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.
I once tried to chase one in my Jet Provost after it appeared out of a flat topped cloud bank a couple of miles away. Not for long, the "constant thrust variable noise" machine I was flying could go nowhere it; it appeared to climb at a 45 degree angle. Very impressive!