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 helical path, approximately maintaining its original direction. It is sometimes described as a "combination of a loop and a roll". The g-force is kept positive (but not constant) on the object throughout the maneuver, commonly between 2 and 3g, and no less than 0.5g. The barrel roll is commonly confused with an aileron roll.
Etymology
The barrel roll is so named because an aircraft executing this maneuver looks as though it were flying with its wheels running around the inside wall of a cylinder, or an imaginary barrel lying on its side. A more common modern visualization is to imagine an airplane trying to fly in a horizontal corkscrew around the line of the direction of travel. Although the maneuver predates the name, the term was first used in 1917, gaining popularity during the early 1930s.
Aviation
In aviation, the barrel roll is an aerobatic maneuver in which an aircraft performs a helical roll around its relative forward motion, with the nose ending up pointed along the original flightpath. It is performed by doing a combination of a roll and a loop. The maneuver includes a constant variation of aircraft attitude (nose orientation) in two or perhaps all three axes. It consists of a rotation along the pitch axis (nose rotates upward, in a direction perpendicular to the wings) through the application of elevator input, followed by aileron input to rotate the aircraft along its roll axis. Sometimes rudder input is applied to help assist the roll through the yaw axis (nose rotates sideways), by swinging the tail over the top. At the midpoint (top) of the roll, the aircraft should be flying inverted, with the nose pointing at roughly a right angle to the general flightpath. The aircraft will have also gained altitude and travelled a short distance from the original flightpath. Flying inverted, the plane continues through the roll, descending in altitude and returning to the original flightpath. Upon completing the roll, the airplane should end up flying along the same flightpath, and at roughly the same altitude at which the maneuver began.
The term "barrel roll" is frequently used, incorrectly, to refer to any roll by an airplane (see aileron roll, slow roll or snap roll).
History
The barrel roll was originally called a "side somersault". It was first performed in 1905 by Daniel Maloney. He was flying a glider owned by John Joseph Montgomery during an exhibition show, which was lifted by balloon and then released. During this particular show, Maloney did a very hard turn, causing the wings to warp, performing the maneuver quite by accident, but was quickly followed by his companion flyer, David Wilke, who did two barrel rolls in a row; one to the left and the other to the right.
Outside of aerobatic competition, the Boeing 367-80 and Concorde prototype were barrel-rolled during testing. The Boeing 367-80 was rolled twice by Tex Johnston in an unauthorized maneuver while demonstrating the aircraft to the International Air Transport Association over Lake Washington, Seattle. The Concorde was rolled multiple times by its test pilots, including Jean Franchi and Brian Walpole. Avro test pilot Roly Falk rolled the Avro Vulcan during a display at the 1955 Farnborough airshow, gaining height during the maneuver.
Execution
To do a barrel roll in its purest form, from the pilot's perspective, it may best be thought of as a roll around a point on the horizon that is 45 degrees off the flightpath. Starting from a level flight, the pilot will usually pick such a point on the horizon as a reference, which is typically between the nose and the wing-tip, out the side window (if the plane has side windows). This point can be anything in that area, like a distant lake, mountain peak, or cloud. The pilot will then pull back on the stick, bringing the plane up into a brief climb. As the nose passes through the horizon, the pilot begins to apply aileron input, which is accomplished by easing the stick to either the right or the left. As the airplane rolls it will continue to pitch in the direction of the lift vector. The pilot will need to carefully control the roll rate, keeping the nose 45 degrees off the reference point on the horizon as the nose traces a circle around this spot. Some planes may require rudder input, while most high powered planes will only need to be guided by aileron and elevator control.