The Split S is an air combat maneuver mostly used to disengage from combat. To execute a Split S, the pilot

Aviator

An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...

 half-rolls his aircraft

Aircraft

An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

 inverted and executes a descending half-loop, resulting in level flight in the exact opposite direction at a lower altitude.

The Split S is taught to be used in dogfight

Dogfight

A dogfight, or dog fight, is a form of aerial combat between fighter aircraft; in particular, combat of maneuver at short range, where each side is aware of the other's presence. Dogfighting first appeared during World War I, shortly after the invention of the airplane...

ing when the pilot has the opportunity to withdraw from battle. Contrary to popular belief, this maneuver is almost never used to evade target-locked air-to-air missile

Air-to-air missile

An air-to-air missile is a missile fired from an aircraft for the purpose of destroying another aircraft. AAMs are typically powered by one or more rocket motors, usually solid fuelled but sometimes liquid fuelled...

s. However, it can be an effective tactic to prevent an enemy behind (between eight o'clock and four o'clock positions) from gaining a missile lock-on

Missile lock-on

Missile lock-on refers to a scenario where the guidance system for a missile can accurately track a target, and a fire-control system can calculate the required flightpath for the missile to hit the target...

 while one is disengaging from a fight.

The Split S maneuver is contrasted with the Immelmann turn

Immelmann turn

The Immelmann turn refers to two different aircraft maneuvers.-In aerobatics:In modern aerobatical parlance, an Immelmann turn is an aerobatic maneuver of little practical use in aerial combat, and is a different maneuver altogether from the original dogfighting tactic of World War I from which it...

, which is an ascending half-loop that finishes with a half-roll out, resulting in level flight in the exact opposite direction at a higher altitude. The Split S is also called a reversed Immelmann turn, or can be listed with a hyphen as Split-S. In basic terms, they are very similar maneuvers, both accomplishing the same goal, 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 always ensure that he/she is starting high enough to complete the half-loop; the exact altitude needed depends on factors such as the aircraft's speed, weight and manoeuvrability. Misjudgments can arise from a lack of situational awareness or from an error in reading instruments.

The reason for starting the Split S maneuver from the inverted position is "If you are flying straight and level and push the nose of the plane down, you will experience your weight lessening. The harder you push the nose down, the more "weightless" you will feel. You are experiencing negative Gs. The effect of negative Gs is to push the blood up into the head, just the opposite of positive Gs. However, while the body can stand up to 9 positive Gs without severe consequences, blood vessels in your eyes will start to rupture when you apply as little as 2 to 3 negative Gs. This is known as redout. A pilot who pushes too many negative Gs will be seeing the world through bloodshot eyes."

However, the Split S without a beginning half-roll was frequently used in early WWII by German pilots seeking to evade British fighters. The Merlin engine

Rolls-Royce Merlin

The Rolls-Royce Merlin is a British liquid-cooled, V-12, piston aero engine, of 27-litre capacity. Rolls-Royce Limited designed and built the engine which was initially known as the PV-12: the PV-12 became known as the Merlin following the company convention of naming its piston aero engines after...

 used in British fighters was carburetted, and the float valves would malfunction under negative g-force

G-force

The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...

 leading to reduced power or a stalled engine (The German fighters were not subject to this problem as they used fuel injection

Fuel injection

Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive petrol engines, having almost completely replaced carburetors in the late 1980s....

). This could be prevented by quarter-rolling the aircraft before starting the dive, but doing so took up enough time to give the German pilots an excellent chance of escaping. The beginnings of a solution was provided by "Miss Shilling's orifice

Miss Shilling's orifice

Miss Shilling's Orifice was a very simple technical device made to counter engine cut-out in early Spitfire and Hurricane fighter aeroplanes during the Battle of Britain...

", a fuel-flow restriction device, and was finally solved by changing from the original S.U. carburetters

SU Carburetter

SU Carburetters were a brand of carburetter usually of the sidedraught type but downdraught variants were used on some pre-war cars....

 to Bendix-Stromberg

Bendix Corporation

The Bendix Corporation was an American manufacturing and engineering company which during various times in its 60 year existence made brake systems, aeronautical hydraulics, avionics, aircraft and automobile fuel control systems, radios, televisions and computers, and which licensed its name for...

 pressure carburettors

Pressure carburetor

A pressure carburetor is a type of fuel metering system manufactured by the Bendix Corporation for piston aircraft engines, starting in the 1940s. It is recognized as an early type of throttle-body fuel injection and was developed to prevent fuel starvation during inverted flight.-Concept:Most...

, and later to S.U. injection carburettors.

Pop culture

• In Top Gun
  Top Gun
  Top Gun may refer to:* Top Gun is a 1986 film starring Tom Cruise.**Top Gun , soundtrack to the movie**Top Gun , a number of games based on the movie...
  
  , Charlie makes reference to footage of an aircraft performing a Split S.
• Numerous video games involving air combat typically provide tutorials on ACMs, including the Split S.