My attempt at a plenum

[Kyle Boatright]

Originally Posted by scsmith

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?

[scsmith]

Originally Posted by Kyle Boatright

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.

[Stewbronco]

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.

[Walt]

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?

[RONSIM]

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

[DanH]

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.

[Stewbronco]

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 .