Sopwith Camel - Free flight scale power model of the British WWI fighter. For .03 - .049 cu engines.
Quote: "Your FREE plan! A 28 inch span free-flight scale model using 0.5 to 0.8 cc engines. Sopwith Camel, by DM Collins.
THE CAMEL, in the eyes of the author, was quite the most fascinating aircraft flown in the First World War and by all accounts also the most effective in terms of enemy aircraft shot down. However it has some very obvious shortcomings, as a flying scale subject which should be borne in mind by the builder. The full size aircraft was tail heavy and the model will be also unless care is taken to keep the fuselage aft of the cockpit, and the tail assembly, as light as possible. Use the lightest balsa available and limit the number of coats of dcipe applied at the tail end. Some relief from the CG problem can be obtained by making a really robust cowling of glass fibre with about, 3/32 in wall thickness, or at least by covering a balsa cowling with a layer of glass fibre.
The other problem is the small tail moment available with the scale tail area. One solution is to have a pendulum operated elevator. Pendulum controls are often justifiably criticised on the grounds that acceleration of the whole model will make the control operate, but remember that the only significant change in forward speed occurs at the launch and in that case the slipstream quickly damps out any such oscillations. Some folk limit the movement of the control surface, but the designer prefers to limit the weight on the pendulum relative to the control surface area, and rely on aerodynamic damping. Do not increase the weight 'for good measure'.
The outline is to scale although the wing section is thickened to improve warp resistance and give more docile flight characteristics. Rigging wires are not needed for flight which speeds up assembly time after hard landings, especially with cold fingers in the winter! Of course they may be added by the meticulous using shirring elastic thread, but on small models this often looks overscale.
Engine installation is a bit of a problem due to the shallowness of the cowling. This does seem to rule out those trusty Mills .75s but the original flew well on a DC Dart .5 cc, and the DC Merlin would also be suitable. Small glow motors are out unless they can swing a 7 x 4 in prop at a reasonable speed. Incidentally the torque of a Dart on a 7 x 4 can be improved by making a con-rod .02 to .05 in longer between the centres of the big and little ends. This reduces the exhaust and transfer periods of the otherwise high speed timing. Fortunately Darts will start and run without any adjustment of the controls once they have been warmed up, so for this reason no external access to needle valve or compression screw is provided. If you must twiddle, you will have to make an extension handle for the compression screw, the gap between the prop and the top wing is too small unless you have unusually high aspect ratio fingers! Alternatively the motor can be inverted, with appropriate adjustment to the thrustline, and the compression screw extended backwards by soldering on a wire to come out of the cowling bottom vent area.
Construction is quick and simple for a scale model but the following points will help guide you on your way. Start the fuselage by cementing a piece of 1/16 in sheet on top of the engine bearers to give the correct spacing, then bind and cement on the pendulum assembly. The cabane and undercarriage wires are bound and cemented to their formers..."
Quote: "Only a small model, but a great flyer with only a little power needed to stay aloft. Glow plug engines are not really suitable for this type of model due to their high revving characteristics - a diesel will turn a larger prop at moderate speeds... "
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Update 30/07/2016: article pages, text & pics added, thanks to RFJ.
Update 06/09/2018: Replaced this plan with a clearer copy, thanks to DBHL, theshadow.
Scan from DBHL, cleanup by theshadow.
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Article pages, text & pics.
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