negative g
 

why does the inverted straight and level flight is -1g can any body help pls

It's relative to whether gravity is going from your head to your feet (+1g) or you are floating in space (0g) or hanging upside down by your ankles (-1g).

S&L inverted flight is only possible in a toy helicopter, as real ones don't have the capacity for negative collective pitch (apart from a couple of navy machines, and only to hold them on the heaving deck). And the fuselage is designed to hang under the rotor system, not stand inverted on it.:confused:

Toy helicopters can't do that either. RC helicopters can though.

The Lynx's "sub min pitch", used for the above(and in some ground runs) is about +2 degrees of positive pitch, rather than negative pitch.

Sub min meaning below normal minimum pitch on the ground.