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Crack fuselage,J430


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I bought J430, 110 hours on the clock. I did only 3 landings with her. Had a hard landing first one, bounced but no problems with rest. After landing, I saw this crack in fuselage. There was no pax in back seats with my flight. Local jabiru agent unaware of similar type of injury. AMO working mainly on jab, said they have seen this before.


I got different opinions on the possible cause of this. I thought that the landing caused it, which would be scary, because it was not THAT hard. The person that fixed it, claims that it was a old crack that became visible after the hard landing ( rest under the cover).


Opinion one: Several hard landings ( previous owner denied) but WITH pax at the back, otherwise there is not an arm to bend the fuselage.


Opinion two: Several landings with aircraft in yawed position causing the back bending of the undercarriage, maybe with a congenital weak spot?







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And that's only what you can see....................................................................024_cool.gif.7a88a3168ebd868f5549631161e2b369.gif

U'r right, it extended underneath the cover for total length of 10 cm, but that's not the point. It was professionally repaired and is flying again.


My question was if somebody had similar damage and what the possible cause could be.



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The 'skinny' legs used to break upon a hard landing in the older Jabs but the newer 'chunky' legs transfer a lot more energy to the fuse, it looked to me as if it had a severe landing at some stage.



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Fortunatly the Jabs are single skin, so the visible crack is all there is, of course, you have to sand off the gell coat to asses the actual crack length. typical repair for structural fibreglass is find out how many plies thick the glass is, (eg 6 plies) sand half the thickness of the glass away along the length of the crack, and taper sand 1 inch min 2 inch max for each layer of the plies you have sanded away, so 3 layers will need 3 steps at in 1 inch wide per step. so the repair should look like a n inverted pyramid. or V shape. lay the first ply (1 inch wide strip) over the crack, then the second ply (2 inch wide) over that, and a third the same. put a layer of silk cloth over the repair to give a smooth finish and place a vacuum bag over the whole lot to compress the layers together.


after this has cured, repeat again for the inside of the skin, only this time, you sand down to remove the crack. which should be the first layer of the outer repair. once the repair is complete, the crack will no longer exist and the original thickness is restored. of course, remove the layer of silk to leave behind a smooth finish, if your good, it wont even require sanding.


Jabiru use an Epoxy resin system, the best high strength high bond and high flexibility resin i have used,( and Boeing use on Hornets, on Hawks, Sea Kings, Sea hawks etc) is HYSOL 9309.3 system. purple in colour.



if i can ill try and scan some of the Boeing/Sikorsky SRM manual showing the typical Fibreglass laminate repair. im Sure Jabiru will use a similar if not identical technique. but the number 1 authority is always the aircraft manufacturer.



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i managed to get hold of the PDF scanner at work and scan in a part of the Sikorsky Sea Hawk Structural repair manual referring to general fibreglass repairs for laminates.




Step B i usually do with the sanding disc, as i dont like the idea of cutting fibres below the intended layer your removing.


This repair is Similar but used for Kevlar laminates, and can be used for Fibreglass.



General tips for working with fibreglass.


mark out the shape of the repair plies on a sheet of plastic. (trace the sanded damaged steps to get accurate repair ply shape)


once you have every layer drawn separately on the sheet of plastic (you should have a series of oval/circle/rectangle shapes representing each individual layer)


use a second sheet and place on the bench, and cut a sheet of fibreglass cloth big enough so that all the drawn layers will be covered by the fibreglass, place this fibreglass on the plastic on the bench.


pour mixed resin over the glass.


place the sheet with the "mud map" of the layers you have drawn over the fibreglass. make sure the ink from the pen is not on the side touching the glass.


use a squeegee to spread the resin through the fibreglass. under the plastic (this way you and your squeegee dont ever touch the resin- a lot less clean up!)


it should be a sandwich of fibreglass/resin in between 2 layers of plastic, one with the repair ply outlines drawn on it.


once the resin has soaked/squeegeed through the fibreglass, push excess resin to the edge.


now you can cut out the fibreglass layers. without getting messy, and the plastic makes sure the shapes remain the same.


put resin on the sanded repair area, and peel one side of the plastic of the repair plies. and put it on the repair area like a sticker. you can then move it into position more accurately etc. then remove the top piece of plastic to leave nothing but the layer behind. repeat with all layers.


this way make sure all repair layers are exactly the correct size and located to give a top quality repair. and a lot less mess.



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you do all layers at the same time. you can leave the last layer of plastic on if you want, it produces a nice gloss finish, but it wont be smooth.


if you cant vacuum bag the repair, the best option is to put a layer of silk over the whole repair area, and wet it on with resin like it was another final layer and use a roller to get it as smooth as possible! no air bubbles. when it cures, the silk will peel off pretty easily and give a smooth silk like finish. use industrial fibreglass peel ply silk.


because you have to use an epoxy resin, you can use any paint.


another little general tip, you can repair a polyester part with epoxy, but you cant repair an epoxy with polyester.



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I have seen a couple being repaired at the factory far worse than that but they had sustained very very hard landings and one was almost cracked all the way across the floor after a down draft of some sort apparently smacked it into the gound in a cart wheel fashion, good news is they can be repaired! one 230 was 30kg heavier after all the repairs (cut and shut) but is still flying and performing in WA apparently.


Man can build great things and he can also break them just as well.



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when the jabiru had the gear ripped off,(see previous thread on jabiru engines), the A/C was damaged in a big way (all the gear ripped off) and the lower fuselage was extensively damaged. The factory had it repaired within a week. I dont think it is a major problem, if you can get the aircraft to the factory. To me it looked like a write off.



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