Message text written by MARK CLARK
>I believe they are havingTORSIONAL RESONANCE problems.<
Correct that to HAVE HAD.
> the
propeller is a form of spring,<
Try getting the manufacturer of a popular =ACexperimental=AC propeller to admit
to this!
>This is due to the torque reversals that occur at resonance point. Any
engine that produces 1 power stroke per revolution is bad news when
it comes to torsional vibration<
Actually the propeller sees little difference btween a geared two cylinder
engine and a direct drive four cylinder of the same power; six or more
cylinders is another story.
>It would take a very complex analysis to determine the
magnitude of this problem.<
An engine propeller combination is actually quite easy to analyse with the
modern availability of PC`s and appropriate software. The difficult bit is
trying to get the propeller maker to nandover data he doesn`t have! Added
to which.........
>This is best analysed empirically on an engine
test stand;<
Which is partly where 102 running hours of testing and development work
went.
See also www.sierra.net/skyranch/article2.htm and
www.prime-mover.org/engines/torsional/sport-av92.html ; the latter confirms
the solution we have taken as being the most appropriate. Compare that with
the alternative engines on the market, some of which have NO torsional
damping device.
For more info., pick up a brochure at Cranfield ( Sportair stand 82 & 83)
Duncan McFadyean
|