20cc Petrol Engine / 82 dB

[Nev Haycox]

Can someone tell me, is it possible to purchase a 20-25cc Petrol Engine that runs at or below 82 decibels with stock silencer?

Nev.

[Codename-John]

probably not

[Reno Racer]

I don't know of any, maybe the Saito FG21 on the assumption that its really just a converted 4 stroke and so the noise should be quiter than a 2 stroke to start with. Just Engines do conversions an conversion kits for 4 strokes, you could get an ASP 120 FS converted to petrol. As a start point my normal nitro ASP 91 FS's measured dB at 7m is 71dB.

These however, are rather more expensive that just buying a RCGF, DLE etc 20cc petrol and then getting a proper silencer like this type

Others may know better, but from what i've seen most petrol's come with a silencer that does nothing more than direct gas flow. Of course, the silencer is only one factor in ensuring your set up in the aircraft is less than 82dB. You should also consider:

• a hydro mount/dampened mounting system - similar to that used in Toni Clark kits.
• foam sound absorption behind the firewall to stop the fuselage (particularly open structures) acting like a drum
• get rid of any rattles, control rods etc etc.
• Right prop, not just balanced put a slighter larger prop and lower rpm can give you enough power, but cut down dB quite a bit.
• use rescue tape to wrap the muffler and stop any tinny sounds as the extracted gasses hit any hard (90 degree) bends.

Hope that helps some. I've been doing the same to fly my 26cc petrol (RCGF with Bisson silencer) in strict dB conditions in Germany.

Edited By Christian Ackroyd on 26/12/2012 12:14:37

[Nev Haycox]

Thanks Christian, Perhapes I should ask-

Can I Buy an off the shelf silencer that will allow me to run a DLE20cc petrol engine (or something similar) at or below 82 dB ?

[Codename-John]

try speaking to someone like just engines, they fabricate exhausts etc and should be able to advise whats available, or what to try to reduce noise in an existing exhaust ?

[Nev Haycox]

Cheers C-J, But, Just Engines don't sell DLE engines (which is favorite at the moment), as a result I'm a little hesitant to ask for their help, but I'm sure they won't mind.

[Turbycat]

Just engines will make an exhaust for just about anything. Also weston uk will make custom manifolds and exhaust systems.

Andy

[Reno Racer]

Not sure. I suspect because theres so many other factors that add to noise, manufacturers don't state dB output for there exhuast, which is frustrating when trying to get a set up.

Can it be done, almost certainly and lots of petrols fly in Germany so must be under 82dB.

Most i've seen have the manifold and cannister type exhaust, HK used to do a 26-30cc canister and manifold for the RCGF 26cc. BTW, the DLE 20 and RCGF 26CC have the same mounting dimensions,so anything for the RCGF26cc will also fit a DLE 20.

This is mine, but I've yet to get it tested.

I'd go for the DLE, and get something like this, which is claimed to be 80dB. Seems expensive but combined cost of this an DLE 20 will be less than a Saito.

If you still need an airframe, this is a good deal for a DLE30 and silencer with 30cc airframe.

Cheers

Chris

[Nev Haycox]

Thanks Christian, Great info and much to look at. If anyone else can help or has any experence with a DLE20cc and silencer then please keep the info coming, I wish to get it down to 82 dB or below.

Cheers, Nev.

[Roby]

Hi, i have a DLE 20 with a silencer from a DLE 30. I put 2 pieces of brass tube, where i drilled few holes, inside the 2 silencer exits and it now runs at 82 db.

Roby

[Nev Haycox]

Hi Roby, Was the silencer you used a stock DLE 30 silencer?

Thanks ,Nev.

[Simon Chambers]

The stock silencers on most petrols are nothing more than sound deflectors. If you want to properly silence them, canisters are the way to go. A friend has silenced his dle55 to under 82dB with a good canister.

I would imagine on a 20cc you should be able to do it with the cheap Chinese canisters. don't forget about the canister mounts as they can make a difference.

Si

[Nev Haycox]

Has anyone achieved 82dB or below with a Pitts Style Muffler on a DLE20cc?

Nev.

[Reno Racer]

The evolution mufflers are supposed to be really good

some good stuff on this thread here, apparantly stock dle20 muffer is 88dB

[Nev Haycox]

Thanks again Christian, you've been most helpful. I'll have a good look at all the links you've provided.

Nev.