Building and Flying the "Cootie"
By: John Worth
Ralph Bradley’s Cootie
PART 1- BUILDING
Ralph Bradley provided the inspiration with his design, Bob Selman provided the
“how to” information via a computer disk with great photos and magnificent
drawings by Ken Spencer, and Plantraco provided their great micro radio system,
so I dusted off my rusty modeling experience to put everything together. The
clincher to the inspiration was seeing a videotape of the Cootie flying
beautifully in a school gym.
The first step was to get the disk ( $6 from
www.BSDmicrorc.com ), put it in my computer, and print out the photos and
drawings. Note: I spent a bit of time on the printing the plans drawing, to get
the size right, to match the scale on the drawing. The first printing came out
smaller than full size, so I had to change the settings shown on the printer
screen—I think I had to go to 120 percent to make 1” equal 1”.
The first of 12 typical instruction photos from the
disk shows step # 1 for building the Cootie
As the photo instruction showed, I got a piece of 3” wide
1/32” sheet about 8 inches long, Using the preprinted and precolored right side
view of Ken Spencer’s fuselage drawing (one of the many on the disk, providing a
choice of color designs), I noted on the balsa sheet where the 1 mm piece of
carbon rod (for the front wing pylon strut) was to go, then carefully cut the
narrow slot (about 1/32” wide) for it in the balsa sheet. I then CA glued the
pylon strut in the slot, leaving 1 ½” of the rod sticking out of the top of the
fuselage (for later mounting to the wing).
Similarly, after noting its location according to the drawings and photographs I
cut another 1/32” wide slot about a half inch deep into the upper part of the
vertical fin, to hold the 1 mm carbon rod for the rear wing pylon strut. After
gluing one end of the carbon rod into the fin, the free end was left sticking
out of the fin about an inch.
Then, with the fuselage on its side, and holding a 90 degree triangle with the
vertical side against the front strut, with the 90 degree corner at the tip of
the strut and the horizontal side of the triangle angled back toward the tail, I
cut off the excess from the rear pylon strut where the horizontal side of the
triangle crossed the strut.
I next sanded the balsa sheet on both sides to assure a smooth surface for
gluing, I then coated one side of it with a glue stick (the instructions said to
use a spray adhesive, but I knew the glue stick would work fine) then applied
and smoothed down the preprinted and precolored left side view of Ken Spencer’s
fuselage drawing. Then I trimmed around the fuselage outline with a sharp razor
to get rid of the surplus balsa and drawing paper.
This view shows the fuselage drawing pasted to the balsa sheet and how the
excess was cut away.
I next glue-coated the other side of the balsa which was
previously cut to the fuselage shape, then applied the left side view fuselage
drawing to it. Then, after light sanding of the fuselage outline shape to get
rid of any fuzzy paper and balsa cuttings, I did as the instructions said and
ran a black felt tip marker pen around the outer fuselage shape to give a neat
and finished look to the profile by coloring the balsa which had been visible
between the paper sheets.
Making the landing gear was next, bending .025” music wire to the shape shown on
the plans. I poked a small hole in the fuselage where a dot showed the landing
gear location, slipped the wire through the hole, then wrapped some fine wire at
the bottom of the fuselage to squeeze the upper part of the landing gear legs
together. A small blob of CA glue on the landing gear wire at the bottom of the
fuselage secured the mounting.
How the landing gear was attached to the fuselage
Next I cut the rudder loose from the vertical fin, then
reattached it with a pair of figure eight cotton thread hinges, after first
using the black marker pen around the outline of the rudder and the cutout of
the vertical fin, to give a finished look to the assembly.
At this point I made a decision to add an elevator the Cootie. Ralph’s original
had controls for the rudder and motor speed, but since I had the Plantraco
system which provided two magnetic actuators I decided on a two control rear
end. I didn’t expect much elevator effectiveness but I thought that if it
provided a little pitch trim that would be worth the addition.
View showing the Worth elevator addition to the
I hacked out a small elevator,as per the photo, attached it
to a short piece of 1/16” dowel with a strip of transparent tape which served to
mount the elevator and provide some self-centering action. I then attached the
dowel to the very tip of the fuselage tail end with a blob of CA glue; a very
simple elevator assembly.
Afterward, when I thought about where to mount the rest of the radio system I
realized that I needed to mount the components as far forward as possible. While
having the elevator adding weight at the tail wasn’t helpful, looking at the
model overall, with the relatively large wing and a very small fuselage, the
elevator wasn’t that far back, so I quit worrying about it. Furthermore, the
very small fuselage leaves very little choice as to where to mount things so I
figured that if there was a balance problem I’d deal with it on the wing itself.
Left front view shows the receiver mounted on
the Cootie nose
I mounted the combined receiver and its Lipo cell as
far forward on the fuselage nose as possible, and I mounted the two
magnetic actuators where there was room. Note: I first had the elevator
actuator way forward on the fuselage close to the rudder actuator, but
there was interaction between the actuators, so I relocated the elevator
actuator toward the tail. I didn’t like have the weight further back but I
liked having the push rod shorter—when the actuator was way forward the
push rod tended to bow too much when moving. As to the motor and prop,
there was no choice at all—their locations were fixed by the design.
Actually, it might not have been necessary to relocate the elevator
actuator. In the process of checking out the RC system I found that if I
put a tiny magnet (1/16: dia x 1/32” thick) on the coil surface in line
with one end of the main actuator magnet, this centered the main magnet
nicely and avoided interaction with the other actuator. Cloud9rc.com has
the tiny magnets ( 2 for $1) and I used a small dab from the glue stick to
hold one magnet to each coil.
The magnet tends to stay on the surface of the coil anyway so it doesn’t
need much adhesive and I didn’t want to use CA glue for this, in case I
wanted to remove or relocate the tiny centering magnet. Note: without the
centering magnets, operating one actuator caused its main magnet to
interact and move the one on the other actuator. But with centering
magnets installed I saw no interaction between actuators.