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A Question About The B2

Wed Jan 28, 2004 6:07 am

I just had a thought cross my mind. How does the B2 maintain yaw control? It has no rudder. Is the vertical axis controlled by differential thrust? If so what happens in case of engine failure. I know this is a true and tested concept but I can't figure it out.

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Thanks in advance.
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RE: A Question About The B2

Wed Jan 28, 2004 6:18 am

The B-2 uses its flaperons, and trailing edge ailerons in the place of rudders to provide yaw control.

provides an image of what part is used as the 'rudder.'
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RE: A Question About The B2

Wed Jan 28, 2004 7:14 am

DUDE!!! Flaperons would be for roll control NOT yaw control. That's why they are called flaperons not flaperrudders or whatever silly name you can think of.

Yaw control in the B2 is provided by a device called a drag rudder. They are attached at the trailing edge where the red circle is located in the graphic above. They open up like clamshells and cause drag on one side of the vehicle. The vehicle then yaws accordingly. The problem with this scheme is that the vehicle does not yaw about its center of gravity as it would with a conventional tail-mounted rudder. But I guess it's not that big of a problem, as Northrop-Grumman has made it work pretty well.

On a related note... The response of drag rudders is not linear. In other words, a pilot may depress the rudder pedals for some distance and the plane may not respond for some time; when it does the response is sudden and unexpected. To counteract this behavior the B2 control system keeps the drag rudders deployed to just the point before they are about to "catch the air". Doing this allows the response of the airplane to more closely approximate the control input of the pilot.

Hope that's not too much info.


[Edited 2004-01-27 23:30:51]
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RE: A Question About The B2

Fri Jan 30, 2004 7:31 am

The B-2 is laterally unstable, so it must be assumed that the drag-rudders work automatically all the time in order to keep the nose pointing in the flight direction.

It's of course a FBW plane, so it is no bigger problem than for instance controlling the elevator on an F-16 fighter plane, which is unstable on the pitch axis.

In principle it has similarities to any FBW Airbus (320 and newer). A "bus driver" does in principle not touch the pedals until he has to land in sidewind. The rudder control is fully automatic even when the plane is flown manually on the sidestick. The computer keeps "the needle in the middle".

It's of course not the same thing since Airbusses are laterally stable. So the B-2 is a far more complicated thing in this respect.

The complications also show up on the price tag.

There is only one major advantage of "missing" vertical fins: Reduced radar signature.

An engine out situation is probably not the nicest thing to experience on a B-2, especially not at low speed where those drag-rudders will have very little effect. A three engine go-around may be a tricky thing involving the need for precise differential thrust. But well, with that price tag that could be automatic too.

Happy landing, Preben Norholm
Always keep your number of landings equal to your number of take-offs

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