Principles of Flight
Flight Principle's
Principles of Flight
Objective: The student will be introduced to the four forces of flight and how each effect the airplane. The student will be able introduced to the theories of lift using Newtons Laws and Bernoulli’s Principle.
Completion Standards: The student will be able to explain the four forces of flight and how each effect the airplane. The student will be able to explain the theories of lift using Newtons Laws and Bernoulli’s Principle.
References: PHAK CH 3-4
Equipment: White Board and markers, iPad/ computer
IP’s Actions:
Assess student
State the objective and completion standards
Writes down references
Provide attention getter
Present content
Assessment
Assign Homework
SP’s Actions:
Take notes
Ask Questions
Introduction:
Show Video of F22:https://www.youtube.com/watch?v=WCP8i-Sm0xE
Motivation: For the student to do maneuvers in the airplane they must learn the basics of flight
Overview:
Basics of an airplane
Aerodynamics of flight:
Wing tip vortices
Wake Turbulence
Stability and Controllability
Turning Tendency
Load Factor
Content:
Basics of an airplane
Discuss 5 elements of an airplane
Aerodynamics of flight:
The Four Forces of Flight:
Draw and label the forces
Ask student what their thoughts are
Weight- Gravity, which all the weight of the aircraft is concentrated, When the CG is forward of the CP, there is a natural tendency for the aircraft to want to pitch nose down. If the CP is forward of the CG, a nose up pitching moment is created. Therefore, designers fix the aft limit of the CG forward of the CP for the corresponding flight speed in order to retain flight equilibrium
Lift- Lift is the force that directly opposes the weight of an airplane and holds the airplane in the air.
Lift is the upward force on the wing acting perpendicular to the relative wind and perpendicular to the aircraft’s lateral axis. Lift is required to counteract the aircraft’s weight. In stabilized level flight, when the lift force is equal to the weight force, the aircraft is in a state of equilibrium and neither accelerates upward or downward. If lift becomes less than weight, the vertical speed will decrease. When lift is greater than weight, the vertical speed will increase
Theories in the Production of Lift
Newton’s Basic Laws of Motion:
“Every object persists in its state of rest or uniform motion in a straight line unless it is compelled to change that state by forces impressed on it.”
Inertia, object at rest stays at rest until acted upon by an outside force. And an object in motion will stay in motion until an outside force act on it
“Force is equal to the change in momentum per change in time. For a constant mass, force equals mass times acceleration.”
Force equals mass X acceleration
“For every action, there is an equal and opposite reaction.”
Lift is the forces acting on an airfoil using F=MA as well as the air turning over the top of the airfoil causing lift to be generated.
Bernoulli’s Principle of Differential Pressure:
States that as the velocity of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases.
This principle explains what happens to air passing over the curved top of the airplane wing.
Venturi, as velocity goes up pressure goes down
Airfoil Design:
An airfoil is constructed in such a way that its shape takes advantage of the air’s response to certain physical laws. This develops two actions from the air mass:
A positive pressure lifting action from the air mass below the wing,
A negative pressure lifting action from lowered pressure above the wing
Low Pressure Above
High Pressure Below
Pressure Distribution:
The pressure distribution along an airfoil at three different angles of attack.
The average of the pressure variation for any given AOA Is referred to as the center of pressure (CP).
Aerodynamic force acts through this CP.
At high angles of attack, the CP moves forward,
while at low angles of attack the CP moves aft.
An airplane’s aerodynamic balance and controllability are governed by
Thrust- is a forward force using the propeller which is similar to an airfoil.
For an aircraft to start moving, thrust must be exerted and be greater than drag. l thrust and drag are equal.
If the engine power is increased, thrust becomes greater than drag and the airspeed increases. As long as the thrust continues to be greater than the drag, the aircraft continues to accelerate. When drag equals thrust, the aircraft flies at a constant airspeed.
Show picture of the propeller shape
Reference desk fan
Drag- Drag is the force that resists movement of an aircraft through the air. There are two basic types: parasite drag and induced drag.
Types: Parasite Drag And Induced Drag
Parasite Drag
Form Drag- generated by the aircraft due to its shape and airflow around it
Examples include the engine cowlings, antennas, and the aerodynamic shape of other components
Interference Drag- The intersection of airstreams that creates eddy currents, turbulence, or restricts smooth airflow.
Example, the intersection of the wing and the fuselage at the wing root has significant interference drag.
Skin Friction Drag- is the aerodynamic resistance due to the contact of moving air with the surface of an aircraft.
Induced Drag
A surface that creates lift will produce drag as a by-product
Also creates wingtip vortices and in turn produces downwash
Wing tip vortices
When the aircraft is viewed from the tail, these vortices circulate counterclockwise about the right tip and clockwise about the left tip.
Since air always moves from high pressure toward low pressure, and the path of least resistance is toward the airfoil’s tips, there is a spanwise movement of air from the bottom of the airfoil outward from the fuselage around the tips. This flow of air results in “spillage” over the tips, thereby setting up a whirlpool of air called a vortex.
Wingtip vortices are greatest when the generating aircraft is “heavy, clean, and slow.”
Wake Turbulence
How to avoid
Avoid flying through another aircraft’s flight path.
Rotate prior to the point at which the preceding aircraft rotated when taking off behind another aircraft. Avoid following another aircraft on a similar flight path at an altitude within 1,000 feet.
Approach the runway above a preceding aircraft’s path when landing behind another aircraft and touch down after the point at which the other aircraft wheels contacted the runway.
Stability and Controllability
Axes of an airplane
Longitudinal
Vertical
Lateral
Stability:
Stability is the inherent quality of an aircraft to correct for conditions that may disturb its equilibrium and to return to or to continue on the original flight path.
Types of stability:
Static Stability- Refers to the initial tendency, or direction of movement.
Positive static stability
The initial tendency of the aircraft to return to the original state of equilibrium after being disturbed
Neutral static stability
The initial tendency of the aircraft to remain in a new condition after its equilibrium has been disturbed
Negative static stability
The initial tendency of the aircraft to continue away from the original state of equilibrium after being disturbed
Dynamic Stability- Defined as the initial tendency to return to equilibrium over time.
Positive dynamic stability-
Over time, the motion of the displaced object decreases in amplitude and, because it is positive, the object displaced returns toward the equilibrium state.
Neutral dynamic stability-
Once displaced, the displaced object neither decreases nor increases in amplitude. A worn automobile shock absorber exhibits this tendency.
Negative dynamic stability-
Over time, the motion of the displaced object increases and becomes more divergent
Turning Tendency
To the pilot, “torque” (the left turning tendency of the airplane) is made up of four elements that cause or produce a twisting or rotating motion around at least one of the airplane’s three axes. These four elements are:
Torque reaction from engine and propeller
Torque reaction involves Newton’s Third Law of Physics for every action, there is an equal and opposite reaction.
Review Newtons 3rd law
As applied to the aircraft, this means that as the internal engine parts and propeller are revolving in one direction, an equal force is trying to rotate the aircraft in the opposite direction.
Corkscrewing effect of the slipstream
The high-speed rotation of an aircraft propeller gives a corkscrew or spiraling rotation to the slipstream. At high propeller speeds and low forward speed (as in the takeoffs and approaches to power-on stalls),
this spiraling rotation is very compact and exerts a strong sideward force on the aircraft’s vertical tail surface.
When this spiraling slipstream strikes the vertical fin, it causes a yawing moment about the aircraft’s vertical axis.
As the forward speed increases
the spiral elongates and becomes less effective.
The corkscrew causes a rolling moment around the longitudinal axis.
Review components of the aircraft and the axes
Gyroscopic action of the propeller
Before the gyroscopic effects of the propeller can be understood, it is necessary to understand the basic principle of a gyroscope.
All practical applications of the gyroscope are based upon two fundamental properties of gyroscopic action:
Rigidity in space and Precession:
Precession is the resultant action, or deflection, of a spinning rotor when a deflecting force is applied to its rim.
when a force is applied, the resulting force takes effect 90° ahead of and in the direction of rotation. The rotating propeller of an airplane makes a very good gyroscope.
Any time a force is applied to deflect the propeller out of its plane of rotation.
Asymmetric loading of the propeller (P-factor)
When an aircraft is flying with a high AOA, the “bite” of the downward moving blade is greater than the “bite” of the upward moving blade.
This moves the center of thrust to the right of the prop disc area,
Causing a yawing moment toward the left around the vertical axis.
Load Factor
In aerodynamics, the maximum load factor (at given bank angle) is a proportion between lift and weight
measured in Gs (acceleration of gravity), force exerted by gravity on a body at rest and indicates the force to which a body is subjected when it is accelerated.
Any force applied to an aircraft to deflect its flight from a straight line produces a stress on its structure.
For example,
A load factor of 3 means the total load on an aircraft’s structure is three times its weight. Since load factors are expressed in terms of Gs, a load factor of 3 may be spoken of as 3 Gs, or a load factor of 4 as 4 Gs
With the structural design of aircraft planned to withstand only a certain amount of overload, a knowledge of load factors has become essential for all pilots.
Load factors are important for two reasons:
It is possible for a pilot to impose a dangerous overload on the aircraft structures.
An increased load factor increases the stalling speed and makes stalls possible at seemingly safe flight speeds
Load Factors and Flight Maneuvers
Turns
Increased load factors are a characteristic of all banked turns
Stalls
As the stall occurs, however, this load factor may be reduced toward zero, the factor at which nothing seems to have weight. The pilot experiences a sensation of “floating free in space.”
Conclusion
Went over the 4 forces
What is involved with creating lift and how airfoils are designed the way the are
Talked about stability and controllability
Turning tendency
Load factor
(Questions to assess student)
What are the 4 forces?
Explain how lift is created either using Bernoulli’s Principle or Newtons Laws?
What is positive static stability?
HW: Review the four forces in the PHAK Ch 3-4