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I found this old spreadsheet that I had been searching for that was developed for Sport Aviation Magazine in 2003 by Neal Willford. It calculates oil cooler sizing, inlet and out cowl areas required based on user inputs including HP, TAS, Altitude, baffle vs plenum, inlet/outlet air ratio assumptions, etc. As is usual, the devil is in the details. I dont know the assumptions. I thought I would share in case one you can enlighten. I am wondering if one uses this do you end up with 350 degree CHT temps or 460 degree CHT temps. Do you end up with 190 degree oil or 240 degree oil. Regardless there is some good knowledge within it. For instance the biggest factor is whether you have standard cowl baffling or a doghouse style baffle (does not include a plenum option but it would be less leakage that the doghouse style and you have the option of using a lower leakage factor).
Was wondering if someone could put in their flying Bearhawks data and see how the calculated areas compare to what you have and tell us what your CHT/Oil temps are. I did this exercise for a Lancair IV and I have exactly the outlet area but too much inlet area and my CHT's would be below 300 degree absent intervention. Intervention in my case was increasing my leak rate intentionally to bring my CHT's above 300 in cruise (as in I have a 4 inch hole in my baffling now with a butterfly valve to allow cooling air to bypass the engine). A better solution is to reduce the inlet area but that would require repainting and I still remember the trauma of painting it 10 years ago.
One little typo, I think, in the spreadsheet is "HP" for the altitude input. It works if you put altitude but not HP in that box.
Was wondering if someone could put in their flying Bearhawks data and see how the calculated areas compare to what you have and tell us what your CHT/Oil temps are. I did this exercise for a Lancair IV and I have exactly the outlet area but too much inlet area and my CHT's would be below 300 degree absent intervention. Intervention in my case was increasing my leak rate intentionally to bring my CHT's above 300 in cruise (as in I have a 4 inch hole in my baffling now with a butterfly valve to allow cooling air to bypass the engine). A better solution is to reduce the inlet area but that would require repainting and I still remember the trauma of painting it 10 years ago.
One little typo, I think, in the spreadsheet is "HP" for the altitude input. It works if you put altitude but not HP in that box.
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