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Old 15th Feb 2003, 15:22   #1 (permalink)
SpaceRanger
 
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Question B747-400 fuel dump rate?

At what rate does a 747-400 dump fuel ? (kg/second, or any other units for that sake)

When is it required that an aircraft has a fuel dump system?

Thank you,

TD
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Old 15th Feb 2003, 16:17   #2 (permalink)
 
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2 tonnes per minute which includes fuel burn. Obviously, that is an averaged figure which is dependent on fuel head etc. Makes 'ball-park' fuel dump time calculation very easy - not really necessary on the -400 since, after 90 seconds the time to dump is displayed on the fuel page.
Fuel dump ability is, in general, required if max landing weight is less than max take-off weight.
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Old 16th Feb 2003, 01:39   #3 (permalink)
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In general, just a tad more involved .. the current US requirements are at FAR 25.1001. If the link only takes you to the index, then cursor down and hyperlink to 25.1001.

The specific requirements for the 744 would be indicated in the regs applicable at the time that the design standard was frozen for the model .. I will leave it to someone else to track that down.
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Old 16th Feb 2003, 09:51   #4 (permalink)
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Thank you for your answers.

FAR25.1001 part (a) and (b) is quoted below, and as far as I can see, is it only approach/go around climb gradients all engines (25.119) and one engine out (25.121(d) ) that dictates whether or not a fuel dump system is required to have on a given aircraft model.

Many aircraft have larger differences between MTOW and MLW w/o fuel dump system intalled, so it seems to concentrate whether or not you can do a go-around at MTOM, ie. you have been attempting to land at a weight over MTOW, in an emergency I suppose.

Anyone care to correct if this is wrong?

Thanks.

FAR 25.1001 a+b (same as JAR 25.1001)

(a) A fuel jettisoning system must be installed on each airplane unless it is shown that the airplane meets the climb requirements of 25.119 and 25.121(d) at maximum takeoff weight, less the actual or computed weight of fuel necessary for a 15-minute flight comprised of a takeoff, go-around, and landing at the airport of departure with the airplane configuration, speed, power, and thrust the same as that used in meeting the applicable takeoff, approach, and landing climb performance requirements of this part.

(b) If a fuel jettisoning system is required it must be capable of jettisoning enough fuel within 15 minutes, starting with the weight given in paragraph (a) of this section, to enable the airplane to meet the climb requirements of 25.119 and 25.121(d), assuming that the fuel is jettisoned under the conditions, except weight, found least favorable during the flight tests prescribed in paragraph (c) of this section.
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Old 16th Feb 2003, 10:26   #5 (permalink)
 
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b747-400 dump rate

At what rate does a 747-400 dump fuel ? (kg/second, or any other units for that sake)


i have had the misfortune to carry this out. with six (ovrrd/ jett) pumps going, the rate was 1000kg/min.

it depends on the no. of pumps running. and of course the burn off at the moment.

i also discovered that it does not take care of fuel imbalance! no, it was not because it came from the dead engine tank!

and oh, er, it does not take 90 seconds to register the 'jettison time'. the moment you push the nozzle buttons, it will give the time to go, and it changes as you go into a bank.

as a point for the academics,the jett time deferred greatly from the book figures. operationally, might be better to give the time reqd after you have hit the two nozz buttons.
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Old 16th Feb 2003, 14:50   #6 (permalink)
 
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Decimal 86
Yes, it does register time to jettison as soon as you start the dump, but it requires the 90 secs to ACCURATELY assess the time by checking the flow rates over that sort of time period.
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Old 17th Feb 2003, 05:32   #7 (permalink)
 
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As fuel in tanks decreases, dump rate decreases.

The ballpark figure I use for dump time is tons to dump / 2 + 5. e.g. for a max weight departure of 397 with max ldg weight 296, approx 100,000kg to lose is 100/2+5 = 55 mins (ballpark).
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