plehrke

plehrke

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Did a preflight this morning with a flashlight and saw this set of cracks in the LH elevator horn steel weldment at the bolt for the centerline hinge.

Thought it looked like a strange looking crack set but it is along the edge of the weld and coming from a screw hole. Thought I should take a closer look. I removed the bolt and started to pick at it and the paint just started to chip off in rather large flakes. I have had this issue before on the weldments supplied by Vans with the red primer paint. When I built 20 years ago I thought maybe I should remove the red primer as I was going to prime and paint anyway. Ended up leaving on the red primer and painted over it with PPG Concept primer and top coat. All seems to have been fine for 20 years but now it appears the red primer is letting loose from the steel. Same flaking happened on some of the steel hinge fitting a year ago. Lesson learned that the red primer stays stuck for about 20 years and next time I should remove it and reprime.
 

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I had the exact same problem with my elevator horns after 1 year of flight. They were not painted by me during build, so still had the original Vans white paint. Sanded down to bare metal, primed and painted. No more problems in 2+ years.
 
Dye penetrant test?

What about attempting a dye penetrant test on the affected area?

I've seen some reasonably priced kits with dye, developer and solvent. But, I'm no expert on the topic. Maybe someone else could chime in.
 
plehrke said:
Did a preflight this morning with a flashlight and saw this set of cracks in the LH elevator horn steel weldment at the bolt for the centerline hinge.

Thought it looked like a strange looking crack set but it is along the edge of the weld and coming from a screw hole. Thought I should take a closer look. I removed the bolt and started to pick at it and the paint just started to chip off in rather large flakes. I have had this issue before on the weldments supplied by Vans with the red primer paint. When I built 20 years ago I thought maybe I should remove the red primer as I was going to prime and paint anyway. Ended up leaving on the red primer and painted over it with PPG Concept primer and top coat. All seems to have been fine for 20 years but now it appears the red primer is letting loose from the steel. Same flaking happened on some of the steel hinge fitting a year ago. Lesson learned that the red primer stays stuck for about 20 years and next time I should remove it and reprime.
Click to expand...

The photos showed no gap between the center bearing and the elevator horn, which is a good sign. Improper shimming here could contribute to cracking but in my opinion, there’s no indication of that in the photos.
Doing a Diepen. inspection would be the way to know for sure, but as clean as the surface is in the second photo, looking at it closely with a 10 times magnifier would probably be sufficient as well.
 
Weld

The slight discoloration around the weld indicates that the part was not properly prepared before painting. Too late now but light bead blasting, followed by cleaning with solvent and then Randolph Rand O Plate primer is the way to go. The Randolph Epoxy was designed decades ago for the Grumman Ag planes and is incredibly durable. Top coat with your choice of color.
 
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