Grid fin

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Soyuz TMA-6 upper level
Lower level of a Falcon 9

Grid fins (also called grid field fins in Russian terminology ) are a variant of control surfaces that are used on various missiles and aerial bombs instead of conventional rudder fins . They were first used around 1964 on the Soviet lunar rocket N1 and since the 1970s as part of the design of Soviet ballistic missiles , the cruise missile family SS-N-27 Sizzler or the US GBU-43 / B MOAB . In the civilian sector, for example, grid fins are used as a stabilizer on the rescue system of the Soyuz spaceships and when landing the reusable first stage of the Falcon 9 and Falcon Heavy rockets .

Design features

Conventional planar control fins correspond to miniaturized wings that are aligned in the direction of the missile's longitudinal axis. In contrast to this, lattice fins consist of many small areas that are lattice-like within a box structure arranged transversely to the longitudinal axis. Their appearance is reminiscent of a wire rack or a potato masher. The elongated box is technologically easier to fold against the body of the missile than a conventional fin, which reduces the space required in the carrier system. This is particularly advantageous for weapons that are z. B. with stealth aircraft in internal weapon bays or should be launched from mobile launchers .

Aerodynamic properties

Grid fins have a much smaller profile depth than conventional control surfaces and can be viewed as a group of small fins arranged in parallel. This reduces the actuating forces to be applied by the control mechanism, which enables the use of smaller actuators. The low profile depth also ensures a reduced susceptibility to stalling at high angles of attack and enables a higher rate of turn and thus maneuverability compared to planar control surfaces .

The aerodynamic effectiveness and the flow resistance of lattice fins depend heavily on the speed of the missile: In the subsonic range and at higher Mach numbers, the flow through the lattice is laminar and leads to reduced counterforces and high rudder effects. However, at transonic velocities between Mach 0.8 and Mach 1.3, shock waves form within the lattice structure, which leads to the air flow being guided around the fin and creating a high flow resistance. Grid fins are therefore not suitable for missiles that travel a large part of their trajectory at transonic speeds.

Examples

Grid fins on the first stage of an SS-20

For control purposes, grid fins were or are used, for example, in the following missiles:

Web links

Individual evidence

  1. ^ Steve Zaloga : "The Scud and Other Russian Ballistic Missile Vehicles" . Concord Publications Co, New Territories, Hong Kong 2000, ISBN 962-361-675-9 .
  2. http://www.spacex.com/news/2015/08/31/grid-fins