I have flown my RV-6A Subaru H-4 since March 2011 but when the heat came last summer, my cooling was insufficient. I have increased my cooling by upsizing the rads from 44 frontal inches each to 72 by having custom radiators made by Eddie at Techweld, Paducah, KY. Our St. Louis heat wave showed 112 OAT when I took off last week and climbed to 3000 AGL before leveling to keep coolant at 220. When tested at 95-100 OAT I climbed to 8000 before leveling with coolant not exceeding 207. For those still trying, custom rads. may be the answer. You can see my photos at kitlog.com/my kitlog/builders/ron burnett.
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Subaru cooling improved
- Thread starter rvator4twa
- Start date
Tandem46
Well Known Member
David-aviator
Well Known Member
Good work, Ron. You have had more success than I did with cooling. Perhaps if I had stuck with the H4 instead of going to the H6, it would have worked out better.
Thanks for your help
Without your help and guidance, I never would have got this project in the air. Thank you.
Without your help and guidance, I never would have got this project in the air. Thank you.
Ron, how do those temperatures compare to the original radiator setup?
The original installation appears to have had simple boxes between cowl intakes and the heat exchangers. Were they sealed to the cowl somehow?
Original rads cooling
Dan,
The origuinal rads had me leveling off at 500 to 1000 (if lucky) agl to keep the coolant below 230 with OAT temps about 90. Multiple flights were out of the question in summertime. Now I am looking to install a controllable butterfly shutter on one of the rads to keep cooling temps higher, especially at cruise.
Ron Burnett
Dan,
The origuinal rads had me leveling off at 500 to 1000 (if lucky) agl to keep the coolant below 230 with OAT temps about 90. Multiple flights were out of the question in summertime. Now I am looking to install a controllable butterfly shutter on one of the rads to keep cooling temps higher, especially at cruise.
Ron Burnett
pierre smith
Well Known Member
Dan, a friend of mine also had a 4 cylinder Subaru on his -7 and yes, there are two square boxes attached to the coolers and no rubber material to the front of the cowl.
During a BFR flight I administered, it always ran over 230 deg or more and 35 MPH slower than the IO-360 he now has in it.
Best,
simpkinsona
Well Known Member
Sealing the radiator boxes is critical for these engines. Mine still has the small radiators but with good seals to the cowling. The oil cooler had one of the seals slip allowing an air leak, oil temps were 10 degrees higher relative to coolant temps until I fixed the seal. Too bad the company didn't stick with the H4. If they had stuck with it and given realistic performance figures, they would have sold many more. My RV-9a has the performance of an O-320 fixed pitch.
-Andy
-Andy
I agree, sealing is very important and most of the problems started when the H6 came along. They are very heavy for an RV6-9. A good H4 will true 150-160 knots and does not weigh much more than the Lyc C/S.
pierre smith
Well Known Member
Ross, I was also told that the Eggenfellner engine package used oil coolers for the coolant, not water radiators and that would be one reason for the lousy cooling, because the design for water cooling rads is different from oil coolers.
What say you?
Thanks,
What say you?
Thanks,
Yeah, the heat exchangers he used on the H4 were not that great for water. I built a special flow bench setup to evaluate several different rad types a couple years back for both air pressure drop (drag) and temp drop per unit volume, unit area etc. The Egg ones were high drag and offered low temperature drop in the tests plus 2 only had 74 square inches of core face area and 268 cubic inches of core volume which is not enough in hot climates in the climb. (I don't consider 230F acceptable BTW).
The early H6s had the same rads so there was no way that was going to work well and it didn't. Proper sealing made a world of difference but few people with the original rads had adequate cooling in high temps without throttling back, step climbing or lowering the nose.
The early H6s had the same rads so there was no way that was going to work well and it didn't. Proper sealing made a world of difference but few people with the original rads had adequate cooling in high temps without throttling back, step climbing or lowering the nose.
rv7charlie
Well Known Member
At one time, the Egg installations were using what looked like either GM or Ford air conditioner evaporator cores. Fairly common for a while in rotary engine installations in RV-x's. But the 'box' for an inlet is just astounding. It's amazing that they didn't all melt something before getting to pattern altitude.
Charlie
Charlie
David-aviator
Well Known Member
The idea of the box was to catch as much air as possible coming in the oval RV inlet. The entire system was initially set up for RV's using the cowl as is. Jan achieved some success with the arrangement in the blue RV-6A at the time however the airplane was tweaked by an expert tweakier. He had no cooling problems with it. The box front was closed except where air entered through the oval inlets.
I flew with Jan one calm morning at OSH and it did better than the 185 he advertised with oil and coolant temps very normal. But it was a finely tuned super charged H4 running about as smooth as wrist watch. He demoed that airplane a lot and it sold engines, more than he could deliver for a few years.
I had a major overheat on the first flight with the H4, never left the traffic pattern. Sitting in front of the hangar running the engine, I discovered if the cabin heater valve was opened, the engine cooled instantly. The problem was the thermostat. Subaru has it at the coolant intake to the engine not at the exit. It was not opening because a small amount of heated by-pass fluid was not getting to it. The heater fluid was and it opened it. Subaru engines are like that, they need heated by-pass fluid to open the thermostat. From then on it was recommended the the heater core valve be open or removed.
Actually, I was getting along quite well with the H4 after that although clearly it was not making 0320 HP. Cooling was an issue but manageable and it was a fun airplane to fly with the Quinti prop system. What did it for me with the H4 was an off field landing after a timing belt failure. I was so satisfied to that point I decided to do it again with the H6 (and its internal timing chain rather that the belted H4) thinking it would certainly duplicate the 0360 in performance. It did not. RV-7A performance was off by at least 15 knots.
The engine also had major cooling problems with the same H4 radiators. I flew it all year 'round for 5 years but never without some special procedure to keep the coolant temp below 230. Once up to 8 or 10 thousand feet it was OK but it took a while to get there. Jan offered to sell a couple of the larger rads that came out later but I was not in a good mood to part with another $900. He made money on the H4 and H6 with me and I was beginning to wonder when it would end.
One day when it was in the 90's the MT electric brush blocks dropped off the rail right after take off, the prop was stuck in fine pitch. One method of getting adequate air through the rads was to set 1700 rpm at WOT. It always caused a drop in coolant temp but that day the prop was churning at 2600-2700 pushing no air at all across the rads. The coolant temp was over 250 by the time I got on the ground. I believe the recommended Subby coolant temp is about 185 - I figured the engine was toast. Actually, it wasn't. I gave the engine to a guy in Atlanta who tore it down and measured everything, it was like new according to him. So go figure....maybe the H6 is tough as a Lycoming. It sure did well at take off power and 2600 with the MT prop but lost some of that guts in cruise.
However that event torqued it for me with Subaru and I don't look back for a minute, I'm glad to be out of it. I had to quit flying or change to Lycoming as this was no fun at all anymore, the problems were not going away.
So, Lycoming it is for me - for as long as I can push the throttle up and not bend metal.
Sube Updates
I think Jan was using oil cooler cores from Niagara for the first few years. The original H4s worked not bad actually as they were lucky to put out 130hp as delivered and geared- they didn't need much cooling because they were pretty weak.
The poor intake and exhaust systems didn't help power output either and these problems migrated into the H6s as well so performance was usually disappointing. One fellow in Hawaii built a proper tuned header system a few months ago and picked up over 20 mph with this change alone on his H6- showing how bad the Egg system really was! He says he now has no problem keeping up with O-360 RVs where before they left him standing.
We suspect the intake manifold design and fabrication is costing 20+hp as well after some study. They are very restrictive.
We have an H6 up here with a couple hundred hours on it now, pretty fast (165-170 knots TAS) and it's been reliable, sounds wonderful and super smooth. A number of others have had valve problems, problems with the poor locking method Jan devised for the AVCS and some melted pistons from too much timing, bad injectors or lean mapping.
When they work, they are actually pretty neat. At this point in time though, I'd say a good 50% have abandoned their Egg engines after encountering various problems. The Subenews forum is invaluable for info and problem sharing. Some who have stuck with it are very happy with their engines now and just fly them like- well a Lycoming...
The STI turbo RV7 up here is accumulating hours, still super fast (180+ knots loafing) and has also been reliable. Three others are being prepped, two in the US and one in Oz, two of these with Aerocharger turbos.
My Turbo EJ22 is getting very tired now and I'll be finally pulling the engine this winter during the annual to rebuild it and see what's going on in there (high oil consumption now). Ten years has flown by fast! I'll be totally revising the cooling system because it evolved (or devolved) into a heavy, draggy mess. Looking at a chin or ventral rad setup to lose weight and drag.
Never a dull moment!
I think Jan was using oil cooler cores from Niagara for the first few years. The original H4s worked not bad actually as they were lucky to put out 130hp as delivered and geared- they didn't need much cooling because they were pretty weak.
The poor intake and exhaust systems didn't help power output either and these problems migrated into the H6s as well so performance was usually disappointing. One fellow in Hawaii built a proper tuned header system a few months ago and picked up over 20 mph with this change alone on his H6- showing how bad the Egg system really was! He says he now has no problem keeping up with O-360 RVs where before they left him standing.
We suspect the intake manifold design and fabrication is costing 20+hp as well after some study. They are very restrictive.
We have an H6 up here with a couple hundred hours on it now, pretty fast (165-170 knots TAS) and it's been reliable, sounds wonderful and super smooth. A number of others have had valve problems, problems with the poor locking method Jan devised for the AVCS and some melted pistons from too much timing, bad injectors or lean mapping.
When they work, they are actually pretty neat. At this point in time though, I'd say a good 50% have abandoned their Egg engines after encountering various problems. The Subenews forum is invaluable for info and problem sharing. Some who have stuck with it are very happy with their engines now and just fly them like- well a Lycoming...
The STI turbo RV7 up here is accumulating hours, still super fast (180+ knots loafing) and has also been reliable. Three others are being prepped, two in the US and one in Oz, two of these with Aerocharger turbos.
My Turbo EJ22 is getting very tired now and I'll be finally pulling the engine this winter during the annual to rebuild it and see what's going on in there (high oil consumption now). Ten years has flown by fast! I'll be totally revising the cooling system because it evolved (or devolved) into a heavy, draggy mess. Looking at a chin or ventral rad setup to lose weight and drag.
Never a dull moment!
I need heat
As winter approached my engineer friend and I were trying to design a radiator bypass system for my very efficient custom radiators that allowed my Subaru powered H-4 to fly 10 kids in eleven flights in the Aug. heat. The simple solution that works great is cutting off swimming pool noodles and stuffing them in the inlet plenum to block air to the lower 2/3 of the radiator. Takes less time on warm up before take off to get the engine to 140 and it barely makes 167 when the thermostat opens. Next spring they wii go back to storage. I chose blue ones that were cute.
As winter approached my engineer friend and I were trying to design a radiator bypass system for my very efficient custom radiators that allowed my Subaru powered H-4 to fly 10 kids in eleven flights in the Aug. heat. The simple solution that works great is cutting off swimming pool noodles and stuffing them in the inlet plenum to block air to the lower 2/3 of the radiator. Takes less time on warm up before take off to get the engine to 140 and it barely makes 167 when the thermostat opens. Next spring they wii go back to storage. I chose blue ones that were cute.
Total radiator area
That is a frontal area comparison. The rads are 3" thick I believe and I quit running a manometer once I installed the new rads.
That is a frontal area comparison. The rads are 3" thick I believe and I quit running a manometer once I installed the new rads.
