In
air combat maneuvering, historically known as
dogfighting, the term "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 flightpath, the purpose of which is to slow the relative forward motion (downrange travel) 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 flightpath.
Rolling scissors 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.
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 excessive elevator pressure and 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.
Displacement roll 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, and 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. 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. Such a displacement roll, also called a "rollaway", uses the geometry of three dimensions by performing a half barrel-roll into the inverted position, then performing the second half of a loop with very little roll, keeping the lift vector aligned with the defender as the aircraft reverses direction.
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 flightpath. 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. The 1966 World War I-setting air combat film
The Blue Max shows a canopy roll being performed by one of the pair of German
Luftstreitkräfte pilots (the characters of Bruno Stachel and Willi von Klugermann), both flying
Fokker Dr.I fighters, just before the tragic "daredevil" under-bridge flight sequence in the film.
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 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.
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 flightpath. 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. 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. ==See also==