GPH increase with 100LL?

[Arizona Aviator]

Just did a XC (3.5 hrs each direction) in the -12. On the flight out, I burned 3.2 to 3.4 GPH in level cruise. On the return flight, I burned 4.4 to 4.5 GPH in level cruise. These measurements were taken from the Dynon D180. I've wracked my brain to figure out what caused the significant increase in GPH. Each flight was nearly identical. Same altitude, same power setting, same time of day (similar temps). The only difference between the flights I can think of was that I burned 91 octane auto fuel on the way out, and 100LL on the way back.

Would the higher octane cause the 912ULS to run richer? Or, any other ideas why it would burn 1+ GPH more during cruise on the return flight? I'm beginning to question the accuracy of the D180 since its "fuel remaining" numbers always disagree with the graphical representations of fuel remaining.

[mturnerb]

I ran various mixtures of mogas and 100LL - 100% each and every combination in between - in my RV-12 with no appreciable difference in fuel flow or performance. I did use decalin when I added 100LL. Only difference I can think of potentially between your situation and mine.

[Paris12Man]

May I ask what your altitude was and outside temp at altitude and RPM setting?

[rvbuilder2002]

Originally Posted by Paris12Man

May I ask what your altitude was and outside temp at altitude and RPM setting?

I am wondering the same...... (and manifold pressure)

3.2 - 3.4 GPH is a very low fuel flow and would only happen at a very low cruise power setting.
Even 4.4 - 4.5 GPH I would consider an economy/best range power setting.

Were these fuel computer displayed value averages, or what you computed based on flight time vs fuel added to the tank?

[dynonsupport]

To add to Scott's question- when you landed and filled up, did the fill up amount match the fuel computer?

[humptybump]

I can't help with explaining the fuel flow difference between 91 zero-e and 100LL.

WHAT I can say is that I've posted the same observation to VAF with regard to my RV-8.

http://www.vansairforce.com/communit...d.php?t=107794

[Weasel]

Originally Posted by Arizona Aviator

Would the higher octane cause the 912ULS to run richer?

NO.

But Non-Ethenol Mogas has 3-5% more energy per unit than 100LL. If there is a measurable difference it should error in favor of the mogas.

[RFSchaller]

I agree, the actual fuel burn from the gas pump reading is what counts. I don't trust gas gages or fancy fuel burn computers. For me at 5100 RPM it's 4.5 GPH and leave an hour margin. Get fancy and you get in trouble!

[Piper J3]

Originally Posted by RFSchaller

I agree, the actual fuel burn from the gas pump reading is what counts. I don't trust gas gages or fancy fuel burn computers. For me at 5100 RPM it's 4.5 GPH and leave an hour margin. Get fancy and you get in trouble!

I like the way you think. Total agreement...