My friends at Flying Aces Club fly gliders at the lower end of the weight spectrum, nearer 2 ounces for scale gliders of 36 inch wingspan.  They will have a one-design competition for this sized models of the Schweizer SGU 2-22 vintage sailplane September 2024 at Muncie as part of their Outdoor Champs Meet.  They are settling on a Hi Start using 1/16 inch rubber for launching at that meet.  The Bird of Time, a model from J&H Aerospace of a model, with 48 inch wing span, is at the 4 ounce end of that weight range, without radio gear, and should need a stronger Hi-Start.

The Hi-Starts for light Gliders (2-4 ounces) for Free Flight without radio gear are available at RetroRC.com.  They sell kits for Hi-Starts with rubber from 1/16 to 1/8 inch wide to cover that weight range.  They use standard FAI Tan Super Sport Rubber that turns propellers in free flight planes. The RetroRC Hi-Start for smallest gliders has 150′ of #30 braided dacron line on a plastic “kite” handle, with 50′ 1/16″ FAI Super Sport Tan II rubber strip (about 25g) providing the energy.  The strongest they provide has 25’of 1/8 inch rubber strip weighing about 1 gram per foot.  It is about 1/24 inch thick, so cross section for the 1/8’ strip is about 0.0052 sq in, and density is a bit over 2 grams/ cu in.  This makes it about 1/12 as strong as a Hi-start for 2 pound planes.  Those sailplanes with 2 meter wingspan use 1/4″ ID x 1/16″ Wall Amber Latex Tubing   ( 0.0614 sq in rubber cross section) to power their Hi-Starts.  RetroRC also sells a kit for a storage reel, with laser cut plywood parts, for their Hi-Starts.

I’d recommend using at least 3/16 inch wide rubber strip to launch a Bird of Time.  Whatever you use, check the launch tension with a Fisherman’s Scale, and start with no more than 3 X the glider’s weight.  Even for gliders with strong wings, tension is best limited to 7 times glider weight. Repairing a wing after a break on launch is no fun.

http://retrorc.us.com/glideraccessories.aspx

https://www.faimodelsupply.com/product-category/tan-super-sport-rubber

Length vs Weight for various sizes of FAI Tan:   1/16 rubber – 230ft/4 oz ; 3/32 rubber – 160 ft/4 oz ; 1/8 rubber – 115 ft/4 oz;   ¼ rubber   – 226 ft /16 oz