Specific Fuel Consumption

[Mike Davis]

Here is some further information I got from Jorge at Crossflow.

Mike

----- Original Message -----
From: "Jorge" <jalonso@crossflow.com>
To: "Mike Davis" <mike.davis@dcsol.com>
Sent: Wednesday, January 24, 2001 8:00 AM
Subject: RE: Specific Fuel Consumption

Mike,
We do have some rates for different power settings, all of our customers
have told us that there is a 20-30% less fuel consumption with the Subaru
than with air-cooled aircraft engines.
Power setting for operation of aircraft seem to vary a lot, the 75% rule

is

only valid for such examples like a Cessna 172 with a 150hp Lycoming. Due

to

the nature of our industry (experimental) there seems to be quite a
different range in power settings for the same kit with the same engine.
It seems that the exact same kit with the exact same powerplant has very
different performance figures. You will have two same models (Murphy Rebel
for example), with the same engine, but one seems to cruise 10 knots

faster

than the other using the same power setting. This seems to be a very

common

occurrence and is mostly associated to builder differences. At completion

of

the same kit, one may be heavier than the other. Wings and control

surfaces

may be aligned slightly different, weight and balances may be different

(and

still be in the envelope), and so on. There also seems to be a very big
difference in proper power matches for kits. We have some Glastars flying
with 200hp and a power setting of 55% for cruise, while others with 180hp
use 55% to achieve the same performance numbers (propeller choice is also

a

huge impact).
Basically to sum things up, the most accurate comparison I can give you,

is

to tell you that when one of our Subaru engines is used side by side to a
Lycoming installation, we have always been about 10% lighter in weight and
consume 20-30% less fuel.

Regards,

Jorge

-----Original Message-----
From: Mike Davis [mailto:mike.davis@dcsol.com]
Sent: Wednesday, January 24, 2001 2:02 AM
To: Jorge
Subject: Re: Specific Fuel Consumption


Thanks, those are pretty decent numbers, I actually suspected a little
better though. The CF4-33 works out to a SFC of about .050 lbs per hour

per

HP, and I think we're all pretty used to figuring .048 for Lycomings, even
if the books says it'll do better. Of course, Lycoming figures this at

65%

and lean of peak.

Do you have rates at different power settings? Full power for take off,

or

55% cruise?

Thanks, Mike

----- Original Message -----
From: "Jorge" <jalonso@crossflow.com>
To: "Mike Davis" <mike.davis@dcsol.com>
Sent: Tuesday, January 23, 2001 5:55 AM
Subject: RE: Specific Fuel Consumption

Mike,

All our figures are metered at 75% engine load, and may vary slightly
according to atmospheric conditions. CF4-33(9.5gph@75%),

CF4-33T(10.5@75%),

CF4-33THO(11.5GPH@75%). I was not aware of the typo. Thanks, I will

correct

it.

Jorge

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