321 stainless megaphone muffler design
 

Thanks for your thoughts on this matter. I have a muffler design I’d like to share and on which I’d REALLY like to hear your thoughts-n-feedback. I have an aviation application where aerodynamics, durability and sound attenuation are key to my success. My exhaust layout consists of two, two inch primaries merged into a two-into-one merge collector (after a 90degree direction change) that then hits a 2.5" ball joint. After the ball joint I have an Inconel 625 inline exhaust baffle. Then a 48-ish degree exhaust gas direction change happens where the exhaust gases will hit my muffler that is outside the cowling of the aircraft. I’ve been looking around for a muffler type that would BOTH be aerodynamic AND durable in the 13b, exhaust gasses as the “flames of Dante” exhaust environment. I believe a megaphone type design would be acceptably aerodynamic *AND*, if it were made from 321SS, be plenty durable enough. To that end, please take a look at my line drawings at http://tripleaser.com/images/reverseCone.jpg and lend me your wisdom. I’d like to know if A) you think the internal cones in the muffler will survive at roughly 19” from the exhaust port opening AFTER the exhaust gasses have already been molested by the Inconel 625 exhaust baffle and having made both a 90degree and 48-ish degree direction turn and B) do you think the sound attenuation would be acceptable for street driving if this design were in a street car. Thanks in advance for your feedback and wisdom.

-J

link returns "forbidden"

Megaphone
 

Well ... in that case how about this attached version. Thanks for taking a look.

-J

Interesting design. It might work. One way to find out. Since this is in a plane I assume you've see the ACRE website?

http://rotaryeng.net/

rotarygod ... I have seen that website. It's provided me much info in this journey of mine. In my muffler design the thing I'm MOST worried about is that it quiets things down. On the power side I have plenty of that to spare so a little flow restriction won't bother things too much. This is why further up in the stack I have an in-line Inconel 625 exhaust baffle. I just want to make sure that after flying I’ll still be able to hear. Any design considerations you think I should observe that I’ve missed? Also …. 321 sheet is getting hard to find. You see any problem using HaselloyX as my sheet material? Thanks for your reply.

-J

I see that still being very loud. A megaphone by design is going to amplify noise. Yes you have muffler packing but only an inch deep. That's not very much. There are lots of rotaries running around on the street that have dual straight through mufflers with a smaller open area than your design that allows more wall to area and also have a couple of inches thick of packing and they are still extremely loud. I see your design being quieter than having no packing but not so much that it isn't still an incredible amount. Then again I've never actually heard a muffler of that design but all things tell me it's going to be very very loud. I'd try building a cheap mockup out of mild steel first just to hear it and see how it works. You don't need to fly with it but at least you won't have tons of money invested in it if it doesn't work. It's also very easy to weld and work with.

How much room do you have to work with? Is this going to be under the cowl or out in the airstream under the plane? Do you have any room to integrate a muffler into the manifold itself at the engine?

rotarygod ... I think you're right. It was a nice thought process but after reading the board and tallying how many times various mufflers were mentioned in a positive "I love my muffler" reference I've decided to go with a 304SS Borla unit with that has the High tem ceramic packing. Sure .... it'll be an odd shape hung under my fuselage but ... I'll be able to hear after every flight. Thanks for your wisdom on this matter.

-J

In case you're wondering ... the model I convinced my wife to buy me for my belated Christmas present is the Borla model -> http://www.jegs.com/i/Borla/157/4066...oductId=744680

We had a Lockheed YO-3 at New Orleans Lakefront Airport that was used by the La Wildlife and Fisheries. It was so quiet that all you could was wind noise as it passed!

As I remember it had a long regular type exhaust pipe and muffler faired into the fuselage.

Your design looks more like a Krisman type 2-stroke spark arrestor.
I would add a support to the front of the cone.

Here is a link to the plane. No muffler pictures were noticed at first glance.
Barry

http://www.google.com/url?sa=t&rct=j...BANc2iNmeU53lg

Here's the Borla Turbo Series Stainless Steel Muffler I chose
 

All,

Here's a pic of the Boral I chose and the place from whence I ordered it. Enjoy.

-J

Didn't you have a different thread on the previous original design? I can't seem to find it.


edit: here is the other thread: https://www.rx7club.com/general-rotary-tech-support-11/321-stainless-extreme-heat-exhaust-978757/


I'm surprised you didn't go with the round version of the Borla. You could have installed a rolled /tapered nose cone on the front (and rear too) to make it a bit more aerodynamic.

the megaphone was a total waste with the internal baffle. The whole point is to enhance power out put through exhaust pulse dynamics, which the baffle completely destroys and it's only sound value is to be loud as freaking hades. They are basically on their way out of racing due to sound restrictions.

.

TeamRX8 .... yea, I snapped to the idea that the megaphone would have given me ear bleeds. On your question regarding the other thread, that thread was dedicated to my choice of materials for an internal, in exhaust stream baffle and NOT to the muffler itself. In that thread we see my design for the baffle I chose to implement AND we learn about the material I chose for such a blazingly hot part. I thought about combining both thoughts into one but since one thought involved 100% life INSIDE Dante's inferno and the other thought involved a large sound dampening cavity stuffed with sound absorbing material I decided to keep them separate. Thanks for your reply.

-J