I am trying to come up with a reasonable estimate of the incremental cost of adding weight to an aircraft, specifically commercial airliners, but I suppose military transport aircraft would be comparable. Since I am looking at marginal costs, the main (only?) factor should be fuel, I guess.

The ideal statement I would like to be able to make is:

"It takes $XXXX to fly 1kg of mass per year"

or, perhaps better,

"It takes XXXX gallons of fuel to fly 1kg of mass per year"

on a commercial airliner.

Any members able to help? A pointer to a reference would be handy, as well as the actual answer.

TIA

Fly over to airliners.net where this kind of stuff is discussed somewhat often. Forums>Technical.

I can't help you with the big kerosene burners, but in 28 years of operating the piston engine V-Tail, I found a difference of 0.3% in TAS per hundred pounds at the same power setting / fuel burn.

TAS is True Air Speed, basically indicated air speed corrected for temperature and pressure (altitude).

To put this in perspective, the empty weight (round numbers) is 2,100 lbs. with a maximum gross weight of 3,300, leaving 1,200 for people, fuel, and "stuff." This would accommodate four average size people and full fuel -- 80 gallons at six pounds / gallon. It is not necessary to depart with full fuel; the regs require sufficient fuel for the planned trip at normal cruise power, plus a 30 minute reserve for daytime VFR, or for IFR it's enough fuel for the planned destination, and if an alternate airport is required an approach at the original destination with a missed approach procedure followed by the flight to the alternate at normal cruise power, all with a 45 minute fuel reserve. Fuel requirements for the big kerosene burners are similar except that extended over water operations have some more convoluted rules.

V-Tail fuel consumption at fastest recommended cruise power is 15.5 to 16 gallons / hour for a TAS of 174 kts. (200 mph) +/- 1 or 2 its, depending on weight.

Otto, Entropy, or some of the others can probably give you more information on the big stuff. Their operating manuals are probably filled with tables, graphs, and charts for this. It's possible that this information is available online, I don't know for sure.

Are you going to assume that weight and balance is maintained at the aft-most CG limit? You have to have something as a constant in that regard, because as CG moves forward, drag will increase due to the higher angle of attack required to maintain the same altitude/speed with aft CG, thus increasing fuel burn at a given speed.

Beyond that suggestion, I'm tapping out...

I suggest that you look at airline pilot forums.com and then you can post in pilot lounge/hanger talk.

Is the weight internal for example baggage or freight or is it an external load?

Depending on the flight plan format used by any particular airline we get a plus or minus penalty for each thousand pounds added or subtracted from the planned flight plan.

The flight plan software is very sophisticated and takes into account the characteristics of each individual aircraft. There can be changes from the original factory baseline for example age of the aircraft, age of the engines, additional external hardware for example satellite domes, etc.

For publicly traded airlines you can go to their investor relations page and look at their 10 K filings. Depending on the break down you'll see the fuel cost per seat mile for example.


Cheers.

quote:

Originally posted by V-Tail:


V-Tail fuel consumption at fastest recommended cruise power is 15.5 to 16 gallons / hour for a TAS of 174 kts. (200 mph) +/- 1 or 2 its, depending on weight.

Ahhh, Bonanzas! You can't go slower on more fuel!!

Thanks, guys, some very useful info.

What I am really trying to quantify is the value of weight reduction in an airframe. If Airbus could knock 1kg out of the weight of the airframe of an A320, what is that worth to an airline?

I believe the rule of thumb we used was 3% fuel/hr. That is, it takes 3% of the weight of the extra item per hour to carry it. A 100 lb increase in weight would cost us 3 lbs of fuel each hour to carry it. We used this to figure out if it made sense to tanker cheaper fuel into a more expensive destination. If the cost of fuel was at least 3% cheaper at our origin, it was cheaper to tanker it.

This was in a large turboprop aircraft.

There are other factors perhaps not as easily calculated. First is bumping revenue. If the increased weight of the aircraft results in becoming weight restricted on takeoff, it hurts the bottom line directly when bumping revenue. The cost to feed, hotel, reroute, deliver late bags, etc can be pretty high. Most airlines don't make money except on the last few seats sold on any given flight. Air cargo is also a money maker, though it may be possible to reroute the cargo at no additional cost to the airline. You don't want to bump revenue!

The next consideration is altitude capability. Every 2000 ft in altitude is approximately a 5% fuel savings for the time at that altitude. This is in my current 90 seat jet. Altitude capability is limited by aircraft weight. If your additional weight of the aircraft mod makes it too heavy to get higher, you burn that extra fuel. We burn about 3500#/hr at cruise altitude. If your mod weighs 350#, we are stuck lower for another 1/10th hour until we can burn off that much weight in fuel. That means we wasted 17.5# of fuel (about 3 gallons, or roughly $10).

Cruise speed is a constant, so in theory the total flight time remains unchanged assuming nothing else changes. But in the event of a large weight difference it could cost a lot more fuel in climb.

Generally in the summer altitude is very correlated to weather deviations. This would be a hidden cost, difficult to quantify. Every 2000 ft in additional altitude can make a very big difference in how much or whether we even need to divert around thunderstorms. If the weight difference is in the 1000# or more arena, yes this could be a factor in our altitude capability.

quote:

Originally posted by JALLEN:

quote:

Originally posted by V-Tail:


V-Tail fuel consumption at fastest recommended cruise power is 15.5 to 16 gallons / hour for a TAS of 174 kts. (200 mph) +/- 1 or 2 its, depending on weight.

Ahhh, Bonanzas! You can't go slower on more fuel!!

You have never flown a C-206?

quote:

Originally posted by V-Tail:

quote:

Originally posted by JALLEN:

quote:

Originally posted by V-Tail:


V-Tail fuel consumption at fastest recommended cruise power is 15.5 to 16 gallons / hour for a TAS of 174 kts. (200 mph) +/- 1 or 2 its, depending on weight.

Ahhh, Bonanzas! You can't go slower on more fuel!!

You have never flown a C-206?

Or a Beechcraft B60 Duke?

Look up "cost per seat mile."

quote:

Originally posted by DrDan:
Thanks, guys, some very useful info.

What I am really trying to quantify is the value of weight reduction in an airframe. If Airbus could knock 1kg out of the weight of the airframe of an A320, what is that worth to an airline?

Is this through ERAU?

Consider the manner which water is carried too.

quote:

Originally posted by DrDan:
Thanks, guys, some very useful info.

What I am really trying to quantify is the value of weight reduction in an airframe. If Airbus could knock 1kg out of the weight of the airframe of an A320, what is that worth to an airline?

About another million a year in stock bonuses for the top 4 and another row of seats for the FAs to referee.

quote:

Originally posted by erj_pilot:

quote:

Originally posted by V-Tail:

quote:

Originally posted by JALLEN:

quote:

Originally posted by V-Tail:


V-Tail fuel consumption at fastest recommended cruise power is 15.5 to 16 gallons / hour for a TAS of 174 kts. (200 mph) +/- 1 or 2 its, depending on weight.

Ahhh, Bonanzas! You can't go slower on more fuel!!

You have never flown a C-206?

Or a Beechcraft B60 Duke?

I'm probably one of the few in here that can saw I have flown a B60 Duke. lol. I've got exactly 0.3 hours in my logbook in a B60 1 take-off, a looooong student pilot sized/airliner pattern, and 1 landing. I told the owner he owed me after an extensive annual. It needed a flight to return to service, and when the owner's pilot showed up and was a MEI...I wasn't taking no for an answer. I already had several landings in 414's, 414A's, an early 310, and a seneca. The duke flies like a dream. As long as you can forget about how awful those engines are once you uncowl them... You truly feel like you're flying a baby airliner. They are the coolest LOOKING twins out there I think. That duke in particular used to spend about 3-4 months in annual every year. It was a maintenance pig, and the owner was hard on it and put it away wet every time. After a couple years of bringing it to me I think he found someone else willing to work on it and turn a blind eye to a few things I wouldn't.

As for -35 bo's being expensive? Some of the most economical $/mile flying you can get. The 36 B0s start to become guzzlers. But for 6 people, it's not bad. Just starts to make a lot more sense to be into a baron. Especially for the price they go today.

A 206 is awfully friendly with the gas pump also. Key is to just get higher where the gear don't matter as much. Any of the 6-pax singles are going to be rough on fuel.

If anyone's looking...my dad is selling his TB-21TC. It's the "1000th" trinidad, was featured in several magazines and did a tour around the states back in 1990. He's had it for about 7 or 8 years now (traded an old -35 Bo), and just moved back up into a baby baron. Dual Aspen panel, and new Garmin center stack, low-time motor, excellent condition. I maintained it myself for 5 years. Full TKS as well. One of the few out there. I know he's motivated to sell.

quote:

Originally posted by LS1 GTO:

Is this through ERAU?

Consider the manner which water is carried too.

No, I am participating in a National Science Foundation program on commercialization of research. I have a technology that might possibly be used to reduce the weight of various transportation structures, with commercial aircraft being a likely early adopter. For the project, I need some rough estimates of the potential commercial value of the technology, if it succeeded.


I don't understand the reference to how water is carried.

quote:

Originally posted by AKSuperDually:

quote:

Originally posted by erj_pilot:

quote:

Originally posted by V-Tail:

quote:

Originally posted by JALLEN:

quote:

Originally posted by V-Tail:


V-Tail fuel consumption at fastest recommended cruise power is 15.5 to 16 gallons / hour for a TAS of 174 kts. (200 mph) +/- 1 or 2 its, depending on weight.

Ahhh, Bonanzas! You can't go slower on more fuel!!

You have never flown a C-206?

Or a Beechcraft B60 Duke?

I'm probably one of the few in here that can saw I have flown a B60 Duke. lol.

Another Duke'r here - 12.3 hrs. The Dr owner had '69 B56TC (small Baron airframe with the same 380 HP Lycoming TIO-540-E1B4) but correctly thought it was more airplane than he could safely fly - so much to my dismay he sold the hot rod Baron and bought a pressurized Duke. Of course, the Duke was just as much if not more airplane to handle so he sold it and bought his old Mooney back

I didn't care much for the Duke, but sure liked the 56TC Baron - I ended up in a 56TC partnership but between 100LL, run out engines and props, we had to sell it

Amazing plane; only 93 56TC's made to prove out the engine and nacelle installation on the Duke. When production began on the Duke, Beech stopped building their factory hot rod.

Had to be some impressive X-country numbers.

Duke's are awesome if someone else is footing the maintenance bill. I've actually never annualed a baron. We were a 414/340 shop, so most of my twin experience was in those cessnas.

Word from my dad about his baby baron is that it's fairly heavy on the controls. That seemed odd to me, the duke was SOO light, like flying a bonanza. I've been wondering if his controls are balanced/rigged properly. Are the baron's heavy on the controls?

quote:

Originally posted by DrDan:

quote:

Originally posted by LS1 GTO:

Is this through ERAU?

Consider the manner which water is carried too.

No, I am participating in a National Science Foundation program on commercialization of research. I have a technology that might possibly be used to reduce the weight of various transportation structures, with commercial aircraft being a likely early adopter. For the project, I need some rough estimates of the potential commercial value of the technology, if it succeeded.


I don't understand the reference to how water is carried.

Makes sense.

For coffee and such airlines used to carry water in fresh water tanks. Then they moved to gallon jugs. Recently some moved to using the pint water bottles. Easy way to tell is look how a customer receives water. Cup or small bottle.

How are you looking at lightening each seat mile? Aircrew typically only carry minimum fuel required.

The manner which seats are manufactured is a great avenue. Lighten each seat by 250 grams, you'll make some moola.

quote:

Originally posted by AKSuperDually:
Had to be some impressive X-country numbers.

Duke's are awesome if someone else is footing the maintenance bill. I've actually never annualed a baron. We were a 414/340 shop, so most of my twin experience was in those cessnas.

Word from my dad about his baby baron is that it's fairly heavy on the controls. That seemed odd to me, the duke was SOO light, like flying a bonanza. I've been wondering if his controls are balanced/rigged properly. Are the baron's heavy on the controls?

The 56TC had a single engine service ceiling > FL180 and service ceiling > FL320. Pretty crazy for a non-pressurized GA twin. Up high we could figure 245KTAS. The one number branded in my head was 95 GPH on take-off. Bird only carried ~150 gallons, so you needed to get it dialed back pretty quick.

All the small Barons I've flown handled similar to the B Bonanzas; delightful. Not as light or responsive as my Tiger, but perfect for the mission they were designed for.

quote:

Originally posted by DrDan:
Thanks, guys, some very useful info.

What I am really trying to quantify is the value of weight reduction in an airframe. If Airbus could knock 1kg out of the weight of the airframe of an A320, what is that worth to an airline?

Quite a bit in an existing airframe because it would allow them to carry more passengers or cargo (or combination) and make more money burning the same fuel (or less when lightly loaded) over the entire lifespan of the airplane.......