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Cowl louvers for RV-8 ?

mcaf

I'm New Here
Hi folks - wondering if anyone has recommendations for a source of cowl louvers for an RV-8?

Our RV-8's CHTs are running hot. We've got a tuned Aerosport Power IO-360, 9.0:1 pistons, plenum under a modified Sam James cowl, dual Pmag ignition and 4:4 Vetterman exhaust. We've used a tube of RTV to plug any air gap we or our A&P can find, have retarded the ignition slightly from the dataplate (to 20 degrees advance), are running the Pmag "B" curve and have even filed down any excess material between cylinder cooling fins. We're still seeing CHTs in the high 380s/low 390s at around 3,000' running 24" 2,400 rpm full rich at 60F OAT.

Scratching our heads a little we now think we might have an exit air area problem. To louver or not to louver seems like a well-debated topic (with some good threads e.g. here and here). Swaying us a bit is the fact that Van's sells a cowl louver kit for the RV-6/-7/-9.

I've poked around a bit but can't find any kind of kit for the -8 - anyone know of a source?

Thank you!
Marco
 
airspeed?

... We're still seeing CHTs in the high 380s/low 390s at around 3,000' running 24" 2,400 rpm full rich at 60F OAT. ...
Some people have installed louvers in their RV-8, and there is nothing magic about the kit that Van's sells for the other models. You could probably use it or something similar.

cat-med_cowl-louver.jpg


Any chance a cowl flap might be a better solution?

https://antisplataero.com/products/ez-cool-cowl-flap

Depends on if it's a problem during climbout or in cruise.
 
Hi folks - wondering if anyone has recommendations for a source of cowl louvers for an RV-8?

Our RV-8's CHTs are running hot. We've got a tuned Aerosport Power IO-360, 9.0:1 pistons, plenum under a modified Sam James cowl, dual Pmag ignition and 4:4 Vetterman exhaust. We've used a tube of RTV to plug any air gap we or our A&P can find, have retarded the ignition slightly from the dataplate (to 20 degrees advance), are running the Pmag "B" curve and have even filed down any excess material between cylinder cooling fins. We're still seeing CHTs in the high 380s/low 390s at around 3,000' running 24" 2,400 rpm full rich at 60F OAT.

Scratching our heads a little we now think we might have an exit air area problem. To louver or not to louver seems like a well-debated topic (with some good threads e.g. here and anhere). Swaying us a bit is the fact that Van's sells a cowl louver kit for the RV-6/-7/-9.

I've poked around a bit but can't find any kind of kit for the -8 - anyone know of a source? Thank you! Marco
What are the CHT's 1, 2, 3 and 4. Usually cylinder #3 Back RHS (passenger side). The fins on the back side of the #3 cylinder are very shallow and your baffling can choke airflow. The trick here is add a little more gap between baffled and cylinder (with spacers). As usual are your CHT probes (I assume bayonet type not spark plug ring types which read high) are calibrated.

Your cruise CHT at 75% power (24/24 at 3500') is at 60F ambient is under 400F, you are golden, which is below Lycs recommended operating limit of 435F. Red line is 500F! For the most part there is no CAUTION limit on Lycs, in theory you can operate at 450F or 465F up to 500F. Continental Red line is 460F. We can agree as owners who would pay the bill for a burned valve or seat that is too high. You are right and I am a big proponent however to keep CHT's below 400F, but it's far from a Lyc limit. However if it get's to 420F or a little higher for a short period that's OK. 420F is my limit for climb. Lycs Tech TIPS does recommend for long engine life, CHT of 400F or less, power settings of 65% or less, OT of 185-210F and CHT never above 435F for continuous operations.

With your high higher compression, full rich at 75% is a good idea. I'd stay full rich to 65% pwr a safe point to lean. You retarded timing and that likely gets you detonation margins back.

Retarding timing, excellent. I assume B-curve is the more conservative advance schedule. Electronic ignition can increase CHT. Retarding timing helps CHT and loss in power is minimal. With 9:1 you have less detonation margins, so retarded timing gives you back margin of safety to detonation.

Sealing gaps, excellent. If you have a Sam James Cowl you should also have round inlets with a flexible sleeve to a pressure plenum. This does not rely on soft baffle seals against the upper engine cowl as in stock Van's installation. Check the inter-cylinder baffle. If your Sam James cowl and cooling plenum are set up well, metal baffle part sealed against engine case, you are getting the max inlet air these inlets can give. You can't increase cooling air IN. The inlets are sized for a stock O-360; your 9:1 is making a little extra power/heat, but you can lower power by throttle and cooling of course by mixture. As stated above check #3 cylinder to baffle gap, increasing it (thickness of a nickle) will lower #3's CHT.

What is your oil temp? The engine is air & oil cooled. How many rows in cooler and what is the air plenum like? Upgrading the oil cooler and improving the airflow (in and out) of cooler, lowering OT will help CHT (a little). In cold weather you want a min OT of 190F. If you are seeing OT in the 210F range, it's probably OK. If you have OT 245F (Lyc max operating) a bigger cooler with better airflow is in order.

Increasing the cowl exit will lower the CHT but at added drag. A lot of piston military and civilian planes for over 80 years have used cowl flaps. The ones you are looking at are fixed it appears to me. That is fine, but you really don't have a cooling issue with 385F (hottest cylinder) at 75% cruise. Climb a different story.... see next Par.

You have a hot home-built, and to go fast you have to minimize cooling drag. The fact you are rocking 9:1 pistons you'd expect these temps or higher. With 385F you are very good. Now on hot day, heavy plane, long climb to altitude, this is the critical test. Over 400F is OK for short periods from time to time. How hot is too hot? Well personally I never like to see over 420F but according to Lycoming you can go much higher (at least for short periods not continuous operations). My RV on really hot summer days, two people, long climb to altitude, I had to shallow the climb or level off momentarily to keep CHT in check. However I had a fast plane which was adequately cooled for most operations.
 
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Our RV-8's CHTs are running hot. We've got a tuned Aerosport Power IO-360, 9.0:1 pistons, plenum under a modified Sam James cowl, dual Pmag ignition and 4:4 Vetterman exhaust.

Parallel valve or angle valve?

What mods to the James cowl? And long or short?
 
Increasing the cowl exit will lower the CHT but at added drag. A lot of piston military and civilian planes for over 80 years have used cowl flaps. The ones you are looking at are fixed it appears to me. That is fine, but you really don't have a cooling issue with 385F.

Install the louvre kit from Vans....it only takes an hour or so. Cheap and I dare say will have no measurable/ noticeable drag component since all is inside cowl, nothing but some openings seen outside. If you ever feel the need to cover, gaffers tape over inside, is a quick easy solution. I am an A model, you being tail dragger will have you a bit more nose high sitting on ground, a bit more noticeable, but far from distracting/distasteful. I got around a 5 degree drop in climb out, not a lot, but beneficial. Also make sure fuel flow is adequate at WOT.
 
Check your lower baffles, the parts that wrap around the bottom of each cylinder. Be sure they are tight to the cylinder to keep cooling air from escaping out the sides instead of through the cooling fins. If needed, use some RTV. The gap at the bottom where the cooling air comes out should be 1.25"-1.5". I typically see this as an overlooked part of the baffling system.

What do you mean by a modified SJ cowl?
 
If your Sam James cowl and cooling plenum are set up well, metal baffle part sealed against engine case, you are getting the max inlet air these inlets can give. You can't increase cooling air IN. The inlets are sized for a stock O-360...

Nope.

Mass flow (cooling air in) is fundamentally determined by exit area, not inlet area. The measure of a cooling inlet is how well it harvests available dynamic pressure. There is no tailoring of inlet size for a particular Lycoming engine. Inlet area can be large or small, depending on the choice of internal or external diffusion.

I got around a 5 degree drop in climb out, not a lot, but beneficial.

A stock RV-8 lower cowl volume cowl will ballpark 1.5 to 3.5 inches H2O internal pressure in the speed range 100 to 175 KTAS. Adding exit area merely reduces that lower cowl pressure, increasing the deltaP across the cylinders...or across the baffle and seal leaks.

Reducing lower cowl pressure will also reduce upper cowl pressure, but to a lesser degree. The net result is that dropping lower cowl pressure by (for example) 2" H2O does not result in a full 2" better deltaP across the cylinders.
 
...I dare say will have no measurable/ noticeable drag component since all is inside cowl, nothing but some openings seen outside...

The added drag from the louvers is not due to skin friction drag over the outside of the airplane. It's added cooling drag due to increased airflow through the cowling. This additional cooling drag is unnecessary in cruise, so you're throwing away top speed if they're present and open full time.
 
The added drag from the louvers is not due to skin friction drag over the outside of the airplane. It's added cooling drag due to increased airflow through the cowling. This additional cooling drag is unnecessary in cruise, so you're throwing away top speed if they're present and open full time.

Some pretty detailed flight testing was done while developing the lovers in parallel with the new design RV-6,7,9 nose gear.

All of the flight testing indicated little to no influence on cruise speed, but the data averages leaned towards possibly a 1 to 2 knot speed loss in cruise (this was on a 160 HP / CS prop RV-9A.

I installed the louvers on my personal 180 / fixed pitch RV-6A and saw the same (little to possibly 1 knot loss).

Theory says that additional flow should cause additional drag. Particularly if in any given flight condition the temps are lower than they were without the louvers.
It is possible, that because of the design of the louver installation (flow exiting the bottom of the cowl some what perpendicular to the high speed free stream vs parallel like it does exiting the rear cowl opening) that at high speed, there is not a large amount of additional flow, but at lower speeds (where the extra cooling is typically need most) the extra amount of flow is larger.
Just a theory.....
Since the main goal was to counter the slight negative impact that the new nose gear had on cooling performance without significantly impacting speed performance, testing to answer the why question was not a high priority once the goal was met.
 
Nope.

Mass flow (cooling air in) is fundamentally determined by exit area, not inlet area. The measure of a cooling inlet is how well it harvests available dynamic pressure. There is no tailoring of inlet size for a particular Lycoming engine. Inlet area can be large or small, depending on the choice of internal or external diffusion.
Well you put the word fundamentally. Yes exit area may be primary but inlet area has to be sized for the engine as well as exit area; there are rules of thumb of inlet/exit ratios. Inlet area is a factor.
Example you will reach a max exit air area where the inlet will limit. To make my point if you use two 4" round inlets and go to 2" you will have less cooling. Absurd example (way roo small inlet area) but inlet and outlet ratios count. Mass flow does count as well as pressure. Many cooling issues are due to poor airflow into the cowl. I bought inlet rings from Dave Anders and modified my stock cowl; he had a larger size for the 200HP vs 180HP. It makes sense a larger engine does need more cooling. Not saying exit does not drive cooling but there are limits based on mass flow and pressure in.
 
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Yes exit area may be primary but inlet area has to be sized for the engine as well as exit area; there are rules of thumb of inlet/exit ratios.

George, do some reading, please.

http://www.n91cz.net/Interesting_Technical_Reports/106-111_BuildingBasics.pdf

Now consider...for any given engine, a designer may select a low velocity ratio inlet, or a high velocity ratio inlet with appropriate internal diffusion. The resulting upper cowl pressure can be the same, thus either choice would have the same exit area for the same mass flow....but the inlet/exit area ratios would be quite different.
 
George, do some reading, please.

http://www.n91cz.net/Interesting_Technical_Reports/106-111_BuildingBasics.pdf

Now consider...for any given engine, a designer may select a low velocity ratio inlet, or a high velocity ratio inlet with appropriate internal diffusion. The resulting upper cowl pressure can be the same, thus either choice would have the same exit area for the same mass flow....but the inlet/exit area ratios would be quite different.
Dan, I have been following your experimentation for over a decade and know you have a passion for this subject. I very much have enjoyed it. We both have read the NASA Rpt 3405 (1981). After decades of research and some experimentation on my RV (no where near as much as you have done), leads me to my point.

Exit is very important and as Chris Zavanson says in the link your provided (I have his web page book marked for a long time), EXIT is the throttle. That is a good way to look at it and why engine cooling cowl flaps have been used almost from the beginning of powered flight, but really took on new meaning in the 30's and 40's during WWII. There really is nothing new under the sun, just variations in the theme. Once jets took over research into cooling of piston engines stopped except for the one off NASA/Ms State Report (which left some loose ends). People like you, Dave Anders, LoPresti and many others have taken the concepts further.

My subtle point which I have come to understand is the cooling of Horz opposed piston engines is a system. In Chris's article he spends a lot of time describing how important the INLET is. That is my point. From the INLET to the EXIT and all points between are important not just the EXIT. The devil is in 100's of details and the system has to be "balanced". As you point out there is Vi/Vo ratios, pressures, mass flow are all in play. Making a system that adequately cools over a wide range of Op conditions with less/least drag is not easy given real physical limitations. "Adequate" cooling is also subjective. That is what makes it a fun topic. There is no one solution. Compromises in drag is needed to get that "adequate" cooling at times. The range of RV inlet/exit area ratios I have seen are all over, from 70% to 200% with reported success. The air has to flow into cowl and exit cowl efficiently, while not creating spillage or interference drag with free air-stream. However some cooling drag is unavoidable since air is bumping around inside the cowl.

Bottom line most don't care about the details as you and I do. The common issue posted on VAF is "My RV has high CHT, OT", or "My RV is slow or does". Three are so many things that can cause high Temp indications or a slow RV including cooling drag. Why some have no issues and others seem to have chronic issues is a fun puzzle. However stuffing an IO-390 into a cowl with 24 sq-in total inlet area (may) be a problem regardless of exit area. I think you have larger inlets on your RV and believe your engine is over cooled.
 
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Total 56.52 sq inches. No, it's not over-cooled. Can you tell us why?
I was reading your post.... in thread: http://www.vansairforce.com/community/showthread.php?t=63952

Post #18:
http://www.vansairforce.com/community/showpost.php?p=478420&postcount=18

".... I'm over-cooling a 390 with about 40 sq in and plan to go smaller. Must be witchcraft"

Your Post #4 you make the same point about how exit is the main factor:
http://www.vansairforce.com/community/showpost.php?p=477865&postcount=4

What Chris Z does not say is INLET is unimportant. Regardless of how big or efficient your exit is, if your inlet is blocked off you engine will over heat. Again my point is it all has to work together and be balanced. Only so much you can do with theory. Craftsmanship and empirical experimentation is needed to optimize. I would not discount the inlets. We have less flexibility with fixed inlets due to the geometry of our SE tractor engine. The exit we have much more room to play with and control. I have seen people put shutters in the inlets. The Russian radials use a shutter to block inlet air.
 
I was reading your post....

Post #18:
http://www.vansairforce.com/community/showpost.php?p=478420&postcount=18

".... I'm over-cooling a 390 with about 40 sq in and plan to go smaller. Must be witchcraft"

56.52 inlet area, 40 sq inches exit area, a ratio of 1/.76, roughly the reverse of the inlet/exit ratio claims of old...which were usually expressed by someone who insisted the exit must be 20% larger "because heated air expands".

The 40 sq in exit was fixed, one of three fabricated to empirically explore appropriate exit area for all conditions. The current exit is variable, with area anything between 30 and 48 inches.

What Chris Z does not say is INLET is unimportant.

The thread is about adding exit area to a cowl which won't cool. I'm running about half the stock exit area to cool a 390 in cruise. Yeah, I think the inlets are important.

The inlets are responsible for pressure. Pressure drives mass. How much mass is determined by the exit throttle.

Regardless of how big or efficient your exit is, if your inlet is blocked off you engine will over heat.

Kinda describes the path taken by a whole lot of folks....not blocked, but a medium to high Vi/Vo inlet with poor pressure recovery, thus a giant exit to compensate.
 
High CHT #3

Hey Can someone go over the baffling remark again in more detail? I have a fairly high #3 CHT relative to the other three(IO-375) do I need to increase baffling on the #3 or decrease baffling.

Same Peak EGT when leaning across #3 and #4 cylinders. Also, #2 is running a little low relative to all the others with same peak EGT across #1 and #2. (they are a little behind the #3 and #4, however, I have some new fuel nozzles on the way so should smooth that out.)
Not really worried about the EGT's just some extra information.

Thanks

Andrew
 
Why don't you just get that Anti Splat louver, that you can open or close at will. I wish I had it. Permanent louvers were installed in my plane (without my knowledge), and now my oil temp runs too cold in winter.
 
Why don't you just get that Anti Splat louver, that you can open or close at will. I wish I had it. Permanent louvers were installed in my plane (without my knowledge), and now my oil temp runs too cold in winter.

Install an oil cooler shutter and that problem will go away.
 
Install an oil cooler shutter and that problem will go away.

Already tried that. Darn thing wouldn't fit. Only thing I've been able to do is partially put (metallic) tape over my oil cooler in winter, and off when it starts getting hot outside.
 
Hey Can someone go over the baffling remark again in more detail? I have a fairly high #3 CHT relative to the other three(IO-375) do I need to increase baffling on the #3 or decrease baffling.

Same Peak EGT when leaning across #3 and #4 cylinders. Also, #2 is running a little low relative to all the others with same peak EGT across #1 and #2. (they are a little behind the #3 and #4, however, I have some new fuel nozzles on the way so should smooth that out.)
Not really worried about the EGT's just some extra information.

Thanks

Andrew
What is your delta-T? Have you opened up the restricted flow area on the back of #3?
 
Delta-T

hey Bill.

The Delta between cyl 2 and 3 is about 60-70
deg C.

I?ll have to look again at the back of cyl 3. Oil cooler comes off behind #3 as well.
 
My old RV 7 had pistol squirters and a Sam James plenum with 10 to 1 pistons. I had the stock exit area and all my CHT's were great always around 360 and even. The issue I had in the summer was high oil temps. I ended up increasing the scat tube to 4 inch and a larger cooler. Before I fixed it it would push 235 if I didnt step climb. The issue with my plenum was that the opening to the cooler did not have enough square inches and it was partially covered up by the rear cylinder.
 
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