There's an article in this month's EAA Experimenter that may be of interest to those that are scratch building their planes. It's a trimmed down version of the NTSB factual report for the 2011 Wright Model B accident with some good pictures of the bad welds. The report does not specify what process was used, so I'm assuming the parts were TIG welded. One news article states that the work was contracted out but did not name the welder.
Full narrative here
PDF of the EAA Experimenter article attached EAA Experimenter - March 2013 - Wright Flyer Weld Failure.pdf
I'm not building anything yet and have only received basic training on oxy-acetylene welding. I'm only bringing this up to satisfy my curiosity. A few questions come to mind:
- What non-destructive methods can be used to inspect welds in 4130 tubing?
- Is there anything about the weld shown in figure 5 (aside from the obvious fracture) that might indicate it would be prone to failure?
- Assuming that a competent welder is doing the work, is any process more likely to have complete penetration of the work (OA vs. TIG)?
It goes without saying that a propeller drive shaft will be under different stresses than a cluster of 4130 fuselage tubing, but I figure there must be something to be learned from this fatal accident.
Figure 1—The two fractured propeller shafts, as received. The left side shaft had completely fractured at the forward weld, while the right side shaft was fractured but still attached in the same location.
Figure 2—The aft fracture surface of the failed forward weld on the left side propeller shaft tube, as received.
Figure 3—The forward fracture surface of the failed forward weld on the left side propeller shaft tube, as received. This is the mating side of Figure 2.
Figure 4—The fractured forward weld of the right side propeller shafttube assembly, showing (a) a side with complete fracture and (b) the small section still intact.
Figure 5—The aft weld of the left propeller shaft, as received, showing a visible crack along the weld line.
Figure 6—Typical section of the forward side fracture surface of the left side propeller shaft forward weld. The areas of fracture, lack of weld penetration, and smearing damage are labeled. Pores were also present on the fractured areas (~50X magnification)
Figure 7—Typical section of the aft side fracture surface of the right side propeller shaft forward weld, after cleaning. The areas of fracture, lack of weld penetration, and smearing damage are labeled. Pores were also present in the fractured areas of this weld (~30X magnification)
Figure 8—Closer view of a typical area of the right side propeller shaft forward weld fracture surface, after cleaning. An area of fatigue could be observed between the unwelded inner area and the rest of the fracture surface.
Figure 9—Secondary electron (SE) micrograph of the left propeller shaft fracture surface, showing fatigue striations near a pore defect, after cleaning. The boxed area is shown in Figure 10.
Figure 10—SE micrograph of the boxed area in Figure 9, showing fatigue striations.
Figure 11—Secondary electron (SE) micrograph of the right propeller shaft fracture surface, showing fatigue striations that developed at the unwelded areas of the forward weld, after cleaning.
Figure 12—SE micrograph of the right propeller shaft fracture surface, showing areas of overstress and post-fracture surface contamination.
Figure 13—Cross-section of an intact section the right side propeller shaft aft weld, showing the depth of the weld penetration relative to the joint (~25X, etched with 4% Nital).
Figure 14—Cross-section of an cracked section the right side propeller shaft aft weld, showing a crack emanating from a gap that had not been welded (~25X, etched with 4% Nital).