Repairing flaperons

[gizmos]

I have a damaged flaperons caused by the hinge. They were laid flat and a couple areas has skin damage. How do you repair it? Drill stop? Can you cover them with fabric and put a patch on with pop rivets?

[Dave S]

Hi Gizmos,

This is a typical repair that is explained in the FAA's Advisory Circular 43.131b Chapter 4, page 4-26.

If you are not familiar with this AC - it is a large document, laid out in chapters that you can find on the FAA's website and you can download as much of it as you want - the entire AC covers just about any kind of repair/modification you can imagine. An excellent document for builders in the first place.

If I did this right - this should be the correct link for your specific repair, but you can drill down from the main FAA website to the Advisory circulars then search for 43.13 1B and find chapter 4

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library%5CrgAdvisoryCircul ar.nsf/0/99C827DB9BAAC81B86256B4500596C4E?OpenDocument

The cut to the chase is if you have a sharp end to the cut it should be stop drilled, then a patch panel can be riveted over the top of the area. Extra strength if you hysol the patch when it is riveted.

I'd stay away from fabric covering of the aluminum flaperon as a repair - the fabric won't be much of a structural repair for aluminum.

Sincerely,

Dave S
KF7 Trigear Flying
912ULS Warp Drive
St Paul, MN

[gizmos]

Thanks Dave for the fast response. I got this kit from another builder, this was the only damage, the photo shows the worse. The other two places are only dented. Any other tips on the flaperons installation I should know? Stripping the protective coating was easy with paint stripper and a sharp plastic putty knife, I used several because they get dull. I found it was best to start pulling the coating off as soon it starts to get loose. If not, the stripper will break down the plastic and you have hundreds of pieces . I got lucky, two sides came off in one sheet. This kit was started in 1994. Thanks again

[jtpitkin06]

From the photo it looks like you have damage around the hinge slot and the trailing edge.


Amateur built aircraft often use practices and standards set by certified aircraft ias a good example. With that said, be aware that many certified aircraft do not allow patches on aluminum skinned flight controls. Many of them require a re-skin or entire control replacement. However, we have the option with amateur built aircraft to do anything we want within reason.


So if you wish to proceed with a repair, press on. I would cut out the damaged area using nibblers and dress the edges smooth with a file. You may need to cut new foam for internal support. Fabricate and contour a suitable patch from aluminum. Bond with Hysol and rivet in place with pulled rivets.


Short of that you would be looking at ordering a new flaperon.



John

[Geowitz]

On some of the original speedster kits in the instructions the builder was actually told to completely sever the flaperon skins ALL the way around at each hinge location. You can see a 1/4 inch gap in the picture and I am drilling rivet holes for a clip to provide continuity at the trailing edge. Supposedly this was to allow the flaperons to flex a little. You were then told to cover over the slot with fabric. After doing this I found out that the need to do this was deemed unnecessary and I devised a way to cover it all up using .016 aluminum and pull rivets. Wish I hadn't cut them in the first place.

Anyways... my point is I would hardly worry about this as a big issue and would just create a simple patch. You could probably just stop drill, use hysol to fill, and sand it all smooth to where it's completely hidden.

[chefwarthog]

Would it be wise to pop an U shape aluminium stopper 1/8 thick at the top of each slots, when we put together the flaperons to prevent dommage? Dose this kind of dommage often occur?

[DesertFox4]

Damage like shown in the photos usually happens when either the flapperons are off the aircraft or the push/pull control tubes have been disconnected for wing folding.

[chefwarthog]

I had in mind that we do not need to disconnect the control horn to fold the wings of a SS-7, do I make things up?

[Dorsal]

Yes you need to disconnect the linkage to the flapperon control horn to fold the wing.

[chefwarthog]

Merci Dorsal!!

I was thinking on the older model like the KF 2,3,4,5 we have to disconect the flaperons, it's not a big deal to disconect them anyway!!!
thanks for the info!!!:D

[Wingover1]

Hi Guy's. Luckily I came across this old article. I have the same fate as many I suppose where, the flaperons gets damaged when folding the wing in incorrectly and or carelessly. Mine was done by a guy that worked on my plane and his staff folded the wings. I understand the repair process although mine was bend on both sides no cuts. I don't have any pictures at this moment. I have 3 questions nl. 1. Will it not be better to just put a patch over the damaged areas with out cutting out the bend damaged sections to keep the structural strength? 2. Is aircraft grade aluminum sheeting required or can normal aluminum sheeting do the trick. 3.What thickness should the plate be?

[jiott]

I think its best to leave the bent parts for structural reasons, straighten as well as possible.
For just a patch I don't think aircraft grade aluminum is necessary. If the patch requires any sharp bends be aware that the stronger, harder grades may crack at the bend line.
Measure the thickness with a micrometer at one of the hinge slots; I think it is 0.012" but not sure.

[patrick.hvac]

Flaperons are 2024 T3 clad ams 4462 Kaiser aluminum .016

[Eric Page]

I'm in the same situation as @gizmos was in back in 2013 (first post, above), with several flaperon hinge slot ends damaged (some dented, some cut) by improper storage/transport. I'm also in the process of devising a solution, but the guidance in AC43.13-1b is, quite frankly, confusing gibberish.

Starting with Figure 4-16, on page 4-32, we see the method for patching stressed sheet metal skins:

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Notice that the crack length is 2.5" and they specify a patch size "not less than 2 times length of crack," so we can assume the patch shown is five inches long, measured "crack-wise." It appears that it might be a bit wider across the crack, but let's say 5" wide also.

Now look at an excerpt from Table 4-10 and its notes, on page 4-38:

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Using their example with a skin thickness of 0.028" and 1/8" rivets, the table requires 4.9 rivets per inch of width. Note c. allows 75% of that number for a single lap sheet joint (3.675 rivets). If the patch is 5" wide, then the minimum number of rivets would be 5 times that number, or 18.375, which I would round up to 19.

Now look at the patch in Figure 4-16 again. They used a total of 8 rivets across the width of the patch, and the note calls out "4 rivets reqd each side." Confusingly, the drawing also shows 4 rivets along each edge of the patch, so the meaning of "side" is somewhat unclear to me, but let's assume it means "on each side of the crack."

The patch shown in Figure 4-16 has 32 total rivets. Does this mean that the calculated minimum of 19 is for the whole patch? If that's the case, then what guidance dictates the minimum of 4 rivets per side, and how is that calculated? What if the patch is much longer than it is wide; then how many rivets?

It gets worse. Looking at paragraph 4-57.c., on page 4-19, and Figure 4-5, on page 4-20, we see that for single and triple/multiple row rivets, edge distance should be at least 2 times rivet diameter and spacing should be at least 3 times rivet diameter. For double row rivets, spacing is 4 times rivet diameter.

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Using the most space-efficient layout, with the rivets staggered to achieve the closest possible lateral spacing (a technique that is not shown in Figure 4-5, but is used in Figure 4-16), there doesn't appear to be any way to get the required number of rivets across any patch. For example:

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A patch of 1.03" width would require 4 rivets (4.9 x 0.75 x 1.03 = 3.78), but only three will fit, and only if they're staggered. The math just doesn't work, no matter what size patch or how many rows of rivets you use. Even a single row doesn't work; it would require 1/2" total width to achieve 1/4" edge spacing, but a 1/2" patch requires 2 rivets.

If someone understands this and can offer a cogent explanation, I would both be very grateful.

[Wingover1]

Hi Guy's Thank you for the info and feedback. I think my repair process will be to fold the patch over the crumpled area with the 2 ends meeting at the bottom end of the trailing edge. Basically like a book over. thereby ensuring minimum airflow disruption over the repaired section. What rivet sizes and spacing and will it be advisable to use an epoxy as well?

[PapuaPilot]

Eric,
I agree that the information on AC43-13 is lacking clarity. This is one of the more frustrating things an A&P has to learn to get the rating. The issue with the number of rivets isn't an issue for what you want to do, that figure is for lap joints. I don't think the flaperon skins would be considered stressed skins, which means it is a simple patch/doubler repair in my eyes.

If I were to do a repair I would stop drill the crack or clean out the damaged area by elongating the slot slightly. The repair needs to be done with 2024-T3 aircraft aluminum of the same thickness. I would make a patch wide enough to cover the slot on both sides and extend in front of the current slot. Size the patch with enough edge distance for 3/32" rivets (2D = 3/16"), which would be approximately 1" wide and 2" long (size as needed). I would make it with a new slot that puts it back in the original position. Drill the holes with the correct edge distance and spacing. Use pull rivets and Hysol to install it.

Here is a drawing I made that might be clearer. BTW I would radius the corners of the patch.


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[Maverick]

Something else to consider, if you haven't already installed the weights is, move the counter balance weight outboard until it is right in front of the outboard hinge and install there. This puts a harder metal at the forward part of the slot creating a stop against over rotating the flaperon when folding the wing.

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Fred

[jrevens]

Just a thought - I think I would be hesitant to relocate the balance weight to that position. There is probably a reason that they are specifically located where they are, directly over an internal foam rib ... stiffness, distribution of forces, conformity of shape? Changes of that nature on a control surface also have to be looked at considering a possible effect on flutter.

[Maverick]

I can understand your reservation and one should follow their own mind about about it. And, this is pertaining to a series 5. I don't know about the later series or the 1-4.

I did this on my first Kitfox and it's still flying 18 years later. As well, I know of others in the Phoenix area that have also done this. So far, none off them have fallen out of the sky. As for the location as advised by the factory, I don't know how they came to that decision. Mabey it was aesthetics. I am not concerned about flutter because the flaperons are well balanced with the two weights on both flaperons and the balance wouldn't change based on the location of the weights on the flying surface, inboard or out board. Many designers add the weights at either the outboard end of the flying surface or inboard at the beginning of the surface. In the case of the Kitfox, it's sort of both. As long as the offsetting weight of the attachment is ahead of the pivot point of the flying surface and there is static balance, flutter is highly unlikely in an airplane that flies the speeds of a Kitfox. The strength of the attachment of the weights isn't going to be affected much by the location because of how they are designed. I can see that it wouldn't be wise to put the two weights close together, i.e. side by side but them being far apart, the stress of the weights would well dispersed.

It's just a suggestion. I've yet to have the problem of the hinges cutting/denting the aluminum.
Fred

[Eric Page]

If I were to do a repair I would stop drill the crack or clean out the damaged area by elongating the slot slightly. The repair needs to be done with 2024-T3 aircraft aluminum of the same thickness. I would make a patch wide enough to cover the slot on both sides and extend in front of the current slot. Size the patch with enough edge distance for 3/32" rivets (2D = 3/16"), which would be approximately 1" wide and 2" long (size as needed). I would make it with a new slot that puts it back in the original position. Drill the holes with the correct edge distance and spacing. Use pull rivets and Hysol to install it.
Thanks for the clarification, Phil. I was hoping one of you A&P guys would chime in. I'll do as you described. Most of my damaged slots are dented/cut at the forward end, so I don't have enough room for the row of three rivets. With that in mind, would you recommend wrapping the patch around the leading edge and putting those three rivets on the bottom side? I could probably dummy up a wood buck with the flaperon nose profile to get the right bend (or maybe use the fiberglass tip to get it close...).


Something else to consider, if you haven't already installed the weights is, move the counter balance weight outboard until it is right in front of the outboard hinge and install there. This puts a harder metal at the forward part of the slot creating a stop against over rotating the flaperon when folding the wing.
That's something to think about. I had the same question as John mentioned, regarding the effect on balance, but it's hard to argue with 18 years of safe flying. Thanks, Fred.

[jrevens]

Those are all good points, Fred. The fact that it has been done by others, and also proven to be OK by you for so many years up to now is a good testimonial to the change probably being safe. The flying and testing is the only way to know for sure. I tend to be, perhaps, over cautious about changes to a design like that, having been privy to an ugly lawsuit where a relatively minor change was made to a homebuilt involved in a fatal crash, and the lawyer(s) jumped all over it even though it had nothing to do with the accident. Flutter is also a complicated issue. It's amazing how a tiny, relatively minor change can make a surface more vulnerable. It's sometimes impossible to predict what will happen if, for instance, someone were to inadvertently dive the aircraft beyond the red line speed and "excite" the surface with a sudden movement of the controls. You might be surprised to see the very simple and tiny change that made the most difference in preventing a flutter issue with the Thorp T-18 stabilator. A very small amount of additional stiffness was created where the anti-servo tab end rib is connected to its hinge by adding a thin (.015") strip of stainless steel between the rib and the hinge. It was stated in print by the designer, after extensive instrumented testing, that the assembly was most probably flutter-proof up to the speed of sound after that. Stiffness between interconnected components can be a huge factor for flutter, and tiny changes can make a world of difference. This is all just an interesting conversation/subject to me, and I don't want you to think that I was trying to make you worry unnecessarily about what you did.

[PapuaPilot]

Thanks for the clarification, Phil. I was hoping one of you A&P guys would chime in. I'll do as you described. Most of my damaged slots are dented/cut at the forward end, so I don't have enough room for the row of three rivets. With that in mind, would you recommend wrapping the patch around the leading edge and putting those three rivets on the bottom side?

Wrapping it around the LE would be fine. It will make it more challenging to bend it right, but .016" is easy for bend and form.

[Eric Page]

Thanks, Phil. I've requested some quotes to have a batch of these laser cut.

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Assuming they're not ruinously expensive, I'll order some and make any leftovers available to others in the same unenviable position.

[Eric Page]

The order is in and the material is on its way to the laser cutter. It looks like I'll get ~45 parts out of a 12" x 12" piece of 0.016" 2024-T3. I should have them in about 10 days, and I'll be happy to share extras with anyone who needs them.

[mike92104]

I could put a set to use.

[Eric Page]

The flaperon hinge slot repair plates have arrived. I got 45 of them out of a 12"x12" piece of 0.016" 2024-T3.

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Here's the cost breakdown: Material (incl. postage): $15.45. Postage (mat'l to cutter): $7.70. Cutting (incl. postage): $103.89. Total: $127.04, or $2.82 ea.


I need 8 of them for my flaperons. The remaining 37 are available for $2.82 ea., plus $0.50 for a padded envelope, plus postage and PayPal fee. If you want some, please send me a private message with your mailing address, your email address and how many you need. I'll send you a PayPal invoice for the total. Please buy only what you need, so these can help as many builders as possible.

If you want to see what you're getting, or if you're reading this well into the future and you need to make your own, here are the design files:

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This .ZIP archive contains the Solidworks .SLDPRT file, as well as .SLDDRW, .DXF and .PDF drawings. The .DXF is the file that should be sent to a laser or water jet cutter for production. The .PDF drawing includes some rudimentary instructions for installation, and for adapting the plates to the trailing end of a hinge slot.

[Eric Page]

Two takers so far. 21 plates remaining. I'll update this thread as they're depleted.

[ken nougaret]

Eric, pieces arrived today in good condition.
Thanks again

[Jfquebec]

Same problem with mine (both)
i just cut the slut more far on each slot,maybe 1/2 inch..
on kitfox 4

[Eric Page]

I fooled around for awhile figuring out the best way to install my hinge slot repair plates and ruined one in the process, so I thought I'd post what I came up with to ease their use for others.

I started by making a wooden buck for shaping the plates. I traced the flaperon's profile, cut away most of the excess wood and finished it by sanding to the line on a belt sander. I ended up with a nicely bent plate that didn't fit the leading edge very well. Don't waste your time with the wood buck; it doesn't help and just makes the job harder.

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Here's the easy way. Locate the plate so the sides and end of the slots match up, then tape the plate to the flaperon. Use another piece of tape to seal the slot so drill swarf doesn't fall inside, then match drill one of the holes nearest to the leading edge to #40 (be careful; drill punch-through can easily damage the opposite side skin) and install a silver cleco. Double check part alignment, match drill the hole on the other side of the slot and install another cleco.

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Caution: The following procedure requires flipping the flaperon onto its top side. Be careful not to press the hinge arms into the skins, doing further damage. Hanging them off the edge of the table worked for me.

Using your thumbs, bend the plate around the leading edge to the bottom side, being careful to keep it in contact with the flaperon throughout the bend. Holding it down with your thumb as close to a hole as you're comfortable with, match drill a hole. A cleco won't hold the plate down tight enough to drill a second hole, so just repeat the thumb-clamp procedure to drill the opposite hole. Now install two clecos, extend the drill bit as far out in the chuck as you dare and drill the center hole.

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Flip the flaperon over, cover the slot with tape again, hold the plate's arms down tight with a finger and match drill the remaining four holes.

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Trace around the plate with a Sharpie to identify the bonding area, then remove the clecos, lightly deburr the holes and bond-prep the surfaces.

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Mix up a tiny amount of Hysol and butter the mating surface of the plate with it.

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Carefully place the plate on the flaperon and install six 3/32" x 1/8" dome-head pop rivets.

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Flip the flaperon over again, install the three bottom-side rivets, then wipe away any Hysol squeeze-out with acetone or alcohol.

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Done!

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[Eric Page]

Here's the procedure for the aft end of a slot:

This wasn't a tear, but it was dented badly enough that I wanted to reinforce it.

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Cut the repair plate down as indicated in the drawing earlier in this thread and deburr the edges.

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Align the plate with the slot, tape it down, match drill one corner and install a cleco.

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Drill the opposite corner, install another cleco, then drill the remaining holes.

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As with the leading edge patch, mark the outline of the plate, pull the clecos, deburr the holes, bond-prep the surfaces, apply Hysol, pull the rivets and clean up the squeeze-out.

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