how hard is it to fly an RC plane?

That depends upon the plane. Some are just gliders with power. They are easy to fly and crash. Others are actual models of planes. They are harder to fly. But once you learn, then you have much more control.
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As was previously said, depends on the plane. Some are harder than others. There is one that I would recommend, it is from hobbyzone and is called a supercub. Stryofoam made so if you crash and break it, it can easily be glued back together. Comes with everything you need including batteries for remote and two different chargers. Very easy to fly and a great one to learn on. Also very fun when you and your buddies each have one and fly them together. Bought one this weekend and paid 149.99 for it. Great beginner plane. Good Luck
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A high wing trainer is your best bet for a starter airplane.It has a flat bottom wing and lots of dihedral(wings are v shaped when you look at them from the front of the plane).Dihedral lets the plane level itself in flight so if you get in trouble release the sticks on the radio and it should level off by itself.A symmetrical winged plane like a fighter will keep in a turn til you stop it.It would be best if you learn to fly before trying a sailplane.If there is a place where people fly near you it should be easy to find someone to help you get started.Getting back on the ground in one piece is the hardest part of learning to fly Good luck
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i have 7 rc planes

It varies upon the plane you buy. Usually 2 channel airplanes and helicopters are very easy and supposibly very sturdy. They should not break easily. I would suggest you go with the Air Hogs product line if you are a beginner pilot.

It is more easier to fly a airplane/plane than a helicopter.
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RC Pilot. Message me if you have more questions!