In the last issue I wrote about cooling, especially based on the shape of the lower cowl. I decided to install a fixed lip at the cowl outlet, and in the process also enlarge the opening by an inch and a half. I had not wanted to make the opening any larger over concerns about how thin the connection area was between the two lower cowl halves, but the new lip served as a doubler so I enlarged the opening. Here are the before and after:






I had hoped to download the EMS recorded data so that I could be more quantitative, but unfortunately it was lost in the fire. Generally, I can say it was a vast improvement. Before, a takeoff with a warm engine would have the CHTs over 400 in the first 1500-2000 feet, climbing at 90 knots. With the new cowl lip, Mike and I were able to climb with our Oshkosh load at 70 knots and the temps started to reach 400 climbing through 6000 feet. At a less steep and more normal climb angle, temps were never a concern, which was the intended design goal. While at Oskhosh, I took photos of several other airplanes for comparison. There is a lot of variety. Bobby Stokes enlarged the intake openings, added the Carbon Cub style louvers, and lower cowl flaps (O-540):


Mark Scott uses more typical louvers with his O-540:





Bill Anton had the largest lower cowl opening of the Oshkosh samples, though I believe he also has the most horsepower and thus BTUs to shed. I also appreciate how he riveted the lip on the top (behind the yellow) of the lower cowl.

The installation is visually appealing. None of this analysis is conclusive enough to say “do it this way,” but hopefully seeing some of the variety will help narrow down the norms of lower cowl configurations.