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Fuel Savings From Cg

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Fuel Savings From Cg

Old 20th May 2008, 06:50
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Fuel Savings From Cg

Hi all,
Can somebody quantify the fuel savings of an aft Cg as opposed to an extrem Fwd Cg? i would really be interested to know what the difference is in real numbers.

we have always been taught that an aft Cg saves fuel and some w&b systems actually suggest an optimal LIZFW (usually around 10pt from aft limit)

Is it worth my while trying to achieve an optimal Cg on a short sector eg dub-fra ??

thanks, john.
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Old 20th May 2008, 07:02
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I have no figures, but whoever 'taught' you was correct and it is worth it on EVERY sector, and more so with every upward $.
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Old 20th May 2008, 12:43
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sounds good i`ll continue as such ... anyone got any ballpark figures?

john?
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Old 20th May 2008, 19:48
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We had correction factors in the old L1011 AFM but I don't recall them off the top of my head. But for sure it was real and on long sectors when loaded aft of that used in the jet plan the savings were considerable.
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Old 20th May 2008, 20:50
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Hope this helps

2%

http://www.nasa.gov/centers/dryden/p...ain_H-2002.pdf
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Old 20th May 2008, 21:30
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1 1/2% for every 5% of CG shift on a GLEX. Had charts for large types like the C-5, 744. It is significant.
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Old 20th May 2008, 21:47
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2% on the data from the 310 tests from AB but the figures are different for each type as G flyer states.

GF do you know Mike McCook?
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Old 20th May 2008, 21:59
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2% ? Wow that is quite significant! Similar to the fuel saved by winglets.

John
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Old 20th May 2008, 22:27
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conversely some manufacturers offer Forward CoG schedules to improve take off perf. Ideally you would like to have it forwards for take off and then shift it back in flight which is what many jets do now.
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Old 20th May 2008, 22:59
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Yeah your welcome Hoppy...feel free to go to that Nasa site link I posted..have a nice day..
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Old 20th May 2008, 23:49
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The pdf you linked talks about a 2% reduction on an A310. so you are welcome.
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Old 21st May 2008, 00:08
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http://iata.org/NR/ContentConnector/...y_Material.pdf

Pages 10-12

All airbus types

DTG
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Old 21st May 2008, 00:13
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ssg might be better off reading this one: http://www.flightlevel400.com/docume...erformance.pdf
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Old 21st May 2008, 00:18
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or this:http://www.smartcockpit.com/pdf/flig...ngtechnique/41
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Old 21st May 2008, 02:15
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FE Hoppy

Nice link to Airbus V1 philosophy. Mike McCook doesn't ring a bell, where might I have met him? I'm an exile from some of ssg's threads.
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Old 21st May 2008, 03:06
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I recall a presentation from a QF fellow at the RAeS some years ago .. relating to a study (which was driven by a pilot's interest, rather than the engineering folk at it turned out) which looked at rescheduling the tailtank usage on the 744 to constrain the aft cg a little more ... long range it was worth a couple of (fare-paying) extra passengers .. over a year, something in excess of a lot of money.
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Old 21st May 2008, 09:37
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GF

He was a Galaxy FE and Instructor. But I guess there are many.
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Old 23rd May 2008, 16:51
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I checked out the Nasa link for aft CG...can't say it applies to all planes, but they seem to make it clear that if you can leave the fuel as far aft for the duration of the flight....2% savings is the approximate result.

Begs to ask the question of why we still hang our tails on the end of the plane the way we do...
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Old 23rd May 2008, 17:11
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Angels,

Don't forget that aft CoG is bad for Vmc so it's not always appropriate to have an aft CoG.
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Old 23rd May 2008, 17:24
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Couldn't agree more Hoppy...I guess in some cases trying to save a buck on fuel, or engines, or whatever, we could end up reducing safety...defeats the purpose if the plane goes in.....
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