From: peon@pacific.net.au
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Date: Wed, 8 Oct 2003 04:48:26 +1000
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Subject: Re: True Displacement of the 13B rotary Egnine
Reply-to: leon@aerota.com
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Hi Guys,

Feel I have to butt in here.   Don't know where whoever came up 
with 321 cc for a 13B chamber swept volume.  Not so I'm afraid. 
Tracey (and Ayn Rand) are right,  "Check your premises" or when 
all else fails,  RTWM (read the workshop manual!). 

The factory manual says they have a swept chamber volume of  
654 cc each.  That makes it 1308 cc for a 2 rotor 13B and 1962 cc 
for a 3 rotor 20B.  

Interrstingly,  like a 2 Stroke,  the Wankel Cycle gives you one 
power pulse (and one suck) per rev per rotor/chamber/pot.  So 
every rev,  a 13B engine (notionally - they tend to have better than 
100 % V.E at higher RPM.) sux 1308  cc of air,  or 2616 cc every 
two revs (to compare what it does to a 4 stroke).  Further,  if fuel 
flow is considered,  a NA 13B uses 4 x 400 cc injectors - about the 
same as a 2.5 Litre 4 cylinder engine.  So both must be using the 
same amount of air??

This is where the arguments start.  Notionally this would make a 
13B equivalent to a 1308 cc 2 stroke or a 2616 cc Otto Cycle (4 
Stroke) engine.

To confirm (sort of) this notion,  and to try to get some sort of 
performance equivalency,  even our local racing sanctioning body, 
CAMS,  bless their little nomex balaclavas,  understands this (sort 
of - they slavishly follow the FIA - which has banned rotary engines 
at Le Mans).  

The CAMS (Confederation of Australian Motor Sport) has therefore 
deemed in its inestimable wisdom that we use a (somewhat 
generous in my opinion) factor of 1.8 times swept volume to (sort 
of) level the racing circuit. (it doesn't - Improved Production is still 
"Rotary Rules" and always has been).

That puts a 13B into the 2 - 3 Litre category (1308 x 1.8 = 2354 
cc), and the 20B in the Over 3 L category ( 1962 x 1.8 = 3532 cc).

Even at a straight 2.0 multilcation factor,  that makes a 13B 2616 
cc,  and a 20B 3934 cc.  Now we COULD argue on this all day, 
(and some people will contnue to perrsist) but in the final analysis,  
the power output is all that really matters,  and will give a rough 
guide to capacity equivalence  (as must air flow and fuel use).

Currently,  any number of good injected 13B bridgeports here in Oz 
 are making in excess of 320 BHP at around 9,500 RPM (I've seen 
350 quoted at over 10,000 RPM - but they tend to not last very 
long).  

The new Renesis engine is making about 240 BHP @ around 
8,500 RPM, (and that's "in the car" - blowing though cat convertors 
and road legal mufflers).  So both types of engines get over 100 
BHP per litre irespective of the porting.  Not bad for an engine that 
weighs in around 120 Kgs wringing wet and fully dressed!

Cheers,

Leon

On 7 Oct 2003, at 10:56, Tracy Crook wrote:

> 
> Always risky to shoot off my mouth before checking for hard facts but
> just from seat of the pants estimates, I'd say the argument rests on
> the accuracy of that single chamber displacement, which was stated as
> 321cc or 19.95 ci. Don't have time to run downstairs and measure the
> actual volume right now but I'd be willing to bet that the
> displacement is more like double that figure.   If this is not true,
> then it would take magic for the 13B to make 180 HP at 6000 rpm.
> 
> As Ayn Rand once said, "There are no contradictions.  If you think you
> see one, check your premis".
> 
> Tracy
> 
> ----- Original Message ----- 
> From: "Ed Anderson" <eanderson@carolina.rr.com>
> To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
> Sent: Tuesday, October 07, 2003 8:56 AM
> Subject: [FlyRotary] True Displacement of the 13B rotary Egnine
> 
> 
> > Ok, guys
> >
> > Time to stir up the pot {:>)
> >
> > If ever there has been something that seems destined to invoke
> > debate and heated argument, it's the issue of the true displacement
> > of the 13B twin rotor Mazda Engine.
> >
> > The official Mazda figure listed for displacement is 1308 cubic
> centimeters
> > for the two rotor 13B model.  However, you may have also heard it
> > characterized as either a 2 cylinder 2 stroke of 80 CID or a 4
> > cylinder 4 stroke of 160 CID displacement.  In reality - none of the
> > above is technically correct, to find out just why this is so, read
> > on:
> >
> > For the 13B engine model, each rotor chamber displaces approx 19.95
> > cubic inches (321 cubic centimeters); there are 3 chambers per rotor
> > and 2
> rotors.
> > That means that in one complete cycle of the rotary engine's six
> > chambers the total displacement is 19.95*3*2 = 120 CID or 1966cc. So
> > where did the 1308cc figure come from?  Where did the 80 CID and 160
> > CID figures come from?
> >
> >  The problem arose when Mazda wanted to provide folks with something
> > familiar to compare the rotary engine with (and perhaps as some
> > folks have suggested artificially reduce the displacement to attain
> > a more favorable tax bracket for a Japanese auto engine).  To fire
> > all six chambers (the rotary's full engine cycle)  takes 1080
> > degrees revolution of the
> eccentric
> > shaft compared to 720 degrees for the full engine cyle of  a  4
> > stroke automobile reciprocating engine.  The 720 deg for a complete
> > 4 stroke
> cycle
> > is the standard for automobile reciprocating engines.  For
> > apparently this reason, Mazda decided to truncate the 1080 degrees
> > of  the full rotary engine cycle to the 720 deg of the standard, 4
> > stroke auto engine - for comparison purposes.  After all, the
> > potential rotary customer would inevitably want to compare the
> > rotary engine to something they were
> familiar
> > with.
> >
> > Well, it turns out that 720 deg is 2/3 of the 13B 1080 degree engine
> cycle.
> > So 2/3 of 120 CID (its actually displacement in its full cycle) = 80
> > CID
> or
> > 1308cc.  This truncation of the rotary's full cycle then became the
> standard
> > reference.  For most purposes this serves just fine as most folks
> implicitly
> > are comparing engines to the 720 deg standard cycle of the
> > reciprocating 4 stroke.  However, one can ask the question of
> > whether you would take 3/4
> of
> > a standard 720 deg 4 stroke engine cycle as a valid basic for
> > comparison.
> I
> > think most would say, "Hey, you can't do that".   If you took an 8
> cylinder
> > reciprocating engine and told someone that you were going to compare
> > it to another engine but would only consider 6 of its cylinders in
> > the
> comparison,
> > most folks would say you are placing the engine at a disadvantage in
> > the comparison.
> >
> > Yet, that is indeed the equivalent of what was done to the
> > displacement of the rotary engine to provide a basis for comparison.
> >
> > Others pointed out that if  you looked at the rotary as a piston
> > engine, then you get the equivalent airflow (and internal combustion
> > engines are nothing more than exotic air pumps) by treating the
> > rotary as either a 2 cylinder 2 stroke of 80 CID displacement or a 4
> > cylinder 4 stroke of 160 CID.  Again, the full cycle of the rotary
> > (1080 deg) is truncated to
> provide
> > a basis of comparison to those engines with which we are most
> > familiar. Indeed, this will not change as it does provide a valid
> > base for comparing the power of the rotary engine with its 
> > reciprocating cousins.   However, just because it is a convenient
> > and not altogether misleading manner of comparison does not mean
> > those figures are the true displacement of the
> 120
> > CID rotary engine.
> >
> > In the end, like most arguments of this type, it really doesn't make
> > a bit of difference.  The rotary engine is blithely unaware of the
> > liberties
> taken
> > with its displacement and could probably care less if it did know. 
> > But, every once in awhile the record needs to be place on notice of
> > the correct facts.  The 13B displaces approx 120 cubic inches over
> > its complete engine cycle or 80 CID over 2/3 of its complete cycle -
> > your choice {:>).
> >
> > FWIW
> >
> > Ed Anderson
> > RV-6A N494BW Rotary Powered
> > Matthews, NC
> > eanderson@carolina.rr.com
> >
> >
> >
> > >>  Homepage:  http://www.flyrotary.com/
> > >>  Archive:   http://lancaironline.net/lists/flyrotary/List.html
> >
> 
> >>  Homepage:  http://www.flyrotary.com/
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