I can confirm that the British 24-ft 'Irvin Oscillator' is a highly unpleasant ride, and the best one can hope is to arrive on the upswing. (I didn't, ankle still twinges occasionally.) The US 'C9' ejection seat canopy was far better and you could kill the tendency to oscillate by releasing the centre rear 4 lines after opening ('four-line cut'), which also gave some forward drive and steerability. The same effect can be achieved on the Irvin, if you have a hookblade knife handy, and after that first ride I always did.