Flight Training Manual Lesson #1: Principles of Flight

this videotape will introduce you to the principles of flight and explain heavier-than-air objects are able to fly you will be shown the physics principles which make flight possible the effect of the atmosphere on flight the four main forces that influence flight equilibrium and stability much of what we deal with in this program is based on Newton's third law of motion simply put it states that for every action there is an equal and opposite reaction how does this apply to an airplane as a propeller moves a massive air backwards there is an equal force that moves the plane forward this is called thrust more about that when the four forces of flight are discussed first we will consider the atmosphere and changes in its properties that affect flight two properties we concern ourselves with our density and pressure density refers to the mass or weight of the air in a given volume changes in that density are measured as air pressure at sea level air pressure average is about fourteen point seven pounds per square inch barometric pressure may also be measured in inches of mercury the pressure at sea level is the pressure required to raise mercury in a barometer to a height of 29.92 inches as altitude increases air pressure decreases looking at the two columns of air one at sea level and the other at 10,000 feet notice the column at 10,000 feet has less air in it therefore less density and a lower air pressure as a matter of fact the air pressure at 10,000 feet is 10.2 pounds or a drop of four and a half pounds before we leave the subject of the atmosphere will consider one other factor temperature as altitude increases temperature drops the reason for is that the sun's heat has little effect on air most of its energy is absorbed by the earth making the earth the nearest heat source to the air therefore air closest to the earth is warmer air higher up is cooler will now consider the four main forces that influence flight we've already mentioned thrust the others include drag weight and lift note how Newton's third law comes into play thrust and drag are opposite forces as our lift and weight first we'll discuss lift and weight the two vertical forces that act on a plane weight the downward force is the total weight of the plane and its contents for the purposes of this discussion it is calculated through a single point known as the center of gravity lift the upward force is generated as the aircraft is thrust through the air as the wing of the plane travels through the atmosphere the air above the wing is traveling faster than the air below it the principle at work here is Bernoulli's theorem it states that as the velocity of air increases its pressure decreases since the air above the wing is moving faster the pressure above the wing is lower the effect of the decreased pressure above the wing is obvious and when the lift force becomes greater than the plane's weight flight is the result like weight the lift is calculated through a single point it is located on the wing and is called the center of pressure there are several observations we can make about lift but first some definitions relative airflow is always parallel to and opposite the flight path of the aircraft the angle of incidence is measured between the plane of the wing chord and the longitudinal axis of the aircraft the angle of attack is the angle between the wing chord and the relative airflow let's go back to Bernoulli's theorem for a moment remembering the pressure on the top surface of the wing is less than that underneath detailed tests have also revealed the pressures are not evenly distributed the lower pressure on the top surface and the higher pressure underneath our greatest over the front of the wing the center of pressure is calculated by deriving a single resultant force the center of pressure moves forward as the angle of attack increases this will continue until it reaches an acute angle well beyond ordinary flight angles when it will move back again if the center of pressure moves far enough back the nose of the aircraft will suddenly pitch downwards as the wing enters a stalled condition the thin layer of air that flows over the wing is called the boundary layer this has two parts the laminar layer and the undesirable turbulent layer as air flows over the wing it conforms to its shape this is the very thin laminar layer between the leading and trailing edges of the wing there is a point of transition where the boundary layer starts to become thick and increasingly turbulent this is the turbulent layer wings have been designed to maintain 11 airflow over as much of the wing surface as possible the laminar flow type wing is generally thinner than conventional wings and the leading edge more pointed the section is nearly symmetrical and the point of maximum camber or greatest convexity is further back than unconventional wings this design results in more even pressure distribution since the airflow is speeded up gradually from the leading edge to the point of maximum camber note as the laminar wing approaches stalling speed the transition point moves forward more rapidly than on a conventional wing will now deal with the other two main forces affecting flight thrust and drag in level flight thrust and drag are the two horrors donto forces acting on the aircraft thrust the forward motion is provided by the aircraft's propeller drag results from the resistance to the aircraft passing through the air we'll consider four types of drag the first form drag is caused by the shape of the aircraft it can be reduced by a more streamlined design skin friction drag results from air resistance to the surface of the aircraft smooth highly polished surfaces have less skin friction mater ice on the aircraft surface increases skin friction drag induced drag is a result of lift high-pressure air from under the wing flows to the lower pressure area above the wing creating a rotary motion at the wingtips this airflow is known as wingtip vortices this disturbed air causes induced drag induced drag is also influenced by the aspect ratio this is the ratio of the wingspan to the mean cord the higher the aspect ratio the lower the induced drag finally the fourth type of drag is called parasitic drag this is caused by wheels struts radio masts and other external attachments to the plane that create resistance to airflow to other forces that affect flight our torque and slipstream torque results from the twisting action produced by the planes engine in response to Newton's third law as the engine rotates the propeller in one direction the plane tries to rotate in the opposite direction most North American planes have a propeller that rotates clockwise when viewed from the cockpit to overcome torque the left wing is given a slightly higher angle of incidence and therefore slightly more lift than the right wing slipstream is the massive air pushed backwards by the propeller as this air moves back it strikes the fin or rudder of the aircraft pushing it to the right this affects the directional and lateral balance of the aircraft and is compensated for by offsetting the fin for normal cruising flight this balance of course will be upset when engine power is changed we now move to the concept of equilibrium this is a state in which an object is neither accelerating nor decelerating examples would be a parked aircraft an aircraft in straight and level flight at a constant speed or an aircraft climbing or descending at a constant speed a plane in a turn at constant height and airspeed however is not in equilibrium that is because during a turning motion the plane is always accelerating towards the center of the turn there are ways to alter a plane's equilibrium role or movement about the plane's longitudinal axis is controlled by the ailerons when an aircraft is rolled one aileron is depressed and the opposite one is raised this down a LaRon increases the camber of the wing giving it more lift pushing that wing up conversely the up aileron reduces the camber and the effective lift which accentuates the roll around the longitudinal axis the ailerons are controlled by the left and right movement of the planes control column when the control column is moved to the left the left aileron is raised and vice versa pitching is movement of the aircraft around the lateral axis and is controlled by the elevators the backward movement of the control column raises the elevators producing a force that causes the nose to rise and the tail to go down forward movement of the control column produces the opposite effect yaw is the movement around the vertical axis and is controlled by the rudder which is hinged to the or vertical stabiliser of the aircraft foot pressure on the left rudder pedal causes the rudder to move to the left this increases the camber of the fin causing a massive air to flow to the left the result is the tail of the plane moves right while the nose moves to the left using the right rudder pedal produces the opposite effect aileron drag or adverse yaw occurs when the ailerons are used for example during a turn the down aileron is subjected to more induced drag as a result of the increased camber this causes a momentary yaw opposite the direction of the turn it usually occurs in a sudden uncoordinated control movement smooth well coordinated turns will avoid this effect there are other devices to help the pilot control the plane they include trim tab flaps and slots and slats trim tabs improve the control and balance of an aircraft and are small auxilary control services attached to the trailing edges of ailerons elevators and the rudder they may be fixed or hinged fixed trim tabs are preset on the ground hinged tabs are controlled by the pilot in larger aircraft hinged tabs are fitted to all control surfaces to compensate for lateral shifts in loading they also provide better rudder control in the event of engine failure in a multi-engine aircraft flaps are controlled by the pilot and improve lift by increasing the camber of a large portion of the wing flaps offer the pilot other advantages such as a decreased stalling speed and a shorter takeoff run they also allow a steeper approach to landing without an increase in airspeed and forward visibility is improved on approach to landing due to the lower nose position when the pilot sets a flat position both flaps go up or down together when fully retracted flaps conform to the shape of the wing flaps must be used precious ly especially when near the ground because of the sudden loss of lift and change in the planes balance that can result there are several types of flaps plane slotted split zap the Fowler flap double slotted and double-slotted flaps and leading-edge slot slots and slats are devices on the leading edge of the wing which improve the airflow or laminar layer of air over the wing at low speeds these may be fixed or controlled by the pilot and are generally found on airplanes with special performance requirements on some aircraft the tail plane can be varied in flight to trim the aircraft longitudinally this is done with a horizontal stabilizer and the effect is similar to trimming the elevators on an aircraft with a fixed tail plane if the plane has differential brakes that is an independent braking system for each main landing wheel they may be used to shorten a landing rule or give directional control on the ground pressure applied to the left brake pedal slows the left wheel and turns the airplane to the left and vice versa to stop straight equal pressure must be applied to both brake pedals one last affect we'll discuss in this section is the gyroscopic effect a spinning gyro will remain rigid in space even though the platform it is pivoted on changes its attitude this is the principle upon which the attitude indicator and heading indicator is based but the gyroscopic effect also has an effect on an aircraft in flight the spinning aircraft engine and propeller act as a gyro wheel and try to remain rigid in space they are also susceptible to gyroscopic precession this occurs when a force is applied to a spinning object the object will react as though the force had been applied at a point 90 degrees from where it was actually applied this effect can be quite noticeable on a tail wheel equipped aircraft because when the tail raises the propeller is pushed forward and because of gyroscopic precession the aircraft yards to the left the final section of this tape deals with stability an aircraft is considered to be stable when it returns to its original position after being subjected to an air disturbance such as an updraft you recall we showed the three planes of rotation of an aircraft pitching or lateral movement yawning or vertical movement and rolling or longitudinal movement stability in an aircraft is achieved through its design lateral stability can be achieved by using a dihedral design in this feature the wing tips are higher than the center section of the wing this causes turbulent air to move to the down wing exposing it to more airflow than the up wing because the down wing also has a higher angle of attack it produces more lift and the aircraft returns to a level state directional stability controls the yaw motion of the aircraft the vertical stabilizer contributes to the directional stability of an airplane longitudinal stability is perhaps the most critical characteristic of an aircraft it is affected by aerodynamic and physical factors including human error the greatest influence on longitudinal stability is the center of gravity other factors that influence it are changes of speed power and attitude turbulent air operation of the flaps and other controls can also affect longitudinal stability this problem is primarily resolved by the horizontal stabilizer and aided by the vertical stabilizer because these stabilizers are a long way from the center of gravity of the aircraft they have a great leverage even a small force on them produces a large correcting movement the basic center of gravity of an aircraft is calculated for an empty plane obviously the center of gravity will change according to how the plane is loaded it is the responsible the of the pilot to make sure the center of gravity remains within the tolerances sent out in the weight and balance report you can seriously affect the controllability of a plane by improperly loading it to simplify loading problems most manufacturers of light aircraft provide pre calculated graphs charts or loading examples careless aft loading can lead to serious balance and control problems even if the maximum permissible weight is not exceeded factors you must consider when calculating the center of gravity include the weight of the fuel pilot passengers baggage and other payload you

Channel: The CFI

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Keywords: flight, trainining, manual, video, canada, private, pilot

Id: SV1Nf9yB7B0

Length: 28min 57sec (1737 seconds)

Published: Wed May 13 2015