Field altitude and runway available? At high altitude, especially with a short runway on a hot day... 0 payload.

You SHOULD be able to lift 2 lbs of payload under normal conditions... but take-off will be trickyer than normal. If you have the right facilities (paved smooth runway... lots of room and no trees...) and good conditions (cool day... at seal level) you might lift 5 lbs. But then the plane would barely be able to climb...