Fuel Burn Computation Question-Cessna 182

Funkeruski

Funkeruski

Pre-takeoff checklist
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Funkeruski
I have a 1978 Cessna 182 which I took out for a cross country joy ride this weekend. This 182 has the 80 gallon tank, with 75 usable and 5 unusable.

Before departing, there was 29g in the left tank, and 30g in the right, for 59g total. When I got back, I put 48 gallons in it, which means there was 32g in the tank when I got back (80-48=32). This indicates that I burned 27g during my 2.5 hour flight. This would come out to 10.8g per hour which I am having a hard time believing. Me thinks it has to be a little higher.

I'm thinking that I may not be correctly accounting for the 5g in unusable fuel that is somewhere in the plane other than the fuel bladders in the wing. When the tanks in the wing are topped off, do they show 40g in each tank or 37.5 in each tank? (Unfortunately, I can't get out to the hangar soon to check this). Do I use 80g in calculating fuel burn or ignore the 5g unusable, and calculate everything off of 75g usable?

I'm confused and am in need of assistance.:mad2:
 
What power setting?

A 182 will happily burn less than 10gph, you just aren't going to be going very fast.
 
You may well be quite close then. I flight plan at 12.5 but seldom burn that much, usually I'm in the 11-12gph range flying between 5 and 7k
 
Funkeruski said:
I was at 8500ft, wide open throttle at 21mp, 2300 rpm.
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Check your POH. That sounds like 60% power or so. ROP or LOP? Factor in that you could have been 2-4 gallons off in your estimate of how much fuel you burned.


PS I remember your video of the engine cutting out and having to put it down in a field. They ever come up with a positive determination of the problem? (I would assume so since you are flying again :) )
 
dell30rb said:
Check your POH. That sounds like 60% power or so. ROP or LOP? Factor in that you could have been 2-4 gallons off in your estimate of how much fuel you burned.


PS I remember your video of the engine cutting out and having to put it down in a field. They ever come up with a positive determination of the problem? (I would assume so since you are flying again :) )
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75 - 100 degrees ROP. The POH reflects that 21/2300 at 8,000 feet (standard temp), is 71% power.

That was my brother/partner who put it down in the field. I think we have 50 or so hours on it since that happened and it is running fine. Mechanic did something with the lifters, although I don't know the specifics.
 
10.8 isn't that unusual. 8,500 cruise, the G1000 that I fly often runs about 11-11.5 gph, take some off for descent and such, and 10.8 is not at all unreasonable.
 
What method was used to determine that you had 59 gallons on departure?
 
JeffDG said:
10.8 isn't that unusual. 8,500 cruise, the G1000 that I fly often runs about 11-11.5 gph, take some off for descent and such, and 10.8 is not at all unreasonable.
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Have to add some for the 20+GPH burned on departure, the new planes also have lycoming 540s so comparison to the TCM 470 may not work 1:1 (but are likely not vastly different either)
 
Skylane81E said:
What method was used to determine that you had 59 gallons on departure?
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Used the dip stick to measure in each wing. That showed 29 in the left, and 30 in the right. The question is whether this includes the 5g in unusable fuel. Did I take off with 59g or 64g? If 64g, then I burned 32g or 12.8 gph.
 
Funkeruski said:
I have a 1978 Cessna 182 which I took out for a cross country joy ride this weekend. This 182 has the 80 gallon tank, with 75 usable and 5 unusable.:
Click to expand...

1977 182Q. Bladders, not wet wing. :wink2:
 
205, IO470 plan for 13, cruise about 9.5. T/O power is around 23.
 
Funkeruski said:
Used the dip stick to measure in each wing. That showed 29 in the left, and 30 in the right. The question is whether this includes the 5g in unusable fuel. Did I take off with 59g or 64g? If 64g, then I burned 32g or 12.8 gph.
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You could run one tank dry in level flight then calibrate the dipstick at a self serve gas pump.
 
A dipstick is not accurate enough for you to make these kind of determinations.


Garbage in....Garbage out!
 
Funkeruski said:
Used the dip stick to measure in each wing. That showed 29 in the left, and 30 in the right. The question is whether this includes the 5g in unusable fuel. Did I take off with 59g or 64g? If 64g, then I burned 32g or 12.8 gph.
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What does the dipstick say when full?

If you have monarch caps they can greatly complicate sticking the tanks
 
kgruber said:
A dipstick is not accurate enough for you to make these kind of determinations.


Garbage in....Garbage out!
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I respectfully disagree....the Fuelhawk I used on my 182 was spot on...between that and the totalizer, I was always within 1 gallon of knowing what I had usable onboard.

FYI to the OP...if you were using a Fuelhawk, it only read usuable in my 182...YMMV
 
Ron Levy said:
And at that altitude and power setting, the POH says the fuel consumption will be _______ gph?
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My 1973 182P's POH calls 7500'/21"/2300RPM a 12.2GPH fuel burn. Of course this depends on where you lean to. I don't know how different this is from the poster's Q though.
 
I have a T182T and have put on over 350 hrs on it since buying it in May 2011. I keep a spreadsheet of everything I put in the plane. I run the plane at 26", and 2000 and lean to maximum TIT. Based on my use of fuel since I purchased the plane I burn an average of 8.4 gallons an hour. This is based on how much fuel on purchased divided on the number of hours flown(hobbs). On ascent based on the G1000 I burn about 16.3 gallons and hour, and in cruise I am usually around 10.8 gallons an hour. So 10.8 gallons an hour seems about right to slightly high to me based on my limited experience with one plane.
 
Sounds like you must have a lot of ground time to get the total burn down in the 8's?
douglas393 said:
I have a T182T and have put on over 350 hrs on it since buying it in May 2011. I keep a spreadsheet of everything I put in the plane. I run the plane at 26", and 2000 and lean to maximum TIT. Based on my use of fuel since I purchased the plane I burn an average of 8.4 gallons an hour. This is based on how much fuel on purchased divided on the number of hours flown(hobbs). On ascent based on the G1000 I burn about 16.3 gallons and hour, and in cruise I am usually around 10.8 gallons an hour. So 10.8 gallons an hour seems about right to slightly high to me based on my limited experience with one plane.
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Basic rule of thumb on non turbo piston engines: Take HP and divide by half to get approximate fuel burn.

250 hp = 12.5gl/hr
200 hp = 10.0gl/hr
etc
 
It is very easy to be +/- a couple gallons per tank on the fill up depending on what you consider "full" to look like, how level the tanks are when full, and whether you switched the fuel selector to one side (so it won't cross feed during fueling to the lower tank, which can be significant if you take your time filling the tank).

~11-12 GPH at your stated altitude/mixture setting sounds about right.
 
wabower said:
Sounds like you must have a lot of ground time to get the total burn down in the 8's?
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Not really. On VFR flights maybe 5 to 10 minutes from turning on the engine to take off, IFR usually about 10 to 15 though on occassion more than that. Also descent and in pattern I am using less fuel. Also, and I completely forgot about this when I first got the plane I was flying 20 squared and that uses about 8 gallons an hour so that 40 or so hours also affects it, though looking at my last 10 or 15 full ups they range from 7.8 gal/hr to 9.1 gal/hr, so it probably it probably more likely slightly higher than 8.4 gal per hour. In any event I use 12 gal/hr for flight planning and with my tanks holding 87 gal usable that gives me 6 hrs with a 1 hour reserve, and I do not have the stamina to spend 6 hours in my plane in one sitting.
 
Funkeruski said:
Used the dip stick to measure in each wing. That showed 29 in the left, and 30 in the right. The question is whether this includes the 5g in unusable fuel. Did I take off with 59g or 64g? If 64g, then I burned 32g or 12.8 gph.
Click to expand...
The only way to know that for certain is to run a tank dry (or drain it) and record the dipstick readings as you add fuel all the way to a full tank on each side. Also IME those dipsticks aren't all that accurate, I suspect your initial fuel could have been off by 5 or more gallons.
 
Kelvin said:
I respectfully disagree....the Fuelhawk I used on my 182 was spot on...between that and the totalizer, I was always within 1 gallon of knowing what I had usable onboard.

FYI to the OP...if you were using a Fuelhawk, it only read usuable in my 182...YMMV
Click to expand...

Wake up, Ace. You are using a totalizer.
 
kgruber said:
Wake up, Ace. You are using a totalizer.
Click to expand...

Yeah, that's great, but it's only as good as the starting point input.

If you measure the tanks +/- 5 gallons, then I don't care how good your totalizer is, you're still +/- 5 gallons at best.
 
For flight planning you should only use the usuable fuel load in calculations. If you are trying to look at how much you burned in flight a calibrated dipstick would be needed. If it is a commercial dipstick it should say if it was calibrated to read usable or unusable. As everyone says the are too many variables to take that as the solid number. More of a ballpark figure. You could make your own dipstick and it would be more accurate, you would have to start with a completely empty tank though. Then add the unusable fuel in the tank and start that as your zero point.
 
Our 182P averages right around 11 GPH, all in. Most flights between 6000-10500' MSL.

Burns considerably more down low if you're not watching the power chart. 13 GPH easy, 15 at takeoff power.

Yours sounds completely normal.

And we've seen scenarios where sticks won't cut it, like a ramp that's not level or the nose gear strut being over or under compressed.

If you're going to stick those big long 80 gal bladders and even somewhat trust it, find a reference point for where the nose gear strut is extended to and put it there if it's not before sticking.
 
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