[Starting a new thread.  The reply nesting level in my mozilla window
 was getting freaky.]

Vivian Meazza wrote:
> The engine I'm trying to specify developed 1140 HP at engine
> revolutions of 2850 rpm at a boost pressure of 9 psi. It was fitted
> with 1:0.477 reduction gearing, which I think means that the
> propeller turned at 1360 rpm.

Hrm, 1360 RPM is very slow for a cruise value, just over idle speed
for a smaller plane.  Likewise, 2850 RPM really isn't that fast for a
piston engine.  It's at the top end of ungeared engines like a
Lycoming O-360 or whatnot, but not really very fast for four stroke
engines as a whole (my Saturn redlines at 6000, for example).

Is it possible that the 2850 number is a *propeller* RPM at max power?
Then you'd get a max power engine speed of 5975, which seems plausible
to me and avoids the problems with solving for a propeller which
"cruises" at a pitch where normal props would be windmilling.

Does anyone have good info on whether the cockpit engine speed gauge
in a Spitfire (which is presumably what most sources will quote for
"RPM") reads engine or propeller speed?

Andy


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