flion
Well Known Member
It's taken me a few days to gain emotional distance enough to deal with a huge setback in my project. I had bought an aircraft lift, which seemed like a great assist, both letting me move both aircraft into the hangar and also positioning the aircraft to work at a convenient height. I had contacted the lift manufacturer for maintenance info (it was purchased from the estate of a pilot here in Flagstaff) and they recommended retro-fitting the jack-screw mechanism with a chain hoist. Well, I should have listened because the lift failed on the 16th while I was lowering it to work on the project. Fortunately, that meant that the -6A was safely outside the hangar and I was not under it because it is operated from the side.
I would estimate the weight of the lift yoke (which the fuselage on gear was strapped to) and the fuselage to be close to 3000 lbs. It did not free-fall due to the geometry of the lift but I came down very fast from between 3 and 4 feet, to a sudden stop on the hangar floor. Due to the added weight and the fact that the wings weren't on (no aerodynamic drag like you'd find in a stall landing at that height), I'm sure it's like stalling in from a greater height.
So, the good news first. You'd definitely survive such an incident. I'm not sure what the wing attachments would look like but the fuselage structure was largely intact. Now the bad news. On closer inspection, the side skins were wrinkled low behind the main spar carry through and the bottom skins were wrinkled behind the mains all the way across. The pictures don't show it too well. The was also slight wrinkling at the panel attachments to the side skin. More good news: I won't know for sure until I disassemble everything but it looks like all the rest of the structure is Ok. The floor and seat pans are fine and I'm hoping the ribs underneath are the same (though I will, of course, check. All lateral forms are fine. I expected to find some stress around the baggage door, which was open, but found none. The entire tail cone, including empennage attachments, show no signs of stress. And likewise on the firewall, which had the mount and engine. The gear also checks out.
The big disappointment is, even if the skins are the only things to replace, it means I will just about have to disassemble the entire project. The fiberglass top (fortunately not bonded) will have to come off, along with the engine and panel, seat and floor pans, tail cone, and likely much of the wiring runs, plus the possibility of finding some hidden damage. If the firewall had shown wrinkles, I would also be sending the engine mount back to be checked - no cracks but I'd worry about deformation.
So I'm not really posting all this to vent (Poor me!) but to give some praise for how tough this structure is. I'm not sure I'll trust a lift again. It worked great while I had it but the consequences of its failure is just too much to risk again. By the way, this thread is not about the lift, either. If you want to discuss the pros and cons of lifts, start a new thread. This really is about how the structure stood up to an unusual situation. Pictures follow:
The wrinkle in the side skin is hard to spot but is about at the third hole in the bottom skin aft of the spar and 'peters out' before the line of rivets about midway up the spar.
Again a little hard to see due to lighting but the wave where the two bottom skins overlap extends all the way across the fuselage.
I would estimate the weight of the lift yoke (which the fuselage on gear was strapped to) and the fuselage to be close to 3000 lbs. It did not free-fall due to the geometry of the lift but I came down very fast from between 3 and 4 feet, to a sudden stop on the hangar floor. Due to the added weight and the fact that the wings weren't on (no aerodynamic drag like you'd find in a stall landing at that height), I'm sure it's like stalling in from a greater height.
So, the good news first. You'd definitely survive such an incident. I'm not sure what the wing attachments would look like but the fuselage structure was largely intact. Now the bad news. On closer inspection, the side skins were wrinkled low behind the main spar carry through and the bottom skins were wrinkled behind the mains all the way across. The pictures don't show it too well. The was also slight wrinkling at the panel attachments to the side skin. More good news: I won't know for sure until I disassemble everything but it looks like all the rest of the structure is Ok. The floor and seat pans are fine and I'm hoping the ribs underneath are the same (though I will, of course, check. All lateral forms are fine. I expected to find some stress around the baggage door, which was open, but found none. The entire tail cone, including empennage attachments, show no signs of stress. And likewise on the firewall, which had the mount and engine. The gear also checks out.
The big disappointment is, even if the skins are the only things to replace, it means I will just about have to disassemble the entire project. The fiberglass top (fortunately not bonded) will have to come off, along with the engine and panel, seat and floor pans, tail cone, and likely much of the wiring runs, plus the possibility of finding some hidden damage. If the firewall had shown wrinkles, I would also be sending the engine mount back to be checked - no cracks but I'd worry about deformation.
So I'm not really posting all this to vent (Poor me!) but to give some praise for how tough this structure is. I'm not sure I'll trust a lift again. It worked great while I had it but the consequences of its failure is just too much to risk again. By the way, this thread is not about the lift, either. If you want to discuss the pros and cons of lifts, start a new thread. This really is about how the structure stood up to an unusual situation. Pictures follow:
The wrinkle in the side skin is hard to spot but is about at the third hole in the bottom skin aft of the spar and 'peters out' before the line of rivets about midway up the spar.
Again a little hard to see due to lighting but the wave where the two bottom skins overlap extends all the way across the fuselage.