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  #1  
Old 11-21-2021, 07:01 PM
wirejock's Avatar
wirejock wirejock is offline
 
Join Date: Oct 2005
Location: Estes Park, CO
Posts: 5,102
Default Cowl inlets

I'm working the cowl and thinking ahead to the plenum very soon.
It seems like there should be some sort of duct connecting the inlets to the plenum so maximum air flow goes into the plenum. However, how would the two cowls come together and seal to the duct? Maybe over thinking again.
I was thinking a horn shaped duct made of fiberglass with a seal of some sort. Since it's wider at the inlets, it wouldn't require overly complicated fastening to keep it from coming out. Easy to seal at the inlet. Assemble the cowls then insert the two ducts through the inlets. I just can't picture how to get a seal at the plenum. Maybe it just dumps with no seal? No idea.
I even considered wet suit material attached to both with a zipper seal between but that would be a real pain.
Any ideas would be appreciated.
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  #2  
Old 11-21-2021, 07:07 PM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
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Default

One of the better setups is to build the entire duct into the bottom cowl, then use neoprene or some other flexible material to convey the air back to the plenum.

The bottom cowl would be similar to the cowl on the Diamond in this video.

https://www.youtube.com/watch?v=3kx7umZZwrI

A bit of fiberglass skill would be required.
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  #3  
Old 11-21-2021, 07:23 PM
Jimmy Cox Jimmy Cox is offline
 
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Location: central Texas
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Look st the JamesAircraft.com website to see how we do the plenum and connection to the inlets. Wetsuit material works good.
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  #4  
Old 11-21-2021, 07:36 PM
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9GT 9GT is offline
 
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My plenum is DIY so a lot is involved in getting the seal right using the stock Van’s cowling. I settled on using two layers of BID impregnated with high temperature RTV silicone and cured in place. They will be two piece, top and bottom with an overlap. Attached to the cowling air inlets as in the plans. Just pull them through the gap when the cowling is in place and they will unfold and open up in place for a good seal. My bottom seal is done and I am working on the upper now. So far I am happy with the results. Gotta have a complete seal with no gaps, otherwise your defeating the main purpose of using a plenum.
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  #5  
Old 11-21-2021, 10:39 PM
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Can you do a plenum with the snorkel air intake or do you have to have the lower cowling direct intake?
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  #6  
Old 11-22-2021, 07:17 AM
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Default Cowl

Quote:
Originally Posted by Foghorn View Post
Can you do a plenum with the snorkel air intake or do you have to have the lower cowling direct intake?
I have an M1B. No scoop. RV Bits plenum. I need a solid seal between the inlets and plenum to be fully effective. I may try impregnatting some fiberglass , as David mentions, with RTV to see what that looks like.
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Donated 12/01/2021, plus a little extra.
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Empennage, wings, fuse, finishing kit done. Working FWF
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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  #7  
Old 11-22-2021, 07:29 AM
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bjdecker bjdecker is offline
 
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Larry,

Just use a small length of SCEET ducting between the back side of the inlets and the front side of the plenum/diffuser.

Make a bell shape for the plenum diffuser similar to what you did for the oil cooler.

Custom duct sizes and lengths available from Jonathan Kinney, Custom Duct -- two zero 7, six three 7, three zero zero zero. kinney AT fairpoint.net

He makes really nice ducts...
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  #8  
Old 11-22-2021, 01:06 PM
BillL BillL is offline
 
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You have just begun to think, so not too much yet.

Since the interface is a racetrack shape, the flat sides would be an issue for wetsuit material. On my James cowl, the gap from the inlet-ring to the diffuser is only 1/8" or a 3/16" max. They don't touch from engine movement. If you try the wetsuit material make a buck the right shape and test it to see if it gets lifted by dynamic air pressures expected.

There is a nice one for Vans cowl on VAF. Edit: Good connection to the cowl, agree with DanH on the upper intersection trip point. It is a good idea to plot the areas for designing the expansion from inlet to head face. It pays off.
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Last edited by BillL : 11-23-2021 at 07:50 AM.
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  #9  
Old 11-22-2021, 02:22 PM
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wirejock wirejock is offline
 
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Quote:
Originally Posted by BillL View Post
You have just begun to think, so not too much yet.

Since the interface is a racetrack shape, the flat sides would be an issue for wetsuit material. On my James cowl, the gap from the inlet-ring to the diffuser is only 1/8" or a 3/16" max. They don't touch from engine movement. If you try the wetsuit material make a buck the right shape and test it to see if it gets lifted by dynamic air pressures expected.

There is a nice one for Vans cowl on VAF.
Wow! That is very nice.
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Larry Larson
Estes Park, CO
wirejock at yahoo dot com
Donated 12/01/2021, plus a little extra.
RV-7A #73391, N511RV reserved (3,000+ hours)
Empennage, wings, fuse, finishing kit done. Working FWF
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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  #10  
Old 11-22-2021, 03:53 PM
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DanH DanH is offline
 
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Larry, Chis did some beautiful work. However, there is one issue. See the sharp, near 90 degree expansion? Flow separation is near guaranteed, which will reduce pressure recovery.

Compare with the plenum in post 31.
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