Some points of interest:

– I did some tests on using a belt 450 tail assembly, and with a bit of modification (adding some idler pulleys to keep the belt from skipping) I achieved just over 1kg of thrust (before belt started skipping) – (my research) and my design of idler pulleys

– I’ve also tried putting a motor directly at the prop shaft, (to eliminate the power transmission through the boom) (my research). The problem I’ve found with putting a motor directly on the shaft is that you can’t get a motor with the proper kv to spin large 200mm blades. Gearing is almost always the best way to get the speed of a motor (at it’s peak efficiency) to a speed those blades can hanle.

– If you’re not looking for inverted flight, I’ve found these heavily cambered blades to produce much more thrust then the symetric 250 sized heli blades. (My research) and still maintain pretty good efficiency. (some photos of my test setup)

– To size your main motor, here’s some numbers I came up with from my test rig. To produce 1.57kg of thrust with the blades mentioned abode, I was sucking back 200W. (my research) For a spreadsheet of thrust numbers (and power required to achieve it) see a spreadsheet I put together. Again, more info to help you size the main motor. (spreadsheet link) Make sure you account for 15-20% losses in drivetrain.

– Another spreadsheet I used to calculate thrust and power (and many more things) (spreadsheet link). Al ot of my initial estimations were done with this. The results of this spreadsheet are not far off from actual tests I did. I’d way within 10-15%.