[RickWoodall]

As I plug away on the baffles and scratch my head at all the fit issues...I cant help by wonder why isnt there just a lid for the top once the sides are built?

Seriously...if you look at several of the builders sites there is the james plenum or some who have made up their own glass/carbon fiber lid.

Why isnt there a pretty easy, commercialy available lid for the top of the baffles. Its pretty universal size isnt it? No floppy little rubber to fit, no gaps to seal, no soft material to pop rivet on or need stitching, no fine tunning, just level it off, ensure clearance with the cowl and install. What am I missing? A simple strong lid for the top that could be fastened with piano hinges like the cowl etc. Easy to remove for inspection, fairly tight seal etc.

Just wondering why there isnt a better solution to this job. Flame away, it just puzzles me.

 

[RV8R999]

I recently completed my baffles with the standard rubber seals. The more I look at it the more I want to remove them. Even if a plenum cover doesn't help with cooling (which i know it will since I did this on my previous plane), it would make install of the top cowl much easier as there would be nothing to compress or ensure is pointed in the right direction.

I was thinking of using my scrap angle alum and riveting through the holes already drilled for the rubber baffle material. Then lay a piece of alum sheet over the top drill, cleco, trim to fit, drill for #8's and install nut plates on the angles. A small bead of red RTV along the perimeter and its done. Would use the rubber material to seal the inlet areas but this would be easy.

 

[lostpilot28]

As I plug away on the baffles and scratch my head at all the fit issues...I cant help by wonder why isnt there just a lid for the top once the sides are built?

Seriously...if you look at several of the builders sites there is the james plenum or some who have made up their own glass/carbon fiber lid.

Why isnt there a pretty easy, commercialy available lid for the top of the baffles. Its pretty universal size isnt it? No floppy little rubber to fit, no gaps to seal, no soft material to pop rivet on or need stitching, no fine tunning, just level it off, ensure clearance with the cowl and install. What am I missing? A simple strong lid for the top that could be fastened with piano hinges like the cowl etc. Easy to remove for inspection, fairly tight seal etc.

Just wondering why there isnt a better solution to this job. Flame away, it just puzzles me.

Don't know "why" a lid, err plenum, isn't standard in the FWF kit...but, I installed the Van's baffle kit pretty much as per plans up to the point where you put the rubber on, then just shoved my James plenum on top, crammed it down until I knew it would clear the cowl, then drilled holes for screws & nutplates. Was simpler than I thought it would be, but still not a fun part of the build for me.

I've read a few posts here and there that talk about maximizing the volume of air above the engine (inside the plenum), but I didn't do much measuring. My temps are all pretty close to each other and it seems to work just fine. I would think making a similar plenum for the square inlets wouldn't be too difficult.

 

[scsmith]

What you are missing is.....

The plenum intake needs to be sealed to the upper and lower cowl cooling intakes. With the standard cowl, this is a bit tricky. It is fussy work. So there is a kind of "conservation of difficulty". Many have done it of course. Check out Kevin Horton's RV-8 website and you will see how he did it.

The one disadvantage of a plenum is that it is nice to be able to see the top half of the engine when the cowl is off. check for leaks, make sure ignition wires are staying put, that sort of thing.

The primary reason for the round inlets on the Sam James cowl, and other similar cowls, is that the connection to the round inlets in the cowl are more straightforward - you have an aluminum ring that engages into shallow slots in the cowl halves, and the ring connects to the plenum with a rubber sleave.

In reality, once you get the baffles trimmed down right, the rubber seals are pretty easy. I spent the most time designing how the baffles would seal around the front of the engine behind the spinner. I think this is a key area where significant leaks can be introduced, and there is more than one workable solution, so lots of head-scratching time. Otherwise, I think it was just as easy, or easier than a plenum.