D L X
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How Necessary Is A Vertical Stabilizer?

Sat Nov 17, 2001 2:13 am

I know that question sounds like a big 'DUH!' but think about it before you answer it. America's B2 Stealth Bomber, and all its ancestor Northrop flying wing prototypes have neither horizontal nor vertical stabilizers. The lack of horizontal sort of makes sense, since it can use the same principals that keep a delta winged jet aloft. (Using elevons, etc.) But, even delta winged jets all have vertical stabilizers. How does the B2 get away without one?

I posted this in the civil aviation forum instead of the military because I'm curious if the plane flying AA587 had any chance at all flying without a vertical stabilizer possibly using the techniques used for the B2.
 
Ikarus
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RE: How Necessary Is A Vertical Stabilizer?

Sat Nov 17, 2001 2:31 am

The B2 can deploy spoilers and elevons differentially, enabling it to create a yawing moment simply by slowing one side of the wing down a bit.

I don't think the A300 has the same capability - it is not designed to fly without vertical stabilizer.

With no vertical stabilizer control, you can still try inducing yawing moments by thrust differentiation (eg the DC10 in Phoenix), but I'm not sure how the complete lack of the surface would affect this manoeuvre. It would be one helluva difficult situation. Probably ending disastrously anyway - maybe if it had ripped off during cruise they could have dumped fuel and attempted a emergency crash landing (survivable bymany) - but at takeoff, this is a pretty tough situation to face. You don't have enough time to realize what's wrong before you hit the ground.

Regards

Ikarus
 
GOT
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RE: How Necessary Is A Vertical Stabilizer?

Sat Nov 17, 2001 2:42 am

I have read that the B2 is stabilized by powerfull computers. Without them the B2 would be impossible to fly.

GOT
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Ikarus
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RE: How Necessary Is A Vertical Stabilizer?

Sat Nov 17, 2001 2:50 am

GOT:

I don't know for sure, but you are probably right. With high-performance (combat) aircraft, the design philosophy is often too tolerate dynamic and static instability (a workload nightmare for pilots) and simply use FBW and computers to stabilize the plane artificially.

But that does not necessarily mean it would be humanly impossible to achieve some control over the plane. It might be the case for the B2, but for a passenger airliner, I would imagine the pilot would still be able to achieve some authority by thrust differentiation and maybe deploying spoilers differentially, too. Landing safely would be a near-impossible task. But achieving a certain control over the flightpath, given a reasonable starting position, would probably be achievable. The thing is, 2 minutes after takeoff is not a reasonable starting position to try and regain control. Also, how do the pilots know they lost their tailfin? There is no "tailfin presence indicator" in a cockpit, is there? Basically, they needed to react to the situation, without necessarily knowing what had gone wrong, thereby being unable to do the right thing. And even if they did the right thing, they were probably too late (human reaction time) and too low to do anything.

If that is the scenario, of course. I still prefer waiting for official theories and reports.

Regards

Ikarus
 
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RE: How Necessary Is A Vertical Stabilizer?

Sat Nov 17, 2001 2:50 am

Ikarus, your answer shows how you can "rudder" a tailless jet, but the vertical stabilizer is more than just the rudder, right? It's like the feathers on an arrow or a dart: even without a control surface, they stabilize the plane from swaying side to side. How does the B2 keep from swaying side to side? By actively countering any yaw encountered?

Does the dihedral help?

Yeah, I figured that would be part of the problem: the pilots probably hadn't even guessed their plane was coming apart.

BTW, A300s can't dump fuel.
 
D L X
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RE: How Necessary Is A Vertical Stabilizer?

Sat Nov 17, 2001 2:54 am

GOT sez : "I have read that the B2 is stabilized by powerfull computers. "

That's probably true, but Flying Wings have been around for more than half a century, long before powerful computers and FBW. Do you know how the old flying wings of the 40s and 50s handled the lack of a tail?
 
spectre242
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RE: How Necessary Is A Vertical Stabilizer?

Sat Nov 17, 2001 2:56 am

The A300 does not have the complex control surfaces or computer fbw system of the B2 to allow it to sustain flight without a v-stab. Once the A300s v-stab came off, it there is no telling what kind of damage may have been done to the rest of the tail, the elevator could have been damaged or hydraulic lines broken or anything like that (which may explain the steep dive of the aircraft), and at that point there isn't a lot you can do. Loss of rudder control can be compenstated by the engines, but at that critical point of the flight just after take off, the airspeed would have been to slow to start reducing engine power on one side to create yaw. Either way the engines came off soon after in the AA A300 case so whatever caused this incident, be it rubulence or whatever, there wasn't any way for the crew to control the pane.
 
Ikarus
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RE: How Necessary Is A Vertical Stabilizer?

Sat Nov 17, 2001 3:06 am

Don't know about the 50s. But from what I've heard, those flying wings back then (few of which made it past prototype) were really really tough to control. So in effect, the pilot probably DID have to counteract each and every gust that swayed the plane by applying differential spoilers...

At least, that's my best guess. Try asking in the Tech/Ops forum. Maybe a more knowledgeable person is around in there...

Regards

Ikarus
 
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VirginFlyer
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RE: How Necessary Is A Vertical Stabilizer?

Sat Nov 17, 2001 4:26 am

The Northrop XB-35 propeller flying wing was able to stay stable becuause of the torque from the turning props. When they built the YB-49, which was a jet variant, they had to add small vertical stabilisers.

The A300, however, was not designed to be able to fly without its vertical stabiliser. Without it, as soon as it was in a banking angle (which would have occured with the turbulence), it would have entered a side slip, and it's all over from there.

As for the B-2 and other Vertical Staberliser-less aircraft (such as the X-36), I am unsure of what prevents a side-slip.
"So powerful is the light of unity that it can illuminate the whole earth." - Bahá'u'lláh
 
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RE: How Necessary Is A Vertical Stabilizer?

Sat Nov 17, 2001 4:29 am

Stabilizers are used to keep the plane from wobbling back and forth in the air, the plane has a vertical stabilizer and two horizontal stabilizers. These stabilizers make up the airplane's tail section. The vertical stabilizer is the wing-like structure jutting out from the top of the plane's fuselage.This keeps the plane's tail from swinging side to side. The plane's horizontal stabilizers are the small wings that jutt out from the sides of the fuselage in the back of the plane. These keep the plane from rolling wildly or tilting up and down, and in most cases the plane's horizontal stabilizers are used to store the elevators or ailerons.

 
D L X
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RE: How Necessary Is A Vertical Stabilizer?

Sat Nov 17, 2001 4:43 am

Umm... thank you 757fan. Care to discuss my question like the others?
 
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RE: How Necessary Is A Vertical Stabilizer?

Sat Nov 17, 2001 4:48 am

in most cases the plane's horizontal stabilizers are used to store the elevators or ailerons.

Just a quick correction, the elevators are usually in the horizontal stabiliser, but the ailerons are actually located in the wings.
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RE: DLX

Sat Nov 17, 2001 5:56 am

Nope... My job is done.