View Full Version : Specific gravity

11th Jan 2004, 06:44
what is the specific gravity of jet a1?

i need the value coz i'm doing an assignment on a/c docs, and fuel prices are quoted in gallons, fuel burn is in lbs,

thanks in advance!

Genghis the Engineer
11th Jan 2004, 06:53

(Aviation Mechanic's Handbook, section 2.4. Book is 10 from AFE and I'd strongly recommend it as a source of such gems).


11th Jan 2004, 14:17
... but, be wary .... the SG depends on a variety of things including crude source and fuel mass temperature.

For planning purposes I would expect 0.80 to be closer to the mark.

For routine use, either measure a sample with an hydrometer or check with the fuel supplier as they pay by weight so they measure the SG accurately at each delivery.

11th Jan 2004, 21:29
Would be inclined to agree with John here rather than Gengis. Working on the ramp SG checks (carried out before each refuel) shows values of 0.8 and slightly below for most UK conditions.

Did work in Canada one winter and SG's of 0.82 were the norm, but the oat and fuel temp were in the -20 degs region.

Genghis the Engineer
12th Jan 2004, 01:55
Fair point. Mind you I'd still recommend that our man has a copy of the ASA Aviation Mechanic Handbook on the shelf, it's a useful reference for such things.


12th Jan 2004, 12:40
Genghis and I are both engineers ... and, as such, we both like to have a well-stocked tech library to track down esoterica .....

Genghis the Engineer
12th Jan 2004, 15:52
There's another way?


13th Jan 2004, 05:30
.. not that I've found to date ......

Flight Detent
13th Jan 2004, 10:45
Hi all,
I understand around 0.77 to 0.85 kg/litre is the norm for operating Boeings about the place, your aircraft OM will specify your exact limits there!


13th Jan 2004, 11:04
I have never seen 0.85 in all my years of flying, 0.82 sometimes in the winter out of Vancouver was the highest.

14th Jan 2004, 22:57
.79 is textbook as I recall.....For JET A1. .....Then depends on conditions of the day, either up or down from that.
Widecuts, JP4 etc may be different.

Dave Gittins
14th Jan 2004, 23:34
Not that this is something I normally get excited about driving a Cherokee but I followed the thread and then tried it on the E6B function on my Palm Pilot.

That alleges (at 10 C) that Jet A has an SG of 0.82 (i.e 8.2 lbs / Imp Gal) Jet B an SG of 0.79 and Avgas 0.70.

It needs a temp of 45 C to get Jet A to 0.79 and -30 C to get to 0.85.

I don't suppose (for my purposes) that I need worry too much and I certainly haven't added anything to the thread but as an engineer (civil not aeronautical) this has exercised my brain somewhat - and I thank you all for adding to my store of knowledge.

DGG :8 :ok:

15th Jan 2004, 06:10

Be wary of ANY "standard" sg figures - unless you are talking comparatively trivial quantities then you must get the actuals from the fuel farm or run a reading yourself.

The real numbers can vary quite a bit. For the GA piston guys and gals this is not too important due to small quantities but do be aware that one can see variations (Australia for example) such a 100/130 down near 0.69 through to 100LL near 0.72.

16th Jan 2004, 17:47
thanks everyone!
i will use 0.80 then. Gengis, thanks for the tip, i think i shall make a small investment!

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