Ed;
I looked it over
to maybe make some comments; but I don’t know what I’m looking at. Maybe
I missed because I haven’t read previous posts, but general questions
are;
What sort of
modeling is this, empirical or theoretical? I don’t see any formulas in
the spreadsheet.
What are the
independant variables (input) and what are the dependant variables
(output)?
Is this for a
specific airplane? Fixed HE configuration?
Only specific
point is the 35% penalty for “thick” radiator, but the thickness is fine as
long as you have sufficient pressure recovery in the inlet duct to overcome PD
across the core and other losses.
Anyway, I don’t
expect you to write a manual, but if you have nothing else to do (yeah..right)
educate me a little.
Al
Hi
Al,
Sorry about the pacuity of information on the model. The Power/fuel flow
and BTU generated are math models that take the BTU in a gallon of
gasoline, your rpm, air/fuel ratio, altitude, temperature/air density and
throttle setting to calculate the output shown in the Results box. I
feel 90-95% confident that those values are within 5% of what a well set up
rotary can do.
However, what I
sent out wasn't the active spreadsheet but simple a cut and paste of the
results of the three cases. I have provide a couple of spreadsheets and
was concerned about getting too many partially completed versions out
there.
The actual
spreadsheet only permits you to input data in the white color (uncolored
cells). The rest are results.
The cooling model
(at this moment) is based on the heat transfer equation Q = W*(Tout-Tin)*Cp
for an air flow mass cooling system. Basically it calculates the CFM of
air flow through the specified radiator (the two evaporator cores in this case
and the RX=7 Stock oil cooler)
As noted I have
"derated" the capacity of the thicker cores by 10% for every inch thick they
are over 1". Its true that they higher dynamic pressure permits us to
successfully use the thicker cores, but everything I have read does indicate
the air flow does meet increase resistance.
I have also found and added a delta T model which shows how much
temperature rise you would have in your air mass flow stream due to the amount
of mass flow AND the amount of BTU of heat you are rejecting into that mass
flow.
I am trying to keep the model based
on simple math relationships and not use any slight of hand tricks.
However, Since a radiator maker provided the rule of thumb of 10% increased
resistance per inch, I decided to incorporate it instead of trying to
calculate the pressure recovery in the plenium and that effect on flow
rate. The cooling model seems to correlate fairly well with what us
folks flying with the cores are experiencing.
There is another gent who is much
better acquainted with such matters than I working on the model to actually
calculate how much heat moves across the aluminum tube walls from the coolant
into the air stream. That way we can calculated the total surface area
for any specified radiator size and get some feel for the adequacy of a
cooling system.
If you would like a copy of the last
spreadsheet I sent out to folks, just let me know. Its cooling model is
not quite to the point of the one I based the Cases on, but you might enjoy
playing with it.
One last point, the model does not
have any "loading" such as a prop so you can get 10,000 rpm no problem.
I have looked into providing such "loading" but just so many variable
inlcuding the prop and the airframe, that I doubt it will ever show up in one
of my models.
I'll be at Shady Bend from tomorrow
until late Sunday.
Best Regards
Ed
Anderson