Guest

Fuel Saving Thru Proper Loading

Wed May 30, 2001 5:05 am

Hi,

It is common knowledge that CG affects fuel consumption.

Can anyone lead me to an info source that relates fuel burn to loading, specifically how much fuel saving can be realised thru loading to ideal CG?

Thanks,

Eli
 
OPNLguy
Posts: 11191
Joined: Tue Jun 15, 1999 11:29 am

RE: Fuel Saving Thru Proper Loading

Wed May 30, 2001 5:34 am

As a starting point, I'd contact the aircraft manufacturer's rep assigned to your airline, and see what publications (in addition to AFM/AOM, etc.) they have. Our Boeing rep provides us all with copies of Boeing's "Airliner" and it commonly has deatiled and in-depth articles on a wide variety of operational topics. I presume Airbus also has something similar.

I'll see what I can find in my own personal archives.. What type of aircraft are you interested in?

ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.
 
Guest

RE: Fuel Saving Thru Proper Loading

Mon Jun 04, 2001 6:42 am

Guys,

5 days and only one righteous in Sodom.

Any ops personnel out there with knowledge to help?

Eli
 
chdmcmanus
Posts: 372
Joined: Wed Mar 21, 2001 12:53 am

RE: Fuel Saving Thru Proper Loading

Mon Jun 04, 2001 7:18 am

I have some generalized CG/Range comparison charts for the Lockheed C-141 in my performance books. I will see if I can scan one of them for you. the relationship is quite dramatic though, with range decreasing very quickly once outside of only a few% of CG, while still remaining in the flight envelope. Hope they will help.

ChD
"Never trust a clean Crew Chief"
 
Top Gun
Posts: 103
Joined: Wed May 19, 1999 8:13 am

RE: Fuel Saving Thru Proper Loading

Mon Jun 04, 2001 2:02 pm

Talking about C of G and W&B can get very detailed.

Here's what I'll tell you in simple terms.

Many Airlines want an aft C of G as possible without going outside the limits (envelope). In order to do this we want to have a heavier tail in cruise which will produce a higher TAS, thus creating a better fuel econ.

The way they work it is relitivly simple, they take fuel from the main tanks and pump it to the one in the tail section. And there you get the heavier tail and aft C of G.

Enjoy.
 
tito
Posts: 122
Joined: Sat Feb 17, 2001 1:39 pm

RE: Fuel Saving Thru Proper Loading

Tue Jun 05, 2001 5:28 am

This can get pretty long... but here's an attempt at a condensed version.

With the exception of some fighters airplanes are always designed so that the entire CG range is forward of the center of lift, thus making the airplane "nose-heavy" , the horizontal stabilizer is always producing some amount of down force to counteract this. This is done to make the aircraft stable in pitch.... If the the aircraft is disturbed, for instance, nose up... the resultant airspeed decrease would render the horizontal stab less effective and allow the nose to drop. And the opposite nose down. OK, so how does loading affect performance?

Because the CG is not co-located with the Center of Lift, any loads being created by the horizontal stabilizer must be carried by the wing in addition to the weight of the aircraft itself. For instance if a light airplane weighs 2000 lbs and its tail is producing 100 lbs of downforce to hold the nose up then the wing must lift 2100 lbs. The location of the center of gravity will effect the amount of downforce that the hor. stab. must produce, and thus the amount of lift the wing must produce. If an a/c is loaded to the aft limit it is a little less nose heavy and the hor. stab. doesn't need to produce as much downforce... if our 2000 lb. light airplane is loaded aft and our hor. stab. is only producing 50 lbs. of downforce then the wing need only lift 2050 lbs.

So in a nutshell... a C.G. further aft means the wing will fly at a lower angle of attack for any given airspeed and will produce less induced drag.... fuel savings.


Hope that helps!
 
ben88
Posts: 1037
Joined: Fri Dec 31, 1999 4:49 pm

RE: Fuel Saving Thru Proper Loading

Tue Jun 05, 2001 6:40 am

Very good explanation Tito. The way I look at it as long as we are within the operational limits in terms of MAC percentage and CG we are fine. It is almost impossible to get a perfect CG when loading A large aircraft, no matter how many hold configuration changes you make.
 
Guest

RE: Fuel Saving Thru Proper Loading

Tue Jun 05, 2001 7:43 am

Guys,
Thanks for taking the time and making the effort to respond.

chdmcmanus:
It will be more than great help if I could get some hard facts to substanciate what is a general knowledge.
I need to have any kind of document that will support my telling management that putting effort into proper loading pays.
If you succeed in scanning the data, please email the files to eliben_ba@hotmail.com.

TopGun:
Why would a heavier tail produce a higher TAS?

Tito:
Thanks for your learned explanation. I understand the theory now. Do you have fuel saving figures relative to CG (@ ZFW or TOW) for the BAe 146? As you can tell from my reply to chdmcmanus, I am looking desperately for tangible figures.

Ben88:
Just another proof that nobody is perfect but airlines do load planning and strive (or should strive) to get as close as possible to ideal c.g.
We use weight & balance software that is capable of load planning to achieve an ideal c.g. It is called LoadMaster - see their website at www.computair.net.
As planned (vs. specified) loading is slower on one hand but saves money on the other - I am looking for the figures that will let us weigh cost/benefit.

Thanks again.

Eli
 
Guest

RE: Fuel Saving Thru Proper Loading

Tue Jun 05, 2001 11:04 am

I don't have a figure for Bae 146 but for the MD-11, fuel flow is 4.5% higher at the forwardmost CG (in cruise ~ 16%) versus the ideal 32% MAC.

Also on the MD-11, if you load cargo to end up with the forward most ZFWCG, the fuel burn will be about 2.7% higher during cruise. That is a huge figure when you calculate based on yearly operation...many thousands of dollars wasted per airplane per year.

Best Regards,
Nut
 
Guest

RE: Fuel Saving Thru Proper Loading

Tue Jun 05, 2001 5:23 pm

MD11nut,

Thank you for your item.
This is the first time I see a figure put to fuel burn vs CG.
Could you please tell me what manual/page carries this information or whether you could scan/fax the page?
I will, naturally, carry any expense incurred.
You can email me direct to OpsManager88@hotmail.com.

Thanks again,
Eli


 
jjbiv
Posts: 1203
Joined: Mon Jan 08, 2001 10:58 am

RE: Fuel Saving Thru Proper Loading

Wed Jun 06, 2001 1:11 am

What is MAC (Mean Aerodynamic Chord)? Thank you.
 
Guest

RE: Fuel Saving Thru Proper Loading

Wed Jun 06, 2001 6:30 am

Jjbiv,

MAC is the chord drawn through the geographic center of the plan area of the wing.
C.G. calculations take into consideration the aerodynamic chord of the wing. In tapered wing aircraft (e.g. jets) the chord changes, hence the need for a mean chord.

Eli
 
musang
Posts: 788
Joined: Sun Apr 08, 2001 4:11 am

RE: Fuel Saving Thru Proper Loading

Wed Jun 06, 2001 6:43 am

Opsmanager88 - I'd be interested if you get any of the data you requested for the 146, as I drive RJ 100s. Please contact me at greendgls@aol.com

Many Thanks, Regards - Musang
 
Guest

RE: Fuel Saving Thru Proper Loading

Thu Jun 07, 2001 7:45 am

OpsManager88,
I got the figures from an article published by Boeing Flight Ops on MD-11 Fuel Conservation.

This was done back in '96 in a booklet form to be distributed to MD-11 operators. I'm not sure about its proprietary. I'll have to look and see. If it's OK, I'll scan and email it to you but it'll take a while. I've been very busy with a newfound passion: scuba diving  Smile/happy/getting dizzy

Best Regards.
Nut

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