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el chubbo

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Please do not send me to a deserted island for this question but...

I was thinking of building a semi-clone of Binders Velociraptor using ***oh god here it goes**** 4" Thinwall PVC.

While I understand that PVC is not good for LPR or MPR - but it seems to be workable for HPR - especially when fiberglassing is not an option (I am dead alergic to resin). Quantum tubing is just too expensive for my projects.

Is it THAT bad of a material or just not the IDEAL material?

Comments?
 

thomasrau

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John Wickman builds just about everything from PVC. Airframes, motor, fins etc. So it is a usable material, just not ideal if you want a low weight, high flying rocket.
 

Manwithbeers

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PVC
I've been working on a 4" PVC Project for a while now. Seemed like a great idea at first, as a challenge and in saving money.

I can tell you now that the PVC does not save money. Commercial tubes are cheap. In any case I've proceeded with my project. Mostly complete I have a 2-stage capable veihicle that can take anything from 38 mm to 75 mm motors. A project goal was versatility.

It's heavy. Very heavy. I'm not sure how it compares to a rocket of similar size made with regular cardboard/Phenolic Tubes. But I'd guess a 40 to 50 percent increase. (Airframe)

Bonding is generally the biggest challenge. Epoxy does not do well but CA does. I picked up a tip from West Systems on Bonding PVC. Put a layer of PVC Glue down before the epoxy and let it cure prior to bonding with epoxy. The Epoxy won't stick to PVC but it will stick to the glue.

I had to build a nose cone as there are none available that I could find to fit the PVC. See more on that here




One good point. If I break something the hardware store has the replacement part. PVC is probably a decent chioce if you like low and slow launches using I/J or larger Impulse classes.

Good Luck!
 

bobkrech

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Matt

You're not banished to a desert island, but I'm not so sure that you will really save any money over purchasing the rocket kit by the time your done with the project.

You don't have to glass the Binder Velociraptor kit for strength. You might want to checkout my comments from the scratchbuilt part of TRF http://www.rocketryforum.com/showthread.php?s=&threadid=6509

If you're set on trying PVC here's some comments.

First, I have to say I don't like the use of PVC for motor casings. PVC is rather brittle and if a motor CATOs, it is likely to send plastic shards all over the place. For an airframe however, it's a different story since it's not pressurized.

The PVC I'm assuming you plan to use is the non-pressure rated gravity drain type. In the 4" size the wall thickness is 0.070" which is comparable to QT. The density of PVC tubing is about 1.38 g/cc which is about 1/3 more than a typical polymer like ABS which is 1.04 g/cc. It has a 4.075" I.D. compared the QT at 3.900" I.D.

I don't think mechanically there would be a great difference between the two. QT is ok for run of the mill rockets that will not exceed M=0.85, and can not be glassed. (Ref PML website) I don't know the composition of QT however if you go to http://ww.matweb.com/ you can get the mechanical of virtually any polymer. My speculation is that the PVC is slightly stiffer than the QT, but I don't have any hard evidence for this.

Gluing to PVC and any other smooth extruded plastic is tricky. At a minimum you have to abrade the surfaces. A nonabrasive scrubber, Skotchbrite(R) or steel wool will work. Some suggestions for adhesives are listed in this thread.

You might consider going all PVC using PVC sheet for the fins and bulkheads. This greatly simplifies the construction and permits the use of standard PVC primer and cement. It will make a bond that is as strong as the material itself. No epoxy or CA required. [Note: PVC primer and cement is a solvent cement (that mean it disolves the surfaces and when the solvent evaporates you are left with one solid mass) will only bond PVC to PVC. It will not bond anything else to PVC]

Also 4" standard PS nosecones will work with 4" PVC. Just build up a masking tape layer to make up the 0.175" diameter difference.

Lastly, all polymer airframes will be effect more by heat than cardboard or phenolic tubes. Do not use a piston ejection stystem. Instead use a Nomex(R) parachute protector. If you keep the airspeed down well below Mach, the non-presure rated PVC pipe should be ok.

Good luck.

Bob Krech
 

zcases

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I completed a project last year with the 4" thin wall PVC, you can see it and view a movie of its flight on a EX J465 on my website. Its 8' tall and weighed in at ~15lb ready to fly with a heavy sch 40 aluminum motor. I also made my own nose cone for it like Manwithbeers, and have a link to VCP on my website which helped with cutting the glass gores out. I found it very cost effective to use, I will fly it again, and have only changed materials for my next project because I couldn't easily find larger thin wall PVC. So the next one will be 8" Quick Tube. Get your gluing process down, theres some good ideas above.

Scott
http://www.zcases.homestead.com/rocket.html
 

Johnnie

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zcases,

good to hear from ya, you must post more often...

All, his PVC rocket flew great, look at his video...

There are a couple of us Sugpro guys here on the forum...
 
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