hello all! i need help with understanding what prop to what engine/plane combination. i understand that lower pitch is for 3-D type flying with hovering and all that fun stuff, and that higher pitch is for speed. What does the prop length do?

and can someone tell me what prop to use with these 2 plane engine combos that i have? and without just suggesting a different engine? lol these 2 engines and planes are all i have and can afford for now. just wanna know what prop to use for the time being untill i can afford better engines. what size prop is best for 3-D type flying for the following:

1) Great Planes U-Can-Do 60 w/ super tigre .61

2) Nitroplanes Zlin Z-50 46 size w/ saito fa80

any help would be greatly appreciated!!!!!!!!!
thanks in advance!!!
=kevin