Re: Do birds, such as Crows and Raptors, stall their wings when they land

Hi Joshua:

I'm not an aeronautical engineer, so I can't really answer your question about adverse yaw. There are, however, quite a lot of resources about the phenomenon on the web. Have a look at this search from google.com, you'll find your explanation there.

Regarding wing attitudes while landing, I think that it's partially true that some birds do stall their wings, but I'm not sure how much it's used in landing. Last week I watched crows stalling their wings while soaring, while I was sitting in a chairlift going up a ski hill. However, the crows were doing it at quite high altitudes and not for landing. Crows are of course very social, and very territorial, and one often sees one crow pursuing another- the pursued crow often abruptly stalls its wings as a way to get its pursuer off its tail (I'm pretty sure that fighter pilots in WWI and II used a similar tactic sometimes). I've also seen the phenomenon when flocks of Canada Geese land- when the flock comes in for a landing the individual birds will spead their wings, apparently stall, drop a few feet quite rapidly and spread their wings out again. It's a really neat behaviour to watch when a whole flock is doing it- I'd speculate that it's a good way to lose altitude quickly without bumping into other birds in the flock.

The birds that I've watched land have generally greatly increased the angle of attack of their wings- in general it appears that they trade thrust for lift. They'll often land into the wind as well, probably because that helps them lose momentum. It has been suggested that in some birds they are at the edge of a stall when landing (turbulent separation at the leading edge of the wing can be seen by a ruffling of the feathers), but that they use several areodynamic tricks (such as altering tail geometry) in order to decrease their stall speed when landing. This is likely a trade-off for the bird, because landing is a fairly risky activity. The bird must trade off between slowing down as much as possible and reducing the risk of injury (i.e. getting as close to stall speed as possible) with the risk of actually stalling and losing control (which will also have an associated risk for injury).
Here's a few links that you should find helpful:

Hope that helps!
Rob Campbell, MAD Scientist