PW5 dive brake repair

Our club PW5 has a problem with the composite material detaching from the aluminum cap on the top of a dive brake (the part that makes the dive brake cap conform to the airfoil shape at that station). Has anybody had actual experience with this type of repair? I emailed the nearest shop and the repairman said he didn't have experience etching the aluminum to prepare the surface for bonding.

-Doug

The major factory (AS, SH, etc) appear to lightly scuff the Al caps and fill them to contour with polyester filler and/or gel coat. Polyester resin systems stick very well to Al in my experience. West Systems sells a conversion primer for Al when applying epoxy.

If the filler layer is thick, many really repairman apply fiberglass, using polyester resin or polyester "gelcoat" to build thickness, prior to applying the topcoat system of choice.

This is a very common repair and I am aware of many instances where the cracks were scarfed out, filled with "bondo", sanded to contour, and top-coated. They have held up for more than a decade, tied down outside in SoCal.

To etch the aluminum, use a product like Jasco Metal-Prep. It's dilute phosphoric acid solution with surfactants, available at Home Depot, Lowes, or probably paint supply shops. If your A&P uses Alodine, he probably has Alumi-Prep as well, which is used first to etch the aluminum. Pretty much the same stuff as Jasco, only more expensive. Either will work.

Probably the best adhesive for this is Loctite 330 Depend. Unlike most epoxies that get hard, 330 retains some elasticity which allows it to work well bonding materials with dissimilar thermal coefficients of expansion (without the need holes or FRP overlays etc). 330 is a fast bonding two part acrylic adhesive that bonds most anything to most anything with few exceptions. You apply the gel to one part, spray the activator on the other, and hold the parts together for a few minutes. No need for clamping and fixtures in most cases. Full strength in 24 hours and as I recall, a strength of 2,000 psi in shear.

It's available on Amazon etc. not cheap, but works wonders. Bad news is shelf life is one year, and they are serious about that - I think on day 366 it stops working, so don't buy a lot more than you'll need.