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Flapperon hinges?

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Posted

so I just got the last of my ribs from Brett and am preparing to start building my wings!!! my question is how strong are the standard rib tail hinge mounts, they seem a bit weak to me. I was thinking about adding thin aluminum pieces to each side of the wood tails but not sure if I should cut slits into the bottom cap strip so they go up into the web of the rib or just bend them and attach them right to the lower cap strip. what are some things others have done or should I just leave them alone. Pics would be awesome

-Robert-

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Posted

I fiberglassed mine.

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Posted

I laminated thin flat aluminum sheet to mine using structural adhesive. I made sure to roughen the bonding side of the aluminum and treated with alumiprep and alodine before doing the glue up.

-- Paul S

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Posted

did you just reinforce the tails or should i cut slits in the lower cap strip and continue them up into the web of the rib? what type and thickness of aluminum or how many layers of fiberglass was used? I'm now thinking of carbon fiber. hmmm the possibilities.

-Robert-

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Posted (edited)

KITFOX SITE had a mod with drawings of the reinforcement that the UK required. Might also be in some manuals?

Believe it was .025 aluminum with several rivets, bent 90 and went full width of hanger and up into rib several inches. Think trailing edge was slit?

Since I am going with BIG flaps and ailerons, I am adding 1/8 x 1 x 9 flat aluminum on each side of hanger, but I tend to overbuild.

Somewhere in between might be a good compromise.

ED in MO

P.S. Added: BELIEVE this was in Service Bulletins.

Edited by Ed In Missouri

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Posted

High Country-

My KF3 had the flaperon hanger mods and I can tell you they are a whole lot beefier than simple, stand-alone ply rib tails. There are many ways to reinforce the flaperon hanger rib tails, but this one has the benefit of manufacturer design, PFA/CAA approval and can be retrofitted to finished wings with minimal effort. The fabric patches from the mod on my wings were fairly discrete and did not stick out at all. I like the way the reinforcements is riveted to the metal trailing edge, seems very strong to me. Here's the SB info and pic.

SERVICE BULLETIN #9

SUBJECT: Flaperon hanger rib-MANDATORY

TO: Kitfoxâ„¢ MODEL I, II, III owners

FROM: Denney Aerocraft Company

There have been two cases of Kitfox™ flaperon hanger rib failure documented in the United Kingdom. In both cases the failure appeared to be from side load overstress. Both aircraft had been in recent prior ground accidents. One was in an automobile accident while being transported on a trailer. The other mishap involved a nose-over upon landing. In both cases it is very likely that there were excessive side loads placed on the flaperon hangers which could have contributed to the subsequent failures. In the latter case the failure occurred on the ground during a period of engine operation at very low RPM’s including engine operation on one cylinder, which caused the entire aircraft to shake violently. There was no personal injury to any persons in either case.

As a result of these occurrences the PFA/CAA in England have grounded the entire Kitfoxâ„¢ fleet, subject to a modification of the flaperon hanger ribs that will meet or exceed United States FAR Part 23 requirements for control surface mass-balance supporting structure.

We have designed and tested reinforcements for the flaperon hanger ribs that can be readily fitted to Kitfox™ wings under construction or retro fitted to wings already completed. These modified ribs will withstand up to 150 lbs side load each when in reality the load will most likely be spread over the 5 hanger ribs. FAR 23 requires a side load capability of 12G’s and 24 G’s normal to the plane of the control surface. The flaperon with the Denney Aerocraft mass balance weighs 7 pounds so you can see that it will withstand a side load of over 21 G’s with the modification. We also tested standard un-modified ribs and they withstood 90 lbs of side load (12G’s). In essence they met the Part 23 requirement for side loads without the reinforcement.

To meet the requirements of FAR 23 for in-plane loads of 24 G’s the reinforcement must be installed on the two outboard ribs. (This assumes you have positioned your Denney Aerocraft Co supplied mass-balance in the prescribed position near the outboard end of the flaperon). You should also install the reinforcement on each inboard rib to compensate for slack in the bearing or failure of the fuselage/turtledeck support bearing. If you desire to reinforce all ten flaperon hanger ribs that is Ok but not necessary UNLESS you have installed the rod type mass-balance inserted in the leading edge of the flaperon as some have done in the U.K. If you have used the rod-type mass balance method then you should reinforce all 10 flaperon hanger ribs.

The reinforcements consist of left and right .025†2024-T3 aluminum angles riveted to each side of each flaperon hanger rib end. Each angle is 8 inches long and tapers from a depth of 1.2 inches to .8 inches with a flange of .4 inch. This flange fits flush against the bottom of the rib cap strip. The reinforcement angles are fastened to the tail of each hanger rib with 6 each 1/8 inch x 5/16 inch long blind “POP†rivets. Each aluminum angle is also riveted to the rib cap strip with 3 each 3/32 inch x 3/16 inch rivets. The builder will have to round the ends of each reinforcement angle to match the rib. He can at his option apply FSA-2 structural adhesive or the equivalent to the mating surfaces for increased joint strength. If this is done the reinforcement angle should be cleaned with acetone or MEK and rough sanded with 100 grit sandpaper.

To retrofit the reinforcement strips to a wing that is already covered, you will have to slit the fabric from the trailing edge about 8 inches forward along the centerline of the bottom of the hanger rib. Slit the fabric along the trailing edge about 6 inches on each side of the rib. Then you can pull the flap of fabric back away from the rib so you can drill rivet holes and install the reinforcement angles.

To repair the fabric you will have to remove the paint and dope down to bare fabric with Stits reducer, MEK, or other suitable solvent. Then use fabric tape to cover the slits and use Stits Poly-Tac, Poly-Brush, and Poly-Spray to attach and coat the tapes. Heat-shrink the patches and repaired areas to restore tautness to those areas. Repaint.

This modification is recommended but not required except in the U.K. It is available to you from Denney Aerocraft Co. at a cost $30.00 which includes shipping costs. You could also fabricate it yourself.

NOTE: Do not idle or run the engine in the low RPM range of 0-2000 RPM except passing through this range in starting and shutdown.

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Posted (edited)

Thanks for all the input. After pricing the aluminum that the Kitfox mod used ouch!!! I've decided to use carbon fiber to reinforce them. I'm wondering if I should just layer each side or wrap a layer over the edges as well. hmmm. Hey Bandit you wouldn't happen to have any pics or input on how you fiber glassed yours by chance would ya? I will post up some pics when I get that far. I've been at POST academy for more training for the sheriffs Dept for the last couple weeks and another to go so it will be a little while.

-Robert-

Edited by High Country

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Posted

Thanks for all the input. After pricing the aluminum that the Kitfox mod used ouch!!! I've decided to use carbon fiber to reinforce them. I'm wondering if I should just layer each side or wrap a layer over the edges as well. hmmm. Hey Bandit you wouldn't happen to have any pics or input on how you fiber glassed yours by chance would ya? I will post up some pics when I get that far. I've been at POST academy for more training for the sheriffs Dept for the last couple weeks and another to go so it will be a little while.

-Robert-

Would think that a complete wrap would be stronger and more weatherproof.

ED in MO (ex SD & Caliber Press grad. too)

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Posted

Would think that a complete wrap would be stronger and more weatherproof.

ED in MO (ex SD & Caliber Press grad. too)

That's kinda what I was thinking, just trying to decide do I wrap it out and around the bottom cap strip and back into the webbing or do i cut small slits in the bottom cap strip against the webbing to allow the layers to just go straight through into the webbing? also I've never worked with carbon fiber before so I'm not to sure how many layers I need I'm thinking two layers per side, does this sound about right.

-Robert-

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Posted

Is that really easier than bending up some aluminum? You don't have to use .025†2024-T3 aluminum angles, any aluminum you put on there who'll be significantly stronger than without. Nothing in the scrap pile that might work?

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Posted (edited)

Is that really easier than bending up some aluminum? You don't have to use .025†2024-T3 aluminum angles, any aluminum you put on there who'll be significantly stronger than without. Nothing in the scrap pile that might work?

Even easier, is to buy some 1 x 1 thin aluminum angle, cut into 8 inch pieces,and trim one leg to suit. Then glue and rivet.

ED in MO

Edited by Ed In Missouri

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Posted

Is that really easier than bending up some aluminum? You don't have to use .025†2024-T3 aluminum angles, any aluminum you put on there who'll be significantly stronger than without. Nothing in the scrap pile that might work?

I do have a piece of fairly stout aluminum that was supposed to be for mounting the side radiator but I plan to relocate it down under the belly so I will not need it. Also have the aluminum door panels for the lower part of the door that I plan to replace with lexan so I could use this as well, Would that do you think. If so should I just slit the lower cap strip slide it in and glue/rivet it in place?

-Robert-

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Posted

I do have a piece of fairly stout aluminum that was supposed to be for mounting the side radiator but I plan to relocate it down under the belly so I will not need it. Also have the aluminum door panels for the lower part of the door that I plan to replace with lexan so I could use this as well, Would that do you think. If so should I just slit the lower cap strip slide it in and glue/rivet it in place?

-Robert-

Anything you do is better than nothing, IMO, that sounds good.

ED in MO

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Posted

Thanks for all the input. After pricing the aluminum that the Kitfox mod used ouch!!! I've decided to use carbon fiber to reinforce them. I'm wondering if I should just layer each side or wrap a layer over the edges as well. hmmm. Hey Bandit you wouldn't happen to have any pics or input on how you fiber glassed yours by chance would ya? I will post up some pics when I get that far. I've been at POST academy for more training for the sheriffs Dept for the last couple weeks and another to go so it will be a little while.

-Robert-

I hope to get over to the airport this week sometime, I'll take pictures. I don't think you will be able to see much though. I glassed bothed sides and edges with the thinest cloth I could buy. Only glassed the rib tail that is exposed to the elements.

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Posted

I hope to get over to the airport this week sometime, I'll take pictures. I don't think you will be able to see much though. I glassed bothed sides and edges with the thinest cloth I could buy. Only glassed the rib tail that is exposed to the elements.

pics would be great thanks. so it sounds like you just wrapped it around the lower cap strip then onto the exposed tail is this correct? I already have some aluminum as i have mentioned and also have some 2x2 twill carbon fiber, still trying to decide which would be best.

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Posted

Yes, I went from the bottom side of the cap strip around to the sides.Then I just brushed resin on the edge of the tail though.

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Posted

pics would be great thanks. so it sounds like you just wrapped it around the lower cap strip then onto the exposed tail is this correct? I already have some aluminum as i have mentioned and also have some 2x2 twill carbon fiber, still trying to decide which would be best.

Sounds like glassing would be good protection from the elements. However, the weak point would still be just forward of the glassing. Believe you could do better by either the metal, and epoxy the edges, or extend the glassing up the rib for about 8 inches from tip of hanger.

ED in MO

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Posted

Hate to leave this post incomplete for the next guy that could use the info so I thought I would give my updates. I decided to go with the aluminum plates, I ordered a 2'x2' piece of .025 2024 T3 from Aircraft Spruce this was more than enough for both wings. i opted to not bend them per the KF sheet that Doug posted as i didn't see how this would do much for the tails.Using a small circular saw like blade in my Dremel and a hacksaw blade I cut a slit along side the tails into the lower cap strip being careful not to cut into the web or tail. I made the aluminum extend aprox 1/16" around the entire parameter of the rib tails then slid them through the slit and glued/ riveted them on then filled this small void all around and made a radius with a file and emery paper, It took much longer than I had expected but was very worthwhile. I was very surprised how much stronger they are. the rivets in the web are pull rivets alternating each way they go through i have 3 holes in the tails for squeeze rivets that still need installed but you get the hint from the pics. on the root ribs i opted to put all rivets in from the end for cosmetic purposes. hope it helps someone else, I sure appreciate all the help I have received form this site and hope I can pass some along as well.

-Robert-

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Posted

Nice job, looks solid! :BC:

Well worth the time IMHO, and a heck of a lot quicker/easier than replacing a broken rib tail on a covered wing. I think I will still use the Kitfox style 'L' bracket reinforcements on my Avid+ though. Probably overkill, but I really like that metal to metal connection when attaching the trailing edge material with rivets.

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Posted

I had not thought about the L part riveting to the trailing edge oops. oh well hindsight's 20/20 I guess. live and learn

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Posted

I had not thought about the L part riveting to the trailing edge oops. oh well hindsight's 20/20 I guess. live and learn

Thanks for the followup - I learned from your photos that your ribs are a lot beefier than my Kitfox hangers. Good Job......

ED in MO

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Posted

one more side note. my original ribs are not quite as thick "strong" as Brett's new ribs, If I had known this to begin with I would have replaced all of the long ribs with the newer ones.

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Posted

Nice job, looks solid! :BC:

 

Well worth the time IMHO, and a heck of a lot quicker/easier than replacing a broken rib tail on a covered wing. I think I will still use the Kitfox style 'L' bracket reinforcements on my Avid+ though. Probably overkill, but I really like that metal to metal connection when attaching the trailing edge material with rivets.

so just to make sure i'm imagining this correctly. When you speak of the benifit of metal on metal, do you mean how the two L brackets are connected on either side of the hangars by rivets? The metel isnt actually touching but connected by the rivet? 

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Posted

I reinforced my ribs with .032 aluminum and bent the bottom edge on each side to put an L to it. I followed the outline of the EXPOSED rib and did not go inside the covering. I was really impressed how much stiffer in side to side movement after only doing 2 ribs. I did all of my ribs and used 3 AN screws to attach the aluminum to the ribs. I am really happy with the way it came out and feel it is much stronger.

Mark

 

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Posted (edited)

Nice job, looks solid! :BC:

 

Well worth the time IMHO, and a heck of a lot quicker/easier than replacing a broken rib tail on a covered wing. I think I will still use the Kitfox style 'L' bracket reinforcements on my Avid+ though. Probably overkill, but I really like that metal to metal connection when attaching the trailing edge material with rivets.

so just to make sure i'm imagining this correctly. When you speak of the benifit of metal on metal, do you mean how the two L brackets are connected on either side of the hangars by rivets? The metel isnt actually touching but connected by the rivet? 

No, not exactly. What I was trying to say is that with the Kitfox hanger reinforcements, the metal trailing edge is riveted to the 'L' brackets rather than wood capstrips. In addition to reinforcing the rib tails this technique provides for a more solid wing structure, IHMO. Although, in reality, adding some Hysol is probably more than enough when riveting the metal trailing edge to wood capstrips. Just personal preference I suppose. Hope that helps.

Kitfox SB-9 Wing Rib Reinforcement.pdf

Edited by dholly
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