- developed by Allard van Wallene


The concept of the 'Russian style' circle towhook is well known. And with the development of electronic timers and servo control I was surprised to see this concept was modified to cooperate with the new electronics. But the well known piston-compression spring combination was initially designed for direct rudder control, i.e. movement of the piston is directly linked to the rudder via the control line. So the question could be asked, do we need such complex systems when the rudder is now controlled by a servo through an electronic timer? Shouldn't we do away with all that complexity?

Ken Bauer must have thought the very same thing when designing his strain gauge hook. However, a strain gauge is a sensitive sensor which is not easy to handle. Bonding to the substrate often imposes a problem as does the temperature sensitivity.

Some weeks ago I designed a novel hook concept. Basically the hook consists of one part cut from 3mm (1/8 ") 7075 aluminium sheet. Due to elastic deformation of the hook at high line tension, a vertical lever moves to trigger a microswitch. The latch is 1 mm steel wire, driven by the servo. It is guided inside a brass M2 threaded screw. This screw is drilled out on a lathe with a 1 mm drill. Consider it the cylinder lining of an engine to guide the piston (latch). Add to that some parts to mount the servo for the latch and some fancy anodizing.

The design has been fine tuned over the last weeks and flown in competitions by Arno Hacken and myself.

- Allard van Wallene


Development history

Technical details

No patent has been filed (hint for the cottage industry ;-) )