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[[File:Barrel roll diagram side view.jpg|thumb|A diagram of a barrel roll]]
[[File:Barrel roll 1.webm|thumb|A barrel roll from the perspective of the wingtip]]
A '''barrel roll''' is an aerial maneuver in which an [[airplane]] makes a complete [[rotation]] on both its longitudinal and lateral axes, causing it to follow a [[helix|helical]] path, approximately maintaining its original direction. It is sometimes described as a "combination of a loop and a [[Aircraft principal axes#Longitudinal axis (roll)|roll]]".<ref>{{cite web |url=https://www.iac.org/legacy/aerobatic-figures |title=Aerobatic Figures |work=[[International Aerobatic Club]] }}</ref> The [[g-force]] is kept positive (but not constant) on the object throughout the maneuver, commonly between 2 and 3''g'', and no less than 0.5''g''. The barrel roll is commonly confused with an [[aileron roll]].
==Etymology==
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A maneuver that greatly resembles a tight barrel-roll is the rudder roll. The rudder roll differs from the barrel roll both in that the application of back-stick pressure (elevator) is usually very high and that aileron input is held neutral throughout the maneuver. Instead, roll is produced by creating a [[sideslip]] through application of rudder combined with elevator. The aircraft will roll in the direction of the rudder. This will cause the aircraft to sideslip through the roll, keeping the nose pointed at only a shallow angle from the flightpath. The aircraft will appear to slide almost sideways at a slight angle around a very narrow, helical path, more like an imaginary pipe than a barrel.
The roll rate of a rudder roll is directly related to the [[angle of attack]] and [[mach number]]. The higher the speed and the greater the angle of attack; the faster the roll will occur. The roll will tend to be more effective if the stick is pulled back until the point of [[Aeroelasticity#Buffeting|buffet]] (the turbulence that precedes a stall), and often to the maximum that the elevators will allow.
The rudder roll is typically more controllable than a barrel roll and can be performed at much higher roll-rates, but usually must be performed at very high speeds to produce the amount of energy needed to carry the slip all the way through the roll. It is generally more effective at combat speeds than a barrel roll due to the lowered effectiveness of aileron authority at higher speeds.<ref>McDonnell Douglas T-45 Gosthawk: Flight Manual 2 By US Navy Air Systems Command, 1997. Page IV-11-7.</ref> The rudder roll is a basic maneuver used by air-to-air and surface-to-air missiles for providing in-flight course corrections, often giving them an erratic-looking flight path that oscillates around its target's track.<ref>''Modern engineering for design of liquid-propellant rocket engines'' by Dieter K. Huzel, David H. Huang. American Institute of Aeronautics and Astronautics, 1992, p. 99, {{ISBN|1-56347-013-6}}.</ref>
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