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GoneWest
25th Aug 2001, 05:19
I read a report recently of a Beech King Air which often travelled from Tennessee to Ft. Lauderdale (Florida).

Don't quote me on the two places - I think it was those two.

Every time, pilot fills up tanks to full and flies himself home to Florida.

Last year, he filled tanks to full AND BOARDED TEN PAX to make the flight. Unfortunately, all eleven of them were killed when the aircraft ran out of fuel, short of destination.

NTSB report says at time of departure they figure he was some 742 pounds overweight. Ouch.

This is not a political question - I am NOT, in any way, criticizing the pilot - what I would like to know FOR STUDENT EDUCATION PURPOSES is just how much extra fuel does it take to carry extra weight (fuel or whatever).

If happy student pilot gets it into his head that the lowly Cessna152 he flies up and down the Florida coast uses six US gallons per hour - how much will it really use when he is x% overweight??

Vandelay
25th Aug 2001, 23:12
As far as Cessna's goes... I know on the cruise performance charts, it is specified to the maximum weight. (i.e. Conditions: 2450)

Elevation
26th Aug 2001, 21:39
Hi there,
I was once told that the extra fuel burned on a Jet for carrying an extra ton of load (fuel or deadload) is around 0.3% of the flight plan fuel.
Not too sure if it is true.

Jetdriver
27th Aug 2001, 03:44
On a 757 its about 4% per hour of cruise of the excess carried.

For example on a 4hr 30 min flight (disregard about 30 mins for descent) it would be about 4x4% of the excess so if the excess fuel was say 4 tonnes the amount of extra fuel consumed in its carriage would be around 640kgs.

Orangewing
27th Aug 2001, 03:59
On the B737-300/700,for every tonne of fuel above flight plan fuel carried,we burn an extra 40kgs. So for 3 extra tonnes on a 2hr flight we burn an extra 240kgs.I think. :D

15/15 flex
27th Aug 2001, 06:43
The L1011 was supposedly 3% per hour (-500). The Jetplan database we have on the 310 works it out for us - but is about the same.

RRAAMJET
27th Aug 2001, 08:49
DEPENDS HOW FAR YOU INTEND TO CARRY THAT EXTRA FUEL:

ie: if you intend to use it on departure delays, not much of a penalty. If you intend the extra fuel to be available for holding at the end of a 14-hr flight, big penalty.

From memory, on the 747-400 if we carried 1000kg over from HKG to LAX, it would require 600-ish for en-route burn to carry it. Therefore, you would have to load on an extra 1600kg to arrive with the extra 1000. It was all printed at the bottom of the plan for the crews' perusal during flt planning.

I'm sure the Cessna has a similar calculation...en-route burn-off v. fuel on arrival...

Elevation
27th Aug 2001, 21:33
Jetdriver,
Thanks, that is what I have been told.
On the 777, it is about 3% per hour for every ton.
Cheers.

stagger
28th Aug 2001, 03:21
RRAAMJET - surely if it carrying an extra 1000kg burns an extra 600kg then you'd need to carry 2500kg extra in order to arrive with an extra 1000kg?

RRAAMJET
29th Aug 2001, 04:03
Stagger:

the 1000kg in my example is, if you wish, cargo for the Capt's pleasure upon arrival...therefore, to carry that 1000 over 14hrs requires 600kg of burn-off fuel.
1000+600 = 1600 = the extra uplift the Capt would order, expecting to arrive with only 1 tonne of it left.

The calculation is not linear, I believe, as the weight of the a/c changes during the long haul, and hence the penalty as a % of total a/c weight changes (clear as mud, eh?). But using the chaps' above example of 3% / hr (for the 777) x 14 hrs gives a burn off penalty of 42%; therefore on the 777 you would have to load 1420 kgs to arrive with 1000.

But wait, there's more....yawn....there was a second calculation at the bottom of the flt plans for extra fuel for en-route burn off ( somewhat less of a penalty ).

Okay, that's enough, I'm going to Starbucks...

quid
29th Aug 2001, 07:27
FWIW, I agree with RRAAMJET across the board. On my DC-8, it's around 4.5%/hr for the tanker fuel.

I agree it's not linear, because at very heavy weights the tanker fuel is a smaller percentage of the total weight. As fuel is burned on a long trip, the tanker fuel becomes a greater % of the total.

FE Hoppy
29th Aug 2001, 07:39
L1011 Fuel burn rules of thumb
1 when excess fuel is carried, extra fuel is burned at aprox 3.5% of the weight above ofp per hour of flight.
eg. An excess 2000kg for 5 hours uses 70x5=350kg of extra fuel.
2 if the intention is to arrive at destination with planned amount of extra fuel above ofp then it is necessary to load the extra fuel plus 5% per hour
eg. to arrive at dest with 2000kg extra after 5 hours flight load 2000+(100x5)=2500kg

note the burn aplies to extra zfw as well as fuel so if the zfw is 2000kg up then to arrive with normal reserves after 5 hours load 5%x2000x5=500kg.
use these figures to check actual weight in flight along with epr settings and you won't go wrong.
Watching the fuel go down is my area of expertise. who's is it on the A330?

[ 29 August 2001: Message edited by: FE Hoppy ]

stagger
29th Aug 2001, 16:23
RRAAMJET - sorry, I was assuming that your figure didn't take into account the cost of taking the 600kg which was the cost of arriving with the 1000kg :confused:

I now realise that what you meant was if you take an extra 1600kg, you'll burn 600kg of this meaning that you'll arrive with only 1000kg extra. :)

[ 29 August 2001: Message edited by: stagger ]

LeadSled
2nd Sep 2001, 18:29
A good computer flight plan program will include information on the precise fuel burn per 1000kg or whatever of extra fuel weight, looking after all the varialbles " on the night". This usually falls out of the part of the program that also works ou the fuel saving ( tankering)/ non saving sectors.

When it's back to basics, a hand cranked plan, for a B744, whatever you take, you will burn in 20 hours, not exact, a little on the conservative side, but near enough for Government work.

jtr
2nd Sep 2001, 18:58
I'm with RRRRRRAMJET.
Our flight plans comes with a figure to increase, or decrease the burn by for changes in weight.

e.g. for every 1000kg inc in ZFW, you will burn about an extra 550kg of fuel on a 15 hour sector.
Cut the sector time to 3 hours, and the inc. is only about 150kg/ton (long time since I took any notice on a short haul, so that may not be 100%, but in the ballpark)

LAN
2nd Sep 2001, 19:25
Works for turboprops as well...

4% burn penalty on the B1900D for the "last 1000 lbs" increase in mass.

According to the performance charts, the burn penalty is less for the lower masses, so if you use the 4% for all mass increases, you are on the safe side.

So today, I once again will tanker and save my company 200 USD :rolleyes: - ooops, 192 USD, that is :D ....

Danmde splelnig...

[ 02 September 2001: Message edited by: Ivan the Horrible ]

eaglet-WestBourne
6th Sep 2001, 11:05
The answer is coefficient of transport which is calculated on the basis: variation of TOM divided by variation of LDM and expressed as a coefficient (1.xx). In most of majorairlines this information is calculated for every route and is a precious tool for readjusting the quantity of fuel in case of variation of load or for a need of extra fuel.
Eaglet WB