Conversion from Edson Cable - to
Open Wire Steering System
Some C250 owners with wheel steering have experienced cable failure and replaced the push/pull system with a two cable pull pull upgrade from Edson. I decided early that an attempt would be made to construct an open wire system.
When first mentioning this, I received pictures from another owner who had made a similar move, even though he had the newer pull/pull system. He was unhappy with the drag and play in the two cable pull/pull system. His comments cemented my concern that an Edson upgrade was not the best course, that while it had solved some of the failure issues, it hadn't fixed the design shortcomings.
His design used a quadrant system and was very well done and accomplished his goals of eliminating drag and play. After pondering replicating his system, I decided it didn't meet all of my design goals.
They were
a simple system to construct, install, and adjust cable tension and wheel centering a system with no steering play a system with no serious drag components
a system easily repairable while cruising one that increased the steering ratio 50-100 % inexpensive left the rudder control arm unloaded so as to easily remove rudder minimized intrusion within the aft berth not requiring removing the aft bulkhead for installation, adjusting or maintenance if possible, have cables lead straight aft where they could passage the hull channel and hug closer to the berth ceiling
After a great many sketches, each idea seemed to leave out a design goal and demand compromise. The final design using a backstay tensioner scheme evolved and matured rapidly after a decision to use a slotted rudder arm was made. All the design goals were met with this design except one. Hoped for was a system which could easily adjust the centering of the king spoke so as to feel the rudder center. The compromise was carefully centering the kink spoke when installing the cable clamps. In favor however is that once centering is done, additional tensioning adjustments don't require concern about centering.
Rudder arm hook up would be done via a slotted arm in lieu of a quadrant. After playing with some models, the slot seemed to make sense as it would solve the problem of loading the rudder arm. A loaded arm would require loosening the cables to remove the rudder and was a design breaker. The slot would need grease but so did Edson's cables and their grease fittings were expensive, as well as requiring special grease. The slot design blossomed with other benefits. The added length to the Edson arm increased the steering ratio which would reduce helm effort, autopilot loading and allow more precise helming which fit a very high priority objective.
Surprise came with an unexpected benefit. While both the Edson hookup and this design offer proportional steering that decreases the rudder travel ratio as it moves away from center, this system has a much greater proportional effect. And, where Edson's system loses lever arm and thrust by perhaps 25% as the rudder moves away from center, this system increases the lever arm by more than three times that of the Edson.
Before disconnecting the old system, I checked the turning ratio and play so that a comparison could be made. Testing after installation, proved that my calculations were close in that lock to lock was now 2 1/4 turns compared to slightly more than one turn previously and this in part because one rudder direction had a great deal more throw than the other. Now, both sides are the same. The ratio is non-linear. At rudder amidships, the ratio is about 60% better than original but near rudder lock the ratio climbs to 115% better than original. This number is even accentuated more when considering that the original lost leverage near rudder lock because of a diminishing thrust line. What this means is that when the rudder is presented with a hard turn which adds load to the rudder, the helm advantage is now increasing to assist with that load rather than decreasing.
Regarding play, the old system had a whopping six inches of wheel play compared with none for the new. I knew it was bad but had never measured it. It was noted when pulling the old system out of the pedestal, that there was some ability to adjust the play but that the adjustment was more of something that would be done at installation rather than routine maintenance as doing so required major surgery into the pedestal.
Conversion Kit Edson Cable Failure Theory Drawing Construction Evaluations
