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  #11  
Old 06-30-2020, 09:35 AM
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Quote:
Originally Posted by rocketbob View Post
I don't see the point of hand wringing over a 3" inlet when you have intake runners that have a 1.75" ID after the airflow makes two 90 degree bends from the servo thru the sump.
Pressure recovery...
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  #12  
Old 06-30-2020, 10:10 AM
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Quote:
Originally Posted by DanH View Post
Pressure recovery...
Perhaps.

My point is there are several chokepoints downstream of the servo.

In this case Jim and I picked the largest cone filter we could find that would work dimensionally in the confines of the F1 intake system.

The shape of the inlet was a compromise between performance, function, and appearance.
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  #13  
Old 06-30-2020, 10:33 AM
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Though the intake should be considered a "system" from intake valve to cowl inlet, the stock updraft sump is indeed a nightmare. Sharp bends, minimal plenum volume - yuk! I'm planning to change to the much superior 300 HP sump eventually, but for now I'm trying to get air "to" the servo (or in my case "throttle body") as efficiently as possible... Whatever the engine can give me after that is simply "what it is", as they say.
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  #14  
Old 06-30-2020, 10:34 AM
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Quote:
Originally Posted by rocketbob View Post
Perhaps.

My point is there are several chokepoints downstream of the servo.
The issue is how to generate maximum inlet pressure, in order to push more air through those restrictions.

Quote:
In this case Jim and I picked the largest cone filter we could find that would work dimensionally in the confines of the F1 intake system.
We're discussing pressure available prior to reaching the filter, throttle plate, intake tubes, etc. How the pressure gets wasted is another discussion.
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  #15  
Old 06-30-2020, 11:29 AM
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Quote:
Originally Posted by rocketbob View Post
I don't see the point of hand wringing over a 3" inlet when you have intake runners that have a 1.75" ID after the airflow makes two 90 degree bends from the servo thru the sump.
The 90 bends inside the sump plenum are fairly low velocity if it is designed well (the horizontal induction sump is a pretty good design) so the losses are lower. I'm not that familiar with the vertical induction sump but I imagine it is not as good. The 1.75" runners are carrying 1/4 or 1/6 of the total flow and are almost 1/3 the area of the throttle body, so those are not much of a restriction.

But as Dan said, the question really is about the inlet, not the rest of the induction system. Fix the things you can, accept the things you can't.
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Last edited by scsmith : 06-30-2020 at 11:31 AM.
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  #16  
Old 06-30-2020, 11:54 AM
sailvi767 sailvi767 is offline
 
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We are sticking with Jim?s 3? intake. Flight testing is delayed a bit because we had a issue with the heater muff and new exhaust. We also had to order a new air filter since the RSA 10 on the new intake reduced the room available between the servo and inlet. Hopefully fly it Thursday of Friday.
George
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  #17  
Old 06-30-2020, 12:24 PM
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Quote:
Originally Posted by Toobuilder View Post
Takeoff was 2700; low approach was 2600.
Calculates as 27.94" for the low approach at 0.9 VE, still close to the 28" reported. However, something isn't accurate. The predicted 27.94 is an airbox pressure. I assume you are tapping manifold pressure at the right rear cylinder's primer port, and as Bob reminds us, there is a loss in between the two points. We're not seeing one here. Better check that MP gauge.

BTW, best I know the Lyc charts assume a 0.9" Hg loss, which would be without a filter. I've measured my total loss, airbox to valve, at 14.4" H2O, or 1" Hg. That's deltaP, airbox vs the #1 primer port, breathing through a flat K&N, an FM200, and a standard Lycoming tuned sump.

What sort of intake system is on your 540?
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Last edited by DanH : 06-30-2020 at 12:48 PM.
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  #18  
Old 06-30-2020, 01:37 PM
scsmith scsmith is offline
 
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Quote:
Originally Posted by DanH View Post
Calculates as 27.94" for the low approach at 0.9 VE, still close to the 28" reported. However, something isn't accurate. The predicted 27.94 is an airbox pressure. I assume you are tapping manifold pressure at the right rear cylinder's primer port, and as Bob reminds us, there is a loss in between the two points. We're not seeing one here. Better check that MP gauge.

BTW, best I know the Lyc charts assume a 0.9" Hg loss, which would be without a filter. I've measured my total loss, airbox to valve, at 14.4" H2O, or 1" Hg. That's deltaP, airbox vs the #1 primer port, breathing through a flat K&N, an FM200, and a standard Lycoming tuned sump.

What sort of intake system is on your 540?
I wonder if a well-designed cold-air sump and tuned runners might get a VE better than 0.9?
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  #19  
Old 06-30-2020, 01:49 PM
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I have a standard D4A5 updraft sump with a machined TB adapter that allows the SDS 80MM TB to bolt to the RSA-5 mount pad. This adapter is an inch high and adds a bit of plenum volume, but is primarily there to allow for the height difference between the updraft sump and the taller 300 HP cold air version. When I change sumps, I don't want to modify my airbox system and pollute my data with multiple changes.

The TB adapter has a MP port incorporated, so I am indeed reading as close to "airbox pressure" as possible without being on the airbox side of the butterfly.
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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
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C

Last edited by Toobuilder : 06-30-2020 at 05:00 PM.
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  #20  
Old 06-30-2020, 03:52 PM
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Quote:
Originally Posted by scsmith View Post
I wonder if a well-designed cold-air sump and tuned runners might get a VE better than 0.9?
I really don't know what VE is typical for a stock Lycoming, and it will change depending on intake style, filter/no filter, etc. I didn't even have VE in my first spreadsheet. 0.9 seems like a reasonable WAG, given Mike said he was using a filter. As noted in a previous post, it doesn't make a lot of difference for intake sizing.

Quote:
Originally Posted by Toobuilder View Post
The TB adapter has a MP port incorporated, so I am indeed reading as close to "airbox pressure" as possible without being on the airbox side of the butterfly.
Ahhhhhh! You tricky devil
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