Looking for ideas on inlet boots for Plenum

[lr172]

I am helping a new owner with some remediation on a 7A he just bought. THe PO built a plenum for it, but chose to put nothing between the inlets and the plenum. Not surprisingly, the CHTs get pretty high in the climb phase. Looking for a hopefully non-invasive way of making an insert and boot to address this. Doesn't need to be perfect, just effective. Plane is panted, so hope not to carve up the fiberglass.

Appreciate any ideas, as I have no experience with plenums.

Larry

 

[agent4573]

Sam James includes a sheet of neoprene to make the boots. You can get 12"x12" sheets of 1/4" thick neoprene and glue on Amazon, or head to your local dive shop, buy a used wetsuit and cut the legs/sleeves off of it if you don't want the glue seam.

 

[rockwoodrv9]

At least put Ducting from Ring to Plenum

Probably more than he wants to do but this worked well for me. Even if he just put the ducting from the back of the ring inlet into the plenum I believe it would be better. Do you have a picture?

Edit - Larry if he wants to come over to Mason or meet sometime to look at mine, let me know.

 

[Webb]

Pictures please

 

[wirejock]

Neoprene

I bought neoprene on Amazon. I have two strips about 3" wide with bra clips. It hasn't flown yet so I can't comment on performance.

 

[Carl Froehlich]

Neoprene is the way to go. Don’t forget the neoprene cement. It holds the butt seam amazingly well.

One ohter suggestion - make the boots at least 3” long to provide for ~1” of separation between the plenum and inlet ring. Less than this and you will impart unnecessary stain on the boot, plenum and cowl. There is a lot of movement between the plenum and cowl.

Carl

 

[wirejock]

Inlet gap

Neoprene is the way to go. Don’t forget the neoprene cement. It holds the butt seam amazingly well.

One ohter suggestion - make the boots at least 3” long to provide for ~1” of separation between the plenum and inlet ring. Less than this and you will impart unnecessary stain on the boot, plenum and cowl. There is a lot of movement between the plenum and cowl.

Carl

1" wow. Guess I need to trim my inlets. I have the gap much closer. Thanks. My Mentor Dave mentioned it as well but no knowing how much gap, I haven't trimmed yet. It's going to be less than 1" on the Frankensnorkel side. Very little left to trim off.

 

[HFS]

What I Did -

Larry -

I too, used wetsuit material - the thickest I could find (mics @~ .250").

I cut the flat pattern so when the ends were drawn together for gluing (using neoprene wetsuit adhesive) the "shape" was a truncated cone, slightly smaller in diameter on the ends so that some "stretching" would have to take place for attachment/sealing. In addition to gluing the end faces, I also cross stitched, with Kevlar (can break it) thread, as a secondary line of support.

I also covered the joint area with clear silicone as a sealer against contaminant intrusion (read oil). I also put a layer of silicone on the end of the "coupling" I didn't want to move against its contact surface. You can just see the silicone "layer" on the inside of the 3rd pic. On that end (silicon side) I used a modified worm drive type hose clamp to increase the "foot print" on the contact area to give better bearing pressure over the area.

21+ years later - still going strong on the second set.

Space between inlet rings and plenum inlet ~ 3/8 - 1/2"

The last picture shows a smaller ring, as it is for the induction inlet.

HFS
HRII S/N 002

 

[lr172]

I probably should have been more clear. This is a std Vans cowl with the rect inlets (no air flow curves installed in top cowl) with a rect shaped plenum inlet with the baffle plenum top combo. The OP left about 1/4" clearance, but am convinced this is spilling a lot of air into the lower cowl during the climb phase and needs something to prevent that.

Looking for how folks deal with this issue when installing plenums with the stock rect inlets. I am not interested in a large F/G project to make the cowl have round inlets.

 

[RWoodard]

I’ll add my endorsement for neoprene… even with the traditional inlets. That’s what I used on the cowling to plenum transition for my Midget Mustang. One potential downside that I discovered is that the neoprene puts out all kinds of black smoke and soot in the event of an engine fire! Downright amazing considering it probably totaled about 40 square inches of material!

 

[D-Dubya]

The neoprene should work just as well with the standard cowl D-shaped openings. And you're absolutely correct in thinking that the CHTs (and probably oil temps) will come down when that gap is sealed. But since it's not round, a gear clamp may not work as well around the oblong shape of the opening. There may be other ways to secure the neoprene to ensure it's a tight fit while still being easily removable for maintenance.

An alternative would be to put silicone baffle sealing material as a lip between the cowling and the plenum, kind of like the "standard" configuration without a plenum. Depending on how the original builder matched the size of the two openings, this may or may not be an easier fix.

 

[andoman]

I’m considering doing the same to my Rocket and keeping its rectangular inlets.
Larry, I’ll be following your pathfinding efforts closely.