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Baffling ??

R

Rolly9

Active Member
I am having trouble trying to decide what the baffles are supposed to look like at the front: #11 & 1 and 3 & 9 where the are next to the Contoured Ramps that are in the Top Cowl Inlet. How does the Baffle Seal Material lay in that area. The instructions are not clear (at least to me).
Thx. Rolly Clark FWF
 
Rolly9 said:
I am having trouble trying to decide what the baffles are supposed to look like at the front: #11 & 1 and 3 & 9 where the are next to the Contoured Ramps that are in the Top Cowl Inlet. How does the Baffle Seal Material lay in that area. The instructions are not clear (at least to me).
Thx. Rolly Clark FWF
Click to expand...

Rolly, the instructions for this are very poor... predating the ramps. Here's a link to a bunch of photos showing how I did it.

my fwf page
 
It's in the name......

Hi Rolly,
Why do you think it's called "Baffling?" :D It takes a lot of looking in the cowling with a mirror and removing the top cowl and cutting a little, feeling a little and so on.

What I'd suggest though, is to cut the rubber material the "short" direction instead of along it's longest direction. Reason for this is that since it was rolled up, it will lay with a perfect curvature after you attach it, instead of standing straight up and you trying to "train" it or coax it to fold horizontally, or possibly lay in the wrong direction after you lay down the cowl.

This little nugget from a six-time repeat offender. ;)

Regards,
 
Vernon, I build my just like you did...

But the layup of the baffle seal along the left side inlet doesn't seem right. I can under stand all the other seal as air pressure increases the seals will be pushed against the cowl sides and make a good seal, but the one next to the flywheel seems like it will just let the air out.

Anyone have a comment on this?

Kent
 
kentb said:
But the layup of the baffle seal along the left side inlet doesn't seem right. I can under stand all the other seal as air pressure increases the seals will be pushed against the cowl sides and make a good seal, but the one next to the flywheel seems like it will just let the air out.

Anyone have a comment on this?

Kent
Click to expand...

My expectation of this area is that there is not much leakage. The area immediately surrounding the inlet is at a low pressure due to the flowing air.

In fact, I've seen RV's with no baffle seal around the bottom and sides of the inlets. I can't claim that this is the right thing to do, but it indicates that the seal in this area may not be critical.

I spent some time early in my career optimizing air flow and cooling in electronic systems. I had the advantage of an expensive thermal imaging system that used LN2 coolant. What I discovered was that 'rules of thumb' can only take you so far. Individual systems needed detailed optimization.

Since we can't optimize the same way in our aircraft, we need to do the best job we can with installation, and then adjust using CHTs and flight testing. I added air dams on cylinders 1&3 with screws and nutplates, and I've experimented with blocking the heater duct and oil cooler with aluminum tape.

By far the biggest effect on CHTs that I found (after rejetting carb, tweaking baffle seals, optimizing air dams) was cleaning the flashings out between the spark plugs to allow better airflow in this area.

This one change dropped CHTs about 35F in cruise. Reflecting on this, it may due to actual CHT reduction, plus more cooling in the area adjacent to the CHT probes which gives an apparent CHT reduction.

So, Vern's rules of thumb:
Do the best job on baffle seals (the ramp area is especially tricky)
If CHTs are high in takeoff/climb, rejet the carb to enrichen the full throttle fuel mixture
If CHTs are high in cruise, check the cylinder flashings
If CHTs are uneven, adjust the air dams in small steps.

There are many more things that can be done and tweaked, but these are the ones that worked for me. I only wished I had cleaned the flashings first, because everything else is minor in comparison.

Vern
 
Air seals around the inlet ramps

Vern,

When I trying to figure out how to cut my baffles up at the nose and around the inlet ramp, I used your web site as a guide. I cut my baffles just as you did but when it came time to add the air seals, I didn?t know how you managed so I tried to get the seals to lay down OVER the inlet ramps but this gave me a free edge to ?scoop? air towards the exit. I am now flying and am having trouble with high CHT?s on #3 and #4. If I don?t lower the nose during climb out and throttle back I will go over 430 degrees in a hurry. I have sealed the inboard side of the inlet ramps but didn?t do much good and looked for blocks in fins as you suggest and found none. I surely would like to know how you made the seals lie down around the inlet ramps. Some pictures would help. I have looked into the air inlets of several RV?s and all seem to have the front air seals lying outside the ramps both on the inboard and outboard side.



The enclosed picture shows how I am trying to get the outboard seals to lie down OVER the ramp and not up along side of the ramp.
 
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