I am building delta flying wing from cardboard and i have A2212 2200kv and i have to buy 6 x4 propeller but don't know about direction.
clockwise or anti clockwise which is right direction for delta flying wing?
Please help  me

What do you mean dude? It doesn't matter as long as the thrust is vectored towards the rear of the plane.

@taksh,
Now that you have the answer, would you like to say why you had this doubt?

@taksh...You can by any CW or CCW...if you are not getting the thrust in the right direction...change any two of the three connections between motor and ESC.

If you are using single motor then no need to worry about prop direction wether it is clockwise or anticlockwise. But if you are using twin motor powered wing (generally no one design) one prop should be spinning clock wise and other to be anticlockwise to avoid roll effect. this is what I know. Please any one can correct me if I'm wrong.