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My attempt at a plenum

CMW

Well Known Member
Here's a few shots of my plenum. This has taken forever. I hope it works well.

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very well done

Chris - honestly I don't think you can say "attempt" at all. You solution looks absolutely superb. Very nice.
 
Very nice work!

The only potential gotcha I see is the amount of air you're stealing at the back of #3. I think you'll find your oil is going to run pretty cool with that monster cooler. I have Van's standard cooler with a 4" SCAT in the same location as you do, and a 2" scat for cabin heat is taken off of my #4 baffle.
My #3 CHT wanted to run hot while my oil was on the cool side. I ended up blocking about 50% of the area of the inlet with perforated aluminum. Oil temp went up 10 deg (to where it should be), and CHT went down by 25 deg.

I'm sure you have more air to work with than me, but something to think about anyway.

Paige
 
Very nice. The transition to the stock cowl inlets (vs. the Sam James "rings") is especially well done.
 
Very nice!!

Chris,

Very Very nice work. Did you lay up the top from the top of the cowl?

What cooler did you use and did you make the plenum for the oil cooler?

The only thing I see that could be an issue is the inlets being aluminum and mating with the glass. The engine moves and the cowl is fixed. Any insulator between the cowl and inlets?

Again, great work!!!
 
Very nice work Chris.

Couple notes...stuff learned in a year with mine.

I'd suggest cutting back the length of the aluminum intake diffusers and increasing the length of the silicone rubber. The engine case torque reaction is significant, and adding length to the silicone tube will reduce load on the aluminum parts. My intakes are glass reinforced urethane. Your unreinforced silicone should give a bit more, a plus.

Same or related issue...make sure you have at least 1/2" cowl clearance at those upper front corners. Your parallel valve heads are easier to package in this regard so it may not be an issue. My angle valve head offers less clearance to work with in the RV8 cowl. I thought it had enough clearance but it still bumps on start-up or rough running.
 
It is a beautiful piece of work

It is a beautiful piece of work and I'm sure you will refine things to account for unforseen stresses as you encounter them. I'm not so sure that some things like the small tab of the rear right side baffle component riveted with two rivets to the forward component is going to hold up for example. I can't see the advantage of the independently closed top plenum and I still use the underside of the top cowl to close mine. I have blast tubes to the mags like you do and a cabin heat port but not the alternator blast tube. I do have my oil cooler mounted on the baffle behind cylinder number 4 instead of the very large duct you have going to your seperately mounted oil cooler. The volume of the plenum independent of the cowl is necessarily smaller and as experienced above with the best of care in development, it may hit the cowl during operation. When I prepare my plane for racing I have cover plates for racing that I install over the mag blast tube and heater ports and I have measured a slight increase in speed.

I know you are at the beginning of your development and I expect you to have a lot of fun refining the design/configuration.

Bob Axsom
 
Sealed Plenum Advantages

I can't see the advantage of the independently closed top plenum and I still use the underside of the top cowl to close mine.

I see the advantages as not having your cowling being constantly beat on by the rubber baffling and better sealing.

Hans
 
Very nice plenum. Do you have also a 4" Scat on the exit side of the oil cooler.In the affirmative how far down did you carry the scat tube: between the exhaust pipe ?
 
Very, very nice work! You've really raised the bar for those of us looking forward to this part of the project. I'm anxious to hear your performance numbers. Please keep posting.
 
Wow!

and to think, we were just going to re-do our baffle material at conditional. Very nice work! Which oil cooler did you use, can you post a couple pictures that show that setup better please?
 
Hmmmmmm

After studying your photos I remembered I too have a TMX-360.:rolleyes:
How much for the used cardboard templates? :eek:
I like yours even better than the Kevlar ones. Outstanding!:)
 
Thanks

Thanks for all the nice comments. I'll try and answer some of the questions:

The only potential gotcha I see is the amount of air you're stealing at the back of #3. I think you'll find your oil is going to run pretty cool with that monster cooler. I have Van's standard cooler with a 4" SCAT in the same location as you do, and a 2" scat for cabin heat is taken off of my #4 baffle.

I agree and I can't tell you how many time I went back and forth on what to do here, but I finally just decided to build it and deal with it during testing. I figured I can always choke down the flow to the oil cooler if I need to but adding flow would be more difficult. The cabin heat scat can also be moved to behind #4 if necessary. I'll have to see how the cabin heat works also, since I have mufflers and am running them in series. More experimenting.

Did you lay up the top from the top of the cowl?

What cooler did you use and did you make the plenum for the oil cooler?

The only thing I see that could be an issue is the inlets being aluminum and mating with the glass. The engine moves and the cowl is fixed. Any insulator between the cowl and inlets?

Yes, I used the top of the cowl as a form to lay up the top of the plenum.

I used some non-reinforced silicone rubber to join the cowl rings to the diffuser. I've posted a link to a video below that shows how much movement the system can accept. I hope its enough.

I'd suggest cutting back the length of the aluminum intake diffusers and increasing the length of the silicone rubber. The engine case torque reaction is significant, and adding length to the silicone tube will reduce load on the aluminum parts. My intakes are glass reinforced urethane. Your unreinforced silicone should give a bit more, a plus.

Same or related issue...make sure you have at least 1/2" cowl clearance at those upper front corners. Your parallel valve heads are easier to package in this regard so it may not be an issue. My angle valve head offers less clearance to work with in the RV8 cowl. I thought it had enough clearance but it still bumps on start-up or rough running.

Dan, first off I want to say that a lot of this design was inspired by if not directly copied from your plenum. I've got a long ways to go to get to your level of craftsmanship and knowledge but it's something to strive for. Thanks for raising the bar.

You may be right about cutting the diffusers back some but right now I think the system should allow sufficient movement of the engine relative to the cowl. The non-reinforced silicone stretches fairly easily. How long it will last is another issue that I'll have to keep a close eye on. Here's a link to a video showing how much movement the system will accept easily.

http://www.youtube.com/watch?v=7WIbDXnEhjU

I have 1/2" of clearance all the way around between the plenum and the upper cowl.

Do you have also a 4" Scat on the exit side of the oil cooler.In the affirmative how far down did you carry the scat tube: between the exhaust pipe ?

No, right now the oil cooler has no exhaust ducting. If I find I need to choke the flow to the cooler, I'll probably make something that will allow me to choke the exhaust rather than the inlet.

Which oil cooler did you use, can you post a couple pictures that show that setup better please?

I have an Aero Classics 8000074 nine row cooler. I'll try and post some in a couple of days.

And, NO! I don't want to go into business making these. This was a ton of extra work. About 3/4 the way into this I was kicking myself for not just building to plans but the first things I made were the cowl rings so I was kind of committed.

Thanks again for the comments,

Chris
 
.....I think the system should allow sufficient movement of the engine relative to the cowl.

The video is illustrative...I think you're right.

So far the fabric-reinforced ducts are holding up fine, but I'll be interested in lifespan for your unreinforced silicone version....internal pressure and membrane tension will be similar, about 100-110 lbs/sq ft at 200 knots down low. Your very low modulus approach is superior if the reinforcement isn't required, as the glass transmits more load to the baffle tin.

Overall your design is much more substantial. I experienced some fatigue cracking in the formed flange (1) and at the front 1/4-20 baffle screw (2).

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There is no structure at all where the urethane ducts meet the glass plenum lid, only a clamp strip with three nutplates. The loads at (1) and (2) are large, much like the anchor points of a rope bridge.

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The flange is highly formed and the material choice (3003) was too soft, so I'll need to replace it. I've already revised (2) for higher local strength.

You've sidestepped all that with significant structure above and around the inlets passages. Flip side will be turbulence behind the section change in the plenum entry if inlet velocity is high (high Vi/Vo). Big deal? I dunno ;) With work that pretty I sure hope you grab some pressure measurements in due course.

Speaking of pretty work, fess up...how did you machine those inlet rings?
 
.......I sure hope you grab some pressure measurements in due course.

Speaking of pretty work, fess up...how did you machine those inlet rings?

Thanks Dan, If I ever finish I will certainly take some pressure measurements. That's what it's all about, education.

The inlet rings I machined on the mill you can see in the background of one of the shots. I've converted it to CNC. It took a little layout work in CAD to get the shape close but then it was pretty easy.

Chris
 
"My Attempt at a Plenum"

Chris,

I have an RV-8 and was researching plenum ideas. I'm mostly interested in ideas like yours that used the stock Vans cowl inlets.

It's been a few years since youve built it. Hows it working? Anything you'd do differently?

Charlie
[email protected]



Here's a few shots of my plenum. This has taken forever. I hope it works well.

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_DSC0287.JPG


_DSC0288.JPG


_DSC0303.JPG


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Love more photos

Do you have a build site with individual part photos?

And how do you remove the top to service plugs/injectors?
 
What up piece of art , nice work Chris and I'll be watching for your disclosure posts on how you got the fibreglass so nice !

Some guys just seam to set the bar too **** high !
 
I'm doing my baffling now so this is really timely for me and I have a stock Vans cowling. I was going to put sheet diffusers to the cowl inlets but now I see where that would likely not have worked.

I like the way the inlet rings have a bead in them for rigidity. I am going to steal that - a good project for my bead roller.

The big difference with mine (or at least the one I have in my head) is that I am doing a split plenum, so the left inlet will feed the left bank of cylinders and the right will feed the right. I think it will be simpler in the long run. But experience may prove otherwise. Thank you for posting this.
 
The big difference with mine (or at least the one I have in my head) is that I am doing a split plenum, so the left inlet will feed the left bank of cylinders and the right will feed the right. I think it will be simpler in the long run. But experience may prove otherwise. Thank you for posting this.

A friend of mine had done it this way on his RV7 and end up removing the middle part to make it all one plenum due to hot temp issues. Once he removed the middle part, his temps were much better.
 
Chris,

I have an RV-8 and was researching plenum ideas. I'm mostly interested in ideas like yours that used the stock Vans cowl inlets.

It's been a few years since youve built it. Hows it working? Anything you'd do differently?

Charlie
[email protected]

I love Plane Porn! Is there an engine installation award category for RV's?
 
On my plenum, a BillL special, the oil dipstick is not in the plenum area. I believe in his photo the dipstick is behind the large orange ducting. At least on a O-320, that is how it works. Here is mine overall, but does not show the oil dipstick. I will see if I can find a picture of it.

[URL=http://s1245.photobucket.com/user/rockwoodrv9a/media/rv9a/plenum6_zpsf2fhhk94.jpg.html][/URL]

Man, that?s nice looking work. I also have Bill?s plenum that?ll be incorporated into my build. I hope mine comes out as nice as yours.
 
On my plenum, a BillL special, the oil dipstick is not in the plenum area. I believe in his photo the dipstick is behind the large orange ducting. At least on a O-320, that is how it works. Here is mine overall, but does not show the oil dipstick. I will see if I can find a picture of it.

[URL=http://s1245.photobucket.com/user/rockwoodrv9a/media/rv9a/plenum6_zpsf2fhhk94.jpg.html][/URL]

Yes, having modified a James plenum to work.........you have done masterful job on this one! congrats.....
 
I realize this is old thread ...but where could a guy get those aluminum " cowl rings ? Thanks. Stew [email protected]

Custom CNC milled, unfortunately. They are pretty aren't they . . . :D

I have been thinking for years about the challenge of mating ducts to the Vans cowl. After looking a some printed RV part porn (Steve Meltons work) I was wondering if some of his carbon material could be used to print some inlets.

Of course, a good design is a prerequisite.
 
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Yes, the rings are the key. If the OP, who invested a lot of effort into getting those right, would just distribute the CAD model for them, others could step up to machine them (or print them?) and many of us would be eternally grateful.
 
Yes, the rings are the key. If the OP, who invested a lot of effort into getting those right, would just distribute the CAD model for them, others could step up to machine them (or print them?) and many of us would be eternally grateful.

Seems like making them out of 'glass would be relatively easy. What am I missing?
 
One challenge of pre-made rings is that not everyone trims their cowl to the same exact closure along the mating line through the intakes. I suppose whatever you end up would be filled/filed/carved/built up to fit the pre-made rings.
 
One challenge of pre-made rings is that not everyone trims their cowl to the same exact closure along the mating line through the intakes. I suppose whatever you end up would be filled/filed/carved/built up to fit the pre-made rings.


That's kind of what I was thinking. Why not mold them in place, then pop 'em out?
 
That's kind of what I was thinking. Why not mold them in place, then pop 'em out?

It would be difficult, but it could be done. Nice thing about composites is that almost anything is possible. But you have to mold in a retention lug that fits into a channel all the way around. So it is a multi-step process.
 
I'd buy them

If something were to be produced....I would certainly be willing to purchase ! Especially given the stage of rework on my cowl that I am at . ....I have a PM into the original poster and hope to entice him into procurement of a pair or CAD ...but need to keep moving along so looking into the option of making my own ... Fingers crossed.
 
Lots of folks go to a ton of trouble to make plenums, my question is do they work?
I know most of my customers with James type cowls/plenums report higher CHT's than I have with a stock cowl.
So is there a real world benefit and is it worth all the extra work?
 
I'm with Walt

My buddies, with the plenums, do not show temps any different than properly baffled engines --- plus, the plenums are a real pain for routine engine maintenance!

Ron
 
Apples and oranges.

A plenum lid is just a sealing device. Unquestionably, a good lid has less leakage than flap seals. A poor lid may not be any better than really good flap seals. Either way, sealing is just one part of the equation.

Mass flow is based on differential pressure. With lots of differential pressure, the system can tolerate huge leaks. It will cool just fine. The excess mass flow will slow the airplane, but that's a price many are willing to pay.

Differential pressure is based on (1) the degree to which available dynamic pressure is converted to static pressure above the engine, and (2) the static pressure below the engine. The first is heavily dependent on inlet design, while the second is heavily dependent on exit size...not rocket science.

To be blunt, some of the past James plenums incorporate terrible duct design between the inlet ring and the upper plenum volume. I'm not guessing; I've seen measured upper plenum pressure 20% lower than stock cowls.

So yep, I am sure some stock cowls with flap seals cool better than some plenum installations. However, be cautious about painting with a broad brush. A good inlet well ducted to a truly sealed lid, providing high pressure air to good baffles, will cool better with less mass flow...and do it while tolerating residual lower cowl pressure, useful for increasing exit velocity.
 
Plenum

I am doing it mainly to off load the force on the upper cowl plus all my baffle seals need a revisit so I have some work either way ....of course intend to seal it well but the transition from inlet to plenum is certainly the most difficult part to get right .
 
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