# TAKE OFF

The purpose of any take-off is to get the wings to generate sufficient lift to hold the weight of the airplane in the the shortest  ground distance ( Equation of lift : L = 1/2 d v s Cl).

DEFINITIONS:

• 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.

Actuation of forces during take off

The take-off maneuver consists of an accelerated movement, in which the aircraft begins with zero speed and ends when the airplane achieves an adequate speed so that it can take off.

Let´s explain the different forces :

• Thrust (T) :It is the main force that provides a positive acceleration. (The strength made of from the engines). The propeller slips causing an slight decrease of this force during the take off run when the speed increases. note :  we will see in future posts with more detail what propeller slip is. For the moment it is just that the propeller performance changes with the speed.
• Lift (L) : It is the force that goes up, it starts as soon as the plane speed increases   (L = 1/2 d v 2 s Cl). It varies between zero at the time of break released and it is equal to the weight at take-off time.

The last part it is very controversial. How is possible that if we have the same amount of lift and weight, the plane can take off?.

the answer is that in an ideal world ( theoric situation), as the first Newton law says that any body is in an unaccelerated straight movent unless we apply a force to  it , which means that all                forces are equivalent (check the following post basic concept of aerodynamics). We are studying the situation of that the acceleration is constant, so all forces are the same .

• Drag (D) : Retarding force whose origin is the aerodynamics of the aircraft. Initially, it is null (D= 1/2 d v 2 s Cd ) , and at takeoff is W (Cl / Cd).
• Friction Force ( Fr) : It is the force caused by the energy losses of the wheels. Fr=m(W-L) .

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