The current issue of Auto Express carries an article on what is essentially active noise reduction (ANR) for a car engine. The physics of it goes that the air intake creates a lot of vibration internally and is therefore responsible for most engine noise. The initial prototype was bulky affair filling a boot, which through a pre-ducting box pulled air through twists, turn and through different size spaces. However prototype two uses a much smaller cylindrical (think it was about 20cm long by about 9cm wide) in which ANR technology is used to produce counteracting in-phase sound to deaden the noise to virtual silence. They even claim to be ablr to add further sounds, e.g a straight 4 sounding like a V8.
(yes I have got the semantics wrong)
I was wondering if such a thing might be feasible for a light aircraft? It’s small, lightweight, non-mission critical, wouldn’t affect engine performance and certainly would keep the NIMBYs happier. Ka-ching?
By: John C - 22nd February 2005 at 10:46
Lotus were doing this 15 years ago! Noise attenuation is only effective in the cabin – you’d probably need an aeroplane covered in loudspeakers to reduce noise emissions to the environent. Big speakers as well. Sort of a reverse Chav effect!
It’s possible to reduce the perceived interior noise but not exterior by this method – it’s down to good old resonators and silencers 🙂
JC
By: Moggy C - 22nd February 2005 at 09:41
Well, they do like talking a load of coblers. Any good engineer will tell you the biggest noise producer on an internal combustion engine is induction roar (i.e. produced by the air inlet system) especially if you do away withj the air filter.
Erm…
Wasn’t that what BR just said :confused:
Moggy
By: Dave Barrell - 21st February 2005 at 23:27
Not wishing to state the obvious but it’s quite handy for a pilot to hear his engine running, especially when it decides to stop – particularly if the aircraft has a VP prop fitted…
On light aircraft, most noise comes from the open, unsilenced exhausts.
If you get a chance, watch a Pawnee with a four blade prop and silenced exhaust – very NIMBY friendly – almost silent in comparison.
DB
By: Kenneth - 21st February 2005 at 22:16
You also still have to attenuate the noise made by the propeller….
By: mike currill - 17th February 2005 at 09:19
Well, they do like talking a load of coblers. Any good engineer will tell you the biggest noise producer on an internal combustion engine is induction roar (i.e. produced by the air inlet system) especially if you do away withj the air filter.
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February 16, 2005 at 9:32 pm