Scytale (oz16120)

About this Plan

Scytale. Free flight sport model. Wingspan 78 in, for 5 cc engine.

Quote: "BEING ONE or the scale fraternity, and with an eye to radio control, Mr Chivrall cast round for a suitable design to provide a model capable of carrying a reed unit for experiments.

The best scale designs having been well 'flogged' he decided on impulse to design a 'scale' model of his own design. This impulse grew as the model progressed, to an urge to make as neat a model as possible, and one which would be worth repairing. Ample room was allowed in the cabin for radio gear, and a 5 cc engine was reckoned to give enough power. Windows being what they are, provision was made for replacing them individually, and the undercarriage made detachable for adjustments on the prototype.

This is no model for the beginner: but one that the experienced sport Hier can really get his teeth into. As a foretaste of the methods of construction, brief building notes follow.

Building: Cement three sheets of 3/32 balsa together edgewise and cut diagonally across corners of middle sheet to form two panels. Add extra sheet to ends to make up length at the tail, and shape to fuselage outline. Splice 1/4 in sq longerons and cement to panels, adding spacers and diagonals for positioning cabin frames, and include ply strut anchorage strengthener, and filling piece at undercarriage position.

Build up cabin frames, trimming longeron gaps to suit slant of front and rear frames. Face root ribs and fin spar with Ile in. ply, and cut out engine mounting assembly and all other plywood bulkheads. The making up of undercarriage and tailwheel assemblies should now he done. The tailwheel assembly must be firmly fixed to the fin spar, but the undercarriage legs can be removed from their bulkhead until the fuselage is completed, when the hinge pin can be inserted through the side and the tensioning hands looped around the dowels.

Join fuselage sides, beginning with the rudder post and fin spar, working forttard inserting cabin frames and undercarriage bulkhead, finishing at the front bulkhead. Fill in the various cross braces and mount the root ribs to the cabin roof, over the tongues left standing out. Slide the engine mount into place and cement dowel tongues behind bulkhead to secure, and then build up front over balsa formers and stringers, sheeting the top from the noseblock back to the instrument panel. Fill in the sides between spacers with 1/4 sheet forward of the undercarriage to strengthen, also the underside. Fill in the sides behind noseblock strongly, as weight does not hurt here.

All other balsa formers are now positioned, the cabin construction completed except for the windscreen framing, and the planking job undertaken. The rear window, side window flaps, and engine hatches can be fitted and the whole papered down smooth.

The tailplane centre section is made and slipped over fin spar, and cemented securely in place, after which the fin is erected and sheeted over, fairing into the fuselage. The tail block completes the job, the rudder being fitted after colouring. Cover the woodwork with lightweight tissue doped on, doped again, and rubbed down prior to colouring.

After the paint job, the window can be cut to shape and fixed in with strips of 3/16 sq balsa. The windscreen shape is found with a card template first, cutting acetate from this and bending to shape. Then the framing is fixed around it and painted.

Mainplanes are built up on a preformed leading edge, adding ribs in slots and fitting trailing edges and wing spars. Wing hooks are fixed in and strut anchorage cemented firmly against spars. After building on the tips, the sheeting is added and the whole covered with silk. Flaps cover the hook apertures after wings are secured. Ohechi would be advisable for the struts.

Tailplanes are built as for wings, and dowels join both halves together through the centre section.

Flying: Get balance on the indicated CG correct. Test in a breeze to save a running launch for glide, and if this is not smooth don't attempt power until it is right, but adjust with weight. The model should turn gently to the left in wide circles. It is not advisable to decrease sidethrust for a turn."

Direct submission to Outerzone.

Supplementary file notes

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