Kite Strings

Dick Reynolds - 1992/11

Lookout Mountain Flight Park had acquired a new Moyes aerotug and I was the pilot - claiming 200 plus tows to date. At 11:00 AM on May 17, 1992 I had decided to take two more tows and then call it quits for the day.

The conditions on this particular morning were very light - great for towing. Takeoff went smoothly, with the glider then the tug lifting off, thus increasing my angle of climb. My airspeed was four mph above stall. I took my eyes off the indicator to watch the hang glider's progress when the engine abruptly seized. I can distinctly remember taking my hand off the throttle to wave the hang glider off, and it was at that point that I fully realized there was no time! I pulled the release and pushed the stick forward.

All this occurred somewhere around fifty feet. The combination of high nose angle plus the pull exerted by the climbing hang glider brought me to a screeching halt, so to speak. I believe my response time was less than a second, but this still me just hanging with very little elevator authority. The nose fell through the horizon to 30 degrees negative and the ground rapidly rushed toward me. I attempted to pull up at approximately 25 to 30 feet, with no response. My feet, butt, and gear impacted simultaneously.

I consider myself fortunate in that my friends were there to immobilize me. The doctors tell me that I'll be walking in a year or so, but that I shouldn't plan on winning any foot races.

Aerotowing Gliders - 2011/06

If there is a problem with the tug, the pilot should immediately release the tow rope.

skysurfer - 2013/10/23 16:47:46 UTC

Just noticed a new version of this has been recently released.

http://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/glider_handbook/

Ground Launch Takeoff Procedures

CG Hooks

Conversely, depending on design, the CG hook may not have sufficient movement to fully release an aerotow line under pressure. If the hook only swings about 90° down, the towline may stay hung on the gliders hook until the pressure is released and slack allows the towline to simply fall off.

Tracy Tillman - 2005/02/08 19:16:10 UTC

The sailplane guys have been doing this for a long time, and there are many hang glider pilots and quite a few tug pilots who don't understand what the sailplane guys have learned over the years. It certainly would help if hang glider towing methods and training were standardized to the degree that they are in the sailplane world.

Dr. Trisa Tilletti - 2012/06

The WT style of weak link performs very consistently, likely due to the extra weak link loops snugging down onto the bridle and not shifting around, and because the knot used to make it is separated far from the pulling pressures.
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A pilot should not expect a weak link to break to prevent a lockout. Sometimes the pressures produced at the start of a lockout are high, and the weak link may break early. Sometimes the pressures are not very high at the start of the lockout and don't get high until the lockout progresses much further--in that case the weak link will break later.
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Dr. Lionel D. Hewitt, professor of physics and developer of the 2-to-1 center-of-mass Skyting bridle for surface towing, is well respected for his knowledge of towing, bridles, and weak links. His position on weak link strength for aerotowing of hang gliders seems to be consistent with ours. He has acknowledged that we especially need to avoid inadvertent weak link breaks while aerotowing, because much of aerotowing takes place over unlandable terrain. That, along with recognizing that towing pressures vary considerably while on aerotow, has led him to suggest the use of a weak link that breaks in the neighborhood of 1.5G of towline pressure.
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