C-172 GPH

[Ddayle]

I have been told that a 172 should burn about 8GPH. I seem to be getting better. As an example today I flew 1.2 hours on the hobbs, I topped off the tanks fuller than when started and still only took 7.7 Gal. I Have only flown club 172's for a few months now, but I have noticed before that used less than 8 GPH almost every time. I lean with an EGT, but as a motorhead I can also lean by sound/feel to about the same %. DaveR

 

[tonycondon]

which engine in the 172? i think they've come from the factory with at least 3 different horsepowers, and who knows how many other after market mods have been approved. and what kind of power settings do you run?

 

[KennyFlys]

Refer to performance numbers in Section 5 of the POH. Then, consider the age on the overhaul, maintenance, etc. As a general rule, I go with the published numbers for teaching flight planning but add a 10% fudge factor for safety's sake beyond required reserves.

 

[ScottM]

As Tony said it will vasry with what engine you are flying. When I was flying the 172R models I got 8 or little under gph. But when I flew the S model I was getting around 9gpg. The S used the O360 while the R used the O0320.

I am currently flying a plane that uses an O320 a O320-D3G to be exact and I often get around 7.8-8.3 gph depending how how much I am leaning.

What you should be doing is using the numbers in your AFM for that aircraft. Then look at your actual usage if it is less, bonus fuel! If it is more then you better start recalculating your fuels consumption or risk running out of gas and making an unscheduled landing.

 

[AuntPeggy]

I'm flying a C-172 with 180 hp Lycoming. Always plan using 8 gph. Usually pull back to 2400 or 2300 rpm and get around 7.5 gph cross country. I believe that T&G results are better.

 

[Ddayle]

the `172 i fly has a 150hp and i ussually run about 2350 -2400 RPM under 3000 '. I do lean it @ 50 degree ROP. I seem to get about 7gph even on 2 hour flights. I have only flown with this club a few months . Prior to that i mostly flew a 150 @ 6gph

 

[tonycondon]

7 gph on an 0-320 at 150 hp sounds about right to me.

 

[Clark1961]

I trained in 172's at an airport with GE of ~5,500. We used 8 gph for planning but usually burned closer to 6-7 gph in the 320's. The 360's burned closer to 8. One particular 360 burned closer to 10 at rental power but the rigging was so bad that it always felt like it was flying sideways.

Most of the flying was 7 to 8 thousand feet and we were taught to pull back a couple hundred rpm once clear of the airport area. We pulled back unless we were flying with the chief pilot who was a binary type guy.

Leaning was typically done to max rpm during run-up. The chief pilot wanted peak egt but most of the instructors said give it a couple twists in from peak.

Glad I'm not flying their machines anymore.

 

[KennyFlys]

So, you've got a 172M or earlier. I can't recall what I was getting on the M but had to be a little better than what I see now.

On the S with the 180HP, we do most training at 2100RPM between 1,500 and 5,000. The average is about 6.3 to 6.7 per hour. If I push it up to 2300 during cross country flights at 6,000-8,000, it's still around 7.0-7.2 GPH.

 

[RotorAndWing]

As a rule of thumb in piston aircraft, divide hp by half and you get the cruise fuel burn. So with 160 hp average burn is 8gph. A 300hp engine will average 15gph.

Of course aggressive leaning will lower the number, but it's a good gouge.

 

[flyingcheesehead]

I have been told that a 172 should burn about 8GPH. I seem to be getting better. As an example today I flew 1.2 hours on the hobbs, I topped off the tanks fuller than when started and still only took 7.7 Gal.

You didn't *fly* 1.2 hours. Idling after startup, during taxi, etc. hardly burns anything.

Next time, write down the actual time as you take the runway for takeoff and again as soon as you land, and it'll be closer. I wouldn't expect a full 8gph on 150hp either.

 

[Richard]

This is danger close to turning into a ROP Vs LOP thread.

Consider this quote from a prior post in this thread, "What you should be doing is using the numbers in your AFM for that aircraft."

I won't advise you to disregard the POH/AFM but as far as it's a LYC powerplant, you may want to research the matter more fully. And that would go deeper than anecdotal experiences as found on an internet forum board.

 

[RotorAndWing]

And that would go deeper than anecdotal experiences as found on an internet forum board.

Really? Gee, by using the internet I've already been told to ignore any information put out by the manufacture because "they (the manufacture) don't know what they're doing anyway"......

 

[Ted]

When I was training in the 172 I generally got a bit under 8 gph in cruise on the 180 hp engine, pulling it back to 2400 RPM. All depends on how you run it and how hard you run it. I tended to get worse fuel burn with the Archer (same engine) because I ran it harder.

 

[Clark1961]

You didn't *fly* 1.2 hours. Idling after startup, during taxi, etc. hardly burns anything.

Next time, write down the actual time as you take the runway for takeoff and again as soon as you land, and it'll be closer. I wouldn't expect a full 8gph on 150hp either.

Another approach: compute the fuel burn is interms of tach hours. It'll be close to the 8 gph planning number.

 

[LearDriver]

The original poster stated that he flew 1.2 hobbs and only burned 7.7 GPH. This amount sounds right when you consider the ground operations time in the averaging of the fuel burn through the various phases of the flight.

If the POH gives a fuel burn of 8 GPH, that is going to be at a given altitude, RPM (which is a constant value), and outside air temperature. I have found over the years that some of the manufacturers performance numbers are overly optimistic. Beech numbers are usually right on where as Piper and Cessna numbers are of by 10% to 15%.

7.7 GPH burn is only 9.6% lower than the 8 GPH amount from the POH. Considering that there was probably about .4 of an hour that was operated at low power settings, I would assume that the engine may actually be burning more than the 8 GPH that was indicated in the POH. Thats just due to the fact that the factory was basing their numbers off of a new airplane (clean and properly rigged), engine (Just broken in) and a test pilot flying the airplane. I don't think any of us are operating the aircraft with those parameters.

I always had my students add an extra 20% to the fuel required amount in addition to the required reserve. With the additional fuel they never burned into their reserves. Its easy to get a higher fuel burn if the headwind picks up, the temperatures change, or the leaning process gets slightly mismanaged.

 

[Lawreston]

With my 0-320 E2d I did a 2.5 hour X-ctry. From start-up to one landing in Portsmouth, NH; and then the return to Maine IFR(I Followed Roads[I-95 and I-295]) at 2500 rpm and dodging a lot of clouds, the top-off was 18.3 gallons. Divided by 2.5 hours(and no leaning) =7.3 gph. The Power Flow tuned exhaust might have had a bearing on the data.
Whatever; I generally flight plan at 9 gph to cma.

HR

 

[Dan Thomas]

As Tony said it will vasry with what engine you are flying. When I was flying the 172R models I got 8 or little under gph. But when I flew the S model I was getting around 9gpg. The S used the O360 while the R used the O0320.

Nope. They both have the O-360. The R model's O-360 was derated to 160 hp. Here's an excerpt from the TCDS (From http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/9f56b5da3feb757e862574780058e45a/$FILE/3A12.pdf )

XI - Model 172R, Skyhawk, 4 PCLM (Normal Category), 2 PCLM (Utility Category), Approved June 21, 1996
Engine Lycoming IO-360-L2A, Rated 160 Horsepower

When Modified by Cessna Modification Kit MK172-72-01 (See NOTE 4)
Lycoming IO-360-L2A, Rated 180 Horsepower

Fuel 100/100LL minimum grade aviation gasoline
Engine Limits For all operations, 2,400 RPM

When Modified by Cessna Modification Kit MK172-72-01 (See NOTE 4)
For all operations, 2,700 RPM


The modification involved a new tach, a new prop, and a POH change to get the 180 HP. All S models started out as 180 hp.

Dan

 

[ScottM]

Nope. They both have the O-360. The R model's O-360 was derated to 160 hp. Here's an excerpt from the TCDS (From http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/9f56b5da3feb757e862574780058e45a/$FILE/3A12.pdf )

XI - Model 172R, Skyhawk, 4 PCLM (Normal Category), 2 PCLM (Utility Category), Approved June 21, 1996
Engine Lycoming IO-360-L2A, Rated 160 Horsepower

When Modified by Cessna Modification Kit MK172-72-01 (See NOTE 4)
Lycoming IO-360-L2A, Rated 180 Horsepower

Fuel 100/100LL minimum grade aviation gasoline
Engine Limits For all operations, 2,400 RPM

When Modified by Cessna Modification Kit MK172-72-01 (See NOTE 4)
For all operations, 2,700 RPM


The modification involved a new tach, a new prop, and a POH change to get the 180 HP. All S models started out as 180 hp.

Dan

Ah yeah, you are correct and I stand corrected. I mistakenly was thinking 160hp = O320 as my Warrior is 160hp and O320

 

[dmccormack]

Nope. They both have the O-360. The R model's O-360 was derated to 160 hp. Here's an excerpt from the TCDS (From http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgMakeModel.nsf/0/9f56b5da3feb757e862574780058e45a/$FILE/3A12.pdf )

XI - Model 172R, Skyhawk, 4 PCLM (Normal Category), 2 PCLM (Utility Category), Approved June 21, 1996
Engine Lycoming IO-360-L2A, Rated 160 Horsepower

When Modified by Cessna Modification Kit MK172-72-01 (See NOTE 4)
Lycoming IO-360-L2A, Rated 180 Horsepower

Fuel 100/100LL minimum grade aviation gasoline
Engine Limits For all operations, 2,400 RPM

When Modified by Cessna Modification Kit MK172-72-01 (See NOTE 4)
For all operations, 2,700 RPM


The modification involved a new tach, a new prop, and a POH change to get the 180 HP. All S models started out as 180 hp.

Dan

The CAP 172R I fly gets 7 GPH no matter what -- TnG, Manuevers, XC -- doesn't matter.

Strangest thing ever.

And yes.. this includes leaning, etc.

 

[poadeleted20]

It all depends how you run the engine. Assuming we're talking a traditional O-320-powered 172, run it leaned for best economy at about 60-65% power, and you can get it to cruise on 8 gph. Run it at 75% power unleaned and you could see 11 gph or more. Of course, 65% power ain't gonna get you high on the speed charts, but you get significantly better miles per gallon.

 

[AuntPeggy]

I just added up the numbers for 2008. Our C-172M (180 hp) used 1484 gallons for 201 hours hobbs time = 7.4 g/h. This includes 25 gallons disposed of at the annual and estimates for 4 topoffs where the amount was not recorded. Mean time between topoffs was 2.7 hrs.

 

[KennyFlys]

I just added up the numbers for 2008. Our C-172M (180 hp) used 1484 gallons for 201 hours hobbs time = 7.4 g/h. This includes 25 gallons disposed of at the annual and estimates for 4 topoffs where the amount was not recorded. Mean time between topoffs was 2.7 hrs.

What power settings are you typically running at for cruise?

 

[flyingcheesehead]

I just added up the numbers for 2008. Our C-172M (180 hp) used 1484 gallons for 201 hours hobbs time = 7.4 g/h. This includes 25 gallons disposed of at the annual and estimates for 4 topoffs where the amount was not recorded. Mean time between topoffs was 2.7 hrs.

Do you know how much tach time that was? That'll give the best number for cruise burn.

 

[Ghery]

The performance chart for our club's C-172N with the Penn Yan 180 hp conversion shows 8.3 gph at 65% power. The number seems about right from memory. My typical cruise power setting for that plane, and it yields 114 KTAS. There are LSAs that will outrun that.

 

[poadeleted20]

The performance chart for our club's C-172N with the Penn Yan 180 hp conversion shows 8.3 gph at 65% power. The number seems about right from memory. My typical cruise power setting for that plane, and it yields 114 KTAS. There are LSAs that will outrun that.

My Grumman Tiger with the same engine as the 172-180 burns 9.3 gph at 70% power turning 130 KTAS. No LSA will outrun that.

 

[LearDriver]

I wouldn't want to outrun that. I fly fast for a living. I like to fly nice and slow for recreation.

By the way. Isn't that baby grumman a light sport aircraft?

Actually they are really nice little planes.

 

[ted gilbertson]

Always do your planning assuming the plane is using the most fuel as possible. I'm sure most people use the book for gph at altitude and rpm, I just don't want Murphy's Law to send me on a trip with a carb that was running rich and I didn't know it. Its much better to come home with extra than empty. On the climb calcuation I sometimes use even 9gph gust to be safe. Alot of the times I get better gph that the POH shows. If you're cutting it close on a flight that extra could save your butt

 

[jmaynard]

My Grumman Tiger with the same engine as the 172-180 burns 9.3 gph at 70% power turning 130 KTAS. No LSA will outrun that.

True. OTOH, I'll only go 15 knots slower while burning 3.5 fewer GPH (though I can't haul as much as you can, either).

 

[brcase]

Always do your planning assuming the plane is using the most fuel as possible. I'm sure most people use the book for gph at altitude and rpm, I just don't want Murphy's Law to send me on a trip with a carb that was running rich and I didn't know it. Its much better to come home with extra than empty. On the climb calcuation I sometimes use even 9gph gust to be safe. Alot of the times I get better gph that the POH shows. If you're cutting it close on a flight that extra could save your butt

Good recommendation, I tell (most) students to find the highest GPH number in the manual and use that for flight planning. After they have 50 hours in that specific airplane the can decide if they need to adjust that number.

I developed that habit after i landed with less than 1 gallon of fuel on board a 172 by using the book numbers. I should have had closer to 10 gallons on board. I probably wasn't very good an leaning like the manual, plus I think the prop had been repitched to a cruise prop so I was burning more fuel to the book RPM's.

Brian
CFIIG/aASEL

 

[AuntPeggy]

Do you know how much tach time that was? That'll give the best number for cruise burn.

Why? Hobbs time is closer to clock time and it is how we gauge our flight time.

To answer another question, we usually cruise around 50 to 60%.

 

[flyingcheesehead]

Why? Hobbs time is closer to clock time and it is how we gauge our flight time.

To answer another question, we usually cruise around 50 to 60%.

Hobbs time is closer to clock time, but it also includes all of your taxi time, when you're burning next to nothing. When you're at cruise power, tach time is very close to (if not exactly) clock time as well, and when you're at lower power settings it slows down, roughly proportional to the lower fuel burn. So, it gives you an excellent representation of cruise fuel burn.

As an example, I generally count on about .2 at the beginning of a flight for taxi and runup time, and .1 at the end of the flight for taxi and shutdown. So on a 1-hour flight, the Hobbs will say it was 1.3 while the tach will say about 1.0, maybe a bit less (.9, or .95) due to lower power settings on approach. Thus, the fuel burn measured against Hobbs time will be lower than that actual cruise fuel burn. Let's say I added 10 gallons after that flight. Divide by hobbs time and you get 10/1.3=7.69. Divide by a tach time of .95 and you get 10.52 and that number is going to be very close to your cruise fuel burn.