ATPL Performance

ATPL

© Atlantic Flight Training

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CHAPTER 1.

Definitions and Abbreviations

Aerodrome Reference Code ...1-1 Definitions ...1-2 Abbreviations ...1-24

CHAPTER 2.

Basic Principles of Flight

Forces on an Aeroplane...2-1 Variation of Coefficient of Lift with Angle of Attack...2-2 Drag ...2-4 Profile Drag ...2-4 Form Drag...2-5 Skin Friction Drag ...2-5 Factors Affecting Skin Friction Drag...2-6 Interference Drag ...2-6 Induced Drag ...2-7 Factors Affecting Induced Drag...2-8 Drag Formula ...2-10 Drag Curves...2-11 Minimum Drag Velocity ...2-12 Effect of Weight on the Drag Curves...2-12 Lift/Drag Ratio ...2-13 Effect of Altitude...2-15 Weight...2-15 Lift/Weight Couple...2-16 Thrust...2-16 Piston Engined Aeroplanes...2-16 The Effects Of Altitude On Engine Performance...2-16 Propeller Aeroplanes...2-18 Jet Engine Aeroplanes ...2-19

CHAPTER 3.

Aerodrome Characteristics

Introduction ...3-1 Aerodrome Reference Code ...3-1 Runway ...3-2 Width...3-2 Declared Distances ...3-2 Take-Off Run Available ...3-3 Clearway ...3-4 Take-Off Distance Available (TODA) ...3-6 Landing Distance Available (LDA) ...3-6 Stopway ...3-6 Runway Alignment ...3-6 Meteorological Data ...3-7 Aircraft Classification Number — Pavement Classification Number (ACN/PCN) ...3-7 Reporting Pavement Bearing Strength...3-8 PCN Reporting...3-8 ACN Reporting...3-10 Overload Operations ...3-10

Runway Strip Strength ...3-11 Runway Contamination ...3-11 JAR Definitions for Runway Contamination ...3-11 Reporting of Contamination ...3-12 Water On A Runway ...3-13 Determination of Friction Characteristics of Wet Paved Runways ...3-13 Snow, Slush Or Ice On A Runway ...3-13 Water Equivalent Depth (WED) ...3-14 Hydroplaning...3-14 Dynamic Hydroplaning ...3-15 Variables that Affect Hydroplaning...3-16 Viscous Hydroplaning ...3-16 Combined Hydroplaning...3-16 Reverted Rubber Hydroplaning...3-16

CHAPTER 4.

Basic Performance – Take-Off

Aerodynamic Forces ...4-1 Variables That Affect the Take-Off...4-3

CHAPTER 5.

Basic Performance – Climb

Basic Aerodynamics...5-1 Forces in a Straight Steady Climb...5-1 Climb Speed ...5-3 Maximum Angle of Climb ...5-3 Maximum Rate of Climb...5-3 Relation between Power and Drag ...5-4 VX and VY...5-5 Climb Performance ...5-6 Ceiling ...5-7

CHAPTER 6.

Basic Performance – Cruise

Forces in the Cruise ...6-1 Variation of Drag ...6-1 Endurance/Range ...6-2 Piston Engined Aeroplanes...6-2 Jet Engined Aeroplanes ...6-3 Range ...6-4 Best Range Speed...6-4 Factors Affecting Range...6-5 Endurance...6-6 Factors Affecting Endurance...6-6

CHAPTER 7.

Basic Performance – Descent

Straight Steady Descent (Dive)...7-1 Steady Glide ...7-2 Forces in a Steady Glide...7-2 Glide Angle ...7-4

The Effect of the Lift/Drag Ratio on Glide Performance ...7-4 The Effect of a Steady Wind on Glide Performance...7-5 The Effect of Weight on Glide Performance...7-5 Summary...7-6

CHAPTER 8.

Basic Performance – Landing

Approach...8-1 Approach Speeds ...8-1 Flap Settings ...8-1 Wind Effect...8-2 Landing Distance ...8-3 Landing Speed...8-4 Weight...8-4 Density ...8-4 CHAPTER 9.

JAR Requirements - General

JAR-OPS 1.470 Applicability...9-1 JAR-OPS 1.475 General...9-1 JAR-OPS 1.475 General...9-2 Take-Off Run Required (TORR) ...9-3 Take-Off Distance Required (TODR) ...9-4 Accelerate Stop Distance (ASD) ...9-5 Aircraft Rotation ...9-7 Balanced Field Operations...9-7 Balanced Take-Off Field Length ...9-8 Contaminated and Wet Runways...9-9 Regulations and Definitions ...9-9 Wet Runways...9-10 Contaminated Runways ...9-11 Optimum Take-Off ...9-11 Reduced Take-Off Thrust...9-12 Assumed Temperature Method...9-12 Noise Abatement ...9-12 Noise Abatement Departure Procedure 1 (NADP 1)...9-13 Noise Abatement Departure Procedure 2 (NADP 2)...9-14 Best Rate of Climb ...9-15 Weight Effect on Optimum and Service Ceiling ...9-15 Buffet Onset Speed...9-16 Buffet Onset Boundary Chart ...9-17 Maximum Altitude ...9-20 Optimum Altitude – Jet Aircraft ...9-20 Rough Air (Turbulence) Speed ...9-20 Terrain Clearance for Performance A Aircraft ...9-21 Service Ceiling ...9-21 Drift Down Procedures ...9-22 En-Route Regulations ...9-24 Payload Versus Range ...9-26

CHAPTER 10.

JAR Performance Class B Aeroplanes

Performance Class B ...10-1 JAR OPS 1 1.525 General ...10-1

Take-Off and Landing Climb ...10-1 Take-off Climb...10-1 Landing Climb ...10-2 JAR OPS 1.530 Take-Off ...10-2 JAR OPS 1.535 Take-Off Obstacle Clearance – Multi Engined Aeroplanes...10-4 Take-Off Flight Path - Visual Course Guidance Navigation ...10-4 Safe Operation With Performance Class B Aeroplanes In Conditions Of Limited Visibility...10-4 Take-Off Flight Path Construction...10-6 JAR-OPS 1.540 - En-Route - Multi-Engined Aeroplanes ...10-6 JAR-OPS 1.542 - En-route - Single-Engine Aeroplanes ...10-7 JAR-OPS 1.545 - Landing - Destination And Alternate Aerodromes ...10-7 JAR-OPS 1.550 - Landing - Dry Runway ...10-7 Steep Approach Procedures ...10-8 Short Landing Operations ...10-8 Landing Distance Correction Factors...10-9 Runway Slope...10-9 Landing - Dry Runway...10-9 JAR-OPS 1.555 - Landing - Wet and Contaminated Runways ...10-10 Landing on Wet Grass Runways...10-10

CHAPTER 11.

JAR Performance Class A Aircraft

Performance Class A ...11-1 JAR-OPS 1.485 – General...11-1 General - Wet and Contaminated Runway Data (JAR – 25 AMJ 25X1591)...11-1 Operation on Contaminated Runways ...11-1 JAR-OPS 1.490 - Take-Off ...11-2 JAR-OPS 1.495 - Take-Off Obstacle Clearance ...11-2 JAR-OPS 1.500 - En-Route - One Engine Inoperative ...11-5 JAR-OPS 1.505 - En-route - Aeroplanes with Three or More Engines, Two Engines Inoperative ...11-6 JAR-OPS 1.510 - Landing - Destination and Alternate Aerodromes...11-6 JAR-OPS 1.515 - Landing - Dry Runways ...11-7 Steep Approach Procedures ...11-8 JAR-OPS 1.520 - Landing - Wet and Contaminated Runways ...11-8

CHAPTER 12.

JAR Performance Class A Aircraft

JAR 25.101 General...12-1 JAR 25.105 Take-off ...12-1 JAR 25.107 Take-off Speeds ...12-2 JAR 25.109 Accelerate-Stop Distance...12-3 JAR 25.111 Take-Off Path ...12-4 The Net Flight Path ...12-5 JAR 25.113 Take-off Distance And Take-off Run ...12-6 JAR 25.115 Take-off Flight Path ...12-7 JAR 25.119 Landing Climb: All-Engines-Operating ...12-7 JAR 25.121 Climb: One-Engine-Inoperative ...12-8 Take-off; landing gear extended ...12-8 Take-off; landing gear retracted ...12-8 Final take-off ...12-9 Approach...12-9 JAR 25.123 En-route Flight Paths...12-9

CHAPTER 13.

JAR Performance Class C Aircraft

JAR-OPS 1.560 - General...13-1 JAR-OPS 1.565 - Take-Off ...13-1 JAR-OPS 1.570 - Take-Off Obstacle Clearance ...13-2 JAR-OPS 1.580 - En-Route - One Engine Inoperative ...13-3 JAR-OPS 1.585 - En-Route - Aeroplanes with Three or More Engines, Two Engines Inoperative..13-3 JAR-OPS 1.590 - Landing - Destination and Alternate Aerodromes...13-4 JAR-OPS 1.595 - Landing - Dry Runways ...13-4 Landing Distance Correction Factors...13-5 JAR-OPS 1.600 - Landing - Wet and Contaminated Runways ...13-5

Chapter 1.

Definitions and Abbreviations

This book is intended to help you study for the JAR-FCL ATPL Performance examination. In this chapter you will find the definitions and abbreviations you require for the course.

A public transport aircraft should proceed safely from departure to destination. The engine and airframe design should ensure that:

¾ It has sufficient power and manoeuvrability for all stages of flight, and ¾ It should be filled with sufficient fuel, including adequate reserves. Fuel considerations are dealt with in Flight Planning. Our concern is with:

¾ Power

¾ Manoeuvrability, and

¾ Performance planning

We shall not concern ourselves with the fuel and time required for the various stages of flight, but solely with the space each stage requires. The object of the performance plan is to ensure that, in every situation, the space required does not exceed the space available; further, that progress is safe whether no incident occurs or whether an incident such as an engine failure occurs at any critical stage of the flight.

Aerodrome Reference Code

All airfields have an aerodrome reference code number and letter which is determined in accordance with the characteristics of the aeroplane for which an aerodrome facility is intended.

Code Number The code number is selected corresponding to the highest value for the aeroplane reference field length of the aeroplanes for which the runway is intended. The aeroplane reference field length is for the selection of the code number and is not intended to influence the actual runway length provided.

Code Letter The code letter is determined by selecting the code letter that corresponds to the greatest wing span or the greatest outer main gear wheel span whichever gives the more demanding code letter of the aeroplane for which the facility is intended.

Code Element 1 Code Element 2 Code Number Aeroplane

Reference Field Length

Code Letter Wing Span Outer Main Gear Wheel Span*

1 Less than 800 m A Up to but not

including 15 m Up to but not including 4.5 m

2 800 m up to but

not including 1200 m

B 15 m up to but not

including 24 m 4.5 m up to but not including 6 m

3 1200 m up to

but not including 1800 m C 24 m up to but not including 36 m 6 m up to but not including 9 m 4 1800 m and

over D 36 m up to but not including 52 m 9 m up to but not including 14 m

E 52 m up to but not

including 65 m 9 m up to but not including 14 m * Distance between the outside edges of the main gear wheels

Definitions

Accelerate/Stop Distance (ASD) The distance an aeroplane takes to accelerate to V1 and brake safely to a halt in the prevailing conditions.

Accelerate/Stop Distance Available (ASDA) See declared distances

Accelerate/Stop Distance Required (ASDR) The calculated distance required for an aircraft to accelerate to V1 and brake to a halt. This figure is calculated from the

aeroplane flight manual and always allows for a factored safety margin.

Aerodrome Elevation

Aerodrome Operating Minima

Landing in precision approach and landing operations, expressed in terms of visibility and/or RVR and DA/DH as appropriate to the category of the operation, and

Landing in non-precision approach and landing operations, expressed in terms of visibility and/or RVR, MDA/MDH and, if necessary, cloud conditions Aerodrome Reference Field Length The minimum field length required for take-off at maximum certificated take-off mass, sea level, standard atmospheric conditions, still air and zero runway slope, as shown in the appropriate aeroplane

flight manual prescribed by the certificating authority or equivalent data from the aeroplane manufacturer. Field length means balanced field length for aeroplanes, if applicable, or take-off distance in other cases

Aerodrome Reference Point The designated geographical location of the aerodrome

Aerodynamic Definitions

Thrust Drag

Weight Lift

Drag The force that opposes thrust

Induced Drag The amount of drag caused by the movement of an aerofoil

Profile Drag The amount of drag caused by: ¾ The aerofoil shape

¾ The boundary layer surface friction ¾ Streamlining of the aircraft

Lift The force acting on an aerofoil which is at right angles to the airflow (acting upwards).

Thrust The force produced by the aeroplane power units acting in a forwards direction

Aeroplane A power-driven heavier than air aircraft, deriving its lift in flight chiefly from aerodynamic reactions on surfaces which remain fixed under given conditions of flight.

Aircraft – Category Classification of aircraft according to specified basic characteristics eg aeroplane, helicopter, glider, free balloon

Aircraft Certified For Single-Pilot Operation A type of aircraft which the State of Registry has determined, during the certification process, can be operated safely with a minimum crew of one pilot

Airspeed

Indicated Airspeed (IAS) The airspeed of an aircraft as shown on its pitot-static airspeed indicator (ASI), that provides vital airspeed information, e.g. stalling and structural limitation airspeeds, to the flight-crew. It is calibrated to reflect standard atmospheric adiabatic compressible flow at sea level, and is uncorrected for airspeed system errors.

Calibrated Airspeed (CAS) The Indicated airspeed of an aircraft corrected for position and instrument errors. CAS is equal to the True Airspeed (TAS) in standard atmosphere at sea level only.

Equivalent Airspeed (EAS) The calibrated airspeed of an aircraft corrected for compressibility error at a particular altitude. EAS is equal to IAS at airspeeds less than 300 knots, and is equal to TAS in standard atmosphere at sea level only.

True Airspeed (TAS) The actual speed of an aircraft through the air relative to the air that is uninfluenced by the aircraft. TAS is important for navigation purposes only. The relationship between EAS and TAS is as follows:

TAS = EAS (ρo / ρ )½

where ρo = density at sea level

ρ = density at altitude

Mach Number The ratio of the TAS of an aircraft to the speed of sound in the surrounding atmosphere, i.e. the local speed of sound (LSS). Mach No = TAS / LSS

All Up Weight (AUW) The total weight of an aeroplane including: ¾ Fuel

¾ Crew ¾ Payload

Alternate Aerodrome An aerodrome to which an aircraft may proceed when it becomes either impossible or inadvisable to proceed to or land at the aerodrome of intended landing. Alternate aerodromes include the following:

Take-off Alternate An alternate aerodrome at which an aircraft can land should this become necessary shortly after take-off and it is not possible to use the aerodrome of departure.

En-route Alternate An aerodrome at which an aircraft would be able to land after experiencing an abnormal or emergency condition while en-route. Destination Alternate An aerodrome to which an aircraft may proceed should it become impossible or inadvisable to land at the aerodrome of intended landing.

Note: The aerodrome from which a flight departs may also be an en-route

or a destination alternate aerodrome for that flight.

Altitude The vertical distance of a level, a point or an object considered as a point measured from mean sea level (MSL).

Approach/Climb Speed The recommended speed for the initial climb after a missed approach is initiated at or above DH. For the situation where the critical power unit is inoperative at MLM and the configuration achieved 15 seconds after initiation (undercarriage up) the aeroplane will be able to maintain the climb gradient required:

Class A

Twin Engined Aeroplane 2.1%

Three Engined Aeroplane 2.4%

Four Engined Aeroplane 2.7%

The speed must not exceed 1.5VS.

Aquaplaning Speed Hydroplaning speed. The speed where a loss of directional control on the ground is caused by a decrease in surface friction due to contaminant on the surface of the runway.

Balanced Field Length Where ASDA equals TODA then it is accepted that the aerodrome has a balanced field length.

Basic Weight The weight of an aircraft and: ¾ All basic equipment

¾ Plus the declared quantity of unusable fuel and oil

Buffet Speed The speed where the aerodynamic airflow over the airframe becomes turbulent and causes vibration in the airframe

Calibrated Airspeed or Rectified Airspeed (RAS) Rectified Air Speed, sometimes known as Calibrated Air Speed (CAS) is IAS corrected for Position and Instrument Error. RAS will equal TAS (True Air Speed) in calibration conditions, sea level temperature +15°C,with pressure 1013.25mb.

Ceiling Split into two definitions:

Absolute Ceiling The pressure altitude where the rate of climb is zero Service Ceiling The pressure altitude where the rate of climb is a defined value:

Jet Engined Aeroplanes 500 fpm (2.5 m/s)

Propeller Driven Aeroplanes 100 fpm (0.5 m/s)

Net Ceiling A artificial figure devised for aircraft safety reasons:

Jet Aircraft 750 fpm

Propeller/Piston Aircraft 150 fpm

The propulsion system and altitude of an aircraft affects an aircraft’s maximum speeds

Clearway A defined rectangular area on the ground or water under the control of the appropriate authority, selected or prepared as a suitable area over which an aeroplane may make a portion of its initial climb to a specified height. The clearway is beyond TORA in the direction of the extended centre line. The first non-frangible obstacle that can endanger an aeroplane in flight restricts the length of the clearway. The clearway cannot exceed 50% of the TORA.

UK The Clearway has a starting semi-width of half the runway strip at the

end of TORA. This expands to 90 m for Code 3 and 4 aerodromes forming a triangular shaped area

ICAO The semi-width is rectangular

Climb Gradient Change in height %

Horizontal distance travelled

Critical Power Unit(s) The power unit(s) failure of which gives the most adverse effect on the aircraft characteristics relative to the case under consideration

D Value This value is the equivalent dry, level, hard surface, still air values of the field lengths when compared accounting for:

¾ Surface condition TORA 90m 90 m Clearway 75m 75 m Clearway

TORA

¾ ACS packs

¾ Runway slope

¾ Wind component

¾ Airworthiness factors

Decision Altitude (DA) or Decision Height (DH) A specified altitude or height in the precision approach at which a missed approach must be initiated if the required visual reference to continue the approach has not been established

Note: DA is referenced to mean sea level, DH is referenced to threshold elevation

Note: The required visual reference means that section of the visual aids or of the approach area which should have been in view for sufficient time for the pilot to have made an assessment of the aircraft position and rate of change of position, in relation to the desired flight path. In Category III operations with a DH the required visual reference is that specified for the particular procedure and operation

Decision Speed (V1) The pilot’s decision to continue or abandon take-off after an engine future will be based on AUW and field lengths. The most direct way of identifying the transition from the “must stop” to the “must continue” situation is a

reading on the ASI. V1 is that speed. Account must be taken for the time delay

between the failure and the pilot’s recognition of it and response to it. Should an engine failure occur at such a time that the pilot can respond below V1 the take-off

must be abandoned. Should the failure occur at such a time that when it is

recognised, the speed is above V1, the take-off must be continued. A Group A

aeroplane is capable of continuing the take-off safely above V1 on the remaining

engines even if they give only net (1 engine inoperative) performance. To summarise:

¾ Engine failure recognised below V1 STOP

¾ Engine failure recognised above V1 CONTINTUE.

¾ Only at exactly V1 is there choice.

V1 is never less than VEF plus the speed increase after an engine failure to the point

where a pilot applies the first means of retardation. The airspeed at the decision point will never be less than VMCG or greater than VR

Declared Distances

Take-Off Run Available (TORA) The length of runway declared available and suitable for the ground run of an aeroplane. The runway having the following uniform characteristics in:

¾ Braking coefficient

¾ Slope

The runway must also be free of non-frangible obstacles.

Take-Off Distance Available (TODA) The declared distance available for an aeroplane to take-off and attain screen height. TODA can comprise of TORA plus clearway. TODA is limited to 1.5 x TORA or to the first non-frangible obstacle liable to damage the aeroplane during a take-off, whichever is the shorter.

Accelerate-Stop Distance Available (ASDA) The length of the take-off run available plus the length of the stopway, if provided. This is the total distance for the aeroplane to accelerate to V1, abandon take-off and to brake

safely. Can be referred to as Emergency Distance Available (EMDA)

Landing Distance Available (LDA) The length of the runway which is declared available and suitable for the ground run of an aeroplane landing. The area has to:

¾ Be free of all non-frangible obstacles ¾ Have uniform characteristics for the:

¾ Slope

¾ Bearing strength

¾ Braking coefficient

The LDA starts at the runway threshold and continues for the length of the runway. Where there is a displaced threshold then the LDA may be less than the physical length of the runway.

Density Altitude The height in ISA which has a density corresponding to the actual density at a specified location. This can also be taken as the pressure altitude corrected for temperature.

Design Minimum Weight The lowest weight that an aeroplane complies with the structural safety requirements necessary for safety

Design Maximum Weight The highest of the weights below at which an aeroplane complies with the structural requirements.

Design Take-Off Weight For taxiing or landing

Design En-Route Weight For conditions other than take-off or landing Design Landing Weight For landing at the maximum velocity of descent

Elevation The vertical distance of a point on or affixed to the surface of the earth, measured from mean sea level

Empty Weight Specified in the flight manual the empty weight includes:

¾ Fixed ballast ¾ Unusable fuel ¾ Undrainable oil ¾ Engine coolant ¾ Hydraulic fluid ¾ Potable water ¾ Lavatory chemicals It excludes: ¾ Fuel ¾ Crew ¾ Payload

Other terms used are Dry Operating Weight or Aircraft Prepared for Service Weight (APS)

Equivalent Air Speed (EAS) Most ASIs are calibrated for an ideal incompressible

air flow (½ρv2). As compression affects all speeds EAS is RAS corrected for

compressibility

Extended Range Twin Operations (ETOPS)

Adequate Aerodrome An adequate aerodrome is an aerodrome which the operator of the aircraft considers to be adequate. In particular it should be expected that at the anticipated time of use:

¾ The aerodrome will be available, and equipped with necessary ancillary services. such as ATC, sufficient lighting, communications, weather reporting, navigation aids, and safety cover, and

¾ At least one letdown aid (ground radar would so qualify) will be available for an instrument approach.

Aerodrome In general terms, an operator may make an appraisal that an aerodrome has long enough runways, and is sufficiently equipped, to be considered adequate for his planned ETOPS routes. The commander must satisfy himself on the day, using criteria provided by the operator, that he has sufficient adequate aerodromes which, taking into account the weather and any equipment unserviceabilities, are suitable for his intended operation.

Extended Range Operations (ETOPS) Extended range operations are those operations intended to be, or actually, conducted over a route that contains a point further than one hour's flying time (in still air) at the normal one-engine-inoperative cruise speed from an adequate aerodrome. When, alternatively, a Threshold Distance has been agreed with the Authority, all non-ETOPS flights shall remain within the Threshold Distance of an adequate aerodrome.

ETOPS Segment The portion of an ETOPS flight that begins when the aeroplane is first more than Threshold Distance from any adequate aerodrome and ends when the aeroplane is last more than Threshold Distance from any adequate aerodrome.

Rule Distance The distance travelled in still air in the Rule Time, at the normal one-engine Inoperative cruise speed.

Rule Time The maximum diversion time that any point on the route may be from a suitable aerodrome for landing, as specified by the Authority and included in the Operations Manual.

Suitable Aerodrome A suitable aerodrome is an adequate aerodrome where at the anticipated time of use weather reports or forecasts, or any combination thereof indicate that the weather conditions are very likely to be at or above the normal operating minima at the time of the intended operation.

A particular aerodrome may be considered to be a suitable aerodrome for flight planning and dispatch purposes for extended range operations if it meets the criteria below:

Single ILS/MLS, or PAR

¾ Cloudbase of 600 feet and a visibility of 3 km (2 statute miles), or ¾ A cloudbase of 400 feet and a visibility of 1.5 km (1 statute mile)

above the lowest authorised landing minima; whichever is higher. Non-precision and circling approaches (including SRA)

¾ Cloudbase of 800 feet and a visibility of 3 km (2 statute miles) or ¾ A cloudbase of 400 feet and a visibility of 1.5 km (1 statute mile)

above the lowest authorised landing minima: whichever is higher.

Two or more ILS/MLS/PAR to separate runways

¾ Where forecast wind and surface conditions indicate that two or more separate runways will be available within the Rule Distance, whether at one or more airfields, the relevant Planning Minima cloudbase may be reduced by 200 feet and the visibility by 1 km (1/2 statute mile).

Threshold Distance The distance travelled in still air in 60 minutes by an aircraft at the normal one-engine-inoperative cruise speed.

Final Take-Off Speed The speed of the aeroplane at the end of the take-off path with the aircraft in en-route configuration with one engine inoperative and all other engines at maximum continuous power

Flap Extended Speed The maximum speed with the wing flaps in a set extended position

Flight Level A surface of constant atmospheric pressure which is related to a specific pressure datum, 1013.2 hPa and is separated from other surfaces by specific pressure intervals.

Note: A pressure type altimeter calibrated in accordance with the Standard Atmosphere:

¾ When set to a QNH altimeter setting, will indicate altitude

¾ When set to a QFE altimeter setting, will indicate height, above the

QFE reference datum

¾ When set to a pressure of 1013.2 hPa may be used to indicate flight

levels.

Note: The terms “height” and “altitude” used in the above note, indicate altimetric rather than geometric heights and altitudes.

Frangibility The ability of an object to retain its structural integrity and stiffness to a specific maximum load but when subject to a load greater than specified or struck by an aircraft will break, distort or yield in such a manner as to present minimum hazard to an aeroplane

Gross Height This is the average height reached by an average aeroplane flown by an average pilot. The height is reduced for safety reasons to obtain net height. The reduction is specified by the JAA and is dependent on the phase of flight

Gross Flight Path (GFP) The path of an aeroplane after reaching the end of the TODR. GFP is calculated using Gross Performance Data (see below) and ends at the same horizontal distance from the take-off point as the Net Flight Path

Gross Performance The average performance that a fleet of aeroplanes should achieve so that any aeroplane has a 50% chance of exceeding that level of performance at any time

Gross Weight The total weight of an aeroplane at the commencement of the take-off run

Ground Effect The effect of downwash is reduced when an aeroplane’s height is within one wingspan of the ground. The angle of attack (AOA) reduces which in turn increases the lift produced. This is “ground effect”

Height The vertical distance of a level, a point or an object considered as a point, measured from a specified datum (NOT msl).

Hydroplaning Speed See Aquaplaning Speed

Indicated Airspeed Indicated air speed is the ASIR corrected for instrument error due to imperfections in manufacture. The aircraft is flown on IAS International Standard Atmosphere, Pressure Settings and Related Matters Based on the International Standard Atmosphere for dry air (ICAO 1964):

¾ At mean sea level pressure 1013.25

¾ Temperature 15°C

¾ From msl to 11 km decrease in temperature 6.5°C/km

¾ From 11 km to 20 km isothermal temperature -56.5°C

¾ From 20 km to 32 km a rise in temperature of about

1°C/km

Landing Approach Speed The CAS in the landing configuration that is maintained to a screen height of 50ft during a stabilised approach. The speed is not less than 1.3VS for any practicable landing weight

Landing-Climb Speed The recommended speed for the initial climb out after a baulked landing. The speed assumes that the aeroplane achieves a minimum gross gradient of climb of 3.2% where:

¾ All power units operative

¾ The aeroplane is in the landing configuration ¾ Power is obtained 8 seconds after initiation

The speed is:

¾ Never less than VMCL, and

¾ Must not exceed the greater of VMCL or 1.3VS

The speed is calculated from AUW and flap setting for landing. The speed is:

Four Engined Aeroplanes 1.15VS

All other Class A Aeroplanes 1.2VS

Landing Gear Extended Speed The maximum speed that an aeroplane can fly with the landing gear extended

Landing Gear Operating Speed The maximum speed that the landing gear can be operated

Landing Weight The gross weight of an aeroplane on landing including all contents but taking into account the expected usage of fuel and oil during the flight to the destination or alternate

Mach Number The ratio of the true airspeed to the local speed of sound Mass The quantity of matter in a body. It determines the force exerted on that body by gravity which is inversely proportional to the mass.

Maximum Brake Energy Speed (VMBE) The maximum speed on the ground from which an aeroplane can be safely stopped within the capabilities of the brakes. This speed may limit V1.

Maximum Landing Weight The highest permissible weight of an aeroplane plus contents on landing. This weight takes into account all regulations, requirements and structural limitations

Maximum Level Off/Height Referred to as the “5 minute point” as this is normally a time limit of 5 minutes from the start of take-off. It is the height where the aircraft must be levelled off to enable it to accelerate and for the flaps to be retracted thus a maximum time limit is imposed on the use of take-off thrust

Maximum Take-Off Weight The maximum take-off weight is the highest permissible weight of an aeroplane including all contents

Maximum Total Weight Authorised (MTWA) For take-off the maximum total weight of an aircraft and contents in accordance with the C of A in the most favourable circumstances anywhere

Maximum Operating Speed/Mach Number (VMO/VMO) This speed must not be deliberately exceeded in any flight condition. The speed has a safety net built in, allowing for minor deviations, which ensures the aeroplane remains free from problems such as buffet or other compressibility effects.

Maximum WAT (Weight, Altitude, Temperature) Limit Weight The highest weight at which all relevant climb minima are achieved

Maximum Weight The lowest of the three weights: ¾ The maximum take-off weight

¾ The maximum weight at which flight other than take-off and landing is permitted

¾ The maximum landing weight (other than an emergency situation)

Maximum Zero Fuel Weight The maximum weight of an aeroplane less the usable fuel that structural limits allows

Measured Performance The average performance of one aeroplane or group of aeroplanes undergoing test conditions

Minimum Control Speed (VMC) The lowest CAS at maximum take-off power that if a critical power unit fails then the aeroplane is controllable within the following limits:

Heading 20° of the original heading

Bank Angle 5° maximum

The speed is always greater than VMCG and not more than 1.2 VS.

Minimum Control Speed on the Ground (VMCG) With engines at maximum take-off power if a critical power unit fails then the following conditions apply using normal piloting skills:

¾ The aeroplane can be steered by the use of aerodynamic means ¾ Nosewheel steering is not used

¾ The aeroplane maintains a parallel path not more than 30 feet from the original path.

Minimum Control Speed on the Approach to Land (VMCL) The lowest speed on the approach to land with all power units operative. The speed is obtainable at all power settings. The speed is such that if a critical power unit fails it is possible to maintain control using no more than 5° bank and continue the approach safely.

One Engine Inoperative - Minimum Control Speed on the Approach to Land (VMCL1) The lowest speed on the approach to land with one power unit inoperative. Straight flight should be maintained using no more than 5° bank and the approach continued safely.

Two Engines Inoperative - Minimum Control Speed on the Approach to Land (VMCL2) The lowest speed on the approach to land with two power unit inoperative for three and four engined aeroplanes. Straight flight should be maintained using no more than 5° bank and the approach continued safely.

Minimum Take-Off Safety Speed (V2min) The minimum speed that V2 is in

terms of CAS. It is never less than: 1.2 VS for

¾ Two or three engined turbo-prop aeroplanes

¾ Turbo-jet aeroplanes without the provision for obtaining a significant reduction in the one-engine inoperative power-on stalling speed

1.15 VS for

¾ Turbo-prop aeroplanes with more than 3 engines

¾ Turbo-jet aeroplanes with the provision for obtaining a significant reduction in the one-engine inoperative power-on stalling speed And

1.1 VMC

Nautical Mile ICAO define the nautical mile as 1852 m. This can also be taken as 6080 ft.

Net Flight Path (NFP) The path of an aeroplane from the end of the TODR until 1500 ft net height above reference zero. NFP is calculated using net performance data

Net Height The gross height reduced by a specified amount for safety reasons. This height is used to determine the compliance with obstacle clearance requirements

Net Performance The gross performance reduced by a set margin. This is set by the Authority.

Obstacle All fixed (whether temporary or permanent) and mobile objects, or parts thereof that are located on an area intended for the surface movement of aircraft or that extend above a defined surface intended to protect aircraft in flight

Obstacle Clearance Altitude (OCA) or Obstacle Clearance Height (OCH) The lowest altitude or the lowest height above the elevation of the relevant runway threshold or the aerodrome elevation as applicable, used in establishing compliance with appropriate obstacle clearance criteria

Note: OCA is referenced to mean sea level and OCH is referenced to the aerodrome elevation or to the threshold elevation if that is more than 2 m (7ft,) below the aerodrome elevation. An OCH for a circling approach is referenced to the aerodrome elevation

Obstacle Elevation/Height The vertical distance of the uppermost point of any non-frangible obstacle. When an elevation is given then the reference is MSL. Where height is given then it is referenced to the Ordnance Datum

Ordnance Datum The horizontal plane that passes through a point on the surface of a particular runway at the centre of the end of TODA. This datum was used to calculate the height of obstacles promulgated in the AIP

Practicable Landing Weight The empty weight plus fuel for a 100 nm diversion plus 30 minutes hold with minimum flight and cabin crew plus 10% of payload

Pressure Altitude The height in the International Standard Atmosphere where the prevailing pressure occurs. The altimeter is set to 1013.2 hPa. Where altitude is used in Performance Charts then this means “pressure altitude”

Pressure Settings The following are the most likely pressure settings that a pilot will encounter:

QFE is air pressure reduced to the datum level of the airport applying corrections for the outside air temperature.

QNH

is QFE reduced to mean sea level using the assumed conditions of

QFF

is QFE reduced to mean sea level with regard to the actual outside

Reference Landing Speed (VREF) The speed in the landing configuration at screen height which is used to calculate the landing distance

Reference Zero (RZ) The imaginary plane passing through a point 35 ft or 50 ft vertically beneath the aeroplane at the end of the TODR. This point is used to reference heights on the take-off flight path

Required Navigation Performance (RNP) A statement of the navigation performance accuracy necessary for operation within a defined airspace. The aircraft remains within the specified distance for 95% of the time of flight

Rotation Speed (VR) If the transition from the take-off run to becoming airborne is to be carried out in the optimum manner, it must be made at the correct speed. Dragging the aeroplane into the air at too low a speed (not necessarily a dangerous one) or holding it down until it fights to leave the ground will both detract from the performance standard. VR is the speed at which the pilot should initiate a

change in attitude with the intention of leaving the ground. It varies with weight and flap setting, and may also be affected by altitude and temperature. It is set at a value

which ensures that the aeroplane becomes airborne and achieves V2 (defined below)

by the screen height. V1 must not exceed VR, but may equal it. VR is never less than

V1 or 1.05VMC. The exact value depends upon:

¾ TOW

¾ Flap setting

¾ Pressure altitude

¾ Temperature

Runway End Safety Area (RESA) An area symmetrical about the extended runway centre line and adjacent to the end of the strip primarily intended to reduce the risk of damage to an aeroplane undershooting or overrunning the aerodrome Runway Strip An area of specified dimensions enclosing a runway intended to reduce the risk of damage to an aircraft running off the runway and to protect aircraft flying over it when taking-off and landing

Screen Height The height of an imaginary screen which the aeroplane would just clear when taking off or landing in an unbanked attitude with landing gear extended.

Slush Water-saturated snow which with a heel-and-toe slap down motion against the ground will be displaced with a splatter; Specific Gravity: 0.5 up to 0.8 Snow (On the ground)

Dry Snow Snow which can be blown if loose or, if compacted by hand, will fall apart again upon release

Specific Gravity Up to but not including 0.35

Wet Snow Snow which, if compacted by hand, will stick together and tend to form a snowball

Compacted Snow Snow which has been compressed into a solid mass that resists further compression and will hold together or break up into lumps if picked up

Specific Gravity 0.5 and over

Stabilising Altitude With one engine inoperative, the maximum altitude that a multi engine aeroplane can maintain level flight

Standard Pressure Setting (SPS) The altimeter sub-scale setting 1013.2 hPa Stopway A defined obstacle free rectangular area on the ground at the end of TORA the same width as the associated runway prepared as a suitable area in which an aeroplane can be stopped in the case of an abandoned take-off. The area is prepared so that the aeroplane can roll without hazard to occupants or structural damage. The following characteristics are similar to the runway:

¾ Braking coefficient

¾ Strength ¾ Slope

Stalling Speeds For all the speeds below the stalling speed is also the minimum steady flight speed when no stalling speed is obtainable.

VS Calibrated stalling speed that is not less than 94% of the speed at

which an aeroplane develops lift equal to its weight for a given configuration. If no stall is obtainable then this is the minimum steady flight speed where the aeroplane remains controllable

VSO The stalling speed with flaps in the landing position

VS1 The stalling speed with the aeroplane in a set configuration under

consideration

VS1g The stalling speed with the aeroplane in a given configuration

VMS The lowest possible stalling speed taking for any combination of AUW and atmospheric conditions with the power at idle. The speed is where pitching or rolling motion occurs that is not immediately controllable

VMS0 The lowest stalling speed, or minimum steady flight speed if no stall is obtainable, when the flaps are in the land setting. This is for any combination of AUW and meteorological conditions

VMS1 The lowest possible stall speed for the configuration under consideration using the conditions above.

VSR Reference stalling speed

VSR0 Reference stalling speed in the landing configuration VSR1 Reference stalling speed in a given configuration VSW The speed where natural or artificial stall warning occurs

Take-Off Distance (TOD) The distance an aeroplane takes to accelerate from the brake release point (BRP) to VR and then climb to screen height

Take-Off Distance Required (TODR) The calculated distance that an aircraft takes to take-off and attain screen height. This figure is calculated from the flight manual and has safety factors inbuilt.

Take-Off Run (TOR) The distance an aeroplane takes to accelerate from the BRP to VLOF

Take-Off Run Required (TORR) The calculated distance required to complete the TOR factored for safety by a specific percentage. The distance is calculated from the flight manual for the specific meteorological conditions and aircraft configuration Take-Off Safety Speed (V2) If the aeroplane is rotated correctly at VR it

will unstick shortly thereafter and climb away. V2 is the minimum speed to which the

aeroplane should accelerate by the screen height with one engine inoperative. Like VR it is determined primarily by AUW and flap setting. It is the speed used widely in

the determination of take-off performance and is linked to VR. We shall see later that

there are occasions when by increasing V2 above “normal”, we may obtain better

performance in the NFP. To achieve the higher V2 we must also increase VR,

lengthening TORR.

Take-Off Weight (TOW) The weight of an aeroplane at the commencement of the take-off. This is the gross weight at this time.

Target Threshold Speed (VAT) The speed at which a pilot aims to cross the threshold in order to land the aeroplane. This speed is an average calculated for light winds and slight turbulence and is determined by AUW and flap setting. The related speeds may also be used:

VAT0 All power units operative This speed is not less than:

¾ VMS1 + 22 knots or 1.3 VMS0

¾ The minimum demonstrated threshold speed + 5 knots

¾ The final steady approach speed – 10 knots ¾ 1.08 x the pre-stall buffet speed in steady flight VAT1 One power unit inoperative

This speed is not less than: ¾ VAT0

¾ VMCL + 5 knots where the critical power unit is

inoperative

¾ VMCL where two power units are inoperative for

three or four engined aeroplanes

¾ The final steady approach speed – 10 knots where the critical power unit is inoperative

VAT2 Two power units inoperative

VTmax The maximum safe threshold speed. The speed is used to check that the performance calculations are within the landing field requirements. The speed is VAT0 plus a set figure (most aircraft use 15 knots).

Where this speed is exceeded it is possible that the required field length will exceed the LDA.

VTmin The minimum safe threshold speed. The lowest approach

speed to be maintained at or before the threshold is reached. VTmin is the

higher figure of VIMD + 5 knots or VS1g + 20%.

Traffic Load The total weight (including non-revenue load) of: ¾ Passengers

¾ Baggage ¾ Cargo

True Airspeed The EAS corrected for density error

Unaccelerated Flight Flight at a constant speed where there is no acceleration in any plane.

Unbalanced Field Length Where ASDA and TODA are different lengths for a particular runway direction then it is considered to be an Unbalanced Field Length Unstick Speed See VLOF.

VMU The lowest possible unstick speed for any combination of AUW and atmospheric conditions. At and above this speed, with all power units operative, the aeroplane can leave the ground and climb safely to screen

height. A 5 knot margin between the lowest nose wheel raising speed and VR

is accepted as normal.

VUS The same as VLOF. The speed where the wheels leave the ground if

the aeroplane is rotated at VR.

V3 The steady initial climb speed with all engines operating, that has to be

achieved by screen height. It is never less than V2 + 10 knots

V4 The steady take-off climb speed with all engines operative using the

scheduled techniques and achieved by 400 ft gross height. It is never less than VMCA

or 1.3 VMS1. The gross flight path does not drop below the gross flight path from which

the net flight path is calculated.

V5 Sometimes used as the one-engine inoperative en-route climb speed

VA Design manoeuvring speed

VB Design speed for maximum gust intensity

VC Design cruise speed VD Design dive speed

VDD Design drag devices speed

VEF Used in performance calculations. The calibrated speed at which it is assumed that the most critical power unit fails. It is never less than VMCG

VF Design flap speed. It is not less than:

¾ 1.6 VS1 at maximum TOM with take-off flap selected

¾ 1.8 VS1 at MLM with approach flap selected

¾ 1.8 VS0 at MLM with land flap selected

VFE Maximum speed to fly safely with flap extended

VFTO Final take-off speed This is the speed of the aeroplane at the end of the take-off path in the fourth segment of a four segment net flight path, where one power unit is inoperative. The remaining engines are set at maximum continuous in the en-route configuration. For aeroplanes the following applies:

Speed Climb Gradient

Twin engined 1.25VS 1.2%

Three engined 1.25VS 1.5%

Four engined 1.25VS 1.7%

VGO The lowest V1 from which a continued take-off is possible within the

TODA

VIMD Minimum drag speed This is the speed achieved at the lowest point of the total drag curve.

VIMP Minimum power speed The speed achieved at the lowest point on the power curve.

VLE The maximum speed that an aeroplane can be safely flown with the landing

gear extended

VLO The maximum speed that landing gear can be safely extended or retracted

VLOF This term is also known as Unstick Speed. The speed at which the landing

gear main wheels leave the ground if the aircraft is rotated at VR. The speed is

directly related to the aeroplane weight and flap setting.

VMAX TYRE The tyres have a maximum rotational speed if this is exceeded theforces generated within the tyre could cause the tyre to disintegrate. This limits the maximum speed for VLOF and therefore can limit the aircraft’s take-off mass.

VMCA Minimum control speed in the climb

VNE Never exceed speed. Set at 0.9 x VD

VNO Maximum structural cruising speed, also referred to as still air speed is set at 0.89 x VNE

VR often termed “rotate” – the speed at which the aircraft is rotated at 3o a second

VRA The recommended turbulence speed. The speed is not less than the maximum gust intensity speed or greater then VMO – 35 knots

VSTOP The highest decision speed that allows an aeroplane to stop within ASDA when a take-off is abandoned

VX1 One engine inoperative maximum gradient of climb speed for a three/four engined aeroplane.

VY The maximum rate of climb speed.

VY1 One engine inoperative maximum rate of climb speed for a three/four

engined aeroplane.

VYse One engine inoperative maximum rate of climb speed for a twin engined aeroplane.

VZF The minimum safe maneouvring speed with zero flap. Mainly used when the

aeroplane is obeying noise abatement procedures.

Water Equivalent Depth (WED) The depth of runway contaminant converted to an equivalent depth of water. This is calculated by the formula:

WED Contaminant depth x SG of contaminant

Weight The force exerted on a body by gravity. The weight is dependent on the mass and the strength of gravity.

Weight = Mass in kg x Gravity in Newtons

The weight of a body will vary with its position and elevation above MSL Abbreviations

ACN Aeroplane Classification Number

AFM Aeroplane flight manual

APS Aeroplane prepared for service

ASD Accelerate stop distance

ASDA Accelerate stop distance available

ASDR Accelerate stop distance required

AUW All up weight

BE Brake energy

BFL Balanced field length

BRP Brake release point

CAS Calibrated airspeed

CDA Mean coefficient of drag in the air

CDG Mean coefficient of drag on the ground

EMD Emergency distance

EMDA Emergency distance available

EMDR Emergency distance required

EPR Engine pressure ratio

ETOPS Extended range twin-jet operations

GFP Gross flight path

FUSS Flaps up safety speed

IAS Indicated airspeed

IAT Indicated temperature

ISA International Standard Atmosphere

LCG Load classification group

LCN Load classification number

LDA Landing distance available

LDR Landing distance required

MAP Manifold air pressure

MAT Mass, altitude, temperature

MCRIT Critical Mach Number

MMO Maximum operating Mach Number

MTWA Maximum total weight authorised

MZFW Maximum zero fuel weight

NFP Net flight path

OCA/H Obstacle clearance altitude/height

ODM Operating data manual

PCN Pavement classification number

RESA Runway end safety area

RNP required navigation performance

RZ Reference zero

SG Specific gravity

SR Specific range

SAR Specific air range

SFC Specific fuel consumption

SPS Standard pressure setting

TAS True airspeed

TOD Take-off distance

TODA Take-off distance available

TODR Take-off distance required

TOR Take-off run

TORA Take-off run available

TORR Take-off run required

TOW Take-off weight

V2 Take-off safety speed

V3 Steady initial climb speed

V4 Steady take-off climb speed

V5 Sometimes used as the on-engine inoperative en-route climb speed

VA Design manoeuvring speed

VAT Target threshold speed

VAT0 Target threshold speed with all power units operative

VAT1 Target threshold speed with one power unit inoperative

VB Design speed for maximum gust intensity

VC Design cruise speed

VD Design dive speed

VEF Assumed speed at the time of engine failure

VF Design flap speed

VFE Maximum flap extended speed

VFTO Final take-off speed

VGO The lowest V1 from which a take-off is possible within the TODA

VLE Maximum landing gear extended speed

VLO Maximum landing gear operating speed

VLOF Lift off speed

VMAX Tyre Maximum structural speed for aircraft tyres

VMBE Maximum brake energy speed

VMC Minimum control speed

VMCA Minimum control speed for take-off and climb

VMCG Minimum control speed on the ground

VMCL Minimum control speed on approach to landing

VMO Maximum operating speed

VMS Minimum stalling speed

VMS0 Minimum stalling speed with flaps in the landing setting

VMS1 Minimum stalling speed for the case under consideration

VMU Minimum unstick speed

VNE Never exceed speed

VN0 Max speed in rough air

VP Aquaplaning/hydroplaning speed

VR Rotation speed

VRA Turbulence speed (rough air airspeed)

VREF Reference landing speed

VS Stall speed

VSO Stall speed with flaps in the landing configuration

VS1 Stall speed in a specified configuration

VS1g Speed at which an aeroplane develops lift equal to the aeroplane weight

VSR0 Reference stalling speed in the landing configuration

VSR1 Reference stalling speed in the specified configuration

VSTOP The highest decision speed from which an aeroplane can stop within ASDA

VSW The speed where the natural or artificial onset of stall warning occurs

VTmax Threshold speed

VTmin Maximum threshold speed

VT Minimum threshold speed

VUS Unstick speed

VX Best angle of climb speed

VY Best rate of climb speed

VZF Minimum safe manoeuvring speed with zero flap

Note: In some cases the prefix M will be used instead of V. The M represents Mach Number.

WAT Weight, altitude, temperature

WC Wind component

WED Water equivalent depth

Chapter 2.

Basic Principles of Flight

The following chapters discuss the segments of flight and the factors that affect them. In the early stage of this course the basic principles of flight and performance details are discussed. Reference to the JAR Performance Classes of aeroplane can be found in the later chapters. Forces on an Aeroplane

There are four basic forces that affect an aeroplane in flight:

THRUST DRAG LIFT WEIGHT ¾ Lift ¾ Drag ¾ Weight ¾ Thrust

Lift acts through the centre of pressure and Weight acts through the centre of gravity.

Thrust and drag act in opposite senses, parallel to the direction of flight, through points, which vary with aircraft attitude and design.

In steady level flight:-

¾ Lift = Weight, and ¾ Thrust = Drag

Lift When air flows around an aerofoil the pressure differential set up over the upper and lower surfaces produces a force. This force acts perpendicular to the relative airflow, and is

known as lift. In steady level flight lift directly balances the aircraft's weight. For a given airspeed the lower the weight, the lower the lift.

Lift depends upon the following factors:

¾ Forward speed

¾ Air density

¾ Air viscosity

¾ Wing shape and wing area ¾ Angle of attack

¾ The local speed of sound

¾ Condition of the surface of the aeroplane wing

Lift acts through the Centre of Pressure (CP) and can be calculated using the following equation:

Lift = CL ½ ρ V2S

Where: CL Coefficient of Lift

ρ Air density

V Free air velocity

S Wing area

CL varies with:

¾ Angle of attack

¾ Wing shape

¾ Weight

Variation of Coefficient of Lift with Angle of Attack

To establish the effect of angle of attack on the lifting ability of a wing, a graph of coefficient of lift against angle of attack can be plotted. This is known as a lift curve and is used to highlight a number of important aerofoil section features.

1.2 1.0 0.8 0.6 0.4 0.2 0 -4° 0° 4° 8° 12° 16° FAST SLOW CRITICAL OR STALL ANGLE (ABOUT 16°) USUAL ANGLES OF FLIGHT (0-16°) ANGLE OF ATTACK

Between 0° and 12° angle of attack The graph is a straight line. This shows that the coefficient of lift, and hence lift is directly proportional to angle of attack in this region.

Above 12° The rate of increase in lift reduces, and the curve eventually culminates in a peak. This peak represents the maximum coefficient of lift (CL max),

which for this particular aerofoil section, occurs at approximately 15°. This angle varies for differing aerofoil sections. For most light aircraft this is a typical value. At angles of attack beyond this point, the lift curve drops rapidly downwards indicating a significant drop in the coefficient of lift and hence lift being developed. The angle of

attack at which CL max is reached is known as the stalling angle of attack of the

aerofoil. The normal flight range is considered to exist between 0° angle of attack and the stalling angle of attack.

The angle of attack is also related to the forward airspeed of the aeroplane: ¾ Low airspeed – high angle of attack

¾ High airspeed – low angle of attack Using the lift formula:

¾ In level flight, at all altitudes, the angle of attack will be constant only if the IAS is constant (remember that if the IAS is constant as the altitude increases then the TAS will increase)

¾ When climbing, the IAS is constant which means that the angle of attack will remain constant. As soon as the climb is related to Mach Number the IAS and the TAS reduce, this will result in a necessary increase in the angle of attack

¾ If any angle of attack the IAS will change in direct proportion to the root of the weight of the aeroplane

¾ The IAS and TAS increase

¾ The angle of attack must decrease accordingly. This decrease in angle of attack will increase both the:

¾ Descent gradient

¾ Pitch angle

Drag

During flight, all of the parts of an aircraft exposed to the airflow produce an aerodynamic force, which opposes the forward motion of the aircraft. This force is known as drag, and is the air resistance experienced by an aircraft as it moves through the air.

RELATIVE AIRFLOW

DRAG

Drag acts parallel to and in the same direction as the relative airflow. In steady level flight (SLF), drag is directly balanced by the thrust produced by an engine or propeller. It follows that, for a given airspeed, the lower the drag the less the thrust required to balance it.

Low drag is therefore beneficial since it leads to reduced fuel consumption and lower operating costs.

The total drag acting on an aircraft in flight comprises of:

¾ Profile drag

¾ Induced drag

¾ Interference drag

Profile Drag

Profile drag can be further separated into:

¾ Form drag

Form Drag

RELATIVE AIRFLOW

ABOVE ATMOSPHERIC

BELOW ATMOSPHERIC

Skin Friction Drag

The reaction to the retardation of the airflow within the boundary layer is known as skin friction. In practice the amount of skin friction depends on the rate at which the air adjacent to the surface is trying to slide relative to it. The retarded air will try to drag the surface along with the flow, in much the same way as two solid surfaces sliding over each other do. This is known as shear stress, and is directly proportional to the speed of flow. The velocity profiles previously used to compare laminar and turbulent boundary layers also represent the shear stress patterns that exist between layers.

LAMINAR PROFILE

TURBULENT PROFILE

LOW SKIN FRICTION DRAG HIGH SKIN FRICTION DRAG

The gradual velocity change associated with the laminar boundary layer shows that low shear stresses exist near the surface, resulting in low skin friction drag. Conversely the rapid velocity change associated with the turbulent boundary layer is evidence of high skin friction drag.

If the conditions of flow were such that either a turbulent or laminar boundary layer could exist, laminar skin friction drag would be about one-third of that of the turbulent flow. Laminar boundary layers are therefore desirable, but the natural transition into a turbulent boundary layer prevents this occurring. The point where transition takes place is therefore important when determining the amount of skin friction drag that exists.

Factors Affecting Skin Friction Drag

The velocity of the airflow and the surface condition over which it is flowing will ultimately effect the position of the transition point.

Effect of Speed With increasing forward airspeed, the transition point moves progressively towards the leading edge resulting in a larger turbulent boundary layer. This causes greater skin friction drag.

Effect of Surface Roughness If the upper surface of a wing has a roughened surface, it may result in a premature transition from a laminar to a turbulent boundary layer; for example the accumulation of ice. This will also cause a large increase in skin friction drag. The degree of skin friction drag may be minimised by polishing and de-icing the surface.

Since all of the aircraft skin is exposed to the airstream, this type of drag will affect all surfaces.

Interference Drag

When an aircraft is considered as a whole, the total drag acting on it may be greater than the sum of the drags of its individual components. This is a result of the airflow being greatly disturbed where the various components are joined together, principally between the wing and fuselage. The disturbance that is imparted to the airflow produces additional drag, known as Interference Drag.

INTERFERENCE DRAG DRAG

DRAG

This type of drag occurs because a large pressure gradient is set up across the junction that causes the boundary layer to prematurely separate from the surface and form a turbulent wake. To minimise this effect suitably shaped fairing or fillet is placed over the intersection to encourage streamline flow, thereby reducing interference drag. Minimising interference drag is particularly important at high airspeeds.

Note: The sum of Profile and Interference Drag is sometimes referred to as Parasite Drag and is attributed to those parts of an aircraft that do not contribute to lift.

Induced Drag

Whenever a wing is producing lift concentrated vortices are formed at the wing tips. These vortices are strongest at the wing tips and become progressively weaker towards the centre-line of the aircraft.

WING

TRAILING EDGE

VORTEX

LEFT-WING VORTEX RIGHT-WING VORTEX

TRAILING EDGE CENTRE-LINE OF AIRCRAFT

These vortices induce downwash to the airflow behind the wing, causing the lift vector to tilt rearwards. The horizontal component of lift opposes the forward flight of the aircraft, and is known as induced drag.

LIFT

DRAG

ANGLE OF INDUCED DOWNWASH FREE STREAM RELATIVE AIRFLOW

EFFECTIVE RELATIVE AIRFLOW CHORD LINE INDUCED DOWNWASH e INDUCED DRAG

The larger the vortex, the greater the induced downwash, and the greater the induced drag. The formula for induced drag is:

Induced Drag (DI ) =

_















where CL = Coefficient Of Lift

A = Aspect Ratio

ρ = Density (kg/m3)

S = Planform Surface Area (m2₎

















π = Coefficient of Induced Drag

Factors Affecting Induced Drag

From the induced drag formula the main factors affecting induced drag are wing planform, aspect ratio, speed and weight/lift.

Effect of Planform This is the principal factor affecting induced drag. The size of the wing tip vortex is directly related to the length of the wing tip chord, and also the larger the vortexes, the lower the sectional effective angle of attack.

14 12 10 8 6 4 2 10 20 30 40 50 60 70 80 90 100 RECTANGULAR TAPERED ELLIPTICAL % SEMI-SPAN EFFECTIVE ANGLE OF ATTACK (°) TIP

Clearly a rectangular planform wing produces a much larger vortex than the tapered section. This is because the wider the tip chord, the greater the spillage of air from the lower surface onto the upper surface, and the larger the wing tip vortex. In aerodynamic terms, the elliptical planform wing is the most aerodynamically efficient because the downwash remains constant across the complete wingspan, giving minimal induced drag.

LIFT

From a practical point of view however, the manufacturing and structural problems associated with an elliptical planform wing preclude its use. For structural reasons, a straight tapered wing provides a good compromise, giving low induced drag.

PREFERRED PLANFORM FOR PURELY STRUCTURAL CONSIDERATIONS

ELLIPTICAL PLANFORM FOR MINIMUM INDUCED DRAG

To preserve the aerodynamic efficiency, the resulting planform is usually tailored, by using wing twist and cross sectional variation, in order to obtain as near as possible the elliptical lift distribution.

Effect of Aspect Ratio Another practical method of minimising induced drag is to make the wingspan as long as possible i.e. increase the aspect ratio. This has the effect of reducing the overall size of the wing tip vortices, and hence induced drag.

LOW ASPECT RATIO HIGH ASPECT

RATIO

Induced drag varies inversely with aspect ratio.

Effect of Airspeed Induced drag is most significant at low airspeeds and high angles of attack i.e. during take-off and landing, when it can account for approximately three-quarters of the total drag. To maintain steady level flight, as the airspeed reduces and the angle of attack increases, the slower passage of air rearwards over the wing will increase the spanwise flow of air around the wing tip. This will result in larger wing tip vortices and greater induced drag.

INDUCED DRAG SLOW SPEED INDUCED DRAG HIGH SPEED INDUCED DRAG _INDUCED DRAG AIRSPEED SLOW HIGH AOA FAST LOW AOA 0

Induced drag is inversely proportional to airspeed².

L

W L

W

SAME SPEED, BUT MANOEUVRING

L

W D

D

W SAME SPEED, BUT HEAVIER

L

Drag Formula

Like lift, a drag formula can also be derived. The drag acting on an aircraft depends on the following factors:

¾ Shape ¾ Angle of attack ¾ Air density (ρ)

¾ Air velocity squared (free stream air velocity) (V2) ¾ Wing planform surface area (S)

Dynamic pressure takes into account the air density and velocity, but when this pressure is combined with the wing planform surface area (S) it produces a force. This force is known as drag. Like lift, drag is not exactly equal to the dynamic pressure times the area, but varies with shape and angle of attack. These factors are represented by the Coefficient of Drag (CD).