MGriffin
Well-Known Member
Lately I've been doing a lot of reading about different airfoils and their applications. All of the math behind it is a bit beyond my abilities but I find the subject fascinating nonetheless.
There are already several threads on here about airfoil selection for ultralight aircraft, I'm not trying to rehash anything that has already been discussed at length, I just want to see if there's a general consensus on this specific issue.
What I have noticed is this:
On here and elsewhere I've seen multiple people say almost the same exact thing; that it doesn't matter what airfoil you choose since you'll be flying at pretty low speeds with an ultralight aircraft anyway. The low cruising speeds and high drag of many ultralight aircraft designs will overwhelm most of the advantages you'd gain from being super selective about which airfoil you will use. This seems to ring true to me, but I'm no aeronautical engineer.
Now let's say you want to build an ultralight motor glider, something that can sort of ride thermal air currents or updrafts. Obviously it would need to be somewhat low drag and somewhat lighter than typical, but at a certain point you can only do so much with strut braced wings and fixed landing gear.
You could of course design and build a cantilever wing like the sky pup, but I am no professional engineer. Even though the sky pup is somewhat aerodynamically "clean" it still has a glide ratio of 12:1 which isn't very good. Good for an ultralight, bad compared to many purpose built gliders.
So do you really need some fancy "S Curve" airfoil with camber like the Easy Riser has or would a simple flat bottom airfoil like the Clark Y work just as well for almost any ultralight, including an ultralight motor glider?
My hypothesis is that wing area/wing loading matters more for the stall performance, low speed stability, and glide performance of ultralight aircraft in general, and even for lower drag designs like ultralight motor gliders.
Mike Sandlin (the guy who designed Bloop and several other light gliders/ultralight aircraft) said almost the same exact thing about airfoil choice:
"I've flown with three different airfoils, they all fly about the same, wing loading seems to be the important factor."
There are already several threads on here about airfoil selection for ultralight aircraft, I'm not trying to rehash anything that has already been discussed at length, I just want to see if there's a general consensus on this specific issue.
What I have noticed is this:
On here and elsewhere I've seen multiple people say almost the same exact thing; that it doesn't matter what airfoil you choose since you'll be flying at pretty low speeds with an ultralight aircraft anyway. The low cruising speeds and high drag of many ultralight aircraft designs will overwhelm most of the advantages you'd gain from being super selective about which airfoil you will use. This seems to ring true to me, but I'm no aeronautical engineer.
Now let's say you want to build an ultralight motor glider, something that can sort of ride thermal air currents or updrafts. Obviously it would need to be somewhat low drag and somewhat lighter than typical, but at a certain point you can only do so much with strut braced wings and fixed landing gear.
You could of course design and build a cantilever wing like the sky pup, but I am no professional engineer. Even though the sky pup is somewhat aerodynamically "clean" it still has a glide ratio of 12:1 which isn't very good. Good for an ultralight, bad compared to many purpose built gliders.
So do you really need some fancy "S Curve" airfoil with camber like the Easy Riser has or would a simple flat bottom airfoil like the Clark Y work just as well for almost any ultralight, including an ultralight motor glider?
My hypothesis is that wing area/wing loading matters more for the stall performance, low speed stability, and glide performance of ultralight aircraft in general, and even for lower drag designs like ultralight motor gliders.
Mike Sandlin (the guy who designed Bloop and several other light gliders/ultralight aircraft) said almost the same exact thing about airfoil choice:
"I've flown with three different airfoils, they all fly about the same, wing loading seems to be the important factor."
