Some questions about fuel consumption.

[Rakshasa]

Hi folks,

Got asked these questions by a sci-fi loving friend of mine but these are way out of my field of expertise. I'd be thankful if anyone could help me answer them.

1) For a typical transcontinental flight (~2000 miles), about what percentage of a normal jumbo jet's fuel is spent taking off and climbing to cruising altitude (~35000ft)?

Also, about what percentage of a jumbo jet's maximum thrust is needed to sustain its cruising speed (~550mph) at cruising altitude?


2)I'll need the following data for a 747

Drag co-efficient.
Power output of the engines at sea level
Power output of the engines at cruise altitude
Average cruise altitude
Fuel consumption rate at maximum power
Fuel consumption rate at cruise power

Link:http://www.concordesst.com/concordeb.html

3)How about for something like Concorde-B (supersonic L/D close to 8 ), but larger (~350 metric tons at takeoff) and following the proposed US SST trend of mach 2.7 (maybe 3.2) cruise.

Roughly what sort of thrust would be needed to sustain mach 2.7 cruise on such an aircraft?

Thanks for any help.

[eckhard]

Hi Rakshasa,

Rough figures from memory:

1) About 8 tonnes (8000kg). The percentage would obviously depend on how much fuel was in the tanks to start with. Using approx 10 tonnes per hour cruise feul flow, the percentage would be 10% for an 8 hour flight, reducing to about 6% for a 14 hour hop (SIN-LHR).

The second part of your question is more tricky, but if we assume each engine produces 60,000 lb of thrust at sea-level, this will have reduced to about 12,000 lb at cruise altitude, i.e. about 20%. (I remember seeing figures like this in the simulator, where we had a 'flight test' screen that could tell you the instantaneous thrust of each engine.)

2) Don't know the Cd, but the lift/drag ratio is about 14:1 in the cruise.
Thrust at sea level is about 60,000 lbs x 4 = 240,000 lbs.
Thrust in the cruise is about 12,000 lbs x 4 = 48,000 lbs.

Power output is obviously quite different! Power = thrust x speed, therefore sitting stationary on the runway at full thrust, the power is zero! At liftoff, assuming 180kts = approx 90mps and 240,000 lbs = 109,000 kgs, then the power is going to be 9.8 megawatts.

In the cruise, assuming TAS of 500kts = 250mps and 48,000 lbs = 22,000 kgs, then power is going to be 5.5 megawatts.

Fuel consumption at take-off is typically 8,000 kgs/hr per engine = 32,000 kgs/hr.

In the cruise, it's typically 2,500 kgs/hr per engine = 10,000 kgs/hr.

Don't know anything about Concorde! However, using your figures and assuming a mid-cruise weight of 300 tonnes and a L/D of 8, then the thrust would have to be 300/8 = 37.5 tonnes. This would be in the order of 83,000 lbs which would equate to nearly 21,000 lbs per engine (assuming 4 engines).

[Rakshasa]

Thanks alot. That really helped.