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Brett82

The Skorpion got stung

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heli_bee

Don't be afraid to try. Here are some photos of a Pike repair. The before photo shows the top surface and the after photo shows the bottom surface.Aftet

20140717_195545.jpg

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satinet

You can use a blue foam rib. That works well.

The mould idea is good but you need to join the skins together well. E.g a chamfer at joint between the old and new skin with cloth. 

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heli_bee

Be prepared to cut decent access if you need to, see photo for access to a damaged joiner box!

20170416_163428.jpg

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Brett82

That's a really nice, clean cut. I might need to do something similar for the right wing to check the spar. Although I think I need to replace the skins front and back of the spar anyway. 

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Witch_1

Sorry to see your Skorp damaged, after you had such a successful outing a few weeks ago.

That's a lot of work (speaking from unfortunate experience....).  If you really want to save the plane I recommend putting a wanted ad in the "for sale" section and on BMFA site for the needed Scorp bits, any of it will save you work. 

(and if anyone has a Race M fuselage or tailplane, please PM me! )

 

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Brett82

Thanks mate, I've always liked the way she flies but after the last race I really have grown attached to her (stupid I know)....

Hence why I'm so keen to fix her. I'm going to try fix it and if any of the damage proves too much then I will see if anyone is willing to sell the section I need.  Must pay for the Fosa first, I'm looking forward to getting that round an F3F course. 

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oipigface

Here's my attempt at wing skin repair. The spar and joiner box were undamaged. The plane has posted a 31.xx since this repair.

Wing repairs.pdf

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Brett82
1 hour ago, oipigface said:

Here's my attempt at wing skin repair. The spar and joiner box were undamaged. The plane has posted a 31.xx since this repair.

Wing repairs.pdf

Now we are talking John, thanks a million. I've saved it and come to the decision this is the method I will use on the left wing which does not seem to have any damage to the spar. I'm sure it will work for the right wing too once the spar is repaired.

I'm going to rebel against Mike and Phil (sorry guys, no offence intended) and start with the left wing. The fuzz is actually quite a mess and although I understand what Phil is saying and agree with it either way I have no option but to hope the spar is repairable. I do think I need to start with the easier option of the 3 just to help me get into it. 

John do you mind if I ask some questions on your method?

1. Will keeping the correct shape be a problem because the root is damaged as I only have one side and the back to glue too? I thought maybe trying to do the top and bottom skin as 1 piece will help keep the correct shape then I can use balsa/foam to form a root with epoxy and microballoons topping it off as mentioned before once the new skin is glued in place. I know the skin might be slightly big as its an outside mold of the existing skin (could try heat and compress the leading edge to get a tighter angle).

2. I think the Skorpions skin if very thin and the foam they have used is strange. I'm worried about trying to burr out a lip to glue it to. Would making the mold slightly bigger and cutting some off the end to use as a lip glued on the inside of the skin but OK? As shown in the drawing I did.

I was also thinking as the root will be open once it has set I might put a some epoxy and microballons inside the leading edge as a filler to give it a little extra strength. Weight is not to much of a problem, I have to do both wings and it will just add to the 900 grams of ballast I can only squeeze into the fuzz...

I can only get the peelply, breather and microballons at the end of the month so anymore suggestions and advice is still more than welcome. 

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oipigface

You won't find out whether the spar is repairable without first figuring out how it is built. You've got a better chance if it's solid moulded carbon fibre structure than if it is built up from multiple shear webs, as some are. (There may be other structures I don't know about.) I've never done a moulded model spar repair myself, but this is what I'd be thinking of doing:

i) find a way of holding the wing so that whatever is left of it is straight. You'll need at least a flat board for this, and probably weights and tape to hold the wing to the board. Spend plenty of time making sure that you can arrange the pieces in such a way as to be sure that any twists or bends have been avoided. You'll need a rule for this, and possibly other measuring devices. As I understand it one wing is relatively intact, so you can possibly use that as a guide.

ii) make sure that you've identified the full extent of the damage to spar. CF structures are made up of tows, and tend to split along their grain, and it is often difficult to know exactly where the damage ends. Doing this is almost certainy going to involve separating the wing skin from the spar, and possible destroying the skin in the process. You shouldn't worry too much about this, but don't destroy more skin than you need.

iii) decide what you are going to do about it. If you can manipulate the spar to make it straight and there are no gaps in it, use thin cyano to hold it. Cyano alone will not suffice for the job though. You will need to add external braces, or Dremel out slots so that you can get some good lengths of carbon tow across the break. You are looking to create full-depth shear webs here, which you can either do with preformed carbon pieces, or by packing epoxy and tows into the spaces you are trying to fill. 

iv) if there are bits missing, or you can't get it straight without removing some material, the same principles apply, only you are probably going to have to be more careful about restoring the strength of the spar. This will usually mean applying pressure to the repair, both vertically and chordwise. I'd be thinking of using wood battens and clamps for the chordwise pressure, and bricks for the vertical pressure. (I've got four bricks in my workshop, which are wrapped in newspaper to stop the dust and make them easier to handle.) It is often difficult to arrange things so you can apply pressure in both directions at the same time, but you'll have to find a way. 

Once you've fixed the spar, you'll need to put the skins back together of course.

 

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Brett82

Thanks again, I will keep this in mind when I look at the right wing.

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oipigface
4 hours ago, Brett82 said:

John do you mind if I ask some questions on your method?

1. Will keeping the correct shape be a problem because the root is damaged as I only have one side and the back to glue too? I thought maybe trying to do the top and bottom skin as 1 piece will help keep the correct shape then I can use balsa/foam to form a root with epoxy and microballoons topping it off as mentioned before once the new skin is glued in place. I know the skin might be slightly big as its an outside mold of the existing skin (could try heat and compress the leading edge to get a tighter angle).

You definitely want the section to be right. Do you know what it is? If you do you can use templates to check. The two roots should be the same, so even if you don't know the section, you may be able to make templates from what you've got left. Alternatively, there's probably soneone on here who has got an undamaged Skorp, who would be willing to trace the root section for you.

It is quite hard to mould CF around sharp corners. It tends to want to straighten itself out, which is why I moulded my tops and bottoms separately. It also helps with the 'oversize' problem, because you can lose some of the excess thickness by taking material off the front edge of your new pieces.

4 hours ago, Brett82 said:

2. I think the Skorpions skin if very thin and the foam they have used is strange. I'm worried about trying to burr out a lip to glue it to. Would making the mold slightly bigger and cutting some off the end to use as a lip glued on the inside of the skin but OK? As shown in the drawing I did.

 

Yes, that seems OK to me. It may be quicker to do as well.....except for this: when I did mine, I was able to adjust the thickness of the lip using a Dremel grinding bit, so that I could get the two surfaces to match pretty closely all the way around. It is likely that your new moulded pieces will be thinner than the original skin, so they would lie below the surface of original skin if they were supported by a lip. This is OK, but requires more filler and more added weight.

4 hours ago, Brett82 said:

I was also thinking as the root will be open once it has set I might put a some epoxy and microballons inside the leading edge as a filler to give it a little extra strength. Weight is not to much of a problem, I have to do both wings and it will just add to the 900 grams of ballast I can only squeeze into the fuzz...

I put quite a lot of epoxy + microballoons onto the leading edge joints when I fitted each of the second patches, then left the wing with the leading edge down, so that the mix would flow into the joint. Two reasons for this: i) it made sure the joint was well glued; ii) it makes it possible to cut the LE  back so that it lines up with the original LE, with little danger of leaving holes.

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Brett82

Awesome, thanks John. You certainly answered my questions there. From what I can see its going to be like skining a cat, I just need to make sure that once I've decided how to proceed I take it slow and think each step through. 

If anyone has a Skorpion and can trace the root for the wing I would really appreciate it. Neither of my wings are suitable for me to do it. Thanks. 

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Brett82

This repair is going to have to be put on hold for a bit while I get the stuff I need but I thought I would take a look inside a wing.  

I decided to open up the left wing to have a good look inside so I could get a better understanding of the damage to the right wing. 

Doing some measurements and guesstimates it looks like the damage to the spar will be where the spar meets the joiner box. I've seen some good stuff online and had a brilliant PM from George on a repair he did. 

I'm going to replace the damaged balsa, sand back the carbon spar caps top and bottom, cut shallow groves and fill with strips of tow, apply layers of overlapping strips of uni carbon (horiz and vert surfaces) then wind kevlar tow  around the whole repair and a bit of the joiner box. 

That's if the damage is how I think it is. It should be a very strong repair, let me know what you think. I will only get the materials this time next month so we have plenty of time for some good advice. Thanks. 

Brett 

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oipigface

One thing you need to be careful of is creating new stress points in the spar. So make sure that whatever you do is feathered out along its length.

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Brett82
12 hours ago, oipigface said:

One thing you need to be careful of is creating new stress points in the spar. So make sure that whatever you do is feathered out along its length.

Will do, thanks mate. 

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satinet

how does a fosa compare?

 

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Brett82
10 minutes ago, satinet said:

how does a fosa compare?

 

There is no comparison... :P

What an awesome weekend we had on the Mynd. The Fosa is amazing (thanks again @jwest532). I had three really nice flights with it and by the last one I was really getting into it. I've still got a long way to go before I am even scrapping the barrel of how much potential it has but even so I could feel a difference. Bring on the next BMFA League race in July...

 

To be fair the Skorpion is still a quick glider. It has to be if I managed to go sub 40 in my last round in Wales. I think they like to be flown in different ways. It definitely feels like I could have good times with the Skorp doing reversals and better times with the Fosa doing EM. I just need to practice the EM turn more with the Fosa. Safe to say Im hooked on Baudis models now.

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Andy_B

you left when it got really good Brett .............

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Brett82
2 hours ago, Andy_B said:

you left when it got really good Brett .............

I guessed that. I even said that too my wife in an attempt to score some extra  brownie points but I don't think it worked. 

I told her I left when it was getting really good so I could be home early enough to help out with the ironing. Then while I was ironing I mentioned there might be an opening at the Welsh open and the reply I got was a short, uninterested "oh"... 

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Les
6 minutes ago, Brett82 said:

I guessed that. I even said that too my wife in an attempt to score some extra  brownie points but I don't think it worked. 

I told her I left when it was getting really good so I could be home early enough to help out with the ironing. Then while I was ironing I mentioned there might be an opening at the Welsh open and the reply I got was a short, uninterested "oh"... 

But was that a "oh" of courts you can go and play for three day's darling or "oh" you can go and get F 😕

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