Module Two: Theory of Flight. In This Module: 789 Lt. R Hampton Gray VC Squadron Ground School 2014...

789 Lt R Hampton Gray VC Squadron Ground School

(2014)

Module Two: Theory of Flight

789 Lt. R Hampton Gray VC Squadron Ground School 2014

In This Module:

2.1 Theoretical Applications

2.2 Flight Instruments

2.1: Theoretical Applications


Four Forces Acting on an Airplane In Flight

When opposing forces are equal, the aircraft is said to be in a state of equilibrium and will maintain constant motion.

If one force becomes greater than it’s opposing force, the aircraft will either accelerate, decelerate, climb, or sink.


Four Forces Acting on an Airplane in Flight


Concept Check

1.Name the four forces acting on an aircraft.

2. If the force of thrust is greater than the force of drag, what will happen?

3. If the force of lift is greater than the force of weight (gravity) what will happen?


Four Forces - Lift

Lift is the force that keeps the airplane in the air, or “lifts” it during flight. The wings of an airplane are designed so that as they move forward through the air, this lifting force is generated. This is accomplished through the use of airfoils.


Airfoils

An airfoil is any surface designed to obtain a reaction from the air through which it moves in order to obtain lift.

The curvature of the upper and lower surfaces is called the camber.

A straight line drawn from the leading edge to the trailing edge is the chord line.


How is Lift Generated?

NEWTON’S 3 LAWS OF MOTION

1) First law: When viewed in an inertial reference frame, an object either remains at rest or continues to move at a constant velocity, unless acted upon by an external force.

2) Second law: The vector sum of the forces F on an object is equal to the mass m of that object multiplied by the acceleration vector a of the object. (F=ma)

3) Third law: When one body exerts a force on a second body, the second body simultaneously exerts a force equal in magnitude and opposite in direction on the first body.



BERNOULLI’S PRINCIPLE

For a flowing fluid, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.



12

3

1) Deflection 2) Downwash 3) Accelerated Air/Fluid



Lift is generated by a combination of:

1) Downwash and Deflection (Newton)2) Reduced Pressure (Bernoulli)

FACT: The ACTUAL mechanism by which lift is created is UNKNOWN to science and only theories exist.


Concept Check

1.What is an airfoil?

2.Explain lift from a Newtonian standpoint.

3.Explain lift relating to Bernoulli’s Principle.


Relative Airflow

Relative airflow describes the motion of the air past the airplane in flight. Relative airflow is not determined by aircraft attitude. It is determined solely by the aircrafts direction of motion through the air.


Angle of Attack (Alpha, α)

Angle of attack (α) describes the angle between the relative airflow and the chord line of the wing.


Effects of Angle of Attack

As angle of attack is increased, the changes in pressure around the wing and the amount of deflection and downwash increase, increasing lift.

At a certain point, any further increase in AoA will result in a sudden and rapid loss of lift. This is called the critical angle of attack.


Center of Pressuree

As AoA increased, the centre of pressure moved forward. Once critical AoA is reached (stall), the centre of pressure moves backwards.


Concept Check

1.What is relative airflow?

2.What is angle of attack?

3.What is critical angle of attack?

4.Explain the relationship between change in angle of attack, lift, and centre of pressure.


Four Forces - Weight

Weight is the force acting towards the centre of the earth and is due to gravity. Whereas lift acts through the centre of pressure, weight acts through the centre of gravity (CoG).


Four Forces - ThrustThrust is provided in powered aircraft by moving a large volume of air or compressed gas backwards, which in turn pushes the aircraft forwards (Newton!)

Gliders technically do not experience thrust. They are moved forward through the air due to their wings opposing the force of gravity.


Concept Check

1.Define weight.

2.Define thrust.

3.Do gliders experience thrust?


Four Forces - Drag

Drag is the resistance that the airplane meets when moving through the air.

Two principal types:• Parasite Drag• Induced Drag


Parasite Drag

Parasite drag is drag resulting from all parts of the airplane that are NOT contributing lift.

Parasite drag is divided into two sub-types, form drag, and skin friction.

Form Drag: Drag created by the form or shape of an object as it moves through the air.

Skin Friction: Refers for the tendency of air flowing over a body to cling to its surface and slow down.


Parasite DragParasite drag can NEVER be eliminated, but it can be reduced through:• Streamlining• Reducing parts exposed to

air stream (i.e. Retractable gear)

• Keeping surfaces clean

Interference drag is parasite drag caused by the joining of two parts. It can be minimized by smoothly blending joints using fairings.


Concept Check

1.What is form drag?

2.What is skin friction?

3.How can parasite drag be reduced?


Induced Drag

Induced drag is drag resulting from all parts of the airplane that ARE contributing lift (i.e. The wings, horizontal stabilizer, lifting-bodies, etc.)

Induced drag is part of lift and can never be eliminated.

Much like lift, it increases as AoA increases and decreases as AoA decreases.


Induced Drag

Induced drag can only be minimized during the design face. A wing with a high aspect ratio (span/chord) produces less induced drag than a wing with a low aspect ratio.


Concept Check

1.What is the difference between induced drag and parasite drag?

2.What is the effect of AoA on induced drag?

3.How can induced drag be reduced in the design process?


Wingtip VorticesWingtip vortices are an example of induced drag. They result from the airflow over the top of the wing being inward and the airflow over the bottom being outward. Wingtip vortices produce a force resisting the forward motion of the airfoil (i.e. Drag).


Wingtip Vortices


Thrust/Drag

As speed increases, so does overall drag. Because of this relationship, as aircraft speed gets higher, the amount of power required to continue increasing speed becomes even higher.

At any given speed, it requires four times the thrust in order to double speed.


Aileron DragWhen ailerons are deployed to bank an aircraft, the down moving aircraft increases lift on that side and thus also increases drag. This asymmetrical drag is known as aileron drag.


Concept Check

1.What are wingtip vorticies?

2.What is a common way of reducing wingtip vortices?

3. What increase in thrust is necessary to achieve a doubling of speed?

4. Explain aileron drag.


Boundary LayerThe boundary layer is a thin layer of air lying over the surface of the wing.


Boundary LayerThe boundary layer begins flowing smoothly over the wing. As it slows due to skin friction and the layer of air has less energy, it separates from the wing and becomes turbulent. The smooth area is called the laminar layer. The separated layer is called the turbulent layer. Where the airflow changes from one to the other is called the transition point.


Boundary Layer


Concept Check

1.What is the boundary layer?

2.What are important aspects of boundary layer?

3. What are some ways to keep the laminar layer attached as long as possible?


Coupling

Most commercial and general aviation aircraft are coupled to create a natural nose down moment.


Wing Design – Conventional Airfoils


Wing Design – Laminar Flow Airfoils

• Designed to allow planes to fly faster.

• Thinner than conventional airfoils and nearly symmetrical.

• Thickest part at ~50% of chord vs 25% for conventional.

• Results in flow separation (transition point) further back on the wing.

• At stall, transition point moves forward very rapidly.


Planform


Aspect Ratio

High Aspect Ratio Low Aspect Ratio

Ratio between wing span and wing chord.


Concept Check

1.What is a laminar flow airfoil?

2.What is the planform of a wing?

3. Describe aspect ratio.


Angle of IncidenceAngle between the longitudinal axis of the aircraft and the chord line of the wing. Angle of incidence is set during design and does not change.


Wash Out/Wash InA slight twist is built into the wing so that the angle of incidence is at the wing tip is less than at the wing root. The result is the wing root flies at a higher AoA and thus will stall earlier.


Concept Check

1.What is the difference between angle of attack and angle of incidence?

2.Describe wash out.


Wing Fences

Wing fences control lateral airflow over the wing and provide better slow speed handling.


Slots, Slats, and Leading Edge Flaps

Slots and slats are designed to provide smoother air flow over the wing at high angles of attack. Slots are fixed gaps built into the wing close to the leading edge. Slats are extendable secondary airfoils.

Leading edge flaps increase the camber of the wing increasing the lift coefficient.


Spoilers

Spoilers are designed to increase drag and decrease lift. They can be used to help control descent, assist with spoiling lift upon landing to increase brake effectiveness, and in some airplanes, to control roll.


Speed Brakes

Speed brakes create additional drag but affect lift minimally or not at all. They are designed to assist with control of descent and control of air speed.


Concept Check

1.What do wing fences accomplish?

2.What is the purpose of slots and slats?

3. What is the difference between spoilers and speed breaks? Which does the cadet glider have?


Flaps

Flaps are high lift devices that increase the camber of the wing. Flaps are deployed during landing, and at takeoff for some airplanes. Flaps produce both lift and drag. At low settings, they produce more lift than drag. Passed the halfway point of their range, they produce more drag and essentially become air brakes.


FlapsFlaps allow for better climb angles on takeoff, and steeper approach angles and lower approach and landing speeds.


Concept Check

1.What are flaps?

2.At roughly what point do flaps produce more drag than lift?

3. When are some times that flaps would likely be deployed?


Axis of an Airplane


Balanced Controls


Concept Check

1.Demonstrate motion about the normal axis of an airplane.

2.Demonstrate motion about the lateral axis of an airplane.

3. Demonstrate motion about the longitudinal axis of an airplane.


Stability

Stability is the tendency of an airplane in flight to remain in straight, level, upright flight and to return to this attitude, if displaced, without corrective action by the pilot.

Static stability is the initial tendency of an airplane, when disturbed, to return to the original position.

Dynamic stability is the overall tendency of an airplane to return to its original position following a series of damped out oscillations.


Static Stability


Dynamic Stability


Concept Check

1.Describe stability.

2.What is the difference between dynamic and static stability?


Longitudinal Stability

• Longitudinal stability is stability about the lateral axis (pitch stability).

• Achieved by making the airplane nose heavy when correctly loaded.

• Nose heavy airplanes have a tendency to pitch down into a normal glide when power is lost.

• Centre of gravity is ahead of centre of pressure.• To counteract the nose down tendency, the horizontal

stabilizer produces negative lift (down force) that keeps the tail down and exactly counters the nose down tendency when trimmed for straight and level flight.


Lateral Stability

•Lateral stability is stability about the longitudinal axis (roll stability).

•Achieved through; 1) dihedral 2) sweepback 3) keel effect and 4) proper distribution of weight.


Dihedral

• Dihedral is the angle between the wings and the horizontal. • If one wing drops, the sideslip effect generated causes the

lower wing to meet the relative flow at a greater angle of attack, causing more lift and lifting the down wing back to a neutral position.

• Negative dihedral is called anhedral.


Keel Effect

In high wing airplanes, keel effect contributes to lateral stability because most of the weight is below the wings. When the plane is disturbed and one wing drops, the weight acts as a pendulum and returns the wings to level.


Concept Check

1.How is longitudinal stability achieved?

2.What are some ways to achieve lateral stability?

3. Describe how dihedral impacts lateral stability.


Directional Stability• Directional stability is

stability about the vertical (or normal) axis.

• The most important factor in directional stability is the vertical stabilizer.

• If the aircraft yaws while in straight flight, side forces on the vertical stabilizer push the aircraft nose back to a neutral position.


Flight Performance Factors

•Torque•Asymmetric Thrust

•Precession•Slipstream

•Climbing•Gliding•Turns•Stall•Spiral Dive

Factors covered in this section:


Torque

The clockwise turning of the spinning propeller creates an equal and opposite rolling effect in the other direction.

Designers combat this by building a right turning tendency into the aircraft. On take-offs, right rudder is required to compensate for torque.


Asymmetric Thrust (P-Factor)

Asymmetric thrust creates a yawing moment to the left at high angles of attack and high power settings. It is corrected for with right rudder input.


PrecessionThe airplane’s propeller acts as a gyroscope, which has the property of rigidity in space.

When an airplane moves suddenly from nose-up to nose-down, gyroscopic procession kicks in and the result is a sharp yawing motion to the left.

This is countered with right rudder.


Slipstream

The rotating air pushed back from the propeller places a force on the left side of the vertical stabilizer inducing yaw to the left. This effect increases as throttle is opened, but decreases as airspeed increases.

This can be corrected with an offset stabilizer, offset engine (thrust line), or rudder trim tab. In flight correction is made using right rudder.


Concept Check

1.Describe torque. How is it corrected for?

2.Describe asymmetric thrust. How is it corrected for?

3. Describe precession. How is it corrected for?

4. Describe slipstream. How is it corrected for?


ClimbingIncreasing power outputs extra energy. That extra energy will turn into either airspeed or altitude. The elevator is used to divide that energy into airspeed or altitude by controlling the angle of attack of the wings.

When the throttle is opened:

• Airspeed will initially increase.• Increased airspeed will result in

higher lift and the airplane will begin to climb.

• As the airplane climbs, energy is expended, and airspeed will drop.

• Airspeed will settle back at what it was trimmed to prior to opening the throttle unless the pilot uses the elevators to change the angle of attack.


Climbing

Best Rate of Climb (VY): The rate of climb at which the airplane will gain altitude in the shortest time.

Best Angle of Climb (Vx): The angle of climb that will produce the most altitude for a given distance.


Concept Check

1.By what mechanism does increasing power initiate a climb?

2.What part of the airplane controls how energy is converted to either airspeed or altitude?

3. Describe best rate of climb and best angle of climb.


GlidingIn a glide, there is no thrust being produced by the engine, so equilibrium is maintained by lift, drag, and weight only.

Airspeed in a glide is controlled by angle. More steeper glide will have a higher airspeed. A shallower dive will have a lower airspeed.


GlidingBest gliding speed (for range) is the airspeed at which the airplane will cover the most horizontal distance for vertical sink. It is achieved at the airspeed with the highest lift to drag ratio.

At airspeeds above best gliding speed, drag is higher, resulting in reduced range. At airspeeds lower than best gliding speed, lift is reduced, resulting in less range.

A gliding aircraft can also be set to best gliding speed for endurance, which is the speed at which it will stay in the air for the longest time.


Concept Check

1.How does a pilot control in a glide?

2.What will happen if a pilot glides a plane at faster than best glide speed? Slower?

3. What is the difference between best glide speed for range vs. endurance?


TurnsTo turn an airplane, the wings are banked from the horizontal. The lift now has a vertical component and a horizontal component. The horizontal component of lift is the mechanism that causes the turn.

Because the horizontal component of lift is no longer countering weight, more total lift must be generated to compensate.


Turns

The steeper the bank angle for any given airspeed:

• The smaller the radius of the turn will be.• The greater the rate of the turn will be. • The higher the stalling speed will be.• The greater the loading will be.

The higher the airspeed for any given bank angle:

• The larger the radius of the turn will be.• The slower the rate of the turn will be.


Turns

When airplanes turn, the total load factor increases beyond 1G due to the centrifugal force generated in the turn.

This load factor is independent of load factor increases from pitching the nose up or down abruptly.


Concept Check

1.Why does banking an airplane cause it to turn?

2. If an airplane in a constant 60 degree bank increases airspeed, will the turn become tighter or wider?

3. Why does load factor go up in a turn?


Stalls

Stall occurs when the angle of attack is increased to the point that the airflow can no longer follow the camber of the wing and detaches, resulting in a loss of lift.

An airplane will stall at any airspeed and any attitude if the critical angle of attack is exceeded.


Stalls

Factors Affecting Stalls:

• Weight• Center of Gravity• Turbulence• Turns

• Flaps• Snow, Frost, and Ice (Contamination)

• Heavy Rain

Stall recovery:Stall recovery can be accomplished by either reducing the angle of attack by pitching the nose down or adding power (if available) to accelerate the airplane.


Stalls

Spins are a stalled condition in which one wing drops and puts the aircraft into a nose down, nearly vertical flight path as the aircraft rotates about the axis of the spin.


Concept Check

1.What causes an airplane to stall?

2.What airspeed and attitude can airplanes stall at?

3. How can a pilot recover from a stall?

4. Describe a spin.


Spiral Dive• Steep descending turn with an

excessive nose down attitude.

• Characterized by excessive bank, rapidly increasing air speed, and rapidly increasing rate of descent.

• May result in structural damage to the plane if airspeed gets too high.

• Different from a spin in that a spin has a constant, low airspeed. A spiral dive has rapidly increasing airspeed.


Airspeed Limitations

Never Exceed Speed (VNE): The maximum speed an airplane can be operated at in smooth air.

Normal Operating Speed (VNO): The cruising speed the airplane was designed to be operated at, and the maximum speed a pilot should ever intentionally fly.

Manoeuvring Speed (VA): The maximum speed at which control surfaces can be safely deflected fully.

Maximum Flaps Extended Speed (VFE): The maximum speed at which the airplane may be operated with the flaps lowered.


Mach Numbers

Mach number is the ratio of the speed of an aircraft to the speed of sound in the surrounding air.

• The speed of sound changes with air temperature (~660Kn at sea level at 15C. ~575 in the stratosphere at -60C)

• Mach number is found by dividing airspeed by the speed of sound in the surrounding temperature.

• An airplane flying at mach 1.3 is flying 1.3 times the speed of sound in the surrounding air.


Concept Check

1.What is a spiral dive?

2.Name four airspeed limitations.

3. Describe mach number.

2.2: Flight Instruments


Pitot-Static SystemThe pitot-static system uses air pressure to power certain instruments.

The pitot tube takes in impact air from the relative airflow.

The static port takes in air at ambient pressure from around the aircraft.

Using these two air pressures, the system provides information to the pilot.


Pitot-Static Instruments

Airspeed Indicator

Vertical Speed Indicator

Altimeter


Altimeter

• Attached to the static port.

• Uses the ambient pressure outside of the airplane.

• Houses a stack of aneroid wafers that expand and contract with change in air pressure.

• Indicates the altitude above sea level.


Altimeter


Altimeter Pressure Error

“From High to Low, Watch Out Below.”

Altimeters use ambient air pressure to gauge altitude. However, because different areas will have naturally varying air pressure, a pilot must adjust his altimeter when flying from one area of pressure to the next. If this is not done, the altimeter will read incorrectly.

When flying from an area of high pressure into to an area of low pressure, the altimeter will indicate a higher altitude than is actually being flown. Pilots must be aware of this danger.


Altimeter Temperature Error

Air temperature has an effect on air density, and as such will affect the altimeter reading. For instance very cold, dense air, will cause the altimeter to under-read.

As a result, the indicated altitude on the altimeter will not show the actual true altitude in air at non-standard temperatures.


Altitude Definitions

Indicated Altitude: The altitude shown on the altimeter when correctly set for barometric pressure.

Pressure Altitude: The altitude when set for 29.92” Hg.

Density Altitude: Pressure altitude corrected for air temperature.

True Altitude: The exact height above sea level.

Absolute Altitude: The actual height above the earth’s surface.


Concept Check

1.Describe how the altimeter works.

2.When flying from a region of high pressure to a region of low pressure will the altimeter over-read or under-read?

3. Describe pressure and temperature errors for altimeters.


Airspeed Indicator

• Attached to the pitot tube and static port.

• Compares the difference in the dynamic pressure (pitot) and static pressure (static).

• Houses an aneroid capsule attached to the pitot tube that expands into a chamber of ambient pressure and moves the dial.


Airspeed Indicator


Airspeed Indicator

Green: Normal Operating Range

White: Safe Flaps Range

Yellow: Caution Range

Red: Never Exceed Speed


Airspeed Indicator Errors

Density Error: Airspeed indicators are calibrated at a standard pressure of 29.92” Hg at a temperature of 15 degrees. As an airplane climbs, the temperature and pressure change, and indicated airspeed will not be the same as true airspeed.

To roughly correct for density error, add 2% to airspeed for every 1000 feet of altitude.

Ex: Indicated airspeed is 150 knots and altitude is 5000 feet. What is the rough true airspeed?


Airspeed Definitions

Indicated Airspeed (IAS): The airspeed shown on the airspeed indicator without any corrections.

Calibrated Airspeed (CAS): Indicated airspeed corrected for any instrument error or installation error in the pitot-static system.

True Airspeed (TAS): Calibrated airspeed corrected for temperature and pressure error.

Equivalent Airspeed (EAS): Calibrated airspeed corrected for compressibility error. Of little importance to pilots of low speed aircraft.


Concept Check

1.How does the airspeed indicator work?

2.What do the four colour bands on the airspeed indicator mean?

3. What is a rough way that a pilot can quickly correct their airspeed for density error?



• Attached to the static port.

• Static pressure is fed to an aneroid wafer which expands or contracts.

• Uses a calibrated leak to allow the pressure in the housing chamber to slowly change.

• The change in pressure between the two provides change in vertical speed.


Concept Check

1.How does the VSI work?

2.What units does the VSI read in?

3. Does the vertical speed indicator show changes in climb/descent rate immediately?


Gyro InstrumentsGyro instruments use the properties of the gyroscope to orient instruments to allow accurate portrayal of the motion of the aircraft.

Engine driven vacuum systems power gyro instruments using a vacuum created by a vacuum pump attached to the engine.

Venturi driven vacuum systems use one or more venturi tubes mounted to the outside of the airplane to generate a low pressure area and partial vacuum.

Electrically driven gyros use electricity from the alternator/battery to drive the gyros.

Common practice is to use a combination of electrically driven and vacuum driven instruments.


Gyro Instruments

Attitude Indicator

Turn and Slip Indicator / Turn Co-Ordinator

Heading Indicator


Heading Indicator

• Indicates the heading of the airplane.

• Provides a steady means of keeping the airplane on a heading.

• Must be set using the magnetic compass.

• Drifts due to precession error, and thus must be reset in ~15 minute intervals.


Heading Indicator


Heading Indicator Limitations

• At bank angles exceeding 85 degrees, heading indicators may tumble and give incorrect readings and thus need to be reset.

• Gyros working on vacuum power need a certain vacuum pressure to operate properly, and so a vacuum driven heading indicator needs about five minutes of operation before it will reach the correct vacuum pressure and operate properly.


Concept Check

1.What does the heading indicator do?

2.How often must a heading indicator be reset?

3. What are some examples of limitations?

4. Demonstrate understanding using FSX.


Attitude Indicator

• Provides the pilot with an artificial horizon for use when the real horizon is not visible..

• Indicates pitch and roll in relation to the horizon.

• Position of “airplane” in relation to the horizon can be adjusted up or down.


Attitude Indicator

Miniature Airplane Nose

Miniature Airplane Wings

Pitch Up/Down Markings

30 Degree Roll Marking



Cage/Adjustment Knob


Attitude Indicator Limitations

• Gyros working on vacuum power need a certain vacuum pressure to operate properly, and so a vacuum driven heading indicator needs about five minutes of operation before it will reach the correct vacuum pressure and operate properly.

• Older AI’s will only read accurately up to about 70 degrees dive or climb and 90 degrees turn. Outside these limits the gyro may tumble.

• Skidding or slipping turns, and acceleration or deceleration will cause the AI to misread briefly.


Concept Check

1.What does the attitude indicator do?

2.Describe the markings on the attitude indicator.

3. What are some examples of limitations?



Turn and Slip Indicator

• Indicates direction and approximate rate of turn (needle) and bank and any slipping or skidding in the turn (ball).

• The indexes on either side indicate a rate 1 turn (3 deg/s, 360 deg/2min).

• The ball is controlled by gravity and centrifugal force.


Turn Co-Ordinator

• Reacts to both roll and yaw due to construction.

• The indexes markings indicate a rate 1 turn (3 deg/s, “two min. Turn).

• The ball is controlled by gravity and centrifugal force.

• Can be used to keep the wings level if the AI fails.


Turn Co-Ordinator


Concept Check

1.What do turn and slip indicators and turn coordinators indicate?

2.What controls the position of the ball?

3. What is the difference between the two?



END OF MODULE 2

Module Two: Theory of Flight. In This Module: 789 Lt. R Hampton Gray VC Squadron Ground School 2014...

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Transcript of Module Two: Theory of Flight. In This Module: 789 Lt. R Hampton Gray VC Squadron Ground School 2014...