I'm on the right - but you knew that...

	This book is the classic, definitive text on the technical aspects of hang gliding.  Covering such topics as aerodynamics, stability and control, structure, performance and glide calculations (including performance in a turn), the physics of landing, slope and thermal soaring, the book translates aeronautical engineering into practical insights from a hang glider pilot's point of view.  Written in a conversational style, the book explains all the important messages in simple rules-of-thumb for those who don't want to get into the technicalities.  However, the book does not run away from algebra:  there are plenty of equations and graphs for those who want to look at the detail behind the rules-of-thumb. Not a training manual, this book does not teach flying techniques, nor is it intended for pilots who just want to know what to do, without wondering why.  This book is for pilots who want more insight into what is happening when they fly. WHAT THIS BOOK IS ABOUT This book is not about hang-gliding. It is about magic. Like many children, when I was young I used to dream I could fly. I would watch the birds and imagine what it would be like to do as they did. They had the power to do something that was clearly impossible. The air is so thin, and gravity pulls so hard, I could not imagine how they could be supported by air alone. Clearly the birds had some magical powers that enabled them to do this. I did not. By the time I had grown up I had almost forgotten the dreams of flight and freedom. Almost, but not quite, because on a dull afternoon a stranger with Dacron wings flying along a mountainside brought them all back with a rush. I watched the stranger float overhead, silently, and knew, just knew, that this was impossible. I was witnessing magic. This book is about the magic. It's not really about how to use the magic. It's not really about the art and skills of flying, although they sometimes appear too. All the air-lore in the world would be useless without wings, and the magic that makes them work. The secrets, the ones the birds knew all along, are what this book is about. Of course, we are modern, technical people. We do not talk about "magic". We talk about "physics", "aerodynamics", "stability", "control", "structures", "algebra", and so on. We talk about cold, hard facts. We have no room anywhere for romantic ideas of freedom or magic, and you will find no such ideas here. This book tells you why hang-gliders work. It is about why they must work, whether you believe it or not. The "laws of physics" apply, and hang-gliders fly no matter how unlikely that may seem. This book is about physics and aerodynamics and why hang-gliders fly, and why they fly the way they do. It's about how the ancient secrets of the birds have been turned into aluminum-and-Dacron wings. It's about magic. HOW THIS BOOK IS ORGANIZED   This book originally started as a series of notes I made to myself when I found the answers to questions I was asking. I wanted to know what determined the glide-angle, and why it was so poor compared to sailplanes, and why high-performance gliders were smaller and more difficult to turn, and why people couldn't get better performance with bigger gliders, and how fast to fly in a headwind, and how much altitude I would lose in a turn, and how much my sink-rate would increase in a turn...   I find I can grasp material best when there isn't much of it. When there's a lot of explanation and "too many words" I find I tend to miss the point occasionally. As a result, I've written these "notes to myself" in a fairly condensed form.   I've organized the notes so that each topic is explained on the left-hand page, with any corresponding diagrams or equations on the right-hand page. If there is no diagram corresponding to the topic on the left, then the right- hand page is blank. Where I've used equations I have summarized the results in the text, so that you can skip all the algebra if you like.

	CONTENTS PAGE Part 1: WHY IT FLIES           1 (I) How to Use Air to Stay Above the Ground 7 1 (II) The Fundamentals of Lift 9 1 (III) The Bad News, or, What a Drag! 11 1 (IV) The Glider Equation, The Magic L/D Ratio, and Minimum Sink 13 1 (V) Performance 15 1 (VI) Taking the Performance Calculations Further 17 I (VII) Conclusions - What we Know about Performance 19 1 (VIII) Wing Loading and the Infamous Stall 21 1 (IX) Downwash, Tip Vortices and Other Cool Terminology 23 1 (X) Taking out the Assumptions 25                               Part 2: WHY IT FLIES UPRIGHT – STABILITY AND CONTROL           2 (I) Stable Relationships and Hang Gliding 27 2 (II) Take a Moment 29 2 (III) Stable Relationships and the Importance of a Good Attitude - Pitch Stability 31 2 (IV) Pitching Moments and You : What about Hang Gliders? 33 2 (V) Rolling with the Punches - Lateral Stability 35 2 (VI) Yaw'll Come Back Now - Directional Stability 37 2 (VII) What about the Pendulum Effect? 39 2 (VIII) But I Want to Go That Way! - Control 41 2 (IX) It's in the Bank - Roll Control 43 2 (X) Twist it All About - Yaw Control 45 2 (XI) You Can't Have One But Not the Other - Roll/Pitch/Yaw Coupling 47 2 (XII) Control Effectiveness at Low Speeds 49 2 (XIII) The Lessons to Learn about Stable Relationships 51                               Part 3: STRUCTURE           3 (1) The Basic Structure, or Keeping it Together 53 3 (II) Secondary Structure, or, I Said Simple, Not Crude! 55 3 (III) Forces and Loads - How Strong Does it Need to Be? 57 3 (IV) Forces and Loads Again - What About the Other Bits? 59 3 (V) Sail Shift, Floating Crosstubes, and the Mysterious Vanishing Keel-Pocket 61 3 (VI) Variable-Geometry Systems - What They Do 63

	Part 4: STRAIGHT AND LEVEL WITH ME!           4 (I) The Minimum-Sink Controversy (Where is it, Really?) 65 4 (II) Are You Flying too S-L-O-W~L-Y? 67 4 (III) Best L/D and Best Glide - Do You Know The Difference? 69 4 (IV) Best Glide, and the Effect of Wind 71 4 (V) Best Glide, and the Effect of Lifting/Sinking Air 73 4 (VI) Closing Remarks on Going Straight 75                               Part 5: TURNING OUR ATTENTION         5 (I) Banking, and What it Has to Do with Flight 77 5 (II) Types of Turn: Steady Co-ordinated 79 5 (III) Types of Turn: Slipping 81 5 (IV) Types of Turn: The Stalled Turn 83 5 (V) Yaw, Lag and Turning Technique 85                               Part 6: UNUSUAL ATTITUDES, STRANGE BEHAVIOR, AND OTHER SPECIAL SITUATIONS             6 (I) Rowdy Conditions 87 6 (II) Final Approach 89 6 (III) Do it With Flare ! (sic) 91 6 (IV) Do it with a bit More Flare 93 6 (V) Spinning: The Tale 95 6 (VI) Tumbling, Whipstalls, and Loops 97 6 (VII) The Great Wingover 99                               Part 7: CAN YOU KEEP IT UP? - SOARING           7 (1) Slope Soaring 101 7 (II) Thermal Soaring 103 7 (III) Getting Down 105

	2 (XIII) The Lessons to Learn About Stable Relationships Here is a summary of what we have seen in Part 2. ---------------------------------------------------------------- The c.g. must be ahead of the a.c. for pitch stability. The wing must be designed with a positive pitching moment for stability. With enough sweep and washout a wing can have positive pitching moment. The more positive the pitching moment, the farther the c.g. is ahead of the a.c. The farther the c.g. is ahead of the a.c., the more pitch stability the glider has. Dihedral is stabilizing in roll. Anhedral is destabilizing. Sweep~back of the wings is stabilizing in roll. Sweep-forward is destabilizing. Vertical surfaces behind the c.g. are stabilizing in yaw. Ahead of it they destabilize. Sweep-back of the wings is stabilizing in yaw. Sweep-forward is destabilizing. Swept-back wings with plenty of washout are stable in all three axes. The Pendulum Effect has very little influence on lateral (roll) stability. The Pendulum Effect has much less influence on pitch stability than most people think. If the pilot uses a light touch on the control bar, the Pendulum Effect disappears entirely. BUT a rigid grip on the control bar is damping in all three axes (slows down any changes). Pitch control is entirely due to weight-shift. Roll control is partly by weight-shift, but mostly by sail-shift - an aerodynamic control. Yaw control is by swinging the pilot's body, and produces temporary yaw only. Roll and Yaw are coupled (affect each other), and, in turns, are coupled to Pitch also. Roll control inputs cause Adverse Yaw, which slows the entry to the turn. When the wing is partially or entirely stalled the glider tends to pitch nose-down. When the wing is partially or entirely stalled, roll stability and control go away.