16 replies to this topic

[ridley]

sssssssssssssssssss

Edited by ridley, 14 February 2015 - 09:58 PM.

[dr thrust]

yeah, make your core longer, your rockets losing power because the cored grain has burned out and your burning the fuel above the core which is burning at a slower rate, we use this fuel above the core as a delay for timing payloads and please be careful drilling bp, if your serious about rockets, make, buy some tooling.65:25:10 works well for me

Edited by chris m, 28 December 2007 - 02:47 PM.

[seymour]

You should have about one and a half ID's worth of fuel above the top of the core. Try this and you can make adjustments to your next rockets if they are required.

[icarus]

i wondered from the flashes / chuffing if they lost pressure because the end hole burnt larger or the end plug popped out and fuel spewed out of the back ignited recover one in daylight to find out. The nozzle hole diameter makes a massive difference to thrust as it sets pressure of burn with 3.2 mm nozzle approx 250 ft height but with 4.5mm hole mine fell out of sky (as they start as core burner then briefly as end burner once in flight ) still burning on ground Ive found alan yates rp propellent mix less pressure dependant than bp i,m still trying to make a casteable fuel grain we can just glue into tubes to rapidly make consistant performing rockets without pressing

[StevenRS]

Hmmm.. First rockets.. Good memories..

A great, small, but ridiculously fast little rocket that I designed a while ago

http://img214.images...bprocketwx7.jpg

Easy to make, cheap, and good to experiment without wasting anything expensive. The plugs are to big, and the casing is overkill, but it allows a lot of experimentation without blowing up. The PVC can be substituted for paper, but I have made thousands of these, and of the few that blew up, only the plugs blew out, no shrapnel. And this size PVC is very cheap.

[cplmac]

I don't know that I would put much of a header on a half inch rocket, but from what I saw in your video either you core is not right or your fuel is weak. Didn't look like the nozzle blew out, and the burn time didn't seem long enough for meaningful nozzle erosion. What did you use for your nozzle and how deep was it? Those flights were pretty good though as best I can tell from that video. Nice job and welcome aboard!

[will-TM]

Hmmm.. First rockets.. Good memories..

A great, small, but ridiculously fast little rocket that I designed a while ago

http://img214.images...bprocketwx7.jpg

Easy to make, cheap, and good to experiment without wasting anything expensive. The plugs are to big, and the casing is overkill, but it allows a lot of experimentation without blowing up. The PVC can be substituted for paper, but I have made thousands of these, and of the few that blew up, only the plugs blew out, no shrapnel. And this size PVC is very cheap.

I have been using PVC for rockets for ages. Everyone said I was going to get CATOs and they were going to shatter the tubes but they were wrong

I genrally only used KNO3/Sugar for them though

[W.P]

It's foolish to assume that just because you haven't had a CATO yet that by chance you won't end up shooting PVC that has a fault across it's center.

[StevenRS]

It's foolish to assume that just because you haven't had a CATO yet that by chance you won't end up shooting PVC that has a fault across it's center.

True, True... Still need to be careful. I heard that wrapping Duct Tape around the rocket acts like the backing on shatter resistant glass, and kind of holds the shrapnel together, stuck on the duct tape. I wonder if anyone has done this, or could test it?
I think it would work, if it does at all, on the smaller rockets, like mine.

Edited by StevenRS, 09 January 2008 - 12:26 AM.

[seymour]

If you must use PVC or other easily shatterable tube materials for rockets please eliminate the chance of injury by placing yourself a great distance from the rocket, behind a large object (vehicle, large tree ect).

It might work, but please do not count on it for your safety. If it fails it will not make much difference to you weather your PVC pipe fragment embedded in your neck has Duct tape on it or not.


Using paper tubes is just so much more simple.

[W.P]

Well, shatter proof glass doesn't have a low order explosive inside it, the force will rupture the tape and at least eject some of the PVC shrapnel.

[StevenRS]

Just simple distance (or a tree) is great protection, unless your rocket wants to give you a kiss. The idea of the DT is not to stop the fragmentation, but hold the fragments together as they fly away, so they slow down faster. Also, you might get hit in the neck with a lump of PVC bits stuck together with duck tape, instead of razors, so you get a bruise instead of a laceration.
Defiantly not foolproof, but add up alot of little precautions like this, and it starts to get safer.
Or you could just use paper.(I do now)

[W.P]

To the OP, why not try a hotter fuel such as RPH in your rockets? I used to play around with 3" long 1/2" ID rockets which lifted +100g shells with ease, it used RPH using 300 mesh spherical aluminium with alder charcoal.

[Mortartube]

I have used pvc electrical conduit tube as rocket mtors and they actually soften with the heat, so much so that if tape one to a stick with insulating tape. The tension of the tape will partially flatten the tube as the propellant burns away. That is with normal BP.

They are a lot easier than paper but I wold only use them after testing repeatedly the fuel in a similar sized paper tube. Even then they are shielded and a long way away. I have never had one CATO into sharp fragments.

[StevenRS]

Ok, I simulated a CATO by packing a tube 3/4 full of BP and filled the remaining 1/4 with loose powder, and capped with a PVC cap. I did several, with and without Duct tape.When lit, anchored to the ground , the DT rockets produced NO sharp shrapnel, it all got clumped together in 3 or 4 chunks, glued together with 1/2 melted duct tape. The normal rockets burst into flower shapes, with a fair amount of shrapnel, but it wasn't sharp. It seems the PVC gets hot, and under the explosive stress, plasticly deforms, not shattering. I also tried a paper rocket, it exploded with the sharpest report, and no shrapnel.