Let’s see, I think it was Bob mentioned assuming .6 #/hp-hr (BSFC) for fuel burn.  Based on what I measured on the dyno on my 20B, that seems a bit high to me.  My numbers ranged from 0.49 for lean cruise settings to 0.54 for WOT 5000 rpm, lambda of about 0.93 (max power mixture).

 

So-o-o . . , when I’m cruising at 7500’ at 170 KTAS and 9.3 gph, I’ll assume a BSFC of about .5 which means a power of about 115 hp (mogas weighs 6.18 #/gal).  That’s a believable number.

 

When I’m taking off at WOT and about 5400 rpm I see about 19 gph.  My dyno hp curve shows about 230 sea level, standard day hp for that rpm.  Adjust that for 1500’ elevation and using a BSFC of .54 says I should burn 18.7 gph.  That’s very consistent.

 

My dyno curve also says 270 hp @ 6200 rpm. Adjust that to 7500’ (about 80%) and varying the speed as the cube root of hp says if I get 170 KTAS at 115 hp, I should get 210 KTAS at WOT and 6200 rpm.  Guess what – when I did that I saw 208 KTAS readout on my GRT EFIS.

 

It all hangs together. (Don’t forget that SAE rated hp is normalized to sea level, 60F day.)

 

These BSFC numbers should be fairly consistent with what a Lycoming could get.  The fact that I get better fuel economy than the Lyc powered Velocitys suggests that I have a bit lower drag.

 

This also suggests that the 20B on my Velocity doesn’t ever have to really work very hard.

 

Al