Originally Posted by paulkinm
Hi all,
I would like to ask about a phenomenon I haev noticed while watching aircraft come into land at Heathrow and other smaller airports.
As an aircraft passes over at about 50 - 60 feet overhead, count to 30 and then there is a strange "ripping of paper" kind of sound in the air. It's very odd and it appears to follow the aircraft. First time I heard it I went
I can only put this down to aircraft slip stream or is it something else?
Any help would be most appreciated!
You are exactly right about the ripping noise! They make you want to duck at times
What you are hearing are the wingtip vorticies. These are super strong mini horizontal tornadoes formed around the wingtips. On a wet/humid day you can physically see them.
There is high pressure under the wings and low pressure on the top surface. This high pressure at the tips effectively leaks around the wingtip edge to the low pressure area and in doing so, creates these spiralling tip vorticies.
They do descend once they are formed, hence why you hear them 30 sec later.
On a very clear still night with low ambient noise, I've heard them several minutes later after aircraft have flown overhead on approach from 2000+ feet up.
From a pilot perspective, if you have a small aircraft, they can literally spin/flip you out of control and there are regulations which state minimum times that smaller aircraft have to wait before following a larger one. It's called a "wake turbulence category".....light/medium/heavy. A bit like a boat plowing thru the water.
Hope this explains your mystery noises!