Ground loop (aviation)
Encyclopedia
In aviation
, a ground loop is a rapid rotation
of a fixed-wing aircraft
in the horizontal
plane
while on the ground. Aerodynamic forces may cause the advancing wing
to rise, which may then cause the other wingtip to touch the ground. In severe cases (particularly if the ground surface is soft), the inside wing can dig in, causing the aircraft to swing violently or even cartwheel.
In powered airplanes, the ground loop phenomenon is predominantly associated with aircraft that have conventional landing gear
, due to the center of gravity being positioned behind the main wheels. It may also occur with tricycle landing gear if excessive load is applied to the nosewheel, a condition known as wheel-barrowing
.
If the aircraft heading is slightly different from the aircraft's direction of motion, a side force is exerted on the wheels. If this force is in front of the center of gravity, the resulting moment rotates the aircraft's heading even further from its direction of motion. This increases the force and the process reinforces itself. To avoid a ground loop, the pilot must respond to any turning tendency quickly, while sufficient control authority is available to counteract it. Once the aircraft rotates beyond this point, there is nothing the pilot can do to stop it from rotating further.
Ground loops occur when the aircraft is moving on the ground—either taxiing
, landing
, or during takeoff
. Ground loops can damage the undercarriage
and wingtips of an aircraft. Several extreme incidents of ground loop have resulted in fatalities.
Ground loops may occur when landing on muddy ground, wet pavement, or frozen surfaces, especially if there are puddles or patches. They may also occur when an aircraft departs a paved surface: for example, after an engine failure on the takeoff roll in a multi-engine aircraft. Another common cause is failure of a tire or wheel brake, causing a loss of directional control. They also commonly occur without outside influence, due entirely to pilot error
.
In gliders
, ground loops can also occur because there is only a single main wheel near the center of gravity, and because the long wings are close to the ground. Any tendency to touch a wingtip to the ground while moving must be quickly counteracted. The leverage from the long wings can apply great stress to the rear fuselage
, sometimes breaking the tail boom, especially on T-tail
gliders.
Pilots may decide to execute a ground loop deliberately, usually as a last resort before hitting an immovable object. In this case it may be a better option to dissipate energy by damaging the wings of the aircraft to protect the occupants seated in the fuselage.
Aviation
Aviation is the design, development, production, operation, and use of aircraft, especially heavier-than-air aircraft. Aviation is derived from avis, the Latin word for bird.-History:...
, a ground loop is a rapid rotation
Rotation
A rotation is a circular movement of an object around a center of rotation. A three-dimensional object rotates always around an imaginary line called a rotation axis. If the axis is within the body, and passes through its center of mass the body is said to rotate upon itself, or spin. A rotation...
of a fixed-wing aircraft
Fixed-wing aircraft
A fixed-wing aircraft is an aircraft capable of flight using wings that generate lift due to the vehicle's forward airspeed. Fixed-wing aircraft are distinct from rotary-wing aircraft in which wings rotate about a fixed mast and ornithopters in which lift is generated by flapping wings.A powered...
in the horizontal
Horizontal plane
In geometry, physics, astronomy, geography, and related sciences, a plane is said to be horizontal at a given point if it is perpendicular to the gradient of the gravity field at that point— in other words, if apparent gravity makes a plumb bob hang perpendicular to the plane at that point.In...
plane
Plane (mathematics)
In mathematics, a plane is a flat, two-dimensional surface. A plane is the two dimensional analogue of a point , a line and a space...
while on the ground. Aerodynamic forces may cause the advancing 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...
to rise, which may then cause the other wingtip to touch the ground. In severe cases (particularly if the ground surface is soft), the inside wing can dig in, causing the aircraft to swing violently or even cartwheel.
In powered airplanes, the ground loop phenomenon is predominantly associated with aircraft that have conventional landing gear
Conventional landing gear
thumb|The [[Piper PA-18|Piper Super Cub]] is a popular taildragger aircraft.thumb|right|A [[Cessna 150]] converted to taildragger configuration by installation of an after-market modification kit....
, due to the center of gravity being positioned behind the main wheels. It may also occur with tricycle landing gear if excessive load is applied to the nosewheel, a condition known as wheel-barrowing
Wheel-barrowing
Wheel-barrowing is a problem that may occur when a pilot places excessive forward pressure on the elevator control of an aeroplane with a nose wheel during takeoff or landing. Forward pressure on the flight controls places an up force on the horizontal tail, thereby transferring weight from the...
.
If the aircraft heading is slightly different from the aircraft's direction of motion, a side force is exerted on the wheels. If this force is in front of the center of gravity, the resulting moment rotates the aircraft's heading even further from its direction of motion. This increases the force and the process reinforces itself. To avoid a ground loop, the pilot must respond to any turning tendency quickly, while sufficient control authority is available to counteract it. Once the aircraft rotates beyond this point, there is nothing the pilot can do to stop it from rotating further.
Ground loops occur when the aircraft is moving on the ground—either taxiing
Taxiway
A taxiway is a path on an airport connecting runways with ramps, hangars, terminals and other facilities. They mostly have hard surface such as asphalt or concrete, although smaller airports sometimes use gravel or grass....
, landing
Landing
thumb|A [[Mute Swan]] alighting. Note the ruffled feathers on top of the wings indicate that the swan is flying at the [[Stall |stall]]ing speed...
, or during takeoff
Takeoff
Takeoff is the phase of flight in which an aerospace vehicle goes from the ground to flying in the air.For horizontal takeoff aircraft this usually involves starting with a transition from moving along the ground on a runway. For balloons, helicopters and some specialized fixed-wing aircraft , no...
. Ground loops can damage the undercarriage
Undercarriage
The undercarriage or landing gear in aviation, is the structure that supports an aircraft on the ground and allows it to taxi, takeoff and land...
and wingtips of an aircraft. Several extreme incidents of ground loop have resulted in fatalities.
Ground loops may occur when landing on muddy ground, wet pavement, or frozen surfaces, especially if there are puddles or patches. They may also occur when an aircraft departs a paved surface: for example, after an engine failure on the takeoff roll in a multi-engine aircraft. Another common cause is failure of a tire or wheel brake, causing a loss of directional control. They also commonly occur without outside influence, due entirely to pilot error
Pilot error
Pilot error is a term used to describe the cause of an accident involving an airworthy aircraft where the pilot is considered to be principally or partially responsible...
.
In gliders
Glider (sailplane)
A glider or sailplane is a type of glider aircraft used in the sport of gliding. Some gliders, known as motor gliders are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off or for extending a flight...
, ground loops can also occur because there is only a single main wheel near the center of gravity, and because the long wings are close to the ground. Any tendency to touch a wingtip to the ground while moving must be quickly counteracted. The leverage from the long wings can apply great stress to the rear fuselage
Fuselage
The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...
, sometimes breaking the tail boom, especially on T-tail
T-tail
thumb|right|Grob motor gliderA T-tail is an aircraft tail stabilizer configuration in which the horizontal surfaces are mounted to the top of the vertical stabilizer. Traditionally, the horizontal control surfaces are mounted to the fuselage at the base of the vertical stabilizer...
gliders.
Pilots may decide to execute a ground loop deliberately, usually as a last resort before hitting an immovable object. In this case it may be a better option to dissipate energy by damaging the wings of the aircraft to protect the occupants seated in the fuselage.