Seeking pilot input on effect of vertical fin on flex-wing hang gliders

Seeking pilot input on the effect of a vertical fin on flex-wing hang gliders

Steve Seibel
www.aeroexperiments.org
steve at aeroexp... dot org

This page was last modified on September 14, 2006

 

I'm interested in the hearing the perceptions of other experienced flex-wing hang glider pilots as to how the handling of various glider models is affected by the presence or absence of a vertical keel fin or wingtip fins. If you are such a pilot, please read on!

I'm interested in hearing whether you perceive that the glider responds more quickly, or more slowly, to your roll control inputs (especially starting from wings-level flight) when a vertical fin is present. Please be as specific as you can about what glider models you are speaking of, and about how these effects vary from low speed to high speed, and from VG full off to VG full on.

My own experience on a Wills Wing Spectrum and Airborne Blade 132 is that I haven't been able to discern that the presence or absence of a fixed vertical affects the roll responsiveness at all. I strongly suspect that a vertical fin will significantly slow a glider's roll response in the VG-off, bar-pulled-in (low angle-of-attack / high airspeed) corner of the flight envelope, where the glider's anhedral geometry should exert a particularly pronounced effect on the glider's handling.

The above questions bear on ideas discussed in "A more 'complete' consideration of adverse yaw in flex-wing hang gliders, with notes on fixed vertical fins: does adverse yaw create a helpful roll torque or an unfavorable roll torque?".

 

I'm also interested in hearing whether you perceive that a fixed vertical fin causes you to need to high-side more, or less, or causes you to need to low-side more, or less, during a constant-banked turn, such as during thermalling. Again please be as specific as you can about what glider models you are speaking of, and about how these effects vary from low speed to high speed, and from VG full off to VG full on.

Again, my own experience on a Wills Wing Spectrum and Airborne Blade 132 is that I haven't been able to discern that the presence or absence of a fixed vertical affects the need for high-siding or low-siding at all. I do suspect that a vertical fin will cause a glider to need a bit more low-siding (or a bit less high-siding) in the VG-off, bar-pulled-in (low angle-of-attack / high airspeed) corner of the flight envelope, where the glider's anhedral geometry should exert a particularly pronounced effect on the glider's handling.

The above questions bear on ideas discussed in "A "holistic" view of how dihedral contributes to roll stability and anhedral contributes to roll instability and "Interpreting in-flight observations: roll torque created by the combined effects of anhedral and sweep in flex-wing hang gliders, VG off versus VG on, high airspeed versus low airspeed".

 

I'm also interested in hearing more general comments about how you perceive that a fixed vertical fin affects a glider's handling. What specifically do you like, and not like, about the way the glider flies with a fixed vertical fin? Again please be as specific as you can about what glider models you are speaking of, and about how these effects vary from low speed to high speed, and from VG full off to VG full on.

My own experience on a Wills Wing Spectrum and Airborne Blade 132 is that I haven't been able to discern any distinct negative aspects about the way these gliders fly with a fixed vertical fin. I do like the way that the gliders generally feel less "yawy" with a fin. And of course, the way that the gliders are less prone to yaw-roll oscillations with the fin in the high-speed, VG-off part of the flight envelope in free flight and on tow is a plus. I suspect that by reducing "yawiness" in general, the fin also tends to create a net decrease in drag, especially during changes in bank angle, throughout the flight envelope, but I don't have any proof that this effect is very significant.

Please email me your thoughts and observations!

 

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