George;
I did some similar calculations, but I –
as Joe is doing – have a tangential manifold muffler which significantly
spreads the pulses. So I did some sort of velocity calculations and chose 2 ¾”
for its outlet. A bit further downstream I have secondary muffler, I guess it
could be called a pulse dampener; which quiets things down another half dozen DBs,
or so. For convenience I kept the same outlet dia., but probably have reduced a bit more for a couple
more DB with little effect on back pressure since the length from there is very
short.
FWIW,
Al G
-----Original Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of George Lendich
Sent: Sunday, May 17, 2009 10:41
PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: 20b
Exhaust
The reason I ask is that I like to
keep the muffler outlet the same area size or a little bigger than the exhaust
outlet in the rotor housing which is usually about 2" dia.
I do understand the 2 and 3 rotors
are staged and the exhaust and the exhaust (shock) waves are in
sequence, but I like to keep the volume of the muffler and muffler exit to the
total of the rotor exits i.e. 3x Pi.r squared (3x Pi 1 x 1) = 9.2 sq" or
Radius of 1.71" = Dia of 3.42".
I thought 2.25 may have a little too
much back pressure, as the rotary doesn't like back pressure.
Probably to do this exercise
properly would be to calculate the volume of the heated and expanded exhaust
gases and calculate the timing of the pulses to see how a particular sized
muffler and exit size coped with the speed and volume of flow. It would be an
interesting exercise.
Too
soon to say really. I have not even had time to assemble the builders log
to get ready for the DAR. Lack of engine power is definitely not what is
keeping this thing grounded though : )
Tracy
On Sun, May 17, 2009 at 6:01 PM, George Lendich <lendich@aanet.com.au> wrote:
Any significant back pressure to
speak of?
----- Original Message -----
Sent: Monday, May
18, 2009 12:11 AM
Subject: [FlyRotary]
Re: 20b Exhaust
In
general, the bigger the exit pipe, the louder the exhaust will be. I used
2.25" which I think is about the minimum for a 20B.
Tracy
On Sat, May 16, 2009 at 9:28 AM, <jewen@comporium.net>
wrote:
I have fabricated my exhaust manifold/tangential
muffler for my 20b. All I have left is to fit and weld the exhaust pipe.
I would like opinions on the size the exhaust pipe should be. This
is in a pusher application (Velocity) with a relatively short run from the
muffler to the exit point. Similar installation to Al G.
Thanks,
Joe
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