Any Sugestions How On How This Happened??

[William]

well I flew my commanche-3 and it flew great. I flew it for the first time singel staged on C6-7, it came back on it's streames great, but when i got to were it landed at first she looked fine, then I noticed that,well it looks like the paper under one fin seperated, or should i say the bt seperated from the glue, the only thing i can think would have caused this is not sanding the the tube before glueing on the fins, now i did sand the bt first. has any one seen this happen,?? was this just bad luck?? if not bad luck how can i prevent this from happening again?? THANKS

 

[Donaldsrockets]

You didn't do anything wrong. This rocket comes down pretty quick on the streamers and unfortunately hits fins first and since they are surface mounted, they do tend to get knocked loose.

I flew my Comanche twice, once as a two stage and as a three stage and on both flights, a sustainer fin popped loose on landing.

Certainly an annoying little quirk if I do say so myself. This is one rocket where TTW fins would be a huge plus.

As a tip, I suppose you could use CA to tack the fin back on and put an epoxy fillet on each side.

 

[Mad Rocketeer]

Search on "double glue", "glue rivets", and "through the wall". I can't quite see what happened from the picture alone, but proper surface preparation and gluing techniques will make a joint that's stronger than the paper and wood that are held by it.

Sand the tube where the fins will attach, and rough up the fin root edge. If you sand a curve or a bevel on your fin edges, be sure to exclude the root edge. To get even better contact, the tube can be temporarily wrapped with sandpaper, and the fin root edges can be briefly sanded against that. Apply good yellow wood glue thinly to both surfaces, and let it dry or nearly so. Then go back, apply another layer of wood glue to one surface (usually the fin is a better choice here), and stick the fins on one at a time, holding them straight until they grip. Small pinholes can be made along the tube where the fin will attach and/or under the fillet area. This allows the glue to fill in the hole like a tiny rivet, greatly increasing the joint strength. In mid-power and up, the fins are often made with tabs that fit into slots in the body tube for a lot of extra strength. Sometimes the tabs go all the way to the motor mount tube, which is stronger yet. Be sure to apply good glue fillets. With yellow glue, you'll want several layers. Fillets can be made all of glue or covered with sandable material for a nicer curve and finish. If your fins go through the tube, be sure to fillet the inside joints too. Reinforcing tissue or lightweight fiberglass can be glued into the joint, overlapping both the fin and the tube as another way to reinforce the joint. In through the wall (TTW), this can be applied to the inside joint for similar strength and better looks.

 

[adrian]

Judging by the photo, William did apply good fillets, epoxy or otherwise. The whole assembly, fin plus fillets, came away. I'm not sure how much paper from the body tube stayed attached to the fillets.

So I'd agree with Donaldsrockets - stick it back on with CA. You don't need to apply fillets, they're already there.

The benefit of surface mount fins is that they come away cleanly like this and are easy to stick back on. A through-the-wall mounted fin is less likely to come off, but if it hits the ground hard enough, it will break the fin instead...

 

[Micromeister]

Yes this looks like a tube paper/glue impact break. Funny we've been discussing CA/Epoxy vs elmer's joints in another thread on "Elmer's glue".
I'll simply say don't repair with CA, or epoxy, both are brittle with very little flex. Use a yellow or brown carpenters glue, Titebond glue, or even Ambroid cement. All of which will give a little before tearing the paper tube on hard landing.
I'd also suggest doubling the commanchee's streamers. I use 2 - 1" x 6' surveyors tape streamers in mine, Haven't broken a fin since increasing the streamer number and length.
Hope this helps.

 

[powderburner]

When you have a design with fins projecting off the rear (that will hit the ground first) you can protect them with a 'bang stick'----I didn't make that up, it's a device I saw in someone's old newsletter.

You add a piece of something strong (like spruce) in the form of a 1/4 x 1/4 piece of stock, attached near a fin root and projecting out the rear a couple inches past the tips of the fins. At touchdown the stick takes the worst part of the beating.

I have only used this feature on a couple designs because it is kind of ugly. But it seems to work---I remember finding a rocket once, standing up in the grass with the stick impaled in the dirt.

 

[William]

YES I want to thank everyone for there sujestions, I will be useing all these the metheds you have all sujested in the future, it was a real bumer for this to happen, mostly becouse it was my 1st rocket i have built in about 10 to 12 years. next it was also the first launch with the club i just joined { SPAAR } and it was the only rocket i had ready to launch, and i planned to launch it till i ran out of engins, owell I will rebuild her better, stronger, and faster. I am very glad to here that it wasent any thing i did wrong,that dose help knowing that, also that there are inprovments i can make in the future. THANKS AGIAN TO EVERY BODY FOR TAKING THE TIME TO HELP!! I LOVE THIS SITE!!

 

[rstaff3]

I have used CA many times to repair fins with this damage up through heavy MPR rockets. It wicks nicely under fins that are still partially attached and once the top layer of paper is pulled it really soaks into the tube, making for a good bond. Just push the fin back into place and apply pressure until it stays in place on its own. If the broken edge is ragged, first clear out chips that will keep the fin from settling easily back. Usually there are a few small gaps in the edge that lifted where chips of fillet/paint may have come off. These can be filled and the root edge repainted.

 

[dragonshiprider]

I used epoxy on mine and they did the exact same thing.

 

[FredT]

I figure I might as well chime in with my technique.

First I lightly sand the tube and mark fin allignment. Then I tack the fins to the body tube with Titebond (or other high quality wood glue). I not to smear glue beyond the thichness of the fin.

Once all fins are tacked and thoroughly dried I start prepareing for the fillet. Using a sharp Xacto I scribe the body tube along the fin root and a parallel line just less than the width of the fillet. Then cut under the scribed area and carefully remote the top layer of paper. This exposes the fuzzy and absorbent under layers.

In cases, like the Comanchee, where there is a thick centering ring underneath, I drill a 1/64 inch hole through the fuzzy area into each ring.

Finally I mask off the area and apply epoxy fillets (I use Bob's 30 minute).

This tends to add a lot of weight which is not necessarily a bad thing.

I did this to the fins on all three stages of the Comanchee and never broke or stripped a fin after several flights.

Eventually I lost the upper stage. The usual fate of Comanchee's that don't loose their fins.

...Fred

 

[astronboy]

My original Goblin (built 1971) loses or cracks a fin on almost every flight. It is just one of he pitfalls of streamer recovery with an 18 or 24 mm powered rocket. I just CA the fin back on and fly again!!

Phred

 

[BobH48]

Originally posted by astronboy
My original Goblin (built 1971) loses or cracks a fin on almost every flight. It is just one of he pitfalls of streamer recovery with an 18 or 24 mm powered rocket. I just CA the fin back on and fly again!!

Phred

I have had the same experience with my Goblins. A few times, in fairly long grass, I get lucky but not that often.

Of course if you use a parachute you don't have to worry about that because you'll never see it again.

 

[cjl]

I have two comanches, and the first one I built with just elmer's glue (briliant idea). I lost one fin because I didn't notice it was missing until I was halfway back to the launchpad. The other one, I built entirely with slow CA and accelerator. I made glue rivets on all of the fin joints as well. It hasn't broken a fin yet, and it's had 6 flights (one to full altitude)

 

[cjl]

Here's the first one lifting off (it broke it's fin on this flight - it was it's last flight)

 

[cjl]

And here's the other on it's full altitude flight to 2600 feet (sorry for the bad quality)