GW,

YES, a flat leading edge will make a difference in the way your plane will fly.

I posted a few pics of a wing being built. There is one pic where the leading edge has not been shaped. If left at this stage and not rounded over, when the air meets that square, flat leading edge surface the air passing over the wing would be quite turbulent and not provide the smoothest airflow over the top of the wing which provides the lower pressure on the top of the wing as compared to the bottom (generation of lift). In other words, leaving the leading edge square is preventing the airfoil to do it's job efficiently and effectively.

You did not mention at what stage you're at in building your wing that you are considering not rounding the leading edge. Pictures always help and clear up any conjectured cures and advice.

If the leading edge material of your wing is balsa, it won't take much time with a block plane (or sanding block, 80-grit if you don't have a plane) to bring the leading edge to a rough rounded shape. Use 120-grit sandpaper to bring it to final shape, and then 220-grit to smooth it out.

Congrats on building your trainer.

EJWash