3mm aircraft ply fin repair

[snrkl]

Firstly, let me say, when my LRV suggested g10 instead of ply, I should have listened. First mistake.

Deadpool flew perfectly on it’s second flight and the dual deploy worked exactly as it should have.

Only problem was, it found two cars on the road to the launch site as this was a public launch.

I joked on the way up to the road: “I hope that car didn’t damage my rocket!”...

It did... a sideways collision of the fincan with a parked car crunched the fin.



A hasty attempted field repair (second mistake) as I was keen to get it back in the race for my L2.. go fever sucks...

This rocket has internal epoxy fillets in all joints (4 internal fillets per fin), I don’t think I’ll EVER get the fin out to just replace it.

So here I sit, contemplating options:

Option 1: trim all 4 fins and refinish. I’ll be updating OR to see how this sims. Don’t like this option as I REALLY like the look of the “as built” fin shape.

Option 2: sand it back and assess the full damage. Look at cleaning up and gluing the fin, then glassing with 200gsm cloth. While I’m there, I might glass all four fins.

What are people’s thoughts?

 

[snrkl]

I know it’s poor form to ask a question then act before hearing responses, but I had some time today and wanted to get a start.

I thought about it for a while and spent some time looking at the rocket and decided that the trim and refinish was the order of the day.

I measured, scribed, simmed in OR to confirm it would be ok (it will be)



Trimmed the damaged fin using the saw attachment for my dremel (which works well for this...)


Trimmed all the others too


On closer inspection, I was worried the fin had popped it’s fillet near the aft root. There was a crack in the paint and I could fee a little movement laterally.

So I stripped the fin root down using the flappy sanding wheel dremel tool (damn, I love my dremel...)


Couldn’t see where the movement was coming from, so I used the one of the fine tipped diamond points to surgically remove the epoxy.

I had a brainwave and used a torch from behind and confirmed my brainwave: it was only an epoxy “pop” off where the fin meets the BT at the end of the fin slot:



More surgical dremelling with diamond points (how long before I’m a qualified dentist?!) and the epoxy in that overhang is out.

A little wiggling confirmed the fin is solid and in good shape, the movement I get was just the epoxy had let go on the fin side of the BT/fin butt joint behind the TTW slot.

Ready for a little clean up, re-filleting, then some paint work.

 

[snrkl]

And on further thinking, I don’t know what the liability situation is over here if I hit a car with a rocket.

So in hind sight, perhaps hitting a car and the ply fin breaking is better than hitting the car and the fin punching a hole in the door...

 

[blackjack2564]

I thought that after reading first post, many times better to break & replace rather than pay for a dent.

 

[DM1975]

I think it looks cool like that. Don’t re paint it either. It matches the Deadpool theme. I’d never paint a repair on that rocket unless it’s a substantial repair.

 

[snrkl]

I think it looks cool like that. Don’t re paint it either. It matches the Deadpool theme. I’d never paint a repair on that rocket unless it’s a substantial repair.

Yeah... no... [emoji12]

 

[boatgeek]

I thought that after reading first post, many times better to break & replace rather than pay for a dent.

My first thought on seeing the first picture was "Yeah, but you shoulda seen the other guy!" I gotta believe you put at least a little dent breaking that much plywood, but maybe I'm wrong. Looks like the repair is well underway though.

 

[snrkl]

Getting my test on with west system 105/206/413 peanut butter mix...

Only problem was, I forgot to start the stopwatch when I added the hardener.

Didn’t start it till long after the fillets were pulled.

Doh...

 

[BDB]

You did the right thing by trimming the fin.

I repaired one of the fins on my L2 rocket with fiberglass after it suffered a somewhat similar fate. It’s “strong enough” but I’m always nervous about it.

 

[snrkl]

9hrs curing and damn - these test fillets are strong!

 

[snrkl]

I fixed the fillets with west system 105/206/413 peanut butter combo. It certainly didn’t drip, but I’m not sure I like it - it was very rough and kept dropping fibres as I tried to sand it..

So I roughed it up, and put a thin coat of BSI mid cure.

These are more like it!

 

[boatgeek]

I loathe microfibers (est 413/403) with a fiery passion. If you have an opportunity, you might try the high density filler (404) or the filleting blend (405) instead. I believe that they make a cleaner surface. I usually end up doing what you did and making most of the fillet with a wood flour structural filler, then cleaning it up a little and putting a thin layer of a microballoon filled epoxy on top. That sands out really nicely. I think West's equivalent is 407.

 

[snrkl]

413 is just about all we can get here in Australia.

I’m going to order some sig microbaloons to have a play with.

The real reason for trying the 413 was to find a mix for BT/CR gluing that does RUN like the wind...

 

[snrkl]

Well - I was ABOUT to move to repaint today, but as I was sanding, I noticed two other fins had cracked fillets the same way.

Given these fillets are on the fin overhang from the TTW tab, it’s not a problem I would normally have bothered with, EXCEPT: I want to L2 with this rocket next weekend. I don’t want to end up in a “but the fillets were cracked like that when I launched it” discussion with the ACO...

So, I ended up reworking the fillets on these other two fins a little more surgically than the first, given I now knew what was going on; this was now keyhole surgery not “exploratory” surgery...




Once they were dealt with, we prime white:



Grey


Then flat black



And de-mask...



There’s a small white paint ridge (can’t believe I didn’t think to start the tape line with a black coat!

Small problem that I’m not too worried about...

Now we let it sit for 3 days, and then I’ll mask the fins and respray the tube between the fins red.

When I do that, I might also spray a little black over that white tape line...

 

[snrkl]

On a side note: a really easy way to make a reusable rail button tee nut shaft shield:

Tip from a bamboo chopstick carefully threaded into the tee nut, then a little heat shrink tube over the lip.. MUCH better than trying to wrap tape on the little sucker!



And when you’re done, just unscrew it and keep for next time...

 

[snrkl]

I’m so tempted to get one of these printed as a vinyl decal for the fin that broke...

(It’s a deadpool thing...)