946 aerodynamic principles for prof pilots

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AERODYNAMICPRINCIPLES

forPROFESSIONAL

PILOTSLES KUMPULAProfessor (Emeritus)

Department of Aeronautical ScienceEmbry-Riddle Aeronautical University

Aircraft Technical Book Company, LLC http://www.ACTechbooks.com

AERODYNAMIC PRINCIPLES


2 AERODYNAMIC PRINCIPLES

AERODYNAMIC PRINCIPLES

For PROFESSIONAL PILOTS

By

Les Kumpula Professor (Emeritus)

Department of Aeronautical Science Embry-Riddle Aeronautical University

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3

Introduction

INTRODUCTION

This book examines the principles of aerodynamics that apply primarily to flight technique issues. Unlike air-craft performance and design, where aerodynamic equa-tions provide numerical data, precision flying requires a thorough understanding of non-numerical aerodynamic principles. In the development of piloting skill, aerody-namic principles are applied qualitatively rather than quantitatively.

While most technical books have many words and a few illustrations, most of the principles explained in this book utilize graphical means. Text comments are mainly used for introductory comments and the summarizing of critical points.

Further applications of aerodynamic principles to flight technique issues can be found in a new book series which emphasizes the development of jet transport flight procedures. The new series expands the content of the Aeronautical Science academic text titled Flight Tech-nique Analysis for Professional Pilots and includes com-puterized demonstrations, tools and additional related sub-ject areas. The first book in the new series, Advanced Air-manship Book 1 Precision Flying, is currently available and the remaining two books are scheduled for release in 2011. Additional information on these new books and up-dated editions of Professor Les Kumpulas current text books is available on the publishers web site: www.cchpublishing.com


4 FLIGHT TECHNIQUE ANALYSIS AERODYNAMIC PRINCIPLES


5

Table of Contents


7

Properties of the Atmosphere


9

Flight Deck Task Management Properties of the Atmosphere


11




The calculations on this and the following pages are not critical for understanding the standard atmosphere. They are used in the creation of a computer program that will cal-culate the standard atmospheric variables at any altitude.


13



15

Review of Aerodynamic Tools Properties of the Atmosphere


17



19



21

Airspeed Measurement


23

Review of Aerodynamic Tools Airspeed Measurement


25


Since equivalent airspeed is an unfamiliar term to many pilots, it may be easier to think of it as perfect indicated airspeed. Equivalent airspeed is what an airspeed indicator would read if it had no errors.


27



29


The drain hole in the pitot tube does not affect airspeed indicator accuracy because the hole is small relative to the volume inside the pitot head.


31



33




In summary, equivalent airspeed and true airspeed are the most important airspeed variables. Equivalent airspeed is used for determining aerodynamic forces while true air-speed is useful for navigation purposes.


35

Transonic Flight Characteristics


37

Speed Stability Transonic Flight Characteristics

Transonic flow is the most complicated of all the flow regions, since it consists of both subsonic and supersonic flow regions whose size and intensity change with angle of attack and airspeed.


39

Basic Equations Transonic Flight Characteristics



Subsonic aircraft are more efficient than supersonic aircraft. However, flight at high Mach numbers for subsonic designed aircraft is limited due to transonic flow effects while flight at high equivalent airspeed is limited due to structural considera-tions. At high altitudes, these two limiting speeds come together at the coffin cor-ner.


41

Constant Velocity Aircraft Control Transonic Flight Characteristics


43

Pitch and Power Relationships Transonic Flight Characteristics


45

Pitch and Power Relationships Transonic Flight Characteristics

Transport aircraft and other airplanes with an air data computer show computed airspeed on the airspeed indi-cator. Computed airspeed is indicated airspeed corrected for errors and is essentially the same as equivalent airspeed.


47

Aerodynamic Force Relationships



The flight controls determine the angles appropriate to their axes of rotation. These angles, along with airspeed and density, determine the aerodynamic forces acting on a par-ticular airplane.


49

Pitch and Power Relationships Aerodynamic Force Relationships



It should be noted that lift and drag are not independent forces. They are perpendicular components of the total aero-dynamic force created by the air flow conditions.


51



53


These facts are direct applications of Newtons laws of motion.



Note that the vector sum of all the forces is zero for both constant velocity flight conditions.


55



57



59



61



63


In a glide, the forward acting parallel component weight takes the place of thrust to keep the airspeed con-stant.


65


It should not be a surprise that lift is less than weight in both a constant velocity climb or descent since lift ap-proaches zero in both vertical climbs and vertical descents.


67

Turn Relationships


69

Turn Relationships



Centrifugal force does not exist. The concept of cen-trifugal force throwing a body to the outside of a turn is not really a force at all. Rather, the tendency of a body to move to the outside of a turn is really its tendency to move in a straight line. For example, as you sit in a car while turning, the tendency of your body to move to the outside of the turn is really your body wanting to move in a straight line while external forces accelerate the car to the center of the circle. People tend to attribute this tendency to a force acting to-ward the outside of the turn, but in reality what is felt is the centripetal force caused by friction of the seat accelerating the body toward the center of the circle. In a banked aircraft, the horizontal component of the force pushing up on your body by the seat provides the centripetal force.


71

Turn Relationships


73

Turn Relationships


75

Turn Relationships


77

Turn Relationships


79

Turn Relationships


81

Turn Relationships


83

The Three Basic Pitch Transition Rules Efficient Use of the Flight Instruments Turn Relationships


84 PRECISION TRANSITIONS FLIGHT TECHNIQUE ANALYSIS AERODYNAMIC PRINCIPLES


85

The Three Basic Pitch Transition Rules Slips and Skids


87

The Three Basic Pitch Transition Rules Efficient Use of the Flight Instruments Slips and Skids


89

Slips and Skids


91

Slips and Skids


92 PRECISION TRANSITIONS PRECISION TRANSITIONS FLIGHT TECHNIQUE ANALYSIS AERODYNAMIC PRINCIPLES


93

Slips and Skids


94 PRECISION TRANSITIONS PRECISION TRANSITIONS FLIGHT TECHNIQUE ANALYSIS AERODYNAMIC PRINCIPLES

Since no acceleration is occurring in this constant ve-locity case, the ball simply sits at the lowest spot in the race-way.


95

Slips and Skids


97

Slips and Skids


99

Adverse and Proverse Yaw


100

TRACKING AND GLIDE SLOPE RULES FLIGHT TECHNIQUE ANALYSIS AERODYNAMIC PRINCIPLES


101



102 TRACKING AND GLIDE SLOPE RULES FLIGHT TECHNIQUE ANALYSIS AERODYNAMIC PRINCIPLES


103



105



107



109



111

Subsonic Aerodynamics


113



115



117

The Lift Equation


119

The Lift Equation


121

The Lift Equation

By definition, stall occurs where the angle of attack effect on lift is a maximum. No other angle of attack will produce more lift. All other stalling variables, such as stall-ing speed, occur when the angle of attack is at the stall angle and the lift coefficient is a maximum.


123

The Lift Equation


125

The Lift Equation


127

The Lift Equation


129

The Lift Equation

From a pilots perspective, this page illustrates an im-portant concept. The point to remember is that lift depends on the combination of angle of attack and EAS (perfect indicated airspeed) for a particular airplane and configura-tion, while keeping in mind that the angle of attack factor reaches its limit at the stall angle of attack.


131

Stall Relationships


133

Stall Relationships


135

Stall Relationships


137

Stall Relationships


139

Stall Relationships


141

Stall Relationships


143

Stall Relationships


145

Stall Relationships


147

Takeoff and Climb Analysis Stall Relationships


149



151



153

Stall Relationships


155

Stall Relationships


157

Takeoff and Climb Analysis Airspeed vs. Angle of Attack


159

Airspeed vs. Angle of Attack

Since a high angle of attack corresponds with low air-speed and vice versa, it is possible to maintain the correct approach speed using either reference. An advantage of us-ing angle of attack as a reference is that its approach value does not change with weight. A disadvantage is that turbu-lence can cause inappropriate autothrottle responses.


161



163



165



167

Takeoff and Climb Analysis Airfoil Shape Effects on Lift


169

Airfoil Shape Effects on Lift


171



173



175

Takeoff and Climb Analysis The Drag Equation


177

The Drag Equation


179

Takeoff and Climb Analysis Airfoil Shape Effect on Drag


181

Airfoil Shape Effect on Drag


183

Lift and Drag Combined - The L/D Ratio


185



187



189

Takeoff and Climb Analysis Propellers


191

Propellers


193

Propellers


195

Propellers


197

Takeoff and Climb Analysis Engine Characteristics


199

Engine Characteristics


201



203



205



207

Performance Airspeeds


209



211




Note that on the following pages, the best performance conditions are found at the maximum or minimum points on the curve and the point where a line drawn from the origin is tangent to the curve.


213



215



217



219



221



223



225



227



229


Although time and effort is needed to find the data de-scribed on the previous pages, no special equipment is re-quired. It is worth the effort to know exactly how an aircraft that you fly regularly really performs.


231

Instrument Approach Profiles High Lift Devices


233

High Lift Devices


235

High Lift Devices


237

High Lift Devices


239

High Lift Devices


241

High Lift Devices


243

High Lift Devices


245

High Lift Devices


247

High Lift Devices


249

High Lift Devices



The computer program used in this example calculates Cessna 172 flight data for any combination of airspeed, flight path angle and flap setting.


251

High Lift Devices


253

High Lift Devices



The use of flaps to slow down while maintaining a con-stant pitch attitude is the most common flap application. Since flaps are extended when the pilot intends to fly slower, it makes sense to utilized flap extension to aid the slowdown.

Extending flaps while pitching down to maintain a con-stant airspeed, thereby increasing the descent angle, is typi-cally used only during partial flap approaches to adjust a final approach that is too high.


255

High Lift Devices


257

Three Dimensional Aerodynamics


259

Wing Shape Effects Three Dimensional Aerodynamics


261

Landing Technique Wing Shape Effects Three Dimensional Aerodynamics


263

Wake Turbulence


265

Wake Turbulence


267

Ground Effect


269

Ground Effect


271

Ground Effect


273

Ground Effect


275

Ground Effect


277

Induced Drag


279

Induced Drag



Downwash changes the flow direction at the wing, thereby causing the lift to be tilted rearward. Lift now has a rearward component relative to the free stream direction. This rearward component of lift is called induced drag.


281

Induced Drag



It is important to note that the strongest wingtip vor-tices and their associated down wash occur at slow speeds. Since down wash is responsible for induced drag, it is great-est at slow speeds and is reduced as air speed increases and wing vortex and down wash strength decrease.


283

Induced Drag

The above drag equation shows the induced and para-site contributions to total drag. Observe that induced drag is proportional to 1 / EAS2, while parasite drag is proportional to EAS2.


285

Speed Stability


287

Speed Stability



In the speed stable region, airspeed tends to remain constant with no pilot action required. In the neutral speed stability region, any airspeed deviation tends to remain unless the pilot changes thrust to return the speed to its original value. In the speed unstable region, airspeed is con-stantly deviating from the desired value and the pilot must continuously work to return the speed to the correct value.


289

Speed Stability


291

Speed Stability


293

Speed Stability


295

Speed Stability


297

Speed Stability


299

Speed Stability


301

Speed Stability



In summary, light airplanes are typically in the speed stable region during approach, especially if operated at a higher than normal approach speed due to traffic considera-tions. Jet transports typically operate in the neutral speed stability region during approach, while fighters normally operate in the speed unstable region, especially during slow carrier approaches. If higher approach speeds are used dur-ing runway approaches, some fighters may operate in the speed neutral region.


303

Wing Shape Effects


305

Wing Shape Effects


307

Wing Shape Effects


309

Wing Shape Effects


311

Wing Shape Effects


313

Aircraft Type Differences


315



317



319



321



323


Additional landing comment: At slower airspeeds, where an increase in angle of at-tack results in a large drag increase with little increase in lift coefficient, raising the nose can cause a speed reduction that more than offsets the increase in lift coefficient, causing a lift reduction and an increase in the rate of descent rather than a decrease.


325

Stability and Control


327



329



331



333



335


Authors note: Most of the remaining diagrams in this section are taken from Aerodynamics for Naval Aviators. Since they are excellent representations of the concepts involved and are in the public domain, I have chosen to add comments to them where appropriate rather than try to duplicate their classic qualities. Other diagrams from Professor Hurts text appear in this book for the same reason.


337



339



341



343



345



347



349

Special Stability & Control Considerations


351

Yaw Factors


353

Yaw Factors


355

Yaw Factors


357

Yaw Factors


359

Yaw Factors


361

Special Comparisons


363

Takeoff and Landing Performance


365




The higher speeds required at increased weights and higher density altitudes affect both takeoff and landing. How-ever, decreased thrust at higher altitudes and increased mass at heavier weights greatly decrease takeoff acceleration. Thrust is not involved in landing distance calculations and heavier weights proportionately increase braking force. Therefore, take-off acceleration is strongly reduced by increased weights and higher density altitudes while landing deceleration is relatively unaffected. For this reason, takeoff distance is more strongly affected by increased weight and density altitude.


367


The worst case method involves computing the take-off distance based on the worst case conditions that you would normally encounter. If none of the worst case condi-tions are exceeded and the runway is adequate for this take-off distance, including an appropriate safety factor, then a takeoff performance data check has essentially been pre-pared and does not need to be done again. If any of the worst case conditions are exceeded, then a new takeoff per-formance data check must be performed.


369

Short Field Landings


371

Short Field Landings


373

Tricycle vs. Tailwheel Airplanes


375



377


Takeoff description using the above corrections: Add significant right rudder pressure as takeoff power is added. Increase right rudder pressure as you begin to raise the tail. Then, re-duce the right rudder pressure after the tail is up. Slightly reduce the right rudder pressure at the beginning of rotation and increase right rud-der pressure as climb pitch attitude is established. Then, continue to hold significant right rudder pressure throughout the climb.


379



381



383



385

Supersonic Aerodynamics



When the tube area begins to constrict, pressure waves radiating at the speed of sound travel forward and accelerate the flow to a higher speed.


387


In supersonic flow, when the tube area begins to con-strict, pressure waves radiating at the speed of sound cannot travel forward to accelerate the flow, so the air molecules bunch up to a higher density and slow down.


389



391




As the supersonic speed of an object increases, the dis-turbances moving at the speed of sound cannot keep up with the source of the disturbances. They bunch up along a shock wave, which is at an angle to the flow. This shock wave is known as an oblique shock wave.


393



395



397


Although similar to subsonic flow, when supersonic flow moves into a larger volume, no change in direction occurs until the first expansion wave. Until this point, the flow does not know that a larger volume is approaching. The flow then changes smoothly across a series of expansion waves. The an-gle of the first expansion wave is determined by the initial flow conditions and the angle of the last expansion wave is deter-mined by the final flow conditions.


399



401



403



405




The changes that take place across shock and expan-sion waves are very complex. Changes are normally deter-mined by computer analysis or by tables such as these illus-trated here or graphs like those shown on the following pages.


407



409



411

Spaceflight Principles


413



415



417




The concept of escape velocity can be understood by imagining the throwing of a ball upward. The faster you throw it upward, the higher it goes. If you throw it fast enough, it will escape gravity and not come back. That speed is the escape velocity.


419



421



423



425



427



429



431

Appendix


433

Summary of Aerodynamic Facts


435

Summary of Aerodynamic Facts



NOTESNOTESNOTESNOTES


AERODYNAMIC PRINCIPLES For PROFESSIONAL PILOTSINTRODUCTIONTable of Contents - 5Properties of the Atmosphere - 7Airspeed Measurement - 21Transonic Flight Characteristics - 35Aerdynamic Force Relationships - 47Slips and Skids - 85Adverse and Proverse Yaw - 99Subsonic Aerodynamics - 111The Lift Equation - 117Stall Relationships - 131Airspeed vs. Angle of Attack - 157Airfoil Shape Effects on Lift - 167

The Drag Equation - 175Airfoil Shape Effect on Drag - 178

Lift and Drag Combined - The L/D Ratio 183Proopellers - 188Engine Characteristics - 196Performance Airspeeds - 206High Lift Devices - 231UntitledThree Dimensional Aerodynamics - 257Wake Turbulence - 263Ground Effect 267Induced Drag - 277Speed Stability - 285Wing Shape Effects - 303Aircraft Type Differences - 313

Stability and Control - 325Yaw Factors - 351Takeoff and Landing Performance - 363Tricycle vs. Tailwheel Airplanes - 373Supersonic Aerodynamics - 385Spaceflight Principles - 411Summary of Aerodynamic Facts - 433

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