Inlet air filters.
To add more information to your recent air filter comparison article (August 2014 Aviation Consumer), I compared the Brackett air filter to the Donaldson air filter on my Beech P-35 Bonanza, equipped with a Continental 10-470N. The data was recorded using a JP1 EDM 800 and a Horizon digital tach. Each test was at full throttle and the tests were performed on the same day to make the conditions between tests as similar as I could. Pressure altitude was 9500 feet and the temperature was 66 degrees.
With the Bracken installed, I recorded fuel flow at 13.4 GPH, manifold pressure was 20.6 inches and the measured RPM was 2450. With the Donaldson, manifold pressure increased to 20.7 inches and I gained 2 MPH in both indicated and true airspeed.
I have the engine oil analyzed each time! change the oil and the oil filter after 45 to 50 hours of use. saw no difference in the silicon readings between the air filters, so I presume the Donaldson and Brackett air filters do an equal job of filtering the engine air.
While there was a slight increase in performance with the Donaldson over the Brackett air filter, I found the Bracken element was much easier than the Donaldson air filter to remove, clean and reinstall. Also, the Bracken foam element is less costly than the Donaldson air filter assembly.
After using the Donaldson filter for 472 hours, 1 switched back to the Brackett. For me, the very slight increase in performance of the Donaldson filter did not justify the extra time in maintenance or cost over the Brackett.
Rick Grossmann Overland Park, Kansas
Excellent air filter comparison in your August issue. You guys did all you could possibly do without getting into expensive lab testing, but in my opinion (as an experienced A&P with an IA certificate) that doesn't matter much. What does matter is that the filter is serviced on a regular basis. To me, it's less about questionable performance gains and more about maintaining air flow to the engine.
Stan Sutton, Jr. via email