Take off Performance:Continued...

[@rajFPV]

Why specifically 0.7Vto? Instead why not write acceleration as vdv/dx and find a differential equation in terms of velocity and displacement and then integrate it? I doubt the 0.7 Vto average acceleration assumption would hold true in case of model airplanes where dynamic thrust matters to a greater extent and cannot be neglected and thereby needs written as a function of propeller exit - aircraft velocity

[@vishalsethi4331]

These assumptions are for preliminary design considerations only.

[@karukkuvelrajd2245]

You can find answer in shevell fundamentals of flight book