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I was going through social media and I came across this GIF image that showed a plane doing some sort of roll.

enter image description here

It was labeled "Barrel Roll" but in the comments to the post, someone said that it was an "Aileron Roll". What is the difference between a barrel roll and an aileron roll?

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    $\begingroup$ Related: aviation.stackexchange.com/questions/22793/… $\endgroup$ – Peter Kämpf Mar 15 '16 at 2:52
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    $\begingroup$ anyone who hasn't seen Bob Hoover pouring tea while doing a roll needs to watch this: youtube.com/watch?v=yO8GyU8asEI $\endgroup$ – rbp Apr 2 '16 at 16:09
  • $\begingroup$ That is one very cool and inspirational video - and not just the pouring-water part. $\endgroup$ – quiet flyer Jul 14 at 17:55
  • $\begingroup$ One uses the aileron as the primary control surface, and one uses the barrel as the primary control surface. Generally only possible in open-cockpit aircraft. Don't forget to bring along a barrel! $\endgroup$ – quiet flyer Jul 14 at 19:13
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The difference between an aileron roll and a barrel roll is that an aileron roll's centre of rotation is very close to or on the aircraft. A barrel roll has its centre of rotation around a point further away from the aircraft itself.

The difference can be appreciated in this image:

Image showing path of plane for barrel and aileron rolls

Image Source You can find out about the difference in feeling that these two manoeuvres have.

Having stated these things, the manoeuvre shown in the GIF is certainly an aileron roll.

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  • $\begingroup$ I noticed in that GIF that at certain points the roll seemed to slow. Is this inherent to an Aileron roll or was that just some quirks of the pilot? $\endgroup$ – David says Reinstate Monica Mar 15 '16 at 14:05
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    $\begingroup$ @DavidGrinberg I see slowing down only at the very end of the video (perhaps also the end of the maneuver). Of course the apparent motion of the wingtips is faster when they are going up or down from the camera's point of view than when they are going directly toward or away from the camera, but that's only apparent motion, not the actual speed of the rotation. $\endgroup$ – David K Mar 15 '16 at 14:56
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    $\begingroup$ @DavidGrinberg: In an aileron roll, the rate of roll is fully controllable by the pilot. With the right aircraft the pilot can literally stop the roll at any point and maintain the aircraft's orientation. There is a precision variant of the aileron roll called the "four point roll" where the pilot rolls 90 degrees then pause then another 90 degrees then pause etc. $\endgroup$ – slebetman Mar 16 '16 at 1:51
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In a barrel roll, the aircraft rotates both in its longitudinal and lateral axes, while in case of aileron roll, the rotation is only about the longitudinal axis.

Barrel roll

A barrel roll, image from flightsimbooks.com

If properly executed, there is no change in alttitude in case of an aileron roll, while during barrel roll, the aircraft follows a helical path.

aileron roll

An aileron roll, image from globalsecurity.org

In short, think like this- in a barrel roll, the aircraft goes along the surface of the barrel, while in an aileron roll, the aircraft corkscrews around inside a barrel, with the wingtips grazing the barrel surface.

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    $\begingroup$ So Peppy got it wrong? $\endgroup$ – corsiKa Mar 15 '16 at 5:33
  • $\begingroup$ I heard that the definition of a barrel roll was that the aircraft was always under positive Gs. Is this accurate? $\endgroup$ – Steve Mar 15 '16 at 12:39
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    $\begingroup$ @Steve Yeah, the definition I've always heard is that a barrel roll (when executed properly) is a constant +1 g downwards manuver (meaning even large planes not capable of high g forces could accomplish one), whereas the aileron roll has an additional acceleration. $\endgroup$ – 0xDBFB7 Mar 15 '16 at 14:46
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    $\begingroup$ @DC177E You must have more than +1G in the pullup between point 3 and 4 in aeroalias diagram. $\endgroup$ – Wirewrap Mar 15 '16 at 19:15
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    $\begingroup$ i posted this above, but you can tell its a +G maneuver bc its possible to pour a glass of tea throughout the roll youtube.com/watch?v=yO8GyU8asEI $\endgroup$ – rbp Apr 2 '16 at 16:11
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There is no precise, universally accepted definition of "aileron roll". If the rotation were purely about the aircraft's longitudinal axis, then any positive angle-of-attack existing at the start of the maneuver would be converted to pure sideslip after 90 degrees of roll, and to a negative angle-of-attack after 180 degrees of roll, at least in the simple case where the wings are attached to the fuselage at zero incidence as measured relative to the longitudinal axis. Such a roll could be done with the aircraft following a nearly linear trajectory. Yet an "aileron roll" is usually described as a maneuver than can be carried out with light positive G all the way around, and no sideslip. This must involve somewhat of an arcing trajectory if the aircraft is to finish the maneuver at the same altitude it starts at, although the arc may be hard to detect in the case of a fast jet.

In short, it is not universally agreed-upon whether the term "aileron roll" should be applied to a maneuver that involves positive G, or negative G, at the point where the aircraft is inverted. The positive-G concept is the more common one.

Still, the most common conception of an aileron roll involves rotation that is MOSTLY around the aircraft's longitudinal axis and involves relatively little change in heading or pitch attitude, while a barrel roll is usually described as a maneuver involving a great deal of heading change, often 90 degrees or nearly so, as well as a great deal of change in pitch attitude.

All things considered, it's complicated. Is the aircraft rolling around its longitudinal axis, or the airspeed vector, or neither? Is the orientation of the aircraft's longitudinal axis staying fixed in space, or is the orientation of the airspeed vector staying fixed in space, or neither? Is flight path linear or arcing? If we had an "x-wing" plane with a set of vertical wings as well as horizontal wings, all with symmetrical airfoils and zero incidence, then starting from an initial slightly nose- high attitude, we could roll around the aircraft's longitudinal axis all day long with very little disturbance to the flight path. We wouldn't be able to pour water into a cup on top of the dash though. Would this be an "aileron roll"? It's hard to argue that it wouldn't be, but it's not what we usually envision when we speak of an "aileron roll".

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