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Technically interesting history: intentionally testing DC-8 at Mach 1.01

Started by Phil Bunch, Tue, 30 May 2017 00:40

Phil Bunch

Apparently they needed to prove that the DC-8 would be recoverable if it accidentally went supersonic.

Here's a brief excerpt from the Smithsonian's "Air and Space" magazine:

http://www.airspacemag.com/history-of-flight/i-was-there-when-the-dc-8-went-supersonic-27846699/?all

"We took it up to 10 miles up, 52,000 feet—that's a record—and put it in a half-a-G pushover. Bill maintained about 50 pounds of push. He didn't trim it for the dive so that it would want to pull out by itself. In the dive, at about 45,000 feet, it went to Mach 1.01 for maybe 16 seconds, then he recovered. But the recovery was a little scary. When he pulled back, the elevator was ineffective; it didn't do anything, so he said, "Well, I'll use the stabilizer," and the stabilizer wouldn't run. It stalled, because of the load. What he did, because he was smart, is something that no other pilot would do: He pushed over into the dive more, which relieved the load on the stabilizer. He was able to run the [stabilizer] motor, with the relieved load, and he recovered at about 35,000 feet."

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There is also an interesting (unrelated) article in the current issue regarding tests of autonomous airliners, apparently aimed at replacing the Pilot Monitoring.  Not your grandfather's autopilot, apparently (?) tested in a real 737 simulator.  I thought that the claim that they do not need hard-wired access to everything in the airliner was interesting.  Here is a brief excerpt:

http://www.airspacemag.com/daily-planet/meet-your-new-copilot-robotic-arm-180963469/

"Siri, Land the Plane"

"This robot controls airplanes the same way people do, so it can fly almost anything people can."

"This is no autopilot upgrade or new line of avionics. Computers, properly programmed, are now smart enough to fly airplanes, and they no longer need hard-wired electronic access to everything."
Best wishes,

Phil Bunch

emerydc8

You could stall the stab motor on the DC-8 at lower speeds too if you loaded it up enough. I had this happen on a DC-8-54 while trying to level off from a rapid descent into Denver's Stapleton airport. I was doing 250 knots and was planning to slow once I leveled off, in order to get the flaps out, so I thought some stab trim would help make the level off a bit easier. I was surprised when the stab motor apparently didn't have enough power when under a load. Unlike the Mach 1.01 situation, I was able to add power and use elevator to level off without any problem. Once the stab was unloaded, the trim began to work again. Maybe the later-series airplanes had a more powerful hydraulic stab motor because that was the only time in 6,500 hours of flying it that it happened to me. Or maybe it was just that the airplane was older than me. Fun days.

United744

"Otto" should remain as a gag in the movie "Airplane!", and not as an actual device in the cockpit.

An autopilot failure is hard enough to prevent, without a physical robot malfunctioning.