Here is a simple design for a Glider Launcher. This particular design is setup for the Kadet Senior, but can be adapted to any plane by scaling it's size and the curvature of the wing saddle. The release servo is attached to Channel #5 which is normally the Landing Gear Switch on your TX.
You can print the plans and enlarge to the 16" x 11" panel. All the parts are cut from .125" (3mm) plywood. I made .125" (3mm) thk balsa doublers for top and bottom and then used .250" (6mm) weather stripping foam tape to cushion all the surfaces. I used triangle stock for the mounting platforms and the servo tray. Note the servo tray is oversized and should be adjusted for the servo you are using. Also you will need to fabricate (2) fusalage saddles to hold the glider, These are different for what you intend to carry. This design seems to fit most applications. The saddles can be .250" (6mm) balsa.
A heavy rubber band #64 is secured on the rear peg, 1 on each side. the rubber is stretched over the glider wing, over the front peg, and then hooked on the servo wire. I use old servo brass eyelets where the servo wires go thru the sides, acting like bushings.When the servo retracts, the rubber band is released and the glider seperates from the mother ship. Normally the mother ship is slowed down to slow flight prior to releasing. There is still substantial forward speed creating a lot of lift for the glider. Seperation is much like a fighter seat being ejected, straight up and well clear of the mother ship.