>      > Help me out here Paul. This is a point that could assist
    > newcomers.
    >      > Perhaps
    >      > a rough explanation proof of this 'equivalent
   displacement' would
    >     be a
    >      > statement akin to:
    >      >
    >      >   " and so if at similar comparative VE the Wankel rotary
    > engine will
    >      > have
    >      > to run at about twice the rpm compared to an RPE to pump
    > (displace)
    >      > the same
    >      > amount of air."
    >      >
    >     Doug,
    >     I wasn't going to say anything anymore.
    >     However, regarding your concern for the new people, above is
   also not
    >     correct.
    >
    >     Both engine run at the same rpm. It is the number one aspect
   to have
    >     equal speed.
    >     Second we have to count two chamber not two rotations of the
    > Rotary to
    >     be equal to the RPE.
    >     I know multiplying it out results in the same, but this would be
    >     incorrect as the rpm number would be double. It is the
    > displacement of
    >     one rotation that needs to be doubled to make things equals
   with the
    >     RPE. That is the same as counting two chamber per rotor.
    >
    >     There is difference between saying we we have to run the
   rotary at
    > twice
    >     the speed and saying we have to calculate its displacement at
   two
    > shaft
    >     rotations.
    >
    >     Your sentence could read:
    >       " and so if at similar comparative VE the Wankel rotary engine
    >     will have
    >     to run at the same rpm compared to an RPE and we have to
   count two
    >     chambers per rotor to pump (displace) the same
    >     amount of air."
    >
    >     Rolf
    >
    >
    >
    > I haven't heard anybody talk about why RPE engines measure
   displacement
    > to start with..
    >
    > I think "displacement" is a way to predict how much air (volume and
    > mass) are going to be moved at a given operating condition (output
    > RPM).  And this is useful because the amount of air moved in a given
    > amount of time is a way to predict engine output.
    >
    > Thus, it makes sense to look at how much air is moved through a
   wankel
    > at a given RPM.  From this come up with a method of comparing
   chamber
    > volume to piston engine displacement.  Anything else is mental
   gyrations
    > for no good purpose.
    >
    >
    > Matt-
    >
    >
   Hello Matt,

   Why measure displacement? you ask.
   You answered your own question.
   Although, you compare engines from their airflow as that is an
   indication of hp.

   The common way is to provide the engine displacement which provides a
   good idea of size and hp without any calculations. From here we
   calculate up.

   In simple terms, I would say, displacement is an indication how big an
   engine is.
   Some Governments use it to assign a tax value to the engine or vehicle.

   Using it to calculate air flow and hp:
   Remember hp is only affected by three things: displacement, mean piston
   pressure (mep) and speed, nothing else.

   Increasing mep is only possible within narrow limits. Speed is also very
   much limited by inertial loads. The only real and easy control one has
   is with engine displacement. ('No replacement for displacement', as one
   saying goes.)

   That is why small model aircraft engine have about 20 cc displacement
   and large ship diesels as much as 1.8 cubic meters or 1,800,000 cc per
   cylinder and as much as 14 cylinders. It is all about hp. With
   displacement we can get an idea of hp quickly. That should give an
   answer to your question in the outset.
   See: http://www.bath.ac.uk/~ccsshb/12cyl/
   <http://www.bath.ac.uk/%7Eccsshb/12cyl/>

   We distinguish between "displacement" (in cc, litre, cuin, cuft), and
   "air flow" in vol/time or in mass/time.
   Air flow in l/s = displacement in litre * rpm / 120. (4-stroke engine)
   Hp is the product of displacement, mep, rpm and a factor. But we talked
   about that already.
   Not being interested in 'mental gyrations' I stop right here. Most has
   been said anyway.

   Rolf

Right, but this lo---ong winded discussion has been about the details of
how to measure displacement on a Wankel, and how to compare that
measured displacement to a conventional 4 stroke piston engine.  My
point was that all of the mechanical discussion about how many chambers
to count, and how many e-shaft revs to use, and and the other
innumerable points were all for naught if the Wankel model that was
devised didn't allow us predict horsepower at an RPM in the same manner
as swept volume displacement does for 4 stroke piston engines.

I guess what I am saying is that my question was loaded (and
rhetorical)..  And that I hoped it would center the discussion towards
things that matter - results.  It seemed to me that we've been drifting.


Matt-


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