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Re:U-2: The veteran spyplane too valuable to replace by areoform on Sunday December 13, 2020 @07:12PM (#25411883)
I admire anyone who flies the U-2. As the article says, it is extremely easy to get yourself killed. The flight envelope of the U-2 was so narrow that the difference between flow separation from the wing (called a buffeting) and stalling is around 20 to 30 knots. It is, as far as I know, the place from where the term "Coffin Corner" came.

https://en.wikipedia.org/wiki/Coffin_corner_(aerodynamics)#/...

From NASA's book on the U-2,

> The U-2 has always been a difficult airplane to fly, challenging even the best pilots. Lightweight construction and long, thin wings give it terrific soaring ability but also make it hard to land. As the airplane approaches the ground, it floats on a cushion of air—known as ground effect—that causes the U-2 to remain airborne even at idle. The pilot almost has to force it down using spoilers to extinguish any remaining lift. A safe touchdown is further complicated by the unusual landing gear configuration. Near or on the ground, the U-2 appears to be a clumsy beast. The mysterious Dragon Lady seems at ease only when soaring to altitude or cruising through the stratosphere. Even there, danger lurks within the thin margin between Mach buffet and stall speed, the dreaded “coffin corner” of the flight envelope. Technological improvements have eased such problems as high-altitude engine flameouts and balky autopilots, but only a select few can hope to admire Earth’s curvature from more than 12 miles above the surface in what has been dubbed the Near-Space Plane.

- https://www.nasa.gov/sites/default/files/atoms/files/unlimit...

It is an extreme craft made for an extreme time.

Re:U-2: The veteran spyplane too valuable to replace by nyolfen on Sunday December 13, 2020 @07:36PM (#25412023)
my grandfather flew one over southeast asia in the 50s, and later was in charge of a team that flew u-2's and a-12's (cia version of sr-71) over china. i transcribed a letter he wrote about it, mostly regarding the mechanical experience of piloting:

https://hyperstition.al/u2-james-black/

he actually mentions a bit about the difficulty of landing:

> The most difficult part of flying the U-2 was to make a good landing. It was a tail-dragger and in order to make a decent landing, you had to come across the threshold at three to five feet and ten knots above the stall speed. And the threshold speed was based on the amount of fuel on board. The aircraft attitude at the threshold had the tail higher than when parked. The residual (idle) RPM was 65% and during the check-outs, only 15% of flaps were used. The trick was to fly down the runway, holding the main wheel one-to-three feet off the runway, while the airspeed dissipated and the attitude of the aircraft rotated from that slightly-tail-high to the parked attitude, without letting the main gear touch the runway. For if the main gear touched too early, you got a bounce and that was a go-around. The same thing is true in a J-3 (40 HP) cub. In other words, you do not make “wheels” landings – placing the main gear on the ground first. It is said, that you can never recover from a bounce. For you will always be 180 degrees out of synchronization. Years later, as a reconnaissance staff officer at the 15th AF Headquarters, March AFB, Calif., I worked for a lieutenant colonel who had been in the RB-47 program at Farber AFB, Kansas for many years and the RB-47 was also a “tail-dragger” and the same was true about it and the bounce. (But it didn’t have a high-aspect wing, such as used on gliders, and the -47 had six engines, so when all six were in idle it settled down very smoothly.)

Re:U-2: The veteran spyplane too valuable to replace by leeoniya on Sunday December 13, 2020 @09:22PM (#25412823)
you might enjoy this story (many pages): https://www.otherhand.org/home-page/area-51-and-other-strang...

the whole site is fantastic, check out his other adventures.

Re:U-2: The veteran spyplane too valuable to replace by nyolfen on Sunday December 13, 2020 @10:32PM (#25413222)
indeed, this is amazing
Re:U-2: The veteran spyplane too valuable to replace by cbsks on Sunday December 13, 2020 @09:58PM (#25413043)
That is amazing. Thanks for posting it and getting the stories from your grandfather!
Re:U-2: The veteran spyplane too valuable to replace by happy_pancake on Sunday December 13, 2020 @09:44PM (#25412969)
fantastic read thank you
Re:U-2: The veteran spyplane too valuable to replace by chiph on Sunday December 13, 2020 @07:28PM (#25411975)
The AF uses muscle cars to chase it down the runway as it lands to give the pilot feedback on their height above the concrete. They have to stall it from 2 feet up (61cm) to have a successful landing. If they do it from 4 feet up (1.2m), they'll probably damage something.

They used to use Pontiac GTOs (aka Holdens), then switched to Camaros. Not sure what they're using now.

https://www.youtube.com/watch?v=BIrZCymyjNY

Re:U-2: The veteran spyplane too valuable to replace by chimpansteve on Monday December 14, 2020 @08:35AM (#25417297)
I've been in one of the chase cars as they talk the plane down. One of the most memorable experiences of my life. This was over 10 years ago, but they were using Subaru Imprezas and Mitsubushi Evos then (this was in Cyprus, btw)
Re:U-2: The veteran spyplane too valuable to replace by garmaine on Sunday December 13, 2020 @09:01PM (#25412687)
Some airman has the most awesome job ever.
Re:U-2: The veteran spyplane too valuable to replace by whoisthemachine on Sunday December 13, 2020 @09:30PM (#25412873)
Electric vehicles would be perfect for this job.
Re:U-2: The veteran spyplane too valuable to replace by numpad0 on Sunday December 13, 2020 @10:56PM (#25413371)
They tested Tesla in 2017 and Camaro don’t seem replaced. Perhaps those were too slow at high speeds.
Re:U-2: The veteran spyplane too valuable to replace by sargun on Monday December 14, 2020 @02:19AM (#25414377)
One of the problem with Tesla’s is they cannot have long periods of sustained acceleration due to the way battery cooling works. They could probably rig up something fancy, but at least none of the models right now do this easily.
Re:U-2: The veteran spyplane too valuable to replace by gambiting on Monday December 14, 2020 @06:50AM (#25415971)
The Porsche Taycan has been specifically engineered to do that sort of thing over and over.The issue there is that I really don't see a reason to get a taycan over some american muscle, a 500hp mustang is like 1/3rd of the price of a base spec Taycan and will do the exact same job. It's not like army bases are short on fuel either.
Re:U-2: The veteran spyplane too valuable to replace by mlindner on Monday December 14, 2020 @09:24AM (#25417845)
This is largely a myth and was only true of early Tesla vehicles.

Also you're not going "long periods of sustained acceleration" here.

The real issue would be Tesla's slow acceleration at high speeds. It has a very very good 0-60 mph, but it's 0-100 mph is more average.

Re:U-2: The veteran spyplane too valuable to replace by numpad0 on Monday December 14, 2020 @03:10AM (#25414635)
Both the cooling and how electric motor works. They lose out power after 60mph or 1/4-mile distance whichever comes first.
Re:U-2: The veteran spyplane too valuable to replace by tolien on Sunday December 13, 2020 @07:29PM (#25411987)
Difficult to get it back on the ground without killing yourself too - to the point that the backup pilot drives behind at ~140mph, calling out helpful information [1].

Saw a U-2 at an airshow and somehow I expected more. It had really badly damaged paint and just looked like some neglected museum exhibit that had been left outside too long.

1: https://jalopnik.com/the-140-mph-chase-cars-of-the-u-s-air-f...

Re:U-2: The veteran spyplane too valuable to replace by cornellwright on Sunday December 13, 2020 @09:53PM (#25413011)
I saw a U-2 at an airshow (California Capitol Airshow at Mather) and it also looked beat up. I asked about it and they said that it's a working airplane, not some show piece. Basically it just had a lot of hours on it since it was last repainted.
Re:U-2: The veteran spyplane too valuable to replace by TigeriusKirk on Sunday December 13, 2020 @10:36PM (#25413244)
The trainer versions go in and out of Mather fairly often. I assume they're based at Beale AFB and just use Mather for short training hops.
Re:U-2: The veteran spyplane too valuable to replace by cornellwright on Monday December 14, 2020 @12:55PM (#25420726)
The U2 I saw at Mather was based a Beale (as were the Air Force folks exhibiting it). They said the U2s get rotated in and out of service/training and that this unit had been all over the world.
Re:U-2: The veteran spyplane too valuable to replace by CalChris on Monday December 14, 2020 @02:32AM (#25414438)
Mather AFB has been closed since 1993.
Re:U-2: The veteran spyplane too valuable to replace by TigeriusKirk on Monday December 14, 2020 @08:26AM (#25417212)
At which point it became Sacramento Mather Airport, where the trainers fly in and out of from time to time.
Re:U-2: The veteran spyplane too valuable to replace by meowster on Sunday December 13, 2020 @07:48PM (#25412087)
I've seen a U-2 up-close in-person (it was actually one of NASA's versions). It looked pretty decent. It's pretty basic and bare-bones though: every pound saved off of it equals one foot higher that it can climb.
Re:U-2: The veteran spyplane too valuable to replace by blackrock on Monday December 14, 2020 @12:53AM (#25414009)
They should get a lighter pilot.
Re:U-2: The veteran spyplane too valuable to replace by t0mas88 on Monday December 14, 2020 @03:42AM (#25414796)
Coffin corner isn't just a thing at 70,000ft in a U2, it applies to regular airliners at much lower altitudes as well. When heavy the maximum altitude for a normal passenger plane can be several thousand feet below it's certified maximum service ceiling.

What helps is that due to procedures nobody flies manually at such altitudes. So it's up to the autopilot to maintain a specific airspeed.

A similar effect exists at very heavy weight on takeoff, the gap between the stall speed and the maximum speed for the flaps can be as little as 20kt in a fully loaded 777. That requires good concentration and constant monitoring in the climb to not get a stall warning or a flap overspeed. This part is often flown manually.

Re:U-2: The veteran spyplane too valuable to replace by geokon on Monday December 14, 2020 @05:05AM (#25415271)
From the article the maximum speed seems to be limited by structural constraints. But surely a loaded 777 at lift off isn't on the verge of disintegrating bc it's going to fast. Maybe it's a different kind of speed limitation?
Re:U-2: The veteran spyplane too valuable to replace by iambateman on Sunday December 13, 2020 @09:08PM (#25412734)
Question on the stall issue: if a pilot starts to stall, wouldn’t they simply maneuver to get the nose down until they get enough speed to break out of the stall?
Re:U-2: The veteran spyplane too valuable to replace by sandworm101 on Sunday December 13, 2020 @10:07PM (#25413095)
Coffin corner is the speed between stall speed and overspeed, some number close to mach 1 that the airframe cannot handle. A stall-induced dive at that altitude risks hitting a speed that will damage the wings. The U2 is essentially a fighter jet with glider wings: two things that dont want to play well together. It is a frankenstien's monster of an aircraft.
Re:U-2: The veteran spyplane too valuable to replace by upofadown on Sunday December 13, 2020 @09:57PM (#25413035)
It might be impossible to recover from the resulting dive without exceeding maximum speed in this particular case.
Re:U-2: The veteran spyplane too valuable to replace by cm2187 on Monday December 14, 2020 @08:58AM (#25417542)
Isn’t Keeping the correct speed a good fit for an autopilot? Plus I would imagine there would be less turbulences and surprises at this altitude.
Re:U-2: The veteran spyplane too valuable to replace by mlindner on Monday December 14, 2020 @09:22AM (#25417824)
Modern autopilots yes, old autopilots weren't nearly as good.