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 “Camber Control” system which he developed more than fulfilled his aims. The leading edge spars have a vertical 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 leading 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 soaring 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 forward. Under similar conditions, the conical will drop its nose sharply and loose about 80 ft of altitude before recovering, 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 outboard 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 nature 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, vertical 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 represents 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.
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.
The Seagull IIIZ has adjustable trim to adjust the control bar pressure in varying positions. It is fitted with split crossbars and padded control bar. The airframe is made from 6061-T6 1.75in x .058 anodised aluminium tubing. Rigging cable is 7 x 19 stainless seel with white vinyl coating, and all hardware is aircraft quality stainless steel.
The sail is made from 3.8oz stabilised dacron and was available in 12 colour combinations. The options for pilot support were seated, supine or prone harness.
The Seagull 4 was almost identical to the Seagull 3. The most conspicuous difference was a cambered, S-shaped keel instead of a straight tube. It also had a two-piece swept-back cross-brace rather than a single tube. 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.
The Seagull IV is a high performance glider designed for Hang Three pilots and for open competition. It is a direct descendant of the Seagull III, using the same truncated conical shape, but with much higher performance characteristics. The Seagull IV has the same nose angle and curved leading edges, but a much shorted, curved keel. The sail is very flat and its trailing edge is roached outward, instead of the normal hollow cut. This was the first glider designed with a shaped, cambered keel and a roached, battened sail.
The Seagull IV has adjustable trim allowing pilots to adjust the control bar pressure for ideal comfort in varying conditions. Split cross bars for convienence, and padded control bar. The airframe is made from 6061-T6 1.75in x .058 anodised aluminium tubuing. Rigging cable is 7 x 19 stainless steel with white vinyl coating. All hardware is aircraft quality stainless steel.
The Seagull IV sail is made from 3.8oz stabilised dacron, in a choice of 12 colours. The Seagull IV was supplied with options of seated, supine or prone harness.
The Seagull VII has adjustable trim allowing pilots to adjust the control bar pressure for ideal comfort in varying conditions. Split cross bars for convienence, and padded control bar. The airframe is made from 6061-T6 1.75in x .058 anodised aluminium tubuing. Rigging cable is 7 x 19 stainless steel with white vinyl coating. All hardware is aircraft quality stainless steel.
The Seagull VII sail is sewn with no billow, the stability being derived from the curved tubing and diffused wingtips. The low sail billow cuts resists prolonged sail inversions in thermal turbulence. The anhedral tips combined with the radial, tapered, foam sandwich battens provide for the lowest tip vortex possible. The Hang Four rated Seagull VII exhibits a smooth, positive pitching moment at any angle of attack.
The cambered keel was not on the Seagull III but on the Seahawk and the Seagull V (Verticle Stabilizer) model.
The Seagull VII has adjustable trim alloing pilots to adjust the control bar pressure for ideal comfort in varying conditions. Split cross bars for convienence, and padded control bar. The airframe is made from 6061-T6 1.75in x .058 anodised aluminium tubuing. Rigging cable is 7 x 19 stainless steel with white vinyl coating. All hardware is aircraft quality stainless steel.
I knew Jack. I was one of the factory pilots from Telluride in those days. Part of the TAF (Telluride Air Force). It was tragic when Jack became a paraplegic from a mishap trying to land on the shore. He was one of the best.
Don Dusatko
Seagull 3
Wing area: 240 sq. ft
Single surface
Nose angle: 90 deg
Glide ratio: 23 – 24:1
Seagull IIIZ
Leading edge: 17 ft
Keel length: 15 ft
Wing span: 26.6 ft
Wing area: 178 sq,ft
Aspect ratio: 3.98
Nose angle: 102˚
Sail billow: 2.5˚
Weight: 36 lb
Pilot weight: 80-145 lb
Takeoff speed: 12 mph
Stall speed: 14 mph
Max speed: 35 mph
Best glide ratio (L/D): 5.5-1
Best L/D speed: 20 mph
Min sink: 320 fpm
Seagull IIIZ
Leading edge: 19 ft
Keel length: 17 ft
Wing span: 29.5 ft
Wing area: 223 sq,ft
Aspect ratio: 3.89
Nose angle: 102˚
Sail billow: 2.5˚
Weight: 40 lb
Pilot weight: 135-200 lb
Takeoff speed: 12 mph
Stall speed: 14 mph
Max speed: 35 mph
Best glide ratio (L/D): 5.5-1
Best L/D speed: 20 mph
Min sink: 320 fpm
Seagull IV 19×17
Leading edge: 19 ft
Keel length: 17 ft
Wing span: 29.5 ft
Wing area: 174 sq,ft
Aspect ratio: 5.0
Nose angle: 102˚
Sail billow: 2˚
Weight: 42 lb
Pilot weight: 130-175 lb
Takeoff speed: 14 mph
Stall speed: 17 mph
Max speed: 45 mph
Best glide ratio (L/D): 6.5-1
Best L/D speed: 22 mph
Min sink: 270 fpm
Seagull VII
Leading edge: 19 ft
Keel length: 11 ft
Wing span: 31.4 ft
Wing area: 161.1 sq,ft
Aspect ratio: 6.13
Nose angle: 110˚
Sail billow: 0˚
Weight: 46 lb
Pilot weight: 130-165 lb
Takeoff speed: 12 mph
Stall speed: 16 mph
Max speed: 50 mph
Best glide ratio (L/D): 8.5-1
Best L/D speed: 24 mph
Min sink: 237 fpm
Seagull VII
Leading edge: 20 ft
Keel length: 12 ft
Wing span: 33 ft
Wing area: 184.9 sq,ft
Aspect ratio: 5.89
Nose angle: 110˚
Sail billow: 0˚
Weight: 48 lb
Pilot weight: 155-220 lb
Takeoff speed: 12 mph
Stall speed: 16 mph
Max speed: 50 mph
Best glide ratio (L/D): 8.5-1
Best L/D speed: 24 mph
Min sink: 234 fpm
All Aero 