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Actually, Tracy I agree with Paul on that matter as well - amazing, we both
do! {:>). But, in any case, you can treat the rotary as a 160 CID 4 cycle 4
cylinder or a 80 CID 2 cycle 2 cylinder equivalent.
Since the rotary (2 rotor) fires twice in 360 of the E shaft or four firings
in 720 degrees (720 deg of course being that required for a reciprocating 4
cycle to make it through all 4 cycles of a four cylinders engine) you can
treat it as either one for some purposes. For example
Take the familiar equation for 4 cycle reciprocating engines for air flow
Air flow CFM = (Total Cubic Inch Displacement) x RPM/(1728*2)
1728 changing the CID to CFM. The 2 divisor because only 1/2 of the
cylinders (or 1/2 the total CID displacement) fire in a 4 cycle
reciprocating engine each 360 turn of the crankshaft, it thereby taking 720
deg before all cylinders fire.
1. From a rotor perspective, a 2 rotor will pump (3faces x 2rotors x 40 CID
displacement) x rpm (rotor rpm) /1728 = CFM. Which at 6000 rpm e shaft =
240*2000 (rotor rpm)/1728 = 278 CFM. Note: We don't divide by "2" as
equation above would suggest as we are treating this as a 2 cycle since 2
rotor faces fire for each 360 of the e shaft just as a 2 cylinder 2 cycle
reciprocating engine would do.
2. If you disregard the rotors rpm and just take its displacement as a two
cycle (2 firings 360 deg e shaft)
At 6000 rpm e shaft = 2*40*e shaft rpm/1728 = 80*6000/1728 = 278 CFM again,
don't divide by the "2" as we are treating it as a 2 cycle.
3. Or if you treat it as a 4 cylinder 4 cycle, the traditional
reciprocating engine approach, then
= (4 x40)*eshaft rpm/(1728*2) = 160*6000/(1728 * 2) = 960,000/(1728 *2) =
278 CFM. For the 4 cycle 4 cylinder reciprocating engine each cylinder
fires on every other stroke, so must divide by the "2"in this case.
So all 4 representations give you the same air flow or power for the engine,
so for some purposes (but not all) you can treat the 2 rotor engine in
several ways (no wonder it can get confusing).
The rotary is of course NOT a two cycle engine as it goes through a 4
cycles, intake, compression, power and exhaust, but it manages to do it in a
single 360 deg turn of the e shaft instead of 720degs as a 4 cycle
reciprociating engine would require. So for air flow/power calculations you
can treat both similarly.
So as I see it we can look at the 2 rotor engine as follows::
1.Three(3) faces on two(2) rotors of 40 CID displacement rotating at rotor
rpm (1/3 eccentric shaft rpm)
Air Flow CFM =No. Faces *No. Rotors * CID(1 face) * rotor rpm/1728
2. Two (2) cylinders of 40 CID displacement acting like a 2 cylinder 2
stroke (this is what the turbo program does)
Air Flow CFM = No. Cylinders * CID (1 Cylinder)* e shaft rpm/1728
3. Four (4) cylinder of 40 CID displacement acting like a 4 clinker 4
cycle.
Air Flow CFM = No. Cylinder * CID (1 cylinder) * e shaft rpm/ (1728 * 2)
must divide by the 2 here.
So there you have it. Either representation can be used for the rotor, just
some are more convient for some purposes than others. Paul, for instance
apparently can't stand anyone taking about the rotary in terms of the rotor
revolution for some reason. But, I find it useful/essential for
understanding some things about the rotary.
I know you many folks already know all this, but for some it may be still
confusing and I hope I have not added to that confusion.
Ed Anderson
Subject: [FlyRotary] Re: Turbo Calculator for the Rotary engine.
> Ed,
> Sounds like a must-have program if you are contemplating a turbo
> installation.
> I'm surprised it works correctly with 80 CID plugged in. One of the few
> things I have agreed with Paul Lamar on is that the 13B is equivalent to a
> 160 CI 4 cyl piston engine in terms of CFM of intake & exhaust volume.
> Perhaps the program is aware of the characteristics of the rotary and
knows
> this relationship?
>
> Tracy
>
> ----- Original Message -----
> From: "Ed Anderson" <eanderson@carolina.rr.com>
>
> >
> > You do have to give the program an NA starting point like 80 CID and
160HP
> > for the rotary. I've checked a couple of the numbers and they come out
> > correct.
> >
> > Ed Anderson
> > Matthews, NC
> > RV-6A N494BW
> > eanderson@carolina.rr.com
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
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