Almost perfect payout winch launch.

Originally Posted by Bill D

On Friday, May 10, 2013 8:59:22 AM UTC-6, Waveguru wrote:
One of the most important things we teach all glider pilots is that it is there responsibility to keep themselves safe at all times, no matter what happens with the launch vehicle, be it winch, or aerotow. At no time should the pilot put himself in a position that he can't recover from in the event of a launch failure. That means you don't climb until you have sufficient airspeed, you limit the climb angle below 200', you abort the tow with enough runway to land straight ahead if you aren't climbing. No matter what happens to the launch vehicle, it is up to the glider pilot to keep himself in a safe place at all times, with safe options. Maybe you guys train differently? Even if my truck blew up, it just means the glider doesn't get as high as he would have. If the brake fails, it just means the glider doesn't get as high as he might. If my truck fails to get up to speed, the truck goes to the left and the glider lands straight ahead. Our payout system has been very dependable, but we train for launch failures just the same. Contrary to your assumptions, our operation is innovative, simple, safe, and really fun, and it doesn't cost a boat load of money.



Boggs

I have no doubt Gary is a highly responsible pilot and instructor who trains pilots to the best of his ability. He is absolutely correct in describing the pilot's responsibility for his own safety.

That said, I think it may be instructive to examine some of the German DAeC Technical Commission's requirements for winches. (I have a copy translated for me by Ulrich Newmann and I can provide a copy to anyone who requested it.) It's a satisfyingly practical document clearly developed from their vast experience and the results show in their absolutely stellar safety record.

Lets start with power,tension and rope speeds where the DAeC sets minimums.


"In dead calm air, the glider has to be controllable around it's longitudinal axis after less than 15 meters and must reach it's takeoff speed after a maximum of 45 meters."

I think Gary's payout winch can meet this requirement since it only depends on how fast the drum brake is engaged.

Now, here's a tough one - minimum rope speed. This is important because a glider launched in thermic conditions can encounter unexpected tailwind gusts or tailwind layers aloft.

"The drum speed (RPM) has to be chosen such that using the drum core diameter and the power to accelerate the glider according to (above), a rope speed of no less than 1.2 x Va is achievable."

Va on many gliders is in excess of 100 knots so let's say 1.2 x Vw which is typically 70% - 75% of Va but this still may require rope speeds near 100 knots. In the case of a payout winch, one has to add whatever the payout speed is to get the truck speed. I think Gary's pickup truck may have some difficulty with this one since it could mean tow vehicle speeds in excess of 100mph.

Here's a crucial one - minimum release height.

"The power of the winch has to be such that at MTOW in dead calm air, a glider launched at maximum permissible (Vw) airspeed for winch launching can achieve a release altitude of at least 25% of the initial rope length. This must assure safe execution of a normal pattern."

While it's possible Gary's payout winch could achieve this, there may be issues with tow vehicle traction when launching the heaviest gliders. Rope tensions up to a ton may be required at tow speeds.

There are a lot more requirements in the DAeC technical documents on winch design which make good reading.

Hi all

Doing a quick search of the DAeC website to find the document Bill is referencing gives the following information translated by Google

"The speed of the drum must be such that, for
Rated power of the motor to the drum core diameter a
Rope speed in the amount of 1.2 times the lift-off speed
is reached to slow aircraft.
When calculating the drum speed is a surcharge of 10% (for
Operating conditions and weather conditions) to consider.
With more than 1000 m elevation sites of the winds is another
Surcharge of 5% per thousand meters of altitude required."

Even with my imperfect understanding of German or of this translation I don't think they are referring to Va when setting rope speed requirements

:-) Colin