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Cowl Duct Modification

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Dave12

Well Known Member
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. http://www.vansairforce.com/communi... I will forward Pete's findings and pictures.
 
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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.
 
Dave12 said:
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. http://www.vansairforce.com/communi...l83/peterk48/Hanger/IMG_3010.jpg[/IMG] Pete
Click to expand...
 
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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.
 
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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/community/showthread.php?t=59578


Just another data point.
 
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Geico266 said:
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/community/showthread.php?t=59578
Click to expand...

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.
 
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.
 
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/community/showthread.php?t=73378
 
Oil Cooler Installed Pics

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.
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Follow up of Oil cooler Pictures.

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.;)
 
Geico266 said:
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.
Click to expand...

I stopped by the Rotax booth and asked the same question as I did the year before. I received the same answer. And that was......red line is red line, do not exceed it. And try to maintain the oil temperature less than 230 degF. Operation above 230 degF should be limited. Maybe a CYA answer but amazingly I did receive the same answer.

I was under the impression that red line was 248 degF not 260 degF per the Rotax manuals and the POH.
 
You Make the Call!

This where it gets a bit confusing,
Yes this is what it says in the POH;
Oil Temperature
Minimum 122? F
Normal in Cruise 190? to 230? F
Caution Range (yellow arc) 230? F to 248? F
Maximum (red line) 248? F
However I can tell you that my red line on my locked settings D-180 is not 248F its 266F. The Rotax Operating Manual, Engine 912 ULS, page 2-5, dated 4/2010, says red line is 266F. Next lets reference the last page of Service Instruction SI-912-016-R4. This bulletin was dated August 2011. It reads as follows:
rotax5017.jpg

:confused:
 
The 912 likes it hot!

Agreed, you make the call. I am not urging anyone to do anything. From where I sit, all of the Rotax oil temps give new meaning to being boiled in oil. I have no problem with the oil heating to 212 degrees for obvious reasons, it's a good thing. Beyond that, I start to become skeptical. Cruising around at 235 or 240 and visiting 255+ is outside of my comfort and I will agree that's a personal thing. This was my issue with my -12 and for peace of mind, it had to be corrected. Some guys were having this issue and some were not, so there was also the lack of consistency.
As Jetguy says, It's your call. The Rotax likes it HOT!
 
Good stuff Dave, and you should be commended for taking the initiative.

I too thought 230 was too high for cruise, and 250 was way outside what I thought was "good". Then I talked to the Rotax reps and Shell Oil lubrication engineers at several OSH seminars. I had my -12 outside the Rotax tent for OSH 2 years ago, the subject came up many times, including Eric Tucker ( "Mr. Rotax" help designed and build the 912 series engines 20 years ago, and is the North America Rep for Rotax) They are perfectly comfortable with the 230F cruise, 260F climb out temps, so I decided to abandon my quest for cooler oil, and just fly. Like Pete I change oil after 40 - 50 hours, cheap insurance.
 
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I moved my oil cooler forward and have not seen oil temps in the yellow since. The OAT's have been around 90 each flight. This mod definitely worked for me and thought I'd pass on my results.

Rick.
 
Jetguy, I don't have pics but my measurements indicate that the bottom of the oil cooler was moved out about one and a half inch and the top about three fourths of an inch. The top moves out less because of the oil line length restriction. The bottom of the cowling slopes up so the oil cooler moved up higher one half of an inch as it came forward. I tack glued it in place and did a trial fit to check for clearances before glassing it in. There are two safety wire tabs on the bottom of the engine that I had to make relief for in the fiberglass just in front of the oil cooler. A trial fit will show any clearance issues and it took me two tries.

Rick
 
Just one more note and then I'll move on... Did another test flight yesterday with ground temps at 92 degrees. I was able to get the oil temps into the yellow by climbing to 4,500' at 1000' per minute (field elevation was 500' msl). Oil temps went to 235 but dropped into the green in a minute or so after I leveled off. I then descended to 1200' and cruised at 5000 rpm for 20 min and oil temps were a consistent 214 - 218. I am pleased.

Rick
 
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morsesc said:
Just one more note and then I'll move on... Did another test flight yesterday with ground temps at 92 degrees. I was able to get the oil temps into the yellow by climbing to 4,500' at 1000' per minute (field elevation was 500' msl). Oil temps went to 235 but dropped into the green in a minute or so after I leveled off. I then descended to 1200' and cruised at 5000 rpm for 20 min and oil temps were a consistent 214 - 218.

Rick
Click to expand...

I'll second that.
 
Oil cooler distance update

Here is a side by side comparison of my oil cooler picture to Dvalcik oil cooler picture. Note the upper spring location.
Mine,
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Daves,
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Side by side,
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John, it's forecast to be 90+ tomorrow. It will be interesting to see what Dave's oil temps are. Dave's clearance is about what you get after the mod..
 
Muffler Shield

Now that I have enough room between my oil cooler and muffler, I have taken a shot at a shield between them. It is 8 inches wide and 10 inches long with two 55% bends at either end. It is attached with "inside" riveted slots and three TBolt clamps around the muffler.

In my enthusiasm to see what I'd done (it was 100 deg today) I climbed out at 1000'/min or more, full power. As I went through 2500' I was elated to see 215 on the oil temp. Oops, forgot about that stuff called anti-freeze. When the CHT's go up, they go up fast! So anyway, I leveled off and made plans to fly to Austin tomorrow (hour and a half) so I will have fun playing with it.

Honestly, my expectations are that I will see little change...Dave's mod already handled it. Unfortunately, there really isn't enough room for a shield until you do move the cooler. At the same time, something makes me think there is still room for improvement. So we'll see.
 
Peterk said:
Honestly, my expectations are that I will see little change...Dave's mod already handled it. Unfortunately, there really isn't enough room for a shield until you do move the cooler. At the same time, something makes me think there is still room for improvement. So we'll see.
Click to expand...

Pete, I have had the same thought. Larry Geiger had some success with one a couple years ago. Since seeing the results and 50 or so hours of summer flying after the mod, my oil temps are solid around 210-217 degrees and I am satisfied with that. One concern I have is that here in Md., we have real winters and I am wondering if I have extended my already long warm up session. I can't believe I am asking this, but will my oil be too cold? I know that my temps will be headed down as fall sets in and it will not reach 212. IMO it still beats 230-240 in the summertime.
 
Dave. For that very reason, I made my shield instantly removable. In fact, even here in Texas, I have to put a piece of aluminum between about half of the oil cooler and the cowling when winter rolls around. Feast or famine huh? Let me know when you design an affordable cabin air conditioner okay? Still 100 deg all week here.
 
Distance between Oil cooler and Muffler!

Thought I would update my last post with one last picture to
use as a reference to gauge the distance between my muffler
and my oil cooler! So I would say that the distance that you see
in my earlier posted picture picture of my plane is about 3/4 inch.
Davids distance is closer to 2 inches. David does not have any oil
cooling problems what so ever. So using the above statements
other builders need at least 1 3/4 inches spacing as a minimum
to get the cooling expected from your set up. It would be nice if
Scott would go out and measure the distance on Vans red RV12
with the lower cowl installed then we would know with out a
doubt. But with out that this is my best estimate.
2012-10-01131109.jpg
 
Blast from the past!

Since the weather has been really cold I thought I would take some time to revisit this problem and make some corrections before summer hits. I won't have time then. As you can see from all my previous posts I had about 3/4 inch between my oil cooler and the muffler. Starting in June and ending in mid September when the first cold front comes though and breaks the summer heat I run some high oil temps. I can usually work around this problem. It becomes a bigger problem when trying to climb high to find cool air on the way home from OSH during the middle of summer. During the climb with OAT in the high 90s I would easily see oil temps above 250F even if I step climbed to altitude. When I flew Dave Valciks plane he had approx 1 3/4 inches spacing. When we did the 75kt climb to 10,000 while doing his flight cards he didn't have any high oil temps so this convinced me to do the mod when I found time. So here it is with some new pics for guys who may want to do it later on.;)
87dbf7c15e6a92f3c1757b69de2c413e_zps8d7549f2.jpg

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6fa5fab909e8806c53c0bde96fa8b0d8_zps768a7605.jpg

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cfb93fa4f63e1c85b46b6f26a4f288ad_zps7ae3029f.jpg
 
Hose lengths with this mod

John,

I'm curious/concerned when moving the radiator forward, as I recall, the hose connecting to it (on the back) is pretty tight and maybe not amenable to another inch of extension. Maybe I have things routed wrong, but there doesn't seem to be any slack for moving it forward, even by 3/4ths of an inch. ?????????
 
Oh I thought of that.;) Last fall during an oil change I rerouted the oil feed hose in anticipation of this mod. Then before starting the mod with the cowl off I manually repositioned the oil radiator to the my best guess.:D It should work fine. You would need 1 inch more to do the mod. This being my first airplane build and as I recall the directions were a little hard to read when routing the hoses. Fast forward to now with a much better understanding and a clear view of where everything goes I could even reroute the hoses one more time and get 2 inches if need be but I think I'm good for now.
 
John - great pics, I may do this. My cowl is painted. How did it look into the fishmouth when you were done before any touchup?

Also a pic of your revised hose routing please!
 
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Bill_H said:
John - great pics, I may do this. My cowl is painted. How did it look into the fishmouth when you were done before any touchup?

Also a pic of your revised hose routing please!
Click to expand...

Bill, I did not have to touch my hoses at all.
 
I'm all done with my cowl mod. Things a learned along the way. You don't want to arch the top part of the tunnel when you reattach the part where the oil cooler attaches as seen in the first pic. I has to go back and redo that area. I had to cut out that area and reglass it with a dip in it as seen in the second pic. There is a point where you can't go any farther forward with out hitting the bottom of the engine because of height of the square frame where the cooler attaches. In the third picture you can compare pics from my earlier post and see now I have about 1 1/2 inches between the cooler and muffler. Before I had about 3/4 inch, use the spring attach point as a reference to compare. The forth pic shows the final product. After I fly it for a while I'll go back and do the cosmetic work and then repaint the inside of the tunnel. I won't know for sure how well it works until the summer kicks end. I'll update when that happens.;)
94dcc8886c6dd20b0820f3df8e7dd04c_zpsf828fcf6.jpg

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5ad4dd4bcc375b2a458adf27111e6a8c_zpsf80ffab7.jpg

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Looking down the throat, seems to be...

a recent tonsillectomy.

Question: you are removing a 1-inch strip, and basically sliding the remainder forward an inch. By forward, I suspect this means "up a bit" also, hence the interference? Sliding it up, do the two edges basically match up on the same level, or is there a step in the glass at that point to join things back together--looks like it is perdy smooth, at least on the top, but a step discontinuity on both of the sides.

NIce thing about this mod is that its just fiberglass--don't have to deal with the pro-seal/devil's snot on this one--will reserve my aggravation for the tank SB :D.


Our machine seems to start out with less clearance--< 1/2", and I don't think we hit any red lines during last summer, but will still be doing the mod.
 
Looks good John. Are you going to leave the insulation on the muffler?
 
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Question: you are removing a 1-inch strip, and basically sliding the remainder forward an inch. By forward, I suspect this means "up a bit" also, hence the interference? Sliding it up, do the two edges basically match up on the same level, or is there a step in the glass at that point to join things back together--looks like it is perdy smooth, at least on the top, but a step discontinuity on both of the sides.

Our machine seems to start out with less clearance--< 1/2", and I don't think we hit any red lines during last summer, but will still be doing the mod.
Click to expand...

Yes that is what I did, cut out a 1inch strip and move it forward 1inch. No, the oil coolers frame won't line up perfectly. Just get it close then glass it in place. You might want to wait through the summer and see how yours does. Here are some pics after my final install of the oil pump for reference. You need at least 1/4inch clearance between the the oil pump and the cowl.
If this cowl mod works out ok Ill take the header wrap off. I didn't really see any cooler temps when using it.:(
bb3fedb4582370f834d4638ce84497e4_zpsd239301a.jpg

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I would prefer to buy new cylinder exhaust pipes which are shaped differently or longer to move the muffler back than all the fiberglass work required mentioned in the above posts. Oh I forgot to mention I hate to fiberglass! With the NEW cylinder exhaust pipes, I guess a new exit hole would need to be made in the lower cowling......just can't get away from fiberglassing and repainting. :mad:
 
Paris12Man said:
With the NEW cylinder exhaust pipes, I guess a new exit hole would need to be made in the lower cowling......
Click to expand...

Maybe not. Looking at the plans, the exhaust pipe seems to exit a little more vertically than before. Worth checking with Vans anyway. If so, it would (could?) be a simple alternative to modifying the cowl.
 
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Cost to Replace?

I wonder how much it would cost to purchase the new system. It does look like you would have to get all 4 pipes and the muffler.

The new EX-000xx part numbers are not on "The List" yet.

I haven't even started my engine yet.
 
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