Paul,

Yes I have Ansdale book. and Kenichi Yamamoto, but non give the Rotor
POCKET
volume.


Thanks Rolf

But my question is not the Chamber swept volume, for this you do not
require
the Rotor POCKET volume, I wanted the pocket volume, of the Rotor, and
as I
say we used to use plasticine to fill it and smooth around the Rotor
Flank
with a steel rule, then take the mould out of the pocket and then measure
the fluid displacement to arrive at the CC of the pocket by computation..

I enclose a screen shot, whilst the FIM accepted the 1.5 rule in 1998 I
accept that this may no longer be true.

The wording was from a Guide for the ACU officials, for post race strip
downs and the like..

Bob



Ok Bob, here it is again from 30/12/2009
Rolf

Hello Bob,

Regarding the calculations for the CR, here is an example of how to go
about it.

Definition of the CR = (displacement + volume at TDC) / volume at TDC,

Mostly known is the displacement calculation = 270.5 R e b

For the small volume at TDC we first calculate a rotor with flat flanks
Straight lines between centre point of apex seal contact.
Here is the calc for the small volume at TDC with straight flanks:

Small volume = [Pi ((e/R)2 + 1/3) - 31/2 /4 (1 + 6 (e/R))] * R2 * b
  = [Pi * ((e/R)2 + 1/3) - 0.433 * (1 + 6 (e/R))] * R2 * b

Example: RX8, e = 1.5 cm, R = 10.5 cm, b = 8 cm,
e/R = 0.14286

Displacement = sqrt (27) * 10.5 * 1.5 * 8 = 654.7 cm3

Small volume = [ 3.1416 *(.14286)2 + 1/3) - .433 * (1 + 6 * .14286)] *
10.52 * 8 cm = [ 1.1113 - .8042 ] * 110.25 * 8 = 270.9 cm3
(flat flanks)

CR = (654.7 + 270.9) / 270.9 = 3.42 having flat flanks,

Reducing the volume at TDC increases the CR.
E.G. 270.9 - 180 = 90.9 thus: CR = (654.7 + 90.9) / 90.9 = 8.2:1,
(270.9 - 190 = 80.9 (654.7 + 80.9 ) / 80.9 = 9.1:1)

We now add a radius to the flank to obtain the additional volume needed
for the selected CR.

Distance d from short axis point to flat rotor flank:
d = (R-e) - (e+ R/2) = R/2 - 2e
d = R/2 - 2e = 105/2 - 2*15 = 22.5

Select clearance to = .5 mm, h = d - clr, h = 22.5 - .5 = 22 mm
Length of ½ flank s = cos 30 * R = .866 * 105 = 90.93 mm

Note : if the clearance is selected differently one must recalculate the
radius and the volume of the circle segment.
Also note that the radius will not have a constant distance to the apex
of the small axis as the rotor turns. In other words, the flank may be
constructed as a curve instead of a radius to minimize the clearance
volume. However, the difference is small.

Radius of arc R1 = (s2 + h2 )/ 2h = (90.932 + 222 ) / (2*22) = 198.92
mm, = 19.89 cm
½ angle = Asin (90.93/198.92) = 27.2 degrees,

Circle sector = R12 * pi * 27.2° / 180° = 187.85 cm2
Area triangle = (R12 - s2 )0.5 * s = 160.85 cm2
Circle segment area = 27.0 cm2
Volume circle segment = area * b = 27 * 8 = 216 cm3

CR without a pocket and with .5 mm clearance radius:
Small volume at TDC = (270.9 - 216) = 54.9 cm3
CR = (654.7 + 54.9) / 54.9 = 12.93 :1

For CR = 9.1 : 1 we need 190 cm3 , where we require a pocket of 216 -
190 = 26 cm3
If the pocket is 0.8 cm deep and 4.5 cm wide on average, it will be
7.2 cm long,
or use any other combination to make up the 26 cm3 .

For a CR = 8.2:1 we need a pocket of 216 - 180 = 36 cm3 using above
radius and 0.5 mm clearance.

Select CR = 10:1. To find the clearance volume : Displacement / (CR - 1),
Volume = 654.7 / (10-1) = 72.75 cm3, [(654.7 + 72.75 ) / 72.75 = 10 : 1]

Pocket size CR 10:1 = 270.9 - 72.75 = 198.15, and 216 - 198.15 =
17.85 cm3
Or: 216 - 270.9 + 72.75 = 17.85 cm3
Or: 72.75 - 54.9 = 17.85 cm3

Regards
Rolf Pfeiffer

Rolf,

If I adjust the Rotor flank clearance to 0.11 cm from 0.05 cm then the CR
figures align to yours, so I must have something wrong with the way I am
dealing with the flank clearance.

However if I set the pocket clearance to Zero I do not match yours

Taking the Geometry used in Ansdale page 52 : 6.3 Calculation of Compression
ratio

e= 1.4 cm : R1=10.2 cm B=6.7 cm

The Author states the maximum theoretical compression ratio CR = 18.95 : 1
and I get CR = 19.02 : 1

I am taking this as without flank clearance and without combustion pockets.

Bob UK