Hi Dan,

 

I think your fuel flow assumptions are overly optimistic. In addition, the power output of the turbine will degrade with altitude just like a normally aspirated piston engine. The exception is if the turbine has a power limit at lower altitudes, often due to inter-turbine temperatures, then it will behave more like a turbonormalized engine where it will produce rated power up to some critical altitude and then degrade with additional altitude.

 

As Gary points out, your fuel flow estimate requires a BSFC of 0.38 (using a Jet A density of ~ 6.9Lbs/Gal) which is very unlikely. In comparison, the Walter only achieves a BSFC around 0.67 Lbs/Hp/Hr. Using this figure, your Innodyne 255TE will be sucking down 24 gal/Hr. On their website, Innodyne reports a flight average fuel consumption of 7 Gal/100 Hp/Hr which equates to an average BSFC of 0.48 Lbs/HP/Hr. This would amount to 17.7 GPH at takeoff and would decrease to 12.4 GPH at 12,000’ which would be equivalent to 70% power, assuming the engine is not derated. I think the new Williams engines, such as the FJ33 and FJ44 are achieving BSFCs around 0.55 (though I can’t confirm the BSFC figure), which is almost 15% higher than the Innodyne BSFC yet 18% lower than the Walter BSFC. Using the 0.55 value, your fuel flows would be ~ 20 GPH at full power and ~ 14 GPH at 12,000’ and maximum power of 70% (or ~180HP). Like Gary, I think these numbers will hit closer to the mark when Innodyne publishes the BSFC for its production turbines.

 

Also, don’t forget that Jet-A weighs about a pound more per gallon than 100LL, so your useful load with full fuel will be less, offsetting some of the weight saved from the lighter engine.

 

We’re getting closer to a practical turbine engine for GA aircraft, and certainly Innodyne may be the closest when it comes to the smaller SHP engines. Unfortunately, I think it may be many years before we see a turbine that rivals the efficiency of our “modern” piston aircraft engines.

 

Best Regards,

Mike