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By permission:

Building and Flying the "Cootie"
By: John Worth
9/1/2005                 


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 Cootie tail

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.