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RV-10 ANTI-SPLAT cowl flaps, etc.

Storch

Member
Hello Everyone,

I've attempted to read all the threads regarding cowl flaps, high CHT's, etc. and there associated solutions and opinions.
Our 10 is stock, have about 900 hrs on it.

Living in the deep south, the summers are pretty hot. My SOP is to attempt to keep the CHT's below 400. Easy to do once cruise flight is established. Climb out is tough. Typically go to 23 square and 120 IAS at the first climb power setting to maintain this limit. Even then it can be difficult to do and only 500 FPM climb.

My baffling is super tight, all holes plugged in an effort to send all air through the cylinder fins.

Has anyone actually installed the cowl flaps and and had an improvement worth the cost and labor?
Did you install one or two?
Did you install them in the original position of the louvers or keep the louvers and install them outboard?

I purchased the big side louvers for the cowling but opted to not install them
after reading a bunch of reviews.


Regarding the oil cooler opening. Our temps run fine. If anything in the lower acceptable range, 175-195.
Was wondering about putting a shutter, slightly raising the temp but redirecting the air to the cylinders?

Thanks,
David
 
Might want to try keeping the throttle at full for the duration of your climb. If I understand correctly, full throttle overly increases fuel flow to aid in cooling. Pulling the throttle off of wide open removes that design benefit.
 
Do you have a CARB.....or FI.
Either way....are you rich enough in the climb phase?
Extra fuel is used for cooling in the climb so if your system is lean....
You could be hot.
 
Hi David,

I just have 30 hours in and I have the cowl flaps installed on the sides of the cowl, at 3 and 9. I have been testing CHT temperatures and it seems like the cowl flaps on a 65 degree day was helping me lower CHT by around 10-12 degrees 412 to 400. That took around 10 minutes to cool down. When I close them CHT starts going up slowly to where it was. And this is not in a climb, this is cruse 60% throttle and no change in mixture.


I am still on very low hours on a new engine, so take this with a grain of salt, it will change as the engine brakes in.


Once I have more hours and more testing I'll update.

I hope this helps.
 
I've heard it said...

that the heat of evaporation of gasoline (its enthalpy) is not sufficient to account for the cylinder head cooling effect observed in a full-rich climb.

The alternative explanation is that full-rich climbs yield cooler CHT's due mostly to the lower engine power output when operated on a mixture very rich of stoich. The rich mixture affords a larger detonation margin of safety, but it cools the engine primarily by reducing available horsepower output versus leaned for optimum combustion. Remember what we're all taught to do with the red knob at Leadville, CO on takeoff.

I could be wrong here, but offer it for discussion. I think it was Deakin or Busch that wrote what I'm recalling here.
 
My engine is fuel injected.
I am a huge advocate and student of Mike Busch. Overall I do not believe my high CHT issue is fuel management related. The CHTs climb into the 390 range within a couple of minutes of applying takeoff power when operating on hot, 90+, days. This occurs even with the fuel boost pump on. Mike recommends maintaining take off power EGT through the climb to cruise altitude, which I do.
 
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By 3 and 9, I assume this means they are mounted on the sides of the cowl?
If so how did you determine this position as opposed to the traditional bottom location?
Thanks.
 
Hi David,

I just have 30 hours in and I have the cowl flaps installed on the sides of the cowl, at 3 and 9. I have been testing CHT temperatures and it seems like the cowl flaps on a 65 degree day was helping me lower CHT by around 10-12 degrees 412 to 400. That took around 10 minutes to cool down. When I close them CHT starts going up slowly to where it was. And this is not in a climb, this is cruse 60% throttle and no change in mixture.


I am still on very low hours on a new engine, so take this with a grain of salt, it will change as the engine brakes in.


Once I have more hours and more testing I'll update.

I hope this helps.

By 3 and 9, I assume this means they are mounted on the sides of the cowl?
If so how did you determine this position as opposed to the traditional bottom location?
Thanks.
 
Cowl flap

I installed one on the bottom of my cowl. I see very little added cooling open or closed. My conclusion is that there is already enough exit area. I have worked hard sealing up baffles and some mods to baffling as discussed in these forums. I am OK with brief excursions to 425 on T/O as I can keep it below 400 in climb.
 

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By 3 and 9, I assume this means they are mounted on the sides of the cowl?
If so how did you determine this position as opposed to the traditional bottom location?
Thanks.

Storch, Years ago when I was working on climb temps like you. I had a conversation with Alex Dominic the RV transition pilot who does lots of hot heavy takeoffs. He sold Louvers on his website and he had success with the 3/9 locations saying to install them just below the bottom of the cylinders to catch that air or to give that air a more direct exit. Rather than having to mix or exit through the bottom which is cluttered with exhaust and in the A model...gear.
In my plane I found my carb was too lean.....based on Deacon's writings and drilled my jet....solved my issues.
 
I decided to leave the louvers off and fly with just a single AntiSplat cowl flap in the side of the cowl, planning to add the louvers later if needed. They aren't, in my installation.

The cowl flap drops CHT's about 10 degrees or so - not particularly worth the effort IMO but it's already there, so it's staying.
 
By 3 and 9, I assume this means they are mounted on the sides of the cowl?
If so how did you determine this position as opposed to the traditional bottom location?
Thanks.

Yes both sides of the cowl, and they open outwards.

I called AntiSplatAero and talked to the owner(forgot his name) he told me that from different tests that were done including tests in Brazil that having them on the side makes the most difference for a 10.

I just took his word and never was able to test the bottom performance
 
Do you have a CARB.....or FI.
Either way....are you rich enough in the climb phase?
Extra fuel is used for cooling in the climb so if your system is lean....
You could be hot.

I lean to 150 ROP during the climb and have no issues keeping CHTs under 400 in the summer in my 10. Better to address the other issues before recommending extra fuel to solve the problem.

That said if I let the EI advance timing as it sees MAP drop in the latter stages of the climb, I will easily get to 425. This amplified by the lower cooling efficiency of the thinner air at higher altitudes. I now manually override the advance while ROP in the climb. Not really possible with Pmags though. The advance is fine if I am climbing LOP. This is a core problem with the preset EI systems. You want the extra advance when LOP but not when ROP at the same MAP.

Larry
 
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I lean to 150 ROP during the climb and have no issues keeping CHTs under 400 in the summer in my 10. Better to address the other issues before recommending extra fuel to solve the problem.

That said if I let the EI advance timing as it sees MAP drop in the latter stages of the climb, I will easily get to 425. This amplified by the lower cooling efficiency of the thinner air at higher altitudes. I now manually override the advance while ROP in the climb. Not really possible with Pmags though. The advance is fine if I am climbing LOP. This is a core problem with the preset EI systems. You want the extra advance when LOP but not when ROP at the same MAP.

Larry

Not to cause thread drift here, but wouldn't the optional fixed/variable mode switch in a p-mag install allow for the same override that you speak of?
 
If your CHTs are below 425, even a bit higher (hottest cylinder) with full power on a hot day climb out, don’t stress it. Keep in mind red line for a Lycoming cylinder is 500 degrees (but I would avoid going there). Climbing out in a mid summer Florida day I may hit 420ish on the initial climb out with about 115kt climb speed. At 1000 feet I bring the prop back to around 2550. You will see the cylinder temp start dropping after 2000 feet. If you have altitude, lower the nose and get to 120 or so knots. Also keep in mind CHT temps drop very slowly so don’t expect to see a drop in temp immediately when you make an adjustment to power or speed. At cruise 65%, especially LOP, your hottest will probably be 365 or less. We are not running Continental engines so avoid getting into the CHT battles. Lycoming recommends under 400 CHT for longevity, but that’s based more on the temps at cruise speed. My hottest to coldest CHT between cylinders is 19 or less degrees. EGT is less then 45. If you have a wide temp spread recheck your baffle and fill any holes or voids with RTV. Make sure your injectors are balanced. Also, I run a 9:1 compression. If you have higher compression cylinders 9.5:1 or better your creating more heat in those cylinders.
 
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I have two of Allen's cowl flaps on bottom of the cowl of my IO-360 RV-7. I was exceeding 425 on a hot climbout, heavy in central California. That was 3 years ago. Now I seldom see over 400. Climb WOT and try to lean a little as I climb. I think they are worthwhile although I did have to replace an actuator once. It might have been heat related so I put some silver tape on the motor. Not sure if that helped but no issues since.
 
If your CHTs are below 425, even a bit higher (hottest cylinder) with full power on a hot day climb out, don’t stress it. Keep in mind red line for a Lycoming cylinder is 500 degrees (but I would avoid going there). Climbing out in a mid summer Florida day I may hit 420ish on the initial climb out with about 115kt climb speed. At 1000 feet I bring the prop back to around 2550. You will see the cylinder temp start dropping after 2000 feet. If you have altitude, lower the nose and get to 120 or so knots. Also keep in mind CHT temps drop very slowly so don’t expect to see a drop in temp immediately when you make an adjustment to power or speed. At cruise 65%, especially LOP, your hottest will probably be 365 or less. We are not running Continental engines so avoid getting into the CHT battles. Lycoming recommends under 400 CHT for longevity, but that’s based more on the temps at cruise speed. My hottest to coldest CHT between cylinders is 19 or less degrees. EGT is less then 45. If you have a wide temp spread recheck your baffle and fill any holes or voids with RTV. Make sure your injectors are balanced. Also, I run a 9:1 compression. If you have higher compression cylinders 9.5:1 or better your creating more heat in those cylinders.

I have 9:1 also and my GAMI FI nozzle spread is .4. I also typically run 65% or less ,LOP, 9,000-11,000, and the CHTs and EGTs are similar to yours in cruise.
What power settings do you run in the climb? Leaning technique in the climb? I notice you only make mention of reducing RPM to 2550. Do you maintain WOT (full throttle) in the climb?
Thanks.
 
I have two of Allen's cowl flaps on bottom of the cowl of my IO-360 RV-7. I was exceeding 425 on a hot climbout, heavy in central California. That was 3 years ago. Now I seldom see over 400. Climb WOT and try to lean a little as I climb. I think they are worthwhile although I did have to replace an actuator once. It might have been heat related so I put some silver tape on the motor. Not sure if that helped but no issues since.
Thank you for the information.
 
So for a comparison: standard Vans cowling, baffle is tight. WOT and 2700 RPM on departure. Once clear of obstacles, I set climb speed for 115 to 120 knots. At 1000 feet I bring the prop back to 2550 at WOT. At cruise altitude, prop set to around 2370-2380 and a big pull to LOP setting with 65 percent power, figuring 9K feet.

Recommendation if you have not done this. Take off the upper cowl, put a bright shop light in the lower cowl area. Close the hanger door. Then look around your engine where the light comes through. Anywhere that light comes through not via the cylinder fins, is an air leak that needs to be filled with RTV. Be very OCD with eliminating any air escape points. If it’s not going through your cylinder fins it not cooling. This includes areas around the aluminum baffle and baffle gasket. Check the middle cylinders lower aluminum baffle for gaps where it meets the case. Make sure the baffle is tight against the fins with no play. Make sure the baffle along the top area is against the fins and has no gap. Air flow need to be forced through the fins so any sloppy tolerance even at the top edge of the baffle will loose cooling effectiveness. Also, I removed the dams that are up front. Others either trim them way down or remove them. And make sure the lower cowl exhaust fins are at a good angle and opened properly. I have seen some that we’re not bent up enough and restricted the out going airflow.
 
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My SOP is to attempt to keep the CHT's below 400. Easy to do once cruise flight is established. Climb out is tough.
Thanks,
David

David,
I agree with Rich in Post #15. "If your CHTs are below 425, even a bit higher (hottest cylinder) with full power on a hot day climb out, don’t stress it."

I too battle keeping CHT's below 400 in climbout, but only on #6 cylinder. It gets to 415 in climbout on hot days. I subscribe to Savvy and have asked them how critical the never exceed 400 mantra is (for all us Mike Busch disciples) They said for short intervals (like early phase of climb out) there's no real harm. So, I quit sweating it and let it get over 400 during climb. I don't think 400 is as hard of a line as I once did.

I also keep throttle wide open during climb (to help with cooling), but set RPM to 2500 very soon after takeoff. I still get over 1,000 fpm most days.
 
As was mentioned earlier, for those running EFI systems you might want to take a close look on the effect of power reductions, prop or mp, on your fuel and ignition maps. My procedure has been to reduce rpm to 2600 at 1000' with WOT and while digging into the maps I discovered that a power reduction generally led to an advance in the timing and a leaning of the mixture. Both of these changes lead to higher temperatures and are counter productive to reducing heat.

Using my air/fuel ratio display I've adjusted my fuel map so that I'm running in the neighborhood of 150 degrees rich of peak (AFR of 11.5) when the RPM is at 2600 and higher since the only time I'll be at those rpms will be during climb. Once I bring the rpm below 2600 the system returns to the normal maps.

I've also adjusted the timing advance to not begin advancing until I retard the rpm below 2600. Both of these adjustments have made a dramatic improvement in CHT, especially at high OATs.

I should mention that my EFI system doesn't have a manual way of overriding the timing advance so that's the reason I've set it up this way.
 
Trying to avoid creating new thread on this matter.
I am relatively new RV10 driver with 40+ hours on new to me engine/airframe. I am located in north-west so the weather here is not that bad in the summer.

On typical summer afternoon with ~80-85F when climbing to say 3500' I often hit 440F CHT on cylinder 2 and 6 for short period of time. Oil is with in 210-215 at its peak.
Cyl 1 usually 420 and cylinders 5,3 and 4 are at 400 or below. The 4 is sometimes 375-385F.
CHTs rapidly goes down as soon as cruise is established. This is when I climb at 100 knots speed. If I climb 120-125 things look much better but still CHT2 and 6 are close to 440.

What I do not understand is while cylinders 2 and 6 are super HOT the number 4 is relatively cold. I can understand number 6 - next to it is large opening for Oil cooling hose. So we loose lots of pressure here. But number 2 is facing the entrance, it should be cold or at least not as hot as it is.

I suspect governors position and baffles around it to be the issue for airflow. There are two lips - air smoothers (whatever they called) attached to the top cowling to ensure that air, which enters the air inlets is smoothed. The one on top of the governor was obviously cut to fit the control arm.
How do you guys go about that particular governor side baffling/air inlet smoothing ? I strongly feel that air which entering the 2-4-6 air inlet side is so turbulent so it does not allow for good cooling at the entrance.

And here is on this thread topic - cowl flaps should technically create negative pressure when opened in the very bottom of the cowl. This should let air at more higher speed to enter the air inlets and make better cooling. I guess there should be a formula to calculate the air entrance size vs air exit size and see what should be the maximum size for best efficiency of the cowl flaps.
 
440 is pretty warm. I'm (obviously) based in Georgia where temperatures can be pretty warm. I climb at 120 knots and don't see temperatures nearly that high.

What is your fuel flow at takeoff?

Have you (or the prior) owner properly sealed all of the gaps in your baffles with RTV?

Are the upper inlet ramps properly installed?

How well are your baffles and baffle seals built?

Pictures of your inlet ramps and baffles/baffle seals might net you a better online diagnosis...
 
440 is pretty warm. I'm (obviously) based in Georgia where temperatures can be pretty warm. I climb at 120 knots and don't see temperatures nearly that high.

What is your fuel flow at takeoff?

Have you (or the prior) owner properly sealed all of the gaps in your baffles with RTV?

Are the upper inlet ramps properly installed?

How well are your baffles and baffle seals built?

Pictures of your inlet ramps and baffles/baffle seals might net you a better online diagnosis...

Thank you Kyle!
My airplane is new, I just built it and only flown 40 hours. All baffles were improved after first flights. I used RTV and sealed all gaps between engine and baffle walls.
Upper inlet ramps - this is what I suspect may be the issue. The right side air inlet ramp is installed and temperatures of cylinders 1-3-5 are more or less OK. The left side air inlet ramp is cut almost 60% due to interference with the governor arm and I feel that this is where problem may be.
Does anyone have a picture of their left side (governor side) air inlet where I can see the inlet ramp ?
I think that my issue can be related to this particular part/location.

I will post few pics this week when get to my hangar again, just returned back after flying :D
 
Here's a construction pic of my upper cowl with the cutout for the governor arm glassed-in to keep the airflow from getting behind the ramp. This basically creates an irregularly shaped box recessed in the ramp profile that fits around the governor and allows full travel of the control arm. I have no idea how effective this is versus doing it as a crude cut-out with no boxing-in of the recess.

See my comments last year in this thread regarding how my setup cools. There is room for improvement as I have yet to do the flashlight tick to see where additional RTV might come in handy to seal leaks, but since it works it's not been a priority...
 

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two questions:
1. Is the air dam in place in front of #2? Many have cut it smaller, or even removed it, to get the front cylinder CHTs lower.
2. Stock fuel injection is not perfect. Have you balanced the injector apertures? e.g., is #4 running richer than the others?
 
Here's a construction pic of my upper cowl with the cutout for the governor arm glassed-in to keep the airflow from getting behind the ramp. This basically creates an irregularly shaped box recessed in the ramp profile that fits around the governor and allows full travel of the control arm. I have no idea how effective this is versus doing it as a crude cut-out with no boxing-in of the recess.

See my comments last year in this thread regarding how my setup cools. There is room for improvement as I have yet to do the flashlight tick to see where additional RTV might come in handy to seal leaks, but since it works it's not been a priority...

Bill Thank you! Yours look different from my and now I think I understand the mistake I made. I simply cut main instead of glassing around the arm and I guess my air is now gets too much turbulent there before even reaching the cylinder 2 fins. Anyway if this is true or not I will re-do my and will review previous posts.
 
two questions:
1. Is the air dam in place in front of #2? Many have cut it smaller, or even removed it, to get the front cylinder CHTs lower.
2. Stock fuel injection is not perfect. Have you balanced the injector apertures? e.g., is #4 running richer than the others?

Bob,
Air dam is in place and I remember cutting it by like 1/4" in the past. Probably you are right and I may need to cut it more or even consider removing it.

I have never balanced my injectors. I will probably start with air dam mod, air inlet ramp mod and see the results. If these wont be enough to fix the situation I will likely get my apertures of injectors balanced.

It is interesting though, CHT 4 is significantly colder than 2 and 6 which does not make much sense. While in cruise all temperatures are well balanced after some time and there are no significant spikes at all.
 
I would suggest getting a seasoned helper to assist in checking out and remediating any baffle sealing issues. I climb at 130 knots in my 10 and never see above 400 (typically closer to 380), at least until I get to around 8-10K, where the ign advance is rising and the air is getting thinner. IMHO, a well sealed 10 should not get anywhere near 440 in low altitude climb if the baffling is done right. Cowl flaps will help, but is just a band aid for ineffective sealing. The 10 can be a bit of a challenge to get the Gov area sealed well. The rubber sealing strips on many builds don't seal well if care is not taking in laying them out, so that may be another area of exploration. Put a light coating of something like crayon all over the rubber seals where they meet the cowl. Fly for a couple hours and examine what wore off (indicator of contact and movement). Large areas where the crayon mark does not wear off needs work. Did you seal the four inter cylinder baffle areas? Also a large leak point. Did you tweak the bends where the rounded area starts to cover the fins? Also a leak area. The bend from the factory usually is not acute enough to seal well and needs some adjustment.

My numbers look like this spread in cruise: 1/2: 340, 3/4: 320, 5/6: 355. 3/4 are always a good bit cooler than the others. The patterns are different in the climb, but not radically different.

Excessive ign advance can cause high temps, so worth checking. In my experience, stock imbalanced injectors will not cause 440 CHTs. That is more about efficiency and economy through balanced AFRs.

If cruise temps are all good and this is just a climb issue, I would also re-examine the inlet ramps and cowl top flow attachments. DId you install the louvers? I am told their primary purpose is to improve air flow in the climb attitude.

Larry
 
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I would suggest getting a seasoned helper to assist in checking out and remediating any baffle sealing issues. I climb at 130 knots in my 10 and never see above 400 (typically closer to 380), at least until I get to around 8-10K, where the ign advance is rising and the air is getting thinner. IMHO, a well sealed 10 should not get anywhere near 440 in low altitude climb if the baffling is done right. Cowl flaps will help, but is just a band aid for ineffective sealing. The 10 can be a bit of a challenge to get the Gov area sealed well. The rubber sealing strips on many builds don't seal well if care is not taking in laying them out, so that may be another area of exploration. Put a light coating of something like crayon all over the rubber seals where they meet the cowl. Fly for a couple hours and examine what wore off (indicator of contact and movement). Large areas where the crayon mark does not wear off needs work. Did you seal the four inter cylinder baffle areas? Also a large leak point. Did you tweak the bends where the rounded area starts to cover the fins? Also a leak area. The bend from the factory usually is not acute enough to seal well and needs some adjustment.

My numbers look like this spread in cruise: 1/2: 340, 3/4: 320, 5/6: 355. 3/4 are always a good bit cooler than the others. The patterns are different in the climb, but not radically different.

Excessive ign advance can cause high temps, so worth checking. In my experience, stock imbalanced injectors will not cause 440 CHTs. That is more about efficiency and economy through balanced AFRs.

If cruise temps are all good and this is just a climb issue, I would also re-examine the inlet ramps and cowl top flow attachments. DId you install the louvers? I am told their primary purpose is to improve air flow in the climb attitude.

Larry

Thank you Larry!
Yes, you are right - in cruise everything becomes normal with CHTs so the issue is in climb only. This exactly points to inlet ramps on top cowl and I did screwed up left side ramp because of the governor's arm. My plan is to re-do it first and see if this helps. Since only two cylinders (2 and 6) are my concern I feel that inlet ramp should be investigated first. This is the plan for this week!
 
You might also try adding a washer between #2 baffle and cylinder creating a space for some air to get to the lower cylinder. This improved the cooling considerably on my RV-7 IO360.
Also check the center baffles behind the prop area have a good seal to the upper cowling. This a difficult area to seal and a bad leak here can affect the intake airflow.
I'm also interested in those who have made a plenum on the RV-10 if there is an improvement to temps.

Rocky
 
Plenum is a very good alternative solution in my opinion. My buddy with his Bushmaster and 540 engine made a plenum - very good cooling results.

I modified my inlet ramp which was likely the cause of the issue at the left side. Also I removed the air dam in the front of cyl 2. Will do some test flying this week and report the results.

I have heard about solution to insert washer in the front of cyl 1 and 2 to improve cooling, so will likely do that as well.
 
Plenum is a very good alternative solution in my opinion. My buddy with his Bushmaster and 540 engine made a plenum - very good cooling results.

I modified my inlet ramp which was likely the cause of the issue at the left side. Also I removed the air dam in the front of cyl 2. Will do some test flying this week and report the results.

I have heard about solution to insert washer in the front of cyl 1 and 2 to improve cooling, so will likely do that as well.

Behind cylinder 5 is where the washer provides the largest benefit.
 
RV7 Cowl Flap experience

I have an RV 7A, not a 10 but…I battled high CHTs for a long time too and had lots of experienced builders check my work. We tried all the standard fixes and some non-standard fixes. Some helped but not enough. Finally put 2 of the anti splat cowl flaps in and it completely solved the problem.
 
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