reinoks:

Having watched the video, I would say that your friend is launching the model wrong. You should aim at the horizon or slightly below, otherwise, as in the video, the plane will loose speed going up and stall and you then try to overcompensate with the elevator and the plane will oscillate (porpoise) up and down.
It is also possible that the CG is too far aft.

The high start should help or find a hill as mentioned before, but make sure you don't launch the model pointing up.

-tychoc