ZAP-O foam safe glue needs kicker to set. It will set fast. Some other foam safe glues (e.g. Bob Smith) will set without kicker, though it takes longer. I've repaired foam planes with Bob Smith glue and no kicker, and it's strong enough: at least as strong as before it broke. Never used ZAP-O on foam, but there's no reason it wouldn't be strong enough. But you do need the kicker for it (doesn't have to be the same brand, I use Bob Smith kicker with ZAP glue).