Previously I posted about the disassembly of the "Oil Hydraulic Struts" as removed from a Curtiss Robin, NR59H. Well, A few weeks ago we finally finished with the repairs and re-assembly of these strut assemblies. Here are some photos of the process...I am happy with the results and believe we have a repair that should last for many years of continued service.
|Portion of tube insert for repair.|
To ensure a proper repair, the design concept for the repair 'insert' tube was to machine a step-down of the outside diameter and to give it a three-inch insertion length to allow the insert to self align to the existing tube. The insert was expertly machined by our friends at Madden Manufacturing, LLC, China Spring TX. We were a little worried about causing too much stress in the upper tube and the potential for cracking during the press-fit-up operation. The shop's owner, Dennis Thom, came up with the right approach for this by effecting a taper of the stepped-down OD from a 0.000 inch fit at the insertion point and gradual taper to 0.0025 interference fit at the last 1.5 -inch of tube to the bottom of its shoulder. The results were spot-on.
At the shoulder, the repair was finished off by welding the interface joint all around. Then the weld bead was ground and polished down smooth and flush with the tube OD. Rosette welds were deemed unnecessary due to the interference fit design which pre-loaded beneficial stress into the assembly.
|Tube 'insert' welded in place and polished smooth.|
|Re-assembly of piston on upper tube with spring-lock clip in place.|
|Installing 'packing' seal.|
|Repaired oleo assemblies with removed portions of upper tube that were replaced.|
|New paint for the re-built oleo struts|
New Lester tires being installed
|The Majestic Curtiss Robin proudly sits on its repaired landing gear|