Hi ae,
Tossing off a hi-start is a lot of fun but as we all know, can be hazardous! For sure, you have to have a strong plane designed to withstand the stress of the launch! A strong spar and a good center section dihedral brace is a must. Post mortumed several hi-start wing folds and they were all because of a poorly constructed center section dihedral brace!! Something else to think about, and I've seen several experienced pilots do this too is just let the plane go and be pulled out of your hand. "NO AIRSPEED" at the critical moment! This could give you what I call a "Firestone Launch!," where instead of the Hi-start hauling your plane to the heavens, you end up where the Hi-start,"Rubber meets the Road!!" I always hold the plane high and behind me a bit and "move" the plane forward a foot or so to get some air moving over the wing so the plane is on its' way to if not at flying speed at "let go."

Blue skyz,
Bill "skybill" Deli AMA-87838