Eric-
OK here goes too
After reading your note several times i have some images in mind, probably totally different from yours. I imagine several intake twists and turns. So a couple of thoughts on cooling air in general, after 500 hours of trouble free DD cooling:
An interesting guest-
A lot of interesting people have leaned on my prop and explained how these airplanes really work. Little known secrets of props, exhaust tuning, cylinder cooling, oil cooling... some useful, some not so much.
One of the most interesting guests loved airplanes but had never been around them or flown one. He looked over the engine and examined my cylinder cooling, oil cooling, and induction tubing. He talked out loud as he figured it all out. His absent-minded comments were fascinating. Surprised at his ability to follow it all, i asked what he did. He said he traveled around the country fixing swimming pool filter installations. He said his corrections usually consist of removing 90 degree elbows. He said that often the installing crews dont really care if it works and just do basic installation. Removing the 90 and replacing it with a curve or a couple of 45 joints usually does the trick. I still enjoy chewing on his last comment- that none of the work is really done by the pump. It is the 14.7 lb/in2, one atmosphere, doing the work. All he did was get things out of the way that interfere with mother nature.
Aircraft cooling is more complex but i find the simple truth useful when my Rube Goldberg virus kicks in. Air and fluids don't like turns. I could make many more descriptive comments about what air does do, one of the truly enjoyable results of having built this plane.
My cylinder cooling has two basic elements. One, the simple, expanding inlets, and two, augmented exhaust. Pics in Featured Canards link here. Some changes but same basic components.
The inlets are each 1x5 inches. They each started out as external 2x9 gorilla nostrils. Those were reduced three times. Tests were run wide open at 2000 ft on 100 degree days. No increase in CHTs with the reductions. Then the inlets were made internal, and reduced three more times. I got a slight increase in CHT with the last reduction. Wide open CHTs at 2000 ft settle at 390. Climbout to 10K, the CHTs start at 390 and reduce to 280 to 320 at 10K peak mixture cruise. So with the cool cruise temps the inlet size could be reduced a little more. Probably not right now.
The exhausts end inside the lower plenums. The exhaust pulls and propells air out the plenum exits. Air has to replace the ejected air and is drawn in the inlets. At idle the flow will suck a string into the inlet. With the plenums the air has to go throught the cylinder fins. So good cooling on the ground too. A friend used to have cooling problems and in hot wx had to shut down and push the plane back to the hangar. He copied my system and was amazed. Once he just went to see if he could sit and idle for 30 minutes. No problem. He came over and told me he thought i had been lieing about my cooling, until he saw it on his plane.
All to say, sounds like your UD/DD mix would have a few twists and turns. One could be enough to make your stomach tighten up on hot days. And following the work Terry Schubert documented in CSA, cylinder wraps on a DD installation could likely give you proper cooling for the cylinders around the exhaust valves.
The Hertzler/Schubert Oshkosh cooling powerpoint slideshow is available here on ez.org somewhere i think. It covers it all in a nutshell.
Through the several years with my system, I can't overheat the engine. It occurs to me that i could have aimed a little more toward the middle and settled for more normal cooling, but then the 31 flights in 31 days during this summer wouldn't have been as comfortable. And what did i build this plane for anyway, straight and level?
Hope i didn't miss your point too much. Thanks for the chance to take a run at it.
