looks your math gives the same result for thrust I found here:

http://www.dept.aoe.vt.edu/~lutze/AOE3104/thrustmodels.pdf

Here are more examples of flight time and efficiency for different types of copters (gasoline, electric, man powered)

]]>i want to design a quad copter that can lift 600kg can tell all about ]]>

This is incorrect. Work is the time integral of power or vie versa power is the rate of change of work. Say you push a block on a surface. Work is how much energy to push from A to B. Power is the rate at w.ich you did it.

]]>If only expensive textbooks were half as good as you!

Or maybe I’m the problem, as my name suggests ]]>