Strengthening the fore and aft ends of the body tube

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MetricRocketeer

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Hi TRF colleagues,

I seem to remember that rocketeers recommend strengthening the aft and especially the fore end of a body tube. Strengthening the forward end of the body tube is especially important to try to prevent zippering. But strengthening even the aft end is useful just because it is prone to wear and tear.

Here is my question, please. What do you recommend to accomplish this strengthening? I think that thin epoxy — like that provided by Bob Smith Industries (BSI) — would be the best. How about white Elmer's glue?

Thank you.

Stanley
 
Since you posted this in the high power rocketry section I’m assuming that’s the use you’re interested in. Elmer’s glue might be helpful for model rockets with Kraft paper tubes, but wouldn’t help much for HPR where all the stresses are greater.
For most HPR, choice of materials is pretty important. If you’re using fiberglass body tubes or if you have wrapped cardboard or phenolic tubes with fiberglass you’ve already protected against most of the stresses. I’ve seen fiberglass shortened near the tube ends and strips of Kevlar or even thin metal wrapped around the very end of the tube.
Of course the best way to avoid zippers is to control the impulse on the rocket when the chute opens. Increasing the area upon which the shock cords act on the edge of the body tube, lengthening the time the chute takes to open, or simply making sure the velocity of the rocket is slight when the chute is ejected will all help. Zipperless construction as described by Stu Barrett all those years ago would be another way.
 
Most of the time when people are talking about damage to the tube ends, it's referencing the ends that are being joined together in a cardboard tube rocket (like LOC/Precision tubes) when assembling the rocket for flight. For that, we typically just put some CA on the edge of the tube to strengthen it and keep it from separating as the coupler is inserted.
 
I seem to remember that rocketeers recommend strengthening the aft and especially the fore end of a body tube. Strengthening the forward end of the body tube is especially important to try to prevent zippering. But strengthening even the aft end is useful just because it is prone to wear and tear.
For LPR cardboard tubes the standard practice is CA. I use thin CA applied with a Q-tip. Be sure to sand it smooth afterwards; else it is extremely abrasive.
Here is my question, please. What do you recommend to accomplish this strengthening? I think that thin epoxy — like that provided by Bob Smith Industries (BSI) — would be the best. How about white Elmer's glue?
White Elmer's glue has low temperature resistance and sands terribly. Do not use it for this.
 
I use Zap thin CA. On the inside leading edge of the tube.

Sometimes I sand, sometimes I don't. I usually wipe the CA down with a gloved hand while it dries.

Sand the wax paper on the outside a bit. Apply CA there too.

Rear of tube, is sealed when I epoxy in the fin can. You can CA the tube edges if you want, but might be unnecessary.

Then I CA'd the fin edges.

I used a small amount of skunky polyurethane to seal the inside of the tubes.
 
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When it comes to the aft end of airframes (assuming paper/carboard body tubes), if the model does not have the fins protruding below the end of the airframe, and if the aft centering ring is inset a bit up into the body tube, then I will use either a thin length of coupler or strip of fiberglass wet out with epoxy applied to the inside diameter to reinforce that lower portion of body tube, making it less likely to ding / crumple upon landing.
 
Assume we are talking cardboard -

If the application is relatively small tubes (say, 2-3 inch or lower) - any CA glue with Q-tips works fine

If you plan to apply the CA to larger tubes (say, 4in and larger) - I would recommend a couple relatively inexpensive options that can make your life easier:

- Get a larger bottle of CA. Forget the tip and just dip your applicator right in the bottle. These 2oz bottles from Starbond work great: https://www.amazon.com/Starbond-Cyanoacrylate-Microtips-Woodturning-Stabilizing/dp/B00C32ME6G?th=1
- Use a larger applicator to preserve your sanity. I like to use either these larger swabs: https://www.amazon.com/gp/product/B07MV465LJ/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1 and/or acid brushes like these: https://www.amazon.com/Pro-Grade-Acid-Brushes-Count/dp/B07PHG2DQY
- I coat the tube way down - past where the coupler tube will end up. I also CA coat the outside of the coupler tube. All of those exposed cardboard areas take a beating from BP charges. Heck, I pretty much CA coat all the exposed cardboard on a rocket, except the outside of the airframe. That I just paint with a thin coat of laminating epoxy.

Epoxy can be used on large tubes - I use it for carboard tubes 6in and larger - that would require a lot of CA, but epoxy is more difficult to work with and will need to be sanded so the parts fit together again. If you go down that route, West Systems 105 has a low viscosity and works well.

All the CA and epoxy coating techniques work pretty well for the phenolic tubing from MAC as well.

When applying CA with any applicator to a big surface area, don't want to insult anyone's intelligence, but I very much recommend wearing nitrile gloves (or equivalent). The CA tends to wick up wood handles or drip down through metal ones and you often end up with a mess of CA on your hands. Not fun to have the wood swab bonded to your hand...
 
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Hi TRF colleagues,

I seem to remember that rocketeers recommend strengthening the aft and especially the fore end of a body tube. Strengthening the forward end of the body tube is especially important to try to prevent zippering. But strengthening even the aft end is useful just because it is prone to wear and tear.

Here is my question, please. What do you recommend to accomplish this strengthening? I think that thin epoxy — like that provided by Bob Smith Industries (BSI) — would be the best. How about white Elmer's glue?

Thank you.

Stanley
Usually, I apply thin C/A and sand it smooth. At the top to help prevent zippering, at joints to prevent coupler damage, and at the rear especially if it lands on the bottom of the tube and not the fins. I've also used epoxy at the rear to improve its heat resistance.
 
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- Snip -

When applying CA with any applicator to a big surface area, don't want to insult anyone's intelligence, but I very much recommend wearing nitrile gloves (or equivalent). The CA tends to wick up wood handles or drip down through metal ones and you often end up with a mess of CA on your hands. Not fun to have the wood swab bonded to your hand...

But but but, that takes all the fun out using thin C/A! o_O
Just kidding, but there is a reason why I keep a bottle of debonder beside me whenever I use C/A. And the last time I used epoxy, I somehow manage to get a little in my moustache. Thankfully I removed it before it set!
 
I've never had a problem with the rear of the airframe. I usually build with the motor sticking out a little bit and of course some designs have swept fins, so the rear of the airframe doesn't hit anything. I also end up with the rear centering ring pretty close to the back of the tube, recessed just enough for a glue fillet.
Now the front of the tube can be a different story although with long enough shock cords I don't get as much impact there as I used to get with short rubber shock cords. Other than a thin layer of glue there isn't a good way to reinforce the front unless you make your own nose cones and can make the shoulder smaller. I suppose you could put another layer of material around the outside of the tube and this would work better with some designs than others.
 
For the zipper prevention, I find it simpler to use the proper shock cord length and type (kevlar is stronger than nylon, but doesn't stretch, so use a longer length or try a Y-harness to split the force) or add something to prevent zippers to the area of the cord that touches the bt (duct taped a few times to widen, foam ear plug, etc.).
 
If CAing a relatively large area, a cross draft from a fan or an outdoor breeze can protect you from the fumes.

Uncured epoxy cleans up well with ordinary vinegar, but don't get it on any epoxy that stays on your rocket.,

It's possible to wipe slow epoxy on paper or cardboard, let it soak in for a few minutes, then wipe it off.

If your nose cone or coupler has a little more thickness than it needs, you could glue thin pre-cured carbon, thin metal, etc. inside the end of the body tube and turn down the coupler or nose cone to match. Maybe use diagonal ends on the reinforcement rather than a butt joint.
 
CA glue will be nice to keep the top of the tube from fraying and degrading over time, but it won't add any significant zipper resistance.

If you want to make your tubes stronger, just bite the bullet and fiberglass them.

IMHO the best way to prevent zippers is to fly with electronics so the parachute is always deployed at apogee.
 
I use extra long cords, and wrap an inch of camper foam tape around the cord where it contacts the tube. The foams adhesive eventually lets go, so add a layer of the tape of your choice.

To save cost, often only the first bit of cord is Kevlar. Usually use any old string fir most of it. Untie and replace when it gets scorched.

1000017613.jpg
 
I have used this stuff: https://www.ebay.com/itm/266834298217 Carbon fiber 12k or 24k tow tape.

Put thin coat of epoxy around tube outside first, then wrap the carbon fiber around the outside and apply more epoxy. Use a very runny slow cure epoxy. You don't need a lot. This is freekin messy though... Before starting cut a piece of thick polyethylene bag into a strip at least three times the width of the reinforcement. after applying the fiber and epoxy, (It will start lifting up...) Wrap the plastic around the tube in the same direction as the fibers. When it is basically tight and smooth tape it with some masking tape. Let cure. The end of the tube will be a little messy, you can grind that smooth after cure with a belt sander, or use a chop saw with a masonry disc. (Hold saw all the way down and use the side of the disc like a sander...as opposed to cutting the tube end off.) When sanding, use vacuum cleaner to suck up any dust during the sanding process. This is no different than dealing with sanding fiberglass...safety in working with anything is important.

Warning:
Carbon fiber can be dangerous in a few ways:
  • Dust
    When cut, machined, or sanded, carbon fiber can break down into a fine dust that can be released into the air. Inhaling this dust can irritate the lungs and eyes, and may cause allergic reactions or long-term respiratory issues. Carbon nanotubes in the dust are similar in size and shape to asbestos fibers, and inhaling them can cause conditions similar to asbestosis.
  • Skin irritation
    Carbon fiber can also irritate the skin, causing an itching sensation similar to fiberglass itch. The fibers can accumulate on the skin, especially at flexure points, beneath clothing, or on the forearms.
  • Chemical irritation
    Most carbon fibers have a coating called a "sizing" that's often made of epoxy or another resin, which can also cause chemical irritation.

  • Carbon fiber can be dangerous in a few ways:
    • Dust
      When cut, machined, or sanded, carbon fiber can break down into a fine dust that can be released into the air. Inhaling this dust can irritate the lungs and eyes, and may cause allergic reactions or long-term respiratory issues. Carbon nanotubes in the dust are similar in size and shape to asbestos fibers, and inhaling them can cause conditions similar to asbestosis.
    • Skin irritation
      Carbon fiber can also irritate the skin, causing an itching sensation similar to fiberglass itch. The fibers can accumulate on the skin, especially at flexure points, beneath clothing, or on the forearms.
    • Chemical irritation
      Most carbon fibers have a coating called a "sizing" that's often made of epoxy or another resin, which can also cause chemical irritation.

      1719070146304.png
 
When it comes to the aft end of airframes (assuming paper/carboard body tubes), if the model does not have the fins protruding below the end of the airframe, and if the aft centering ring is inset a bit up into the body tube, then I will use either a thin length of coupler or strip of fiberglass wet out with epoxy applied to the inside diameter to reinforce that lower portion of body tube, making it less likely to ding / crumple upon landing.
I just give that area a thin coat of epoxy, has worked well. This also prevents the BT from scorching.
 
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