Crack in AFT

[mre3333]

I have a crack on the side of my AFT near the front. Do you think this is fixable with a fiberglass repair kit?
https://1drv.ms/u/s!As8mzMk7VnPaxVmbFCdqTjYLOsu4
Thanks
Rich

[g8dhe]

You might want to fix some metal strengthening plate on the inside first, possibly glued into place.

[Doone]

As Geoff said, but yes it is fixable with fibreglass.

[mikeonb4c]

As Geoff said, but yes it is fixable with fibreglass.

I've always wondered how well fibreglass bonds with the AFT material - are there old repairs that are lasting well?

[mikeonb4c]

Useful article here on bonding dissimilar materials

https://www.engineering.com/AdvancedMan ... astic.aspx

Also, depending on type of location and crack, maybe carbon fibre cloth and resin could be a good option

[Tessie]

I repaired mine with fibreglass in mid 2014 and it is still good as it was then even though it has been used regularly, sometimes in strong winds. There is a fact sheet, look for Auto Free Top. It covers everything to putting the roof up, getting it down manually, common faults and one or two bits on repairing cracks. If yours is cracked in a place where the crack is together and not been pulled apart, which it might be being at the front, then it will be fairly straightforward as long as you can get to the inside of the roof. You might not have to remove the gas struts and other bits. Have a look at the fact sheet, it will help you to do the job easier.

P.S. Just looked at your photo. Go for it, I reckon that will be a fairly easy repair. Mine went up the side and onto the top of the roof and was is in a place that gets pressure put on it when raising the roof.

[mikeonb4c]

I repaired mine with fibreglass in mid 2014 and it is still good as it was then even though it has been used regularly, sometimes in strong winds. There is a fact sheet, look for Auto Free Top. It covers everything to putting the roof up, getting it down manually, common faults and one or two bits on repairing cracks. If yours is cracked in a place where the crack is together and not been pulled apart, which it might be being at the front, then it will be fairly straightforward as long as you can get to the inside of the roof. You might not have to remove the gas struts and other bits. Have a look at the fact sheet, it will help you to do the job easier.

P.S. Just looked at your photo. Go for it, I reckon that will be a fairly easy repair. Mine went up the side and onto the top of the roof and was is in a place that gets pressure put on it when raising the roof.

Ah yes, just looked at the OPs photo. Wonder what caused a crack like that. Did you use a metal plate as part of your repair Tessie or just woven glasscloth? Also did you use polyester resin or epoxy resin?

[mre3333]

That's for the advice guys,
I will give it a go when we next get a dry weekend.
So fiberglass repair both sides of the crack followed by bracing the inside by gluing a piece of metal over the repair.
Will let you know how it goes!

Rich

[mikeonb4c]

That's for the advice guys,
I will give it a go when we next get a dry weekend.
So fiberglass repair both sides of the crack followed by bracing the inside by gluing a piece of metal over the repair.
Will let you know how it goes!

Rich

Personally I would rough up the metal and the mating roof surface and (with clamping highly desirable) and bond/glue the metal plate to the roof first. I would then when set roughen the relevant area before overlaying glasscloth and resin. I'm not sure though that a metal plate is necessary, and it could risk transferring stresses abruptedly to where the metal plate ends. Also, for me, the tidier the repair the better. And after all, if not using one results in the crack reappearing, the metal plate option can always be revisited. Instead of the metal plate I'd probably opt for reasonably heavyweight glasscloth tape (maybe tapering from two thicknesses to one to grade out stress joint) or even carbon fibre tape. And i would try and find out what plastic the roof is made of (could be reinforced ABS?) and research for my best shot at best resin to use (probably polyester but....there used to be some great stuff for modellers called Stabilit Express but it aint cheap and technology has probably developed since the 1970s anyway!). All this probably isnt supercritical (e.g. Tessie's experience) esp on a minor looking Bongo AFT crack, but my background is/was jointing competition model glider composite structures so you were focused on light strong long lasting repairs so your wings didnt fold in flight, which is why i always try and go the extra mile. And using the right glue for the right material is a key aspect. Good luck & keep us posted

P.S. Oh and although it might give a stronger repair, I'd really want to avoid fibreglass on the outside surface as it'll ruin the look of the AFT.

[Tessie]

I have to agree with Mike about most of what he says above, I don't know about model gliders but hopefully your AFT won't be crashing to the ground from a height

I didn't bother putting a metal plate in for strengthening and didn't fibreglass on the outside, in agreement with Mike there for the reasons he gave. Luckily I have a good friend who has his own fibreglass company so could get the stuff I needed for free. I used a fairly heavy grade f/glass matting with polyester resin, and of course the catalyst (hardener). If you have a company anywhere near you that manufactures fibreglass goods they might be good enough to let you have some matting, the amount you require will be off-cuts in the waste bin to them, and if you take a couple of jars you should be able to get some resin and hardener ( you will be amazed how little hardener you require) You won't need loads of any of the items so they may give it to you or charge you a minimal amount. I don't suppose you are anywhere in the West Yorkshire area are you? If so I have all the stuff you will need. F.O.C of course as it is to repair a Bongo

Here is most of what I wrote (in Sept 2015) about repairing mine that was inserted into the Fact Sheet. I don't think you will have to remove anything to repair your roof apart from pulling the rubber seal away in the area of the crack.

My roof cracked when one of the motors came loose from the mountings and pressure was foolishly put on the roof to try to close it instead of doing it the proper way. I repaired mine in-situ and it is more than twelve months since now, been up and down quite a few times, been up for two weeks in one period in the Isle of Man when awnings were being destroyed by the wind and has shown no
signs of giving any problems or cracking again.

I raised the roof and propped it in place with lengths of timber at that side before removing the gas strut and the hefty aluminium beam with the roof lifting mechanism. Take your time looking at all this gubbins noting what goes where, but remember you can always look at the other side of the roof to check. Removing the rubber seal from this section will help with the rest of the work. Once you have all the metalwork free you may have to adjust the timber props slightly to make sure the roof aligns correctly where it has cracked, i.e. it is straight and not bent. If you are lucky the cracked pieces will fall into place but more likely you will have to do some manipulating. If needs be you can align them by clamping strips of thin wood or metal on the inside and outside but do not cover all the crack. I suppose you could rivet or screw strips of metal across the cracks to be removed later but this just gives extra holes to be filled.

When you are happy that the area is as close to its normal position as possibly start fibre-glassing on the inside, I slightly roughened the surface first to give a bit of 'hold'. I used fairly heavy duty matting and overlapped the crack by a fair amount. Once the repair has hardened the strips that were clamped or riveted/screwed to hold the crack together can be removed and these areas then fibre-glassed. It may not be necessary but once it had all hardened I gave it another coat of resin mix and also ran resin into the cracks on the outside of the roof.

Once you are happy that all your hard work has hardened off you can put all the metal work back and the gas strut and lifting mechanism. All that is left then is to rub down the repair on the outside, possibly a little filling and some repainting, although I must admit I haven't got around to doing mine yet as I thought I would wait to see if the repair stood up to the rigours of use ( that is my excuse anyway), which it has.

Good luck, go for it you can do it

[mikeonb4c]

Great advice from Tessie - i'd back that 100%. The only reason i don't use matting is its horrible stuff to work with for what i used to do. But its better stuff for blending+evening out stresses. It should all be easy to do job. Treat yourself to a box of disposable plastic gloves, disposable paintbrushes, and things like polythene (not too thin and maybe sprayed / wiped with suitable release agent) to lay over wet repairs so you can then placed any clamping batons and / or work the matting a bit without it getting into a mess, lifting onto your hands etc. This kind of trick can help give a fairer faced repair also, with the polythene acting as a 'mould face'. But since its hidden, its not crucial.