10-24-2020

Reading the Bearhawk forums it is clear that Bearhawks with the -540 engines which are operated in warmer climates suffer from engine cooling problems. To solve this problem, most folks seemed to have increased the size of the exit air and/or added cowl flaps.

I've read portions of the book "Engines" by Tony Bingelis where he offered a basic formula of hp x 0.35 to determine the size of the incoming cooling air scoops for an engine based on horsepower. 

In my case my engine is rated at 250 hp so I need a minimum of 87.5 square inches of incoming cooling air. 

I measured the periphery of the openings in my nose cowl and was surprised to find that each side measured 33 square inches for a combined total of 66 square inches of incoming air. That is quite a bit lower than recommended for my size engine. As the Bearhawk does not fly at high speeds that would benefit with a higher ram air effect in cruise, I felt the it would be prudent to increase the openings to obtain at least the recommended 87.5 square inches.

For my measurements I used a string that I ran along the radius of the opening and marked it after completing the entire periphery. Next I measured the overall length of this string and divided that number by four to mimic a square area. Using the formula Area= Length x Heigth, I determined the area of the nose cowl opening.

To obtain the additional cooling inlet area, I sketched an outline on the nose cowl and played with the look until I was happy because after all, cooling air is important but so are the looks!

Each time I changed the outline I would re-measure the area until I had a combined total of 88 square inches marked out. I concentrated extending the opening outward rather than simply up and down because there is more air coming off the prop blades at the outboard locations than there is from the prop blade roots.

To ensure consistancy between each side, I must now trace the final shape onto posterboard and transfer the outline to the RH side. 

I will then make a mold of the inlet area and use that to make the new shape.