Kyler

Another true (War) story.

T-28A

7 cyl 900 HP engine. (128+ HP per cyl)
2 blade Aero-Products prop (big wide paddle blades to absorb HP)
Prop shaft cut with a square corner where it transitioned to throw.
At original cruise rpm viborations/stresses caused prop shaft to break
off and prop depart plane.
Result - dead stick with prop missing.

Fixes tried.

1. Tried 3 blade prop which reduced stress on crank - worked but cost
too much to throw away the relatively new 2 blade props and get
new 3 blade props.

2. Dissambled engine and under cut (rounded) square corner betweem
shaft and throw. More failures.

3. Set up a restricted rpm range that could be transitioned but not
fly steady state in.

4. Raised cruise rpm 150 rpm changing stress on crank. These two
worked but reduced range and duraation a lot. Had to refuel after
every training mission vs flying two missions on one load of fuel.

Looks like this true life story supports both sides of the argument?

Big John


On Mon, 01 Dec 2003 20:09:35 GMT, Kyler Laird
wrote:

"Mike Rapoport" writes:

But do you agree that components that require maintenance (propeller,
cylinders, engine mounts, ...) can cause/accelerate crankshaft
failures?

I suppose that I agree to a limited extent, but virtually all
crankshaft/connecting rod failures are caused by a flaw/fault in
design/manufacture or installation. Once the crank or connecting rod is
installed, nothing is done to it and it is unseen until overhaul time. A
failure of either of these components is not going to put much, if any,
metal into the oil until the bitter end either..

I was thinking less of metal in the oil than the forces exerted on the
crankshaft. An out-of-balance prop or even a faulty spark plug can
cause out-of-spec. impluses to be exerted on the crankshaft.

I sure don't know how significant that is likely to be though. ('course
you can consider the stories of pilots taking off after prop. strikes as
an extreme.)

--kyler