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Old 06-24-2019, 04:59 AM
flysrv10 flysrv10 is offline
Join Date: Jan 2010
Location: Florida
Posts: 244

I struggled with high CHT and oil temps for many years. I was almost ready to replace the oil cooler with a larger one as couple of companies have large oil cooler recommendations for RV10 owners.

I decided to check my Vernatherm and sure enough, it was stuck closed (or is it open?). Fixed the vernatherm and the difference is day and night for CHT and oil temps. Interestingly, Vernatherm is an item that is not checked during engine overhauls.

I do not have louvers or cowl flaps and now do not have cooling issues. I think before you decide to install louvers or cowl flaps, you need to be sure that your CHT readings are accurate and your baffling is tight, then check Vernatherm.
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Old 06-24-2019, 06:29 AM
DanH's Avatar
DanH DanH is offline
Join Date: Oct 2005
Location: 08A
Posts: 9,328

Given the wide speed range of an RV model, variable exit area will far superior to fixed louvers.

I'd suggest arranging things so exit area varies from 25% less than stock to 50% more than stock, fully closed to fully open.
Dan Horton
Barrett IO-390
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Old 06-24-2019, 06:57 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is offline
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 2,486

Just another data point.

RV-10 with stock engine, James Cowl and Plenum. I used the louvers from Cleaveland tool instead of the stock Van?s ones as I did not like them.

Biggest test was flying out of Phoenix in the summer time directly up to 13K?. Take off was a little under gross. CHTs and oil temp stayed in the green.

Note - I did climb out at a reasonable 120 kts or so.
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Old 06-24-2019, 07:17 AM
lr172 lr172 is offline
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,068

Originally Posted by BillL View Post
My 10 Friend built his stock to the plans and has no cooling issues. We did a good job of sealing the leaks, and the same climate you will see. I am a good sealer . No timing advance.

You should have no trouble.
By stock, do you mean with the kit provided louvers installed in the cowl?

N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019

Last edited by lr172 : 06-24-2019 at 07:24 AM.
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Old 06-24-2019, 07:21 AM
lr172 lr172 is offline
Join Date: Oct 2013
Location: Schaumburg, IL
Posts: 5,068

Originally Posted by rvbuilder2002 View Post
One comment that will do little to answer the original question but will help understand the issues involved.....

There is no one absolute configuration that will work perfectly on every RV-10 (or other models for that matter). Every engine has a different personality. It is not uncommon for two exact matching airplanes (with the exact same level of workmanship regarding baffle installation, etc.), to have differences in temperatures.

I have experience with removing an engine, having it overhauled, and reinstalling it exactly the same as it was before, and having totally different CHT and oil temperatures.

The louvers were added to the RV-10 based on the limited testing that could be done with a couple of prototypes. In service experience seems to have shown that on most RV-10's having louvers installed will be preferable to not having them.

In the recent flight testing done with the louver installation for the new nose gear on the RV-6,7,9, all of the speed test data indicated that after adding the louvers, if there was a speed penalty, it was so small that it was lost in the data noise. I can't say for sure why, because in theory it should cause some drag. Possibly this type of flow path (one where the flow is not exiting parallel to the external flow) is throttled somewhat at high speed, but at lower speed in a climb it increases the mass flow enough for a cooling improvement (we didn't take the time to instrument and see what the differences were at different airspeeds). The goal was to improve cooling in a climb and that is what they did. Some amount of speed loss was expected but there was none. This could be because the louvers were offsetting a loss in flow caused by the new (more restrictive) nose gear.
FWIW, I recently installed the louvers on my personal RV-6A, which does not have the new nose gear installed, and in the limited testing I have done so far the cruise speed seems to be unchanged.
As a comparison, these louvers are slightly larger in total area than what is supplied in the RV-10 kit.
Thanks. Very helpfull.

N64LR - RV-6A / IO-320, Flying as of 8/2015
N11LR - RV-10, Flying as of 12/2019
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Old 06-24-2019, 08:01 AM
falcon900guy falcon900guy is offline
Join Date: Jan 2014
Location: Vero Beach
Posts: 110

i have a rv10 with io540 built with 10:1 compression, port and polished, blah blah blah. there is EFII ignition and injection on the airplane, and still will make a couple of changes after paint to the system but have battled high temps for a while until we did some science experiment. we had got in touch with DanH and he coached us through some different trails and narrowed down some weaknesses in my airplane. 1st thing, we hooked up a manometer to some piccolo tubes measuring differential pressure on top and bottom of engine, and we had a temp sensor near the exit area. he had us fly a triangle pattern at different settings, altitudes, speeds, etc and record the data. biggest thing i learned was a lot of holes in baffle as well as in efficiency of air on my showplaces cowl air inlet entry. we reworked the air inlet on showplaces cowl, closed up every hold possible on baffle, and changed the rubber on baffle. this made a huge difference and dropped temps but didn't cure my problem 100%. i spent a day at jet guys out of covington, tn and owner shared a tip with me how to make a lip on aft exit of cowl, and also we put a half piece of pipe on bottom of firewall each side of cowl at the exhaust to create a low pressure sucking the hot air out. he said not a guarantee this would do anything but wouldn't cost anything to try the experiment. we taped the parts on cowl and firewall, and my temps were down 20 degrees lower from previous flights. i was having to add mixture just to keep CHT's down under 400 prior to this low pressure experiment, but i was running 24 square at 4500' the flight test with no mixture at all. i have no cowl flaps or louvers and will do a couple more flight tests to verify our results, but looks like through experimentation have found a positive result for cooling on "my airplane" without cowl flaps and louvers. I'm not saying it will work on everyone's airplane, but through experiments while flying think we have it licked. i have some pictures to show what we did. don't know if this helps but there you have it

Last edited by falcon900guy : 06-24-2019 at 08:07 AM.
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Old 06-24-2019, 11:09 AM
AviatorJ AviatorJ is offline
Join Date: Feb 2015
Location: Oklahoma City
Posts: 909

Originally Posted by falcon900guy View Post
i have some pictures to show what we did. don't know if this helps but there you have it
Not to hijack the thread but I would like to see those pictures!
RV-10, N10JW
First Flight 2/14/2019
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Old 06-25-2019, 05:25 AM
falcon900guy falcon900guy is offline
Join Date: Jan 2014
Location: Vero Beach
Posts: 110

PM me your email address and I'll send them your way. Going out of town on a trip so give me a day or two, but I will send you what i have.

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Old 06-25-2019, 08:19 AM
TShort TShort is offline
Join Date: Jan 2005
Location: Indianapolis, IN (KUMP)
Posts: 1,008

If it's ok, could Justin post them here? I am curious as well.
Thomas Short
KUMP - Indianapolis, IN / KAEJ - Buena Vista, CO
RV-10 N410TS bought / flying
RV-8 wings / fuse in progress ... still
1948 Cessna 170 N3949V
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Old 06-25-2019, 08:20 AM
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NovaBandit NovaBandit is offline
Join Date: Feb 2011
Location: Hastings, MN
Posts: 582

I think I was one of the first to put the AntiSplat cowl flaps in a 10 in lieu of the traditional louvers.

I battle a little with high CHTs, especially if I'm heat soaked... even in moderate temperatures. I absolutely have room for improvement on my baffling, and I'm hoping that will help a lot when I redo the baffling material, but the cowl flaps are not a magic bullet.

Mine are on the very bottom of the cowl, in the place of the stock louvers. The difference between them open (fully) and closed (fully) is only a few degrees at high power settings. I'd really like to tuft the area, as I think they might be opening TOO far for the AOA at a 120kt climb, and possibly creating a lot of turbulence at the cowl exit... reducing cooling potential.

Here is my blog post showing where I have them installed:
Ed Kranz
RV-10 N829EC - Flying
First Flight: 8/29/15
KSGS - Fleming Field, South Saint Paul, Minnesota
-- Build Timelapse and Travel Videos . . -- Build and Travel Blog
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