fuel burn queston

[lowtimedriver]

I work right next to KSNA and often watch the traffic there. I have noticed that the SWA 737 pilots seem to use substantially less runway on take-off than Alaska, American 737's, etc. I am going to take a guess and say it is because SWA flies shorter segments, on most occasions, than the other airlines and they probably carry less fuel on takeoff.

I was wondering if fuel efficiency with turbofans increases with a reduction in gross weight due to fuel burn?

 

[Andy Neill]

I work right next to KSNA and often watch the traffic there. I have noticed that the SWA 737 pilots seem to use substantially less runway on take-off than Alaska, American 737's, etc. I am going to take a guess and say it is because SWA flies shorter segments, on most occasions, than the other airlines and they probably carry less fuel on takeoff.

I was wondering if fuel efficiency with turbofans increases with a reduction in gross weight due to fuel burn?

I don't know if that wouldn't be true for any power source or engine. Less weight means less power required means less fuel needed means increased performance.

 

[super88]

I'd say its because Southwest pilots do everything faster- stop, taxi, gate turn... They probably just punch it, no reduced power take offs, get up and get out.

I used to freightdog it in and out of MDW and the only guys taxiing as fast as we did were SWA.

 

[Stifler's Mom]

I like Super88's answer. They probably have TO Power set before they're even lined up on runway heading...

...or their special blend of "hedged" fuel is better performing compared to other airlines.

 

[flyalot]

Yes,
Less weight, Less power needed to push the beast.
Heavy, high relative angle of attack= more drag
Light, low relative angle of attack= less drag
This equals less fuel burn.
Burns start high. Get lower as the plane gets lighter.
IE-1st hour, 7,000 lbs
2nd hour, 6,500 lbs
3rd hours, 6,000 lbs
Just a simple answer. You can get much more into it if you want.

 

[lowtimedriver]

So if fuel efficiency increases with a decrease in gross weight, do the airlines fly with less than a full load of fuel when they are able?

 

[time builder]

So if fuel efficiency increases with a decrease in gross weight, do the airlines fly with less than a full load of fuel when they are able?

Yes. A SWA 737 will typically take less than 12000 lbs. of fuel for an hour long flight into good weather, 35000 to 42000 will top it off.

Go for a long flight, need to plan for an alternate, or for any other reason need to add fuel, "it takes fuel to carry fuel."

Another consideration, in additon to those listed above, is the amount of time spent with climb power. A 737 will burn significantly less fuel in cruise than during climb. So.... geting up to altitude quicker equals fuel savings. Trudge along with a minimal climb rate and you burn more fuel.

It's not all about efficiency though, you have to consider other things like landing weight. You may be able to take off at max gross, but you need to burn off enough fuel to meet your landing weight requirements. I don't remember the exact numbers, but there can be over 15000 pounds difference between takeoff weight and landing weight on a 737, with differences from model to model.

In which case, a 737 on a short leg will be much more limited on their takeoff weight than one going on a 4 hour trip.