The fourth generation hang gliders may not have exhibited a great step forward in performance, though it cannot be denied that some progress was made. It was in the area of handling and safety that the benefit came. These gliders were strong, stable and well behaved with only questions about pitch stability left unanswered. It was widely acknowledged that the Hiway Super Scorpion possessed the best handling to date. This machine included in its design innovations that distinguished the third generation glider. The keel was contained, in its rear portion, in a deep keel pocket, an arrangement which returned some of the yaw stability that had been lost when near zero billow was introduced. Another feature of this particular machine, which was almost universally adopted by designers of gliders with radial tips, was the washout retaining tip rods. These allowed the wing tips to assume whatever angle that was dictated by the air flow at lower speeds but came into play as minimum washout stops when the glider was dived and therefore played a part in dive limitation and recovery.
Sail design at this time had became quite a complex and sophisticated subject as no longer were they made as a flat sheet which assumed a curved shape due to flight loads and built in billow angles. Now the required airfoil or camber was sewn into the sail by the sail maker, this naturally had a profound effect on the performance and handling of the machine but also dictated that the airframe should retain its geometry with some exactness. Up to this point most second generation gliders had incorporated deflexers in order to cope with the problem of flight loads deforming the airframe but progress demanded that such drag inducing structures should be dispensed with. Many designs lengthened the cross boom in order to supply extra support to the leading edge tubes and also increased their diameter, therefore stiffening them.
Ken Messenger with his design, the Cherokee, resisted the complete removal of the deflexer and fitted a single wire and post as he had concern about the effects that differing pilots weights would have on the washout of the sail. A heavy pilot, it was pointed out would induce more washout due to greater flex of the wing booms and therefore lose performance whilst a light pilot would perhaps not have sufficient to be safe. He further suggested that the small amount of drag induced by a single deflexer was probably less than that produced by an increased length of cross boom - which would also have to be of a larger diameter to retain column strength. Despite this reservation the age of the deflexer had faded and as the hey day of the third generation glider arrived at the end of the seventies any pilot flying a deflexer type hang glider was dismissed a novice. Battens were still of the flexible type and it was believed in some quarters that the preformed rigid battens, when applied to a flex wing design, could proved dangerous. Birdman however, had begun to experiment with battens which had a preformed section at the leading edge and a flexible part from there back to the trailing edge.
. a system that was to be utilised on many subsequent designs. As noted, at the end of the decade of the seventies some excellent gliders were appearing and it seemed that they would dominate the scene for some years to come.
General Specification of fourth generation gliders
Aspect ratio 5.0-7.0.
Nose angle 120 degrees or higher.
Sail planform Flying wing. Often with very slight tail to fair keel pocket shape.
Tips almost exclusively radial.
Sail shaping Always cut and sewn into the sail by means of external and internal camber.
Keel and leading edges Stronger than previous generation and no wire bracing to control flex. Adoption of keel pocket across all models.
Cross tubes Two piece, exposed but sometimes moved into slower moving air above the leading edge juncture.
Sail slackness None.
Top rigging Kingpost always.
Battens Full length chordwise battens across entire wing, Many models utilising preformed.
Pitch stability Mainly planform stability reinforced by tip struts to limit blow down.
Duration of type 1978 to 1980.
Examples Hiway Super Scorpion, Birdman Cherokee, Chargus Vortex and Flexiform Skyline.