The Ram Air
Turbine emergency power system, known as RAT, is one of the backup power
sources that are designed to automatically engage to ensure that those systems
needed for continued safe operation of the airplane are powered, in case a
failure of the power from both engines and the aircraft speed is above 100 Knots.
Theoretically, there is no time limitation for flying with the RAT. The Emergency Generator should remain supplying until touchdown; so the
aircraft should never become 'Batteries Only'.
This small
generator is required in the event of power failure and should be tested before
the first flight
A ram air turbine (RAT) is a self contained turbine
unit with a hydraulic pump attached that are generally only used in emergency
situations.
RAT is deployed automatically when main system pressure
drops below a predetermined value, and could also be deployed into the airflow
by selection of a switch on the flight deck.
The RAT must be capable of operation over a broad
speed range, maintaining normal hydraulic pressure, whether the aeroplane is at
maximum speed and height or slowing for landing.
A volumetric flow control valve is usually fitted to
the RAT allowing the propeller to attain operating speed, before being loaded
by the pump, this allows full system pressure to be achieved approximately 4-5
seconds after deployment into the air stream.
In the 787 (above) the RAT is stowed in the flap track fairing. In the A350 XWB, the place of stowage was initially under the left wing as shown in this old image below, but currently is under the fuselage fairing (belly fairing).
In the
extremely rare loss of power from the engines, the RAT deploys into the
airstream and produces power for the cockpit and flight controls to safely land
the aircraft.
The RAT is designed&manufactured
by American supplier Hamilton Sundstrand Electric Systems (a subsidiary of UTC)
located in Rockford Illinois (USA) that also provides the A350 XWB’s Electric
Power Generation System.
“We are proud
to support Airbus’ latest advanced commercial aircraft. As the world’s leading
RAT systems supplier, we strive to provide the best competitive and technical
solutions for our customers, and we’re pleased to be selected for the A350
XWB.”
Airbus is
using the same 21-year-old original A340-300 as development testbed for its
investigation of acoustic transmission after installing a carbonfibre fuselage
panel that could be seen in the same photo.
Based on the
article “Airbus teste la RAT de l'A350 sur son A340-300 d'essai ” published in
AeroWeb-fr.net