9 replies to this topic

[newtoolsmith]

Hi friends,

today I didnt know what to do with me, so I decided to manufacture some motors.

I usually used KNO3/sugar motors but I didnt want so much work today.

As I had heard about DJ?s nozzleless motors, I quickly made a simple tooling (alu-tube, welding wire, ...) and hoped, my BP would be fast enough.

It is!

The casing is 12mmID and 79mm long PVC tube.

The lower 12mm are empty, above 55mm with 4mm core and the rest up to the top massive rammed as endplug and timedelay.

BP is made with BBQ charcoal (not briquettes) and milled for lets say 12 hours, maybe 15.

This works great, quite noisy but without catos yet (5 tests).

For a testflight a 55 gram piece of steel was mounted as payload and reached approx 10m hight. The real payload will be only 30...35 gram so the hight will increase.

Any other experiences with this size and construction?


MfG
newtoolsmith

[FrankRizzo]

Congratulations! Once you make a successful rocket, you're addicted.

Now, if your BP works for nozzleless rockets, it will carry much more weight *with* a nozzle. The advantage with DJ's design is that you can take an otherwise too hot powder, and make a nice rocket wth inexpensive tooling. OTOH, if your powder is slow enough to use a nozzle, you really should. Nozzled rockets also have the advantage of being able to use a BP with a higher percentage of charcoal or other adjuncts that give an excellent tail but a slower burn...an advantage that nozzleless rockets don't have.

Edited by FrankRizzo, 10 September 2006 - 02:47 AM.

[newtoolsmith]

Hi FrankRizzo,

thanks for your nice words but the reason why I decided to try nozzleless rockets is not to manage to build a working rocket. It seems you thought that.

I built great working KNO3/sugar rockets before and tried to increase their efficiency by increasing the chamber pressure and optimizing the nozzle design.

By the way, I am an mechanical engineer and usually use maths before tools because I dont like catos.

I used the same book, calculations and equations as Richard Nakka does. He uses the book "rocket propulsion elementes" and has great experience - even much more than me.

While testing much different constructions I managed to allow chamber pressures of 40bar and a thrust of over 400 newton with thin pvc casings.

That seemed to be enough for more than a kilo of payload but far, far, far to much work for every single motor.

A totally different way had to be gone.

At this point the nozzleless design seemed to be great but as you said, the thrust is not very high (measurements are done theese days by a friend of mine, who developed and built a full electronic thrust measuring equipment with automatically data transfer to MS Excel and ASCII file...).

The nozzles were often blown out so I crimped the tube inwards and used quick cement. That worked great but was laborous too.

Now I'm going to test pvc tubes with 28mm ID and see how the thrust grows.

How can I manage to lock the nozzle easier? Glue it? I know, most of you use cardboard tubes which build up better contact to the pressed clay nozzle.

MfG
newtoolsmith

[ActionTekJackson]

I know what you mean, I too am trying to find easier ways to get the nozzle to withstand higher pressures in PVC casings. Paper is no problem, but a slight bit expensive, and laborous to roll my own, not to mention I have loads of 3/4" ID PVC just laying around with no other use. Drying time isn't so much an issue, patients is a neccissity with pyrotechnics, so I was thinking possibly tile grout, or is there something I can add to the bentonite without making it stick to the tooling sets I have?

[Mortartube]

If you get a Dremel (or similar) with a cutting wheel, just put a few diagonal grooves on the inside of each PVC tube, where the clay nozzle will go. It works for me.

[newtoolsmith]

Hi friends,

last days I found a way:

I made a tool from 4mm steel rod and oak plywood. The wood has a hole only 3mm deep witch fits the outer diameter of the pvc pipe and a second hole, exactly centered in the first, wich goes all the way through the wood. The diameter is only 3mm and the steel rod is sharpened at one end and pressed into.

The pvc pipe is guided in the bigger hole and cant move outwards there.

When you press the clay nozzle into the pipe, the pvc will expand slightly - but not the lowest 3mm as they are guided. The diameter of the resulting nozzle decreases downwards and it cant move out.

This works well.

MfG
newtoolsmith

[BlackSky]

Yes my dear newtoolsmith , This is the way that I always did.
When I press the cat litter into the PVC pipe it will expand a little preventing the cat litter from slide when the PB burn inside the pipe.

I think this is much better than depending on the friction factor between the pipe and the cat litter.

I used to use it for both types BP and Sugar rockets. And I think it is the best way too.

By the way , I also use a technique that gives the nozzle a super strength. I press it in 2 stages.
First , I press 1cm of the nozzle and insert a thin layer of aluminum washer and then press another 1cm. The washer will prevent the internal core of the nozzle from collapse. Thus, It wil be more stronger than the regular nozzle.
I used Cola cans body by cutting it and then punch it as a washer.

Regards
BS

Edited by BlackSky, 04 March 2007 - 06:47 PM.

[ActionTekJackson]

By the way , I also use a technique that gives the nozzle a super strength. I press it in 2 stages.
First , I press 1cm of the nozzle and insert a thin layer of aluminum washer and then press another 1cm. The washer will prevent the internal core of the nozzle from collapse. Thus, It wil be more stronger than the regular nozzle.
I used Cola cans body by cutting it and then punch it as a washer.

Interesting... wouldn't that just melt? I've heard of people using steel wire mesh, is the clay that heat resistant to keep the aluminium from melting?

[BlackSky]

Interesting... wouldn't that just melt? I've heard of people using steel wire mesh, is the clay that heat resistant to keep the aluminium from melting?

Yes it is durable, at least it can stand until the fuel finish burning.

[bonzoronnie]

Hi to all that have made posts on this topic.

I am pleased to find that I am not alone. As I too, have been making use of PVC tubes.

The power to weight ratio over paper tubes must be quite substantial.

I resolved the problem of the tube distorting when the nozel was rammed by making use of a 15mm id brass ferral. Namely a standard 15 mm compression fitting. The beveled olive edge was removed to leave it nice and flat.

For an extra bit of grip I found a coarse threaded tap, slightly larger than the id of the tube and cut a few mm of thread.

As I am making end burners, I can ram the nozel plug and the first two powder rammings before I remove the tube from the ferral. I then continue to fill without the ferral.

I think the PVC tube is incredibly stong in view of the relative thin wall thickness