Flap Modification for Hand held Wings

[Matteo V]

Windsurfing sails used to have a line embedded in the trailing edge which could be tensioned (not sure if they still have them). Something similar could perhaps be done for wings? Also those wings that use a boom could have an "outhaul" tensioner to adjust the camber of the wing, similar to what we used to install on windsurfing race booms.

But do you agree that "flaps" are horribly inefficient for a soft sail? I mean a sailboat doesn't have any use for flaps. - you can change area by reefing the sail, and adjust downhaul or outhaul to change the camber.

I like the ingenuity and determination of the OP, but I think thier approach is to tackle a problem from the wrong end. I'd focus on adjusting camber and/or area of the wing.

[Schietwedder]

Yes exactly! Camber.
Same goes for sailboats as for windsurfers which I would say are more familiar to a Wing (Surfer) than a kite besides the tube kite construction. If you look at sail racing development which is around for 200 Years or more, way before people knew how to fly almost everything has being tried and tested.

Sailmakers spend most of the time finding the best position and amount of the max. depth or camber of a profile and do everything they possibly can on the cunningham outhaul mast and Rigg trim in order to have the camber at the optimal percentage and depth. Draft aft profiles are 99% relying on the principle of laminar flow in order to work well and that is not the case on any wingsurfer I'm afraid.
They attach little tell tales at the Trailing edge of every sail just to make sure the flow is attached which is the most important trim indicator.

The lift of a surface is created 80% ish on the front half of the wing/sail surface, the first 30% of chord are the most important for generating lift.
The back halve of the profile is just there to reunite upper and lower surface flow streams as smooth as possible.
Not saying a flap when used rightly is not increasing lift as you also change the camber, but doing so with a soft sail in a clean manner is way more complicated than changing the camber with the outhaul, otherwise sailing boats would have them.

Other story with rigid wings if you look at the flaps on hydrofoils of recent America's cup boats because you can't deform a wing in cross sectional shape without a flap. It's Airplanes engineers wet dreams to have a flexible or morphable adjustable profile which is then also stiff in span direction.

Whenever you say the word flap to make sure the flow stays attached, you should also say slot like on solid wingsails of racing catamarans/Airplane flaps (re energising the boundary layer in the back part where otherwise flow seperation is happening.

Great literature for the Kite and Windsurf can be found in following books:

"The Art and Science of Sails, revised edition", Tom Whidden, Michael Levitt (Written by many smart people of North Sails)
For flexible sails

And "Fundamentals of sailplane design"by Fred Thomas
if you're more into the aeronautical stuff


I think there will be some development in this area for sure in Wingding design, but more in the sense of trim possibilities seen on a modern windsurfer like outhaul, cunningham and maybe some camber inducing stuff.

[Matteo V]

Other story with rigid wings if you look at the flaps on hydrofoils of recent America's cup boats because you can't deform a wing in cross sectional shape without a flap. It's Airplanes engineers wet dreams to have a flexible or morphable adjustable profile which is then also stiff in span direction.

Thanks for letting me know my idea is not crazy. But it's pretty easy to come to that conclusion when you realize the first step of wing design (selecting an initial foil section) must be completely undone if that shape winds up being unsuitable. Being able to vary the foil section would eliminate the need for trailing edge or leading edge flaps. And these flaps are definetly an inefficient (but necessary) workaround for most rigid wings.