Ed,
 The problem here is that the formula used for displacement. The real solution is that the racing sanctioning bodies want the rotary to be at a slight disadvantage to piston engines! It, (the formula), has no relation to actual reality!
Bill Jepson


In a message dated 2/10/2005 4:18:02 PM Eastern Standard Time, "Ed Anderson" <eanderson@carolina.rr.com> writes:

>
>> Ed, I think you've blinded yourself with science 8*)
>>
>> Each face of the rotor will cycle 40cid of air on each revolution.  You
>> can ignore the eshaft.  Every time the rotor turns around, each face
>> will have processed 40cid. If a rotor is turning at 2000 RPM, then three
>> faces will each cycle 2000*40cid of air.  You bring in referencing off
>> the eshaft, and all of a sudden only 4 faces are processing air.  I
>> think that is the mistake.
>>
>> You reference 720 degrees of eshaft rotation.  But all that means is
>> that the rotors haven't completed their cycle.  You're just ignoring
>> every third rotor face.
>>
>>
>
>Ernest, I think you are making my very point.
>
>1.  Each rotor has 3*40 = 120 cid of volume displace per 360 deg rotation and with two rotor that is 2*120 = 240 CID each revolution.
> so we have 2000*240 cid/1728 = 277.77 CFM exactly what quantity the formula gives  when treating the rotary as a 160 CID 4 stroke engine with e shaft at 6000 rpm - but that is for a FULL 360 deg rotation of the rotor.  See part 2 next {:>).
>
>2.  Example
>
>160*6000/(2*1728)  = 277.77 CFM which agrees with the above but if the 160 CID  figure is correct then that means that 160/4 = 4 , only 4 rotor faces worth of displacement have been considered in the formula.  Which if that is correct then the rotor have only turned 240 degs  and not 360 deg.  But if the rotor has only turned 240 deg (240*3 = 720Deg Checks!) then that means that to make a valid comparison with 1 above, we need to reduce the amount of rotation in statement 1 to 240 deg instead of 360 which means that we only have 277.77*4/6 = 185 CFM which leaves me back where I started.
>
>There is no question that if the two rotors have completed their 360 deg rotation - then all six faces have completed the cycle.
>That gives 40*6*2000/1728 = 277.77 CFM, so lets not debate that point - we both agree! .
>
>My problem has been the use of the 160 CID equivalent in the formula.  I understand how it was arrived at ( I believe) its simply the amount of displacement occurring in the rotary at 720 deg of e shaft rotation  which is the standard of comparison with other engines.
>
>At 720 deg of e shaft rotation then indeed 160 CID of displace has occurred.  If I calculate using the 240 deg of rotor rotation I again get 240/360 * 6 = 4 rotor faces.  But if that is indeed the actually amount of displacement of the rotor then according to our calculations in 1 above we need to use 240 deg not 360 and that gives 185 cfm not 277.77.
>
>I mean I don't care if we use 240 CID (the total displacement  across 1080) or 160 CID (the total displacement across 720 deg - the standard for comparison) but there should be some logical consistency between the two.
>
>WAIT! Stop the presses I  Finally Understand!  The key is the 240 CID total displacement for 360 rotor degrees or for 1080 deg of e shaft rotation.
>
>It was not a math problem or logic problem, my problem was a reference transformation problem!
>
>
>             Using the rotor representation we have Air flow = 240 * 2000/1728 = 277.77 this is rotary based on 360 deg of rotation.  Now if we  take that formula (which I think we agree on),  I then want to convert it into a formula that conforms to the 720 deg standard.  So I can compare apples and apples.
>
>Here's what happens.
>
>1.   First the e shaft rpm is the e shaft rpm and is the standard reference point for rpm of engines.  So we can simply multiply our 2000 rpm rotor rpm by 3 to reference it to the eshaft. So 3* 2000 = 6000.  That "transformation" gives us the rpm figure in the "Standard" equation.
>
>2.  However, to  reference the 240 CID displacement to the 720 deg standard we must use the ratio of the transformation from 1080 to the 720 reference system.  Because the amount of displacement IS affected by the choice of reference.   This gives 720/1080 * 240 = 160 CID referenced to the standard.
>
>So now the formula should migrate from rotor reference of 240*2000/1728 = 277.77 to e shaft reference of 160*6000/1728 = 277.77 by reference system transformation.  To do that:
>
>1.   We multiply the rotor rpm by 3 - the rpm does not care whether its 720 or 1080 referenced, one revolution/min is one revolution/min.
>2.   The 720 deg standard DOES affect the amount of displacement so 720/1080 *240 = 160 CID.
>
>Taking the rotor reference formula above we can directly transform it to the e shaft reference standard.  Doing so gives us
>
>     [720/1080*240]*[3*2000]/1728 = [0.666*240]*[6000]/1729, taking the first factor 0.6666* 240 = 159.9999 = 160 and we have
>
>  Airflow = 160CID*6000/1728 = 277.77  So the rotor reference is transformed to the e shaft reference of 720 deg.
>
>Thanks all for helping me out of my problem area.  I just knew there had to be a connection someway.  If this is not correct - please refrain from informing me {:>).
>
>
>Be  heartened, Ernest,  I have been faithfully using the 160 formula - just wanted to understand what appeared to me to be a difference when looking at it from two different perspectives.  If the "reference" transformation is applied to the rotor equation then it translates into the  720 reference state.
>
> Best Regards and thanks for your input
>
>Ed
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