- •Textbook Series
- •Contents
- •1 Overview and Definitions
- •Overview
- •General Definitions
- •Glossary
- •List of Symbols
- •Greek Symbols
- •Others
- •Self-assessment Questions
- •Answers
- •2 The Atmosphere
- •Introduction
- •The Physical Properties of Air
- •Static Pressure
- •Temperature
- •Air Density
- •International Standard Atmosphere (ISA)
- •Dynamic Pressure
- •Key Facts
- •Measuring Dynamic Pressure
- •Relationships between Airspeeds
- •Airspeed
- •Errors and Corrections
- •V Speeds
- •Summary
- •Questions
- •Answers
- •3 Basic Aerodynamic Theory
- •The Principle of Continuity
- •Bernoulli’s Theorem
- •Streamlines and the Streamtube
- •Summary
- •Questions
- •Answers
- •4 Subsonic Airflow
- •Aerofoil Terminology
- •Basics about Airflow
- •Two Dimensional Airflow
- •Summary
- •Questions
- •Answers
- •5 Lift
- •Aerodynamic Force Coefficient
- •The Basic Lift Equation
- •Review:
- •The Lift Curve
- •Interpretation of the Lift Curve
- •Density Altitude
- •Aerofoil Section Lift Characteristics
- •Introduction to Drag Characteristics
- •Lift/Drag Ratio
- •Effect of Aircraft Weight on Minimum Flight Speed
- •Condition of the Surface
- •Flight at High Lift Conditions
- •Three Dimensional Airflow
- •Wing Terminology
- •Wing Tip Vortices
- •Wake Turbulence: (Ref: AIC P 072/2010)
- •Ground Effect
- •Conclusion
- •Summary
- •Answers from page 77
- •Answers from page 78
- •Questions
- •Answers
- •6 Drag
- •Introduction
- •Parasite Drag
- •Induced Drag
- •Methods of Reducing Induced Drag
- •Effect of Lift on Parasite Drag
- •Aeroplane Total Drag
- •The Effect of Aircraft Gross Weight on Total Drag
- •The Effect of Altitude on Total Drag
- •The Effect of Configuration on Total Drag
- •Speed Stability
- •Power Required (Introduction)
- •Summary
- •Questions
- •Annex C
- •Answers
- •7 Stalling
- •Introduction
- •Cause of the Stall
- •The Lift Curve
- •Stall Recovery
- •Aircraft Behaviour Close to the Stall
- •Use of Flight Controls Close to the Stall
- •Stall Recognition
- •Stall Speed
- •Stall Warning
- •Artificial Stall Warning Devices
- •Basic Stall Requirements (EASA and FAR)
- •Wing Design Characteristics
- •The Effect of Aerofoil Section
- •The Effect of Wing Planform
- •Key Facts 1
- •Super Stall (Deep Stall)
- •Factors that Affect Stall Speed
- •1g Stall Speed
- •Effect of Weight Change on Stall Speed
- •Composition and Resolution of Forces
- •Using Trigonometry to Resolve Forces
- •Lift Increase in a Level Turn
- •Effect of Load Factor on Stall Speed
- •Effect of High Lift Devices on Stall Speed
- •Effect of CG Position on Stall Speed
- •Effect of Landing Gear on the Stall Speed
- •Effect of Engine Power on Stall Speed
- •Effect of Mach Number (Compressibility) on Stall Speed
- •Effect of Wing Contamination on Stall Speed
- •Warning to the Pilot of Icing-induced Stalls
- •Stabilizer Stall Due to Ice
- •Effect of Heavy Rain on Stall Speed
- •Stall and Recovery Characteristics of Canards
- •Spinning
- •Primary Causes of a Spin
- •Phases of a Spin
- •The Effect of Mass and Balance on Spins
- •Spin Recovery
- •Special Phenomena of Stall
- •High Speed Buffet (Shock Stall)
- •Answers to Questions on Page 173
- •Key Facts 2
- •Questions
- •Key Facts 1 (Completed)
- •Key Facts 2 (Completed)
- •Answers
- •8 High Lift Devices
- •Purpose of High Lift Devices
- •Take-off and Landing Speeds
- •Augmentation
- •Flaps
- •Trailing Edge Flaps
- •Plain Flap
- •Split Flap
- •Slotted and Multiple Slotted Flaps
- •The Fowler Flap
- •Comparison of Trailing Edge Flaps
- •and Stalling Angle
- •Drag
- •Lift / Drag Ratio
- •Pitching Moment
- •Centre of Pressure Movement
- •Change of Downwash
- •Overall Pitch Change
- •Aircraft Attitude with Flaps Lowered
- •Leading Edge High Lift Devices
- •Leading Edge Flaps
- •Effect of Leading Edge Flaps on Lift
- •Leading Edge Slots
- •Leading Edge Slat
- •Automatic Slots
- •Disadvantages of the Slot
- •Drag and Pitching Moment of Leading Edge Devices
- •Trailing Edge Plus Leading Edge Devices
- •Sequence of Operation
- •Asymmetry of High Lift Devices
- •Flap Load Relief System
- •Choice of Flap Setting for Take-off, Climb and Landing
- •Management of High Lift Devices
- •Flap Extension Prior to Landing
- •Questions
- •Annexes
- •Answers
- •9 Airframe Contamination
- •Introduction
- •Types of Contamination
- •Effect of Frost and Ice on the Aircraft
- •Effect on Instruments
- •Effect on Controls
- •Water Contamination
- •Airframe Aging
- •Questions
- •Answers
- •10 Stability and Control
- •Introduction
- •Static Stability
- •Aeroplane Reference Axes
- •Static Longitudinal Stability
- •Neutral Point
- •Static Margin
- •Trim and Controllability
- •Key Facts 1
- •Graphic Presentation of Static Longitudinal Stability
- •Contribution of the Component Surfaces
- •Power-off Stability
- •Effect of CG Position
- •Power Effects
- •High Lift Devices
- •Control Force Stability
- •Manoeuvre Stability
- •Stick Force Per ‘g’
- •Tailoring Control Forces
- •Longitudinal Control
- •Manoeuvring Control Requirement
- •Take-off Control Requirement
- •Landing Control Requirement
- •Dynamic Stability
- •Longitudinal Dynamic Stability
- •Long Period Oscillation (Phugoid)
- •Short Period Oscillation
- •Directional Stability and Control
- •Sideslip Angle
- •Static Directional Stability
- •Contribution of the Aeroplane Components.
- •Lateral Stability and Control
- •Static Lateral Stability
- •Contribution of the Aeroplane Components
- •Lateral Dynamic Effects
- •Spiral Divergence
- •Dutch Roll
- •Pilot Induced Oscillation (PIO)
- •High Mach Numbers
- •Mach Trim
- •Key Facts 2
- •Summary
- •Questions
- •Key Facts 1 (Completed)
- •Key Facts 2 (Completed)
- •Answers
- •11 Controls
- •Introduction
- •Hinge Moments
- •Control Balancing
- •Mass Balance
- •Longitudinal Control
- •Lateral Control
- •Speed Brakes
- •Directional Control
- •Secondary Effects of Controls
- •Trimming
- •Questions
- •Answers
- •12 Flight Mechanics
- •Introduction
- •Straight Horizontal Steady Flight
- •Tailplane and Elevator
- •Balance of Forces
- •Straight Steady Climb
- •Climb Angle
- •Effect of Weight, Altitude and Temperature.
- •Power-on Descent
- •Emergency Descent
- •Glide
- •Rate of Descent in the Glide
- •Turning
- •Flight with Asymmetric Thrust
- •Summary of Minimum Control Speeds
- •Questions
- •Answers
- •13 High Speed Flight
- •Introduction
- •Speed of Sound
- •Mach Number
- •Effect on Mach Number of Climbing at a Constant IAS
- •Variation of TAS with Altitude at a Constant Mach Number
- •Influence of Temperature on Mach Number at a Constant Flight Level and IAS
- •Subdivisions of Aerodynamic Flow
- •Propagation of Pressure Waves
- •Normal Shock Waves
- •Critical Mach Number
- •Pressure Distribution at Transonic Mach Numbers
- •Properties of a Normal Shock Wave
- •Oblique Shock Waves
- •Effects of Shock Wave Formation
- •Buffet
- •Factors Which Affect the Buffet Boundaries
- •The Buffet Margin
- •Use of the Buffet Onset Chart
- •Delaying or Reducing the Effects of Compressibility
- •Aerodynamic Heating
- •Mach Angle
- •Mach Cone
- •Area (Zone) of Influence
- •Bow Wave
- •Expansion Waves
- •Sonic Bang
- •Methods of Improving Control at Transonic Speeds
- •Questions
- •Answers
- •14 Limitations
- •Operating Limit Speeds
- •Loads and Safety Factors
- •Loads on the Structure
- •Load Factor
- •Boundary
- •Design Manoeuvring Speed, V
- •Effect of Altitude on V
- •Effect of Aircraft Weight on V
- •Design Cruising Speed V
- •Design Dive Speed V
- •Negative Load Factors
- •The Negative Stall
- •Manoeuvre Boundaries
- •Operational Speed Limits
- •Gust Loads
- •Effect of a Vertical Gust on the Load Factor
- •Effect of the Gust on Stalling
- •Operational Rough-air Speed (V
- •Landing Gear Speed Limitations
- •Flap Speed Limit
- •Aeroelasticity (Aeroelastic Coupling)
- •Flutter
- •Control Surface Flutter
- •Aileron Reversal
- •Questions
- •Answers
- •15 Windshear
- •Introduction (Ref: AIC 84/2008)
- •Microburst
- •Windshear Encounter during Approach
- •Effects of Windshear
- •“Typical” Recovery from Windshear
- •Windshear Reporting
- •Visual Clues
- •Conclusions
- •Questions
- •Answers
- •16 Propellers
- •Introduction
- •Definitions
- •Aerodynamic Forces on the Propeller
- •Thrust
- •Centrifugal Twisting Moment (CTM)
- •Propeller Efficiency
- •Variable Pitch Propellers
- •Power Absorption
- •Moments and Forces Generated by a Propeller
- •Effect of Atmospheric Conditions
- •Questions
- •Answers
- •17 Revision Questions
- •Questions
- •Answers
- •Explanations to Specimen Questions
- •Specimen Examination Paper
- •Answers to Specimen Exam Paper
- •Explanations to Specimen Exam Paper
- •18 Index
Limitations 14
The Negative Stall
If the angle of attack of the wing is ‘increased’ in the negative direction, it will eventually reach an angle at which it will stall. (If the wing section is symmetrical this angle will be the same as the positive stall angle, but for a cambered wing, the angle and the negative CLMAX will usually be lower). The line OH in Figure 14.1 represents the negative CLMAX boundary. For large aircraft a limit load factor of -1 must be considered up to VC. From VC to VD the negative load factor varies linearly from -1 to 0.
Manoeuvre Boundaries
Taking into account the limiting values of positive and negative load factor, and the maximum speed to be considered, the aircraft is therefore safe to operate within the boundaries shown in Figure 14.5.
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Figure 14.5 Manoeuvre boundaries |
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Line SL represents level 1g flight. Line SA shows the load factors that could be produced by pitching the wing to its stalling angle. Line ACD is the limit set by the maximum positive ‘g’ which the airframe is required to withstand. Line OH shows the negative load factors that could be produced with the wing at its negative stalling angle, and line HFE is the negative ‘g’ limit.
The design speeds VC and VD, already defined, are used for the purpose of assessing the strength requirements of the aircraft in various flight conditions. These speeds are not scheduled in the aircraft’s Flight Manual, but the operational speed limits which are scheduled, are related to them.
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14 Limitations
Operational Speed Limits
Limitations 14
The maximum airspeed at which an aircraft is permitted to fly is VMO for ‘large aircraft’ (CS-25) or VNE for other aircraft (CS-23) other than turbine engined aircraft. (For certification, a large aircraft is defined as one of more then 5700 kg Maximum Certificated Take-off Mass).
Maximum Operating Speed (Large Aircraft) VMO / MMO : VMO is a speed that may not be deliberately exceeded in any regime of flight (climb, cruise or descent). VMO must not be greater than VC and must be sufficiently below VD to make it highly improbable that VD will be inadvertently exceeded in operations.
Because VMO is an Indicated Airspeed, as altitude increases the Mach number corresponding to VMO will increase. There will be additional limitations on the aircraft because of compressibility effects. In a climb VMO will be superceded by MMO (maximum operating Mach number) at about 24 000 to 29 000 ft, depending on atmospheric conditions.
Mach/Airspeed Warning System (Large Aircraft): Two independent Mach/Airspeed warning systems provide a distinct aural warning (clacker) any time the maximum speed of VMO/MMO is exceeded. The warning clackers can be silenced only by reducing airspeed below VMO/MMO.
When Climbing at Constant IAS
It is Possible to Exceed MMO
When Descending at Constant Mach No.
It is Possible to Exceed VMO
Never Exceed Speed (Small Aircraft) VNE : VNE is set below VD to allow for speed upsets to be recovered. (VNE = 0.9VD). VNE will be shown by a radial red line on the airspeed indicator at the high speed end of the yellow arc.
Maximum Structural Cruise Speed (Small Aircraft) VNO : VNO is the normal operating cruise speed limit and must be not greater than the lesser of VC or 0.89VNE.
On the airspeed indicator VNO is the upper limit of the green arc.
From VNO to VNE there will be a yellow arc, which is the caution range. You may fly at speed within the yellow arc only in smooth air, and then only with caution.
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Limitations 14
Gust Loads
The structural weight of an aircraft must be kept to a minimum while maintaining the required strength. The following gust strengths were first formulated in the late 1940s and their continued effectiveness has been verified by regular examination of actual flight data recorder traces.
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50 ft/sec |
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Figure 14.6
Aircraft are designed to be strong enough to withstand a 66 ft/sec vertical gust at VB (the design speed for maximum gust intensity). If an aircraft experienced a 66 ft/sec vertical gust while flying at VB, it would stall before exceeding the limit load factor. In turbulence an aircraft would receive maximum protection from damage by flying at VB.
VB is quite a low airspeed and it would take some time for an aircraft to slow from VC (the design cruising speed) to VB if it flew into turbulence. Therefore, another design strength requirement is for the aircraft also to be strong enough to withstand a vertical gust of 50 ft/ sec (EAS) at VC.
Protection is also provided for the remote possibility of a vertical gust during a momentary upset to a speed of VD (the design diving speed). The aircraft must also be strong enough to withstand a vertical gust of 25 ft/sec at VD. (VB, VC and VD are design speeds and are not quoted in an aircraft’s Flight Manual).
In practice, a slightly higher speed than VB is used for turbulence penetration. This speed is VRA/ MRA (the rough-air speed). VRA / MRA will give adequate protection from over-stressing the aircraft plus give maximum protection from an inadvertent stall.
Limitations 14
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14 Limitations
Effect of a Vertical Gust on the Load Factor
Limitations 14
Vertical gusts will affect the load factor (n) by changing the angle of attack of the wing, Figure 14.7.
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EFFECTIVE AIRFLOW |
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Figure 14.7
The following example illustrates the effect of a vertical gust on the load factor (n).
An aircraft is flying straight and level at a CL of 0.42. A 1° change in angle of attack will change the CL by 0.1. If the aircraft is subject to a vertical gust which increases the angle of attack by 3°, what load factor will the aircraft experience?
Load Factor = |
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A 3° increase in angle of attack will give: 3 × 0.1 = 0.3
the CL will increase by 0.3: 0.42 + 0.3 = 0.72 n = 0.720.42 = 1.7
A gust which increases the angle of attack by 3° will increase the load factor to 1.7
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