Fins Assy

[ptx]

Hi

after finishing my launcher (under forum topic "Portable Launcher Project") I am now doing my first rocket. I opted for a mini rocket using 0,5L bottles in order to practice assembly techniques and do not waste much material.

I just made the nosecone and now I will draw and assemble 3 fins using corrugated plastic, however I am not very comfortable on how to glue them to the main bottle using sikaflex 11 (could not find PL Premium on local stores). In the future I am planning to do a jig but now I would like to avoid it and glue all the 3 fins at the same time. I am thinking on using tape to keep them in position during cure but I am not sure if it will work.

How do you usually glue your fins? In the same position as pic below, lay down, or with nozzle upwards? Do you use tape to fix them during cure? What do you use?

Thx for the help!

[Nick B]

I use hot melt, and foam fins.


It's fast and dries fast, hold good for most pressure launches, and the fins can shear off in most cases during a tree incursion.

The hot melt sticks have an infinite shelf life and can sit in the glue gun forever and still be usable. Silkflex and pl premium is junk if the tube is not used up soon after opened and has a short shelf life.


I also have a collection of small water rockets to use for recreation without worrying about them going too high, too far, hitting an auto, or collecting on the neighbors roof. They are good fun.

[bugwubber]

Gorilla duct tape for me. If I smash a bottle, I want those fins to be reusable. And if I tear up a fin, I want to be able to replace it.

[ptx]

Thanks! With good reasons you guys are not polyurethane fans ..

Does someone uses PL Premium or Sikaflex and how do you do it?

[Nick B]

Thanks! With good reasons you guys are not polyurethane fans ..

Does someone uses PL Premium or Sikaflex and how do you do it?

PL Premium and Sikaflex are great adhesives. it just depends on your application and preference. If you have no trees within your flight range and a perfect chute recovery system, then a perfect hobby rocket with perfect fins and adhesive is great. PL Premium Sikaflex is great for splicing bottles, bulkheads and other uses. It's just a matter of variable ease of purchase, preference and time.

[bugwubber]

Nice jig for fins that will work with multiple bottle diameters...



Might want to pressurize the bottle a bit while you glue them in place.

[ptx]

Hi again,

as I already bought the sikaflex, I am now willing to use it. I was just looking for some information on people who are using it and how do they glue the fins. Also if tape to fix them during cure was enought or too risky (? seems not a good solution ?)

I really appreciate your input but I was looking for polyurethane experiences, probably on this one I will have to learn by myself.

Nevertheless you were the only 2 guys who tryed to help me so far. Many thx for that!

[bugwubber]

I have used pl premium to do fins in the past. It does require some set time so you will have to come up with a way to hold them in place for a couple hrs. You do want the glue to breathe so dont cover it up while it is setting. Drill cross holes along the edge of your fins for a mechanical lock and sand the mating surfaces. Coroplast is hard to glue so you want to give plenty of mechanical grip for the glue.

You can also just glue footings on the fins, or a fin can if you like the idea of removable fins

Hope that helps

[Blenderite]

Hi nunopt!

I have used PLP in the past and it works great, until you crash. Currently, I am using a system composed of a duct tape band which has the fins hot glued to that. The duct tape band is made up of two layers of duct tape. One layer is applied directly to the bottle with the sticky side facing out. The next layer is applied sticky side down. Then I just hot glue the fins in place. I usually will put a extra bead of hot glue on where the fin meets the bottle. That provides a spec more strength. If you wrap the layers slightly tight, the fins will stay in place on the way up. One thing that is kinda nice is that when the rockets inevitably crash, the band of duct tape will slide up the rocket. I believe this reduces the stress put on the glue joint. (Warning: That last sentence has not been proven. I am not responsible if your fins still break off even if the duct tape band slides down the rocket!)

-DogLover

[ptx]

bugwubber, once again you gave a great help to me! I had the feeling that it was a bit more dificult than just tape it to keep in position ... but thats the fun of it. I am already thinking on a simple fixture to keep them in position (and I will do several small holes at the root edge). Thanks for sharing your experience.

DogLover thats an interesting concept, but to be honest I did not get it completly, however it seems that you are using duct tape between the fin and the bottle: 2 layers-OK / 1st with sticky side facing out-???, and then hot glue the fin to the tape.
I was avoiding the hot glue because of temperature deforming the bottle and your concept probably will avoid it. Is that so?
Can you give more details/photos?

Thx

[Asupremeflight]

I use 3 pieces of angle iron I make a jig. One angle iron to sit on rocket and the other 2 to hold the fin. Just like this one. It works great. http://www.aircommandrockets.com/images ... s_07_s.jpg there are better, more elaborate, jigs but this one is easy and accurate. Also to avoid trashing the fins with a damaged rocket make a sleeve to fit over your most commonly used bottle and glue the fins to it. Then you can transfer the fins to different rocket bodies.

[SaskAlex]

I'm surprised to hear about people having fins ripped off on landing when using PL. I use PL on my fins, and even on my ballistic rockets which always land at high speed, I've never had a fin ripped off. Just make sure to give the root edge of the fin and the bottle a good sanding where the fillet of glue will be. Of course, it also helps that I use small fins, but I still would trust PL over just about any other means of attachment. I can't speak for sikaflex, but the creator of this site recommends it- http://waterrocket.uh-lab.de/laminated_fins.htm. He also uses a little "helping hand" clamp to hold fins while the glue cures.

I've never tried any way of holding the fins other than a purpose made jig. You can see mine here- http://www.wra2.org/forum/viewtopic.php ... +jig#p6966. It's quite simple to make and very easy to use. I've also made what I believe is called a "half the diameter" type jig for T8 FTCs. Both give nice straight fins every time. I think trying to hold the fins with tape would be even more work than making a jig. One thing you could do, is glue one side of the fin with a fillet of hot glue and hold it until it hardens. Glue the other side with a good PU glue, and when that cures, tear off the hot glue fillet and re-do it with PU. I've compared hot glue and PL on the same fins on the same rocket, and the hot glue fins ripped off at launch. A good PL job would never do that. Still, hot glue is great for temporary jobs that need to be separated later. And when gluing to PET bottles, you have to be careful not to let the gun get to full temperature. If you are careful, you can get it to adhere without deforming the bottles.

Hope you find something that works well for you,

Alex

[Blenderite]

Here is what I meant by sticky side to sticky side.

duct tape illustration.png (45.51 KiB) Viewed 113 times

Naturally you could put several pieces of duct tape side by side, overlapped by a 1/4" or so, to make a wider band. Then you can put the top layer, sticky side down, onto the first layer. That creates a ring that can be removed from the rocket. The duct tape is enough of a insulator that the hot glue won't shrink the bottle.

-DogLover

[ptx]

It is great to have you guys when we are starting this hobbie!

Good jig ideias (Alex unfortunately the link to your jig pic is wrong).

Now I see what you meant DogLover. That band is an interesting concept, I suppose that it will work like a sleeve that Asupremeflight mentioned above. Isnt it too flexible? I may try it later after my Sykaflex tube dry.

But now I have several ideias running through my head for a jig. Currently I am thinking on a bigger wood board than my current one and add 3 metal L on top at the right positions to fix the fins with spring clamps during cure (similar to the "L" in pic below), preferably adjustable.

I will think a bit more about it and start looking for the needed materials.

I will let you know on the results. It might take some time because I like to do these things slowly ..

Thx

[Asupremeflight]

[youtube][/youtube]

This is the best one I've seen to date.