embrider
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Joined: Fri Mar 26, 2010 10:17 pm

Weight Difference Between Early And Late Frames

Tue Sep 27, 2011 12:35 pm

I read all the time that for a certain new aircraft- 787 for exemple- the first frames are ^heavy^and some weight loss and consequent performance improvement is expected for future frames. How does this "weight loss" happen? What parts/component loose weight and why this can not happen in the first frames? What is the magnitude of weight loss, 0.5%, 2% 5%?
 
tdscanuck
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RE: Weight Difference Between Early And Late Frames

Tue Sep 27, 2011 2:01 pm

Quoting embrider (Thread starter):
How does this "weight loss" happen? What parts/component loose weight and why this can not happen in the first frames?

Mostly redesign of structural components and cleaning up systems. That takes time and data, both of which you don't have when you build the first frames. You may discover that this rib is 2% stronger than it needs to be and you can take this material away, or that you put three fans in this cooling system but it's performance is better than you thought and you only really need two.

In some cases, there may also be provisions for system modifications that you think you might need (e.g. Rolls Royce originally had a clutch between two of the spools on the Trent 1000 but it turned out it wasn't required). Once you have the data to know if you need that system or not, you can get rid of the system and the provisions that were supporting the option.

There's no inherent technical reason you can't refit earlier frames with weight-saving modifications after they're built but, in the case of big structural changes, it's economically prohibitive.

Quoting embrider (Thread starter):
What is the magnitude of weight loss, 0.5%, 2% 5%?

As much as you can get away with...weight is everything.

Tom.
 
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lightsaber
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RE: Weight Difference Between Early And Late Frames

Tue Sep 27, 2011 2:25 pm

Quoting tdscanuck (Reply 1):
As much as you can get away with...weight is everything.

Yep. About $500 per kg. For every kilogram removed, the sales value of the airframe increases.

Weight removed is added payload (assuming same MTOW, MZFW, and MLW) or free range.

Quoting tdscanuck (Reply 1):
There's no inherent technical reason you can't refit earlier frames with weight-saving modifications after they're built but, in the case of big structural changes, it's economically prohibitive.

   I've seen it done for easy changes and special cases, but the trade is always cost per pound removed. The older the airframe, the less likely money will be spent due to the shorter expected flying life.

Lightsaber
"They did not know it was impossible, so they did it!" - Mark Twain
 
lhcvg
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RE: Weight Difference Between Early And Late Frames

Tue Sep 27, 2011 2:36 pm

This even happens in cars all the time. In addition to incremental, year over year changes, don't forget the mid-lifecycle "refresh" where they institute a number of changes of varying degrees at once, creating in effect a "model 1.5".
 
embrider
Topic Author
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RE: Weight Difference Between Early And Late Frames

Wed Sep 28, 2011 2:47 am

This is all very informative; Thank you
 
tdscanuck
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RE: Weight Difference Between Early And Late Frames

Wed Sep 28, 2011 3:02 am

Quoting lightsaber (Reply 2):
Yep. About $500 per kg.

It's come down then...I thought it used to be about $500/lb.

Tom.

[Edited 2011-09-27 20:03:06]