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Darren_O

Ocelot wing saddle cracked

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Darren_O

Bit miffed with this, it's only had a few flights and the landings were absolutely lovely, slid in gently. Wicked pink zap into the crack after second flight, but after landing the third time it's really opened up as you see in the pics. If I hold the nose and gently twist the tail/boom it seems so easy to twist :( No strength at all.

I'm new to mouldies, is there anything I have done to cause this? 

On to repairs....thanks to East Coast Fibreglass I am well armed with repair materials. I have carbon twill sheet, tow, carbon and f/glass tape, fibreglass sheet and West epoxy.
My initial idea was to throw a sheet of carbon cloth over the whole area, I'm not too fussed abut looks as long as it flies :)
I've seen a few ocelots with cracks in same place, one on rc groups detailed his repair but it seemed long winded...
How would you repair this?

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Darren_O

Sorry, forgot to add pics.

_E8cxOnM.jpg

64QL8uUo.jpg

c8Nqr7nr.jpg

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satinet

The ocelot was very thinly built. Not typical.

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Darren_O

Thanks, I was beginning to think I was cursed. Fuse feels very easy to twist, nothing like the banana.

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satinet

They're both fragile compared to most bigger models.

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Phil.Taylor

jiggle the cracks back into place & wick thin cyano in there to start

then add several carbon tows across the hole & beyond the cracks - in the "corner" at the top of the fus

and several layers of carbon or glass across the hole & beyond on the inside of each side - enough to make up the thickness of the original lay-up - and then some more - see if you can make the hole into a lot less wide than whats there - the current hole is too big & that's what's causing the problems - not enough strength left so it breaks in the corners. Strongest would be to do away with the hole completely & have a self-connecting "plug n play" plug/socket set into whats currently the middle of the hole.

that wing connector - someone has soldered it up wrong - you're supposed to solder to the other side of that part of the connector ! (have a look at a few installation pics of MPX greenies)

have fun!

Phil.

 

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Darren_O

Previous owner did the wiring, I think I'll rewire it completely whilst it's in the workshop. Thank's for the advice, The hole is weak and the amount of flex there is incredible. Fully ballasted on the Orme it just couldn't cope.

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swarrans
11 hours ago, Phil.Taylor said:

 

that wing connector - someone has soldered it up wrong - you're supposed to solder to the other side of that part of the connector ! (have a look at a few installation pics of MPX greenies)

have fun!

Phil.

 

Just when you thought you had seen every possible mistake!!!....

.Simon

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pete beadle

Hi Darren

I don't want to dump cold water on to all your good work but, if you're going to completely rewire the Ocelot and, with the info that your one is probably a fragile one because of the thin moulding, don't you think it might be worth beefing every part of the fuselage - or even replacing it with a stronger one, not necessarily an Ocelot one?

I looked at your pic of the wiring of the MPX connectors and, for a while, simply couldn't see what the fault was, because it was such a basic and frankly unbelievable mistake it made me think this plane has probably been built by someone who had never built an R/C glider before - and worse, what other mistakes are there, but still not discovered yet:(

Regards

Pete

BARCS1702 

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Darren_O

I can see in places where far too much epoxy has been left on, part of the wing saddle is all epoxy and no cloth in the corners. Not brilliantly put together by manufacturer.

As for the builder...lots of slop in linkages and wiring desperately needs sorting, control link to elevator is slightly on the cock. 

BUT...it was £100 servos included so I don't mind a bit of work. Once done it will be a nice glider for not much money and I'll have improved my building skills and knowledge a bit. 

The MPX connector..I didn't notice, I would have happily copied that I reckon :)

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isoaritfirst

Just maybe, and I'm trying hard to give the original builder some credit, he has done this wiring deliberately.

Plugging the solder tags into the socket may (and I haven't tried this) allow the connection to come apart much easier in the event of a heavy landing and a wing being knocked off.

But I'm really clutching at straws, because if that was the thinking then the wing bolts should be replaced by thin plastic ones. 

 

Using plastic bolts is something you should adopt Darren, breaking a bolt rather than putting all the shock into the fuselage will save your model.

Beyond that - you could look at adding a ballast tube, installed correctly they will add significant strength to that area of the fuselage, and improve you flights.

 

Lastly - around 15 years ago my lads shooting star developed a similar crack. A quick fix with X-weave tape kept it flying. If after you're repair it still feels weak - add some tape. its a remarkably strong and light way to add strength

 

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Phil.Taylor
5 hours ago, Darren_O said:

I can see in places where far too much epoxy has been left on, part of the wing saddle is all epoxy and no cloth in the corners. 

The MPX connector..I didn't notice, I would have happily copied that I reckon :)

Epoxy&microbaloons in the corners is standard practice - cant get the glass laid up into the sharp corners.

Theres another fairly easy way of fixing it - square hardwood suitably shaped & epoxied in the corners across the hole & beyond

Phil.

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oipigface

Hardwood maybe, but I would be thinking about moulding a carbon fibre channel, to fit inside and under the saddle. Make it the same width as the inside of the fus, as long as will fit between the wing retention screws and 5-10mm deep. Use two or, preferably, three layers of carbon. Cut out as little of the original material to enable fitting of the new channel, and before you fit it in place fix a new MPX plug into it (wired up of course). Glue it in. Lots of epoxy and microballoons.

You'll need to do some work on the mating MPX plug in the wing.

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Phil.Taylor

But then - you could achieve the same thing with a 3mm ply plate - but not as bling as carbon 😏

Isnt it great - fixing other folks planes

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oipigface
24 minutes ago, Phil.Taylor said:

But then - you could achieve the same thing with a 3mm ply plate - but not as bling as carbon

Not as  bulky and not as light, more to the point. I don't know what else has to fit inside the fus at that point, but there may be issues about fitting it all in.

You're right about having the power but none of the responsibility!

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Darren_O

Thanks for all the advice, I've sanded back the cracks a little with a mini drum on the sides of the fuse then put a little cloth in. The top of the saddle I've cut across the cracks with a mini diamond disk and put carbon tow across. Once this has cured I'll lay carbon across the saddle and down the side.

@ Isoaritfirst Plastic bolts is on my list of things to pick up at Webbs next time I go. Also it has a ballast tube fitted.

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Darren_O

Flew it fully ballasted in a good blow on Boxing Day, went well.

Took it up yesterday barely a breath of wind and the saddle went again. Cracked the tow I'd inlaid! Sides bowed out slightly. Beginning to think the wing doesn't mate well.

Will wrap in carbon this time and very thin foam tape the saddle for a better fit.

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Scram

When applying epoxy for strength, I would not mix micro balloons. These do not add strength (in fact they make the epoxy much more brittle), they just lighten the mix.

For strength, use micro fibres or milled carbon or glass fibres.

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oipigface

The other thing you should remember about carbon fibre is that, as long as the fibres are all thoroughly wetted out, material made from it is stronger the greater the ratio of carbon to the matrix resin (epoxy in your case). It helps if, when you are applying tows to a surface, you can apply some pressure to it and use a breather layer over peel ply to absorb the epoxy that is forced out. What I have done with cracked fuselage repairs several times in the past is Dremel grooves into the general area of the cracks, and lay CF tows into them. Wrap the relevant area with peel ply, and then breather. (Purpose made breather quilt can be got from Easy Composites. Some people are contented to use wads of bog roll as a substitute.) The next step is important. Get some strong tape and wrap it as tightly round the repair as you possibly can. Then leave it somewhere warm to go off.

When you unwrap it, you should find a surface that requires little extra work prior to whatever finishing you want to do.

Later today, I'll post a photo of a Pitbull inner nose that had this treatment. Tolerances on these noses are small, so the job needs to wind up almost exactly the same size as the original. It doesn't look very pretty, but it does the job, and if you are concerned with the looks of the thing, get out the spray cans and wet-and-dry.

Since the wing saddle takes quite a lot of stress, I would also suggest that you follow my previous advice and mould a piece that will fit inside. (Or follow Phil Taylor's alternative suggestion of strips of wood fitted internally.) That, and reinforcement of the fuselage skin with tows in grooves, may well beef it up enough to last a little longer.

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