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  #51  
Old 09-07-2021, 07:48 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by sahrens View Post
What material did you use to fabricate the ramp area?
https://vansairforce.net/community/s...light=urethane
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  #52  
Old 09-08-2021, 12:09 PM
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sahrens sahrens is offline
 
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Thank you for the link
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  #53  
Old 09-08-2021, 05:48 PM
wawrzynskivp wawrzynskivp is offline
 
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Default Another example

Here is a pic of a homeshaped plenum, following the path illuminated by Dan Horton.

Method used here was to lightly lay up the plenum lid inside the cowl, release, then induce a bend so that the sides are 1/2" lower than the center relative to the cowl and then glass up for stiffness.

1/4" clearance was built in for the center to cowl which should give 3/4" on the sides for startup and shut down engine wobble.

Only contact point seen so far is close to center and very minor. This supports Dan's caution that the plenum will bulge at higher speeds.

I am in the camp that wants the most space in the plenum above the engine as is possible. The slower you get that plenum air the more pressure you'll develop, and more space will allow for greater pressure distribution. (No pressure drops as air goes over cylinders)

Couldn't be happier with the cooling flow provided. In fact I was able to reduce the standard Van's cowling exit area. I threw in some cowl flaps for extreme conditions but rarely open them.
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  #54  
Old 09-10-2021, 09:14 AM
motodave motodave is offline
 
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My mold is taking shape (since this photo I've done some additional blending) and I plan on doing the fiberglass layup this weekend once I coat the plug with epoxy so I can remove it later! Plan is ~2 layers of 8oz, then some Soric and then another couple layers as needed to stiffen it up. Using high temp epoxy and will install with nut plates on the plenum with screws through the standard Van's baffles.

Plenum mold by Dave Hock, on Flickr
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  #55  
Old 09-29-2021, 08:10 AM
motodave motodave is offline
 
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After a TON of work of making and re-making the plug for my Plenum I glassed it with the initial 2 layers of 8oz & Soric (more around intakes) and was able to remove (and save my hard earned plug) the plenum last night! Feels great to have this off the mold:



Next step is to apply 2 more layers on the inside, trim and add nut plates. Lots more pics on my Flickr site below.
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  #56  
Old 09-29-2021, 02:32 PM
BillL BillL is offline
 
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Nice buck and part, Dave! This type of buck is much better than what I tried. I had several failures and parts before getting something that looked that good.

I hope you will install some piccolo tubes above and below the barrels to measure your recovery performance. That will validate your design and aid in any troubleshooting that might me needed into Phase 1.

GOOD JOB!!
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  #57  
Old 09-29-2021, 09:41 PM
crabandy crabandy is offline
 
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Kudos for the quality plenum you made, looks like it will serve you better than what you started with!
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  #58  
Old 09-30-2021, 06:45 AM
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Dave, what is the inlet ring ID?
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  #59  
Old 09-30-2021, 08:26 AM
motodave motodave is offline
 
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Quote:
Originally Posted by DanH View Post
Dave, what is the inlet ring ID?
Same as std James aluminum inlets, dia is 4.8"

I will say while pleasing to make on my own from scratch this is a bunch of work and not inexpensive to do. The plenum is a good solution but the Van's baffles work fine for hundreds of builders and probably less expensive and maybe lighter. I'm happy picking the James cowl but with any deviation from the std plans has a lot of downstream effects... the James cowl forced me to a plenum and a more expensive Hartzel prop (extended hub) but I'm happy with the choice for now.
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Last edited by motodave : 09-30-2021 at 08:35 AM. Reason: added comment
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  #60  
Old 09-30-2021, 01:23 PM
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Quote:
Originally Posted by motodave View Post
Same as std James aluminum inlets, dia is 4.8"
Got it. I do hope you'll measure upper and lower pressures after you get flying. I'll be happy to help you with a standardized method which allows comparison with similar applications.

I asked about the inlet ring size because of the shape of the plenum inlet necks. Cowl exit area sets mass flow, so given two cowls with the same exit, inlet size sets inlet velocity. Our goal is to convert dynamic pressure to increased static pressure by smoothly slowing the flow. It can be done externally, out in front of a large area, low velocity inlet, or internally, with a smooth expansion of duct area. Given significant velocity, sharply diverging expansions have the potential for flow separation, resulting in less static pressure (sketch below).

So returning to inlet size, a 4.8" inlet is 18 sq inches. A 6" inlet (for example) has roughly 50% more area, while a 4" inlet is roughly 50% smaller. Given the same cowl exit, the three inlet velocities are very different, smaller being much higher.

In practical application (i.e. cowls for airplanes like ours), inlets in the 6" range are so insensitive to separation that they are often seen with no duct at all, just a nicely shaped lip around a hole dumping into the upper cowl volume. At the other end of the spectrum, applications with small inlets require carefully shaped ductwork.

Take a look at one of the plenum lids Bill Lane has done, like Rockwood's in post#15. I think they use the same 4.8 ring, but expand more gradually. I'm not saying yours is not going to work. It will, the question being how well, i.e. coefficient of pressure per CR3405. I'd love to see pressure data for the two otherwise similar installations.
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