44 replies to this topic

[jermain]

Hi,

First post etc. bit of a newbie and looking for some help. I made this rocket recently out of ball milled (7-8hrs) 75/15/10 composition. It was one of my first experiments with rocket motors. Though it took of it seemed to lack the power to gain enough elevation and then veered at a 45 degree angle. Can anyone help me as to why this happened.

Also before setting of this rocket I had made numerous attempts at making motors. Some instantanously exploded and others burnt for 4-5 seconds without taking off.

This rocket was not cored as I have found that most cored rockets just explode without any burn time.

Any help would be appreciated.

[Atom Fireworks]

Hey buddy and welcome,


Right first of all lets talk safety, i take it that was your garden? if so i would assume there houses nearby? Judging by the video i would say you do not have a big enough test area yet especially for your first test, you need a bigger area but thats up 2 you, ive seen people do this kinda stuff in allot smaller spaces and it can be very dangerous.

Right now for the fun bit I take it your motor was an end burner, now ime not very experienced with rocket motors and compositions ( i like shells more) but from my limited experience using the same mix as lift, with a clay nozzle drilled out to the " optimum diameter" you can achieve allot more powerfull motors than the one displayed in your video, Do you nozzle them? i would suspect you do if you are having some of them just explode on you. Its trial and error really, get your mix right first and stick to it then try different nozzle diameters to see what you can get away with before they just pop. Another thing is make sure your casings are strong a reliable and also maybe adjust the pressure your ramming them at, i just used to ram them with a raw hide mallet and brass rod and hit it a few times per half teaspoon of powder not rocket science some of the lads on here are very clued up on them maybe have a read through the rocketry threads? Also do a power test with some scales and a vid recorder, try and see how much thrust you are achieving consistantly, only when you can create many motors and test say 5 of 1 batch and they all perform within reason the same, then start attaching sticks and headers.



Hope that helped,



Jay

Edited by dumper truck, 16 May 2011 - 09:58 AM.

[Mortartube]

Welcome to the forums. What is the ID of your rocket tube in mm? I think the choke hole is too big. You are nearly there. What size was the choke?

I make end burners with a 16mm ID and only use a 3mm choke. Try making the choke 1mm smaller in Diameter. If that doesn't work try 2mm smaller. 2mm may result in a CATO so try 1mm smaller first.

BTW cored rocket need a slower mix as the core creates a much bigger surface area so gas pressure builds more quickly. For your size of rocket, if it was cored, you would need a mix of about 65% kno3, 15%s and 20% charcoal. That would need fine tuning of course and that would be about an 8mm dia choke.

Looking at your video again, I would say this: But before you try any of that, try a slightly longer stick. You should be able to balance the rocket on your finger with your finger literally just below the bottom of the motor with the stick on your finger. It may be as simple as that. Give that a go first.

Edited by Mortartube, 16 May 2011 - 10:09 AM.

[jermain]

Thanks for the answers guys, great help!!

Firstly, yes that was my back garden, however there is a field about 2mins walk away where i went for my previous 15 tests. For this one i just couldnt be bothered to walk over there again. Sod's law it was the only one that actually took of!!

Second of all, I ram the composition pretty hard (could this be the reason they are blowing up, I'm guessing the harder you ram the more quickly the pressure builds up.

Thirdly yes it is nozzled using bentonite clay. I can't remember the exact size of the nozzle but my guess was that it was to large and the escape velocity of the gasses not fast enough therefore not giving it enough lift. Your points have confirmed this. I think I'll buy some more chemicals and try some more experimenting for batch 2 (already used 2kg of KNO3!) For the casing's i simply used paper and selotape. I sawed of the top of a broomstick for a rammer and wrap 4-5 sheets of A4 paper around the circumference and then simply selotape it into place and fill it up with composition. Is this not suitable?

One question, do you think the rockets keep exploding as the paper is to weak or perhaps the pressure build up in the rocket is just to much (most explosions blew the top out even though it was blocked with 1/2inch of clay).

On another note, i did try 60/30/10 composition core burner and it didnt move :|. Admittedly it was 8 inches long and was pretty heavy!!

[Mortartube]

Firstly, I would do everything you did to make the one in the video but increase the stick length, This is the easiest option and may be the cause. After all it flew a good distance and may just be out of balance.

If that doesn't work, then play with mixes and nozzle sizes. The tube should be glued, rockets produce high pressure and bad tubes are too variable in quality to get consistent results.

[jermain]

Ok ill try to do that. Btw does it make much difference mixing the BP with water and then pushed through a screen to make crystals? Does it increase a rockets power?

I'm just concerned looking ahead considering these motor's barely lifted themselves off the ground let alone be able to carry any sort of weight for a header.

[Mortartube]

Well if you look at your video again, you will see that the rocket seemed to maintain power throughout it's flight. It didn't explode or pop out the choke, so I think the motor is just about right. However you did it before, do the same again. I really think it's just a matter of too short a stick meant it wasn't balanced. If you get some flying straight up making them exactly as you did before, then you can play about with fine tuning afterwards to try to increase power. Eliminate one thing at a time and remember to keep notes on everything you do. Notes can save you a lot of messing about when you come to repeat experiments many months later.

Use a stick of te same dimensions but try about 200mm longer.

[dr thrust]

hello
firstly welcome to the forum, and yippee for amateur rocket action!, there's been a serious "pyro" drought over the last six months !!!
heres a useful link skylighter end burner
hope your playing with rockets safely, dont forget your ppe whilst ramming , protective clothing, face shield , thick work gloves consistency is the key to successful rockets, noting milling times,accurate measuring of ramming increments ,ie make "measuring scoops"
and consider, making/ buying basic tooling to form your nozzle , no drilling please!

Edited by dr thrust, 16 May 2011 - 09:31 PM.

[Peret]

Ball milled 75:15:10 will be much too hot for a core burner and almost invariably explodes, though I'm surprised at the poor result for an end burner. 60:30:10 is what most people use with cores, or for a nice silver tail, 60:22:10 and 8% aluminium coarse flake (20-40 mesh), but it needs to be ball milled and not just screened or it will do the same thing yours did. Here are a couple of mine - you'll relate to the first one, which was not ball milled. The second was so fast away that the camera couldn't follow it. These were both 1/2 inch by 5 inch tubes, with about a 4 inch core and 1/4 inch nozzle. Both had a header and a 33 inch by 1/4 inch square stick, and an all-up weight (including stick) of about 75 grams.

[jermain]

Though I do take extreme care whilst ramming (as I'm aware of what 'could' happen) I do not have a face shield or thick gloves etc. I do use gardening gloves and were eye protection. Is everything else essential? Is there much of a chance of the powder going up whilst ramming bearing in mind i use a wooden mallet and wooden stave.

Thanks

hello
firstly welcome to the forum, and yippee for amateur rocket action!, there's been a serious "pyro" drought over the last six months !!!
heres a useful link skylighter end burner
hope your playing with rockets safely, dont forget your ppe whilst ramming , protective clothing, face shield , thick work gloves consistency is the key to successful rockets, noting milling times,accurate measuring of ramming increments ,ie make "measuring scoops"
and consider, making/ buying basic tooling to form your nozzle , no drilling please!

[Atom Fireworks]

When you " play" with fire you will inevitably get burnt, i know what your saying about using wooden tools and the chances of an ignition are very VERY slim, however in this hobbie theres a concept to be adheard to at all times, "Better to be safe than sorry" you may get away with it 100 times and then it only takes 1 accident to cost you dearly, personally i have run the risk when ramming motors but if anything did happen it would be soley my own fault and i would expect no sympathy. I think its fair to say youve taken a reasonable safety approach using the ppe you have, you could and maybe should go one step further and buy a face shield, that will also come in handy if you ever get involved in profesional pyrotechnics.

Oh and ide buy good quality rocket casings, its 1 less variable for you to worry about, atleast then when youve finally made your most impressive rocket with a good header that youve taken a while to construct it doesnt cato because your casing failed. I know it feel good to build something from nothing but i have built shells that i have taken so much time and effort to find out when fired i did not prime my stars enough, or the burst wasent as hard as it should have been, do it right the first time is my motto now

[Gavin]

Hey Peret, nice sized back yard you got there

[jermain]

When you " play" with fire you will inevitably get burnt, i know what your saying about using wooden tools and the chances of an ignition are very VERY slim, however in this hobbie theres a concept to be adheard to at all times, "Better to be safe than sorry" you may get away with it 100 times and then it only takes 1 accident to cost you dearly, personally i have run the risk when ramming motors but if anything did happen it would be soley my own fault and i would expect no sympathy. I think its fair to say youve taken a reasonable safety approach using the ppe you have, you could and maybe should go one step further and buy a face shield, that will also come in handy if you ever get involved in profesional pyrotechnics.

Oh and ide buy good quality rocket casings, its 1 less variable for you to worry about, atleast then when youve finally made your most impressive rocket with a good header that youve taken a while to construct it doesnt cato because your casing failed. I know it feel good to build something from nothing but i have built shells that i have taken so much time and effort to find out when fired i did not prime my stars enough, or the burst wasent as hard as it should have been, do it right the first time is my motto now

Sorry to probably ask a stupid question. What do you mean by a header?

Thanks

[Creepin_pyro]

.

Edited by Creepin_pyro, 08 October 2011 - 10:09 PM.

[jermain]

Ok, thanks!!