13 replies to this topic

[a2wpyro]

tubes

for my bp rockets
i have been looking at this site for a bit and was woundering what size tube i should get.
The dimensions i have been using are as followed:

id: 11mm
length:6cm
walls: 1.5 mm

i dont want to get to many of this size because i will more than likely want to upgrade my rockets, for bigger loads.

Edited by a2wpyro, 11 January 2004 - 04:13 PM.

[Yugen-biki]

I?m sure they will work. They are plastic right?
I have used plastic fore some time but slightly larger:

id: 13mm
length:7cm
walls: 1.5 mm

Maby the walls are a little to thin for paper tubes...? When I used paper tubes I used a wall thickness of 2mm (hand made). With the right BP and technic they will surely fly.

[alany]

Do not use plastic!

It is not a good match for BP if you are case bonding the grain. Kraft is an much better match for BP, it is rough and bonds fairly well to the grain. It also poses no shrapnel hazard if the motor catos.

Those PVC motors you see all the high power rocketry guys using are fairly well designed and have an internal paper liner/inhibitor into which the grain is cast. They still suffer the odd grain/liner delamination and cato explosively scattering bits of jagged PVC and burning propellant everywhere.

Start with 2 oz rocket tubes 3/8" x 3 1/2" (9.5mm x 89 mm), cat litter nozzle and bulkhead plug and greenmix BP as the propellant. A 3-4 mm nozzle hole bored about 50 mm deep into the grain should work, but is by no means optimal. You can use any size you like, but 8-10 x ID long is a good starting point unless you are using a more energetic propellant and ~10 mm ID is physically quite a good size to work with, wasting less propellant and making smaller catos while you are getting the details worked out.

Another, probably more sensible, option would be to start with 'bottle rocket' size devices. They are much more forgiving of packing density and geometry. You can virtually funnel and wire load them, then stab a metal skewer up their bottom to form the nozzle and core. A 5-6 mm ID (around the 1/4" or less), about 45-50 mm long works well. The tubes can be rolled from typing paper, but newsprint will work and it often used in commercial '1 gross in a box' ones. Unfortunately larger devices are easier to make physically with poor tooling.

When I was in highschool I made rockets using nothing but a piece of cardboard from a matchbox, wrapped around an 8 mm Aluminium rod and taped in place. This completely dry-rolled tube was then rammed with a small piece of Aluminium foil to make a primitive nozzle-end plug, BP prepared by mortar and pestle was then rammed in with hand-strength, some paper wadding and hot-melt sealed the top. Then I forced a 2.4 mm philllips screwdriver through the Aluminium foil ball and almost all the way to the top of the grain. The motor was taped to a kebab stick about 6 times longer than iitself, and a fuse of BP meal twisted up in kitchen paper was added. They worked quite well for their 'field expedient' construction, on my website under "Small Experimental Rocket Motors" you can see my recreation of them last year when I was just getting back into pyro. (This doesn't mean you should try to replicate this design! It is only to say primitive designs made with virtually no tooling or materials can work quite well.)

[Yugen-biki]

My plastic tube have never exploded in to shrapnels. The nozzle or the top of the rocket goes first. One time the plastic melted and a opening formed with a pop. If green powder is used the plastic will surely hold. On the other hand I don?t think my tubes are made off PVC...?
Maby paper is the best, because you never know when the plastic you have got may explode.

[Pyromaster2003]

I used a plastic tube a year or two ago to make a rocket and it failed badly. The tube melted in the middle and the rocket lost power and shot back to earth still burning! The tube walls was 3mm thick. Never used plastic since...

[Yugen-biki]

Many off todays rockets are made from plastic with some paper wraped around. They don`t melt and then I got the id? off me useing plastic. The most important thing is to get the BP verey well compacted, or else it will cato.
68:23:9 milled for 3-4h is near optimum.

[Jerronimo]

I use PVC for my rocketmotors (18mm ID 20mm OD)for a long time now.
I think I made around 50 of them and not a single one cato'ed, so I must be doing something right.

The secret is to use slow BP with a coredesign, and as Yugen allready stated
ram it realy hard.

[lord_dranack]

The problem with pvc is that if there is an explosion, the shrapnel (or splinters) do not show up on x-rays and so if you do get hurt, then you face explorative surgery so find all the bits, or a nasty infection from them.

[bernie]

Life is just so much more simple when you use paper. Do yourself a favor and take the advice. Please.

[Matt]

Im with Bernie.. as a rule...
Just a note on PVC though. Im sure he is using rammed clay plugs, Have you felt the inside of pvc? seriously if the pressure builds up its just gonna shoot the plugs out before the casing will go. this is all in the first 2 seconds. Anything after that the pvs goes spongy from heat, i make my 23mm engines with teleflite propellant with pvc. The only catos have been plugs blown out.
But when you go the full length and do what them rocket boys do and use customised reducers as nozzles and use pvc end caps and all, thats when i would be scared.

-Matt

[Yugen-biki]

Just a note on PVC though. Im sure he is using rammed clay plugs, Have you felt the inside of pvc? seriously if the pressure builds up its just gonna shoot the plugs out before the casing will go. this is all in the first 2 seconds. Anything after that the pvs goes spongy from heat, i make my 23mm engines with teleflite propellant with pvc. The only catos have been plugs blown out.
But when you go the full length and do what them rocket boys do and use customised reducers as nozzles and use pvc end caps and all, thats when i would be scared.

If you have a slow burning BP the tube will melt and the rocker becomes a "side fountain". If the BP is to fast the preasure will escape at the ends. I use a 3mm thick sugar and KNO3 dealy and end plugg for my rockets (hard as a candy). If the Rockets cato:es the sugar will fly upp in the air lika a single mortat in a cake.

But allways safety first!! If you are going to "go the full length" use paper.

[sasman]

What causes the rockets to go cato? is it due to the Bp not being pressed into the tube correctly?..

sasman

[Richard H]

A CATO can be caused by a number of things. The most common is poor consolidation of the propellant, and the second most common is a fractured grain. Any hairline cracks can cause the motor to simply explode when it comes up to pressure.

[dfk]

To add to the list:

fuel that is too hot,
ramming large increments of powder at once,
weak end plugs,
a core that is too long for your rocket or the speed of your fuel,
using too course a material for your tail(charcoal, titanium or any other metal for that mater)

The list goes on, thats what I do and don't like about rockets;
they can be very challenging, frustrating at times but are equally rewarding when everything suddenly fits together and work just as they are supposed to.