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Could be, Barry
I start to lose track when loads change, rpm changes and
fuel consumption stays the same {:>). Burning the same fuel would
certainly imply producing the same HP (all other factors being constant).
I have recorded dozens of flights MP fuel flow and rpm, so should be able to
check back and find some apple and apple comparisons.
You are right rpm is not the entire story as your example
points out. That is why its essentially useless to try and program the EC2
without a prop load. RPM,airflow (manifold pressure) and fuel
flow generally tell the story (that's assuming you have the air flow/manifold
pressure to combust the fuel flow).
ED
----- Original Message -----
Sent: Sunday, December 11, 2005 10:42
AM
Subject: [FlyRotary] Re: Elippse
Propeller
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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