Ram air turbine

Lore & Background

In some early aircraft, including airships, small RATs were permanently mounted and operated a small electrical generator or fuel pump. Some constant-speed propellers, such as those of the Argus As 410 engines used in the Focke-Wulf Fw 189, used a propeller turbine on the spinner to power a self-contained pitch governor. Modern aircraft generate power in the main engines or an auxiliary power unit; the RAT generates power from the airstream due to aircraft speed, producing less power at low speeds. In normal conditions the RAT is retracted into the fuselage or wing and is deployed manually or automatically following complete power loss, with batteries used in the interim.

RATs are common in military aircraft, which must survive sudden power loss. They also power pod-fitted systems such as the M61A1 Vulcan cannon. Some free-fall nuclear weapons, such as the British Yellow Sun and Red Beard, used RATs to power radar altimeters and firing circuits as a more reliable alternative to batteries. High-powered electronics like the AN/ALQ-99 jamming system can be self-powered by a RAT in standard operation, allowing installation on a standard hardpoint without a pod-specific power supply. As many as five such systems can be mounted on a Boeing EA-18G Growler, each containing two transmitters with directional antennas, and they stay deployed continuously during flight.

Many modern commercial airliners, from the Vickers VC10 of the 1960s onwards, are equipped with RATs. The VC10 used a RAT driving an electrical generator due to its packaged hydraulically powered flying controls. The Airbus A380 has the largest RAT in the world at 1.63 metres in diameter. RATs have also been used to power centrifugal pumps on crop-duster aircraft, chosen for safety and to avoid modifying the FAA-certified engine and power systems.

Reader's Guide

The ram air turbine serves as a critical emergency power source in modern aviation, providing hydraulic or electrical power when both primary and auxiliary systems fail. Its significance is underscored by its use in numerous civilian incidents, including the Gimli Glider incident (Air Canada Flight 143), the Azores Glider incident (Air Transat Flight 236), and US Airways Flight 1549, among others listed in the source article. In military aircraft, RATs enable survival after sudden power loss and power pod-mounted systems like the M61A1 Vulcan cannon and AN/ALQ-99 jamming pods. The RAT's legacy includes its role in early aircraft and airships, as well as in free-fall nuclear weapons where it provided more reliable power than batteries. In civilian agriculture, RATs drive spray system pumps without modifying the aircraft's certified engine, simplifying plumbing and ensuring gravity feed. The RAT's design varies widely, from the 1.63-metre unit on the Airbus A380 to smaller models producing as little as 400 watts, reflecting its adaptation to diverse aircraft and power requirements.

Did You Know?

• As many as five AN/ALQ-99 jamming systems with built-in RATs can be mounted on a Boeing EA-18G Growler.
• A typical large RAT on a commercial aircraft can produce 5 to 70 kW, while smaller low-airspeed models may generate as little as 400 watts.