Long-EZ Cylinder Head Cooling

October 1996

by Mike Melvill

Here we go again! This has been an on-going nagging problem, that has been by far the most common question I have received here at RAF over the years. Those of you who read the Canard Pusher are well aware that cylinder head cooling, and to some extent, oil cooling, have been on-going problems for many EZ flyers, and we have addressed these problems many times with some of our ideas and some builder-submitted ideas, with varying degrees of success.

I myself have made an amazing number of changes to the cooling system on N26MS, including four complete changes of engine baffling, a bigger NACA inlet, a smaller NACA inlet with larger lip radius, and two small NACA inlets cut into the top cowling cheeks.

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I have had my oil cooler in five different locations in the cowling, and it is now back in the plans called-out position, where it works best.

Recently I spent a lot of money on a major engine overhaul, and the uneven cylinder head temperatures (number 4 is always hottest!) really began to bug me. A couple of months ago I was talking to Dave Ronneberg (Berkut designer) and he is cooling a Lycoming IO-540 with two small "armpit" inlets and allowing the engine to breathe and the oil to cool through a small "pitot" armpit inlet on the bottom of the fuselage. I frankly did not believe his cylinder head temperatures! Dave gave me a pair of the small "pitot" type "armpit' inlets and although they did not fit the Long-EZ cowling very well, they were adequate for some flight testing. I flew the airplane at 11,500 feet with an outside air temperature of 9-degm C. I set the RPM at 2660, and leaned it to a fuel flow of 9.6 GPH, and 17.3-inches of manifold pressure. I used these settings for all subsequent test flights.

The first test was with all of my cooling inlets, the normal NACA on the bottom of the fuselage, plus two small NACA inlets in the top cowling, plus the two Berkut "armpit" inlets. Cooling was worse!! (see chart) My number 4 cylinder really worried me! I was disappointed to say the least, but I persevered and tried a small vane in the right "armpit" inlet To my amazement this reduced the temperature across the board, but especially reduced #4 by 140degrees! (see chart)

I then began a series of iterations of vanes and ducting within the "armpit" inlets and I also sealed up the two small NACA inlets in the top cowl. I still had my original NACA inlet as well as the Berkut armpit inlets and now the cylinders were actually a little too cool!! So I sealed up my NACA inlet and flew with just the two Berkut armpit inlets, which incidentally together had 10 square inches less inlet area than my original NACA inlet! The result was a very gratifying 342-degrees; 345degrees; 344-degrees; and 345-degrees with the oil temperature stable at 185-degrees F. (see chart)

I am so impressed with the results of my testing that I am currently building a new cowling, incorporating the Berkut style "armpit" inlets, designed to fit the shape of the Long-EZ cowling. This cowl will be made entirely out of Carbon Fiber saving about 15 lbs, and I will have excellent cylinder head and oil cooling, together with a slightly lower drag cowling. I will report on the results of the new cowling in the next CP (Jan '97), but I thought that this was such a significant improvement over the original NACA inlet that it would be of interest to many of our builder/flyers.

Long-EZ N2MS with Lyc 0-360 and Airflow performance fuel injection system. All data obtained at 11,500 ft, pressure altitude. Power set at 2660 RPM and 9.6 GPH fuel flow
Date Comments Cyl #1 Cyl #2 Cyl #3 Cyl #4 Oil Temp Deg F
8/30/96 Baseline - 12" Wide NACA inlet plus two small NACA inlets in top cowl 366 390 397 411 188
9/8/96 Original NACA inlet, plus two Berkut "armpit" inlets 363 398 386 429 188
9/10/96 As above, with flow ducted to cylinder #4 357 345 360 287 184
9/13/96 As above, but with ducted flow to all cylinders 322 334 329 282 185
9/20/96 As above, but with each duct modified to try to even temperature 344 351 355 316 188
9/20/96 As above, with ducts #3 and #4 modified a little more 345 345 353 330 185
9/21/96 NACA inlet glassed shut, only Berkut inlets functional 354 347 340 317 183
9/23/96 Berkut inlets only, with optimized restrictor nozzles 1340/342 1335/345 1351/344 1350/345 185

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