cowl inlet to baffle ramp clearance?

[Desert Rat]

This is with regard to the gap between the fwd edge of the baffle ramps and the lower cowl inlet aft edge; I understand that there needs to be a gap there because the baffle material gets fastened to the under side of the cowl lip and then laps up onto the surface of the baffle ramp to bridge the gap between the two.

But how big is that gap? It obviously needs to be big enough that I can get the baffle rubber tucked up in there while installing the cowl, but what distance works well for that?

 

[rv8ch]

Hi Terry, it kind of depends on the kind of rubber you are using for your baffles. If you use the very flexible silicon rubber like that sold by McFarlane, you need about a 1/4" or so. I think it would be fine up to about an inch. If you use the very stiff black rubber material, you might need more.

The two considerations are that you don't want so much of a gap such that the rubber material can be pushed down below the ramp and spill air on the hot side of the engine, but you need enough space to move the rubber up into place when installing the cowl. I guess you know this since you are asking the question.

 

[Carl Froehlich]

I use 3/8”, but I also have removable ramp gap seals (three screws attach it to the bottom cowl inlet).

Carl

 

[Carl Froehlich]

Here are some photos of my ramp gap seal. Not shown is the strip of aluminum on the underside to rivet the nutplates. A little JB weld (or pro-seal) holds the strip in place while removing and installing.
Carl

 

[Bavafa]

I have used the thickness of my fingers as a guide, about 1/2".
You will need enough gap to make sure the engine does not come in contact with the cowl when it shakes. The shaking is often the hardest when one shut down the engine.

 

[PilotjohnS]

Removable ramp seals

I did removable ramp seals too. Never saw a way to have the seals permanently attached and be able to remove lower cowl. Also, the area the seal rests against needs some wear tape.
The ramp flex material is glued to the 1/2” wide aluminum reinforcement strip. The strip contains 3 nutplates. The alum strip forms a u shape that goes up both sides of the lower cowl air inlet.

 

[Desert Rat]

thanks guys- very helpful