Grid fins are a type of flight control surface used on missile

Missile

Though a missile may be any thrown or launched object, it colloquially almost always refers to a self-propelled guided weapon system.-Etymology:The word missile comes from the Latin verb mittere, meaning "to send"...

s and bomb

Bomb

A bomb is any of a range of explosive weapons that only rely on the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy...

s in place of more conventional control surfaces, such as planar fin

Fin

A fin is a surface used for stability and/or to produce lift and thrust or to steer while traveling in water, air, or other fluid media, . The first use of the word was for the limbs of fish, but has been extended to include other animal limbs and man-made devices...

s. They have been used since the 1970s in various Soviet ballistic missile

Ballistic missile

A ballistic missile is a missile that follows a sub-orbital ballistic flightpath with the objective of delivering one or more warheads to a predetermined target. The missile is only guided during the relatively brief initial powered phase of flight and its course is subsequently governed by the...

 designs such as the SS-12 Scaleboard, SS-20 Saber, SS-21 Scarab, SS-23 Spider, SS-25 Sickle, the N-1

N1 rocket

N-1 was a heavy lift rocket intended to deliver payloads beyond low Earth orbit, acting as the Soviet counterpart to the NASA Saturn V rocket. This heavy lift booster had the capability of lifting very heavy loads into orbit, designed with manned extra-orbital travel in mind...

 (the intended rocket for the Soviet moon program

Soviet Moonshot

The Soviet manned lunar programs were a series of programs pursued by the Soviet Union to land a man on the Moon in competition with the United States Apollo program to achieve the same goal set publicly by President John F. Kennedy on May 25, 1961...

), and the abort system for the Soyuz spacecraft. In Russia, they are referred to as grid fins.

Grid fins have also been used on conventional missiles and bombs such as the Vympel R-77

Vympel R-77

The Russian R-77 Missile is a medium range, air-to-air, active radar-guided missile system. It is the Russian counterpart to the American AIM-120 AMRAAM missile, thus gaining a nickname: Amraamski....

 air-to-air missile; the 3M-54 Klub

3M-54 Klub

The Russian 3M-54 Klub is a multi-role missile system developed by the Novator Design Bureau. Its NATO reporting name is SS-N-27. Both submarine and surface ship launched versions exist. The system is designed to accept various warheads, allowing its use against surface and subsurface naval...

 (SS-N-27 Sizzler) family of cruise missile

Cruise missile

A cruise missile is a guided missile that carries an explosive payload and is propelled, usually by a jet engine, towards a land-based or sea-based target. Cruise missiles are designed to deliver a large warhead over long distances with high accuracy...

s; and the American Massive Ordnance Air Blast

GBU-43 Massive Ordnance Air Blast bomb

The GBU-43/B Massive Ordnance Air Blast bomb is a large-yield conventional bomb developed for the United States military by Albert L. Weimorts, Jr. At the time of development, it was touted as the most powerful non-nuclear weapon ever designed...

 (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

Air brake (aircraft)

In aeronautics, air brakes or speedbrakes are a type of flight control surface used on an aircraft to increase drag or increase the angle of approach during landing....

 on the Soyuz

Soyuz spacecraft

Soyuz , Union) is a series of spacecraft initially designed for the Soviet space programme by the Korolyov Design Bureau in the 1960s, and still in service today...

 TM-22 spacecraft.

Design characteristics

Conventional "planar" control fins are shaped like miniature wing

Wing

A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...

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 to potato masher

Potato masher

A potato masher or bean masher is a food preparation utensil used to crush soft food for such dishes as mashed potatoes, apple sauce, or refried beans.-Construction:...

s or waffle iron

Waffle iron

A waffle iron is a cooking appliance used to make waffles.It usually consists of two hinged metal plates, molded to create the honeycomb pattern found on waffles...

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

Stealth aircraft

Stealth aircraft are aircraft that use stealth technology to avoid detection by employing a combination of features to interfere with radar as well as reduce visibility in the infrared, visual, audio, and radio frequency spectrum. Development of stealth technology likely began in Germany during...

. 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

C-130 Hercules

The Lockheed C-130 Hercules is a four-engine turboprop military transport aircraft designed and built originally by Lockheed, now Lockheed Martin. Capable of using unprepared runways for takeoffs and landings, the C-130 was originally designed as a troop, medical evacuation, and cargo transport...

 cargo bay for deployment while the craft is in flight.

Grid fins have a much shorter "chord

Chord (aircraft)

In aeronautics, chord refers to the imaginary straight line joining the trailing edge and the center of curvature of the leading edge of the cross-section of an airfoil...

" (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

Torque

Torque, moment or moment of force , is the tendency of a force to rotate an object about an axis, fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....

 exerted on the steering mechanism by high-speed airflow, allowing for the use of smaller fin actuators, and a smaller tail assembly overall. Their small chord also makes them less prone to stall

Stall (flight)

In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...

 at high angles of attack

Angle of attack

Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...

, allowing for tighter turns.

Grid fins perform very well at subsonic and supersonic speeds, but poorly at transonic

Transonic

Transonic speed is an aeronautics term referring to the condition of flight in which a range of velocities of airflow exist surrounding and flowing past an air vehicle or an airfoil that are concurrently below, at, and above the speed of sound in the range of Mach 0.8 to 1.2, i.e. 600–900 mph...

 speeds; the flow causes a normal shockwave to form within the lattice, causing much of the airflow to pass completely around the fin instead of through it and generating significant wave drag

Wave drag

In aeronautics, wave drag is a component of the drag on aircraft, blade tips and projectiles moving at transonic and supersonic speeds, due to the presence of shock waves. Wave drag is independent of viscous effects.- Overview :...

. However, at high Mach number

Mach number

Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...

s, grid fins flow fully supersonic and can provide lower drag

Drag (physics)

In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...

and greater maneuverability than planar fins.

External links

• Missile Grid Fins, Aerospaceweb.org
• Conventional Weapons Technology Group, Defense Technical Information Center
• "It's the Big One", Aviation Week
• KLUB (SS-N-27) ASCM, Bharat-Rakshak.com
• Small Smart Bomb with Range Extension, Air Force Research Laboratory
• Medical Missile Prepped for Launch, DefenseTech.org