have hard data to explain why. We experimented with outside-thebox
designs using non-Stunt power plants and flap-free wings. Our
aim was to fly the pattern to the specified dimensions so accurately
that we had to get top points. (Yeah, right.)
The wingspan was limited to 54 inches so that they would fit into
Bob’s Volvo sedan! I had determined that wings with zero quarter
chord sweep angles didn’t
react to wind by chattering
in roll, so we held this
criterion.
After a suitable period,
we realized that the judging
cadre was not using the
book dimensions and had
no intention of ever
measuring them by any
equipment other than the
trained eyeball.
By 1975 it was clear
that Bob would have to fly a traditional airplane to stay in the top
five at major meets. He joined the campaign with his Avanti series:
a conventional flapped machine with conventional styling. I waded
into the flap-analysis swamp armed with a TI-59 programmable
calculator. Progress was slow because flap calculations are tedious
and complex. We applied each of my research breakthroughs to the
Avanti and tested the accuracy of my progress.
There were also several major configurations to idealize the yaw
January 2004 29
BareCat 650-C
THIS AIRPLANE and document are my sentimental journey to
honor the memory of Bob Baron (1944-1999) and our long
collaboration to design and compete with cutting-edge Control Line
Precision Aerobatics equipment.
It started when Bob showed up on my doorstep in Pasadena,
California, sometime during 1965. He was able to feel and analyze
things about the airplane in flight where my calculations only
showed variation in the second decimal place.
We knew that flaps were difficult to keep in tune, but we didn’t
A bottom view of the BareCat shows the no-frills approach that
Bill prefers. The trim scheme is simple.
Sometimes
function yields
unusual forms
■ Bill Netzeband
01sig1.QXD 10/27/03 2:00 pm Page 29
30 MODEL AVIATION
axis, the power-plant package, the landing gear, the Rabe rudder, and
search for the magic flap-elevator relationship. Along with the
aerodynamic package criterion, we added simple structure with
maximum longevity.
In 1984 I tiptoed into the computer era and was able to get
answers more rapidly. Unfortunately I developed all of my programs
using arcane software, so I won’t be able to provide the math for
your design efforts.
It became clear that flaps introduce forces that vary widely with
any center of gravity (CG) shift or a minor velocity change, and
while making a possible 40% more lift available to the wing, they
load the elevator excessively and demand lots of extra thrust! I kept
looking for ways to compete without flaps because I like simple
solutions, and my skill level peaked out a little bit above average.
Bob and I left off anything that did not contribute to flying the
AMA rule-book pattern dimensions, such as labor-intensive
decorations and artistic shapes and high finishes, which add up to
weight and cost.
The Humbug series, initiated in 1968, was based on 7:1-aspectratio
wings controlled by 10:1-aspect-ratio stabilators, and it had
minimal fuselage and appendages. The stabilators were later
replaced by using stabilizer-elevator surfaces. They were also based
on low power-to-weight-ratio airframes.
The original Humbug used a Fox .19 to power 490 square inches
of wing at 39 ounces. Subsequent versions backed down to 6:1-
aspect-ratio wings and 8:1 stabilizers, and the late Tom Warden
styled a couple of them. They produced positive comments from the
general population but missed the winner’s circle too often.
The 1⁄2A BareCat was designed in 1980, to achieve the lowest
practical wing loading and take advantage of reducing the wing
aspect ratio to 4:1 and the tail to 6:1. The tail became 30% of the
wing, and the tail moment arm was 14 inches.
We added a practical problem by storing fuel on the CG in a
bladder tank since a tank in the 11-inch nose would upset the CG
during flight. We were looking for the 5-foot corner, but the whole
1⁄2A project went too far outside the box to become a popular
configuration.
In 1993 I wrote a story called “The Stunt Ace” and designed a
theoretically optimized machine that would do a book pattern. It
required a super .09 engine to save dead weight and fuel and to allow
.012-inch-diameter lines. Fuel was stored in a high-pressure bladder
mounted on the CG, as in the 1⁄2A BareCat. I had to specify several
unobtanium space-age materials to keep the weight down. It flew
great on paper, but, as in real life, Ace missed qualifying at its first
Nats by a half point.
The machine had a 600-square-inch wing, huge centerline fin
surfaces, a single wheel, booms, a stabilator, etc., and only weighed
15 ounces. Bob enjoyed the story and asked me if it would fly with a
Spar and trailing-edge pieces are attached to the foam cores.
Don’t omit the panel-identification marks!
Leading- and trailing-edge planking has been added. Masking
tape is used to hold everything down tight.
The wing takes shape with the addition of capstrips and centersection
planking. Notice the splice-plate cutouts.
The bellcrank assembly, with attached pushrod, is glued in
place. Take extra care to ensure smooth movement.
01sig1.QXD 10/27/03 2:00 pm Page 30
.15 engine. He built the BareCat 600 from my sketches using a
Nelson .15 Combat engine.
The puzzlement came when the 40-ounce machine flew off the
bench, and the few times Bob and the Nelson got together with the
needle valve and the experimental bladder fuel system, it handled
like an eagle! Those happy moments were too few, and Bob shelved
it.
I got my hands on the airframe in 1998 and tried a Norvel .15. I
replaced the stabilator and nonlinear bellcrank with a 50%
stabilizer-elevator assembly. The thing teased me by flying all of the
maneuvers, but it couldn’t deliver adequate confidence. It ended up
with a Double Star .40, a conventional fuel tank in the nose, it
gained 7 ounces, and it became a better-than-average performer.
There was not enough sizzle, though.
Bob had a final adventure using the BareCat ’98 that was
published in the June 1999 Model Aviation. He took it to the 1998
Nationals for recreation. Tragically, his Spartan broke up during a
test flight after he had qualified for the finals! Being a consummate
competitor, Bob decided to fly the BareCat.
Several problems in addition to being first up to fly the next day
prompted an all-nighter. He’d been flying with .008 lines on the
airplane powered by a 1cc engine! The last trimming trauma was a
frantic session to install a combat-tuned VA .049. He had help from
Larry Driskill and “Sleepy” Dawson.
After little real sleep, they got in a fast test flight at 6 a.m. Bob’s
first flight was humming along when the engine mount broke and
the VA sailed off into the boondocks. Bob finessed it back to the
runway with no further damage.
The next frantic fix involved reinstalling the 1cc engine and a set
of “equivalent” .012-diameter lines. With no test flight, Bob racked
up a 500-point score from the Nationals judges—not too shabby for
an outside-the-box machine.
In 1998 Tom Dixon was producing a Double Star 50, and we
decided to give the BareCat another shot. We used the 1⁄2A BareCat
geometry and enlarged it to produce 650 square inches of wing.
After reviewing the layout, we adjusted the tail moment arm and
stabilizer aspect ratio to more reasonable sizes for a large airplane.
Bob constructed the first model and used an inverted Double Star
50 engine and spinner. This airplane was almost finished when he
passed away in September 1999. Tom Dixon finished Bob’s model
and flew it a few times. It needed flight trimming, but Tom and I
decided that Bob’s last project shouldn’t be put at any more risk.
To make Bob’s airplane unique, I modified the drawings to use
an upright engine and aluminum two-wheel landing gear. I built the
“A” model and powered it with a Double Star 50. While putting up
with nose-heavy trim, I crashed it inverted, broke the engine, and
cracked a few major joints.
The cowl-free nose allows easy access to the removable tank for
height adjustments. Notice the engine-mount pads.
The engine mounts and lower firewalls assemble on a flat
surface. Clamp them tightly and let the epoxy cure.
The top and bottom planks and the nose-block wedge piece have
been assembled and smoothed into the spinner shape.
Photos by the author
January 2004 31
The doublers have been joined to the fuselage sides. Check out
the 1⁄4 triangle stock reinforcement pieces.
01sig1.QXD 10/27/03 2:01 pm Page 31
During the repair phase I shortened the nose to move the CG to
the design location, and Tom replaced the engine. The next flight
series was truncated at four. The partially tuned BareCat was
feeling good, and I tried an Hourglass. I ham-handedly executed the
first corner and the model came loose on the second corner, quickly
hiding behind my hat, and augered into the unyielding ground
before I could turn around.
There were several large pieces, but none of them had joints that
lent themselves to reconstruction. Besides that, the new engine was
split open after the fuel tank mashed around it, and the engine beam
mounts made a wishbone out of the engine crankcase.
Post-mortem analysis revealed that the twin-finned design had
excessive yaw stability but inadequate side area to generate enough
yaw torque to recover from extreme adverse yaw. Bob never
overcontrolled a model, so the problem didn’t show up until I got
my hands on one. So the twin-finned BareCat 650 project ended
with two prototypes, and I moved on to the B model.
The BareCat 650-B incorporated the single-finned side view of
the old 600, a sidewinder engine on a Radio Control engine mount,
and it preserved the now-proven 650 plan-view geometry. I used a
4-year-old Silver Foxx .40 to take advantage of the .015-diameter
cable. This is a powerful engine. I settled on 10% fuel and an APC
12.25 x 3.75 propeller.
This allows a rich, level flight and plenty of reserve thrust for
the vertical maneuvers. It comes on and off reliably, and with a 20%
oil blend it needs less than 4 ounces to complete the pattern.
Trimming the model was straightforward and surprise-free. I
cleaned up the slight tendency to turn tighter outside by sliding the
lines down on the handle to adjust my leverage and feel. The 650-B
at 54 ounces competes in the Advanced class with good results for
me. I currently fly it with a Tom Dixon-prepared O.S. .46 LA and
use 66 feet of that dreaded .018-diameter cable required by rules.
We sincerely believe that too much horsepower is about right.
I wouldn’t expect those competing in the Expert class to use
BareCat 650-C
It’s time for a dry-assembly test to ensure that all parts fit
together properly before gluing. Looks good!
A clean, functional front end. Look at neat fuel-line routing and
muffler installation. Details make the difference!
Type: CL sport Stunt
Wingspan: 541⁄4 inches
Engine: Double Star 50
Flying weight: 49 ounces
Construction: Balsa, plywood, foam
Covering/finish: MonoKote/modeling paints
32 MODEL AVIATION
The wingtip braces and leadout guide have been installed on the
inboard wing panel. Braces do not touch the covering.
01sig1.QXD 10/27/03 2:02 pm Page 32
January 2004 33
something as simple as this machine as their
competition mount. This is an excellent
airplane with which to work your way up
through the ranks before you have to start
the arduous task of keeping a flap model in
tune.
The C model is presented with three
different nose configurations. I selected the
inverted engine for personal reasons. (It
looks the best.) Cut the nose you want from
sheet two of the plans and tape the paper
doll to the main drawing. The attach point is
the firewall at the leading edge. The plan
width is set for beam mounts and stock
tanks, and once you blend in the shapes you
can have as fancy a nose as anyone’s.
However, the totally external engine
system (the B model) is ideal for running
power-plant experiments. The fuel-mixture
symmetry on my B model was adjusted with
the tank raised 1⁄8 inch.
The covering and decoration are
MonoKote. The foam wing core is available
from Tom Dixon. The C model had a dry
weight of 49 ounces using a carbon-fiber
landing-gear strut, the lightweight Double
Star 50 engine, and a 12 x 6 wood propeller.
On 68 feet (handle to airplane centerline) x
.018-diameter cables, there is plenty of
reserve line tension overhead. The best CG
is per the plans, and the prototype nailed it
without adding dead weights.
CONSTRUCTION
This is not a beginner’s project; you
should have experience with handling
standard materials and construction
procedures. There are no major kinks in
assembling the BareCat 650. (Well, you do
need to get the assembled parts square to
each other.) I have laid out the major parts
to provide self-alignment features between
the fuselage and wing and the tail and the
airplane.
As you browse through the construction
photos you will see a lot of masking tape. It
does much more than block off paint! It
clamps around things, across flat joints, over
wingtips, along edges you don’t want to
sand, and many places you don’t want to
leave pinholes.
I like putting a 2-inch-wide strip over the
end of my shaping block and sliding the
taped end along a tip rib to blend in the
wingtip. I use 100-grit garnet sandpaper
with light pressure for fast removal to
rough-shape. I follow this with 150-grit
paper to take out the tool marks, 280 grit,
then 400 grit to polish the wood.
Using plastic film covering all over
forces me to make joints fit superclose,
which is essential to solid glue joints
anyway. It requires extra planning during
covering to leave it off where parts fit
together rather than cut away film after
covering. I get nervous cutting through film
on top of balsa, particularly over 1⁄16 balsa
planking.
The foam wing cores you buy from Tom
Dixon are geared toward his exoskeleton
planking system, and the cored-out portions
save 4 ounces of dead weight. Tom
publishes a comprehensive assembly
procedure, which you can download when
you order the cores on his Web site.
I prefer to cut the main spar on the
centerline and add splice plate caps during
final wing assembly. One convenience is
being able to block-sand the center face of
both panels to gain the best glue joint and
alignment. The caps carry the major bending
loads anyhow.
I keep the waste-foam material handy to
hold the cores during work and storage.
They prevent a lot of hangar rash and make
nice, stable support fixtures. With the 24-
inch panel cores, you don’t have to order
48-inch lumber. I purchased 24-inch
selected stock from Lone Star Models.
Have someone there select the stabilizer
and elevator in 3⁄16, 6- to 8-pound stock—
one 4 x 36 inches and one 3 x 36 inches.
The 1⁄4 stock for fins, tips, and top and
bottom planks needs to be 4 inches wide and
36 inches long in 6- to 8-pound density. I
used four pieces altogether.
I stripped the leading edge from a 1⁄4
sheet to get it dead straight in the relaxed
state. Logical sequence of adding parts
yielded a 15.3-ounce fully covered wing
with controls and an ounce of permanent tip
weight. If you noticed that my tip-weight
box cover is on top, don’t sweat it. The first
time I did it was an accident, and I got used
to it on future airplanes.
After you complete the wooden parts
assembly, do the wingtips, line guide, tipweight
box, and the bellcrank dry assembly.
Put these pieces aside until the rest of the
uncovered parts are ready to cover.
Before and after you cover the stabilizer
and elevator pieces, make sure that both
mating edges are dead straight—not just
mated to the same curvature. You will be
01sig2.QXD 10/27/03 10:40 am Page 33
34 MODEL AVIATION
Full-Size Plans Available—see page 191
01sig2.QXD 10/27/03 10:41 am Page 34
January 2004 35
rewarded with an elevator that drops freely
by its own weight. Careful location and
cutting hinge slots will save you problems
during final assembly, when the parts are all
covered and polished.
The control-horn base takes a bit of skill
but gives a clean, fuelproof assembly. (See
the plans for details.) Make sure that the
horn is located on the bottom and the
inboard side before you cut the pocket. (I
didn’t do it once.) I cut out the fin parts at
the same time as the stabilizer parts and get
into a rhythm of rounding edges, blocksanding,
and polish-sanding these parts.
I drilled a series of 1⁄2-inch-diameter
holes along the engine mounts to save dead
weight. Using a Forstner drill bit I let the
center point just break out of the hole’s
bottom, which leaves a solid glue surface. I
use 1⁄8-inch dowel pins to key the fuselage
sides and doublers during their glue process.
I use epoxy, well-squeegeed, and apply a
great deal of pressure between flat surfaces
to gain the optimum joint strength. The pins
are sanded on both sides until flush to both
surfaces.
I make a subassembly of the engine
mounts, two subfirewalls and the spacer
block, and the filler piece, assembled
squarely and flat using epoxy. This group is
used to square and align the fuselage sides
and top assembly on a nice, flat surface. If
this assembly is true, the final product
works better.
Thoroughly coat with epoxy the inside
surfaces that will be exposed to fuel. Do the
engine mounting holes and spacer plates,
then tape up the engine. Mount it and a
sacrificial spinner and carve the nose. Here
you should have the uncovered wood parts
ready for final assembly.
Final Assembly: Tape the wing halves
together, dry-assemble the fuselage to the
wing, then use the flat tabletop to fit the top
fin and the booms and stabilizer together.
Once these joints are tuned to firm slip fits,
proceed with covering the parts. The closer
these joints fit, the better the strength, and
you really can get quality without fillets to
cover the gaps.
Final assembly is straightforward,
requiring care to align parts and make solid
glue joints. Once the assembly is finished,
add all of the deadweight parts: landing-gear
assembly, control horn, pushrod half, fuel
tank and padding, and plumbing.
The covering and decorations are up to
you and your comfort level. I went beyond
my usual level of decoration, but don’t
expect this all the time. One thing Bob and I
learned is that the 20 appearance points we
could get now far outweigh the 80 points
awarded in the beginning days of Stunt to
turn the design direction away from the ugly
barndoor machines. It is also clear that the
appearance judging has saved the event
from becoming easy.
Flying: If your finished CG is within 1⁄8
inch of the design location, you might as
well proceed to flight tests. The lines’
location on the plans are for the design CG
and a 50-ounce dry weight. You can tune
your model from there as you get used to it.
I was able to hit the design CG right on
with a wood propeller, and so far the lines
rake is correct using 66-foot x .018-diameter
cables, eyelet to eyelet. This delivers a flight
radius, including 2.5 feet for my extended
arm, of 70.8 feet.
I have an ounce of tip weight in the box,
for a total of 2 ounces. I am still playing the
propeller, tank-height game while feeling
safe to ease through all of the pattern
maneuvers. I learned that 6.0-second laps are
too slow and that 5.5 seconds brings up safe
tension and controls force.
The Double Star 50 is performing
routinely with no bad habits on 10%-nitro
fuel. I still need to stabilize the power-plant
components before determining the ideal
fuel capacity. It will probably be less than 5
ounces.
Since Bob is no longer available to make my
numbers sing, will there be more BareCat
type projects? The three models presented
here represent optimal geometry under the
present pattern specifications. Someone
could probably shave off a few ounces with
carbon fiber and a Lost Foam wing structure.
Frankly, the resulting machinery would not
present better enough than the present
structure to warrant the additional effort.
I believe that any of the top-10 pilots
could compete successfully with a BareCat
650. Brave words, for sure, but I don’t
believe any of them will try it. Don’t feel
sorry for me; I had my time in the barrel and
am ready to coast a bit. Please try the
BareCat. You’ll like it!
Thanks, Bob. It was a fun run. MA
Bill Netzeband
23978 Villa Pamilla
Murrieta CA 92562
$3900
+ $450 S/H
DAKOTA
Joe Wagners, Classic
Free Flight design.
24" wingspan for
.02 or .049 engine
BMJR Model Products
Box 1210
Sharpes, FL 32959-1210
321-537-1159
www.BMJRModels.com
Materials Sources:
Foam wing cores (BareCat), Bolly landing
gear (KA-10), Double Star 50 engine:
Tom Dixon
Box 671166
Marietta GA 30062
Tel./Fax: (770) 592-3279
http://members.tripod.com/~TomDixon/tom
dixon.htm
Fuel tank, controls, wheels, propellers:
Brodak Mfg. & Distributing Co. Inc.
100 Park Ave.
Carmichaels PA 15320
(724) 966-2726
Fax: (724) 966-5760
www.brodak.com
Fuel tank, controls, wheels, propellers:
RSM Distribution
21899 Heliotrope Ln.
Wildomar CA 92595
(714) 931-6038
www.rsmdistribution.com
Selected-density balsa (see plans):
Lone Star Models
115 Industrial
Lancaster TX 75134
(972) 218-9663
(800) 687-5555 (to order)
Fax: (972) 218-9211
www.lonestar-models.com
01sig2.QXD 10/27/03 10:41 am Page 35
Edition: Model Aviation - 2004/01
Page Numbers: 29,30,31,32,33,34,35
Edition: Model Aviation - 2004/01
Page Numbers: 29,30,31,32,33,34,35
have hard data to explain why. We experimented with outside-thebox
designs using non-Stunt power plants and flap-free wings. Our
aim was to fly the pattern to the specified dimensions so accurately
that we had to get top points. (Yeah, right.)
The wingspan was limited to 54 inches so that they would fit into
Bob’s Volvo sedan! I had determined that wings with zero quarter
chord sweep angles didn’t
react to wind by chattering
in roll, so we held this
criterion.
After a suitable period,
we realized that the judging
cadre was not using the
book dimensions and had
no intention of ever
measuring them by any
equipment other than the
trained eyeball.
By 1975 it was clear
that Bob would have to fly a traditional airplane to stay in the top
five at major meets. He joined the campaign with his Avanti series:
a conventional flapped machine with conventional styling. I waded
into the flap-analysis swamp armed with a TI-59 programmable
calculator. Progress was slow because flap calculations are tedious
and complex. We applied each of my research breakthroughs to the
Avanti and tested the accuracy of my progress.
There were also several major configurations to idealize the yaw
January 2004 29
BareCat 650-C
THIS AIRPLANE and document are my sentimental journey to
honor the memory of Bob Baron (1944-1999) and our long
collaboration to design and compete with cutting-edge Control Line
Precision Aerobatics equipment.
It started when Bob showed up on my doorstep in Pasadena,
California, sometime during 1965. He was able to feel and analyze
things about the airplane in flight where my calculations only
showed variation in the second decimal place.
We knew that flaps were difficult to keep in tune, but we didn’t
A bottom view of the BareCat shows the no-frills approach that
Bill prefers. The trim scheme is simple.
Sometimes
function yields
unusual forms
■ Bill Netzeband
01sig1.QXD 10/27/03 2:00 pm Page 29
30 MODEL AVIATION
axis, the power-plant package, the landing gear, the Rabe rudder, and
search for the magic flap-elevator relationship. Along with the
aerodynamic package criterion, we added simple structure with
maximum longevity.
In 1984 I tiptoed into the computer era and was able to get
answers more rapidly. Unfortunately I developed all of my programs
using arcane software, so I won’t be able to provide the math for
your design efforts.
It became clear that flaps introduce forces that vary widely with
any center of gravity (CG) shift or a minor velocity change, and
while making a possible 40% more lift available to the wing, they
load the elevator excessively and demand lots of extra thrust! I kept
looking for ways to compete without flaps because I like simple
solutions, and my skill level peaked out a little bit above average.
Bob and I left off anything that did not contribute to flying the
AMA rule-book pattern dimensions, such as labor-intensive
decorations and artistic shapes and high finishes, which add up to
weight and cost.
The Humbug series, initiated in 1968, was based on 7:1-aspectratio
wings controlled by 10:1-aspect-ratio stabilators, and it had
minimal fuselage and appendages. The stabilators were later
replaced by using stabilizer-elevator surfaces. They were also based
on low power-to-weight-ratio airframes.
The original Humbug used a Fox .19 to power 490 square inches
of wing at 39 ounces. Subsequent versions backed down to 6:1-
aspect-ratio wings and 8:1 stabilizers, and the late Tom Warden
styled a couple of them. They produced positive comments from the
general population but missed the winner’s circle too often.
The 1⁄2A BareCat was designed in 1980, to achieve the lowest
practical wing loading and take advantage of reducing the wing
aspect ratio to 4:1 and the tail to 6:1. The tail became 30% of the
wing, and the tail moment arm was 14 inches.
We added a practical problem by storing fuel on the CG in a
bladder tank since a tank in the 11-inch nose would upset the CG
during flight. We were looking for the 5-foot corner, but the whole
1⁄2A project went too far outside the box to become a popular
configuration.
In 1993 I wrote a story called “The Stunt Ace” and designed a
theoretically optimized machine that would do a book pattern. It
required a super .09 engine to save dead weight and fuel and to allow
.012-inch-diameter lines. Fuel was stored in a high-pressure bladder
mounted on the CG, as in the 1⁄2A BareCat. I had to specify several
unobtanium space-age materials to keep the weight down. It flew
great on paper, but, as in real life, Ace missed qualifying at its first
Nats by a half point.
The machine had a 600-square-inch wing, huge centerline fin
surfaces, a single wheel, booms, a stabilator, etc., and only weighed
15 ounces. Bob enjoyed the story and asked me if it would fly with a
Spar and trailing-edge pieces are attached to the foam cores.
Don’t omit the panel-identification marks!
Leading- and trailing-edge planking has been added. Masking
tape is used to hold everything down tight.
The wing takes shape with the addition of capstrips and centersection
planking. Notice the splice-plate cutouts.
The bellcrank assembly, with attached pushrod, is glued in
place. Take extra care to ensure smooth movement.
01sig1.QXD 10/27/03 2:00 pm Page 30
.15 engine. He built the BareCat 600 from my sketches using a
Nelson .15 Combat engine.
The puzzlement came when the 40-ounce machine flew off the
bench, and the few times Bob and the Nelson got together with the
needle valve and the experimental bladder fuel system, it handled
like an eagle! Those happy moments were too few, and Bob shelved
it.
I got my hands on the airframe in 1998 and tried a Norvel .15. I
replaced the stabilator and nonlinear bellcrank with a 50%
stabilizer-elevator assembly. The thing teased me by flying all of the
maneuvers, but it couldn’t deliver adequate confidence. It ended up
with a Double Star .40, a conventional fuel tank in the nose, it
gained 7 ounces, and it became a better-than-average performer.
There was not enough sizzle, though.
Bob had a final adventure using the BareCat ’98 that was
published in the June 1999 Model Aviation. He took it to the 1998
Nationals for recreation. Tragically, his Spartan broke up during a
test flight after he had qualified for the finals! Being a consummate
competitor, Bob decided to fly the BareCat.
Several problems in addition to being first up to fly the next day
prompted an all-nighter. He’d been flying with .008 lines on the
airplane powered by a 1cc engine! The last trimming trauma was a
frantic session to install a combat-tuned VA .049. He had help from
Larry Driskill and “Sleepy” Dawson.
After little real sleep, they got in a fast test flight at 6 a.m. Bob’s
first flight was humming along when the engine mount broke and
the VA sailed off into the boondocks. Bob finessed it back to the
runway with no further damage.
The next frantic fix involved reinstalling the 1cc engine and a set
of “equivalent” .012-diameter lines. With no test flight, Bob racked
up a 500-point score from the Nationals judges—not too shabby for
an outside-the-box machine.
In 1998 Tom Dixon was producing a Double Star 50, and we
decided to give the BareCat another shot. We used the 1⁄2A BareCat
geometry and enlarged it to produce 650 square inches of wing.
After reviewing the layout, we adjusted the tail moment arm and
stabilizer aspect ratio to more reasonable sizes for a large airplane.
Bob constructed the first model and used an inverted Double Star
50 engine and spinner. This airplane was almost finished when he
passed away in September 1999. Tom Dixon finished Bob’s model
and flew it a few times. It needed flight trimming, but Tom and I
decided that Bob’s last project shouldn’t be put at any more risk.
To make Bob’s airplane unique, I modified the drawings to use
an upright engine and aluminum two-wheel landing gear. I built the
“A” model and powered it with a Double Star 50. While putting up
with nose-heavy trim, I crashed it inverted, broke the engine, and
cracked a few major joints.
The cowl-free nose allows easy access to the removable tank for
height adjustments. Notice the engine-mount pads.
The engine mounts and lower firewalls assemble on a flat
surface. Clamp them tightly and let the epoxy cure.
The top and bottom planks and the nose-block wedge piece have
been assembled and smoothed into the spinner shape.
Photos by the author
January 2004 31
The doublers have been joined to the fuselage sides. Check out
the 1⁄4 triangle stock reinforcement pieces.
01sig1.QXD 10/27/03 2:01 pm Page 31
During the repair phase I shortened the nose to move the CG to
the design location, and Tom replaced the engine. The next flight
series was truncated at four. The partially tuned BareCat was
feeling good, and I tried an Hourglass. I ham-handedly executed the
first corner and the model came loose on the second corner, quickly
hiding behind my hat, and augered into the unyielding ground
before I could turn around.
There were several large pieces, but none of them had joints that
lent themselves to reconstruction. Besides that, the new engine was
split open after the fuel tank mashed around it, and the engine beam
mounts made a wishbone out of the engine crankcase.
Post-mortem analysis revealed that the twin-finned design had
excessive yaw stability but inadequate side area to generate enough
yaw torque to recover from extreme adverse yaw. Bob never
overcontrolled a model, so the problem didn’t show up until I got
my hands on one. So the twin-finned BareCat 650 project ended
with two prototypes, and I moved on to the B model.
The BareCat 650-B incorporated the single-finned side view of
the old 600, a sidewinder engine on a Radio Control engine mount,
and it preserved the now-proven 650 plan-view geometry. I used a
4-year-old Silver Foxx .40 to take advantage of the .015-diameter
cable. This is a powerful engine. I settled on 10% fuel and an APC
12.25 x 3.75 propeller.
This allows a rich, level flight and plenty of reserve thrust for
the vertical maneuvers. It comes on and off reliably, and with a 20%
oil blend it needs less than 4 ounces to complete the pattern.
Trimming the model was straightforward and surprise-free. I
cleaned up the slight tendency to turn tighter outside by sliding the
lines down on the handle to adjust my leverage and feel. The 650-B
at 54 ounces competes in the Advanced class with good results for
me. I currently fly it with a Tom Dixon-prepared O.S. .46 LA and
use 66 feet of that dreaded .018-diameter cable required by rules.
We sincerely believe that too much horsepower is about right.
I wouldn’t expect those competing in the Expert class to use
BareCat 650-C
It’s time for a dry-assembly test to ensure that all parts fit
together properly before gluing. Looks good!
A clean, functional front end. Look at neat fuel-line routing and
muffler installation. Details make the difference!
Type: CL sport Stunt
Wingspan: 541⁄4 inches
Engine: Double Star 50
Flying weight: 49 ounces
Construction: Balsa, plywood, foam
Covering/finish: MonoKote/modeling paints
32 MODEL AVIATION
The wingtip braces and leadout guide have been installed on the
inboard wing panel. Braces do not touch the covering.
01sig1.QXD 10/27/03 2:02 pm Page 32
January 2004 33
something as simple as this machine as their
competition mount. This is an excellent
airplane with which to work your way up
through the ranks before you have to start
the arduous task of keeping a flap model in
tune.
The C model is presented with three
different nose configurations. I selected the
inverted engine for personal reasons. (It
looks the best.) Cut the nose you want from
sheet two of the plans and tape the paper
doll to the main drawing. The attach point is
the firewall at the leading edge. The plan
width is set for beam mounts and stock
tanks, and once you blend in the shapes you
can have as fancy a nose as anyone’s.
However, the totally external engine
system (the B model) is ideal for running
power-plant experiments. The fuel-mixture
symmetry on my B model was adjusted with
the tank raised 1⁄8 inch.
The covering and decoration are
MonoKote. The foam wing core is available
from Tom Dixon. The C model had a dry
weight of 49 ounces using a carbon-fiber
landing-gear strut, the lightweight Double
Star 50 engine, and a 12 x 6 wood propeller.
On 68 feet (handle to airplane centerline) x
.018-diameter cables, there is plenty of
reserve line tension overhead. The best CG
is per the plans, and the prototype nailed it
without adding dead weights.
CONSTRUCTION
This is not a beginner’s project; you
should have experience with handling
standard materials and construction
procedures. There are no major kinks in
assembling the BareCat 650. (Well, you do
need to get the assembled parts square to
each other.) I have laid out the major parts
to provide self-alignment features between
the fuselage and wing and the tail and the
airplane.
As you browse through the construction
photos you will see a lot of masking tape. It
does much more than block off paint! It
clamps around things, across flat joints, over
wingtips, along edges you don’t want to
sand, and many places you don’t want to
leave pinholes.
I like putting a 2-inch-wide strip over the
end of my shaping block and sliding the
taped end along a tip rib to blend in the
wingtip. I use 100-grit garnet sandpaper
with light pressure for fast removal to
rough-shape. I follow this with 150-grit
paper to take out the tool marks, 280 grit,
then 400 grit to polish the wood.
Using plastic film covering all over
forces me to make joints fit superclose,
which is essential to solid glue joints
anyway. It requires extra planning during
covering to leave it off where parts fit
together rather than cut away film after
covering. I get nervous cutting through film
on top of balsa, particularly over 1⁄16 balsa
planking.
The foam wing cores you buy from Tom
Dixon are geared toward his exoskeleton
planking system, and the cored-out portions
save 4 ounces of dead weight. Tom
publishes a comprehensive assembly
procedure, which you can download when
you order the cores on his Web site.
I prefer to cut the main spar on the
centerline and add splice plate caps during
final wing assembly. One convenience is
being able to block-sand the center face of
both panels to gain the best glue joint and
alignment. The caps carry the major bending
loads anyhow.
I keep the waste-foam material handy to
hold the cores during work and storage.
They prevent a lot of hangar rash and make
nice, stable support fixtures. With the 24-
inch panel cores, you don’t have to order
48-inch lumber. I purchased 24-inch
selected stock from Lone Star Models.
Have someone there select the stabilizer
and elevator in 3⁄16, 6- to 8-pound stock—
one 4 x 36 inches and one 3 x 36 inches.
The 1⁄4 stock for fins, tips, and top and
bottom planks needs to be 4 inches wide and
36 inches long in 6- to 8-pound density. I
used four pieces altogether.
I stripped the leading edge from a 1⁄4
sheet to get it dead straight in the relaxed
state. Logical sequence of adding parts
yielded a 15.3-ounce fully covered wing
with controls and an ounce of permanent tip
weight. If you noticed that my tip-weight
box cover is on top, don’t sweat it. The first
time I did it was an accident, and I got used
to it on future airplanes.
After you complete the wooden parts
assembly, do the wingtips, line guide, tipweight
box, and the bellcrank dry assembly.
Put these pieces aside until the rest of the
uncovered parts are ready to cover.
Before and after you cover the stabilizer
and elevator pieces, make sure that both
mating edges are dead straight—not just
mated to the same curvature. You will be
01sig2.QXD 10/27/03 10:40 am Page 33
34 MODEL AVIATION
Full-Size Plans Available—see page 191
01sig2.QXD 10/27/03 10:41 am Page 34
January 2004 35
rewarded with an elevator that drops freely
by its own weight. Careful location and
cutting hinge slots will save you problems
during final assembly, when the parts are all
covered and polished.
The control-horn base takes a bit of skill
but gives a clean, fuelproof assembly. (See
the plans for details.) Make sure that the
horn is located on the bottom and the
inboard side before you cut the pocket. (I
didn’t do it once.) I cut out the fin parts at
the same time as the stabilizer parts and get
into a rhythm of rounding edges, blocksanding,
and polish-sanding these parts.
I drilled a series of 1⁄2-inch-diameter
holes along the engine mounts to save dead
weight. Using a Forstner drill bit I let the
center point just break out of the hole’s
bottom, which leaves a solid glue surface. I
use 1⁄8-inch dowel pins to key the fuselage
sides and doublers during their glue process.
I use epoxy, well-squeegeed, and apply a
great deal of pressure between flat surfaces
to gain the optimum joint strength. The pins
are sanded on both sides until flush to both
surfaces.
I make a subassembly of the engine
mounts, two subfirewalls and the spacer
block, and the filler piece, assembled
squarely and flat using epoxy. This group is
used to square and align the fuselage sides
and top assembly on a nice, flat surface. If
this assembly is true, the final product
works better.
Thoroughly coat with epoxy the inside
surfaces that will be exposed to fuel. Do the
engine mounting holes and spacer plates,
then tape up the engine. Mount it and a
sacrificial spinner and carve the nose. Here
you should have the uncovered wood parts
ready for final assembly.
Final Assembly: Tape the wing halves
together, dry-assemble the fuselage to the
wing, then use the flat tabletop to fit the top
fin and the booms and stabilizer together.
Once these joints are tuned to firm slip fits,
proceed with covering the parts. The closer
these joints fit, the better the strength, and
you really can get quality without fillets to
cover the gaps.
Final assembly is straightforward,
requiring care to align parts and make solid
glue joints. Once the assembly is finished,
add all of the deadweight parts: landing-gear
assembly, control horn, pushrod half, fuel
tank and padding, and plumbing.
The covering and decorations are up to
you and your comfort level. I went beyond
my usual level of decoration, but don’t
expect this all the time. One thing Bob and I
learned is that the 20 appearance points we
could get now far outweigh the 80 points
awarded in the beginning days of Stunt to
turn the design direction away from the ugly
barndoor machines. It is also clear that the
appearance judging has saved the event
from becoming easy.
Flying: If your finished CG is within 1⁄8
inch of the design location, you might as
well proceed to flight tests. The lines’
location on the plans are for the design CG
and a 50-ounce dry weight. You can tune
your model from there as you get used to it.
I was able to hit the design CG right on
with a wood propeller, and so far the lines
rake is correct using 66-foot x .018-diameter
cables, eyelet to eyelet. This delivers a flight
radius, including 2.5 feet for my extended
arm, of 70.8 feet.
I have an ounce of tip weight in the box,
for a total of 2 ounces. I am still playing the
propeller, tank-height game while feeling
safe to ease through all of the pattern
maneuvers. I learned that 6.0-second laps are
too slow and that 5.5 seconds brings up safe
tension and controls force.
The Double Star 50 is performing
routinely with no bad habits on 10%-nitro
fuel. I still need to stabilize the power-plant
components before determining the ideal
fuel capacity. It will probably be less than 5
ounces.
Since Bob is no longer available to make my
numbers sing, will there be more BareCat
type projects? The three models presented
here represent optimal geometry under the
present pattern specifications. Someone
could probably shave off a few ounces with
carbon fiber and a Lost Foam wing structure.
Frankly, the resulting machinery would not
present better enough than the present
structure to warrant the additional effort.
I believe that any of the top-10 pilots
could compete successfully with a BareCat
650. Brave words, for sure, but I don’t
believe any of them will try it. Don’t feel
sorry for me; I had my time in the barrel and
am ready to coast a bit. Please try the
BareCat. You’ll like it!
Thanks, Bob. It was a fun run. MA
Bill Netzeband
23978 Villa Pamilla
Murrieta CA 92562
$3900
+ $450 S/H
DAKOTA
Joe Wagners, Classic
Free Flight design.
24" wingspan for
.02 or .049 engine
BMJR Model Products
Box 1210
Sharpes, FL 32959-1210
321-537-1159
www.BMJRModels.com
Materials Sources:
Foam wing cores (BareCat), Bolly landing
gear (KA-10), Double Star 50 engine:
Tom Dixon
Box 671166
Marietta GA 30062
Tel./Fax: (770) 592-3279
http://members.tripod.com/~TomDixon/tom
dixon.htm
Fuel tank, controls, wheels, propellers:
Brodak Mfg. & Distributing Co. Inc.
100 Park Ave.
Carmichaels PA 15320
(724) 966-2726
Fax: (724) 966-5760
www.brodak.com
Fuel tank, controls, wheels, propellers:
RSM Distribution
21899 Heliotrope Ln.
Wildomar CA 92595
(714) 931-6038
www.rsmdistribution.com
Selected-density balsa (see plans):
Lone Star Models
115 Industrial
Lancaster TX 75134
(972) 218-9663
(800) 687-5555 (to order)
Fax: (972) 218-9211
www.lonestar-models.com
01sig2.QXD 10/27/03 10:41 am Page 35
Edition: Model Aviation - 2004/01
Page Numbers: 29,30,31,32,33,34,35
have hard data to explain why. We experimented with outside-thebox
designs using non-Stunt power plants and flap-free wings. Our
aim was to fly the pattern to the specified dimensions so accurately
that we had to get top points. (Yeah, right.)
The wingspan was limited to 54 inches so that they would fit into
Bob’s Volvo sedan! I had determined that wings with zero quarter
chord sweep angles didn’t
react to wind by chattering
in roll, so we held this
criterion.
After a suitable period,
we realized that the judging
cadre was not using the
book dimensions and had
no intention of ever
measuring them by any
equipment other than the
trained eyeball.
By 1975 it was clear
that Bob would have to fly a traditional airplane to stay in the top
five at major meets. He joined the campaign with his Avanti series:
a conventional flapped machine with conventional styling. I waded
into the flap-analysis swamp armed with a TI-59 programmable
calculator. Progress was slow because flap calculations are tedious
and complex. We applied each of my research breakthroughs to the
Avanti and tested the accuracy of my progress.
There were also several major configurations to idealize the yaw
January 2004 29
BareCat 650-C
THIS AIRPLANE and document are my sentimental journey to
honor the memory of Bob Baron (1944-1999) and our long
collaboration to design and compete with cutting-edge Control Line
Precision Aerobatics equipment.
It started when Bob showed up on my doorstep in Pasadena,
California, sometime during 1965. He was able to feel and analyze
things about the airplane in flight where my calculations only
showed variation in the second decimal place.
We knew that flaps were difficult to keep in tune, but we didn’t
A bottom view of the BareCat shows the no-frills approach that
Bill prefers. The trim scheme is simple.
Sometimes
function yields
unusual forms
■ Bill Netzeband
01sig1.QXD 10/27/03 2:00 pm Page 29
30 MODEL AVIATION
axis, the power-plant package, the landing gear, the Rabe rudder, and
search for the magic flap-elevator relationship. Along with the
aerodynamic package criterion, we added simple structure with
maximum longevity.
In 1984 I tiptoed into the computer era and was able to get
answers more rapidly. Unfortunately I developed all of my programs
using arcane software, so I won’t be able to provide the math for
your design efforts.
It became clear that flaps introduce forces that vary widely with
any center of gravity (CG) shift or a minor velocity change, and
while making a possible 40% more lift available to the wing, they
load the elevator excessively and demand lots of extra thrust! I kept
looking for ways to compete without flaps because I like simple
solutions, and my skill level peaked out a little bit above average.
Bob and I left off anything that did not contribute to flying the
AMA rule-book pattern dimensions, such as labor-intensive
decorations and artistic shapes and high finishes, which add up to
weight and cost.
The Humbug series, initiated in 1968, was based on 7:1-aspectratio
wings controlled by 10:1-aspect-ratio stabilators, and it had
minimal fuselage and appendages. The stabilators were later
replaced by using stabilizer-elevator surfaces. They were also based
on low power-to-weight-ratio airframes.
The original Humbug used a Fox .19 to power 490 square inches
of wing at 39 ounces. Subsequent versions backed down to 6:1-
aspect-ratio wings and 8:1 stabilizers, and the late Tom Warden
styled a couple of them. They produced positive comments from the
general population but missed the winner’s circle too often.
The 1⁄2A BareCat was designed in 1980, to achieve the lowest
practical wing loading and take advantage of reducing the wing
aspect ratio to 4:1 and the tail to 6:1. The tail became 30% of the
wing, and the tail moment arm was 14 inches.
We added a practical problem by storing fuel on the CG in a
bladder tank since a tank in the 11-inch nose would upset the CG
during flight. We were looking for the 5-foot corner, but the whole
1⁄2A project went too far outside the box to become a popular
configuration.
In 1993 I wrote a story called “The Stunt Ace” and designed a
theoretically optimized machine that would do a book pattern. It
required a super .09 engine to save dead weight and fuel and to allow
.012-inch-diameter lines. Fuel was stored in a high-pressure bladder
mounted on the CG, as in the 1⁄2A BareCat. I had to specify several
unobtanium space-age materials to keep the weight down. It flew
great on paper, but, as in real life, Ace missed qualifying at its first
Nats by a half point.
The machine had a 600-square-inch wing, huge centerline fin
surfaces, a single wheel, booms, a stabilator, etc., and only weighed
15 ounces. Bob enjoyed the story and asked me if it would fly with a
Spar and trailing-edge pieces are attached to the foam cores.
Don’t omit the panel-identification marks!
Leading- and trailing-edge planking has been added. Masking
tape is used to hold everything down tight.
The wing takes shape with the addition of capstrips and centersection
planking. Notice the splice-plate cutouts.
The bellcrank assembly, with attached pushrod, is glued in
place. Take extra care to ensure smooth movement.
01sig1.QXD 10/27/03 2:00 pm Page 30
.15 engine. He built the BareCat 600 from my sketches using a
Nelson .15 Combat engine.
The puzzlement came when the 40-ounce machine flew off the
bench, and the few times Bob and the Nelson got together with the
needle valve and the experimental bladder fuel system, it handled
like an eagle! Those happy moments were too few, and Bob shelved
it.
I got my hands on the airframe in 1998 and tried a Norvel .15. I
replaced the stabilator and nonlinear bellcrank with a 50%
stabilizer-elevator assembly. The thing teased me by flying all of the
maneuvers, but it couldn’t deliver adequate confidence. It ended up
with a Double Star .40, a conventional fuel tank in the nose, it
gained 7 ounces, and it became a better-than-average performer.
There was not enough sizzle, though.
Bob had a final adventure using the BareCat ’98 that was
published in the June 1999 Model Aviation. He took it to the 1998
Nationals for recreation. Tragically, his Spartan broke up during a
test flight after he had qualified for the finals! Being a consummate
competitor, Bob decided to fly the BareCat.
Several problems in addition to being first up to fly the next day
prompted an all-nighter. He’d been flying with .008 lines on the
airplane powered by a 1cc engine! The last trimming trauma was a
frantic session to install a combat-tuned VA .049. He had help from
Larry Driskill and “Sleepy” Dawson.
After little real sleep, they got in a fast test flight at 6 a.m. Bob’s
first flight was humming along when the engine mount broke and
the VA sailed off into the boondocks. Bob finessed it back to the
runway with no further damage.
The next frantic fix involved reinstalling the 1cc engine and a set
of “equivalent” .012-diameter lines. With no test flight, Bob racked
up a 500-point score from the Nationals judges—not too shabby for
an outside-the-box machine.
In 1998 Tom Dixon was producing a Double Star 50, and we
decided to give the BareCat another shot. We used the 1⁄2A BareCat
geometry and enlarged it to produce 650 square inches of wing.
After reviewing the layout, we adjusted the tail moment arm and
stabilizer aspect ratio to more reasonable sizes for a large airplane.
Bob constructed the first model and used an inverted Double Star
50 engine and spinner. This airplane was almost finished when he
passed away in September 1999. Tom Dixon finished Bob’s model
and flew it a few times. It needed flight trimming, but Tom and I
decided that Bob’s last project shouldn’t be put at any more risk.
To make Bob’s airplane unique, I modified the drawings to use
an upright engine and aluminum two-wheel landing gear. I built the
“A” model and powered it with a Double Star 50. While putting up
with nose-heavy trim, I crashed it inverted, broke the engine, and
cracked a few major joints.
The cowl-free nose allows easy access to the removable tank for
height adjustments. Notice the engine-mount pads.
The engine mounts and lower firewalls assemble on a flat
surface. Clamp them tightly and let the epoxy cure.
The top and bottom planks and the nose-block wedge piece have
been assembled and smoothed into the spinner shape.
Photos by the author
January 2004 31
The doublers have been joined to the fuselage sides. Check out
the 1⁄4 triangle stock reinforcement pieces.
01sig1.QXD 10/27/03 2:01 pm Page 31
During the repair phase I shortened the nose to move the CG to
the design location, and Tom replaced the engine. The next flight
series was truncated at four. The partially tuned BareCat was
feeling good, and I tried an Hourglass. I ham-handedly executed the
first corner and the model came loose on the second corner, quickly
hiding behind my hat, and augered into the unyielding ground
before I could turn around.
There were several large pieces, but none of them had joints that
lent themselves to reconstruction. Besides that, the new engine was
split open after the fuel tank mashed around it, and the engine beam
mounts made a wishbone out of the engine crankcase.
Post-mortem analysis revealed that the twin-finned design had
excessive yaw stability but inadequate side area to generate enough
yaw torque to recover from extreme adverse yaw. Bob never
overcontrolled a model, so the problem didn’t show up until I got
my hands on one. So the twin-finned BareCat 650 project ended
with two prototypes, and I moved on to the B model.
The BareCat 650-B incorporated the single-finned side view of
the old 600, a sidewinder engine on a Radio Control engine mount,
and it preserved the now-proven 650 plan-view geometry. I used a
4-year-old Silver Foxx .40 to take advantage of the .015-diameter
cable. This is a powerful engine. I settled on 10% fuel and an APC
12.25 x 3.75 propeller.
This allows a rich, level flight and plenty of reserve thrust for
the vertical maneuvers. It comes on and off reliably, and with a 20%
oil blend it needs less than 4 ounces to complete the pattern.
Trimming the model was straightforward and surprise-free. I
cleaned up the slight tendency to turn tighter outside by sliding the
lines down on the handle to adjust my leverage and feel. The 650-B
at 54 ounces competes in the Advanced class with good results for
me. I currently fly it with a Tom Dixon-prepared O.S. .46 LA and
use 66 feet of that dreaded .018-diameter cable required by rules.
We sincerely believe that too much horsepower is about right.
I wouldn’t expect those competing in the Expert class to use
BareCat 650-C
It’s time for a dry-assembly test to ensure that all parts fit
together properly before gluing. Looks good!
A clean, functional front end. Look at neat fuel-line routing and
muffler installation. Details make the difference!
Type: CL sport Stunt
Wingspan: 541⁄4 inches
Engine: Double Star 50
Flying weight: 49 ounces
Construction: Balsa, plywood, foam
Covering/finish: MonoKote/modeling paints
32 MODEL AVIATION
The wingtip braces and leadout guide have been installed on the
inboard wing panel. Braces do not touch the covering.
01sig1.QXD 10/27/03 2:02 pm Page 32
January 2004 33
something as simple as this machine as their
competition mount. This is an excellent
airplane with which to work your way up
through the ranks before you have to start
the arduous task of keeping a flap model in
tune.
The C model is presented with three
different nose configurations. I selected the
inverted engine for personal reasons. (It
looks the best.) Cut the nose you want from
sheet two of the plans and tape the paper
doll to the main drawing. The attach point is
the firewall at the leading edge. The plan
width is set for beam mounts and stock
tanks, and once you blend in the shapes you
can have as fancy a nose as anyone’s.
However, the totally external engine
system (the B model) is ideal for running
power-plant experiments. The fuel-mixture
symmetry on my B model was adjusted with
the tank raised 1⁄8 inch.
The covering and decoration are
MonoKote. The foam wing core is available
from Tom Dixon. The C model had a dry
weight of 49 ounces using a carbon-fiber
landing-gear strut, the lightweight Double
Star 50 engine, and a 12 x 6 wood propeller.
On 68 feet (handle to airplane centerline) x
.018-diameter cables, there is plenty of
reserve line tension overhead. The best CG
is per the plans, and the prototype nailed it
without adding dead weights.
CONSTRUCTION
This is not a beginner’s project; you
should have experience with handling
standard materials and construction
procedures. There are no major kinks in
assembling the BareCat 650. (Well, you do
need to get the assembled parts square to
each other.) I have laid out the major parts
to provide self-alignment features between
the fuselage and wing and the tail and the
airplane.
As you browse through the construction
photos you will see a lot of masking tape. It
does much more than block off paint! It
clamps around things, across flat joints, over
wingtips, along edges you don’t want to
sand, and many places you don’t want to
leave pinholes.
I like putting a 2-inch-wide strip over the
end of my shaping block and sliding the
taped end along a tip rib to blend in the
wingtip. I use 100-grit garnet sandpaper
with light pressure for fast removal to
rough-shape. I follow this with 150-grit
paper to take out the tool marks, 280 grit,
then 400 grit to polish the wood.
Using plastic film covering all over
forces me to make joints fit superclose,
which is essential to solid glue joints
anyway. It requires extra planning during
covering to leave it off where parts fit
together rather than cut away film after
covering. I get nervous cutting through film
on top of balsa, particularly over 1⁄16 balsa
planking.
The foam wing cores you buy from Tom
Dixon are geared toward his exoskeleton
planking system, and the cored-out portions
save 4 ounces of dead weight. Tom
publishes a comprehensive assembly
procedure, which you can download when
you order the cores on his Web site.
I prefer to cut the main spar on the
centerline and add splice plate caps during
final wing assembly. One convenience is
being able to block-sand the center face of
both panels to gain the best glue joint and
alignment. The caps carry the major bending
loads anyhow.
I keep the waste-foam material handy to
hold the cores during work and storage.
They prevent a lot of hangar rash and make
nice, stable support fixtures. With the 24-
inch panel cores, you don’t have to order
48-inch lumber. I purchased 24-inch
selected stock from Lone Star Models.
Have someone there select the stabilizer
and elevator in 3⁄16, 6- to 8-pound stock—
one 4 x 36 inches and one 3 x 36 inches.
The 1⁄4 stock for fins, tips, and top and
bottom planks needs to be 4 inches wide and
36 inches long in 6- to 8-pound density. I
used four pieces altogether.
I stripped the leading edge from a 1⁄4
sheet to get it dead straight in the relaxed
state. Logical sequence of adding parts
yielded a 15.3-ounce fully covered wing
with controls and an ounce of permanent tip
weight. If you noticed that my tip-weight
box cover is on top, don’t sweat it. The first
time I did it was an accident, and I got used
to it on future airplanes.
After you complete the wooden parts
assembly, do the wingtips, line guide, tipweight
box, and the bellcrank dry assembly.
Put these pieces aside until the rest of the
uncovered parts are ready to cover.
Before and after you cover the stabilizer
and elevator pieces, make sure that both
mating edges are dead straight—not just
mated to the same curvature. You will be
01sig2.QXD 10/27/03 10:40 am Page 33
34 MODEL AVIATION
Full-Size Plans Available—see page 191
01sig2.QXD 10/27/03 10:41 am Page 34
January 2004 35
rewarded with an elevator that drops freely
by its own weight. Careful location and
cutting hinge slots will save you problems
during final assembly, when the parts are all
covered and polished.
The control-horn base takes a bit of skill
but gives a clean, fuelproof assembly. (See
the plans for details.) Make sure that the
horn is located on the bottom and the
inboard side before you cut the pocket. (I
didn’t do it once.) I cut out the fin parts at
the same time as the stabilizer parts and get
into a rhythm of rounding edges, blocksanding,
and polish-sanding these parts.
I drilled a series of 1⁄2-inch-diameter
holes along the engine mounts to save dead
weight. Using a Forstner drill bit I let the
center point just break out of the hole’s
bottom, which leaves a solid glue surface. I
use 1⁄8-inch dowel pins to key the fuselage
sides and doublers during their glue process.
I use epoxy, well-squeegeed, and apply a
great deal of pressure between flat surfaces
to gain the optimum joint strength. The pins
are sanded on both sides until flush to both
surfaces.
I make a subassembly of the engine
mounts, two subfirewalls and the spacer
block, and the filler piece, assembled
squarely and flat using epoxy. This group is
used to square and align the fuselage sides
and top assembly on a nice, flat surface. If
this assembly is true, the final product
works better.
Thoroughly coat with epoxy the inside
surfaces that will be exposed to fuel. Do the
engine mounting holes and spacer plates,
then tape up the engine. Mount it and a
sacrificial spinner and carve the nose. Here
you should have the uncovered wood parts
ready for final assembly.
Final Assembly: Tape the wing halves
together, dry-assemble the fuselage to the
wing, then use the flat tabletop to fit the top
fin and the booms and stabilizer together.
Once these joints are tuned to firm slip fits,
proceed with covering the parts. The closer
these joints fit, the better the strength, and
you really can get quality without fillets to
cover the gaps.
Final assembly is straightforward,
requiring care to align parts and make solid
glue joints. Once the assembly is finished,
add all of the deadweight parts: landing-gear
assembly, control horn, pushrod half, fuel
tank and padding, and plumbing.
The covering and decorations are up to
you and your comfort level. I went beyond
my usual level of decoration, but don’t
expect this all the time. One thing Bob and I
learned is that the 20 appearance points we
could get now far outweigh the 80 points
awarded in the beginning days of Stunt to
turn the design direction away from the ugly
barndoor machines. It is also clear that the
appearance judging has saved the event
from becoming easy.
Flying: If your finished CG is within 1⁄8
inch of the design location, you might as
well proceed to flight tests. The lines’
location on the plans are for the design CG
and a 50-ounce dry weight. You can tune
your model from there as you get used to it.
I was able to hit the design CG right on
with a wood propeller, and so far the lines
rake is correct using 66-foot x .018-diameter
cables, eyelet to eyelet. This delivers a flight
radius, including 2.5 feet for my extended
arm, of 70.8 feet.
I have an ounce of tip weight in the box,
for a total of 2 ounces. I am still playing the
propeller, tank-height game while feeling
safe to ease through all of the pattern
maneuvers. I learned that 6.0-second laps are
too slow and that 5.5 seconds brings up safe
tension and controls force.
The Double Star 50 is performing
routinely with no bad habits on 10%-nitro
fuel. I still need to stabilize the power-plant
components before determining the ideal
fuel capacity. It will probably be less than 5
ounces.
Since Bob is no longer available to make my
numbers sing, will there be more BareCat
type projects? The three models presented
here represent optimal geometry under the
present pattern specifications. Someone
could probably shave off a few ounces with
carbon fiber and a Lost Foam wing structure.
Frankly, the resulting machinery would not
present better enough than the present
structure to warrant the additional effort.
I believe that any of the top-10 pilots
could compete successfully with a BareCat
650. Brave words, for sure, but I don’t
believe any of them will try it. Don’t feel
sorry for me; I had my time in the barrel and
am ready to coast a bit. Please try the
BareCat. You’ll like it!
Thanks, Bob. It was a fun run. MA
Bill Netzeband
23978 Villa Pamilla
Murrieta CA 92562
$3900
+ $450 S/H
DAKOTA
Joe Wagners, Classic
Free Flight design.
24" wingspan for
.02 or .049 engine
BMJR Model Products
Box 1210
Sharpes, FL 32959-1210
321-537-1159
www.BMJRModels.com
Materials Sources:
Foam wing cores (BareCat), Bolly landing
gear (KA-10), Double Star 50 engine:
Tom Dixon
Box 671166
Marietta GA 30062
Tel./Fax: (770) 592-3279
http://members.tripod.com/~TomDixon/tom
dixon.htm
Fuel tank, controls, wheels, propellers:
Brodak Mfg. & Distributing Co. Inc.
100 Park Ave.
Carmichaels PA 15320
(724) 966-2726
Fax: (724) 966-5760
www.brodak.com
Fuel tank, controls, wheels, propellers:
RSM Distribution
21899 Heliotrope Ln.
Wildomar CA 92595
(714) 931-6038
www.rsmdistribution.com
Selected-density balsa (see plans):
Lone Star Models
115 Industrial
Lancaster TX 75134
(972) 218-9663
(800) 687-5555 (to order)
Fax: (972) 218-9211
www.lonestar-models.com
01sig2.QXD 10/27/03 10:41 am Page 35
Edition: Model Aviation - 2004/01
Page Numbers: 29,30,31,32,33,34,35
have hard data to explain why. We experimented with outside-thebox
designs using non-Stunt power plants and flap-free wings. Our
aim was to fly the pattern to the specified dimensions so accurately
that we had to get top points. (Yeah, right.)
The wingspan was limited to 54 inches so that they would fit into
Bob’s Volvo sedan! I had determined that wings with zero quarter
chord sweep angles didn’t
react to wind by chattering
in roll, so we held this
criterion.
After a suitable period,
we realized that the judging
cadre was not using the
book dimensions and had
no intention of ever
measuring them by any
equipment other than the
trained eyeball.
By 1975 it was clear
that Bob would have to fly a traditional airplane to stay in the top
five at major meets. He joined the campaign with his Avanti series:
a conventional flapped machine with conventional styling. I waded
into the flap-analysis swamp armed with a TI-59 programmable
calculator. Progress was slow because flap calculations are tedious
and complex. We applied each of my research breakthroughs to the
Avanti and tested the accuracy of my progress.
There were also several major configurations to idealize the yaw
January 2004 29
BareCat 650-C
THIS AIRPLANE and document are my sentimental journey to
honor the memory of Bob Baron (1944-1999) and our long
collaboration to design and compete with cutting-edge Control Line
Precision Aerobatics equipment.
It started when Bob showed up on my doorstep in Pasadena,
California, sometime during 1965. He was able to feel and analyze
things about the airplane in flight where my calculations only
showed variation in the second decimal place.
We knew that flaps were difficult to keep in tune, but we didn’t
A bottom view of the BareCat shows the no-frills approach that
Bill prefers. The trim scheme is simple.
Sometimes
function yields
unusual forms
■ Bill Netzeband
01sig1.QXD 10/27/03 2:00 pm Page 29
30 MODEL AVIATION
axis, the power-plant package, the landing gear, the Rabe rudder, and
search for the magic flap-elevator relationship. Along with the
aerodynamic package criterion, we added simple structure with
maximum longevity.
In 1984 I tiptoed into the computer era and was able to get
answers more rapidly. Unfortunately I developed all of my programs
using arcane software, so I won’t be able to provide the math for
your design efforts.
It became clear that flaps introduce forces that vary widely with
any center of gravity (CG) shift or a minor velocity change, and
while making a possible 40% more lift available to the wing, they
load the elevator excessively and demand lots of extra thrust! I kept
looking for ways to compete without flaps because I like simple
solutions, and my skill level peaked out a little bit above average.
Bob and I left off anything that did not contribute to flying the
AMA rule-book pattern dimensions, such as labor-intensive
decorations and artistic shapes and high finishes, which add up to
weight and cost.
The Humbug series, initiated in 1968, was based on 7:1-aspectratio
wings controlled by 10:1-aspect-ratio stabilators, and it had
minimal fuselage and appendages. The stabilators were later
replaced by using stabilizer-elevator surfaces. They were also based
on low power-to-weight-ratio airframes.
The original Humbug used a Fox .19 to power 490 square inches
of wing at 39 ounces. Subsequent versions backed down to 6:1-
aspect-ratio wings and 8:1 stabilizers, and the late Tom Warden
styled a couple of them. They produced positive comments from the
general population but missed the winner’s circle too often.
The 1⁄2A BareCat was designed in 1980, to achieve the lowest
practical wing loading and take advantage of reducing the wing
aspect ratio to 4:1 and the tail to 6:1. The tail became 30% of the
wing, and the tail moment arm was 14 inches.
We added a practical problem by storing fuel on the CG in a
bladder tank since a tank in the 11-inch nose would upset the CG
during flight. We were looking for the 5-foot corner, but the whole
1⁄2A project went too far outside the box to become a popular
configuration.
In 1993 I wrote a story called “The Stunt Ace” and designed a
theoretically optimized machine that would do a book pattern. It
required a super .09 engine to save dead weight and fuel and to allow
.012-inch-diameter lines. Fuel was stored in a high-pressure bladder
mounted on the CG, as in the 1⁄2A BareCat. I had to specify several
unobtanium space-age materials to keep the weight down. It flew
great on paper, but, as in real life, Ace missed qualifying at its first
Nats by a half point.
The machine had a 600-square-inch wing, huge centerline fin
surfaces, a single wheel, booms, a stabilator, etc., and only weighed
15 ounces. Bob enjoyed the story and asked me if it would fly with a
Spar and trailing-edge pieces are attached to the foam cores.
Don’t omit the panel-identification marks!
Leading- and trailing-edge planking has been added. Masking
tape is used to hold everything down tight.
The wing takes shape with the addition of capstrips and centersection
planking. Notice the splice-plate cutouts.
The bellcrank assembly, with attached pushrod, is glued in
place. Take extra care to ensure smooth movement.
01sig1.QXD 10/27/03 2:00 pm Page 30
.15 engine. He built the BareCat 600 from my sketches using a
Nelson .15 Combat engine.
The puzzlement came when the 40-ounce machine flew off the
bench, and the few times Bob and the Nelson got together with the
needle valve and the experimental bladder fuel system, it handled
like an eagle! Those happy moments were too few, and Bob shelved
it.
I got my hands on the airframe in 1998 and tried a Norvel .15. I
replaced the stabilator and nonlinear bellcrank with a 50%
stabilizer-elevator assembly. The thing teased me by flying all of the
maneuvers, but it couldn’t deliver adequate confidence. It ended up
with a Double Star .40, a conventional fuel tank in the nose, it
gained 7 ounces, and it became a better-than-average performer.
There was not enough sizzle, though.
Bob had a final adventure using the BareCat ’98 that was
published in the June 1999 Model Aviation. He took it to the 1998
Nationals for recreation. Tragically, his Spartan broke up during a
test flight after he had qualified for the finals! Being a consummate
competitor, Bob decided to fly the BareCat.
Several problems in addition to being first up to fly the next day
prompted an all-nighter. He’d been flying with .008 lines on the
airplane powered by a 1cc engine! The last trimming trauma was a
frantic session to install a combat-tuned VA .049. He had help from
Larry Driskill and “Sleepy” Dawson.
After little real sleep, they got in a fast test flight at 6 a.m. Bob’s
first flight was humming along when the engine mount broke and
the VA sailed off into the boondocks. Bob finessed it back to the
runway with no further damage.
The next frantic fix involved reinstalling the 1cc engine and a set
of “equivalent” .012-diameter lines. With no test flight, Bob racked
up a 500-point score from the Nationals judges—not too shabby for
an outside-the-box machine.
In 1998 Tom Dixon was producing a Double Star 50, and we
decided to give the BareCat another shot. We used the 1⁄2A BareCat
geometry and enlarged it to produce 650 square inches of wing.
After reviewing the layout, we adjusted the tail moment arm and
stabilizer aspect ratio to more reasonable sizes for a large airplane.
Bob constructed the first model and used an inverted Double Star
50 engine and spinner. This airplane was almost finished when he
passed away in September 1999. Tom Dixon finished Bob’s model
and flew it a few times. It needed flight trimming, but Tom and I
decided that Bob’s last project shouldn’t be put at any more risk.
To make Bob’s airplane unique, I modified the drawings to use
an upright engine and aluminum two-wheel landing gear. I built the
“A” model and powered it with a Double Star 50. While putting up
with nose-heavy trim, I crashed it inverted, broke the engine, and
cracked a few major joints.
The cowl-free nose allows easy access to the removable tank for
height adjustments. Notice the engine-mount pads.
The engine mounts and lower firewalls assemble on a flat
surface. Clamp them tightly and let the epoxy cure.
The top and bottom planks and the nose-block wedge piece have
been assembled and smoothed into the spinner shape.
Photos by the author
January 2004 31
The doublers have been joined to the fuselage sides. Check out
the 1⁄4 triangle stock reinforcement pieces.
01sig1.QXD 10/27/03 2:01 pm Page 31
During the repair phase I shortened the nose to move the CG to
the design location, and Tom replaced the engine. The next flight
series was truncated at four. The partially tuned BareCat was
feeling good, and I tried an Hourglass. I ham-handedly executed the
first corner and the model came loose on the second corner, quickly
hiding behind my hat, and augered into the unyielding ground
before I could turn around.
There were several large pieces, but none of them had joints that
lent themselves to reconstruction. Besides that, the new engine was
split open after the fuel tank mashed around it, and the engine beam
mounts made a wishbone out of the engine crankcase.
Post-mortem analysis revealed that the twin-finned design had
excessive yaw stability but inadequate side area to generate enough
yaw torque to recover from extreme adverse yaw. Bob never
overcontrolled a model, so the problem didn’t show up until I got
my hands on one. So the twin-finned BareCat 650 project ended
with two prototypes, and I moved on to the B model.
The BareCat 650-B incorporated the single-finned side view of
the old 600, a sidewinder engine on a Radio Control engine mount,
and it preserved the now-proven 650 plan-view geometry. I used a
4-year-old Silver Foxx .40 to take advantage of the .015-diameter
cable. This is a powerful engine. I settled on 10% fuel and an APC
12.25 x 3.75 propeller.
This allows a rich, level flight and plenty of reserve thrust for
the vertical maneuvers. It comes on and off reliably, and with a 20%
oil blend it needs less than 4 ounces to complete the pattern.
Trimming the model was straightforward and surprise-free. I
cleaned up the slight tendency to turn tighter outside by sliding the
lines down on the handle to adjust my leverage and feel. The 650-B
at 54 ounces competes in the Advanced class with good results for
me. I currently fly it with a Tom Dixon-prepared O.S. .46 LA and
use 66 feet of that dreaded .018-diameter cable required by rules.
We sincerely believe that too much horsepower is about right.
I wouldn’t expect those competing in the Expert class to use
BareCat 650-C
It’s time for a dry-assembly test to ensure that all parts fit
together properly before gluing. Looks good!
A clean, functional front end. Look at neat fuel-line routing and
muffler installation. Details make the difference!
Type: CL sport Stunt
Wingspan: 541⁄4 inches
Engine: Double Star 50
Flying weight: 49 ounces
Construction: Balsa, plywood, foam
Covering/finish: MonoKote/modeling paints
32 MODEL AVIATION
The wingtip braces and leadout guide have been installed on the
inboard wing panel. Braces do not touch the covering.
01sig1.QXD 10/27/03 2:02 pm Page 32
January 2004 33
something as simple as this machine as their
competition mount. This is an excellent
airplane with which to work your way up
through the ranks before you have to start
the arduous task of keeping a flap model in
tune.
The C model is presented with three
different nose configurations. I selected the
inverted engine for personal reasons. (It
looks the best.) Cut the nose you want from
sheet two of the plans and tape the paper
doll to the main drawing. The attach point is
the firewall at the leading edge. The plan
width is set for beam mounts and stock
tanks, and once you blend in the shapes you
can have as fancy a nose as anyone’s.
However, the totally external engine
system (the B model) is ideal for running
power-plant experiments. The fuel-mixture
symmetry on my B model was adjusted with
the tank raised 1⁄8 inch.
The covering and decoration are
MonoKote. The foam wing core is available
from Tom Dixon. The C model had a dry
weight of 49 ounces using a carbon-fiber
landing-gear strut, the lightweight Double
Star 50 engine, and a 12 x 6 wood propeller.
On 68 feet (handle to airplane centerline) x
.018-diameter cables, there is plenty of
reserve line tension overhead. The best CG
is per the plans, and the prototype nailed it
without adding dead weights.
CONSTRUCTION
This is not a beginner’s project; you
should have experience with handling
standard materials and construction
procedures. There are no major kinks in
assembling the BareCat 650. (Well, you do
need to get the assembled parts square to
each other.) I have laid out the major parts
to provide self-alignment features between
the fuselage and wing and the tail and the
airplane.
As you browse through the construction
photos you will see a lot of masking tape. It
does much more than block off paint! It
clamps around things, across flat joints, over
wingtips, along edges you don’t want to
sand, and many places you don’t want to
leave pinholes.
I like putting a 2-inch-wide strip over the
end of my shaping block and sliding the
taped end along a tip rib to blend in the
wingtip. I use 100-grit garnet sandpaper
with light pressure for fast removal to
rough-shape. I follow this with 150-grit
paper to take out the tool marks, 280 grit,
then 400 grit to polish the wood.
Using plastic film covering all over
forces me to make joints fit superclose,
which is essential to solid glue joints
anyway. It requires extra planning during
covering to leave it off where parts fit
together rather than cut away film after
covering. I get nervous cutting through film
on top of balsa, particularly over 1⁄16 balsa
planking.
The foam wing cores you buy from Tom
Dixon are geared toward his exoskeleton
planking system, and the cored-out portions
save 4 ounces of dead weight. Tom
publishes a comprehensive assembly
procedure, which you can download when
you order the cores on his Web site.
I prefer to cut the main spar on the
centerline and add splice plate caps during
final wing assembly. One convenience is
being able to block-sand the center face of
both panels to gain the best glue joint and
alignment. The caps carry the major bending
loads anyhow.
I keep the waste-foam material handy to
hold the cores during work and storage.
They prevent a lot of hangar rash and make
nice, stable support fixtures. With the 24-
inch panel cores, you don’t have to order
48-inch lumber. I purchased 24-inch
selected stock from Lone Star Models.
Have someone there select the stabilizer
and elevator in 3⁄16, 6- to 8-pound stock—
one 4 x 36 inches and one 3 x 36 inches.
The 1⁄4 stock for fins, tips, and top and
bottom planks needs to be 4 inches wide and
36 inches long in 6- to 8-pound density. I
used four pieces altogether.
I stripped the leading edge from a 1⁄4
sheet to get it dead straight in the relaxed
state. Logical sequence of adding parts
yielded a 15.3-ounce fully covered wing
with controls and an ounce of permanent tip
weight. If you noticed that my tip-weight
box cover is on top, don’t sweat it. The first
time I did it was an accident, and I got used
to it on future airplanes.
After you complete the wooden parts
assembly, do the wingtips, line guide, tipweight
box, and the bellcrank dry assembly.
Put these pieces aside until the rest of the
uncovered parts are ready to cover.
Before and after you cover the stabilizer
and elevator pieces, make sure that both
mating edges are dead straight—not just
mated to the same curvature. You will be
01sig2.QXD 10/27/03 10:40 am Page 33
34 MODEL AVIATION
Full-Size Plans Available—see page 191
01sig2.QXD 10/27/03 10:41 am Page 34
January 2004 35
rewarded with an elevator that drops freely
by its own weight. Careful location and
cutting hinge slots will save you problems
during final assembly, when the parts are all
covered and polished.
The control-horn base takes a bit of skill
but gives a clean, fuelproof assembly. (See
the plans for details.) Make sure that the
horn is located on the bottom and the
inboard side before you cut the pocket. (I
didn’t do it once.) I cut out the fin parts at
the same time as the stabilizer parts and get
into a rhythm of rounding edges, blocksanding,
and polish-sanding these parts.
I drilled a series of 1⁄2-inch-diameter
holes along the engine mounts to save dead
weight. Using a Forstner drill bit I let the
center point just break out of the hole’s
bottom, which leaves a solid glue surface. I
use 1⁄8-inch dowel pins to key the fuselage
sides and doublers during their glue process.
I use epoxy, well-squeegeed, and apply a
great deal of pressure between flat surfaces
to gain the optimum joint strength. The pins
are sanded on both sides until flush to both
surfaces.
I make a subassembly of the engine
mounts, two subfirewalls and the spacer
block, and the filler piece, assembled
squarely and flat using epoxy. This group is
used to square and align the fuselage sides
and top assembly on a nice, flat surface. If
this assembly is true, the final product
works better.
Thoroughly coat with epoxy the inside
surfaces that will be exposed to fuel. Do the
engine mounting holes and spacer plates,
then tape up the engine. Mount it and a
sacrificial spinner and carve the nose. Here
you should have the uncovered wood parts
ready for final assembly.
Final Assembly: Tape the wing halves
together, dry-assemble the fuselage to the
wing, then use the flat tabletop to fit the top
fin and the booms and stabilizer together.
Once these joints are tuned to firm slip fits,
proceed with covering the parts. The closer
these joints fit, the better the strength, and
you really can get quality without fillets to
cover the gaps.
Final assembly is straightforward,
requiring care to align parts and make solid
glue joints. Once the assembly is finished,
add all of the deadweight parts: landing-gear
assembly, control horn, pushrod half, fuel
tank and padding, and plumbing.
The covering and decorations are up to
you and your comfort level. I went beyond
my usual level of decoration, but don’t
expect this all the time. One thing Bob and I
learned is that the 20 appearance points we
could get now far outweigh the 80 points
awarded in the beginning days of Stunt to
turn the design direction away from the ugly
barndoor machines. It is also clear that the
appearance judging has saved the event
from becoming easy.
Flying: If your finished CG is within 1⁄8
inch of the design location, you might as
well proceed to flight tests. The lines’
location on the plans are for the design CG
and a 50-ounce dry weight. You can tune
your model from there as you get used to it.
I was able to hit the design CG right on
with a wood propeller, and so far the lines
rake is correct using 66-foot x .018-diameter
cables, eyelet to eyelet. This delivers a flight
radius, including 2.5 feet for my extended
arm, of 70.8 feet.
I have an ounce of tip weight in the box,
for a total of 2 ounces. I am still playing the
propeller, tank-height game while feeling
safe to ease through all of the pattern
maneuvers. I learned that 6.0-second laps are
too slow and that 5.5 seconds brings up safe
tension and controls force.
The Double Star 50 is performing
routinely with no bad habits on 10%-nitro
fuel. I still need to stabilize the power-plant
components before determining the ideal
fuel capacity. It will probably be less than 5
ounces.
Since Bob is no longer available to make my
numbers sing, will there be more BareCat
type projects? The three models presented
here represent optimal geometry under the
present pattern specifications. Someone
could probably shave off a few ounces with
carbon fiber and a Lost Foam wing structure.
Frankly, the resulting machinery would not
present better enough than the present
structure to warrant the additional effort.
I believe that any of the top-10 pilots
could compete successfully with a BareCat
650. Brave words, for sure, but I don’t
believe any of them will try it. Don’t feel
sorry for me; I had my time in the barrel and
am ready to coast a bit. Please try the
BareCat. You’ll like it!
Thanks, Bob. It was a fun run. MA
Bill Netzeband
23978 Villa Pamilla
Murrieta CA 92562
$3900
+ $450 S/H
DAKOTA
Joe Wagners, Classic
Free Flight design.
24" wingspan for
.02 or .049 engine
BMJR Model Products
Box 1210
Sharpes, FL 32959-1210
321-537-1159
www.BMJRModels.com
Materials Sources:
Foam wing cores (BareCat), Bolly landing
gear (KA-10), Double Star 50 engine:
Tom Dixon
Box 671166
Marietta GA 30062
Tel./Fax: (770) 592-3279
http://members.tripod.com/~TomDixon/tom
dixon.htm
Fuel tank, controls, wheels, propellers:
Brodak Mfg. & Distributing Co. Inc.
100 Park Ave.
Carmichaels PA 15320
(724) 966-2726
Fax: (724) 966-5760
www.brodak.com
Fuel tank, controls, wheels, propellers:
RSM Distribution
21899 Heliotrope Ln.
Wildomar CA 92595
(714) 931-6038
www.rsmdistribution.com
Selected-density balsa (see plans):
Lone Star Models
115 Industrial
Lancaster TX 75134
(972) 218-9663
(800) 687-5555 (to order)
Fax: (972) 218-9211
www.lonestar-models.com
01sig2.QXD 10/27/03 10:41 am Page 35
Edition: Model Aviation - 2004/01
Page Numbers: 29,30,31,32,33,34,35
have hard data to explain why. We experimented with outside-thebox
designs using non-Stunt power plants and flap-free wings. Our
aim was to fly the pattern to the specified dimensions so accurately
that we had to get top points. (Yeah, right.)
The wingspan was limited to 54 inches so that they would fit into
Bob’s Volvo sedan! I had determined that wings with zero quarter
chord sweep angles didn’t
react to wind by chattering
in roll, so we held this
criterion.
After a suitable period,
we realized that the judging
cadre was not using the
book dimensions and had
no intention of ever
measuring them by any
equipment other than the
trained eyeball.
By 1975 it was clear
that Bob would have to fly a traditional airplane to stay in the top
five at major meets. He joined the campaign with his Avanti series:
a conventional flapped machine with conventional styling. I waded
into the flap-analysis swamp armed with a TI-59 programmable
calculator. Progress was slow because flap calculations are tedious
and complex. We applied each of my research breakthroughs to the
Avanti and tested the accuracy of my progress.
There were also several major configurations to idealize the yaw
January 2004 29
BareCat 650-C
THIS AIRPLANE and document are my sentimental journey to
honor the memory of Bob Baron (1944-1999) and our long
collaboration to design and compete with cutting-edge Control Line
Precision Aerobatics equipment.
It started when Bob showed up on my doorstep in Pasadena,
California, sometime during 1965. He was able to feel and analyze
things about the airplane in flight where my calculations only
showed variation in the second decimal place.
We knew that flaps were difficult to keep in tune, but we didn’t
A bottom view of the BareCat shows the no-frills approach that
Bill prefers. The trim scheme is simple.
Sometimes
function yields
unusual forms
■ Bill Netzeband
01sig1.QXD 10/27/03 2:00 pm Page 29
30 MODEL AVIATION
axis, the power-plant package, the landing gear, the Rabe rudder, and
search for the magic flap-elevator relationship. Along with the
aerodynamic package criterion, we added simple structure with
maximum longevity.
In 1984 I tiptoed into the computer era and was able to get
answers more rapidly. Unfortunately I developed all of my programs
using arcane software, so I won’t be able to provide the math for
your design efforts.
It became clear that flaps introduce forces that vary widely with
any center of gravity (CG) shift or a minor velocity change, and
while making a possible 40% more lift available to the wing, they
load the elevator excessively and demand lots of extra thrust! I kept
looking for ways to compete without flaps because I like simple
solutions, and my skill level peaked out a little bit above average.
Bob and I left off anything that did not contribute to flying the
AMA rule-book pattern dimensions, such as labor-intensive
decorations and artistic shapes and high finishes, which add up to
weight and cost.
The Humbug series, initiated in 1968, was based on 7:1-aspectratio
wings controlled by 10:1-aspect-ratio stabilators, and it had
minimal fuselage and appendages. The stabilators were later
replaced by using stabilizer-elevator surfaces. They were also based
on low power-to-weight-ratio airframes.
The original Humbug used a Fox .19 to power 490 square inches
of wing at 39 ounces. Subsequent versions backed down to 6:1-
aspect-ratio wings and 8:1 stabilizers, and the late Tom Warden
styled a couple of them. They produced positive comments from the
general population but missed the winner’s circle too often.
The 1⁄2A BareCat was designed in 1980, to achieve the lowest
practical wing loading and take advantage of reducing the wing
aspect ratio to 4:1 and the tail to 6:1. The tail became 30% of the
wing, and the tail moment arm was 14 inches.
We added a practical problem by storing fuel on the CG in a
bladder tank since a tank in the 11-inch nose would upset the CG
during flight. We were looking for the 5-foot corner, but the whole
1⁄2A project went too far outside the box to become a popular
configuration.
In 1993 I wrote a story called “The Stunt Ace” and designed a
theoretically optimized machine that would do a book pattern. It
required a super .09 engine to save dead weight and fuel and to allow
.012-inch-diameter lines. Fuel was stored in a high-pressure bladder
mounted on the CG, as in the 1⁄2A BareCat. I had to specify several
unobtanium space-age materials to keep the weight down. It flew
great on paper, but, as in real life, Ace missed qualifying at its first
Nats by a half point.
The machine had a 600-square-inch wing, huge centerline fin
surfaces, a single wheel, booms, a stabilator, etc., and only weighed
15 ounces. Bob enjoyed the story and asked me if it would fly with a
Spar and trailing-edge pieces are attached to the foam cores.
Don’t omit the panel-identification marks!
Leading- and trailing-edge planking has been added. Masking
tape is used to hold everything down tight.
The wing takes shape with the addition of capstrips and centersection
planking. Notice the splice-plate cutouts.
The bellcrank assembly, with attached pushrod, is glued in
place. Take extra care to ensure smooth movement.
01sig1.QXD 10/27/03 2:00 pm Page 30
.15 engine. He built the BareCat 600 from my sketches using a
Nelson .15 Combat engine.
The puzzlement came when the 40-ounce machine flew off the
bench, and the few times Bob and the Nelson got together with the
needle valve and the experimental bladder fuel system, it handled
like an eagle! Those happy moments were too few, and Bob shelved
it.
I got my hands on the airframe in 1998 and tried a Norvel .15. I
replaced the stabilator and nonlinear bellcrank with a 50%
stabilizer-elevator assembly. The thing teased me by flying all of the
maneuvers, but it couldn’t deliver adequate confidence. It ended up
with a Double Star .40, a conventional fuel tank in the nose, it
gained 7 ounces, and it became a better-than-average performer.
There was not enough sizzle, though.
Bob had a final adventure using the BareCat ’98 that was
published in the June 1999 Model Aviation. He took it to the 1998
Nationals for recreation. Tragically, his Spartan broke up during a
test flight after he had qualified for the finals! Being a consummate
competitor, Bob decided to fly the BareCat.
Several problems in addition to being first up to fly the next day
prompted an all-nighter. He’d been flying with .008 lines on the
airplane powered by a 1cc engine! The last trimming trauma was a
frantic session to install a combat-tuned VA .049. He had help from
Larry Driskill and “Sleepy” Dawson.
After little real sleep, they got in a fast test flight at 6 a.m. Bob’s
first flight was humming along when the engine mount broke and
the VA sailed off into the boondocks. Bob finessed it back to the
runway with no further damage.
The next frantic fix involved reinstalling the 1cc engine and a set
of “equivalent” .012-diameter lines. With no test flight, Bob racked
up a 500-point score from the Nationals judges—not too shabby for
an outside-the-box machine.
In 1998 Tom Dixon was producing a Double Star 50, and we
decided to give the BareCat another shot. We used the 1⁄2A BareCat
geometry and enlarged it to produce 650 square inches of wing.
After reviewing the layout, we adjusted the tail moment arm and
stabilizer aspect ratio to more reasonable sizes for a large airplane.
Bob constructed the first model and used an inverted Double Star
50 engine and spinner. This airplane was almost finished when he
passed away in September 1999. Tom Dixon finished Bob’s model
and flew it a few times. It needed flight trimming, but Tom and I
decided that Bob’s last project shouldn’t be put at any more risk.
To make Bob’s airplane unique, I modified the drawings to use
an upright engine and aluminum two-wheel landing gear. I built the
“A” model and powered it with a Double Star 50. While putting up
with nose-heavy trim, I crashed it inverted, broke the engine, and
cracked a few major joints.
The cowl-free nose allows easy access to the removable tank for
height adjustments. Notice the engine-mount pads.
The engine mounts and lower firewalls assemble on a flat
surface. Clamp them tightly and let the epoxy cure.
The top and bottom planks and the nose-block wedge piece have
been assembled and smoothed into the spinner shape.
Photos by the author
January 2004 31
The doublers have been joined to the fuselage sides. Check out
the 1⁄4 triangle stock reinforcement pieces.
01sig1.QXD 10/27/03 2:01 pm Page 31
During the repair phase I shortened the nose to move the CG to
the design location, and Tom replaced the engine. The next flight
series was truncated at four. The partially tuned BareCat was
feeling good, and I tried an Hourglass. I ham-handedly executed the
first corner and the model came loose on the second corner, quickly
hiding behind my hat, and augered into the unyielding ground
before I could turn around.
There were several large pieces, but none of them had joints that
lent themselves to reconstruction. Besides that, the new engine was
split open after the fuel tank mashed around it, and the engine beam
mounts made a wishbone out of the engine crankcase.
Post-mortem analysis revealed that the twin-finned design had
excessive yaw stability but inadequate side area to generate enough
yaw torque to recover from extreme adverse yaw. Bob never
overcontrolled a model, so the problem didn’t show up until I got
my hands on one. So the twin-finned BareCat 650 project ended
with two prototypes, and I moved on to the B model.
The BareCat 650-B incorporated the single-finned side view of
the old 600, a sidewinder engine on a Radio Control engine mount,
and it preserved the now-proven 650 plan-view geometry. I used a
4-year-old Silver Foxx .40 to take advantage of the .015-diameter
cable. This is a powerful engine. I settled on 10% fuel and an APC
12.25 x 3.75 propeller.
This allows a rich, level flight and plenty of reserve thrust for
the vertical maneuvers. It comes on and off reliably, and with a 20%
oil blend it needs less than 4 ounces to complete the pattern.
Trimming the model was straightforward and surprise-free. I
cleaned up the slight tendency to turn tighter outside by sliding the
lines down on the handle to adjust my leverage and feel. The 650-B
at 54 ounces competes in the Advanced class with good results for
me. I currently fly it with a Tom Dixon-prepared O.S. .46 LA and
use 66 feet of that dreaded .018-diameter cable required by rules.
We sincerely believe that too much horsepower is about right.
I wouldn’t expect those competing in the Expert class to use
BareCat 650-C
It’s time for a dry-assembly test to ensure that all parts fit
together properly before gluing. Looks good!
A clean, functional front end. Look at neat fuel-line routing and
muffler installation. Details make the difference!
Type: CL sport Stunt
Wingspan: 541⁄4 inches
Engine: Double Star 50
Flying weight: 49 ounces
Construction: Balsa, plywood, foam
Covering/finish: MonoKote/modeling paints
32 MODEL AVIATION
The wingtip braces and leadout guide have been installed on the
inboard wing panel. Braces do not touch the covering.
01sig1.QXD 10/27/03 2:02 pm Page 32
January 2004 33
something as simple as this machine as their
competition mount. This is an excellent
airplane with which to work your way up
through the ranks before you have to start
the arduous task of keeping a flap model in
tune.
The C model is presented with three
different nose configurations. I selected the
inverted engine for personal reasons. (It
looks the best.) Cut the nose you want from
sheet two of the plans and tape the paper
doll to the main drawing. The attach point is
the firewall at the leading edge. The plan
width is set for beam mounts and stock
tanks, and once you blend in the shapes you
can have as fancy a nose as anyone’s.
However, the totally external engine
system (the B model) is ideal for running
power-plant experiments. The fuel-mixture
symmetry on my B model was adjusted with
the tank raised 1⁄8 inch.
The covering and decoration are
MonoKote. The foam wing core is available
from Tom Dixon. The C model had a dry
weight of 49 ounces using a carbon-fiber
landing-gear strut, the lightweight Double
Star 50 engine, and a 12 x 6 wood propeller.
On 68 feet (handle to airplane centerline) x
.018-diameter cables, there is plenty of
reserve line tension overhead. The best CG
is per the plans, and the prototype nailed it
without adding dead weights.
CONSTRUCTION
This is not a beginner’s project; you
should have experience with handling
standard materials and construction
procedures. There are no major kinks in
assembling the BareCat 650. (Well, you do
need to get the assembled parts square to
each other.) I have laid out the major parts
to provide self-alignment features between
the fuselage and wing and the tail and the
airplane.
As you browse through the construction
photos you will see a lot of masking tape. It
does much more than block off paint! It
clamps around things, across flat joints, over
wingtips, along edges you don’t want to
sand, and many places you don’t want to
leave pinholes.
I like putting a 2-inch-wide strip over the
end of my shaping block and sliding the
taped end along a tip rib to blend in the
wingtip. I use 100-grit garnet sandpaper
with light pressure for fast removal to
rough-shape. I follow this with 150-grit
paper to take out the tool marks, 280 grit,
then 400 grit to polish the wood.
Using plastic film covering all over
forces me to make joints fit superclose,
which is essential to solid glue joints
anyway. It requires extra planning during
covering to leave it off where parts fit
together rather than cut away film after
covering. I get nervous cutting through film
on top of balsa, particularly over 1⁄16 balsa
planking.
The foam wing cores you buy from Tom
Dixon are geared toward his exoskeleton
planking system, and the cored-out portions
save 4 ounces of dead weight. Tom
publishes a comprehensive assembly
procedure, which you can download when
you order the cores on his Web site.
I prefer to cut the main spar on the
centerline and add splice plate caps during
final wing assembly. One convenience is
being able to block-sand the center face of
both panels to gain the best glue joint and
alignment. The caps carry the major bending
loads anyhow.
I keep the waste-foam material handy to
hold the cores during work and storage.
They prevent a lot of hangar rash and make
nice, stable support fixtures. With the 24-
inch panel cores, you don’t have to order
48-inch lumber. I purchased 24-inch
selected stock from Lone Star Models.
Have someone there select the stabilizer
and elevator in 3⁄16, 6- to 8-pound stock—
one 4 x 36 inches and one 3 x 36 inches.
The 1⁄4 stock for fins, tips, and top and
bottom planks needs to be 4 inches wide and
36 inches long in 6- to 8-pound density. I
used four pieces altogether.
I stripped the leading edge from a 1⁄4
sheet to get it dead straight in the relaxed
state. Logical sequence of adding parts
yielded a 15.3-ounce fully covered wing
with controls and an ounce of permanent tip
weight. If you noticed that my tip-weight
box cover is on top, don’t sweat it. The first
time I did it was an accident, and I got used
to it on future airplanes.
After you complete the wooden parts
assembly, do the wingtips, line guide, tipweight
box, and the bellcrank dry assembly.
Put these pieces aside until the rest of the
uncovered parts are ready to cover.
Before and after you cover the stabilizer
and elevator pieces, make sure that both
mating edges are dead straight—not just
mated to the same curvature. You will be
01sig2.QXD 10/27/03 10:40 am Page 33
34 MODEL AVIATION
Full-Size Plans Available—see page 191
01sig2.QXD 10/27/03 10:41 am Page 34
January 2004 35
rewarded with an elevator that drops freely
by its own weight. Careful location and
cutting hinge slots will save you problems
during final assembly, when the parts are all
covered and polished.
The control-horn base takes a bit of skill
but gives a clean, fuelproof assembly. (See
the plans for details.) Make sure that the
horn is located on the bottom and the
inboard side before you cut the pocket. (I
didn’t do it once.) I cut out the fin parts at
the same time as the stabilizer parts and get
into a rhythm of rounding edges, blocksanding,
and polish-sanding these parts.
I drilled a series of 1⁄2-inch-diameter
holes along the engine mounts to save dead
weight. Using a Forstner drill bit I let the
center point just break out of the hole’s
bottom, which leaves a solid glue surface. I
use 1⁄8-inch dowel pins to key the fuselage
sides and doublers during their glue process.
I use epoxy, well-squeegeed, and apply a
great deal of pressure between flat surfaces
to gain the optimum joint strength. The pins
are sanded on both sides until flush to both
surfaces.
I make a subassembly of the engine
mounts, two subfirewalls and the spacer
block, and the filler piece, assembled
squarely and flat using epoxy. This group is
used to square and align the fuselage sides
and top assembly on a nice, flat surface. If
this assembly is true, the final product
works better.
Thoroughly coat with epoxy the inside
surfaces that will be exposed to fuel. Do the
engine mounting holes and spacer plates,
then tape up the engine. Mount it and a
sacrificial spinner and carve the nose. Here
you should have the uncovered wood parts
ready for final assembly.
Final Assembly: Tape the wing halves
together, dry-assemble the fuselage to the
wing, then use the flat tabletop to fit the top
fin and the booms and stabilizer together.
Once these joints are tuned to firm slip fits,
proceed with covering the parts. The closer
these joints fit, the better the strength, and
you really can get quality without fillets to
cover the gaps.
Final assembly is straightforward,
requiring care to align parts and make solid
glue joints. Once the assembly is finished,
add all of the deadweight parts: landing-gear
assembly, control horn, pushrod half, fuel
tank and padding, and plumbing.
The covering and decorations are up to
you and your comfort level. I went beyond
my usual level of decoration, but don’t
expect this all the time. One thing Bob and I
learned is that the 20 appearance points we
could get now far outweigh the 80 points
awarded in the beginning days of Stunt to
turn the design direction away from the ugly
barndoor machines. It is also clear that the
appearance judging has saved the event
from becoming easy.
Flying: If your finished CG is within 1⁄8
inch of the design location, you might as
well proceed to flight tests. The lines’
location on the plans are for the design CG
and a 50-ounce dry weight. You can tune
your model from there as you get used to it.
I was able to hit the design CG right on
with a wood propeller, and so far the lines
rake is correct using 66-foot x .018-diameter
cables, eyelet to eyelet. This delivers a flight
radius, including 2.5 feet for my extended
arm, of 70.8 feet.
I have an ounce of tip weight in the box,
for a total of 2 ounces. I am still playing the
propeller, tank-height game while feeling
safe to ease through all of the pattern
maneuvers. I learned that 6.0-second laps are
too slow and that 5.5 seconds brings up safe
tension and controls force.
The Double Star 50 is performing
routinely with no bad habits on 10%-nitro
fuel. I still need to stabilize the power-plant
components before determining the ideal
fuel capacity. It will probably be less than 5
ounces.
Since Bob is no longer available to make my
numbers sing, will there be more BareCat
type projects? The three models presented
here represent optimal geometry under the
present pattern specifications. Someone
could probably shave off a few ounces with
carbon fiber and a Lost Foam wing structure.
Frankly, the resulting machinery would not
present better enough than the present
structure to warrant the additional effort.
I believe that any of the top-10 pilots
could compete successfully with a BareCat
650. Brave words, for sure, but I don’t
believe any of them will try it. Don’t feel
sorry for me; I had my time in the barrel and
am ready to coast a bit. Please try the
BareCat. You’ll like it!
Thanks, Bob. It was a fun run. MA
Bill Netzeband
23978 Villa Pamilla
Murrieta CA 92562
$3900
+ $450 S/H
DAKOTA
Joe Wagners, Classic
Free Flight design.
24" wingspan for
.02 or .049 engine
BMJR Model Products
Box 1210
Sharpes, FL 32959-1210
321-537-1159
www.BMJRModels.com
Materials Sources:
Foam wing cores (BareCat), Bolly landing
gear (KA-10), Double Star 50 engine:
Tom Dixon
Box 671166
Marietta GA 30062
Tel./Fax: (770) 592-3279
http://members.tripod.com/~TomDixon/tom
dixon.htm
Fuel tank, controls, wheels, propellers:
Brodak Mfg. & Distributing Co. Inc.
100 Park Ave.
Carmichaels PA 15320
(724) 966-2726
Fax: (724) 966-5760
www.brodak.com
Fuel tank, controls, wheels, propellers:
RSM Distribution
21899 Heliotrope Ln.
Wildomar CA 92595
(714) 931-6038
www.rsmdistribution.com
Selected-density balsa (see plans):
Lone Star Models
115 Industrial
Lancaster TX 75134
(972) 218-9663
(800) 687-5555 (to order)
Fax: (972) 218-9211
www.lonestar-models.com
01sig2.QXD 10/27/03 10:41 am Page 35
Edition: Model Aviation - 2004/01
Page Numbers: 29,30,31,32,33,34,35
have hard data to explain why. We experimented with outside-thebox
designs using non-Stunt power plants and flap-free wings. Our
aim was to fly the pattern to the specified dimensions so accurately
that we had to get top points. (Yeah, right.)
The wingspan was limited to 54 inches so that they would fit into
Bob’s Volvo sedan! I had determined that wings with zero quarter
chord sweep angles didn’t
react to wind by chattering
in roll, so we held this
criterion.
After a suitable period,
we realized that the judging
cadre was not using the
book dimensions and had
no intention of ever
measuring them by any
equipment other than the
trained eyeball.
By 1975 it was clear
that Bob would have to fly a traditional airplane to stay in the top
five at major meets. He joined the campaign with his Avanti series:
a conventional flapped machine with conventional styling. I waded
into the flap-analysis swamp armed with a TI-59 programmable
calculator. Progress was slow because flap calculations are tedious
and complex. We applied each of my research breakthroughs to the
Avanti and tested the accuracy of my progress.
There were also several major configurations to idealize the yaw
January 2004 29
BareCat 650-C
THIS AIRPLANE and document are my sentimental journey to
honor the memory of Bob Baron (1944-1999) and our long
collaboration to design and compete with cutting-edge Control Line
Precision Aerobatics equipment.
It started when Bob showed up on my doorstep in Pasadena,
California, sometime during 1965. He was able to feel and analyze
things about the airplane in flight where my calculations only
showed variation in the second decimal place.
We knew that flaps were difficult to keep in tune, but we didn’t
A bottom view of the BareCat shows the no-frills approach that
Bill prefers. The trim scheme is simple.
Sometimes
function yields
unusual forms
■ Bill Netzeband
01sig1.QXD 10/27/03 2:00 pm Page 29
30 MODEL AVIATION
axis, the power-plant package, the landing gear, the Rabe rudder, and
search for the magic flap-elevator relationship. Along with the
aerodynamic package criterion, we added simple structure with
maximum longevity.
In 1984 I tiptoed into the computer era and was able to get
answers more rapidly. Unfortunately I developed all of my programs
using arcane software, so I won’t be able to provide the math for
your design efforts.
It became clear that flaps introduce forces that vary widely with
any center of gravity (CG) shift or a minor velocity change, and
while making a possible 40% more lift available to the wing, they
load the elevator excessively and demand lots of extra thrust! I kept
looking for ways to compete without flaps because I like simple
solutions, and my skill level peaked out a little bit above average.
Bob and I left off anything that did not contribute to flying the
AMA rule-book pattern dimensions, such as labor-intensive
decorations and artistic shapes and high finishes, which add up to
weight and cost.
The Humbug series, initiated in 1968, was based on 7:1-aspectratio
wings controlled by 10:1-aspect-ratio stabilators, and it had
minimal fuselage and appendages. The stabilators were later
replaced by using stabilizer-elevator surfaces. They were also based
on low power-to-weight-ratio airframes.
The original Humbug used a Fox .19 to power 490 square inches
of wing at 39 ounces. Subsequent versions backed down to 6:1-
aspect-ratio wings and 8:1 stabilizers, and the late Tom Warden
styled a couple of them. They produced positive comments from the
general population but missed the winner’s circle too often.
The 1⁄2A BareCat was designed in 1980, to achieve the lowest
practical wing loading and take advantage of reducing the wing
aspect ratio to 4:1 and the tail to 6:1. The tail became 30% of the
wing, and the tail moment arm was 14 inches.
We added a practical problem by storing fuel on the CG in a
bladder tank since a tank in the 11-inch nose would upset the CG
during flight. We were looking for the 5-foot corner, but the whole
1⁄2A project went too far outside the box to become a popular
configuration.
In 1993 I wrote a story called “The Stunt Ace” and designed a
theoretically optimized machine that would do a book pattern. It
required a super .09 engine to save dead weight and fuel and to allow
.012-inch-diameter lines. Fuel was stored in a high-pressure bladder
mounted on the CG, as in the 1⁄2A BareCat. I had to specify several
unobtanium space-age materials to keep the weight down. It flew
great on paper, but, as in real life, Ace missed qualifying at its first
Nats by a half point.
The machine had a 600-square-inch wing, huge centerline fin
surfaces, a single wheel, booms, a stabilator, etc., and only weighed
15 ounces. Bob enjoyed the story and asked me if it would fly with a
Spar and trailing-edge pieces are attached to the foam cores.
Don’t omit the panel-identification marks!
Leading- and trailing-edge planking has been added. Masking
tape is used to hold everything down tight.
The wing takes shape with the addition of capstrips and centersection
planking. Notice the splice-plate cutouts.
The bellcrank assembly, with attached pushrod, is glued in
place. Take extra care to ensure smooth movement.
01sig1.QXD 10/27/03 2:00 pm Page 30
.15 engine. He built the BareCat 600 from my sketches using a
Nelson .15 Combat engine.
The puzzlement came when the 40-ounce machine flew off the
bench, and the few times Bob and the Nelson got together with the
needle valve and the experimental bladder fuel system, it handled
like an eagle! Those happy moments were too few, and Bob shelved
it.
I got my hands on the airframe in 1998 and tried a Norvel .15. I
replaced the stabilator and nonlinear bellcrank with a 50%
stabilizer-elevator assembly. The thing teased me by flying all of the
maneuvers, but it couldn’t deliver adequate confidence. It ended up
with a Double Star .40, a conventional fuel tank in the nose, it
gained 7 ounces, and it became a better-than-average performer.
There was not enough sizzle, though.
Bob had a final adventure using the BareCat ’98 that was
published in the June 1999 Model Aviation. He took it to the 1998
Nationals for recreation. Tragically, his Spartan broke up during a
test flight after he had qualified for the finals! Being a consummate
competitor, Bob decided to fly the BareCat.
Several problems in addition to being first up to fly the next day
prompted an all-nighter. He’d been flying with .008 lines on the
airplane powered by a 1cc engine! The last trimming trauma was a
frantic session to install a combat-tuned VA .049. He had help from
Larry Driskill and “Sleepy” Dawson.
After little real sleep, they got in a fast test flight at 6 a.m. Bob’s
first flight was humming along when the engine mount broke and
the VA sailed off into the boondocks. Bob finessed it back to the
runway with no further damage.
The next frantic fix involved reinstalling the 1cc engine and a set
of “equivalent” .012-diameter lines. With no test flight, Bob racked
up a 500-point score from the Nationals judges—not too shabby for
an outside-the-box machine.
In 1998 Tom Dixon was producing a Double Star 50, and we
decided to give the BareCat another shot. We used the 1⁄2A BareCat
geometry and enlarged it to produce 650 square inches of wing.
After reviewing the layout, we adjusted the tail moment arm and
stabilizer aspect ratio to more reasonable sizes for a large airplane.
Bob constructed the first model and used an inverted Double Star
50 engine and spinner. This airplane was almost finished when he
passed away in September 1999. Tom Dixon finished Bob’s model
and flew it a few times. It needed flight trimming, but Tom and I
decided that Bob’s last project shouldn’t be put at any more risk.
To make Bob’s airplane unique, I modified the drawings to use
an upright engine and aluminum two-wheel landing gear. I built the
“A” model and powered it with a Double Star 50. While putting up
with nose-heavy trim, I crashed it inverted, broke the engine, and
cracked a few major joints.
The cowl-free nose allows easy access to the removable tank for
height adjustments. Notice the engine-mount pads.
The engine mounts and lower firewalls assemble on a flat
surface. Clamp them tightly and let the epoxy cure.
The top and bottom planks and the nose-block wedge piece have
been assembled and smoothed into the spinner shape.
Photos by the author
January 2004 31
The doublers have been joined to the fuselage sides. Check out
the 1⁄4 triangle stock reinforcement pieces.
01sig1.QXD 10/27/03 2:01 pm Page 31
During the repair phase I shortened the nose to move the CG to
the design location, and Tom replaced the engine. The next flight
series was truncated at four. The partially tuned BareCat was
feeling good, and I tried an Hourglass. I ham-handedly executed the
first corner and the model came loose on the second corner, quickly
hiding behind my hat, and augered into the unyielding ground
before I could turn around.
There were several large pieces, but none of them had joints that
lent themselves to reconstruction. Besides that, the new engine was
split open after the fuel tank mashed around it, and the engine beam
mounts made a wishbone out of the engine crankcase.
Post-mortem analysis revealed that the twin-finned design had
excessive yaw stability but inadequate side area to generate enough
yaw torque to recover from extreme adverse yaw. Bob never
overcontrolled a model, so the problem didn’t show up until I got
my hands on one. So the twin-finned BareCat 650 project ended
with two prototypes, and I moved on to the B model.
The BareCat 650-B incorporated the single-finned side view of
the old 600, a sidewinder engine on a Radio Control engine mount,
and it preserved the now-proven 650 plan-view geometry. I used a
4-year-old Silver Foxx .40 to take advantage of the .015-diameter
cable. This is a powerful engine. I settled on 10% fuel and an APC
12.25 x 3.75 propeller.
This allows a rich, level flight and plenty of reserve thrust for
the vertical maneuvers. It comes on and off reliably, and with a 20%
oil blend it needs less than 4 ounces to complete the pattern.
Trimming the model was straightforward and surprise-free. I
cleaned up the slight tendency to turn tighter outside by sliding the
lines down on the handle to adjust my leverage and feel. The 650-B
at 54 ounces competes in the Advanced class with good results for
me. I currently fly it with a Tom Dixon-prepared O.S. .46 LA and
use 66 feet of that dreaded .018-diameter cable required by rules.
We sincerely believe that too much horsepower is about right.
I wouldn’t expect those competing in the Expert class to use
BareCat 650-C
It’s time for a dry-assembly test to ensure that all parts fit
together properly before gluing. Looks good!
A clean, functional front end. Look at neat fuel-line routing and
muffler installation. Details make the difference!
Type: CL sport Stunt
Wingspan: 541⁄4 inches
Engine: Double Star 50
Flying weight: 49 ounces
Construction: Balsa, plywood, foam
Covering/finish: MonoKote/modeling paints
32 MODEL AVIATION
The wingtip braces and leadout guide have been installed on the
inboard wing panel. Braces do not touch the covering.
01sig1.QXD 10/27/03 2:02 pm Page 32
January 2004 33
something as simple as this machine as their
competition mount. This is an excellent
airplane with which to work your way up
through the ranks before you have to start
the arduous task of keeping a flap model in
tune.
The C model is presented with three
different nose configurations. I selected the
inverted engine for personal reasons. (It
looks the best.) Cut the nose you want from
sheet two of the plans and tape the paper
doll to the main drawing. The attach point is
the firewall at the leading edge. The plan
width is set for beam mounts and stock
tanks, and once you blend in the shapes you
can have as fancy a nose as anyone’s.
However, the totally external engine
system (the B model) is ideal for running
power-plant experiments. The fuel-mixture
symmetry on my B model was adjusted with
the tank raised 1⁄8 inch.
The covering and decoration are
MonoKote. The foam wing core is available
from Tom Dixon. The C model had a dry
weight of 49 ounces using a carbon-fiber
landing-gear strut, the lightweight Double
Star 50 engine, and a 12 x 6 wood propeller.
On 68 feet (handle to airplane centerline) x
.018-diameter cables, there is plenty of
reserve line tension overhead. The best CG
is per the plans, and the prototype nailed it
without adding dead weights.
CONSTRUCTION
This is not a beginner’s project; you
should have experience with handling
standard materials and construction
procedures. There are no major kinks in
assembling the BareCat 650. (Well, you do
need to get the assembled parts square to
each other.) I have laid out the major parts
to provide self-alignment features between
the fuselage and wing and the tail and the
airplane.
As you browse through the construction
photos you will see a lot of masking tape. It
does much more than block off paint! It
clamps around things, across flat joints, over
wingtips, along edges you don’t want to
sand, and many places you don’t want to
leave pinholes.
I like putting a 2-inch-wide strip over the
end of my shaping block and sliding the
taped end along a tip rib to blend in the
wingtip. I use 100-grit garnet sandpaper
with light pressure for fast removal to
rough-shape. I follow this with 150-grit
paper to take out the tool marks, 280 grit,
then 400 grit to polish the wood.
Using plastic film covering all over
forces me to make joints fit superclose,
which is essential to solid glue joints
anyway. It requires extra planning during
covering to leave it off where parts fit
together rather than cut away film after
covering. I get nervous cutting through film
on top of balsa, particularly over 1⁄16 balsa
planking.
The foam wing cores you buy from Tom
Dixon are geared toward his exoskeleton
planking system, and the cored-out portions
save 4 ounces of dead weight. Tom
publishes a comprehensive assembly
procedure, which you can download when
you order the cores on his Web site.
I prefer to cut the main spar on the
centerline and add splice plate caps during
final wing assembly. One convenience is
being able to block-sand the center face of
both panels to gain the best glue joint and
alignment. The caps carry the major bending
loads anyhow.
I keep the waste-foam material handy to
hold the cores during work and storage.
They prevent a lot of hangar rash and make
nice, stable support fixtures. With the 24-
inch panel cores, you don’t have to order
48-inch lumber. I purchased 24-inch
selected stock from Lone Star Models.
Have someone there select the stabilizer
and elevator in 3⁄16, 6- to 8-pound stock—
one 4 x 36 inches and one 3 x 36 inches.
The 1⁄4 stock for fins, tips, and top and
bottom planks needs to be 4 inches wide and
36 inches long in 6- to 8-pound density. I
used four pieces altogether.
I stripped the leading edge from a 1⁄4
sheet to get it dead straight in the relaxed
state. Logical sequence of adding parts
yielded a 15.3-ounce fully covered wing
with controls and an ounce of permanent tip
weight. If you noticed that my tip-weight
box cover is on top, don’t sweat it. The first
time I did it was an accident, and I got used
to it on future airplanes.
After you complete the wooden parts
assembly, do the wingtips, line guide, tipweight
box, and the bellcrank dry assembly.
Put these pieces aside until the rest of the
uncovered parts are ready to cover.
Before and after you cover the stabilizer
and elevator pieces, make sure that both
mating edges are dead straight—not just
mated to the same curvature. You will be
01sig2.QXD 10/27/03 10:40 am Page 33
34 MODEL AVIATION
Full-Size Plans Available—see page 191
01sig2.QXD 10/27/03 10:41 am Page 34
January 2004 35
rewarded with an elevator that drops freely
by its own weight. Careful location and
cutting hinge slots will save you problems
during final assembly, when the parts are all
covered and polished.
The control-horn base takes a bit of skill
but gives a clean, fuelproof assembly. (See
the plans for details.) Make sure that the
horn is located on the bottom and the
inboard side before you cut the pocket. (I
didn’t do it once.) I cut out the fin parts at
the same time as the stabilizer parts and get
into a rhythm of rounding edges, blocksanding,
and polish-sanding these parts.
I drilled a series of 1⁄2-inch-diameter
holes along the engine mounts to save dead
weight. Using a Forstner drill bit I let the
center point just break out of the hole’s
bottom, which leaves a solid glue surface. I
use 1⁄8-inch dowel pins to key the fuselage
sides and doublers during their glue process.
I use epoxy, well-squeegeed, and apply a
great deal of pressure between flat surfaces
to gain the optimum joint strength. The pins
are sanded on both sides until flush to both
surfaces.
I make a subassembly of the engine
mounts, two subfirewalls and the spacer
block, and the filler piece, assembled
squarely and flat using epoxy. This group is
used to square and align the fuselage sides
and top assembly on a nice, flat surface. If
this assembly is true, the final product
works better.
Thoroughly coat with epoxy the inside
surfaces that will be exposed to fuel. Do the
engine mounting holes and spacer plates,
then tape up the engine. Mount it and a
sacrificial spinner and carve the nose. Here
you should have the uncovered wood parts
ready for final assembly.
Final Assembly: Tape the wing halves
together, dry-assemble the fuselage to the
wing, then use the flat tabletop to fit the top
fin and the booms and stabilizer together.
Once these joints are tuned to firm slip fits,
proceed with covering the parts. The closer
these joints fit, the better the strength, and
you really can get quality without fillets to
cover the gaps.
Final assembly is straightforward,
requiring care to align parts and make solid
glue joints. Once the assembly is finished,
add all of the deadweight parts: landing-gear
assembly, control horn, pushrod half, fuel
tank and padding, and plumbing.
The covering and decorations are up to
you and your comfort level. I went beyond
my usual level of decoration, but don’t
expect this all the time. One thing Bob and I
learned is that the 20 appearance points we
could get now far outweigh the 80 points
awarded in the beginning days of Stunt to
turn the design direction away from the ugly
barndoor machines. It is also clear that the
appearance judging has saved the event
from becoming easy.
Flying: If your finished CG is within 1⁄8
inch of the design location, you might as
well proceed to flight tests. The lines’
location on the plans are for the design CG
and a 50-ounce dry weight. You can tune
your model from there as you get used to it.
I was able to hit the design CG right on
with a wood propeller, and so far the lines
rake is correct using 66-foot x .018-diameter
cables, eyelet to eyelet. This delivers a flight
radius, including 2.5 feet for my extended
arm, of 70.8 feet.
I have an ounce of tip weight in the box,
for a total of 2 ounces. I am still playing the
propeller, tank-height game while feeling
safe to ease through all of the pattern
maneuvers. I learned that 6.0-second laps are
too slow and that 5.5 seconds brings up safe
tension and controls force.
The Double Star 50 is performing
routinely with no bad habits on 10%-nitro
fuel. I still need to stabilize the power-plant
components before determining the ideal
fuel capacity. It will probably be less than 5
ounces.
Since Bob is no longer available to make my
numbers sing, will there be more BareCat
type projects? The three models presented
here represent optimal geometry under the
present pattern specifications. Someone
could probably shave off a few ounces with
carbon fiber and a Lost Foam wing structure.
Frankly, the resulting machinery would not
present better enough than the present
structure to warrant the additional effort.
I believe that any of the top-10 pilots
could compete successfully with a BareCat
650. Brave words, for sure, but I don’t
believe any of them will try it. Don’t feel
sorry for me; I had my time in the barrel and
am ready to coast a bit. Please try the
BareCat. You’ll like it!
Thanks, Bob. It was a fun run. MA
Bill Netzeband
23978 Villa Pamilla
Murrieta CA 92562
$3900
+ $450 S/H
DAKOTA
Joe Wagners, Classic
Free Flight design.
24" wingspan for
.02 or .049 engine
BMJR Model Products
Box 1210
Sharpes, FL 32959-1210
321-537-1159
www.BMJRModels.com
Materials Sources:
Foam wing cores (BareCat), Bolly landing
gear (KA-10), Double Star 50 engine:
Tom Dixon
Box 671166
Marietta GA 30062
Tel./Fax: (770) 592-3279
http://members.tripod.com/~TomDixon/tom
dixon.htm
Fuel tank, controls, wheels, propellers:
Brodak Mfg. & Distributing Co. Inc.
100 Park Ave.
Carmichaels PA 15320
(724) 966-2726
Fax: (724) 966-5760
www.brodak.com
Fuel tank, controls, wheels, propellers:
RSM Distribution
21899 Heliotrope Ln.
Wildomar CA 92595
(714) 931-6038
www.rsmdistribution.com
Selected-density balsa (see plans):
Lone Star Models
115 Industrial
Lancaster TX 75134
(972) 218-9663
(800) 687-5555 (to order)
Fax: (972) 218-9211
www.lonestar-models.com
01sig2.QXD 10/27/03 10:41 am Page 35
Edition: Model Aviation - 2004/01
Page Numbers: 29,30,31,32,33,34,35
have hard data to explain why. We experimented with outside-thebox
designs using non-Stunt power plants and flap-free wings. Our
aim was to fly the pattern to the specified dimensions so accurately
that we had to get top points. (Yeah, right.)
The wingspan was limited to 54 inches so that they would fit into
Bob’s Volvo sedan! I had determined that wings with zero quarter
chord sweep angles didn’t
react to wind by chattering
in roll, so we held this
criterion.
After a suitable period,
we realized that the judging
cadre was not using the
book dimensions and had
no intention of ever
measuring them by any
equipment other than the
trained eyeball.
By 1975 it was clear
that Bob would have to fly a traditional airplane to stay in the top
five at major meets. He joined the campaign with his Avanti series:
a conventional flapped machine with conventional styling. I waded
into the flap-analysis swamp armed with a TI-59 programmable
calculator. Progress was slow because flap calculations are tedious
and complex. We applied each of my research breakthroughs to the
Avanti and tested the accuracy of my progress.
There were also several major configurations to idealize the yaw
January 2004 29
BareCat 650-C
THIS AIRPLANE and document are my sentimental journey to
honor the memory of Bob Baron (1944-1999) and our long
collaboration to design and compete with cutting-edge Control Line
Precision Aerobatics equipment.
It started when Bob showed up on my doorstep in Pasadena,
California, sometime during 1965. He was able to feel and analyze
things about the airplane in flight where my calculations only
showed variation in the second decimal place.
We knew that flaps were difficult to keep in tune, but we didn’t
A bottom view of the BareCat shows the no-frills approach that
Bill prefers. The trim scheme is simple.
Sometimes
function yields
unusual forms
■ Bill Netzeband
01sig1.QXD 10/27/03 2:00 pm Page 29
30 MODEL AVIATION
axis, the power-plant package, the landing gear, the Rabe rudder, and
search for the magic flap-elevator relationship. Along with the
aerodynamic package criterion, we added simple structure with
maximum longevity.
In 1984 I tiptoed into the computer era and was able to get
answers more rapidly. Unfortunately I developed all of my programs
using arcane software, so I won’t be able to provide the math for
your design efforts.
It became clear that flaps introduce forces that vary widely with
any center of gravity (CG) shift or a minor velocity change, and
while making a possible 40% more lift available to the wing, they
load the elevator excessively and demand lots of extra thrust! I kept
looking for ways to compete without flaps because I like simple
solutions, and my skill level peaked out a little bit above average.
Bob and I left off anything that did not contribute to flying the
AMA rule-book pattern dimensions, such as labor-intensive
decorations and artistic shapes and high finishes, which add up to
weight and cost.
The Humbug series, initiated in 1968, was based on 7:1-aspectratio
wings controlled by 10:1-aspect-ratio stabilators, and it had
minimal fuselage and appendages. The stabilators were later
replaced by using stabilizer-elevator surfaces. They were also based
on low power-to-weight-ratio airframes.
The original Humbug used a Fox .19 to power 490 square inches
of wing at 39 ounces. Subsequent versions backed down to 6:1-
aspect-ratio wings and 8:1 stabilizers, and the late Tom Warden
styled a couple of them. They produced positive comments from the
general population but missed the winner’s circle too often.
The 1⁄2A BareCat was designed in 1980, to achieve the lowest
practical wing loading and take advantage of reducing the wing
aspect ratio to 4:1 and the tail to 6:1. The tail became 30% of the
wing, and the tail moment arm was 14 inches.
We added a practical problem by storing fuel on the CG in a
bladder tank since a tank in the 11-inch nose would upset the CG
during flight. We were looking for the 5-foot corner, but the whole
1⁄2A project went too far outside the box to become a popular
configuration.
In 1993 I wrote a story called “The Stunt Ace” and designed a
theoretically optimized machine that would do a book pattern. It
required a super .09 engine to save dead weight and fuel and to allow
.012-inch-diameter lines. Fuel was stored in a high-pressure bladder
mounted on the CG, as in the 1⁄2A BareCat. I had to specify several
unobtanium space-age materials to keep the weight down. It flew
great on paper, but, as in real life, Ace missed qualifying at its first
Nats by a half point.
The machine had a 600-square-inch wing, huge centerline fin
surfaces, a single wheel, booms, a stabilator, etc., and only weighed
15 ounces. Bob enjoyed the story and asked me if it would fly with a
Spar and trailing-edge pieces are attached to the foam cores.
Don’t omit the panel-identification marks!
Leading- and trailing-edge planking has been added. Masking
tape is used to hold everything down tight.
The wing takes shape with the addition of capstrips and centersection
planking. Notice the splice-plate cutouts.
The bellcrank assembly, with attached pushrod, is glued in
place. Take extra care to ensure smooth movement.
01sig1.QXD 10/27/03 2:00 pm Page 30
.15 engine. He built the BareCat 600 from my sketches using a
Nelson .15 Combat engine.
The puzzlement came when the 40-ounce machine flew off the
bench, and the few times Bob and the Nelson got together with the
needle valve and the experimental bladder fuel system, it handled
like an eagle! Those happy moments were too few, and Bob shelved
it.
I got my hands on the airframe in 1998 and tried a Norvel .15. I
replaced the stabilator and nonlinear bellcrank with a 50%
stabilizer-elevator assembly. The thing teased me by flying all of the
maneuvers, but it couldn’t deliver adequate confidence. It ended up
with a Double Star .40, a conventional fuel tank in the nose, it
gained 7 ounces, and it became a better-than-average performer.
There was not enough sizzle, though.
Bob had a final adventure using the BareCat ’98 that was
published in the June 1999 Model Aviation. He took it to the 1998
Nationals for recreation. Tragically, his Spartan broke up during a
test flight after he had qualified for the finals! Being a consummate
competitor, Bob decided to fly the BareCat.
Several problems in addition to being first up to fly the next day
prompted an all-nighter. He’d been flying with .008 lines on the
airplane powered by a 1cc engine! The last trimming trauma was a
frantic session to install a combat-tuned VA .049. He had help from
Larry Driskill and “Sleepy” Dawson.
After little real sleep, they got in a fast test flight at 6 a.m. Bob’s
first flight was humming along when the engine mount broke and
the VA sailed off into the boondocks. Bob finessed it back to the
runway with no further damage.
The next frantic fix involved reinstalling the 1cc engine and a set
of “equivalent” .012-diameter lines. With no test flight, Bob racked
up a 500-point score from the Nationals judges—not too shabby for
an outside-the-box machine.
In 1998 Tom Dixon was producing a Double Star 50, and we
decided to give the BareCat another shot. We used the 1⁄2A BareCat
geometry and enlarged it to produce 650 square inches of wing.
After reviewing the layout, we adjusted the tail moment arm and
stabilizer aspect ratio to more reasonable sizes for a large airplane.
Bob constructed the first model and used an inverted Double Star
50 engine and spinner. This airplane was almost finished when he
passed away in September 1999. Tom Dixon finished Bob’s model
and flew it a few times. It needed flight trimming, but Tom and I
decided that Bob’s last project shouldn’t be put at any more risk.
To make Bob’s airplane unique, I modified the drawings to use
an upright engine and aluminum two-wheel landing gear. I built the
“A” model and powered it with a Double Star 50. While putting up
with nose-heavy trim, I crashed it inverted, broke the engine, and
cracked a few major joints.
The cowl-free nose allows easy access to the removable tank for
height adjustments. Notice the engine-mount pads.
The engine mounts and lower firewalls assemble on a flat
surface. Clamp them tightly and let the epoxy cure.
The top and bottom planks and the nose-block wedge piece have
been assembled and smoothed into the spinner shape.
Photos by the author
January 2004 31
The doublers have been joined to the fuselage sides. Check out
the 1⁄4 triangle stock reinforcement pieces.
01sig1.QXD 10/27/03 2:01 pm Page 31
During the repair phase I shortened the nose to move the CG to
the design location, and Tom replaced the engine. The next flight
series was truncated at four. The partially tuned BareCat was
feeling good, and I tried an Hourglass. I ham-handedly executed the
first corner and the model came loose on the second corner, quickly
hiding behind my hat, and augered into the unyielding ground
before I could turn around.
There were several large pieces, but none of them had joints that
lent themselves to reconstruction. Besides that, the new engine was
split open after the fuel tank mashed around it, and the engine beam
mounts made a wishbone out of the engine crankcase.
Post-mortem analysis revealed that the twin-finned design had
excessive yaw stability but inadequate side area to generate enough
yaw torque to recover from extreme adverse yaw. Bob never
overcontrolled a model, so the problem didn’t show up until I got
my hands on one. So the twin-finned BareCat 650 project ended
with two prototypes, and I moved on to the B model.
The BareCat 650-B incorporated the single-finned side view of
the old 600, a sidewinder engine on a Radio Control engine mount,
and it preserved the now-proven 650 plan-view geometry. I used a
4-year-old Silver Foxx .40 to take advantage of the .015-diameter
cable. This is a powerful engine. I settled on 10% fuel and an APC
12.25 x 3.75 propeller.
This allows a rich, level flight and plenty of reserve thrust for
the vertical maneuvers. It comes on and off reliably, and with a 20%
oil blend it needs less than 4 ounces to complete the pattern.
Trimming the model was straightforward and surprise-free. I
cleaned up the slight tendency to turn tighter outside by sliding the
lines down on the handle to adjust my leverage and feel. The 650-B
at 54 ounces competes in the Advanced class with good results for
me. I currently fly it with a Tom Dixon-prepared O.S. .46 LA and
use 66 feet of that dreaded .018-diameter cable required by rules.
We sincerely believe that too much horsepower is about right.
I wouldn’t expect those competing in the Expert class to use
BareCat 650-C
It’s time for a dry-assembly test to ensure that all parts fit
together properly before gluing. Looks good!
A clean, functional front end. Look at neat fuel-line routing and
muffler installation. Details make the difference!
Type: CL sport Stunt
Wingspan: 541⁄4 inches
Engine: Double Star 50
Flying weight: 49 ounces
Construction: Balsa, plywood, foam
Covering/finish: MonoKote/modeling paints
32 MODEL AVIATION
The wingtip braces and leadout guide have been installed on the
inboard wing panel. Braces do not touch the covering.
01sig1.QXD 10/27/03 2:02 pm Page 32
January 2004 33
something as simple as this machine as their
competition mount. This is an excellent
airplane with which to work your way up
through the ranks before you have to start
the arduous task of keeping a flap model in
tune.
The C model is presented with three
different nose configurations. I selected the
inverted engine for personal reasons. (It
looks the best.) Cut the nose you want from
sheet two of the plans and tape the paper
doll to the main drawing. The attach point is
the firewall at the leading edge. The plan
width is set for beam mounts and stock
tanks, and once you blend in the shapes you
can have as fancy a nose as anyone’s.
However, the totally external engine
system (the B model) is ideal for running
power-plant experiments. The fuel-mixture
symmetry on my B model was adjusted with
the tank raised 1⁄8 inch.
The covering and decoration are
MonoKote. The foam wing core is available
from Tom Dixon. The C model had a dry
weight of 49 ounces using a carbon-fiber
landing-gear strut, the lightweight Double
Star 50 engine, and a 12 x 6 wood propeller.
On 68 feet (handle to airplane centerline) x
.018-diameter cables, there is plenty of
reserve line tension overhead. The best CG
is per the plans, and the prototype nailed it
without adding dead weights.
CONSTRUCTION
This is not a beginner’s project; you
should have experience with handling
standard materials and construction
procedures. There are no major kinks in
assembling the BareCat 650. (Well, you do
need to get the assembled parts square to
each other.) I have laid out the major parts
to provide self-alignment features between
the fuselage and wing and the tail and the
airplane.
As you browse through the construction
photos you will see a lot of masking tape. It
does much more than block off paint! It
clamps around things, across flat joints, over
wingtips, along edges you don’t want to
sand, and many places you don’t want to
leave pinholes.
I like putting a 2-inch-wide strip over the
end of my shaping block and sliding the
taped end along a tip rib to blend in the
wingtip. I use 100-grit garnet sandpaper
with light pressure for fast removal to
rough-shape. I follow this with 150-grit
paper to take out the tool marks, 280 grit,
then 400 grit to polish the wood.
Using plastic film covering all over
forces me to make joints fit superclose,
which is essential to solid glue joints
anyway. It requires extra planning during
covering to leave it off where parts fit
together rather than cut away film after
covering. I get nervous cutting through film
on top of balsa, particularly over 1⁄16 balsa
planking.
The foam wing cores you buy from Tom
Dixon are geared toward his exoskeleton
planking system, and the cored-out portions
save 4 ounces of dead weight. Tom
publishes a comprehensive assembly
procedure, which you can download when
you order the cores on his Web site.
I prefer to cut the main spar on the
centerline and add splice plate caps during
final wing assembly. One convenience is
being able to block-sand the center face of
both panels to gain the best glue joint and
alignment. The caps carry the major bending
loads anyhow.
I keep the waste-foam material handy to
hold the cores during work and storage.
They prevent a lot of hangar rash and make
nice, stable support fixtures. With the 24-
inch panel cores, you don’t have to order
48-inch lumber. I purchased 24-inch
selected stock from Lone Star Models.
Have someone there select the stabilizer
and elevator in 3⁄16, 6- to 8-pound stock—
one 4 x 36 inches and one 3 x 36 inches.
The 1⁄4 stock for fins, tips, and top and
bottom planks needs to be 4 inches wide and
36 inches long in 6- to 8-pound density. I
used four pieces altogether.
I stripped the leading edge from a 1⁄4
sheet to get it dead straight in the relaxed
state. Logical sequence of adding parts
yielded a 15.3-ounce fully covered wing
with controls and an ounce of permanent tip
weight. If you noticed that my tip-weight
box cover is on top, don’t sweat it. The first
time I did it was an accident, and I got used
to it on future airplanes.
After you complete the wooden parts
assembly, do the wingtips, line guide, tipweight
box, and the bellcrank dry assembly.
Put these pieces aside until the rest of the
uncovered parts are ready to cover.
Before and after you cover the stabilizer
and elevator pieces, make sure that both
mating edges are dead straight—not just
mated to the same curvature. You will be
01sig2.QXD 10/27/03 10:40 am Page 33
34 MODEL AVIATION
Full-Size Plans Available—see page 191
01sig2.QXD 10/27/03 10:41 am Page 34
January 2004 35
rewarded with an elevator that drops freely
by its own weight. Careful location and
cutting hinge slots will save you problems
during final assembly, when the parts are all
covered and polished.
The control-horn base takes a bit of skill
but gives a clean, fuelproof assembly. (See
the plans for details.) Make sure that the
horn is located on the bottom and the
inboard side before you cut the pocket. (I
didn’t do it once.) I cut out the fin parts at
the same time as the stabilizer parts and get
into a rhythm of rounding edges, blocksanding,
and polish-sanding these parts.
I drilled a series of 1⁄2-inch-diameter
holes along the engine mounts to save dead
weight. Using a Forstner drill bit I let the
center point just break out of the hole’s
bottom, which leaves a solid glue surface. I
use 1⁄8-inch dowel pins to key the fuselage
sides and doublers during their glue process.
I use epoxy, well-squeegeed, and apply a
great deal of pressure between flat surfaces
to gain the optimum joint strength. The pins
are sanded on both sides until flush to both
surfaces.
I make a subassembly of the engine
mounts, two subfirewalls and the spacer
block, and the filler piece, assembled
squarely and flat using epoxy. This group is
used to square and align the fuselage sides
and top assembly on a nice, flat surface. If
this assembly is true, the final product
works better.
Thoroughly coat with epoxy the inside
surfaces that will be exposed to fuel. Do the
engine mounting holes and spacer plates,
then tape up the engine. Mount it and a
sacrificial spinner and carve the nose. Here
you should have the uncovered wood parts
ready for final assembly.
Final Assembly: Tape the wing halves
together, dry-assemble the fuselage to the
wing, then use the flat tabletop to fit the top
fin and the booms and stabilizer together.
Once these joints are tuned to firm slip fits,
proceed with covering the parts. The closer
these joints fit, the better the strength, and
you really can get quality without fillets to
cover the gaps.
Final assembly is straightforward,
requiring care to align parts and make solid
glue joints. Once the assembly is finished,
add all of the deadweight parts: landing-gear
assembly, control horn, pushrod half, fuel
tank and padding, and plumbing.
The covering and decorations are up to
you and your comfort level. I went beyond
my usual level of decoration, but don’t
expect this all the time. One thing Bob and I
learned is that the 20 appearance points we
could get now far outweigh the 80 points
awarded in the beginning days of Stunt to
turn the design direction away from the ugly
barndoor machines. It is also clear that the
appearance judging has saved the event
from becoming easy.
Flying: If your finished CG is within 1⁄8
inch of the design location, you might as
well proceed to flight tests. The lines’
location on the plans are for the design CG
and a 50-ounce dry weight. You can tune
your model from there as you get used to it.
I was able to hit the design CG right on
with a wood propeller, and so far the lines
rake is correct using 66-foot x .018-diameter
cables, eyelet to eyelet. This delivers a flight
radius, including 2.5 feet for my extended
arm, of 70.8 feet.
I have an ounce of tip weight in the box,
for a total of 2 ounces. I am still playing the
propeller, tank-height game while feeling
safe to ease through all of the pattern
maneuvers. I learned that 6.0-second laps are
too slow and that 5.5 seconds brings up safe
tension and controls force.
The Double Star 50 is performing
routinely with no bad habits on 10%-nitro
fuel. I still need to stabilize the power-plant
components before determining the ideal
fuel capacity. It will probably be less than 5
ounces.
Since Bob is no longer available to make my
numbers sing, will there be more BareCat
type projects? The three models presented
here represent optimal geometry under the
present pattern specifications. Someone
could probably shave off a few ounces with
carbon fiber and a Lost Foam wing structure.
Frankly, the resulting machinery would not
present better enough than the present
structure to warrant the additional effort.
I believe that any of the top-10 pilots
could compete successfully with a BareCat
650. Brave words, for sure, but I don’t
believe any of them will try it. Don’t feel
sorry for me; I had my time in the barrel and
am ready to coast a bit. Please try the
BareCat. You’ll like it!
Thanks, Bob. It was a fun run. MA
Bill Netzeband
23978 Villa Pamilla
Murrieta CA 92562
$3900
+ $450 S/H
DAKOTA
Joe Wagners, Classic
Free Flight design.
24" wingspan for
.02 or .049 engine
BMJR Model Products
Box 1210
Sharpes, FL 32959-1210
321-537-1159
www.BMJRModels.com
Materials Sources:
Foam wing cores (BareCat), Bolly landing
gear (KA-10), Double Star 50 engine:
Tom Dixon
Box 671166
Marietta GA 30062
Tel./Fax: (770) 592-3279
http://members.tripod.com/~TomDixon/tom
dixon.htm
Fuel tank, controls, wheels, propellers:
Brodak Mfg. & Distributing Co. Inc.
100 Park Ave.
Carmichaels PA 15320
(724) 966-2726
Fax: (724) 966-5760
www.brodak.com
Fuel tank, controls, wheels, propellers:
RSM Distribution
21899 Heliotrope Ln.
Wildomar CA 92595
(714) 931-6038
www.rsmdistribution.com
Selected-density balsa (see plans):
Lone Star Models
115 Industrial
Lancaster TX 75134
(972) 218-9663
(800) 687-5555 (to order)
Fax: (972) 218-9211
www.lonestar-models.com
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