Junkflyer:
But it sounds great when it lights off.
30 years ago I was conducting a flt ops survey on newly-delivered 747s - a flock of mechs were on a fam tour of the cockpit as the a/c wasn't scheduled to go for an hour or so. So rather than add to the confusion I took a pax seat in the upper deck, enjoying a bit of breeze from an open hatch.
Then I heard a sustained foghorn-like sound. At first I thought "What ARE those guys doing that makes that noise? - hydraulics, or what"??
After a bit I noted a TriStar 1/2 km down the ramp blowing a BIIIG cloud of fuel vapor out #2 exhaust. When the vapor finally stopped, so did the noise.
