KGARS - Kiting Glider Automatic Relase System

I wonder if the existing back release mechanism(s) used on CG hooks would not already perform the needed function. Maybe an existing CG hook from a glider, chosen to match the towplane's structural limits, and mounted at an appropriate orientation and angle, would be sufficient.

A more sophisticated and complicated system would not only measure the rope angle, but would also sense impending loss of elevator (or even rudder) authority and release immediately.

On Sunday, May 17, 2020 at 10:41:24 AM UTC-7, Wit Wisniewski wrote:
I wonder if the existing back release mechanism(s) used on CG hooks would not already perform the needed function. Maybe an existing CG hook from a glider, chosen to match the towplane's structural limits, and mounted at an appropriate orientation and angle, would be sufficient.

A more sophisticated and complicated system would not only measure the rope angle, but would also sense impending loss of elevator (or even rudder) authority and release immediately.

It might be possible to make some sort of back-release-type mechanism on the tow plane. However, I don't think that an existing glider release would work.

I also don't like the idea of releasing at a particular angle. For example, a 1,000 pound pull at 20 degrees may over-power the tow plane, while a 10 pound pull from 40 degrees may not. The real culprit is a pitching moment that's a function of both force and angle.

The cable pulls with some force (F) and angle (theta). The vertical component of this force is Fsin(theta). The tow plane is forced into a dive when Fsin(theta) exceeds the control authority of the tow plane.

The back release mechanism could have some length (X) such that the tow rope exerts a torque on it of XFsin(theta). The device could be designed to release at an appropriate torque, rather than at a particular angle. This would release when the glider is in danger of exceeding the control authority of the tow plane; not just because the glider is high.

Another thought... most of our tow aircraft were not designed exclusively for glider towing. If one were to design a tow plane from the ground-up, it may be possible to provide a bit more control authority to resist ballooning gliders. One could also locate the tow hook closer to the center of gravity, although this may not be feasible with a conventional configuration.

On Sunday, May 17, 2020 at 6:41:18 PM UTC-7, wrote:
On Sunday, May 17, 2020 at 10:41:24 AM UTC-7, Wit Wisniewski wrote:
I wonder if the existing back release mechanism(s) used on CG hooks would not already perform the needed function. Maybe an existing CG hook from a glider, chosen to match the towplane's structural limits, and mounted at an appropriate orientation and angle, would be sufficient.

A more sophisticated and complicated system would not only measure the rope angle, but would also sense impending loss of elevator (or even rudder) authority and release immediately.

It might be possible to make some sort of back-release-type mechanism on the tow plane. However, I don't think that an existing glider release would work.

I also don't like the idea of releasing at a particular angle. For example, a 1,000 pound pull at 20 degrees may over-power the tow plane, while a 10 pound pull from 40 degrees may not. The real culprit is a pitching moment that's a function of both force and angle.

The cable pulls with some force (F) and angle (theta). The vertical component of this force is Fsin(theta). The tow plane is forced into a dive when Fsin(theta) exceeds the control authority of the tow plane.

The back release mechanism could have some length (X) such that the tow rope exerts a torque on it of XFsin(theta). The device could be designed to release at an appropriate torque, rather than at a particular angle. This would release when the glider is in danger of exceeding the control authority of the tow plane; not just because the glider is high.

Another thought... most of our tow aircraft were not designed exclusively for glider towing. If one were to design a tow plane from the ground-up, it may be possible to provide a bit more control authority to resist ballooning gliders. One could also locate the tow hook closer to the center of gravity, although this may not be feasible with a conventional configuration.

An automatic release system does not need to be all that complex. At the minimum I would combine pitch attitude with altitude: if nose-down pitch exceeded a preset limit and the altitude was less than 1,000 ft AGL the rope would be released. A further refinement would include a load cell to detect a load on the rope. If the load is increasing above a preset rate and the pitch angle is increasing above a preset rate and the altitude is less than 1,000 ft AGL the rope is released.

The bottom line is such a system is not all that complex and could be developed by the talent that exists in the glider community. I don't care how often these accidents occur, one life lost is one life too many.

Tom