How to calculate flight time from time at full throttle?
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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