Repairing flaperons

[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!!!

[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.

[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

[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.

1-8-2021 9-33-41 AM.jpg
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.

[ken nougaret]

Eric, pieces arrived today in good condition.
Thanks again

[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.