Thrust vectoring

Thrust vectoring, also known as thrust vector control (TVC), is the ability of an aircraft, rocket or other vehicle to manipulate the direction of the thrust from its engine(s) or motor(s) to control the attitude or angular velocity of the vehicle. In rockets and ballistic missiles that fly outside the atmosphere, aerodynamic control surfaces are ineffective, so thrust vectoring is the primary means of attitude control. Exhaust vanes and gimbaled engines were used in the 1930s by Robert Goddard. For aircraft, the method was originally envisaged to provide upward vertical thrust as a means to give aircraft vertical (VTOL) or short (STOL) takeoff and landing ability. Subsequently, it was realized that using vectored thrust in combat situations enabled aircraft to perform various maneuvers not available to conventional-engined planes. To perform turns, aircraft that use no thrust vectoring must rely on aerodynamic control surfaces only, such as ailerons or elevator; aircraft with vectoring must still use control surfaces, but to a lesser extent. In missile literature originating from Russian sources, thrust vectoring is referred to as gas-dynamic steering or gas-dynamic control.

Thrust vectoring, also known as thrust vector control (TVC), is the ability of an aircraft, rocket or other vehicle to manipulate the direction of the thrust from its engine(s) or motor(s) to control the attitude or angular velocity of the vehicle. In rockets and ballistic missiles that fly outside the atmosphere, aerodynamic control surfaces are ineffective, so thrust vectoring is the primary means of attitude control. Exhaust vanes and gimbaled engines were used in the 1930s by Robert Goddard. For aircraft, the method was originally envisaged to provide upward vertical thrust as a means to give aircraft vertical (VTOL) or short (STOL) takeoff and landing ability. Subsequently, it was realized that using vectored thrust in combat situations enabled aircraft to perform various maneuvers not available to conventional-engined planes. To perform turns, aircraft that use no thrust vectoring must rely on aerodynamic control surfaces only, such as ailerons or elevator; aircraft with vectoring must still use control surfaces, but to a lesser extent. In missile literature originating from Russian sources, thrust vectoring is referred to as gas-dynamic steering or gas-dynamic control. ====Gimbaled thrust==== Thrust vectoring for many liquid rockets is achieved by gimbaling the whole engine. This involves moving the entire combustion chamber and outer engine bell as on the Titan II's twin first-stage motors, or even the entire engine assembly including the related fuel and oxidizer pumps. The Saturn V and the Space Shuttle used gimbaled engines. A later method developed for solid propellant ballistic missiles achieves thrust vectoring by deflecting only the nozzle of the rocket using electric actuators or hydraulic cylinders. The nozzle is attached to the missile via a ball joint with a hole in the centre, or a flexible seal made of a thermally resistant material, the latter generally requiring more torque and a higher power actuation system. The Trident C4 and D5 systems are controlled via hydraulically actuated nozzle. The STS SRBs used gimbaled nozzles. ====Propellant injection==== Another method of thrust vectoring used on solid propellant ballistic missiles is liquid injection, in which the rocket nozzle is fixed, however a fluid is introduced into the exhaust flow from injectors mounted around the aft end of the missile. If the liquid is injected on only one side of the missile, it modifies that side of the exhaust plume, resulting in different thrust on that side thus an asymmetric net force on the missile. This was the control system used on the Minuteman II and the early SLBMs of the United States Navy. ====Vernier thrusters==== An effect similar to thrust vectoring can be produced with multiple vernier thrusters, small auxiliary combustion chambers which lack their own turbopumps and can gimbal on one axis. These were used on the Atlas and R-7 missiles and are still used on the Soyuz rocket, which is descended from the R-7, but are seldom used on new designs due to their complexity and weight. These are distinct from reaction control system thrusters, which are fixed and independent rocket engines used for maneuvering in space. ====Exhaust vanes==== One of the earliest methods of thrust vectoring in rocket engines was to place vanes in the engine's exhaust stream. These exhaust vanes or jet vanes allow the thrust to be deflected without moving any parts of the engine, but reduce the rocket's efficiency. They have the benefit of allowing roll control with only a single engine, which nozzle gimbaling does not. The V-2 used graphite exhaust vanes and aerodynamic vanes, as did the Redstone, derived from the V-2. The Sapphire and Nexo rockets of the amateur group Copenhagen Suborbitals provide a modern example of jet vanes. Jet vanes must be made of a refractory material or actively cooled to prevent them from melting. Sapphire used solid copper vanes for copper's high heat capacity and thermal conductivity, and Nexo used graphite for its high melting point, but unless actively cooled, jet vanes will undergo significant erosion. This, combined with jet vanes' inefficiency, mostly precludes their use in new rockets. ===Aircraft=== FA.2 ZA195 front (cold) vector thrust nozzle An example of 2D thrust vectoring is the Rolls-Royce Pegasus engine used in the Hawker Siddeley Harrier, as well as in the AV-8B Harrier II variant. Widespread use of thrust vectoring for enhanced maneuverability in Western production-model fighter aircraft didn't occur until the deployment of the Lockheed Martin F-22 Raptor fifth-generation jet fighter in 2005, with its afterburning, 2D thrust-vectoring Pratt & Whitney F119 turbofan. F-35B taking off with thrust-vectored nozzle. While the Lockheed Martin F-35 Lightning II uses a conventional afterburning turbofan (Pratt & Whitney F135) to facilitate supersonic operation, its F-35B variant, developed for joint usage by the US Marine Corps, Royal Air Force, Royal Navy, and Italian Navy, also incorporates a vertically mounted, low-pressure shaft-driven remote fan, which is driven through a clutch during landing from the engine. Both the exhaust from this fan and the main engine's fan are deflected by thrust vectoring nozzles, to provide the appropriate combination of lift and propulsive thrust. It is not conceived for enhanced maneuverability in combat, only for VTOL operation, and the F-35A and F-35C do not use thrust vectoring at all. The Sukhoi Su-30MKI, produced by India under licence at Hindustan Aeronautics Limited, is in active service with the Indian Air Force. The TVC makes the aircraft highly maneuverable, capable of near-zero airspeed at high angles of attack without stalling, and dynamic aerobatics at low speeds. The Su-30MKI is powered by two Al-31FP afterburning turbofans. The TVC nozzles of the MKI are mounted 32 degrees outward to longitudinal engine axis (i.e. in the horizontal plane) and can be deflected ±15 degrees in the vertical plane. This produces a corkscrew effect, greatly enhancing the turning capability of the aircraft. A few computerized studies add thrust vectoring to extant passenger airliners, like the Boeing 727 and 747, to prevent catastrophic failures, while the experimental X-48C may be jet-steered in the future. ===Other=== Examples of rockets and missiles which use thrust vectoring include both large systems such as the Space Shuttle Solid Rocket Booster (SRB), S-300P (SA-10) surface-to-air missile, UGM-27 Polaris nuclear ballistic missile and RT-23 (SS-24) ballistic missile and smaller battlefield weapons such as Swingfire. The principles of air thrust vectoring have been recently adapted to military sea applications in the form of fast water-jet steering that provide super-agility. Examples are the fast patrol boat Dvora Mk-III, the Hamina class missile boat and the US Navy's Littoral combat ships.

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