turbine sound effects - boring
obviously what you need is a real helicopter a Bell 47 3B1 which is still fairly warm from its arrival at - the convenient location.
scene - strike up a converstaion with 'the guard', wander over to said machine and con him into sticking his head nearly into the end of the big exhaust pipe, while hero fiddles inside.
Fiddling means - master electrics on - the throttle is given three good primes - wait a half second - hit the start button - just as its going past TDC (top dead centre) of the first compression - throw both mags on.
There will be an ear splitting explosion - followed by the sound of a real engine winding up - guard will be laying flat on the ground with mild concussion - jump in - thirty seconds later as you continue winding up - lift the collective - make like you're just learning to hover - all over the flat like - the other gurads will - take cover - at that point - full throttle - cyclic forward and piss off.
Not that I ever would have done that in real life with those real helpful bloody stickybeaks!