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Here is a spreadsheet program that I have used for a long time in messing
around with dreams of rotary engine power. I have simplified and added to
the original that some of you may have. This spreadsheet calculates the a
number of factors based on your input. The out put is the horsepower, fuel
burn and BTU of waste heat need to be disposed of. You can choose 1, 2 or
3 rotors to play with as well as your gear box. All the gear box selection
does is provide the correct prop rpm. This is a calculaton model not a
simulation.
I have now added a section on cooling capacity based on two GM evaporator
cores (which a number of you are using) and a stock RX-7 Oil cooler. The
assumption here is that you have a good cooling configuration that provides
maximum airflow to the radiators and cooler. The cooling capacity
calculations are based on cooling airflow air mass going through your
radiator and cooler based on the forward indicated airspeed of the aircraft.
Note that the cooling capacity permits you to select both an indicated
airspeed and an engine rpm. However, that engine rpm must be contained in
the RESULTS table of the HP and BTU data. You can set up your engine power
in the first section and then enter your airspeed AND the RPM you intend to
operate at in the cooling section.
So you can choose 100 mph airspeed (such as during take off) and say 5600
rpm producing 160 HP (you must configure your engine in the first section to
produce 160 HP at 5600 rpm by adjusting Air/Fuel Ratio and throttle
position. Also, you can adjust for altitude and OAT.
Then entering 5600 below your airspeed entry in the cooling section, you
will likely find that at that power setting and airspeed, the cooling system
is not rejecting enough heat, but as you increase the airspeed at the same
power setting (climb cruise perhaps) you will likely find some point where
there is sufficient airflow to provide adequate cooling.
Play with it a while and I think you will get the hang of it. For those of
you who know how to use the "Goal Seeking" function under Tools on the
spreadsheet menu. You can for example set up the "goal seek" to seek the
airspeed at which you have just enough cooling capacity with no reserve or
deficit = zero.
Enjoy the toy - no, you can't see all the calculations, they are hidden. I
have found folks changing the previous program and sometimes the changes
were good but other times not so.
I have found that based on my experience and checking with other folks that
the calculations are not just WAGs and come fairly close to actual
operations. I would be interested in how close it may come to your
operational experience - assuming you have the same cooling set up.
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
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