DStuntz
Topic Author
Posts: 40
Joined: Thu Oct 30, 2003 9:13 am

### Measuring Fuel-efficiency

I imagine that the 2 main factors in determining fuel efficiency would be the carrying capacity and the rate of fuel consumption, but how is it measured? For example, I know that the B757 is more fuel-efficient that the B707, but by how much?

Is there such a rating system where each aircraft type would have a certain number to specifically and accurately indicate the fuel-efficiency? (In the same way that "500 deg F." is more specific and accurate than just saying "hot"). I would greatly appreciate a response. Thanks.

StanstedFlyer
Posts: 113
Joined: Sat Jul 28, 2001 4:48 pm

### RE: Measuring Fuel-efficiency

I think it would be hard to define, as even within types, certain aircraft are more efficient. Each aircraft has it's own efficiency, so you can't say all 747's are exactly the same. And surely it would also depend on loads, range etc. If you broke each plane down into efficiency per passenger per mile, that might help. No idea how you'd do it though!!!
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ramerinianair
Posts: 1452
Joined: Tue Nov 11, 2003 6:03 am

### RE: Measuring Fuel-efficiency

I think they have a figure of fuel burn per hour. Depending on how you will configure the A/C, you can compare the burn per seat. Just divide the burn per hour by the amount of seats. It sounds like it works but I'm not totally sure.
SR
W N = my Worst Nightmare!!!!!

timz
Posts: 6265
Joined: Fri Sep 17, 1999 7:43 am

### RE: Measuring Fuel-efficiency

Yeah, it's surprising how hard it is to get anyone to answer a simple question like that. Put equal numbers of people and payload in a 757-200 and a 707-131, fly them both from LAX to JFK, same weather, same delays-- how will the fuel burn compare? I'm guessing in the 50% range, but I've never seen a good answer.

OldAeroGuy
Posts: 3301
Joined: Sun Dec 05, 2004 6:50 am

### RE: Measuring Fuel-efficiency

Two ways really:

Individual airplane fuel mileage is usually expressed as Nautical Miles per Lb.(or Kg.) of fuel in cruise, usually referred to in the shortened form of NAM's. This figure is never a constant as it varies with Mach, Airplane Weight and Cruise Altitude.

For airplane to airplane comparisons, Timz is on the right track. The favored method is to compare the Block Fuel per Seat used on a specific mission with a full passenger payload and no cargo that is consistent with the general range characteristics of the two airplanes being compared. A320 vs B737 might use 1000 n.m. while A346 vs 773ER might use 4000 n.m. Block fuel includes fuel used for Taxi Out/In, Takeoff, Climb, Cruise, Descent, and Approach.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis

ramerinianair
Posts: 1452
Joined: Tue Nov 11, 2003 6:03 am

### RE: Measuring Fuel-efficiency

I just recieved an e-mail from a fellow a.netter . . . Here is the real anwser.
easy..... i study physics at the no.1 college in London St Francis Xaixer college so yeah heres the answer>>> "energy" the waste factor of energy being produce is are unwanted heat, drag, noise>(low A380,a350 and 7E7 noise saving more fuel). you could save more fuel and go longer routes if you cut down on these factors. for a better example a normal light bulb> 100Watts 10% light & 90% heat, efficent light bulb>11watts 95% light 5% heat. you'll have the same amount of light but save way more energy and money. can you post this up please? i hope this has been any use to you cause i know it can help everyones answer on the a380/a350/7e7 noise level. need any more info contact me at kenzydelightfm@hotmail.com thankz
SR
W N = my Worst Nightmare!!!!!

lightsaber
Crew
Posts: 12706
Joined: Wed Jan 19, 2005 10:55 pm

### RE: Measuring Fuel-efficiency

RamerinianAir's answer is technically correct. But there needs to be more of an applied perspective:

 Quoting OldAeroGuy (Reply 4):The favored method is to compare the Block Fuel per Seat used on a specific mission with a full passenger payload and no cargo that is consistent with the general range characteristics of the two airplanes being compared. A320 vs B737 might use 1000 n.m. while A346 vs 773ER might use 4000 n.m. Block fuel includes fuel used for Taxi Out/In, Takeoff, Climb, Cruise, Descent, and Approach.

Correct, but the analysis I have participated always use "target routes" with varying winds and such. CO did it the most straight forward way to decide which regional jet they preferred. They had a CRJ-200 and an ERJ-145 take off within minutes of each other loaded with the same number of "volunteers" and the luggage was weighted to have within a few pounds the same. The FAA was in on the test as they assigned the two the exact same flight levels per CO request.

For most sales orders, everything was done at TSFC and appropriate thrust levels the airframe required at Takeoff, Takeoff +27F, initial climb, mid-climb, end of climb, start of cruise, mid-cruise, end of cruise, and approach. From this most customers could predict fuel consumption to within 0.5% (on an annualized average). All of these numbers were produced for light loads, max pax (no cargo), and max payload plus any subsets a customer would require.

If it seems overly complicated, its because it is complicated. An airbus 320 is very efficient for long haul, but the 738 gains on the short haul just because its lighter. Its a constant trade. But it does come down to mass fuel consumed per distance traveled per pax.

Oh, a 757 uses less than half the fuel of a 707, the best link I found. Note how efficiency is a function of range on slide 16:

The space is messing up the link:
www.tc.gc.ca/programs/environment/ Freight/training/pdf/Mark%20Janes.pdf

Lightsaber
"They did not know it was impossible, so they did it!" - Mark Twain

OldAeroGuy
Posts: 3301
Joined: Sun Dec 05, 2004 6:50 am

### RE: Measuring Fuel-efficiency

 Quoting Lightsaber (Reply 6):Correct, but the analysis I have participated always use "target routes" with varying winds and such. CO did it the most straight forward way to decide which regional jet they preferred.

You're correct if a specific airline is doing a purchasing decision study. The generalized data I was referring to is what you see in brochures. No airline should ever select an airplane from what they see in brochure-to-brochure comparison of airplane types, although sometimes you wonder.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis

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