Thrust vectoring

Thrust vectoring, also known as thrust vector control (TVC), is a vital technology for steering vehicles. It allows an aircraft, rocket, or missile to change the direction of its engine thrust. By manipulating this thrust, a vehicle can control its attitude, which refers to its orientation in space. It can also control its angular velocity, or how fast it rotates. This is especially important for rockets and ballistic missiles traveling outside the Earth's atmosphere. In space, there is no air to push against wings or fins. Therefore, thrust vectoring becomes the primary method for controlling the vehicle's direction.

To understand how this works, imagine a rocket's line of action. Normally, the thrust from a rocket nozzle passes directly through the vehicle's center of mass. When this happens, there is zero net torque, meaning the rocket does not rotate. To steer, the vehicle must create pitch or yaw moments. This is done by deflecting the thrust vector so it no longer passes through the center of mass. This deflection creates a turning force. While gimbaling can handle pitch and yaw, roll control usually requires different methods. These include using two or more separate nozzles or vanes placed in the exhaust plume.

Engineers use four basic methods to achieve thrust vectoring. The first is gimbaling the engine or the nozzle. In liquid rockets, the entire combustion chamber and engine bell might move. For example, the Titan II used twin first-stage motors that gimbaled the whole engine. The Saturn V and the Space Shuttle also used gimbaled engines. Another method is reactive fluid injection. This is used in solid propellant missiles like the Minuteman II. It works by injecting liquid into the exhaust flow through injectors. This modifies the exhaust on one side, creating an asymmetric force that steers the missile.

A third method uses auxiliary Vernier thrusters. These are small, separate combustion chambers that can gimbal on one axis. They were used on the Atlas and R-7 missiles. The Soyuz rocket, which is descended from the R-7, still uses them today. However, they are rarely used in new designs because they are heavy and complex. The fourth method involves exhaust vanes, also called jet vanes. These are small parts placed directly in the exhaust stream. They deflect the thrust without moving any engine parts. The V-2 rocket used graphite vanes for this purpose.

While exhaust vanes are useful, they have specific drawbacks. They reduce the overall efficiency of the rocket engine. They must also be made of refractory materials to prevent them from melting. For example, the Sapphire rocket used copper vanes for their high heat capacity. The Nexo rocket used graphite because of its high melting point. Without active cooling, these vanes will suffer from significant erosion. Because of these issues, most modern rockets avoid using them. However, small tactical missiles like the AIM-9X Sidewinder still use mechanical vanes. These allow the missile to steer even at very low speeds right after launch.

Thrust vectoring also enables unique flight capabilities for aircraft. One major goal was to provide vertical thrust for vertical takeoff and landing (VTOL). This allows aircraft to operate from very short runways. Some modern aircraft, like the V-22 Osprey, use a tiltrotor design. This means the engine nacelles rotate 90 degrees after takeoff. This allows the craft to transition from hovering to forward flight.

Other aircraft use rotating nozzles to deflect exhaust by as much as 90 degrees. This helps them perform combat maneuvers that conventional planes cannot do.

Looking toward the future, scientists are researching Fluidic Thrust Vectoring (FTV). This method uses secondary fluid injections to divert the main thrust. Tests show that forcing air into an exhaust stream can deflect thrust by up to 15 degrees. This technology could be much better than moving parts. It could reduce mass and cost by up to 50 percent. It also reduces the radar cross section, which helps with stealth. This makes it a very promising tool for 6th generation fighter aircraft and unmanned aerial vehicles.

In 1949, Percy Walwyn submitted a jet design featuring thrust vectoring to the British Air Ministry. Today, the field continues to grow as we seek more efficient ways to move through the air and into space.