Guided Whistle (oz16086)

About this Plan

Guided Whistle. Control line stunt model. Wingspan 42 in.

Quote: "Uniquely different, this large stunt model has skin stress construction. Guided Whistle, by Walton Hughes.

Full size airplanes started out with wood frame constructions. This all began with the Wright Brothers. They built a wooden frame and covered it like a kite for their lifting surface. When metal such as aluminum became cheap enough to use as framework material, this early principle of a separate frame and covering didn’t work very well.

Engineers started using tubes and beams and finally struck on the idea of making the fuselage one big tube held in shape with bulkheads. This worked very successfully and became known as skin stress or monocoque construction. Rather than a frame and covering, one structure or skin serves both purposes. Later on plywood was perfected for aircraft use. Many excellent skin stress wood ships have been built, the English Mosquito bomber is a good example.

But in the model world most builders still use the old frame and cover system. Why shouldn’t we build skin stress models? The stunt ship presented here is very close to full monocoque construction. The resulting durability is well worth considering.

An intensive study of existing model wing types and application of structural design engineering theories produced a new idea for a wing. The Navy’s Wildcat fighter used a skin stress leading edge and spar assembly for most of its strength; I set out to build a similar wing of balsa wood. The result was an 8 x 40 wing made with a 1/32 sheet balsa spar and 1/32 sheeting on the leading edge. This formed an irregular tube or 'D' spar.

In the conventional wing (see plan illustration) bending or torsion causes horizontal shear between spars. Ribs cannot stand this stress, so they deflect. This deflection allows paper to tear, then wing deflects farther and cracks ribs. With the skin stress wing design, the leading edge sheets, nose block and sheet spar form a tube which is main strength of the wing. Rear half of ribs and trailing edge 'hang' on the tubular spar. Using the tubular spar leading edge reduces deflection of wood frame in torsion and bending. As structure is 'loaded,' wood and paper develop stress evenly, thus increasing strength.

Tying the landing gear and motor together confines most of the strain in the mounts and leaves only the problem of attaching the mount to the wing. Since the wing under discussion is a skin stress structure the strain Should be distributed over the entire wing skin. Plywood gussets were finally chosen to carry strains from the motor mount and landing gear to the fuselage and wing surface. (See Motor Mount Detail). The best skin stress fuselage would be a tapered' tube, but this couldn’t be built effectively of balsa wood, so the first job was hexagon shape.

A design was evolved for a hand- launched .49 engine stunt ship using j mostly 1/16 and 1/32 sheet. The completed job weighed 26 ounces with ignition and turned out to be the hottest stunt ship in the vicinity. The plane was far better than my flying ability. I kept trying but piled into the soft earth again and again. The neighborhood flyers would watch me ram it into the ground right up to the wing, then I’d pull it out, put on a new prop and fly again..."

Direct submission to Outerzone.

Update 16/6/2025: Added alternate plan, thanks to theshadow. Maybe slightly clearer and easier to read. This is a reprint from RCMW, Aug 2016. Note this plan is stamped as Archive #003791 from the Cooperative Plans Service. See their website at www.co-op-plans.com

Supplementary file notes

Alternate plan.
Article.

Corrections?

Did we get something wrong with these details about this plan (especially the datafile)? That happens sometimes. You can help us fix it.
Add a correction