|Quoting Texfly101 (Reply 47):|
Yes, and Yes. That's the case and what will happen. The first part of the model design, until validation during testing, will have had some increased margins due to the uncertainty of how disparate assemblies actually work together, both in manufacture and assembly. The partners that actually design and build the parts usually leave some extra materials in areas like webs, fillets, etc as they are both difficult to model and design, and it gives some room when B comes calling saying "gotta reduce weight, give me 2%". Actual flight will produce another round of refinements that will reduce weight but sometimes adds weight, so I would call it at worst to be a wash, but as Zvezda states, I agree with him.
I would expect the first group of airframes, I can't say how many that encompasses, to be at best, close to the target weight. I would expect the follow on airframes of the initial model to be on target for weight and performance. The next models will benefit from the lessons learned and will meet their target weight and performance, probably exceeding it, as has typically been the case for B's models. That was the way it went for 772LR and 773ER with their actual SFB to be even better than planned.
|Quoting 787engineer (Reply 45):|
Absolutely correct, there are several procedures for initiating change on parts that have already been released. Just because a part has been released doesn't mean Boeing can't go back and change it. How else do we continually make minor improvements to keep planes competitive? There are even plans for "re-releases" in which large numbers of parts can be replaced by newer releases. Early on re-releases are necessary because through testing many things may need to change.
You are absolutly correct, design continues to evolve even past design freeze.
Irtysh-Avia (Kazakhstan)">IT IS
TAKE WEIGHT OUT OF
FILLET RADIUS AND
WEBS AFTER MONEY HAS BEEN SPENT ON
PARTNERS HAVE COMMITTED TO
GUARANTEED WEIGHTS. In my career, I have yet to see this happen unless an overweight issues threatens the very existance of the program.
My experience in airframe testing is usually used for validation and not for optimization.
If I left extra material in my designs, I'd be a terrible aerospace engineer and my weights engineer would be very mad.
I'd love to have the opportunity to work for Boeing and see how the experts do it