Fixing fins and Repairing Parachutes

My daughter and I flew rockets this morning, and had a very good time. Unfortunately, on one of the last flights some parachute leads on the Semroc Vega pulled loose, and the rocket plummeted to the ground and broke a fin.

Couple of newbie questions:

1. I used wood glue to fix the fin, using the double glue method. I clamped it with a ruler to hold it straight and it seems fine. Do I need to reinforce the break area with anything else?
2. The Semroc parachute has loops of thread under a gummed label circle. It appears one thread pulled loose and another label came off. I reattached them, but now I'm thinking I should punch holes and tie the leads on. What do you all think?

Edit: For some reason the pictures show up upside down.

If your fin feels strong enough you should be okay. I would punch holes in the parachute.

Answer 1:
You'll probably be fine, but if you REALLY wanted to, or if the fins break again, you could sand the paint off and paper the fins to reinforce them. (There are many threads on the forum covering how to do this. I think Luke Strawalker probably has one of the more comprehensive write-ups of this method.) I would sand the paint off so that you get a good bond between the paper and the balsa. (as opposed to the paint.)

Answer 2:
Punching holes runs the risk of the holes eventually being torn through. A pack of binder paper reinforcement rings will help if you decide to do it. Again, you'd probably be fine just reattaching them under the label circles. Although I might use new stickers instead of the ones that came loose. (cut up old floppy disk labels work well...)

That's my two cents. Honestly you are probably fine the way things are now. I guess it depends on how much work you feel like doing.

gna said:

I used wood glue to fix the fin, using the double glue method. I clamped it with a ruler to hold it straight and it seems fine. Do I need to reinforce the break area with anything else?

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Once the glue dries try to wiggle it (gently!) with your fingers. If it feels tight, it probably is.

The Semroc parachute has loops of thread under a gummed label circle. It appears one thread pulled loose and another label came off. I reattached them, but now I'm thinking I should punch holes and tie the leads on. What do you all think?

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Definitely punch holes and tie the shrouds. Get some paper reinforcing rings for loose leaf binder sheets, stick them in position on the 'chute canopy and tie the shrouds through them. If you are going to replace them all, I would recommend making the shroud lengths 1.5 time the canopy diameter. e.g. for a 12" 'chute, make the shrouds 18" long. Cut your shroud material, good kit string works well, to ~40" and tie each end of a piece to adjacent corners. The extra length leaves enough for the knots and to keep the lines equal length. Trim the excess and fly some more!

rbelknap said:

Answer 1:
You'll probably be fine, but if you REALLY wanted to, or if the fins break again, you could sand the paint off and paper the fins to reinforce them. (There are many threads on the forum covering how to do this. I think Luke Strawalker probably has one of the more comprehensive write-ups of this method.) I would sand the paint off so that you get a good bond between the paper and the balsa. (as opposed to the paint.)

Answer 2:
Punching holes runs the risk of the holes eventually being torn through. A pack of binder paper reinforcement rings will help if you decide to do it. Again, you'd probably be fine just reattaching them under the label circles. Although I might use new stickers instead of the ones that came loose. (cut up old floppy disk labels work well...)

That's my two cents. Honestly you are probably fine the way things are now. I guess it depends on how much work you feel like doing.

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I hadn't read about papering fins yet while I was building this rocket, but I think it would have helped strengthen them. I also tried to airfoil the fins, too, but I gather that's a waste of time.

mikemech said:

Once the glue dries try to wiggle it (gently!) with your fingers. If it feels tight, it probably is.

Definitely punch holes and tie the shrouds. Get some paper reinforcing rings for loose leaf binder sheets, stick them in position on the 'chute canopy and tie the shrouds through them. If you are going to replace them all, I would recommend making the shroud lengths 1.5 time the canopy diameter. e.g. for a 12" 'chute, make the shrouds 18" long. Cut your shroud material, good kit string works well, to ~40" and tie each end of a piece to adjacent corners. The extra length leaves enough for the knots and to keep the lines equal length. Trim the excess and fly some more!

Click to expand...

I bought some paper reinforcing rings. Just one in each corner, or one on each side? Also, if I understand you correctly, the shrouds should be 36" long, tied to adjacent corners? So when gathered together, they will hang 18" below the 'chute?

gna said:

I hadn't read about papering fins yet while I was building this rocket, but I think it would have helped strengthen them. I also tried to airfoil the fins, too, but I gather that's a waste of time.

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Unless you are trying for a high performance / competition model, airfoiling is probably not needed. I usually just round the leading and trailing edges on balsa fins. Sometimes (if I'm feeling feisty, )I'll try to hand bevel them.

I bought some paper reinforcing rings. Just one in each corner, or one on each side? Also, if I understand you correctly, the shrouds should be 36" long, tied to adjacent corners? So when gathered together, they will hang 18" below the 'chute?

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The One Ring (<gollum>my precious...</gollum> ) on each corner is fine. For the shroud lines on a hexagonal chute, cut 3 36" long lines and tie one end to each corner. Mike suggested 40" to account for slack in tying the loops. (you'll have a bit of a tail at each end after you've tied them off.)

Instead of going to adjacent corners, I take one of the lines across the middle of the chute to the opposing corners, like this:

(see method 2)

works for larger numbers of shroud lines too, if you picture it as starting on one side of the chute and working your way across the middle....


Also, I use a small fishing swivel at the end to help quickly attach/swap chutes and keep the shroud lines from getting quite so tangled up.

I'm puzzled why you would bridge one of the shroud lines across the longest dimension of the parachute? When all the instructions say to tie to adjacent corners with three, equilateral loops (of about 18"). What benefit do you see from doing this?

And, yes, I invested in a 200 paper punch reinforcement ring roll of adheasive rings for my jump kit rocket tackle box. I always use them when making up a new parachute (mylar) from Jon-ROcket.
It's a cheap and easy investment.

Kirk G said:

I'm puzzled why you would bridge one of the shroud lines across the longest dimension of the parachute? When all the instructions say to tie to adjacent corners with three, equilateral loops (of about 18"). What benefit do you see from doing this?

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When you do the 3 loops to adjacent corners, one of the shroud lines will always end up "crossed" when you gather them up to attach them to the shock cord/nose cone/snap swivel. When you pass one of the loops across the longes dimension, the shroud lines don't get crossed when you gather them at their attachment point. Your loops are still all the same length, just change where they are attached to the chute. I've noticed that the pre-made estes chutes have started doing it this way as well. (My 6-year-old earned himself a Sky Hawker from the club at the last launch he attended for helping clean up.)

Not sure my explanation makes sense. I'll see if I can take pictures of a couple of chutes to illustrate what I mean when I get home.

edit: I annotated my previous image let me see if I can use it to explain:


with 3 loops to adjacent corners (method one) to gather the lines you would take
purple loop EF and
blue loop CD so that

points C and F are next to each other and
points D and E are next to each other and

the loops are aligned so you can pass an object through them.

now you need to take green loop AB and line it up so that either
points A,E,D are all a together or
points B,E,D are.

In either case the Loop AB has to cross over the nearest attachment point of either EF or CD in order for the loops to be aligned so that an object can be passed through all three loops.


with the loops attached as they are in method 2, the loops are already aligned to allow passage. just gather them up, pass them through whatever attachment point you are using and pull the loops back over to secure.

I would use a self adhesive disk on both sides of the parachute. The clear ones are a bit tougher than the paper ones.
Also, don't tie a slip not in the shroud lines to the chute. Look up and use the Double or Box knot. Just try and make them all the same size as possible.

If you have a paper or leather punch, you can actually punch the holes through the provided paper stick on disks, then tie your shroud lines through the holes. You can do the same thing with scotch tape, put a little piece folded around the edge at each corner (folded over top and bottom of chute edge) and punch a hole through the edge. The paper reinforcing rings are even better if you have them, but the above works in a pinch if you don't have the rings. What you SHOULDN'T do it use a needle or pencil to poke a little hole and thread the shroud line through the hole. The small hole is much more likely to tear than the larger one made by a paper or leather hole punch. Something to do with focusing the stress on a smaller area with a poked versus punched hole.

Thanks for all the advice. I will follow rbelknap's shroud alignment. Yet another follow up question:

I checked all the sewing thread in the house, but none of it is very strong. My daughter has a kite with plenty of string, but it seems to be a nylon string. If I use it I'd be worried it could get melted. Should I hold out for heavy duty cotton thread, such as carpet thread?

Thank you for the explanation on the new shroud line lay-out. I'm going to try that on my next chute.

As for the plastic shroud line question, I think you're wise to give pause and think about this, but I would think any heat that could melt the braided plastic line could just as easily burn the cotton thread or line as well. If it's only the matter of waiting a day or two until Mom or Dad can get to the store to select some really tough, strong lines in a spool, I would wait. But if it's the difference between flying today or waiting an undetermined number of days... I say, get that bird in the air. That's what it's all about.

Your mileage may vary!

gna said:

Thanks for all the advice. I will follow rbelknap's shroud alignment. Yet another follow up question:

I checked all the sewing thread in the house, but none of it is very strong. My daughter has a kite with plenty of string, but it seems to be a nylon string. If I use it I'd be worried it could get melted. Should I hold out for heavy duty cotton thread, such as carpet thread?

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I'd get the heavy carpet thread, if you can. I've also heard of people use dental floss, but I haven't done that myself.

on an unrelated side note: My wife found out this past summer that a pack of dental floss can be taken on a plane in your carry-on and (usually won't be confiscated) and makes a serviceable yarn cutter for knitting/crochet projects. (you can also generally take dull bamboo/plastic knitting needles/crochet hooks on planes again now too - check your airline's rules before flying...)

The question about melting the nylon got me thinking. I've honestly never considered that before. I don' think it would be an issue. If you are in danger of melting the nylon kite string, you are also in danger of burning the cotton thread, not to mention melting holes your chute canopy.

I think the nylon kite string would be fine.

I also dug this up a few minutes ago: https://ojames3.tripod.com/tccnarcontesttips/BobKaplowNAR18LCompParachute.pdf

It's a duration competition chute making article by Bob Kaplow, and he mentions using nylon shroud lines as well.

Cotton thread burns through slower than the nylon melts, assuming they are the same thickness.

I have a spool of braided nylon that I use sometimes... as long as I keep it from getting melted, it never frays. I wish I could get more of it, but it came from the dollar store and by the time I realized how nice it was they were out. I'd have cleaned them out if I had known. Y'see, I have this rip-resistant, slippery plastic "fabric" that I use for parachutes, and the braided nylon is perfect for those chutes. I attach the strings with a bit of epoxy brushed on with disposable acid brushes.

I fixed my parachute with reinforcing rings, a hole punch, and kite string. I tried to square knot loops through the holes. I also used a fishing swivel on the end to avoid the twists and tangles. I didn't get the leads exactly the same; how important is it to get the leads the same, or is "close enough," good enough?

Was hoping to fly this weekend, but it was a little windy. Maybe next weekend...

Obviously, the more even the line lengths are, the better, but honestly I don't think I've ever gotten my loops tied 100% identically. Close enough is probably good enough. As long as you don't have one side of the canopy flapping in the wind, it should be fine.

Probably a good call on not flying with too much wind. I've had rockets drift off never to be seen again under chute. Of course in days like that you could alway switch the chutes out for streamers. (Easier to do on the field with this fishing swivels in place - assuming you have some appropriately sized streamers with you.) if it's not too windy to fly safely that is.

gna said:

I fixed my parachute with reinforcing rings, a hole punch, and kite string. I tried to square knot loops through the holes. I also used a fishing swivel on the end to avoid the twists and tangles. I didn't get the leads exactly the same; how important is it to get the leads the same, or is "close enough," good enough?

Was hoping to fly this weekend, but it was a little windy. Maybe next weekend...

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The tieing of the parachute lines to the 'chute is one of my pet peeves I have cut the lines off nylon parachutes to re-attach them the proper way.

Tieing the small knot then placing the dot over the line would have worked....providing they didn't supply disks with Post-It adhesive Dang things barely stuck to plastic. It's like some Duck-brand Painters Blue Low Stick tape, the crap won't even stick to itself...what crap...

I even tried to correct some tutorials on youtube. They like turned their noses up, sniffed, and said, "well, that's what the instructions said to do." All I wanted to do was scream, "You people are idiots!" Continuing to spread Estes mis-information is not rocket science, it's just stupid, the same way Estes thinks we're stupid and can't figure out the correct way.

I bought 100 16" parachutes off eBay, all with the wrong instructions...I'm such a rule-breaker

dave carver said:

The tieing of the parachute lines to the 'chute is one of my pet peeves I have cut the lines off nylon parachutes to re-attach them the proper way.

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So what is the proper way?

Tieing the small knot then placing the dot over the line would have worked....providing they didn't supply disks with Post-It adhesive Dang things barely stuck to plastic. It's like some Duck-brand Painters Blue Low Stick tape, the crap won't even stick to itself...what crap...

Click to expand...

The parachute instructions had me putting a loop under the disk; two failed that way. I've since found reference to running the leads through holes in the disks, knotting, and pressing down; is that the right way?