Model Airplanes And The Real Thing Are Controlled By The Same Factors
Article by Dale R Smith
One of the first things that is likely to be noticed during a visit to the local airport is the wide variety of airplane styles and designs. No matter what each looks like they all depend on the the same four factors which are lift, weight, thrust, and drag
And precisely in the same manner, model airplanes are affected in a like matter. For example, a model of a Piper Cub performs in almost the identical ways as the full grown Piper. And the same applies to all aircraft. In a similar manner, of course, but with small differences.
Lift is the upward force created by the effect of airflow as it passes over and under the wings. It supports the airplane in flight. Weight opposes lift. It is caused by the downward pull of gravity. Thrust is the forward force which propels the airplane through the air. It varies with the amount of engine power being used. Opposing thrust is drag, which is a backward, or retarding, force that limits the speed of the airplane.
Lift is the key aerodynamic force. It is the force that opposes weight. In straight-and-level, unaccelerated flight, when weight and lift are equal, an airplane is in a state of equilibrium. If the other aerodynamic factors remain constant, that airplane neither gains nor loses altitude. When an airplane is stationary on the ramp, it is also in equilibrium, but the aerodynamic forces are not a factor. In calm wind conditions, the atmosphere exerts equal pressure on the upper and lower surfaces of the wing. Movement of air about the airplane, particularly the wing, is necessary before the aerodynamic force of lift becomes effective.
During flight, however, pressures on the upper and lower surfaces of the wing are not the same. Although several factors contribute to this difference, the shape of the wing is the principal one. The wing is designed to divide the airflow into areas of high pressure below the wing and areas of comparatively lower pressure above the wing. This pressure differential, which is created by movement of air about the wing, is the primary source of lift.
The weight of the airplane is not a constant. It varies with the equipment installed, passengers, cargo, and fuel load. During the course of a flight, the total weight of the airplane decreases as fuel is consumed. Additional weight reduction may also occur during some specialized flight activities, such as crop dusting, fire fighting, or sky diving flights.The direction in which the force of weight acts is constant. It always acts straight down toward the center of the earth. Thrust is the forward-acting force which opposes drag and propels the airplane. In most airplanes, this force is provided when the engine turns the propeller. Each propeller blade is cambered like the airfoil shape of a wing. This shape, plus the angle of attack of the blades, produces reduced pressure in front of the propeller and increased pressure behind it. As is the case with the wing, this produces a reaction force in the direction of the lesser pressure. This is how a propeller produces thrust, the force which moves the airplane forward. To increase thrust by using the throttle to increase power, thrust exceeds drag, causing the airplane to accelerate. This acceleration, however, is accompanied by a corresponding increase in drag. The airplane continues to accelerate only while the force of thrust exceeds the force of drag. When drag again equals thrust, the airplane ceases to accelerate and maintains a constant airspeed.
However, the new airspeed is higher than the previous one. When the thrust is reduced thrust, the force of drag causes the airplane to decelerate. But as the airplane slows, drag diminishes. When drag has decreased enough to equal thrust, the airplane no longer decelerates. Once again, it maintains a constant airspeed. Now, however, it is slower than the one previously flown. As it has been seen, drag is associated with lift. It is caused by any aircraft surface that deflects or interferes with the smooth airflow around the airplane. A highly cambered, large surface area wing creates more drag and lift than a small, moderately cambered wing. If the airspeed is increased, or angle of attack, the drag and lift increases. Drag acts in opposition to the direction of flight, opposes the forward-acting force of thrust, and limits the forward speed of the airplane. Drag is broadly classified as either parasite or induced.
In conclusion, all planes, model and real size, need the four forces of flight so that they can fly. These things are quite unique in their own way but without these factors, the planes would never be able to fly.
About the Author
Dale R Smith drsmith7684@sbcglobal.nethttp://www.dalzmoneytree.comCareer spent in teaching and training, both as a civilian and military trainer. Mr Smith has been a teacher in public schools, college and university and both the US Army and US Navy. “>More info
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