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pa201
Topic Author
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Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 3:41 am

Looking at the 777LR and 777F operating stats of:

MTOW: LR = 766K pounds F= 766K pounds (same)
Fuel Cap: LR = 53K gallons F= 48K gallons (nearly same)
Range: LR= 9,400 miles F= 4,900 miles (huge difference - 55% less)

So in that the same airframe carries the same amount of fuel, and has the exact same Max Takeoff weight, why is there such a vast difference in two's range capabilities? If the same airplane is carrying the same weight with the same amount of gas, why can't the F go as far as the LR, and by such a wide margin ? Noticed the same for the 748F v. 748I - same operating stats but half the range. Thanks for any info on this minor mystery that has been bugging me for months !  confused 
 
beech19
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RE: Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 3:51 am

My understanding is because a F usually runs at near MTOW where as a pax hardly ever does. Pax range is not at MTOW but a combination of something less (max fuel but not MTOW). I beleive a PAX version at MTOW will be limited to a range near the same as the F.

Can anyone verify this?
KPAE via KBVY
 
Lemurs
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RE: Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 3:54 am

Most obvious answer would be where that weight is put. A fully loaded 777LR with a typical pax/cargo load can carry a lot more fuel up to it's MTOW than a full 777F. As WidebodyPhotog has said multiple times, the 777LR runs out of space to put fuel in typical pax operations, not weight to carry.

DfwRevolution mentioned in one of the 777-conversion threads that the structural weight limits of the 777F allow it to carry more than 50,000lbs more "stuff" than a 777ER. (i.e. non-fuel) That's 50,000lbs less fuel in the tanks before it hits MTOW, which is a whole boatload of miles...hence much shorter range.

[Edited 2006-11-10 19:56:19]
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OldAeroGuy
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RE: Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 3:56 am

Quoting PA201 (Thread starter):
MTOW: LR = 766K pounds F= 766K pounds (same)
Fuel Cap: LR = 53K gallons F= 48K gallons (nearly same)
Range: LR= 9,400 miles F= 4,900 miles (huge difference - 55% less)

The range for the 777F is shown at the payload for max zero fuel weight (MZFW) ie carrying max. payload.

The range for the 772LR is shown with full pax and bags only. Although both airplanes are at the same takeoff weight, the 772LR has a lot more fuel on board and is close, if not at it's fuel capacity limit.

If the 772LR were at it's MZFW, its range would be closer to that quoted for the 777F.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
bringiton
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RE: Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 3:56 am

Quoting PA201 (Thread starter):
So in that the same airframe carries the same amount of fuel, and has the exact same Max Takeoff weight, why is there such a vast difference in two's range capabilities? If the same airplane is carrying the same weight with the same amount of gas, why can't the F go as far as the LR, and by such a wide margin ? Noticed the same for the 748F v. 748I - same operating stats but half the range. Thanks for any info on this minor mystery that has been bugging me for

Did you by any chance happen to ask that question to Randy Baseler?


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ikramerica
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RE: Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 3:58 am

That's because you are not reading those numbers right, or more to the point, they are not the whole picture.

The range of the 772LR is with pax only, and the max range. No cargo, not even a realistic interior config. It's full of fuel, but not of revenue. Full of fuel and 3 belly tanks. This is because the primary purpose of a pax aircraft is to fly pax around.

The 777F range quoted is range at max payload, and is fuel limited. This is because the primary purpose of a freighter is to carry freight.

It can fly much further with less payload, as the curves for the 777F and 772LR are similar (since they are similar planes).

The pax version has a max landing weight of 492k lbs, while the 777F has a max landing weight of 575k lbs. The MZFW of the 772LR is 460k, and the 777F is about 540k. The ranges you quote are not for the 772LR at that weight, but are for the 777F at that weight.

The max range for a 772LR without belly tanks at it's MZFW is under 7000nm. The 777F also has a range similar to this at 460k ZFW. FX is going to operate their 777Fs in this way, according to their PR.
Of all the things to worry about... the Wookie has no pants.
 
OldAeroGuy
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RE: Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 4:00 am

Quoting Beech19 (Reply 1):
My understanding is because a F usually runs at near MTOW where as a pax hardly ever does.

The range quote for the 772LR is at or very close to MTOW, the same as the 777F. The difference is that 777F trades fuel weight for payload weight.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
beech19
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RE: Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 4:06 am

Quoting OldAeroGuy (Reply 6):
The difference is that 777F trades fuel weight for payload weight.

I see that now... good to know.  Smile Makes sense!
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kc135topboom
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RE: Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 4:17 am

Quoting OldAeroGuy (Reply 6):
The range quote for the 772LR is at or very close to MTOW, the same as the 777F. The difference is that 777F trades fuel weight for payload weight.

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brilondon
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RE: Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 6:32 am

My twocents  are that a frieghter would probably be loaded to capacity in order to maximize its profit.
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warreng24
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RE: Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 6:37 am

Remember that freighters usually are heavier (larger empty weight) than a passenger model.

This is because of the strengthened floor of the main deck to accomondate all the weight.

Therefore, the freighter will reach the MTOW with less fuel than a passenger model.

Less fuel & more weight equals less range.
 
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LAXintl
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RE: Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 6:49 am

Quoting Warreng24 (Reply 10):
Remember that freighters usually are heavier (larger empty weight) than a passenger model.
This is because of the strengthened floor of the main deck to accomondate all the weight.

Actually its the other way around. Freighter aircraft weight a lot less by themselves compared to the passenger version of the equivalent type.

Freighters for all essential purposes are a bare bones aircraft while the passenger versions are weighed down with added cabin furnishings such as seats, sidewalls, galleys, lavs, entertainment systems, added ventilation etc..

For instance an empty passenger 747-400 weights about 45,000lbs more than its freighter cousin.


The difference in range as mentioned has to do with payload. A full passenger aircraft weights significantly less then the same aircraft with a full load of cargo.
For instance using the B744, 400 passengers and their bags would weight roughly 85,000lbs, while the same aircraft full of cargo could accomodate well over 200,000lbs of cargo which in turn eats into the range performance quite a bit.
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OldAeroGuy
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RE: Pax V. Freighter, Why Range So Different?

Sat Nov 11, 2006 6:53 am

Quoting Warreng24 (Reply 10):
Remember that freighters usually are heavier (larger empty weight) than a passenger model.

This is because of the strengthened floor of the main deck to accomondate all the weight.

Any floor strengthening on a Freighter is far out weighted by passenger seats and support equipment like galleys on a Pax airplane.

Pax OEW is higher than the same model airplane Freighter OEW by a wide margin.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
widebodyphotog
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RE: Pax V. Freighter, Why Range So Different?

Wed Nov 15, 2006 3:55 am

Quoting PA201 (Thread starter):
So in that the same airframe carries the same amount of fuel, and has the exact same Max Takeoff weight, why is there such a vast difference in two's range capabilities? If the same airplane is carrying the same weight with the same amount of gas, why can't the F go as far as the LR, and by such a wide margin ? Noticed the same for the 748F v. 748I - same operating stats but half the range. Thanks for any info on this minor mystery that has been bugging me for months !

Actually at the specified ranges and payloads the airplanes carry vastly different amounts of fuel. The 777-200LR at a still air range of ~9,700nm and a nominal 64,000lbs of payload, (301 Pax), also carries its maximum fuel load of 356,000lbs plus taxi allowance. 48% of the total takeoff weight is fuel and the airplane can fly very far...

For the freighter at its MZFW of 547,000lbs, it can only carry 219,000lbs of fuel plus taxi allowance at certificated MTOW. Only 29% the total takeoff weight is fuel and the range is considerably less than the passenger aircraft.

Works the same way for the 747-8's as well...


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