Best material to use for airframe

[rocket_troy]

The weakness of cardboard tubes going mach is greatly exaggerated.

Probably gets that reputation from people trying to push non-reinforced Estes kits (designed for C & D engines) past Mach with larger engines. I've seen that done so many times with a 100% failure rate.
However, I've flown 90mm cardboard post-pack tubing (non reinforced) on large hybrids that have exceeded Mach maybe 30 times without a single structural failure from flight; although hybrids (being a typically longer burn) generally exceed it a bit later than solids in slightly less dense air.

TP

 

[GlueckAuf]

Hi Tamir,

To the great advice you've gotten so far, let me offer my suggestion.

Another airframe material your team might want to consider researching that's far stronger than Kraft paper tubing, less expensive than carbon fiber tubing, and offers some advantages (but with some disadvantages, too) over fiberglass is Blue Tube 2.0 by Always Ready Rocketry. It is created from ribbons of vulcanized cellulose that are layered and bonded into spiral-formed tubing. It is sized into all of the usual coupler, airframe, and motor tube diameters used in consumer-level rocketry, and in varying lengths. It accommodates standard nose cones, motor retainers, rail guides, and other build components.



I've used Blue Tube exclusively for several years in my self-designed and built rockets that took me from NAR Level 1 through 3, and a personal best flight that exceeded Mach 1 and rose to 2,017 meters on a K-class, 38mm motor, the Loki K-627LR. In my experience, Blue Tube requires no bonding of a fiberglass outer layer to raise it to a stress-resistant strength capable of surviving Mach flights. It's Mach-ready right out of the box.

Blue Tube's cost is pretty similar to that of fiberglass. Its main advantage is that, like cardboard, it is easy to work with woodworking power tools when drilling, sanding, and fin-slotting. Cutting it is very easy to do, as it will not chip or crack from using a copper pipe cutter (just back up the cutting area with a piece of scrap coupler or a stack of plywood bulkhead disks). Adhesives soak into it, providing a very strong bond for centering rings, fins, and couplers. But do rough-up sand the bonding surface, though, for best adhesion.

Blue Tube's disadvantages are few, but significant. It will not tolerate getting soaking wet, lest it soften and delaminate. To prevent this, its maker suggests sealing the surface with an oil-based sanding sealer, but I don't do that because I believe epoxy (my main buildng adhesive) wouldn't soak in well after that treatment.

Secondly, Blue Tube can become deformed if subjected to high heat and bending stress (such as left inside a car trunk on a hot, summer day) or intense, direct sunlight.

But avoiding these two of Blue Tube's Achilles Heels will help you produce a tough, resilient, high-altitude-capable project rocket. (Pictured below, production of my 75mm NAR Level 3 achiever, the Mach Schnell SLK 75m.







Best of luck with your project! And be sure to keep us posted on the progress.

 

[Hobie1dog]

I would recommend just buying fiberglass airframe tube and be done with it if you are able. Avoid the time sucking activities....

What he said, it's ready right out of the box, tougher than a Navy SEAL, proven time and again to be one of the most cost effective , bullet-proof airframes to use for any High Power.

 

[Not Quite Nominal]

Strength is determined as much by structure as by material. An open tube is similar to a cantilevered beam, and a closed tube is a monocoque. Squeeze the end of a long carbon tube with your fingers, and it will deform. Squeeze the end of a cardboard tube that has a centering ring mounted in that end, and even a clamp won't deform it.

In the case of rocket airframes going moderately past M1, you have two concerns - stiffness, and compressive strength.

Stiffness is the key here - A tube that ovals out could lead to an off-nominal flight profile, failure to separate, etc. Thankfully, that's easy to fix. In your lower body tube, either mount a bulkhead as high as you can while still fitting your recovery, or simply go zipperless. Keep the upper tube relatively short.

If you have a stiff airframe, plain old LOC tube is more than strong enough (in compression) for your flight profile. There are plenty of youtube videos of completely unreinforced cardboard kits going much faster.

Fins, on the other hand, are a different story.

 

[Tamir Friedman]

You could use 90mm PVC downpipe and get Mach 1.23. Is that available to you. Is 3D printing available at the university/ What's the capacity?

I will have to check for the capacity, but I don't I will be able to print a full airframe tube in a single piece. We did however started looking into plumbing companies who sell industrial sewage tubes to see if any sell something we could use.

 

[Tamir Friedman]

Thank you everyone with all the advices and support. I think I have a better grasp now at what we are looking for.

I will continue to update about our build as it evolve over time, and hopefully it won't be long before we start the actual building phase

 

[OzHybrid]

I will have to check for the capacity, but I don't I will be able to print a full airframe tube in a single piece. We did however started looking into plumbing companies who sell industrial sewage tubes to see if any sell something we could use.

Go to the plumbing depot and tell us what sizes are available in PVC downpipe. You can either use it as a mandrel to produce a fiberglass tube or directly as the airframe if it's light enough. I can get 90mmOD PVC rainwater downpipe in Australia that's thin enough to fly. I've not done it as I have better options available to me. So take a visit to the plumbers and post some pictures with a tape measure across the end. I've simmed a rocket made of 90mm and it gets Mach 1.23 with realistic weights and paint finishes on the K805.
So you tell us what's available. Don't print the tube. It would not be structurally sound without a lot of work.......

 

[Not Quite Nominal]

I will have to check for the capacity, but I don't I will be able to print a full airframe tube in a single piece. We did however started looking into plumbing companies who sell industrial sewage tubes to see if any sell something we could use.

A printed PVC tube is nowhere near as strong as plain old plumbing PVC pipe.

The strength of the joins between each layer is nowhere near as strong as a monolithic pipe - and you've got that fracture plane at every single layer.

If the cost of getting actual rocket tubing shipped (probably from the US?) is prohibitive, consider mailing tubes. They often thicker, heavier, and yet weaker than rocket tubes, but will probably survive a K flight. It's inferior in every way to rocket tubing, but will work if it's the only thing available to you.

 

[OzHybrid]

There are usually 3 types of pvc piping.
Rainwater downpipe. Usually 90mm or 102mm These are the thinnest. The 90mm is thinner than the 102.
Sewerage underground. Thicker. Will survive a blockage. You could use as a mandrel to make a fiberglass tube or Carbon tube.

Plastic pressure pipe. Used for pool piping generally. Same as above. Can be used as a mandrel.

Other things can be used as a mandrel too.....

I googled plumbing supplies in Israel ( I was probably on a watch list anyway). It seems a lot different to me being able to look at the Bunnings catalogue here and phone up the store that's got my pipe in stock to get them to put my name on it.......

Make contact with a yachting supplies place. ( Marine chandler ) for epoxy and fiberglass/ carbon cloth.

If you have the budget though, the spiral wound and ground fiberglass tube is really the stuff to get. I had a chute fail and ploughed into hard packed clay. Dug 150mm clay out from the inside of the tube, trimmed it back 50mm and flew again the same day. It's amazingly strong and perfectly finished.
Again this depends on budget, import issues and availability to you for whatever your timescale is.

What is your timescale?

 

[Tamir Friedman]

There are usually 3 types of pvc piping.
Rainwater downpipe. Usually 90mm or 102mm These are the thinnest. The 90mm is thinner than the 102.
Sewerage underground. Thicker. Will survive a blockage. You could use as a mandrel to make a fiberglass tube or Carbon tube.

Plastic pressure pipe. Used for pool piping generally. Same as above. Can be used as a mandrel.

Other things can be used as a mandrel too.....

I googled plumbing supplies in Israel ( I was probably on a watch list anyway). It seems a lot different to me being able to look at the Bunnings catalogue here and phone up the store that's got my pipe in stock to get them to put my name on it.......

Make contact with a yachting supplies place. ( Marine chandler ) for epoxy and fiberglass/ carbon cloth.

If you have the budget though, the spiral wound and ground fiberglass tube is really the stuff to get. I had a chute fail and ploughed into hard packed clay. Dug 150mm clay out from the inside of the tube, trimmed it back 50mm and flew again the same day. It's amazingly strong and perfectly finished.
Again this depends on budget, import issues and availability to you for whatever your timescale is.

What is your timescale?

Yes, here if we wanted to get plumbing tubes it would be contracting directly the manufacturer because there isn't really a public market for this kind of stuff. We wanted to had the rocket ready by August (take notice that most of us are students which mean we can't focus out entire time on it). In our last project the time it took us to assemble to rocket from the moment all the materials we needed arrived was about a month.

 

[Zeta]

blue tube 2.0 is great stuff

 

[JohnCoker]

Here's a survey of airframe materials:
http://jcrocket.com/body-tubes.shtml
I doubt you need to fiberglass your tubes, but if you want to:
http://jcrocket.com/tube-wrapping.shtml

 

[GlueckAuf]

Here's a survey of airframe materials:
http://jcrocket.com/body-tubes.shtml

An impressive list, John, and (as is your whole site) very helpful toward understanding the advantages and disadvantages inherent to each air frame material. Thanks for maintaining it for our community.

One minor correction, though. Blue Tube 2.0, as I understand it, is constructed from pure vulcanized cellulose, not "vulcanized paper phenolic." Its formula and properties are very different from phenolic. Property wise, phenolic reminds me of thin, brittle plastic. Great as a liner encased within an aluminum alloy motor tube, but much too fragile as a stand-alone air frame material for high-powered missiles, in my view. Blue Tube--vulcanized cellulose--is like a thin coil of rawhide. (It makes for a very tough, survivable rocket. Just don't let your pooch use it as a chew toy,)



Thanks again for the contribution to the discussion!

 

[Hobie1dog]

Here's a survey of airframe materials:
http://jcrocket.com/body-tubes.shtml

I wish carbon fiber was also included to see the weight difference

 

[Tractionengines]

I have a follow-up question for Fiberglass tubes. If you had 2 fiberglass tubes with exactly the same ID, OD, wall, epoxy, etc. But 1 was convolute wound from S-glass fabric, the other was Filament Wound (FW) S-glass. Which would be the better choice for airframe material?

It seems to me convolute wound would be slightly better since the long fibers are aligned with the axis of the tube, giving best support to bending stress. Then the cross fibers are directly around the tube to carry hoop stress. In a FW tube the fibers are carrying a mix of bending and hoop stresses. Having a mix of winding angles gives some more "along", and some more "around", but they are always a combination of loads.

I know most "roll your own" are cloth, and most "commercial" FW. This is from available processes. Just curious how the 2 types compare. Everything else being equal.

Mike

 

[JohnCoker]

One minor correction, though. Blue Tube 2.0, as I understand it, is constructed from pure vulcanized cellulose, not "vulcanized paper phenolic." Its formula and properties are very different from phenolic. Property wise, phenolic reminds me of thin, brittle plastic.

Cellulose is a plant material, most commonly harvested from trees. I'm not sure what the right wording is exactly and the BT facts page isn't much help:
https://alwaysreadyrocketry.com/blue-tube-2-0/

 

[JohnCoker]

I have a follow-up question for Fiberglass tubes. If you had 2 fiberglass tubes with exactly the same ID, OD, wall, epoxy, etc. But 1 was convolute wound from S-glass fabric, the other was Filament Wound (FW) S-glass. Which would be the better choice for airframe material?

Good question. Hopefully someone with more knowledge than I will chime in here.

 

[GlueckAuf]

Cellulose is a plant material, most commonly harvested from trees. I'm not sure what the right wording is exactly and the BT facts page isn't much help:
https://alwaysreadyrocketry.com/blue-tube-2-0/

Blue Tube 2.0 is a spiral-wound, laminated, tubular form of what is sometimes termed fish paper (though it has nothing to do with fish other than resemble the paper that was once used to wrap fish) or leatheroid. Fish paper is produced from paper that is treated with an acid to change its fibers into a sticky, gelatinous form which is then...well, here's how one maker of the product describes its manufacture of fish paper in sheet or roll form. (Always Ready Rocketry's supplier finishes the product as spirally-wound tubes.)

Making Vulcanex Vulcanized Fiber (from https://oliner.com/vulcanex-vulcanized-fibre/how-vulcanex-is-made/)

Vulcanized Fiber is made from plies of paper. More than 99% of the finished product is Cellulose, so Vulcanized Fiber, although it is not paper, is made almost entirely of paper. There are no glues, resins or binders in Vulcanized Fiber.

The number of plies of Base Paper depends on the thickness of the Vulcanized Fiber that is being produced. Please refer to the diagram below as we proceed with the explanation.



In the Laminator, the plies of paper pass through a bath of Zinc Chloride, which is an acid. The Zinc Chloride bath makes the surfaces of the individual fibers, which make up the paper, gummy and sticky. These gummy plies of paper are then pressed together.

The gelatinous fibers create both a stronger bond within each ply of paper and a stronger bond between the plies of paper. They bind together to form Vulcanized Fiber, a chemically pure product of unmatched physical and electrical properties, and unique bond strength.

Once the plies are bonded together, the Vulcanized Fiber enters the Leaching Tanks. In this process, the Zinc Chloride is gradually leached out of the Fiber in a series of water baths. These water baths have gradually decreasing concentrations of Zinc Chloride in them. After the Fiber has finished its path through the Leaching Tanks, it has only a trace amount of Zinc Chloride (typically less than 0.1%) left in it.

The Fiber then passes through the Drying section. In this process, the Fiber passes over a series of large heated rolls which dry the Fiber to its final Moisture Content.

After that, the Fiber is Calendered. The Calender is a pair of rollers which compress the Fiber significantly, making it smoother and denser.

After the Calender, the Fiber is either wound into Master Rolls or Cut into Flat Sheets. Fiber which is made into Master Rolls can also be slit into tight tolerance coils, to virtually any width, but that process is done after the fact, not as part of the overall manufacturing process.

Vulcanex Vulcanized Fiber, made by this process, is almost completely pure cellulose, free from any artificial glues, resins or binders. Other than trace elements, it contains entirely natural components.

Phenolic tubing [on the other hand] is produced from a dielectric Kraft paper that has been pre-impregnated with a special Phenolic resin and cured to the Class “B” stage. After forming, the tubes are baked to complete the resin cure. In this process, the Phenolic and the special adhesive coalesce to form a complete homogenous product. Phenolic tubing has excellent mechanical strength as well as good electrical properties. Strength for strength, Phenolic tubing provides a much thinner wall than Kraft alone. Phenolic tubing will also hold its shape better than Kraft; particularly under humid conditions. (taken from https://paramounttube.com/phenolic-paper/)

To my knowledge, there is NO Phenolic resin used in the production of fish paper, which is a virtually 100% pure cellulose product.

Now you know!

 

[Zeta]

...

 

[JohnCoker]

Now you know!

Thanks for the detailed quote! Now what's a 3-word description of it?

To me it seems like phenolic from a working perspective, in that ordinary woodworking tools are used with it and it's in the same range in mechanical properties. I don't want to have incorrect statements, but I also don't want a raft of words that don't provide useful info for comparison purposes.

 

[GlueckAuf]

Thanks for the detailed quote! Now what's a 3-word description of it?

To me it seems like phenolic from a working perspective, in that ordinary woodworking tools are used with it and it's in the same range in mechanical properties. I don't want to have incorrect statements, but I also don't want a raft of words that don't provide useful info for comparison purposes.

I suggest simply "Vulcanized cellulose." Materially accurate. Descriptively terse.