The
Super
Marval
560
by Marvin Mace
An AMA
2007 Model
of the Year
26 MODEL AVIATION
THE SUPER MARVAL is not a Power model for beginners. It is a
fairly sophisticated bunting airplane that can be easily built and
flown by a modeler who has previously built and flown “locked-up”
Power models. If you make the investment of time and money to
construct a Super Marval, you will have a model that, if well built
and adjusted, is fun to fly and a competitive AMA Category III
performer.
I hope your competitive attitude will encourage you to master the
bunting technique. Perhaps the observations and confessions in this
article will encourage you if you have reservations about taking the
leap and sharing the challenge and joy a bunter offers. You probably
won’t be sorry if you do.
The use of a high-strength, round, lightweight carbon-fiber
fuselage raises building issues that do not occur with an all-balsa
fuselage. For safety reasons, special construction provisions must be
made to ensure the engine mounting’s integrity in the carbon-fiber
fuselage.
There are several building tools you will find useful for working
on this model: a scroll saw, a drill press, an electric hand drill, a disc
sander, a Dremel motor tool with a cutoff wheel, a 2-56 tap and
wrench, and a 5-foot-long, 2-inch aluminum 90° angle.
CONSTRUCTION
Carbon-Fiber Fuselage Preparation: I chose a carbon-fiber FIC
tailboom, made by Hans Seelig in Germany, for the fuselage. As
purchased, the tailboom is roughly 47.5 inches long and the outer
surface is a spiral wrap that must be sanded smooth to the touch
using 100-grit sandpaper.
06sig1.QXD 4/22/09 2:10 PM Page 26
Photos by the author and Larry Kruse
The Norvel .21 is the power plant of choice. The carbon-fiber fuselage is painted
brightly with a two-part fuelproof paint system such as epoxy.
The rudder’s size and shape are important, but how it’s built is
your choice. It is screw-adjustable for left tab in the power mode
and right tab in the glide.
The author holds his Super Marval under a shade tree while the
Texas sun blazes. The wing and stabilizer are covered with light
iron-on film.
Use the 5-foot aluminum angle and a couple of
Rex Hinson’s Alignment Jig plywood bulkheads to
mark 90° points on the round fuselage.
That usually takes one to two hours of vigorous sanding and is
best done outdoors, to avoid breathing the sanding dust. Wear a
mask, regardless of where you do this job.
Sand only until the tube is smooth to the touch. Do not overdo it.
When finished and cleaned with acetone, the spiral markings should
still be visible on the tube.
Place four strips of narrow masking tape on the top, bottom, left,
and right sides of the tube. Use the 5-foot aluminum angle and a
couple of Rex Hinson’s Alignment Jig plywood bulkheads to mark
the 90° points on the masking tape at the front and rear ends of the
tube.
Use a pen to draw straight lines on the tape, connecting the points.
The top line will be used to line up the firewall, wing pylon, stabilizer
mount, rudder, and bunt mechanism. The bottom line helps locate the
lower side of the timer cutout and the landing skid.
Add the Seelig timer mounting assembly to the fuselage. Put the
assembly in the fuselage and push it to a point where the center of the
timer box is 5 inches from the front of the tube. Use a motor tool with
a cutoff wheel to make a small opening in the lower quadrant of the
left side of the fuselage until you can see the timer box.
Rotate the assembly until the bottom edge is on the bottom line of
the fuselage. Enlarge the opening as necessary with the cutoff wheel.
Firewall Plug and Front-End Fabrication: The firewall, engine
mounting system, landing skid, fuel access, and engine retaining
system are built as a unit. You can use a beam or backplate mount.
The firewall is 13/4 inches in diameter; it is made from two pieces of
1/8 plywood and a 1/32 plywood spacer.
Use epoxy to join the front disk and the 1/32-inch disk. When
cured, the four quadrant lines on the sides of the fuselage are marked
on the edge of the disks. The face of the front disk is marked with the
upper end of the landing skid’s shape, and the skid’s shape is cut out
with a scroll saw.
This cutout permits the landing skid to be retained, removed,
straightened, or replaced by removing the engine mount. Epoxy the
rear 1/8 plywood disk to the front piece and place the assembly in a Cclamp
to cure.
Make the two 1/4-inch, five-ply plywood disks that will fit snugly
inside the fuselage. They are epoxied and C-clamped together to cure.
When dry, the 1/2-inch plug is epoxied to the firewall and C-clamped
until cured.
June 2009 27
06sig1.QXD 4/22/09 3:21 PM Page 27
The pylon is constructed using a backbone of 1/8 square balsa, to
which formers are attached. The bottom former is made from 1/2
or 5/8 balsa, while the middle and top formers are 1/8 balsa.
The plywood firewall sandwich forms the engine mount bolt
locations and undercarriage strut location. The plug portion is
relieved for the fuel-line pass.
The stabilizer is straightforward in its construction. The Oliver
stabilizer mount is modified to accommodate VIT hardware. The Seelig timer mounting assembly is put in the fuselage and
pushed to a point where the center of the timer box is 5 inches
from the front of the tube.
Type: A/B FF Gas
Skill level: Advanced
Wingspan: 72.17 inches
Wing area: 557 square inches
Stabilizer area: 94 square inches
Overall length: 51.18 inches
Weight: 26.4 ounces
Engine: Nelson .21
Construction: Carbon-fiber fuselage, balsa, plywood
Finish: Ultra-light film, epoxy paint
Other: Seelig timer or Texas Timers 3F-1, four-function conversion kit
The
Super
Marval
560
28 MODEL AVIATION
06sig1.QXD 4/22/09 2:29 PM Page 28
five or six points on the tube, roughly 1/4 inch behind the backside
of the firewall, that will not interfere with previously installed
hardware. Drill shallow 1/4-inch-diameter holes through the tube into
the plug with a 13/64 bit.
Put a drop of epoxy in each drilled hole, and lightly drive a 3/8-
inch-long, 13/64 dowel into the holes, leaving approximately 1/8 inch of
the dowel sticking out above the tube. These dowels will pin the plug
and firewall to the tube, to assure that the engine is secure on the front
of the tube.
To complete the front end, use cyanoacrylate to adhere small balsa
wedges, which are approximately 13/4 inches long and 1/4 inch high, to
the nose of the tube, against the back of the firewall, and on each side
of the dowels.
Fill spaces between the wedges with carpenter’s wood filler, and
then sand the front of the tube until smooth. Apply six to eight strips
of fiberglass to the front end of the tube, and spread epoxy on the front
3 inches of the tube and the firewall.
Place a piece of waxed paper on the firewall. Attach the engine
mount to the firewall using the 4-40 bolts, which have had the threads
coated with a thick grease, to prevent the epoxy from sticking to the
bolts and the T-nuts. Tighten the 4-40 bolts and hang the fuselage
nose-down to cure.
When dry, remove the bolts, engine mount, and waxed paper. Sand
A small box to house the Walston radio transmitter is installed in
the left side of the pylon; an exit tube runs from the back of the
box out the rear.
Sand the fuselage smooth prior to any installation. The engine
assembly is aligned with quadrant marks and pinned with dowel
rods epoxied into several points.
The engine mount is flaired into the fuselage with firm balsa; the
wood grain running lengthwise increases the airframe’s torqueload
strength.
To accommodate the VIT hardware, the stabilizer’s center rib will
support the stabilizer pivot wire, hold-down rubber-band hook,
bunt line, and glide-DT line.
To ensure the integrity of the epoxy joint between the firewall and
plug, mount a 4-40 Phillips-head bolt with washers and nut through
both the firewall and plug (countersunk both front and back). Tighten
them so they cannot come apart.
Place the engine mount on the firewall, and place a drop of thin
cyanoacrylate glue in the joint. Put the unit in a drill press and make
the four mounting holes for the 4-40 mounting bolts. After slightly
countersinking the holes on the back of the firewall, put T-nuts in the
holes and tighten the 4-40 bolts to seat them.
Place the firewall assembly in a machinist’s vise and drill a 1/4-
inch-diameter hole at an angle from the lower left edge of the engine
mount (near the landing skid) to a point near the center of the plug.
This hole serves as the access to the fuel compartment and fuel
bladder.
You can separate the engine mount from the firewall by forcing a
knife blade a short distance in between the two.
Sand the front of the carbon-fiber fuselage tube square to the
thrustline. Carefully sand roughly an inch of the inside of the tube to
remove any mold-release residue and clean with acetone.
Brush epoxy onto the outside of the plug and the inside of the tube.
Mate the two parts, taking care to line up the top and bottom marks of
the firewall and tube.
After the epoxy has cured for at least 24 hours, carefully choose
June 2009 29
06sig1.QXD 4/22/09 3:33 PM Page 29
For this article I used the popular Seelig timer, which is no
longer available new. A suitable substitute is the Texas Timers’
3F-1, modified with the available four-function conversion kit.
Set the timer disks beginning with the fuel shutoff wire under
the first disk. Let the timer run until the wire just jumps out from
under the notch in the disk. Halt the timer by using the start/stop
plunger.
Loosen the small nut holding the disks. While holding the
bottom disk, rotate the second and third disk so that the notch in
the top disk is roughly 1/16 inch from the end of the power-line
trip wire and the notch in the middle disk is 1/8 inch from the
bunt-line trip wire. Retighten the small nut while holding all the
disks in place.
The stabilizer is installed and all timer lines are connected.
The timer is fully wound, set on a short engine-run mark, and
cycled to see how things work.
If they work correctly, the engine cutoff wire should
escape the first disk at approximately two seconds. A second
later, the power line should release and the stabilizer should snap
down to the bunt position. Then one second later, the bunt line
should release the stabilizer, which will jump up and be stopped
by the glide adjustment nut.
As the timer continues to run, the DT release wire will follow
the grooves in the timer scroll until it reaches the exit point, at
which time that line is released. The cycle is completed when the
timer is reset to the two-second mark and the timer is rewound.
Now the wing should be mounted on its platform and the
bunt line to the stabilizer released. The stabilizer will rise to the
glide-DT stop nut.
Test-glide the aircraft. Adjust the stop nut as needed to obtain
a safe, floating glide. The model should be ready for short power
flights as you begin trimming.
If possible, have a fellow modeler who flies bunters do a
preflight check of your airplane and be present for your first few
power flights. When you are ready for the first flight, the
observer should be 30-40 feet away from the launch site so that
he/she has a different perspective of the model than you do as it
ascends.
This second opinion about when and if the model leaves the
expected flight path and whether it begins as a turn or a pitch
over or back is critical in knowing what adjustments need to be
made. Rotating the power-adjustment screw for one-eighth or
one-quarter turn is usually all the adjustment necessary for pitch
corrections, and small adjustments of the left rudder tab usually
take care of excess turn.
When making the first few flights, hook up only the engine
cutoff line, the power line, and the rudder line to the timer. The
bunt line and the glide-DT line are permitted to hang loose.
This arrangement lets you have a short engine run and a
small selected amount of left rudder for the first flight. You can
observe the pattern of the flight. Then the aircraft goes directly
to a quick DT.
Upon retrieval, set the timer to the engine run time you are
using and wind it fully. Reattach the lines to the timer, and make
any necessary adjustments.
Continue the test flights until the model is flying a straight-up
pattern. Now engine run times can be increased in small
increments and proper adjustments can be made so that the
airplane stays on pattern until the engine stops.
On the first bunting flight, hook up the bunt line but leave the
glide-DT line hanging loose. This permits you to observe the
bunt’s force and duration.
Did the model go too far over or not far enough? Does the
bunt need to be held longer or held for a shorter period? You can
make the needed adjustments by carefully loosening the small
nut on the Seelig disk, slightly moving the appropriate disk, and
retightening the nut.
When the bunt looks good, it is time to check the airplane’s
glide. Hook up all the lines to the timer. Loosen the nut holding
the DT scroll on the timer and reposition it so that the wire in the
scroll grooves will escape nearly 15 seconds after the engine is
stopped. Retighten the scroll nut. The model is flown with a
four- or five-second engine run, to assure that it has plenty of
altitude for the first test glide.
Assuming that the power pattern is good and the bunt is
timely and correctly done, the bunt line will release the stabilizer
so that it pops up and is stopped by the glide adjustment nut.
Observe the glide and make minor adjustments with the glide
adjustment nut as needed.
When you are satisfied that the glide is safe, loosen the scroll
nut again and set the scroll’s exit point so that when the DT wire
is placed in the proper groove, DT will occur at approximately
2:05. The glide is now fine-tuned. MA
—Marvin Mace
Trimming
a Bunter
30 MODEL AVIATION
06sig1.QXD 4/22/09 2:32 PM Page 30
away any excess epoxy, and sand the front of
the fuselage until smooth.
Rudder: The rudder’s size and shape is
important, but how you build it is your
choice. I cut mine to shape from a sheet of 1/8
balsa and cyanoacrylate-glue three layers of
1/64 plywood that are 1/8 inch wide around the
perimeter.
I sand the rudder to a streamlined shape.
Then I cover it with fiberglass cloth using
epoxy, which has Model Research Labs
fluorescent red pigment dissolved in it for
visibility.
Use whatever system of rudder control
you are comfortable with, but make sure it is
screw-adjustable for left tab in the tab power
mode and right tab in the glide.
The rear of the rudder is located 5 inches
from the rear of the fuselage. Before
mounting the rudder, using the top fuselage
line as a guide, randomly drill eight to 10 1/16-
inch-diameter holes along the top of the
fuselage where the rudder will be placed.
Using a No. 50 wire drill, carefully make a
similar number of holes in the bottom of the
rudder.
Cut and remove the masking tape where
the rudder will be mounted. Lightly sand the
top of the fuselage and clean it with acetone.
Mount the rudder directly on top of the
fuselage with a bead of epoxy on both the top
of the fuselage and the bottom of the rudder,
so that the adhesive is forced into the small
holes when they are pressed together. This
results in a strong joint.
Using the aluminum angle, the Hinson
Alignment Jig system, and a couple of
drafting triangles will ensure that the rudder is
properly aligned on the top of the tube.
Stabilizer and Stabilizer Mount: The
stabilizer’s construction is straightforward. A
couple of modifications are made to
accommodate the Variable Incidence
Tailplane (VIT) hardware.
The stabilizer’s center rib is cut from a
medium-light sheet of 1/2 balsa. This rib
supports the stabilizer pivot wire, the holddown
rubber-band hook, the bunt line, the
glide-DT line, and, on the underside of the
rib, a small stainless-steel plate.
The VIT system’s power-adjustment
screw rests on the steel plate. The single rib
provides the strength required to maintain the
stabilizer’s integrity for hundreds of bunts.
A portion of the stabilizer’s LE and
approximately 3/8 inch of the center rib are
removed to permit the installation of a piece
of .062 music wire, which will be fitted into
the groove in the back of the Oliver stabilizer
mount.
That short piece of music wire is supported
June 2009 31
Full-Size Plans Available—see page 183
06sig1.QXD 4/22/09 3:31 PM Page 31
in the stabilizer LE by 1/16 plywood half
ribs and is tricky to install. When the half
ribs are made, holes slightly larger than
the .062 music wire are drilled in each of
the two, approximately 1/8 inch from the
front edge and centered top to bottom.
Then the half ribs are installed in the front
part of the stabilizer, which has been cut
to fit the Oliver stabilizer mount.
Sharpen a 1/2-inch piece of .062 music
wire and insert it into the half rib holes, to
increase the depth of the holes in the balsa
LE. Cut another piece of .062 music wire
to 11/2 inches, and slightly sharpen both
ends. Grasp this wire portion with pliers
and ease one end a short distance into one
of the holes in the half rib.
When the other end clears the opposite
short rib, maneuver the other end into the
opposite hole. The wire can be slid back
and forth, and a drop of epoxy is put in
each hole. Center the wire and set the
stabilizer aside for the epoxy to cure.
The stabilizer is completed when a
cutout is made on the centerline of the
thick rib for the glide-DT post and the
stabilizer capture button. Epoxy a small
stainless-steel plate, made from a razor
blade, to the underside of the rib, just
behind the stabilizer-capture button hole.
Drill a small hole on the centerline of
the wide rib, just behind the front spar,
and epoxy a short piece of dowel in the
hole, to serve as a hook for the rubber
bands that hold the stabilizer.
When you epoxy the stabilizer mount
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in position, be sure to put the stabilizer in
its mount and place the fuselage tube in
the aluminum angle so the stabilizer mount
can be aligned 90° from the rudder. Use a
bubble level on the stabilizer to ensure
accurate positioning. The LE of the
stabilizer mount should be located
approximately 1 inch behind the rudder.
Ken Oliver makes a well-constructed,
efficient stabilizer mount, and it is
designed for bunting models. Judiciously
sanding the mounting hole in the base will
increase the inner diameter and provide a
perfect fit on the tube.
The stabilizer mount’s exact location
will be determined after the completed
stabilizer is fitted on the fuselage with the
VIT system in place. When positioned
properly, the mount will be roughly 31/2
inches from the end of the tube.
Lynch VIT Assembly: I like the VIT unit
that Bill Lynch, an excellent California
Power flier, developed, because it is
located at the end of the fuselage and is
trouble free when properly installed and
rigged. It also permits visual inspection of
important VIT system parts after you have
attached the lines to the Seelig timer and
before you fly the model. The information
brochure Bill provides with his unit is
invaluable when installing it and its lines.
Using the top line marked on the tube,
use the cutoff wheel to make a slice that is
nearly as long and as wide as the top of the
VIT frame (less the front tang). Use a
small file to enlarge the cutout so that the
VIT frame fits.
It is now necessary to mount a short
piece of 3/32-inch-diameter aluminum
tubing through the fuselage at a location so
that the notch in the VIT frame will fit
perfectly on the tubing when the short tang
bolt is tightened.
To determine where the holes for the
3/32 tubing are located on the sides of the
fuselage, I start with my best guess, use a
tiny drill bit, and enlarge the holes in the
proper direction until the tubing is a
perfect fit in the notch of the VIT unit.
When I find the proper location, I install
the 3/32 tubing (which is slightly longer
than the fuselage tube is wide) and epoxy
it in place (both on the inside and outside
of the fuselage).
When cured, slip the VIT frame into
position with the notch over the 3/32
aluminum tube. Drill a small hole in the
top of the fuselage, matching the hole in
the tang.
Screw a 1/4-inch-long 2-56 bolt, on
which you place a small flat washer and a
lock washer, through the hole in the top of
the tube and into the hole in the tang of the
frame, so that the frame is held firmly in
place when the bolt is tightened.
Wing: The balsa D-box wing spans 72
inches and is constructed in five panels.
The main spar is an I-beam with 1/4 x .007
carbon-fiber strips on the insides of the 1/4
x 1/8 balsa spar caps.
Covered with ultra-light plastic film
and with balsa Hoerner-type tips, the wing
weighs 8.8 ounces. It is dead stiff, as it
must be.
Pylon Construction and Attachment: The
pylon is constructed using a backbone of
1/8 square balsa, to which formers are
attached. The bottom former is made from
1/2 or 5/8 balsa, while the middle and top
formers are 1/8 balsa.
A small box to house the Walston radio
transmitter is installed in the left side of
the pylon with an exit tube running from
the back of the box out the rear of the
pylon. Then the pylon is covered with 1/16
balsa sheet. Cover the left side of the pylon
first, so that the hole for the transmitter box
can be easily marked from the backside
and then cut out.
The bottom of the pylon must be sanded
to a curved shape so that it will fit against
the fuselage tube. You can do this by
wrapping a sheet of 100-grit sandpaper
around the fuselage and then sliding the
base of the pylon back and forth in a
straight line over the sandpaper, to remove
the excess balsa. It is difficult, but it works
and, finally, a good fit is achieved.
Put the pylon on the fuselage using a
couple of rubber bands to hold it. Check to
see what incidence is on the wing platform.
To do so, return the fuselage to the
aluminum angle and jack up the rear of the
tube until its centerline is parallel to the
top of your workbench. Using an accurate
ruler, measure the distance from the top of
the table to the front and rear of the wing
platform.
If the front is roughly 1/8 inch higher
than the rear, you are home free. If not,
you must continue the back-and-forth
sanding, with pressure applied as needed,
until the platform incidence is 1/8 inch.
With the correct wing incidence, the
model can be assembled and the final
pylon location can be determined.
Make a permanent mark on the edge of
the platform at 58% of the wing chord.
Install the engine, propeller, spinner, wire
skid, timer, and radio transmitter. The
wing with the pylon and stabilizer are
attached to the fuselage with rubber bands.
Balance the model at 58% of the wing
chord by sliding the wing pylon back and
forth on the tube until a balance point is
found and the fuselage is parallel to the
floor. Mark the masking tape on the top
line of the fuselage where the front and
back of the pylon are. Randomly drill a
series of small holes along the top line of
the fuselage between the marks, and drill
several small holes in the bottom of the
pylon.
Remove the masking tape where the
pylon is to be located. Lightly sand the top
of the tube, and clean it with acetone. Coat
the top of the fuselage and the bottom of
the pylon with epoxy, and join them. As
with the rudder, the adhesive will be
forced into the small drilled holes,
improving the joint strength.
Three or four strong rubber bands are
used to hold the pylon tightly to the
fuselage, and then it is placed in the
aluminum angle. Line up the pylon with
the remaining top line marks on the
fuselage and with the rudder while using a
bubble level on the top of the wing
platform. When everything is properly
aligned, allow the epoxy to cure for 24
hours.
When cured, fair the pylon into the
fuselage tube using a mixture of epoxy
and microballoon filler, and then sand.
Mask off the rudder, and paint the
fuselage. I prefer to use white epoxy paint
on the fuselage, because it is highly
visible and cooler in the summertime.
Flight Preparation: Before heading to
the flying field for the first test flight, it is
mandatory that you check the model, in
the shop, for decalage. To do this, draw a
48-inch straight line on the workbench.
Then lay the fuselage on its side, with its
centerline located precisely on the straight
line. Draw a line on the workbench from
the front to the back of the wing platform.
Go to the back of the fuselage, and
make a dot on the workbench that
corresponds with the wire groove of the
Oliver stabilizer mount. Using a drafting
triangle pressed against the top of the
power adjustment screw, make a mark
indicating the top of that screw.
Accurately measure the distance
between the front and back of the wing
platform to the fuselage centerline, and
measure from the two dots, which
represent the distance from the front and
back of the stabilizer to the centerline. The
difference between the measurements
represents the model’s decalage.
Recall that we built 1/8 inch of
incidence into the wing platform when we
mounted it on the fuselage. Since we
would like to start our trimming with 1/16
inch of decalage, we can adjust the power
adjustment screw up or down as needed to
achieve this 1/16 difference.
You should be ready to trim your Super
Marval for competition. Repeatable, safe
engine runs are extremely important—
especially at four and five seconds. The
penalty for overruns during flyoffs is a
zero time, and nothing could be worse. Err
on the side of a safe engine run.
You must keep your timer clean and
oiled and all of your model’s parts in
perfect shape and in good working order.
Have confidence in your timer and your
ability to accurately set it for any engine
run.
That confidence comes from making
many test flights with the help of fellow
modelers who know how to accurately
time an engine run. The watch starts when
the aircraft leaves the flier’s hand and ends
when you hear the engine’s last audible
power stroke.
I take this opportunity to acknowledge the
invaluable help and advice I have received
from my fellow bunters in the past few
years as I have tried to get up to speed.
Insights or clever ideas that I appear to
claim as my own are the result of
conversations I have had with guys such as
Doug Galbreath, Bill Lynch, Ken Oliver,
the late Bob Johannes, Dick Covalt, Bob
Mattes, Gil Robbins, Ronnie Thompson,
Don DeLoach, Faust Parker, Henry
Spence, Mark Troutman, Reid and Roger
Simpson, C.C. Johnson, and Dick Hall.
I also thank Larry Kruse for helping me
put this construction article together in a
format for publication. The Super Marval
is as much your model as it is mine. MA
Marvin Mace
107 Country Ln.
Seguin TX 78155
(830) 379-0036
[email protected]
Sources:
Seelig carbon-fiber tube:
Reid C. Simpson
115 Trail Ridge Dr.
Athens TX 75751
(903) 677-8525
[email protected]
Oliver stabilizer mount:
Ken Oliver
2213 El Cejo Cir.
Rancho Cordova CA 95670
(916) 363-2017
Lynch VIT system:
Bill Lynch
2279 Auburn Ravine Dr.
Lincoln CA 95648
(916) 645-3337
[email protected]
Alignment Jig:
Rex Hinson
1141 S. Waterview Dr.
Inverness FL 34450
(352) 344-5931
[email protected]
Red fluorescent pigment:
Model Research Labs/Curt Stevens
25108 Marguerite Parkway #160
Mission Viejo CA 92692
[email protected]
Walston Retrieval Systems:
Jim Walston
725 Coopers Lake Rd. SE
Smyrna GA 30082
(770) 434-4905
[email protected]
Texas Timers (Request model 3F 1 and
four-function conversion kit)
3317 Pine Timbers Dr.
Johnson City TN 37604
(423) 282-6423
www.texastimers.com
Edition: Model Aviation - 2009/06
Page Numbers: 26,27,28,29,30,31,32,34,36
Edition: Model Aviation - 2009/06
Page Numbers: 26,27,28,29,30,31,32,34,36
The
Super
Marval
560
by Marvin Mace
An AMA
2007 Model
of the Year
26 MODEL AVIATION
THE SUPER MARVAL is not a Power model for beginners. It is a
fairly sophisticated bunting airplane that can be easily built and
flown by a modeler who has previously built and flown “locked-up”
Power models. If you make the investment of time and money to
construct a Super Marval, you will have a model that, if well built
and adjusted, is fun to fly and a competitive AMA Category III
performer.
I hope your competitive attitude will encourage you to master the
bunting technique. Perhaps the observations and confessions in this
article will encourage you if you have reservations about taking the
leap and sharing the challenge and joy a bunter offers. You probably
won’t be sorry if you do.
The use of a high-strength, round, lightweight carbon-fiber
fuselage raises building issues that do not occur with an all-balsa
fuselage. For safety reasons, special construction provisions must be
made to ensure the engine mounting’s integrity in the carbon-fiber
fuselage.
There are several building tools you will find useful for working
on this model: a scroll saw, a drill press, an electric hand drill, a disc
sander, a Dremel motor tool with a cutoff wheel, a 2-56 tap and
wrench, and a 5-foot-long, 2-inch aluminum 90° angle.
CONSTRUCTION
Carbon-Fiber Fuselage Preparation: I chose a carbon-fiber FIC
tailboom, made by Hans Seelig in Germany, for the fuselage. As
purchased, the tailboom is roughly 47.5 inches long and the outer
surface is a spiral wrap that must be sanded smooth to the touch
using 100-grit sandpaper.
06sig1.QXD 4/22/09 2:10 PM Page 26
Photos by the author and Larry Kruse
The Norvel .21 is the power plant of choice. The carbon-fiber fuselage is painted
brightly with a two-part fuelproof paint system such as epoxy.
The rudder’s size and shape are important, but how it’s built is
your choice. It is screw-adjustable for left tab in the power mode
and right tab in the glide.
The author holds his Super Marval under a shade tree while the
Texas sun blazes. The wing and stabilizer are covered with light
iron-on film.
Use the 5-foot aluminum angle and a couple of
Rex Hinson’s Alignment Jig plywood bulkheads to
mark 90° points on the round fuselage.
That usually takes one to two hours of vigorous sanding and is
best done outdoors, to avoid breathing the sanding dust. Wear a
mask, regardless of where you do this job.
Sand only until the tube is smooth to the touch. Do not overdo it.
When finished and cleaned with acetone, the spiral markings should
still be visible on the tube.
Place four strips of narrow masking tape on the top, bottom, left,
and right sides of the tube. Use the 5-foot aluminum angle and a
couple of Rex Hinson’s Alignment Jig plywood bulkheads to mark
the 90° points on the masking tape at the front and rear ends of the
tube.
Use a pen to draw straight lines on the tape, connecting the points.
The top line will be used to line up the firewall, wing pylon, stabilizer
mount, rudder, and bunt mechanism. The bottom line helps locate the
lower side of the timer cutout and the landing skid.
Add the Seelig timer mounting assembly to the fuselage. Put the
assembly in the fuselage and push it to a point where the center of the
timer box is 5 inches from the front of the tube. Use a motor tool with
a cutoff wheel to make a small opening in the lower quadrant of the
left side of the fuselage until you can see the timer box.
Rotate the assembly until the bottom edge is on the bottom line of
the fuselage. Enlarge the opening as necessary with the cutoff wheel.
Firewall Plug and Front-End Fabrication: The firewall, engine
mounting system, landing skid, fuel access, and engine retaining
system are built as a unit. You can use a beam or backplate mount.
The firewall is 13/4 inches in diameter; it is made from two pieces of
1/8 plywood and a 1/32 plywood spacer.
Use epoxy to join the front disk and the 1/32-inch disk. When
cured, the four quadrant lines on the sides of the fuselage are marked
on the edge of the disks. The face of the front disk is marked with the
upper end of the landing skid’s shape, and the skid’s shape is cut out
with a scroll saw.
This cutout permits the landing skid to be retained, removed,
straightened, or replaced by removing the engine mount. Epoxy the
rear 1/8 plywood disk to the front piece and place the assembly in a Cclamp
to cure.
Make the two 1/4-inch, five-ply plywood disks that will fit snugly
inside the fuselage. They are epoxied and C-clamped together to cure.
When dry, the 1/2-inch plug is epoxied to the firewall and C-clamped
until cured.
June 2009 27
06sig1.QXD 4/22/09 3:21 PM Page 27
The pylon is constructed using a backbone of 1/8 square balsa, to
which formers are attached. The bottom former is made from 1/2
or 5/8 balsa, while the middle and top formers are 1/8 balsa.
The plywood firewall sandwich forms the engine mount bolt
locations and undercarriage strut location. The plug portion is
relieved for the fuel-line pass.
The stabilizer is straightforward in its construction. The Oliver
stabilizer mount is modified to accommodate VIT hardware. The Seelig timer mounting assembly is put in the fuselage and
pushed to a point where the center of the timer box is 5 inches
from the front of the tube.
Type: A/B FF Gas
Skill level: Advanced
Wingspan: 72.17 inches
Wing area: 557 square inches
Stabilizer area: 94 square inches
Overall length: 51.18 inches
Weight: 26.4 ounces
Engine: Nelson .21
Construction: Carbon-fiber fuselage, balsa, plywood
Finish: Ultra-light film, epoxy paint
Other: Seelig timer or Texas Timers 3F-1, four-function conversion kit
The
Super
Marval
560
28 MODEL AVIATION
06sig1.QXD 4/22/09 2:29 PM Page 28
five or six points on the tube, roughly 1/4 inch behind the backside
of the firewall, that will not interfere with previously installed
hardware. Drill shallow 1/4-inch-diameter holes through the tube into
the plug with a 13/64 bit.
Put a drop of epoxy in each drilled hole, and lightly drive a 3/8-
inch-long, 13/64 dowel into the holes, leaving approximately 1/8 inch of
the dowel sticking out above the tube. These dowels will pin the plug
and firewall to the tube, to assure that the engine is secure on the front
of the tube.
To complete the front end, use cyanoacrylate to adhere small balsa
wedges, which are approximately 13/4 inches long and 1/4 inch high, to
the nose of the tube, against the back of the firewall, and on each side
of the dowels.
Fill spaces between the wedges with carpenter’s wood filler, and
then sand the front of the tube until smooth. Apply six to eight strips
of fiberglass to the front end of the tube, and spread epoxy on the front
3 inches of the tube and the firewall.
Place a piece of waxed paper on the firewall. Attach the engine
mount to the firewall using the 4-40 bolts, which have had the threads
coated with a thick grease, to prevent the epoxy from sticking to the
bolts and the T-nuts. Tighten the 4-40 bolts and hang the fuselage
nose-down to cure.
When dry, remove the bolts, engine mount, and waxed paper. Sand
A small box to house the Walston radio transmitter is installed in
the left side of the pylon; an exit tube runs from the back of the
box out the rear.
Sand the fuselage smooth prior to any installation. The engine
assembly is aligned with quadrant marks and pinned with dowel
rods epoxied into several points.
The engine mount is flaired into the fuselage with firm balsa; the
wood grain running lengthwise increases the airframe’s torqueload
strength.
To accommodate the VIT hardware, the stabilizer’s center rib will
support the stabilizer pivot wire, hold-down rubber-band hook,
bunt line, and glide-DT line.
To ensure the integrity of the epoxy joint between the firewall and
plug, mount a 4-40 Phillips-head bolt with washers and nut through
both the firewall and plug (countersunk both front and back). Tighten
them so they cannot come apart.
Place the engine mount on the firewall, and place a drop of thin
cyanoacrylate glue in the joint. Put the unit in a drill press and make
the four mounting holes for the 4-40 mounting bolts. After slightly
countersinking the holes on the back of the firewall, put T-nuts in the
holes and tighten the 4-40 bolts to seat them.
Place the firewall assembly in a machinist’s vise and drill a 1/4-
inch-diameter hole at an angle from the lower left edge of the engine
mount (near the landing skid) to a point near the center of the plug.
This hole serves as the access to the fuel compartment and fuel
bladder.
You can separate the engine mount from the firewall by forcing a
knife blade a short distance in between the two.
Sand the front of the carbon-fiber fuselage tube square to the
thrustline. Carefully sand roughly an inch of the inside of the tube to
remove any mold-release residue and clean with acetone.
Brush epoxy onto the outside of the plug and the inside of the tube.
Mate the two parts, taking care to line up the top and bottom marks of
the firewall and tube.
After the epoxy has cured for at least 24 hours, carefully choose
June 2009 29
06sig1.QXD 4/22/09 3:33 PM Page 29
For this article I used the popular Seelig timer, which is no
longer available new. A suitable substitute is the Texas Timers’
3F-1, modified with the available four-function conversion kit.
Set the timer disks beginning with the fuel shutoff wire under
the first disk. Let the timer run until the wire just jumps out from
under the notch in the disk. Halt the timer by using the start/stop
plunger.
Loosen the small nut holding the disks. While holding the
bottom disk, rotate the second and third disk so that the notch in
the top disk is roughly 1/16 inch from the end of the power-line
trip wire and the notch in the middle disk is 1/8 inch from the
bunt-line trip wire. Retighten the small nut while holding all the
disks in place.
The stabilizer is installed and all timer lines are connected.
The timer is fully wound, set on a short engine-run mark, and
cycled to see how things work.
If they work correctly, the engine cutoff wire should
escape the first disk at approximately two seconds. A second
later, the power line should release and the stabilizer should snap
down to the bunt position. Then one second later, the bunt line
should release the stabilizer, which will jump up and be stopped
by the glide adjustment nut.
As the timer continues to run, the DT release wire will follow
the grooves in the timer scroll until it reaches the exit point, at
which time that line is released. The cycle is completed when the
timer is reset to the two-second mark and the timer is rewound.
Now the wing should be mounted on its platform and the
bunt line to the stabilizer released. The stabilizer will rise to the
glide-DT stop nut.
Test-glide the aircraft. Adjust the stop nut as needed to obtain
a safe, floating glide. The model should be ready for short power
flights as you begin trimming.
If possible, have a fellow modeler who flies bunters do a
preflight check of your airplane and be present for your first few
power flights. When you are ready for the first flight, the
observer should be 30-40 feet away from the launch site so that
he/she has a different perspective of the model than you do as it
ascends.
This second opinion about when and if the model leaves the
expected flight path and whether it begins as a turn or a pitch
over or back is critical in knowing what adjustments need to be
made. Rotating the power-adjustment screw for one-eighth or
one-quarter turn is usually all the adjustment necessary for pitch
corrections, and small adjustments of the left rudder tab usually
take care of excess turn.
When making the first few flights, hook up only the engine
cutoff line, the power line, and the rudder line to the timer. The
bunt line and the glide-DT line are permitted to hang loose.
This arrangement lets you have a short engine run and a
small selected amount of left rudder for the first flight. You can
observe the pattern of the flight. Then the aircraft goes directly
to a quick DT.
Upon retrieval, set the timer to the engine run time you are
using and wind it fully. Reattach the lines to the timer, and make
any necessary adjustments.
Continue the test flights until the model is flying a straight-up
pattern. Now engine run times can be increased in small
increments and proper adjustments can be made so that the
airplane stays on pattern until the engine stops.
On the first bunting flight, hook up the bunt line but leave the
glide-DT line hanging loose. This permits you to observe the
bunt’s force and duration.
Did the model go too far over or not far enough? Does the
bunt need to be held longer or held for a shorter period? You can
make the needed adjustments by carefully loosening the small
nut on the Seelig disk, slightly moving the appropriate disk, and
retightening the nut.
When the bunt looks good, it is time to check the airplane’s
glide. Hook up all the lines to the timer. Loosen the nut holding
the DT scroll on the timer and reposition it so that the wire in the
scroll grooves will escape nearly 15 seconds after the engine is
stopped. Retighten the scroll nut. The model is flown with a
four- or five-second engine run, to assure that it has plenty of
altitude for the first test glide.
Assuming that the power pattern is good and the bunt is
timely and correctly done, the bunt line will release the stabilizer
so that it pops up and is stopped by the glide adjustment nut.
Observe the glide and make minor adjustments with the glide
adjustment nut as needed.
When you are satisfied that the glide is safe, loosen the scroll
nut again and set the scroll’s exit point so that when the DT wire
is placed in the proper groove, DT will occur at approximately
2:05. The glide is now fine-tuned. MA
—Marvin Mace
Trimming
a Bunter
30 MODEL AVIATION
06sig1.QXD 4/22/09 2:32 PM Page 30
away any excess epoxy, and sand the front of
the fuselage until smooth.
Rudder: The rudder’s size and shape is
important, but how you build it is your
choice. I cut mine to shape from a sheet of 1/8
balsa and cyanoacrylate-glue three layers of
1/64 plywood that are 1/8 inch wide around the
perimeter.
I sand the rudder to a streamlined shape.
Then I cover it with fiberglass cloth using
epoxy, which has Model Research Labs
fluorescent red pigment dissolved in it for
visibility.
Use whatever system of rudder control
you are comfortable with, but make sure it is
screw-adjustable for left tab in the tab power
mode and right tab in the glide.
The rear of the rudder is located 5 inches
from the rear of the fuselage. Before
mounting the rudder, using the top fuselage
line as a guide, randomly drill eight to 10 1/16-
inch-diameter holes along the top of the
fuselage where the rudder will be placed.
Using a No. 50 wire drill, carefully make a
similar number of holes in the bottom of the
rudder.
Cut and remove the masking tape where
the rudder will be mounted. Lightly sand the
top of the fuselage and clean it with acetone.
Mount the rudder directly on top of the
fuselage with a bead of epoxy on both the top
of the fuselage and the bottom of the rudder,
so that the adhesive is forced into the small
holes when they are pressed together. This
results in a strong joint.
Using the aluminum angle, the Hinson
Alignment Jig system, and a couple of
drafting triangles will ensure that the rudder is
properly aligned on the top of the tube.
Stabilizer and Stabilizer Mount: The
stabilizer’s construction is straightforward. A
couple of modifications are made to
accommodate the Variable Incidence
Tailplane (VIT) hardware.
The stabilizer’s center rib is cut from a
medium-light sheet of 1/2 balsa. This rib
supports the stabilizer pivot wire, the holddown
rubber-band hook, the bunt line, the
glide-DT line, and, on the underside of the
rib, a small stainless-steel plate.
The VIT system’s power-adjustment
screw rests on the steel plate. The single rib
provides the strength required to maintain the
stabilizer’s integrity for hundreds of bunts.
A portion of the stabilizer’s LE and
approximately 3/8 inch of the center rib are
removed to permit the installation of a piece
of .062 music wire, which will be fitted into
the groove in the back of the Oliver stabilizer
mount.
That short piece of music wire is supported
June 2009 31
Full-Size Plans Available—see page 183
06sig1.QXD 4/22/09 3:31 PM Page 31
in the stabilizer LE by 1/16 plywood half
ribs and is tricky to install. When the half
ribs are made, holes slightly larger than
the .062 music wire are drilled in each of
the two, approximately 1/8 inch from the
front edge and centered top to bottom.
Then the half ribs are installed in the front
part of the stabilizer, which has been cut
to fit the Oliver stabilizer mount.
Sharpen a 1/2-inch piece of .062 music
wire and insert it into the half rib holes, to
increase the depth of the holes in the balsa
LE. Cut another piece of .062 music wire
to 11/2 inches, and slightly sharpen both
ends. Grasp this wire portion with pliers
and ease one end a short distance into one
of the holes in the half rib.
When the other end clears the opposite
short rib, maneuver the other end into the
opposite hole. The wire can be slid back
and forth, and a drop of epoxy is put in
each hole. Center the wire and set the
stabilizer aside for the epoxy to cure.
The stabilizer is completed when a
cutout is made on the centerline of the
thick rib for the glide-DT post and the
stabilizer capture button. Epoxy a small
stainless-steel plate, made from a razor
blade, to the underside of the rib, just
behind the stabilizer-capture button hole.
Drill a small hole on the centerline of
the wide rib, just behind the front spar,
and epoxy a short piece of dowel in the
hole, to serve as a hook for the rubber
bands that hold the stabilizer.
When you epoxy the stabilizer mount
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in position, be sure to put the stabilizer in
its mount and place the fuselage tube in
the aluminum angle so the stabilizer mount
can be aligned 90° from the rudder. Use a
bubble level on the stabilizer to ensure
accurate positioning. The LE of the
stabilizer mount should be located
approximately 1 inch behind the rudder.
Ken Oliver makes a well-constructed,
efficient stabilizer mount, and it is
designed for bunting models. Judiciously
sanding the mounting hole in the base will
increase the inner diameter and provide a
perfect fit on the tube.
The stabilizer mount’s exact location
will be determined after the completed
stabilizer is fitted on the fuselage with the
VIT system in place. When positioned
properly, the mount will be roughly 31/2
inches from the end of the tube.
Lynch VIT Assembly: I like the VIT unit
that Bill Lynch, an excellent California
Power flier, developed, because it is
located at the end of the fuselage and is
trouble free when properly installed and
rigged. It also permits visual inspection of
important VIT system parts after you have
attached the lines to the Seelig timer and
before you fly the model. The information
brochure Bill provides with his unit is
invaluable when installing it and its lines.
Using the top line marked on the tube,
use the cutoff wheel to make a slice that is
nearly as long and as wide as the top of the
VIT frame (less the front tang). Use a
small file to enlarge the cutout so that the
VIT frame fits.
It is now necessary to mount a short
piece of 3/32-inch-diameter aluminum
tubing through the fuselage at a location so
that the notch in the VIT frame will fit
perfectly on the tubing when the short tang
bolt is tightened.
To determine where the holes for the
3/32 tubing are located on the sides of the
fuselage, I start with my best guess, use a
tiny drill bit, and enlarge the holes in the
proper direction until the tubing is a
perfect fit in the notch of the VIT unit.
When I find the proper location, I install
the 3/32 tubing (which is slightly longer
than the fuselage tube is wide) and epoxy
it in place (both on the inside and outside
of the fuselage).
When cured, slip the VIT frame into
position with the notch over the 3/32
aluminum tube. Drill a small hole in the
top of the fuselage, matching the hole in
the tang.
Screw a 1/4-inch-long 2-56 bolt, on
which you place a small flat washer and a
lock washer, through the hole in the top of
the tube and into the hole in the tang of the
frame, so that the frame is held firmly in
place when the bolt is tightened.
Wing: The balsa D-box wing spans 72
inches and is constructed in five panels.
The main spar is an I-beam with 1/4 x .007
carbon-fiber strips on the insides of the 1/4
x 1/8 balsa spar caps.
Covered with ultra-light plastic film
and with balsa Hoerner-type tips, the wing
weighs 8.8 ounces. It is dead stiff, as it
must be.
Pylon Construction and Attachment: The
pylon is constructed using a backbone of
1/8 square balsa, to which formers are
attached. The bottom former is made from
1/2 or 5/8 balsa, while the middle and top
formers are 1/8 balsa.
A small box to house the Walston radio
transmitter is installed in the left side of
the pylon with an exit tube running from
the back of the box out the rear of the
pylon. Then the pylon is covered with 1/16
balsa sheet. Cover the left side of the pylon
first, so that the hole for the transmitter box
can be easily marked from the backside
and then cut out.
The bottom of the pylon must be sanded
to a curved shape so that it will fit against
the fuselage tube. You can do this by
wrapping a sheet of 100-grit sandpaper
around the fuselage and then sliding the
base of the pylon back and forth in a
straight line over the sandpaper, to remove
the excess balsa. It is difficult, but it works
and, finally, a good fit is achieved.
Put the pylon on the fuselage using a
couple of rubber bands to hold it. Check to
see what incidence is on the wing platform.
To do so, return the fuselage to the
aluminum angle and jack up the rear of the
tube until its centerline is parallel to the
top of your workbench. Using an accurate
ruler, measure the distance from the top of
the table to the front and rear of the wing
platform.
If the front is roughly 1/8 inch higher
than the rear, you are home free. If not,
you must continue the back-and-forth
sanding, with pressure applied as needed,
until the platform incidence is 1/8 inch.
With the correct wing incidence, the
model can be assembled and the final
pylon location can be determined.
Make a permanent mark on the edge of
the platform at 58% of the wing chord.
Install the engine, propeller, spinner, wire
skid, timer, and radio transmitter. The
wing with the pylon and stabilizer are
attached to the fuselage with rubber bands.
Balance the model at 58% of the wing
chord by sliding the wing pylon back and
forth on the tube until a balance point is
found and the fuselage is parallel to the
floor. Mark the masking tape on the top
line of the fuselage where the front and
back of the pylon are. Randomly drill a
series of small holes along the top line of
the fuselage between the marks, and drill
several small holes in the bottom of the
pylon.
Remove the masking tape where the
pylon is to be located. Lightly sand the top
of the tube, and clean it with acetone. Coat
the top of the fuselage and the bottom of
the pylon with epoxy, and join them. As
with the rudder, the adhesive will be
forced into the small drilled holes,
improving the joint strength.
Three or four strong rubber bands are
used to hold the pylon tightly to the
fuselage, and then it is placed in the
aluminum angle. Line up the pylon with
the remaining top line marks on the
fuselage and with the rudder while using a
bubble level on the top of the wing
platform. When everything is properly
aligned, allow the epoxy to cure for 24
hours.
When cured, fair the pylon into the
fuselage tube using a mixture of epoxy
and microballoon filler, and then sand.
Mask off the rudder, and paint the
fuselage. I prefer to use white epoxy paint
on the fuselage, because it is highly
visible and cooler in the summertime.
Flight Preparation: Before heading to
the flying field for the first test flight, it is
mandatory that you check the model, in
the shop, for decalage. To do this, draw a
48-inch straight line on the workbench.
Then lay the fuselage on its side, with its
centerline located precisely on the straight
line. Draw a line on the workbench from
the front to the back of the wing platform.
Go to the back of the fuselage, and
make a dot on the workbench that
corresponds with the wire groove of the
Oliver stabilizer mount. Using a drafting
triangle pressed against the top of the
power adjustment screw, make a mark
indicating the top of that screw.
Accurately measure the distance
between the front and back of the wing
platform to the fuselage centerline, and
measure from the two dots, which
represent the distance from the front and
back of the stabilizer to the centerline. The
difference between the measurements
represents the model’s decalage.
Recall that we built 1/8 inch of
incidence into the wing platform when we
mounted it on the fuselage. Since we
would like to start our trimming with 1/16
inch of decalage, we can adjust the power
adjustment screw up or down as needed to
achieve this 1/16 difference.
You should be ready to trim your Super
Marval for competition. Repeatable, safe
engine runs are extremely important—
especially at four and five seconds. The
penalty for overruns during flyoffs is a
zero time, and nothing could be worse. Err
on the side of a safe engine run.
You must keep your timer clean and
oiled and all of your model’s parts in
perfect shape and in good working order.
Have confidence in your timer and your
ability to accurately set it for any engine
run.
That confidence comes from making
many test flights with the help of fellow
modelers who know how to accurately
time an engine run. The watch starts when
the aircraft leaves the flier’s hand and ends
when you hear the engine’s last audible
power stroke.
I take this opportunity to acknowledge the
invaluable help and advice I have received
from my fellow bunters in the past few
years as I have tried to get up to speed.
Insights or clever ideas that I appear to
claim as my own are the result of
conversations I have had with guys such as
Doug Galbreath, Bill Lynch, Ken Oliver,
the late Bob Johannes, Dick Covalt, Bob
Mattes, Gil Robbins, Ronnie Thompson,
Don DeLoach, Faust Parker, Henry
Spence, Mark Troutman, Reid and Roger
Simpson, C.C. Johnson, and Dick Hall.
I also thank Larry Kruse for helping me
put this construction article together in a
format for publication. The Super Marval
is as much your model as it is mine. MA
Marvin Mace
107 Country Ln.
Seguin TX 78155
(830) 379-0036
[email protected]
Sources:
Seelig carbon-fiber tube:
Reid C. Simpson
115 Trail Ridge Dr.
Athens TX 75751
(903) 677-8525
[email protected]
Oliver stabilizer mount:
Ken Oliver
2213 El Cejo Cir.
Rancho Cordova CA 95670
(916) 363-2017
Lynch VIT system:
Bill Lynch
2279 Auburn Ravine Dr.
Lincoln CA 95648
(916) 645-3337
[email protected]
Alignment Jig:
Rex Hinson
1141 S. Waterview Dr.
Inverness FL 34450
(352) 344-5931
[email protected]
Red fluorescent pigment:
Model Research Labs/Curt Stevens
25108 Marguerite Parkway #160
Mission Viejo CA 92692
[email protected]
Walston Retrieval Systems:
Jim Walston
725 Coopers Lake Rd. SE
Smyrna GA 30082
(770) 434-4905
[email protected]
Texas Timers (Request model 3F 1 and
four-function conversion kit)
3317 Pine Timbers Dr.
Johnson City TN 37604
(423) 282-6423
www.texastimers.com
Edition: Model Aviation - 2009/06
Page Numbers: 26,27,28,29,30,31,32,34,36
The
Super
Marval
560
by Marvin Mace
An AMA
2007 Model
of the Year
26 MODEL AVIATION
THE SUPER MARVAL is not a Power model for beginners. It is a
fairly sophisticated bunting airplane that can be easily built and
flown by a modeler who has previously built and flown “locked-up”
Power models. If you make the investment of time and money to
construct a Super Marval, you will have a model that, if well built
and adjusted, is fun to fly and a competitive AMA Category III
performer.
I hope your competitive attitude will encourage you to master the
bunting technique. Perhaps the observations and confessions in this
article will encourage you if you have reservations about taking the
leap and sharing the challenge and joy a bunter offers. You probably
won’t be sorry if you do.
The use of a high-strength, round, lightweight carbon-fiber
fuselage raises building issues that do not occur with an all-balsa
fuselage. For safety reasons, special construction provisions must be
made to ensure the engine mounting’s integrity in the carbon-fiber
fuselage.
There are several building tools you will find useful for working
on this model: a scroll saw, a drill press, an electric hand drill, a disc
sander, a Dremel motor tool with a cutoff wheel, a 2-56 tap and
wrench, and a 5-foot-long, 2-inch aluminum 90° angle.
CONSTRUCTION
Carbon-Fiber Fuselage Preparation: I chose a carbon-fiber FIC
tailboom, made by Hans Seelig in Germany, for the fuselage. As
purchased, the tailboom is roughly 47.5 inches long and the outer
surface is a spiral wrap that must be sanded smooth to the touch
using 100-grit sandpaper.
06sig1.QXD 4/22/09 2:10 PM Page 26
Photos by the author and Larry Kruse
The Norvel .21 is the power plant of choice. The carbon-fiber fuselage is painted
brightly with a two-part fuelproof paint system such as epoxy.
The rudder’s size and shape are important, but how it’s built is
your choice. It is screw-adjustable for left tab in the power mode
and right tab in the glide.
The author holds his Super Marval under a shade tree while the
Texas sun blazes. The wing and stabilizer are covered with light
iron-on film.
Use the 5-foot aluminum angle and a couple of
Rex Hinson’s Alignment Jig plywood bulkheads to
mark 90° points on the round fuselage.
That usually takes one to two hours of vigorous sanding and is
best done outdoors, to avoid breathing the sanding dust. Wear a
mask, regardless of where you do this job.
Sand only until the tube is smooth to the touch. Do not overdo it.
When finished and cleaned with acetone, the spiral markings should
still be visible on the tube.
Place four strips of narrow masking tape on the top, bottom, left,
and right sides of the tube. Use the 5-foot aluminum angle and a
couple of Rex Hinson’s Alignment Jig plywood bulkheads to mark
the 90° points on the masking tape at the front and rear ends of the
tube.
Use a pen to draw straight lines on the tape, connecting the points.
The top line will be used to line up the firewall, wing pylon, stabilizer
mount, rudder, and bunt mechanism. The bottom line helps locate the
lower side of the timer cutout and the landing skid.
Add the Seelig timer mounting assembly to the fuselage. Put the
assembly in the fuselage and push it to a point where the center of the
timer box is 5 inches from the front of the tube. Use a motor tool with
a cutoff wheel to make a small opening in the lower quadrant of the
left side of the fuselage until you can see the timer box.
Rotate the assembly until the bottom edge is on the bottom line of
the fuselage. Enlarge the opening as necessary with the cutoff wheel.
Firewall Plug and Front-End Fabrication: The firewall, engine
mounting system, landing skid, fuel access, and engine retaining
system are built as a unit. You can use a beam or backplate mount.
The firewall is 13/4 inches in diameter; it is made from two pieces of
1/8 plywood and a 1/32 plywood spacer.
Use epoxy to join the front disk and the 1/32-inch disk. When
cured, the four quadrant lines on the sides of the fuselage are marked
on the edge of the disks. The face of the front disk is marked with the
upper end of the landing skid’s shape, and the skid’s shape is cut out
with a scroll saw.
This cutout permits the landing skid to be retained, removed,
straightened, or replaced by removing the engine mount. Epoxy the
rear 1/8 plywood disk to the front piece and place the assembly in a Cclamp
to cure.
Make the two 1/4-inch, five-ply plywood disks that will fit snugly
inside the fuselage. They are epoxied and C-clamped together to cure.
When dry, the 1/2-inch plug is epoxied to the firewall and C-clamped
until cured.
June 2009 27
06sig1.QXD 4/22/09 3:21 PM Page 27
The pylon is constructed using a backbone of 1/8 square balsa, to
which formers are attached. The bottom former is made from 1/2
or 5/8 balsa, while the middle and top formers are 1/8 balsa.
The plywood firewall sandwich forms the engine mount bolt
locations and undercarriage strut location. The plug portion is
relieved for the fuel-line pass.
The stabilizer is straightforward in its construction. The Oliver
stabilizer mount is modified to accommodate VIT hardware. The Seelig timer mounting assembly is put in the fuselage and
pushed to a point where the center of the timer box is 5 inches
from the front of the tube.
Type: A/B FF Gas
Skill level: Advanced
Wingspan: 72.17 inches
Wing area: 557 square inches
Stabilizer area: 94 square inches
Overall length: 51.18 inches
Weight: 26.4 ounces
Engine: Nelson .21
Construction: Carbon-fiber fuselage, balsa, plywood
Finish: Ultra-light film, epoxy paint
Other: Seelig timer or Texas Timers 3F-1, four-function conversion kit
The
Super
Marval
560
28 MODEL AVIATION
06sig1.QXD 4/22/09 2:29 PM Page 28
five or six points on the tube, roughly 1/4 inch behind the backside
of the firewall, that will not interfere with previously installed
hardware. Drill shallow 1/4-inch-diameter holes through the tube into
the plug with a 13/64 bit.
Put a drop of epoxy in each drilled hole, and lightly drive a 3/8-
inch-long, 13/64 dowel into the holes, leaving approximately 1/8 inch of
the dowel sticking out above the tube. These dowels will pin the plug
and firewall to the tube, to assure that the engine is secure on the front
of the tube.
To complete the front end, use cyanoacrylate to adhere small balsa
wedges, which are approximately 13/4 inches long and 1/4 inch high, to
the nose of the tube, against the back of the firewall, and on each side
of the dowels.
Fill spaces between the wedges with carpenter’s wood filler, and
then sand the front of the tube until smooth. Apply six to eight strips
of fiberglass to the front end of the tube, and spread epoxy on the front
3 inches of the tube and the firewall.
Place a piece of waxed paper on the firewall. Attach the engine
mount to the firewall using the 4-40 bolts, which have had the threads
coated with a thick grease, to prevent the epoxy from sticking to the
bolts and the T-nuts. Tighten the 4-40 bolts and hang the fuselage
nose-down to cure.
When dry, remove the bolts, engine mount, and waxed paper. Sand
A small box to house the Walston radio transmitter is installed in
the left side of the pylon; an exit tube runs from the back of the
box out the rear.
Sand the fuselage smooth prior to any installation. The engine
assembly is aligned with quadrant marks and pinned with dowel
rods epoxied into several points.
The engine mount is flaired into the fuselage with firm balsa; the
wood grain running lengthwise increases the airframe’s torqueload
strength.
To accommodate the VIT hardware, the stabilizer’s center rib will
support the stabilizer pivot wire, hold-down rubber-band hook,
bunt line, and glide-DT line.
To ensure the integrity of the epoxy joint between the firewall and
plug, mount a 4-40 Phillips-head bolt with washers and nut through
both the firewall and plug (countersunk both front and back). Tighten
them so they cannot come apart.
Place the engine mount on the firewall, and place a drop of thin
cyanoacrylate glue in the joint. Put the unit in a drill press and make
the four mounting holes for the 4-40 mounting bolts. After slightly
countersinking the holes on the back of the firewall, put T-nuts in the
holes and tighten the 4-40 bolts to seat them.
Place the firewall assembly in a machinist’s vise and drill a 1/4-
inch-diameter hole at an angle from the lower left edge of the engine
mount (near the landing skid) to a point near the center of the plug.
This hole serves as the access to the fuel compartment and fuel
bladder.
You can separate the engine mount from the firewall by forcing a
knife blade a short distance in between the two.
Sand the front of the carbon-fiber fuselage tube square to the
thrustline. Carefully sand roughly an inch of the inside of the tube to
remove any mold-release residue and clean with acetone.
Brush epoxy onto the outside of the plug and the inside of the tube.
Mate the two parts, taking care to line up the top and bottom marks of
the firewall and tube.
After the epoxy has cured for at least 24 hours, carefully choose
June 2009 29
06sig1.QXD 4/22/09 3:33 PM Page 29
For this article I used the popular Seelig timer, which is no
longer available new. A suitable substitute is the Texas Timers’
3F-1, modified with the available four-function conversion kit.
Set the timer disks beginning with the fuel shutoff wire under
the first disk. Let the timer run until the wire just jumps out from
under the notch in the disk. Halt the timer by using the start/stop
plunger.
Loosen the small nut holding the disks. While holding the
bottom disk, rotate the second and third disk so that the notch in
the top disk is roughly 1/16 inch from the end of the power-line
trip wire and the notch in the middle disk is 1/8 inch from the
bunt-line trip wire. Retighten the small nut while holding all the
disks in place.
The stabilizer is installed and all timer lines are connected.
The timer is fully wound, set on a short engine-run mark, and
cycled to see how things work.
If they work correctly, the engine cutoff wire should
escape the first disk at approximately two seconds. A second
later, the power line should release and the stabilizer should snap
down to the bunt position. Then one second later, the bunt line
should release the stabilizer, which will jump up and be stopped
by the glide adjustment nut.
As the timer continues to run, the DT release wire will follow
the grooves in the timer scroll until it reaches the exit point, at
which time that line is released. The cycle is completed when the
timer is reset to the two-second mark and the timer is rewound.
Now the wing should be mounted on its platform and the
bunt line to the stabilizer released. The stabilizer will rise to the
glide-DT stop nut.
Test-glide the aircraft. Adjust the stop nut as needed to obtain
a safe, floating glide. The model should be ready for short power
flights as you begin trimming.
If possible, have a fellow modeler who flies bunters do a
preflight check of your airplane and be present for your first few
power flights. When you are ready for the first flight, the
observer should be 30-40 feet away from the launch site so that
he/she has a different perspective of the model than you do as it
ascends.
This second opinion about when and if the model leaves the
expected flight path and whether it begins as a turn or a pitch
over or back is critical in knowing what adjustments need to be
made. Rotating the power-adjustment screw for one-eighth or
one-quarter turn is usually all the adjustment necessary for pitch
corrections, and small adjustments of the left rudder tab usually
take care of excess turn.
When making the first few flights, hook up only the engine
cutoff line, the power line, and the rudder line to the timer. The
bunt line and the glide-DT line are permitted to hang loose.
This arrangement lets you have a short engine run and a
small selected amount of left rudder for the first flight. You can
observe the pattern of the flight. Then the aircraft goes directly
to a quick DT.
Upon retrieval, set the timer to the engine run time you are
using and wind it fully. Reattach the lines to the timer, and make
any necessary adjustments.
Continue the test flights until the model is flying a straight-up
pattern. Now engine run times can be increased in small
increments and proper adjustments can be made so that the
airplane stays on pattern until the engine stops.
On the first bunting flight, hook up the bunt line but leave the
glide-DT line hanging loose. This permits you to observe the
bunt’s force and duration.
Did the model go too far over or not far enough? Does the
bunt need to be held longer or held for a shorter period? You can
make the needed adjustments by carefully loosening the small
nut on the Seelig disk, slightly moving the appropriate disk, and
retightening the nut.
When the bunt looks good, it is time to check the airplane’s
glide. Hook up all the lines to the timer. Loosen the nut holding
the DT scroll on the timer and reposition it so that the wire in the
scroll grooves will escape nearly 15 seconds after the engine is
stopped. Retighten the scroll nut. The model is flown with a
four- or five-second engine run, to assure that it has plenty of
altitude for the first test glide.
Assuming that the power pattern is good and the bunt is
timely and correctly done, the bunt line will release the stabilizer
so that it pops up and is stopped by the glide adjustment nut.
Observe the glide and make minor adjustments with the glide
adjustment nut as needed.
When you are satisfied that the glide is safe, loosen the scroll
nut again and set the scroll’s exit point so that when the DT wire
is placed in the proper groove, DT will occur at approximately
2:05. The glide is now fine-tuned. MA
—Marvin Mace
Trimming
a Bunter
30 MODEL AVIATION
06sig1.QXD 4/22/09 2:32 PM Page 30
away any excess epoxy, and sand the front of
the fuselage until smooth.
Rudder: The rudder’s size and shape is
important, but how you build it is your
choice. I cut mine to shape from a sheet of 1/8
balsa and cyanoacrylate-glue three layers of
1/64 plywood that are 1/8 inch wide around the
perimeter.
I sand the rudder to a streamlined shape.
Then I cover it with fiberglass cloth using
epoxy, which has Model Research Labs
fluorescent red pigment dissolved in it for
visibility.
Use whatever system of rudder control
you are comfortable with, but make sure it is
screw-adjustable for left tab in the tab power
mode and right tab in the glide.
The rear of the rudder is located 5 inches
from the rear of the fuselage. Before
mounting the rudder, using the top fuselage
line as a guide, randomly drill eight to 10 1/16-
inch-diameter holes along the top of the
fuselage where the rudder will be placed.
Using a No. 50 wire drill, carefully make a
similar number of holes in the bottom of the
rudder.
Cut and remove the masking tape where
the rudder will be mounted. Lightly sand the
top of the fuselage and clean it with acetone.
Mount the rudder directly on top of the
fuselage with a bead of epoxy on both the top
of the fuselage and the bottom of the rudder,
so that the adhesive is forced into the small
holes when they are pressed together. This
results in a strong joint.
Using the aluminum angle, the Hinson
Alignment Jig system, and a couple of
drafting triangles will ensure that the rudder is
properly aligned on the top of the tube.
Stabilizer and Stabilizer Mount: The
stabilizer’s construction is straightforward. A
couple of modifications are made to
accommodate the Variable Incidence
Tailplane (VIT) hardware.
The stabilizer’s center rib is cut from a
medium-light sheet of 1/2 balsa. This rib
supports the stabilizer pivot wire, the holddown
rubber-band hook, the bunt line, the
glide-DT line, and, on the underside of the
rib, a small stainless-steel plate.
The VIT system’s power-adjustment
screw rests on the steel plate. The single rib
provides the strength required to maintain the
stabilizer’s integrity for hundreds of bunts.
A portion of the stabilizer’s LE and
approximately 3/8 inch of the center rib are
removed to permit the installation of a piece
of .062 music wire, which will be fitted into
the groove in the back of the Oliver stabilizer
mount.
That short piece of music wire is supported
June 2009 31
Full-Size Plans Available—see page 183
06sig1.QXD 4/22/09 3:31 PM Page 31
in the stabilizer LE by 1/16 plywood half
ribs and is tricky to install. When the half
ribs are made, holes slightly larger than
the .062 music wire are drilled in each of
the two, approximately 1/8 inch from the
front edge and centered top to bottom.
Then the half ribs are installed in the front
part of the stabilizer, which has been cut
to fit the Oliver stabilizer mount.
Sharpen a 1/2-inch piece of .062 music
wire and insert it into the half rib holes, to
increase the depth of the holes in the balsa
LE. Cut another piece of .062 music wire
to 11/2 inches, and slightly sharpen both
ends. Grasp this wire portion with pliers
and ease one end a short distance into one
of the holes in the half rib.
When the other end clears the opposite
short rib, maneuver the other end into the
opposite hole. The wire can be slid back
and forth, and a drop of epoxy is put in
each hole. Center the wire and set the
stabilizer aside for the epoxy to cure.
The stabilizer is completed when a
cutout is made on the centerline of the
thick rib for the glide-DT post and the
stabilizer capture button. Epoxy a small
stainless-steel plate, made from a razor
blade, to the underside of the rib, just
behind the stabilizer-capture button hole.
Drill a small hole on the centerline of
the wide rib, just behind the front spar,
and epoxy a short piece of dowel in the
hole, to serve as a hook for the rubber
bands that hold the stabilizer.
When you epoxy the stabilizer mount
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in position, be sure to put the stabilizer in
its mount and place the fuselage tube in
the aluminum angle so the stabilizer mount
can be aligned 90° from the rudder. Use a
bubble level on the stabilizer to ensure
accurate positioning. The LE of the
stabilizer mount should be located
approximately 1 inch behind the rudder.
Ken Oliver makes a well-constructed,
efficient stabilizer mount, and it is
designed for bunting models. Judiciously
sanding the mounting hole in the base will
increase the inner diameter and provide a
perfect fit on the tube.
The stabilizer mount’s exact location
will be determined after the completed
stabilizer is fitted on the fuselage with the
VIT system in place. When positioned
properly, the mount will be roughly 31/2
inches from the end of the tube.
Lynch VIT Assembly: I like the VIT unit
that Bill Lynch, an excellent California
Power flier, developed, because it is
located at the end of the fuselage and is
trouble free when properly installed and
rigged. It also permits visual inspection of
important VIT system parts after you have
attached the lines to the Seelig timer and
before you fly the model. The information
brochure Bill provides with his unit is
invaluable when installing it and its lines.
Using the top line marked on the tube,
use the cutoff wheel to make a slice that is
nearly as long and as wide as the top of the
VIT frame (less the front tang). Use a
small file to enlarge the cutout so that the
VIT frame fits.
It is now necessary to mount a short
piece of 3/32-inch-diameter aluminum
tubing through the fuselage at a location so
that the notch in the VIT frame will fit
perfectly on the tubing when the short tang
bolt is tightened.
To determine where the holes for the
3/32 tubing are located on the sides of the
fuselage, I start with my best guess, use a
tiny drill bit, and enlarge the holes in the
proper direction until the tubing is a
perfect fit in the notch of the VIT unit.
When I find the proper location, I install
the 3/32 tubing (which is slightly longer
than the fuselage tube is wide) and epoxy
it in place (both on the inside and outside
of the fuselage).
When cured, slip the VIT frame into
position with the notch over the 3/32
aluminum tube. Drill a small hole in the
top of the fuselage, matching the hole in
the tang.
Screw a 1/4-inch-long 2-56 bolt, on
which you place a small flat washer and a
lock washer, through the hole in the top of
the tube and into the hole in the tang of the
frame, so that the frame is held firmly in
place when the bolt is tightened.
Wing: The balsa D-box wing spans 72
inches and is constructed in five panels.
The main spar is an I-beam with 1/4 x .007
carbon-fiber strips on the insides of the 1/4
x 1/8 balsa spar caps.
Covered with ultra-light plastic film
and with balsa Hoerner-type tips, the wing
weighs 8.8 ounces. It is dead stiff, as it
must be.
Pylon Construction and Attachment: The
pylon is constructed using a backbone of
1/8 square balsa, to which formers are
attached. The bottom former is made from
1/2 or 5/8 balsa, while the middle and top
formers are 1/8 balsa.
A small box to house the Walston radio
transmitter is installed in the left side of
the pylon with an exit tube running from
the back of the box out the rear of the
pylon. Then the pylon is covered with 1/16
balsa sheet. Cover the left side of the pylon
first, so that the hole for the transmitter box
can be easily marked from the backside
and then cut out.
The bottom of the pylon must be sanded
to a curved shape so that it will fit against
the fuselage tube. You can do this by
wrapping a sheet of 100-grit sandpaper
around the fuselage and then sliding the
base of the pylon back and forth in a
straight line over the sandpaper, to remove
the excess balsa. It is difficult, but it works
and, finally, a good fit is achieved.
Put the pylon on the fuselage using a
couple of rubber bands to hold it. Check to
see what incidence is on the wing platform.
To do so, return the fuselage to the
aluminum angle and jack up the rear of the
tube until its centerline is parallel to the
top of your workbench. Using an accurate
ruler, measure the distance from the top of
the table to the front and rear of the wing
platform.
If the front is roughly 1/8 inch higher
than the rear, you are home free. If not,
you must continue the back-and-forth
sanding, with pressure applied as needed,
until the platform incidence is 1/8 inch.
With the correct wing incidence, the
model can be assembled and the final
pylon location can be determined.
Make a permanent mark on the edge of
the platform at 58% of the wing chord.
Install the engine, propeller, spinner, wire
skid, timer, and radio transmitter. The
wing with the pylon and stabilizer are
attached to the fuselage with rubber bands.
Balance the model at 58% of the wing
chord by sliding the wing pylon back and
forth on the tube until a balance point is
found and the fuselage is parallel to the
floor. Mark the masking tape on the top
line of the fuselage where the front and
back of the pylon are. Randomly drill a
series of small holes along the top line of
the fuselage between the marks, and drill
several small holes in the bottom of the
pylon.
Remove the masking tape where the
pylon is to be located. Lightly sand the top
of the tube, and clean it with acetone. Coat
the top of the fuselage and the bottom of
the pylon with epoxy, and join them. As
with the rudder, the adhesive will be
forced into the small drilled holes,
improving the joint strength.
Three or four strong rubber bands are
used to hold the pylon tightly to the
fuselage, and then it is placed in the
aluminum angle. Line up the pylon with
the remaining top line marks on the
fuselage and with the rudder while using a
bubble level on the top of the wing
platform. When everything is properly
aligned, allow the epoxy to cure for 24
hours.
When cured, fair the pylon into the
fuselage tube using a mixture of epoxy
and microballoon filler, and then sand.
Mask off the rudder, and paint the
fuselage. I prefer to use white epoxy paint
on the fuselage, because it is highly
visible and cooler in the summertime.
Flight Preparation: Before heading to
the flying field for the first test flight, it is
mandatory that you check the model, in
the shop, for decalage. To do this, draw a
48-inch straight line on the workbench.
Then lay the fuselage on its side, with its
centerline located precisely on the straight
line. Draw a line on the workbench from
the front to the back of the wing platform.
Go to the back of the fuselage, and
make a dot on the workbench that
corresponds with the wire groove of the
Oliver stabilizer mount. Using a drafting
triangle pressed against the top of the
power adjustment screw, make a mark
indicating the top of that screw.
Accurately measure the distance
between the front and back of the wing
platform to the fuselage centerline, and
measure from the two dots, which
represent the distance from the front and
back of the stabilizer to the centerline. The
difference between the measurements
represents the model’s decalage.
Recall that we built 1/8 inch of
incidence into the wing platform when we
mounted it on the fuselage. Since we
would like to start our trimming with 1/16
inch of decalage, we can adjust the power
adjustment screw up or down as needed to
achieve this 1/16 difference.
You should be ready to trim your Super
Marval for competition. Repeatable, safe
engine runs are extremely important—
especially at four and five seconds. The
penalty for overruns during flyoffs is a
zero time, and nothing could be worse. Err
on the side of a safe engine run.
You must keep your timer clean and
oiled and all of your model’s parts in
perfect shape and in good working order.
Have confidence in your timer and your
ability to accurately set it for any engine
run.
That confidence comes from making
many test flights with the help of fellow
modelers who know how to accurately
time an engine run. The watch starts when
the aircraft leaves the flier’s hand and ends
when you hear the engine’s last audible
power stroke.
I take this opportunity to acknowledge the
invaluable help and advice I have received
from my fellow bunters in the past few
years as I have tried to get up to speed.
Insights or clever ideas that I appear to
claim as my own are the result of
conversations I have had with guys such as
Doug Galbreath, Bill Lynch, Ken Oliver,
the late Bob Johannes, Dick Covalt, Bob
Mattes, Gil Robbins, Ronnie Thompson,
Don DeLoach, Faust Parker, Henry
Spence, Mark Troutman, Reid and Roger
Simpson, C.C. Johnson, and Dick Hall.
I also thank Larry Kruse for helping me
put this construction article together in a
format for publication. The Super Marval
is as much your model as it is mine. MA
Marvin Mace
107 Country Ln.
Seguin TX 78155
(830) 379-0036
[email protected]
Sources:
Seelig carbon-fiber tube:
Reid C. Simpson
115 Trail Ridge Dr.
Athens TX 75751
(903) 677-8525
[email protected]
Oliver stabilizer mount:
Ken Oliver
2213 El Cejo Cir.
Rancho Cordova CA 95670
(916) 363-2017
Lynch VIT system:
Bill Lynch
2279 Auburn Ravine Dr.
Lincoln CA 95648
(916) 645-3337
[email protected]
Alignment Jig:
Rex Hinson
1141 S. Waterview Dr.
Inverness FL 34450
(352) 344-5931
[email protected]
Red fluorescent pigment:
Model Research Labs/Curt Stevens
25108 Marguerite Parkway #160
Mission Viejo CA 92692
[email protected]
Walston Retrieval Systems:
Jim Walston
725 Coopers Lake Rd. SE
Smyrna GA 30082
(770) 434-4905
[email protected]
Texas Timers (Request model 3F 1 and
four-function conversion kit)
3317 Pine Timbers Dr.
Johnson City TN 37604
(423) 282-6423
www.texastimers.com
Edition: Model Aviation - 2009/06
Page Numbers: 26,27,28,29,30,31,32,34,36
The
Super
Marval
560
by Marvin Mace
An AMA
2007 Model
of the Year
26 MODEL AVIATION
THE SUPER MARVAL is not a Power model for beginners. It is a
fairly sophisticated bunting airplane that can be easily built and
flown by a modeler who has previously built and flown “locked-up”
Power models. If you make the investment of time and money to
construct a Super Marval, you will have a model that, if well built
and adjusted, is fun to fly and a competitive AMA Category III
performer.
I hope your competitive attitude will encourage you to master the
bunting technique. Perhaps the observations and confessions in this
article will encourage you if you have reservations about taking the
leap and sharing the challenge and joy a bunter offers. You probably
won’t be sorry if you do.
The use of a high-strength, round, lightweight carbon-fiber
fuselage raises building issues that do not occur with an all-balsa
fuselage. For safety reasons, special construction provisions must be
made to ensure the engine mounting’s integrity in the carbon-fiber
fuselage.
There are several building tools you will find useful for working
on this model: a scroll saw, a drill press, an electric hand drill, a disc
sander, a Dremel motor tool with a cutoff wheel, a 2-56 tap and
wrench, and a 5-foot-long, 2-inch aluminum 90° angle.
CONSTRUCTION
Carbon-Fiber Fuselage Preparation: I chose a carbon-fiber FIC
tailboom, made by Hans Seelig in Germany, for the fuselage. As
purchased, the tailboom is roughly 47.5 inches long and the outer
surface is a spiral wrap that must be sanded smooth to the touch
using 100-grit sandpaper.
06sig1.QXD 4/22/09 2:10 PM Page 26
Photos by the author and Larry Kruse
The Norvel .21 is the power plant of choice. The carbon-fiber fuselage is painted
brightly with a two-part fuelproof paint system such as epoxy.
The rudder’s size and shape are important, but how it’s built is
your choice. It is screw-adjustable for left tab in the power mode
and right tab in the glide.
The author holds his Super Marval under a shade tree while the
Texas sun blazes. The wing and stabilizer are covered with light
iron-on film.
Use the 5-foot aluminum angle and a couple of
Rex Hinson’s Alignment Jig plywood bulkheads to
mark 90° points on the round fuselage.
That usually takes one to two hours of vigorous sanding and is
best done outdoors, to avoid breathing the sanding dust. Wear a
mask, regardless of where you do this job.
Sand only until the tube is smooth to the touch. Do not overdo it.
When finished and cleaned with acetone, the spiral markings should
still be visible on the tube.
Place four strips of narrow masking tape on the top, bottom, left,
and right sides of the tube. Use the 5-foot aluminum angle and a
couple of Rex Hinson’s Alignment Jig plywood bulkheads to mark
the 90° points on the masking tape at the front and rear ends of the
tube.
Use a pen to draw straight lines on the tape, connecting the points.
The top line will be used to line up the firewall, wing pylon, stabilizer
mount, rudder, and bunt mechanism. The bottom line helps locate the
lower side of the timer cutout and the landing skid.
Add the Seelig timer mounting assembly to the fuselage. Put the
assembly in the fuselage and push it to a point where the center of the
timer box is 5 inches from the front of the tube. Use a motor tool with
a cutoff wheel to make a small opening in the lower quadrant of the
left side of the fuselage until you can see the timer box.
Rotate the assembly until the bottom edge is on the bottom line of
the fuselage. Enlarge the opening as necessary with the cutoff wheel.
Firewall Plug and Front-End Fabrication: The firewall, engine
mounting system, landing skid, fuel access, and engine retaining
system are built as a unit. You can use a beam or backplate mount.
The firewall is 13/4 inches in diameter; it is made from two pieces of
1/8 plywood and a 1/32 plywood spacer.
Use epoxy to join the front disk and the 1/32-inch disk. When
cured, the four quadrant lines on the sides of the fuselage are marked
on the edge of the disks. The face of the front disk is marked with the
upper end of the landing skid’s shape, and the skid’s shape is cut out
with a scroll saw.
This cutout permits the landing skid to be retained, removed,
straightened, or replaced by removing the engine mount. Epoxy the
rear 1/8 plywood disk to the front piece and place the assembly in a Cclamp
to cure.
Make the two 1/4-inch, five-ply plywood disks that will fit snugly
inside the fuselage. They are epoxied and C-clamped together to cure.
When dry, the 1/2-inch plug is epoxied to the firewall and C-clamped
until cured.
June 2009 27
06sig1.QXD 4/22/09 3:21 PM Page 27
The pylon is constructed using a backbone of 1/8 square balsa, to
which formers are attached. The bottom former is made from 1/2
or 5/8 balsa, while the middle and top formers are 1/8 balsa.
The plywood firewall sandwich forms the engine mount bolt
locations and undercarriage strut location. The plug portion is
relieved for the fuel-line pass.
The stabilizer is straightforward in its construction. The Oliver
stabilizer mount is modified to accommodate VIT hardware. The Seelig timer mounting assembly is put in the fuselage and
pushed to a point where the center of the timer box is 5 inches
from the front of the tube.
Type: A/B FF Gas
Skill level: Advanced
Wingspan: 72.17 inches
Wing area: 557 square inches
Stabilizer area: 94 square inches
Overall length: 51.18 inches
Weight: 26.4 ounces
Engine: Nelson .21
Construction: Carbon-fiber fuselage, balsa, plywood
Finish: Ultra-light film, epoxy paint
Other: Seelig timer or Texas Timers 3F-1, four-function conversion kit
The
Super
Marval
560
28 MODEL AVIATION
06sig1.QXD 4/22/09 2:29 PM Page 28
five or six points on the tube, roughly 1/4 inch behind the backside
of the firewall, that will not interfere with previously installed
hardware. Drill shallow 1/4-inch-diameter holes through the tube into
the plug with a 13/64 bit.
Put a drop of epoxy in each drilled hole, and lightly drive a 3/8-
inch-long, 13/64 dowel into the holes, leaving approximately 1/8 inch of
the dowel sticking out above the tube. These dowels will pin the plug
and firewall to the tube, to assure that the engine is secure on the front
of the tube.
To complete the front end, use cyanoacrylate to adhere small balsa
wedges, which are approximately 13/4 inches long and 1/4 inch high, to
the nose of the tube, against the back of the firewall, and on each side
of the dowels.
Fill spaces between the wedges with carpenter’s wood filler, and
then sand the front of the tube until smooth. Apply six to eight strips
of fiberglass to the front end of the tube, and spread epoxy on the front
3 inches of the tube and the firewall.
Place a piece of waxed paper on the firewall. Attach the engine
mount to the firewall using the 4-40 bolts, which have had the threads
coated with a thick grease, to prevent the epoxy from sticking to the
bolts and the T-nuts. Tighten the 4-40 bolts and hang the fuselage
nose-down to cure.
When dry, remove the bolts, engine mount, and waxed paper. Sand
A small box to house the Walston radio transmitter is installed in
the left side of the pylon; an exit tube runs from the back of the
box out the rear.
Sand the fuselage smooth prior to any installation. The engine
assembly is aligned with quadrant marks and pinned with dowel
rods epoxied into several points.
The engine mount is flaired into the fuselage with firm balsa; the
wood grain running lengthwise increases the airframe’s torqueload
strength.
To accommodate the VIT hardware, the stabilizer’s center rib will
support the stabilizer pivot wire, hold-down rubber-band hook,
bunt line, and glide-DT line.
To ensure the integrity of the epoxy joint between the firewall and
plug, mount a 4-40 Phillips-head bolt with washers and nut through
both the firewall and plug (countersunk both front and back). Tighten
them so they cannot come apart.
Place the engine mount on the firewall, and place a drop of thin
cyanoacrylate glue in the joint. Put the unit in a drill press and make
the four mounting holes for the 4-40 mounting bolts. After slightly
countersinking the holes on the back of the firewall, put T-nuts in the
holes and tighten the 4-40 bolts to seat them.
Place the firewall assembly in a machinist’s vise and drill a 1/4-
inch-diameter hole at an angle from the lower left edge of the engine
mount (near the landing skid) to a point near the center of the plug.
This hole serves as the access to the fuel compartment and fuel
bladder.
You can separate the engine mount from the firewall by forcing a
knife blade a short distance in between the two.
Sand the front of the carbon-fiber fuselage tube square to the
thrustline. Carefully sand roughly an inch of the inside of the tube to
remove any mold-release residue and clean with acetone.
Brush epoxy onto the outside of the plug and the inside of the tube.
Mate the two parts, taking care to line up the top and bottom marks of
the firewall and tube.
After the epoxy has cured for at least 24 hours, carefully choose
June 2009 29
06sig1.QXD 4/22/09 3:33 PM Page 29
For this article I used the popular Seelig timer, which is no
longer available new. A suitable substitute is the Texas Timers’
3F-1, modified with the available four-function conversion kit.
Set the timer disks beginning with the fuel shutoff wire under
the first disk. Let the timer run until the wire just jumps out from
under the notch in the disk. Halt the timer by using the start/stop
plunger.
Loosen the small nut holding the disks. While holding the
bottom disk, rotate the second and third disk so that the notch in
the top disk is roughly 1/16 inch from the end of the power-line
trip wire and the notch in the middle disk is 1/8 inch from the
bunt-line trip wire. Retighten the small nut while holding all the
disks in place.
The stabilizer is installed and all timer lines are connected.
The timer is fully wound, set on a short engine-run mark, and
cycled to see how things work.
If they work correctly, the engine cutoff wire should
escape the first disk at approximately two seconds. A second
later, the power line should release and the stabilizer should snap
down to the bunt position. Then one second later, the bunt line
should release the stabilizer, which will jump up and be stopped
by the glide adjustment nut.
As the timer continues to run, the DT release wire will follow
the grooves in the timer scroll until it reaches the exit point, at
which time that line is released. The cycle is completed when the
timer is reset to the two-second mark and the timer is rewound.
Now the wing should be mounted on its platform and the
bunt line to the stabilizer released. The stabilizer will rise to the
glide-DT stop nut.
Test-glide the aircraft. Adjust the stop nut as needed to obtain
a safe, floating glide. The model should be ready for short power
flights as you begin trimming.
If possible, have a fellow modeler who flies bunters do a
preflight check of your airplane and be present for your first few
power flights. When you are ready for the first flight, the
observer should be 30-40 feet away from the launch site so that
he/she has a different perspective of the model than you do as it
ascends.
This second opinion about when and if the model leaves the
expected flight path and whether it begins as a turn or a pitch
over or back is critical in knowing what adjustments need to be
made. Rotating the power-adjustment screw for one-eighth or
one-quarter turn is usually all the adjustment necessary for pitch
corrections, and small adjustments of the left rudder tab usually
take care of excess turn.
When making the first few flights, hook up only the engine
cutoff line, the power line, and the rudder line to the timer. The
bunt line and the glide-DT line are permitted to hang loose.
This arrangement lets you have a short engine run and a
small selected amount of left rudder for the first flight. You can
observe the pattern of the flight. Then the aircraft goes directly
to a quick DT.
Upon retrieval, set the timer to the engine run time you are
using and wind it fully. Reattach the lines to the timer, and make
any necessary adjustments.
Continue the test flights until the model is flying a straight-up
pattern. Now engine run times can be increased in small
increments and proper adjustments can be made so that the
airplane stays on pattern until the engine stops.
On the first bunting flight, hook up the bunt line but leave the
glide-DT line hanging loose. This permits you to observe the
bunt’s force and duration.
Did the model go too far over or not far enough? Does the
bunt need to be held longer or held for a shorter period? You can
make the needed adjustments by carefully loosening the small
nut on the Seelig disk, slightly moving the appropriate disk, and
retightening the nut.
When the bunt looks good, it is time to check the airplane’s
glide. Hook up all the lines to the timer. Loosen the nut holding
the DT scroll on the timer and reposition it so that the wire in the
scroll grooves will escape nearly 15 seconds after the engine is
stopped. Retighten the scroll nut. The model is flown with a
four- or five-second engine run, to assure that it has plenty of
altitude for the first test glide.
Assuming that the power pattern is good and the bunt is
timely and correctly done, the bunt line will release the stabilizer
so that it pops up and is stopped by the glide adjustment nut.
Observe the glide and make minor adjustments with the glide
adjustment nut as needed.
When you are satisfied that the glide is safe, loosen the scroll
nut again and set the scroll’s exit point so that when the DT wire
is placed in the proper groove, DT will occur at approximately
2:05. The glide is now fine-tuned. MA
—Marvin Mace
Trimming
a Bunter
30 MODEL AVIATION
06sig1.QXD 4/22/09 2:32 PM Page 30
away any excess epoxy, and sand the front of
the fuselage until smooth.
Rudder: The rudder’s size and shape is
important, but how you build it is your
choice. I cut mine to shape from a sheet of 1/8
balsa and cyanoacrylate-glue three layers of
1/64 plywood that are 1/8 inch wide around the
perimeter.
I sand the rudder to a streamlined shape.
Then I cover it with fiberglass cloth using
epoxy, which has Model Research Labs
fluorescent red pigment dissolved in it for
visibility.
Use whatever system of rudder control
you are comfortable with, but make sure it is
screw-adjustable for left tab in the tab power
mode and right tab in the glide.
The rear of the rudder is located 5 inches
from the rear of the fuselage. Before
mounting the rudder, using the top fuselage
line as a guide, randomly drill eight to 10 1/16-
inch-diameter holes along the top of the
fuselage where the rudder will be placed.
Using a No. 50 wire drill, carefully make a
similar number of holes in the bottom of the
rudder.
Cut and remove the masking tape where
the rudder will be mounted. Lightly sand the
top of the fuselage and clean it with acetone.
Mount the rudder directly on top of the
fuselage with a bead of epoxy on both the top
of the fuselage and the bottom of the rudder,
so that the adhesive is forced into the small
holes when they are pressed together. This
results in a strong joint.
Using the aluminum angle, the Hinson
Alignment Jig system, and a couple of
drafting triangles will ensure that the rudder is
properly aligned on the top of the tube.
Stabilizer and Stabilizer Mount: The
stabilizer’s construction is straightforward. A
couple of modifications are made to
accommodate the Variable Incidence
Tailplane (VIT) hardware.
The stabilizer’s center rib is cut from a
medium-light sheet of 1/2 balsa. This rib
supports the stabilizer pivot wire, the holddown
rubber-band hook, the bunt line, the
glide-DT line, and, on the underside of the
rib, a small stainless-steel plate.
The VIT system’s power-adjustment
screw rests on the steel plate. The single rib
provides the strength required to maintain the
stabilizer’s integrity for hundreds of bunts.
A portion of the stabilizer’s LE and
approximately 3/8 inch of the center rib are
removed to permit the installation of a piece
of .062 music wire, which will be fitted into
the groove in the back of the Oliver stabilizer
mount.
That short piece of music wire is supported
June 2009 31
Full-Size Plans Available—see page 183
06sig1.QXD 4/22/09 3:31 PM Page 31
in the stabilizer LE by 1/16 plywood half
ribs and is tricky to install. When the half
ribs are made, holes slightly larger than
the .062 music wire are drilled in each of
the two, approximately 1/8 inch from the
front edge and centered top to bottom.
Then the half ribs are installed in the front
part of the stabilizer, which has been cut
to fit the Oliver stabilizer mount.
Sharpen a 1/2-inch piece of .062 music
wire and insert it into the half rib holes, to
increase the depth of the holes in the balsa
LE. Cut another piece of .062 music wire
to 11/2 inches, and slightly sharpen both
ends. Grasp this wire portion with pliers
and ease one end a short distance into one
of the holes in the half rib.
When the other end clears the opposite
short rib, maneuver the other end into the
opposite hole. The wire can be slid back
and forth, and a drop of epoxy is put in
each hole. Center the wire and set the
stabilizer aside for the epoxy to cure.
The stabilizer is completed when a
cutout is made on the centerline of the
thick rib for the glide-DT post and the
stabilizer capture button. Epoxy a small
stainless-steel plate, made from a razor
blade, to the underside of the rib, just
behind the stabilizer-capture button hole.
Drill a small hole on the centerline of
the wide rib, just behind the front spar,
and epoxy a short piece of dowel in the
hole, to serve as a hook for the rubber
bands that hold the stabilizer.
When you epoxy the stabilizer mount
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in position, be sure to put the stabilizer in
its mount and place the fuselage tube in
the aluminum angle so the stabilizer mount
can be aligned 90° from the rudder. Use a
bubble level on the stabilizer to ensure
accurate positioning. The LE of the
stabilizer mount should be located
approximately 1 inch behind the rudder.
Ken Oliver makes a well-constructed,
efficient stabilizer mount, and it is
designed for bunting models. Judiciously
sanding the mounting hole in the base will
increase the inner diameter and provide a
perfect fit on the tube.
The stabilizer mount’s exact location
will be determined after the completed
stabilizer is fitted on the fuselage with the
VIT system in place. When positioned
properly, the mount will be roughly 31/2
inches from the end of the tube.
Lynch VIT Assembly: I like the VIT unit
that Bill Lynch, an excellent California
Power flier, developed, because it is
located at the end of the fuselage and is
trouble free when properly installed and
rigged. It also permits visual inspection of
important VIT system parts after you have
attached the lines to the Seelig timer and
before you fly the model. The information
brochure Bill provides with his unit is
invaluable when installing it and its lines.
Using the top line marked on the tube,
use the cutoff wheel to make a slice that is
nearly as long and as wide as the top of the
VIT frame (less the front tang). Use a
small file to enlarge the cutout so that the
VIT frame fits.
It is now necessary to mount a short
piece of 3/32-inch-diameter aluminum
tubing through the fuselage at a location so
that the notch in the VIT frame will fit
perfectly on the tubing when the short tang
bolt is tightened.
To determine where the holes for the
3/32 tubing are located on the sides of the
fuselage, I start with my best guess, use a
tiny drill bit, and enlarge the holes in the
proper direction until the tubing is a
perfect fit in the notch of the VIT unit.
When I find the proper location, I install
the 3/32 tubing (which is slightly longer
than the fuselage tube is wide) and epoxy
it in place (both on the inside and outside
of the fuselage).
When cured, slip the VIT frame into
position with the notch over the 3/32
aluminum tube. Drill a small hole in the
top of the fuselage, matching the hole in
the tang.
Screw a 1/4-inch-long 2-56 bolt, on
which you place a small flat washer and a
lock washer, through the hole in the top of
the tube and into the hole in the tang of the
frame, so that the frame is held firmly in
place when the bolt is tightened.
Wing: The balsa D-box wing spans 72
inches and is constructed in five panels.
The main spar is an I-beam with 1/4 x .007
carbon-fiber strips on the insides of the 1/4
x 1/8 balsa spar caps.
Covered with ultra-light plastic film
and with balsa Hoerner-type tips, the wing
weighs 8.8 ounces. It is dead stiff, as it
must be.
Pylon Construction and Attachment: The
pylon is constructed using a backbone of
1/8 square balsa, to which formers are
attached. The bottom former is made from
1/2 or 5/8 balsa, while the middle and top
formers are 1/8 balsa.
A small box to house the Walston radio
transmitter is installed in the left side of
the pylon with an exit tube running from
the back of the box out the rear of the
pylon. Then the pylon is covered with 1/16
balsa sheet. Cover the left side of the pylon
first, so that the hole for the transmitter box
can be easily marked from the backside
and then cut out.
The bottom of the pylon must be sanded
to a curved shape so that it will fit against
the fuselage tube. You can do this by
wrapping a sheet of 100-grit sandpaper
around the fuselage and then sliding the
base of the pylon back and forth in a
straight line over the sandpaper, to remove
the excess balsa. It is difficult, but it works
and, finally, a good fit is achieved.
Put the pylon on the fuselage using a
couple of rubber bands to hold it. Check to
see what incidence is on the wing platform.
To do so, return the fuselage to the
aluminum angle and jack up the rear of the
tube until its centerline is parallel to the
top of your workbench. Using an accurate
ruler, measure the distance from the top of
the table to the front and rear of the wing
platform.
If the front is roughly 1/8 inch higher
than the rear, you are home free. If not,
you must continue the back-and-forth
sanding, with pressure applied as needed,
until the platform incidence is 1/8 inch.
With the correct wing incidence, the
model can be assembled and the final
pylon location can be determined.
Make a permanent mark on the edge of
the platform at 58% of the wing chord.
Install the engine, propeller, spinner, wire
skid, timer, and radio transmitter. The
wing with the pylon and stabilizer are
attached to the fuselage with rubber bands.
Balance the model at 58% of the wing
chord by sliding the wing pylon back and
forth on the tube until a balance point is
found and the fuselage is parallel to the
floor. Mark the masking tape on the top
line of the fuselage where the front and
back of the pylon are. Randomly drill a
series of small holes along the top line of
the fuselage between the marks, and drill
several small holes in the bottom of the
pylon.
Remove the masking tape where the
pylon is to be located. Lightly sand the top
of the tube, and clean it with acetone. Coat
the top of the fuselage and the bottom of
the pylon with epoxy, and join them. As
with the rudder, the adhesive will be
forced into the small drilled holes,
improving the joint strength.
Three or four strong rubber bands are
used to hold the pylon tightly to the
fuselage, and then it is placed in the
aluminum angle. Line up the pylon with
the remaining top line marks on the
fuselage and with the rudder while using a
bubble level on the top of the wing
platform. When everything is properly
aligned, allow the epoxy to cure for 24
hours.
When cured, fair the pylon into the
fuselage tube using a mixture of epoxy
and microballoon filler, and then sand.
Mask off the rudder, and paint the
fuselage. I prefer to use white epoxy paint
on the fuselage, because it is highly
visible and cooler in the summertime.
Flight Preparation: Before heading to
the flying field for the first test flight, it is
mandatory that you check the model, in
the shop, for decalage. To do this, draw a
48-inch straight line on the workbench.
Then lay the fuselage on its side, with its
centerline located precisely on the straight
line. Draw a line on the workbench from
the front to the back of the wing platform.
Go to the back of the fuselage, and
make a dot on the workbench that
corresponds with the wire groove of the
Oliver stabilizer mount. Using a drafting
triangle pressed against the top of the
power adjustment screw, make a mark
indicating the top of that screw.
Accurately measure the distance
between the front and back of the wing
platform to the fuselage centerline, and
measure from the two dots, which
represent the distance from the front and
back of the stabilizer to the centerline. The
difference between the measurements
represents the model’s decalage.
Recall that we built 1/8 inch of
incidence into the wing platform when we
mounted it on the fuselage. Since we
would like to start our trimming with 1/16
inch of decalage, we can adjust the power
adjustment screw up or down as needed to
achieve this 1/16 difference.
You should be ready to trim your Super
Marval for competition. Repeatable, safe
engine runs are extremely important—
especially at four and five seconds. The
penalty for overruns during flyoffs is a
zero time, and nothing could be worse. Err
on the side of a safe engine run.
You must keep your timer clean and
oiled and all of your model’s parts in
perfect shape and in good working order.
Have confidence in your timer and your
ability to accurately set it for any engine
run.
That confidence comes from making
many test flights with the help of fellow
modelers who know how to accurately
time an engine run. The watch starts when
the aircraft leaves the flier’s hand and ends
when you hear the engine’s last audible
power stroke.
I take this opportunity to acknowledge the
invaluable help and advice I have received
from my fellow bunters in the past few
years as I have tried to get up to speed.
Insights or clever ideas that I appear to
claim as my own are the result of
conversations I have had with guys such as
Doug Galbreath, Bill Lynch, Ken Oliver,
the late Bob Johannes, Dick Covalt, Bob
Mattes, Gil Robbins, Ronnie Thompson,
Don DeLoach, Faust Parker, Henry
Spence, Mark Troutman, Reid and Roger
Simpson, C.C. Johnson, and Dick Hall.
I also thank Larry Kruse for helping me
put this construction article together in a
format for publication. The Super Marval
is as much your model as it is mine. MA
Marvin Mace
107 Country Ln.
Seguin TX 78155
(830) 379-0036
[email protected]
Sources:
Seelig carbon-fiber tube:
Reid C. Simpson
115 Trail Ridge Dr.
Athens TX 75751
(903) 677-8525
[email protected]
Oliver stabilizer mount:
Ken Oliver
2213 El Cejo Cir.
Rancho Cordova CA 95670
(916) 363-2017
Lynch VIT system:
Bill Lynch
2279 Auburn Ravine Dr.
Lincoln CA 95648
(916) 645-3337
[email protected]
Alignment Jig:
Rex Hinson
1141 S. Waterview Dr.
Inverness FL 34450
(352) 344-5931
[email protected]
Red fluorescent pigment:
Model Research Labs/Curt Stevens
25108 Marguerite Parkway #160
Mission Viejo CA 92692
[email protected]
Walston Retrieval Systems:
Jim Walston
725 Coopers Lake Rd. SE
Smyrna GA 30082
(770) 434-4905
[email protected]
Texas Timers (Request model 3F 1 and
four-function conversion kit)
3317 Pine Timbers Dr.
Johnson City TN 37604
(423) 282-6423
www.texastimers.com
Edition: Model Aviation - 2009/06
Page Numbers: 26,27,28,29,30,31,32,34,36
The
Super
Marval
560
by Marvin Mace
An AMA
2007 Model
of the Year
26 MODEL AVIATION
THE SUPER MARVAL is not a Power model for beginners. It is a
fairly sophisticated bunting airplane that can be easily built and
flown by a modeler who has previously built and flown “locked-up”
Power models. If you make the investment of time and money to
construct a Super Marval, you will have a model that, if well built
and adjusted, is fun to fly and a competitive AMA Category III
performer.
I hope your competitive attitude will encourage you to master the
bunting technique. Perhaps the observations and confessions in this
article will encourage you if you have reservations about taking the
leap and sharing the challenge and joy a bunter offers. You probably
won’t be sorry if you do.
The use of a high-strength, round, lightweight carbon-fiber
fuselage raises building issues that do not occur with an all-balsa
fuselage. For safety reasons, special construction provisions must be
made to ensure the engine mounting’s integrity in the carbon-fiber
fuselage.
There are several building tools you will find useful for working
on this model: a scroll saw, a drill press, an electric hand drill, a disc
sander, a Dremel motor tool with a cutoff wheel, a 2-56 tap and
wrench, and a 5-foot-long, 2-inch aluminum 90° angle.
CONSTRUCTION
Carbon-Fiber Fuselage Preparation: I chose a carbon-fiber FIC
tailboom, made by Hans Seelig in Germany, for the fuselage. As
purchased, the tailboom is roughly 47.5 inches long and the outer
surface is a spiral wrap that must be sanded smooth to the touch
using 100-grit sandpaper.
06sig1.QXD 4/22/09 2:10 PM Page 26
Photos by the author and Larry Kruse
The Norvel .21 is the power plant of choice. The carbon-fiber fuselage is painted
brightly with a two-part fuelproof paint system such as epoxy.
The rudder’s size and shape are important, but how it’s built is
your choice. It is screw-adjustable for left tab in the power mode
and right tab in the glide.
The author holds his Super Marval under a shade tree while the
Texas sun blazes. The wing and stabilizer are covered with light
iron-on film.
Use the 5-foot aluminum angle and a couple of
Rex Hinson’s Alignment Jig plywood bulkheads to
mark 90° points on the round fuselage.
That usually takes one to two hours of vigorous sanding and is
best done outdoors, to avoid breathing the sanding dust. Wear a
mask, regardless of where you do this job.
Sand only until the tube is smooth to the touch. Do not overdo it.
When finished and cleaned with acetone, the spiral markings should
still be visible on the tube.
Place four strips of narrow masking tape on the top, bottom, left,
and right sides of the tube. Use the 5-foot aluminum angle and a
couple of Rex Hinson’s Alignment Jig plywood bulkheads to mark
the 90° points on the masking tape at the front and rear ends of the
tube.
Use a pen to draw straight lines on the tape, connecting the points.
The top line will be used to line up the firewall, wing pylon, stabilizer
mount, rudder, and bunt mechanism. The bottom line helps locate the
lower side of the timer cutout and the landing skid.
Add the Seelig timer mounting assembly to the fuselage. Put the
assembly in the fuselage and push it to a point where the center of the
timer box is 5 inches from the front of the tube. Use a motor tool with
a cutoff wheel to make a small opening in the lower quadrant of the
left side of the fuselage until you can see the timer box.
Rotate the assembly until the bottom edge is on the bottom line of
the fuselage. Enlarge the opening as necessary with the cutoff wheel.
Firewall Plug and Front-End Fabrication: The firewall, engine
mounting system, landing skid, fuel access, and engine retaining
system are built as a unit. You can use a beam or backplate mount.
The firewall is 13/4 inches in diameter; it is made from two pieces of
1/8 plywood and a 1/32 plywood spacer.
Use epoxy to join the front disk and the 1/32-inch disk. When
cured, the four quadrant lines on the sides of the fuselage are marked
on the edge of the disks. The face of the front disk is marked with the
upper end of the landing skid’s shape, and the skid’s shape is cut out
with a scroll saw.
This cutout permits the landing skid to be retained, removed,
straightened, or replaced by removing the engine mount. Epoxy the
rear 1/8 plywood disk to the front piece and place the assembly in a Cclamp
to cure.
Make the two 1/4-inch, five-ply plywood disks that will fit snugly
inside the fuselage. They are epoxied and C-clamped together to cure.
When dry, the 1/2-inch plug is epoxied to the firewall and C-clamped
until cured.
June 2009 27
06sig1.QXD 4/22/09 3:21 PM Page 27
The pylon is constructed using a backbone of 1/8 square balsa, to
which formers are attached. The bottom former is made from 1/2
or 5/8 balsa, while the middle and top formers are 1/8 balsa.
The plywood firewall sandwich forms the engine mount bolt
locations and undercarriage strut location. The plug portion is
relieved for the fuel-line pass.
The stabilizer is straightforward in its construction. The Oliver
stabilizer mount is modified to accommodate VIT hardware. The Seelig timer mounting assembly is put in the fuselage and
pushed to a point where the center of the timer box is 5 inches
from the front of the tube.
Type: A/B FF Gas
Skill level: Advanced
Wingspan: 72.17 inches
Wing area: 557 square inches
Stabilizer area: 94 square inches
Overall length: 51.18 inches
Weight: 26.4 ounces
Engine: Nelson .21
Construction: Carbon-fiber fuselage, balsa, plywood
Finish: Ultra-light film, epoxy paint
Other: Seelig timer or Texas Timers 3F-1, four-function conversion kit
The
Super
Marval
560
28 MODEL AVIATION
06sig1.QXD 4/22/09 2:29 PM Page 28
five or six points on the tube, roughly 1/4 inch behind the backside
of the firewall, that will not interfere with previously installed
hardware. Drill shallow 1/4-inch-diameter holes through the tube into
the plug with a 13/64 bit.
Put a drop of epoxy in each drilled hole, and lightly drive a 3/8-
inch-long, 13/64 dowel into the holes, leaving approximately 1/8 inch of
the dowel sticking out above the tube. These dowels will pin the plug
and firewall to the tube, to assure that the engine is secure on the front
of the tube.
To complete the front end, use cyanoacrylate to adhere small balsa
wedges, which are approximately 13/4 inches long and 1/4 inch high, to
the nose of the tube, against the back of the firewall, and on each side
of the dowels.
Fill spaces between the wedges with carpenter’s wood filler, and
then sand the front of the tube until smooth. Apply six to eight strips
of fiberglass to the front end of the tube, and spread epoxy on the front
3 inches of the tube and the firewall.
Place a piece of waxed paper on the firewall. Attach the engine
mount to the firewall using the 4-40 bolts, which have had the threads
coated with a thick grease, to prevent the epoxy from sticking to the
bolts and the T-nuts. Tighten the 4-40 bolts and hang the fuselage
nose-down to cure.
When dry, remove the bolts, engine mount, and waxed paper. Sand
A small box to house the Walston radio transmitter is installed in
the left side of the pylon; an exit tube runs from the back of the
box out the rear.
Sand the fuselage smooth prior to any installation. The engine
assembly is aligned with quadrant marks and pinned with dowel
rods epoxied into several points.
The engine mount is flaired into the fuselage with firm balsa; the
wood grain running lengthwise increases the airframe’s torqueload
strength.
To accommodate the VIT hardware, the stabilizer’s center rib will
support the stabilizer pivot wire, hold-down rubber-band hook,
bunt line, and glide-DT line.
To ensure the integrity of the epoxy joint between the firewall and
plug, mount a 4-40 Phillips-head bolt with washers and nut through
both the firewall and plug (countersunk both front and back). Tighten
them so they cannot come apart.
Place the engine mount on the firewall, and place a drop of thin
cyanoacrylate glue in the joint. Put the unit in a drill press and make
the four mounting holes for the 4-40 mounting bolts. After slightly
countersinking the holes on the back of the firewall, put T-nuts in the
holes and tighten the 4-40 bolts to seat them.
Place the firewall assembly in a machinist’s vise and drill a 1/4-
inch-diameter hole at an angle from the lower left edge of the engine
mount (near the landing skid) to a point near the center of the plug.
This hole serves as the access to the fuel compartment and fuel
bladder.
You can separate the engine mount from the firewall by forcing a
knife blade a short distance in between the two.
Sand the front of the carbon-fiber fuselage tube square to the
thrustline. Carefully sand roughly an inch of the inside of the tube to
remove any mold-release residue and clean with acetone.
Brush epoxy onto the outside of the plug and the inside of the tube.
Mate the two parts, taking care to line up the top and bottom marks of
the firewall and tube.
After the epoxy has cured for at least 24 hours, carefully choose
June 2009 29
06sig1.QXD 4/22/09 3:33 PM Page 29
For this article I used the popular Seelig timer, which is no
longer available new. A suitable substitute is the Texas Timers’
3F-1, modified with the available four-function conversion kit.
Set the timer disks beginning with the fuel shutoff wire under
the first disk. Let the timer run until the wire just jumps out from
under the notch in the disk. Halt the timer by using the start/stop
plunger.
Loosen the small nut holding the disks. While holding the
bottom disk, rotate the second and third disk so that the notch in
the top disk is roughly 1/16 inch from the end of the power-line
trip wire and the notch in the middle disk is 1/8 inch from the
bunt-line trip wire. Retighten the small nut while holding all the
disks in place.
The stabilizer is installed and all timer lines are connected.
The timer is fully wound, set on a short engine-run mark, and
cycled to see how things work.
If they work correctly, the engine cutoff wire should
escape the first disk at approximately two seconds. A second
later, the power line should release and the stabilizer should snap
down to the bunt position. Then one second later, the bunt line
should release the stabilizer, which will jump up and be stopped
by the glide adjustment nut.
As the timer continues to run, the DT release wire will follow
the grooves in the timer scroll until it reaches the exit point, at
which time that line is released. The cycle is completed when the
timer is reset to the two-second mark and the timer is rewound.
Now the wing should be mounted on its platform and the
bunt line to the stabilizer released. The stabilizer will rise to the
glide-DT stop nut.
Test-glide the aircraft. Adjust the stop nut as needed to obtain
a safe, floating glide. The model should be ready for short power
flights as you begin trimming.
If possible, have a fellow modeler who flies bunters do a
preflight check of your airplane and be present for your first few
power flights. When you are ready for the first flight, the
observer should be 30-40 feet away from the launch site so that
he/she has a different perspective of the model than you do as it
ascends.
This second opinion about when and if the model leaves the
expected flight path and whether it begins as a turn or a pitch
over or back is critical in knowing what adjustments need to be
made. Rotating the power-adjustment screw for one-eighth or
one-quarter turn is usually all the adjustment necessary for pitch
corrections, and small adjustments of the left rudder tab usually
take care of excess turn.
When making the first few flights, hook up only the engine
cutoff line, the power line, and the rudder line to the timer. The
bunt line and the glide-DT line are permitted to hang loose.
This arrangement lets you have a short engine run and a
small selected amount of left rudder for the first flight. You can
observe the pattern of the flight. Then the aircraft goes directly
to a quick DT.
Upon retrieval, set the timer to the engine run time you are
using and wind it fully. Reattach the lines to the timer, and make
any necessary adjustments.
Continue the test flights until the model is flying a straight-up
pattern. Now engine run times can be increased in small
increments and proper adjustments can be made so that the
airplane stays on pattern until the engine stops.
On the first bunting flight, hook up the bunt line but leave the
glide-DT line hanging loose. This permits you to observe the
bunt’s force and duration.
Did the model go too far over or not far enough? Does the
bunt need to be held longer or held for a shorter period? You can
make the needed adjustments by carefully loosening the small
nut on the Seelig disk, slightly moving the appropriate disk, and
retightening the nut.
When the bunt looks good, it is time to check the airplane’s
glide. Hook up all the lines to the timer. Loosen the nut holding
the DT scroll on the timer and reposition it so that the wire in the
scroll grooves will escape nearly 15 seconds after the engine is
stopped. Retighten the scroll nut. The model is flown with a
four- or five-second engine run, to assure that it has plenty of
altitude for the first test glide.
Assuming that the power pattern is good and the bunt is
timely and correctly done, the bunt line will release the stabilizer
so that it pops up and is stopped by the glide adjustment nut.
Observe the glide and make minor adjustments with the glide
adjustment nut as needed.
When you are satisfied that the glide is safe, loosen the scroll
nut again and set the scroll’s exit point so that when the DT wire
is placed in the proper groove, DT will occur at approximately
2:05. The glide is now fine-tuned. MA
—Marvin Mace
Trimming
a Bunter
30 MODEL AVIATION
06sig1.QXD 4/22/09 2:32 PM Page 30
away any excess epoxy, and sand the front of
the fuselage until smooth.
Rudder: The rudder’s size and shape is
important, but how you build it is your
choice. I cut mine to shape from a sheet of 1/8
balsa and cyanoacrylate-glue three layers of
1/64 plywood that are 1/8 inch wide around the
perimeter.
I sand the rudder to a streamlined shape.
Then I cover it with fiberglass cloth using
epoxy, which has Model Research Labs
fluorescent red pigment dissolved in it for
visibility.
Use whatever system of rudder control
you are comfortable with, but make sure it is
screw-adjustable for left tab in the tab power
mode and right tab in the glide.
The rear of the rudder is located 5 inches
from the rear of the fuselage. Before
mounting the rudder, using the top fuselage
line as a guide, randomly drill eight to 10 1/16-
inch-diameter holes along the top of the
fuselage where the rudder will be placed.
Using a No. 50 wire drill, carefully make a
similar number of holes in the bottom of the
rudder.
Cut and remove the masking tape where
the rudder will be mounted. Lightly sand the
top of the fuselage and clean it with acetone.
Mount the rudder directly on top of the
fuselage with a bead of epoxy on both the top
of the fuselage and the bottom of the rudder,
so that the adhesive is forced into the small
holes when they are pressed together. This
results in a strong joint.
Using the aluminum angle, the Hinson
Alignment Jig system, and a couple of
drafting triangles will ensure that the rudder is
properly aligned on the top of the tube.
Stabilizer and Stabilizer Mount: The
stabilizer’s construction is straightforward. A
couple of modifications are made to
accommodate the Variable Incidence
Tailplane (VIT) hardware.
The stabilizer’s center rib is cut from a
medium-light sheet of 1/2 balsa. This rib
supports the stabilizer pivot wire, the holddown
rubber-band hook, the bunt line, the
glide-DT line, and, on the underside of the
rib, a small stainless-steel plate.
The VIT system’s power-adjustment
screw rests on the steel plate. The single rib
provides the strength required to maintain the
stabilizer’s integrity for hundreds of bunts.
A portion of the stabilizer’s LE and
approximately 3/8 inch of the center rib are
removed to permit the installation of a piece
of .062 music wire, which will be fitted into
the groove in the back of the Oliver stabilizer
mount.
That short piece of music wire is supported
June 2009 31
Full-Size Plans Available—see page 183
06sig1.QXD 4/22/09 3:31 PM Page 31
in the stabilizer LE by 1/16 plywood half
ribs and is tricky to install. When the half
ribs are made, holes slightly larger than
the .062 music wire are drilled in each of
the two, approximately 1/8 inch from the
front edge and centered top to bottom.
Then the half ribs are installed in the front
part of the stabilizer, which has been cut
to fit the Oliver stabilizer mount.
Sharpen a 1/2-inch piece of .062 music
wire and insert it into the half rib holes, to
increase the depth of the holes in the balsa
LE. Cut another piece of .062 music wire
to 11/2 inches, and slightly sharpen both
ends. Grasp this wire portion with pliers
and ease one end a short distance into one
of the holes in the half rib.
When the other end clears the opposite
short rib, maneuver the other end into the
opposite hole. The wire can be slid back
and forth, and a drop of epoxy is put in
each hole. Center the wire and set the
stabilizer aside for the epoxy to cure.
The stabilizer is completed when a
cutout is made on the centerline of the
thick rib for the glide-DT post and the
stabilizer capture button. Epoxy a small
stainless-steel plate, made from a razor
blade, to the underside of the rib, just
behind the stabilizer-capture button hole.
Drill a small hole on the centerline of
the wide rib, just behind the front spar,
and epoxy a short piece of dowel in the
hole, to serve as a hook for the rubber
bands that hold the stabilizer.
When you epoxy the stabilizer mount
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in position, be sure to put the stabilizer in
its mount and place the fuselage tube in
the aluminum angle so the stabilizer mount
can be aligned 90° from the rudder. Use a
bubble level on the stabilizer to ensure
accurate positioning. The LE of the
stabilizer mount should be located
approximately 1 inch behind the rudder.
Ken Oliver makes a well-constructed,
efficient stabilizer mount, and it is
designed for bunting models. Judiciously
sanding the mounting hole in the base will
increase the inner diameter and provide a
perfect fit on the tube.
The stabilizer mount’s exact location
will be determined after the completed
stabilizer is fitted on the fuselage with the
VIT system in place. When positioned
properly, the mount will be roughly 31/2
inches from the end of the tube.
Lynch VIT Assembly: I like the VIT unit
that Bill Lynch, an excellent California
Power flier, developed, because it is
located at the end of the fuselage and is
trouble free when properly installed and
rigged. It also permits visual inspection of
important VIT system parts after you have
attached the lines to the Seelig timer and
before you fly the model. The information
brochure Bill provides with his unit is
invaluable when installing it and its lines.
Using the top line marked on the tube,
use the cutoff wheel to make a slice that is
nearly as long and as wide as the top of the
VIT frame (less the front tang). Use a
small file to enlarge the cutout so that the
VIT frame fits.
It is now necessary to mount a short
piece of 3/32-inch-diameter aluminum
tubing through the fuselage at a location so
that the notch in the VIT frame will fit
perfectly on the tubing when the short tang
bolt is tightened.
To determine where the holes for the
3/32 tubing are located on the sides of the
fuselage, I start with my best guess, use a
tiny drill bit, and enlarge the holes in the
proper direction until the tubing is a
perfect fit in the notch of the VIT unit.
When I find the proper location, I install
the 3/32 tubing (which is slightly longer
than the fuselage tube is wide) and epoxy
it in place (both on the inside and outside
of the fuselage).
When cured, slip the VIT frame into
position with the notch over the 3/32
aluminum tube. Drill a small hole in the
top of the fuselage, matching the hole in
the tang.
Screw a 1/4-inch-long 2-56 bolt, on
which you place a small flat washer and a
lock washer, through the hole in the top of
the tube and into the hole in the tang of the
frame, so that the frame is held firmly in
place when the bolt is tightened.
Wing: The balsa D-box wing spans 72
inches and is constructed in five panels.
The main spar is an I-beam with 1/4 x .007
carbon-fiber strips on the insides of the 1/4
x 1/8 balsa spar caps.
Covered with ultra-light plastic film
and with balsa Hoerner-type tips, the wing
weighs 8.8 ounces. It is dead stiff, as it
must be.
Pylon Construction and Attachment: The
pylon is constructed using a backbone of
1/8 square balsa, to which formers are
attached. The bottom former is made from
1/2 or 5/8 balsa, while the middle and top
formers are 1/8 balsa.
A small box to house the Walston radio
transmitter is installed in the left side of
the pylon with an exit tube running from
the back of the box out the rear of the
pylon. Then the pylon is covered with 1/16
balsa sheet. Cover the left side of the pylon
first, so that the hole for the transmitter box
can be easily marked from the backside
and then cut out.
The bottom of the pylon must be sanded
to a curved shape so that it will fit against
the fuselage tube. You can do this by
wrapping a sheet of 100-grit sandpaper
around the fuselage and then sliding the
base of the pylon back and forth in a
straight line over the sandpaper, to remove
the excess balsa. It is difficult, but it works
and, finally, a good fit is achieved.
Put the pylon on the fuselage using a
couple of rubber bands to hold it. Check to
see what incidence is on the wing platform.
To do so, return the fuselage to the
aluminum angle and jack up the rear of the
tube until its centerline is parallel to the
top of your workbench. Using an accurate
ruler, measure the distance from the top of
the table to the front and rear of the wing
platform.
If the front is roughly 1/8 inch higher
than the rear, you are home free. If not,
you must continue the back-and-forth
sanding, with pressure applied as needed,
until the platform incidence is 1/8 inch.
With the correct wing incidence, the
model can be assembled and the final
pylon location can be determined.
Make a permanent mark on the edge of
the platform at 58% of the wing chord.
Install the engine, propeller, spinner, wire
skid, timer, and radio transmitter. The
wing with the pylon and stabilizer are
attached to the fuselage with rubber bands.
Balance the model at 58% of the wing
chord by sliding the wing pylon back and
forth on the tube until a balance point is
found and the fuselage is parallel to the
floor. Mark the masking tape on the top
line of the fuselage where the front and
back of the pylon are. Randomly drill a
series of small holes along the top line of
the fuselage between the marks, and drill
several small holes in the bottom of the
pylon.
Remove the masking tape where the
pylon is to be located. Lightly sand the top
of the tube, and clean it with acetone. Coat
the top of the fuselage and the bottom of
the pylon with epoxy, and join them. As
with the rudder, the adhesive will be
forced into the small drilled holes,
improving the joint strength.
Three or four strong rubber bands are
used to hold the pylon tightly to the
fuselage, and then it is placed in the
aluminum angle. Line up the pylon with
the remaining top line marks on the
fuselage and with the rudder while using a
bubble level on the top of the wing
platform. When everything is properly
aligned, allow the epoxy to cure for 24
hours.
When cured, fair the pylon into the
fuselage tube using a mixture of epoxy
and microballoon filler, and then sand.
Mask off the rudder, and paint the
fuselage. I prefer to use white epoxy paint
on the fuselage, because it is highly
visible and cooler in the summertime.
Flight Preparation: Before heading to
the flying field for the first test flight, it is
mandatory that you check the model, in
the shop, for decalage. To do this, draw a
48-inch straight line on the workbench.
Then lay the fuselage on its side, with its
centerline located precisely on the straight
line. Draw a line on the workbench from
the front to the back of the wing platform.
Go to the back of the fuselage, and
make a dot on the workbench that
corresponds with the wire groove of the
Oliver stabilizer mount. Using a drafting
triangle pressed against the top of the
power adjustment screw, make a mark
indicating the top of that screw.
Accurately measure the distance
between the front and back of the wing
platform to the fuselage centerline, and
measure from the two dots, which
represent the distance from the front and
back of the stabilizer to the centerline. The
difference between the measurements
represents the model’s decalage.
Recall that we built 1/8 inch of
incidence into the wing platform when we
mounted it on the fuselage. Since we
would like to start our trimming with 1/16
inch of decalage, we can adjust the power
adjustment screw up or down as needed to
achieve this 1/16 difference.
You should be ready to trim your Super
Marval for competition. Repeatable, safe
engine runs are extremely important—
especially at four and five seconds. The
penalty for overruns during flyoffs is a
zero time, and nothing could be worse. Err
on the side of a safe engine run.
You must keep your timer clean and
oiled and all of your model’s parts in
perfect shape and in good working order.
Have confidence in your timer and your
ability to accurately set it for any engine
run.
That confidence comes from making
many test flights with the help of fellow
modelers who know how to accurately
time an engine run. The watch starts when
the aircraft leaves the flier’s hand and ends
when you hear the engine’s last audible
power stroke.
I take this opportunity to acknowledge the
invaluable help and advice I have received
from my fellow bunters in the past few
years as I have tried to get up to speed.
Insights or clever ideas that I appear to
claim as my own are the result of
conversations I have had with guys such as
Doug Galbreath, Bill Lynch, Ken Oliver,
the late Bob Johannes, Dick Covalt, Bob
Mattes, Gil Robbins, Ronnie Thompson,
Don DeLoach, Faust Parker, Henry
Spence, Mark Troutman, Reid and Roger
Simpson, C.C. Johnson, and Dick Hall.
I also thank Larry Kruse for helping me
put this construction article together in a
format for publication. The Super Marval
is as much your model as it is mine. MA
Marvin Mace
107 Country Ln.
Seguin TX 78155
(830) 379-0036
[email protected]
Sources:
Seelig carbon-fiber tube:
Reid C. Simpson
115 Trail Ridge Dr.
Athens TX 75751
(903) 677-8525
[email protected]
Oliver stabilizer mount:
Ken Oliver
2213 El Cejo Cir.
Rancho Cordova CA 95670
(916) 363-2017
Lynch VIT system:
Bill Lynch
2279 Auburn Ravine Dr.
Lincoln CA 95648
(916) 645-3337
[email protected]
Alignment Jig:
Rex Hinson
1141 S. Waterview Dr.
Inverness FL 34450
(352) 344-5931
[email protected]
Red fluorescent pigment:
Model Research Labs/Curt Stevens
25108 Marguerite Parkway #160
Mission Viejo CA 92692
[email protected]
Walston Retrieval Systems:
Jim Walston
725 Coopers Lake Rd. SE
Smyrna GA 30082
(770) 434-4905
[email protected]
Texas Timers (Request model 3F 1 and
four-function conversion kit)
3317 Pine Timbers Dr.
Johnson City TN 37604
(423) 282-6423
www.texastimers.com
Edition: Model Aviation - 2009/06
Page Numbers: 26,27,28,29,30,31,32,34,36
The
Super
Marval
560
by Marvin Mace
An AMA
2007 Model
of the Year
26 MODEL AVIATION
THE SUPER MARVAL is not a Power model for beginners. It is a
fairly sophisticated bunting airplane that can be easily built and
flown by a modeler who has previously built and flown “locked-up”
Power models. If you make the investment of time and money to
construct a Super Marval, you will have a model that, if well built
and adjusted, is fun to fly and a competitive AMA Category III
performer.
I hope your competitive attitude will encourage you to master the
bunting technique. Perhaps the observations and confessions in this
article will encourage you if you have reservations about taking the
leap and sharing the challenge and joy a bunter offers. You probably
won’t be sorry if you do.
The use of a high-strength, round, lightweight carbon-fiber
fuselage raises building issues that do not occur with an all-balsa
fuselage. For safety reasons, special construction provisions must be
made to ensure the engine mounting’s integrity in the carbon-fiber
fuselage.
There are several building tools you will find useful for working
on this model: a scroll saw, a drill press, an electric hand drill, a disc
sander, a Dremel motor tool with a cutoff wheel, a 2-56 tap and
wrench, and a 5-foot-long, 2-inch aluminum 90° angle.
CONSTRUCTION
Carbon-Fiber Fuselage Preparation: I chose a carbon-fiber FIC
tailboom, made by Hans Seelig in Germany, for the fuselage. As
purchased, the tailboom is roughly 47.5 inches long and the outer
surface is a spiral wrap that must be sanded smooth to the touch
using 100-grit sandpaper.
06sig1.QXD 4/22/09 2:10 PM Page 26
Photos by the author and Larry Kruse
The Norvel .21 is the power plant of choice. The carbon-fiber fuselage is painted
brightly with a two-part fuelproof paint system such as epoxy.
The rudder’s size and shape are important, but how it’s built is
your choice. It is screw-adjustable for left tab in the power mode
and right tab in the glide.
The author holds his Super Marval under a shade tree while the
Texas sun blazes. The wing and stabilizer are covered with light
iron-on film.
Use the 5-foot aluminum angle and a couple of
Rex Hinson’s Alignment Jig plywood bulkheads to
mark 90° points on the round fuselage.
That usually takes one to two hours of vigorous sanding and is
best done outdoors, to avoid breathing the sanding dust. Wear a
mask, regardless of where you do this job.
Sand only until the tube is smooth to the touch. Do not overdo it.
When finished and cleaned with acetone, the spiral markings should
still be visible on the tube.
Place four strips of narrow masking tape on the top, bottom, left,
and right sides of the tube. Use the 5-foot aluminum angle and a
couple of Rex Hinson’s Alignment Jig plywood bulkheads to mark
the 90° points on the masking tape at the front and rear ends of the
tube.
Use a pen to draw straight lines on the tape, connecting the points.
The top line will be used to line up the firewall, wing pylon, stabilizer
mount, rudder, and bunt mechanism. The bottom line helps locate the
lower side of the timer cutout and the landing skid.
Add the Seelig timer mounting assembly to the fuselage. Put the
assembly in the fuselage and push it to a point where the center of the
timer box is 5 inches from the front of the tube. Use a motor tool with
a cutoff wheel to make a small opening in the lower quadrant of the
left side of the fuselage until you can see the timer box.
Rotate the assembly until the bottom edge is on the bottom line of
the fuselage. Enlarge the opening as necessary with the cutoff wheel.
Firewall Plug and Front-End Fabrication: The firewall, engine
mounting system, landing skid, fuel access, and engine retaining
system are built as a unit. You can use a beam or backplate mount.
The firewall is 13/4 inches in diameter; it is made from two pieces of
1/8 plywood and a 1/32 plywood spacer.
Use epoxy to join the front disk and the 1/32-inch disk. When
cured, the four quadrant lines on the sides of the fuselage are marked
on the edge of the disks. The face of the front disk is marked with the
upper end of the landing skid’s shape, and the skid’s shape is cut out
with a scroll saw.
This cutout permits the landing skid to be retained, removed,
straightened, or replaced by removing the engine mount. Epoxy the
rear 1/8 plywood disk to the front piece and place the assembly in a Cclamp
to cure.
Make the two 1/4-inch, five-ply plywood disks that will fit snugly
inside the fuselage. They are epoxied and C-clamped together to cure.
When dry, the 1/2-inch plug is epoxied to the firewall and C-clamped
until cured.
June 2009 27
06sig1.QXD 4/22/09 3:21 PM Page 27
The pylon is constructed using a backbone of 1/8 square balsa, to
which formers are attached. The bottom former is made from 1/2
or 5/8 balsa, while the middle and top formers are 1/8 balsa.
The plywood firewall sandwich forms the engine mount bolt
locations and undercarriage strut location. The plug portion is
relieved for the fuel-line pass.
The stabilizer is straightforward in its construction. The Oliver
stabilizer mount is modified to accommodate VIT hardware. The Seelig timer mounting assembly is put in the fuselage and
pushed to a point where the center of the timer box is 5 inches
from the front of the tube.
Type: A/B FF Gas
Skill level: Advanced
Wingspan: 72.17 inches
Wing area: 557 square inches
Stabilizer area: 94 square inches
Overall length: 51.18 inches
Weight: 26.4 ounces
Engine: Nelson .21
Construction: Carbon-fiber fuselage, balsa, plywood
Finish: Ultra-light film, epoxy paint
Other: Seelig timer or Texas Timers 3F-1, four-function conversion kit
The
Super
Marval
560
28 MODEL AVIATION
06sig1.QXD 4/22/09 2:29 PM Page 28
five or six points on the tube, roughly 1/4 inch behind the backside
of the firewall, that will not interfere with previously installed
hardware. Drill shallow 1/4-inch-diameter holes through the tube into
the plug with a 13/64 bit.
Put a drop of epoxy in each drilled hole, and lightly drive a 3/8-
inch-long, 13/64 dowel into the holes, leaving approximately 1/8 inch of
the dowel sticking out above the tube. These dowels will pin the plug
and firewall to the tube, to assure that the engine is secure on the front
of the tube.
To complete the front end, use cyanoacrylate to adhere small balsa
wedges, which are approximately 13/4 inches long and 1/4 inch high, to
the nose of the tube, against the back of the firewall, and on each side
of the dowels.
Fill spaces between the wedges with carpenter’s wood filler, and
then sand the front of the tube until smooth. Apply six to eight strips
of fiberglass to the front end of the tube, and spread epoxy on the front
3 inches of the tube and the firewall.
Place a piece of waxed paper on the firewall. Attach the engine
mount to the firewall using the 4-40 bolts, which have had the threads
coated with a thick grease, to prevent the epoxy from sticking to the
bolts and the T-nuts. Tighten the 4-40 bolts and hang the fuselage
nose-down to cure.
When dry, remove the bolts, engine mount, and waxed paper. Sand
A small box to house the Walston radio transmitter is installed in
the left side of the pylon; an exit tube runs from the back of the
box out the rear.
Sand the fuselage smooth prior to any installation. The engine
assembly is aligned with quadrant marks and pinned with dowel
rods epoxied into several points.
The engine mount is flaired into the fuselage with firm balsa; the
wood grain running lengthwise increases the airframe’s torqueload
strength.
To accommodate the VIT hardware, the stabilizer’s center rib will
support the stabilizer pivot wire, hold-down rubber-band hook,
bunt line, and glide-DT line.
To ensure the integrity of the epoxy joint between the firewall and
plug, mount a 4-40 Phillips-head bolt with washers and nut through
both the firewall and plug (countersunk both front and back). Tighten
them so they cannot come apart.
Place the engine mount on the firewall, and place a drop of thin
cyanoacrylate glue in the joint. Put the unit in a drill press and make
the four mounting holes for the 4-40 mounting bolts. After slightly
countersinking the holes on the back of the firewall, put T-nuts in the
holes and tighten the 4-40 bolts to seat them.
Place the firewall assembly in a machinist’s vise and drill a 1/4-
inch-diameter hole at an angle from the lower left edge of the engine
mount (near the landing skid) to a point near the center of the plug.
This hole serves as the access to the fuel compartment and fuel
bladder.
You can separate the engine mount from the firewall by forcing a
knife blade a short distance in between the two.
Sand the front of the carbon-fiber fuselage tube square to the
thrustline. Carefully sand roughly an inch of the inside of the tube to
remove any mold-release residue and clean with acetone.
Brush epoxy onto the outside of the plug and the inside of the tube.
Mate the two parts, taking care to line up the top and bottom marks of
the firewall and tube.
After the epoxy has cured for at least 24 hours, carefully choose
June 2009 29
06sig1.QXD 4/22/09 3:33 PM Page 29
For this article I used the popular Seelig timer, which is no
longer available new. A suitable substitute is the Texas Timers’
3F-1, modified with the available four-function conversion kit.
Set the timer disks beginning with the fuel shutoff wire under
the first disk. Let the timer run until the wire just jumps out from
under the notch in the disk. Halt the timer by using the start/stop
plunger.
Loosen the small nut holding the disks. While holding the
bottom disk, rotate the second and third disk so that the notch in
the top disk is roughly 1/16 inch from the end of the power-line
trip wire and the notch in the middle disk is 1/8 inch from the
bunt-line trip wire. Retighten the small nut while holding all the
disks in place.
The stabilizer is installed and all timer lines are connected.
The timer is fully wound, set on a short engine-run mark, and
cycled to see how things work.
If they work correctly, the engine cutoff wire should
escape the first disk at approximately two seconds. A second
later, the power line should release and the stabilizer should snap
down to the bunt position. Then one second later, the bunt line
should release the stabilizer, which will jump up and be stopped
by the glide adjustment nut.
As the timer continues to run, the DT release wire will follow
the grooves in the timer scroll until it reaches the exit point, at
which time that line is released. The cycle is completed when the
timer is reset to the two-second mark and the timer is rewound.
Now the wing should be mounted on its platform and the
bunt line to the stabilizer released. The stabilizer will rise to the
glide-DT stop nut.
Test-glide the aircraft. Adjust the stop nut as needed to obtain
a safe, floating glide. The model should be ready for short power
flights as you begin trimming.
If possible, have a fellow modeler who flies bunters do a
preflight check of your airplane and be present for your first few
power flights. When you are ready for the first flight, the
observer should be 30-40 feet away from the launch site so that
he/she has a different perspective of the model than you do as it
ascends.
This second opinion about when and if the model leaves the
expected flight path and whether it begins as a turn or a pitch
over or back is critical in knowing what adjustments need to be
made. Rotating the power-adjustment screw for one-eighth or
one-quarter turn is usually all the adjustment necessary for pitch
corrections, and small adjustments of the left rudder tab usually
take care of excess turn.
When making the first few flights, hook up only the engine
cutoff line, the power line, and the rudder line to the timer. The
bunt line and the glide-DT line are permitted to hang loose.
This arrangement lets you have a short engine run and a
small selected amount of left rudder for the first flight. You can
observe the pattern of the flight. Then the aircraft goes directly
to a quick DT.
Upon retrieval, set the timer to the engine run time you are
using and wind it fully. Reattach the lines to the timer, and make
any necessary adjustments.
Continue the test flights until the model is flying a straight-up
pattern. Now engine run times can be increased in small
increments and proper adjustments can be made so that the
airplane stays on pattern until the engine stops.
On the first bunting flight, hook up the bunt line but leave the
glide-DT line hanging loose. This permits you to observe the
bunt’s force and duration.
Did the model go too far over or not far enough? Does the
bunt need to be held longer or held for a shorter period? You can
make the needed adjustments by carefully loosening the small
nut on the Seelig disk, slightly moving the appropriate disk, and
retightening the nut.
When the bunt looks good, it is time to check the airplane’s
glide. Hook up all the lines to the timer. Loosen the nut holding
the DT scroll on the timer and reposition it so that the wire in the
scroll grooves will escape nearly 15 seconds after the engine is
stopped. Retighten the scroll nut. The model is flown with a
four- or five-second engine run, to assure that it has plenty of
altitude for the first test glide.
Assuming that the power pattern is good and the bunt is
timely and correctly done, the bunt line will release the stabilizer
so that it pops up and is stopped by the glide adjustment nut.
Observe the glide and make minor adjustments with the glide
adjustment nut as needed.
When you are satisfied that the glide is safe, loosen the scroll
nut again and set the scroll’s exit point so that when the DT wire
is placed in the proper groove, DT will occur at approximately
2:05. The glide is now fine-tuned. MA
—Marvin Mace
Trimming
a Bunter
30 MODEL AVIATION
06sig1.QXD 4/22/09 2:32 PM Page 30
away any excess epoxy, and sand the front of
the fuselage until smooth.
Rudder: The rudder’s size and shape is
important, but how you build it is your
choice. I cut mine to shape from a sheet of 1/8
balsa and cyanoacrylate-glue three layers of
1/64 plywood that are 1/8 inch wide around the
perimeter.
I sand the rudder to a streamlined shape.
Then I cover it with fiberglass cloth using
epoxy, which has Model Research Labs
fluorescent red pigment dissolved in it for
visibility.
Use whatever system of rudder control
you are comfortable with, but make sure it is
screw-adjustable for left tab in the tab power
mode and right tab in the glide.
The rear of the rudder is located 5 inches
from the rear of the fuselage. Before
mounting the rudder, using the top fuselage
line as a guide, randomly drill eight to 10 1/16-
inch-diameter holes along the top of the
fuselage where the rudder will be placed.
Using a No. 50 wire drill, carefully make a
similar number of holes in the bottom of the
rudder.
Cut and remove the masking tape where
the rudder will be mounted. Lightly sand the
top of the fuselage and clean it with acetone.
Mount the rudder directly on top of the
fuselage with a bead of epoxy on both the top
of the fuselage and the bottom of the rudder,
so that the adhesive is forced into the small
holes when they are pressed together. This
results in a strong joint.
Using the aluminum angle, the Hinson
Alignment Jig system, and a couple of
drafting triangles will ensure that the rudder is
properly aligned on the top of the tube.
Stabilizer and Stabilizer Mount: The
stabilizer’s construction is straightforward. A
couple of modifications are made to
accommodate the Variable Incidence
Tailplane (VIT) hardware.
The stabilizer’s center rib is cut from a
medium-light sheet of 1/2 balsa. This rib
supports the stabilizer pivot wire, the holddown
rubber-band hook, the bunt line, the
glide-DT line, and, on the underside of the
rib, a small stainless-steel plate.
The VIT system’s power-adjustment
screw rests on the steel plate. The single rib
provides the strength required to maintain the
stabilizer’s integrity for hundreds of bunts.
A portion of the stabilizer’s LE and
approximately 3/8 inch of the center rib are
removed to permit the installation of a piece
of .062 music wire, which will be fitted into
the groove in the back of the Oliver stabilizer
mount.
That short piece of music wire is supported
June 2009 31
Full-Size Plans Available—see page 183
06sig1.QXD 4/22/09 3:31 PM Page 31
in the stabilizer LE by 1/16 plywood half
ribs and is tricky to install. When the half
ribs are made, holes slightly larger than
the .062 music wire are drilled in each of
the two, approximately 1/8 inch from the
front edge and centered top to bottom.
Then the half ribs are installed in the front
part of the stabilizer, which has been cut
to fit the Oliver stabilizer mount.
Sharpen a 1/2-inch piece of .062 music
wire and insert it into the half rib holes, to
increase the depth of the holes in the balsa
LE. Cut another piece of .062 music wire
to 11/2 inches, and slightly sharpen both
ends. Grasp this wire portion with pliers
and ease one end a short distance into one
of the holes in the half rib.
When the other end clears the opposite
short rib, maneuver the other end into the
opposite hole. The wire can be slid back
and forth, and a drop of epoxy is put in
each hole. Center the wire and set the
stabilizer aside for the epoxy to cure.
The stabilizer is completed when a
cutout is made on the centerline of the
thick rib for the glide-DT post and the
stabilizer capture button. Epoxy a small
stainless-steel plate, made from a razor
blade, to the underside of the rib, just
behind the stabilizer-capture button hole.
Drill a small hole on the centerline of
the wide rib, just behind the front spar,
and epoxy a short piece of dowel in the
hole, to serve as a hook for the rubber
bands that hold the stabilizer.
When you epoxy the stabilizer mount
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in position, be sure to put the stabilizer in
its mount and place the fuselage tube in
the aluminum angle so the stabilizer mount
can be aligned 90° from the rudder. Use a
bubble level on the stabilizer to ensure
accurate positioning. The LE of the
stabilizer mount should be located
approximately 1 inch behind the rudder.
Ken Oliver makes a well-constructed,
efficient stabilizer mount, and it is
designed for bunting models. Judiciously
sanding the mounting hole in the base will
increase the inner diameter and provide a
perfect fit on the tube.
The stabilizer mount’s exact location
will be determined after the completed
stabilizer is fitted on the fuselage with the
VIT system in place. When positioned
properly, the mount will be roughly 31/2
inches from the end of the tube.
Lynch VIT Assembly: I like the VIT unit
that Bill Lynch, an excellent California
Power flier, developed, because it is
located at the end of the fuselage and is
trouble free when properly installed and
rigged. It also permits visual inspection of
important VIT system parts after you have
attached the lines to the Seelig timer and
before you fly the model. The information
brochure Bill provides with his unit is
invaluable when installing it and its lines.
Using the top line marked on the tube,
use the cutoff wheel to make a slice that is
nearly as long and as wide as the top of the
VIT frame (less the front tang). Use a
small file to enlarge the cutout so that the
VIT frame fits.
It is now necessary to mount a short
piece of 3/32-inch-diameter aluminum
tubing through the fuselage at a location so
that the notch in the VIT frame will fit
perfectly on the tubing when the short tang
bolt is tightened.
To determine where the holes for the
3/32 tubing are located on the sides of the
fuselage, I start with my best guess, use a
tiny drill bit, and enlarge the holes in the
proper direction until the tubing is a
perfect fit in the notch of the VIT unit.
When I find the proper location, I install
the 3/32 tubing (which is slightly longer
than the fuselage tube is wide) and epoxy
it in place (both on the inside and outside
of the fuselage).
When cured, slip the VIT frame into
position with the notch over the 3/32
aluminum tube. Drill a small hole in the
top of the fuselage, matching the hole in
the tang.
Screw a 1/4-inch-long 2-56 bolt, on
which you place a small flat washer and a
lock washer, through the hole in the top of
the tube and into the hole in the tang of the
frame, so that the frame is held firmly in
place when the bolt is tightened.
Wing: The balsa D-box wing spans 72
inches and is constructed in five panels.
The main spar is an I-beam with 1/4 x .007
carbon-fiber strips on the insides of the 1/4
x 1/8 balsa spar caps.
Covered with ultra-light plastic film
and with balsa Hoerner-type tips, the wing
weighs 8.8 ounces. It is dead stiff, as it
must be.
Pylon Construction and Attachment: The
pylon is constructed using a backbone of
1/8 square balsa, to which formers are
attached. The bottom former is made from
1/2 or 5/8 balsa, while the middle and top
formers are 1/8 balsa.
A small box to house the Walston radio
transmitter is installed in the left side of
the pylon with an exit tube running from
the back of the box out the rear of the
pylon. Then the pylon is covered with 1/16
balsa sheet. Cover the left side of the pylon
first, so that the hole for the transmitter box
can be easily marked from the backside
and then cut out.
The bottom of the pylon must be sanded
to a curved shape so that it will fit against
the fuselage tube. You can do this by
wrapping a sheet of 100-grit sandpaper
around the fuselage and then sliding the
base of the pylon back and forth in a
straight line over the sandpaper, to remove
the excess balsa. It is difficult, but it works
and, finally, a good fit is achieved.
Put the pylon on the fuselage using a
couple of rubber bands to hold it. Check to
see what incidence is on the wing platform.
To do so, return the fuselage to the
aluminum angle and jack up the rear of the
tube until its centerline is parallel to the
top of your workbench. Using an accurate
ruler, measure the distance from the top of
the table to the front and rear of the wing
platform.
If the front is roughly 1/8 inch higher
than the rear, you are home free. If not,
you must continue the back-and-forth
sanding, with pressure applied as needed,
until the platform incidence is 1/8 inch.
With the correct wing incidence, the
model can be assembled and the final
pylon location can be determined.
Make a permanent mark on the edge of
the platform at 58% of the wing chord.
Install the engine, propeller, spinner, wire
skid, timer, and radio transmitter. The
wing with the pylon and stabilizer are
attached to the fuselage with rubber bands.
Balance the model at 58% of the wing
chord by sliding the wing pylon back and
forth on the tube until a balance point is
found and the fuselage is parallel to the
floor. Mark the masking tape on the top
line of the fuselage where the front and
back of the pylon are. Randomly drill a
series of small holes along the top line of
the fuselage between the marks, and drill
several small holes in the bottom of the
pylon.
Remove the masking tape where the
pylon is to be located. Lightly sand the top
of the tube, and clean it with acetone. Coat
the top of the fuselage and the bottom of
the pylon with epoxy, and join them. As
with the rudder, the adhesive will be
forced into the small drilled holes,
improving the joint strength.
Three or four strong rubber bands are
used to hold the pylon tightly to the
fuselage, and then it is placed in the
aluminum angle. Line up the pylon with
the remaining top line marks on the
fuselage and with the rudder while using a
bubble level on the top of the wing
platform. When everything is properly
aligned, allow the epoxy to cure for 24
hours.
When cured, fair the pylon into the
fuselage tube using a mixture of epoxy
and microballoon filler, and then sand.
Mask off the rudder, and paint the
fuselage. I prefer to use white epoxy paint
on the fuselage, because it is highly
visible and cooler in the summertime.
Flight Preparation: Before heading to
the flying field for the first test flight, it is
mandatory that you check the model, in
the shop, for decalage. To do this, draw a
48-inch straight line on the workbench.
Then lay the fuselage on its side, with its
centerline located precisely on the straight
line. Draw a line on the workbench from
the front to the back of the wing platform.
Go to the back of the fuselage, and
make a dot on the workbench that
corresponds with the wire groove of the
Oliver stabilizer mount. Using a drafting
triangle pressed against the top of the
power adjustment screw, make a mark
indicating the top of that screw.
Accurately measure the distance
between the front and back of the wing
platform to the fuselage centerline, and
measure from the two dots, which
represent the distance from the front and
back of the stabilizer to the centerline. The
difference between the measurements
represents the model’s decalage.
Recall that we built 1/8 inch of
incidence into the wing platform when we
mounted it on the fuselage. Since we
would like to start our trimming with 1/16
inch of decalage, we can adjust the power
adjustment screw up or down as needed to
achieve this 1/16 difference.
You should be ready to trim your Super
Marval for competition. Repeatable, safe
engine runs are extremely important—
especially at four and five seconds. The
penalty for overruns during flyoffs is a
zero time, and nothing could be worse. Err
on the side of a safe engine run.
You must keep your timer clean and
oiled and all of your model’s parts in
perfect shape and in good working order.
Have confidence in your timer and your
ability to accurately set it for any engine
run.
That confidence comes from making
many test flights with the help of fellow
modelers who know how to accurately
time an engine run. The watch starts when
the aircraft leaves the flier’s hand and ends
when you hear the engine’s last audible
power stroke.
I take this opportunity to acknowledge the
invaluable help and advice I have received
from my fellow bunters in the past few
years as I have tried to get up to speed.
Insights or clever ideas that I appear to
claim as my own are the result of
conversations I have had with guys such as
Doug Galbreath, Bill Lynch, Ken Oliver,
the late Bob Johannes, Dick Covalt, Bob
Mattes, Gil Robbins, Ronnie Thompson,
Don DeLoach, Faust Parker, Henry
Spence, Mark Troutman, Reid and Roger
Simpson, C.C. Johnson, and Dick Hall.
I also thank Larry Kruse for helping me
put this construction article together in a
format for publication. The Super Marval
is as much your model as it is mine. MA
Marvin Mace
107 Country Ln.
Seguin TX 78155
(830) 379-0036
[email protected]
Sources:
Seelig carbon-fiber tube:
Reid C. Simpson
115 Trail Ridge Dr.
Athens TX 75751
(903) 677-8525
[email protected]
Oliver stabilizer mount:
Ken Oliver
2213 El Cejo Cir.
Rancho Cordova CA 95670
(916) 363-2017
Lynch VIT system:
Bill Lynch
2279 Auburn Ravine Dr.
Lincoln CA 95648
(916) 645-3337
[email protected]
Alignment Jig:
Rex Hinson
1141 S. Waterview Dr.
Inverness FL 34450
(352) 344-5931
[email protected]
Red fluorescent pigment:
Model Research Labs/Curt Stevens
25108 Marguerite Parkway #160
Mission Viejo CA 92692
[email protected]
Walston Retrieval Systems:
Jim Walston
725 Coopers Lake Rd. SE
Smyrna GA 30082
(770) 434-4905
[email protected]
Texas Timers (Request model 3F 1 and
four-function conversion kit)
3317 Pine Timbers Dr.
Johnson City TN 37604
(423) 282-6423
www.texastimers.com
Edition: Model Aviation - 2009/06
Page Numbers: 26,27,28,29,30,31,32,34,36
The
Super
Marval
560
by Marvin Mace
An AMA
2007 Model
of the Year
26 MODEL AVIATION
THE SUPER MARVAL is not a Power model for beginners. It is a
fairly sophisticated bunting airplane that can be easily built and
flown by a modeler who has previously built and flown “locked-up”
Power models. If you make the investment of time and money to
construct a Super Marval, you will have a model that, if well built
and adjusted, is fun to fly and a competitive AMA Category III
performer.
I hope your competitive attitude will encourage you to master the
bunting technique. Perhaps the observations and confessions in this
article will encourage you if you have reservations about taking the
leap and sharing the challenge and joy a bunter offers. You probably
won’t be sorry if you do.
The use of a high-strength, round, lightweight carbon-fiber
fuselage raises building issues that do not occur with an all-balsa
fuselage. For safety reasons, special construction provisions must be
made to ensure the engine mounting’s integrity in the carbon-fiber
fuselage.
There are several building tools you will find useful for working
on this model: a scroll saw, a drill press, an electric hand drill, a disc
sander, a Dremel motor tool with a cutoff wheel, a 2-56 tap and
wrench, and a 5-foot-long, 2-inch aluminum 90° angle.
CONSTRUCTION
Carbon-Fiber Fuselage Preparation: I chose a carbon-fiber FIC
tailboom, made by Hans Seelig in Germany, for the fuselage. As
purchased, the tailboom is roughly 47.5 inches long and the outer
surface is a spiral wrap that must be sanded smooth to the touch
using 100-grit sandpaper.
06sig1.QXD 4/22/09 2:10 PM Page 26
Photos by the author and Larry Kruse
The Norvel .21 is the power plant of choice. The carbon-fiber fuselage is painted
brightly with a two-part fuelproof paint system such as epoxy.
The rudder’s size and shape are important, but how it’s built is
your choice. It is screw-adjustable for left tab in the power mode
and right tab in the glide.
The author holds his Super Marval under a shade tree while the
Texas sun blazes. The wing and stabilizer are covered with light
iron-on film.
Use the 5-foot aluminum angle and a couple of
Rex Hinson’s Alignment Jig plywood bulkheads to
mark 90° points on the round fuselage.
That usually takes one to two hours of vigorous sanding and is
best done outdoors, to avoid breathing the sanding dust. Wear a
mask, regardless of where you do this job.
Sand only until the tube is smooth to the touch. Do not overdo it.
When finished and cleaned with acetone, the spiral markings should
still be visible on the tube.
Place four strips of narrow masking tape on the top, bottom, left,
and right sides of the tube. Use the 5-foot aluminum angle and a
couple of Rex Hinson’s Alignment Jig plywood bulkheads to mark
the 90° points on the masking tape at the front and rear ends of the
tube.
Use a pen to draw straight lines on the tape, connecting the points.
The top line will be used to line up the firewall, wing pylon, stabilizer
mount, rudder, and bunt mechanism. The bottom line helps locate the
lower side of the timer cutout and the landing skid.
Add the Seelig timer mounting assembly to the fuselage. Put the
assembly in the fuselage and push it to a point where the center of the
timer box is 5 inches from the front of the tube. Use a motor tool with
a cutoff wheel to make a small opening in the lower quadrant of the
left side of the fuselage until you can see the timer box.
Rotate the assembly until the bottom edge is on the bottom line of
the fuselage. Enlarge the opening as necessary with the cutoff wheel.
Firewall Plug and Front-End Fabrication: The firewall, engine
mounting system, landing skid, fuel access, and engine retaining
system are built as a unit. You can use a beam or backplate mount.
The firewall is 13/4 inches in diameter; it is made from two pieces of
1/8 plywood and a 1/32 plywood spacer.
Use epoxy to join the front disk and the 1/32-inch disk. When
cured, the four quadrant lines on the sides of the fuselage are marked
on the edge of the disks. The face of the front disk is marked with the
upper end of the landing skid’s shape, and the skid’s shape is cut out
with a scroll saw.
This cutout permits the landing skid to be retained, removed,
straightened, or replaced by removing the engine mount. Epoxy the
rear 1/8 plywood disk to the front piece and place the assembly in a Cclamp
to cure.
Make the two 1/4-inch, five-ply plywood disks that will fit snugly
inside the fuselage. They are epoxied and C-clamped together to cure.
When dry, the 1/2-inch plug is epoxied to the firewall and C-clamped
until cured.
June 2009 27
06sig1.QXD 4/22/09 3:21 PM Page 27
The pylon is constructed using a backbone of 1/8 square balsa, to
which formers are attached. The bottom former is made from 1/2
or 5/8 balsa, while the middle and top formers are 1/8 balsa.
The plywood firewall sandwich forms the engine mount bolt
locations and undercarriage strut location. The plug portion is
relieved for the fuel-line pass.
The stabilizer is straightforward in its construction. The Oliver
stabilizer mount is modified to accommodate VIT hardware. The Seelig timer mounting assembly is put in the fuselage and
pushed to a point where the center of the timer box is 5 inches
from the front of the tube.
Type: A/B FF Gas
Skill level: Advanced
Wingspan: 72.17 inches
Wing area: 557 square inches
Stabilizer area: 94 square inches
Overall length: 51.18 inches
Weight: 26.4 ounces
Engine: Nelson .21
Construction: Carbon-fiber fuselage, balsa, plywood
Finish: Ultra-light film, epoxy paint
Other: Seelig timer or Texas Timers 3F-1, four-function conversion kit
The
Super
Marval
560
28 MODEL AVIATION
06sig1.QXD 4/22/09 2:29 PM Page 28
five or six points on the tube, roughly 1/4 inch behind the backside
of the firewall, that will not interfere with previously installed
hardware. Drill shallow 1/4-inch-diameter holes through the tube into
the plug with a 13/64 bit.
Put a drop of epoxy in each drilled hole, and lightly drive a 3/8-
inch-long, 13/64 dowel into the holes, leaving approximately 1/8 inch of
the dowel sticking out above the tube. These dowels will pin the plug
and firewall to the tube, to assure that the engine is secure on the front
of the tube.
To complete the front end, use cyanoacrylate to adhere small balsa
wedges, which are approximately 13/4 inches long and 1/4 inch high, to
the nose of the tube, against the back of the firewall, and on each side
of the dowels.
Fill spaces between the wedges with carpenter’s wood filler, and
then sand the front of the tube until smooth. Apply six to eight strips
of fiberglass to the front end of the tube, and spread epoxy on the front
3 inches of the tube and the firewall.
Place a piece of waxed paper on the firewall. Attach the engine
mount to the firewall using the 4-40 bolts, which have had the threads
coated with a thick grease, to prevent the epoxy from sticking to the
bolts and the T-nuts. Tighten the 4-40 bolts and hang the fuselage
nose-down to cure.
When dry, remove the bolts, engine mount, and waxed paper. Sand
A small box to house the Walston radio transmitter is installed in
the left side of the pylon; an exit tube runs from the back of the
box out the rear.
Sand the fuselage smooth prior to any installation. The engine
assembly is aligned with quadrant marks and pinned with dowel
rods epoxied into several points.
The engine mount is flaired into the fuselage with firm balsa; the
wood grain running lengthwise increases the airframe’s torqueload
strength.
To accommodate the VIT hardware, the stabilizer’s center rib will
support the stabilizer pivot wire, hold-down rubber-band hook,
bunt line, and glide-DT line.
To ensure the integrity of the epoxy joint between the firewall and
plug, mount a 4-40 Phillips-head bolt with washers and nut through
both the firewall and plug (countersunk both front and back). Tighten
them so they cannot come apart.
Place the engine mount on the firewall, and place a drop of thin
cyanoacrylate glue in the joint. Put the unit in a drill press and make
the four mounting holes for the 4-40 mounting bolts. After slightly
countersinking the holes on the back of the firewall, put T-nuts in the
holes and tighten the 4-40 bolts to seat them.
Place the firewall assembly in a machinist’s vise and drill a 1/4-
inch-diameter hole at an angle from the lower left edge of the engine
mount (near the landing skid) to a point near the center of the plug.
This hole serves as the access to the fuel compartment and fuel
bladder.
You can separate the engine mount from the firewall by forcing a
knife blade a short distance in between the two.
Sand the front of the carbon-fiber fuselage tube square to the
thrustline. Carefully sand roughly an inch of the inside of the tube to
remove any mold-release residue and clean with acetone.
Brush epoxy onto the outside of the plug and the inside of the tube.
Mate the two parts, taking care to line up the top and bottom marks of
the firewall and tube.
After the epoxy has cured for at least 24 hours, carefully choose
June 2009 29
06sig1.QXD 4/22/09 3:33 PM Page 29
For this article I used the popular Seelig timer, which is no
longer available new. A suitable substitute is the Texas Timers’
3F-1, modified with the available four-function conversion kit.
Set the timer disks beginning with the fuel shutoff wire under
the first disk. Let the timer run until the wire just jumps out from
under the notch in the disk. Halt the timer by using the start/stop
plunger.
Loosen the small nut holding the disks. While holding the
bottom disk, rotate the second and third disk so that the notch in
the top disk is roughly 1/16 inch from the end of the power-line
trip wire and the notch in the middle disk is 1/8 inch from the
bunt-line trip wire. Retighten the small nut while holding all the
disks in place.
The stabilizer is installed and all timer lines are connected.
The timer is fully wound, set on a short engine-run mark, and
cycled to see how things work.
If they work correctly, the engine cutoff wire should
escape the first disk at approximately two seconds. A second
later, the power line should release and the stabilizer should snap
down to the bunt position. Then one second later, the bunt line
should release the stabilizer, which will jump up and be stopped
by the glide adjustment nut.
As the timer continues to run, the DT release wire will follow
the grooves in the timer scroll until it reaches the exit point, at
which time that line is released. The cycle is completed when the
timer is reset to the two-second mark and the timer is rewound.
Now the wing should be mounted on its platform and the
bunt line to the stabilizer released. The stabilizer will rise to the
glide-DT stop nut.
Test-glide the aircraft. Adjust the stop nut as needed to obtain
a safe, floating glide. The model should be ready for short power
flights as you begin trimming.
If possible, have a fellow modeler who flies bunters do a
preflight check of your airplane and be present for your first few
power flights. When you are ready for the first flight, the
observer should be 30-40 feet away from the launch site so that
he/she has a different perspective of the model than you do as it
ascends.
This second opinion about when and if the model leaves the
expected flight path and whether it begins as a turn or a pitch
over or back is critical in knowing what adjustments need to be
made. Rotating the power-adjustment screw for one-eighth or
one-quarter turn is usually all the adjustment necessary for pitch
corrections, and small adjustments of the left rudder tab usually
take care of excess turn.
When making the first few flights, hook up only the engine
cutoff line, the power line, and the rudder line to the timer. The
bunt line and the glide-DT line are permitted to hang loose.
This arrangement lets you have a short engine run and a
small selected amount of left rudder for the first flight. You can
observe the pattern of the flight. Then the aircraft goes directly
to a quick DT.
Upon retrieval, set the timer to the engine run time you are
using and wind it fully. Reattach the lines to the timer, and make
any necessary adjustments.
Continue the test flights until the model is flying a straight-up
pattern. Now engine run times can be increased in small
increments and proper adjustments can be made so that the
airplane stays on pattern until the engine stops.
On the first bunting flight, hook up the bunt line but leave the
glide-DT line hanging loose. This permits you to observe the
bunt’s force and duration.
Did the model go too far over or not far enough? Does the
bunt need to be held longer or held for a shorter period? You can
make the needed adjustments by carefully loosening the small
nut on the Seelig disk, slightly moving the appropriate disk, and
retightening the nut.
When the bunt looks good, it is time to check the airplane’s
glide. Hook up all the lines to the timer. Loosen the nut holding
the DT scroll on the timer and reposition it so that the wire in the
scroll grooves will escape nearly 15 seconds after the engine is
stopped. Retighten the scroll nut. The model is flown with a
four- or five-second engine run, to assure that it has plenty of
altitude for the first test glide.
Assuming that the power pattern is good and the bunt is
timely and correctly done, the bunt line will release the stabilizer
so that it pops up and is stopped by the glide adjustment nut.
Observe the glide and make minor adjustments with the glide
adjustment nut as needed.
When you are satisfied that the glide is safe, loosen the scroll
nut again and set the scroll’s exit point so that when the DT wire
is placed in the proper groove, DT will occur at approximately
2:05. The glide is now fine-tuned. MA
—Marvin Mace
Trimming
a Bunter
30 MODEL AVIATION
06sig1.QXD 4/22/09 2:32 PM Page 30
away any excess epoxy, and sand the front of
the fuselage until smooth.
Rudder: The rudder’s size and shape is
important, but how you build it is your
choice. I cut mine to shape from a sheet of 1/8
balsa and cyanoacrylate-glue three layers of
1/64 plywood that are 1/8 inch wide around the
perimeter.
I sand the rudder to a streamlined shape.
Then I cover it with fiberglass cloth using
epoxy, which has Model Research Labs
fluorescent red pigment dissolved in it for
visibility.
Use whatever system of rudder control
you are comfortable with, but make sure it is
screw-adjustable for left tab in the tab power
mode and right tab in the glide.
The rear of the rudder is located 5 inches
from the rear of the fuselage. Before
mounting the rudder, using the top fuselage
line as a guide, randomly drill eight to 10 1/16-
inch-diameter holes along the top of the
fuselage where the rudder will be placed.
Using a No. 50 wire drill, carefully make a
similar number of holes in the bottom of the
rudder.
Cut and remove the masking tape where
the rudder will be mounted. Lightly sand the
top of the fuselage and clean it with acetone.
Mount the rudder directly on top of the
fuselage with a bead of epoxy on both the top
of the fuselage and the bottom of the rudder,
so that the adhesive is forced into the small
holes when they are pressed together. This
results in a strong joint.
Using the aluminum angle, the Hinson
Alignment Jig system, and a couple of
drafting triangles will ensure that the rudder is
properly aligned on the top of the tube.
Stabilizer and Stabilizer Mount: The
stabilizer’s construction is straightforward. A
couple of modifications are made to
accommodate the Variable Incidence
Tailplane (VIT) hardware.
The stabilizer’s center rib is cut from a
medium-light sheet of 1/2 balsa. This rib
supports the stabilizer pivot wire, the holddown
rubber-band hook, the bunt line, the
glide-DT line, and, on the underside of the
rib, a small stainless-steel plate.
The VIT system’s power-adjustment
screw rests on the steel plate. The single rib
provides the strength required to maintain the
stabilizer’s integrity for hundreds of bunts.
A portion of the stabilizer’s LE and
approximately 3/8 inch of the center rib are
removed to permit the installation of a piece
of .062 music wire, which will be fitted into
the groove in the back of the Oliver stabilizer
mount.
That short piece of music wire is supported
June 2009 31
Full-Size Plans Available—see page 183
06sig1.QXD 4/22/09 3:31 PM Page 31
in the stabilizer LE by 1/16 plywood half
ribs and is tricky to install. When the half
ribs are made, holes slightly larger than
the .062 music wire are drilled in each of
the two, approximately 1/8 inch from the
front edge and centered top to bottom.
Then the half ribs are installed in the front
part of the stabilizer, which has been cut
to fit the Oliver stabilizer mount.
Sharpen a 1/2-inch piece of .062 music
wire and insert it into the half rib holes, to
increase the depth of the holes in the balsa
LE. Cut another piece of .062 music wire
to 11/2 inches, and slightly sharpen both
ends. Grasp this wire portion with pliers
and ease one end a short distance into one
of the holes in the half rib.
When the other end clears the opposite
short rib, maneuver the other end into the
opposite hole. The wire can be slid back
and forth, and a drop of epoxy is put in
each hole. Center the wire and set the
stabilizer aside for the epoxy to cure.
The stabilizer is completed when a
cutout is made on the centerline of the
thick rib for the glide-DT post and the
stabilizer capture button. Epoxy a small
stainless-steel plate, made from a razor
blade, to the underside of the rib, just
behind the stabilizer-capture button hole.
Drill a small hole on the centerline of
the wide rib, just behind the front spar,
and epoxy a short piece of dowel in the
hole, to serve as a hook for the rubber
bands that hold the stabilizer.
When you epoxy the stabilizer mount
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in position, be sure to put the stabilizer in
its mount and place the fuselage tube in
the aluminum angle so the stabilizer mount
can be aligned 90° from the rudder. Use a
bubble level on the stabilizer to ensure
accurate positioning. The LE of the
stabilizer mount should be located
approximately 1 inch behind the rudder.
Ken Oliver makes a well-constructed,
efficient stabilizer mount, and it is
designed for bunting models. Judiciously
sanding the mounting hole in the base will
increase the inner diameter and provide a
perfect fit on the tube.
The stabilizer mount’s exact location
will be determined after the completed
stabilizer is fitted on the fuselage with the
VIT system in place. When positioned
properly, the mount will be roughly 31/2
inches from the end of the tube.
Lynch VIT Assembly: I like the VIT unit
that Bill Lynch, an excellent California
Power flier, developed, because it is
located at the end of the fuselage and is
trouble free when properly installed and
rigged. It also permits visual inspection of
important VIT system parts after you have
attached the lines to the Seelig timer and
before you fly the model. The information
brochure Bill provides with his unit is
invaluable when installing it and its lines.
Using the top line marked on the tube,
use the cutoff wheel to make a slice that is
nearly as long and as wide as the top of the
VIT frame (less the front tang). Use a
small file to enlarge the cutout so that the
VIT frame fits.
It is now necessary to mount a short
piece of 3/32-inch-diameter aluminum
tubing through the fuselage at a location so
that the notch in the VIT frame will fit
perfectly on the tubing when the short tang
bolt is tightened.
To determine where the holes for the
3/32 tubing are located on the sides of the
fuselage, I start with my best guess, use a
tiny drill bit, and enlarge the holes in the
proper direction until the tubing is a
perfect fit in the notch of the VIT unit.
When I find the proper location, I install
the 3/32 tubing (which is slightly longer
than the fuselage tube is wide) and epoxy
it in place (both on the inside and outside
of the fuselage).
When cured, slip the VIT frame into
position with the notch over the 3/32
aluminum tube. Drill a small hole in the
top of the fuselage, matching the hole in
the tang.
Screw a 1/4-inch-long 2-56 bolt, on
which you place a small flat washer and a
lock washer, through the hole in the top of
the tube and into the hole in the tang of the
frame, so that the frame is held firmly in
place when the bolt is tightened.
Wing: The balsa D-box wing spans 72
inches and is constructed in five panels.
The main spar is an I-beam with 1/4 x .007
carbon-fiber strips on the insides of the 1/4
x 1/8 balsa spar caps.
Covered with ultra-light plastic film
and with balsa Hoerner-type tips, the wing
weighs 8.8 ounces. It is dead stiff, as it
must be.
Pylon Construction and Attachment: The
pylon is constructed using a backbone of
1/8 square balsa, to which formers are
attached. The bottom former is made from
1/2 or 5/8 balsa, while the middle and top
formers are 1/8 balsa.
A small box to house the Walston radio
transmitter is installed in the left side of
the pylon with an exit tube running from
the back of the box out the rear of the
pylon. Then the pylon is covered with 1/16
balsa sheet. Cover the left side of the pylon
first, so that the hole for the transmitter box
can be easily marked from the backside
and then cut out.
The bottom of the pylon must be sanded
to a curved shape so that it will fit against
the fuselage tube. You can do this by
wrapping a sheet of 100-grit sandpaper
around the fuselage and then sliding the
base of the pylon back and forth in a
straight line over the sandpaper, to remove
the excess balsa. It is difficult, but it works
and, finally, a good fit is achieved.
Put the pylon on the fuselage using a
couple of rubber bands to hold it. Check to
see what incidence is on the wing platform.
To do so, return the fuselage to the
aluminum angle and jack up the rear of the
tube until its centerline is parallel to the
top of your workbench. Using an accurate
ruler, measure the distance from the top of
the table to the front and rear of the wing
platform.
If the front is roughly 1/8 inch higher
than the rear, you are home free. If not,
you must continue the back-and-forth
sanding, with pressure applied as needed,
until the platform incidence is 1/8 inch.
With the correct wing incidence, the
model can be assembled and the final
pylon location can be determined.
Make a permanent mark on the edge of
the platform at 58% of the wing chord.
Install the engine, propeller, spinner, wire
skid, timer, and radio transmitter. The
wing with the pylon and stabilizer are
attached to the fuselage with rubber bands.
Balance the model at 58% of the wing
chord by sliding the wing pylon back and
forth on the tube until a balance point is
found and the fuselage is parallel to the
floor. Mark the masking tape on the top
line of the fuselage where the front and
back of the pylon are. Randomly drill a
series of small holes along the top line of
the fuselage between the marks, and drill
several small holes in the bottom of the
pylon.
Remove the masking tape where the
pylon is to be located. Lightly sand the top
of the tube, and clean it with acetone. Coat
the top of the fuselage and the bottom of
the pylon with epoxy, and join them. As
with the rudder, the adhesive will be
forced into the small drilled holes,
improving the joint strength.
Three or four strong rubber bands are
used to hold the pylon tightly to the
fuselage, and then it is placed in the
aluminum angle. Line up the pylon with
the remaining top line marks on the
fuselage and with the rudder while using a
bubble level on the top of the wing
platform. When everything is properly
aligned, allow the epoxy to cure for 24
hours.
When cured, fair the pylon into the
fuselage tube using a mixture of epoxy
and microballoon filler, and then sand.
Mask off the rudder, and paint the
fuselage. I prefer to use white epoxy paint
on the fuselage, because it is highly
visible and cooler in the summertime.
Flight Preparation: Before heading to
the flying field for the first test flight, it is
mandatory that you check the model, in
the shop, for decalage. To do this, draw a
48-inch straight line on the workbench.
Then lay the fuselage on its side, with its
centerline located precisely on the straight
line. Draw a line on the workbench from
the front to the back of the wing platform.
Go to the back of the fuselage, and
make a dot on the workbench that
corresponds with the wire groove of the
Oliver stabilizer mount. Using a drafting
triangle pressed against the top of the
power adjustment screw, make a mark
indicating the top of that screw.
Accurately measure the distance
between the front and back of the wing
platform to the fuselage centerline, and
measure from the two dots, which
represent the distance from the front and
back of the stabilizer to the centerline. The
difference between the measurements
represents the model’s decalage.
Recall that we built 1/8 inch of
incidence into the wing platform when we
mounted it on the fuselage. Since we
would like to start our trimming with 1/16
inch of decalage, we can adjust the power
adjustment screw up or down as needed to
achieve this 1/16 difference.
You should be ready to trim your Super
Marval for competition. Repeatable, safe
engine runs are extremely important—
especially at four and five seconds. The
penalty for overruns during flyoffs is a
zero time, and nothing could be worse. Err
on the side of a safe engine run.
You must keep your timer clean and
oiled and all of your model’s parts in
perfect shape and in good working order.
Have confidence in your timer and your
ability to accurately set it for any engine
run.
That confidence comes from making
many test flights with the help of fellow
modelers who know how to accurately
time an engine run. The watch starts when
the aircraft leaves the flier’s hand and ends
when you hear the engine’s last audible
power stroke.
I take this opportunity to acknowledge the
invaluable help and advice I have received
from my fellow bunters in the past few
years as I have tried to get up to speed.
Insights or clever ideas that I appear to
claim as my own are the result of
conversations I have had with guys such as
Doug Galbreath, Bill Lynch, Ken Oliver,
the late Bob Johannes, Dick Covalt, Bob
Mattes, Gil Robbins, Ronnie Thompson,
Don DeLoach, Faust Parker, Henry
Spence, Mark Troutman, Reid and Roger
Simpson, C.C. Johnson, and Dick Hall.
I also thank Larry Kruse for helping me
put this construction article together in a
format for publication. The Super Marval
is as much your model as it is mine. MA
Marvin Mace
107 Country Ln.
Seguin TX 78155
(830) 379-0036
[email protected]
Sources:
Seelig carbon-fiber tube:
Reid C. Simpson
115 Trail Ridge Dr.
Athens TX 75751
(903) 677-8525
[email protected]
Oliver stabilizer mount:
Ken Oliver
2213 El Cejo Cir.
Rancho Cordova CA 95670
(916) 363-2017
Lynch VIT system:
Bill Lynch
2279 Auburn Ravine Dr.
Lincoln CA 95648
(916) 645-3337
[email protected]
Alignment Jig:
Rex Hinson
1141 S. Waterview Dr.
Inverness FL 34450
(352) 344-5931
[email protected]
Red fluorescent pigment:
Model Research Labs/Curt Stevens
25108 Marguerite Parkway #160
Mission Viejo CA 92692
[email protected]
Walston Retrieval Systems:
Jim Walston
725 Coopers Lake Rd. SE
Smyrna GA 30082
(770) 434-4905
[email protected]
Texas Timers (Request model 3F 1 and
four-function conversion kit)
3317 Pine Timbers Dr.
Johnson City TN 37604
(423) 282-6423
www.texastimers.com
Edition: Model Aviation - 2009/06
Page Numbers: 26,27,28,29,30,31,32,34,36
The
Super
Marval
560
by Marvin Mace
An AMA
2007 Model
of the Year
26 MODEL AVIATION
THE SUPER MARVAL is not a Power model for beginners. It is a
fairly sophisticated bunting airplane that can be easily built and
flown by a modeler who has previously built and flown “locked-up”
Power models. If you make the investment of time and money to
construct a Super Marval, you will have a model that, if well built
and adjusted, is fun to fly and a competitive AMA Category III
performer.
I hope your competitive attitude will encourage you to master the
bunting technique. Perhaps the observations and confessions in this
article will encourage you if you have reservations about taking the
leap and sharing the challenge and joy a bunter offers. You probably
won’t be sorry if you do.
The use of a high-strength, round, lightweight carbon-fiber
fuselage raises building issues that do not occur with an all-balsa
fuselage. For safety reasons, special construction provisions must be
made to ensure the engine mounting’s integrity in the carbon-fiber
fuselage.
There are several building tools you will find useful for working
on this model: a scroll saw, a drill press, an electric hand drill, a disc
sander, a Dremel motor tool with a cutoff wheel, a 2-56 tap and
wrench, and a 5-foot-long, 2-inch aluminum 90° angle.
CONSTRUCTION
Carbon-Fiber Fuselage Preparation: I chose a carbon-fiber FIC
tailboom, made by Hans Seelig in Germany, for the fuselage. As
purchased, the tailboom is roughly 47.5 inches long and the outer
surface is a spiral wrap that must be sanded smooth to the touch
using 100-grit sandpaper.
06sig1.QXD 4/22/09 2:10 PM Page 26
Photos by the author and Larry Kruse
The Norvel .21 is the power plant of choice. The carbon-fiber fuselage is painted
brightly with a two-part fuelproof paint system such as epoxy.
The rudder’s size and shape are important, but how it’s built is
your choice. It is screw-adjustable for left tab in the power mode
and right tab in the glide.
The author holds his Super Marval under a shade tree while the
Texas sun blazes. The wing and stabilizer are covered with light
iron-on film.
Use the 5-foot aluminum angle and a couple of
Rex Hinson’s Alignment Jig plywood bulkheads to
mark 90° points on the round fuselage.
That usually takes one to two hours of vigorous sanding and is
best done outdoors, to avoid breathing the sanding dust. Wear a
mask, regardless of where you do this job.
Sand only until the tube is smooth to the touch. Do not overdo it.
When finished and cleaned with acetone, the spiral markings should
still be visible on the tube.
Place four strips of narrow masking tape on the top, bottom, left,
and right sides of the tube. Use the 5-foot aluminum angle and a
couple of Rex Hinson’s Alignment Jig plywood bulkheads to mark
the 90° points on the masking tape at the front and rear ends of the
tube.
Use a pen to draw straight lines on the tape, connecting the points.
The top line will be used to line up the firewall, wing pylon, stabilizer
mount, rudder, and bunt mechanism. The bottom line helps locate the
lower side of the timer cutout and the landing skid.
Add the Seelig timer mounting assembly to the fuselage. Put the
assembly in the fuselage and push it to a point where the center of the
timer box is 5 inches from the front of the tube. Use a motor tool with
a cutoff wheel to make a small opening in the lower quadrant of the
left side of the fuselage until you can see the timer box.
Rotate the assembly until the bottom edge is on the bottom line of
the fuselage. Enlarge the opening as necessary with the cutoff wheel.
Firewall Plug and Front-End Fabrication: The firewall, engine
mounting system, landing skid, fuel access, and engine retaining
system are built as a unit. You can use a beam or backplate mount.
The firewall is 13/4 inches in diameter; it is made from two pieces of
1/8 plywood and a 1/32 plywood spacer.
Use epoxy to join the front disk and the 1/32-inch disk. When
cured, the four quadrant lines on the sides of the fuselage are marked
on the edge of the disks. The face of the front disk is marked with the
upper end of the landing skid’s shape, and the skid’s shape is cut out
with a scroll saw.
This cutout permits the landing skid to be retained, removed,
straightened, or replaced by removing the engine mount. Epoxy the
rear 1/8 plywood disk to the front piece and place the assembly in a Cclamp
to cure.
Make the two 1/4-inch, five-ply plywood disks that will fit snugly
inside the fuselage. They are epoxied and C-clamped together to cure.
When dry, the 1/2-inch plug is epoxied to the firewall and C-clamped
until cured.
June 2009 27
06sig1.QXD 4/22/09 3:21 PM Page 27
The pylon is constructed using a backbone of 1/8 square balsa, to
which formers are attached. The bottom former is made from 1/2
or 5/8 balsa, while the middle and top formers are 1/8 balsa.
The plywood firewall sandwich forms the engine mount bolt
locations and undercarriage strut location. The plug portion is
relieved for the fuel-line pass.
The stabilizer is straightforward in its construction. The Oliver
stabilizer mount is modified to accommodate VIT hardware. The Seelig timer mounting assembly is put in the fuselage and
pushed to a point where the center of the timer box is 5 inches
from the front of the tube.
Type: A/B FF Gas
Skill level: Advanced
Wingspan: 72.17 inches
Wing area: 557 square inches
Stabilizer area: 94 square inches
Overall length: 51.18 inches
Weight: 26.4 ounces
Engine: Nelson .21
Construction: Carbon-fiber fuselage, balsa, plywood
Finish: Ultra-light film, epoxy paint
Other: Seelig timer or Texas Timers 3F-1, four-function conversion kit
The
Super
Marval
560
28 MODEL AVIATION
06sig1.QXD 4/22/09 2:29 PM Page 28
five or six points on the tube, roughly 1/4 inch behind the backside
of the firewall, that will not interfere with previously installed
hardware. Drill shallow 1/4-inch-diameter holes through the tube into
the plug with a 13/64 bit.
Put a drop of epoxy in each drilled hole, and lightly drive a 3/8-
inch-long, 13/64 dowel into the holes, leaving approximately 1/8 inch of
the dowel sticking out above the tube. These dowels will pin the plug
and firewall to the tube, to assure that the engine is secure on the front
of the tube.
To complete the front end, use cyanoacrylate to adhere small balsa
wedges, which are approximately 13/4 inches long and 1/4 inch high, to
the nose of the tube, against the back of the firewall, and on each side
of the dowels.
Fill spaces between the wedges with carpenter’s wood filler, and
then sand the front of the tube until smooth. Apply six to eight strips
of fiberglass to the front end of the tube, and spread epoxy on the front
3 inches of the tube and the firewall.
Place a piece of waxed paper on the firewall. Attach the engine
mount to the firewall using the 4-40 bolts, which have had the threads
coated with a thick grease, to prevent the epoxy from sticking to the
bolts and the T-nuts. Tighten the 4-40 bolts and hang the fuselage
nose-down to cure.
When dry, remove the bolts, engine mount, and waxed paper. Sand
A small box to house the Walston radio transmitter is installed in
the left side of the pylon; an exit tube runs from the back of the
box out the rear.
Sand the fuselage smooth prior to any installation. The engine
assembly is aligned with quadrant marks and pinned with dowel
rods epoxied into several points.
The engine mount is flaired into the fuselage with firm balsa; the
wood grain running lengthwise increases the airframe’s torqueload
strength.
To accommodate the VIT hardware, the stabilizer’s center rib will
support the stabilizer pivot wire, hold-down rubber-band hook,
bunt line, and glide-DT line.
To ensure the integrity of the epoxy joint between the firewall and
plug, mount a 4-40 Phillips-head bolt with washers and nut through
both the firewall and plug (countersunk both front and back). Tighten
them so they cannot come apart.
Place the engine mount on the firewall, and place a drop of thin
cyanoacrylate glue in the joint. Put the unit in a drill press and make
the four mounting holes for the 4-40 mounting bolts. After slightly
countersinking the holes on the back of the firewall, put T-nuts in the
holes and tighten the 4-40 bolts to seat them.
Place the firewall assembly in a machinist’s vise and drill a 1/4-
inch-diameter hole at an angle from the lower left edge of the engine
mount (near the landing skid) to a point near the center of the plug.
This hole serves as the access to the fuel compartment and fuel
bladder.
You can separate the engine mount from the firewall by forcing a
knife blade a short distance in between the two.
Sand the front of the carbon-fiber fuselage tube square to the
thrustline. Carefully sand roughly an inch of the inside of the tube to
remove any mold-release residue and clean with acetone.
Brush epoxy onto the outside of the plug and the inside of the tube.
Mate the two parts, taking care to line up the top and bottom marks of
the firewall and tube.
After the epoxy has cured for at least 24 hours, carefully choose
June 2009 29
06sig1.QXD 4/22/09 3:33 PM Page 29
For this article I used the popular Seelig timer, which is no
longer available new. A suitable substitute is the Texas Timers’
3F-1, modified with the available four-function conversion kit.
Set the timer disks beginning with the fuel shutoff wire under
the first disk. Let the timer run until the wire just jumps out from
under the notch in the disk. Halt the timer by using the start/stop
plunger.
Loosen the small nut holding the disks. While holding the
bottom disk, rotate the second and third disk so that the notch in
the top disk is roughly 1/16 inch from the end of the power-line
trip wire and the notch in the middle disk is 1/8 inch from the
bunt-line trip wire. Retighten the small nut while holding all the
disks in place.
The stabilizer is installed and all timer lines are connected.
The timer is fully wound, set on a short engine-run mark, and
cycled to see how things work.
If they work correctly, the engine cutoff wire should
escape the first disk at approximately two seconds. A second
later, the power line should release and the stabilizer should snap
down to the bunt position. Then one second later, the bunt line
should release the stabilizer, which will jump up and be stopped
by the glide adjustment nut.
As the timer continues to run, the DT release wire will follow
the grooves in the timer scroll until it reaches the exit point, at
which time that line is released. The cycle is completed when the
timer is reset to the two-second mark and the timer is rewound.
Now the wing should be mounted on its platform and the
bunt line to the stabilizer released. The stabilizer will rise to the
glide-DT stop nut.
Test-glide the aircraft. Adjust the stop nut as needed to obtain
a safe, floating glide. The model should be ready for short power
flights as you begin trimming.
If possible, have a fellow modeler who flies bunters do a
preflight check of your airplane and be present for your first few
power flights. When you are ready for the first flight, the
observer should be 30-40 feet away from the launch site so that
he/she has a different perspective of the model than you do as it
ascends.
This second opinion about when and if the model leaves the
expected flight path and whether it begins as a turn or a pitch
over or back is critical in knowing what adjustments need to be
made. Rotating the power-adjustment screw for one-eighth or
one-quarter turn is usually all the adjustment necessary for pitch
corrections, and small adjustments of the left rudder tab usually
take care of excess turn.
When making the first few flights, hook up only the engine
cutoff line, the power line, and the rudder line to the timer. The
bunt line and the glide-DT line are permitted to hang loose.
This arrangement lets you have a short engine run and a
small selected amount of left rudder for the first flight. You can
observe the pattern of the flight. Then the aircraft goes directly
to a quick DT.
Upon retrieval, set the timer to the engine run time you are
using and wind it fully. Reattach the lines to the timer, and make
any necessary adjustments.
Continue the test flights until the model is flying a straight-up
pattern. Now engine run times can be increased in small
increments and proper adjustments can be made so that the
airplane stays on pattern until the engine stops.
On the first bunting flight, hook up the bunt line but leave the
glide-DT line hanging loose. This permits you to observe the
bunt’s force and duration.
Did the model go too far over or not far enough? Does the
bunt need to be held longer or held for a shorter period? You can
make the needed adjustments by carefully loosening the small
nut on the Seelig disk, slightly moving the appropriate disk, and
retightening the nut.
When the bunt looks good, it is time to check the airplane’s
glide. Hook up all the lines to the timer. Loosen the nut holding
the DT scroll on the timer and reposition it so that the wire in the
scroll grooves will escape nearly 15 seconds after the engine is
stopped. Retighten the scroll nut. The model is flown with a
four- or five-second engine run, to assure that it has plenty of
altitude for the first test glide.
Assuming that the power pattern is good and the bunt is
timely and correctly done, the bunt line will release the stabilizer
so that it pops up and is stopped by the glide adjustment nut.
Observe the glide and make minor adjustments with the glide
adjustment nut as needed.
When you are satisfied that the glide is safe, loosen the scroll
nut again and set the scroll’s exit point so that when the DT wire
is placed in the proper groove, DT will occur at approximately
2:05. The glide is now fine-tuned. MA
—Marvin Mace
Trimming
a Bunter
30 MODEL AVIATION
06sig1.QXD 4/22/09 2:32 PM Page 30
away any excess epoxy, and sand the front of
the fuselage until smooth.
Rudder: The rudder’s size and shape is
important, but how you build it is your
choice. I cut mine to shape from a sheet of 1/8
balsa and cyanoacrylate-glue three layers of
1/64 plywood that are 1/8 inch wide around the
perimeter.
I sand the rudder to a streamlined shape.
Then I cover it with fiberglass cloth using
epoxy, which has Model Research Labs
fluorescent red pigment dissolved in it for
visibility.
Use whatever system of rudder control
you are comfortable with, but make sure it is
screw-adjustable for left tab in the tab power
mode and right tab in the glide.
The rear of the rudder is located 5 inches
from the rear of the fuselage. Before
mounting the rudder, using the top fuselage
line as a guide, randomly drill eight to 10 1/16-
inch-diameter holes along the top of the
fuselage where the rudder will be placed.
Using a No. 50 wire drill, carefully make a
similar number of holes in the bottom of the
rudder.
Cut and remove the masking tape where
the rudder will be mounted. Lightly sand the
top of the fuselage and clean it with acetone.
Mount the rudder directly on top of the
fuselage with a bead of epoxy on both the top
of the fuselage and the bottom of the rudder,
so that the adhesive is forced into the small
holes when they are pressed together. This
results in a strong joint.
Using the aluminum angle, the Hinson
Alignment Jig system, and a couple of
drafting triangles will ensure that the rudder is
properly aligned on the top of the tube.
Stabilizer and Stabilizer Mount: The
stabilizer’s construction is straightforward. A
couple of modifications are made to
accommodate the Variable Incidence
Tailplane (VIT) hardware.
The stabilizer’s center rib is cut from a
medium-light sheet of 1/2 balsa. This rib
supports the stabilizer pivot wire, the holddown
rubber-band hook, the bunt line, the
glide-DT line, and, on the underside of the
rib, a small stainless-steel plate.
The VIT system’s power-adjustment
screw rests on the steel plate. The single rib
provides the strength required to maintain the
stabilizer’s integrity for hundreds of bunts.
A portion of the stabilizer’s LE and
approximately 3/8 inch of the center rib are
removed to permit the installation of a piece
of .062 music wire, which will be fitted into
the groove in the back of the Oliver stabilizer
mount.
That short piece of music wire is supported
June 2009 31
Full-Size Plans Available—see page 183
06sig1.QXD 4/22/09 3:31 PM Page 31
in the stabilizer LE by 1/16 plywood half
ribs and is tricky to install. When the half
ribs are made, holes slightly larger than
the .062 music wire are drilled in each of
the two, approximately 1/8 inch from the
front edge and centered top to bottom.
Then the half ribs are installed in the front
part of the stabilizer, which has been cut
to fit the Oliver stabilizer mount.
Sharpen a 1/2-inch piece of .062 music
wire and insert it into the half rib holes, to
increase the depth of the holes in the balsa
LE. Cut another piece of .062 music wire
to 11/2 inches, and slightly sharpen both
ends. Grasp this wire portion with pliers
and ease one end a short distance into one
of the holes in the half rib.
When the other end clears the opposite
short rib, maneuver the other end into the
opposite hole. The wire can be slid back
and forth, and a drop of epoxy is put in
each hole. Center the wire and set the
stabilizer aside for the epoxy to cure.
The stabilizer is completed when a
cutout is made on the centerline of the
thick rib for the glide-DT post and the
stabilizer capture button. Epoxy a small
stainless-steel plate, made from a razor
blade, to the underside of the rib, just
behind the stabilizer-capture button hole.
Drill a small hole on the centerline of
the wide rib, just behind the front spar,
and epoxy a short piece of dowel in the
hole, to serve as a hook for the rubber
bands that hold the stabilizer.
When you epoxy the stabilizer mount
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in position, be sure to put the stabilizer in
its mount and place the fuselage tube in
the aluminum angle so the stabilizer mount
can be aligned 90° from the rudder. Use a
bubble level on the stabilizer to ensure
accurate positioning. The LE of the
stabilizer mount should be located
approximately 1 inch behind the rudder.
Ken Oliver makes a well-constructed,
efficient stabilizer mount, and it is
designed for bunting models. Judiciously
sanding the mounting hole in the base will
increase the inner diameter and provide a
perfect fit on the tube.
The stabilizer mount’s exact location
will be determined after the completed
stabilizer is fitted on the fuselage with the
VIT system in place. When positioned
properly, the mount will be roughly 31/2
inches from the end of the tube.
Lynch VIT Assembly: I like the VIT unit
that Bill Lynch, an excellent California
Power flier, developed, because it is
located at the end of the fuselage and is
trouble free when properly installed and
rigged. It also permits visual inspection of
important VIT system parts after you have
attached the lines to the Seelig timer and
before you fly the model. The information
brochure Bill provides with his unit is
invaluable when installing it and its lines.
Using the top line marked on the tube,
use the cutoff wheel to make a slice that is
nearly as long and as wide as the top of the
VIT frame (less the front tang). Use a
small file to enlarge the cutout so that the
VIT frame fits.
It is now necessary to mount a short
piece of 3/32-inch-diameter aluminum
tubing through the fuselage at a location so
that the notch in the VIT frame will fit
perfectly on the tubing when the short tang
bolt is tightened.
To determine where the holes for the
3/32 tubing are located on the sides of the
fuselage, I start with my best guess, use a
tiny drill bit, and enlarge the holes in the
proper direction until the tubing is a
perfect fit in the notch of the VIT unit.
When I find the proper location, I install
the 3/32 tubing (which is slightly longer
than the fuselage tube is wide) and epoxy
it in place (both on the inside and outside
of the fuselage).
When cured, slip the VIT frame into
position with the notch over the 3/32
aluminum tube. Drill a small hole in the
top of the fuselage, matching the hole in
the tang.
Screw a 1/4-inch-long 2-56 bolt, on
which you place a small flat washer and a
lock washer, through the hole in the top of
the tube and into the hole in the tang of the
frame, so that the frame is held firmly in
place when the bolt is tightened.
Wing: The balsa D-box wing spans 72
inches and is constructed in five panels.
The main spar is an I-beam with 1/4 x .007
carbon-fiber strips on the insides of the 1/4
x 1/8 balsa spar caps.
Covered with ultra-light plastic film
and with balsa Hoerner-type tips, the wing
weighs 8.8 ounces. It is dead stiff, as it
must be.
Pylon Construction and Attachment: The
pylon is constructed using a backbone of
1/8 square balsa, to which formers are
attached. The bottom former is made from
1/2 or 5/8 balsa, while the middle and top
formers are 1/8 balsa.
A small box to house the Walston radio
transmitter is installed in the left side of
the pylon with an exit tube running from
the back of the box out the rear of the
pylon. Then the pylon is covered with 1/16
balsa sheet. Cover the left side of the pylon
first, so that the hole for the transmitter box
can be easily marked from the backside
and then cut out.
The bottom of the pylon must be sanded
to a curved shape so that it will fit against
the fuselage tube. You can do this by
wrapping a sheet of 100-grit sandpaper
around the fuselage and then sliding the
base of the pylon back and forth in a
straight line over the sandpaper, to remove
the excess balsa. It is difficult, but it works
and, finally, a good fit is achieved.
Put the pylon on the fuselage using a
couple of rubber bands to hold it. Check to
see what incidence is on the wing platform.
To do so, return the fuselage to the
aluminum angle and jack up the rear of the
tube until its centerline is parallel to the
top of your workbench. Using an accurate
ruler, measure the distance from the top of
the table to the front and rear of the wing
platform.
If the front is roughly 1/8 inch higher
than the rear, you are home free. If not,
you must continue the back-and-forth
sanding, with pressure applied as needed,
until the platform incidence is 1/8 inch.
With the correct wing incidence, the
model can be assembled and the final
pylon location can be determined.
Make a permanent mark on the edge of
the platform at 58% of the wing chord.
Install the engine, propeller, spinner, wire
skid, timer, and radio transmitter. The
wing with the pylon and stabilizer are
attached to the fuselage with rubber bands.
Balance the model at 58% of the wing
chord by sliding the wing pylon back and
forth on the tube until a balance point is
found and the fuselage is parallel to the
floor. Mark the masking tape on the top
line of the fuselage where the front and
back of the pylon are. Randomly drill a
series of small holes along the top line of
the fuselage between the marks, and drill
several small holes in the bottom of the
pylon.
Remove the masking tape where the
pylon is to be located. Lightly sand the top
of the tube, and clean it with acetone. Coat
the top of the fuselage and the bottom of
the pylon with epoxy, and join them. As
with the rudder, the adhesive will be
forced into the small drilled holes,
improving the joint strength.
Three or four strong rubber bands are
used to hold the pylon tightly to the
fuselage, and then it is placed in the
aluminum angle. Line up the pylon with
the remaining top line marks on the
fuselage and with the rudder while using a
bubble level on the top of the wing
platform. When everything is properly
aligned, allow the epoxy to cure for 24
hours.
When cured, fair the pylon into the
fuselage tube using a mixture of epoxy
and microballoon filler, and then sand.
Mask off the rudder, and paint the
fuselage. I prefer to use white epoxy paint
on the fuselage, because it is highly
visible and cooler in the summertime.
Flight Preparation: Before heading to
the flying field for the first test flight, it is
mandatory that you check the model, in
the shop, for decalage. To do this, draw a
48-inch straight line on the workbench.
Then lay the fuselage on its side, with its
centerline located precisely on the straight
line. Draw a line on the workbench from
the front to the back of the wing platform.
Go to the back of the fuselage, and
make a dot on the workbench that
corresponds with the wire groove of the
Oliver stabilizer mount. Using a drafting
triangle pressed against the top of the
power adjustment screw, make a mark
indicating the top of that screw.
Accurately measure the distance
between the front and back of the wing
platform to the fuselage centerline, and
measure from the two dots, which
represent the distance from the front and
back of the stabilizer to the centerline. The
difference between the measurements
represents the model’s decalage.
Recall that we built 1/8 inch of
incidence into the wing platform when we
mounted it on the fuselage. Since we
would like to start our trimming with 1/16
inch of decalage, we can adjust the power
adjustment screw up or down as needed to
achieve this 1/16 difference.
You should be ready to trim your Super
Marval for competition. Repeatable, safe
engine runs are extremely important—
especially at four and five seconds. The
penalty for overruns during flyoffs is a
zero time, and nothing could be worse. Err
on the side of a safe engine run.
You must keep your timer clean and
oiled and all of your model’s parts in
perfect shape and in good working order.
Have confidence in your timer and your
ability to accurately set it for any engine
run.
That confidence comes from making
many test flights with the help of fellow
modelers who know how to accurately
time an engine run. The watch starts when
the aircraft leaves the flier’s hand and ends
when you hear the engine’s last audible
power stroke.
I take this opportunity to acknowledge the
invaluable help and advice I have received
from my fellow bunters in the past few
years as I have tried to get up to speed.
Insights or clever ideas that I appear to
claim as my own are the result of
conversations I have had with guys such as
Doug Galbreath, Bill Lynch, Ken Oliver,
the late Bob Johannes, Dick Covalt, Bob
Mattes, Gil Robbins, Ronnie Thompson,
Don DeLoach, Faust Parker, Henry
Spence, Mark Troutman, Reid and Roger
Simpson, C.C. Johnson, and Dick Hall.
I also thank Larry Kruse for helping me
put this construction article together in a
format for publication. The Super Marval
is as much your model as it is mine. MA
Marvin Mace
107 Country Ln.
Seguin TX 78155
(830) 379-0036
[email protected]
Sources:
Seelig carbon-fiber tube:
Reid C. Simpson
115 Trail Ridge Dr.
Athens TX 75751
(903) 677-8525
[email protected]
Oliver stabilizer mount:
Ken Oliver
2213 El Cejo Cir.
Rancho Cordova CA 95670
(916) 363-2017
Lynch VIT system:
Bill Lynch
2279 Auburn Ravine Dr.
Lincoln CA 95648
(916) 645-3337
[email protected]
Alignment Jig:
Rex Hinson
1141 S. Waterview Dr.
Inverness FL 34450
(352) 344-5931
[email protected]
Red fluorescent pigment:
Model Research Labs/Curt Stevens
25108 Marguerite Parkway #160
Mission Viejo CA 92692
[email protected]
Walston Retrieval Systems:
Jim Walston
725 Coopers Lake Rd. SE
Smyrna GA 30082
(770) 434-4905
[email protected]
Texas Timers (Request model 3F 1 and
four-function conversion kit)
3317 Pine Timbers Dr.
Johnson City TN 37604
(423) 282-6423
www.texastimers.com
Edition: Model Aviation - 2009/06
Page Numbers: 26,27,28,29,30,31,32,34,36
The
Super
Marval
560
by Marvin Mace
An AMA
2007 Model
of the Year
26 MODEL AVIATION
THE SUPER MARVAL is not a Power model for beginners. It is a
fairly sophisticated bunting airplane that can be easily built and
flown by a modeler who has previously built and flown “locked-up”
Power models. If you make the investment of time and money to
construct a Super Marval, you will have a model that, if well built
and adjusted, is fun to fly and a competitive AMA Category III
performer.
I hope your competitive attitude will encourage you to master the
bunting technique. Perhaps the observations and confessions in this
article will encourage you if you have reservations about taking the
leap and sharing the challenge and joy a bunter offers. You probably
won’t be sorry if you do.
The use of a high-strength, round, lightweight carbon-fiber
fuselage raises building issues that do not occur with an all-balsa
fuselage. For safety reasons, special construction provisions must be
made to ensure the engine mounting’s integrity in the carbon-fiber
fuselage.
There are several building tools you will find useful for working
on this model: a scroll saw, a drill press, an electric hand drill, a disc
sander, a Dremel motor tool with a cutoff wheel, a 2-56 tap and
wrench, and a 5-foot-long, 2-inch aluminum 90° angle.
CONSTRUCTION
Carbon-Fiber Fuselage Preparation: I chose a carbon-fiber FIC
tailboom, made by Hans Seelig in Germany, for the fuselage. As
purchased, the tailboom is roughly 47.5 inches long and the outer
surface is a spiral wrap that must be sanded smooth to the touch
using 100-grit sandpaper.
06sig1.QXD 4/22/09 2:10 PM Page 26
Photos by the author and Larry Kruse
The Norvel .21 is the power plant of choice. The carbon-fiber fuselage is painted
brightly with a two-part fuelproof paint system such as epoxy.
The rudder’s size and shape are important, but how it’s built is
your choice. It is screw-adjustable for left tab in the power mode
and right tab in the glide.
The author holds his Super Marval under a shade tree while the
Texas sun blazes. The wing and stabilizer are covered with light
iron-on film.
Use the 5-foot aluminum angle and a couple of
Rex Hinson’s Alignment Jig plywood bulkheads to
mark 90° points on the round fuselage.
That usually takes one to two hours of vigorous sanding and is
best done outdoors, to avoid breathing the sanding dust. Wear a
mask, regardless of where you do this job.
Sand only until the tube is smooth to the touch. Do not overdo it.
When finished and cleaned with acetone, the spiral markings should
still be visible on the tube.
Place four strips of narrow masking tape on the top, bottom, left,
and right sides of the tube. Use the 5-foot aluminum angle and a
couple of Rex Hinson’s Alignment Jig plywood bulkheads to mark
the 90° points on the masking tape at the front and rear ends of the
tube.
Use a pen to draw straight lines on the tape, connecting the points.
The top line will be used to line up the firewall, wing pylon, stabilizer
mount, rudder, and bunt mechanism. The bottom line helps locate the
lower side of the timer cutout and the landing skid.
Add the Seelig timer mounting assembly to the fuselage. Put the
assembly in the fuselage and push it to a point where the center of the
timer box is 5 inches from the front of the tube. Use a motor tool with
a cutoff wheel to make a small opening in the lower quadrant of the
left side of the fuselage until you can see the timer box.
Rotate the assembly until the bottom edge is on the bottom line of
the fuselage. Enlarge the opening as necessary with the cutoff wheel.
Firewall Plug and Front-End Fabrication: The firewall, engine
mounting system, landing skid, fuel access, and engine retaining
system are built as a unit. You can use a beam or backplate mount.
The firewall is 13/4 inches in diameter; it is made from two pieces of
1/8 plywood and a 1/32 plywood spacer.
Use epoxy to join the front disk and the 1/32-inch disk. When
cured, the four quadrant lines on the sides of the fuselage are marked
on the edge of the disks. The face of the front disk is marked with the
upper end of the landing skid’s shape, and the skid’s shape is cut out
with a scroll saw.
This cutout permits the landing skid to be retained, removed,
straightened, or replaced by removing the engine mount. Epoxy the
rear 1/8 plywood disk to the front piece and place the assembly in a Cclamp
to cure.
Make the two 1/4-inch, five-ply plywood disks that will fit snugly
inside the fuselage. They are epoxied and C-clamped together to cure.
When dry, the 1/2-inch plug is epoxied to the firewall and C-clamped
until cured.
June 2009 27
06sig1.QXD 4/22/09 3:21 PM Page 27
The pylon is constructed using a backbone of 1/8 square balsa, to
which formers are attached. The bottom former is made from 1/2
or 5/8 balsa, while the middle and top formers are 1/8 balsa.
The plywood firewall sandwich forms the engine mount bolt
locations and undercarriage strut location. The plug portion is
relieved for the fuel-line pass.
The stabilizer is straightforward in its construction. The Oliver
stabilizer mount is modified to accommodate VIT hardware. The Seelig timer mounting assembly is put in the fuselage and
pushed to a point where the center of the timer box is 5 inches
from the front of the tube.
Type: A/B FF Gas
Skill level: Advanced
Wingspan: 72.17 inches
Wing area: 557 square inches
Stabilizer area: 94 square inches
Overall length: 51.18 inches
Weight: 26.4 ounces
Engine: Nelson .21
Construction: Carbon-fiber fuselage, balsa, plywood
Finish: Ultra-light film, epoxy paint
Other: Seelig timer or Texas Timers 3F-1, four-function conversion kit
The
Super
Marval
560
28 MODEL AVIATION
06sig1.QXD 4/22/09 2:29 PM Page 28
five or six points on the tube, roughly 1/4 inch behind the backside
of the firewall, that will not interfere with previously installed
hardware. Drill shallow 1/4-inch-diameter holes through the tube into
the plug with a 13/64 bit.
Put a drop of epoxy in each drilled hole, and lightly drive a 3/8-
inch-long, 13/64 dowel into the holes, leaving approximately 1/8 inch of
the dowel sticking out above the tube. These dowels will pin the plug
and firewall to the tube, to assure that the engine is secure on the front
of the tube.
To complete the front end, use cyanoacrylate to adhere small balsa
wedges, which are approximately 13/4 inches long and 1/4 inch high, to
the nose of the tube, against the back of the firewall, and on each side
of the dowels.
Fill spaces between the wedges with carpenter’s wood filler, and
then sand the front of the tube until smooth. Apply six to eight strips
of fiberglass to the front end of the tube, and spread epoxy on the front
3 inches of the tube and the firewall.
Place a piece of waxed paper on the firewall. Attach the engine
mount to the firewall using the 4-40 bolts, which have had the threads
coated with a thick grease, to prevent the epoxy from sticking to the
bolts and the T-nuts. Tighten the 4-40 bolts and hang the fuselage
nose-down to cure.
When dry, remove the bolts, engine mount, and waxed paper. Sand
A small box to house the Walston radio transmitter is installed in
the left side of the pylon; an exit tube runs from the back of the
box out the rear.
Sand the fuselage smooth prior to any installation. The engine
assembly is aligned with quadrant marks and pinned with dowel
rods epoxied into several points.
The engine mount is flaired into the fuselage with firm balsa; the
wood grain running lengthwise increases the airframe’s torqueload
strength.
To accommodate the VIT hardware, the stabilizer’s center rib will
support the stabilizer pivot wire, hold-down rubber-band hook,
bunt line, and glide-DT line.
To ensure the integrity of the epoxy joint between the firewall and
plug, mount a 4-40 Phillips-head bolt with washers and nut through
both the firewall and plug (countersunk both front and back). Tighten
them so they cannot come apart.
Place the engine mount on the firewall, and place a drop of thin
cyanoacrylate glue in the joint. Put the unit in a drill press and make
the four mounting holes for the 4-40 mounting bolts. After slightly
countersinking the holes on the back of the firewall, put T-nuts in the
holes and tighten the 4-40 bolts to seat them.
Place the firewall assembly in a machinist’s vise and drill a 1/4-
inch-diameter hole at an angle from the lower left edge of the engine
mount (near the landing skid) to a point near the center of the plug.
This hole serves as the access to the fuel compartment and fuel
bladder.
You can separate the engine mount from the firewall by forcing a
knife blade a short distance in between the two.
Sand the front of the carbon-fiber fuselage tube square to the
thrustline. Carefully sand roughly an inch of the inside of the tube to
remove any mold-release residue and clean with acetone.
Brush epoxy onto the outside of the plug and the inside of the tube.
Mate the two parts, taking care to line up the top and bottom marks of
the firewall and tube.
After the epoxy has cured for at least 24 hours, carefully choose
June 2009 29
06sig1.QXD 4/22/09 3:33 PM Page 29
For this article I used the popular Seelig timer, which is no
longer available new. A suitable substitute is the Texas Timers’
3F-1, modified with the available four-function conversion kit.
Set the timer disks beginning with the fuel shutoff wire under
the first disk. Let the timer run until the wire just jumps out from
under the notch in the disk. Halt the timer by using the start/stop
plunger.
Loosen the small nut holding the disks. While holding the
bottom disk, rotate the second and third disk so that the notch in
the top disk is roughly 1/16 inch from the end of the power-line
trip wire and the notch in the middle disk is 1/8 inch from the
bunt-line trip wire. Retighten the small nut while holding all the
disks in place.
The stabilizer is installed and all timer lines are connected.
The timer is fully wound, set on a short engine-run mark, and
cycled to see how things work.
If they work correctly, the engine cutoff wire should
escape the first disk at approximately two seconds. A second
later, the power line should release and the stabilizer should snap
down to the bunt position. Then one second later, the bunt line
should release the stabilizer, which will jump up and be stopped
by the glide adjustment nut.
As the timer continues to run, the DT release wire will follow
the grooves in the timer scroll until it reaches the exit point, at
which time that line is released. The cycle is completed when the
timer is reset to the two-second mark and the timer is rewound.
Now the wing should be mounted on its platform and the
bunt line to the stabilizer released. The stabilizer will rise to the
glide-DT stop nut.
Test-glide the aircraft. Adjust the stop nut as needed to obtain
a safe, floating glide. The model should be ready for short power
flights as you begin trimming.
If possible, have a fellow modeler who flies bunters do a
preflight check of your airplane and be present for your first few
power flights. When you are ready for the first flight, the
observer should be 30-40 feet away from the launch site so that
he/she has a different perspective of the model than you do as it
ascends.
This second opinion about when and if the model leaves the
expected flight path and whether it begins as a turn or a pitch
over or back is critical in knowing what adjustments need to be
made. Rotating the power-adjustment screw for one-eighth or
one-quarter turn is usually all the adjustment necessary for pitch
corrections, and small adjustments of the left rudder tab usually
take care of excess turn.
When making the first few flights, hook up only the engine
cutoff line, the power line, and the rudder line to the timer. The
bunt line and the glide-DT line are permitted to hang loose.
This arrangement lets you have a short engine run and a
small selected amount of left rudder for the first flight. You can
observe the pattern of the flight. Then the aircraft goes directly
to a quick DT.
Upon retrieval, set the timer to the engine run time you are
using and wind it fully. Reattach the lines to the timer, and make
any necessary adjustments.
Continue the test flights until the model is flying a straight-up
pattern. Now engine run times can be increased in small
increments and proper adjustments can be made so that the
airplane stays on pattern until the engine stops.
On the first bunting flight, hook up the bunt line but leave the
glide-DT line hanging loose. This permits you to observe the
bunt’s force and duration.
Did the model go too far over or not far enough? Does the
bunt need to be held longer or held for a shorter period? You can
make the needed adjustments by carefully loosening the small
nut on the Seelig disk, slightly moving the appropriate disk, and
retightening the nut.
When the bunt looks good, it is time to check the airplane’s
glide. Hook up all the lines to the timer. Loosen the nut holding
the DT scroll on the timer and reposition it so that the wire in the
scroll grooves will escape nearly 15 seconds after the engine is
stopped. Retighten the scroll nut. The model is flown with a
four- or five-second engine run, to assure that it has plenty of
altitude for the first test glide.
Assuming that the power pattern is good and the bunt is
timely and correctly done, the bunt line will release the stabilizer
so that it pops up and is stopped by the glide adjustment nut.
Observe the glide and make minor adjustments with the glide
adjustment nut as needed.
When you are satisfied that the glide is safe, loosen the scroll
nut again and set the scroll’s exit point so that when the DT wire
is placed in the proper groove, DT will occur at approximately
2:05. The glide is now fine-tuned. MA
—Marvin Mace
Trimming
a Bunter
30 MODEL AVIATION
06sig1.QXD 4/22/09 2:32 PM Page 30
away any excess epoxy, and sand the front of
the fuselage until smooth.
Rudder: The rudder’s size and shape is
important, but how you build it is your
choice. I cut mine to shape from a sheet of 1/8
balsa and cyanoacrylate-glue three layers of
1/64 plywood that are 1/8 inch wide around the
perimeter.
I sand the rudder to a streamlined shape.
Then I cover it with fiberglass cloth using
epoxy, which has Model Research Labs
fluorescent red pigment dissolved in it for
visibility.
Use whatever system of rudder control
you are comfortable with, but make sure it is
screw-adjustable for left tab in the tab power
mode and right tab in the glide.
The rear of the rudder is located 5 inches
from the rear of the fuselage. Before
mounting the rudder, using the top fuselage
line as a guide, randomly drill eight to 10 1/16-
inch-diameter holes along the top of the
fuselage where the rudder will be placed.
Using a No. 50 wire drill, carefully make a
similar number of holes in the bottom of the
rudder.
Cut and remove the masking tape where
the rudder will be mounted. Lightly sand the
top of the fuselage and clean it with acetone.
Mount the rudder directly on top of the
fuselage with a bead of epoxy on both the top
of the fuselage and the bottom of the rudder,
so that the adhesive is forced into the small
holes when they are pressed together. This
results in a strong joint.
Using the aluminum angle, the Hinson
Alignment Jig system, and a couple of
drafting triangles will ensure that the rudder is
properly aligned on the top of the tube.
Stabilizer and Stabilizer Mount: The
stabilizer’s construction is straightforward. A
couple of modifications are made to
accommodate the Variable Incidence
Tailplane (VIT) hardware.
The stabilizer’s center rib is cut from a
medium-light sheet of 1/2 balsa. This rib
supports the stabilizer pivot wire, the holddown
rubber-band hook, the bunt line, the
glide-DT line, and, on the underside of the
rib, a small stainless-steel plate.
The VIT system’s power-adjustment
screw rests on the steel plate. The single rib
provides the strength required to maintain the
stabilizer’s integrity for hundreds of bunts.
A portion of the stabilizer’s LE and
approximately 3/8 inch of the center rib are
removed to permit the installation of a piece
of .062 music wire, which will be fitted into
the groove in the back of the Oliver stabilizer
mount.
That short piece of music wire is supported
June 2009 31
Full-Size Plans Available—see page 183
06sig1.QXD 4/22/09 3:31 PM Page 31
in the stabilizer LE by 1/16 plywood half
ribs and is tricky to install. When the half
ribs are made, holes slightly larger than
the .062 music wire are drilled in each of
the two, approximately 1/8 inch from the
front edge and centered top to bottom.
Then the half ribs are installed in the front
part of the stabilizer, which has been cut
to fit the Oliver stabilizer mount.
Sharpen a 1/2-inch piece of .062 music
wire and insert it into the half rib holes, to
increase the depth of the holes in the balsa
LE. Cut another piece of .062 music wire
to 11/2 inches, and slightly sharpen both
ends. Grasp this wire portion with pliers
and ease one end a short distance into one
of the holes in the half rib.
When the other end clears the opposite
short rib, maneuver the other end into the
opposite hole. The wire can be slid back
and forth, and a drop of epoxy is put in
each hole. Center the wire and set the
stabilizer aside for the epoxy to cure.
The stabilizer is completed when a
cutout is made on the centerline of the
thick rib for the glide-DT post and the
stabilizer capture button. Epoxy a small
stainless-steel plate, made from a razor
blade, to the underside of the rib, just
behind the stabilizer-capture button hole.
Drill a small hole on the centerline of
the wide rib, just behind the front spar,
and epoxy a short piece of dowel in the
hole, to serve as a hook for the rubber
bands that hold the stabilizer.
When you epoxy the stabilizer mount
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in position, be sure to put the stabilizer in
its mount and place the fuselage tube in
the aluminum angle so the stabilizer mount
can be aligned 90° from the rudder. Use a
bubble level on the stabilizer to ensure
accurate positioning. The LE of the
stabilizer mount should be located
approximately 1 inch behind the rudder.
Ken Oliver makes a well-constructed,
efficient stabilizer mount, and it is
designed for bunting models. Judiciously
sanding the mounting hole in the base will
increase the inner diameter and provide a
perfect fit on the tube.
The stabilizer mount’s exact location
will be determined after the completed
stabilizer is fitted on the fuselage with the
VIT system in place. When positioned
properly, the mount will be roughly 31/2
inches from the end of the tube.
Lynch VIT Assembly: I like the VIT unit
that Bill Lynch, an excellent California
Power flier, developed, because it is
located at the end of the fuselage and is
trouble free when properly installed and
rigged. It also permits visual inspection of
important VIT system parts after you have
attached the lines to the Seelig timer and
before you fly the model. The information
brochure Bill provides with his unit is
invaluable when installing it and its lines.
Using the top line marked on the tube,
use the cutoff wheel to make a slice that is
nearly as long and as wide as the top of the
VIT frame (less the front tang). Use a
small file to enlarge the cutout so that the
VIT frame fits.
It is now necessary to mount a short
piece of 3/32-inch-diameter aluminum
tubing through the fuselage at a location so
that the notch in the VIT frame will fit
perfectly on the tubing when the short tang
bolt is tightened.
To determine where the holes for the
3/32 tubing are located on the sides of the
fuselage, I start with my best guess, use a
tiny drill bit, and enlarge the holes in the
proper direction until the tubing is a
perfect fit in the notch of the VIT unit.
When I find the proper location, I install
the 3/32 tubing (which is slightly longer
than the fuselage tube is wide) and epoxy
it in place (both on the inside and outside
of the fuselage).
When cured, slip the VIT frame into
position with the notch over the 3/32
aluminum tube. Drill a small hole in the
top of the fuselage, matching the hole in
the tang.
Screw a 1/4-inch-long 2-56 bolt, on
which you place a small flat washer and a
lock washer, through the hole in the top of
the tube and into the hole in the tang of the
frame, so that the frame is held firmly in
place when the bolt is tightened.
Wing: The balsa D-box wing spans 72
inches and is constructed in five panels.
The main spar is an I-beam with 1/4 x .007
carbon-fiber strips on the insides of the 1/4
x 1/8 balsa spar caps.
Covered with ultra-light plastic film
and with balsa Hoerner-type tips, the wing
weighs 8.8 ounces. It is dead stiff, as it
must be.
Pylon Construction and Attachment: The
pylon is constructed using a backbone of
1/8 square balsa, to which formers are
attached. The bottom former is made from
1/2 or 5/8 balsa, while the middle and top
formers are 1/8 balsa.
A small box to house the Walston radio
transmitter is installed in the left side of
the pylon with an exit tube running from
the back of the box out the rear of the
pylon. Then the pylon is covered with 1/16
balsa sheet. Cover the left side of the pylon
first, so that the hole for the transmitter box
can be easily marked from the backside
and then cut out.
The bottom of the pylon must be sanded
to a curved shape so that it will fit against
the fuselage tube. You can do this by
wrapping a sheet of 100-grit sandpaper
around the fuselage and then sliding the
base of the pylon back and forth in a
straight line over the sandpaper, to remove
the excess balsa. It is difficult, but it works
and, finally, a good fit is achieved.
Put the pylon on the fuselage using a
couple of rubber bands to hold it. Check to
see what incidence is on the wing platform.
To do so, return the fuselage to the
aluminum angle and jack up the rear of the
tube until its centerline is parallel to the
top of your workbench. Using an accurate
ruler, measure the distance from the top of
the table to the front and rear of the wing
platform.
If the front is roughly 1/8 inch higher
than the rear, you are home free. If not,
you must continue the back-and-forth
sanding, with pressure applied as needed,
until the platform incidence is 1/8 inch.
With the correct wing incidence, the
model can be assembled and the final
pylon location can be determined.
Make a permanent mark on the edge of
the platform at 58% of the wing chord.
Install the engine, propeller, spinner, wire
skid, timer, and radio transmitter. The
wing with the pylon and stabilizer are
attached to the fuselage with rubber bands.
Balance the model at 58% of the wing
chord by sliding the wing pylon back and
forth on the tube until a balance point is
found and the fuselage is parallel to the
floor. Mark the masking tape on the top
line of the fuselage where the front and
back of the pylon are. Randomly drill a
series of small holes along the top line of
the fuselage between the marks, and drill
several small holes in the bottom of the
pylon.
Remove the masking tape where the
pylon is to be located. Lightly sand the top
of the tube, and clean it with acetone. Coat
the top of the fuselage and the bottom of
the pylon with epoxy, and join them. As
with the rudder, the adhesive will be
forced into the small drilled holes,
improving the joint strength.
Three or four strong rubber bands are
used to hold the pylon tightly to the
fuselage, and then it is placed in the
aluminum angle. Line up the pylon with
the remaining top line marks on the
fuselage and with the rudder while using a
bubble level on the top of the wing
platform. When everything is properly
aligned, allow the epoxy to cure for 24
hours.
When cured, fair the pylon into the
fuselage tube using a mixture of epoxy
and microballoon filler, and then sand.
Mask off the rudder, and paint the
fuselage. I prefer to use white epoxy paint
on the fuselage, because it is highly
visible and cooler in the summertime.
Flight Preparation: Before heading to
the flying field for the first test flight, it is
mandatory that you check the model, in
the shop, for decalage. To do this, draw a
48-inch straight line on the workbench.
Then lay the fuselage on its side, with its
centerline located precisely on the straight
line. Draw a line on the workbench from
the front to the back of the wing platform.
Go to the back of the fuselage, and
make a dot on the workbench that
corresponds with the wire groove of the
Oliver stabilizer mount. Using a drafting
triangle pressed against the top of the
power adjustment screw, make a mark
indicating the top of that screw.
Accurately measure the distance
between the front and back of the wing
platform to the fuselage centerline, and
measure from the two dots, which
represent the distance from the front and
back of the stabilizer to the centerline. The
difference between the measurements
represents the model’s decalage.
Recall that we built 1/8 inch of
incidence into the wing platform when we
mounted it on the fuselage. Since we
would like to start our trimming with 1/16
inch of decalage, we can adjust the power
adjustment screw up or down as needed to
achieve this 1/16 difference.
You should be ready to trim your Super
Marval for competition. Repeatable, safe
engine runs are extremely important—
especially at four and five seconds. The
penalty for overruns during flyoffs is a
zero time, and nothing could be worse. Err
on the side of a safe engine run.
You must keep your timer clean and
oiled and all of your model’s parts in
perfect shape and in good working order.
Have confidence in your timer and your
ability to accurately set it for any engine
run.
That confidence comes from making
many test flights with the help of fellow
modelers who know how to accurately
time an engine run. The watch starts when
the aircraft leaves the flier’s hand and ends
when you hear the engine’s last audible
power stroke.
I take this opportunity to acknowledge the
invaluable help and advice I have received
from my fellow bunters in the past few
years as I have tried to get up to speed.
Insights or clever ideas that I appear to
claim as my own are the result of
conversations I have had with guys such as
Doug Galbreath, Bill Lynch, Ken Oliver,
the late Bob Johannes, Dick Covalt, Bob
Mattes, Gil Robbins, Ronnie Thompson,
Don DeLoach, Faust Parker, Henry
Spence, Mark Troutman, Reid and Roger
Simpson, C.C. Johnson, and Dick Hall.
I also thank Larry Kruse for helping me
put this construction article together in a
format for publication. The Super Marval
is as much your model as it is mine. MA
Marvin Mace
107 Country Ln.
Seguin TX 78155
(830) 379-0036
[email protected]
Sources:
Seelig carbon-fiber tube:
Reid C. Simpson
115 Trail Ridge Dr.
Athens TX 75751
(903) 677-8525
[email protected]
Oliver stabilizer mount:
Ken Oliver
2213 El Cejo Cir.
Rancho Cordova CA 95670
(916) 363-2017
Lynch VIT system:
Bill Lynch
2279 Auburn Ravine Dr.
Lincoln CA 95648
(916) 645-3337
[email protected]
Alignment Jig:
Rex Hinson
1141 S. Waterview Dr.
Inverness FL 34450
(352) 344-5931
[email protected]
Red fluorescent pigment:
Model Research Labs/Curt Stevens
25108 Marguerite Parkway #160
Mission Viejo CA 92692
[email protected]
Walston Retrieval Systems:
Jim Walston
725 Coopers Lake Rd. SE
Smyrna GA 30082
(770) 434-4905
[email protected]
Texas Timers (Request model 3F 1 and
four-function conversion kit)
3317 Pine Timbers Dr.
Johnson City TN 37604
(423) 282-6423
www.texastimers.com