Sopwith Triplane (oz3028)

About this Plan

Sopwith Triplane. Scale WWI fighter for CO2 power.

Quote: "TAKING UP AEROMODELLING again after a long absence, I was horrified to discover how scarce flying fields were and how small the available few were.

Having built a modified version of Ken McDonough's all sheet Triplane for 020 power it seemed a natural for shrinkage to the smaller and much more flexible CO2 motors. Trimmed down to low revs on a calm evening it is a delight to watch a small scale model performing at near scale speed This model is as near scale con-strricticn as is possible though the riblets are not essential.

Wings: The wings are made in the conventional manner but there are possible problems with wing rib construction. The small size of the requires some very nifty work with a scalpel round a metal template.

Make a template of the wing rib from brass or aluminium sheet. Select 1/32 soft for the riblets and medium hard sheet balsa for the complete ribs. If you wish, sand the 1/32 sheet down a little but use sharp sandpaper as the idea is to remove balsa and not compress it. Cut out extra rib blanks to allow for wastages.

When all the rib blanks are cut, pin down a strip of x 1/8 in. and join a shorter'/. x in. strip at right angles. Glue in hatches of ribs pushing them firmly up to both pieces of/, x 1/8 in. Put a weight on top of the ribs to stop the pressure pushing the ribs up. Glue more 1/4 x 1/8 in. strip at other end and side to frame all the rib blanks together. Sand the complete assembly to produce a smooth profile top and bottom. When making up the rib pack, be sure to mix the differing hard-nesses of balsa as all soft at one end can cause a taper.

If you have a saw bench cut the spar slots with the ribs still clamped together. You can of course use a hand saw for this job, but be careful not to cut too deep. Push two lengths of wing spar into the rib block and sand the leading and trailing edges square Separate the ribs and use as normal. The trailing edge is laminated from three sheets of 1/64 veneer and is sliced and then mounted so that the glue lines are vertical to the plan. This gives a very stiff TE and avoids that ugly trailing ege warping. If you wish to use larger section balsa for the TE, adjust the wing rib template accordingly.

Fuselage: Fuselage construction is normal box and former method and should present no problems. It helps to pin down the centre section struts unsanded and complete fuselage side in the normal manner. When making the second side over the top of the first, place a spacer in between the cabane struts so as to get the two struts flush with the outside of the fuselage halves.

The lower wing position pieces are laminated round three wing ribs pinned to a board. Sand the centre section struts before you assemble fuselage sides; also fill grain.

Covering sheet can be grain filled and sanded before gluing to model.

Tailskid is formed by laminating thin strips of veneer round a curve and sanding to shape - be warned! Balsa skids break and are awkward to replace. The extra weight of veneer is worth it.

Rear deck stringers and side panel stringers are made from soft balsa offered up to the fuselage and then cut and trimmed to shape before glueing on.

Fin and Tailplane: These should present no problems but be sure that the fin laminations are wet or steamed before bending round former. Use light balsa and keep weight as low as possible.

Undercarriage: Epoxy 18 swg aluminium tube to rear of front bulkhead and front of front lower wing spar before covering. Bend undercarriage wire to shape and bind and solder axle. Remove undercarriage and fit joining strips; I use slotted 1/16 soft sheet epoxied into place and then filled and sanded, trim joining strips to length, then epoxy under-carriage into tubes. While undercarriage is off the model, cover the bottom of fuselage and lower wing centre section.

Wheels Cut a 1/8 soft balsa disc slightly over-size. Epoxy a length of 18 swg brass tube into the centre hole ensuring that the disc spins true. Leave some of the tube protruding at each end. Epoxy triangles of obeche veneer or thin balsa to make the spokes. When dry clamp end of tube in drill chuck or lathe and sand disc true and spokes smooth. Cover wheel with Jap
tissue and dope well. The tyre is made from rubber tube joined with cyano adhesive and lightly epoxied to the wheel disc. A better fit is obtained by sanding a groove into the wheel disc.

Cowling This is made from papier mache. Find or make a suitable former, cut strips of news-paper with the forward edges slit closely. Using heavy duty wallpaper paste, wrap the former with paper, brushing the slit edges over the front curvature. Do not try to do the whole cowling in one go. Offer it up, sand off high spots and apply more paper as required. Do not sand until thoroughly dry. Finally dope and sand until smooth, when the finishing colour can be applied.

Cover the entire model in Jap tissue using green for the upper surtaces and white for the lower, water or steam shrink. Apply one coat of thin dope 50/50 or two coats of very thin dope. Spray or hand paint to correct colour scheme. The model should weigh in at less than two ounces.

Test fly over long grass. Don't worry about a flat glide as the model has a glide like a brick, but trim out any stalling or turning tendency. Set the CO2 motor to its lowest power setting and adjust down and sidethrust to give a suitable flight pattern. With the twelve of these models that I have built so far, I have used all sorts of flight patterns and it is very forgiving. There is one thing to beware of If the model descends in a diving spiral, use the rigging wires to increase the dihedral slightly, or reduce the fin area. "

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