Baffling evolution

My Q-200 started out with the off-the-shelf baffling. It went through lots of changes which I don’t need to bore you with. I’ll try and keep it to the bottom line.

First – I don’t like oil coolers on the Q-200 installation. They are costly, heavy and are a possible failure point. In addition, they take up valuable cowling space, and when mounted on the firewall, make it that much harder to pull the engine for service.

So, the trick is to not have an oil cooler, but still keep the engine cool. Lighten and simplicate.

Enter the plenum. I saw plenum installations on two guys airplanes, Lynn French and Bruce Cranium and kind of liked the idea. My feeling was, though, that they weren’t getting all benefits available to them.

For that reason, when I decided to do the plenums, I chose to have it cover the crankcase split line. This way, cooling air will be forced over the crankcase and help cool the engine oil. I overhauled my engine a couple of years ago, and this was the logical time to make the new plenum baffling. The plenums were pretty easy to make. I just uploaded my plenum fabrication photos to my web log: http://samhoskins.blogspot.com/ so you can see how I did it.

The plenum really helped my engine cooling, and my oil temps dropped at least 20 degrees! I think I may have also picked up a knot or two. I did seem to have a high EGT on my #3 cylinder, which I chalked up to uneven fuel distribution.

I thought it was all better, but I met a guy named Sam James at Oshkosh. He makes cowlings for the RVs and he talked me into ordering a set of trick inlet rings. He said it would improve the cooling and maybe get me a little more speed. You can see his products here: http://www.jamesaircraft.com/ Notice that his plenums COVER THE ENTIRE CRANKCASE. His web site says about the full plenum cowl and rings: http://www.jamesaircraft.com/South_Shop.html He claims:

Average speed increase with the cowl and cooling plenum alone is 7-10 m.p.h.

“The increased speed is made possible through improved internal and external aerodynamic flow. This is accomplished in part by a slightly longer cowl which requires either a 4" prop extension or an extended hub propeller.

“The inlet design, influenced by NASA funded research conducted at Mississippi State, resulted in a 40% reduction in size while ensuring improved cooling in climb and cruise configurations.

“Overall drag is substantially reduced. Pressure loss in the upper chamber is negligible while cylinder head temperature variations are controlled uniformly to within a few degrees”.

Last spring I installed modified my cowling and installed the inlet rings. I didn’t notice any speed increase (rats!), but the engine is even cooler and now all of the cylinder temps are quite even. And you know what? That high EGT on #3 came down in line with the rest of my cylinders!

At this year’s AirVenture Cup race I ran around 1,000 feet AGL on a 90 degree day, wide open throttle, for two hours and twenty minutes. The oil temp never got over 210 degrees.

So, what works for me is: Full cover plenum baffling and no oil cooler!