Another broken flaperon hanger

34 posts in this topic

Posted (edited)

I agree with Leni, definitely add rivets through the aluminum forward of the flaperon brackets. I reinforced mine all with aluminum during the wing build just to strengthen them. The aluminum does not glue well, that is why Avid insists on the high powered aluminum treatment when glueing the ribs to the spars.  Good work on the repair job.

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Edited by SuberAvid

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Posted

I went with bolts in three locations. I have built and repaired several things through the years and i'm not a fan of pull rivets into wood. If the rivet goes clear through the structure and uses metal or a backing washer then I would use them. I will post a picture of how I installed the bolts. 

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Posted

For what it is worth I made these printouts in Autocad. I chose to go around the trailing edge on my model one kitfox. I included two files, one with the notch and one without. I found that each ribtail had to be fitted seperately, mainly because making the 90 degree bend perfect is difficult ( I think thats why atleast). I can also send the dxf file if you choose to send it to a Waterjet. let me know if ayone see's a problem with these. I havent put them in yet. 

ribtail hangar pdf 2.pdf

Ribtail hangar without notch PDF.pdf

I realize this thread is a bit old, but unfortunately it has resurfaced with paramount importance for me... I'll post pictures later, but long story short I found a broken flaperon hanger this spring when swapping over from skis to wheels. And this one broke right at the trailing edge of my wing, so I'll definitely be opening up some fabric to splice in a new rib tail :(

A few years ago I had to do the same thing on a different flaperon hanger and this thread helped me make that repair! So thank you guys! But ever since then I've been meaning to go back and reinforce the rest of them with with aluminum, but... flying is just too much fun so naturally I procrastinated the project and now... well.. here we are... "another broken flaperon hanger".

Durham66, I happen to have access to a waterjet and I like the idea of cutting a bunch of these aluminum covers out all at once. I admit I'm a little confused as to where the bend lines are on your template though. If you still have that dxf file, I would love to see it and maybe use it for my repair/reinforcements if able. Did you end up putting these on your Kitfox? If so how did you like them, and do you have any pictures?

Here's a picture of my previous broken hanger from 2020. I'll keep you all updated and send more pictures of the current repair as it progresses.

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Update:

I've made some good progress over the last month. I ended up making a CAD drawing of the stiffeners shown in the Denney Aerocraft Service Bulletin #9, and had 20 of them waterjet, bent, and primed. However since I have an Avid Flyer Model C, I knew I'd have to modify them somewhat to make them work for the slightly different rib tail design. But still, it significantly sped up the process having all these parts made in advanced. I was then able to borrow a friends hangar to do the repair and started the long and painful process of opening up the wing at each rib tail.

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I started out by stripping off the paint and silver down to the fabric with MEK on all but three of the rib tails. Loosening the glue with more MEK and peeling back the tape, and surgically cutting a line down the top and bottom of the wing fabric. I typically only had to cut 2 or 3 rib stitches to gain enough access to the rib.

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The broken flaperon hanger with evident dry-rot. What I believe caused this was the fiberglass wrapping that the previous owner had put on all the hangars trying to reinforce them without having to open up the wing... Over time, water seeped into parts of the fiberglass that were cracking or hadn't been sealed up very well, then was trapped inside the fiberglass shell that now surrounded the original wooden rib tail.

Let this be a warning to all Avid/Kit Fox owners: DO NOT WRAP YOUR FLAPERON HANGERS WITH FIBERGLASS! (unless you do a professional job of vacuum sealing during the curing process, moisture WILL get in and compromise the strength of your hangers.

I ended up leaving 1 hanger on each wing that appeared to be well sealed with fiberglass and gave no sign of reduced strength. The remaining 8 have now all been reinforced or replaced.

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More dry-rot found on two of the right wing hangers. I cut them out and spliced in new 3/16" plywood tails. I'll show more pictures in the next post.

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Posted

After cleaning the fabric and peeling it back I warmed the epoxy holding the capstrips with a heat gun and used a razor to cut through and release them from the rib joint. I used aluminum foil to keep the heat off the wing fabric as much as possible during this process. It was a pretty delicate balance of applying enough heat to release the epoxy without darkening/burning the wood. I found it better to just go slow, apply some heat while pushing the razor along the capstrip, letting it cool off, then continue with more heat.

I then used a hacksaw blade to cut about a 45 deg notch 10 or 11 inches up the rib, removing the old broken rib tail. Using that as a template, I cut out a matching replacement and sanded in to fit snug in the notch. I also made two scabs to cover the seam on each side of the rib. All of this, with the two aluminum stiffeners, cut from 2024 T3C - .025, were positioned in place and clamped, making small adjustments until the tip of the new rib tail was centered on a string that I tied from the outboard rib tail to the most inboard rib tail, such that all the rib tails would be in alignment. This was done on all the broken and/or rotted rib tails, 3 of them in my case.

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Posted (edited)

All of the aluminum stiffeners I pre-made ended up having to be trimmed down to fit correctly. In hindsight, I would have made the bent flange 0.3 inches shorter and left out the cap strip holes (for the -3 rivets) so that I could have just match drilled through everything after it was glued up, but I worked with what I had. I did not want to remake all those stiffeners again! This pattern should work well for a Kit Fox though, and can be easily modified for any Avid, so I'll attach it at the end of this post along with the DXF.

Another thing, the Kit Fox rib tails all have a slight taper down to the flaperon attach holes, whereas the Avid's are straight. I ended up preferring the added strength of the tapered skag, so I kept it that way on all the stiffeners and just had to cut the notch deeper into the bottom capstrip. The root of the rib ends up being visible further along the underside of the wing, but I didn't think it was very noticeable.

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For the rib tails that seemed to be intact, I cut and sanded off all the fiberglass and sanded them down to clean wood, making sure there was no dry-rot. Then I trimmed the bottom capstrip notch to allow room for the stiffeners to be inserted. Because the Avid's rib tails were not tapered, but the stiffeners were, I could not use the pre-drilled rivet holes along the bottom edge, so I drilled new ones through both stiffener and existing rib tail. See the picture below with the rivets inserted but not driven.

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Next step, gluing!

rib tail stiffener.pdf

rib stiffener.DXF

Edited by sndye117
Add dxf and stiffener drawing
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With careful preparation, having all the rivet holes pre-drilled, pieces cut, sanded, and cleaned up, and everything clamped in place (so I knew it would all fit correctly once glued), the gluing process went pretty smoothly. Of course I was basically fighting cure time the whole way, with the epoxy starting out very runny and dripping everywhere but cleaning up nicely, to the last one being thick and sticky, easy to pack in and fillet around corners but just smearing everywhere when trying to clean it up. It took me 3 rounds of mixing epoxy to get all 8 of them done. I drove the rivets while the epoxy was still wet, and then clamped the "scabs" over the new spliced in rib tails with more epoxy as the last step. Not much else to say about it, the pictures speak for themselves.

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Before glue:

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After glue:

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The next day after everything was good and dry, I drilled holes for a screw on each side of the "scab" and bolted them tight, to prevent them from ever peeling away from the rib in the future.

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Overall I was very happy with how they turned out. Very strong!!

Next step, stitching up the fabric....

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Posted

 I hand stitched the seam on the top and bottom of the wing which helped draw the fabric tight across the rib, then did the rib stitches (hidden modified seine knot). I laid a piece of 4" tape over that and another over the trailing edge seam, so there was 2" overlap on all the cut fabric edges. Then  I laid the old tape back down over everything to help hide the rough edges of the repair. I was able to iron out most of the wrinkles and tighten up the fabric with an iron set to 250F. After applying 3 coats of silver, some sanding, and a top coat, it all blended together very nicely!   Finally got to fly it yesterday!

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Posted

Nice repair!

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