Longbow by Bill Brooks

The inventor was Bill Brooks, who is now chief technical officer for the BMAA. At the time, 1992, he was working for Solar Wings. Basically (like me) he was looking for something with the portability and convenience of a paraglider and the performance of a hang glider. Also, like me, he wondered if a curved, preloaded bow for the LE would eliminate the necessity for a cross tube, kingpost and upper rigging, and allow the LE to be removed and broken down for easy transport. Interestingly, like me, he also got the idea from looking at windsurfers,but unlike me took it a lot further than the model stage and beat me to it.

The LE bow had a radius of 14.8 meters and used 2 5/8' diameter 17swg HT30TF tube with 2 1/2' inner sleeve progressively tapering to 60mm 7075-t6 tube with 1mm wall thickness at the tips. The LE broke down to 5 sections of 2.4m and rolled inside the sail with the batons remaining inside, and fit inside a small car for transport. With a tube this large (to control washout) it was able to tolerate negative loads without support (maybe the first true topless?).

The LE tube was posted (slid) into the wing sleeve and loaded (bent) with a winch that was built into the sail to provide the 180KG of preload required - taking about ten turns to fill the sail. It was then held securely in place with a winch pin. The lower lines were then attached to the leading edge boom and you're ready to go.

The tension in the wing was such that there was little tip washout in flight so weight shift-only roll control was poor, and reflex was required in the wing batons. D handles were added to the A frame with lines that lifted the tip trailing edge to provide good roll control and ground handling so you could fly it on the ground. With the reflex the wing mushed rather than stalled.

The wing was pitch tested to 400kg positive 150kg negative and proved stable up to 50 mph with no "hole' in the pitch curve at low incidences that you find with flex wings due to luff lines. Internal struts held the trailing edge up at low incidences (the first sprogs?)

The glide was estimated at 9:1 at the time of writing the wing had only been tested in straight line glides off bunny hills. There had been no soaring flights as the author was concerned with spiral dive tendency shown in models (low sweep back and washout?).

The designer felt the weight and convenience could be further enhanced with a composite LE tube and kevlar lines. He also felt the reflex could be reduced and glide improve with a short V tail. Solar wings liked the idea but declined to take it any further as it was felt the flying public would consider the concept too radical. This is the last I've heard of it.

 

Specifications

Area ?? m2
Weight ?? kg.
Span
14.8 m (length of the bow)

Folded length 2.4 m

Pictures of the Longbow

If you have any, please send me a copy!