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Kyri

F3F repairs

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Kyri

I love repair threads, and  always learn new things from people who have breathed new life into damaged or crashed planes. Some of the techniques, for example like the creased tail repair with threaded cf tows and ca, are novel and I can't wait to try that. 

I acquired a very (very) nice F3F plane and repaired it, trying to make the repair both cosmetically good but also structurally sound, to cope with future unplanned but hard landings.

I have some pictures of the repair which I will describe and hope it helps someone else as I have been helped by those who share their work. 

Anyway here is the broken nose:

 

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Kyri

It is interesting to see how the break happened around the area where the carbon finishes. It is also quite a thick cross section. 

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Kyri

In the past I have tried a single layer of cloth or a few tows. That was insufficient, as I found out later. This time the thickness of the area to be repaired is reduced with a demel and sanding tools. The vacuum cleaner nozzle is close by, as this debri should not be breathed in.

 

 

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Kyri

I took away about 1/3 of the thickness of the fuz, which was thickest at the bottom. as it will be built up with cf tows and dont want a bulge. Also the outside will be reduced too so need enough cross section left to join. 

The parts need mating straight, so I used a metre long metal ruler as a jig. Taping the parts to the ruler to hold them in place, whilst the cyano tacks them together ahead of the proper repair. The snakes were taped, to prevent glue getting down them. The front of the nose has a hole that will also need repairing.

 

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Kyri

The outside is not very neat, but this can be sorted afterwards.

In the meantime tows are prepared. they have been made long enough to bring the carbon strengthening ahead of the original position. However I did debate whether this is a design feature, ie. it is meant to break there, but went ahead with "serious" strengthening anyway.

The tows are pulled through the epoxy to ensure maximum concentration of tows whilst making sure all the fibres are wetted out. I used the non stick backing of the film used to cover books, to keep the prepared tows before applying them to the inside of the tacked together fuz. Multiple layers were prepared and put inside,  of 12K tows, in around 5-6 layers which should be plenty!

 

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Kyri

The weak areas where the canopy corners are, were strengthened in all four corners.

 

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Kyri

Now, a layer of kevlar and a latex innertube from a bike - very elastic, and able to fill gaps but balloons easily so kept in place with strapping tape during the cure and inflation. It was covered in film to prevent sticking or snagging. 

Then in a warm place for a while...

 

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Mikeb52

Very informative Kyri, and great photos.Looking forward to seeing the finished fuselage. 

Mike. 

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Munch197

Fantastic job on this, looking forward to the final finish. 

Trying to work out which model it is?

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isoaritfirst

Nice job Kyri. 

Once all the inner is set I would grind back the outer layers enough to put a couple of biased cloth layers across the joint and flared back into existing fuselage sides.You should be able to remove enough material to do this without putting any bulge on the outside. Currently you have a break repair that is just patched on one side, not great at surviving a sideways bang. 

Although you could of course consider also the servo tray as part of the structure, making sure it runs back well past the break point. 

Cut a deep U into the end of the tray and take ends of the U back to front incidence pins. 

Dont put too much strength there though as it’s better to break the fuselage than the wing boxes in a impact. Hence the deep U cut out. 

I like to make trays out of layered 1/64 ply. 

Very quick to work with, cut with scissors, and doesn’t need to be tight fit as differences between the layers give good areas for epoxy to grab. Several layers = lots of ply layers and lots of strength as well as an easy install.  Final class cloth layer to complete the tray and finish it to the fuselage. 

Lastly if you haven’t got a vacuum pump, I haven’t. Try this. 

With the outer wrap of cloth. 

Sit cloth on newspaper and wet out. Leave for a while, then scrape off all you can. Then blott off the rest. Get it as dry as you can, then dry it a bit more. 

Put it to the surface and then put it all into a plastic sleeve. A bag with the end cut off. Then squeeze it hard from the centre outwards, keep doing it every 5 minutes . Keep it warm and keep squeezing for 30 minutes ish. I’ve found the air gets pushed out and the vacuum is formed. The end results loook and feel like they have been bagged. 

To keep it warm put it all in another bag and put in a bucket of warm water. Water will apply some pressure as well 

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Andy_B
2 hours ago, Munch197 said:

Fantastic job on this, looking forward to the final finish. 

Trying to work out which model it is?

I guess its a Needle 124

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Brett82

Really nice repair thread Kyri, and great pictures. 

Looking forward to seeing the next steps. 

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Kyri
7 hours ago, Andy_B said:

I guess its a Needle 124

Quite right - it is!

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Kyri
10 hours ago, isoaritfirst said:

Nice job Kyri. 

Once all the inner is set I would grind back the outer layers enough to put a couple of biased cloth layers across the joint and flared back into existing fuselage sides.You should be able to remove enough material to do this without putting any bulge on the outside. Currently you have a break repair that is just patched on one side, not great at surviving a sideways bang. 

This post of yours Mike, (all of it) is excellent, you have a really nice way of explaining things. I have done a variation on basically what you have suggested, so as I go through the next posts and show what I did I will try to reference the reasoning. There may be slight differences, so for example instead of hot water I put the part in a warm place (on top of a cast iron storage cooker) but I like the fact that the water applies a bit of pressure.

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Kyri
9 hours ago, isoaritfirst said:

 

Although you could of course consider also the servo tray as part of the structure, making sure it runs back well past the break point. 

Cut a deep U into the end of the tray and take ends of the U back to front incidence pins. 

Dont put too much strength there though as it’s better to break the fuselage than the wing boxes in a impact. Hence the deep U cut out. 

I like to make trays out of layered 1/64 ply. 

Very quick to work with, cut with scissors, and doesn’t need to be tight fit as differences between the layers give good areas for epoxy to grab. Several layers = lots of ply layers and lots of strength as well as an easy install.  Final class cloth layer to complete the tray and finish it to the fuselage. 

Lastly if you haven’t got a vacuum pump, I haven’t. Try this. 

With the outer wrap of cloth. 

Sit cloth on newspaper and wet out. Leave for a while, then scrape off all you can. Then blott off the rest. Get it as dry as you can, then dry it a bit more. 

Put it to the surface and then put it all into a plastic sleeve. A bag with the end cut off. Then squeeze it hard from the centre outwards, keep doing it every 5 minutes . Keep it warm and keep squeezing for 30 minutes ish. I’ve found the air gets pushed out and the vacuum is formed. The end results loook and feel like they have been bagged. 

To keep it warm put it all in another bag and put in a bucket of warm water. Water will apply some pressure as well 

Really useful info!!! - as it turns out I had a servo tray, servos and inner pushrods from the blue needle in which I had put the servos in the tail because the original pushrod sleeves got broken as that fuz was snapped behind the wing.  I did make a tray out of some glass fibre board for the nose but your method with ply and glassing / vacuuming it looks simple and I like the fact that it keys better to the sides of the fuz. I will try this method. 

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Kyri

Here is how I fast cured the epoxy. I used the space above the cooker which is nice and warm.

 

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Kyri

Removal of the tape, inner tube, and a bit of tidying up. Here is how it looks.

 

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isoaritfirst

Thanks Kyri,

I also always go through a variation of what i posted,

Theres no fun in following a set routine, I enjoy the exploration into new ideas. 

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Kyri

Indeed, I like the journey of a repair - if not the disappointment of breaking something!

Here is the removal of some material to strengthen the outside of the broken area:

 

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isoaritfirst

Probably doesn't need it but if there areas that look weak, I have in the past dremelled in slots across the break and fed in carbon tows before wrapping.

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