Lesson 1A: Basic structure of airplane

Lesson 1:  AIRFRAME of an airplane

 

AIRFRAME of an airplane

Judging from the story of Daedalus and Icarus, humans have been interested in  aerodynamics and flying for thousands of years, although flying in a heavier-than-air  machine has been possible only in the last hundred years. Aerodynamics affects the  motion of a large airliner, a model rocket, a beach ball thrown near the shore, or a kite  flying high overhead. The curveball thrown by big league baseball pitchers gets its  curve from aerodynamics. In this lesson, we will discuss the basics of aircraft  aerodynamics, flight control surfaces for airplanes and helicopters, and maintaining  those flight controls.




Subscribe here to our Youtube Channel ... And you will have the advantage of asking questions specific to you and you get quick answers to your situations ....


Click here for the previous lessons, to learn about: Principle of Airframe; Principles of Aerodynamics; Airfoil Characteristics; Primary Flight Control Surfaces; Description and Operation of Helicopter; Miscellaneous Components of an Aircraft…

PRINCIPLES OF AERODYNAMICS 

What is aerodynamics? The word comes from two Greek words: aerios,  concerning the air, and dynamis, meaning powerful. Simply stated, aerodynamics is the  study of forces and the resulting motion of objects through the air. 

Forces Exerted On An Aircraft In Flight 

 In order to understand how an aircraft flies, we must first discuss the four forces  that affect the aircraft in flight, figure 1-1. These forces are manipulated by the pilot,  through the use of engine and flight controls, to produce a desired response from the  aircraft. 

.  

Forces Exerted On An Aircraft In Flight

Figure 1-1, Four Forces  



LIFT.

One of the fundamental forces studied in aerodynamics is lift, or the force  that keeps an airplane in the air. Lift is produced by the effect of air passing over an airfoil. The net force produced is perpendicular to the relative wind, which will be  discussed later in this section. Lift directly opposes gravity. 

WEIGHT.

Weight is a measurement of the force that gravity exerts on a given  object. Weight is also the force that offsets lift, because it acts in the opposite direction.  The weight of the airplane must be overcome by the lift produced by the wings. If an  airplane weighs 70,000 pounds, then the lift produced by its wings must be greater than  70,000 pounds in order for the airplane to leave the ground. 

THRUST.

 Thrust is the force that propels an airplane forwa

rd through the air.  The airplane’s propulsion system, either a propeller or jet engine or combination of the  two, provides thrust. Thrust is used to overcome the opposing forces of drag and  inertia. Inertia is a property of matter that causes it to remain stationary or remain in  uniform motion in a straight line. Consequently, thrust overcomes inertia by setting the  aircraft in motion and defeats drag by keeping the aircraft in motion. 

DRAG

. Another important aspect of aerodynamics is the drag, or resistance,  acting on solid bodies moving through air. The thrust force developed by either the jet  engine or the propellers, for example, must overcome the drag forces exerted by the air  flowing over the airplane. In this section we will discuss two types of drag: Induced and  parasitic. 

Induced Drag.


Induced Drag.


 This drag is caused by the development of lift. As a difference in  pressure is caused about an airfoil, attempts to equalize this pressure at the wing tip  cause a circular motion called vortices. This phenomenon creates, or induces drag. 

Parasitic.

The second type of drag, parasitic, is found in three forms: Skin  friction, interference drag, and form drag. 

Skin Friction.


Skin Friction.


Consider the air passing over a surface to be made up of thin  sheets of molecules of air. The sheet of air on the surface of the skin will lodge in the  minute pits and crevices found on all surfaces. As this sheet of air is stopped, a mass is  decelerating which will cause a force to be exerted. The molecules of air do not remain  in the thin sheets but bounce from one sheet to another. Consequently, as the now  slower-moving molecules on the surface move to the next layer, they slow that layer  also. The overall picture will be that of many sheets of air moving across the skin. The  layer on the skin will be stopped and each adjacent layer will be moving somewhat  faster until a short distance away all of the layers will be moving at the normal speed. 

Interference Drag.

 This drag is generated by the collision of airstreams creating  turbulence. It is reduced by conforming external appendages to surface of the fuselage  as much as possible. If you take a clean aircraft and determine its drag at a given  airspeed and then take an external store like a fuel tank or bomb and measure its drag  at the same airspeed, the total drag of the aircraft with the external store attached  exceeds the sum of the individual drag values. Interference drag also occurs as a result  of external engine nacelles and at the junction of the wing and tail surfaces with the  fuselage.

Form Drag.

 This drag is caused by the relative low pressure in the area behind  any object in a moving airstream. The difference in pressure between the front and the  rear of the object acts on the profile area and causes a force aft. An example would be  putting your hand out the window of a fast moving vehicle. Form drag results in a force  aft, which causes your hand to move toward the rear of the vehicle.