I have two systems, one for gear-less combat flying wings, and one for planes that ROG.
This is the spring-loaded stooge for "hand-launch" planes--it doesn't catapult, but only releases; requires an engine strong enough to pull the plane directly into the air--as I said, combat wings. Pick up the handle, give it a tug, and off you go. The "spring-loaded" part is a transverse spring that holds the yoke on the catch until you pull (against the spring) to release.
These are old pictures; I have made improvements a couple of times since then--most notably 45 d. elbows at the top of the arms to insure the plane doesn't prematurely jump out. It never did; but at least the now-bent arms give a better perception of security!
Hmmm, upon seeing the pix, the release catch isn't all that clear, is it? I need to go take some pix of the current setup. Same principle though.