Quiet Flight

Homebuilt Aircraft & Kit Plane Forum

Help Support Homebuilt Aircraft & Kit Plane Forum:

autoreply

Well-Known Member
Joined
Jul 7, 2009
Messages
10,765
Location
Rotterdam, Netherlands
As far as I know (I'm not a silencer-geek) the main problem in muffling motorcycles (and cars) is the different speeds and loads the engine revs at. Isn't there a way to simply make use of that (fine tune it for one speed) to make a very quit engine?
 

David and Goliath

New Member
Joined
May 11, 2010
Messages
1
Location
Coupeville, WA / USA
Update on the Quiet Star at Skagit airport. It is going to the Boeing Air Museum this summer. I know this because I spoke to the owner of the aircraft, telling him of my intention to steal the airplane and restore it. The agreement with the museum was made only a month before my call to him.

The muffling system on this plane is truly exceptional. The plane was virtually silent from any distance more than 200-300 feet. The "muffler" system is about 12 feet long and covered with a large insulated chamber that mixed ambient air from outside with the pulses coming through a muffler chamber then exiting via a piccolo tube. It is quite impressive. In addition to the quieting effect of this system, its tail-aspect IR signature must have been both diffuse and very very low. The YO-3 was way ahead of its time on many levels.

It is good to see this airplane will be restored and put on display in a great home. As the final custodial agent for the last F-4 Phantoms in the U.S. inventory (four of which were demiled for use as targets on the FRTC bombing range, the fifth is on display on the USS Midway) it is good to know others will get to see this marvelous bird.
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
15,217
Location
Port Townsend WA
A friend told me that the YO-3 was used in Vietnam to land unseen and unheard at night on back roads. Can you imagine landing on a road at night... with 60 feet of span.
 

DarylP

Well-Known Member
Joined
Mar 22, 2010
Messages
352
Location
CO

DarylP

Well-Known Member
Joined
Mar 22, 2010
Messages
352
Location
CO
A big, slow turning prop is quieter than a mall, fast turning prop.
-Dana
Not from what I have read. According to Areo Sound shield and tests they ran, the long two bladed props were much louder. The reason is, according to good sources, loading is where half the sound comes from, while the thickness of the blade is the rest.

I saw an engine (not an aircraft engine) that used a gas expansion chamber, that allowed all the pressure to stabilize before exiting to the exhaust. I think that Swiss muffler idea is real close to what you could do to get a really quiet plane. Inside sound is another matter, but having the exhaust dumping out right under the cabin causes a lot of noise in the cabin, so having a long exhaust tube under the cabin would really help with that too.
 

DarylP

Well-Known Member
Joined
Mar 22, 2010
Messages
352
Location
CO
I have been waiting for just the right moment to revolutionary muffler design. Basically the design takes each exhaust pulse and causes it to be divided up into numerous micro pulses that are released one at a time, over a period of time.

Because fluid flow is similar in many ways to the flow of electricity for descriptive purposes. I can describe this muffler as a phase splitter and capacitor. The phase splitting happens by causing the sound shock wave to travel through a long perforated tube. It takes time for the pulse to travel the length of the tube. A small amount of that pulse is released each time it passes over a hole. By the time the pulse reaches the end of the tube, the pulse should have been disipated. At the outlet, those micro pulses are of much less amplitude than the original pulse, and the frequency of the pulses are an order of magnitude higher, i.e. smoother.

Traditional mufflers primarily rely on a mumbo-jumbo system of baffles and/or acoustic material to convert shock wave energy into heat by shear flow and friction.

My design relies primarily on taking big pulses and splitting them up into little ones and spreading them out over time.

I believe the greatest noise reduction will result from a combination of the two methods...phase splitting within an acoustic chamber.

This is all theory, to be tested in a few years when I get to that point in the construction of my machine.

Noise reduction is very important to me because I have lost some hearing already. It's especially noticable in noisy environments which make it difficult for me to hear conversations when it is relatively easy for others.

You are totally on the right track.
 

Hot Wings

Grumpy Cynic
HBA Supporter
Log Member
Joined
Nov 14, 2009
Messages
7,934
Location
Rocky Mountains
You are totally on the right track.
Yes, I think he is.

Years ago I used similar theory in the construction of experimental silencers for a 9mm. They were light weight, had no packing or wipers, good heat dissipation, low volume, and were very quiet in full auto mode. Didn't work well in single shot mode and the project got scrapped due to lack of market, and too much BATF paper work.

Since aircraft engines aren't very often operated in single shot mode the idea may have merit for aircraft exhaust and could be worth the time to try someday. I might have some spare time around 2017:tired:
 

rtfm

Well-Known Member
Joined
Jan 3, 2008
Messages
3,649
Location
Brisbane, Australia
I have been waiting for just the right moment to revolutionary muffler design. Basically the design takes each exhaust pulse and causes it to be divided up into numerous micro pulses that are released one at a time, over a period of time.
Gotta say, mate - this sounds very simple and elegant. Kudos.

Duncan
 

GESchwarz

Well-Known Member
Joined
Oct 23, 2007
Messages
1,179
Location
Ventura County, California, USofA.
Dave,

This is the first I've heard of the Quiet Star. I would sure like to learn more about that muffler. It sounds similar to my design, except that the flow through my design reverses direction through the outer tube. This effectively doubles the length/effect of the piccolo tube.

Are there any web sites in particular where I can learn more about the muffler of the Quiet Star.

The piccolo tube is the first half of my design. The second half is to incase the piccolo tube in a larger diameter tube. The downstream end of the piccolo is capped off. The outer tube is capped off at the same location. The exhaust end of the large tube is about where the piccolo tube enters the large tube. The effect of this is that a single exhaust pulse from the engine will begin to escape from the assembly through the first hole in the piccolo tube which is very near the large diameter exit. The last part of the pulse will exit through the most downstream hole of the piccolo tube...that last part must travel all the way back up the length of the large tube in order to exit to the atmosphere.
 

GESchwarz

Well-Known Member
Joined
Oct 23, 2007
Messages
1,179
Location
Ventura County, California, USofA.
I just did some looking into this and learned that most of the exhaust noise reduction on the YO-3 was with the help of a large automotive muffler. Although the piccolo by itself is a a form of muffler, in this design it appears as though the piccolo tube was used primarilly for mixing with ambient air to get the temperature down.
 

GESchwarz

Well-Known Member
Joined
Oct 23, 2007
Messages
1,179
Location
Ventura County, California, USofA.
Duncan, It will be awhile before I'll be cranking up my rotary, but I have been noticing the sorry state of the muffler on my lawn edger. I may take a little time out from my work on the aeroplane to fabricate a scaled down prototype of the Schwarzpipe and stick it on that Briggs & Stratton and see how it does.

I think I'm going to go out and look at that thing right now.
 

rtfm

Well-Known Member
Joined
Jan 3, 2008
Messages
3,649
Location
Brisbane, Australia
Excellent. An engine is an engine for the purposes of the proof of concept. We want video with lots of sound... :)
Duncan
 

GESchwarz

Well-Known Member
Joined
Oct 23, 2007
Messages
1,179
Location
Ventura County, California, USofA.
Already I have run the edger with the existing muffler. I captured the run with a digital camcorder at a distance of 2 feet. The RPM was measured using a photoelectric meter I picked up years ago. It's nice to have these tools put away where I can find them. I then removed the old muffler to learn what I need to mate to the engine (1/2" pipe thread; that's easy). In the next day or so I'll assemble the materials to weld up some rudimentary prototype mufflers. I just wish I had a better device for measuring or comparing sound levels besides a camcorder.
 

rtfm

Well-Known Member
Joined
Jan 3, 2008
Messages
3,649
Location
Brisbane, Australia
Great news... I really think this might work. If the initial camcorder test is promising, perhaps a more controlled test can be conducted later. Good luck.

Duncan
 

BBerson

Light Plane Philosopher
HBA Supporter
Joined
Dec 16, 2007
Messages
15,217
Location
Port Townsend WA
I have a Radio Shack sound meter. I think they are about $35, but I might be wrong about the price because it was a birthday gift. (a little hint sometimes works)
 
Top