FAB to cowl snout interface for carbureted RV-7 ? fiberglass work

McFly · #1 07-12-2006, 09:58 AM

I am having trouble visualizing what the fiberglass inside the cowl snout should look like. Can some someone please direct me to a website or post some pictures. Thanks.

Scott Will · #2 07-12-2006, 12:19 PM

Me, too... I'm hung up on this as well. What length of "snout" does everyone end up with? I trimmed my FAB and I hardly need any length of "snout" and I can get my cowl off straight down. Need to get this finished so I can fly soon!

pierre smith · #3 07-12-2006, 12:31 PM

We had a fairly close fit but you need to add the flexible rubber skirt around the airbox front end in order to not have a gap between the cowl and the airbox. It's one of those fit and remove over and over deals. The cowl then becomes a little more difficult to remove/install but we made a 'hook' from an awl and work the skirt into place after the cowl is on.

We also had to extend our lower cowl snout half an inch or so with more fiberglass cloth,

McFly · #4 07-12-2006, 01:08 PM

Quote:

We had a fairly close fit but you need to add the flexible rubber skirt around the airbox front end in order to not have a gap between the cowl and the airbox.

I dont understand what the cowl scoop should look like. Should I be making a tube that extends from the cowl scoop mouth to just shy of the FAB mouth? This directions mention making a ledge for the top of the FAB skirt to rest on? I'm sure as soon as I see a picture or website the light will go on but in the mean time, I'm lost.

kevinh · #5 07-12-2006, 02:04 PM

Quote:

Originally Posted by McFly

I dont understand what the cowl scoop should look like. Should I be making a tube that extends from the cowl scoop mouth to just shy of the FAB mouth?

Yes. The procedure I used:

1) install cowl & FAB - stick in ruler to measure gap X" between the existing cowl lip and the front of the FAB.

2) Use hacksaw blade to cut foam block so that it is X-.25" deep - make it plenty wide and high though.

3) Glue foam block to back of cowl opening with 5 min epoxy/bondo whatever

4) Reinstall cowl then insert hacksaw blade through the opening and cut out a 'tunnel' through the foam. Then use files/sand paper to shape the tunnel to nicely match the FAB inlet. This only takes about 30 minutes. Remove cowl.

5) Lay up fiberglass inside the tunnel (bonding onto the existing cowl inlet). After fiberglass cures, trim off aft side using the foam as a guide. Then remove the foam with your fingers/hacksaw. You are now done with the fiberglass (except filling).

6) I split the inlet rubber seal into two parts. The top flatish part I attached to the FAB. The bottom U shaped part I attached to the cowl (with a little bit of inward 'preload'). It still seals quite tight, but it makes installing the cowl much easier than if all the rubber is attached to the cowl side.

McFly · #6 07-12-2006, 02:31 PM

Thanks kevinh that helps but I want to make sure I have this right.

The tube is a cantilevered structure only attached to the cowl inlet mouth? It is not boxed in in any way?

kevinh · #7 07-12-2006, 02:38 PM

Quote:

Originally Posted by McFly

Thanks kevinh that helps but I want to make sure I have this right.

The tube is a cantilevered structure only attached to the cowl inlet mouth? It is not boxed in in any way?

Yes, it is supported only by the cowl inlet. A few layers of 8-10oz ish BID fiberglass is plenty strong - in my case it only ended up being about 1" deep. Make sure to scuff up the existing cowl inlet real good before gluing on the foam block. This allows you to layup the fiberglass in one sitting. It only took a few hours to do all of the FAB to cowl inlet stuff this way.

sf3543 · #8 07-12-2006, 02:58 PM

On my RV6, in order to facilitate installation of the cowl and still have a good seal between the FAB snout and the cowling ram air inlet, I fastened the rubber seal (U shaped) around the inlet, with no rubber seal at the top, which is fairly flat. This was held on with a big hose clamp. The top part of the seal was actually mounted to the top of the FAB snout, sticking forward. The cowl went on and off much easier and sealed just fine. I believe the spacing between the FAB and cowl inlet was about 1/4 to 3/8 inch. Things do move around there so don't get them too close.
I have also seen where someone mounted a thick rubber hose around the FAB snout and this basically jammed up against the inlet when you installed the cowl. Not too pretty, but effective and simple.