Indecisive Analysis???

[Lawreston]

During my initial flight, with CFI, in the C-172 Skyhawk with newly-added Power Flow Systems tuned exhaust we flew for 2.5 hours. We departed with full tanks.
Today, prior to flying to Concord, NH to leave the plane for panel upgrades, I filled the tanks from the prior flight: 11.8 gal.
11.8 gal. / 2.5 flight hours = 4.72gph. I'm hesitant to believe that initial result in view of the 2.5 hours having been little cruise mode, primarily slow flight, med bank turns, steep turns, and other maneuvers the CFI needed to see from his "new" student. Could the seemingly fuel-efficiency have been effected (partially) by the recent MOH on which there are now, at best, 10 or 12 hours?

Opinions??

HR

 

[infotango]

If you look at the tach time you will have a better idea of how much time you actually spent at cruise power.
I know that when I do pattern work or manuvers the tach time is far less for a two hour flight, than it would be for a xc flight of the same time. The engine simply isn't working as hard. Fuel flows calculated out over a set of manuvers are mostly useless because then engine is almost never at a constant power.
I'll leave the question about overhaul effecting engine efficency to those who know more than I do.

 

[poadeleted20]

The PowerFlow system is pretty good, but it won't cut fuel consumption in half. You'd have to compare what you got with what you had before on a flight of similar profile. In addition, you'd have to make sure that whoever fueled the plane fueled it to the same "full" point as the previous fueler -- I've noticed that "full" isn't the same for all line crews. Some pack it to the top, some leave a little headspace for expansion, and some don't recognize the collars in Cessnas with long range tanks and think "full" is to the bottom of the collar.

 

[Lawreston]

The PowerFlow system is pretty good, but it won't cut fuel consumption in half. You'd have to compare what you got with what you had before on a flight of similar profile. In addition, you'd have to make sure that whoever fueled the plane fueled it to the same "full" point as the previous fueler -- I've noticed that "full" isn't the same for all line crews. Some pack it to the top, some leave a little headspace for expansion, and some don't recognize the collars in Cessnas with long range tanks and think "full" is to the bottom of the collar.

I surmised from the outset that an analysis will need more than one tracking; the initial check just surprised me. Whenever permitted, only I put fuel nozzle to the opening(careful to keep the hose off the leading edge's paint), and I always fill to the same level. It'll be interesting to continue tracking the PFS aftermath[is that a pun?]. CFI remains impressed with the PFS, in comparison to stock C-172 w/0-320/E2D.

HR

 

[flyingcheesehead]

If you look at the tach time you will have a better idea of how much time you actually spent at cruise power.

Bingo. Tach time is the best way to find what your fuel burn really is, assuming your tach actually is proportional to engine power and not the ones that is "off" below 800 RPM (or some other limit) and "on" above.

FWIW, the worst ratio of tach to hobbs time I've ever had was 1.08, best was well over 1.4, average is 1.35 (this is for 15 months of club flying, much of which was instrument training, so that's a bit higher than you'd expect from "normal" flight ops).

For VFR cross country flights, which have the worst tach-to-Hobbs ratio (extended periods at high power, no lengthy approaches at lower power), I average just shy of 1.2.

So, I'd expect your cruise fuel burn to be more like 5.3 gph, and at worst 6.6, which is still pretty darn good for a 172.