Twister,


I can agree to neither formula!

The 2D + P formula is way too simplistic.
It can make one think a 10x6 and an 11x4 offer the same load, which is pretty far from the truth...

...as Brian (downunder) found out a couple of months ago.

Your formula also gets pretty close results (less than 2.5% difference) for these two prop sizes; so it must also be simplistically wrong.