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Plenum Seal

SeanB

Well Known Member
I've got a carbon plenum that is designed for the stock intakes (not SJ round ones) of the Van's cowl for my RV-7. Wonder how folks are handling the intake seals. I could use traditional strips of silicon fabric, like for traditional baffle seals. Curious if neoprene could be used with the odd shape of the stock intakes.

Also, to seal the other edges of the plenum, I plan to create an Ultra Black RTV seal. I would like to have the plenum removeable for service. Can I just use packing tape as a release for one side, like when laying down fiberglass? Make the RTV adhere to the plenum, or adhere to the associated baffling?

Thank you!
 
Plenum

I've got a carbon plenum that is designed for the stock intakes (not SJ round ones) of the Van's cowl for my RV-7. Wonder how folks are handling the intake seals. I could use traditional strips of silicon fabric, like for traditional baffle seals. Curious if neoprene could be used with the odd shape of the stock intakes.

Also, to seal the other edges of the plenum, I plan to create an Ultra Black RTV seal. I would like to have the plenum removeable for service. Can I just use packing tape as a release for one side, like when laying down fiberglass? Make the RTV adhere to the plenum, or adhere to the associated baffling?

Thank you!
RTV doesn't stick to packing tape. Works great to layup seals. Also RTV impregnated fiberglass works great to seal the cylinder fins.
Or
You could get really serious and do this. The inlets will be sealed with thin neoprene. The rest is sealed with RTV. I taped off the plenum then applied RTV. When removed, it left a form fitting seal.
20220514_074653.jpg
 
Also, to seal the other edges of the plenum, I plan to create an Ultra Black RTV seal. I would like to have the plenum removeable for service. Can I just use packing tape as a release for one side, like when laying down fiberglass? Make the RTV adhere to the plenum, or adhere to the associated baffling?

Thank you!
FWIW I went with the aluminum tape used to seal air conditioning/heater ducts for the edges of my plenum. It is very cheap and works incredibly well.

Plenum2.jpg

Plenum.jpg
 
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Urethane rubber layup

You can get some two part urethane and some cloth and layup whatever shape you like.

I did my intakes on a temporary foam core with kevlar and used some black die to make them look tidy.
 

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Thanks for all the replies and great suggestions. You guys all have nice looking results.
 
RTV doesn't stick to packing tape. Works great to layup seals. Also RTV impregnated fiberglass works great to seal the cylinder fins.
Or
You could get really serious and do this. The inlets will be sealed with thin neoprene. The rest is sealed with RTV. I taped off the plenum then applied RTV. When removed, it left a form fitting seal.
View attachment 31650

Have you tried removing that lower cowl with the prop and spinner on yet? It looks like it is going to be tight.

Larry
 
Bottom cowl

Have you tried removing that lower cowl with the prop and spinner on yet? It looks like it is going to be tight.

Larry

Nope. I build in 3/8" gap per Whirlwind recommendation. I did borrow their faux spinner to check final fit. The "A" model new gear design has a pretty big slot with close out panels. It should drop far enough to clear the spinner. The inlets don't have to clear. They don't slip on top of the baffles like a traditional set up. The tiny gap between the cowl inlets and the plenum inlets is sealed with a neoprene sock. The cowl can drop straight down. I suspect it won't be fun! :D
<fingers crossed>
 
Plenum Intake Seals

Including pics of the rough fit version of my plenum from a few years ago. Now it's time to figure out good intake seals as I near first flight.

As you will see, it follows the same shape as the stock cowl inlets. There is a small step on the carbon inlet to aid with a seal. I'm having difficulty coming up with a good solution in this case. A Neoprene "Sock" seems like a great candidate, but I'm not sure how to get it to stay in place.

Glue neoprene to the ID of the plenum intakes so it won't balloon with air pressure? Then overlap the two cowl OD halves on the forward side with metal strips holding the neoprene in place? It's a challenge not being round like a Sam James and a band clamp. Trying to imagine a mechanical captive fastener with this odd shape.

Try silicon baffle material and make two pieces that overlap? Similar to stock application. Wondering what will keep the pieces from spreading apart at the overlap (longitudinally). This one to me seems most practical...so far.

Larry's looks nice/interesting to me...but I don't have the same fancy mod he did on the cowl.

Sure will appreciate any additional ideas! Thank you!!!!
 

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Sean,
I am trying to come up with an idea that would work other than some wet suit material and a couple large pipe clamps. Maybe zip tied on? You would have to replace them each time you took the bottom off but may be worth it.

One thought - maybe some rubber U channel like on the panel shelf edge? It could nest up against the shelf and not cause issues when the engine shakes at start and stop. It there is a slight gap between the plenum and the cowl shelf, it may not be that big of an issue?

Mine are round so I just used the black tubing and it flex fits on. It isnt perfect but works.

Nice work on the plenum. The inlets look like they will let in max air so it should be great for cooling.

Email me if you want to see my pictures. They may help?
 
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Sean, that design looks like it would seal well with simple strip seals...like a stock lower seal and a mirror copy on the top cowl. They get attached to the backside of the cowl flanges and overlap into the plenum inlets. Might need to shorten the plenum ramps.
 
Thanks Rocky and Dan! Yes, thinking I’ll try the more traditional seals (mirrored) and shorter. I appreciate your ideas.
 
Plenum

Thanks Rocky and Dan! Yes, thinking I’ll try the more traditional seals (mirrored) and shorter. I appreciate your ideas.

That's very nice work Sean.
I have one concern with my solution. I don't have a prop so I wake up at night wondering if I will be able to R&R the bottom cowl. Go figure. It looks like it will clear. I did fit the neoprene seals. They go on and come off but, as you pointed out, they are accessible after removing my top cowl. They are 3" wide. Yours is a little different. Point I'm not making well is the cowls have to come off. Whatever you use has to clear the ramps or flex.
How about a seal the shape of the inlets? Assemble everything then slip the seals in the inlets. Seems like Dan has a set up like that. A fiberglass layup with a thin seal bonded to it. A fastener to keep it from slipping back out. It can't go in because it's the shape of the inlet and wider than the hole.
Just a thought.
 
Seal Rings

That's very nice work Sean.
I have one concern with my solution. I don't have a prop so I wake up at night wondering if I will be able to R&R the bottom cowl. Go figure. It looks like it will clear. I did fit the neoprene seals. They go on and come off but, as you pointed out, they are accessible after removing my top cowl. They are 3" wide. Yours is a little different. Point I'm not making well is the cowls have to come off. Whatever you use has to clear the ramps or flex.
How about a seal the shape of the inlets? Assemble everything then slip the seals in the inlets. Seems like Dan has a set up like that. A fiberglass layup with a thin seal bonded to it. A fastener to keep it from slipping back out. It can't go in because it's the shape of the inlet and wider than the hole.
Just a thought.

This ^^^^ is what I have done. I started by laying-up 4 plies in the inside of each inlet to make thin "rings". Then, I made rubber boots that slip over the rings, covering about half the length of each ring and secured with hose clamps. Next, each cowl inlet was shortened 3/4" to provide clearance for the boot & clamp. I faired the inlet surfaces with some micro so that the rings are not noticeable when looking into the inlets, although not really necessary. Now, I can remove the top cowl with the inlet rings and rubber boots remaining attached to the bottom cowl.

Ron B.
 
Thanks for the additional replies, Everyone! Ron...do you have pics of what you did?
 
Inlet Rings

Thanks for the additional replies, Everyone! Ron...do you have pics of what you did?

Here are a few pics of the parts during the build process. However, I do not have pics of the rubber boots or the finished product and I do not plan to visit the hangar for a few weeks...

The rings are 1/16" thick, so the inlet size is slightly reduced. Also, the rings are somewhat flimsy until they are installed between the upper & lower cowl. Once installed, the rings become very stiff.

When installed, the rings are trapped by the micro fairing (fwd movement) and the inlet draft angle (aft movement). I added a couple of screws to affix the rings to the lower cowl as an added measure of security.
 

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RTV and a couple of layers of fiberglass cloth works well and seems to be pretty durable.
 

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Here are a few pics of the parts during the build process. However, I do not have pics of the rubber boots or the finished product and I do not plan to visit the hangar for a few weeks...

The rings are 1/16" thick, so the inlet size is slightly reduced. Also, the rings are somewhat flimsy until they are installed between the upper & lower cowl. Once installed, the rings become very stiff.

When installed, the rings are trapped by the micro fairing (fwd movement) and the inlet draft angle (aft movement). I added a couple of screws to affix the rings to the lower cowl as an added measure of security.

Those inlets are a nice piece of work. My compliments sir.
 
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