13x 4 W is a BAD prop for Irvine53 but it just about works for the West T50.

12.25 x 3.75 is best combo on capishe with irvine 53 (although you have to maintain quite a high throttle during normal flight as the forward thrust is slow on this prop ie your in second gear all the time)

as for putting 12.25 x 3.75 on a 36 you will kill it stone ded in 5 flights!!

Malc your electric is done just waiting for cells, do you want me to charge some cells so you can fly it on holls (not high discharge cells but it will fly ok)