The thing I find fascinating about the U2 is how close to coffin corner it cruises.
Just a big jet powered glider really, flying in the thinnest of air, right on the stall for hours on end.
Filmed an ER2 taking off from Christchurch Airport once to do atmospheric sniffing for NOA over Antarctica.
We were in a Squirrel with the doors off, hovering halfway down the runway off to one side.
I'd heard the jet had a very steep climb out rate and said the the chopper pilot, "you'll need to pull full collective mate just to keep him in shot."
The jet rolled, lifted, the Squirrel pilot hauled his left hand to the roof, and in about 3 seconds the ER2 just shot right upwards past us, heading for the clouds.
We didn't stand a chance.