Flyfast1

My Feedback: (1)

I have an FPE 3.4 (55cc) in a 1/5 scale spitfire with a stock wrap around pitts muffler and need to make it quieter. My home field has a max noise limit of 98db and this plane is at 104db with a Zoar 21x10 prop. I am tight on room in the cowl and can't really go with a larger muffler. Are there any suggestions for quieting my plane? Will adding some tubing to the end of the muffler pipes significantly reduce the noise, or is this a waste of time? I've attached some pictures.

Thanks,

-Ed B.

jedijody

My Feedback: (1)

Roll the opening of the muffler down tubes in to reduce the opening size or just squeeze them with pliers but rolling them will work better. Use a 3 blade orlarger and or different brand prop to reduce RPM, Xoar are not the quietest props out there.

aussiesteve

Contact JTec and see if they have "Snufflers" to fit it.

Otherwise - can you find a decent welding shop? - here is a cheap way to make a glass pack outlet.

drill a series of 1/8" holes around the existing outlet tubes
Weld some larger diameter tubes around the exisiting outlets
Fill the cavity between the two tubes with fibreglass wool
Weld a cap over the cavity end

There you have a glass pack muffler that will quieten the exhaust quite a bit and not take up any additional room.

Also heed the advice about the propeller making a lot of noise.

OR

Go Electric
"HK" does some decent electric sets nowadays[sm=biggrin.gif]

(Oops - did I say that? LOL)

Lifer

My Feedback: (1)

I usually stuff some stainless steel pot scrubber material (from the local hardware store) into the opening of the muffler and tamp it into the chamber. Not stuffed, but loosely fill the chamber. This will lower the tone and to a degree, the volume of noise. I've had some that blew out quickly, and some that remain after several years.

If there is a drop in performance, it is marginal. You may also try different props, as well.

Hope it works for you. Good luck.

Charlie P.

Wow! 104 dB is durned loud.

T'were it me I'd try an APC 21 x 10, which is a pattern/IMAC prop and won't look as appealing as the Xoar but should reduce the sound.

Flyfast1

My Feedback: (1)

Thanks for all the suggestions. I have been in contact with Jtec about their snufflers and they say that they cannot be added to my two exhaust pipes directly, but that I would have to mount the snufflers remotely and use flexible tubing to connect the snufflers to my existing down pipes. Given the tight spacing, they may or may not be able to make a snuffler muffler that would replace the existing muffler. They need some additional pictures, so I will get those this weekend.

Yes, I know the plane is loud. It's got a high pitch tone or "bark" to it that makes it noisy at all rpm levels. It is not a deep throaty sound. I have also tried a Zoar 22x10, which reduced the prop speed, but it was still too loud. Does anyone have a recommendation for brands of props that tend to be quieter?

Jody, how would I roll in the ends of the tubes? Is there a special tool for this? Are the ends of the tubes sliced vertically before rolling?

Lifer, do you insert the steel wool go into the top of the muffler where it mounts to the engine, so that the steel wool sits in the large chamber to which the exit pipes connect?

Steve, thanks for the suggestion. There must be some local welding shops around me, so I will try your suggestion if the other steps don't work.

-Ed B.

Lifer

My Feedback: (1)

Remove the muffler and insert the steel wool from the exhaust port. You will be surprised at the difference. The effect is similar to the sound of the "glass pack" mufflers I used on my cars when I was a kid. The principle is the same. I do this to all the engines I own.

Charlie P.

That's why I suggested APC. They use(d) the same design elements that the Navy uses on submarine props for noise reduction. I'm one of the safety officers at our club and APC is usually good for two or three decibels off. But I like wood props for gas (which I hand-start) and don't use them in the larger sizes. Six decibels drop is a huge goal. That means you have to quiet it by double-digits percentage wise!

I've been using 18 x 10 Xoars, though, and they're no louder than the same sized ProZingers.

I might also suggest a call to Dick Bennett at B&B Specialties 574-277-0499 (Bennettbuilt.com) to see if he has an after-market muffler for the FPE. Doesn't list them on his website, but he is a helpful cuss with such things. I'm thinking, though, that gas mufflers are all pretty simple and similar. What RPM are you hitting with that prop?

earlwb

The only thing I can think of is to get a right angle bend in the down tubes on the muffler and mount a couple of snufflers on to the ends.
it is a little ugly but it would work. Yeah our flying field has noise limits too. Many of the gasoline engine guys have run afoul of it too.
usually whenever possible try to use the expensive canister mufflers.

One thought is to use a silencer to go on the tips or outlets to your down tubes.
They do this with the boats a lot. But they are commonly used on the ends of tuned pipes for all sorts of engines.
There are quite a few of them being sold on Ebay and through other sources. Both insteel and Aluminum.

mmattockx

You need to reduce prop speed with more pitch or more blades, not diameter. It is tip speed that makes the noise and a bigger diameter prop at lower rpm will still be noisy. Try a 20x12 or a 3 blade and see what that does for you.

Mark

Flyfast1

My Feedback: (1)

Thanks very much for all the suggestions. Someone asked what performance I am getting with the Xoar 21X10. The engine runs at 6950 rpm on the ground and the engine is new. I think I will start by inserting some steel scrubbing wire into the muffler as suggested by Lifer, followed by closing the ends of the two exhaust pipes as suggested by Jody. I also have a Menz 21X12 prop that I can try. If that doesn't work, then I will need to proceed to more difficult solutions. I'll follow up with the results.

-Ed B.

Scota4570

The pot scrubber pad idea works good. Make sure there is a baffel to keep it out of the cylinder. Just put one inside the muffler can. If it pops out drill a small hole cross ways in the pipe and put a wire through it to block the srubbie's exit.

I also experimented with the length of the exhaust pipe. I made a slide affair like trombone. I found that at different lengths you could hear the sound coming in and out of resonance. With the right length it became very quiet.

For the couple of DB you are talking you could turn a couple of restrictors and stuff them in the end of the pipes, or just crimp the end of the pipes, as stated before.

It is a small gas engine, 7000 explosions a minuet is going to be loud, isn't it supposed to be?

I guess I'm lucky. My club does not care, I have asked. I do own a DB meter but would never bring it to the club. The readings vary drastically as you increase the distance and where you check in a radius around the airplane. A foot further away will make the difference you are looking for. Simply pointing the exhaust down makes a huge difference as versus measuring in line wih the outlet. Running on grass vs asphalt is a big difference. Getting a reading of so many DBs at some distance is going to be arbritrary. If someone tries to bust your chops over this ask to see the meter calibration documentation!

I can not imagine someone walking around the flight line with a DB meter. Imagine somebody checking this stuff, " My readings show you are 4 DB over the limit, no flying until you fix it" How petty is that? If you do have such folks, they obvioulsy have way too much time on their hands and a poor attitude. Is this person constantly looking for a fight? There are probably lots of arguments about trivial matters? Being dragged into such bickering is not my idea of fun. Frankly, if I had such busy bodies at my club I would leave and find someplace else to fly.

dubs1946

Hi I would be a bit cautious of the pot scrubber idea as there is a certain amount of "suck and blow" from the engine exhaust box.
In every club you get the "Nazi" who is full of self importance and rules. Be very careful if they get anywhere near the club committee. Most often these guys fly once or twice a year and make rules that are impossible to keep, its worse then the traffic road rules it gets to a point wear you cannot fly without breaking some rule or other.
But here in Australia there is a noise problem especially from the large gas engines coming out now,and flying fields have been lost because of it.
So common sense should prevail to try and keep the noise down.
Perhaps it would be worth trying a tube insert into the 2 down pipes that has baffles with uneven holes in them to try and break up the sound waves.
Dave.

billhass

My Feedback: (1)

Go to a Hardware Store and buy a SS Lint trap that goes over the discharge of a washing machine.
You get two in a package.  Do not unroll.  Cut off the end and also a piece about 1"long. Cut that in half.
Now take what is left and just stuff it in the end of each exhaust. Then take the 1" peice that you cut in half,
put it over the end to keep the piece you stuffed in the exhaust and secure it with a hose clamp.
I have done this to a 30 CC and a 20 CC gasser and the quitness unblievable. Lost of power in nil.
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jedijody

My Feedback: (1)

Need to take the muffler off and gently clamp it in a vise, doesn't need to be tight. Use a propane torch to anneal just the very tip of the down tube, about 1/4". You need to get it up to about 800* F and it will melt at about 1200* F so be a little careful. Use a small hammer to lightly tap the edge of the tube into theopening, the face of the hammer striking the edge of the tube at roughly a 45* angle and just work your way around the tube a little at a time. It will deform very easily, as it cools it will get tougher to move so keep bringing the heat back to it every couple of minutes.

In the picture the tube ID went from 18mm down to 14mm in about 10-12 minutes, it's very easy to do and effective.

Flyfast1

My Feedback: (1)

Jody, thanks for the description and the picture. I should be able to do that.

Did this significantly reduce the sound?

-Ed B.

jedijody

My Feedback: (1)

I've never done it to reduce sound emissions, I did it here just to demo for you, almost all Bisson Pitts mufflers come with the tips rolled in specifically to reduce noise. I cut the tips off to get the 100-150 RPM they cost you back. How many db I couldn't say but there is a significant difference in the noise level and tone.

rc34074

My Feedback: (5)

Take a look at two possibilities:

1. Get a Master Airscrew Scimitar prop. I use a 17-8 on my GS mustang and it seems pretty quiet to me. You can get them in a 20-10 and a 22-10 from Tower.

2. Talk to either/both Jtec or Slimline about a muffler with a bigger sound chamber. The one you are using looks pretty small to me- the bigger sound chamber mufflers will definitely reduce the bark of the engine - I know that it did on my 2 cycle engines so it will on your gasser.
Jtec has a "Large Wrap Around Pitts Muffler for FPE 3.2" for $140. They will make you a custom muffler for your plane for about the same price - they are doing it for me right now.
Slimline doesn't have much for a web site but I have used their large volume mufflers and they really do reduce engine "bark". So maybe you could call them and find out what they have. Their telephone numer is 480 967 5053 on their temporary web site. I tried to put their number i my message but for some reason it doesn't show when I click Ok - weird eh?

I have never tried to get dba data though so I have no data on what the actual noise effect is from these items. But I know they worked for me for what I wanted to do.

Good Luck

Ed

tkg

My Feedback: (1)

Go to a hardware store and get a copper pipe cap the correct size to fit over one of your exhaust pipes.
See what that does for noise/power. If you cant make the noise limit with one pipe then most of the suggestions are not going to work either.
Then you will need a better muffler or after mufflers and will have to modify the plane.
Sorry your wants and desires cant argue with mother nature and her laws.

rc34074

My Feedback: (5)

Hey - welcome back!!

How are you doing?

Ed

Gooseman240

@ Scota4570


If you have a community that says no louder than <Defined number>db, then it pays to have a picky club member so you do not loose your flying field.

Sorry to spoil your rant.

jaka

Hi!
First a 55cc engine is way too large in a 1/5 scale Spit! Brian Taylors 1/5 Spitfire uses a 1.50 four stroke and weights a little more than 7,5kilos.
You will never be able to quiet that big gasser enough.

Get a smaller engine like a 26cc gas engine and use a large cannister silencer buried in the fuselage or get a 1.50-1,80 four stroke.
Picture below shows my MVVS 45cc engine with small MVVS cannister silencer. Engine spins a Menz 24x8 wood prop at 6600rpm on 2,5% synthetic oil and 95 okt fuel.

Flyfast1

My Feedback: (1)

Jaka,

I think you might have this plane confused with another plane. This is a Yellow Spitfire. The typical weight range is 25 to 30 lbs. Mine is 27lbs. The smallest engine anyone uses with this plane is a G38 or a ZDZ40, and many consider the plane to be either marginally powered or underpowered with either of these engines. I have flown one with a G38 and it would fall out of the top of long vertical maneuvers. A 50cc class engine, e.g., 50-55cc, is considered typical for good performance. Some are even using 60 and 70cc engines. I know the MVVS engines are good, especially on a pipe (I have owned a 26cc MVVS), but it is not enough for this plane. Besides, a header and canister are not practical for this application.

Thanks,

-Ed B.

nonstoprc

My Feedback: (90)

21x10 prop on a 55cc engine is way too small. The noise is from the ripping prop tips. Try a Xoar 23X10.

DoubleDD

Have a Brisson 3.2 in a 30% Edge and ran a carbon fibre 22x10 and changed to a Vess 23B. Power curve much better. Prop noise is gone and also gives a more natural sound in flight. Vess is the way to go.