Aero Vintage Books

I've got a question I bet the experts on here can help me with? In many stories of bomber missions I've read about an engine starting to "Windmill", or " Runaway". What exactly is this condition, and what is the right actions to correct it?

Windmilling of the engine is when the airstream turns the propeller/engine combination. It happens when the propeller can't be feathered, i.e. the propeller blades turned into the airstream leading edge forward to prevent the air from turning the propeller. This can happen if the oil supply is gone or feathering pump disabled. A run-away propeller/engine is when the propeller overspeeds and can't be controlled and can be caused by a lack of oil supply which controls the propeller (like power steering fluid in your car), governor failure, or failure of the propeller itself. With the engine running away it can and will tear itself apart (like over reving of your car engine) and the propeller may depart the engine and possibly cutting through the fuselage. Either way, the engine will be damaged and may catch on fire due to lack of oil.

The procedure to prevent it is to feather the propeller.

A windmilling propeller creates an enormous amount of drag. That is the main reason to feather a propeller.

With a propeller spinning, centrifical force tends to turn the blades to a flat or low pitch angle which causes a higher RPM. The oil pressure/electrical motors oppose this.

One more point, some propellers were electrically operated, they had a small electric motor and gearing to controll the propeller angle. If you lose electrical power you will be unable to feather the propeller or control it. The electrical propellers had a brake built in to them to prevent the blade angle from changing if electrical power was lost, but like all things mechanical, it will fail.

Thank you very much for clearing that up for me , and maybe many others. It never ceases to amaze me the expertise of the members on this fine web-site. Thanks again !!!