A-8 Student Handout

STUDENT HANDOUT

147 Part 66 Basic Licensing

Subject A-8: Basic Aerodynamics

Copyright © 2007 Aviation Australia

Unit C1a OH&S

All rights reserved. No part of this document may be reproduced, transferred, sold, or otherwise disposed of, without the written permission of Aviation

Australia.

MEAC01B revised 18/04/232 – PPE

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Subject A-8 Basic Aerodynamics

CONTENTS

Page

Definitions 4

Study Resources 5

Introduction 6

Topic 2 – Basic Aerodynamics 9

Topic 3 – Theory of Flight 15

Topic 4 – Stability 19

Topic 5 – Flight Controls 21

Topic 6 – High Speed Flight 27

Issue A – September 2006 Revision 1 Page 4 of 29


DEFINITIONS

Define

To describe the nature or basic qualities of.

To state the precise meaning of (a word or sense of a word).

State

Specify in words or writing.

To set forth in words; declare.

Identify

To establish the identity of.

List

Itemise.

Describe

Represent in words enabling hearer or reader to form an idea of an object or process.

To tell the facts, details, or particulars of something verbally or in writing.

Explain

Make known in detail.

Offer reason for cause and effect.



STUDY RESOURCES

Jeppesen General

Jeppesen Powerplant

Jeppesen Airframe

Student Handout – Subject 7



INTRODUCTIONThe purpose of this subject is to familiarise you with basic aerodynamics and the theory of flight. It also covers flight controls and conditions which affect the aerodynamics of aircraft

On completion of the following topics you will be able to:

Topic 1 Atmosphere and Airspeed

State the application of the International Standard Atmosphere (ISA) to aerodynamics.

Topic 2 Basic Aerodynamics

Identify airflow around a body and define the following terms: Boundary layer Laminar and turbulent flow Free stream flow Relative airflow Upwash and downwash Vortices Stagnation

Define the following terms and list their interaction with related forces: camber chord mean aerodynamic chord (MAC) profile (parasite) drag induced drag centre of pressure angle of attack wash in and wash out fineness ratio wing shape and aspect ratio

State the relationship between thrust, weight and aerodynamic resultant.

State how lift and drag are generated and define the following associated terms: Angle of attack Lift coefficient Drag coefficient Polar curve Stall

Identify aerofoil contamination including ice, snow and frost.



Topic 3 Theory of Flight

State the relationship between lift, weight, thrust and drag.

Define glide ratio.

Identify steady state flight and define performance.

State the theory of the turn.

Define load factor and define its influence on stalling, flight envelope and structural limitations.

List methods of lift augmentation.

Topic 4 Stability

Define the following types of flight stability (active and passive): longitudinal lateral directional

Topic 5 Flight Controls

Define the operation and list the effects of primary control systems:

roll control (ailerons and spoilers)

pitch control (elevators, stabilators, variable incidence stabilisers and canards)

yaw control and rudder limiters

Define flight control using elevons and ruddervators.

Define the operation and list the effects of high lift devices, slots, slats, flaps and flaperons.

Define the operation and list the effects of: Drag inducing devices (spoilers, lift dumpers and speed brakes) Wing fences and saw tooth leading edges

List methods of boundary layer control: Vortex generators Stall wedges Leading edge devices.

Define the operation and list the effects of the following: Trim tabs Balance and antibalance (leading) tabs Servo tabs Spring tabs Mass balance Control surface bias Aerodynamic balance panels



Topic 6 High Speed Flight

Define the following: Speed of sound Subsonic flight Transonic flight Supersonic flight Mach number Critical mach number Compressibility buffet shock wave aerodynamic heating area rule

State the airflow conditions in engine intakes of high speed aircraft and the factors which affect them.

List the effects of sweepback on critical mach number.



TOPIC 2 – BASIC AERODYNAMICS

BOUNDARY LAYER

This is the layer of air next to the surface of an airfoil where the velocity is slowed by friction due to the air’s viscosity.

Laminar & Turbulent Flow

Laminar flow is flow over a surface in smooth layers and particles do not go from layer to layer. Turbulent flow is random or unsteady flow, creating eddies.

In turbulent flow, air does not remain in layers and particles go from one layer to another


LAMINAR FlOW


The attached laminar flow is located at the forward area of the airfoil, and the separated turbulent flow forms at the rear.

Upper and lower layers merge at the trailing edge and form the wake.

STAGNATION POINT

The stagnation point is the first point of contact of relative airflow, or, the point on the leading edge of an airfoil where the airflow divides, some going over the surface and some going below.

The pressure distribution shows how static pressure varies at different points over the wing.


PRESSURE DISTRIBUTION


PRESSURE & ANGLE OF ATTACK

The angle of attack is between the relative airflow and airfoil chord.

The angle of attack will determine the airfoil centre of pressure (CP).

Increasing the angle of attack moves the CP forwards until the stall when it moves back quickly.

MEAN AERODYNAMIC CHORD MAC

All these wings taper in chord length from root to tip. There will be a mean chord between these two values. One way to define the MAC is to add root chord to tip chord, and divide by 2.



FINENESS RATIO

The fineness ratio is a measure of the thickness of the airfoil.

WASH IN and WASH OUT

condition of rigging in which a wing has an increase in it’s angle of incidence near the tip is called “wash in.”

With “wash out”, the wing has a decrease in it’s angle of incidence near the tip.



INDUCED DRAG

This is the part of the total drag which is caused by the same dynamic factors that create lift. Vortices are formed whose strength depend on the angle of attack.

As airspeed increases INDUCED DRAG decreases because the AoA is reduced.

As airspeed increases, Parasite drag, i.e. FORM DRAG and SKIN FRICTION increases.

AIRFOIL ICING

Icing is detrimental to aircraft performance in two ways, changing the aerodynamic shape, and increasing weight

Rime IceIs a milky type ice similar to that which can be found in a domestic freezer. It is formed on leading edges by immediate freezing on contact, of moisture contained within the air. There is no flow of water.

Glaze IceIs a clear and smooth type ice, formed just below freezing.


http://www.aopa.org/images/asf/topics/ice.jpg%00%E5%A1%B9%EF%92%81%E1%B4%BB%E4%A1%BF%E2%B2%AF%E5%B6%82%E8%97%84%E6%8C%A7%00%00%EA%AE%A5





TOPIC 3 – THEORY OF FLIGHT

CLIMB

In a steady climb, thrust must balance the drag plus a portion of the weight.

So, lift is less than weight Thrust is greater than drag

DESCENT

In a powered descent, thrust may be reduced as gravity supplies some of the energy.

Lift is less than weight. Drag is balanced by the reduced thrust and a part of the weight



GLIDE

In a glide there is no thrust, and the pilot adopts the descent angle that gives the best Lift to Drag ratio (L/D) and the lowest rate of descent.

Glide Ratio = L/D

= Distance Height

Gravity provides all of the energy to remain flying

LOAD FACTOR

During turning manoeuvres, the weight of the aircraft and centrifugal force combine into a resultant which is greater than aircraft weight alone. This additional load imposed on the aircraft wings thereby increases the stress on the wing, which is also felt by the pilot. This is commonly known as “pulling g”.

LOAD FACTOR = TOTAL LIFT WEIGHT

As angle of bank increases, the total lift to achieve the turn rate required without losing altitude or speed must be increased by the pilot increasing the angle of attack. This will increase the Load Factor, and the aircraft pulls more ‘g’

At 60° of bank the lift is doubled and the load factor is 2. The stall speed also increases.



CHANGE OF STALL SPEED WITH WEIGHT

With increases in weight there must be compensation.This is achieved by increasing the angle of attack, this increase in angle of attack in turn increases the total lift of the aircraft. The reverse is true also with the loss of weight. Increased weight increases stall speed.

LIMITATIONS

As load factor increases, the stress on the airframe increases. All aircraft will have “g” limits to avoid damage.

It is also possible that a particular aircraft could be designed to reach its Critical Angle and stall before it reaches a dangerous load factor.

Another structural limitation is Gross Weight.There will always be a maximum weight above which the wings cannot provide enough lift for safe flight.






TOPIC 4 – STABILITY

SWEEPBACK

A wing is swept when the leading edge of the wing angles backward or forward from the fuselage.

These planforms allow high speed flight and promote lateral and directional stability.

LATERAL/DIRECTIONAL DYNAMIC STABILITY

Two modes are possible; Dutch Roll and Spiral Instability

Dutch roll is a complex oscillation combining roll and yaw which can be unstable (gets worse)

Spiral Instability is a result of negative static stability in roll and yawThe aircraft continues to roll and yaw after a disturbance and spirals into a dive

A Yaw Damper is an example of an active stability system used to increase the natural (passive) stability, and reduce Dutch roll.






TOPIC 5 – FLIGHT CONTROLS

CONTROL ABOUT TWO AXES - RUDDERVATORS

A combination of rudder and elevator mounted on a Vee tail which provides simultaneous longitudinal and directional control

Also known as a Butterfly tail.

CONTROL ABOUT TWO AXES - ELEVONS

DELTA WINGS

Elevons provide simultaneous control about the lateral axis and the longitudinal axisi.e. pitch and roll.



AERODYNAMIC BALANCING and TRIMMING

Control forces depend on the airspeed2 and area of surface, The larger and/or faster the aircraft the higher the force required to manoeuvre.

For this reason controls are often balanced to assist the pilots input force during manoeuvres. (Reduce forces)

Trimming however, means removing all control forces during steady flight using a separate control in the cockpit.

AERODYNAMIC BALANCING - HORN BALANCE

A portion of the control surface is extended out ahead of the hinge line. This utilises the airflow about the aircraft to aid in moving the surface.

Although very simple, it does create drag.



AERODYNAMIC BALANCING - BALANCE PANELS

The hinged balance panel moves inside a sealed space ahead of the aileron.

When the aileron is deflected upward, (as seen above) the air over the bottom surface speeds up and produces a low pressure below the balance panel. (Venturi effect)

This low pressure pulls the balance panel down and puts a force on the leading edge of the aileron in such a direction that it assists the pilot in holding the aileron deflected upward. There is no extra drag.

DRAG INDUCING DEVICES

Spoilers & Lift Dumpers

Spoilers are flight controls that raise up from the upper surface of the wing to destroy, or spoil, lift.

Flight spoilers are used at high speed to decrease lift on one wing and roll the aircraft.

As lift dumpers, they are used to destroy the lift of the aircraft after touchdown to aid in slowing the aircraft



Speed Brakes

Speed brakes, also called dive brakes,are large drag panels used for airspeed control.

They can also be used to slow anaircraft after touchdown, and reducethe landing roll.

BOUNDARY LAYER CONTROL

Wing Fences

Boundary layer control devices are designed to delay airflow separation over the wing.

Wing fences are fixed vanes that extend chord wise across the wing of swept wing aircraft.

Their purpose is to prevent air from flowing outward along the span of the wing, for this in turn is likely to cause airflow separation near the wing tips and so lead to tip stalling and pitch-up


WING FENCE

http://www.airforce.dnd.ca/airforce/grfx/equip_gallery/historic_gallery/wallpaper/runway.jpg%00%E5%A1%B9%EF%92%81%E1%B4%BB%E4%A1%BF%E2%B2%AF%E5%B6%82%E8%97%84%E6%8C%A7%00%00%EA%AE%A5


Saw Tooth Leading Edge

Tip separation and stall can also be delayed reduced by introducing a notch or saw tooth in the leading edge.

Each notch generates a strong vortex which controls the boundary layer in the tip region

Vortex Generators

These are small plates or wedges, projecting an inch or so from the top surface of the wing, Each plate generates a vortex adding energy to the boundary layer

The boundary layer travels further along the surface before being slowed up and separating from the wing.


NOTCH

http://www.aerospaceweb.org/aircraft/fighter/javelin/javelin_18.jpg%00%E5%A1%B9%EF%92%81%E1%B4%BB%E4%A1%BF%E2%B2%AF%E5%B6%82%E8%97%84%E6%8C%A7%00%00%EA%AE%A5





TOPIC 6 – HIGH SPEED FLIGHT

MACH NUMBER

The ratio of the speed of the airplane to the speed of sound in the same atmospheric conditions.

True Airspeed = Flight Mach No. Local Speed of Sound M = 1 is called SONIC flow

High speed flight is measured in terms of Mach Number, which is the ratio of the speed of the aircraft to the speed of sound.When the aircraft is flying at Mach •75 it is flying at 75% of the speed of sound at the ambient air temperature.

The Speed of Sound varies with temperature, and the temp varies with altitude.So aircraft reach Mach 1 earlier at higher altitudes.

CRITICAL MACH NUMBER

The flight Mach number at which there is the first indication of sonic airflow, over the wing.

At Mach 0.5 All airflow over the aircraft wing is less than M =1. As the aircraft accelerates, the Flight Mach No. at which the airflow over the wing, (due to the venturi effect), becomes sonic, is known as the Critical Mach Number.



SHOCK INDUCED STALL

Beyond Mcrit, the shock wave grows. Airflow through this region undergoes a sudden static pressure increase.

The effect of the sudden pressure rise is to cause the boundary layer to separate from the wing immediately behind the shock, taking with it the layers of air above it, so precipitating a “Shock Stall”.

The shock wave causes earlyairflow separation. (partial stall)

The “Shock Stall “and the ordinary\ stall, although having different causes have certain points in common:-

A sudden increase in drag often accompanied by compressibility buffeting which increases in intensity with growth of stall, and a loss of lift.

SHOCK INDUCED DRAG

The sudden extra drag which is a marked feature of shock stall, is of the same nature as form drag and skin friction.

Overcoming this sudden drag rise gives rise to the expression, “breaking the Sound Barrier”.


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A-8 Student Handout