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Comment by tyingq | Hacker News Reader

I don't think that's unusual at all for any jet aircraft that's around for decades. They almost all get new engines, avionics, etc. That the B-52 still has 8 engines is somewhat surprising...that's not terribly desirable.

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The Air Force considered replacing the 8 engines with 4 more powerful ones. However, they determined that the loss of one of those engines on take-off would cause a dangerous thrust asymmetry. Dealing with that would have required more extensive changes like moving the engine mounts, so they dropped the idea. But they are going to replace the engines with newer models.

https://www.thedrive.com/the-war-zone/42517/rolls-royce-will...

I had seen/heard/read that the thrust asymmetry was a design feature to help with yaw, and that fewer engines would overpower the design limits of other parts of the airplane, to the extent that everything else would need to be redesigned to handle them (mounts, tail, rudder, etc.)

edit: I believe this is the original video where I saw the above https://www.youtube.com/watch?v=02_geGISTLg

You can use thrust asymmetry to help with yaw, yes.

But here we're talking about unplanned sudden thrust asymmetry, causing a massive yaw force at a critical phase of flight, takeoff, where you're engines are likely to be near their full power and you're close to/on the ground.

If you go from 8 engines to 4, loosing one engine goes from causing 25% thrust loss on the wing to 50%.

Makes sense, but must be also tied to something else unique about the B-52. There are certainly much larger aircraft with 4 engines.

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