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Fuselage stiffeners F786B F786C

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dwollen89

Well Known Member
I’m working on a 7A fuselage. I’m trying to figure out how to trim the F786 stiffeners. The plans show details for how to trim the F786B aft end, however, it doesn’t specify how to trim the aft end of F786C, or the fore end of any of the stiffeners. I’ve looked all over the instructions and plans and can’t find anything other than what’s on drawing 18.

I’m assuming that both ends of all the stiffeners get trimmed to fit the bulkheads. Is there some place on the plans that I’m missing?
 

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If you download Service Letter SL-00014 it shows dwg's for the install. As I recall after laying out the rivet hole locations and drilling the top and bottom holes it was relatively easy to locate and trim the stiffeners to fit. A little awkward riveting but not a big deal. Did it on both my 7 & 8 without too much difficulty.
 
RV7 To Go said:
If you download Service Letter SL-00014 it shows dwg's for the install. As I recall after laying out the rivet hole locations and drilling the top and bottom holes it was relatively easy to locate and trim the stiffeners to fit. A little awkward riveting but not a big deal. Did it on both my 7 & 8 without too much difficulty.
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Actually - SL00014 - RV-789-Tail-Cone-Stiffener 8-26-2020 is for Tail dragger versions, not "A"'s, and is for stiffening the most aft bay against deformations from tail wheel side loads. It does not address F-786 long stiffeners...
 
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From memory, the overall length dimensions on DWG 18 will give you tons of spare to play with. I cut the aft end with slightly wider and longer tabs, then trimmed them back to suit. (There's not much edge distance with the 15/32" width, so I initially cut 17/32".)
The forward ends will be trimmed in a similar way—it will make more sense when you come to fit them.
Here's a photo of the B and C stringers, but hidden from view are the tabs that slot in between F-706 bulkhead and the skin.
Stringers.jpg
 
gregmc said:
From memory, the overall length dimensions on DWG 18 will give you tons of spare to play with. I cut the aft end with slightly wider and longer tabs, then trimmed them back to suit. (There's not much edge distance with the 15/32" width, so I initially cut 17/32".)
The forward ends will be trimmed in a similar way—it will make more sense when you come to fit them.
Here's a photo of the B and C stringers, but hidden from view are the tabs that slot in between F-706 bulkhead and the skin.
View attachment 74029
Click to expand...
Thank you very much for the reply. That helps a lot! On the aft most bulkheads, do the stiffener “tabs” extend all the way to the furthest bulkhead? Or do they stop at the first of the two? I’m not at home, but I think it’s F711 and 712 bulkheads if I remember right. I can’t figure it out judging from the plans.
 
I searched my project file and found some pictures that may be insightful for your F786 fabrication, bear in mind that mine is a tail dragger however the F786 end fabrications should be the same. The aft most tab for the bottom stiffener is involved with the rudder travel stops you will fab somewhere down the road... a larger tab than Van's left me on my QB would be helpful for riveting edge distance reasons.
 

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AZSteve053's photos are better than I can manage, and the stringers are the same as on my 7A.
Re the aft tab of the stringer, the main problem I had was ensuring sufficient overlap between the stringer and the tab on F-712 to maintain edge distance. You can see on AZSteve053's photos that the F-712 tab may stick out at a funny angle. The shape of the tab indicated on DWG 18 is merely a "serving suggestion". If you get the aft end right, then trim the forward end as required.
 
AZSteve053 said:
I searched my project file and found some pictures that may be insightful for your F786 fabrication, bear in mind that mine is a tail dragger however the F786 end fabrications should be the same. The aft most tab for the bottom stiffener is involved with the rudder travel stops you will fab somewhere down the road... a larger tab than Van's left me on my QB would be helpful for riveting edge distance reasons.
Click to expand...
Thank you very very much for the pics! That answers my questions. I’ve been at a stand still for several days trying to figure this out. As others have said before, the fuse instructions leave a lot to be desired.
 
I made a “template” from a spare piece of stringer that had the funky shape on it. One side was for left and the other for the right. Once the aft hole was drilled, I popped the template over the stringer and marked the exact cut point that I needed. I think there is a part in my build log on this. If not, let me know and I’ll post a picture or video explaining if you like.
 
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