Look up stress to failure tests on commercial airplanes.
They know how much peak load is supposed to be for the airframe, then they go well beyond it to see how the plane fails. Generally you want the wings to break not the fuselage.
You can in a lot of situations land a plane with 1.5 wings. But once the spine cracks you’re just a ballistic object.
The parts are designed for "ultimate load" which is 150% of the worst case maximum load expected to ever see in service.
I used to work at Boeing on the 757 stabilizer trim system. There's the design group and the stress group. I was in the design group, the stress group double checks the design work.
One day the stress group called me on the carpet, and asked me why my designs consistently just barely exceeded 150%. I said I started with the ultimate load, and worked backwards to size the part. The stress groups said they prefered designs to be 10% over the ultimate load. I replied that I designed to the requirements, as adding 10% makes the airplane overweight. If they didn't like the design requirements, change them.
They grumbled, but I got my way :-/
A few months later, they offered me a position on the stress group. It was a nice compliment, as they normally required a masters' degree and I only had a bachelors. I told them I was honored by the offer, but my heart was in design.
Some time later, my parts were put on the torture rack to see if they passed the ultimate load test. All of them passed on the first try.
I also had the privilege in being mentored by some really fine engineers at Boeing, such as J Burton Berlin and Erwin Schweizer.
Am I proud of that? Yes. I love flying in the 757. Best airplane Boeing ever made. Whenever I fly in them I chat a bit with the flight crew, and they love it, too.
P.S. the jackscrew turned out to be stronger than I'd anticipated. The credit for that goes to Saginaw Gear, who made them. SG makes kick-ass airplane parts, beautifally made.
> If they didn't like the design requirements, change them.
If anyone is wondering, this is always the correct answer when there’s a disagreement between reality and the specification and you’re following the spec.
I always thought of you as the C++/D compiler guy - wow you did work in aerospace too!
Thanks for making the D programming language. If it did not insist on a GC and had a robust and stable GC-free stdlib, I believe it could have conquered the world.
I've probably posted a hundred messages here on MCAS! Most were downvoted to hell. The actual 737 pilots I talked to agreed with me, nobody else did. Classic Gell-Mann Effect. The only truthful account of the crashes is the official NTSB report.
The 737 is an electric drive, with a manual backup. The 757 is a scaled down version of the 747's dual hydraulic drive, no manual backup.
More efficient wings and engines obsoleted the 757.
Oh I was an aeronautical engineer (BS, MS aerospace engineering, concentration in fluid mechanics) for 8 years. Any pithy explanation of aircraft flight/engineering concepts that I post gets downvoted or ignored. Better yet, sometimes a java programmer tries to mansplain it to me in a worse way.
When I talk to airplane crews, their faces say "oh crap, another nut I have to be nice to". So I let slip into the conversation things only insiders would know, and they then relax and open up.
I also love the 757, but never had as good a reason as you other than knowing the flight characteristics of the plane. Sad to see them disappearing from the icelandair fleet, is there anything else comparable? The modern 737 variants sure don't seem to be.
I would submit to you that it’s impossible to load the wings at 150% of max load without transferring any of that force into the fuselage. Look at any finite element analysis of complex shapes. The force spreads out from areas of max tension or compression, and goes around corners.
They know how much peak load is supposed to be for the airframe, then they go well beyond it to see how the plane fails. Generally you want the wings to break not the fuselage.
You can in a lot of situations land a plane with 1.5 wings. But once the spine cracks you’re just a ballistic object.