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"Morgans" <jessmorgan@cJhUaNrKter.net> wrote in message
news:zjTXf.291$38.91@fe07.lga...
>
> "ADK" <aklettke@okanagan.net> wrote in message
> news:X6TXf.28774$%H.11944@clgrps13...
> > This is probably going to open old wounds. What I'd like is
> > experienced input on the advantages, for economic, efficiency and
> > longevity etc. of different types of redrives.
> >
> > I'm leaning towards a cog-belt reducer in a 6 cylinder, liquid cooled,
> > configuration driving a long drive shaft to the prop.
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
>
> Warning,Warning, Danger, Danger, Will Robinson!
>
> Yep, that is a really big can of worms.
>
> The redrive isn't as big a problem as you think. You get into a mess
when
> you start talking about long drive shafts.
>
> Torsional resonance has brought many of the great minds of the flying
> industry to their knees. No joke. I do not have all of the links at hand,
> but someone here does. Start by googling torsional resonance.
>
> Then, be afraid. Be very afraid.
> I you do not get afraid, keep looking, until you get afraid, because you
need
> to get afraid, or you do not understand the problem.
> --
> Jim in NC
>
Yes, Sir! Lots of old wounds, etc, etc ...
Actually, I believe that a driveshaft can be part of the problem, solution,
or both--although, in and of itself, I agree that a long driveshaft is far
more likely to be a problem than a solution. Also, do not forget that all
resonance applied through the engine mount to the airframe will still
apply--there is a famous "Contact!" magazine article describing some of both
problems during the [attempted] development of the BD-5. The point here is
that, although a loss of power is the most obvious
And keep in mind that, although the redrive isn't a source of torsional
resonance, the redrive isn't inherently dampening. However, many redrives
can be a source of considerable shear and bending loads applied to the
crankshaft. I do not know how much is too much in either case.
As additional food for thought: I was a long time advocate of automotive
conversions, but I'm now leaning away from them--as well as from many of
the more modern engine packages now available. I believe that they can be
just about as reliable in service, and that the probable weight penalty is
acceptable--if a slightly heavier airplane does the same job, burns a little
more fuel, and has a lower initial cost; it may still be the best value,
especially if you enjoy the education that you will achieve through the
development work. However, I'm now leaning back toward the "traditional"
type certified engines because it may be much easier to get approval for IFR
operation. For some time to come, at least in the US, TFRs are going to
continue as a fact of life; and an IFR flight plan gives that greatest
assistance in staying out of difficulty on cross country flights. Just my
$.02, and YMMV.
Peter
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Re: PSRU design advantages
