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Comment by rob74 | Hacker News Reader

Let me quote from the Wikipedia article https://en.wikipedia.org/wiki/Lockheed_Constellation:

> One of the reasons for the elegant appearance of the aircraft was the fuselage shape, a continuously variable profile with no two bulkheads the same shape. This construction was expensive and was replaced by mostly tube-shaped modern airliners. The tube is more resistant to pressurization changes and cheaper to build.

With blended wing bodies, you would again need a continuously variable profile for the whole fuselage (rather than only the wing, as in modern "tube-and-wing" planes). To build a larger or smaller variant, you would have to redesign the whole fuselage, rather than just adding/removing a few tube segments. So, even with updated tools, there will still be a lot of challenges...

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In todays world of most high value things being CNC machined rather than made from hand crafted moulds and templates, every part being different is less of a concern. Just download the set of designs to the machine, do a test run of the smallest and largest part, and then hit 'start' and come back in the morning.

Yeah, a passenger aircraft is somewhat more complex in manufacture than a MacBook Pro.

Also in today's world it is cheaper for one machine to produce 1.000 identical parts than for the same machine produce 10 times 100 different parts. You need stock of each, tests of each.

Imagine how efficient car maintenance would be of only we'd use one standardized car. You can have the larger model, but all components are the same, every garage has them...

Like Tesla is doing with one engine for all cars and a mono frame pressed out of a metal sheet. Cybertruck deliverable in every color you like as long as it's metal. I have read somewhere the complexity in production lines are similar as the big O notation. Henry Ford would be proud of Elon.

Most car manufacturers are massively reducing complexity. Toyota's Next Generation Architecture is reducing total manufacturing costs by 20% by simplifying their entire platform of vehicles into a common set of types and using similar hardware wherever possible.

3D printing.

This is so, so not the case! If anything it's the opposite.

First of all, nobody is CNC machining airplanes from billet. They're sheet metal structures. But that aside...

For handmade structures with little tooling, the difference is less because it takes only a bit more training and about the same amount of time to make a bunch of unique parts as to make a bunch of identical parts. The economies of scale are there, but less so.

But even for CNC parts, extra shapes means extra CNC programming time (expensive but amortizes over the number of pieces made, so n unique parts costs n times as much to setup and amortizes n times less). It means more inspection gauges. More tooling. Significantly more inventory costs.

Design a machine from a single modular piece, and all else equal it will be much cheaper than one made from a bunch of unique parts.

Modern aircraft, as in 787 and a350 are mostly carbon composite structures by now. I image that would be even more the case for a blended wing body Design

You're not machining large surfaces like wings, windmill blades and the like, not just because it's hard to make machine tools that size but because the structure and performance of the materials depend on not being machined.

When you machine an amorphous or crystalline material like a metal alloy you aren't always simply removing material, but can be putting a specific finish on the surface for mechanical reasons. Sometimes you want to cast again for performance (or cost) reasons because machining can't get you what you want.

When you build a shape from a composite material such as fibreglass in epoxy you want the longitudinal fibres to run long distances to distribute the stresses. Machining it would defeat the purpose. They are cast.

I like these blended wing designs; I'm just pointing out that your argument is not applicable to this application.

They are made from composites. The moulds are machined.

Airliner structures are very conservative. They still use a lot of fasteners, lowering manufacturing and structural efficiency.

There is a lot of room to improve. There is a huge space for innovation in composites. It just takes a lot of time and money to ensure the more modern methods are also durable and safe.

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