Seagull Aircraft Seagull
Pacific Kites Seagull

In 1972, Mike Riggs, president of Seagull Aircraft Inc of Santa Monica in California, commenced a 14 month study which resulted in the semi-cylindrical Seagull III. Riggs, a graduate of the Northrop Institute of Aeronautics, saw the merits and demerits of both conical and cylindrical and set out to develop a Rogallo wing which, if possible, would combine the virtues of both and none of the vices. The patented “Cam-ber Control” system which he devel-oped more than fulfilled his aims. The leading edge spars have a verti-cal curve running out from the nose for about one-third of their length which in flight impart a cylindrical form to the inboard wing sections. The outboard two-thirds of the lead-ing edges are straight, although not in the same plane as the keel, and thus the outboard wing sections adopt a conical form in flight. This configuration allows for a higher aspect ratio than is possible with the conical type. It has a 25 per cent improvement in L/D ratio, allowing it to fly much more slowly than a conical but retaining the ability to fly as fast at similar wing loadings. This makes it not only much easier to learn to fly on but also greatly extends the scope of the skilled soar-ing pilot. The angle of incidence, which caries along the length of the leading edge, is greater through the curved nose section than out at the wing tips. Thus in a nose up attitude the nose will reach a stall mode but lift is still being generated further outboard and aft towards its wing tips. Thus the centre of pressure moves aft inducing stall recovery. Under these conditions stall recovery can be made immediately without any height loss simply by pulling back on the control bar i.e. pulling the pilot’s weight for-ward. Under similar conditions, the conical will drop its nose sharply and loose about 80 ft of altitude before recover-ing, and is susceptible to dropping one wing and spinning at such a time. The semi-cylindrical in a dive mode also provides full recoverability. When a point is reached where there is zero angle of attack through the out-board sections of the leading edges there is still a sufficient angle of attack through the inboard curved sections to generate lift thus moving the centre of pressure forward allowing the nose to rise. Even in a vertical dive the curved leading edges and the multi-plane nat-ure of the airframe ensure that the wing sail does not collapse and thus it remains controllable.

Captain Chuck Stahl, a United Airlines 707 pilot, who test flies commercially produced hang gliders in the United States, was unable to make the Seagull III fall out of the sky. In his test report he credited it with full recoverability from the following: high speed stall, low speed stall, verti-cal dive, chandelle and tail slide, and like all Rogallo wings it can be used as a parachute when the pilot runs out of room or wants to descend vertically.

The semi-cylindrical Seagull III rep-resents the state of the art in Rogallo wing flying. Whereas conicals, with their narrow airspeed range and consequently critical wing loadings, need to be sized according to pilot weight, the Seagull Ill allows for as wide a range of pilot weights as is likely to be encountered. The difficulty in DIY for Seagull III was the shaping of the leading edge tube; such was a doorway for buying full ship or parts from Seagull Aircraft.

A Seagull III has been recorded as having gained 2,000 ft of altitude from a foot launch in California’s Santa Ana Valley using the combined effects of thermal and ridge lift. It has the ability to remain aloft on ridge lift all day long and can safely be put through a great variety of manoeuvres, although no hang glider yet could be described as fully aerobatic.