Foils Lift to Drag and NEW Options

[Beasho]

The reduction in Drag from foiling is significant.

Does anyone have the calculations.  I suspect a lift/drag ratio of 10:1 but maybe more.

Either way the reduction in drag is changing how we can surf and possibly how we enjoy flat-water as well.

The Wind Weapon is back:

[Beasho]

This source suggests a T foil (similar to our GoFoil / other wing designs) may provide a Lift/Drag ratio of 20:1.

The ladder foil would be interesting allowing for low speed flight and high speed control since the L/D ratio drops as speed increases.

http://www.tspeer.com/Hydrofoils/generic.pdf

[TallDude]

A ladder foil makes a lot of sense. Wonder if 2 would be to abrupt? Maybe 3?

[supuk]

i would think your first guess of 10:1 would be closer but I would not be surprised if it was less maybe between 4 and maybe 6 :1.  When you consider ridged wing gliders have a ratio of between 20-30:1 and paragliders are 8-10 in the air I think we would be way closer to a paraglider than anything else.

[PonoBill]

Ladder foils are a bit complicated and the transitions are abrupt. The Geezer foil is a V-foil and as confessed previously, very hard to steer. I could probably make it more steerable by using a more extreme angle. For what we're doing the stabilized T-foil is pretty good. It needs some development to give it a broader speed range. Surface sensing would help but it's too complicated for a surfboard. I'm interested in soft leading and trailing edges, both for safety and for automatic tuning. Working on it.

[jondrums]

The main wing might approach 20:1 (maybe?) but when the extra drag of the fuselage and the tail is factored in, it'll be significantly lower.  Then you have to subtract off the fact that the tail is actually providing slight negative lift, which is what makes the system stable. 

Tail and fuse probably adds 20-25% more wetted surface area (just a guess - could be pretty easily measured).  This extra drag would take a 20:1 L/D down to 16:1.  I guess the rear wing downforce counteracts about 10% of the lift of the front wing, taking it down again to maybe 14:1.

I'd be willing to bet that the reference you shared that has a T-wing at 20:1 is counting on quite a bit higher aspect ratio than a typical surfing foil.  So there would be some deduction for that if true.

So, I'd say 10:1 might be about right.

[jondrums]

Oh, and I was going to mention - why hasn't anyone tried a "canard" style foil? (or have they?) That way the stabilizer could be adding lift to the system and achieve an overall higher L/D.

<edit> hadn't seen Zeeko foils before, so it has been tried!

[PonoBill]

I've seen single wing foils--stabilized with a lot of sweep to the wings. They tend to be pretty stable, but hard to manage the pitch since AOA changes affect the wing uniformly.  The fundamental problem with Canards is that the leading wing leaves a lot of the front wing in downwash that screws with lift--or at least with disturbed flow. They also move the center of lift forward of the center of gravity which can make pitch control more difficult. It could be done, but I suspect you'd be fighting the hobby horse issue that canard wing airplanes often need wing tweaks to deal with.

[jondrums]

found this too - looks interesting.   Probably doesn't surf too well without any anhedral

https://projet-dared.com/2017/04/03/new-foil-km-special-sup-surf/