Plastic Fin Repair?

[RadioFlyer]

We have a couple of RTF kits that have a one-piece set of plastic fins. We've had a couple of crashes that broke a fin off at the base or very close to the base. Does anyone have any advice on fixing a plastic fin - type of glue, prep, etc.? And for our surviving (for now) plastic finned rockets, is there anything we can do to strengthen them to reduce the chance of them breaking off?

 

[BlueCollar Rocketeer]

I had to do a fin repair on my Rubicon which has all plastic fins. I cut out a new fin from balsa that was the same diameter (or close) to the original. I ca'd the root edge of the new fin to the old and then laminated printer paper on both sides with thin epoxy. If you look real close you can see the outline of the original fin through the printer paper. Came out great and still flies.

Good luck with your repair.

 

[Micromeister]

We have a couple of RTF kits that have a one-piece set of plastic fins. We've had a couple of crashes that broke a fin off at the base or very close to the base. Does anyone have any advice on fixing a plastic fin - type of glue, prep, etc.? And for our surviving (for now) plastic finned rockets, is there anything we can do to strengthen them to reduce the chance of them breaking off?

Yes there are a couple things you can do to reattach broken RTF Styene fins on most of the Estes fincans. some Quest RTF fincans are a different polyproplene injection molded type material that is harder to bond.

Best solvent welder for styrene or acrylic operations would be Methylene chloride (MC) which can be had by the gallon at most Sign Supply places. Smaller quantities can by had of Weld-on 3 or 4 as a decent alternatives that can be purchased from most industrial supply companies like McMaster-Carr.

It's important to do a very good job matching up the break or getting solid contact between the mating parts. Solvent welding reforms the material at the mating parts so it's a good Idea to apply solvent to BOTH parts for the best bond. As the part are pressed together will be some bulging around all sides of the joint. After the material has been allowed to completely reharden (Usually overnight) bulges can be sanded flat.
Better yet leave the bluge as is with an overlaying small epoxy fillet which will releave some of the landing force placed on the new joint reinforcing the repair. Rememeber to rough up the surfaces that will recieve the fillet with heavy 80-120grit sandpaper. These Scratch grooves will give the epoxy a good bit more surface to grab & hold.

 

[boomtube]

The hardest part about fixing a plastic fin is determining what kind of plastic it is and thus what type of glue is needed.

I work with model trains and the number of different types of plastics I encounter is enough to drive you batty; which admittedly is a very short drive for me but is nonetheless true.

The problem with all these different plastics is that the glue that works great for one type is completely useless for another; or worse it appears to have bonded but in fact really hasn’t. You’ll discover this when the fin flies off moments after ignition.

Some of these plastics are utterly unaffected by styrene glue or other “solvent glues” while others repel epoxies and ACCs like eggs off Teflon.

And then there are resin castings.

 

[Scott S]

I broke a fin on my Aerotech Strong Arm and used CA on it but it breaks off everytime it lands. Any recomendations on which product to use?

Thanks

 

[mwtoelle]

I broke a fin on my Aerotech Strong Arm and used CA on it but it breaks off everytime it lands. Any recomendations on which product to use?

Thanks

Where is the fin broken? CA is not a very good choice for a repair because it is fairly brittle.

 

[Scott S]

The fin is broken along the root cord about 1/2 inch away from the body tube.

 

[mwtoelle]

I would probably use epoxy and some lightweight fiberglass (1/2 oz. - 1 oz.) to fix that fin. If you can get the root section of the fin out, try replacing the fin. Just my :2:.

I had a fin break at the break line on the fin tab during landing. That fin was a real pain to fix.

 

[GregGleason]

I broke a fin on my Aerotech Strong Arm and used CA on it but it breaks off everytime it lands. Any recomendations on which product to use?

Thanks

One fin on my AeroTech initiator broke off. I used Aeropoxy adhesive to fix. In leiu of that, a good 15 minute epoxy should help. Do some light sanding on the broken area (don't sand to change the shape, you are just sanding to surface to remove any "gloss" to give the adhesive more "bite"). Then clean the area to be glued with alcohol (being careful not to get it on any painted area). Then mix the epoxy and apply it to both surfaces (not globbed on), then let set for a few minutes, before it "kicks". Then attach it.

If there is significant part of fin that stayed on the rocket, as in half of the fin broke off, you can use it to help set the re-attached fin. You can do that with two straight wooden blocks, a clamp, and some parchment paper. Place the parchment paper over the glue joint (epoxy will not stick to parchment paper, unlike wax paper). Place the wooden blocks on either side of the "good" half of the fin, seat the broken part of the fin, then clamp it. That assures proper alignment. Let cure for 24 hours, then remove clamp, blocks, and paper. You should have a strong fin that is ready for flight.

Greg

 

[BlackBrant2]

I have the same rocket with the same problem, Karl at Aerotech said to use a glue that works on ABS plastics

 

[Rex R]

Consider 'abs' pipe cement. Don't go hogwild with it*, a cotton swab works nicely to apply it.
*To much will melt the fin.

 

[DeltaVee]

I have the same rocket with the same problem, Karl at Aerotech said to use a glue that works on ABS plastics

I successfully fixed a similar break on my aerotech HV arcas... snapped off nearly on the root. First I cleanened the joint, trying to clear any paint... then fit the parts together as best you can and flowed in Plastruct MEK being careful not to get it all over... I did this a couple of times to ensure a decent but not excessive softening of the plastic would occur. Once it all dried up, I applied my favorite filler... Bondo spot putty and sanded away down to the surface... then repainted.

You can hardly tell (after painting) and the fin seems remarkably solid... it has survived once or two flights so far. The moral of the story is that there is always hope!

 

[Back_at_it]

I've used BSI epoxy a coupl eof times when I've broken Estes RTF fins on things like the Alpha III, etc. Works pretty well.

 

[DeltaVee]

I forgot the final result. As you can see, not perfection, but pretty decent... With plastruct, the fin seems pretty solid at least. It certainly complies with the 20 ft rule