Barrel roll

For other uses, see Barrel roll (disambiguation).

Barrel roll

A barrel roll is an aerial maneuver in which an airplane makes a complete rotation on its longitudinal axis while following 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 2-3 G, and no less than 0.5 G.^[1]

Etymology

The barrel roll is so named because an aircraft executing this maneuver looks as though it were flying with its wheels running along the inside edge of a barrel. 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.

Aviation

In aviation, the maneuver includes a constant variation of attitude in all three axes, and at the midpoint (top) of the roll, the aircraft is flying inverted, with the nose pointing at a moderate angle to the general path of flight. The term "barrel roll" is frequently used, incorrectly, to refer to any roll by an airplane (see aileron roll). Most often, a barrel roll refers to a helical roll around the relative forward motion of the aircraft, in which the nose ends up pointed along the flight path. It is performed by doing a combination of a roll and a loop.^[2]

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 her test pilots, including Jean Franchi and Brian Walpole.^[3]

Execution

To do a barrel roll 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.^[4] Starting from a level flight, the pilot will usually pick such a point on the horizon as a reference. 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 upward. The pilot will need to control the roll rate, keeping the nose 45 degrees off the reference point on the horizon as the plane rolls 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.^[5][6]

When the aircraft has rolled 90 degrees, and the wings are vertical, the nose should be pitched about 45 degrees directly above the reference point on the horizon. As the plane continues to roll upside-down it will begin to level out, and the horizon will appear to rise to meet the nose. When in the completely inverted position, the aircraft should be level and the nose should still be 45 degrees to the side of the reference point, putting it 90 degrees off of the original flightpath. As the nose drops through the horizon, the pilot may need to reduce the elevator pressure, to counter-act the force of gravity and the loss of lift. Still keeping the nose 45 degrees off the reference point, the plane should roll into level flight along the same flightpath and at the same altitude at which the maneuver began.^[6]

Military attack

In air combat maneuvering, historically known as dogfighting, a barrel roll may refer to one of many maneuvers. These maneuvers are often simply called barrel rolls, but many fall into the category of "displacement rolls."

Barrel roll

The term barrel roll, by itself, most often refers to a helical roll around a straight flight path, the purpose of which is to slow the relative forward motion of the aircraft. This can help a defender to force an attacker, who is usually behind the defender, to fly out in front, called overshooting. This can also help an attacker to prevent an overshoot. This often forces both planes to continue through a series of rolls known as a rolling scissors maneuver. A barrel roll is also often used to check blind spots while remaining on a steady flight path.

Rolling scissors

Rolling scissors

The rolling scissors, also called vertical scissors or simply "rollers," is usually an undesirable maneuver to be caught in, both for the attacker and the defender. The advantage usually goes to the aircraft with the higher turn rate, especially when pulling the nose through the top and bottom of the turns. Correct placement of the lift vector during the maneuver is crucial to keep from moving ahead, relative to the opponent. There are many optical illusions that affect the pilot's ability to determine the relative position of the opponent, and mistakes can easily be made. It is extremely difficult to get a suitable firing solution during the rolling scissors. If the aircraft have a thrust-to-weight ratio of less than one, each consecutive roll will be lower than the previous, and the pilots can quickly find themselves at ground level. Any advantage is usually lost by the first pilot that attempts to disengage.^[7]

High g barrel roll

A high g barrel roll is a last ditch defensive maneuver, performed when the attacker has achieved a suitable firing solution. The maneuver is performed when the attacker is very close, and a barrel roll performed by the defender may cause an overshoot. The maneuver begins by cutting the throttle, extending the speed brakes, or turning very hard to encourage an overshoot. The maneuver is then executed by applying hard rudder input during the barrel roll to assist with the roll. The sudden change in the relative forward speed may cause a surprised attacker to fly out in front of the defender. Depending on the situation, a high g barrel roll can be performed "over the top," by beginning the roll like a normal barrel roll. The roll can also be performed "underneath," by doing a half aileron roll into the inverted position and beginning the barrel roll while upside-down.^[8]

Displacement roll

Displacement roll, providing a reduction in turn radius.

There are a variety of maneuvers that can be described as displacement rolls. A displacement roll is a barrel roll that moves the aircraft laterally, displacing it from its projected flightpath and moving it onto a new flightpath. Depending on how a displacement roll is executed, it may provide a shift laterally onto a parallel flightpath, or more aggressive rolls can be used to provide a reduction in turn radius.

By moving the fighter more into the vertical plane, the pilot can use gravity to assist the aircraft in turn performance. In vertical or oblique geometric planes, the turn will be much slower over the top, but the turn radius will be much smaller. Conversely, the turn radius will be much larger through the bottom of the turn, but the turn rate will be faster.^[9] Displacement rolls make full use of this assistance provided by gravity. By moving the fighter into more of the vertical plane, the pilot can then control the roll rate and yaw to provide a sharp reduction in turn radius, helping the attacker to prevent an overshoot and remain inside of the defender's turn.^[10]

Canopy roll

Canopy roll

A canopy roll is the simplest form of displacement roll. The roll is used to provide lateral displacement while maintaining the original heading. The maneuver begins like a normal barrel roll, but when the plane is nearly inverted, the pilot places the elevators and ailerons close to the neutral position. Called "unloading," this allows the inverted aircraft to fly momentarily in a fairly straight arc. When the pilot has achieved enough lateral displacement, the pilot continues through the second half of the barrel roll.

This type of roll is called a canopy roll, because it is often used as a way for aircraft to quickly change positions, by rolling over the top of an airplane and coming down on the other side. Canopy rolls are often used in combat, to displace the attacker in relation to the defender's flight path. An attacker following inside the defender's turn may need to displace the aircraft to the outside of the defender's turn in order to prevent an overshoot. Similarly, if following outside the turn of a defender that is much more maneuverable, the attacker may be unable to pull the nose up into a suitable firing position. By using a canopy roll, the attacker can shift the aircraft laterally away from the defender's flightpath. This will cause the flightpaths of both airplanes to cross, using geometry to change the attacker's aim. Canopy rolls are often used by the attacker when the defender reverses the turn, allowing the attacker to follow the reversal while keeping the correct relative position.^[11]

Lag displacement roll

A lag displacement roll, or "lag roll," helps improve the firing position of the attacking aircraft, and helps to increase range. The attacker performs the roll during a hard, turning chase, rolling both up and away from the turn. Typically performed a little slower than a normal displacement roll, the attacker achieves the proper reduction in turn radius on, or just outside of the defender's turn. Upon completing the roll, when the aircraft's lift vector points directly at the enemy, the pilot pulls back on the stick, reentering the turn with the ability to achieve a better firing position.^[12][13][14]

Barrel roll attack

Barrel roll attack

A barrel roll attack is a military maneuver that improves the attacker's offensive position and prevents the attacker from overshooting. In this maneuver the defender breaks one direction and so the attacker performs a barrel roll in the opposite direction. The attacker pulls back on the stick more than a normal barrel roll, performing a tighter loop than the roll. It is the three dimensional equivalent of a 90 degree turn, and the attacker finishes the loop, having completed three quarters of a roll, with the nose pointed along the defender's flight path.^[15][16]

The maneuver is performed when an overshoot is imminent and cannot be corrected with a normal displacement roll. Much more aggressive than a normal displacement roll, the maneuver begins by rolling slightly toward the direction of the defender's break, and then pulling up sharply. At roughly 30 degrees from the horizon, the pilot begins the barrel roll away from the defender's break, applying more elevator pressure than roll. When inverted, the pilot then uses the assistance provided by gravity combined with rudder control to bring the fuselages of both aircraft into alignment. As the nose passes through the horizon, the pilot will then align the lift vector ahead of the defender, to bring the fighter back into the correct geometric plane, inside of the defender's turn.^[16]

The success of a barrel roll attack depends greatly on the aircraft's ability to zoom climb.^[16] As the attacker is coming down, the defender may counter by pulling up unto a barrel roll, resulting in a rolling scissors.^[7]

See also

• Aileron roll
• Inline twist
• Roller coaster
• Skiing
• Star Fox 64

External links

• Aerobatic maneuver website
• Avro Vulcan Roll
• Flight training video

References

1. ^ "Barrel Roll". Full Deflection:Aerobatic website. http://www.fulldeflection.com/index.php/manoeuverscatalogue/42-catalogue/48-barrel-rolls. 
2. ^ http://www.iac.org/begin/figures.html#Barrel%20Rolls
3. ^ http://www.youtube.com/watch?v=KYQS3qAIjAo
4. ^ Aeronautical Dictionary: With Emphasis on ATC Communications Terms By J. Deborah Balter - Trafford Publishing 2004 Page 94
5. ^ Angels and Airspeed: World War Two Air Combat Theory and Tactics By Paul William Forbes - Trafford Publishing 2007 Page 52
6. ^ ^{a b} Douglas A-1H Skyraider Pilot's Flight Operating Instructions By United States Navy 2008 4-17
7. ^ ^{a b} http://www.tpub.com/content/aviation2/P-1222/P-12220034.htm
8. ^ http://www.tpub.com/content/aviation2/P-1222/P-12220045.htm
9. ^ http://www.tpub.com/content/aviation2/P-1222/P-12220016.htm
10. ^ http://www.tpub.com/content/aviation2/P-1222/P-12220028.htm
11. ^ http://www.tpub.com/content/aviation2/P-1218/P-12180033.htm
12. ^ An Illustrated Guide to Modern Fighter Combat By Mike Spick - Prentence Hall Trade 1987 Page 147
13. ^ http://www.tpub.com/content/aviation2/P-821/P-8210225.htm
14. ^ http://www.352ndfightergroup.com/virtual/protac/acm/maneuver.html
15. ^ An Illustrated Guide to Modern Fighter Combat By Mike Spick - Prentence Hall Trade 1987
16. ^ ^{a b c} http://www.tpub.com/content/aviation2/P-1222/P-12220033.htm