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Weight Difference Between Early And Late Frames  
User currently offlineembrider From United States of America, joined Mar 2010, 26 posts, RR: 0
Posted (2 years 9 months 2 weeks 4 days 12 hours ago) and read 2590 times:

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%?

5 replies: All unread, jump to last
 
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 1, posted (2 years 9 months 2 weeks 4 days 11 hours ago) and read 2431 times:

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.


User currently offlinelightsaber From United States of America, joined Jan 2005, 12781 posts, RR: 100
Reply 2, posted (2 years 9 months 2 weeks 4 days 11 hours ago) and read 2359 times:
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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



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User currently offlineLHCVG From United States of America, joined May 2009, 1535 posts, RR: 1
Reply 3, posted (2 years 9 months 2 weeks 4 days 10 hours ago) and read 2323 times:

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".

User currently offlineembrider From United States of America, joined Mar 2010, 26 posts, RR: 0
Reply 4, posted (2 years 9 months 2 weeks 3 days 22 hours ago) and read 1953 times:

This is all very informative; Thank you

User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 5, posted (2 years 9 months 2 weeks 3 days 22 hours ago) and read 1927 times:

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]

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