[GLPalinkas]

OK, I know I have been asking a lot of questions lately but that means I'm seriously building again, right? I'm in the home stretch (hopefully).

I have a 1998 vintage RV-6 cowl which has the foam core really close to the trailing edge of the cowl. I'm guessing the newer cowls don't have this problem.

I am installing Skybolt Camlocs and have made the scalloped .063 firewall support. I do plan on cutting it down a little (around the camloc receptacles) when I get the camlocs installed and everything lines up OK.

As you can see from the photos, the camlocs will overlap the foam core. My thinking is that if the newer cowls allow a larger mounting area then I should just be able to cut the foam core down, (thinning it) then seal it with a layer of glass and epoxy and call it a day. The foam core is approx. 1/8" thick.

What are the thoughts on my plan. I don't want the cowl structurally compromised as it gets really messy leaving the airplane in cruise flight. LOL

Firewall strip:

Looking under the cowl and up at the camlocs/cowl:

Any help appreciated.

 

[flion]

Well, first of all, your picture shows the camloc strip between the firewall and the top skin. Did you re-bend the flange for this, because the firewall flange is supposed to be against the skins all the way around and any fastener strips/hinge material/shims/etc. are supposed to be to the inside.
Once the strips are in their proper location, how does the cowl rest. If the cowl rests even with the fuselage skins, then I'd leave it alone. If it sits high, I'd shim where necessary, between the camloc strips and the firewall flange, until the cowling sits even with the fuselage skins while clecoed to the camloc strips.

Next, I'd look inside the cowl where the clecos are and see if drilling for the camlocs will take you from thick to thin material (it's hard to tell from your photo but it looks like it'll all be in the thick area). If not, put some packing tape on the camloc mounting strips, dab some flocking on the thin areas around the cleco holes, and cleco the cowling to the strips until the flox sets. That should give you a good mounting base around the camloc holes. Again, looking at your photo, I don't think you'll need to do this.

Next, drill the holes for the camlocs. I can only speak with regard to the Milspec but they float so you can just use the templates and drill without worrying. Install per the instructions but before you install the grommets fill the edges of the holes in the fiberglass. I'd recommend a filler here; flox and micro are both difficult to use neatly. Don't worry too much about the finish; you want to seal the edges but they'll be hidden by the grommets.

Others will disagree (this is the VAF forums, after all. ) but I'd rather see you shim the strips inward than trim the cowl thickness down. If your grommets are not 'deep' enough, though I think they are, you can get others for your material thickness. Same goes for the camlocs themselves, though the adjustable receptacles should accommodate your application.

 

[Vlad]

Shim

I agree with Patrick on this. Take your time and shim it.

 

[GLPalinkas]

Camlocs Help

Patrick,

Thanks for the reply and the help. Luckily you saw my post and error. I don't know how I got the idea in my "builder's mind" that the camloc strip went between the top skin and the firewall. I just switched them to the inside as suggested and it looks like when I dimple the firewall the cowl and skin should be good. The way I had it the cowl was really close but I had to push to line it up (firewall thickness). I think this will be much better. I rant about the old RV-6 instructions (or lack there of) but when I double checked, there it was on drawing 63 with the hinge on the inside of the firewall.

Some camloc receptacles will definitely be partially into the foam core. I like your idea of making a build up. It seems like the better option. I believe my Skybolt units have a lot of vertical adjustment, float and that should not be a problem.

What kind of filler would you use around the grommet holes?

VAF is immensely valuable to a lot of us although sometimes just a getting a thorough yet simple answer like yours is tough. Wading through all of the opinions sometimes boggles the mind of us first time airplane builders.

Thanks again Patrick and Vlad for you help here.

 

[Mark Bolton]

I am at the same stages as GLPalinkas and am wondering what manner of filling / reinforcing the fibreglass on the cowls will need ? They are the RV 4 style cowls about 1/8 thick. the holes for the camloc pins are aboutt 1/4 inch from the edge of the glass. I am told a glassing strip of sheet ally as a backing plate will probably not be that effective since it doesnt bond nicely and it will crack away from the epoxy . Is this true ? Would using proseal to fasten a reinforcing strip work ? Does it need reinforcing at all.

I have been poring over pictures of camloc application and they all show the firewallside but not much mention of the cowl side.

THX in Advance

Mark

http://rv-4builder.blogspot.com/2010/10/oil-cooler.html

BTW Love your work with the camera GLPalinkas! Beautifull place you live

 

[flion]

Your cowl should need no reinforcing at all. If you run into interference with the honeycomb layer, as described above, you can build the the area with flox. Other than that, the cowl is plenty sturdy enough to handle camlocs without reinforcing. When you install them, you will be inserting a metal grommet, captured with a split ring, into the holes in the cowl; this will transfer the loads from the fastener to the cowl and prevent abrading the edges of the hole. I do suggest an application of thin CA (superglue) to the edges of the hole before installing the grommet (apply some glue and quickly wipe the excess away) to help seal the edges. If you've drilled through the honeycomb layer, use thick CA or epoxy instead to fill gaps in the honeycomb and keep fluids from seeping in.

 

[Mark Bolton]

Greatly apreciated Patrick,

I wasnt sure what sorts of stresses the cowl would be under.

The superglue is an excellent idea to seal the glass reinforcing and to prevent abrading.

Cheers!

 

[DanH]

Ya'll are talking about shims between the mount strip and the firewall flange equal in thickness to the foam core? That foam core is, what, 1/8" -3/16" thick? I dunno guys....don't think I'd shim the mounting strip that much. Anyway, moving the edge of the foam away from the tab strip is fast and easy.

Chuck a coarse 3" sanding disk in your die grinder. Hold it at an angle like so and re-cut the tapered edge of the foam, then lay on a few plies of new glass:



When cured, block with a coarse paper to flatten any lumps or wrinkles so you have a nice seating surface for the aluminum tabs.

Speaking of which....you may or may not need an additional thin shim between the tab strip and the firewall flange. Your initial cowl fit may lead you to think you need one, but first check to see if the tabs are flat against the inside surface of the cowl. They may (probably) need to be bent a little, and then the outer surfaces may be flush. If not, only then add a shim strip.