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  #11  
Old 11-20-2022, 12:10 PM
Paul Thomas Paul Thomas is offline
 
Join Date: Jun 2005
Location: Fort Myers, FL
Posts: 516
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Quote:
Originally Posted by Toobuilder View Post
[...] I was going to chime in and tell you that removing the pitot style scoop on the bottom of the cowl in favor of the snorkle in the the cooling inlet will actually cost you speed due to the loss of MAP. I[...]
How much MAP did you lose? I've read about the ram air effect from multiple people here but engine builders have told me horizontal induction would make a bit more power when I discussed engine option for the -7 I'm building.

I like the smooth cowl look but I want to be as efficient as possible.
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  #12  
Old 11-20-2022, 02:12 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 3,354
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Quote:
Originally Posted by Toobuilder View Post
after the first few posts I was going to chime in and tell you that removing the pitot style scoop on the bottom of the cowl in favor of the snorkle in the the cooling inlet will actually cost you speed due to the loss of MAP. I just did this mod to my Rocket in the hopes that the loss of MAP would be offset by lower airframe drag. It was not to be. Looks like the pitot is going back on.

That said, your MAP is not dependant on a ram rise because of the turbo so the pitot scoop is not contibuting anything but drag (but it isnt much). I would not expect to see much, if any, gains in speed with the removal of the scoop. Airflow management and cooling exit size, sure.
Michael,

Evidence from Dan Chekaway (sp?) when he did a lot of testing on inlet snorkels was that if you do a good design of the snorkel intake that incorporates a filter on the left cooling ramp, you get the "almost" the same manifold pressure as a ram intake with a filter. The key is to have nice radiused lips around the perimeter of the air filter to improve the flow into the filter. You don't want the flow to have to turn around square corners.

Of course you lose a little bit of manifold pressure in the filter, and it is not easy to design a filter bypass for the snorkel intake like you can for a ram intake (Rod Bower, others).

My point is that the external diffusion in front of the cooling intake, plus a well-designed snorkel intake, can achieve "almost" the same pressure as a ram intake.

Sorry for the thread drift.

To address the OP's original question, the devil is in the details. We have seen as much as 7 kt of speed increase on normal Lycoming installations by putting a radius lip on the bottom corner of the cowl where the cooling flow exits, and reducing the exit size appropriately. This is achieved by a combination of moderate reduction of actual cooling mass flow, and a substantial increase in exit flow velocity. On the other hand, we have also seen a case where the Lycoming engine was baffled so closely, and the cooling was so efficient, that there was not much cooling flow to work with at the exit, and could not get much exit velocity. In that case, there was little or no speed increase, IIRC.

For your installation, the devil is very much in the details. If you can get good flow with little pressure loss through your intercooler and coolant radiators, and collect that heated flow into a well-designed exit, you will see very low cooling drag. If you have rather haphazard flow paths into and out of your radiators inside the cowl, and then expect to expel that flow with any significant velocity at the exit, you will probably be disappointed. Ross Farnham has been very successful with his Subaru installation using a fully external radiator system, because it is well thought out and executed. There is potential to do better if you can keep the radiators at least partially inside the normal aircraft shape, so that the cooling intake adds less frontal area. It would be challenging, but possible, to install radiators inside the norma cowl, and provide good internal ducting into and out of the radiators.
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RV-8 N825RV
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"The Magic Carpet" Flying since Sept. 2009
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Last edited by scsmith : 11-20-2022 at 02:27 PM.
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  #13  
Old 11-20-2022, 03:21 PM
Toobuilder's Avatar
Toobuilder Toobuilder is offline
 
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Steve - Don't mean to derail an RV-9 thread, but here is a brief rundown of my journey:

First picture is my attempt at a "perfect" FAB. It houses a 2x14x7 inch K&N filter feeding into the standard updraft 540 sump through the SDS throttle body. This setup provided more MP in a side by side comparison with another Rocket buddy. This worked well.

Second picture is a water manometer plumbed into that same FAB (about 7 inches from the inlet), and also a pressure tap into the left cooling inlet (also about 7 inches back - right where I intended to pull induction air). This picture is at 5000 feet and about 180 KIAS. This is standard 1/4 inch graph paper and "I" is cooling inlet while "P" is the pitot inlet of the FAB. This led me to believe that the resulting loss in MAP would be slight, and the aero gains would overcome the loss in power.

So that led me to picture 3, where I built an inlet for the induction tube, intended to mount at the bottom of the left side cooling air intake. Note the very generous inlet radius and smooth interior finish.

Picture 4 brings it all together. Note the airbox is now bolted directly to the sump (this is the same airbox and filter as picture #1, BTW), and the throttle body is now on the front. The tube is 3" diameter and mandrel bent. There is no filter, screen or any other obstruction between the inlet and the TB.

Initial testing shows that the setup in picture #4 cost me about an inch of MAP compared to the picture #1 setup. Still need more data. Once I'm satisfied there is enough data, I'll cut a hole in the cowl and stick a pitot right out the front and see what I get.
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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
______________
Harmon Rocket II -SDS EFI
1940 Taylorcraft BL-65
1984 L39C - SOLD
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  #14  
Old 11-21-2022, 03:02 PM
scsmith scsmith is offline
 
Join Date: Jan 2008
Location: Ashland, OR
Posts: 3,354
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Michael,
sending you a PM to take the intake discussion out of the thread.

Quote:
Originally Posted by Toobuilder View Post
Steve - Don't mean to derail an RV-9 thread, but here is a brief rundown of my journey:

First picture is my attempt at a "perfect" FAB. It houses a 2x14x7 inch K&N filter feeding into the standard updraft 540 sump through the SDS throttle body. This setup provided more MP in a side by side comparison with another Rocket buddy. This worked well.

Second picture is a water manometer plumbed into that same FAB (about 7 inches from the inlet), and also a pressure tap into the left cooling inlet (also about 7 inches back - right where I intended to pull induction air). This picture is at 5000 feet and about 180 KIAS. This is standard 1/4 inch graph paper and "I" is cooling inlet while "P" is the pitot inlet of the FAB. This led me to believe that the resulting loss in MAP would be slight, and the aero gains would overcome the loss in power.

So that led me to picture 3, where I built an inlet for the induction tube, intended to mount at the bottom of the left side cooling air intake. Note the very generous inlet radius and smooth interior finish.

Picture 4 brings it all together. Note the airbox is now bolted directly to the sump (this is the same airbox and filter as picture #1, BTW), and the throttle body is now on the front. The tube is 3" diameter and mandrel bent. There is no filter, screen or any other obstruction between the inlet and the TB.

Initial testing shows that the setup in picture #4 cost me about an inch of MAP compared to the picture #1 setup. Still need more data. Once I'm satisfied there is enough data, I'll cut a hole in the cowl and stick a pitot right out the front and see what I get.
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 725
also
1/4 share in 1959 C-182B (tow plane)
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2022
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