Acknowledgements and origins of ideas

Acknowledgements and origins of ideas

Steve Seibel
steve at



I am highly indebted to the members of the Kansas Soaring Association and the Wichita Soaring Association for making the nation's most affordable (sailplane) soaring available to people of all ages. And particularly to the volunteer instructors of the Wichita Soaring Association, chiefly (during my time of learning) Bill Brown and Frank O'Donnell.


Other acknowledgements: to Dennis Pagen for outlining his view of hang glider aerodynamics so clearly and concisely in all his various writings--this provided the spark that got me thinking about many of the sideslip-related issues very early in my hang gliding training process, when my feet had barely left the sand dune. Also his flight training guides were essential, practical tools for my journey into the real world of hang gliding.


To a handful of people who had the knowledge, and took the time, to respond over the internet or over the telephone or in person to a large collection of physics-oriented questions I had early in my hang gliding career, and a few more in more recent years. These people include David Phillips of Australia and Stephen Morris and Steve Pearson of California.


My initial exposure to a few of the fine points of spiral stability issues, and to the "airflow curvature" concept, came from a series of articles called "Spiral Stability and the Bowl Effect" by Blaine Beron-Rawdon that appeared in Model Aviation in September and October 1990, and also in articles by the same author in the same magazine in August through November of 1988. These articles discuss "airflow curvature" in relation to stability and efficiency in rudder-controlled model sailplanes, but the ideas within apply to all aircraft.


Some of the most invaluable texts for furthering my informal education in aeronautics are listed on the "recommended reading" page of this website.


After being interested in some of these issues for well over a decade, in many cases it is difficult to know which ideas were arrived at truly independently and which ideas were initially encountered somewhere in the vast literature of aviation and later made "my own" in some sense through careful thought and/or experimental confirmation. Of the former, it is almost impossible to know which ideas (if any) are truly entirely new to this earth, and which are not. Some of the ideas that were in fact arrived at independently include: *The experimental discovery of the safest heading quadrant for using a magnetic compass as an emergency blind-flying aid (the results were in conflict with what I had previously encountered in aircraft flight manuals). *The experimental confirmation (to my initial surprise) that the modern understanding of the role of pitch and yaw inputs in the world of "conventional" aviation also applies well to the world of hang gliding and triking, and that the "inadequate pitch 'coordination' input creates a sideslip" model, though widely accepted among hang glider and trike pilots, does not. *The idea that a short-coupled rudder on a swept-wing aircraft with no fixed vertical tail and minimal cross-sectional area (as seen in a side view) can actually end up creating a net aerodynamic sideforce in the same direction--not the opposite direction--as the rudder is deflected. *By logical extension, the conclusions about the rather "interesting" crosswind landing characteristics that such an aircraft would have. *The thoughts on the fundamental reason for the "drift" that begins when a pilot "kicks out the crab" during a crosswind landing. *The "hang glider rack" paradox. *The independent (but not new) experimental discovery that a flex-wing hang glider exhibits a net negative coupling between yaw (sideslip) and roll, harnessing the sideways airflow created by adverse yaw to create a helpful roll torque. *The idea that sail billow contributes greatly to the "net geometric anhedral" of a flex-wing hang glider, and the related idea that tightening the variable geometry system of a flex-wing hang glider decreases, rather than increases, the glider's "net geometric anhedral" (even in the case of a standard pulley VG system), and the obvious corollary that it is entirely inadequate to define the anhedral as the droop in the leading edge tubes in relation to the keel tube, even when the flying wires are tight. *The closely related idea that when any flap or spoiler or elevon or other moving surface is lowered from an aircraft, if it is mounted on an aft-swept hinge line, this will create a dihedral effect, and if it is mounted on a forward-swept hinge line, this will create an anhedral effect. Likewise the corollary idea that when any flap or spoiler or elevon or other moving surface is raised from an aircraft, if it is mounted on an aft-swept hinge line, this will create a anhedral effect, and if it is mounted on a forward-swept hinge line, this will create an dihedral effect, all of which can be seen by visualizing how a sideways (slipping) airflow component will interact with the object to create a roll torque. *And of course, the reverse-engineering observations regarding the mysterious workings of the Brauniger IQ Comp GPS vario. (Note: many of the above ideas are not yet adequately explored on the Aeroexperiments website!)


Thanks also to Jim Norton for website hosting and to John Matylonek for imparting many skills, but more importantly for imparting so much enthusiasm and vision, during my time as student/novice hang glider pilot.

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