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engine cooling fix

Nomadflyer

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My RV6 has a heating problem on 600fpm climb out, the CHT's are high above 400degs. I have high compression pistons in the engine. I just bought two electric cowl flaps form Anti Slapt Aero. Now at a 1000fpm climb out CHT's are 360 to 370degs more than 40degs cooler. (Homerun) I installed them with their directions, it was easy. I was a little apprehensive to cut my painted cowl it just took a little time to make a nice fit. Their directions were simple and easy, and I made more work out of it than I should have. More then 50degs at 600fpm. You made me very happy thanks Anti Slapt Aero
 
That is impressive.

What engine do you have?
Do you have EI's or mags?
If so what timing is set?
What fuel flow are you getting at what MP/RPM?

This could be a very interesting thread. :)
 
Not much mystery here. Ever blow on your soup? More air flow, more cooling. If more cooling is your only goal, additional outlet area always works.
 
General comment reg. cowl flaps.

There are thousands of RV's flying, that have entirely acceptable engine temps (CHT, Oil, etc.), even in hot climates.

When temps are not acceptable, there are two basic possible causes.
1. There is not enough cooling airflow available for the specific engine installation.
2. The cooling air that is available is not being fully/properly utilized.

Over the years I have had the opportunity to look at a lot of engine installations in RV's. If it has been to help someone diagnose a cooling problem, the majority of the time it is resolved by fixing problems resulting from cause # 2.

It has been extremely rare to see one that couldn't have some level of improvement in the baffling/cooling system. Countless times I have helped people that were adamant that their installation was as good as it could be done, but it was far from it.

Adding cowl flaps to improve cooling, before doing a very detailed analysis of problems that may exist in the entire system, is similar to installing a fifth leg on a wobbly 4 legged table.
This is not meant as a cut down to those that have installed them (or manufacture them). There are instances that it is probably the only remedy (engine modifications producing more power, etc.), but the number of RV's flying successfully without cooling mods is evidence that in most instances it is probably a short cut method to resolve a problem.

My opinion anyway....
 
Not much mystery here. Ever blow on your soup? More air flow, more cooling. If more cooling is your only goal, additional outlet area always works.

...With the accompanying reduction in speed from extra drag.
 
A well tuned fuel delivery system has a huge impact on temps. Had a 3878 carb on 55BC and it would hit 420 on takeoff, and would settle down to 350 in cruise. With the Rotec am now seeing 390 typically on departure and in cruise up high CHTs will drop to 275-290. Big temp drop especially at altitude.
 
A well tuned fuel delivery system has a huge impact on temps. Had a 3878 carb on 55BC and it would hit 420 on takeoff, and would settle down to 350 in cruise. With the Rotec am now seeing 390 typically on departure and in cruise up high CHTs will drop to 275-290. Big temp drop especially at altitude.

Good point Bob.
I was speaking just in the context of the air cooling system.
Proper fuel delivery is also part of the equation.
 
Not much mystery here. Ever blow on your soup? More air flow, more cooling. If more cooling is your only goal, additional outlet area always works.

Indeed. Adequate temps are easy;

Adequate temps with minimum drag is another story.
 
There are thousands of RV's flying, that have entirely acceptable engine temps (CHT, Oil, etc.), even in hot climates.

When temps are not acceptable, there are two basic possible causes.
1. There is not enough cooling airflow available for the specific engine installation.
2. The cooling air that is available is not being fully/properly utilized.

Over the years I have had the opportunity to look at a lot of engine installations in RV's. If it has been to help someone diagnose a cooling problem, the majority of the time it is resolved by fixing problems resulting from cause # 2.

It has been extremely rare to see one that couldn't have some level of improvement in the baffling/cooling system. Countless times I have helped people that were adamant that their installation was as good as it could be done, but it was far from it.

Adding cowl flaps to improve cooling, before doing a very detailed analysis of problems that may exist in the entire system, is similar to installing a fifth leg on a wobbly 4 legged table.
This is not meant as a cut down to those that have installed them (or manufacture them). There are instances that it is probably the only remedy (engine modifications producing more power, etc.), but the number of RV's flying successfully without cooling mods is evidence that in most instances it is probably a short cut method to resolve a problem.

My opinion anyway....

I am one of those that believe my baffles are as good as I can get it and with no apparent leaking area. I have no complaint about my temp in cruise but on climb out, I am limited to about 2500 before I have to reduce power or I will hit 400. My CHT and EGT are very uniform, max spread of CHT is less than 10 F and EGT is within or less than .2G

I would really like to find a way to improve the cooling in the climb out short of creating more exit area if all possible.
 
Not to put down anybodys fixes or ideas but--years ago when I was doing speed mods on my RV6 I was told one of the best you can do is to merely cut the exit opening of the lower cowl back 45 degrees and then straight across to let more air exit. We put an airspeed tube in the opening before and after the mod and the results were incredible. Before cutting the exit air was about 50 mph. After the mod the airflow increased to over 90 mph. I have done this on all three of my 6's and had the same results. An increase in speed (about 2 knots) and radically improved cooling. This year I forgot to uncover the oil cooler fins (we duct tape them in the winter months about halfway) and we still ran cool temps except on radical climb outs. At cruise, I normally see temps between 350-355 on all cyls. That is running 2450 rpm with a fixed pitched prop. JMTCW. Allen makes great products, by the way.
 
I am one of those that believe my baffles are as good as I can get it and with no apparent leaking area. I have no complaint about my temp in cruise but on climb out, I am limited to about 2500 before I have to reduce power or I will hit 400. My CHT and EGT are very uniform, max spread of CHT is less than 10 F and EGT is within or less than .2G

I would really like to find a way to improve the cooling in the climb out short of creating more exit area if all possible.

... You are not alone! We have sold several hundred of the EZ-Cool Flaps in the short time we have been offering them and can honestly say, not one customer is unhappy or sorry with his or her purchase. I have seen many of these beautiful aircraft and had conversations with many builders / owners. I can assure you these are not ignorant uneducated people by any means. Most have addressed this problem with all the standard tests and checks and still the temperature issue persists. I have personally fought this for a long time on my airplane and found very minimal gains at best until I made and installed the EZ-Cool flaps. This issue isn't just common to RVs and we see increasing sales to the Super Cubs and many other experimental aircraft. Few people have the facilities at their disposal that ASA has to address this problem and we saw little gains. Almost all certified GA aircraft, especially the tight cowled, high performance ones, that fly at similar speeds to the RVs, are equipped with cowl flaps. This is to regulate temperatures on climb, helping to save the engine without compromising the speed performance or efficiency in cruise configuration. I doubt the engineers at Beach, Cessna, Grumman, Rockwell and others would have added this feature if not necessary, or at least felt it added more versatility to their aircraft. Thanks, Allan...:D
 
........years ago when I was doing speed mods on my RV6 I was told one of the best you can do is to merely cut the exit opening of the lower cowl back 45 degrees and then straight across to let more air exit. .........

"Woodman", I am trying to picture this mod in my head, unsuccessfully! :eek: Any photos or drawings? Thanks,
 
I am one of those that believe my baffles are as good as I can get it and with no apparent leaking area...

...I would really like to find a way to improve the cooling in the climb out short of creating more exit area if all possible...

2 comments:

1. 400 as a transient condition in climb is not a big issue IMO.

2. Do you have the cylinder #2 and #3 bypass ducts installed as shown in this thread and others?
 
Adding cowl flaps to improve cooling, before doing a very detailed analysis of problems that may exist in the entire system, is similar to installing a fifth leg on a wobbly 4 legged table.
This is not meant as a cut down to those that have installed them (or manufacture them). There are instances that it is probably the only remedy (engine modifications producing more power, etc.), but the number of RV's flying successfully without cooling mods is evidence that in most instances it is probably a short cut method to resolve a problem.
Fair enough, Scott.

But for many of us who do not have your or DanH's expertise (which I wholeheartedly respect and appreciate), knowing how to solve these temp issues is indeed the problem. It's not that the problems can't be solved, its that pilots like myself don't have the expertise or, in some cases the time, to do so even if we do have a genuine interest in learning how to do so. For two years I've been chasing higher-than-desired CHTs and occasionally higher-than-desired oil temps and trying to figure out what the problems are. Yes, I'm sure my baffles could even still use a bit more work, but I also know that there are other issues involved: for example, a carb that distributes the fuel very poorly. In any case, the result of this has been that I have not yet had the opportunity to fully enjoy and get full utility from my plane.

So, sure, adding cowl flaps might be a band-aid approach that doesn't fully address the root of the problem, but so long as we're willing to sacrifice a couple knots in order to gain full utility and enjoyment of our $60K+ aircraft, it seems to me to be a reasonable tradeoff.

P.S. I do not (yet) have any cowl flaps nor have I increased the amount of exit air.
 
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We put an airspeed tube in the opening before and after the mod and the results were incredible. Before cutting the exit air was about 50 mph. After the mod the airflow increased to over 90 mph.

Where did you locate your static source?
 
I remember a thread somewhere that when flying, the pressure inside the cowl causes it to expand outward slightly. There are also small leaks normal to the aircraft into the airstream and these cause additional drag and loss of speed. The baffling may look good, but may react differently when the plane if flying.
Rog, can you give us pictures of your cut outs in the cowl exit. Mine will be painted in a few weeks and then it will be harder to modify.
 
2 comments:

2. Do you have the cylinder #2 and #3 bypass ducts installed as shown in this thread and others?

I had followed that thread with great interest and no, I don't. My cylinder #2 and #1 (in that order) are the hottest during the climb outs but only by a few degree (less than 10) so I wasn?t sure if this was going to help me as it is not only those two cylinder.
 
I remember a thread somewhere that when flying, the pressure inside the cowl causes it to expand outward slightly. ....
I think the cowl lift has to do more with Bernoulli's principle than anything else. I have a plenum on my engine and yet the cowl still tries to lift a little bit. Since there is no air pressure on the inside, I suspect it is "lifting" and not being pushed.
 
I had followed that thread with great interest and no, I don't. My cylinder #2 and #1 (in that order) are the hottest during the climb outs but only by a few degree (less than 10) so I wasn?t sure if this was going to help me as it is not only those two cylinder.

I can say with near certainty that regardless of how well your engine cools now, boosting the airflow through the "blocked fins" on #2 and #3 will show you lower CHT on those two cylinders.
 
I have a plenum on my engine and yet the cowl still tries to lift a little bit. Since there is no air pressure on the inside, I suspect it is "lifting" and not being pushed.

Upper plenum pressure is roughly 0.6~0.8 available dynamic pressure, some of which is dropped across the engine fins, leaving residual pressure to move air out the exit. That residual lower cowl pressure is what inflates your cowl.

How much pressure? Looking at a random line of data from a few years ago, I measured 5.5" H2O in the lower cowl at 166 TAS, or roughly 29 lbs per sq ft of cowl with a moderately large exit area.
 
nice change

I commute from Portland Oregon to Southern California. So when I stop for fuel for 20 minutes the engine hasn't had time to cool down. With warm outside temps and climbing out creates a problem high CHT's. I just flew to SoCal today from Portland. What a difference the temps were a lot lower in a normal range on climb out. My temps were always good in flight. The Cowl Flaps work Awesome.
 
Not to put down anybodys fixes or ideas but--years ago when I was doing speed mods on my RV6 I was told one of the best you can do is to merely cut the exit opening of the lower cowl back 45 degrees and then straight across to let more air exit. We put an airspeed tube in the opening before and after the mod and the results were incredible. Before cutting the exit air was about 50 mph. After the mod the airflow increased to over 90 mph. I have done this on all three of my 6's and had the same results. An increase in speed (about 2 knots) and radically improved cooling. This year I forgot to uncover the oil cooler fins (we duct tape them in the winter months about halfway) and we still ran cool temps except on radical climb outs. At cruise, I normally see temps between 350-355 on all cyls. That is running 2450 rpm with a fixed pitched prop. JMTCW. Allen makes great products, by the way.

Would you have a picture you can share with us please ?
 
Here are a couple of pics of the cut cowl. I had to make a support in the center to replace the original but no big deal. The pitot tube done in testing was set about 2" aft of the opening between the exhaust pipes. As you can see, I also cut the exhaust pipes back for both esthetics and drag.

 
years ago when I was doing speed mods on my RV6 I was told one of the best you can do is to merely cut the exit opening of the lower cowl back 45 degrees and then straight across to let more air exit. We put an airspeed tube in the opening before and after the mod and the results were incredible. Before cutting the exit air was about 50 mph. After the mod the airflow increased to over 90 mph. I have done this on all three of my 6's and had the same results. An increase in speed (about 2 knots) and radically improved cooling. T

IMG_2856_zps9ed9f966.jpg


This is going to get interesting.
lurk5.gif
 
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So I have a question about exit volume. With my 4 pipes also in this space, how much less area do I have and should I open up the exit area anyway? Yes I can figure out the volume of the pipes and do the math but this is just a rhetorical question for the scientist among us.

I am having slightly elevated CHTs in long climbs and plan to work on it this winter so am beginning to pay attention to what others are discovering.
 
So I have a question about exit volume. With my 4 pipes also in this space, how much less area do I have and should I open up the exit area anyway? Yes I can figure out the volume of the pipes and do the math but this is just a rhetorical question for the scientist among us.

I am having slightly elevated CHTs in long climbs and plan to work on it this winter so am beginning to pay attention to what others are discovering.

Do you have any numbers to share, Paul? Like airspeed, CHT, and ambient temps? I'm assuming you are running at WOT. oh- oil temp too.

I know your baffles and plenum well, so surely you must have sealed every square mm for losses.
 
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Bill,

Because it really hasn't been much of a problem, I haven't really kept any data and have not compared my performance to ano others numbers. In general;

-CHTs in cruse average 330 ish with differentials between cylinders of about 20 to 40

-in long climbs, 1800 plus fpm sustained, one or two cylinders will exceed 425 so I try not to climb this hard.

- I run WOT and full rich in all climbs but not in cruse. In cruse I adjust for about 8 gph burn rate and about 162 knots indicated. Also lean to about 50 LOP.

- I have not modified the factory baffles to open up air movement at the cylinder fins (or lack of) yet.

Other than my home made plenum, it is a totally factory installation, all baffles RTVed in every visible gap and nothing unique beyond that.

None of this has any value because it is totally unscientific! Too much fun flying to get serious about data collection :)

Here is a photo of what it looks like "under the hood"
photo%25204-1.JPG


photo%25204%2520copy.JPG


An effective seal is achieved between the front of the plenum and the rear of the cowl inlets using baffle seal materials. It fits nice but very tight!
 
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