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  #11  
Old 10-03-2017, 12:29 PM
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Toobuilder Toobuilder is offline
 
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Agree with most of the above with the subtle, but important distinction that cowl flaps are generally an engineered solution which provide both large exit airflow for high demand situations AND a small exit for drag reduction at cruise. The RV cowl is a compromise between these two and favors excess cooling at the expense of drag reduction. This is evidence with those that pinch off the exits and see speed increases and proper temps, and those like me who have the stock exit size, but see our CHT "too cool" at cruise.

So in essence, your cowl flap adds exit area to a cowl design that is already too large for the cruise configuration. Yes it works, but to say there is no speed penalty requires the qualification: "...compared to a stock RV cowl..."
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  #12  
Old 10-03-2017, 12:49 PM
Bicyclops Bicyclops is offline
 
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Location: LA, California
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Default During the build?

As others have mentioned, the standard RV cowling works pretty well for most people with proper attention to sealing. One thing I have noticed on many RVs that I have inspected is that the little tab on the baffle which is supposed to be bent to be very close to the cylinder base of #3 is often left wide open. Even if the tab is bent properly, that whole area should be sealed with RTV and often isn't.

I modified my cowl during build a la Dan Horton's "Shrinking Exit" by increasing inlet size and decreasing exit area. I was concerned that I would have excessive CHTs and oil temps during taxi and climb so I took drastic measures to increase airflow through an oversize cooler and I cut in very large cowl flaps. As it turns out, I have to choke off most of the air to the oil cooler just to get into the green and don't need the cowl flaps for taxi and climb even on 100 degree days. Now that the weather has cooled to about 90 degrees (much cooler than that today), my hottest cylinder is about 340 down low with high power set. So - I definitely have excess cooling capacity. My intent is to shrink and extend my exit scoop further which will enclose my exhaust pipe and add some augmentation to the mix. My hope is that I'll reach a point where I do need the cowl flaps for ground ops and climb but not for cruise.

As pertains to this thread, I wouldn't do cowl flaps during build on a standard installation. If attention to detail is employed, it'll cool ok. If it runs hot anyway, then the addition of cowl flaps is a viable method of adding mass airflow for cooling.

Ed Holyoke
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  #13  
Old 10-03-2017, 01:08 PM
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PerfTech PerfTech is offline
 
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Quote:
Originally Posted by Toobuilder View Post
Agree with most of the above with the subtle, but important distinction that cowl flaps are generally an engineered solution which provide both large exit airflow for high demand situations AND a small exit for drag reduction at cruise. The RV cowl is a compromise between these two and favors excess cooling at the expense of drag reduction. This is evidence with those that pinch off the exits and see speed increases and proper temps, and those like me who have the stock exit size, but see our CHT "too cool" at cruise.

So in essence, your cowl flap adds exit area to a cowl design that is already too large for the cruise configuration. Yes it works, but to say there is no speed penalty requires the qualification: "...compared to a stock RV cowl..."
...I am aware and in agreement with most of the above. This being said, it doesn't change the fact that many people are experiencing very high CHTs on climb-out on hot days. They are finding it necessary to compromise their flight path to accommodate temperature issues. This is not necessary and to us is unacceptable! The cowl flaps only address this climb-out issue, and cruise speed is an altogether different subject. We have looked at cruise airflow as well, and are working on a product package to address this also. Our prototype is in testing now and showing very favorable results. Our 9-A is seeing cruise speeds of 205 to 210 true at altitude, with fuel burn of 7 GPH with a stock 0-320 160 HP. We hope to offer this package for purchase in a couple of months. Thanks, Allan...
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  #14  
Old 10-03-2017, 01:18 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by PerfTech View Post
...I am aware and in agreement with most of the above. This being said, it doesn't change the fact that many people are experiencing very high CHTs on climb-out on hot days. They are finding it necessary to compromise their flight path to accommodate temperature issues. This is not necessary and to us is unacceptable! The cowl flaps only address this climb-out issue, and cruise speed is an altogether different subject. We have looked at cruise airflow as well, and are working on a product package to address this also. Our prototype is in testing now and showing very favorable results. Our 9-A is seeing cruise speeds of 205 to 210 true at altitude, with fuel burn of 7 GPH with a stock 0-320 160 HP. We hope to offer this package for purchase in a couple of months. Thanks, Allan...
And some of the rest of us have tried to to convey that there are many ways to resolve over heating problems.

One extreme would be to sell the airplane and buy one that doesn't overheat.
The other would be to zero in on the root cause of the problem and fix it.

Adding a cowl flap (or two) to a cooling system design that the major majority of the same airplanes cool well without, is another method of solving the problem, but not the best way in my opinion.
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  #15  
Old 10-03-2017, 01:21 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by PerfTech View Post
...I am aware and in agreement with most of the above. This being said, it doesn't change the fact that many people are experiencing very high CHTs on climb-out on hot days...
We are in agreement. The standard Vans cowl is a compromise and there are going to be a few outliers that have issues. That, and I think their continuing baffle treatment of #2 and #3/5 is borderline irresponsible...

That said, many of the people who "think" their baffles are good are in error. There is a lot more to it than just aiming some air in the general direction and hoping for the best. Every molecule of air that comes out the exit needs to have gone through a cooling fin first or its a waste.

I'm doing a true cowl flap on the Rocket to address the significant cooling needs of the engine at high power/low speed flight as well as sealing things up to keep the heat IN when I'm high and LOP. I'll be interested to see what you come up with.
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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.

Michael Robinson
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RV-8 - Flying
1940 Taylorcraft BL-65 -flying
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  #16  
Old 10-03-2017, 02:20 PM
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rvator51 rvator51 is offline
 
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Default My take on cowl flaps

I sure appreciate everyone's point of view on this. I have done everything I could to get temps down on my two RV's except for putting in a solid plenum and cicular inlets. Here in Phoenix, I was unable to keep below 400 degrees on climbout in both the RV-4 and RV-6a. Addition of electric cowl flaps solved the problem on both airplanes.

The RV-4 used to cool fine with the O-320 in it, but when we went to an O-360 with 9:1 compression cylinders, it runs real hot on climbout without use of cowl flaps.

Sure would be nice to know what I was doing wrong with the baffling so I could fix it. Baffling fits good all the way around, Liberal use of RTV everywhere I could. My no 2 cylinder has small fins in front so no need to do a bypass around it.
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  #17  
Old 10-03-2017, 02:44 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by rvator51 View Post
...My no 2 cylinder has small fins in front so no need to do a bypass around it...
Can you define "small fins"? There is some variation between manufacturers, but the deepest I've seen so far (on the 360/540) is only about 1/8 inch - not nearly enough. And how about the rear of your #3 - same?
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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.

Michael Robinson
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Harmon Rocket II -SDS EFI instalation in work
RV-8 - Flying
1940 Taylorcraft BL-65 -flying
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  #18  
Old 10-03-2017, 03:02 PM
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Low Pass Low Pass is offline
 
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Two cowl flaps installed. Adds significant operating (temp) flexibility. Does cost money, weight, noise, and drag when open. Am I'm just about trained to connect the power to the actuators when reinstalling the cowling now after a year.

One issue with the EZ Cool devices. The fasteners need Loctite, and I felt like the actuator needs insulation. I strapped a small piece of foil backed cloth on each one of mine.
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Last edited by Low Pass : 10-03-2017 at 03:05 PM.
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  #19  
Old 10-03-2017, 05:44 PM
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Front fin on no 2 is about 1/8 in deep. Used washer in back of no 3 cylinder. All four cylinders run about same temp.
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Thomas Velvick
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  #20  
Old 10-03-2017, 06:03 PM
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PerfTech PerfTech is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
And some of the rest of us have tried to to convey that there are many ways to resolve over heating problems.

One extreme would be to sell the airplane and buy one that doesn't overheat.
The other would be to zero in on the root cause of the problem and fix it.

Adding a cowl flap (or two) to a cooling system design that the major majority of the same airplanes cool well without, is another method of solving the problem, but not the best way in my opinion.
... The majority of these aircraft do not operate in the extreme heat like Ca.Tex. Az. etc. It would stand to reason that most or many don't have the problem in cooler climates. In our testing I took off from Lake Havasu City AZ. 117 degree day, 800 foot elevation, pretty much an ideal test location for heating issues. I rotated at max power to 70 kts. 2400 ft. pr min, held that speed to 12k ft. Temps never passed 380. I closed the flaps pushed the nose over to cruise configuration and a true airspeed exactly on my VNE. at less than 7 GPH. I don't know of another RV that can do this without cowl flaps. Whats not to like? I like you deal with, and talk to a lot of RV owners as well as other extremely high performance aircraft owners/builders. Most report back big reductions in climb temperatures, usually in the 50 degree range with no penalty in speed or efficiency. We currently have over 800 aircraft out there with "Easy Cool Flaps" and have yet to receive a performance report from an unhappy customer. This speaks volumes in itself, and unlike "many suppliers" we offer a 100% guarantee of satisfaction on all products and purchases! I wish everybody in this business operated this way, as it would make the flying and owning an aircraft much more enjoyable. Thanks, Allan..
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AntiSplatAero.com
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Products, Tools & Services
Info@AntiSplatAero.com
Southern California (KREI)
RV-9A / Edge-540
(909) 824-1020
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