Hi Kevin, I think I was a bit surprised as well. I looked at screw penetrations of the cap strips as critical weak points, which they are but not to the degree I assumed before doing tests. I was also surprised that my first rib (second test) with its' non-straight screws breaking the ply, held up under the near 90kg weight. Where there is glue, it seems the function of screws is mostly alignment and pressure while the glue sets. It seems the glue (or at least modern glues) more than carries the weight. Unknowable is how this test would have gone using 1917 ply and caesin glue. On the spar (not glued), my take (but very interested in other views) is that the spar screws are resisting lateral forces, so depth doesn't need to be deep (ie. half inch is ok). Mostly those screws are about isolating the stress on one side from the other. The first rib failed at 50kg and in hindsight I believe the lack of screws into the spar was a major contributing factor, putting 30kg of stress on a weak point in the cap strip (poor material, no glue plus a screw penetration). I got a good view in the video of a bottom screw appearing to resist (hold onto) the cap strip from being pulled off. After reflection, I'm no longer convinced it contributed much on that front. More likely is that the top cap strip resisted the downward pull and that it was at the limit of the "stretch" it could provide (possibly that is where the rib would have broken if I had more weight to add). Part of that assessment is that the bottom screw partially pulled out and given it is a tapered wood screw, extended this far it's grip would be considerably weakened. All this is me thinking out aloud, happy for my thoughts to be critiqued!
Fabulous. 😂 I am wondering if the blocks that locate the ribs on the spar will, in final assembly, also be glued to the rib? Seems that would greatly increase the strength.. no?
Short answer, yes (give or take the quality of glues in 1917). Longer answer is that they weren't glued to facilitate field repairs. With the blocks keying the ribs in they are pretty stable. That last rib was severely bowed but at the spar, still vertical.
Given the first on broke at 50kg and the second one was of poorer material and assembly (being the first one I made), I expected it to fail with less than a 50kg load but hopefully learning more about aspects I discuss in the video.before tackling my third test rib.
Is testing to destruction a requirement to getting certified for flight? I don't think a single rib in flight will see that amount of force up to the limits specified by Sopwith.
In short, it's not required for getting certified, however my workmanship will be inspected with a view to safety. With that said, things like insufficient glue probably won't get picked up in an inspection which in my mind makes testing worthwhile and a lot better than discovering I made a mistake at 2000 ft :-) The test weight is based on the aircraft loaded weight divided by the area of the wings. The load each rib carries is based on the area of wing it supports. The answer to that (12.24kg) is then multiplied by a loading factor (think G forces) plus a significant safety margin. In this case x7 (so 86kg per rib).
I was surprised at the end. Those screws both impressed me and make me wonder how much results are being affected.
Hi Kevin, I think I was a bit surprised as well. I looked at screw penetrations of the cap strips as critical weak points, which they are but not to the degree I assumed before doing tests. I was also surprised that my first rib (second test) with its' non-straight screws breaking the ply, held up under the near 90kg weight.
Where there is glue, it seems the function of screws is mostly alignment and pressure while the glue sets. It seems the glue (or at least modern glues) more than carries the weight. Unknowable is how this test would have gone using 1917 ply and caesin glue.
On the spar (not glued), my take (but very interested in other views) is that the spar screws are resisting lateral forces, so depth doesn't need to be deep (ie. half inch is ok). Mostly those screws are about isolating the stress on one side from the other. The first rib failed at 50kg and in hindsight I believe the lack of screws into the spar was a major contributing factor, putting 30kg of stress on a weak point in the cap strip (poor material, no glue plus a screw penetration).
I got a good view in the video of a bottom screw appearing to resist (hold onto) the cap strip from being pulled off. After reflection, I'm no longer convinced it contributed much on that front. More likely is that the top cap strip resisted the downward pull and that it was at the limit of the "stretch" it could provide (possibly that is where the rib would have broken if I had more weight to add). Part of that assessment is that the bottom screw partially pulled out and given it is a tapered wood screw, extended this far it's grip would be considerably weakened.
All this is me thinking out aloud, happy for my thoughts to be critiqued!
Fabulous. 😂
I am wondering if the blocks that locate the ribs on the spar will, in final assembly, also be glued to the rib? Seems that would greatly increase the strength.. no?
Short answer, yes (give or take the quality of glues in 1917). Longer answer is that they weren't glued to facilitate field repairs. With the blocks keying the ribs in they are pretty stable. That last rib was severely bowed but at the spar, still vertical.
I guess CONGRATULATIONS is in order. So, CONGRATULATIONS 🎈🎊🍾
It definately wasn't the result I expected :-)
@@MattProject the twisting of the rib ?? Or at the point of failure?
Surviving much beyond 50kg :-)
@@MattProject 50k , was that good news?? I don’t know
Given the first on broke at 50kg and the second one was of poorer material and assembly (being the first one I made), I expected it to fail with less than a 50kg load but hopefully learning more about aspects I discuss in the video.before tackling my third test rib.
Is testing to destruction a requirement to getting certified for flight? I don't think a single rib in flight will see that amount of force up to the limits specified by Sopwith.
In short, it's not required for getting certified, however my workmanship will be inspected with a view to safety. With that said, things like insufficient glue probably won't get picked up in an inspection which in my mind makes testing worthwhile and a lot better than discovering I made a mistake at 2000 ft :-)
The test weight is based on the aircraft loaded weight divided by the area of the wings. The load each rib carries is based on the area of wing it supports. The answer to that (12.24kg) is then multiplied by a loading factor (think G forces) plus a significant safety margin. In this case x7 (so 86kg per rib).
Hey!.. other viewers.. 73 views, only seven likes before me? Give the guy a like at least!😂😋
lol, it's all good :-)