Dave Jackson, after you have solved the problems of the blades, rotor head (there will be some serious forces hanging around the blade attachments!!) and negative collective, don't forget to redesign the engine.
It will need an inverted flight sump, to keep oil going to the oil pump, different scavenge system because the oil will no longer drain to the bottom, and an inverted fuel system to again keep the pump supplied with fuel as it sloshes from side to side and to the top.
Ensure the aircraft gets vacuumed after every flight - get zero or negative g and all the dust and grit comes up off the floor.
Design map pockets that are very tight, to stop them coming loose. Buy a pile of new maps, because now the pilots will tear them pulling them out, and ruin them when stuffing them back in. Forget designing inverted flight coffee cup holders, I think Lockheed made one some years ago for a Hercules, and each one cost $20k.
Add to that the coffee percolator that will keep going after a thermonuclear magnetic pulse, and I think we are complete.
