Flexhook timer requirements

An electronic timer needs the following to operate with this hook:

• servo control for the hook servo (open and closed positions)
• servo control for rudder and stabilizer
• a 'bump filter'. This is a timer which starts counting the moment the release tension has been reached. After the bump filter time expires the timer signals the servo to open the latch. The bump filter is set for about 0,5 seconds.
• a timer which starts counting once the line tension reduces below the critial line tension. Once this timer expires (after about 0.3 seconds), the hook should close again and the timer should allow the flier to continue towing
• the hook position can be ignored during bunt transition. This will prevent any switch or hook bouncing from affecting the bunt.
• possibly a system that allows the use of Hall sensors for straight tow and high line tension. Microswitches might also work, but are less reliable.

Here's Ken Bauer's description of using of a gust filter plus tension reduction timer to re-latch the hook:

Also, the OLA timer does not need to start at the moment of high force and last for a long period like 4 seconds. Rather, I do this: start the OLA timer when the hook force DECREASES below the threshold, just after the maximum OLA pull and just before the hook goes back at launch. The OLA time window can now be very short, like 1 second, I'm using about 1.4 seconds. So if the launch does not happen in this very small 1 second window, the hook relatches and normal towing continues. The logic of my system works like this:

1. Hook pull threshold exceeded (10kg) for more than 0.5 seconds (jerk filter), system then goes to "ARM" state indefinitely as long as the force remains high.
2. The moment the pull drops below the threshold, a one second launch timer is started.
3. If the hook goes back within this one sec time, the system goes to bunt mode for glider launch.
4. If the hook does not go back within this one sec window, then the system goes back to normal towing mode.

I believe that this system makes it much easier to avoid unwanted launches. It is only necessary to hold the line tight for one second following a hard line pull event. It is much more difficult and dangerous to hold the line tight for 3 or 4 seconds to avoid a launch.

In fact, the time window for re-latching can be as short as a few tenths of a second.