View Full Version : Why do helicopters sound so "choppy" on windy days?
Tickle
4th Jul 2018, 13:20
It's very windy tonight here in Melbourne, Australia (since last night, in fact!). The VicPol Dauphin just flew over and the rotor blades were so loud (rotor slap?) even though it was just flying forward at speed, not turning or hovering.
I am wondering if anyone can explain the physics as to what causes this extra sound dynamic on a windy day?
Thanks.
Ascend Charlie
4th Jul 2018, 18:51
All the lift is getting blown away, so the blades have to work harder.:8
John Eacott
5th Jul 2018, 01:19
All the lift is getting blown away, so the blades have to work harder.:8
Silly sod......
Everyone knows that it's because VPAW operate those funny French helicopters with the rotors going round the wrong way, and Melbourne has the bathwater going down the plughole in the opposite direction so the two conflict and give a louder noise :ok:
BOBAKAT
5th Jul 2018, 02:19
North Hemispher helicopter brand used in south hemispher and main rotor runing in the wrong way . What else ?
Tickle - google BVI - that's not the British Virgin Islands but Blade Vortex Interaction:ok:
Ascend Charlie
5th Jul 2018, 05:46
Pilot Murphy forgot to go to Whisper Mode. JAFO should have reminded him.
Tickle
6th Jul 2018, 02:13
Thank you for the replies, Crab's suggestion helped explain it well.
Love the Blue Thunder reference. :)
Pilot kzn
2nd Aug 2018, 08:12
Dis-symmetry of lift I'd say is the cause. Wind gusts temporarily increase lift on the advancing blade which causes blade flapping and increased noise. This is compounded by decreased lift on the retracting blade.
I'm getting retreating brain stall.....
Supersonics...
tartare
2nd Aug 2018, 23:06
Remember flying many years ago to the scene of a light plane crash in Canterbury.
A poor stude had speared in, flying a Tomahawk solo cross country in a terrifying Nor-Wester - he should never have left the aero club.
Two things still stick in my mind decades later.
The hand still holding a map sticking out of the compacted wreckage as it rocked gently back and forward in that hot wind.
And that same wind blowing in howling gusts up through the disc of Alan Bond's 500 (may he rest in peace) as we flew back to Christchurch hugging the hillsides.
Was the first time I really thought about how those rotors really do look like one solid wing to the airflow, and how they're also a giant shock absorber when it's really windy.
Hence the noise I suppose...