This is about Bill Collum's story in Soaring, "New Sailplane
Material". I respect Bill's knowledge and enjoy reading his stories
in Soaring. In it he suggests a 50 Lb 15 meter glider will be
possible and I don't doubt it.

Certainly assembling it would be much easier, but to get reasonable
penetration, wouldn't it need water ballast? Now, many fly without
water but with a 50 Lb airframe, that wouldn't be an option. Every
flight would be 'wet' offsetting the ease of assembly with the water
filling hassle.

You might see an increase in the number of the 12 meter gliders but I
don't see many 12 meter gliders entered in 15 meter contests. No
matter how light, I don't think the performance is really there.

Ultimately, if you reduce the density of a glider to that of air, you
have a glider shaped balloon. What's the L/D of a balloon?