Content:

1. Physics of Flights

2. Lift

3. Weight

4. Thrust

5. Drag

1. Physics of Flights

i. The Four Forces of Flights

• Lift

• Weight

• Thrust

• Drag

ii. Vectors

• Quantities that have both magnitude and direction

• Two or more vectors acting on an object at the same time can be added or subtracted to create a resultant vector

iii. Equilibrium

• Equilibrium exists when?

• Lift equals weight

• Drag equals thrust

iv. Newton's Laws of Motion

1. An object at rest will remain at rest unless acted on by an outside force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an outside force

2. When a force is applied to a mass, the mass will accelerate

3. Whenever one body exerts a force on another, the second body always exerts an equal force in the opposite direction

v. Bernoulli's Principle

• As the velocity of a fluid increases, its pressure decreases

2. Lift

i. Airfoil

• An airfoil is any surface that provides lift when it interacts with a moving stream of air

• Relative wind is always directly opposite to the flight path

• Angle of attack?is the angle between the chord line of an airfoil and the relative wind

• The angle of attack can change based on pilot input or external factors such as undrafts or wind gusts

• Creating Lift:

• The shape of the airfoil:

• Causes the air flowing over the upper surface to speed up, which decreases the pressure above the airfoil

• Causes the air flowing beneath it to slow down, which increases pressure

• The air pressure on the bottom surface of the wing is greater than the pressure on the upper surface. This pressure difference creates lift

• The airfoil causes the air moving past it to curve downward, creating a strong downwash behind the airfoil

• How Air velocity Affects Lift

• When there is no air flowing over an airfoil, there is no lift

• To generate lift, an airfoil needs motion relative to the air

• The faster an airfoil moves relative to the air, the more lift it generates

• If all other factors remain the same, doubling the airspeed quadruples the amount of lift

• Angle of Attack and Coefficient of Lift

• Coefficient of lift (CL) is a way to measure lift as it relates to angle of attack. CL is determined by airfoil design and angle of attack

• As angle of attack increases, CL increases

• The point of maximum lift is called CLmax

• If the maximum coefficient of lift is exceeded, lift decreases rapidly and a stall occurs

ii. Wing Design

• Factors that Affect Wing Design:

• Airfoil camber

• Changing camber affects lift

• Aspect ratio

• In general, the higher the aspect ratioin, the higher the lift efficiency of the wing

• Wing area

• The greater the wing area, the more lift it produces

• Wing planform

• Shape of an airplane wing when viewed from above or below

• Straight

• Elliptical

• Tapered

• Sweptback

• Delta

• Angle of Incidence: the upward angle formed between the chord line and a line parallel to the longitudinal axis

• Places the wing at the best angle of attack at cruising airspeed

• Keeps the fuselage aligned with the flight path to minimize drag

• Stall Strips: disrupt the airflow at high angle of attack, which:

• Causes the wing roots to stall before the wingtips

• Helps to preserve aileron effectiveness, providing an opportunity for recovery before the stall progresses to the wingtips

• Wing Twist: creates a lower angle of incidence at wingtip than the wing root

• Results in the wingtip having lower angle of attack than the root when approaching a stall

• Causes the wing root to stall first and preserves wingtip and aileron effectveness at the beginning of a stall

iii. Introduction to Stalls

• Stall: the sudden decreases in lift that occurs when the airfoil exceeds the angle of attack for CLmax

• At any angle above CLmax, lift decreases rapidly as the smooth airflow over the upper surface of the wing becomes turbulent and separates

• For any given airplane, a stall always occurs at the same angle of attack, regardless of airspeed, flight attitude, or weight. This angle is the critical angle of attack

iv. Pilot Control of Lift

• Pilots can control lift by:

• Increasing or decreasing the angle of attack

• Changing the airspeed

• Changing the wing shape by lowering the flaps

• Increasing lift also increases drag, which is a byproduct of lift

• High-lift Devices:

• Flaps: a surface at the trailing edge of a wing that has hinges or tracks so its trailing edge can move downward

• Changes camber to increase the coefficient of lift

• Changes the chord line and increases the angle of attack

• Helps maintain lift at low airspeed, such as during approach and landing

• Increases the lifting efficiency and decreases stall speed

• Using full flaps during approach allows for steep descent angles without gaining airspeed

• Slots: allows the airflow to remain attached over the outer portion of the wings after the roots have stalled

• Slats: portions of the leading edge that can move forward and down to create a path for air similar to a slot

• Flaps and Configurations: the position of the landing gear and flaps

• Raising or lowering the gear

• Moving the flaps (clean configuration when the flaps are up)

• Types of Flaps:

• Plain flaps

• Split flas

• Slotted flaps

• Flowler flaps

3. Weight

• Weight is the force of gravity, which acts vertically toward the center of the earth

• Can be thought of as acting through a single point called the center of gravity

• Factors that Affect Weights:

• Fuel

• Baggage

• Pilot and Passengers

4. Thrust

i. Generating Thrust

• The propeller accelerates a mass of air backward.?An equal and opposite force results. This force is thrust acting in a forward direction

• The blades rotate in circular path called the plane of rotation

• The angle of the propeller blade relative to the plane of rotation is the blade angle, or pitch

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ii. Propeller Characteristics

• Each propeller blade works like an airplane wing

• The propeller blade twists slightly from root to tip and is thicker at the root. These design features help compensate for the fact that the blade tips travel at a higher speed than the roots

• Near the root, each blade has a thick airfoil optimized for low rotational speeds and set at a high angle of attack

• At the tip, the blade has a thin airfoil designed for high speeds and is set at a relatively low angle of attack

• The airfoil shape and the angle of attack change smoothly between the root and the tip so each section has the optimum airfoil shape and angle of attack for its rotational speed at that point

5. Drag

• Drag: a backward, or retarding, force that limits the forward speed of an aircraft

• Types of drags:

• Induced drag: A?result of the wings producing lift; it decreases as the airplane goes faster

• Low airspeed requires a higher angle of attack to generate enough lift to support the airplane. The greater pressure difference between the upper and lower wing surfaces generates more powerful wingtip vortices, which are the primary cause of induced drag

• At higher airspeeds, a lower angle of attack generates sufficient lift, so the wingtip vortices are less powerful and create less induced drag

• Parasite drag: Any drag that is unrelated to the production of lift; it increases with speed

• Three types of Parasite drags:

• Form Drag: Results from the turbulent wake that occurs when airflow separates from the surface of an object

• Interference Drag: Created when the air flowing around one part of the airplane interacts with air moving at a different speed or in a different direction around an adjacent part

• Skin Friction Drag: Caused by the roughness of the airplane's surfaces

• Parasite drag is proportional to the square of the airspeed: doubling your airspeed quadruples parasite drag

• An airplane's top speed is limited by the rapid increase in parasite drag

• Total Drag: sum of parasite and induced drag

• Lift-to-Drag Ratio (L/D): Lift/Drag

• The L/D ratio varies with the angle of attack of the airfoil

• L/Dmax is the angle of attack where the lift-drag ratio reaches its maximum value

• L/Dmax corresponds to the lowest point on the total drag curve. This is the airspeed at which total drag is at its minimum

• L/Dmax corresponds to the power-off glide speed that provides the best glide ratio of the airplane

• L/Dmax also provides the most efficient fuel economy

• The airspeed for achieving?L/Dmax varies with the weight of the airplane; however, the angle of attack for?L/Dmax does not vary significantly

• Ground Effect: when an airplane flies within one wingspan's distance from the ground or water, the earth's surface alters the three-dimensional airflow around the airplane and reduces induced drag

• There is a reduction in upwash, downwash, and wingtip vortices. This phenomenon is called ground effect

• Ground effect is more noticeable in low-wing airplanes because the wings are closer to the ground

• Causes more of the wing's lift to act vertically

• Decreases induced drag

• Allows the wings to create enough lift at a lower speed to support the weight of the airplane

• Because of ground effect, your airplane can take off at a lower-than-normal airspeed

• However, when you fly out of ground effect:

• More thrust is required to sustain lift (normally already maximum thrust)

• Induced drag suddenly increases

• Increased drag slows the airplane and reduces lift

• Ground effect is also responsible for "floating" during the landing flare

• Reduce thrust to continue slowing the airplane for landing

• On a short field, ground effect could cause the airplane to float so far down the runway that you wouldn't have room enough to stop after touchdown