Aircraft Take off Forces

Aircraft Take off Forces





This post written in the aircraft performances part for all the Private pilot and Air transport pilots is an introduction of the first part of each flight.

First, we must differentiate between take off run and take off distance.

Take off run: Horizontal distance between the brake release point and the moment the airplane goes into the air.

Take off Distance: Horizontal distance between the brake release point and the moment the airplane is 50 ft above the ground level.


Why a plane takes off ?


The main goal of every take off is to get enough amount of lift to win all the forces that are against the movement.

For increasing the lift we must increase the speed, in concrete the True Air Speed (TAS) as we can check in the lift equation L = 1/2 d TAS^2 S Cl.



Which forces appears during the take of run?


The forces that are taking part during the take off  run are:

Thrust (T): It is the main force that provides a positive acceleration. Thrust is related with the power of the engine. For studying the take off run we consider we are performing an static take off. which means that we increase the power of the aircraft to the maximum with the breakes set on, and when the power reaches the maximum we release the breaks. That is why at the beginning the thrust is maximum and at the take off point it is a little bit less, due to an error of the propeller 

Lift (L): It is the force that goes up, it starts as soon as the plane speed increases. It varies between zero at the time of break released and it is equal to the weight at the moment the wheels start to leave the ground. 

Drag (D): Retarding force whose origin is the aerodynamics of the aircraft. Initially, it is null (D= 1/2 d TAS^2  S Cd) , and at the moment of taking off is W (Cl / Cd).

Friction Force (Fr): It is the force caused by the energy losses of the wheels. Fr=m(W-L), or the runway conditions.







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