C172 - Fuel consumption @ 65-70%

[bliksimpie]

To all the real life pilots.
what is your fuel consumption round about with the C172 for cruse flight @ 65-75% (yeah I know there are many variables)

just looking for some ball park figure ? My current average is about 7.5 GpH

can 8 or 9 Gal per hour be right for flight planning purposes, or do you use your average consumption as a base for flight planning ?

[aikichris]

sent you a PM

[Oracle427]

Generally speaking I use 9GPH and that has served me very well. I usually come within a gallon or two of my expected consumption on a 2 hour flight when I drop the dipstick into the tanks. I'm usually cruising at 2400RPM on a 180HP 172 at an average of 6000'.

[Great Ozzie]

To all the real life pilots.
what is your fuel consumption round about with the C172 for cruse flight @ 65-75% (yeah I know there are many variables)

I would use book figures -- I never really knew *exact* fuel burns as for the vast majority of flights I did not refuel after landing. The ones I did must have been a 'yeah that's about right' as I never recall an 'off' fuel burn.

Also, and this is *extremely* important, when I landed and after shutting down the engine, my absolute minimum amount of fuel would be 1 hour (planned) fuel remaining... that was *never* (ever) dipped into. Typical to be much more generous w/ the reserve.

Start the engine, start a clock... and then you know what time you have to be back on the ground with the 1 hour + fuel reserve.

Also, really just one main variable with percent power for gph used. You pick a percent, fuel burn is going to be roughly the same for whatever altitude. The main variable for % power will be how you lean (Best Power vs. Best Economy). The variables come in as e.g. KTAS and rpm setting.

can 8 or 9 Gal per hour be right for flight planning purposes, or do you use your average consumption as a base for flight planning ?

The way I always did this for a 'cross-country' flight:

I went to the Performance Chart knowing what % power I was going to use, picked an altitude, then found what rpm setting I needed. Then lean appropriately. I never used an average as I knew what the 'book burn' would be.

Fuel mismanagement accidents are a perennial problem within GA. One way to avoid is to know the fuel burn for the power setting to be used and be conservative with how much fuel is loaded and the amount of fuel reserve.

Generally speaking I use 9GPH and that has served me very well. I usually come within a gallon or two of my expected consumption on a 2 hour flight when I drop the dipstick into the tanks.

This a very wise check.

[Oracle427]

I do consult the books as noted by Great Ozzie, but so often I land on 9GPH.

After a flight, I always like to check on how I did on several parameters, as that is the only way to learn if you can improve. Otherwise, what is the point of planning in advance at all?

If the fuel is off, I have to check my density altitude estimates and time between checkpoints to see if I was making the expected groundspeed. It can be fun to check all these things as you revisit a recent flight.

[bliksimpie]

Thanks a lot for all the in depth answers given.
I really appreciate your willingness to share your knowledge.

[Great Ozzie]

I do consult the books as noted by Great Ozzie, but so often I land on 9GPH.

Yeah I should have mentioned that... one flies a certain series airplane enough, like the C172 R model, certain numbers will stick in your head because, for example with the fuel burn, you know what % power you will be using.

I would buy a POH for the airplane I was flying so I had "the book" I could lug around. Mostly, the general POH varied from the Airplane Flight Manual (the AFM -- what is actually in the airplane) by the Weight & Balance info.

But you have to be careful the POH you have matches the airplane's AFM. Not a problem if you own (like we do ). If you rent, one needs to look up / verify those numbers in the airplane's actual AFM. This brings up an interesting point that we have experience with re: our C172R that enables us to swap in the "S" prop / Horsepower upgrade.

I've posted this link once before (worth posting again I feel). There is a youtube of the Top 10 Causes Of General Aviation Accidents (2012)... the 'Number 7' (Begins at 8:20) is a very interesting example of "Fuel Related" where the C172 accident being described was due to the Airplane Flight Manual *not* being appropriately updated after an STC mod that raised the horsepower by 10hp or so. Pilot goes to the AFM expecting such and such fuel burn, but gets another (higher) fuel burn due to the STC mod (AFM was not updated to reflect the STC change).

This is part where the Oracle was saying the importance to verify the numbers to actual use.