Cowl Duct Modification

[Dave12]

Considering the numerous plans that I have sent out I thought I would start a separate thread on this subject. Pete just finished his mod. and was good enough to send me pictures. Too bad I don't know how to get them on this thread. Maybe Pete can get them on. Anyway, he reports that the mod has helped. If you have any questions about how this started, look up "Boiling Mad" from several weeks ago. [url]http://www.vansairforce.com/community/showthread.php?t=88612[/

If you pm me your email I will forward Pete's findings and pictures.

[Andy J]

Dave,
I modified mine last summer, as did a friend, in a manner similar to what you describe in the mentioned thread. I think I brought the cooler forward 1.25", which as I recall was about as far as it could go due to other clearance issues. It did help both of our plane's oil temps. I believe mine improved by 10 deg f, and I don't have any worries now. We also added an aluminum heat shield to the muffler. I can't seem to find the photos I had - Would like to see yours.

[Peterk]

Originally Posted by Dave12

Considering the numerous plans that I have sent out I thought I would start a separate thread on this subject. Pete just finished his mod. and was good enough to send me pictures. Too bad I don't know how to get them on this thread. Maybe Pete can get them on. Anyway, he reports that the mod has helped. If you have any questions about how this started, look up "Boiling Mad" from several weeks ago. [url]http://www.vansairforce.com/community/showthread.php?t=88612[/

If you pm me your email I will forward Pete's findings and pictures.

I'll try to explain what I told Dave (who was nice enough to tell me what he'd done) about modifying my oil cooler box. There are differences among us in how much room remains between the oil cooler and muffler. In my case it was about the width of my hand. Others have trouble getting a small finger in the space. Since I live in Texas where the temps exceed 100 several days in a row each summer we are very attuned to oil temperature mgt. Dave was convinced that moving the cooler box forward an inch made a considerable difference in his temps. I can always use temp relief so I followed his lead and it does indeed make a difference. Because there are so many factors involved (OAT, density alt, manifold pressure etc) I cannot offer engineering before/after results. I do have 360 hours on my RV12 though and there is no doubt that I can generate higher MP at lower oil temps than previously. As an example, my first flight was 104 ambient air, 4000' density altitude and I climbed at 70kts to 2500' (from 620) and never exceeded 230 degrees. I could cruise at 24.5 MP and 225 degrees. I have no idea how warm it was inside the bubble but my IPhone was flashing the yellow road sign screaming Temperature. I would conservatively say I gained 5 degrees and perhaps 10 at best. Dave asked me to post some pictures of my work with his technique. Thanks again Dave.

This is the "box" with the inch wide cut lines marked.



This is what's left when the box is out.



This is the box glassed back in one inch forward



And this is all done, ready for sanding and paint




Pete

[MartySantic]

Very nice description and photo set. At Oshkosh, Scott McDaniels was looking for others to perform the modification as described initially by Dave Farmer. Seems as though the distance between the oil radiator and the muffler is MOST critical and could explain why some see higher than the average oil temperatures with high ambient temperatures in the RV-12, and, others do not.

For the builders out there, when you set the position of the muffler, set it as far aft as you can get it!!

You are a true experimenter!! Next....maybe a heat shield on the forward side of the muffler?? Anyone? Ideas?

Maybe Scott will now comment.

[Geico266]

What temps are you seeing? Oil temps up to 260F on climb out and 230F in cruise are fine according to the oil companies and Rotax.

Before people start modifying the cowling please read the thread I started a couple of years ago on the same subject. While I agree the muffler is too close to the oil cooler the temps I am seeing with no mods are well within tolerances.

Also, it takes a couple hundred hours on your engine to break it in. Temps are reduced after that.

http://www.vansairforce.com/communit...ad.php?t=59578


Just another data point.

[Dave12]

Originally Posted by Geico266

What temps are you seeing? Oil temps up to 260F on climb out and 230F in cruise are fine according to the oil companies and Rotax.

http://www.vansairforce.com/communit...ad.php?t=59578

Larry, The bottom line on my temps? Very rarely do I see yellow. OAT has to be mid to high 90's and even then I only "visit" the very low yellow's. I have been wondering if that ingenious heat shield you made would help with that "visit". I flew several hours yesterday and my oil temps in cruise were 210-215 and the oat was around 90.

BTW, I did speak with a very interested Ken Krueger and at Osh regarding this and my gut feeling is that they will address it.

[Peterk]

No, I don't encourage everyone to run out and modify their cowling. There is no safety issue involved here. It is simply an annoyance issue. Yes, the tolerances allow much "yellow" flying. To me, it's kinda like changing your oil. Rotax says 100 hours. My preference is 50 simply because common everyday engine knowledge tells me that few things do more to prolong engine life than changing your oil. I fly in extremely hot ambient air many months of the year and simply prefer to run a cooler engine. This offers that opportunity. Its simple to do (thanks to Dave's creative mind) and doesn't compromise any structural issues. Many people up north put thermostats on their oil lines so they can avoid the annoyance of waiting 30 minutes for warm oil. If Dave's mod helps you sleep better at night, go for it. If you are happy flying in the yellow, that's fine as well, according to Rotax. (keep in mind, this is the company that approved a fuel line hose that didn't like gasoline and threw chunks of rubber into the carbs!) Anyway, what Dave did is one of the parts of "experimental" that really hit the nail on the head.

[Andy J]

I agree with Larry and Pete. I would encourage new builders to build per the plans, and especially be careful fitting the cowl so that it is not shorter than the scribe lines, as this will further reduce the clearance between the oil cooler and the muffler(Also affects the header pipe clearances) . Also as Marty mentioned: When mounting the muffler position it as far aft as possible. I think those of us in the hotter climates felt we needed a little extra cooling.

Just for reference sake here is another good old thread on the topic:
http://www.vansairforce.com/communit...ad.php?t=73378

[Jetguy]

I think Dave is on to something here. See the following Pictures of My oil cooler clearance with the lower cowl installed. As you can see it pretty close. I wasn't able to get a ruler in the picture but your looking at about an 1 1/4 inches between the two. I just thought about it and anybody who has access to their oil cooler could measure the aluminum braket at the right side of the picture to use as a measurement reference and then post it here.

[Jetguy]

As a follow up to my previous post. Right now I'm not going to modify my cowl like Dave's because my plane is done and painted. Ive developed my own strategies to deal with this problem. I only have high oil temps from June through August. As with Pete and Larry and the Rotax manual I keep the oil temp below 250f over most of the operating period. If operating in OAT temps of 90F to 100F I may have to make a reduced power climb no matter what the speed I fly to keep the temps down, I may run Mobil 1 synthetic for the summer months which is recommended by Rotax if I intend to operate above 250F for most of the flights.
Having said that, If I were to build another RV12 I would absolutely do the modification. Furthermore I think Vans should change to cooling duct to give more clearance between the muffler and the oil cooling radiator. At the least they should put a note in the directions letting builders know that this clearance is important during assembly.