Vivek1979 From United States of America, joined May 2002, 50 posts, RR: 0 Posted (9 years 8 months 1 week 4 days 15 hours ago) and read 15482 times:
Hello friends,
I recently heard something which I don't think made any sense but was unsure. Does a 747 consume more fuel taxing or in flight. I was watching a documentary on Discovery I think on cargo jumbos and I came across that. Im not sure if they were just trying to emphasize the actual ratio of consumption between the two and exagerrated a bit or what. Does anyone know how much does it cost to fill all 747 tanks?
Prebennorholm From Denmark, joined Mar 2000, 5744 posts, RR: 56 Reply 1, posted (9 years 8 months 1 week 4 days 13 hours ago) and read 15471 times:
40,000 dollars.
Turbojet and jurbofan engines are indeed very thirsty creatures in the thick air at sea level. They are designes to operate economically at cruising altitude.
But to say that taxiing consumes more fuel than cruising... Per mile, for sure! Per hour or minute, aeh... It depends on a lot of circumstances.
Taxiing is sometimes a fast run with engines at idle. But very often at congested airports before take-off it's a stop-go-stop-go. The latter is very expensive on fuel, especially on a heavily loaded plane.
On the other hand, after landing many airports have fast roll-off taxiways. Planes often turn off half of the engines when brakes are released and roll all way to the gate with the remaining engine(s) at idle.
Engine type? Some engine types idle better than others. I have been told that some old JT9 engines on early 747's have a very powerful idle. I have flown on such a plane only once, a 747-100. And sure enough, during taxiing for take-off the wheel-brakes were engaged much of the time to keep the speed down. But then we were very lightweight, around 100 pax of our way for a 50 minutes flight.
Also in cruise... It's a lot more expensive on fuel to cruise with almost full fuel tanks than at the end of a long flight when the plane is light.
I think that the Discovery over-simplified the situation. Very few things are that simple in aviation.
Always keep your number of landings equal to your number of take-offs, Preben Norholm
AJ From Australia, joined Nov 1999, 2358 posts, RR: 31 Reply 2, posted (9 years 8 months 1 week 4 days 13 hours ago) and read 15468 times:
We allow one ton taxi fuel for ground operations (fixed), 300kg an hour for APU burn, about 35 ton an hour through the take off roll, and approximately 10 ton an hour during cruise. These are grossly generalised figures, as it depends on altitude, temperature, weight etc. I'm sure if you taxied to your destination you would burn more fuel than if you flew, maybe that's what they're getting at?
FDXmech From United States of America, joined Mar 2000, 3251 posts, RR: 45 Reply 5, posted (9 years 8 months 1 week 3 days 18 hours ago) and read 15399 times:
Jet engines, though fuel burn in pounds per hour is high compared to other type aero engines, relatively speaking. In fact it's much more efficient than face value because of the massive distance covered during that hour due to its high speed.
These high cruising speeds (true air speed [TAS], not indicated airspeed[IAS]) are possible because of high altitude flight.
Raw number wise, fuel consumption during taxi/idle are the about as low as you can go.
The best bang for the buck though is during descent when engines are at idle and speeds are high and the jet is a glider. This is one of the primary duties of the FMS. To determine the most efficient point to begin descent.
Vivek1979 From United States of America, joined May 2002, 50 posts, RR: 0 Reply 6, posted (9 years 8 months 1 week 3 days 15 hours ago) and read 15381 times:
B747skipper From , joined Dec 1969, posts, RR: Reply 7, posted (9 years 8 months 1 week 2 days 17 hours ago) and read 15371 times:
Fuel burn (planning) 747-200s or 747-300s...
We account for some 1,000 kg (2,200 lbs) for the taxi-out for takeoff...
Assuming a heavy aircraft at 377,000 kg (833,000 lbs) takeoff weight, it will burn some 15,000 kg (33,000 lbs) to initial cruise level FL290 or 310...
First hours of cruise, expect some 13,000 kg (28,000 lbs) FF per hour...
As the plane gets lighter, at the end of cruise, maybe at FL370 or 390, the FF will decrease to under 10,000 kg (21,000 kg) per hour...
Descent, approach, landing, generally burn 3,000 kg (6,000 lbs) total...
Taxi-in will be anywhere from 500 to 1000 kg (1,000 to 2,000 lbs)...
Our company policy is plan landing at destination with 14,000 kg (30,000 lbs) which leaves us enough to proceed to an alternate destination + reserves...
The cost of a fill-up on a 747-200 or 300 varies with fuel prices, but be the capacity of these airplanes is generally 155,000 kg (345,000 lbs) with the 7 tanks configuration, or 165,000 kg (367,000 lbs) with 9 tanks...
Hope it helps...
B747skipper From , joined Dec 1969, posts, RR: Reply 9, posted (9 years 8 months 1 week 1 day 12 hours ago) and read 15321 times:
Dear Mr.BA...
I dont have data for the 747-400s, I discussed the savings of lower fuel consumption with many, and correct, they burn a little less, and have more range... To do so, bear in mind that the 400s have -
(1) newer versions or higher engine "dash numbers" slightly more efficient...
(2) refined aerodynamics (reduced drag) - see the winglets...
(3) their tanks also have more fuel capacity (extra tank in tail)...
The 747-400 max takeoff weight is much more than the 200/300s which are certified up to 377,000 kg (833,000 lbs), some I hear are some 20,000 kg (or 45,000 lbs) heavier for max takeoff weight...
Been often in flight deck visits in cruise, of 400s, their fuel flows dont appear less than the 200/300s I fly... maybe they save, wild guess 500 kg (1,200 lbs) FF at equal weights... their fuel burn for taxi must be same as a 200/300...
Keep in mind, that a 400 can be an expensive airplane to buy (or lease) for that minimal fuel savings... US$100 million vs US$12 million for an older 747...
The seating capacity for a 400 is the same as a 300...
Crew cost savings for the 400, neither are justified really by "suppressing" the flight engineers. On a 200/300 the crew of three can legally fly up to 12 hrs without need for additional relief crew members, in a 400 with a crew of two, legs are not legal to fly 12 hrs legs, so they must at least provide a third crewmember for legs of 12 hrs, and that "third" crewmember must be... a fully qualified captain by regulations... which is a crewmember with a higher salary than the flight engineers they conveniently sent to unemployment...
Few airlines can really justify replacing 200/300s by... 400s...
I am a pilot, not an airline chief financial officer...
All the best... (s) Skipper
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. But would be very interested to get figures for the B744 too. Anyone?
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