Rene Bubberman

Rene Bubberman

Well Known Member
Hello Folks,

Just trimmed the baffle tops exactly to the upper cowl. Next step is to remove 3/8 to get the correct clearance. After that I'll have to make a pattern for the Airseal fabric. My question is: I guess I will have to make the distance the airseal sticks out above the baffles a little bit more than 3/8, in order to be sure of a seal against the cowl. How much do you advise and what is the effect of the engine sag on this number?

Thanks!
 
2"

Previous builders recommended having 2" of airseal stick up above the aluminum baffle edges, and that worked fine for me. I wouldn't go any less than 1", but 1.5" would probably be fine. Consider this...you can always trim away excess later if you don't need it.

)_( Dan
RV-7 N714D
http://www.rvproject.com
 
The seal should extend about 1" above the baffle plates, and will bend over inward toward the incoming airflow. That way the airflow "inflates" the seals to hold them up against the underside of the cowl to form the seal. The slight amount of engine sag will not affect the seal. This is not a compression type seal where the cowl forces down on the seal edges. This is actually rather loose until the airflow pressurizes the seals as they are force upward against the cowl. You need the initial looseness or the rockin' rollin' engine during startup would damage the cowl if the fit was too tight.

Roberta
 
Whoa, that's a lot!

Thanks Dan,

If I read you correctly there will be maximum 1 5/8 inch (2-3/8) of extra material curled up to the inside of the cowl? Doesn't this make it very hard to place the Top cowl on the Bottom cowl?

kind regards,
 
Nope

Nah, it's not hard at all. Here's another trick I learned from Gary Sobek which works great...

When you first install the airseal, it will tend to stick up straight. You want it to curl over into the plenum like Roberta said. So what you can do is this...

In the corners, take a piece of masking tape and tape the corners together so that it holds the baffles bent into the plenum chamber. This keeps the airseal bent over in the right direction those first few times you put the cowl on.

After you run the engine and fly once or twice, the baffles will conform nicely, and you can take the masking tape off if it's not off (blown off, worn off, whatever) already.

The masking tape doesn't hurt a thing, and it's a good alternative to lacing or using tie wraps or safety wire or rivets or... I've seen a lot of cases where builders use something like that to "bind" the corners together, and in my opinion it's not necessary. Anything you use to bind the corners could wear against the top cowl. No need for that. Use masking tape and it'll work out great!

)_( Dan
 
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