In the build video Josh stresses that the numbers on the prop should be pointed in the direction of flight, or, towards the front of the wing. I ask why? What difference does it make if you mount them rearward and just reverse the rotation of the shaft???
It won't break anything, but you'll get an unmistakeable sound, and you'll notice a dramaticly weaker pull. The props we use are desigend to pull fresh air in from the side with the writing and throw air the other direction. Reverse it and you've got that thin weak side trying to slice fresh air and it will flatten and vibrate instead of cleanly generating thrust.
After you've heard that sound once, you'll remember it, so if you have a prop running backwards again, it's impossible to miss as you throttle up.