The Lift Formula

You have to know the lift formula as a PPL by heart, so take the time to learn it. Here it is:

L = Lift
CL = Co-efficient of Lift

1
/2 p = half rho (rho relates to air density)

..2
v = velocity squared (velocity is a vector quantity made up of speed and direction)

s = surface area of the wing

Just in case you can't quite remember what each part of the formula represents, the next picture should give you a little reminder:

CL - the Co-efficient of Lift
This is a number between 0 and 2 worked out by the clever folk who are involved in aircraft design and engineering. Us pilots don't have to worry too much about this number, just that it is a part of the all important Lift Formula, and that it is affected by the Angle of Attack of the wing, and the Shape of the wing.

Can you, as the pilot have an effect on the Angle of Attack of the wing? Can you change it in any way?

Can you as the pilot of a light training aircraft change the shape of the wing in any way? Turn it into a Delta Wing? Can you increase it's Camber?

1
/2 p - Rho

Rho relates to the density of the air at the level and in the conditions in which you are currently flying.

Can you, as the pilot change the density of the air that you are busy flying in?

..2
v - Velocity squared

Velocity relates to the speed at which you are flying. Notice its effect is squared, so it has a very significant impact on the creation of lift.

Can you as the pilot change the speed of the aircraft in any way?

s - the Surface Area of a Wing

This is the square foot / meter of the wing.

Can you, as the pilot, change the surface area of your light training aircraft?

In your training aircraft, the only elements in the Lift Formula that you have any direct control over are the :

Angle of Attack - when you pitch the aircraft. This controls your attitude and speed - it is your attitude, (and power), and not your aptitude that determines your altitude;

Wing Shape on the inboard section - when you extend your flaps, you increase the Camber / Curvature of the inboard wing section;

Speed - which is determined by a combination of Power (throttle input), and Attitude. Note it is squared, and has a very significant effect on lift.


All put together

Bring everything together, and you will find that everything affects everything.

If you increase the Angle of Attack,(AoA), you increase the Lift, and you will climb. Increase the AoA too much, and your CL begins to decrease as Drag increases.

Flaps down, increased Camber, increased Lift, and visa versa.

Increase your Speed, keeping your AoA constant, and you will also increase Lift. Decrease Speed, AoA constant, decrease Lift.

We will talk more about this in Exercise 6 - Straight and Level Flight

For more detailed info on the elements that make up lift, visit Exercise 4 - The Effects of Controls

Fly from the Lift Formula back to the Flight Lessons Briefings.


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Exercises 4 to 18

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