Swallow P-30 (oz4212)

About this Plan

Swallow P-30. Rubber tailless pusher sport model.

Quote: "Swallow P-30, by Barnaby Wainfan. A Tailless P-30 Rubber Model.

An improved version of the model that won the Open P-30 event at the 1984 bats, the Swallow is an unusual but effective tailless model. A unique detherrnalizer setup helps get it down.

The Swallow is a tailless P-30 class rubber-powered model which is the latest in a long series of tailless models built and flown by the author. It is a direct evolution of the Cyrano II flying plank which won Open P-30 at the 1984 Reno Nats. The Swallow is a distinct improvement over the Cyrano II in both appearance and performance. It incorporates improvements in planform and airfoil evolved in the past two wars, building on the experience gained with the Cyrano. The unusual planform makes it slightly more complicated to build than the constant chord Cyrano, but, due to the lack of tail surfaces, a Swallow will still take less time to build than a conventional P-30 model.

DESIGN The eye-catching planform of the Swallow's wing was not designed for the sake of appearance only. Its shape was inspired by a Society of Automotive Engineers (SAE) technical paper (SAE Paper #851770) by CP van Dam entitled 'wept-Wing Tip Shapes for Low-Speed Airplanes.' This paper presented theoretical results suggesting that a wing with a highly swept and tapered tip would have an unusually high span efficiency and hence low induced drag.

Low induced drag is important for a free flight model since the majority of its drag is induced drag. The normal method of reducing the induced drag of a model is to increase its wingspan and aspect ratio. In a class like P-30 where the span is limited by the rules this is not possible and the only way to reduce induced drag is to increase span efficiency. Winglets are one way to do this, but they add non-lifting area to the wing and increase its parasite drag while decreasing its induced drag. The winglets only pay off if the increase in parasite drag is smaller than the reduction in induced drag they provide. The wing shape suggested by van Dam promised to have the low induced drag of a wingletted wing without the para-site drag penalty.

The optimum leading sweep angle at the tips was found by Mr van Dam to be 60 degrees, and this is the value used on the wing of the Swallow. The inboard panel of the wing was lightly tapered but left with very little sweep so that the model would retain the easy trimming and good stall characteristics of the pure plank unwept flying wing. This effort was successful. If anything, the Swallow has better stability and stall characteristics than the earlier Cyrano.

In addition to the new planform, the Swallow uses a new airfoil which has more nose camber and a slightly greater maximum camber than the Cyrano airfoil..."

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