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Do I need Louvers

lr172

Well Known Member
I am wondering if anyone has successfully gone without louvers on the 10 or if they are really required to keep temps in line. I suspect that they will add some drag and would like to avoid that penalty if possible. My issue is break in heat and a lack of desire to experiment with this during break in. However, getting rid of the louvers latter will require a bunch of glass work.

Anyone leave them out with success? Anyone know what the drag/speed penalty is for these louvers? I am curious if the louvers are a crutch for poor baffle sealing or truly a necessary component for airflow.

I could make a cowl flap, but trying to accelerate the build process to get in the air before the cold weather.

Thanks for the input.

Larry
 
I have an Anti-Splat cowl flap and am seriously considering starting out with no louvers to see how it goes - or perhaps a modified set of louvers without as many slots - for the reasons you list (drag).
 
Larry, after flying my -10 for a year and seeing cylinder head temps consistently on the cool side, I removed the louvers and covered the slots with an aluminum blanking plate. Results over the past four years are acceptable......the worst case situation is a quick fuel stop on a hot day, and in a case like that, with a heat soaked engine and high OAT I need to cruise climb or step climb. Cool weather and a cold engine, no problem with a high performance climb. I would not advise going without louvers if one flies a lot in hot weather, but for those of us that do most of our flying in cooler weather, it works out. I wish I had not cut my cowl, it will be a lot of work to fill those slots.

Cowl flaps would be even better, and are on my long term project list.

Andy
 
I asked the same question some time back to Scott McDaniels. He indicated that the factory prototypes showed a need for additional cooling and louvers were the solution.
 
Larry, after flying my -10 for a year and seeing cylinder head temps consistently on the cool side, I removed the louvers and covered the slots with an aluminum blanking plate. Results over the past four years are acceptable......the worst case situation is a quick fuel stop on a hot day, and in a case like that, with a heat soaked engine and high OAT I need to cruise climb or step climb. Cool weather and a cold engine, no problem with a high performance climb. I would not advise going without louvers if one flies a lot in hot weather, but for those of us that do most of our flying in cooler weather, it works out. I wish I had not cut my cowl, it will be a lot of work to fill those slots.

Cowl flaps would be even better, and are on my long term project list.

Andy

Thanks for the input. Did you notice a speed increase when you covered them up? Trying to quantify the drag penalty.

Larry
 
I asked the same question some time back to Scott McDaniels. He indicated that the factory prototypes showed a need for additional cooling and louvers were the solution.

This is what I was afraid of. Assuming they did a good job on the baffling (likely, I think), that is probably the confirmation I was looking for.

Thanks,

Larry
 
I have an Anti-Splat cowl flap and am seriously considering starting out with no louvers to see how it goes - or perhaps a modified set of louvers without as many slots - for the reasons you list (drag).

Have you compared the area of the cowl flap vs. the louvers? I would expect the cowl flow to eliminate the need for louvers.

Larry
 
I have cowl flaps in lieu of louvers.... I?ve been working on baffle and cowl improvements and recently got my temps where full power take offs are manageable on a 95 degree day.

Still working on a few things and if I can?t to where I can do a solid 120 knot full power climb and keep all CHTs below 400 then I might try some louvers as well.
 
No Louvers & no cowlflaps. I fly in San Joaquin valley CA with CHTs all well below 400 even in climb with OAT >100 F. Standard Vans construction with VERY careful attention to sealing all possible air leaks. I do have to cruise climb a bit faster in hot weather (120 to 130 kt) to keep oil temps under 220
 
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.
 
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.
 
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.
 
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.
http://www.cleavelandtool.com/ALUMINUM-PUNCHED-LOUVER/productinfo/4680/#.XRDGxsopChA

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.
Carl
 
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 :D. No timing advance.

You should have no trouble.

By stock, do you mean with the kit provided louvers installed in the cowl?

Larry
 
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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.

Larry
 
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
 
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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.

kenny
 
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:
http://www.goodplaneliving.com/cowl-flaps-finished/
 
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.

You got it. If the air is bypassing the hot parts, it contributes only drag. Exit area as big as a garbage can won't solve an underlying problem with poor heat transfer. Cold air in, only lukewarm out, and the engine stays hot.

It's why I ask folks to measure exit temperature.
 
I have stock 8.5:1 io540 and feel I have tight baffling and rtv?d gaps . I struggled with whether to put in louvers based on others that have gone before and decided not to. I?m in Michigan but have flown in Florida with 90+ temps and am comfortable with my cylinder temps in cruise and simply don?t climb as quick if temps get around 400 but usually that?s not a problem. Oil temps not an issue with butterfly valve which works well and can keep oil temps where I want them. I have dual ei and not sure if that makes a difference or not. Just more info to ponder.
 
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.

I don't exactly follow you on this. Did you fair the lip on the firewall with that piece of pipe to get a smoother transition (and better exit velocity)?

Thanks,
 
Anti-splat Cowl Flap

I put one anti-splat cowl flap on the right side of my cowl because the #3 cylinder of my 6A's O320 runs hottest. One nice thing about Anti-splat is that it is very easy to install. I see a CHT reduction of about 5 degrees F when I open it in straight and level cruise.

I need to work on baffling to get more balanced CHTs but I'm glad I have the cowl flap for those real hot days. John
 
I have stock 8.5:1 io540 and feel I have tight baffling and rtv?d gaps . I struggled with whether to put in louvers based on others that have gone before and decided not to. I?m in Michigan but have flown in Florida with 90+ temps and am comfortable with my cylinder temps in cruise and simply don?t climb as quick if temps get around 400 but usually that?s not a problem. Oil temps not an issue with butterfly valve which works well and can keep oil temps where I want them. I have dual ei and not sure if that makes a difference or not. Just more info to ponder.

Thanks for sharing.

Larry
 
I had the same problem in climb with CHT's (400) when I was in phase one. I used Nick Nafsinger's cowl flap design and added cowl flaps outboard of the cowling exit on the bottom. My temps dropped to 380 during climb and I was able to climb out at 110kts and 800-1000 fpm.
These cowl flaps were added after the -10 was painted. Very little touch up was needed.
I have drawings and pictures on my web site http://www.nwacaptain.com/cowl_flap.html if you are interested.
 
I've been battling with higher than desired CHTs (>400). At the time I only had two cowl flaps in the same location as the default RV-10 louvers. Typically my hot cylinders were 1,2,5,6. At times a few of these would push towards 440 on my earlier flights. Here were some of the steps I took which incrementally improved things.

- Ensured baffling material was flat, especially in the rear corners.
- RTV'd obvious openings.
- Did the 'washer trick' behind #5.
- Trimmed 1 & 2 baffle dams.

The above along with pulling power out faster, managing climb speed (125 knots) helped but I was still seeing 1,2 & 6 get into the 430s (5 was good) and I didn't really like reducing power so fast and it started to get hotter out which started to drive the temps back up. So next I-

- Went through a ton of RTV, putting it on every gap, between the cylinders, all over my hands, floor... it was a mess but hey it has to be sealed at this point right?
- I also replaced the outboard lower baffle rods with some ends I fabricated out of bolts and used hose covered safety wire to pull them in nice and tight.
- I shimmed the space behind #6 to ensure there was an adequate gap.
- A major improvement was fiber-glassing in the top cowl inlets especially around the prop governor.

This got me able to full power climb in about 80 OAT with 1&2 just a bit over 420... still high but easily manageable.

The latest, and the reasoning for me posting here, was the installation of stock louvers in the not stock area. I'm post paint so the idea of installing something that would botch that up didn't set well with me. I noticed Vans now sells a louver kit for the 7&9 which looked as if they could be replicated on the 10. So that's what I did, I installed two louvers in the bottom area on the most outboard part of the lower cowling.

Here are some pictures but all in all it took me maybe 10 hours, most of that being the fiberglass work. These louvers in conjunction with my cowl flaps open seemed to really improve airflow. Today 91 OAT, full power climb at 95 knots (was doing this on purpose) and the hottest cylinder was 410. My intent was to push it hard and see the results. I'm really happy with the results of the louvers. I look forward to sub 400 climb outs!







 
Looks good, did you buy and adapt the louvers from Van's or was this 100% roll your own?

Lynn
 
Looks good, did you buy and adapt the louvers from Van's or was this 100% roll your own?

Lynn

They're the stock RV-10 louvers.


Do you have data to compare cruise before / after?
Curious how it affects the top end.

Next time I download all my log data (Oil change typically), I can compare my current cruise speeds with some previous trips. If there are any major delta's I'll put them out there. I would have gladly given up a few knots for a cooler engine. I did find a picture I took of my EFIS, I was at 65% power 2350 props going 151 TAS.
 
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