The trailing edge is the thinner edge, usually a knife edge as opposed to the rounded, blunt edge of the leading edge.

The easy way to remember is to think of an airplane wing. The thick edge is to the front and the back has thin flaps which is obvious when you look at one.

Just one way to understand without having to understand how it works.

Tom

The Truth is the Truth, even if no one believes it; and a lie is a lie even if everyone believes it

I think the question that you are asking refers  to weather you are making clockwise or counterclockwise rotation blades. For CCW, as the blades are laying round side up, the trailing edge would be on the right. Fat side to your left, skinny side to right. For clockwise rotation it would be reversed. That would be as you are looking at the "end" view. Flat side faces the wind.

Good Luck

Which web site? Nunbers-r30, r60 don't know.

Upper Right corner on this site, go to FAQs section, homebrew, Blades 101, good pics and info there. The blades are CCW rotation.

You ask which is up. As you are making the blades the round side is up, flat side down. Just as Tom W said about the airplane wing.

CCW or CW rotation. Are you following a plan from this site??

Good Luck