Naked Science Forum
General Science => Question of the Week => Topic started by: thedoc on 05/05/2009 19:11:49
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Can you do aerobatic stunts like a loop-the-loop or a barrel roll in large aeroplanes such as Airbus A380s and Boeing 747s?
Asked by Dave, Essex
Hear this Question on our Podcast (http://www.thenakedscientists.com/HTML/podcasts/show/2009.04.25/)
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We put this firstly to Disk Schleh, of Boeing Commercial Airplanes in Seattle, Washington:
Well a large passenger jet such as the Boeing 747 or almost, almost any large passenger jetliner was not designed nor was it tested, nor was it certified to perform aerobatic manoeuvres like a loop-the-loop or a barrel roll.
[img float=left]/forum/copies/RTEmagicC_800px-Utterly.butterly.aerobatics.arp_02.jpg.jpg[/img]Certainly the wings of the airplane would be put under quite a bit of stress and some of the tail structure and so forth, doesn’t mean it couldn’t do it but they were not designed that way and they were certainly not certified with that in mind. In the early days of the jetliners when the jetliner was being developed at the Boeing company in the 1950s there was a prototype called the 367-80, that was the 707 prototype and the original test pilot on that airplane was Tex Johnston and one day he was asked to fly the aeroplane over a major event here in Seattle which was called the Hydroplane Races, so he did in fact fly the aeroplane at a fairly low altitude over the crowd but then he decided to really impress the crowd so he did a barrel roll with that airplane, much to the surprise of the Boeing officials who were watching from down below.
But he felt that it was a good demonstration of the aeroplane’s capability but he was strongly reminded never to do that again and indeed, as far as I know, it has not been done again at least certainly not as part of our test operation here at Boeing.
We then asked Peter Merton, Resident Research Officer at the Imperial War Museum at Duxford.
The simple answer is frankly, no. The critical points about, well not just modern passenger jet airliners but airliners built in the past during the 20s and 30s coming forward in time is that they are designed to be load carriers. So they are designed to withstand the quite severe adverse weather conditions, to be able to carry passengers and cargo in safety and especially now-a-days of course with the long-range jets to carry a lot of fuel.
So they are perfectly capable of some quite violent manoeuvres in terms of things like steep turns and I have seen them being flown with a very graceful positional flying, doing quite steep dives and climbs but not of course with passengers or cargo on board. This is the big difference that they are designed to be strong and robust and particularly to have a good survivability factor in case of an accident or a crash landing whereas the purpose designed aerobatic aircraft or even other aircraft types like fighter aircraft, can cope with the stresses and that is the critical difference really.
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"Can you do aerobatic stunts like a loop-the-loop or a barrel roll in large aeroplanes such as Airbus A380s and Boeing 747s?"
Once.
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I would imagine any stunts would have to be done quite slowly, if at all, as the large planes won't be very maneouvreable.
That said, I have seen a DHL-branded 747 cargo plane flying extremely slowly and extremely low over the sea at the Eastbourne Airshow...
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Is he asking about people inside the plane or the actual planes doing the tricks?
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As long as the manoeuvre is within the g ratings of the aircraft, no problem. A barrel roll is an approx 1G manouevre.
+3g to -1 appears to be a typical recommended operating envelope on a very quick web search. That has intrigued me, and I may update this post further.
Here is the most famous example:
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Can you do aerobatic stunts like a loop-the-loop or a barrel roll in large aeroplanes such as Airbus A380s and Boeing 747s?
Asked by Dave, Essex
For the most part, nope.
The vid that Edster links to is worth watching, and listening to; you'll hear Tex Johnson clearly describing the maneuver he performed in the Boeing 707 prototype as a Chandelle. While this may look a bit like a barrel roll it's actually a lot different and isn't actually classed as an aerobatic maneuver but as a turning maneuver. Having said that, it's not usually extended so far.
There are three main reasons why an airliner can't/shouldn't perform aerobatics: The airframe isn't designed to handle the stresses, they lack sufficient power (unless empty), and the flight controls lack sufficient authority to maintain the maneuvers.
Let's use a true barrel roll as an example, where the aircraft rotates about its longitudinal axis. As the aircraft starts to roll, a centrifugal force is applied sideways to the engine nacelles, and while the nacelles are designed to transfer the power generated by the engines to the wing, the forces they must withstand are always along the axis of the engine, not sideways to it. Thus, as a consequence, unless the roll is very slow, the centrifugal force will detach the engines.
However, trying to roll the aircraft very slowly brings its own problems. Because gravity always acts downwards, regardless of the attitude of the aircraft, as soon as the wings are not level they generate less lift than normal, and of course, when the wings are vertical, they generate no lift at all. In a slow roll then, as the roll approaches 90 degrees, the only things generating any lift are the fuselage and the rudder, and to get sufficient lift from them would require a relatively high Angle of Attack (AoA - this is the angle of the lifting surface relative to direction of movement through the air), which as the axis of the aircraft have been translated 90 degrees, is equivalent to extreme yaw, which in turn results in very high drag. As the airliner approaches this point it'll find that the rudder lacks sufficient authority to maintain the AoA needed, and the induced drag, combined with effective yaw relative to the engines, effectively reduces the available power. There is also a very good chance that the AoA required could stall the tailfin/rudder, leaving no effective flight controls.
A loop is more feasible, for a lightly loaded airliner, because the major forces act in the 'normal' directions i.e. along the axis of the aircraft, and effectively downwards, even when the aircraft is at the top of the loop. Even then though, the size of the loop must be carefully chosen; too tight a loop will increase the G-forces experienced to the point where the aircraft may either break up or end in a G-stall (this is where, due to G-forces, the effective weight of the aircraft increases beyond the lift available to support it). Too large a loop, on the other hand, means that the aircraft won't be able to maintain sufficient speed as it climbs up the loop and will stall.
There are also issues concerned with things like the thickness of the skins covering the airframe; these are no thicker (and stronger) than normally needed on an airliner to save weight, but all the aerodynamic forces that we've been discussing act via the aircraft skin, and once the skin strength limits are exceeded the skin will start to disintegrate.
Some large military aircraft have been rolled and looped, but only the very strongest ones; the Vulcan being a good example. It was, in any case, a very rigid and strong design, but the engines were sited inboard, close to the fuselage, so suffered relatively little during rolls. The Low Altitude Bombing System (LABS) used by Vulcans and developed during the cold war after ground-to-air missiles developed that could reach the highest flying bombers, involved approaching the target at low level, typically a few hundred feet agl, and then pulling up in to a loop, with the bomb being released just before the aircraft reached the vertical. The bomb was therefore lobbed up in the air, and towards the target, while the bomber continued on it's loop, rolling back level at the top of the loop and facing away from the target (I was lucky enough to see this demonstrated at an airshow and it's quite a sight - there are some clips on u-tube).
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The vid that Edster links to is worth watching, and listening to; you'll hear Tex Johnson clearly describing the maneuver he performed in the Boeing 707 prototype as a Chandelle. While this may look a bit like a barrel roll it's actually a lot different and isn't actually classed as an aerobatic maneuver but as a turning maneuver. Having said that, it's not usually extended so far.
This edited piece of film inserted in the interview has caused so much argument on forums. The edit does not align the pictures with the voice over or give an explanation of the terms
The description in the interview of a roll, preceded by a Chandelle applies to this better quality piece you may find here:
http://www.avpics.de/mov/civ/tex_roll.avi
My post started from my memory of 25 years ago I`m sorry I was lazy and picked the first google illustration.
In the film you can see a powered banked climbing turn, followed by a roll, in which the axis of roll is substantially higher than the axis of the fuselage.
This still equates to a chandelle followed by a barrel roll in all the limitations of both definitions I`m aware of that haven`t changed since after the web.
If the roll axis falls within the fuselage area, it is a flavour of aileron roll as there is no helical movement about an external axis. Sorry.
The manouvre was repeated on the same flight too.
25 years ago with some other engineer friends over beer, we discussed the same topic, one of our number had then become a Resarch Aerodynamicist, and his pronouncement was any 1G manoeuver is unconditionally safe, and having seen that film (incidentally described as a barrel roll) as part of his undergrad aero degree, said he admired the bravery of the pilot; not for the move, but for the chewing out on landing by those that didn`t understand how safe it was.
Airliners.net have a general for g not too far from that I remembered: http://www.airliners.net/aviation-forums/tech_ops/read.main/233503/?threadid=233503&searchid=236256&s=aerobatic#ID236256
Reply 7, posted Tue Aug 26 2008 03:55:26 your local time (8 months 2 weeks 3 days 16 hours ago) and read 1220 times: Support Airliners.net - become a First Class Member!
Modern aircraft certified in transport & normal catagories are designed to withstand approximately 3.5 positive (wings bend up) & 1.5 negitive (wings bend down) G forces. If you are in a non aerobatic airplane wings bending down would be a very bad situation.
During the certfication process on the 777 Boeing demonstrated an approximate wing bend of 19 feet in the up direction at the tip. That was over 150% of the design load limit.
This is normal flight envelope. There are transient g ratings including g bump landings in excess of these by far larger margins than 150%.
ALL of the aircraft must be able to withstand this, from the overhead lockers to the wings and fuselage, the fixing of the cabling inside the aircraft etc. Oh and the engines.
It would appear that more modern airliners will not be able to do any "aerobatic" manoeuvres due to set limits in the fly by wire, for example most airbus aircraft have a fixed bank limit of around 60 degrees so a roll would be off the menu ( except on the inflight catering) [:)]
So for those 2 mentioned it looks like no.
Sorry. no rolling aibuses at shows then.
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One thing that nobody mentioned- Concorde could do barrel rolls; they actually did it.
During the test program the French test pilot (I think Turcat) was sitting next to the British one (Walpole) and he rolled it; and then invited the British pilot to 'unroll it' again, so he did.
They didn't ever do it with passengers onboard though; strangely they thought it might make them nervous. [;D]
See:
But as others have implied, I'm pretty sure that all aircraft can do a barrel roll or similar; this is a maneuver that can be done at 1g throughout; and basically all aircraft can take it; although you might have to turn off some of the computers in some of the modern ones.
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If memory serves me, they should be rated at +3\-1.5g's. If you can maintain these limits they will all do it. I have always been told that the 707 is structually sound enough to do the loop, but the circle, up and down air space needed to complete it the 707 wouldn't make it, just can't fly high enough to do it and not strong enough to pull out at the end of it, the harder you pull the more g's created, eventually the wings say, enough for me, I'm going somewhere else.