About this Plan
Finch. Simple profile rubber biplane model.
Quote: "The Finch. A beginner's model biplane built especially for Meccano Magazine, by Ray Malmstrom.
BIPLANE models always arouse interest on the flying field because, like their full-size counterparts, they are something of a rarity. A properly trimmed biplane climbs well, is very steady in flight and has a good glide. The little Finch featured here has all these biplane virtues and, moreover, it is very easy to build.
To commence construction, cut the fuselage shape from 1/8 sheet balsa. Bend the undercarriage wire to shape and slip into position (front 'V' cut in fuselage). Secure with thin strips of tape, cemented firmly in position. Note the forward slope of the legs called 'rake'. Bend over the ends of the axles to retain the wheels.
Next cut out two nose pieces (A) from 1/8 sheet. Add one to side of nose and place the 20 swg (standard wire gauge) bush into the slot in the nose. Cement it in and then add the other nose piece A. Hold pieces in place with modelling pins until set.
Cut the upper (X) and lower (Y) wing mounts from ith sheet and cement accurately into their respective fuselage slots. Bend the rear rubber motor anchorage and skid and slide over rear part of fuselage (rear 'V' cut in fuselage). It is secured by a skin of cement. Add the reinforcing tape pieces to fuselage at places shown. Sandpaper round edges of nose pieces.
Cut tailplane and fin from ,nth sheet, sandpaper edges to section and cement in position, tailplane first. Bend the propeller driving shaft hook and insert into bush from the rear. Slip on two cup washers and then the 5 in. diameter K.K. plastic propeller, from your model shop, price lid. Bend the front end of the shaft over as shown to engage the propeller. The fuselage of your Finch is now complete.
Fitting the wings: Cut wings from 1/16 sheet. Mark the position of the interplane struts on the wings with a soft pencil. Lightly sandpaper the wings to sections shown on side view, using only very fine sandpaper. The method of obtaining the upward slope of the wings (dihedral angle) is shown in the 'easi-build' sketches and photographs. The jig pieces M and N are cut from 1/8 or 3/16 sheet. Use plenty of modelling pins to keep the wing panels in the correct positions while drying. Add strips of tape along the centre sections of both wings.
When wings are ready, cement them to the upper and lower wing mounts and fuselage. Please check for correct alignment of both wings to each other and to the tailplane. If your wings are twisted or warped your Finch will not fly! When the wings are dry, cement the interplane struts, cut from fth sheet and sandpapered to section, between the marks on the wings. Pin in position until set.
Power for the model: Now for the rubber motor. You can choose either a 20 in length of 3/16 wide strip rubber, which you thread through the rear anchorage wire, tie and slip on to the driving shaft hook, or a 40 in length of 1/8 wide strip, which you make into a loop and then thread through the rear anchorage, slipping the two loops on to the driving shaft hook.
The first motor is best for testing. It will take up to 450 turns and your model will fly at a good height. If you use the second motor you can only put on about 225-50 turns, but you will get a very rapid climb, a short cruise and a long glide down.
Both motors must be lubricated with rubber lubricant, 4d a tube, and with the rubber motor in position, you must balance your model. This is important and must be done before any flying is attempted. Suspend the model from the balance point marked on the plan. It should hang level. If it is nose or tail heavy add small pieces of Plasticine to nose or tail to achieve correct balance.
Choose a calm day and some long grass for flight testing. Glide test first. Face into wind and launch. If your model dives, bend up the rear edges of the tailplane slightly. if it climbs too steeply and falls backwards (stalls), add weight to the nose. Correct turns to left or right by slightly bending the rear edge of the fin on the opposite direction. Now wind up your motor by putting about a quarter of the number of turns previously mentioned. If flight is successful add 20-30 extra turns on each subsequent flight, up to the maximum."
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User commentsDouble check the dihedral angle of the upper wing mount. Plans are approximately 7-1/5 degrees. Using upper and lower dihedral jigs will give a 10 degree dihedral. The upper wing mount is a bit shallow. The lower wing mount is correct.
JD - 25/08/2020
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