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Would you being willing to elaborate on what makes it special to you? I'd love to know more! Years ago I worked at Ames on the ACES system (minor but fixes and

Would you being willing to elaborate on what makes it special to you? I'd love to know more! Years ago I worked at Ames on the ACES system (minor but fixes and a Greenfield projects involving data/flight path visualization), but I felt the airplanes themeselves were these magical black boxes. I'd would appreciate having a deeper understanding about how they differentiate from one another in a non-superfical sense.

WalterBright 7y ago
Simply, what makes it special is I had a hand in it. Every time you fly on one, you're betting your life on my parts. I know how it works, and I know why it's safe. I worked specifically on the stabilizer trim system (like the one in the news on the 737MAX), and did some work on the elevator system. In particular on the latter, I did many calculations to prove it would not flutter (dynamic instability). My very first assignment was to size the stabilizer trim jackscrew. I panicked and told my lead I had no idea how to do that. He laughed and said of course you do, it's a simple column buckling problem. Which of course it was, and I sized it. A couple years later, and the first jackscrew gearbox assembly came off the line, and was doomed to be subjected to the ultimate load test. Any buckling, cracks, deformation, etc., would be a failure. The test guys told me they were gonna bust my jackscrew. They hooked it up to this big ugly iron I-beam with a hydraulic ram to compress my green BMS10-11 painted gearbox and shiny chrome steel jackscrew (made by Saginaw Gear, who made the best kick-ass forgings). They started cranking up the pressure, while I stood around anxiously watching it. Slowly, the I-beam bent into a nice curve. We didn't have to make any changes to any of the stab trim system due to test failures. Whaddya know, the math works! So I am not a bit afraid to fly on a 757. The seating can be cramped, but that's the way it goes these days. As far as know, there have been no in-service failures of that system. The 757 itself has a fantastic safety record, of which I am proud to have contributed to. The last D conference I flew to on a 757 operated by Iceland Air, yay! At the time I bought a bunch of Boeing stock as a result of my confidence in Boeing, and it has paid off handsomely.
- taneq 7y ago
  Maybe a dumb question, but wouldn’t you have expected it to break at the target max load? I would have thought it being stronger than required would mean it was heavier than necessary?
  - WalterBright 7y ago
    That is a fun question. Boeing had two groups - the design group, and the stress group. The design group does the design, the stress group checks it. I was in the former. One day, I got called into the stress group, where they told me they were unhappy with my parts. I asked why, they said there just barely strong enough for the ultimate load, only about 1% over. They said they'd feel more comfortable with 10% extra strength. I said this was no coincidence, I used math to size the part to the load, rather than guessing at a size and checking to see if it was strong enough. The requirement was the ultimate load, which is 150% of the maximum load that could ever be expected. I asserted that I designed to the design requirement, and an extra 10% would make it overweight. Brat that I was, I said if you guys were unhappy with the design requirement, increase it. They grudgingly signed off on it. The reason it didn't break on the test stand is because all parts vary in size due to manufacturing tolerances. It was sized to pass the ultimate load test under the most adverse size allowed under the tolerances. Odds are, it'll be a little stronger. For comparison, spacecraft have (I think) an ultimate load of 110% of the max load. The margins are awfully thin, but they have little choice. If you really want a math heavy engineering job, design spacecraft. BTW, the stress group signed off on the jackscrew size. If it had failed the ultimate load test, both them and I would have had a black eye. As it turned out, the test guys were embarrassed by their bent rig :-) and fortunately that wasn't really a problem.
    - rayiner 7y ago
      Thank you for sharing these stories, they’re amazing.
    - caust1c 7y ago
      Thanks for sharing! This was super interesting :-)

WalterBright 7y ago

Simply, what makes it special is I had a hand in it. Every time you fly on one, you're betting your life on my parts. I know how it works, and I know why it's safe. I worked specifically on the stabilizer trim system (like the one in the news on the 737MAX), and did some work on the elevator system. In particular on the latter, I did many calculations to prove it would not flutter (dynamic instability). My very first assignment was to size the stabilizer trim jackscrew. I panicked and told my lead I had no idea how to do that. He laughed and said of course you do, it's a simple column buckling problem. Which of course it was, and I sized it. A couple years later, and the first jackscrew gearbox assembly came off the line, and was doomed to be subjected to the ultimate load test. Any buckling, cracks, deformation, etc., would be a failure. The test guys told me they were gonna bust my jackscrew. They hooked it up to this big ugly iron I-beam with a hydraulic ram to compress my green BMS10-11 painted gearbox and shiny chrome steel jackscrew (made by Saginaw Gear, who made the best kick-ass forgings). They started cranking up the pressure, while I stood around anxiously watching it. Slowly, the I-beam bent into a nice curve. We didn't have to make any changes to any of the stab trim system due to test failures. Whaddya know, the math works! So I am not a bit afraid to fly on a 757. The seating can be cramped, but that's the way it goes these days. As far as know, there have been no in-service failures of that system. The 757 itself has a fantastic safety record, of which I am proud to have contributed to. The last D conference I flew to on a 757 operated by Iceland Air, yay! At the time I bought a bunch of Boeing stock as a result of my confidence in Boeing, and it has paid off handsomely.

taneq 7y ago
Maybe a dumb question, but wouldn’t you have expected it to break at the target max load? I would have thought it being stronger than required would mean it was heavier than necessary?
- WalterBright 7y ago
  That is a fun question. Boeing had two groups - the design group, and the stress group. The design group does the design, the stress group checks it. I was in the former. One day, I got called into the stress group, where they told me they were unhappy with my parts. I asked why, they said there just barely strong enough for the ultimate load, only about 1% over. They said they'd feel more comfortable with 10% extra strength. I said this was no coincidence, I used math to size the part to the load, rather than guessing at a size and checking to see if it was strong enough. The requirement was the ultimate load, which is 150% of the maximum load that could ever be expected. I asserted that I designed to the design requirement, and an extra 10% would make it overweight. Brat that I was, I said if you guys were unhappy with the design requirement, increase it. They grudgingly signed off on it. The reason it didn't break on the test stand is because all parts vary in size due to manufacturing tolerances. It was sized to pass the ultimate load test under the most adverse size allowed under the tolerances. Odds are, it'll be a little stronger. For comparison, spacecraft have (I think) an ultimate load of 110% of the max load. The margins are awfully thin, but they have little choice. If you really want a math heavy engineering job, design spacecraft. BTW, the stress group signed off on the jackscrew size. If it had failed the ultimate load test, both them and I would have had a black eye. As it turned out, the test guys were embarrassed by their bent rig :-) and fortunately that wasn't really a problem.
  - rayiner 7y ago
    Thank you for sharing these stories, they’re amazing.
  - caust1c 7y ago
    Thanks for sharing! This was super interesting :-)