I attempted 3 times to post the
new spreadsheet to the list, but it is a few KB too large. So those of
you who may want it, send me an e mail to eanderson@carolina.rr.com with
the subject : Spreadsheet . I will send you a
copy.
Details of latest
revisions.
In the past, I have provided a
spreadsheet to aid in determining power, fuel flow, heat produced, etc, and
have also attempt to provide some rudimentary cooling calculations.
You can entertain yourself with it as well with your dream engine
{:>)
Since there was no engine load
component in earlier spreadsheets, I had provided % throttle opening
factor as a substitute. However, that was never satisfactory
because who of us know exactly what % throttle opening we have at any
point and besides that throttle opening does not necessarily correspond to
load.
In any case, I recent revised
the spreadsheet, so that a user may now put in his manifold pressure.
That is generally a parameter available to most folks. It also
eliminates potential errors from altitude, air density, temperature
etc. It and rpm also provide a better indicator of LOAD than does
throttle position. It will also works for N/A and turbo
engines.
All you do is enter your
manifold pressure (and the other engine operating parameters)
and the calculations will use that to calculate the air density in the
intake and from that the power, flow rates,BTU, etc. So now the
manifold air density is separate from the cooling air density which is
dependent on altitude. So manifold pressure and altitude (ambient
pressure) are now separate for engine operation and cooling
operations.
So in the cooling section you
must now enter your altitude for cooling calculations. Also, I have
now provided for the user to enter the dimensions of his cooling cores and
the number rather than the default Gm cores and RX-7 oil cooler I had been
using. You can change these parameters on the second sheet titled
"Cooling Calculations", it shows recommended default values (the GM
cores and Stock Rx-7 cooler) just to get you started or if your project is
still in the dream stage.
Also there is provision on the
cooling calculations sheet to have your coolant flow rate proportional to
engine rpm (more realistic). The flow rate is based on Racing Beat
information for 1974 and later coolant pump flow rate. If you
have changed the pulley ratio to non-stock then these flow rates may be off
a bit - but still more realistic than assuming a 40 gpm flow rate at idle
and at 6000 rpm {:>).
So these changes mean you can
now simulate a partial throttle operation say at 19" Hg and a cooling
altitude at 7500 MS. You can now see if your system should be cooling
at that power setting and then you could change the power setting to 22" Hg
and see if you installation should still cool at that selected air
speed and altitude and power setting. Manifold pressure and Air Fuel
Ratio can make a considerable difference in the amount of heat
produced. So pay attention to the values you are
using.
Now here is the potential
problem I can see. If you tell the spreadsheet you are flying at 7500
MSL in the cooling data input, but you decide to use WOT for your engine,
you must realize that the ambient pressure (and therefore your manifold
pressure) at that altitude will not be 29.92 " HG. Your
manifold pressure (for N/A engine) would never be that high for
an N/A engine at that altitude - but, it could be for a
turbo engine. So unless you selected YES for
turbocharged in the data entry area, an error message will be displayed
"Manifold Pressure exceeds
ambient". It can also happen if you have
already selected a manifold pressure say 29" while at sea level, but then
you enter 2000 MSL for altitude in the cooling section. The
warming message will inform you that your manifold pressure now exceeds
the ambient pressure at 2000 MSL ( unless you enter
If you select an RPM value for
the cooling section and it is outside the limits of the rpm values in
your calculated data table, then an error message
"Invalid
RPM" will be shown in the cooling data entry
area. So that would mean either change the rpm OR change the range of
rpm in the table by adjusting the rpm start value or the rpm step
value.
As always, if anyone finds an
error or problem please let me know.
Ed Anderson
Rv-6A N494BW
Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://www.andersonee.com
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.dmack.net/mazda/index.html