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> Richard Lamb wrote:
>
> > But then the topic is resonance, is not it.
> > And?
> > With the exception of combinations which are known to have
> > engine/prop/AIRFRAME
> > resonance issues (hint, hint, hint), certified engines avoid that trap
> > entirely
> > (well, mostly?).
> >
"Ernest Christley" <echristley@nc.rr.com> wrote in message
news:hKkYf.56420$915.53670@southeast.rr.com...
>
> I am glad to add the "(well, mostly?)", because I could read that as "not
> at all". What you do have with a certified engine is a situation where
> the prop manufacturer has tested their prop with that engine. It's a
> well studied combination that everyone knows how to work with.
>
> For instance, you cannot cut a metal prop down but so far. Why? Because
> everyone knows where that resonant point is, and cutting the prop down
> to 70" will land you smack-dab in the middle of patooky when one of the
> blades comes off.
>
> But build a new prop of your own design, sufficiently different from the
> typical prop...then it doesn't matter if you put it on a certified
> powerplant or the front of your Oldsmobile. Unless you have the
> facilities to test it, its longevity is just guesswork.
>
>
> --
> This is by far the hardest lesson about freedom. It goes against
> instinct, and morality, to just sit back and watch people make
> mistakes. We want to help them, which means control them and their
> decisions, but in doing so we actually hurt them (and ourselves)."
I think that the point of "(well mostly)" may have been that even the tried
and true combinations, such as certain Lycoming engines with approved
constant speed props, failures can occur long after the design appears to be
mature, and some of the failures may yet prove to be related to resonance.
The moral may be that everything is experimental, but some things are less
experimental than others.
At least, that would have been my point...
Peter
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Re: PSRU design advantages
