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The term Immelmann turn, named after German World War One Eindecker fighter ace Leutnant Max Immelmann, refers to two different aircraft maneuvers. In World War I aerial combat, an Immelmann turn was a maneuver used after an attack on another aircraft to reposition the attacking aircraft for another attack.
An Immelmann trades airspeed for altitude during a 180 degree change in direction. The aircraft performs the first half of a loop, and when completely inverted, rolls to the upright position. The Immelmann is a good offensive maneuver for setting up a high-side guns pass against a lower altitude, slow moving opponent, going in an opposite direction. However, an Immelmann is a poor defensive maneuver, turning the defender into a slow moving target.
To successfully execute the aerobatic Immelmann turn, the pilot accelerated to sufficient speed to perform a loop in the aircraft. The pilot then pulls the plane into a climb, and continues to pull back on the controls as the aircraft climbs. As the plane passes over the point at which the climb was commenced, it should be inverted and a half loop will have been executed. Sufficient speed must be maintained to recover without losing altitude, and at the top of the loop the pilot then executes a half-roll to regain normal, upright aircraft orientation. As a result, the fighter is now at a higher altitude and has changed course 180 degrees.
A Chandelle, also called a Pitchback, is an Immelmann that is executed in some plane other than the vertical. Basically just a pitch turn, the fighter will be at some angle of bank before performing the half loop and roll. Unlike the Immelmann, a Chandelle depletes less kinetic energy and is harder for an adversary to track.
A chandelle is a climbing turn, performed in the clean configuration, with a 180-degree change in course. It begins near the maneuvering speed of the aircraft and finishes close to its stalling speed. The first half of the chandelle features a constant bank attitude and increasing pitch attitude. During the second half of the maneuver, the pitch attitude stays constant and the bank continuously decreases to a level attitude.
The scissors are a series of turn reversals and flight path overshoots intended to slow the relative forward motion (downrange travel) of the aircraft in an attempt to either force a dangerous overshoot, on the part of the defender, or prevent a dangerous overshoot on the attacker's part. The defender's goal is to stay out of phase with the attacker, trying to prevent a guns solution, while the attacker tries to get in phase with the defender. The advantage usually goes to the more maneuverable aircraft. There are two types of scissor maneuvers, called flat scissors and rolling scissors.
Rolling Scissors: Rolling scissors, also called vertical scissors, tend to happen after a high-speed overshoot from above. The defender reverses into a vertical climb and into a barrel roll over the top, forcing the attacker to attempt to follow. The advantage lies in the aircraft that can pull its nose through the top or bottom of the turn faster. In battles with aircraft that have a thrust-to-weight ratio of less than one the aircraft will quickly lose altitude, and crashing into the ground becomes a possibility. According to author Mike Spick, "Disengagement from a vertical rolling scissors is best made with a split-s and a lot of hope.
Flat Scissors: Flat scissors, also called horizontal scissors, usually occur after a low-speed overshoot in a horizontal direction. The defender reverses the turn, attempting to force the attacker to fly out in front and to spoil aim. The attacker then reverses, trying to remain behind the defender, and the two aircraft begin a weaving flight pattern.
The opposite of an Immelmann is the Split-S. This maneuver consists of rolling inverted and pulling back on the stick, diving the aircraft into a half loop, which changes the aircraft's direction 180 degrees. The split-s is rarely a viable option in combat as it depletes kinetic energy in a turn and potential energy in a dive. It is most often used to set up a high-side guns pass against a lower but fast moving opponent that is traveling in the opposite direction. Also, the split-s is sometimes used as a disengagement tactic.
The Split S is contrasted with the Immelmann turn, which is an ascending half-loop that finishes with a half-roll out, resulting in level flight in the opposite direction at a higher altitude. The Split S is also called a reversed Immelmann turn and can also be written with a hyphen: Split-S. In basic terms, the Immelmann and Split S are very similar, both accomplishing the same reversal in course, but the Split S exchanges altitude to gain speed, while the Immelmann turn exchanges speed to gain altitude.
The Split S, being a descending maneuver, means that the pilot must ensure that it is started high enough to complete the half-loop; the exact minimum altitude depends on factors like the aircraft's speed, weight and maneuverability, likewise the terrain below the plane. Misjudgements can arise from a lack of situational awareness or from an error in reading instruments
If the attacker has a significant altitude advantage, a high-side guns pass is usually prudent. Sometimes called a "swoop", "boom and zoom", "hit and split", plus a variety of other names, it consists of a powered dive toward the rear quarter of a lower flying opponent. Shooting with the cannons in a single, high-speed pass, the attacker uses excess kinetic energy to disengage from the fight in a zoom climb back to a safe altitude, restoring the potential energy. This allows the attacker to set up another attack and dive again. Surprise is often a key element in this type of attack, and the attackers will often hide in the sun or clouds, stalking their opponents until a good opportunity is presented. A high-side guns pass is a very effective tactic against a more maneuverable opponent, where the turning battle of a dogfight is best avoided.
Spotting an attacker approaching from behind, the defender will usually break. The maneuver consists of turning sharply across the attacker's flight path, to increase AOT (angle off tail). The defender is exposed to the attacker's guns for only a brief instant (snapshot). The maneuver works well because the slower moving defender has a smaller turn radius and bigger angular velocity, and a target with a high crossing speed (where the bearing to the target is changing rapidly) is very difficult to shoot. This can also help to force the attacker to overshoot, which may not be true had the turn been made away from the attacker's flight path.
The counter to a break is often a displacement roll called a barrel roll attack. A barrel roll consists of performing a roll and a loop, completing both at the same time. The result is a helical roll around a straight flight path. The barrel roll attack uses a much tighter loop than the roll, completing a full loop while only executing 3/4 of a roll. The result is a virtual 90 degree turn, using all three dimensions, in the direction opposite of the roll. Rolling away from the defender's break, the attacker completes the roll with the aircraft's nose pointed in the direction of the defender's travel.
This maneuver differs from the defensive high-g barrel roll in that a great loss of speed to force an attacking fighter to overshoot is not necessary. The g forces can therefore often be quite small. Closely resembling the roll-away, the barrel roll attack is used to alter the angle of approach to the defender without losing a lot of speed. It is used when the attacker becomes aware that he is going to overshoot a turning target. He rolls the wings level, pulls the nose hard up, then rolls away from the direction of turn. This three- dimensional maneuver is completed by sliding in astern of the target.
The high Yo-Yo is a very effective maneuver, and very difficult to counter. The maneuver is used to slow the approach of a fast moving attacker while conserving the airspeed energy. The maneuver is performed by reducing the angle at which the aircraft is banking during a turn, and pulling back on the stick, bringing the fighter up into a new plane of travel. The attacker then rolls into a steeper pitch turn, climbing above the defender. The trade-off between airspeed and altitude provides the fighter with a burst of increased maneuverability. This allows the attacker to make a smaller turn, correcting an overshoot, and to pull in behind the defender. Then, by returning to the defenders plane, the attacker restores the lost speed while maintaining energy.
The low Yo-Yo is one of the most useful maneuvers, which sacrifices altitude for an instantaneous increase in speed. This maneuver is accomplished by rolling with the nose low into the turn, and dropping into a steeper slice turn. By utilizing some energy that was stored in the vertical plane, the attacker can quickly decrease range and improve the angle of the attack, literally cutting the corner on the opponent's turn. The pilot then pulls back on the stick, climbing back to the defender's height. This helps slow the aircraft and prevents an overshoot, while placing the energy back into altitude. A defender spotting this maneuver may try to take advantage of the increase in AOT by tightening the turn in order to force an overshoot. The low Yo-Yo is often followed by a high Yo-Yo, to help prevent an overshoot, or several small low Yo-Yos can be used instead of one large maneuver.
A lag displacement roll, also called a "lag roll", is a maneuver used to reduce the angle off tail by bringing the attacker from lead pursuit to pure, or even lag pursuit. The maneuver is performed by rolling up and away from the turn, then, when the aircraft's lift vector is aligned with the defender, pulling back on the stick, bringing the fighter back into the turn. This maneuver helps prevent an overshoot caused by the high AOT of lead pursuit, and can also be used to increase the distance between aircraft.
Superiority in the rolling plane could be used to defeat a better-turning opponent. Rolling away from the direction of the turn allowed the pursuing fighter to cut the corner. This was, however, a double-edged sword: American Thunderbolts often used the vector roll against Bf 109s.