Noise reduction

[Timothy]

I have been long resentful that in the certified world it is not permitted (without the 5-6 figure cost of recertification) to be a good citizen and put four blade props and silencers on my MEP. Just for altruism.

With the purchase of my lovely Emeraude, I am new to this whole uncertified world.

But I do feel that, if I can, I should put my money where my mouth is and quieten her down.

Where do I start? Is there a light four short blade C90 prop I can just fit? Similarly a silencer? Or would it be a huge deal under the LAA as well?

[Ian Melville]

I doubt there is a 'just fit' option anywhere. I know of a 3 blade prop on a O-200* powered WAR FW190. I also think that Airboats in Florida sometimes use 4 blades on a O-200. Have a chat to Rupert at Hercules Props

Best to speak to LAA engineering as things are never simple when making what are significant changes. The first question is, where is the noise from? Prop or engine. Does your aircraft have a silencer or straight pipes? Consideration needs to be made regarding the weight and and changes to power output. Have a look for Swiss Pipe Mufflers used on the continent, but as far as I know not on the small continentals. Example here https://www.airliners.net/photo/Untitle ... 2BHw%3D%3D

I suspect you won't have enough margins to make the changes without making your aircraft a single seater.

Cheers
Ian
* C90 and O-200 are cosely related. C90 producing power at a lower RPM is the better choice for quietness.

[Timothy]

Thank you. I feared as much!

[Boxkite]

The LAA produce a list (downloadable from this site) of all approved props, together with details of the aircraft and engine.

[tnowak]

Probably 10-15 years ago, an LAA member submitted plans for a new exhaust system for small Continental engines.
From memory, I believe the tailpipe mod. resulted in a 3-4 db noise reduction.
Perhaps LAA engineering still has the info?
Tony

[Ian Melville]

Was that the one where there was a short length of pipe added with holes drilled in the side?

Cheers
Ian

[tnowak]

Ian,

I don't think so but will have to check the drawing (if I can find it)..
Tony

[John Dean]

Was that the one where there was a short length of pipe added with holes drilled in the side?

I seem to remember that some years ago a competition was held for the design of an exhaust muffler and it was won by a Kent Strut member.

I could be very wrong but I can ask the person involved when I next see him.

[JimCrawford]

I'm currently running a VW 'open port' on my Nipper and would be interested in any simple noise reduction exhaust scheme as I hope to move to a farm strip in a year or so and it seems like a good idea to keep the neighbours happy.

Jim

[tnowak]

John,

That is the exhaust system I was referring to.
Designed by Gary Smith - the "GS2000 exhaust silencing system".

I also have a copy of an article published in the July/Aug 2001 of Popular Flying titled "Quiet Aircraft".
Contains some good info on aircraft noise and how to reduce it.

Tony

[dmcnicholl]

Jim Crawford,

My RF3 has a VW based engine with these mufflers on either side. Pretty standard on all Fourniers.

Not a full silencer but they are effective, as I found out many years ago when the manacle clamp on one side loosened and the pair fell off on take off!

Material is 35m diameter 1mm wall thickness 316 stainless steel tube. I think they are about 350mm long. They don't weigh much.
The row of holes are 5mm in diameter and the fishtail ends are not fully flattened but have a 4-5mm gap.
At the connection to the exhaust stubs the tube is slotted to allow a reduction in diameter to match the stubs. The 'reducer' length of the slot is welded (to itself not the exhaust stub).

It seems to me that not pointing exhaust pipes, perforations, open or fishtail ends at the ground a makes a huge contribution to minimising noise nuisance.

[Ian Melville]

Sadly Timothys kite is resting in the trees near Rochester

[Alan George]

It may be academic now but this is the neat arrangement on a C90 I am involved with. 4 into 2 steel headers leading to a collector/silencer with a single outlet plus a stainless muff for cabin and carb heat. Its very quiet in operation but unfortunately I cannot see a maker's name.