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Aircraft empty weight vs number of passenger seats

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Aircraft empty weight vs number of passenger seats

Old 10th Jan 2015, 08:01
  #41 (permalink)  
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Using the data from the spreadsheet of Gilles, the following graph indicates that the payload rises as the OWE increases. There is a sense of diminishing returns as the OWE rises, which reflects the increasing structural weight needed per kg of extra payload as the aircraft gets larger; it might also be related to range.

The black trend line deviates increasingly from the linear as the OWE increases. There is less scatter than I had expected from the discussion above.

There is the obvious exception with the Boeing 747SP.



Then when the aircraft are divided by range, they show the effect of fuel capacity on the OEW/payload relationship.

The aircraft have been divided into short range (<5000 km), long range (5,000 - 10,000 km), and ultra-long range (>10,000km). These are my arbitrary divisions, with divisions approximately at the 737-800 and 767-300ER ranges.

The linear trend lines show the differing OEW/payload relationships. As expected, the longer the range, the less "efficient" is the structural weight needed per kg of extra payload.

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Old 11th Jan 2015, 13:31
  #42 (permalink)  
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Interesting. I'll try to get more reliable numbers and add more aircraft to the list, when I have time...
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Old 12th Jan 2015, 01:18
  #43 (permalink)  
 
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Smile Maybe a good academic conversation, but useless

This whole discussion maybe a nice academic conversation but really only produce conversation not productive information. In some of the examples with a full load of fuel, moves the all the numbers. JAL at one time had 747's flying relatively short legs, but with something around or over 500 seats. Then throw in the 380, (one of the ugliest airframes in the sky, MHO) with a couple of showers with hot running water.


A better conversation would center around the direct operating cost of the airframe. The 777, 787 and maybe the 350 are fuel savers, that's why the airlines want them. The 380 maybe dead in less than five years, just cost to many liters of jet fuel to move the beast.
Fuel cost per seat would be a much better conversation. Or, how about cost per hundred kilos?


As long as the aircraft is above a relative size the passenger is more interest in frequency, than number of seats it carries. An airline offering four departures a day in a 737/320 as opposed to one 330 departure.
The 737/320 carrier wins.


Just my couple of pennies.
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Old 12th Jan 2015, 03:11
  #44 (permalink)  
 
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You have to look at total cost per ASM (ASK), not just fuel. Certainly the 380 is a fuel hog, but if fuel stays below $75 other factors begin to become more significant, driving the seat mile costs closer to that of a big twin. I fly for an A380 operator...passengers actively demand it over the well-appointed 747s we also fly.

Your comparison on frequency is broadly correct, but your example is based on short haul realities rather than long haul. Over great distances frequency is often once a day.

If you compared a carrier operating four 737s, you'd need to compare than to one operating three A330-200s. No prize for guessing who wins that one on passenger appeal.

Passengers in most parts of the world prefer wide bodies. Enough to overcome a slight frequency disadvantage on routes of over, say, two hours. And passenger behaviour cannot be predicted on purely rational expectations.
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Old 12th Jan 2015, 16:05
  #45 (permalink)  
 
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When I worked in research we looked at the same figures. We had pretty good and reliable data for a couple of aircraft, including very detailed OEW figures that took into account operational items and stuff.

Result was equally inconclusive. There was no appreciable weight benefit over history. We have identified the following reasons:
  1. I know it is often said, but seats: you simply cannot find a 100% comparable layout. Using floor area as metric may make more sense, but may also not.
  2. You never find two equal aircraft: some may have same capacity, but widely different range or field performance. A real 1-on-1 comparison is never possible. That is because aircraft are products of their time and technology, and one would be an idiot to build a 1965-aircraft in the 2000s with similar range-payload (see evolution of the B737, for example -200, -500, -600, -6MAX: all same capacity, became best sold model, second best sold model, worst sold model, discontinued model).
  3. Modern aircraft are not lighter, but they are sometimes much more durable in terms of fatigue lifecycle. They also require less maintenance in terms of inspections.
  4. Aircraft tend to have always a comparable relationship between empty weight and take-off weight. That is not because it is a physical law, but because only those that have are designed, built and put in service. If some technology makes something lighter, the saved weight usually re-invested (for example in more range).
  5. Weight is no benefit in itself, it is about cost and performance. Weight may factor in airport charges, but that is about it. And you can always paper an aircraft down. Hence, aircraft are built for minimum cost and the added weight often decreases the cost of operation.

By the way: I like these threads and find them very useful. Just because the result is inconclusive doesn't mean the question and the analysis isn't justified.
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Old 13th Jan 2015, 13:26
  #46 (permalink)  
 
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mustangsally:
...JAL at one time had 747's flying relatively short legs, but with something around or over 500 seats. Then throw in the 380, (one of the ugliest airframes in the sky, MHO) with a couple of showers with hot running water.
JAL also had DC-10-40s dedicated to this market. It fact, they lightened the aircraft by REMOVING the center MLG, and operating at DC-10-10 max weights.

ANA jumped on the bandwagon too with their own 747SR (short range) ships about 1979. I rode a couple survey flights with them; average stage length was 45 minutes, and we had several legs loaded with 500 paying pax plus babes in arms. Wonder if the A380 has a market here?
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Old 13th Jan 2015, 15:04
  #47 (permalink)  
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When new aircraft types are under development, and especially when the first production series are built, there is always ample talk about the manufacturer being able, or not, to meet expected empty weight goals. Being able to meet or failing to meet that goal affects all the rest: payload, fuel burn, range, endurance, landing and take off performance and especially the CASM.
When the manufacturer fails to meet the target Empty Weight, the ZFW is bumped to compensate and maintain the expected payload. This requires an increase in MTOW to maintain expected range. This requires more Power which increases fuel burn. The increased weights increases the take off and landing distances as well, and all this can and has, in the past, compromised certain sales.

Last edited by Gilles Hudicourt; 13th Jan 2015 at 16:28.
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Old 13th Jan 2015, 15:13
  #48 (permalink)  
 
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Originally Posted by LoadMan View Post
When I worked in research we looked at the same figures. We had pretty good and reliable data for a couple of aircraft, including very detailed OEW figures that took into account operational items and stuff.

Result was equally inconclusive. There was no appreciable weight benefit over history. We have identified the following reasons:
  1. I know it is often said, but seats: you simply cannot find a 100% comparable layout. Using floor area as metric may make more sense, but may also not.
  2. You never find two equal aircraft: some may have same capacity, but widely different range or field performance. A real 1-on-1 comparison is never possible. That is because aircraft are products of their time and technology, and one would be an idiot to build a 1965-aircraft in the 2000s with similar range-payload (see evolution of the B737, for example -200, -500, -600, -6MAX: all same capacity, became best sold model, second best sold model, worst sold model, discontinued model).
  3. Modern aircraft are not lighter, but they are sometimes much more durable in terms of fatigue lifecycle. They also require less maintenance in terms of inspections.
  4. Aircraft tend to have always a comparable relationship between empty weight and take-off weight. That is not because it is a physical law, but because only those that have are designed, built and put in service. If some technology makes something lighter, the saved weight usually re-invested (for example in more range).
  5. Weight is no benefit in itself, it is about cost and performance. Weight may factor in airport charges, but that is about it. And you can always paper an aircraft down. Hence, aircraft are built for minimum cost and the added weight often decreases the cost of operation.

By the way: I like these threads and find them very useful. Just because the result is inconclusive doesn't mean the question and the analysis isn't justified.
You are correct on the OEW development of newer types. Look at the OEW of B737-300 - B737-700 - B737-7MAX (if not stillborn), OEW for these similar sized a/c will go from around 30t to close to 45t!
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Old 13th Jan 2015, 17:22
  #49 (permalink)  
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I updated the file with a few more Boeing aircraft. Cannot find the OEW of the B787-9 or the the A350 anywhere..... They seem to be a closely guarded secret.

IF anyone has them........

https://dl.dropboxusercontent.com/u/...ht%20data.xlsx

Last edited by Gilles Hudicourt; 14th Jan 2015 at 08:30.
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Old 14th Jan 2015, 10:52
  #50 (permalink)  
 
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The B787-9 is about 122t OEW.
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Old 14th Jan 2015, 12:15
  #51 (permalink)  
 
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From OWE per seat ... to Fleet Yield per 24h ?

Hello folks ! The discussion here is driving fleet strategies and route marketing policies at airlines round the world ! Thanks Gilles !

But I recommend :
- to break aircraft types into sector type categories (RJ, feeder, VLA, WBMH, WBLH ...) and do segment analysis ... otherwise we are comparing all Y-class types with three class types or apples with bananas
- to look closely at the respective types' groundworthiness ie airport turn-around time, to compute 24h productivity : an A321 @ 218 pax turns around eg in 41' whereas its sister H21QR turns in 24'5 or 16.5' less, with 199 pax. OWE/pax are apprx. 236 kg vs 221 kg, but H21QR can take 6 AKH with payfreight on top of 4 AKH with checked-in luggage, against only 3 + 7 AKH for A321 so at the payfreight-to-pax revenue contribution conversion factor, the capacity of H21QR is 199 maindeck pax plus 6 x 10 = 60 other 'virtual' (underdeck) pax, total 259 'aggregate' pax (OWE = 181 kg/pax), which compares with 194 kg/pax for A321.

We can conclude that measured on Gilles scale - reinterpreted to include lower deck, H21QR is more efficient than A321 ... but there is a lot more to come enlargening the scope to 24h yields ... the perspective gets wider as you go through all the ingredients one by one to construct 24h-yields !
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Old 14th Jan 2015, 19:11
  #52 (permalink)  
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A little context

Articles : Aircraft Interiors International
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