How to calculate flight time from time at full throttle? I'm building an electrically powered paraglider,  and I'm trying to reach one hour of flight time.  I've resolved to using 2 18-kilowatt motors. I could use one 35-kilowatt motor, but I'd wrather not kick out my spine on a hard start.

Anyway,  with 6 x 504Wh packs,  I'd get 6 minutes at full throttle.  

But powered paragliders don't use full throttle the whole time. How can i calculate aproximate flight time from time that i can have full throttle?  

You can assume that my glider has a forward rate of 9:2, and a climb rate of 9:4.
You say mention a 'forward rate' of 9:2. If I get you right, that means L/D = 4,5 The mass of your body, plus electric motor, battery and parachute is probably around 110 kg. Assuming you may glide with an airspeed of 15 m/s at L/D = 4,5, the vertical component of the airspeed is 15/4,5 = 3,33 m/s, and the 'gravitational power' involved is 110 x 9,8 x 3,33 = 3600 W. The conversion efficiency of motor + propeller is probably 0,5, so the electric power needed to fly level at L/D = 4,5 and 15 m/s would be 7200 W. If the capacity of your batteries is 6 x 504 Wh = 3024 WH, then your flight time would be 3024/7200 = 0,42 hours = 25 minutes...

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