Topic: Vector III Wing/Spar repair.

Royally stuffed my Vek in t'other month snapping fuz and a wing
I thought wing spar repairs are not the norm so here's a thread to gather advice and provide future reference.
I know it's commonly said that wing spars are bit of a questionable repair but let's remember. This glider does not launch from a winch, is not a carbon affair and appears to be a viable repair considering the materials.

Here's some pics.

1) Post last repair glory!



2) Upper port side



3) port underside



4) Whoops no control surfaces!



5) Ah, let the dog see the rabbit



6) 2 spars eh?




So we have 2 x endgrain balsa.  The balsa spar uprights are glassed. The upper and lower surfaces are bonded to multiple carbon layers. my measurements from sticking a rule inside are 8mm x 15mm (the front spar is a bit lower). The gap between is about 18mm.

As you can see from the initial upper and lower surface shots the skins are holding it together.  I managed to push it back together to align it true. i've CA'd the LE and underside to give me a datum.
Im happy repairing skins but am pondering the actual spar repairs. Each spar has broken through to the underside carbon. The grain does not jigsaw back together as it appears some material has been lost as the wing bent over. Consequently there is a small gap < 1mm in each spar so that rules out a quick CA and reinforce approach.
Thoughts are to cut out the broken sections and splice in new sections?
Splint each spar either side with a narrow spruce section?
Cut a section of balsa (?) to fit inbetween the spars?
I personally think splicing is the easiest option. Reinforced with some carbon around the spar sides and skin and a new carbon spar cap.

Im completely open to ideas as to effecting the strongest and lightest job.
I need a plan to complete my repair shopping list.

Oh yes, I don't have vac bag equipment so will be completing the skins in the old fashioned way.

Regards

MooSey - Destroyer of Vectors
 

I've just noticed my 'Evil monkey' Avatar is pointing right at the pic of my Vek, accusing me of inhumane glider treatment
Best I do a reet good job here lads!

Looks like a challenge , Its always hard making it worse before you can make it all better again.
Will be watching

Lee

It's had more crashes than ZX spectrum!

Watching this with interest - its a bit like the Falcon centre section - broken spar.

FWIW - its the carbon spar "caps" that provide the real strength, so a repair to the spar caps has to be able to take the tension & compression loads. I'd thought about taking out the spar web, epoxying in some pre-preg carbon strips across the breaks in the spar caps, then rebuilding the spar web. Hope that makes sense? The strength would depend on how good the bond between the existing carbon & new carbon reinforcement was. You have an advantage in that the break is quite a way along the wing, where the stresses are much less than at the root.

Phil.

...wot Phil said

however you need to spread the loads away from the break

I would cut a slot in the skins away from the opened up area, and remove the spar cap completely around the crunched area. Replace the crunched balsa webbing, then pack wetted tows in the slot.

Then reinforce the webbing either side with carbon or tapered glass cloth to spread the stresses.

My personal preference is for wetted cloths as I think you'll get a better adhesive-able area

There's absolutely no reason not to stuff a foam support between the skins here and there - it's a 'bodge' to a mouldie but so what - it works

Interesting.
I like the approach mentioned by Phil and Paul (great diagram btw ) I had previously discussed this with Tony Fu (another model!) and his drift was the same. He did mention that heat and pressure where the key but thats tio effect the strongest repair without adding more weight.
I also feel it's entirely possible to completely overcomplicate matters and take Steves approach.
My thoughts are:
The endgrain spars provide the means to attach the spar caps in the correct place without weighing too much.
The carbon spar caps work in compression and tension to provide rigidity.
There are 2 to provide the strength derived from the LE D box and increase torsional rigity over the wing.
The skin being attached to the sparcaps also becoming a stressed member in compression and tension.
Light simple and strong with a bit of give whe needed.
Thats my understanding?

Hence to benefit from the spar repair as suggested it's crucial I can bond on a new surface skin to attain former strength?
If I merely reinforce the 2 spars splint style then the spars themselves bear more of the forces acted upon the wing rather than the structure as a whole?

Still pondering this one but some great advice so far to help me

the spars / spar caps take the bending loads on the wing - big loads - so need to be strong - need to get the stresses to go from one broken spar cap part to the other for continuity - just adding splints to the sides of the spar web won't do that

the skins take the torsional / twisting loads - not so big loads

(purists would say the wing skins also contribute to bending strenght - but its the broken spar that's the real problem here)

Phil.

Have at a look at this repair project which resurrected a Nyx Furio wing that had suffered bad damage. It was borrowed from the old Sailplane and Electric Aeromodellers of Tasmania site a few years ago and no longer exists on their new one, so thanks to them. The model was apparently winch launched in F3B comps afterwards. 3 parts because of file size limitations

excellent attachments

Need to order some carbon tow then im ready to get repairing.

Just fill it up with carbon and stick a lead weight into the opposite wing tip......................

Carbon is a bit pricey these days.
I was thinking plumbers expanding foam and duct tape

There is one tip I can offer - going back to balsa bashing days - where you've cut your skins way in a 'nice neat' square box - bad news - stress lines etc.

Better to cut a star shape or just random 'wiggly' lines then put your 'new skin' under the hole and draw onto that what you've cut out etc

The Vector is a big thick wing which helps - I'd 'cobble' the existing spar(s) just to get the wing straight again - follow that up with a hefty Spruce spar either side of the original and overlapping as much as you can either way from the break and loads of epoxy and Colloidal or filler to adhere it - an infill of foam under the hole to support the skin repair (balsa then glass cloth and you'll be fine.

Oh aye - next time you fly her - just keep aiming for the planet and missing 

It's not my fault it keeps breaking 
Honest
I blame JimBone for designing a glider that makes me fly it like a chav in a nicked car under hot pursuit from the law. Always ends with a good smack

It's not my fault it keeps breaking 
Honest
I blame JimBone for designing a glider that makes me fly it like a chav in a nicked car under hot pursuit from the law. Always ends with a good smack

ooooooohhh...I love EVERYTHING that ends with a good smack!

I of course fly mine like a Gentle Lady....

I accept the blame though...

Cheers Moose.

Boneham

Ok, here's a tip to repair spars and joiner boxes:

I now preform 'c' shaped braces in 2 layers of 200g carbon (laid at 45 degrees) over a wood plug slightly smaller than the depth of the sheer web. I heat and vac but could do with a wrap of pvc tape. The plug has the corners of the 'C' rounded, say 1-2mm. This is because sheer webs are often put in with splodges of epoxy and micro balloons and you want to clear these.

When cured (don't need to be fully done), cut to length to give a generous overlap of the break. Lay tows on the corner of the skin and sheer web and some along the skin. This makes the spar wider at the break. Coat the sheer web and bottom skin (or which ever skin is opposite to the opening you made) with splodge mix. Do both sides of the sheer web and clamp in your braces. Clean up any oozes especially on the top part of the 'C'. Now let that fully cure.

Then it's just a matter of putting in more tows and splodge when you replace the skin on the opening side. You have an in built flexible lip to sit the new skin on. Cure that.

Take your dremel sand bevel down the spar caps on one side first by going through the skin. You have a very stable surface to work on with the new bracing either side. Taper your dremelling. Then fill with straight tows of varying lengths to fill the 'V' you've just made.

Cure, then do the same to the opps side.

Finish and paint!

Obviously, you need to be careful of creating stress risers and use different length 'C' braces and make them undesized enough to accomodate extra tows on the skin. Laying tows needs to be done without creating risers too.

The beauty about using this preformed shape is that you will be bracing the sheer web and widening the spar and strengthening the skin all at the same time.  Not only that your spar should be thicker too as you will be filling in with tows to the depth of the skin. Well you might not need that many tows but use your judgement!




 

Tony, any chance of a sketch of that?

Phil.

Tony ,
             Are you saying make some carbon channels with curvy edges , use a carved wooden spar a bit smaller than the depth of the sheer web with a 2mm radius on the edge and use this as a plug for 2 layers of 200 g carbon at 45 degrees ,  ?


                            Bob

Tony, any chance of a sketch of that?

Phil.

I can't visualize either. Sorry Tony I know your'e a busy man!

Tony ,
             Are you saying make some carbon channels with curvy edges , use a carved wooden spar a bit smaller than the depth of the sheer web with a 2mm radius on the edge and use this as a plug for 2 layers of 200 g carbon at 45 degrees ,  ?


                            Bob

Yes, simple eh?

Plug is any scrap square timber I have, which is planed down if necessary. I put parcel tape on the 3 moulding faces, maybe wax up once and mould the 'channel' as you call it. Cure, release and trim.

Here's a piccie of the plug for a Sting joiner box I recently did.

Its 14mm thick. The sides width is immaterial.

The arrows point to the side I moulded from.

I laid my carbon on a flat cutting board and stuck on a piece of 2'' tape and cut the cloth to the size of the masking tape.  Wetted it out and rolled hard. Cut this in half and laid these on top of each out to make 2 layers. You can pick the masking tape off one side if wetted out without disturbing the weave. The carbon was then laid on the mould, taped side down. The edges held with more tape and a layer of peel ply and kitchen paper on the 'outside' surface. A sheet of poly over that to act as a release film. Whole lot in a vac bag and into the heat box.

When cured you release a 'channel' which you have made twice the length you need. This is trimmed and cut in half to give 2 'channels one for each side of the shear web or joiner box you are repairing.

Very, very strong.

What I was please about most with this technique is that you don't need the exact shape of the sheer web/joiner box you are bracing (or the same taper spanwise). Slightly undersized and radiused in the corners is the key. Of course I trim the'channel' to reduce stress risers before splodge and tows. (and remove masking tape!)

Tony

So if I've got this right, the C-shapes go either side of the spar?
like:

[ [] ]         or         ] [] [

or do they go top & bottom?
like:

___
|    |
  []
|__|


Phil.
(and his bad ascii art)

 

Gotcha Tony.
All becomes clear now reading your previous explanation.

       ] [] [



Phil.
(and his bad ascii art)
[/quote]

That there!. C's verticats brace web sides, C's horizontals brace skins.

Relative to the fuz of this repair project. Does anyone know a chemical capable of sofening foam P.U glue without damaging the surrounding fibreglass?
I understand acetone will sofen  P.U? I've just tried some MEK and that softens it but it will also make the epoxy tacky in the fuz.
I have successfully removed the stuff from the tailboom half of my snapped fuz by poking and rumaging a very long screwdriver around to dislodge it.
The nose half has limited access due to the ballast tube sat in the way.  A thin screwdriver may be the only way without softening the fuz itself but im open to any labour saving shortcut

Im removing the broken snakes to replace btw.

Leave the broken snakes in place - they're not hurting any - replace with carbon pushrods whilst you're mid repair - golden opportunity to 'upgrade and improve' 

poking around with a long screwdriver (like a chimp with a twig rooting for termites) sorted the dratted snakes.
no need for nasty chemicals.
not sure if rods would go. The gap between the ballast tube and fuz sides is minimal, well snake size!
Should be receiving some carbon supplies soon so progress will be made.