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
- 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.
- 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.
Adapted from here!
