The Flapping Sail.

On a windy day when I hear a flapping flag or something I can’t help but think of early cliff launches at Cromer.

The flapping sail was an integral part of glider design and pilots used to use this as an airspeed indicator. The more you pulled in the more the sail flapped. Imagine the sound of a cigarette card on bicycle spokes x 10 and you will get the idea. Often the sound could be heard on the beach.
At each end of the flight range there was ‘no flap‘ (you were stalled) and ‘flapping like buggery’ (you were in a dive).
Paul Whitely used to amply demonstrate both ends of this scale when he was in ‘acrobatic mode’.
We used to watch open mouthed as Paul would nose up until a full-blown stall developed and then he would fall into a steep dive. The sail would actually collapse and be nothing more then a flapping fluttering sheet. We would all be holding our breath while Paul plummeted towards the ground. Then, just in time, the wing would miraculously recover and Paul would climb up and do it all again, giving us watchers hardly enough time to catch our breath.

These gliders had no tip struts, no luff lines, no reflexed battens or sweep+washout to stabilise the dive. Instead the sail was always tight at the front and flappy at the back. As the sail flapped it killed lift at the back, the faster you went the more lift was killed, eventually stabilising a dive.

That’s right dive recovery on these early gliders was down to a flapping sail. Don’t you just love ’70s hang gliding?

Mike Lake

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