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New optional plans OP-58 - Lower cowl louvers for RV-6/7/9

greghughespdx

Well Known Member
Advertiser
Van's has published OP-58, an optional (OP) plan set which describes the installation of lower-cowl louvers in the RV-6/6A. RV-7/7A and RV-9/9A engine cowls (note: this kit does not fit other model cowls). The louvers may be used where additional exit air flow, such as for cooling purposes, is desired.

You can order kit "COWL LOUVER KIT" from the Van's Aircraft online store or by calling the Van's order desk. Cost for the kit is $8.00 plus shipping and it includes parts for creating louvers on both sides of the lower cowl. Complete instructions describing cowl modifications and installation of the aluminum parts included in this kit are found in the OP-58 document. The builder/installer will need to modify the lower cowl and will supply fiberglass fabric and other materials used during installation.

You may download the OP-58 plans/assembly instructions at this link.

greg
 
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Louvers

I think this is a great option. Any idea how much CHT will drop?
Interesting that the louvers bend inwards ( inside of the cowl) iso outwards. What would be the reason for that?
 
Wow. There is a welcome underlying shift in messaging with this addition.
 
Wow. There is a welcome underlying shift in messaging with this addition.

Agreed. Instead of "you're doing it wrong" now we are getting "here is how to do it better, since you're going to do it anyway."
 
Test results

Now somebody hurry up and do a good job testing this new "option" for effectiveness in lowering CHTs and speed penalty after installation.
 
Since in all instances where the owner was asking for help in improving cooling, I have never inspected an RV that didn't have at least some level of issue with the baffling / cowling installation, and most of the time it was more than just minor leakage (Even though they were sure that it was as good as it could be), so this shouldn't be considered a Van's endorsed method of resolving cooling issues.
This is for instances where the rest of the cowl/plenum system has been optimized but other factors make adding additional cooling flow path area, beneficial.
 
I think this is a great option. Any idea how much CHT will drop?

about 30 degrees CHT difference on N540VF, IO-540 F1 Rocket on hot days.

It's easy to install an inside track(s) to hold an aluminum sheet to block these off in the Winter.
 
Since in all instances where the owner was asking for help in improving cooling, I have never inspected an RV that didn't have at least some level of issue with the baffling / cowling installation, and most of the time it was more than just minor leakage

Same here.

Scott, curiosity questions please. Assuming our intrepid owner is forced to fly with crappy baffling and too much timing advance...

(1) Why not just remove the core, make the 4 ply 9-oz layup, and cut the slots, skipping the metal louver?

(2) Or, why not enlarge the standard exit? A simple 45 degree cut increases exit area by 41%. Costs nothing and can be done in 15 minutes.
 
Louvers

I installed louvers during my build. I found them to be very effective in keeping the CHTs and oil temperatures in check during the summer months here in Arizona.

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Just to clarify, if one does a good job of baffling, they should not need this option? I am getting close to my first engine start, FAA inspection, paint shop date, etc. Don?t need another project. I installed a pressure plenum and everything else stock, hoping that it would be sufficient.
 
Just to clarify, if one does a good job of baffling, they should not need this option? I am getting close to my first engine start, FAA inspection, paint shop date, etc. Don?t need another project. I installed a pressure plenum and everything else stock, hoping that it would be sufficient.

You'd really only want/need to install these if, after flying and optimizing baffle seals etc., you find you need them.
 
Same here.

Scott, curiosity questions please. Assuming our intrepid owner is forced to fly with crappy baffling and too much timing advance...

(1) Why not just remove the core, make the 4 ply 9-oz layup, and cut the slots, skipping the metal louver?

(2) Or, why not enlarge the standard exit? A simple 45 degree cut increases exit area by 41%. Costs nothing and can be done in 15 minutes.



Dan,
Good point.
Did #2 and made all the difference after I installed louvers. Should of opened exit first.

Boomer
 
How to open outlet

Does anyone have pictures, or drawing of the ?45 degree? cut that is mentioned? Unclear on how this is implemented.
Thanks,
Wayne

N1179J. Purchased flying.
2019 donation.
 
Does anyone have pictures, or drawing of the ?45 degree? cut that is mentioned? Unclear on how this is implemented.
Thanks,
Wayne

N1179J. Purchased flying.
2019 donation.

I would also like to see some pictures to better understand how the cut would impact the interface with the center bottom support on the A models. Would a half-round cut on the sides of the exit be effective? That would prevent changing the center support. Maybe some kind of scalloped edge?
 
I will look on this sight. There are pics somewhere.

I cut mine about 1 inch down and then toward the front of the exit.
Both sides, then open up about 2 inches and then reglass.
With the A model it opens it up as Dan said ~41%.

Boomer
 
Does anyone have pictures, or drawing of the ?45 degree? cut that is mentioned? Unclear on how this is implemented.

45%20Degree%20Cut.jpg


I would also like to see some pictures to better understand how the cut would impact the interface with the center bottom support on the A models. Would a half-round cut on the sides of the exit be effective? That would prevent changing the center support. Maybe some kind of scalloped edge?

Yes, you would need to modify and/or eliminate the A-model brackets. What do they support?
 
45%20Degree%20Cut.jpg




Yes, you would need to modify and/or eliminate the A-model brackets. What do they support?

Thanks for pic Dan.
Found the old thread but no pics.
Dans way is great if you don?t want to extend bracket.
On mine I made the cut at second piece of yarn, forward ~12 inches
Pulled it down 2.5 inches and reglasses.
Extended the brace.
If you take off the gear leg fairing it will slide down and rebuild brace.

I did have a Vettermans 4 pipe and it was real tight.

Look at RV-8 OR TD and you will see the exit difference.

Boomer
 
The OP-58 kit may require less fabrication on an A-model. I realize some owners are not builders.
 
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Same here.

Scott, curiosity questions please. Assuming our intrepid owner is forced to fly with crappy baffling and too much timing advance...

(1) Why not just remove the core, make the 4 ply 9-oz layup, and cut the slots, skipping the metal louver?

That is an option that the installer could choose. Including the louvers give the installation a more purposeful / finished look (less of an after thought), and I think there is a very slight performance increase regarding flow volume (air doesn't like to exit an opening perpendicular to high speed dynamic flow) but I admit not a lot of effort was invested in proving that.

(2) Or, why not enlarge the standard exit? A simple 45 degree cut increases exit area by 41%. Costs nothing and can be done in 15 minutes.

Ease of installation and low impact on already painted cowls was a consideration. Along with other details and changes that could be involved with supporting the bottom of the cowl on "A" model installations ;)
 
45%20Degree%20Cut.jpg




Yes, you would need to modify and/or eliminate the A-model brackets. What do they support?

This is what I did - but I only ended up taking 1.5" off rather than the nearly 12" shown. I trimmed .5" at a time up to the 1.5" where the CHT's came under control for cruise, and then added the servo-louvers from Anti-Splat for hard climb scenarios to keep the oil temp happy.
 
Since in all instances where the owner was asking for help in improving cooling, I have never inspected an RV that didn't have at least some level of issue with the baffling / cowling installation, and most of the time it was more than just minor leakage (Even though they were sure that it was as good as it could be), so this shouldn't be considered a Van's endorsed method of resolving cooling issues.
This is for instances where the rest of the cowl/plenum system has been optimized but other factors make adding additional cooling flow path area, beneficial.

Scott - you're absolutely correct that, if done correctly, this is not needed. Reality and a large portion of your customer set seems to indicate that it is either very difficult to do correctly, or very difficult to motivate the builders to do it correctly. Either of those cases gives the same result - which is the cooling crutch. They are trading a few knots of drag for a few hours of modification and testing. It's not ideal but it is reality, and it's well for the kit provider to recognize trends amongst the customer set, even if it's distasteful. Not all builders are efficiency fanatics.
 
#3 baffle next?

Now when will the engine baffle kit be modified to fix the #3 0-fin depth issue?

I really like this new approach by van's. It says a lot that #1 is willing to invest in getting better, whether actually better or just perceived as better.
 
Needed with new mount

If i convert to the new style RV9a front gear, do I really need the louvers, or will a careful baffling job be enough?
 
If i convert to the new style RV9a front gear, do I really need the louvers, or will a careful baffling job be enough?

We included the new louvers in the kit with the new gear. Personally, I’d try without them first and then add them if needed - but note that the new gear assembly is bulkier in physical size and as a result does tend to block the exit area a bit more than the original Wittman style gear. On our RV-9A demonstrator the teamfirst flew the new gear without louvers and then found it was necessary to add them for cooling purposes. The net result between the aircraft before the new gear and mount vs. after new gear/mount and louvers were installed was a slightly cooler-running engine compared to when the project started.

The fact of the matter is every airplane is a little different. My perspective is that it’s a good idea to optimize sealing and airflow first, see what the results are, and work from there. There a higher likelihood with the new gear you’ll need extra airflow. I’m sure others will want to just install them from the get go. Your airplane, your decision!
 
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We included the new louvers in the kit with the new gear. Personally, I?d try without them first and then add them if needed - but note that the new gear assembly is bulkier in physical size and as a result does tend to block the exit area a bit more than the original Wittman style gear. On our RV-9A demonstrator the teamfirst flew the new gear without louvers and then found it was necessary to add them for cooling purposes. The net result between the aircraft before the new gear and mount vs. after new gear/mount and louvers were installed was a slightly cooler-running engine compared to when the project started.

The fact of the matter is every airplane is a little different. My perspective is that it?s a good idea to optimize sealing and airflow first, see what the results are, and work from there. There a higher likelihood with the new gear you?ll need extra airflow. I?m sure others will want to just install them from the get go. Your airplane, your decision!
Can you report on the effect on airspeed with the louvers installed?
 
Is there a reason this kit would not work on the rv-8?

If using the 45 degree cut method, what is the speed penalty?

Thanks.
 
Is there a reason this kit would not work on the rv-8?

Dimensionally the kit parts don?t fit in the space on the RV-8 cowl. You could of course fabricate something similar if you wanted to. The RV-8 is usually a well-cooled engine though. Have you already analyzed and optimized sealing of the existing cowl? What are you trying to address, oil temp or CHT or?
 
time for an experiment

But I think louvers are Ugly with a capital U. I will probably try all the tricks like streamlining the internal cowl airflow and such before resorting to louvers. I think I will flight test unpainted without louvers. Heck, I will be flying wide open anyway to break the engine in.:D JMHO. to each there own.

I am really thrilled Vans came out with this mod. so so very grateful.
 
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It?s high CHT for me. Oil temp has been a non issue. I?ve looked at baffling and made some adjustments. I?ve tidied up everything I?ve been able to locate to this point. I?m running electronic ignition but still set at a fixed 25 degrees BTDC. AFR on the fuel indicates a 12:1 ratio on a parallel valve IO-360. Cruise temps are typically ok but climb temps will jump up above 420 without much effort. I?ve got to level off, power back, and/or richen the mixture within 1500-2000? of a climb at 110 knots. Was thinking increasing airflow might be the next thing to try? I have the 4 pipe exhaust so the air exit looks pretty packed in there.
 
I have the 4 pipe exhaust so the air exit looks pretty packed in there.

If you?ve addressed everything else and know you have heavily restricted exit area, seems like you could be a reasonable candidate.

There are of course other options you can consider as well, especially if you like experimenting. DanH has done some really cool stuff on his RV-8, for example, and you can find detailed info about his ideas and results here on the forums.
 
On our RV-9A demonstrator the team first flew the new gear without louvers and then found it was necessary to add them for cooling purposes.

Ahhhh, the new gear. That explains a lot. Mind posting some photos of the new gear? It would be interesting to compare the degree of exit blockage, old vs new.

It’s high CHT for me. Oil temp has been a non issue. I’ve looked at baffling and made some adjustments. I’ve tidied up everything I’ve been able to locate to this point. I’m running electronic ignition but still set at a fixed 25 degrees BTDC. AFR on the fuel indicates a 12:1 ratio on a parallel valve IO-360. Cruise temps are typically ok but climb temps will jump up above 420 without much effort. I’ve got to level off, power back, and/or richen the mixture within 1500-2000’ of a climb at 110 knots. Was thinking increasing airflow might be the next thing to try? I have the 4 pipe exhaust so the air exit looks pretty packed in there.

Just for fun, make some measurements. What are the pipe diameters? What are the cowl exit dimensions?

There are well known build issues which can be corrected on a checklist basis. The top items are baffling and sealing, mixture, and ignition timing. I may add "four pipes blocking the exit" to the list.

Operational changes may also be appropriate, like pulling RPM to 2500 with a constant speed, and adding a bit more climb airspeed. Just going from 110 KTAS to 125 KTAS can add more than 2" H2O to cooling pressure, the magic of velocity squared.

This is a Lycoming chart for the O-360 parallel valve (same for IO-360 parallel). I've included an example. Plot a 4" baffle pressure drop rather than 6", and see where the CHT is predicted to be:

COOL%20O-360%20Revised%20w%20example.jpg


Increasing the exit area (per this thread) generally means a reduction in lower cowl pressure, thus an increase in baffle pressure drop.

With the usual suspects rounded up, I'd encourage pressure and temperature measurement rather than guessing. Upper and lower cowl pressures at a known air density and aircraft velocity tell a lot, as does exit temperature. For example, upper cowl pressure at 60% of available dynamic pressure says there is an inlet problem, or huge leaks bypassing the engine. High upper cowl pressure and zero lower cowl pressure says baffling/sealing is very tight, and adding louvers would be a waste of time. Low exit temperature indicates leakage or other cause of poor heat transfer. Email privately for a white paper if you want to do the work.
 
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For the record: Dan Horton and people like him are a big part of what makes the RV world an amazing place!
 
This will probably take it off on a tangent but what CHTs are we shooting for? For 12 years my -6 (O-360 normally aspirated) virtually never got above 400 then I switched engine monitor systems and all of a sudden they're going above 420 on climbout on a warm day! Obviously that's some difference in the probes not the temps themselves but I'm confident the new system is accurate.

Anyway is it bad to get into the 420s for the 5 minutes or so it takes to get to altitude? In cruse I'm always below 400, and by "the book" (Lycoming's), that's no problem. But I've read some articles that say you should never let it get above 400 more than momentarily. What's the common wisdom?

And Scott, you can expect me to drop by sometime and have you show me where I can improve my baffling!
 
On this same topic, I see a lot of variations in CHT issues from one build to the next. While in many cases it may be baffling, tuning, or exhaust configuration, I am curious if there are cowl variations impacting this as well.

For example, my CHTs are running really high. Now, the engine is still in break-in and it is summer, so that doesn't help, but I can barely get to pattern altitude under and stay under 450. I have a cooling plenum and have gone through it multiple times and made sure every leak is plugged.

When I fitted my cowl and airbox (vertical induction) I noticed that the clearance from the airbox to the cowl (pepto pink version) was very tight. Enough so that I left out the alternate air for lack of clearance. Also, the entire snorkel was a good 3/4" off center. I was at the airport yesterday and decided to trim a small amount from the cowl exit, but if I started short on exit area that could make a difference. Next Time I am at the airport I am going to measure the exit area for comparison.

I make pick up a couple pressure transducers so I can measure plenum vs lower cowl differential.
 
I have completed my install up to bending lovers from flat to 45 degrees and riveting down. Not a builder , so question is how to properly bend the tabs/louver. I cleco?d down and am hesitant to try to bend as the material between each opening is not all that stout and afraid it may flex and break. No reason they cannot be pre bent to 45 before riveting in place, just unsure of best way to do. I have access to straight blade seaming plyers......should I lightly score a line to help with bend or should I use some other better method. Have bench vise too. Thanks
 
I have completed my install up to bending lovers from flat to 45 degrees and riveting down. Not a builder , so question is how to properly bend the tabs/louver. I cleco?d down and am hesitant to try to bend as the material between each opening is not all that stout and afraid it may flex and break. No reason they cannot be pre bent to 45 before riveting in place, just unsure of best way to do. I have access to straight blade seaming plyers......should I lightly score a line to help with bend or should I use some other better method. Have bench vise too. Thanks

I used my thumbs, then seaming pliers on mine. I did them off the airplane.
 
Thanks Kyle. I took a scrap piece of 2x6 and some drywall screws and mounted it, got fingers under edge enough to come back with borrowed seamer plyers. All finished about remount cowl.
 
Sounds like you got it sorted but for future reference, never score aluminum for bending (or for any other reason except maybe to mark for a cut) -- that'll just set it up for a crack there in the future.
 
Thanks Randell , a good friend and 7A builder texted me the same. I appreciate builders looking out for us buyers :)
 
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