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Al,
Have a look at my velocity calculations and see if
the compare well with yours, of course the real world outcomes are the
proof.
George (down under)
----- Original Message -----
Sent: Tuesday, May 19, 2009 3:47 AM
Subject: [FlyRotary] Re: 20b
Exhaust
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
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