[Davepar]

1. How do the baffles seal to the sides of the cowl inlets? The plans seem to call out an approach like this one from Vern's pictures:

Won't the air pressure push the flexible seal material away from the inlet? Along the tops of the baffles, the seal material curves inward and the air pressure pushes it into a good seal. But along the sides of the inlets the seal material can't curve inward. Or am I just worrying about nothing here?

2. This is related to the horz induction airbox. I've noticed from a few pictures now that everybody seems to use angle plus washers to attach the airbox to the baffle floor. From Mark's site:

Is there a reason why nobody is using the funky double-Z-channel that Van's supplies?

Thanks,
Dave

 

[vlittle]

Dave:

As for question (1), I think you mean what happens right at the inlet on the inside and outside edges.

I haven't had a chance to look at what happens in flight (!), but here is my educated guess.

As the air passes through the inlet, it speeds up relative to the air in the cowling volume outside of the baffles. This means that the moving air will have a lower relative pressure.

In effect, the higher velocity air 'sucks' the baffle material closed at the inlet. There may be some minor leaks, but it has no significant affect*.

When the air slows down in the plenum, it's pressure increases relative to the pressure outside the baffles, and pushes the baffle material up against the cowling, thus providing a tight seal.

*If air leaking from inside the cowling in this low pressure area were to occur, it would reduce the cowling air pressure.... and improve cooling flows around the cylinders. Theoretically of course, and it's probably not significant.

Vern Little, a baffling expert (not!)

 

[Bob Axsom]

Question 1 only

This is just some operational experience and not an answer to your question directly. After 176 hours of operation I performed the annual condition inspection on my RV-6A. The baffeling was one of the things on my checklist in the engine area. I observed the gaps between the metal and the rubber seal material and I applied Dow Corning 736 in this all around the upper seal area as I see that you have done. I also added some "736" at the rear edge of the vertical strip at the inboard edge of the inlets because I saw that the overlap rubber aft of the rivet line was lifted from the metal by quite a bit (maybe 3/16"). A few days later I made one "after maintenance" test flight and the low voltage light came on as reported elsewhere so off came the cowling again. I found that the RTV that I added to the top seal strips outside the plenum did fine but the bond at the trailing edge of the vertical strip was broken and the rubber strip was completely free to move in and out without opposition. Something is going on in this area that I can't associate with a linear flow, high velocity, low pressure image. I do not have a solution for it and I do not know if it is significant. I have observed some round inlet, independent plenum designs that employ what amounts to a large hose interface between the inlet and the plenum which would eliminate leaks in this area.

Added comment - I would minimize the upper corner of the vertical metal forward of the last rivet at the outside edge of the inlet. I did mine per plans similar to yours and I have contact marks on the inside if the upper cowl where they have hit during operation. I cut it as a fairly large and well deburred radius during the annual to eliminate the corner protrusion.

Bob Axsom

 

[N916K]

Question #1

When you put the top cowl in place it will cause the forward most piece of baffle to curve. This curve will hold the baffle material in place quite well. Also make the flap that attaches to the lower cowl curve up around the sides. This will create an overlap of that material and the material attached to the baffles. Once you get it all together there will be so much going on in that area, no large amount air will be able to get through.

Also I wouldn't glue all your baffle material together. It will need to float a bit to make a good seal. If you glue it together it won't lay flat when the upper cowl is on.

It's one of those jobs that everything makes sense after you're done.

Good luck

 

[Davepar]

It's one of those jobs that everything makes sense after you're done.

I believe that. As I get further and further into the baffles and filtered airbox, it's making more sense. Thanks for the advice all.

I think I've answered my own second original question. It seems that Vans may have re-designed the filtered airbox kit. The instructions were written late 2005 and the drawings are dated mid-2005. So far, it's going together really easily and seems very solid.

 

[Rene Bubberman]

You lucky devil!!!!!!!!!!

Hi Dave,

I looked at your site tonight and I was amazed by the quality and especially the fit of your FAB!
It seems like VAN's finally adapted the fit to the much more common IO-360, and made some improvements as well. The quality, fit AND instructions of the FAB kit I have are absolutely crap and needed a lot of hair-pulling and improvising, as you may have seen on my site ;-)
I'm glad for you, keep up the good work!

all the best,

 

[Davepar]

I did luck out. I was expecting to have a miserable time with the FAB, but it has been going together very easily. And the instructions have been nearly perfect. I didn't trim the width of the left baffle floor at all, so it flares out a bit. I'm not sure how it's exactly going to seal to the cowl inlet yet, but I'll have it figured out by the time I'm done! I'd rather deal with that problem than do major surgery on the FAB.

Just imagine the lucky devils that will get an updated baffle kit. At least I hope Vans updates the baffles some day.

Dave

 

[godspeed]

plug wires

where are yall getting those blue things
that hold the plug wires through the baffle?

I didn't get those in my kit.. and if I don't use those
whats the other options ?



Danny..

 

[RV_7A]

where are yall getting those blue things
that hold the plug wires through the baffle?

I didn't get those in my kit.. and if I don't use those
whats the other options ?



Danny..

Aircraft Spruce PN- 07-01014 2 wire 5mm wire seal.

-Jeff

 

[roadrunner20]

I believe Vans has modified the FAB for the horizontal induction.
I fit mine last week and it fit perfectly. While at snf today, I inspected Superiors and they had to add an extension.

 

[Scott Hersha]

baffle seal

I think it would help, when building your baffles/seals to visual a balloon with the cowl inlet being the 'nozzle' of the balloon. Air begins to slow right there and therefore, pressure begins to build. Any opening aft of this inlet in the baffle or seal will allow pressure to vent to the exit/low pressure of the lower cowl. A one square inch leak in this area can reduce cooling efficiency by as much as 20%. With this in mind, the baffle seal should be forced out against either the cowl or the baffle, depending on where it is mounted. My baffle seal in the lower inlet area is mounted to the cowl per plans and seals against the sloping front baffle in front of the cylinders. High pressure (because of slowing relative velocity) pushes it down against the front baffle, insuring a tight seal. All other baffle seal material is mounted on the baffles and curves inward so the positive pressure can force it against the cowl. Use talcom powder (baby powder works) every so often when you take off your cowl to insure a slick surface on the seal so it slides into a tight position under pressure. Cooling efficiency is a result of pressure differential not airflow.
Be cool.....Scott

 

[godspeed]

parts question

I have a left over part (or one I have not figured out where goes) anyone remember a part # VA-192B ?
little round part with two ears with holes ? anyone know where that ones goes.. maybe its for another
part of the fwf kit but I figured it goes with the
baffling ? not found a good place for it yet.. ideas ?

Danny..

 

[Hawkeye7A]

I have a left over part (or one I have not figured out where goes) anyone remember a part # VA-192B ?
little round part with two ears with holes ? anyone know where that ones goes.. maybe its for another
part of the fwf kit but I figured it goes with the
baffling ? not found a good place for it yet.. ideas ?

Danny..

When you described the part it sounded familiar to me and I confirmed it. It's part of the vertical air induction bypass system (which I believe is an optional installation.) VA-192B is a sort of rotating "trap door" to allow air to bypass the filter in the event it gets clogged with icing.