karel wrote:
Out of curiosity I started to look for fuel consumption figures for the
Jabiru 3300.
I found a figure of 0.46 lbs/HP/hr which is not particularly meaningful to
me.

This is actually a pretty reasonable number. Most of the big bore
lycomings are in this range, if I remember the discussions I have had
recently on power and fuel consumption.

The value being discussed here is "BSFC" or brake specific fuel
consumption. This is part of the universal "truth" regarding horsepower
in internal combustion engines. HP takes fuel. More HP takes more fuel.

Is this way of calculating correct and do the numbers seem reasonable?
I had expected this engine to be less fuel hungry than the Lycomings &C...
Do not Rotax claim something like 15 liters/hour?

As others have already pointed out, you had one decimal out of place..
(36 pph) but the rest of the math was about right..

As for the 15 liter per hour claim.. that is likely the power setting
(and fuel flow) for max range/best economy. Airframe and engine
manufacturers like to "play" with the numbers to suit their needs. None
of this overrides the fact that you have to burn more fuel for more HP.

With a BSFC of 0.45 (essentially the same as your engine, and similar to
Lyc's and continentals). I am not positive at what mixture this is being
computed at, but stoichiometric (1:14.7) seems to be the most logical.

250 hp = 18.75 gal/hr
200 hp = 15 gal/hr
150 hp = 11.25 gal/hr
100 hp = 7.5 gal/hr

The way you can use this BSFC to your benefit is in evaluating engine
efficiency claims on your own, independently of marketing claims. Your
fuel burn for given power setting can be calculated.

If an engine maker, particularly a new-comer, wont release their values,
then their claims of power and efficiency should be viewed as suspect
and with skepticism.

Dave


TIA

PS do not tell me that the rated power of 120 HP is not for
continued application, I knew that. Seems similar to the Rotax 914S.