Originally Posted by
Cat 1
I think there might be something else at play here too Bert - The engine ran fine at the "summer setting" on the ground run ups but was just slightly lean in the Air - My in flight CHT's were also low as the engine is uncowled.. I did try a few minutes of WOT and then I could dial out the additional fuel until it cooled again.. I don't think we are currently compensating for a "cooler" engine.. Had trouble getting above 120 deg and wouldn't stay there. Had the big prop on (18-6 wide) and it had lots of power.
Two things of note also: The engine ran very clean - Very little residue and was very light.
The fuel burn was incredible - I only filled the tank once and wanted to run it dry as I was using my Wife's SUV for transport. Bet I flew over 20 total minutes on 8 oz of fuel. Some putting around but lots of high power stuff too.. In the end to run dry - I set up a turn of about 700m in diameter and was trying to see how many I could do without correction - air was so smooth I had a few intervals where I counted 5 uncorrected circuits that were almost superimposed.
Everything plays a role, but so far I have not yet seen much influence from an engine running 80 degrees HT all the way up to 135 (this is the range I pass when doing a tow, and it never requires any correction)So I think the main influence is fuel viscosity making the engine a bit leaner.
Diesel (only a slight bit more viscous than gasoline/oil mix) easily changes a half to a full point of CentiStokes on a tempperature change of say, from freezing to 20 deg C, and that is noticable in things like pumping speed or filter differential pressures.
So yes, I think the viscositiy is the main issue. But that is relatively unimportant, because both engine running temp and fuel viscosity are affected by the same parameter: ambient temperature.
It could be worth a try. You progged your own driver, it should be easy to do an experiment. Tthe nasty thing is, it takes a minimum of 6 months to change progging, test in summer, then wait for winter to check the veracity of the claim....
The 20 minutes WOT on 8 oz, I think is pretty close. I have a variable timer as an emulation of a fuel gauge, and it is set at 13,5 minutes for aprox a 25% reserve fuel. Since I can "tune" my fuel curve, this timer is "fairly accurate" regardless of throttle position. So I am inclined to say that yeah, you probably would be running 20 minutes on a single 8 oz tank.