[John Cleese]
Look, if I’m to argue with you I have to take a contrary position…
[/John Cleese]
Ring, you still had a stabilizer, though, right?
Also, according to a Wings episode on the flying wings, the YB-49 actually was stable, from an aerodynamic point of view. But it was not stable from a bombing platform point of view.
A pilot described how when coming out of a turn your conventional aircraft will swing two degrees wide, then one degree the other way, then a half degree back, and then settles down. In contrast, the YB-49 will occilate a degree back and forth for quite awhile before damping out.
So, it flew just fine. But it made some bombadiers sick when looking through the bomb sight.
JAL 123 is the flight I thought of when I read the post. I always wondered if that aircraft could have been landed despite the damage to the tail assby if they had not lost hydraulics. The aircraft had lost the rudder but I think about half of the vertical stabilizer was still in place.
With operable control surfaces the pilots of JAL123 would have probably had a chance. Despite losing control and fighting severe oscillations and a dutch roll condition (easiest way to describe is the wingtips moving like bicycle pedals, for more info see here) the crew was able to keep the plane at an attitude that allowed a couple of folks to survive when it finally hit the mountains.
Speaking of losing major flight surfaces, Peter Garrison in this month’s Flying tells and analyzes the flight dynamics involved with an Israeli F-15 that lost an entire wing in a mid-air collision and was flown home. His column isn’t on line, yet, but read a version of the story here: http://www.tailslide.firelight.dynip.com/f15wing.asp (pictures included)
A few things I haven’t seen mentioned, yet.
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The vertical fin has got to be fairly heavy. Once it comes off, the plane’s center of gravity is going to move forward, maybe too much for the elevator to compensate for.
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All the independent hydraulic systems on the plane (I’ve been hearing that the A300 has three) must have lines going up the fin to the rudder actuators. When the fin comes off, that would sever the hydraulic lines and all the systems could lose pressure. Combined with #1, that could be a real handful for the pilots.
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Swept-wing aircraft are susceptible to a phenomenon called dutch rolls. Say the plane yaws slightly to the left (gust of wind, whatever), now the right wing is meeting the oncoming air at a more direct angle than the left. That makes the right wing generate more lift, so that wing starts to lift. Adverse yaw kicks in at this point, that slows the right wing. That yaws the plane to the right and now the left wing is meeting the airflow more directly. Left wing now lifts, adverse yaw, etc., setting up a kind of oscilation. Without a vertical stabilizer, the oscilations can increase in magnitude until something very bad happens. That could also explain why World War II bombers could survive similar damage, they had straight wings.
(I just previewed and saw Boxcar’s post, but I’m leaving mine as it is.)
Keeping in mind I fly small planes…
It’s true, rudder is not absolutely essential to flight. My husband once lost a rudder cable in a two-axis ultralight and still managed to land safely and walk away. While studying for my license my instructors took me through various drills to simulate serious failures, including loss of rudder control.
Improper use of rudder (including lack of use) results in sashaying of the airplane in a turn, deviation from course in climbs or descents, and various other less-than-perfect results of steering inputs. The further you are from the center of gravity the worse the swaying and “wallowing” sensations. A lot of people find the motion disturbing and/or nauseating. It can result in a reappearance of breakfast.
So, I don’t need a rudder. I also don’t need to clean puke out of the interior of the airplane which is why I use one.
You can get away with the no-rudder trick in a model plane much easier than a full size one because there’s no one aboard the model to complain. And an RC model may have more power-to-weight and the RC modeler is probably not as concerned with maximum fuel efficiency as an airline is.
We have an unmodified Ercoupe at my field which flies very well - but it was designed to fly without rudder pedals and, in fact, does have rudders, just not under direct pilot control.
Another problem with not using the rudder is that the “sloppiness” that results reduces the efficiency of the airplane. In cruise flight this is not such an issue because you have power to spare and you’re pretty much maintaining a straight line. On climb-out, just after take-off, you’re typically at maximum power, or close to it, so have none to spare. A reduction in aerodynamic efficiency at that point in the flight can render the plane uncontrollable.
At one point on the cockpit voice recorder one of the pilots call for “max power” - my WAG is that was an attempt to use power to compensate for the control problems.
On this flight, they were also turning (a less stable situation than level flight, which requires compensating rudder input) and part of the plane had physically come off - altering the weight and balance of the airplane (and that, by itself, can render a plane uncontrollable). The hydraulics may have also failed. THEN an engine falls off, furthering altering the weight and balance of the airplane. (A DC-10 in 1979 had an engine drop off just after take-off and was not controllable even though it had a fully functional tail and hydraulics)
In other words, these guys had several problems to deal with, and several of them just by themselves could cause a crash. To have them happen simultaneously… well, this is not a situation anyone wants to be in.
I seem to recall an incident that a B-52 lost almost all of its tail and landed without much difficulty. The crew didn’t even know there was a problem until they were radioed and told it was missing.
I’ll try to find a link/cite.
I didn’t intend to weigh in on this, but I wanted to point out that with the current (as of the last news broadcast I watched this morning) theory, the rudder and stabilizer detached, and the severe yaw that resulted caused the engines to separate. Not quite simultaneous, more of a cause-and-effect.
Now, it should be pointed out that the engines are designed to separate under situations of extreme stress, the idea being that dealing with sudden asymmetrical thrust is better than having a burning engine hanging on to a wing full of fuel. Unfortunately, the violent forces at work on the airframe in this case (caused by loss of the vertical stabilizer and rudder) caused both engines to detach right when they were needed the most…and both engines were apparently in perfect working order right up to the point where they hit the ground.
Take a closer look at your YB-49 pictures. The YB-49 actually did have vertical stabilizers (although I don’t know if they had rudder controls on those stabilizers or not). Instead of one big vertical stabilizer the plane had 4 (I think) little ones.
If you go even further back than that, the Gotha brothers in Germany (prior to and during WW2) had some very advanced flying wing designs. Almost all of them had stubby stablizers but a couple didn’t (The GOO9 for example).
Amazing aircraft if you remember they’re 50ish year old designs.
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- There’s two questions here: if a jet can survive losing its rudder in flight, and if any airplane needs a stab/rudder to maintain flight. The first I don’t know, but the second I have seen multiple references that it is false. I don’t have any cites, but if a stabilizer is necessary then how come birds don’t have them? - MC
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While in the business I talked to a DC-10 Captain who had flown that problem (along with Sioux City) in a simulator. The loss of the engine on the DC-10 did not affect the controllability of the aircraft directly. In fact, the aircraft could have been safely flown to a landing. The pilots, trained in these emergencies, flew as they were taught, but the book was wrong and they didn’t have the altitude or time to figure it out. 5kts of airspeed killed that airplane.
From the NTSB Report
The book says that on engine loss in takeoff configuration the aircraft was to be flown at 154kts (IIRC). So after takeoff, the aircraft continued to accelerate through 160kts and then began to slow to the recommended speed.
When the pylon seperated, hydraulic pressure that locked the slats in place on the left wing was lost and the slats were pushed back into their retracted mode. This changed the stall speed of that wing to 159kts. As the aircraft speed dropped below 159kts to the recommended 154kts, the left wing dropped, the nose went over, and all was done.
After the accident, American and other DC-10 operators rewrote their books to recommend a higher engine out speed.
They do have them. They’re variable-geometry two-axis units located aft of the exhaust outlet.
Second question first - birds DO have stabilizers. Johnny LA put it more poetically, but basically we’re talking tails here. But do keep in mind that birds, in addition to making constant adjustments while in flight (just as we make constant adjustments while walking or running) have variable geometry - meaning their wings/feathers/tails change shape and aerodynamics while in flight - and are propelled by flapping, not propellors or jet-thrusting. There ARE some significant differences between bird-flight and machine-flight.
First question second - IF an aircraft is designed to fly without a rudder and/or vertical stabilizer then yes, it can maintain flight without one. IF, however, an aircraft is designed to have a rudder/vertical stabilizer then it requires one for normal flight and lack of one, under at least some circumstances, can have disasterous effects. So it depends on the aircraft. An Airbus 300 is designed to have and use both a rudder and vertical tailfin so the loss of them would have pretty serious effects. Would it doom a flight? Well, maybe not for certain, but having other things go wrong at the same time or shortly thereafter would make a Bad Thingsub[/sub] very much worse.
Well, I don’t think anyone used the “simultaneous” word. Sure, severe yaw could contribute to the breakup. But, wow, it would have to be amazingly severe.
If wake turbulence contributed/caused the breakup that alone - without yaw, could have theorectically caused a breakup as well.
Or maybe it was the combination of the wake AND the “severe yaw” - neither of which sufficient alone - which caused the breakup.
Huh? Never heard of that. Where did you get that?
There are means to cut the fuel flow off to a burning engine - I’ve even been aboard a DC-10 where this was done. That’s usually sufficient to put out the fire.
Now - dropping an engine would most definitely alter the weight and balance. I can’t imagine that being the first choice for dealing with a burning engine.
Most high-bypass jet engines are designed to detach from the aircraft in extreme circumstances - I think the issue has nothing to with the engine burning, but with the very high drag those huge engines would create if the fan stopped spinning (normally when at idle or shut down the fans still rotate. It still causes some drag, but not nearly as much as if the engine were to fail catastrophically and the fan came to a dead stop).
In fact, I seem to recall an incident a few years ago with an engine on a 747 that fell off in flight because the shear pin wasn’t in place (the shear pin being the device that is designed to fail and let the engine go).
I guess I’m too late to jump into this one with much gusto, I think the pilots here have done a pretty good job.
But, Sam and Kiltman, engines designed to drop off under stress? You gotta be kidding.
A comment on news coverage - I have a running joke with a few of my fellow engineers at work. A few years ago, the NBC “Science correspondent” (can’t remember his name, but he’s still around) was talking about an airline crash. He referred to the horizontal stabilizer as “that flat part on the back”. Now, whenever we’re talking about tail surfaces at work, somebody always brings up - “you know, that flat part on the back”.
The breakaway engine mounts on airliners are designed and engineered as a last resort to prevent even further damage to the plane. For example, the rotating parts of a jet engine have signifigant mass, and if the bearings were to suddenly seize, the engine would tend to twist very violently. You want the pylon to break away at a force below that which would bend the wing. Losing an engine is bad, bending a wing is worse.
Kelly: If you engineer the engine pod to break away only under enough force that would damage the wing structure if it didn’t, then you really aren’t giving up anything. If the engine generates that much force on the structure through some malfunction, *something very bad is about to happen. It turns out that often the best thing to do under such circumstances is to just let the engine go on its way.
I imagine another reason for breakaway pods would be in case the engine hits an obstacle on the ground. You’d rather have the engine rip off than the entire wing, or even worse perhaps pull the whole aircraft and cause it to cartwheel.
I’m going to have to say this sounds like complete and utter nonsense to me. Really. Unless you can come up with something other than “I heard from somewhere…” to support this.
I have actually been on an airliner with a sudden engine stoppage and fire (on take-off, yet). Yes, when the engine got hit the entire airplane yawed to the right. It was a distinct and unpleasent jerk. The fire was contained (probably the fuel feed shut off) but the engine did not drop off. Although the airplane clearly did not fly as efficiently as before, fly it did, under control, to a safe landing.
Yes, a stopped engine causes drag. But I completely do not understand how dropping said engine is going to improve things - it will drastically alter the weight and balance of the airplane. Keep in mind that the wing acts as a lever - the mass of the engine, mounted out on the wing, exerts quit an effect and losing it will make that wing rise - to counteract it you’ll need to use rudder and aileron, both of which will cause drag and reduce flight efficiency even further than the asymetrical thrust.
How are you going to detatch it neatly? If it just tears loose at the very least your going to have fuel pouring out - combine that with a fire it’s going to get even uglier. If it just rips loose you risk damaging other parts of the wing.
Also, when an engine quits, although you do get a yaw, it’s not strong enough to rip engines loose - so… what’s the point, here? If it’s to eliminate the drag of a dead engine, and the dead engine usually doesn’t drop off…?
On the face of it, this just does not make sense to me.
I hope this isn’t a silly question, and I’ve a feeling we’ve addressed it (partially) before, but to what extent can a large jet glide? How would its ability to glide be affected if its engines were lost/jettisoned?