Bill Pendergrass and I spent about an hour walking the lines at Triple Tree last Saturday, camera in hand, peering into the cowls of a great many RV's (and a few others).
The average baffle seals are
abysmal.
Can't see very far back into the upper volume, so I didn't bother looking at seals above the cylinders and along the back wall. Here the focus was on sealing around the inlets.
This poor soul conveniently removed his cowl and went off somewhere. Sealing against the upper cowl appears to be non-existent at "A". The flap at "B" is riveted to the center baffle aluminum, so pressure blows the flap open, rather than against a hard surface for sealing. The outer end at "C" is just sort of stuffed into the area between the end of the upper fiberglass ramp and the inner cowl.
Predictably, given the state of sealing, the installation required louvers in the lower cowl:
Riveting the inboard seal to the aluminum wall (and hoping it will somehow seal against the backside of the fiberglass) must be on a published drawing somewhere, because it sure is common. If the wall and the fiberglass are offset from each other just so, and the aluminum extends up to or behind the fiberglass, it is possible to use the baffle rubber as a sort of gasket. It's not a good seal, just ok. Here you can just see wear marks at "A", indicating this seal runs in close contact with the glass. However, the upper seal, the one that runs around the upper edge of the wall, is a mess where it meets the ramp at "B":
The builder did not get the inboard flap
just so on the other side, and the result is predictable. Pressure simply blows the flap in, away from the glass. It's a very common leak indeed.
Not all seals were terrible. Here's a nicely done outboard inlet. Note the curved piece at "A", which gives the seal on the lower cowl lip something to seal against. "B" is nice and tight against the ramp, and pressure blows it even tighter. The end tucks under the upper cowl lip at "C", and matches its curve. Although the tuck-under doesn't allow pressure sealing at this point, the fold doesn't allow it to blow open either, and the inlet flow can't blow it away from the ramp. Note the overlap at "D".
BTW, let's hope the builder injected some silicone sealant behind the curved aluminum piece at "A", or the air will just leak behind it.
This one is Bill's. It's an inboard doppelganger of the outboard seal shown above. Same nice tight fit, same lower seal overlap (gray), same tuck.
These are
not the only bad and good ways to seal, but merely a few examples from this weekend's fly-in visit.