Unknown Propellor

PETERTHEEATER;166691 wrote:

I will stand corrected but the pitch gears would have been covered by the propeller spinner.

Those props are bent the wrong way. The gears you can see are the propeller reduction gears. This cutaway of a Bristol Pegasus shows what I mean.

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The propeller is attached to the shaft on the left of the picture.

The only reason I suggested it might have been a stationary undercarriage collapse is in a tail dragger the forces might be directed forwards as the blades touch the ground

Another option is the prop and gears came separately and have been put back together the wrong way around.

Right; I see now that the blades are bent forward. If that cluster is a reduction gear I would expect either the front bevel gear or the rear to be a different diameter to provide the necessary ratio for reduction of the prop speed yet they appear to be the same size like a differential.

Where are our golden oldie Engine Fitters when you need them:)

Here's a typical assembly...



Should buff out Chief..

Bigbear;166677 wrote:

The blades seem to be bent the wrong way. If the aircraft was travelling forward wouldn't they be bent towards the gears? Is this because of an undercarriage collapse perhaps?

If an engine is producing power on impact, the blades tend to bend forwards.
If no power is being produced, they bend backwards.

P wrote:

If an engine is producing power on impact, the blades tend to bend forwards.
If no power is being produced, they bend backwards.

Mmmmmm not sure I agree with that, look at the beaufighter example in the last post. If the engines are producing power and the aircraft is travelling forwards the blades bend back (ye cannie change the laws of physics Jim). If the plane is not moving forward I might agree.

If the engines aren't producing power then only the lower blades bend back on impact, again if the plane is moving forward. The blades or blades above the level of the bottom of the fuselage tend to remain straight.

That's certainly how I've seen it in pictures of crashed planes.

It also makes sense from basic mechanics and action and reaction of the forces acting on a spinning blade tip touching the ground with forward velocity.

This isn't from one of those German pusher props is it? If so then the blades are actually bent backwards as the engine is in front of the propeller.

Sounds crazy, but it's true.
Think about the pitch angle each blade will be at when the prop is rotating and producing thrust, and how that thrust is directed.

Props, such as this one, where the engine was operating at normal flight power settings on impact with water seem to show the most forward bending, as water is denser than air.
Ground impacts under the same conditions show less forward bending, as the angle of the blades causes them to try to dig themselves up out of the ground.

As you say, the most commonly-seen result is blades bent backwards, which is caused when the prop is just spinning at idle or under no power at all, i.e not producing thrust.

OK, see your logic, however I'd like to see some pictures. I've never seen any bent forward like that before including water landings.

I still think the resultant force produced when a spinning prop, under power hits the water at speed with several tons of aircraft behind it will be rearward rather than forward.

Do we have any good photo's of the blade tips to see the damage pattern ?

The extreme angle of blade bending with out damaging the prop roots would indicate that it hit a relatively soft object.