Fuel / KG

[Skystar320]

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

[Bevan666]

AVGAS is around 0.71 Kg..

[Wizofoz]

...At SL in a standard atmoshere.

[Skystar320]

Brilliant, I had the idea of around 0.78 so I was close. Thanks for the heads up

[Mere Mortal]

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

[rutan around]

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.

[cavok123]

check the ersa, says its 0.72

[Xcel]

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...

[YPJT]

Hi .6s are common up north. Especially when it cooks for a while in the tanker on it's way to the distributor.

[FRQ Charlie Bravo]

Last time I checked the MSDS for AVGAS coming out of the Kwinana refinery was at 0.70 kg/L @ 15°C. I can't find refinery specific info but:

According to BP Aust MSDS (http://www.bp.com/sectiongenericarticle.do?categoryId=9012966&contentId=7015036) for AVGAS you're looking at 0.70 kg/L @ 15°C.:8

And for those of you playing at home Jet A1 (with fizzy) is 0.80 kg/L @ 15°C (ibid).:8

FRQ CB

[Ex FSO GRIFFO]

Well, I've only EVER used 7.2 lbs / Gallon.....

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

Still alive though....

Cheers:ok:

[mattyj]

..Eurocopter Tiger?...cool!:ok:

[displaced gangster]

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.:ok:

[baswell]

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...

[Mainframe]

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.

[tpad]

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'

[djpil]

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.

[baswell]

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...

[Mainframe]

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 ?

[rutan around]

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.

[Xcel]

^^ rutan

weird...

Best way I understood it was - we used to put the fuel samples in the fridge for 5 minutes cause otherwise even our @15 temps wouldn't make sense on those hot days and with the friction on the front container from the tanker it was way off. Cool the sample down so the sg was within spec so we could accept the fuel. If hotter than his calculated @15 we would be getting ripped off cause the volume over such a large amount of fuel would be out and theoretically wouldn't fit in the tank... As the sample was from the owest point it was closest the road and the front so was the hottest. By the time we let the fuel in and it mixed with the colder fuel it would always fit. :)

[Ex FSO GRIFFO]

Hey 'Rutan' I never thought of that when I was flying higher performance, 'carby' pistons.

However, if it works for you...I wonder just how much fuel you actually saved?
Care to elaborate?

Half a circuit's worth...or more..?

The only comment I would make is that the use of the Carby Heat delivers unfiltered air - so you wouldn't want to have any 'dust' around....

Cheers:ok:

[rutan around]

Griffo, back in those days I didn't fly enough to think about quantifying fuel savings. Perhaps the Piper Comanche association could help here. We didn't use carby heat till we were above the dust layer. I think what was at play was that the heated induction air weighed less, so the MP decreased, which meant the mixture (fuel flow) could be reduced. The power remained the same because the better atomized fuel/air mix burned more completely and sooner. A bit like modern coal powered ships. They don't shovel lumps of coal in - they crush it to a talc-like powder and blow it in, achieving quick and complete combustion. Another 'trick' that helps is not quite full throttle. The following excerpt from the Cessna Pilots Association elaborates.

Lean of Peak (LOP) In A 182

Tech Support,
In a recent E-ATIS (13:51), Mike Busch answered a question regarding LOP operation in a 182Q (see below). However, he did not address the advantage, if any, of operating full throttle LOP given the difficulty of operating LOP at all in the 182Q. Is there an advantage? I operate my 1977 182Q LOP on most flights. I take a cautious approach by operating in the 62-64% range where per the POH I have the freedom to operate lean. Fuel flows are, say, 8.4-9.2 gph depending on weather and altitude and I make about 110 knots. The CHTs are acceptable; the EGT diff reading varies... 60 is great, 80 is typical, and I switch to ROP if I can't stay under 100. Of course, with a Skylane this requires partial carb heat such as 46-48 degrees IAT. These settings seem to keep my plugs clean, valves cool, fuel costs low, etc. I have tried the transition to full throttle LOP operation but given the above and at my typical altitudes (2,500-4,500), it seemed difficult. Is there sufficient additional advantage to switch to the full throttle settings?

Here is what was said in E-ATIS

“Your O-470 engine is very difficult to operate LOP without unacceptable roughness. It is only possible to control power with the mixture control when you're operating LOP. You cannot practically use the LOP procedures I was discussing in ATIS on your O-470.”

Thanks in advance,
David R.

David,
For O-470 engines operated LOP, it's best to operate them at "almost WOT." Starting at wide-open throttle, pull the throttle back slowly until there just the slightest reduction in indicated MP(a needle's width at most). This provides "almost WOT" operation, but cocks the throttle plate in the carburetor throat just enough to cause turbulent airflow, which improves fuel atomization and mixture distribution.

The other O-470 "trick" for operating LOP is to use just a touch of carb heat, again to improve atomization and mixture distribution.

Mike Busch, CPA Tech Rep.



Mike,
Thank you for responding to my question. I can certainly try the almost WOT. Given my current numbers with just carb heat, would you expect a noticeable improvement if I can position the throttle plate? Also, since the difference between 22-23 MP and almost WOT is big at 2,500 ft, are there tricks to help smooth the transition? Would it help to lean ahead of time to flows that are typical of either ROP or LOP operation? Since I am able to fly LOP with the settings I posted in my first message, I wondered whether I would see any improvement in efficiency or smooth engine operation by adding WOT on top of carb heat. For me at least, the transition from cruise power to WOT at 2,500 ft. is difficult. I wondered whether I should lean to my typical LOP fuel flows first before changing the throttle. Difficult = Like flooring the car, steering, and trying to adjust the radio at the same time! Having established cruise altitude and prepared for my leaning procedure (close cowl flaps, adjust carb heat, etc.), I have my hands full just scanning for traffic, maintaining altitude, and tracking my EDM readouts.

Thanks in advance,
David

David,
Operating at or near WOT is always more efficient, all other things being equal. The difference in efficiency can be large with turbocharged engines, is much smaller with normally aspirated engines.

For normally aspirated engines, the major loss of efficiency comes in flying at low altitudes where partial throttle is a consideration. If you are flying at efficient higher altitudes, you'd never consider operating at less than WOT anyway.

Mike Busch, CPA Tech Rep
Cheers RA
PS For the record back then we didn't dream of running LOP because it was "verboten"

[Ex FSO GRIFFO]

Thanks for that - and especially for the references.

Mike Busch certainly, is well regarded.

Cheers:ok: