A minor quibble. What you described in your answer was an aileron roll. I once saw an interview with the pilot who performed the barrel roll in the 707. He points out that a barrel roll is a 1G maneuver. IOW, the wings generate lift towards the top of the aircraft the entire time. Almost any plane should be able to perform one.
Here’s how it works. As you start the maneuver you pull the nose above the horizon. Then you apply back pressure at the same time as you apply roll input. If done correctly, the angle of attack (the direction from which the air hits the wings) should remain constant throughout the roll.
Since you have to start with a climb, some aircraft may not be able to perform several barrel rolls in quick succession. An aircraft without a lot of excess power might lose airspeed and/or altitude with each roll. Eventually, the ground will get in the way.
Another pilot on that same show (sorry, it was years ago and I don’t remember where I saw it) pointed out that an expertly executed barrel roll is imperceptible to passengers. He gave an anecdote where he proved this to his co-pilot by performing a barrel roll without provoking comment from the businessmen who were deep in conversation in the back of the plane. He also demonstrated on-camera that he could pour a cup of coffee while performing a barrel roll.
One addition I should make might help people visualize the difference.
With an aileron roll, the fuselage of the aircraft goes pretty much straight and the plane just spins about that axis.
A barrel roll can best be described as a corkscrew threw the sky. It’s as though the plane is flying around a huge barrel, thus the name. If you think about it, the only way to get the plane to rotate and move around the barrel and keep the top of the plane pointing at the barrel all at the same time is if there’s some back pressure on the stick. That back pressure produces the percieved G force, making this a 1G maneuver.
The pilot to which Drake refers to as the other pilot on the show was the legendary Bob Hoover. I, too, have seen the same show and have seen several videos of Hoover pouring water or coffee from a pitcher into a cup sitting on the top of the instrument panel while the plane was in a roll. Hoover was the only one at the controls at the time and was flying a Rockwell Commander, a twin-engine turbo-prop business aircraft. It was without any modification for aerobatics. He also used this same aircraft to perform a standard airshow routine, including loops, rolls, Cuban 8s, and Lomcervaks (sp?) with one engine feathered.
Drake is also right about the 1G stress of a properly performed roll, as stated by the pilot who rolled the Dash 80 (prototype 707) at its 1st public showing. Now, can you loop a 747? An entirely different question.
Actually, he didn’t do Lomcervaks (who knows? but he did do all the rest. And it wasn’t one prop feathered. It was both props feathered. He was demonstrating energy management and did something like a four-minute routine without engines, all momentum. I think he finished it off with a dead-stick landing.
Not just any old dead-stick landing, but a dead stick landing after coming out of the bottom of a loop, followed by rolling the aircraft without power off of the runway, up to the airshow flight line, and stopping it within a couple of feet of the fence.
I’ve seen Hoover do this routine a couple of times at the Reno Air Races.
He also does aileron rolls in the Commander with one engine feathered and the other producing power. If you ask me, that would be more difficult than doing it with both engines shut down.
Well, ok. What’s the quibble again? Cecil was describing an aileron roll when what he meant to describe was a barrel roll? I don’t think so. Show me how you made that determination.
Or perhaps you meant he was wrong about it being “an extremely foolish action” to attempt a barrel roll in a 747, or do you mean it would be foolish only if what he was describing is an aileron roll? Why? Because you have determined that “almost any airplane should be able to perform one”? (Which? Both?)
Maybe it was Cecil’s “loss of lift” and “when the wings cease to function” statements that threw you. Did you think he meant the aircraft stalled? Perhaps quibble with Cecil’s use of the word “lift” to describe “(cease to) hold the aircraft up,”
but it was quite obvious to me what he meant.
In any event, why would an aircraft stall during a properly executed aileron roll? The angle of attack does not change. Unlike your barrel roll, an aileron roll will result in momentary negative g’s - but the barrel roll is technically not a 1 G maneuver, either, unless you don’t count the “pull the nose above the horizon” part of it, during which you have not only increased the angle of attack, but the G load as well.
Tell me again what that minor quibble was?
Here’s the original article, for those of you interested.
> Enough forward speed must be maintained during the roll to compensate for the loss of lift that occurs when, in effect, the wings cease to function.
Basically, he’s mixing in his description of an aileron roll with the discussion of the barrel roll done by the 707. In a barrel roll, one is actually gaining altitude in the first quarter of the roll even though the wings are perpendicular to the ground. That’s because one has been raising the nose and climbing while rotating up until that point.
The reason I mentioned raising the nose at the beginning of the maneuver in order to gain altitude to compensate for how much altitude would be lost while the plane was upside down while still maintaining something near 1G. If one doesn’t care about the loss in altitude then one could start from straight and level.
I guess the main point of confusion is that the original question was worded imprecisely. Todd J. simply asked if a large plane could be rolled. If one allows barrel rolls then most any aircraft can safely perform one. I’ve even seen video of a helicopter do one.
I agree with Drake, I also cringed at the wording used. Technically, the wings are functioning throughout the roll (aileron or barrel). One wing is providing positive lift and the other negative, hence the roll. Explaining that lift and therefore roll rate is a function of indicated airspeed and relating that to the aileron roll dynamics would have been more appropriate than the ‘forward speed to compensate …’ explanation. Of course Bernoulli, adverse yaw, etc. have been left out but I’ll let some experts jump in now.
Assuming the wings are at a positive angle of attack then the downward-moving wing is still providing a net positive lift even during the roll. It’s simply providing less lift than the upward-moving wing.
After reading Cecil’s explanation one more time, what bothers me is he goes through three ideas in that one paragraph. He starts off with the discussion of the Dash-80 barrel roll. He changes to a description of an aileron roll. Then he states that the plane must have enough velocity for knife-edge flight (using the fuselage for lift) in that one sentence. In a barrel roll, that’s just not the case.
Changing to the other subject of the question, I’m wondering myself if one of those aircraft could perform a successful (read: survivable) loop. What came to mind just this minute is the NASA KC-135 “Vomit Comet.” http://zeta.grc.nasa.gov/kjenks/kc-135.htm
Hmm, according to the accompanying text, the plane only pitches up to 50 degrees and down to -45 degrees on the other side. That’s a long way from going past 90 degrees. It’s hard to say whether it would be controllable at the top of the loop. And then of course there’s the question of whether they can get the nose of the plane back up to level on the bottom side of the loop before the speed got so high that it ripped something important off.
Waffling back the other way, they’ve had aircraft plummet out of control for tens of thousands of feet a couple of times and survive. I think it just might be possible with an exceptional pilot and a little luck.
Forget the LOOP! In an aircraft as heavy as a B747 (even if it’s almost empty), by the time you are a quarter of loop-up, your airspeed will be so low, that the wing will be stalling. Notwithstanding the powerful engines (Rolls-Royce RB211 for a typical B747-200), it just won’t climb to complete the first half of the loop before you reach stall speed. I don’t think there’s a pilot crazy enough to try to do a loop with an airliner.
Now, regarding the roll, maybe a barrel roll is feasible for a B747, although it is definitely NOT recommendable! There have been other large aircraft known to have done similar stuff but under very different circumstances. For example, a B727 “performed” a spin after stalling at high altitude, and the pilots recovered it. But an aileron roll would be a little trickier, although not impossible (maybe).
Now, to call a maneuver a “1G” maneuver is just pilots lingo. There’s no such thing as that. Even if momentarily, but you will always exert a force of a little more and a little less than 1G whenever you change your flying conditions (remember Newton laws?).
And please, the wings never cease to function! At least not as long as they are attached to the fuselage, and you have enough speed. What happens is that when the roll angle equals 90°, the whole lift is perpendicular to the direction of the weight of the aircraft, that’s all. To say that the wings “cease to function” is misleading.
And, Cecil: increasing the speed increases the lift OVER the wing, and THAT is what holds the airplane in the air. The pressure under the wing helps a bit, but it is a very small help compared to the lift created in the upper camber. It is a common misconception to think that it is the other way around.
Drake, I thought that the downward traveling wing actually had a negative AOA (angle of attack) due to the upward deflected aileron. Or is this in reference to the dynamics for a barrel roll only. IOW are you saying the ‘pitch up’ AOA is greater than the aileron down -AOA. Is this due to the fact that most ailerons are not full span, angle of incidence & asymetrical camber ? Do most aircraft wings (w/asymetrical camber) in general have a net positive AOA even with full up aileron ? Of course, I realize this is all in reference to roll/looping big iron, but I was hoping for some additional insight as to the dynamics of a barrel roll.
Thanks, Oblio
A point in every direction is like no point at all
I’d be careful here especially when you really don’t know any more than what you see on the discovery channel. It all depends on the camber, AOA, and type of airfoil. A flat plate for example could be more accurately descibed to fly by increasing the pressure below. Finally seperating the pressure below and above the airfoil is foolish in that they are directly related, in relative terms the pressure above cannot decrease with out the pressure increase below. Relative terms are the only ones that apply in discussing lift/drag.
The facts expressed here belong to everybody, the opinions to me. The distinction is
yours to draw…
E1skeptic, I checked your profile, so I’ll take back that Discovery Channel smack. But, I think you’ll agree that your response was extremely narrow and over simplified.
Obilo is the one at Raytheon. E1skeptic, he has this thread pretty well covered, and assuming he’s not some schmuck Comp. E at Raytheon he’ll be a bit more experienced than I.
E1skeptic, even though I got the wrong profile last time, the pilot title should still warrant my retraction.
E1skeptic, yes, the 747 is heavy. But that also means massive. That’s a heck of a lot of inertia at .8 mach. Considering that the KC-135 can get to 50 degrees with enough inertia to “coast” for about 15-20 secs before hitting the top of the parabola, I think it just might be possible for one of those to get past 90 degrees under power.
Now, will it still be controllable at or near 180 degrees? Or will it pretty much just stall and flop over the top? The latter seems likely, though not certain. A good pilot who is careful to conserve his energy could probably keep it controllable much longer that one would initally guess. Keep in mind Bob Hoover in his business twin. He might not produce a nice, pretty near-circular loop, but he should be able to get over the top.
Oh, and the “1G maneuver” phrase is intended to mean, “no undue stress beyond what would likely be experienced in straight-and-level flight.” IOW, no high positive G’s and nothing close to zero or negative G’s. For all practical purposes, 1G.
Oblio, yes, the downward moving wing is producing lift. Think of it this way. The plane is being held in the air by the wings. A 747 weighs over 500,000 pounds. A fully-loaded 747-400 approaches one million pounds. If the downward-moving wing was not producing lift then all 500,000+ pounds of lift would be coming from the upward-moving wing. That much differential would cause an enourmous roll rate With the mechanical advantage of the ailerons out on the tip of the wing I suspect it doesn’t take more than a few hundred to a few thousand pounds of differential lift to induce a roll.
OTOH, an aerobatic plane might experience negative lift on the downward-moving wing. I’m not sure about that.
at Raytheon he’ll be a bit more experienced than I.