Winching - Reverse Auto Tow

On Thursday, July 21, 2016 at 3:18:23 PM UTC+3, Martin Gregorie wrote:
On Thu, 21 Jul 2016 10:30:00 +0000, Peter Higgs wrote:

That is quite true, except with the winch you have the full runway
length of rope between winch and glider.

With the Car, you can only start with half that distance from car to
glider.

That assumes the end of the rope is anchored at the launch point, which
looks like a worst case scenario. If the anchor is somewhere along the
runway, in theory at least, you can do a lot better. Putting the anchor
at the midpoint with the car starting at the 3/4 mark should launch to a
height of half the rope length.

That doesn't make sense. The anchor point can be anywhere at all at or behind where the car starts from, including next to the glider, or behind it. It's only dead (unused, wasted) rope length from the car to the anchor point..

If you want to be able to reel in (nearly) the entire length of rope after glider release, as is commonly done with a winch, then you're limited to the car starting at most half way along the runway so that the rope is fully retrieved as the car nears the far end of the runway.

It's hard to figure out what release height you might get.

Assuming a standard winch launch gets 33.33% of the runway length in height, and assuming the glider averages the same climb angle with a 2:1 auto launch with the car starting from the runway mid point, then release will occur with the car about 75% of the way down the runway, and the glider at a height 25% of the runway length.