Steve Leonard wrote:

On Thursday, February 20, 2014 5:48:43 PM UTC-6, Colin Wray wrote:
Most people posting here do not understand the word "instantaneous". Chris
Rollings, and the CofG hook exponents, are the only people who get it.

Glad to see you chose my post to respond to when you decide to imply that most of us (myself included) don't know what "instantaneous" means, Colin. I work a lot with electrical guys and your idea of "instantaneous" is an eternity to them. Half a second? That is a lifetime in the world of electrical system responses. I work with regulations and know about human reaction times. I know that the event being discussed will go from start to disaster in less than typical event to recognition to reaction time. Even for someone who is expecting it and knows exactly when it starts.

I understand the dynamics of it at least as well as you do. Maybe better. I know that cambered wing sections can generate higher C/L max than symmetric sections. I know what a C/L versus Alpha curve is. I know its slope. I can tell you what it takes in terms of AOA change to go from 1 g to minus 1 g. I know that a wing that is 5 times the size of the tail on the towplane, and attached to the towplane via the tow rope roughly 20 times further back from the towplane aerodynamic center than the tail will be able to produce more than 30 times the pitching moment to the towplane than the tail on the towplane can. I know that if the glider does this, there is NO way the towplane pilot can do anything to stop it. Again, I don't think the tail on the towplane stalls. I think the glider effectively becomes the "tail" of the tug, and it can and does overpower anything the elevator might do.

I agree that a system based on angular displacement of the rope likely won't work, as the relative angle between the two planes doesn't change much and you can slowly go higher than this and not cause a problem to the tug. Longer ropes can damp the response, but not eliminate it. I read what Chris wrote, and I get it. I get it that you can do this and not break a proper strength rope. You have once again assumed that because someone is proposing an automatic system to try and minimize (notice, I know I can NOT prevent it) the impact, you assumed that "he doesn't get it".

Design thoughts. When is a towplane nose down? In an upset or on descent. If the towplane is in its descent, where is the elevator? It certainly won't be more than half way to full nose up! It might be a quarter to half way up during a normal tow, but the nose will not be below the horizon. And if a kiting event starts, the towpilot will no doubt start pulling back. What I have proposed is a starting point for evaluation of an automatic system to MINIMIZE the risk to the tuggie in the event of kiting. I strongly suspect that 10 degrees nose down is too much, as the tug will already have gone negative load factor, and the event must be stopped before then. But, I am proposing a starting point.

Have you got a better proposal for a starting point for a system to MINIMIZE the risk to the tuggie? In case you are wondering, autothrottle won't Minimize it. :-)

End of rant.

Steve Leonard

Steve, I bow to your vatly superior knowledge of aerodynamics, and I
can now see that you really do 'get it'. (Sorry). I was basing my
comments on little more than my involvement in two of these episodes.

I guess that in real kiting accidents, where the rope remains
reasonably tight throughout, there will be a measurable time before it
becomes unrecoverable. My upset as the tug pilot featured a slack rope
which snapped tight, so any kiting must have been akin to a sling shot
for the glider.