Hi Bob and Rich,

Does a speeder spring failure always result in a propeller going to course, or is this just the case for a counterweighted propeller (Hartzell) which relies on oil pressure to drive it to fine?

Question 9 from GK2 pg 2.17, - Q9) Failure of the speeder spring in the governor of a CSU will cause the blades to move a) fully coarse with a drop in RPM.

As there are a number of different systems out there, I assume they will explain the type of CSU if they ask a question this specific.

Many thanks,
Cheers Ned..

Yes, there are a number of different systems but they are in the propeller hub and are different ways of moving the propeller blades to fine or coarse pitch. The speeder spring is part of the propeller governor and its failure would always have the same result - the propeller would move to fully coarse.

Whatever the system in the propeller hub, the speeder spring is always opposing the spinning fly weights in the governor. A failure of the speeder spring will 'fool' the governor into believing that the engine is overspeeding because the spinning flyweights will have no resistance. The governor will respond with the action to remedy overspeed. It will try to slow the engine down, that is, it will make the propeller harder to turn.

Very clear! - thanks Bob

Further to this topic, do the flyweights themselves ever fail?

When people say propeller run away is due to the governor failing (and hence the natural tendency of the propeller to seek fine pitch due to the Centrifugal twisting moment) is it due to the flyweights failing?

I guess the type of system, whether the fixed force in the prop hub pushes the prop towards fine or coarse pitch would also be a factor aswell? E.g. if the fixed force was towards fine pitch, and the oil pressure to push the blade towards coarse pitch failed, then the prop would have a tendency to overspeed? I guess thats what the counterweights are for?

Does the fixed force in the prop hub ever fail for some reason?

Thanks.

The most likely cause of failure in a propeller governor would be the speeder spring breaking and allowing the flyweights to send a false 'overspeed' command. This would cause the blades to go fully coarse.

Many singles do not have flyweights at all. They have a strong spring supplying the fixed force that acts towards fine pitch, while oil pressure moves towards coarse. A loss of oil pressure in the hub would result in the blades going to fully fine. Multi engine aircraft will have a hub arrangement where, in the event of a failure in the hub, the fixed force will move the blades towards coarse pitch i.e. towards the feather position.

Thanks Bob, that makes sense.

My question stemmed from watching ice pilots and during the coarse of one episode the crew had a an oil leak in their engine which caused the prop to overspeed! So was trying to figure out how it worked!