I wonder: I have purchased 9 planes. But I don’t seem to be able to pick the plane I want to use in a game. 

I rarely get to fly the Seimans plane. . And the Hawker Hurricane, I don’t understand the shots coming out of the plane, when I shoot. They go in a circle and don’t hit the target. . What is that all about?
 

Are you not able to pick which side you want? If you are premium, on the server selection you can see 3 boxes, Allied, Central and Random

To select a side, use the appropriate button ( allied or central power ), NOT THE RANDOM GAME button 
This only works if you’re premium ( I assume you are ), otherwise it balances the game you’re about to enter ( say it’s a 5v4, if you hit “random” it puts you in the side with minimum players, here it’s the one with 4 )
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now if you meant I can’t select plane in the hangar  simply use the arrows on the sides
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As for the “bullets go in circles”, I can’t understand that. Can you make it more clearer? Because they just fire straight and drop down like normal