BeFore We BUILD SkyCrawler, I
would like to share a few thoughts on
coming up with this type of airplane in the
first place.
I live in Cache Valley, which is located
at 4,500 feet elevation in Northern Utah.
We are blessed, for the time being, to be
able to fly on an abandoned runway at our
local airport. That situation may change in
the future, and our club has been very
worried about that possibility.
I decided to try a so-called “park flyer” to
see what flying at a local park is all about. My
experience was basically good; however, I
wasn’t satisfied with the total flight time so I
started changing things, such as the motor and
the battery pack, which greatly increased
performance and flight time.
The basic airframe couldn’t handle the
extra weight, so I strengthened that. Then I
ended up changing the wings and the tail,
and a totally new model was born; I call it
the SkyCrawler.
This airplane can take a light breeze, and
it will climb as high as you want. I have an
altimeter watch that weighs two ounces. I
With a planform reminiscent of the French Demoiselle, the SkyCrawler is very easy to
build and deceptively rugged. It’s a great daily flier!
26 M ODEL AVIATION
n Clark Salisbury
May 2001 27
The SkyCrawler model doing what it does the best: flying slowly and precisely, with a maximum fun factor!
RC gear and batteries are mounted to the 1⁄4-inch-diameter dowel
fuselage substructure. Construction is light and strong.
strapped the watch on the model one time, and started it climbing.
My watch recorded a 400-foot altitude gain.
The main word used to describe this airplane is “fun.” I have
flown it at more than 25 locations, all within five miles of where I
live, and even Radio Control (RC) pilots who have flown Pattern
airplanes and everything else imaginable love it, because it is so
easy to fly and field setup is a thing of the past.
I even use this model when my wife sends me on errands; it fits
nicely in the back seat, and I can stop at any park and fly for six to
10 minutes in the middle of the trip.
CONSTRUCTION
All the pieces should be cut out with a scroll saw before putting
anything together. Note that all plywood pieces are actually made
from Lite Ply or poplar plywood.
Cut all of the wing ribs at the same time, after stacking sixteen 1⁄8
sheet balsa pieces together. Use a small amount of glue on the
outside edges to hold the stack together.
Build the tail surfaces by laying all the pieces over the plan,
pinning, and gluing, as with any conventional airplane. After
these structures have dried, it is good to install the nylon hinges.
Slot the balsa very carefully, since these surfaces are only 1⁄8-
inch thick.
Start the fuselage stick construction by gluing the firewall and
the plywood engine mounts in place.
Glue the 1⁄8 plywood reinforcing pieces along the entire length of
the fuselage stick. Make sure these parts are glued to the bottom of
the stick, and notch the balsa stick, as shown on the plans, where the
nylon battery ties hold the battery.
If you are going to do the parachute-drop option, this is a
good time to glue in the 1⁄8 plywood piece that will hold the
parachute servo.
Glue the tail skids to the back of the fuselage stick. Make sure
the two-degree angle of incidence is held with respect to the
fuselage stick when gluing these pieces in place.
Glue a piece of 1⁄8 balsa to the inside of both tail skids, to
help hold the vertical stabilizer in place. These pieces should
be 1⁄4 x 2 inches each.
After that entire assembly is dry, glue the wood dowel to the left
tail skid piece, as shown on the plan.
The landing gear support structure can be built by laying the 1⁄4
Photos by the author Graphic design by Carla Kunz
To make ribs, tack-glue 16 blanks of 1⁄8 sheet balsa. Lay the rib
shape on the top blank and cut the stack with a scroll saw.
Assemble ribs and 1⁄4-inch-diameter dowel leading and trailing
edges over plan. Flats on rib bottoms ensure accuracy.
The two wing panels are joined with the dihedral braces.
Clothespins are used to clamp this assembly until the glue dries.
The wingtips are fabricated from several pieces of 1⁄4 scrap
balsa. Note spanwise braces. Sand tips smooth after assembly.
dowels on the plan’s front view and cutting as necessary. The lower
ends can even be beveled to better fit the crosspiece.
This is also a good time to glue the 1⁄8 plywood wheel hubs to the
wheels you have cut out, on both sides.
Start the wing by laying the entire second sheet of plans down
with plastic or wax paper over them. Both wings can be built at the
same time. Basically glue the ribs to the wood dowels, holding the
ribs in place with pins at the front and back of the wing.
Make sure the wood dowels lay flat on the surface, or you will
introduce a warp into the wing that won’t be easy to correct later.
When the panels are complete, add the diagonal wing braces.
It’s time to build the wingtips. This is a five-part process and the
most time-consuming part of the construction, but it must be done
one piece at a time. However, both wings can be worked on
simultaneously with a two- to three-hour wait between each step.
Start with the front of the wing, and roll the wing to the rear as
each piece is added.
Glue the dihedral joiners in place at the front and the rear of the
wing. Make sure the dihedral is held. If you lay a 2 x 4-inch piece of
lumber at a point 81⁄2 inches from the center of the wing, on both
sides, the dihedral will be held perfectly.
Sand the wingtips carefully, to achieve a nice, rounded shape.
Glue the wing-mount plywood pieces in place.
Glue the wing plywood butterfly pieces in place, then glue the
oak wing mounts. Glue the landing gear-support structure to the
firewall and to the fuselage stick.
The 1⁄4 dowels coming from the axle to the fuselage stick need to
be sanded on an angle to meet the fuselage stick.
After the landing gear structure is dry, you could wrap some
thread around where the three dowels meet, on each side, and add
cyanoacrylate (CyA) glue to strengthen the joint.
Glue in place the front oak motor mounts and the oak servo-mounting
“I” piece. Also glue on the plywood radio platform.
Epoxy the 1⁄16-inch-diameter axle rod to the bottom of the lower
1⁄4-inch-diameter dowel.
Finishing: Covering with Oracover presents some unique challenges,
since I was used to using MonoKote®. Oracover does not shrink with
heat, and all the surfaces to be covered must first be coated with a heatsensitive
adhesive that can be brushed on.
I didn’t check for warpage of the wings until I had made my first
flight, which was a near disaster. When I got the model down, luckily
still intact, I looked at the wings more carefully and learned that the left
wing had considerable warp.
I would normally just twist the wing into proper shape and heat the
covering material to bring it in, but this doesn’t work with Oracover.
I took most of the covering off, put on new adhesive, then
twisted the wing. While holding the twist, I put the covering back
on with my iron.
28 MODEL AVIATION
May 2001 29
Stabilizer/elevator and fin/rudder assemblies are made from 1⁄8
sheet and strip balsa, by pinning the pieces over the plan.
The 1⁄8 Lite Ply motor mount frames are attached to the 3⁄8 square
balsa fuselage stick. Clamp until the epoxy cures.
The completed framework is light, strong, and accurate. The
author covered the original SkyCrawler with popular Oracover.
Pieces of 1⁄8 Lite Ply glued to either side of the aft end of the
fuselage stick serve as tail assembly, tail-skid mounts.
That worked fine, and my flights since then have been great.
Final Preparations: The gearbox must be modified before you
install it and the motor. Grind away the plastic where the motor
“can” sits, and enlarge the hole in the small gear to 1⁄8-inchdiameter,
to fit the 480 motor.
You will also have to use longer 2.5mm screws, and slot the
mounting holes outward where the motor bolts to the gearbox. Install
the motor and gearbox onto the oak motor mounts with small screws,
and epoxy the servos in place into the servo-mounting “I” piece.
The battery is held in place with two nylon ties, and the radio is
mounted to the plywood platform with nylon ties. The servos are
connected to the control surfaces with the thread.
Glue the 1⁄8-inch “horn” dowels into the rudder and the elevator
if you haven’t already, and glue the horizontal and vertical
stabilizers to the rear of the fuselage stick.
When attaching the threads from the servos to the control
surfaces, make sure you end up with the amount of travel
shown on the plans.
Install the 3⁄16-inch wood dowel wing struts as follows. Drill 1⁄16-
Type: rC slow flyer
Wingspan: 48 inches
Power: Graupner Speed 480 with 2.5:1 red gearbox and
eight-cell 1200 mAh battery pack
Flying weight: 22 ounces
Construction: Sheet and stick balsa, plywood
Covering/finish: oracover
inch-diameter holes into both ends of
the dowels. Insert 1⁄16-inch threaded rods
into both ends of the dowels. Put epoxy
on the threaded rods as you screw them
into the dowels.
Adjust the nylon clevises to meet the
wing, and slide a small piece of silicone
fuel line over the clevises so they don’t
come off in flight.
The wing is held in place with four 8-32
nylon screws, as shown on the plan. Drill
and tap the oak wing mounts on the
fuselage to 8-32, and drill holes in the
plywood pieces at the center of the wing so
the nylon screws can be installed.
Flying: This is the best part of the
project. I have been amazed at how much
fun this airplane is to fly. It is not
aerobatic, and it can’t be flown in
anything but a light breeze—no more
than three to four mph—but that doesn’t
mean it can’t be a heck of a lot of fun.
Because of SkyCrawler’s slow flying
speed (five to 10 mph), it can be handlaunched
at just a walk. Make sure it is a
straight-and-level launch if you are
launching with your right hand, but holding
your radio with your left hand.
It takes two to three seconds to
transfer the radio from your left hand to
your right hand after the launch, so
make absolutely sure the trim
adjustments on your radio are correct so
the airplane will fly level.
I made this mistake once, and the
consequence was that I had to build a
new airplane.
You should be able to fly the
SkyCrawler in any park as large as a
regulation baseball diamond, even if there
are big floodlights around the field.
Enjoy, and don’t be surprised when
people stop to watch.
Parachute-drop Option: For the fun of it, I
decided to try dropping a parachute from
the model, since it could easily carry my
two-ounce altimeter watch to 400 feet.
I installed a third servo that pulls a pin
into a hole, thereby releasing a rubber band
that holds a parachute.
I made the parachute by cutting a 28-
inch-diameter circle in a plastic grocery bag
and attaching a 2/3-ounce weight using six
strings. The parachute is held under the
battery with the rubber band.
I installed the parachute-drop servo with
a “Y” harness and mounted it so that it is
common with the elevator servo. This way,
a three-channel radio can still be used.
When I push the elevator stick all the way
forward (down control), it also pulls the pin
into the hole, with the parachute servo.
It only takes a half-second to do this and
the airplane hardly even noses down, but the
parachute is dropped. It is a lot of fun—
especially if your kids are with you; they will
have a blast going after the parachute. MA
Clark Salisbury
671 E. 2160 N.
North Logan UT 84341
30 MODEL AVIATION
