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

Paul - check my input on the KIS letter - I combined data from their web
page and stuff from the article. Actually you can make a fair estimate of
shaft horsepower from static test - the clue is you need the dia (70 in)
and check the perfect pump jet hp, and back in a reasonable efficiency
of a variable pitch prop pumping eff (I used 85 percent I will check
for more detail with my prop program)
the  data equate to:           thrust  est shaft hp  bsfc
                                300       50          1.5
                                375       69          1.12
                                450       91          0.98
                                525      115          0.87
                                600      140          0.79
This assumes that they reported data truthfully, and makes reasonable sense
BSFC gets better at higher power settings, and the flat 1.2 reported by
Avon Aero in their sales page is suspect because it did not change with
rating

By the way, you will be pleased to hear that my current Road and Track
came with a magazine size RX 8 pamphlet nice copy- PR - but nice
Vance Jaqua

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