the trick to getting them to climb ......all of the above posts + you need extra power but increase that power slowly or the plane will start flipping over on itself rather than spinning

also, use an apc prop....they are not the best for every 3d maneuver (heavier than wood)) but they are the best at maximizing torque/power and that's what you need to get the climbing part of the climbing flat spin.....

trying them with the tank closer to empty doesn't hurt either...(less weight)