The Aerodynamics Forces of Flight Module

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## Gravity

#### How does gravity affect an aircraft in flight?

When an airplane flies, it must first overcome two primary forces--weight and drag. Weight is the force of gravity acting to pull the plane to the ground, and it is overcome through lift. Lift results in the plane rising into the air. What is the center of gravity?

With lift and gravity in opposition to each other, it is obvious that increased lift and decreased weight are objectives in both the designing and flying of aircraft.

What kind of materials are used to construct airplanes? Today, most airplanes are built of metal, with aluminum alloy being used extensively because of its strength and light weight.

The weight of the load the airplane carries also receives very careful consideration. Click here to find out how the weight of the load the airplane carries effects the forces of lift and gravity.

Are there any circumstances in which lift can no longer overcome weight? Well, consider these two cases

For more information on the force of gravity and some nice diagrams click here!

#### Center of Gravity

The center of gravity (CG) of an aircraft is the point where all of the weight of the aircraft is considered to be located. Where the weight is placed in the airplane is a factor that has a tremendous effect on how well the airplane will fly. This is because the CG of the airplane must be maintained within certain limits prescribed by the manufacturer, in order for the aircraft to be flown safely. If the CG gets too far forward or too far backward the aircraft will be out of balance and difficult, if not impossible, to control.

#### The Effect of an Airplane's load

Each airplane has a total weight limitation called maximum gross weight, above which the airplane is unsafe for flight. It is possible to keep putting luggage or other cargo into an airplane until it is so heavy it will not fly. Since the pilot cannot put the airplane on a scale to make sure it doesn't exceed the maximum gross weight, another approach must be used. This involves computations that were begun during the design and testing of the airplane since the maximum gross weight is established by the manufacturer. Then, as each airplane is completed, it is weighed at the assembly plant and this weight is entered in certain documents (which must remain with the airplane at all times) as the empty weight. Thus, the difference between empty weight and maximum gross weight tells the pilot how much weight can be put in the airplane without overloading. Incidentally, this amount of weight is called useful load.

This information was found here.

#### Two Cases

1. There is a point in this relationship of airfoil to angle of attack where lift is destroyed and the force of gravity (weight) takes command. This is called stall. The air can no longer flow smoothly over the wing's upper surface. Instead, the air burbles over the wing and lift is lost. You might wonder why the force of power from the engine can't take the place of the loss of lift from the airfoil. Very simply, there just isn't enough of this force available from a conventional aircraft's engine. Some of the more powerful jet fighters and acrobatic sport airplanes can, for a short time and distance, climb straight up without any significant help from their airfoils. However, these airplanes will eventually stall and start to fall toward Earth. The stalled condition is one from which recovery (and continued flight) is fairly easy.

2. No matter how efficient the airfoils and power plant of an aircraft may be, there is still a limit as to how high in the atmosphere it can go. This limit is called the aircraft's ceiling. At its ceiling, the aircraft's power plant is producing all possible power, and the airfoils are producing all possible lift just to equal the force of the aircraft's weight. Why? The atmosphere, you will remember, becomes less and less dense as altitude increases. The aircraft's ceiling is that point in the atmosphere where the air is too thin to allow further increase in lift.