Axial load strength of PVC pipe

[jetman]

Hello,

I design high powered rockets in our Tripoli rocket club. A particular plastic type of tube used is the Quantum 3.9 in dia plastic (sewer pipe) it is a thin wall design. http://www.publicmissiles.com/ They state that this basic tube is good for just .86 mach for compression loads. Basically this nearly 4in dia tubing is used for rockets that are between 6 and 9 ft tall. To go above mach 1 we have the option to use fiberglass tubes or better yet carbon fiber, steel etc.

Before I spend all that money on fiberglass or carbon, I want to know what axial strength I would have roughly, if I used an outer pvc sleeve over the previous mention PML tube. (good for mach.86) The resulting double walled pvc tube would now be good for what in compression axis? 1.5 mach 2 mach etc..

The known is: The PML tube alone is good for .86 mach airspeed for compression load..BUT if i use the below listed outer tube (a white thin wall sewer pipe)..it will be stronger.

The outer tube I want to use just fits nicely over the PML tube and specifically, the outer tube is: Made by Cresline pvc DS- 3000LB CRUSH PVC sewer pipe MS ASTM D 2729.

Obviously, when you slide a PVC tube inside another tube, it becomes stronger.


Also in general, If say a known tube A for example has an axial load strength of 2000lb then tube B of axial strength 1500...if bonded together with epoxy or silicone etc..and tubes cut flush on ends...will the new load simply be A+B= 3500? or is there a higher increase, a synergistic effect when tubes are layered? I realize an accurate way to find out is load test a 12 in piece of tubing that has the tube glued inside another...but, I don't have such testing equipment.

*My current rocket design will reach mach one almost at 700MPH for just a few secs..then the speed will decrease over 30 sec to just 30 mph at apogee.

The main point is, I need stronger tubing for my rocket project that will just barely reach 700mph. The PML tube alone is not quite good enough (.86 mach) I will be at least 1 mach...can my double tube do it...surely it can, but I need Data!

Thanks,

Michael Tampa
Tripoli Cert Level 2

 

[cjl]

Honestly, QT is fine for mach 1 or so. I've seen it flown in that region many times, and flown it myself. The issue with most PML kits is the fins. The included fiberglass fins are very prone to flutter at high speeds. If you do genuinely need more compressive strength than the QT can provide, then look into glass, glassed paper, blue tube, glassed phenolic, or similar, but if you're only looking at 700mph, the PML tube should be fine alone (Oh, and I wouldn't try your suggested reinforcement method - PVC is very heavy, and it would be nearly impossible to get a decent bond between the QT and the PVC, since they are different types of plastic)

What kind of rocket design is this anyways?

Chris
(TRA 11233 L3, NAR 84281 L3)

 

[jetman]

Hi Chris,

haha another rocketeer on the forum..cool For my cert 2, used pml Quantum, with lots of couplers inside.was stiffer. The fins wer 3/16 ply sanded/painted and bolted to aluminum brackets..BUT the PML lower scratch built fincan was sleeved with the white pvc sewer pipe...this way the brackets were firm..did not budge when you tried to move the fins.

I still don't have any TAPS selected yet..need a field good for 15k at least. Some people have said at mach 1..may get more stress..vibration etc,,so you should glass. I plan on using the long burn 11 sec..Aerotech M650..it should not go like a bat out of hell..should be a nice less aggressive launch...Will TAPS sign off for a cert 3 if pml tubes are used?? Has anyone ever done cert 3 on 4in dia pml??

If PML quantum is good for .86 mach...I wouold like to know what the axial 'max load' would be with the outer white thinwall sewer pipe. When I smack it with a hammer..it won't break,,seems tough. I need some strength vaules, I I double wall it..to relay to my future TAPs

Thanks,

Michael

 

[cjl]

Oh, this is for an L3? I wouldn't recommend quantum for an L3, reinforced or otherwise. It's decent tubing, but there are better choices. MagnaFrame or Blue Tube would probably be my first choice for something like that. They'll do just fine without any reinforcement. They aren't that expensive either - MagnaFrame is $10 more per 48 inch section, and Blue Tube is $9 more per 48 inch section. I doubt that you could reinforce the PML QT for any less than that. Besides, I still don't think that the sewer pipe would really be able to be bonded to the QT very well, so I think its main weakness would be the fact that you couldn't really join them with any kind of strength.

(Of course, glass tubing is the way to go for the most strength, but it's not really needed for the flight profile you've mentioned so far. It's great stuff to work with, but quite pricy - $76 for a 4 foot by 4 inch section)

 

[batman394]

jetman, I don't want to hijack your topic. Not trying to anyway.

Where did you find the compression strength data for PVC pipe?

I'm thinking about building a vacuum chamber for some quick tests from PVC. It'd be schedule 40 pipe, 6" diameter, a 12" length of it.

Maximum water pressure inside the pipe at schedule 40 is 130 psi. But pushing out on the pipe isn't the same as pushing in.

 

[Windnsails]

Solvent welded joints on Sched 40 PVC pipe can withstand full atmospheric vacuum (only 14.7psi and hoop stress is practically negligible for all diameter-thickness ratios). However, gasketed PVC pipe joints should not be relied upon to withstand vacuum since buckling at the pipe ends may occur and loss of seal will result. Google:" Uni-Bell PVC Pipe Association" and look for the PVC design manual.