Slip slidin' away.

The right hand rudder cable on Angel Paula’s JS-1 was cut through; the rudder then went full left. There is no quick obvious way to get control of the rudder when that happens. The glider was about 3,000 ft. AGL then.

The cable was cut by the sharp end of the S tube through which the cable passes. The end of the S tube is normally flared out, or bell shaped. Some manufacturers also run a plastic tube through the S tube and have the cable routed in the plastic. The JS-1 that Angel bailed out of and a sister ship owned by Barton Tate, also at Moriarty, had S tubes with no plastic tube and no flare on the end. The end was apparently cut with some kind of rotary cutter, probably an abrasive disk and the sharp end that resulted was not dressed smooth. I have cut steel tube this way and the end is so sharp you can almost shave with it. It will cut your flesh quite easily.

That sharp end is at the bottom of the tube where the cable exits and goes forward to an anchor point on a bulkhead. Each time the rudder pedal was pressed forward the sharp end of the steel tube cut into the cable. The cable is made of many small diameter wires bundled together. The sharp end of the steel tube simply cut, over many applications of right pedal, the cable one small strand at a time. Soon there were not enough strands to withstand the tension loads and the remaining strands, probably already nicked a bit, broke under that load. The tension spring on the LH rudder pedal then pulled the rudder to full left deflection.

The rudder did not lock out nor did the cable break, it was cut. The breaking strength of stainless steel 7x19 aircraft cable is 1760 lbs, galvanized is 2,000 lbs. The forward anchor point of the cable would fail before the cable reached its breaking point. The pictures of the wreckage show the forward anchor point to be intact. The glider hit almost level, almost no forward movement; the cable did not break during impact. Pictures do show the cut cable.

Jonkers so much admitted the correctness of this description when they sent Barton Tate new rudder pedals with a plastic tube in the S tube. After Angel’s accident Barton sat in his glider and cycled the rudder pedals from stop to stop, his already frayed cable was cut through even further.
This was a sobering moment for Barton.

I have designed and built and flown a rudder pedal assembly, Genesis prototype and production units, I know the critical design points. Those pedals have proven to be trouble free, they have a flared end and a plastic tube. I have pictures of Angle’s cut cable and Barton’s almost severed cable. I have felt the sharp end of the S tube. There is no other scenario that is viable.

Robert Mudd
Composite Aircraft Repair LLC
Moriarty, New Mexico USA