Finn Lassen wrote:

Just read the April 2003 issue of Sport Aviation.
Claims 14 GPH at 200 HP.
Assuming the fuel they burn also weighs 6 pounds per gallon, that's

[BSFC] 0.42.

Explain again to me why that's impossible in a small turbine.

Finn

No way. Sport Aviation mag is becoming editorial ignorant and irrelevant.
Uniformed articles like this facilitate the scam artist out there.

Several reasons. The main one I think is the limited compression ratio
one can obtain with a single stage of centrifugal compressor
is only about 3:1. These APU engines are made from glorified turbo

chargers.

Fuel consumption was of little consequence.

The Mazda rotary is up to about 10:1 CR and a diesel
is up to about 20:1 Modern axial flow turbo fan compressors are over
8:1 I think. Another is the compressor and turbine clearance
is critical and as you make it smaller the clearance gap becomes a larger
and larger percentage of the total leakage. The third thing is turbine

inlet

temperature. Efficient high temp turbines are very expensive indeed.

Hopefully Vance will jump in an explain it better as he gave a very good
forum on the subject at Sun & Fun. You should have attended.

Paul Lamar

Good summary Paul. Modern large turbofan's are up to around 40:1 compression
(RR Trent and GE90).

I think the PT-6 is quoted at around 0.65 BSFC. Does anyone really believe
you can take a 30 year old APU, designed for the military, have a reduction
gearbox bolted on and produce a powerplant with 50% lower fuel burn then the
industry standard?

Snip>Assuming the fuel they burn also weighs 6 pounds per gallon, that's
[BSFC] 0.42.
Jet fuel has a specific gravity of about .80 as compared to .72 for AVGAS.

Mark Wrathall

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