was climbing at max rate in an Issacs Fury. The engine failed and the Fury stalled and spun immediately
Yeah, there is a less than universally understood concept, which most of us have been guilty of ignoring, to our own peril;
The steeper the climb, the slower the airspeed. The slower the speed, the higher the drag. The higher the drag, the faster the plane will slow down when you take the power away. There comes a point where the pilot just will not get the nose down fast enough, and a stall is assured.
A pilot should expect that the plane can be easily glided from at engine failure at Vy. An engine failure at Vx may be somewhat different, and extra skill will have to be applied. Slower than Vx (which is certainly possible) is much worse. It might not be possible following, a sudden engine failure, to lower the nose fast enough to accelerate to glide speed. In that case, you're going to stall before you can establish a glide. Game over.
There are phases of flight which we get into, which we will not be able to get out of following an engine failure. All helicopters have them - it's called a height/velecity curve. Airplanes have them too, but they are not documented. This is probably because airplanes are not expected to be operating in those regions of flight. Aside from slow flight training, there just is no reason. In slow flight training, you should have lots of altitude to recover the stall which will result.
I have done this testing in a modified Cessna Grand Caravan, and it was very scary! My experience with microlights is limited. I do know that they have less inertia, and so are even more vulnerable to this than certified light planes.
Vx to assure that the obsticle is cleared. Vy or faster after that. Yes, altitude is your friend, but not if you foresake airspeed to get it!