Strengthening A Luna Fus Around The Fin.

[Mr Ed]

Well the first cracks in the gel coat were there, so time to heed the signs and get a fix in before its really needed.

First we need access. Keyholes are for keys, not my meaty fingers, so lets make a hole or two. Note: I did hold the fus up to a bright light and drew where the rudder snake was glued to the fus side. In retrospect I could have finished the back of the cutout forward of where I did and still managed to undo the elevator pushrod clevis.

Right, here's whats inside your Luna guys.

A pushrod to the bellcrank and a thin rudder snake.

With the pushrod disconnected and removed we can now see the front balsa brace up the fin about a couple of cm back.

But what's that white splogdge in front of it? Microballoons and epoxy, all that is holding the fin halves together, and to be honest its not too bad at that. But if we look further forward we can see that the sploodge goes right round the corner at the front of the fin and ends just about where all the flexing is.

Here is the sploodge on the bit I cut out.

So the plan seems to be grind down a bit of that micro balloon stuff and add some cloth to stiffen things and strengthen the seams. Thrown in a 3/16 play bulkhead. Feed the pushrod back!!!! And only then seal it all up again.

Lets see how it goes over the next few days.

[RGPuk]

Snap! - except I had to go further forward to deal with the extra damage from leaving the proper repair for too long.

Ro.

[Mr Ed]

Great minds etc....

[Mr Ed]

Prior to the bulkhead fix: a few strips of 200g carbon to reinforce the the bits that have been flexing in case the resin has been crumbling. The epoxy is out of the store warming up now...

[Mr Ed]

Right just had an hour on it this evening.

trimmed off excess carbon. Made a 3/16 ply bulkhead with a hole for the pushrod (amazing what one can forget) and a slot for the rudder snake. Ran a lot of thin CA into the porous wood before making the hole as the centre laminate is a bit crumbly.

Glued it in place with 30min epoxy/Cabosil.

I'll trim off the excess wood tomorrow as I refit the missing piece of outer skin.

Re-coupled elevator pushrod while I remembered. Added a drop of CA to be sure of minimal slop.

Doodled a beach scene on the iPod whilst waiting for glue to set...

[Mr Ed]

OK, after a couple of days of overload at work its back to the fixin'

First up, add a few bits of thin carbon and balsa around the inside of the void to bond the removed bit of skin to. Luckily I am never able to throw away those little squares of wing skin that are left when you cut out the servo bays.

A bit of epoxy/microballoons mix is added to the locating lip we jus made and a bit more is added to the edges of the piece to be re-attached and it is taped securely in place. This 'after' shot shows the two iittle carbon pegs I glued to the old skin. They are there to stop the refitted piece getting squished into the hole when the repair was bound with tape while the balloons went off.

Now it is part cured to the green stage I remove the tape and use a knife to cut off any excess lumps of epoxy mix. Much easier than sanding it later.

All thats needed now is a bit of filler, sanding, primer and paint.

Sander du jour

Simples.

The result is rather pleasing. The 200g carbon cloth laminated inside the skin has spread out the local stresses from that vertical rib in the tail and the mini bulkhead at the point where the curvature of the fus met the flat sides of the fin has moved the stresses elsewhere. No doubt we'll discover where that point is further down the timeline...

[Bobbyr]

looks good John ,

Get it maidened m8 , im awaiting the re maiden of the new black Willow , which is nice.

But weather is not playing ball . :mad:

Bob

[Mr Ed]

I'm looking forward to coming down over the next couple of weeks. She'll fly then at the latest. CG moved back a tad but I was moving it back to 107MM anyway so only a tiny bit of extra noseweight needed.

Look forward to seeing the Willow. I have to admit I'm very, very tempted by one. I could get Willow and a Valenta Volcano for the price of a Needle 124.

(BTW: I'm also down for the final week of the sailing Olympics as a dog sitter, so a lot of partying and flying then hopefully.)

[Woodstock]

Andy B is most impressed with his Willow...

[Mr Ed]

Well it makes a sensible idea not to buy a very expensive race machine when I have no intention of ever entering an F3F race.

But when has commonsense ever stopped someone buying a Ferrari if they have the money?

Edit: Just to clarify, I am in no way being dismissive of the Willow's proven abilities. More a comment on my liking the shiniest of toys.

[Jerry Lunt]

John, a tip given to me by Tony Fu.

When you are making joints which require some strength, it is better to use epoxy / microfibre mix. Fibres give much more strength to the epoxy as glass balloons are of course brittle.

[Mr Ed]

Thanks for that Jerry.

I think I had it covered though. The only joint needing extra strength was the one on the skin and the carbon sheet bracing took care of that. The colloidal silica was only used to thicken the mix to stop it sliding elsewhere and the microballons just to pad out the join when I banged the skin back in. If I had fibres I may have used them but they weren't really a priority on any part of this as the joins all seemed well worked out. The only structural stuff was the skin reinforcement and the bulkhead install

Of course the events of the next few weeks will decide if I got that right.