Hi Dave
The RB211 (747) has Variable Inlet Guide Vanes just behind the big Fan at the front, to guide the airflow smoothly into the rest of all the whizzing bits further downsteam.
The best and most impressive feature of this is the VIGV controller, a pressure driven device that works really well except when pushed a little i.e. Typhoon conditions, big crosswinds etc, combined with large throttle movement. It can then deliver the most spectacular results, throwing a doughnut shaped fireball out of the intake beyond the nose of the A/C with accompanying sound effects that make one wish for a quiet lightning strike!
Fortunately the bark is much worse than the bite, and I've only had one run down after the stall/surge, and even then, no damage----Thanks to all the chaps at RR, you build them well.
