So I zippered my 4" LOC Goblin

[Joshua F Thomas]

I haven't been doing much rocketry lately, as an internship thing sucked up all my time; and then I've been learning to design models for 3D printing. Too many hobbies.

Anways, the last time on the 4" LOC Goblin was last November, when it was in the local "pumpkin lofting" competition. This did not end well for the Goblin, as you can see below. A solid 9" zipper right through the sidewall.

How the heck do I fix this?

Thanks in advance!

 

[tim cubbedge]

Easiest fix is to just cut tube off at bottom of zipper and fly a shorter rocket. Another option would be to cut it off below zipper and add new airframe connected with a coupler. I’m sure there are more options but those are fairly easy fixes.

 

[MidOH]

Coupler and a tube.

 

[cwbullet]

That about sums it up. Make it shorter by cutting it off, or longer with a tube and coupler.

 

[Joshua F Thomas]

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That about sums it up. Make it shorter by cutting it off, or longer with a tube and coupler.

It’s already pretty short as a Goblin. Any shorter and it’ll be a nosecone with fins!

Guess I’ll make into a “stretch” Goblin, after I recheck the sim for stability.

This works how I think it does? Cut off the broken section; glue a coupler and a body tube together; glue the new combo to the old frame? There’ll be a seam but I guess that can’t be helped.

 

[TRWXXA]

What kind of shock cord were you using for a recovery system? The LOC tubing is very prone to zippering, especially if the part of the harness that anchors into the tube is narrow. I'd go with 2" webbing for a 4" cardboard tube.

Cut the old tube low -- ~1/2 a coupler tube length above the MMT centering ring. Epoxy in the coupler, and new body tube above (gives you a chance to modify your shock cord mounting too). Putting in a coupler up high, just below the zipper, just makes a snag point for the parachute.

Just my €0.019.

 

[Joshua F Thomas]

What kind of shock cord were you using for a recovery system? The LOC tubing is very prone to zippering, especially if the part of the harness that anchors into the tube is narrow. I'd go with 2" webbing for a 4" cardboard tube.

Cut the old tube low -- ~1/2 a coupler tube length above the MMT centering ring. Epoxy in the coupler, and new body tube above (gives you a chance to modify your shock cord mounting too). Putting in a coupler up high, just below the zipper, just makes a snag point for the parachute.

Just my €0.019.

The shock cord came with the kit - LOC’s 3/8” nylon webbing.

I’m a dummy because I have a shock cord bumper for zipper protection but forgot to install it on that day.

 

[tim cubbedge]

This works how I think it does? Cut off the broken section; glue a coupler and a body tube together; glue the new combo to the old frame? There’ll be a seam but I guess that can’t be helped.

That’s all you need to do but be careful when gluing. The coupling will grab the airframe once you have applied glue so you want to make sure you have a good fit before gluing. What I have seen happen from my own experience is the coupling will seize up before you get it into correct position. You need to be pretty fast even if you’re using glue with long set time.

 

[TRWXXA]

The shock cord came with the kit - LOC’s 3/8” nylon webbing.

I’m a dummy because I have a shock cord bumper for zipper protection but forgot to install it on that day.

I have seen those bumpers, and was wondering how effective they would be. Zero effective, if not installed, right?
Seems like they would take up a lot of airframe space on a rocket like the Goblin.

BTW: Your Goblin is the exact color scheme of the Estes Goblin I built as a kid.

Here's the 4", PML "Quantum Tube", Goblin I built 25 years ago (before everyone started making upscale, Goblin kits), and never flew. Going to try an recertify L1 with it on an H242 next month.

 

[Joshua F Thomas]

That’s all you need to do but be careful when gluing. The coupling will grab the airframe once you have applied glue so you want to make sure you have a good fit before gluing. What I have seen happen from my own experience is the coupling will seize up before you get it into correct position. You need to be pretty fast even if you’re using glue with long set time.

I’ve had this happen on small rockets. The solution is fairly easy: use a lot more glue! It needs to be a lubricant until it dries.

 

[Joshua F Thomas]

I have seen those bumpers, and was wondering how effective they would be. Zero effective, if not installed, right?
Seems like they would take up a lot of airframe space on a rocket like the Goblin.

BTW: Your Goblin is the exact color scheme of the Estes Goblin I built as a kid.

Here's the 4", PML "Quantum Tube", Goblin I built 25 years ago (before everyone started making upscale, Goblin kits), and never flew. Going to try an recertify L1 with it on an H242 next month.
View attachment 581920

Very clean! I used the orange because I wanted a more “Halloween” feel.

I also should have sanded the fins smoother. The decals have always been a little rough.

 

[TRWXXA]

Very clean! I used the orange because I wanted a more “Halloween” feel.

I also should have sanded the fins smoother. The decals have always been a little rough.

Just look at this as the "opportunity" to refinish it. I'm going to replace the launch lugs on mine, with surface-mounted, rail guides. Then I'll repaint it with an orange or copper metallic (whichever Autozone has).and clear. Already got new vinyl decals from LOC. I'll probably do that after the cert. flight. For that, the old John Deer Yellow is good enough.

 

[Joshua F Thomas]

Just look at this as the "opportunity" to refinish it. I'm going to replace the launch lugs on mine, with surface-mounted, rail guides. Then I'll repaint it with an orange or copper metallic (whichever Autozone has).and clear. Already got new vinyl decals from LOC. I'll probably do that after the cert. flight. For that, the old John Deer Yellow is good enough.

I used button rails, ones that are teardropes shaped. The rails represent a significant amount of drag, so a few bucks for fancy low-drag ones seemed like a cheap upgrade

 

[thzero]

Can also sand down the paint on the tubing down to a couple inches below the end of the zip, then wrap a few layers of fiberglass cloth around the top section. Then repaint.

 

[cwbullet]

I have seen those bumpers, and was wondering how effective they would be. Zero effective, if not installed, right?
Seems like they would take up a lot of airframe space on a rocket like the Goblin.

BTW: Your Goblin is the exact color scheme of the Estes Goblin I built as a kid.

Here's the 4", PML "Quantum Tube", Goblin I built 25 years ago (before everyone started making upscale, Goblin kits), and never flew. Going to try an recertify L1 with it on an H242 next month.

I make my own with a piece of pipe insultation and zip ties. They are pretty effective if they are placed on the shock cord where it hits the body tube.

 

[Back_at_it]

That actually looks like a pretty clean rip. It doesn't look jagged with huge holes missing. Since this is a heavy wall LOC tube I would try the following.

Put the nose cone inside the tube so that it keeps the correct shape while you do the next steps.

- Wrap the outside of the rocket with wax paper then wrap the wax paper with your choice of tape. You will want the tape to be tight as you want to pull the torn bits of the tube back into place.
- Remove the nose cone and sand the inside of the tube with some rough sandpaper. Something like 60 grit to open up the fibers.
- Use thin epoxy to repair the tube from the inside. I'd spread on a couple of coats with an junk paint brush and let it cure.
- Remove the tape/wax paper then paint on a couple of coats of thin epoxy on the outside.
- Sand / Fill and paint.

This happened to me on a 4" LOC kit a couple years ago. Ejection on an F67 was instant and it zippered about 10 inches of the tube.

 

[KenECoyote]

Orange duct tape?

 

[Titan II]

That’s all you need to do but be careful when gluing. The coupling will grab the airframe once you have applied glue so you want to make sure you have a good fit before gluing. What I have seen happen from my own experience is the coupling will seize up before you get it into correct position. You need to be pretty fast even if you’re using glue with long set time.

Use epoxy. Problem solved.

I have seen those bumpers, and was wondering how effective they would be. Zero effective, if not installed, right?
Seems like they would take up a lot of airframe space on a rocket like the Goblin.

They work great. Just install it/them correctly. It is not rocket science.

 

[thzero]

That’s all you need to do but be careful when gluing. The coupling will grab the airframe once you have applied glue so you want to make sure you have a good fit before gluing. What I have seen happen from my own experience is the coupling will seize up before you get it into correct position. You need to be pretty fast even if you’re using glue with long set time.

As someone else also mentioned, use epoxy...like Bob Smith's 30 minute epoxy.

 

[Jowayen]

THE reason to use zipper-less couplers..
But, to repair, I have used aluminum foil or saran wrap to cover the nosecone shoulder. Then insert into the body tube. I like to use JB Weld and epoxy the zipper together on the outside of the body tube, then cover with foil and tape tight. Let dry then remove the nosecone. Take a thin piece of kraft paper and make a patch for the inside of the body tube. CA it in place and then place the foil covered nosecone back in position to "clamp" the patch. Let dry then remove the nosecone and all of the tape/foil from the rocket. Then sand, prime, sand, and finish until you're pleased.

 

[Jowayen]

Orange duct tape?

I love that dude... and it's good stuff.
I've used flex-seal a lot on my duck hunting boats. They take a beating.

 

[Philip Tiberius D.]

Easiest fix is to just cut tube off at bottom of zipper and fly a shorter rocket. Another option would be to cut it off below zipper and add new airframe connected with a coupler. I’m sure there are more options but those are fairly easy fixes.

Cut, add a coupler and airframe. Maybe have a longer / thicker line or zip tie a piece of material where the cord impacts the rocket. Double check the ejection timing. Notice the repair using a coupler and new airframe.

 

[Joshua F Thomas]

So I ended up taking a different approach to fixing this zipper. Over the past year I'd obtained a 3D printer, done a number of upgrades, and learned basic 3D modeling. I decided to fix this with a 3D print.

The design uses a 2.5mm sleeve that fits around the Goblin's body over the zipper'd area. The total vertical distance was 95mm. The material is ASA, which is otherwise known as "ABS, but less of a pain in the ass". ASA also has good UV and heat resistance; the sleeve won't weather or deform in outdoor conditions.

The sleve has a chamfer on each end to help aerodynamics a little. However this made printing it as one piece problematic - my print failed halfway through despite precautions. I split the sleeve into three parts - upper and lower chamfer sections and a central section - and printed each of them seperately, with no issue.

The parts were preped on the inside with 60 grit sandpaper, and the same was done to the rocket body area to be covered. 30 minute epoxy (Bob Smith) was prepared and a very light layer was applied on the surface of the body, and the rings slid into place. They were already fitted to have a fairly tight friction fit. Isopropyl alcohol cleaned up excess epoxy.

Because of slight differences in each print, they don't align precisely at the edges, but good enough for my purposes. The Goblin isn't exactly the most aerodynamic to begin with so I'm not terribly worried about performance. The sleeve adds ~ 75g to a 1500g (unloaded) rocket.

As an exercise in seeing what I could do with 3D printed parts this seems like a good start. I have yet to launch it, so I'll report back after that if anything unusual happens.

 

[Back_at_it]

So I ended up taking a different approach to fixing this zipper. Over the past year I'd obtained a 3D printer, done a number of upgrades, and learned basic 3D modeling. I decided to fix this with a 3D print.

The design uses a 2.5mm sleeve that fits around the Goblin's body over the zipper'd area. The total vertical distance was 95mm. The material is ASA, which is otherwise known as "ABS, but less of a pain in the ass". ASA also has good UV and heat resistance; the sleeve won't weather or deform in outdoor conditions.

The sleve has a chamfer on each end to help aerodynamics a little. However this made printing it as one piece problematic - my print failed halfway through despite precautions. I split the sleeve into three parts - upper and lower chamfer sections and a central section - and printed each of them seperately, with no issue.

The parts were preped on the inside with 60 grit sandpaper, and the same was done to the rocket body area to be covered. 30 minute epoxy (Bob Smith) was prepared and a very light layer was applied on the surface of the body, and the rings slid into place. They were already fitted to have a fairly tight friction fit. Isopropyl alcohol cleaned up excess epoxy.

Because of slight differences in each print, they don't align precisely at the edges, but good enough for my purposes. The Goblin isn't exactly the most aerodynamic to begin with so I'm not terribly worried about performance. The sleeve adds ~ 75g to a 1500g (unloaded) rocket.

As an exercise in seeing what I could do with 3D printed parts this seems like a good start. I have yet to launch it, so I'll report back after that if anything unusual happens.

I like the idea and it should prevent any future zippers.

Question. Does the ring interfere with the launch rod/ rail?

 

[Joshua F Thomas]

I like the idea and it should prevent any future zippers.

Question. Does the ring interfere with the launch rod/ rail?

Good question. It should be a very close clearance. If necessary I can print some small shims and add them to the base of the launch rail lugs to push them up a millimeter or so.

 

[sed6]

Love your solution! Looks like black duct tape though. Solution to prevent future zippers, piston ejection! Ejects an inverted "cup" to push your chute out. Read about it here www.ApogeeRockets.com/Educa-tion/Downloads/Newsletter290.pdf

 

[SolarYellow]

So I ended up taking a different approach to fixing this zipper. Over the past year I'd obtained a 3D printer, done a number of upgrades, and learned basic 3D modeling. I decided to fix this with a 3D print.

I just had an epiphany. I like the Little John, probably spend too much time thinking about how to model it. I just realized that the 12.5-inch band below the nose cone on the otherwise 12.25-in airframe could be reasonably replicated with a wrap of composite reinforcement, which should help resist zippering vs. just cardboard. Just need to figure out what to do with the NC, if you're using a COTS NC.

 

[Joekeyo]

That’s all you need to do but be careful when gluing. The coupling will grab the airframe once you have applied glue so you want to make sure you have a good fit before gluing. What I have seen happen from my own experience is the coupling will seize up before you get it into correct position. You need to be pretty fast even if you’re using glue with long set time.

Use lots of glue to prevent seizing. It acts as a lubricant. Small amounts at your peril. I use Elmer's. Doesn't have tite, quick, or bond in the glue name.

 

[CaptHaywire]

I make my rockets longer when using a coupler for repair. Rockets always get shorter over the years from repairs. As others have mentioned, use plenty of glue when installing the coupler or it will seize in the airframe.

 

[sr205347d]

Using a Jolly Logic Chute Release can prevent zippers.