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Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 9:01 am
by airplanecrazy
Does the fuel consumption (and thereby range) of an aircraft change as the aircraft ages? Cars will get better gas mileage after they are broken in, so I was wondering if a similar effect happens with airplanes. Perhaps the range actually decreases as the aircraft skin gets dirty or dinged?

RE: Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 9:45 am
by fr8mech
Quoting AirplaneCrazy (Thread starter):
Perhaps the range actually decreases as the aircraft skin gets dirty or dinged?

Don't you just love it when you answer your own question? Also, as the engine ages, it gets less efficient because the clearances open up.

RE: Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 10:10 am
by LAXintl
Aircraft performance in general declines after a few years of ownership due to both airframe engine degradation.

Everything from engine EGT margin loss, flight control surface rigging issues, aircraft weight gain etc.. all serve to reduce performance.

RE: Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 10:36 am
by airplanecrazy
Quoting Fr8Mech (Reply 1):
Aircraft performance in general declines after a few years of ownership due to both airframe engine degradation.

Do you know how signficant the change can be? Are we talking 1-2%, or more?

Thanks

RE: Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 11:24 am
by liedetectors
Quoting AirplaneCrazy (Reply 3):

Do you know how signficant the change can be? Are we talking 1-2%, or more?

Depends no how whipped you let your engine become.

A big killer is fan blade deterioration. As the fan tip wear down, they create gaps. These gaps cause a drop in EPR and a result, N2 must increase to maintian EPR. This, of course, would drive up fuel flow as the engine is now running faster and hotter.

RE: Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 11:35 am
by LAXintl
Quoting AirplaneCrazy (Reply 3):
Do you know how signficant the change can be? Are we talking 1-2%, or more?

Performance deterioration tends to stabilise in mid age aircraft. Its not uncommon for middle age Airbus and Boeing types to be 5% or more percent from aircraft book performance values.
Many airlines have proactive engine and airframe maintenance programs to win back some of the degradation particularly these days with the high cost of fuel.

RE: Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 11:40 am
by airplanecrazy
Quoting Liedetectors (Reply 4):
A big killer is fan blade deterioration. As the fan tip wear down, they create gaps

I know the latest GE engine blades are made of a carbon-reinforced epoxy with titanium leading edges. Is there any noticeable difference in the blade wear between these blades and more traditional blades?

RE: Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 12:41 pm
by 2H4


I've always wondered how much weight could be removed from a 40-year-old airliners if you could somehow turn it upside-down and shake out the years and years of dirt, pens, grime, trash, and assorted debris that have collected in all the nooks and crannies...




2H4



RE: Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 12:47 pm
by kdeg00
I was thinking along similar lines last week, looking at the various patches on the engine cowling of my 752. My question was how much additional drag an older airframe had because of the repairs to normal bumps and bruises.

RE: Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 3:38 pm
by Molykote
Quoting AirplaneCrazy (Thread starter):
Does the fuel consumption (and thereby range) of an aircraft change as the aircraft ages? Cars will get better gas mileage after they are broken in, so I was wondering if a similar effect happens with airplanes. Perhaps the range actually decreases as the aircraft skin gets dirty or dinged?

Yes.

Aircraft performance deteriorates for a number of reasons with age.

- "Dust Bunnies" and other junk accumulated in nooks and crannies of the airframe.

- Repairs will add weight and be somewhat detrimental to aerodynamics if external.

- Engine deterioration

- Slop in the rigging of flight controls, gear doors, etc.

I'm sure others will have more to add. A deterioration of 2-3% is in the ballpark of "normal" after a few to several years.

RE: Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 6:12 pm
by pavlin
Quoting AirplaneCrazy (Thread starter):
Cars will get better gas mileage after they are broken in

I am not sure about that. You should take a look at those valves after 100.000km

RE: Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 7:36 pm
by AvionicMech
Every airline should produce either fuel flow factor and drag factor charts or maybe just a fuel flow factor chart for each aircraft to be entered into the FMC. When a navigational database is loaded to the FMC on older systems it will wipe out the FF and drag factors and they will need to be re entered once the update is complete. At my airline we only enter a FF factor and leave the drag factor at 0.0. This FF figure is updated every 3 months I believe, using actual fuel used for a flight and comparing it to the expected fuel burn.

Most of our aircraft have a figure of around 2-3 but some with a couple of old engines may be as high as 5, but that is unusual.

RE: Fuel Consumption As Aircraft Ages

Posted: Thu May 11, 2006 8:03 pm
by F14D4ever
Quoting Liedetectors (Reply 4):
A big killer is fan blade deterioration. As the fan tip wear down, they create gaps.

A bigger killer is turbine blade deterioration. After initial rubs, fan blades aren't as prone to continued tip wear as turbine blades, because in addition to mechanical growth/shrinkage, turbine blades suffer airfoil degradation due to thermal stress, which obviously happens continuously through their life cycle.