flyrotary@lancaironline.net Mailing List Archive

Hi Neil,

To save Bill some time, here ya go:

https://en.wikipedia.org/wiki/Helmholtz_resonance

https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=helmholtz%20resonator

If you've ever blown across the mouth of a bottle to hear it resonate, that's an example. A ported loudspeaker enclosure is another. Most intake manifolds these days have them somewhere in there, as well; sometimes for induction tuning, other times to silence the noise of the intake.

Many years ago, Monty Roberts & I played around with a real time spectrum analyzer at one of Tracy Crook's flyins with the (stillborn) goal of doing what Bill's group has apparently accomplished.

There are other ways to strip off the nasty high frequencies, but most of them are heavy. A builder here in the USA once ran a stock cast iron manifold without a muffler (just a ~8" stub pipe on the end) on a canard pusher, and it had a very pleasant sound similar to a small block V-8.

Charlie

On 10/17/2016 6:38 PM, Neil Unger wrote:

Bill, what are Helmholtz principles?? The muffler at 6000 rpm was so quiet it does not even sound like a rotary. Do you have diagram of a description?? Allow that I am an idiot so all details needed. Neil.

On 10/18/2016 10:34 AM, William Jepson wrote:

Neil,
The muffler in the video. It was designed using Helmholtz principles and it works very well at reducing the high frequencies from the rotary.

Bill

On Mon, Oct 17, 2016 at 4:18 PM, Neil Unger <flyrotary@lancaironline.net> wrote:

Bill, Now you have got my interest, What muffler and where?? Everything else on the Rotary can be handled, Cooling, mounting, P porting etc, but mufflers have me beaten. They are the next for me to investigate particularly how to keep small if possible, The size in most cases affects how the engine mount can be constructed on that side.

Thanks in anticip[ation, Neil.

On 10/18/2016 9:58 AM, William Jepson wrote:

Charlie,
Pardon my haste in the original reply. The butterflies are very similar to the original, with the exception that we have devised a new way to make them that doesn't require drilling through the housings. Can't say more right now other than we do NOT use epoxy in the housings and NO sealing problems. Don't expect any. Also we DO NOT weld to the liner as sometimes pushed by others. I do not believe you can weld to the liner without catastrophic failure later. I believe you will either fail your apex seals or crack the weld due to crystallization of the steel. The muffler is a MAJOR win. It is quieter than a unmuffled Lyc, and successfully kills the annoying hi frequencies. It is more restrictive than some but only costs us a few HP. It also fits in an RV-3! I am experimenting with a larger version in hopes of repeating the success with a bit less restriction on cowls that aren't as tight as the RV-3

Bill

On Mon, Oct 17, 2016 at 3:15 PM, Charlie England <flyrotary@lancaironline.net> wrote:

Hi Bill,

Thanks for the link. I've been following it on the Homebuilt Airplanes forum; are you 'billsrv4' over there?

I've been trying to find a throttle mechanism in the video, but don't see one. Are they using the custom 'in the housing' butterflies, like the original Powersport engine?

Have you heard it run in person? If so, does the muffler work as well as it seems to in the video? (Hard to know how much the audio is clipped in level on a recording.)

Thanks,

Charlie

On Mon, Oct 17, 2016 at 4:52 PM, William Jepson <flyrotary@lancaironline.net> wrote:

Since it has been so quiet thought I would make some noise.
Try this package on for size.

https://www.youtube.com/watch?v=EfreUJt-Fsk.

Think you will find it interesting.

Bill