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What is a Ram Air Turbine (RAT)?
In the case of a flight emergency where all power may be lost, it is paramount that pilots can still have functional flight systems and instruments so that a safe landing may be conducted. Despite many modern aircraft having two sources of power, there is always a possibility that both may fail or be inoperable. In such emergencies, the aircraft may be able to rely on a structure known as a ram air turbine (RAT) which can be used as an alternate source of power during flight.
The ram air turbine often comes in the form of a small wind turbine that may be deployable from the aircraft wing or fuselage. Generally, the ram air turbine is attached to either a hydraulic pump or generator in order to provide its functionality as a power source. When the ram air turbine is deployed, it is placed within the airstream in order to generate power from the ram pressure resulting from the aircraft moving through the atmosphere at high speeds. As such, the speed of the aircraft is directly tied to the power output of the ram air turbine.
As stated beforehand, the ram air turbine is an emergency system, only operated when the primary and secondary aircraft power system fail. As an example of its operation, the RAT may automatically deploy from the aircraft wing or fuselage in the event that the auxiliary power unit and other power sources all fail. With the power created by the RAT, the hydraulic pump or generator can create the energy needed to operate flight controls, hydraulics, and flight instruments. If the turbine is a type only capable of creating hydraulic power, that power may then be used to power generators on the aircraft.
Across aircraft types, the most common application for the ram air turbine is for military aircraft due to the stringent emergency requirements that demand their operability even in the instance of a complete loss of power. Despite this, many civilian aircraft also may rely on the ram air turbine as well for emergency situations, including the Airbus A380 which features a ram air turbine with the largest propeller diameter. On larger civilian aircraft, ram air turbines will often generate 5 to 70 kW of power depending on the generator. With smaller models, on the other hand, around 400 watts of produced AC power is common. Aircraft that are centered around agriculture can benefit from the use of the RAT as well, as such devices can power centrifugal pumps so that spray systems may be pressurized for crop-dusting applications. RATs in particular are very beneficial for agriculture, due to the fact that the Federal Aviation Administration allows their use with approved engines and power systems without the need for modifications.
While ram air turbines are emergency systems that are not often used, they have saved countless civilian lives since their invention. From the 1983 Gimli Glider incident to US Airways Flight 1549 in 2009, ram air turbines have assisted pilots in daring landing procedures so they could best ground an aircraft during an emergency and prevent the loss of lives. Since the advent and implementation of ram air turbines, they have aided in saving over 1,700 lives over 16 documented emergency situations.
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