splischke
Scott Plischke Sonerai IIL N994SP
About a year ago I posted some pictures of a crack that developed in the rudder horn of my Sonerai IIL. I thought I'd give everyone an update.
First let's revisit the problem. One day on a preflight inspection I noticed that the right side rudder horn appeared slightly bent down. When I tugged on the horn, the right side deflected slightly more than the left. Although there was no sign of damage, it just didn't seem right. I decided to take the rudder home and strip the covering. Once the covering was removed, the problem was obvious. A crack had developed along the periphery of the weld just under the covering material and out of sight. Here's a picture:
Closer view:
As you can see, the crack developed on the right side of the horn where the tailwheel tiller rod is connected. Apparently the repeated force applied to the horn from the tailwheel/tiller rod caused the crack to develop. Total time on the airframe was only 102 hours when the crack was detected.
There has been some speculation as to why the crack developed so quickly on my Sonerai while other high time Sonerais with tiller rods never had a horn crack. Some people have said that I had a cold weld. Some said that the angle of the tiller rod is too great. I think it's a combination of these plus flying off rough fields and several hard landings.
So what did I do? Obviously the old horn had to be cut off and replaced. The new horn was fabricated from the same thickness material but I designed it slightly wider than what is specified on the plans so that it wraps around the forward side of the rudder spar. This gave me more to weld to. I also welded 0.090" 4130 steel triangular gussets on the top side of the horn and rudder spar.
In addition to the redesigned horn, I also reduced the angle of the tiller rod by connecting it to the bottom of the horn. Why I did it the other way originally I don't know. Here's a picture of the tiller rod before repositioning:
I have about 35 hours on the new horn and repositioned tiller rod and so far so good. I check it carefully before flight. I also inspect the rudder hinge for cracks too. If you have a similar tiller rod setup on your Sonerai, you may want to inspect the horn for signs of stress and possible cracks!
-Scott
First let's revisit the problem. One day on a preflight inspection I noticed that the right side rudder horn appeared slightly bent down. When I tugged on the horn, the right side deflected slightly more than the left. Although there was no sign of damage, it just didn't seem right. I decided to take the rudder home and strip the covering. Once the covering was removed, the problem was obvious. A crack had developed along the periphery of the weld just under the covering material and out of sight. Here's a picture:
Closer view:
As you can see, the crack developed on the right side of the horn where the tailwheel tiller rod is connected. Apparently the repeated force applied to the horn from the tailwheel/tiller rod caused the crack to develop. Total time on the airframe was only 102 hours when the crack was detected.
There has been some speculation as to why the crack developed so quickly on my Sonerai while other high time Sonerais with tiller rods never had a horn crack. Some people have said that I had a cold weld. Some said that the angle of the tiller rod is too great. I think it's a combination of these plus flying off rough fields and several hard landings.
So what did I do? Obviously the old horn had to be cut off and replaced. The new horn was fabricated from the same thickness material but I designed it slightly wider than what is specified on the plans so that it wraps around the forward side of the rudder spar. This gave me more to weld to. I also welded 0.090" 4130 steel triangular gussets on the top side of the horn and rudder spar.
In addition to the redesigned horn, I also reduced the angle of the tiller rod by connecting it to the bottom of the horn. Why I did it the other way originally I don't know. Here's a picture of the tiller rod before repositioning:
I have about 35 hours on the new horn and repositioned tiller rod and so far so good. I check it carefully before flight. I also inspect the rudder hinge for cracks too. If you have a similar tiller rod setup on your Sonerai, you may want to inspect the horn for signs of stress and possible cracks!
-Scott
