The flaps, like all the other control surfaces, feature a glass-to-glass bond along the aftmost 1".  If it has popped (debonded) it might be because there are no vent provisions, and the air pressure poped the surface open at the weakest point.  So before you fly the repaired part, make sure there are vent provisions.

Having said that, all you really need to do is to glue it back together.  If possible, scuff up both surfaces.  I have a tool made by Permagrit which is essentially a thin sheet of aluminum with grit on one side (I think it is the F-101 from Aircraft Spruce).  You might need to slip a Dremel cutting disk in there to make a slot first, or maybe just a hacksaw blade.  Anything you can do to clean up the suface and rough it up a little will help.  If you can't even do that, then it might still be okay.

Next, the technigue you friend suggests (hypodermic needle with glue) is fine, but crazy glue is the wrong stuff.  Use Hysol structural adhesive.  You will need a big needle -- 16 or 18 gauge.  (If a physician comes at you with one of those, RUN!  I get mine at veterinary supply stores.)  Let it cure for a week at 70 F before flying.  Or put a heat lamp on it, get it to 140F or so, and fly the next day.  DO NOT let it get to 50F at night -- a shop lamp with a 60 watt bulb about a foot away will be fine.  Save the cup of adhesive stored at the same temperature as the repair job and check that for hardness.  When you sand it and get dust, instead of stickum, let it cure for the same amount of time again before you fly.

If al else fails, you can cut out the broken trailing edge and do a major repair (not that big a job) but I'd get professional help on that one if you are not a eperienced builder of fiberglass aircraft.  Plus, you'll need to repaint.

- Rob Wolf