you might think about a 3-bladed prop. it'll reduce the tip speed per given RPM, thus the noise. bonus, more prop clearance -since power won't be an issue. also, might help be an 'air-brake' at low idle. These are some of the reason's the H9 Alpha uses a 3-blade prop.

I looked for a three blade prop. APC makes a 9x6 - too small, and 10x8 - too big.

I'd need something that has about the same load as an 11x5 two blade.

I've read that tip noise is not excessive until you get past about 0.7 mach. Round tip prop's such as APC's are supposedly better (less noise). I'm running an 11 inch prop around 14500. That is ~ 0.62 according to my chart. So I expect that it is a large contributor, but not extreme.

Talking about air brakes.... I ready in the "Bolly Book", on Bolly's web site, that a quiet pipe can aid in downline braking. That's the first and only reference I read to a pipe helping slow the engine..... yet another thing to understand

Go to --->

http://www.flyquiet.com/


Francis

Just barely a differance, hardly close to a Db. 3Db is about twice or half the power level.

I have only done this with Cox .049's. How many fingers do you still own?

Sport_Pilot, I was trying to put across the point to those new to diesels that holding them in their hands with a bit of fuel in them can give a big surprise.

I've still got all 10 fingers but I won't go into details about what I've done except to say I've never done it with anything as small as an .049

Check out this pic of an old Leasure Amptique with a PAW .09 r/c.

Yes thats just over three feet of tubing.

Oily in Germantown

Francis

I've noticed that models that have a lot of open bays (i.e. just covered with Monokote or somethign) make a lot of noise from vibration. Might do a soft mount for my upcoming 40 size project if I had an easy, cheap way to do it.

I am playing with the idea of making a large, light wooden muffler built into the fuselage so it's larger and less ugly.

My Scooter 2 had an FP40 with 11" instead of 10" prop, and the optional baffles and extension for the muffler. Couldn't hear it if other people were up. I've got to think if homework is done on the LA 15 and soft mount is used it could be made almost arbitrarily quiet without going to diesel or electric

I know this great way to quiet a engine and get a lot of power! ...... Ear plugs!

I saw a pattern contest once, back when they still used .60 2 strokes, but after the noise rules came in. 200 foot square loops and almost inaudible (I admit there was a light breeze blowing towards the planes). It can be done.

If you go over the the diesel posts I have a 54" VMAR cub with an OS10 davis
head I fly at an electric site it is quieter than the gear electrics

This .21 4 stroke is claimed to rival an electric:

http://www.mecoa.com/hp/vt/vt.htm#hpfs

The HP four strokes are so quiet that when my dad put the electric starter on his .49 and turned it on, he kept on going because he thought it wasn't firing. Giving up, he removed the starter and realized the engine was running fine. They are the quietest thing ever! Not great powerhouses but definitely quiet!

Max

Putting a piece of rubber behind the engine pount won't reduce noise, because there is still "hard to hard" contact (the mounting screws).

If you want to achieve noise reduction this way you have to completely isolate the engine from the airframe.

Try this: http://home.online.no/~ofremmi/HowTo.../HydeMount.htm
This "Hyde mount" is mostly used on pattern planes, but can be scaled down for your application... it will just take a little experimenting.

A properly set up (calculated) mousse can pipe is a sure to way to succes, and will even increase engine power.

Like other people said, induction noise from the carb may not be overlooked... it is a much bigger noise factor than most people realise.
There's absolutely no use in quieting everything down if you do nothing about the carb... since the human ear will always pick out the loudest noise.
Try to get your air from inside the fuse one way or another, that will do the trick. Just don't use a hose the size of you throttle opening all the way to the fuse, that's too restrictive and will kill performance.

I seriously doubt you can make is as quiet as a brushless though... unless there's something terribly wrong with the brushless you're comparing it to.

Finally, I do not own a diesel engine, but I'm looking into it. If everything I've read is correct, than a diesel is probably the easiest way to really quiet things down... but you will still need a flex mount of some sort.