By Tommy H. Thomason

Monday, January 26, 2009


Aircraft manufacturers tried in vain to avoid the weight and complexity of hydraulic control systems. Some also tried to provide a manual backup, such as an extendable control stick to allow the pilot to contend with the loads. The F7U-1 Cutlass had a complex system with an automatic switch over to manual control via spring-loaded tabs on the ailevators. This proved troublesome and at least one pilot was killed as a result of an unnecessary and ineffective switch. As a result, the production F7U-3 wound up with four hydraulic pumps for the flight controls.

Eventually, the fallback for a hydraulic pump or engine failure on most aircraft was the Ram Air Turbine or RAT, which was extended into and turned by the air stream to provide hydraulic (and/or electric) power. These were released by unlatching an uplock, so no hydraulic or electric power was required to bring them into play.

The F8U RAT was unusual in that it had large number of blades of high activity factor and the fan was shrouded.  Most RATs now have only two blades and are not shrouded. This picture of an RF-8 with the RAT extended was taken by Joe Youngerman at the National Air and Space Museum.

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