I've seen pictures of wing taping where the fiberglass completely encircles the wing joint. Is this really necessary? Wouldn't a few strips on the botton going lengthwise with the wing be good enough?

You are correct at least from my experience, the wing tape goes completely around the wing. This greatly strengthens the wing joint. I don't know as I would build a plane where the wing halves are joined together without doing a full taping. I know some ARF's for example don't call for the use of fiberglass tape when joining the wing halves, but since I don't assemble ARF's, I can't speak from any experience along those lines.

It depends...

It is the job of an Engineer to determine what is needed structurally to hold a wing (or whatever) together, while making it as light as possible.

If the Engineer says to wrap a #" wide piece of Fiberglass around the center section, I do as he says.

Case in point...

Before the advent of newer kits, my dad and I used to mostly scratch build. Back in the late 80's, my dad got a Goldberg Chipmunk. When joining the wings, he didn't "trust" the thin plywood wing joiner, so he made his own out of 1/4" plywood, and made it much longer than the one supplied.

Having done that modification, he though he didn't need the fiberglass tape (which, under normal circumstances, he wouldn't have) but what he failed to realize was that the fiberglass also reinforced the LE where the forward wing mounting dowels were located.

The plane flew successfully many times, until one day when he did an outside loop. When the loop was just passed halfway done, and the plane was starting the up-swing, the dowels ripped right through the wing. needless to say, the plane (and engine) were a total loss.

To this day, I never second-guess an engineer.

Is the tape as good as the epoxy/cloth method? The manual for the avistar doesn't call for any reinforcement but I've read a few threads where the wings have failed. I don't know if a few isolated incidences is making me paranoid or not. After losing my pt40, I was going to use an ultrastick that I had already bought in anticipation of soloing but decided against it.

In many trainers, the glass cloth or tape on the center section also helps reduce crushing from rubberbands. (trainers that don't have glassed center sections frequently use thicker sheeting and seem to have an extra rib or two in the center to stop crushing, or so it seems) So, if it's called for, I'd do it.

If you wanted to replace the cloth and save weight, look at some carbon fiber cloth.

I've been doing glass and epoxy jobs on most of my combat planes, and it doesn't add that much weight, and the strength is worth it. I do it in two parts, the bottom first, overlapping around the LE and TE by about 1-2", then the top, overlapping on to hte bottom by the same amount. This doubles the glass at the LE and TE, and really reduces rubber band crush. Not the only way, but works for me.