Can a jet not remain airborne without a vertical tail fin?

Factual Questions
1

Hypothetically, if a plane loses it’s vertical tail fin, can it still fly? I realize that the pilot would have a bitch of a time steering the thing, but I can’t see why it would not remain airborne. Yes or no?

Disclaimer: This thread was, of course, inspired by the crash of flight 587, but posts should not be limited to the known or speculated details of just that event. The leading theory is that the vertical tail fin snapped off the body of the plane. There were other mechanical events (engines/wings breaking off, etc.) but for the sake of this Q, let’s ignore those.

2

There are aircraft without vertical stabilizers. The B-2 comes to mind immediately. The purpose of the vertical stab. is to keep the pointy end in front. The rudder, which is attached to the stab, controls yaw. In a twin engine fixed-wing aircraft, yaw can also be controlled using differential thrust. Then there is “adverse yaw”. Adverse yaw occurs when the ailerons (controlling bank) are deflected. I fly helicopters and it’s been a long time since I’ve flown fixed-wing, but IIRC adverse yaw moves the nose in the direction opposite the bank. Which would make sense, since you need to use rudder (and elevator) to make a coordinated turn.

Given all of that, I would assume that a jet aircraft could be flown without a vertical stabilizer or rudder under ideal conditions. Yaw might be controllable with differential thrust. As long as you do things very gently, my guess is that it might work out. But if the aircraft was put into an unusual attitude and/or there is a loss of one or both engines, I don’t think it would fly without a tail.

3

As Johnny L.A. pointed out the B2 flies without a vertical stabilizer so yes, it is possible.

However, the B2 was built to fly that way and it requires the input of some fairly sophiscated computers and software to keep the plane flying and stable. Totally outside of the pilots input or control the plane constantly monitors itself and makes endless little adjustments via the ailerons to stay stable. The original flying wing, even with some minimal vertical stabilizers, was very unsteady (no computers helping out) which is one of the reasons it was cancelled. If you turned off the B2’s computers while in flight (which I doubt is possible) the plane would surely crash.

Same goes for commercial jets. While the plane could theoretically be controlled there is no way pilots could make adjustments quickly enough or finely enough to keep the plane flyable.

That said you can often continue flying as long as you have at least a little of the tail left. I remember seeing pictures of B-17 bombers than landed safely after having a good hunk of their tail-fin shot off.

4

Here are some photos of tail damage sustained by B-17’s that still made it home (it’s amazing some of those planes were able to land safely).

5

The OP didn’t ask about flying the thing WELL, just about keeping it AIRBORNE. The news media are showing that the plane suddenly fell straight down, nose first.

This totally unknowledgeable nonpilot doesn’t understand why a missing tail rudder would cause that. The plane could still have used wing flaps to bring the nosedive to something less steep than straight down.

That’s why I’m going with the theory that when the engine fell off they lost the hydraulics and couldn’t do a thing to prevent the plane from simply falling like a brick.

Eagerly waiting for someone with half a brain to show me the light…

6

Keeve: Loss of hydraulic power can be a bitch, as was proven when that DC-10 crashed in Suoix City back in '89. The pilots were only able to keep it airborne with differential thrust. And they still lost it at the end due to a gust of wind. (Still, it was an excellent job of flying.)

Now what about the latest crash? Why couldn’t the pilots keep it under control? Remember that the aircraft is in its takeoff profile. That means that there is a lot of thrust, a high pitch angle, relatively low altitude, and relatively low speed. Depending on the airspeed (I don’t know what it was) a sudden, violent yaw caused by the rending of the vertical stab could have stalled one wing. In that case, the aircraft would roll into that wing and the nose would fall. Without a rudder to stop the spin, the pilots may not have had enough room to bring the aircraft under control. Could it have been brought under control? I don’t know. If an engine departed the airframe, which could have happened in a violent lateral maneuver, then they’re doomed no matter what they do.

This is all speculation, of course.

7

Now, now, Keeve. Chill a bit.

Yes, I asked this Q to learn if the media simulations of the plane dropping once the tail fin snaps are accurate. But there’s no need to antagonize our fellow Dopers who have the answers. Give them a break and ask politely for clarification.

8

thanx

9

The Funamentals of Aerodynamics page can help you understand how an aircraft is controlled. A shockwave animation explains the functions of the elevators, ailerons and rudder.

“Wing flaps” do exist, but we simply call them “flaps”. Some aircraft have leading edge flaps. Most have trailing edge flaps. Flaps come in different designs. The simplest is just a trailing edge flap that droops down. There are also split flaps. With split flaps, the upper surface is fixed (part of the wing proper) and the lower surface drops into the airstream. Fowler flaps, as found on the popular Cessna 172 Skyhawk and others, roll backwards on tracks so that they increase the surface area of the wing as they drop.

Why are there flaps? Vintage aircraft often do not have them. Flaps dp a couple of things. If they are not extended too much, they increase lift. Drop them more, and they act as brakes. As mentioned, Fowler flaps are very efficient and can be used to help get the aircraft airborne on short runways or if you’re heavy. I found that the Cessna’s flaps were very good at slowing down dad’s Skyhawk and steepening the final approach. Flaps affect the pitch axis.

The other flappy things on wings are the ailerons. These are used to control movement around the longitudinal axis.

On the rear of the airframe, called the empannage, are the horizontal and vertical stabilizers. The vertical stab almost always contains a rudder, which is a seperate moveable surface attached to the fixed vertical stab. There are some “exotic” designs that have an all-moving vertical stab. The rudder controls movement around the yaw axis. this is a very important control if you are in a spin. The other surface is the horizontal stab/elevators or the stabilator. The former has a fixed stabilizer with a moveable elevator. In the latter case, the whole unit moves. The elivator or stabilator conrols pitch.

Now here’s the problem. If you are in a nose-down attitude and are in a spin, what do you do? Stop the spin, of course, and pull out of the dive. In a spin, the inboard wing is stalled. You need to move it through the air to make it generate lift. The drill is to and neutralize the ailerons and elevator and apply opposite rudder. The rudder stops the spin by allowing the inboard wing to gain flying speed. At the same time, the nose drops more. Pull off the power so you don’t rip the wings off. Now you’re diving steeply, but at least both of your wings are flying. Slowly pull back on the stick/yoke. If you pull to fast your wings will fail and depart the airframe. This is not a good thing. When you gradually bring the nose to the horizon, you can apply power and keep flying.

But what if you’re low and slow? Plus you don’t have a rudder? Suppose the problem is compounded by the loss of an engine? Basically, you’re screwed.

10

Gotta remember - 99% of the media aren’t pilots, either. Including the guys doing the 3-D animations.

OK, first lesson. The part of the tail that sticks up vertically is actually two parts. One part is the vertical stabilizer and it does, indeed, stabilize the airplane. It keeps it from swinging left and right (from the perspective of someone aboard the plane) in an uncontrolled manner. The other part is the rudder, which is used to counteract adverse yaw. In laymen’s terms - it helps with the steering. Now, there is no question that a plane can fly with part of this apparatus missing - passenger airliners are engineered with an ample margin of safety in as many systems as possible - but the whole damn vertical stabilizer and rudder snapped off

Now, we also know that there was some sort of engine problem at some point in this short flight. In a multiengine plane, when one engine quits the half of the plane it’s attached to slows down and the other half continues on it’s merry way. So, from inside the plane, the airplane is yanked to either the right or the left until the pilot gets things sorted out. How does he do that? With the rudder… oh, wait, in this case the rudder is missing…

IF the two engines had remained running the plane MIGHT have been controllable – but as soon as the first engine quit, with no rudder available, the pilots would not be able to regain control. At best, the plane would turn in a tighter and tighter circle until it ceased to fly for a variety of aerodynmic reasons I won’t attempt to explain unless you’re really really interested.

Also - flaps will invariably steepen a descent. In a “nosedive” situation extending them will have little, if any, effect. In fact, in the planes I fly (admittedly, not jets or airliners) the FIRST thing you do in a “nosedive” is get rid of the flaps as soon as possible because they will delay your recovery and resumption of normal flight.

If that isn’t clear I’ll try again. I usually manage to piss off both pilots and non-pilots at the same time with my explanations (too detailed for the former, not enough for the latter).

Well, they might indeed have lost hydraulics, but I’d say having the jet disassemble itself in mid-air was really the heart of the problem here. It IS possible to survive a complete and total hydraulic failure - the (in)famous Sioux City crash is an example. Which is not to minimize the seriousness of such a circumstance - hydraulic failure is a Bad Thing.

11

simulpost!

Well, if we can’t get that cleared up between Johnny and me I just don’t know what we’re gonna do…

12

In 1985 a Japan AirLines 747 suffered a failure of the aft pressure bulkhead that resulted in loss of the vertical stabilizer (and the hydraulic system).

The crew fought and struggled with the airplane for quite some time, actually got it turned around in the general direction of the airport, using engine thrust, but finally called out that the plane had become “uncontrollable” shortly before hitting a mountain.

A brief report:

http://aviation-safety.net/database/1985/850812-1.htm

13
      • As I understand it, no aircraft specifically needs a rudder to maintain flight, and it is possible to fly any airplane without using the rudder: what controls its left-right movement is how much it is banked, and a rudder is just an easy way to make quick adjustments to that. - MC
14

MC, a conventional aircraft can be flown without rudder but not without a vertical stabilizer. Note conventional. Exotic aircraft like the X-31 have other devices to control yaw. The Japanese 747 demonstrates that problem.

Assuming both engines are working, adverse yaw is the real culprit. It’s pretty easy to understand.

When you want to roll right you want the right wing to go down and the left wing to go up. So the aileron on the right wing goes up, reducing lift on that side. The aileron on the left wing goes down, increasing lift on that side.

By dropping the left aileron down that causes increased drag. On the right, the aileron doesn’t cause as much drag. So even though you’re rolling right the nose goes left at first. Normally you use rudder to counteract that yaw.

Possibly some aircraft can fly without rudder, given enough altitude to practice. But the vast majority will be uncontrollable.

15

An airplane can be designed to fly without a vertical stabilizer, but if it isn’t, then it won’t fly without one. Sounds simple enough, eh?

Airplanes are designed to have positive stability. That means that when they are upset from straight and level flight, they will tend to return to it on their own (there are some unstable aircraft, but they require active computer control to fly. There are also planes designed with neutral stability, like jet fighters and aerobatic planes, but they aren’t certifiable for commercial passenger flight). But you don’t want to have TOO much stability, because it makes the plane sluggish on the controls, burns more fuel, etc.

Now, when you are designing a plane, you don’t over-design it. You put just the stuff on it that it needs to fly. There are directional-stability certification requirements, and the tail surface will be added to the airplane in order to provide it. No more, no less. So if the tail is there, it needs to be there.

Without the Stab, you might be able to maintain some kind of directional control with just the engines, or the aircraft might be totally uncontrollable. I wouldn’t hazard a guess without seeing engineering data for the plane’s design. But it’s not guaranteed that it will be controllable with the engines for one simple reason: the engines have a spool-up time, kind of like the mother of all turbo lag. If the period of oscillation of the instability is faster than the spool up time of the engines, then they will lag behind and won’t do the job. Plus, the pilots have to be up to it. And they have to realize what’s going on. And they have to have enough reserve thrust.

The Sioux City crash was different. Yes, the pilots used the engines to control the airplane. But the basic stability of the airplane wasn’t affected by the damage - the movable control surfaces were just frozen. So gradual power inputs could be used to slowly turn the plane. That’s a far cry from trying to keep an unstable aircraft in the air.

Think of the difference between hanging a pencil from your fingers, and trying to balance the pencil from below on the tip of your finger. In the first case, the pencil is stable. In the second, it’s unstable. Now if you wanted to move that pencil to the left, in the case of the stable one you could give it a nice, slow gentle push. The unstable one requires sharp inputs, and trying to move it in a certain direction takes a complex series of rapid adjustments. Now imagine that whenever you tell your finger to move there is a 3 second delay before your finger actually moves. That wouldn’t have much effect on the stable pencil - you could still get it where you want it to go. But it becomes completely impossible to balance the unstable one.

16

MC: Some aircraft need very little rudder to turn. Others require a lot of rudder. “Step on the ball!” That’s what some instructors are fond of saying. (They also like to say things like “Come on! This is supposed to be fun!” and “Look outside of the airplane!”) The ball is part of the turn coordinator, an instrument that depicts wings to show the angle of bank and a ball to show sideslip. A coordinated turn is made when the tail of the airplane follows the same arc as the nose, and the airplane does not change altitude. If you don’t use rudder, adverse yaw causes the tail to slide into the turn and the nose to point outside. You need to use the rudder to make the tail track correctly. When you bank, you also change the direction of the lift vector. Let’s assume you’re flying an airplane that weighs 1,750 pounds and that you are in level flight. The wing is generating 1,750 pounds of lift. If you bank, the wing is still generating 1,750 pounds of lift, but it is generated in a direction that is not perpendicular to the 1,750 pounds of gravity that is pulling you down. Thus, you need to increase the pitch (with the elevators/stabilator) to increase the lift vector such that you maintain your altitude. Well, you don’t get something for nothing. Now you have to increase power to keep everything in equilibrium. So there’s a lot of things going on, and rudder control is very important in most airplanes to make a coordinated turn.

There’s also the matter of torque and “P-factor”. Torque can be attenuated somewhat by mounting the engine such that the thrust vector is off-centre. “P-factor” is noticed on takeoff when the air swirling off of the prop hits the airframe and causes it to roll. On takeoff, you need to put in a little rudder to keep things straight. (I’ve read a couple of articles debating the effects of torque and “P-factor”, but as a heli pilot the debate doesn’t affect me. Helicopters have “anti-torque pedals” instead of rudder pedals.)

The Alon Ercoupe was unique in that it was originally built without rudder pedals. The rudders (it had an “H” tail with two vertical stabs) were interconnected to the yoke and it did not have rudder pedals. Many of these aircraft were retro-fitted with rudder pedals so that the pilot would have direct control.

Rudders are also very important when you’re flying a conventionally-geared aircraft (i.e., a “taildragger”). You need some way to keep the nose pointed foreward when the tailwheel (assuming it’s steerable) is off the ground.

As I’ve already mentioned, rudder control is necessary for spin recovery. Rudder is also used in stall situations, as levelling the aircraft with ailerons will cause adverse yaw and may cause a spin.

So rudder control is something that is needed in almost all airplanes. Airplanes can be flown without rudder. They can even be flown without elevators. I remember reading about single-channel R/C flyers who controlled pitch with the rudder by allowing the model to bank and then using “up-rudder” to climb. People tend to think of airplanes as extremely complicated, precision machines. Which they are. But it’s really amazing how much can go wrong and the aircraft can still fly. Look at the bombers on the site Whack-a-Mole linked. The problem is that while a severely damaged aircraft can often still fly, it’s the landing that everyone is worried about. Landing is a precision maneuver where the goal is to run out of flying speed and altitude over a specific spot, in a specific direction, and at a fairly specific descent rate. To do this successfully, a rudder is generally considered “necessary”.

I have the same problem Broomstick does. Either I’m too detailed, or not enough. I often omit things for what I consider clarity, then someone comes in and says, “Yeah, but…” Also, I haven’t flown a fixed-wing aircraft in 9 years (helis are so much more fun! :slight_smile: ) so I may misstate things from time to time. But there are 20 or 30 pilots who post to these boards, and I’m sure that between us we can answer anything flying related.

17

Heh. Triple simulpost!

FWIW, helicopters are inherently unstable (much like their pilots? :wink: ). That is, they have “negative stability”.

18

You are quite mistaken! In fact, vertical stabilizers are very undesirable in combat aircraft. They contribute hugely to the radar crossection of a jet and therefore its chances of being located and targeted by enemy weapons systems. Nasa has been working on the X-36, an experimental “tailess” aircraft for almost five years.

It isn’t just the Northrup YB-49 “flying wing” style (the B2’s grandaddy) of of aircraft, or even the modern B2 bomber. They are working on aircraft that fly perfectly well without a vertical stabilizer of any sort. Much of this work began on the X-31A, a development platform that had a very truncated vertical stabilizer. A lot of the recent work is dependent upon “vectored thrust” technology. The net result will be even more low-observable profile planes than we already have. Say hello to the next generation of stealth!

19

As Drake Christensen and Sam Stone pointed out, an aircraft can be designed without a vertical stabilizer (or horizontal ones for that matter). Aircraft design is a study in compromise. The examples you give can certainly fly without tails. That’s the way they were designed. But that comes at a price. Tailless aircraft are often designed to be fighters. Fighters require maneuverability. As Sam said, the less stability in an airframe, the more maneuverable it is. Modern fighters are designed to be unstable in flight. This is compensated for by computers that input the correct control movements to make them appear stable to the pilot. The trade off is that you need more complex and more expensive systems than you would have in, say, a typical GA aircraft. They also tend to have much more powerful engines, which are also an added expense. (I mentioned that helicopters are inherently unstable, but the instability is easily compensated for by their mechanical control systems. The pilot learns to subconsciously apply the correct control inputs. Quite Zen, actually. :wink: ) Also, low observability is not desireable in civilian aircraft. They even carry transponders to make them easier to “see” on radar.

However the OP is asking whether an aircraft designed with a tail can fly without one. The short answer (as can be seen by the larger answers previously posted) is No.

20

Many years ago I used to fly R/C model airplanes and unless I wanted to do a slow roll or a spinning dive I never ever used the rudder. Bank with the ailerons and pull up on the elevator and you could make any turn you wanted. Plus we had a small paved landing strip and I could set that baby down as soft as a baby’s ass anywhere on that little strip.

Now flying model airplanes is obviously a lot different from flying the real thing, but why did I find rudder control almost entirely useless?