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  #1  
Old 10-01-2017, 01:00 PM
NYTOM NYTOM is offline
 
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Default Cowl flap advice

Reading through the archive's it seems a cowl flap can be a good investment towards to control of cylinder head temps. And I see some have installed two. My question is if one cowl flap is good, is two cowl flaps better? Would rather take the time now to install a second flap if it's going to make a readonable difference. We have about 40 days over 90 here and the heat can be brutal.
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  #2  
Old 10-01-2017, 01:32 PM
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Toobuilder Toobuilder is offline
 
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The first thing to ask is if you have your baffles and seals working properly to begin with. And this includes addressing the zero fin depth areas on the front of #2 and the back of #3 (remedied with bypass ducts). Generally, the standard Vans cowl provides plenty of differential pressure to cool effectively. My 200 HP -8 has a stock cowl and cools just fine in 110+ temps. I did have to take it easy leaving Arizona one day, but the OAT was 121...

Next thing to look at is ignition advance. If you are EI, do you know what the timing is doing at TO power? If you have a CPI for example, you can retard timing (from data plate values) and help your CHT right off the bat with no loss of power.

A cowl flap can be a good thing if its used to pinch down the exit at altitude to reduce drag and increase temps, but if you're adding one to increase exit area, that's probably a bandaid fix for another problem.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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Last edited by Toobuilder : 10-01-2017 at 01:36 PM.
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  #3  
Old 10-01-2017, 02:30 PM
Kyle Boatright Kyle Boatright is online now
 
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Quote:
Originally Posted by NYTOM View Post
Reading through the archive's it seems a cowl flap can be a good investment towards to control of cylinder head temps. And I see some have installed two. My question is if one cowl flap is good, is two cowl flaps better? Would rather take the time now to install a second flap if it's going to make a readonable difference. We have about 40 days over 90 here and the heat can be brutal.
Have you flown the airplane? Since I adjusted the cylinder blockers properly during the first year or so of flight, CHT's have never been a problem on my -6.

Where I'm going is that I wouldn't spend the time and money on a flap or flaps unless you have flown the airplane and have tweaked things for proper cooling.

But to answer your question, yes, two would be more effective than one IF you need the additional airflow.
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  #4  
Old 10-01-2017, 04:33 PM
NYTOM NYTOM is offline
 
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Not looking to solve any current problem, just want to do it as best as I can the first time. Have read all I can on baffles and problems and hope to avoid the usual stuff. Already planning fabricating bypass ducting on the problem areas and hope my sealing is more than sufficient. It's just so darn hot here most of the year that I wanted to get some insight on cowl flaps and if having them would be a wise decision. Have looked at many baffle installation on RV 's and it's amazing how different they can be. I guess it's all in the fine detail.
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  #5  
Old 10-01-2017, 06:39 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by NYTOM View Post
Not looking to solve any current problem, just want to do it as best as I can the first time.
Making an RV the best it can be means different things to different people.....

To one it means not doing any more build effort, spend more money, or add any additional operating complexity to the airplane beyond what is necessary.

To another it means installing every gadget possible.

Since it is rare I have inspected an RV that the engine baffling system couldn't be improved (regardless of what the owner thought), my recommendation would be to not install cowl flaps until you have determined that you are unable to resolve a cooling problem any other way.
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  #6  
Old 10-02-2017, 10:39 AM
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jjconstant jjconstant is offline
 
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I understand your desire to head off as many "problems" as possible during construction, but I think it would be best to embrace the notion of build, then test, then adjust. I speak from experience here.

During construction I had 2 friends whose engine oil temps were lower than they wanted, even during mild temperatures so I thought I would head off that problem during the build and just install the louvered oil shutter. My thinking was that there was no real downside to having it. Well, from day one my problems were too much heat rather than not enough. In the process of trying to fix the problem, I wound up taking the oil shutters off because I realized that in the open position they still cut off some of the air flow across the cooling fins of the oil cooler and I needed all of cooling I could get. It still wasn't enough. I then resorted to installing a larger oil cooler, then installing two cowl flaps. Both oil temperature problems and cylinder temperature problems were fixed, but only after testing, getting lots of advice and implementing EVERY suggestion that implied I had screwed up the baffles and/or installation.

Every build is different. With all of the choices we have, we have to acknowledge that, even when done as well as humanly possible, the result of the choices will yield differences in performance, many of which are hard to predict until you test it. Both my friends who had too-cool running engines came over and helped address whatever faults they could think of with my installation. Ultimately, they acknowledged that on my plane, with my engine, ignition, compression ratio, nickel cylinders, etc, etc, etc, my plane ran much hotter than theirs.

Build to the best of your abilities. Then have lots of experienced eyes look for issues. Then test PROPERLY. Don't just fly off the hours. And folks who imply that you didn't build it right if you have problems just got lucky with their build or are forgetting or minimizing things they needed to address. Yes, use their suggestions to check if you in fact did screw up, but filter out the implications that "if it isn't perfect right out of the box, you suck as a builder".

You will also need to figure out both who knows what they're talking about AND does that advice work with my priorities. I have another friend who does stunningly beautiful work try to convince me that I needed to paint everything before initial assembly. He was speaking from experience in how to MOST EFFICIENTLY make an airplane beautiful. I ignored his advice because I knew that me building an airplane wasn't about efficiency in the build (7 years!) and also that I knew of planes with problems that should have been addressed but weren't because the owners didn't want to screw up the paint job. I didn't want to be that guy. Just embrace the concept that this is a hobby and is supposed to suck up all your time

In the case of cowl flaps, I don't see a downside to installing them during the build, except of course cost, weight and complexity but remember that I didn't see the downside of the oil shutter and wound up needing to remove it, so me not seeing too much of a downside should not give you much comfort. I wound up installing them after I knew I had a problem and implemented every other suggestion on how to fix the problem.

And of course, I only discovered the effective solution AFTER the plane was painted
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  #7  
Old 10-02-2017, 11:46 AM
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larrynew larrynew is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
...my recommendation would be to not install cowl flaps until you have determined that you are unable to resolve a cooling problem any other way.
+1. After 400 hrs of reasonably cool engine temps, I decided to seal up the baffles as best I could during some maintenance. I thought I had done a good job initially as I only had to lower the nose occasionally to keep the CHTs below 400 after a quick turn during the summer months in Texas. $14 at NAPA for red RTV and 3 hours later, temps are now consistently 20 degrees cooler.
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Last edited by larrynew : 10-06-2017 at 09:36 AM.
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  #8  
Old 10-02-2017, 06:56 PM
NYTOM NYTOM is offline
 
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Like they say, there's no substitute for experience and this is exactly the type of reply I was hoping for. Thank you gentlemen. I will proceed as you suggested.
You can learn so much from others experience here, all you have to do is ask.
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  #9  
Old 10-03-2017, 08:43 AM
moll780 moll780 is offline
 
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I've installed one flap and love it! No worries about rising temps on extra long taxies around Texas airports on hot summer days.
That's the perfect use-case.

Quote:
Originally Posted by NYTOM View Post
Reading through the archive's it seems a cowl flap can be a good investment towards to control of cylinder head temps. And I see some have installed two. My question is if one cowl flap is good, is two cowl flaps better? Would rather take the time now to install a second flap if it's going to make a readonable difference. We have about 40 days over 90 here and the heat can be brutal.
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  #10  
Old 10-03-2017, 10:43 AM
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PerfTech PerfTech is offline
 
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Quote:
Originally Posted by NYTOM View Post
Like they say, there's no substitute for experience and this is exactly the type of reply I was hoping for. Thank you gentlemen. I will proceed as you suggested.
You can learn so much from others experience here, all you have to do is ask.
...Well tom, I agree that baffling, timing, mixture and all the normal possible causes for excessive heat should be addressed, and corrected if possible first. One would assume this to be the case prior to any further modification. I also wholeheartedly agree that there is no substitute for experience, especially in the aviation world. Cowl flaps have been in use on virtually every commercially manufactured general aviation, as well as military aircraft throughout the world since the conception of the cowl itself. Definitely not a revolutionary concept by any means. They are without any doubt the most ideal method of obtaining large gains in cooling airflow, as in a climb, taxiing, operating in elevated air temperatures etc. All of this advantage and control at your fingertips with no penalty in cruise speed whatsoever. The "Easy Cool Flaps" are a very simple, quick installation, that really doesn't add much complexity or maintenance concerns to your aircraft. They increase the utility, reliability, and lifespan of your engine, by keeping the temperatures down when it is working hard and the demands are the greatest. They also add a considerable increase in comfort level, knowing you don't have to worry about excessive climb out temperatures, the need to push the nose over or pull off the power off to control them. You shouldn't be required to fly with any special maneuvers or odd practices to keep the temperatures in check! You wouldn't accept this in your car every time you wanted to go somewhere or came to a hill? Why have the power if you can't use it? Thanks, Allan..
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