Low aspect ratio wings

[yuri_base]

When designing wings with low aspect ratio, should the wing profile be thicker or thinner for maximum lift to drag ratio?

[Sparky Paul]

What'ya wanna do with the plane?

[yuri_base]

it's not a plane, it's a wingsuit. The wingspan is limited by your armstretch.

[Ollie]

Wingsuit? Or, perhaps wingnut? Go to the gym. Hold 100 pounds in each hand and see how it works for the wing span and lift.

[Sparky Paul]

Be sure to include the weight of the anti-splat!

[TurboThruster]

When designing wings with low aspect ratio, should the wing profile be thicker or thinner for maximum lift to drag ratio?

So can anyone answer his question? Assuming cruise flight at high Reynolds number, how does wing profile thickness affect performance?

As far as I know a thin profile is always best for L/D performance at cruise, and I don't recall seeing any fighter jets with particularly thick sections. The fact that the leading edge is your arm sets a lower bound on the profile thickness though.

[DT56]

I thought wing suits were just panels of fabric stretched between the arms, the torso and the legs. If that's the case, then your section thickness is limited by the fabric thickness.

What reynolds numbers are you designing for? A 6 foot root chord (height of pilot) and a 6 inch tip chord (hand), at perhaps 150 MPH, does not yield very high reynolds numbers by full scale standards.

[TurboThruster]

No, wingsuit wings are inflatable airfoils, just like paragliders and skydiving canopies, so they can be designed for any thickness and shape. Can't imagine a panel of fabric flying very well.

Anyway, I'm contemplating a rigid gliding wing for skydiving, constructed similarly to EPP combat/DS wings but with much higher strength (hence the desire for a thick section). The biggest problem/effort is designing the safety systems to be reliable enough. I often fly rc sailplanes with dodgy servos, cracks in fuse, poorly repaired wings, etc., which is an attitude that obviously won't cut it in this new scenario. Also not sure how to ensure roll stability without dihedral, which I'd rather not do. Control in roll axis will be via weight shift.

Unfortunately wingspan is limited to <6 ft by the plane door - not considering a fancy folding wing at this stage. Winglets might be an option but I can't imagine how to make them strong enough. Should be able to outperform the best wingsuits pretty easily though. Just getting up to speed with XLRF5, I hope it's reasonably accurate for this application.

[kcaldwel]

At the Re of a wingsuit, you can probably go up to 15% thickness without compromising the L/D. XLRF5 should work pretty well for your application.

I don't think you will need too much roll stability, so dihedral isn't likely necessary. Most hang gliders have a fair bit of anhedral, to make them roll unstable enough for weight shift to work. They also have movable airframes that allow billow shift in the wing that actually causes the roll.

On a rigid wing, weight shift usually only causes a bit of adverse yaw, and very little roll. I've tried it on some proto hang glider designs. Your span is a lot smaller, but I've never got much of a turn out of rigid wing gliders (hand launch to hang glider) with offset weight. Your span is a lot smaller than a hang glider, so that might allow you to shift the CG a much greater % of the span. But I've had problems trying to make it work on 12" rigid models of hang gliders.

Weight shift roll control isn't a straightforward thing - it may require a lot of experimentation to make it work. Are you sure some spoilers like most of the rigid wing hang gliders use wouldn't be possible?

I can't imagine how you launch a 6' wing out an aircraft door at 50 or 60 knots?!! What do you do for pitch stability and control? Good luck!

Kevin

[T.D.]

I asked the Aerodynamics grad. at my work your question and he said to approach wingsuit design more as a lifting body problem than a true wing/glider/airfoil problem.

He also told me to tell you to spend your money on a commercial wingsuit as the pain bill has already been paid by those who came before.


T.D.

[TurboThruster]

Thanks guys.

kcaldwel, I was hoping to avoid control surfaces because of the complexity and possibility of failure, but thanks for the info re roll control for rigid wings. You're right.
I don't really need roll control as such, just steering. Maybe simply putting an arm in the wind at these speeds would create sufficient differential drag to yaw me around. Does that make sense? Might need more thought..
One aspect is that if I somehow end up on my back without roll control I'll have no choice but to cut the wing away, in which case it's unlikely I'd ever see it again (it will have a drogue chute to slow its descent, the upper winds could carry it for miles).

Pitch control is no problem, It's just a matter of building sufficient reflex into the wing and increasing/decreasing the lift generated by the feet.
A lot of this stuff has already been worked out by the awesome Yves Rossy. http://www.jet-man.com/prod/index.html. He has ailerons and a folding wing, not to mention four turbojets, which is all a bit too fancy for my budget and building skills, but I'm trying to learn as much as possible from his pictures and videos.

Exit speed is more like 85 knots from the plane I have in mind (Shorts Skyvan). That's fine, it's just a matter of keeping low AoA.

I plan to do at least 90 more skydives (I only have 110), then at least 50 wingsuit flights before trying the rigid wing. That's about 8-12 months to develop and build the wing, including a bombproof cutaway system in case of unrecoverable instability.

T.D. That's a fair argument about taking advantage of the R&D that's already gone into commercial wingsuits. It also applies to model aircraft, but there will always be some who keep looking for better performance, plus the pleasure of simply doing their own thing.
Very strong wingsuit pilots with tons of experience only get 3.5:1 glide at very best - I want better performance than that!

[tommyeflight89]

I thought wing suits were just panels of fabric stretched between the arms, the torso and the legs. If that's the case, then your section thickness is limited by the fabric thickness.


I don't think that is correct. The first fabric wing that comes to my mind is the Rogallo. I am pretty sure this is the basis for most any hang glider, paraglider etc. The geometry of the structure creates the wing thickness, how much undercamber etc..