This appears to be a forged crank but it is lacking
the large radii in the journal area necessary to
lower the stress concentrations and make the crank last
the requisite number of hours for aircraft use. All aircraft
cranks that I have seen have large radii in this area that is
known to reduce stress concentrations.

 I agree that the large radii will reduce stress concentractions. But I was
lead to believe that their primary function was to take the thrust loads.
This is one reason they're not on automotive cranks and are present on all
direct drive aircraft piston engines. Does this make sense from an
engineering standpoint or is it just an over simplification from A&P school?

James Phillips

I think somebody mis informed you in A & P school. There are separate
plane thrust bearings in all aircraft engines. There is a chart in Taylor
on this subject of crank radii verses stress concentration and I will
scan it in and up load it as soon as Robin stops using her computer.
In the mean time here is another interesting chart from the Sky Ranch
Engineering Manual I think.

Paul Lamar

Opps, here is the chart I mentioned above. A forgot I already had it scanned
in. A bit marginal to read I am afraid. I will scan in a newer version in
higher rez soon.

Paul Lamar
 
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