Matt,

There has been a lot of good advice posted here in response to your question. If you are on a budget, stay with your trainer on floats and your .40 until you develop your own opinon of what works. In relation to the power available from your .40 and the added weight and drag of the floats. The nice thing about using your trainer is that it doesn't require much speed to fly, and it probably had a very low wing loading to begin with. Drag is a function of the square of the speed, so your drag won't be that much greater if you aren't trying to fly real fast. Trainers are pretty high drag planes to begin with.

So, the thing that you need to be concerned with is propeller efficiency to get the most out of your existing rig. Try using the larger diameter, low pitch propellers that will fit your engine's effective RPM range. Such a propeller will have a higher efficiency rating and will make much more use of the power you do have available. Your .40 should be able to swing an 11x4, without any real problems. the plane won't fly as fast, but takeoffs and landings will be much easier. The lower pitch propeller will help the plane slow down to make your landings much easier. Experiment a little with the exact diameter/pitch combination. You want the engine to be able to come up to speed, without over-revving. The larger the diameter, the more volume of air you will move . . . the more air you move, the more thrust you have. The law of conservation of momentum is Mass (1) X Velocity(1) = Mass (2) x Velocity (2). Therefore, thrust developed by your engine is equally weighted to the quantity(mass) of air that the propeller moves and the velocity imparted on the air by the pitch of the propeller. But the area of the propeller is proportional to the square of the diameter. So, if your .40 can spin an 11x4 at the same rpm that it can spin a 10x5, it will develop more pounds of thrust with the 11x4. The limitation to this analysis is the useable rpm range of your engine.

If the engine has enough power to get the floats up on the steps, then your trainer will probably have plenty power to fly.

Good Luck and have fun.