Armstrong Whitworth FK3 (oz14158)

About this Plan

Armstrong Whitworth FK3. Free flight scale model WWI biplane. Wingspan 40 in. Scale is 1/12.

Quote: "Full Size Plans! For the Plane on the Cover. Armstrong Whitworth FK3. A 40 in span free flight scale model by G Elsegood.

Looking through the April 1953 issue of Model Aircraft I came across a solid scale plan of the Armstrong-Whitworth FK3. The article accompanying the drawing read: This aircraft has a lot to recommend it for a flying scale model. It has pronounced dihedral (4°), a rugged undercarriage with that prop-saving device the forward skid, and a cowling sufficiently deep to bury a diesel motor. More important than these, however, is the long moment arm and generous tail surfaces, which should all add up to a very successful model.

I decided to build a 1 in to 1 ft scale replica, and the completed plane weighed only 12-1/2 oz. This, with a wing area of over 400 sq in, has proved to be an almost 'unprangable' model, that has fully lived up to the Model Aircraft prediction.

Fuselage: Cut the sides from 1/8 sheet and cement on the longerons, spacers and engine bearers. Bind the 16 swg centre section struts to formers 2 and 4 before assembling. The forward decking is now planked with 1/16 sheet.

Fit the pendulum rudder controls, before adding the stringers to the rear decking. Assemble the undercarriage components, bind the front V struts to former 1B and cement and Araldite in position. When the undercarriage is complete, fill in the underside of the fuselage with 1/16 sheet.

Wings and Tailplane: Construction is quite straightforward, but care should be taken over the selection of wood for the ribs. Use hard wood for the bottom and soft wood for the top, the camber of top surface will be obtained more easily if the wood is first damped. Fill in the more heavily stressed ribs with sheet and bind the wing boxes and strut tubes with thread.

The original model, which is powered with an ancient Mills 75, is finished as a training aircraft, no colour dope being required. To get the correct creamy colour of clear doped fabric, mix a little yellow ochre water colour paint, with the water used for shrinking the tissue. Use heavyweight Modelspan for the fuselage and wings, lightweight for the tailplane and rudder and give two coats of clear dope.

Cover the nose with aluminium foil stuck on with Pliobond or Evostik and paint the cylinders, exhaust pipes and aircraft number black. Shirring elastic should be used for rigging.

Flying: Test glide in calm conditions over long grass if possible and adjust the glide by adding ballast to the nose or tail. Do not adjust tailplane incidence. The original required about 1/2 oz of weight in the nose. Start powered flights with reduced power and watch for any violent turns. The pendulum rudder should take care of them but, as an extra precaution, fit an acetate trim tab (turned up) to the lower starboard wing. The original required very little trimming, except for the ballast and is a most realistic, stately flyer."

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