How does a B-2 flys with out a rudder?

[jet-ster]

Hi I was wondering, how does a B-2 flys without a rudder? Most models of the B-2 seems to have some kind of rudder add to it. For example the GWS
B-2 has , I guess cheater rudders on the bottom of it.
My question is, can this be done on a model without rudder?
Is it the size of the real B-2 that makes the difference?
Or just the way it's flown?

thanks
Dan

[nmasters]

If you look closely at the trailing edge of the control surface nearest the tips you'll see a slot that's always slightly open. That's called a drag rudder (http://www.rcgroups.com/forums/showthread.php?t=229775) . It's simply two flaps, one on top of the other, that spread apart to make drag on the side that the plane needs to yaw toward. A lot of models don't have enough room inside the tip for a mechanism to work drag rudders so they deviate from pure flying wings

--Norm

[Tom Harper]

Dan,

The drag rudder provides control but not lateral stability. The B-2 gets that from a mega-bucks worth of electronics.

A model with a swept wing will fly without a rudder. It does not work well for free flights but is OK for RC where the pilot makes corrections. Check out the venerable Zagnutz.

Tom

[Brandano]

I think that the B2 is probably intrinsically stable. The computer will keep it from reaching unrecoverable attitudes, but since it isn't a fighter there's little reason to make it into an excessively unstable design. It's not meant to dogfight. The Horten Ho 229 flying wing wing used the same control method, had a comparable wing sweep, and no computer assistance to speak of, but apparently it flew just fine (http://www.nasm.si.edu/research/aero/aircraft/horton_229.htm)

[macboffin]

Check out the Carbon Falcon. Also several of the Horten flying wings.

[nmasters]

The Hortens used a more complex drag rudder mechanism than Northrop but the result was pretty much the same. BTW I was looking at the Horten restoration page (http://www.twitt.org/Berlin.htm#top) today and I had forgotten how huge the H-III was. The root chord looks like it's about 9 ft and I think that airfoil is 18%.

[macboffin]

Here is 3-view of the Horten 229. Several succesful turbine powered scale models have been flown.

[macboffin]

BTW, no cheater fins/rudders on the B2. It cheats by using computer control!

[Brandano]

As I was saying, I don't think the B2 needs a computer to be flyable, but it probably needs one for carefree handling. Probably only relies on the computer to avoid reaching unrecoverable attitudes, like flat spins or extreme AOA's. It might well be possible to fly it even in the event of a complete computer failure, as long as the pilot is VERY careful about the flight parameters

[summerkc]

As I was saying, I don't think the B2 needs a computer to be flyable, but it probably needs one for carefree handling. Probably only relies on the computer to avoid reaching unrecoverable attitudes, like flat spins or extreme AOA's. It might well be possible to fly it even in the event of a complete computer failure, as long as the pilot is VERY careful about the flight parameters


That, and if he (or she) isn't too tired after the 55 hour misson!

[nmasters]

I don't think the B2 needs a computer to be flyable, but it probably needs one for carefree handling.

I believe the B-2 has a dangerously aft CG. On the bomber it's done for efficiency. Those of us who can't afford to design our airplanes around multi-million dollar computer networks must rely on old fashioned aerodynamic design and pay for stability with higher induced drag. :(

[The Other Dave]

As I was saying, I don't think the B2 needs a computer to be flyable, but it probably needs one for carefree handling. Probably only relies on the computer to avoid reaching unrecoverable attitudes, like flat spins or extreme AOA's. It might well be possible to fly it even in the event of a complete computer failure, as long as the pilot is VERY careful about the flight parameters

The B2 absolutely needs it's flight control system active to fly.

It would be out of control without it.

Same for the F-16, F-22, F-35, F-117, F-18 (I think)

Most modern military aircraft are dynamically unstable and require computer control to make them fly.

[Brandano]

This is generally true for fighters, where the instability pays out as increased agility. Not quite so important for dedicated bombers, like the B1 or B52. That said, I can see how having the CG far aft might allow the plane to have better efficiency. However, the trade back could be that the continuously moving control surfaces are more likely to be seen on a radar.

[50+AirYears]

There has been a number of reports written about how the original Northrup flying wing bombers were marginally stable in pitch and yaw. In fact, one of the early company pilots reported the B-49 (Turbojet version) could start flipping tail over nose if the angle of attack went too negative, such as during a stall. The YB-49 also needed stub fins added after the loss of the effective side area of the original recip nacels to try to correct the loss of yaw control.

The B-2 obviously has a typical double or triple redundant computer system to overcome these instabilities that reputably made the Northrup wings unstable bombing platforms. The computer can sense vvariations and make corrections many times before a human pilot can even sense the variations starting.

The B-2 is still an awesome and impressive flying machine.

[BMatthews]

.... The YB-49 also needed stub fins added after the loss of the effective side area of the original recip nacels to try to correct the loss of yaw control.......

Not just the little nacelle stubs but the props as well. Propeller discs have a goodly amount of "side area" effect. I remeber reading something about the later Spitfire varients requireing a larger fin and rudder when they went to the counter rotating props for the later Griffin engine options that put out too much power for even a single 5 bladed prop.

[Wayne V]

Well i tried to cut down my vertical stab a little at at a time til it wouldn't fly anymore, then i just added a little back, so on my B2 model i needed the stab to make it fly extemely stable, next time it will be clear so from 10' you can't see it.

http://www.rcgroups.com/forums/showthread.php?t=586728&highlight=8+b2

[nuevo]

How does a B2 handle cross-winds on landing? It it like flying an aileron/elevator only plane, where a roll, then slight elevator input is required?

[Brandano]

the B2 has a swept wing, so the wing toward the wind will have more lift. However, since it doesn't have a vertical surface to feathercock it in the wind probably the rudder input to keep it i line with the runway is moderate, and needs a little aileron toward the wind. It still has to fly "sideways" to the runway, (to keep the approach path in line with the runway) but maybe is a bit less sensitive to wind gusts.

[murmur]

As yet, nobody has offered the standard answer to the title of the thread ("Just fine, thank you!"), so that'll be my contribution.

[squeakywaffle]

I think the B-2 exhibits 'relaxed stability'- that is, even trimmed to a specific attitude, without continuous adjustment, it would tend to oscillate around that attitude with increasing amplitude, which could cause the aircraft to become uncontrollable.

I believe the name for this is 'pilot induced oscillation'- the pilot tends to overcorrect slightly in these situations in an attempt to restore the aircraft to normal flight, and when this is coupled with the aircraft's tendency to increasingly deviate from its trimmed attitude, the oscillations can quickly take the aircraft out of its normal flight envelope and cause an unrecoverable situation.

This is what happened in the X-15 program, causing a fatal crash (those guys had balls...).

I imagine these aircraft can be flown by hand (for instance, I know the F-117 prototypes were flown by hand) but doing so is made extremely difficult because the aircraft is more or less inherently unstable, as opposed to a traditional design which always tends to correct itself toward its trimmed attitude in case of deviation.

In any case, flying something like that for a long period of time would be very tiring and probably not possible over any significant time scale.

[murmur]

The fatal X-15 crash I know about (I think there was only one, but I'm not sure) was the result of an autopilot problem. NASA was trying to move forward on the "adaptive autopilot" front, in which the autopilot attempts to learn what the correct controls gains are, in flight, the way a human pilot has to learn what the appropriate sizes of control movements are for various maneuvers and for corrections following disturbances. This is advanced stuff, and the theory is still in development to this day! Development of adaptive autopilots languished for years (decades?) following the X-15 crash, and probably for good reason; the onboard computing power required to really do a good adaptive autopilot has only been available in the last 10-15 years.