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jrd4198
05-14-2009, 02:00 PM
I am looking at purchasing a KFII that has been ground looped. Part of the repairs insclude rib replacement and compression strut repair. My question is this. How diffucult is it to replace the ribs and repair the struts. Is this something that can be completed with a high degree of strength and reliability. I don't believe the current owner has photos of the repair. With out removing fabric this seems a little trusting. Any thoughts on this.

They also mentioned repairing the landing gear which I would most likely upgrade anaway so I am not to concerned with this.

Are there any other points, tweeks or repairs to look for in this situation?

Mark
05-15-2009, 03:10 AM
I have replaced ribs on wings following a ground loop. The ribs and drag/antidrag tubes can be removed and replaced fairly easily. HOWEVER, if the spar was bent, it is trash. It may be very difficult to determine the integrity of the spar with it being covered. You can view inside the wing with the wingtip removed but could only see major damage that way.

The FAA 43.13 is a great source of information, but useless if the builder / repairer doesn't follow it.

jrd4198
05-15-2009, 07:13 AM
Thanks for the replies.

I wasnt sure how you would re attach the ribs to the spar. are they mechanically fastened or are they epoxied or?

mclayton
05-15-2009, 03:14 PM
I am in the middle of rebuilding a KitFox II that was pretty badly trashed in a departure stall. The damage to the wings was very severe on one side, and bad on the other side. After salvaging the good ribs, I am building a new wing, with a new spar, and many new drag/anti-drag braces, as well as new trailing edge and leading edge.

To properly repair the damage, any broken ribs will have to be replaced. If any drag/anti-drag braces are damged, they will also have to be replaced. If the spar is buckled, it will have to be replaced for sure. If it is only very slightly bent, you may be able to straighten it out successfully. The ribs are epoxied to the spars, and so you will need to use a heat gun to loosen the epoxy, then it has to be cleaned from the spar, and a new undamaged rib installed. If the damaged rib is surrounded by good ribs, you will either have to disassemble the wing, or remove and replace ribs. Effectively, if the damage is very severe, you will have to build a new wing. None of this is difficult to do, but you have to be careful to end up with a structurally sound wing, and one that has the proper amount of washout.

I purchased some needed ribs, a copy of the KitFox II manual, and the spar and the internal stiffener from John McBean. He has also been really helpful in helping me to understand what needs to be done.

As far as the landing gear goes, mine was trashed, and I have replaced it with the Bush Gear from John as well.

SkyPirate
05-15-2009, 03:32 PM
here is a trick some of you might of heard of ,..first make sure the inside of the spar is clean,..then take some fine metal dust,.. and dump them down the wing spar,..take a strong magnet and drag the metal shavings all the way around and down the wing spar from the outside,..in doing this flex your wing,..have someone lift slightly and pull down slightly on the wingtip end,..if there is a crack,..the metal dust will go into the crack and stay there,..you will see a faint line on the inside of the spar where the metal was sucked in and stuck,..it's a rather tedious method of looking for a crack ,..but it does work,..if you do see a fine line ..clean the inside of the spar again..taking note of the area the dust stayed,..then try to apply it again in the same area,.. working the magnet all around that area ,..and someone flexing the spar,..it will define the crack again in the same area if there is a crack,..this is on a wing that is coverd of course..

jrd4198
05-15-2009, 10:32 PM
What if a center rib is broke. Do you have to remove the preceding ribs to fix it or can it be fixed by removing and replacing that rib only?

SkyPirate
05-16-2009, 08:51 AM
if I've got the fabric off the wings,..and I see broken ribs,..I'd be replacing them,..and anything else that was broke,..wood is not like steel,..where as if you weld a crack,..it's suppose to be stronger if welded properly,..wood ..if it has a fracture,..you see the fracture,..but you do not see where the ply's of the rib where stressed during the fracture,..if the ply's were stressed and not visible to the naked eye ,..that is a potential place for moisture to inhibit the rib,..

Steve
05-19-2009, 03:10 AM
Does anyone have any experience in fixing wing struts? I have the two long beams that are bent and I guess need eigher replaced or welded. Any have one forsale?

Skybolt
05-19-2009, 04:57 AM
Steve.

Very important....Replace them with new.
Get the side you want from Kitfox aircraft.

Eric

SkyPirate
05-19-2009, 07:39 PM
Steve ..although 4130 is a very strong material,..in the application of a wing strut I wouldn't trust straightening it ,..especially if it has a split in it and you want t oweld it ,..in flight it doesn't only support your wing ..but it supports your life,..let me ask you this ..when it bent the strut ..what damage did it do to the wing spars at the point where they meet the fuselage..the aluminum being softer,..I'd expect it elongated the holes by stretching the material,..this would also have to be inspected and repaired if it is damaged,. you can not weld this area either ,..but you might be able to insert a smaller tube and attach it to the spar..never attach or rivet on top or bottom of the spar ...attach front and back,...ie the sides,..you might have to file the fuselage attach points to fit the smaller tube,..the other option is to replace it completely.
The reason for this repair being crucial ..if you ever went with a negative G load,..and this point is elongated ,..your wing could seperate from the fuselage at that point.
Since the strut was bent ..drawing the wing down,..chances are there is something that got stressed at that point where the wing meets the fuselage.

SkyPirate
05-20-2009, 09:51 AM
I haven't read ac 43-13 1b ,..I'm just curious if there is something that brings that attention to the fuselage,..I'd be willing to repair a section with in the fuselage with a splice and an internal or external sleeve,.and feel all warm and fuzzy about it,..the fuselage is a conglomerant of several structural sections,..
And don't take this wrong ,..I'm speaking personally here,..the strut and my knowing the stress's it is exposed to,..I would weld any crack or break close to the ends of a strut,..because vibration is buffered by the connection points of the strut ..which are on each end ,.and the repair would not be exposed to severe vibration,..in the center of the strut,..you have the jury strut which does buffer vibration,.. at the point that the jury strut is attached,..but ..because both ends of a repair in the middle of a strut would be exposed to that vibration ,..more so then an on end,..and welds are very suseptible to vibration,..there is allot going on there at that point ,..wind induced vibration at speed being the major culprit,..personally I would not repair a strut in the middle ,and get that warm and fuzzy feeling ,..I would get a new piece of 4130 and rebuild the strut before welding it in the center.
that is just my personal feeling about it.

SkyPirate
05-20-2009, 10:26 AM
point taken,..it is up to the owner,.
I have held certification in all phases of welding ..including nuclear,..I was just stating my own personal feeling concerning a strut.

(I want to clarify something . we are talking about a round strut here ,..not an aerodynamic strut)

Chase

SkyPirate
05-20-2009, 01:00 PM
right ,..I was saying the round strut because it is round ..which makes it more suspeptible to the air induced vibration,..a strut that is extruded or formed into an aerodynamic shape has less vibration induced by air flow.
a round strut with a dressing on it to make it aerodynamic has less vibration then just an exposed round strut,..but it is still a round strut ..the added cosmetics does not increase its integrity,..where as an extruded or formed strut is stronger.,.. :) and yes..more expensive to boot.

SkyPirate
05-20-2009, 03:30 PM
yes .that is to make your splice cut on an angle,.and bring the seam to a point,...try your best to never cut a splice joint at 90 degree's ,..unless we are doing pipe fitting for pressures less then 120 lbs psi..but then your welding the same joint at least 3 passes ..a root then fillet then finish

SkyPirate
05-21-2009, 12:17 AM
well ,..my not ever reading that article you posted prior to your posting it ,,and what I have said prior to the post gives merit to what I have said,..and after reading the posted article,,I can see it is a little outdated in welding tech.
From what it is saying ,,it is explaining a flame welded joint which will need annealing to relax any weld induced stress,..now I did not look at the link to see if there were any photos of a correct weld application.
If I were to weld anything on an aircraft today,..I'd be tig welding it ,..not flame welding.
Tig welding is 100% perosity free,..and it does not need to be annealed after a weld is completed,..although some still do,..it's an operator option :)
the one thing in your article that made my sphincter tighten a little was the statement basically saying ..watch the strut during flight for failure ..this is why I would not weld a strut..personally :)
but it is the owners choice,..

and thanks for posting that article ..it backed up everything I said :)

Skybolt
05-21-2009, 04:19 AM
Does anyone have any experience in fixing wing struts? I have the two long beams that are bent and I guess need eigher replaced or welded. Any have one forsale?

SkyPirate.
It looks like you have vast experience with how a strut can be welded per FAA procedures for airworthiness and probably are very good with the welding (making a quality weld)
This is how I see this thread unfold.
But the question is; can your average kit builder tackle such a job?

Steve, the person who asked the original question is looking on.
Can the long beam be welded. from what I read= No. It should be spliced or a big chunk removed from the center and a new tube welded in.
What If Steve can not weld, he can buy chromoly steel tube, the correct thickness and fabricate the repair, then he can take it to a weldor. But will that weldor take on the responsibility of a job that keeps an airplane in flight?, maybe not.
If I were that weldor I would not take on the job.

I would price the wing strut at Kitfox Aircraft and go from there.

Skybolt
05-21-2009, 07:03 AM
airhawg, what are you guys doing with kit planes?

From what I can gather you guys have a wealth of knowledge....A plans built would suite you just fine.
Maybe it's the flying you find the most enjoyable?
I am working on a Skybolt, plans.
Some seriouse thought everytime I work on it, but it is a blast, big difference to the Kitfox, especially the way Kitfox has made the components go together and the easy construction manual. Yeh' I know, a little head scratching but nothing like a plans build.

Sorry to get off topic.
Cheers

SkyPirate
05-21-2009, 09:24 AM
My point was ,.. the strut is not an area for some one with limited welding experience to be messing with,..there are too many forces going on that MUST be accounted for ..replace it.

I'd like to add,..because the strut was bent and put downward forces on the spar at the point where it connects to the fuselage,..this area is just as important..check it for stress cracks ..elongation ,..check the bolt for cracks..the attach point on the fuselage for stress cracks .etc

from the photo it looks like the front strut took a pretty severe hit and it was bent more then 30 degrees at impact,..for it to spring back to what looks like 20 degrees plus minus,..the jury strut looks to be still intact..meaning connected ..so the spar was not allowed to flex between the outer strut connection and the fuselage at the impact moment

dang it carnt spell carwreckly edit edit edit

Steve
05-22-2009, 12:48 PM
I am still trying to find someone that can do welding in or around Arlington, WA. I am wanting a remake the wing strut useing my existing hardware, which is what Kitfox recongmends. I have a welding job needed on the rear tire brace so I need to find a local welder that I can trailer it to.

SkyPirate
05-22-2009, 12:56 PM
Hey Steve,..just curious of the spar was damaged at the fuselage connect points too?