withak
Posts: 219
Joined: Thu Apr 19, 2007 5:29 pm

Tailless Aircraft And Crosswind Landings

Tue May 08, 2007 2:50 pm

How to tailless aircraft (such as the B2) perform crosswind landings given that they don't have a rudder?

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WithaK
 
2H4
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RE: Tailless Aircraft And Crosswind Landings

Tue May 08, 2007 2:56 pm



I'd imagine they have a much easier time negotiating crosswind landings, as there is no vertical surface and thus, little or no weathervaning effect.

Yaw can still be controlled, just not through the traditional means of a rudder.


2H4




[Edited 2007-05-08 07:58:18]
Intentionally Left Blank
 
boeingfixer
Posts: 573
Joined: Fri Jul 29, 2005 2:02 am

RE: Tailless Aircraft And Crosswind Landings

Tue May 08, 2007 2:58 pm

What you'll notice is that the B-2 has split ailerons. It uses these for yaw control in much the same way as a normal rudder. The flight control computers take rudder pedal inputs and decides how much the split ailerons will be deflected causing the desired yaw.

Cheers,

John

[Edited 2007-05-08 08:01:00]
Cheers, John YYC
 
withak
Posts: 219
Joined: Thu Apr 19, 2007 5:29 pm

RE: Tailless Aircraft And Crosswind Landings

Tue May 08, 2007 3:38 pm

Quoting Boeingfixer (Reply 2):
What you'll notice is that the B-2 has split ailerons. It uses these for yaw control in much the same way as a normal rudder. The flight control computers take rudder pedal inputs and decides how much the split ailerons will be deflected causing the desired yaw.

Cheers,

John

Thanks. That makes alot of sense.

Quoting 2H4 (Reply 1):
I'd imagine they have a much easier time negotiating crosswind landings, as there is no vertical surface and thus, little or no weathervaning effect.

Correct me if I'm wrong but wouldn't there still be a considerable weathervaning effect because of the changed lift and drag characteristics due to the crosswind itself (ie the aircraft will still want to point into the wind.)
I thought the vertical stabiliser although contributing to the weathervaning effect was used to straighten out the aircraft again after crabbing.

WithaK
 
rwessel
Posts: 2448
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RE: Tailless Aircraft And Crosswind Landings

Tue May 08, 2007 4:27 pm

Quoting WithaK (Reply 3):
Correct me if I'm wrong but wouldn't there still be a considerable weathervaning effect because of the changed lift and drag characteristics due to the crosswind itself (ie the aircraft will still want to point into the wind.)

Aircraft in coordinated flight do not weathervane, they are, by definition, flying straight already, and there’s no direction to weathervane to. If an aircraft is landing in a steady crosswind, and it’s crabbing, the aircraft is flying exact straight through the air, but at an angle to its desired ground track. That angle (hopefully) exactly cancels out the “drift” from the crosswind.

But, in uncoordinated flight, or if hit with a sudden crosswind (same thing), then sure, since the B-2 has a swept wing, the upwind wing would generate more lift and drag, and the aircraft would yaw into the wind, while rolling away from it. The pilots will use the drag rudders and ailerons to counteract that.

Now that changes once the landing gear is on the ground, since the gear will hold the aircraft on a straight path, so the crosswind will cause the aircraft to weathervane. If the pilot does now keep the tendency to yaw into the wind under control at that point, a very embarrassing ground loop may develop.

Quoting WithaK (Reply 3):
I thought the vertical stabiliser although contributing to the weathervaning effect was used to straighten out the aircraft again after crabbing.

On the B-2 that function is performed by the drag rudders on the wingtips (which you can see open in the photo up thread). The aircraft will yaw towards the more open drag rudder.

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