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Comment by CitizenKane | Hacker News Reader

It's a fascinating read, and makes a lot of sense why it's so hard to develop a commercial aircraft that actually ends up being profitable. One thing that got me wondering, and maybe someone here might know this, is why hasn't Boeing attempted to miniaturize the 787 as opposed to continually re-purposing the 737? From the outsider's (and complete layman's) view it seems like this would be a more sensible way to build a successful modern aircraft in that vein as opposed to trying to repurpose a design which is now well over half a century old.

I fly a fair amount an honestly the 787 is an impressive aircraft. I'm surprised that Boeing hasn't tried to take what they learned from their developments there and apply them in a way that could potentially help them recoup the costs of that program.

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Scaling up and down aircraft is usually done by changing their length since that's both structurally very straight forward, and it can usually be done with relatively benign aerodynamic impacts.

The 787 is significantly larger than the 737. It's not just built to have more passengers, but also to carry way more fuel so it can go more than twice as far. While you can always take off with less fuel to stave off the worst of the penalty when making shorter flights, a penalty remains.

Scaling down a 787 to hit the 737's operating niche likely means:

* Reducing the body diameter/width * Shrinking the wings (the 787 wing has 3x the area of the 737 wing) * Reducing the length

The first two operations are really non-trivial. Certainly not impossible, but challenging enough that calling it a "787 redesign/miniaturization" vs "clean sheet model with 787 heritage" gets really blurry.

The weight and efficiency benefits of current composites vs aluminum lithium (AlLi) frames are not enough to justify their costs.

Also wide-bodies are just different from narrow bodies in length or diameter. Narrow bodies are designed to go through more and frequent pressurization cycles, fit and weigh enough for certain gates and runways, carry different amounts of cargo.

The other variable is the cost to build the plane you describe. The reason Boeing decided to rengine the 737 for the NG instead of the 757 is the 737 costs less to build and operate. The 737 MAX 8-200 and the MAX 10 are very economical to fly on a level a shrunken 787 couldn't reach.

It's also important to remember the 737 Max was kind of a stop gap on the higher capacity variants for the NMA. If Boeing had been willing to give the MAX a slightly different type rating and difference training for the MAX, MCAS would not have been necessary. Then the MAX 9 and 10 could be replaced by the NMA and bought Embraer with stretched E2 jets replacing the MAX 7 and 8 if executives were concerned with more than their annual stock comp.

> If Boeing had been willing to give the MAX a slightly different type rating and difference training for the MAX, MCAS would not have been necessary.

I see this a lot, but MCAS would still be needed to comply with the regulations on control column force curves so I don't think Boeing could have just gotten a different type rating and done that.

The 737 and 787 are fundamentally different designs. The 737 is made to be small enough to deplane using stairs to the tarmac at smaller airports while the 787 is exclusively for modern airports with walkways. The 737 is about 12 meters tall and the 787 is 17 meters tall as a result.

That was the driving factor behind the 737 Max disaster. The most efficient engines are high bypass turbofans which are getting taller and taller to fit the main rotor so they had to place the engine nacelles in front of the wings rather than below in order to fit them. This changed the flight envelope and necessitated retraining which Boeing avoided by implementing MCAS which caused the crashes.

Boeing could recycle some of the core 787 technology to design a new single-aisle airliner. But the concern is that by the time it is certified it might already be obsolete. They are in a holding pattern now, waiting for research results on truss-braced wings. If those work then they could significantly reduce fuel costs.

https://www.seattletimes.com/business/boeing-aerospace/boein...

The article mentions that at the time they were looking at the 737 replacement in the early 2000s they didn't think they could scale up the production to the volume needed for the 737's market. I think this fits the general theme of the article - they probably could if they started work now, but they had to make the decision on replacing the 737 or creating the 737 Max whilst guessing on the future years down the line.

I’m not 100% sure but I think there are some fundamental differences between wide-body and narrow-body aircraft (things aren’t just a different size but different shapes) that mean you couldn’t just shrink it down and change the seat pattern, but I expect they definitely could base a new aircraft on the same materials tech, avionics, etc. as the 787.

The problem is the airlines. They can't be bothered to do any kind of retraining for their pilots. They'll just buy another brand if this is needed. Which is why the whole MCAS thing happened.

Even 787 pilots will have to be retrained if they scale it down to the size of a 737.

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