TomW wrote: ↑
Fri Apr 20, 2018 9:58 pm
I thought it was variable amount of lift at variable AoA. Then at certain AoA lift decreases, a stall. Some wing designs, thus curve is falling drastically and deep, like cliff. Other wings the curve is more like a hill.
The cliff curve is difficult to recover from, the hill is easier.
Eventhough on the "stalled" side, any wing will behave quite erratic meaning difficult to predict what will happen.
Huge difference on dynamic stall as you can smoothly get some wings to a high stall angle, but if too rapid they will drop.
Also, the SPECIFIC stall angle of attack is of no use for comparison at all.
The high lift wings often stall at a lower AOA than the faster ones, because they have a lot of lift at zero angle of attack, as opposed to more flat/fast wings, which often outweighs the surplus lift.
Generally though, very low drag wings will have a steep polar curve, both before and after the stall point.
And thicker more blunt, high drag wings, will have a gentle hill instead, so be way easier in terms of the stall - meaning you can push too much and it still dont stall, as opposed to the faster wing that will just drop you.
What happens in reality though, is that when a beginner push too much with the rear foot (or ride too slow) without having the wing fly up, it goes past the stall point, but it still has lots of lift even when way over the "ideal" max lift point, so it will not stall immediately.
But because the drag will increase HUGELY now, riding speed goes down, and you drop anyways, because lift is squared with riding speed.
So apart from muscle memory kangarooing because one can not control pitch, you also see this stall kangarooing we know so well from the learning phase.
Lower aspect wings can be pushed to a higher AOA without stalling, because the "overall" polar gets even more blunt (hill and not steep).
This is why they stall so gently and can be recovered, especially because they often have more lifting profiles, so used for beginners, or wave wings where these characteristics are a must eventhough for two different reasons.
As opposed to race wings, high AR and faster profile, so the stall will be violent, compared.
But doesnt mean a thing for racing, so perfect