In the 1970s when I used to occasionally inhabit the spectators' gallery at Gatwick, one could often see a Bristow Whirlwind or two bashing the circuit at Redhill, presumably schooling Bell 47 graduates rather than ab initio students. As far as I remember from surreptitious visits to Redhill, one was piston, the other two turbines. They never seemed to fly during my visits. (A very belated Thank You Tiger Club for always letting us spotty teenagers roam your hangar which usually meant we then had tacit approval to be on what was otherwise a rather unfriendly aerodrome!)