- Grid fin
Grid fins (or lattice fins) are a type of flight control surface used on
missile s andbomb s in place of more conventional control surfaces, such as planarfin s. They have been used since the 1970s in variousSoviet ballistic missile designs such as the SS-12 "Scaleboard", SS-20 "Saber", SS-21 "Scarab", SS-23 "Spider", SS-25 "Sickle", and the N-1 (the intended rocket for the Soviet moon program). In Russia, they are referred to as "Belotserkovskiy" grid fins [cite book |last=Zaloga |first=Steve |authorlink= |title="The Scud and Other Russian Ballistic Missile Vehicles" |year=2000 |publisher=Concord Publications Co |location=New Territories, Hong Kong |isbn=962-361-675-9 ] .Grid fins have also been used on conventional missiles and bombs such as the
Vympel R-77 air-to-air missile; theSS-N-27 ("Klub") family ofcruise missile s; and the American Massive Ordnance Air Blast (MOAB) large-yield conventional bomb. They have also been used on specialized devices such as the Quick-MEDS delivery system and as emergency air brakes on the Soyuz TM-22 spacecraft.Design characteristics
Conventional "planar" control fins are shaped like miniature
wing s. By contrast, grid fins are a lattice of smaller aerodynamic surfaces arranged within a box. Their appearance has sometimes led them to be compared topotato masher s orwaffle iron s.Grid fins can be folded against the body of a missile more easily than planar fins, allowing for more compact storage of the weapon; this is of importance for craft which store weapons in internal bays, such as
stealth aircraft . Shortly after release, the fins are swiveled into place for use as control surfaces. In the case of the MOAB, grid fins allow the weapon to fit inside a C-130 cargo bay for deployment while the craft is in flight.Grid fins have a much shorter "chord" (the distance between leading and trailing edge of the surface) than planar fins, as they are effectively a group of short fins mounted parallel to one another. Their reduced chord reduces the amount of
torque exerted on the steering mechanism by high-speed airflow, allowing for the use of smaller finactuators , and a smaller tail assembly overall. Their small chord also makes them less prone to stall at high angles of attack, allowing for tighter turns.Grid fins perform very well at subsonic and supersonic speeds, but poorly at
transonic speeds; the flow causes anormal shock wave to form within the lattice, causing much of the airflow to pass completely around the fin instead of through it and generating significantwave drag . However, at highMach number s, grid fins flow fully supersonic and can provide lower drag and greater maneuverability than planar fins.Notes
References
* [http://www.aerospaceweb.org/question/weapons/q0261.shtml Missile Grid Fins, "Aerospaceweb.org"]
* [http://www.dtic.mil/ttcp/wpn.htm Conventional Weapons Technology Group, "Defense Technical Information Center"]
* [http://www.aviationweek.com/aw/generic/story_generic.jsp?channel=awst&id=news/03173news.xml "It's the Big One", "Aviation Week"]
* [http://www.bharat-rakshak.com/NAVY/Klub.html KLUB (SS-N-27) ASCM, "Bharat-Rakshak.com"]
* [http://www.afrlhorizons.com/Briefs/Jun02/MN0206.html Small Smart Bomb with Range Extension, "Air Force Research Laboratory"]
* [http://www.defensetech.org/archives/001044.html Medical Missile Prepped for Launch, "DefenseTech.org"]
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