What is automatic control connections and how does it work?

Question

The Rolladen-Schneider LS4B control connections are automatic. This feature, also called automatic control hookup seems to be common. The last time I assemble a glider was more than a decade ago, and controls had to be mechanically (re)connected one by one.

What is automatic control connection? (I imagine it is some mechanism connecting controls when assembling wings). How does it work?

Answer 1

The automatic hookup uses a catchment area to mechanically force the pushrod into a receptacle to ensure a proper mechanical connection when the parts of the plane are connected.

As an example, I have sketched below how the ailerons would be connected. The blue structure is the fuselage-side part, and the green structure is the wing-side part of the control linkage. The pushrod coming from the stick is connected to a trapezoidal cone which is hinged at the same point as the wing-mounted pivot lever which is moving the pushrod connected to the aileron.

The opening of the trapezoidal cone is sized such that the end of the pivot lever will always be caught by it, regardless of the stick position and the aileron deflection. At the base where the end of the pivot lever rests when both parts are connected, the exact position and play between both can be adjusted, so the automatic connection will not have an adverse effect on handling.

I once witnessed an aborted winch launch of the SB-8 in which the linkages to the ailerons were interchanged. The pilot noticed the wrong operation of his ailerons before becoming airborne and released the rope quickly, but could not avoid a ground-loop, because he had pushed the low wing into the ground when trying to correct the plane's attitude. I was glad not to have been in his position, because I am not sure I had reacted as quickly. Automatic connections would have made this mishap impossible.

Answer 2

Automatic control hookup means that when the wing or tail are fully inserted into the aircraft fuselage, that the control rods for the airlerons, flaps, speedbrakes, elevator, etc., are all guaranteed to be fully and properly connected to the control handles inside the cockpit.

Without automatic control hookups, the control rods coming from the wing or tail control surfaces had to be manually connected, one by one, to the control rods coming from the cockpit. This system led to many accidents, when pilots forgot to connect a control rod during assembly, and they didn't find out until the glider was launched:

Source: http://www.blackmountainsgliding.co.uk/cfidocs/accidentreviewbga12.pdf

Another type of manual control rode failure is associated with the L'Hotellier connector, which would seem to be fully connected, but would fall apart, even after a positive control check.

Automatic control hookups are designed to reduce, if not eliminate, these kinds of problems. Needless to say, even with automatic control hookups, a positive control check must still be performed before every flight.