Hi Mark,
My Rotorshape weighs 10.5 oz with a 3 cell 910mah Lipo. The disc radius is 13 3/8 inches. By my calculations that yields a Disc Loading of 2.7 oz/ sq ft.
From what I have read, a good rule of thumb is to stay under 6 oz per sq ft. And stay in the range of 5 to 6 watts per ounce.
Jim Baxter has provided some excellent information on all of this, which can be found at
http://www.autogyro.com/
Regards,
Frank