Quiet Flight

[delta]

It's kind of humbling to see the scope of Kelly's work.

Rick

 

[GESchwarz]

GESchwarz,

Any updates/news on the exhaust system?

Trying to figure out how I'm going to do something similar on my O-320Lycoming.

Thanks

Max, No, I think that's about it. Those two devices, the centrifuge and the piccolotube individually are effective in their own right, and combined the effect is absolutesilence. You look at the way a typicalmuffler is designed and all they aredoing is some random baffling in an attempt to break down the exhaust pulses byshear turbulence, which in itself generates its own noise, and some canceling. The centrifuge sends the pulses to the circumference ofthe can and venting from the center of the vortex where the pulses are weak. The piccolo with the reverse flow jacket takes each pulse and cuts it up into little pieces and spreads it over time; so instead of hearing one big “pop”, you hear lots of very small pops.

 

[fadec]

There's a YO-3a for sale for 85K:

I was considering this project a while back but decided to leave it for someone with deeper pockets, not to mention the shear hassle of trying to get a warbird out of the US these days.

Stan Hall of sailplane fame was the airframe design manager for the YO-3A. Not sure how much input Kelly Johnson had as it was developed away from the main skunk works.

On a practical level the pilot flies from the rear seat so the view fwd isn't as good as it could be.

 

[pictsidhe]

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:

That'd be now, how's it going?

 

[TFF]

Stardate 11232017; we have gone back in time to the year 2012. Our concern is accidentally altering the timeline of people using the search function...

 

[pictsidhe]

Marty, you have to go back to September 1945 and give Fred Trump a condom!

 

[Hot Wings]

That'd be now, how's it going?

Filled with other projects. The beavers keep fixing the dam...........Makes it hard to drain the pond.

 

[BJC]

Marty, you have to go back to September 1945 and give Fred Trump a condom!

Back in the 1980’s prince Charles was in the news for learning aerobatics in a Chipmunk. He was invited to come across the pond and participate in an aerobatic contest, but he was a no-show. I won’t say any more about his family, since I’m not British.


BJC

 

[Victor Bravo]

Marty, you have to go back to September 1945 and give Fred Trump a condom!

Might as well have him take that time machine back 50 or 60 years and fix a few problems on the other side of the aisle as well. At least with the current (imperfect) situation, the pendulum is swinging back toward the middle where things are in balance, instead of further off the rails in the direction it had been going. Maybe his time machine can go into the future a few years and stop the pendulum from swinging too far in either direction, eh?

Uh Oh... what's that red dot doing on my chest?

 

[pictsidhe]

That's a sign of the times, VB!

 

[MolsonB]

Here's a picture of my Mazda Renesis Rotary 3-port exhaust manifold that I've trimmed to accept the "can" in which the exhaust pulses will spin around the circumference while the flow exits the can through a perforated pipe (not shown in this photo) that runs down the center of the can.

I'm going to build this in Jan. Just sourcing out the 321. Did you end up going with 5"? 4" is all I can find so far, in either 16ga or 20ga.

 

[pictsidhe]

I'm going to build this in Jan. Just sourcing out the 321. Did you end up going with 5"? 4" is all I can find so far, in either 16ga or 20ga.

Mufflers are best concocted with witchcraft and luck: Test with mild and scrap whatever. When you get something that works, then go hunt the stainless.

 

[MolsonB]

I quickly put a sketch together. I'm assuming the holes in the inner pipe, you want the area to be twice the area of the exiting pipe. 2.5" in my case. And will try not to put the holes in the path of the primaries. Let it swirl around first before getting pushed out the middle.

Couldn't find any 321 in 5" tube (probably 0.050 thick), so will buy a flat plate from McMaster-Carr and put in the rollers. Any one else have a good source for 321?

 

[lr27]

I'm sure all this stuff has been worked out completely, and someone knows how to make really good mufflers without a lot of testing. Or, at least, not a lot of testing once the engine has been characterized. I'm pretty sure mufflers can be tuned to work best at a particular rpm. Probably the rpm at a full power climb would be best if you're trying to save the airport.
Here is an exploded diagram of a muffler which I know from previous experience is very quiet:
https://www.rcuniverse.com/forum/glow-engines-114/10993462-k-b-sportster-club.html?styleid=7#&gid=1&pid=1
The Sportster 20 had problems, but noise wasn't one of them.
The model airplane guys have been messing around with "mousse can" mufflers for years. That's not my part of the hobby, but I think some of them have hit on some methods for making quite mufflers that aren't too complicated. Plus some rough calculations to determine dimensions based on rpm. Unfortunately, I can't remember where I saw the latter. Keep in mind that adding cylinders is like increasing the rpm, and going from two to four stroke may be like halving the rpm. Anyway, I'm sure someone with more patience than me can find this.

----------------

If I was making some kind of cockpit lining with two layers of aluminum, I'd consider joining them with foam tape with acrylic adhesive. 3M claims that some truck trailer bodies are assembled with their version of this stuff. Specs imply that aluminum is the ideal surface. I think the foam is made of silicone, but I'm not sure. I might also look into using their transfer tape, which is the same adhesive without a carrier, and making cork tape to join the two panels. It may be a good idea to have mechanical fasteners at the ends of the tape to prevent peeling.

I seem to recall reading about airplanes (a particular version of the King Air?) that use some kind of resonant device to quite the inside panels. Apparently, they can be tuned so that the panel will have very little response at the desired frequency. One of the few things I remember from the vibrations course I took was that you can tune systems to do this. Also, that pickup truck manufacturers had figured this out so they could make commercials like this one:

no need to turn the sound on. You may want to start at 27 seconds.

 

[lr27]

Looks like it doesn't start at 27 seconds, like I wanted it to. That's when the fun begins.

 

[Spencer Fisher]

Hey Molson, I do not claim to be a thermodynamic engineer but my gut tells me that design is going to result in back pressure IMMEDIATELY. The rotating flow is going to create a high pressure directed out from the center, so not much flow is going to go through the holes in the center.

That being said I think a centrifugal muffler design is very interesting. I think you'll need to bleed off flow from the outside however.

 

[Bill Welter]

I built a muffler for my 13B, had the exhaust come out of the ports into two circular pipes. One pipe was pointed clockwise, the other pointed CCW, so the exhaust from one port would come round and the sound waves would hit the sound waves from the other port head on. They would theoretically cancel each other out. Then the exhaust gas would go out a few perforated tubes like your drawing. It worked well, but was too big to fit under my LongEZ cowl if I had sufficient insulation. On a Cozy it might have worked since there's more under-cowl room. Yours will work, just make the holes in the tube big enough to not restrict flow. Then you'll need to find some really good insulation

 

[Sockmonkey]

I kinda wanna stick that vortex muffler out in the airstream with a merideth shroud around it so it can produce some auxiliary thrust.

 

[rv7charlie]

I kinda wanna stick that vortex muffler out in the airstream with a merideth shroud around it so it can produce some auxiliary thrust.

Extremely unlikely that it will help; extremely likely that it'll cost several knots. True Merideth effect is so difficult that it approaches myth.

 

[Sockmonkey]

Extremely unlikely that it will help; extremely likely that it'll cost several knots. True Merideth effect is so difficult that it approaches myth.

Ordinarily yes, but with the exhaust flow blasting out the back it's acting like a shrouded pulse jet.