RR Viper jet pipe
A bit of a niche subject this, but looking at HS125-600B, some aircraft had a straight, simple jet pipe, others had a diffuser. Why was there a difference?
https://www.prints-online.com/new-im...-32230610.html https://abpic.co.uk/pictures/view/1736019 |
Hush kits?
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I believe the diffuser was a customer option (or retrofit) to reduce the viper's noise output. At one time such 'Hush-kits' were quite common on various jet aircraft as airports became increasingly sensitive to noise.
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I recall that husk kits on One-Elevens made no discernible difference. I imagine that it must have been measurable but my human ear couldn't detect anything.
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Originally Posted by Quemerford
(Post 11519007)
I recall that husk kits on One-Elevens made no discernible difference. I imagine that it must have been measurable but my human ear couldn't detect anything.
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I was at Gatwick when the first 1-11 hush kits appeared, Tarom I think. The difference was only noticeable when the aircraft got some distance away. The noise seemed to be the same on take-off but the hush kit fitted ones faded away quite soon whereas the unfitted aircraft could still be heard when they were near Seaford.
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Originally Posted by Allan Lupton
(Post 11519098)
We were always a bit puzzled that the One-Eleven was so much noisier than our Tridents. I think I recall a member of the Weybridge opposition (later colleagues) telling us that most of the One-Eleven's noise was from the air-driven CSDs in which case a hush kit would indeed make no difference.
Trident-wise, I seem to recall early mornings hearing Tridents running engines post-maintenance at Hatton Cross from my house in Hersham. Maybe seven or eight miles away. The aircraft on the Cullum mufflers too! |
I'm glad to hear that my mind wasn't entirely playing tricks: I do seem to recall seeing a noise footprint at some point, which showed how the dB should have been reduced (possibly in an aft-wards direction as dixi188 alluded to above).
However, slightly off-topic, I really miss the sight and sound of a low-level SOAF One-Eleven! |
A couple things to keep in mind. First, the human ear is not a particularly good sensor when it comes to determining the relative loudness of noise. It takes roughly a 3db change in noise level before the human ear can even detect it (which, given the logarithmic nature of the decibel scale means a doubling (or halving) of the sound energy level - yet obtaining a 3db reduction is a huge engineering challenge. Further, the human ear doesn't detect all frequency levels the same - hence there is a db scale that is "weighted" for certain frequencies.
Second, the official jet aircraft Takeoff and Landing noise levels are determined at fairly specific points along the aircraft flight path - so getting a meaningful reduction in noise level at the official measurement sites doesn't necessarily mean the same thing at other locations along the flight path. |
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