AP wrote:
I dissagree with your specs. The calculator below can be found at
http://www.hamuniverse.com/jpole.html

I don't have the exact specs of a B-17s rudder, but My C-172 was taller than
5 ft

Just eyeballing it it looks to be about 7' for the B-17 rudder. With the
active part of a J-pole at about 5', just where in your C-172 (assuming it
wasn't made of metal) were you planning to put it? Where do you think the
OP's going to manage to put his? Did you actually think about this problem
or do you just like to argue to hear yourself talk?