Simple lightweight muffler

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

poormansairforce

Well-Known Member
Joined
Mar 28, 2017
Messages
1,129
Location
Just an Ohioan
So we got the muffler built for my son's go kart with a Predator 212 and it works pretty well. I know this isn't an airplane but it will carry over and since this was being discussed on another thread I thought I would start a new thread rather than take away from that thread.

I took some decibel readings while standing 10' behind the straight pipe. I measured about 80db and after the muffler was mounted it measured about 72db. The sharpness was noticeably muted. The header pipe is SS and measures 1" od and has .6 sq in of area inside. The muffler was made from a 1 1/2" id exhaust pipe joiner section that measures 3 3/4" long. I welded a SS nut to a SS washer that had the same diameter as the header pipe and in turn that was fusion welded to the end of the header pipe with the nut on the inside. One end of the outer can was reamed to slip snuggly over the header pipe and the other end was drilled for a 1/4" SS bolt that holds the muffler onto the end of the header via the nut. The header pipe has 4" straight section after the 90 degree bend that was drilled with 16-1/4" holes in a pattern of 4 rows with 4 holes each. Each row was drilled incrementally 3/16" farther back so the exhaust gets broken up into 16 pulses with each one having to take a different length path to the exhaust port on the bottom front end of the outer can. Another can over the outside of the first can with staged holes would really quite it down. We also could have added to the header pipe length and the extra distance would have toned it down more. It weighs mere ounces. The road had too much traffic to get any speed readings but my son didn't think it hurt the power at all.

Note: This is a brand new engine so he is not running it very hard.

[video=youtube_share;s-EBwXcc918]https://youtu.be/s-EBwXcc918[/video]
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
Interesting baffle. If you bleed energy from a sound wave travelling down a pipe, the first hole will leak more energy than subsequent holes as the wave will decrease in energy as it passes holes. You can balance it by increasing the size of later holes, or using more. The maths and physics to calculate it is a bit nasty, but nothing wrong with taking a guess, probably faster to make test pipes..
 

poormansairforce

Well-Known Member
Joined
Mar 28, 2017
Messages
1,129
Location
Just an Ohioan
Interesting baffle. If you bleed energy from a sound wave travelling down a pipe, the first hole will leak more energy than subsequent holes as the wave will decrease in energy as it passes holes. You can balance it by increasing the size of later holes, or using more. The maths and physics to calculate it is a bit nasty, but nothing wrong with taking a guess, probably faster to make test pipes..
I thought about doing that but didn't feel like rechucking 4 different times. That's an improvement for the next time. For the time being I wanted to see the benefits of staggering the holes.
 

TFF

Well-Known Member
Joined
Apr 28, 2010
Messages
14,741
Location
Memphis, TN
Doing can within a can within a can, reversing direction, can make it quiet that all you will hear is the clutch shoes ringing the housing. Maybe a little steel wool packing in the last can. 10 oz to 16 oz to 24 oz. reversing and expanding is how many people get smaller squirrel cage blowers to run pipe organs without the whoosh sounds or quiet air compressors in small shops. A friend and I made a different than standard race pipe for our race cart. It mostly was a smaller diameter than the regular; I think limited to 18" long. It made a lot more torque but did limit the RPM. we were spinning 5 hp briggs 6000 rpm.
 

poormansairforce

Well-Known Member
Joined
Mar 28, 2017
Messages
1,129
Location
Just an Ohioan
Doing can within a can within a can, reversing direction, can make it quiet that all you will hear is the clutch shoes ringing the housing. Maybe a little steel wool packing in the last can. 10 oz to 16 oz to 24 oz. reversing and expanding is how many people get smaller squirrel cage blowers to run pipe organs without the whoosh sounds or quiet air compressors in small shops. A friend and I made a different than standard race pipe for our race cart. It mostly was a smaller diameter than the regular; I think limited to 18" long. It made a lot more torque but did limit the RPM. we were spinning 5 hp briggs 6000 rpm.
Agreed. An extra can was in the plans if it was too loud but he has been running it around the house and it is not any louder that the GY6 with it's heavy muffler. It's been sitting for 2 years so he is 30 lbs heavier and he said it has more get up and go in the mid range for sure. It handled 2 people better than before so we are good. The top speed still needs to be determined but that's not as important to him.

The pipe organ operations are an interesting idea. Thanks for that.
 

Himat

Well-Known Member
Joined
May 5, 2011
Messages
2,868
Location
Norway
Interesting baffle. If you bleed energy from a sound wave travelling down a pipe, the first hole will leak more energy than subsequent holes as the wave will decrease in energy as it passes holes. You can balance it by increasing the size of later holes, or using more. The maths and physics to calculate it is a bit nasty, but nothing wrong with taking a guess, probably faster to make test pipes..
Looking at it as an energy distribution that will be the answer, yes the first holes bleed of most of the sound energy. The impedance of the ports, or load of the holes in other words, are then not taken into account. Even if the holes are the same diameter and area, the impedance may change with placement relative the ends, walls, geometry and other aspects of the tubes involved. In this example the second row of ports may bleed of just as much energy as the first, but maybe at a different frequency due to the spacing.

I do find this a fine example of an easy built, light and cost effective silencer/muffler.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
Looking at it as an energy distribution that will be the answer, yes the first holes bleed of most of the sound energy. The impedance of the ports, or load of the holes in other words, are then not taken into account. Even if the holes are the same diameter and area, the impedance may change with placement relative the ends, walls, geometry and other aspects of the tubes involved. In this example the second row of ports may bleed of just as much energy as the first, but maybe at a different frequency due to the spacing.

I do find this a fine example of an easy built, light and cost effective silencer/muffler.
"is a bit nasty"
 

choppergirl

Banned
Joined
Jan 30, 2015
Messages
1,682
Location
air-war.org
If you aim the exhaust pipe straight up, the sound wave will not have anything to hit (short of the air molecules itself) to bounce back to the listener and your noise level will be substantially reduced.

So why aren't all exhaust pipes aimed straight up? Rain. Rain going down them right into the cylinder head which leads to rust, hydrolock, etc.

However, when not in use, like an airplane parked in a hanger, or not flying, exhaust pipes pointing straight up could be capped (with a cap that perhaps slides or screws on) to keep out the rain


I discovered this phenomenon when playing around with the idea of designing silencers.

A blank gunshot shot straight up is deathly quiet.

A gunshot shot at the ground at a 45 degree angle, will hit the ground, and bounce upward into space away from the shooter at another 45 degree angle, and also be very quiet to the shooter.

However, a gun shot, shot down range in a forest level, produces a lot of noise, as every tree reflects sound back to the shooter.

A gun shot shot in an open field down range, will be mostly quiet, until the sound wave hits something down range and bounces back to the shooter.

Therefore, my design was to design a silencer that allowed the bullet to go straight forward down range, but the baffle "rings" would be at a 45 degree angle and bounce the sound straight upwards through vertical pipes from the silencer unit. Outdoors, it would work to silence most of the sound by directing it upwards, but indoors, with a ceiling overhead, it would not produce the same leveling of silencing power as the ceiling would reflect the sound back downwards.

Most gun shots however, occur outdoors, so it would be a very effective silencer for the most part, as long as you were not shooting with a canopy of trees overhead.

I've never seen any silencer design do any such thing, attempt to reflect the gunshot sound wave and expanding gases "upwards", so I considered my silencer idea and design rather unique.

~

When I angle my own plane exhaust, I plan to aim it straight up, or perhaps straight up and rearward pointing up and backwards away from the pilot seat. Cover it up when the engine is not flying, as a habit or checklist item, just in the same way you might do other things when you are done flying, like parking the prop at the right angle, draining the gas, etc. You definitel don't want water go down into your cylinder head, as I've seen small engines where that has happened going down the air intake manifold (when the air filter box unit was taken off and left off, and the engine left to the mercy of the elements) and rusted them tight.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
14,968
Location
Port Townsend WA
My tractor exhaust is straight up with a rain guard flapper.
Just make sure the exhaust fumes doesn't hit the pilot.
 

akwrencher

Well-Known Member
HBA Supporter
Joined
Oct 16, 2012
Messages
1,324
Location
Gustavus, AK
My first Comercial fishing boat had a worn out muffler on an old Jimmy diesel, pointing up. Could hear it from miles away until I replaced it. After that, only the noise from the engine was screaming in my ear. Straight pipes are straight pipes, unless turboed.
 

poormansairforce

Well-Known Member
Joined
Mar 28, 2017
Messages
1,129
Location
Just an Ohioan
A blank gunshot shot straight up is deathly quiet.
I have several 12 gauge shotguns and and a 7mm rifle. If you stood anywhere around me when I shoot it straight up you will not be saying that it is "deathly quiet"!

It will help but you still have a pressure wave impacting the atmosphere sending a wave in all directions. Go to a tractor pull with the alkys having straight pipes pointing up. We need to either lower the peak pulse by stringing it into many small ones that arrive at different intervals or use a negative/positive cancellation.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
14,968
Location
Port Townsend WA
VW Beetles have two 8" long silencers clamped on the tailpipe end. I just tried one on my V-twin, it really absorbs the sharp pop.
 

pictsidhe

Well-Known Member
Joined
Jul 15, 2014
Messages
8,812
Location
North Carolina
A regular gunshot has the bullet/shot to bounce the wave off. I've never used blanks, so can't comment on how big the effect is.
Saying that, sound is directional. The problem with tailpipes pointing up is that the small wavefront will encourage diffraction. You will get a few dB reduction, but not 'deathly silence'. A megaphone pointed up would help, but that's bulky, draggy and a rain magnet.
A simple compromise could be an upward kinked tailpipe with a small drain hole.
 

Armilite

Well-Known Member
Joined
Sep 5, 2011
Messages
3,517
Location
AMES, IA USA
A regular gunshot has the bullet/shot to bounce the wave off. I've never used blanks, so can't comment on how big the effect is.
Saying that, sound is directional. The problem with tailpipes pointing up is that the small wavefront will encourage diffraction. You will get a few dB reduction, but not 'deathly silence'. A megaphone pointed up would help, but that's bulky, draggy and a rain magnet.
A simple compromise could be an upward kinked tailpipe with a small drain hole.
===========================================

With a Gun Shot, you have the Sound of the Hammer & Firing Pin Striking the Primmer, the Bolt if Semi/Full Auto, the Hot Gas following the Bullet that hits the Cooler Atmospheric Air, and then the Sonic Crack if the Bullet is traveling roughly over 1150fps, and if it hits a Target Close by, the Sound of Bullet Impact. If Shooting towards the Woods and Shooting Normal Ammo that Sonic Crack can also echo back towards you. Take one of them DB Aps for your Smart Phone. Dry Fire you Gun to get the DB Reading of the Hammmer & Firing Pin. If Semi Auto, pull Slide Back and let go to get that DB Reading. Then Shoot some Normal Rounds and get that DB Reading, then Shoot some Subsonic Rounds and get that DB Reading. If, you live in a State where Suppressors are Leagal, you can also Test their DB Data. Last I new, All 50 States but 6 they are Legal in, but you have to check your State, County, City, Laws. The same goes for Machineguns.

A Muffler and a Suppressor are very similar, they Absorb Heat, and Slow the Hot Gas down to give it Time to Cool, before it exits the Muffler or Suppressor. Each Gun and Motor is different.

This guy puts out some Nice Video Reviews. Here is a 300 black out Suppressed.
https://www.youtube.com/watch?v=Q5ALp8-d3dQ&t=698s

A Pistol
https://www.youtube.com/watch?v=s4qaZATtYiU

See Through Suppressor.
https://www.youtube.com/watch?v=7pOXunRYJIw

What some Suppressors look like inside and what your Typical Mufflers looks like inside. They Both do the same Thing, Absorb Heat, and Slow the Hot Gases down, giving them Time to Cool. If you Noticed, on the Suppressor, you don't see any Hot Flash come out the end. Fire needs Oxygen to Burn. So with a Suppressor you not only lower your Sound Signature, you lower your Flash Signature.
 

Attachments

Last edited:
Top