Sssshhwept (oz7943)

About this Plan

Sssshhwept. Geoff Dallimer's 'Sssshhwept' from May 1969 RCM&E.

Quote: "A rudder, elevator and throttle control sportster designed for GG control and suitable for the latest lightweight multis. Sssshhwept, by Geoff Dallimer.

THOSE of you who know the designer may be surprised to find me building R/C - however, having spent two hours in a fruitless search downwind for a lost Wakefield model, my thoughts on the long walk back centred around the application of R/C to 'free flight' events! However, a little reflection on the problems of 'penetration', and a visit to the 'other half' of our club - largely single channel sport flyers - convinced me of the need for a single channel design that was a little different, and could give a lively performance on a limited budget.

Since I had flown GG as long back as 1958 (before 'advancing' to free flight competition flying incidentally!), the many advantages of pulse proportional were not lost upon me. That engine control is also available now from actuators of the Rand type makes this kind of control system very competitive indeed on a cost/value basis for the sport flyer.

The basic design parameters set were simple, ie single channel pulse proportional control, light airframe, adequate power, and an 'out of the rut' appearance if possible.

In the event Sssshhwept met these requirements reasonably well, weighing in at 28 oz complete with 500 DID DEAC driving home-built receiver and Rand actuator. Swept wing configuration was adopted in an endeavour to smooth out any tendency to 'gallop' by increasing longitudinal stability, whilst vortex tips can be claimed to be advantageous during fast circuits! The airframe is quite conventional perhaps traditional would be a better word - and since the construction is to be light, its strength must come from spreading impact loads evenly into the structure, and by avoiding localised highly stressed areas. Two load-bearing members bridge the wing cut-out between engine mounting and aft sections of the fuselage, and serve the double purpose of providing a mounting rail for the Rand/Rx unit a la Boddington!

Sssshhwept has withstood a high speed dive into the ground, most damage resulting from the power pack going through the i in. ply bulkhead. In this particular instance the model had got into an uncontrollable dive with the dive steepening as airspeed increased - a state not unknown with other swept wing designs including full-size aircraft as the late John Derry demonstrated in the DH108 when unexpectedly achieving the first British faster than sound flight during a near vertical dive. Like the swept wing DH108, Sssshhwept will recover if the power is throttled back - and you have enough height!

Wing: Commence construction with the wing by sandwiching the required number of blanks between root and tip ribs, then carve the resulting block to shape. Lightly sand each rib separately to trim its outline to match the wing taper. Ensure that the assembly is true before cementing the joints - warps are troublesome enough without building them in. It is particularly fatal to force fit the webbing between the mainspars, since this is almost certain to result in a twisted wing. To fit the LE sheeting I prefer to butt joint it first to the LE, and when the joint has set, pull it down on to the mainspar..."

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