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Ed,
If you're burning the same amount of fuel and the efficiency of your
engine hasn't changed (i.e., BSFC constant), doesn't that just mean
that you're producing the same horsepower at the higher RPM? That could
be a consistent finding if your manifold pressure is lower than it used
to be when you were running lower revs.
RPM isn't the whole story. For instance, one could race a car engine in
neutral at high RPMs but produce very little horsepower. It's the
reason that a dyno needs to put a load on the engine in order to
generate a meaningful horsepower/torque curve.
Your advantage in running the higher RPMs is that you are in the higher
output part of your horsepower/torque curve when you are in rev-limited
situations like climbing or takeoff. And theoretically, if allowed by
your prop pitch, you could generate higher maximum horsepower because
you could get to the upper revs (e.g., 8500 or so) if you wanted it,
subject to the limit of your prop tip speed going supersonic.
Barry Gardner
Wheaton, IL
Ed Anderson wrote:
Hi Todd,
Actually, No - not anything significant.
Although I now cruise at 5600 rpm vice 5200 rpm with the 2.17 the fuel
burn is identical. I think the 2.85 puts less load on the engine
permitting it to turn faster at the same fuel burn. Just a theory.
Ed
-----
Original Message -----
Sent:
Sunday, December 11, 2005 3:06 AM
Subject:
[FlyRotary] Re: Elippse Propeller
Hi Ed;
I know that it has been stated in the past, but
refresh my memory. Have you observed any fuel consumption change from
the 2.17 to the 2.85????
Todd (tough game tonight, so too tired to
check the archives)
Also looking at the power difference at
the two different rpms, I calculate 160 at 5200 and 180HP at 6000,
whether that is accurate absolute power it shows a possible 12.5%
increase. The disc area carved out by the 74" prop is approx 18% more
although its speed is approx 13% less. So I think more area, more HP
and more pitch appears to add up in my case to considerably better low
speed performance. The top speed appears not to have changed, still a
shade under 200 MPH around 197MPH for both props.
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