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Fuel / KG

Old 30th Apr 2011, 05:50
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Fuel / KG

Really stupid question... In piston aircraft what is the approx value that a liter of aviation fuel weighs in kilo's?

Trying to do some calculations, but I'm not making sence
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Old 30th Apr 2011, 05:53
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AVGAS is around 0.71 Kg..
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Old 30th Apr 2011, 06:08
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...At SL in a standard atmoshere.
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Old 30th Apr 2011, 06:26
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Brilliant, I had the idea of around 0.78 so I was close. Thanks for the heads up
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Old 30th Apr 2011, 06:32
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0.72kg/lt in the ERSA. I have seen some weight and balance test questions in the past give a particular weight they wanted you to use, e.g. convert fuel kgs to litres(SG 0.69).

Cheers MM
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Old 30th Apr 2011, 08:35
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Temp.effects the SG O.70 is easy to use and probably closest to the mark if you operate in the tropics especially in summer.
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Old 30th Apr 2011, 08:37
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check the ersa, says its 0.72
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Old 30th Apr 2011, 08:46
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0.7 if it's hot or doing it in your head
0.72 if it's cold or if doing a Casa exam

have had sg's as low as 0.67 when doing the transfer calculations...

0.78 is closer to jeta1 perhaps why it was in your head...
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Old 30th Apr 2011, 09:32
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Hi .6s are common up north. Especially when it cooks for a while in the tanker on it's way to the distributor.
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Old 30th Apr 2011, 09:36
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Last time I checked the MSDS for AVGAS coming out of the Kwinana refinery was at 0.70 kg/L @ 15C. I can't find refinery specific info but:

According to BP Aust MSDS for AVGAS you're looking at 0.70 kg/L @ 15C.

And for those of you playing at home Jet A1 (with fizzy) is 0.80 kg/L @ 15C (ibid).

FRQ CB
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Old 1st May 2011, 01:17
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Well, I've only EVER used 7.2 lbs / Gallon.....

But then I AM a 'dinosaur'......(Works in the Tiger...)

Still alive though....

Cheers
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Old 1st May 2011, 03:02
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..Eurocopter Tiger?...cool!
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Old 1st May 2011, 05:07
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SG of Avgas

I used a SG of .72 (legacy of training/CASA exams), during a CASA audit the FOI (good bloke) indicated an SG of .69 is appropriate in the tropics.

In a C310 with full mains this increased the payload by 12kg.
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Old 1st May 2011, 06:46
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In a C310 with full mains this increased the payload by 12kg
Another "stupid" question:

Doesn't fuel get burned in the engine by volume? So if the fuel expands when it's hot and weighs less per litre, your endurance on full tanks goes down.

In your case it would be the equivalent of a whole 16 litres in ISA, which I doubt makes a significant difference, but still...
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Old 1st May 2011, 08:03
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Typical values for AvGas specific gravity vs temperature are as follows.

Temp C, S.G.
10 , .712
15 , .707
20 , .701
25 , .695
30 , .69
35 , .684
40 , .678


Due to manufacturing tolerances, additives and time of year, there will always be variations from the typical values.

Talk to your local refueller, not only does he have an actual S.G. for each batch of avgas, he also has a whiz wheel for computing the S.G.

Under ISA conditions (15 degrees C) the typical value is .707

The figure of .72 has a safety fudge factor and is not indicative of the S.G. as supplied by the fuel supplier.

Baswell is correct regarding volume, at higher temperatures the volume of fuel is less.

TAA / QANTAS used to take advantage of this fact to enable extra fuel to be loaded.

For a Sydney - Perth flight, originating from Melbourne, the technique was to cruise as high as possible MEL - SYD,
then refuel as soon as possible after landing SYD while the wings / fuel tanks were still chilled.

Racing cars use a similar method, refuelling from chilled containers to get more fuel (volume) into the fuel tank.

As for exams, unless specified, stick to .72, whether its right or wrong, its what is expected.

and finally, a repeat of earlier, for the actual S.G. ask the refueller what was the S.G. when he did his daily dips and tests.
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Old 1st May 2011, 10:15
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Mainframe,

You quote Baswell as correct that fuel volume is less when temperatures are high.

I thought it was the other way around. Ex DXB in the A300-600R we used to
" hide " a couple of tonnes in the tail tank to get the volume of gas aboard when it came out of the ground hot.

Just wonderin'
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Old 1st May 2011, 11:12
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I know I've forgotten most of the stuff that I learnt in high school physics. Something about things expanding when they heat up (until they change state). There was also something about the calorific content of fuel. Of course, the container may have limits of mass and volume but it is the energy in the fuel which is partially converted into work done by the powerplant .... I need more red wine.
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Old 1st May 2011, 11:44
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tpad/mainframe.

Bit of confusion I think:

Baswell is correct regarding volume, at higher temperatures the volume of fuel is less.
What I meant: when hot, the weight of the same volume of fuel is less. But at cruise, the fuel cools down again, so the volume shrinks. And you can put the extra tonnes you put in the tail back into the mains because there is room again? (not to mention fuel burnt making space, of course)

That why you heavy drivers put fuel in by the tonne instead of litres.

Also: if the fuel didn't significantly cool, e.g. you go power line inspecting in a chopper on a 40 degree day, you actually have less endurance in the tanks then you would if you did the same job on a 10 degree day? Just because the fuel expands, doesn't magically give it more energy...
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Old 1st May 2011, 23:17
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Tpad, djpil and Baswell,

apologies, the weight, not volume, is less with temp increase, so calorific value suffers.

I used to gain in intelligence after a few Crownies, or so it seemed.

Not the first on PPRuNe to respond after imbibing ?

Last edited by Mainframe; 1st May 2011 at 23:19. Reason: typo
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Old 1st May 2011, 23:20
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Re 'at higher temperatures the volume of fuel is less'
I think Mainframe may have had one Crownie above gross. Perhaps he had it hot in order to get more volume for the same weight. I think he meant that at higher temperatures the weight is less for a given volume of fuel.

Re fuel, my experience with an IO520 Continental has been that when I operate in cold places with cold fuel I require a higher fuel flow for my usual power settings. I'm probably getting more power but I need it to push through the cold dense air. In hot climates I can run further lean of peak (probably due to better atomization of the the hot fuel in the hot intake air) . My indicated airspeed is down slightly but my TAS is just as good if not better than it is when flying in cold air. I may have been dudded in the amount of energy I purchased (high volume low weight) but it balances out by the more efficient use of the hot fuel in hot air.
Cheers RA

PS We used to use the principle of better atomization in hot air in a Comanche I flew long ago. In cruise we used to operate partial carby heat which gave us smoother operation and better economy.
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