given enough speed, you can create the lift you want. The questions you need to know,

1. What's the maximum lift coefficient of the airfoil that you will use? (flying wings use symmetrical or reflexed airfoils that don't generally lift as much as highly cambered ones do)

2. What will it weigh including the payload?

3. What are the dimensions of the wing?

4. What power are you going to use? (thrust must overcome drag or the plane won't be able to climb)

The lift equation is, (from Andy Lennon's book, applicable to models)

Lift (oz) = Lift Coefficient x relative density x velocity^2 x Wing Area / 3519

Relative Density = 1 at sea level, 0.8616 at 5000 ft, 0.7384 at 10000 ft