Cheeky (oz15083)

About this Plan

Cheeky. Radio control sport biplane model. All-sheet construction.

Quote: "20 in span, all-sheet, 0.5cc IC powered, RC backyard flyer. Cheeky, by David Boddington.

Before you ask, yes, it probably would fly electric-powered, but I haven't tried it, so let me know how it performs with amps instead of ether. 'Cheeky' is a simple, quick build biplane, which will only take up a small area of your car; you could even pack it in a suitcase and take it on holiday (designed for free flight, or strap-on lightweight R/C (or fitting the radio for trimming, before reverting to free flight), the choice is yours. For sure it won't take a month of Sundays to build, or cost a fortune in materials, or fuel for flying.

The prototype flew with a venerable DC Dart in the nose. These engines can be picked up for a very modest cost, but any engine around the half cc mark will suffice - the RC version can cope with slightly larger motors. Incidentally, if you do obtain a second hand diesel engine which feels solid and hasn't been run for a score of years, take out the needle valve and put it, and the whole engine, in a jar of cellulose thinners (the cheap type, not the anti-chill variety) overnight. Turn it over in the morning, put it back in the thinners give it a good shake. By the following day it will be nice and free and ready to start, if not then a dose of WD40 should do the trick.

Construction: Take a bit of trouble in selecting and matching the 1/16 sheet for the wings and fuselage sides, you don't have to go for heavy, hard balsa, medium grades will suffice. Cut out all the parts before commencing construction, it's more fun and faster that way.

I edged the wing and tailplane leading edges with strips of 1/16 x 1/8 spruce, although 1/16 sq would suffice, to make them more 'ding' proof. When the wing and tailplane panels have been cut out and anti-warp strips inserted in the tailplane, the edges should be rounded. At this stage I apply lightweight filler (One Strike Lightweight Filler) to both sides, using a damp sponge. This dries rapidly and is easily sanded to a super smooth finish.

Ribs are cut from firm 3/32 and they extend far enough beyond the wing chord to allow the ends to be pinned down. Before pinning the 1/16 wing panels to the ribs, give them a coat of cellulose sanding sealer and when it is sufficiently dry, sand smooth. Pinning and gluing the panels before they are totally dried allows them to bend more readily. Leave overnight to set thoroughly.

The root ribs are sanded (or canted during building) to the dihedral angle of 7°. To join the panels, prop up one tip rib by 48mm, the other panels, prop up one tip rib by 48mm, the other panel being pinned flat; when set, the centre joint is reinforced with nylon, or bandage, doped in place. Trim the underside of the top wing centre ribs, so that the wing sits flat on the top platform. Reinforce the centre trailing edge with small pieces of 1/32 (0.8mm) ply to prevent the wing retaining bands from damaging the balsawood.

Whether you have operating elevator and rudder, or small trim tabs, will depend on the type of model you build, I used adhesive tape to hinge the surfaces and made small control horns from thin ali sheet.

Starting in the fuselage, mark the position of the doublers, longerons, uprights and fin on the inside of the starboard fuselage side, spacing the engine bearers to suit the motor to be used. Balance on the prototype model was slightly in front of the ideal location, so if you are using a heavier engine than a 'Dart' you should move it back.

When the framing has dried, place a piece of scrap 3/32 hard balsa behind the last upright and plane and sand the framework, from the rear of the wing platforms, down to 3/32 at the fin location. Sand and grain-fill the fin and glue to the fuselage side, the port side can now be glued in position, checking that the fin aligns with the fuselage centre. Sand and grain-fill the fuselage and drill holes for dowels, engine bolts etc, before adding the wing and tailplane seating platforms and undercarriage assembly.

I formed the lower wing seating platform from 0.4mm ply, cutting through the centre line for all but 1/2 at the high point of the curvature. This was glued to the fuselage with the lower wing in position and some thin polythene between, to prevent the wing being glued to the plywood. When dry, the lower gap was filled with Bondfilla, which was also used to form a fairing above the wing seating.

Form the undercarriage as shown on the drawings, remembering to slip the piece of tubing onto the crosspiece before completing the bends. Bind and epoxy the tubing to a piece of 1/16 (1.5mm) plywood and glue this to the fuselage. The top hooks of the undercarriage are retained by small dental rubber bands through a length of ali tubing glued to the fuselage..."

Direct submission to Outerzone.

Cheeky from R/C Model Flyer November 2004.

Supplementary file notes

Article pages, thanks to RFJ.

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