A ram air turbine (RAT) is a small wind turbine that is connected to a

hydraulic pump Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic. A hydraulic pump is a mechanical source of power that converts mechanical power into hydraulic energy ( hydrostatic energy i.e. flow, pressure). It genera ...

, or

electrical generator In electricity generation, a generator is a device that converts motive power ( mechanical energy) or fuel-based power ( chemical energy) into electric power for use in an external circuit. Sources of mechanical energy include steam turbines, ...

, installed in an

aircraft An aircraft is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or by using the Lift (force), dynamic lift of an airfoil, or in ...

and used as a power source. The RAT generates power from the airstream by

ram pressure Ram pressure is a pressure exerted on a body moving through a fluid medium, caused by relative bulk motion of the fluid rather than random thermal motion. It causes a drag force to be exerted on the body. Ram pressure is given in tensor form as ...

due to the speed of the aircraft.

Operation

Modern aircraft generally use RATs only in an emergency. In case of the loss of both primary and auxiliary power sources the RAT will power vital systems (flight controls, linked hydraulics and also flight-critical instrumentation). Some RATs produce only hydraulic power, which is in turn used to power electrical generators. Argus AS 410

In some early aircraft (including airships), small RATs were permanently mounted and operated a small electrical generator or

fuel pump A fuel pump is a component in motor vehicles that transfers liquid from the fuel tank to the carburetor or fuel injector of the internal combustion engine. Carbureted engines often use low pressure mechanical pumps that are mounted outside the f ...

. Some

constant-speed propeller In aeronautics, a variable-pitch propeller is a type of propeller (airscrew) with blades that can be rotated around their long axis to change the blade pitch. A controllable-pitch propeller is one where the pitch is controlled manually by the p ...

s, such as those of the

Argus As 410 The Argus As 410 was a German air-cooled inverted V-12 light aircraft engine that was first produced by Argus Motoren in 1938. Design and development The engine marked a departure from earlier Argus engines in that it had new construction tech ...

engines used in the

Focke-Wulf Fw 189 The Focke-Wulf Fw 189 ''Uhu'' ("Eagle Owl") is a German twin-engine, twin-boom, three-seat tactical reconnaissance and army cooperation aircraft. It first flew in 1938 (Fw 189 V1), entered service in 1940 and was produced until mid-1944. In ad ...

, used a propeller turbine on the

spinner Technology *Spinner (aeronautics), the aerodynamic cone at the hub of an aircraft propeller * Spinner (cell culture), laboratory equipment for cultivating plant or mammalian cells * Spinner (computing), a graphical widget in a GUI * Spinner (MIT Med ...

to power a self-contained pitch governor controlling this constant speed. Modern aircraft generate power in the main engines or an additional fuel-burning

turbine engine A gas turbine, also called a combustion turbine, is a type of continuous flow internal combustion engine. The main parts common to all gas turbine engines form the power-producing part (known as the gas generator or core) and are, in the direct ...

called an

auxiliary power unit An auxiliary power unit (APU) is a device on a vehicle that provides energy for functions other than propulsion. They are commonly found on large aircraft and naval ships as well as some large land vehicles. Aircraft APUs generally produce 115& ...

, which is often mounted in the rear of the fuselage or in the main-wheel well. The RAT generates power from the airstream due to the speed of the aircraft. If aircraft speeds are low, the RAT will produce less power. In normal conditions the RAT is retracted into the fuselage (or wing), and is deployed manually or automatically following complete loss of power. In the time between power loss and RAT deployment, batteries are used.

Military use

RATs are common in military aircraft which must be capable of surviving sudden and complete loss of power. In other military uses, pod-fitted systems such as the M61A1 Vulcan cannon or high-powered electronics such as the

AN/ALQ-99 The AN/ALQ-99 is an airborne electronic warfare system, found on EA-6B and EA-18G military aircraft. The ALQ-99E version of the system was carried on the EF-111A Raven aircraft as an escort or standoff jammer. Description The ALQ-99 is an airb ...

jamming system can be powered by a RAT in standard operation. This allows their installation on a standard

hardpoint A hardpoint is an attachment location on a structural frame designed to transfer force and carry an external or internal structural load, load. The term is usually used to refer to the mounting points (more formally known as a weapon station or ...

, without requiring a pod-specific power supply. Also, some free-fall nuclear weapons, such as the British Yellow Sun and

Red Beard is a 1965 Japanese ''jidaigeki'' film co-written, edited, and directed by Akira Kurosawa, in his last collaboration with actor Toshiro Mifune. Based on Shūgorō Yamamoto's 1959 short story collection, '' Akahige Shinryōtan'', the film takes pl ...

, used RATs to power

radar altimeter A radar altimeter (RA), also called a radio altimeter (RALT), electronic altimeter, reflection altimeter, or low-range radio altimeter (LRRA), measures altitude above the terrain presently beneath an aircraft or spacecraft by timing how long it t ...

s and firing circuits; these were a more reliable alternative to batteries.

Civilian use

Many modern types of commercial airliners, from the

Vickers VC10 The Vickers VC10 is a mid-sized, narrow-body long-range British jet airliner designed and built by Vickers-Armstrongs (Aircraft) Ltd and first flown at Brooklands, Surrey, in 1962. The airliner was designed to operate on long-distance route ...

of the 1960s, are equipped with RATs. A ram air turbine driving an electrical generator was chosen for the VC10 because of its use of "

packaged Packaging is the science, art and technology of enclosing or protecting products for distribution, storage, sale, and use. Packaging also refers to the process of designing, evaluating, and producing packages. Packaging can be described as a ...

" hydraulically-powered flying controls, rather than a centralised hydraulic system. The individual package units of the VC10 were each powered electrically and so emergency redundancy for the VC10 relied on quadruple generators and a backup RAT generator at a time when most RATs drove hydraulic pumps. The

Airbus A380 The Airbus A380 is a large wide-body airliner that was developed and produced by Airbus. It is the world's largest passenger airliner and only full-length double-deck jet airliner. Airbus studies started in 1988, and the project was annou ...

has the largest RAT in the world at in diameter, but around is more common. A typical large RAT on a commercial aircraft can be capable of producing , depending on the generator. Smaller, low airspeed models may generate as little as 400 watts. RATs have also been used to power

centrifugal pump Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. They are a sub-class of dynamic ...

s to pressurize the spray systems on aircraft that are used as

crop duster A crop is a plant that can be grown and harvested extensively for profit or subsistence. When the plants of the same kind are cultivated at one place on a large scale, it is called a crop. Most crops are cultivated in agriculture or hydroponi ...

s to deliver liquid agents to cropland. The major reason for choosing a RAT is safety; using a RAT in the United States allows an FAA-certified engine and power systems on the aircraft to remain unmodified. There is no need to use an engine

power takeoff A power take-off or power takeoff (PTO) is one of several methods for taking power from a power source, such as a running engine, and transmitting it to an application such as an attached implement or separate machine. Most commonly, it is a s ...

to drive the pump, as the pump can be placed low or below the exterior of the airframe, greatly simplifying plumbing. Being the lowest point in the plumbing, it will have gravity feed from the spray tanks and never need to be primed. In the event of a pump failure that could result in seizure, there is no effect on the flying ability of the aircraft or its systems apart from the fact that the spray systems are non-functional.

Civilian incidents involving RAT deployment

The following aviation incidents involved the deployment of a ram air turbine: * 1974:

British Airways British Airways (BA) is the flag carrier airline of the United Kingdom. It is headquartered in London, England, near its main hub at Heathrow Airport. The airline is the second largest UK-based carrier, based on fleet size and passengers ...

Flight 910 * 1983: Air Canada Flight 143, also known as the

Gimli Glider Air Canada Flight 143, commonly known as the Gimli Glider, was a Canadian scheduled domestic passenger flight between Montreal and Edmonton that ran out of fuel on Saturday, July 23, 1983, at an altitude of , midway through the fli ...

incident * 1996: The hijacking of

Ethiopian Airlines Flight 961 Ethiopian Airlines Flight 961 was a scheduled flight serving the route Addis Ababa–Nairobi–Brazzaville–Lagos–Abidjan. On 23 November 1996, the aircraft serving the flight, a Boeing 767-200ER, was hijacked en route from Addis Ababa to Na ...

* 2000:

Hapag-Lloyd Flight 3378 Hapag-Lloyd Flight 3378 (HF-3378) was a passenger service operated by Hapag-Lloyd Flug from Chania, on the island of Crete, Greece, to Hannover, Germany. On 12 July 2000, the aircraft flying the route, an Airbus A310-304, registration wit ...

* 2001: Air Transat Flight 236, also known as the Azores Glider incident * 2004:

Pinnacle Airlines Flight 3701 On October 14, 2004, Pinnacle Airlines Flight 3701 (ICAO: FLG3701, IATA: 9E3701, or Flagship 3701) crashed near Jefferson City, Missouri, while flying from Little Rock National Airport to Minneapolis–Saint Paul International Airport. Flight 37 ...

* 2009:

US Airways Flight 1549 US Airways Flight 1549 was a regularly scheduled US Airways flight from New York City (LaGuardia Airport), to Charlotte and Seattle, in the United States. On January 15, 2009, the Airbus A320 serving the flight struck a flock of birds short ...

* 2010: Cathay Pacific Flight 780 * 2016:

Air Canada Air Canada is the flag carrier and the largest airline of Canada by the size and passengers carried. Air Canada maintains its headquarters in the borough of Saint-Laurent, Montreal, Quebec. The airline, founded in 1937, provides scheduled an ...

Flight 361 * 2018: SmartLynx Estonia Flight 9001 * 2020:

Pakistan International Airlines Flight 8303 Pakistan International Airlines Flight 8303 was a scheduled domestic flight from Allama Iqbal International Airport in Lahore to Jinnah International Airport in Karachi, Pakistan. On 22 May 2020, the Airbus A320 crashed into Model Colony, a de ...

* 2022:

LATAM Paraguay Transportes Aéreos del Mercosur S.A, d/b/a LATAM Airlines Paraguay (formerly known as TAM Paraguay and previously ''Líneas Aéreas Paraguayas'') is the flag carrier and the national airline of Paraguay with its headquarters in Asunción, Para ...

Flight 1325

References

External links

*
A survey on the use of ram air turbine in aircraft
/ AIP Conference Proceedings > Volume 1831, Issue 1 (2017) doi:10.1063/1.4981189
Emergency Airplane RATs – IEEE
{{Aircraft components Electrical generators Aircraft components