RE: Biplane problem
Didn't a lot of these types of layouts in full size require a LOT of right rudder during takeoff? Are you running out of right rudder and it's still doing the swing and flip thing? How much rudder travel do you have?
Normally our models have such little toothpicks for props compared to the originals that it's not really an issue but in this case you may be suffering from P effect and trying to lift off too soon as Dick and the others suggested. You may need to get the tail up and let it get up to a higher speed before trying to lift off at a shallower angle. This sort of thing was common with the higher powered fighters. I read one story about the Mustang in particular that the P effect was horrendous and flipped more than a few planes that tried to lift off too soon. The cure for them was lots of right rudder and lots of speed before liftoff.