If you go with one of the lighter engines and kits out there and do a few lightning mods, you can get close to a 3:1 thrust to weight ratio with a light wing loading (under 30 oz per sq ft).

example (31% CA Extra 300L, carbon gear, LIon batteries, ZDZ 80 single) just under 20 lbs with a 93" wingspan and over 50 lbs of thrust.

If you go with a heavier engine with a spring start and a heavy kit and add extra uneeded weight, you can get closer to a 1:1 thrust to weight ratio with a very heavy wingloading (around 40 oz/sq ft)

example 2 (73" Cap ARF, G-23 engine, heavy nicad batteries, tires, pilot, etc.) 16 lbs and real close to a 1:1 thrust to weight ratio.

If you do everything the "light" way and don't try to save on an engine or any other part, you can get a 78" plane around 12-14 lbs. mostly depending on whether you go gas or glow.

If you get closer to a 90" wingspan plane (84" or above), the decision to go gas is clear.

Hope this helps

John