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Fuel Saving Thru Proper Loading  
User currently offlineOpsManager88 From , joined Dec 1969, posts, RR:
Posted (13 years 2 months 6 days 6 hours ago) and read 2056 times:

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


13 replies: All unread, jump to last
 
User currently offlineOPNLguy From , joined Dec 1969, posts, RR:
Reply 1, posted (13 years 2 months 6 days 5 hours ago) and read 1989 times:

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?



User currently offlineOpsManager88 From , joined Dec 1969, posts, RR:
Reply 2, posted (13 years 2 months 1 day 4 hours ago) and read 1940 times:

Guys,

5 days and only one righteous in Sodom.

Any ops personnel out there with knowledge to help?

Eli


User currently offlineChdmcmanus From United States of America, joined Mar 2001, 374 posts, RR: 2
Reply 3, posted (13 years 2 months 1 day 3 hours ago) and read 1937 times:

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"
User currently offlineTop Gun From Canada, joined May 1999, 101 posts, RR: 2
Reply 4, posted (13 years 2 months 21 hours ago) and read 1913 times:

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.


User currently offlineTito From United States of America, joined Feb 2001, 125 posts, RR: 1
Reply 5, posted (13 years 2 months 5 hours ago) and read 1907 times:

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!


User currently offlineBen88 From United States of America, joined Dec 1999, 1093 posts, RR: 3
Reply 6, posted (13 years 2 months 4 hours ago) and read 1895 times:

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.

User currently offlineOpsManager88 From , joined Dec 1969, posts, RR:
Reply 7, posted (13 years 2 months 3 hours ago) and read 1898 times:

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


User currently offlineMD11nut From , joined Dec 1969, posts, RR:
Reply 8, posted (13 years 2 months ago) and read 1891 times:

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


User currently offlineOpsManager88 From , joined Dec 1969, posts, RR:
Reply 9, posted (13 years 1 month 4 weeks 1 day 17 hours ago) and read 1875 times:

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




User currently offlineJjbiv From United States of America, joined Jan 2001, 1226 posts, RR: 5
Reply 10, posted (13 years 1 month 4 weeks 1 day 10 hours ago) and read 1867 times:

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

User currently offlineOpsManager88 From , joined Dec 1969, posts, RR:
Reply 11, posted (13 years 1 month 4 weeks 1 day 4 hours ago) and read 1859 times:

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


User currently offlineMusang From United Kingdom, joined Apr 2001, 861 posts, RR: 7
Reply 12, posted (13 years 1 month 4 weeks 1 day 4 hours ago) and read 1860 times:

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


User currently offlineMD11nut From , joined Dec 1969, posts, RR:
Reply 13, posted (13 years 1 month 4 weeks 3 hours ago) and read 1848 times:

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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