Best airfoil for high stall angle?
Best airfoil for high stall angle?
(OP)
Hey guys,
I'm looking for the airfoil that has the highest lift/drag ratio at the highest possible angle of attack. It would be preferabbly symmetric, even better if it's a NACA 4 digit (or something that would be easy to model).
Any ideas? Thanks in advance :)
I'm looking for the airfoil that has the highest lift/drag ratio at the highest possible angle of attack. It would be preferabbly symmetric, even better if it's a NACA 4 digit (or something that would be easy to model).
Any ideas? Thanks in advance :)





RE: Best airfoil for high stall angle?
That is, which is better, one with an L/D of 19 at 20 degrees, or one with an L/D of 18 at 21 degrees?
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Best airfoil for high stall angle?
I guess my question is poorly stated, and does not reveal the the true intent of my investigation.
X = (lift)cos(90-a) - (drag)cos(90-a)
(a = maximum angel of attack)
The angle of attack will be swept through (nearly sinusoidally) from -a -> a, so it would be very nice not to have it act erracticly inbetween.
I've been thumbing through some of the NACA 4 series... it seems like the 00xx is a good range ot look through but I thought I'd consult the expertise of the members here before I take too many steps in the wrong direction ;)
Thanks again.
RE: Best airfoil for high stall angle?
but then you know what you're doing, just looks funny that two forces at 90deg to one another would have the same trig function (rather than sin and cos) ...
reading your post again, i think you're doomed to failure. first the lift force is going to dominate (being much bigger than drag), second, lift is linear with aoa (but then maybe that's not behaving erractically), third, drag is not usually expressed as a function of aoa (but maybe you could transform the Cd plot to achieve this)
good luck
RE: Best airfoil for high stall angle?
X = (lift)sin(a) - (drag)cos(a) is what I meant to say
I choose ended up going with the NACA 0012, but just out of curiosity... if it is a symmetric airfoil, why is it that programs such as designFOIL and xFOIL generate different lift coefficients for +/- angles of attack?
For example, for
AoA: -10 degrees
Cl: -1.193 <----
Cd: 0.0114
AoA: 10 degrees
Cl: 1.239 <----
Cd: 0.0114
If the airfoil is symmetric would it really matter if the anlge of attack is positive or negative? Or is it just bad programming? Th
RE: Best airfoil for high stall angle?
RE: Best airfoil for high stall angle?
It may also be using a zero lift unit conversion to bring it back to a unitless coefficient. It may be adjusting the incidence angle to compensate.
Does the Cl show zero at 0 AOA?
As for the lower Cl vs Cd, it appears that you are looking for a wide drag bucket.
Check out Theory of Wing Sections, Ira G Abbott and Albert E. Von Doenhoff Library of Congress # 60-1601.
There are coordinates for the NACA series airfoils so you can manually input the points and spline the curves. This way you won't be restricting yourself to 1000 series symmetrical airfoils.
By the way...the highest Lift/Drag ratio is the holy grail of aerodynamics. The airfoil selection all depends on your flight envelope and the Reynolds Number you plan to use it.
RE: Best airfoil for high stall angle?
Just when you thought it was complicated enough...
You'd better read Abbott & von Doenhoff's Theory of Wing Sections. It's not expensive, and easily obtained because I think it's still in print (Dover Press).
Steven Fahey, CET
RE: Best airfoil for high stall angle?
RE: Best airfoil for high stall angle?
You will get vortex lift at high AoA and they are
typically good up to 25degress AoA