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backing strips for fiberglass tips?

O

odens_14

Well Known Member
I'm working on my emp tips while waiting for my QB and I've noticed on some builders websites they have put aluminum doublers on their fiberglass tips. However, I don't see this in van's instructions...is this somthing I should be doing?
 
Yes

You need something to shoulder the rivet. Fiberglas has a tendency to crack. Most use .025 strips, 1/2" wide or so glued into place with proseal or something of the sort.
 
I had a hard time getting the aluminum strip to stick with epoxy. I used a layer of carbon fiber tape this made for a super strong backing . The carbon fiber tape is a little pricey but I don't think I will have to worry about cracks .
 
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I epoxied aluminum strips on the elevator tips and aluminum washers on the HS tips as rivet backups. I bought the 1/8" i.d. AL washers at HoDe. They're Arrow brand, stocked with the pop rivets.

Steve
 
I used T-88 epoxy to glue my AL strips to the tips...doesn't work well. I'll be re-gluing mine with tank sealant at some point. Epoxy has worked for some, but if the fiberglass flexes at all during installation, it easily pops the AL strip off. Use something flexible like sealant or the carbon fiber tape idea...I like that idea a lot!:cool:
 
Prep

Scuff the metal with 80 grit then clean with acetone. Clean the inside of the tips with acetone then use your Dremel with sanding drum to scuff the area to be glued. Clean again with acetone.

I used 5 minute epoxy with some West Systems 410 microfiller mixed in. Clamp in place and wait about 10 minutes to remove the clamps. You can do them all in about 30 minutes with this method. Very secure if prepped properly.
 
Jeff is correct assuming you are using nutplates for screws. Cleco everything together and rivet the nutplates to the AL strips and fiberglass. Nothing is going anywhere after this.
 
I used 3M 5200 adhesive to hold my strips in. Clamp in place with those spring clips from Office Depot.
 
I had no problem riveting my nutplates on; I followed with a dab of epoxy over the rivet and nutplate tab. That's sufficient to hold the nutplate while a screw is installed; once the screw is in, it's not going anywhere. On the tail fairing, I countersunk a little deep and capture it with 100 degree washers from ACS. For the empennage tip fairings, which will not be coming off, I glued them in (Hysol is good for this) before setting the pop rivets. The rivets were set before the glue cured.
 
Agree with Darwin...scuff up the strips. For the emp. I used .016 and for the wingtips with nutplates I used .025 alum. I drilled "litering" holes all along the strips between where I thought the rivets would go....so it kinda looked like swiss cheese....Then used a combination of west system expoxy and a slurry of Cotton flox to kind of bed the strip in ...the flox oozed out of the litering holes and over the strip...while drying I clamped the strip down about every 1/2 inch using ordinary wooden clothing pins...
 
Seems like WAY overkill to use an aluminum strip with nutplates, at least that's my opinion. I used strips on the emp tips to give the pop rivets something to grip on, but used nutplates with no strip on the wing tips. I used basically the same technique on the strips as Darwin. I think I also stuffed some crumpled newspaper in the tips to hold them in the proper shape (mine wanted to flatten out) while the epoxy set up. That way there was less flexing when they were installed.
 
If you consider pop rivets as 'single use fasteners' and don't mind the idea of drilling them out and using new ones when you reassemble, they make sense.
They are lighter, faster to install and cheaper, three of the top criteria for aircraft building.
Used in conjunction with the grip washers that are made for them (previous post) you have a tried and true fastening system.
I marvel at the enginuity of some builders to invent high quality alterations to Van's designs (I have a few myself) but I always consider weight, simplicity and cost when I think about changing something.
Also, until I worked with a sheet metal journeyman, I had thought pop rivets were inferior to traditional fasteners....It turns out pop rivets are cheaper, lighter, quicker to install, more vibration resistant than a sheet metal screw, and reassembly is done with all new fasteners so you can forget about trying to keep track of the ones you removed, or if they are suitable for reuse.
The cockpit floors are a case in point here. I was all set to plate nut the floors like so many of us do, until I learned about pull rivets and considered how often I might remove the floors. I know sometimes when drilling one out they might spin, but over-all Van probably got it right (again).
 
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