View Full Version : Strange engine noise
boguing
7th Jan 2009, 11:16
An aircraft, sounding much like any other twin jet engined airliner, passed over me yesterday (above cloud - so no ID). Climbing away from a Heathrow departure.
The only way I can really describe what I heard is to say that it sounded just like when a boat's propellor cavitates - revs rise very quickly but no thrust increase, caused by applying too much power at low speed, bit like a wheelspin. This happened three times in rapid succession.
The rpm increase was far quicker than a normal jet engine can. rpm decrease was equally rapid.
Any ideas? I've heard it once before.
PPRuNeUser0215
7th Jan 2009, 15:04
Might not be that but when the 146 retracts or extend its flaps, there is a high(ish) pitch noise due to the aerodynamics changes.
boguing
7th Jan 2009, 16:39
No, it's not that, definitely engine.
Groundloop
8th Jan 2009, 08:28
Well, the first time I heard it while aboard a 146 I thought the pilot was slamming the throttle levers back and forward. It definitely sounds like thrust changes but is in fact airflow separation as the flaps move through a particular position.
boguing
8th Jan 2009, 18:17
I suppose I'll just have to wait until I hear it again on a clear day, and can give a type.
Why would a 146, at several thousand feet, on departure and 25 miles from takeoff, be playing with flaps?
As I said earlier, I'm positive it was engines - there was a clear absence of engine noise in between the 'runaways'.
PPRuNeUser0215
8th Jan 2009, 20:13
Why would a 146, at several thousand feet, on departure and 25 miles from takeoff, be playing with flaps?
Perhaps you could have given more details. You said climbing away from LHR departure and never mentioned a distance or a height.
Never heard jet engines cavitating and never suffered that kind of pretty critical situation.
boguing
10th Jan 2009, 18:59
I live a few miles South of Dorking, and a few miles North of Gatwick's airspace.
I normally have descents into Heathrow, but if on Easterlies, I get the West bound traffic cruising or climbing gently.
I didn't say that the engine was cavitating, it was an analogy which a boat user might understand. The engine rpm rose far more quickly than normal. I wondered if I was hearing a compressor stall, or some other precursor to the demise of my local school/hospital.