33 replies to this topic

[Sparky]

Hi all

 

I've been away from the hobby for a little while for no other reason than my many other hobbies got in the way. Anyway I'm back at it again and once again my hand rammed rockets are the bane of my life.

I have some nicely made aluminium tooling and the best concentric, STRONG tubes money can buy but still I have issues with reliability. I won't go into too much detail about my multiple failures and multiple attempts to build a motor I can trust well enough to lift the equivalent header to about a 3 inch size shell or close to that. Strangely when I started out with inferior tubes and chemicals and experience I had greater reliability. All I will say is that over the many attempts I have tried all the obvious tweaks but I still get a significant number failing. Too many to trust putting a header on that is going to break quite hard.

 

The usual failure is the tube splitting but I've had the nozzle blow out and occasionally the bulkhead.

I've not given up and I will go back to basics with my ramming techniques, compositions, construction etc so I'm not seeking more advice there yet. One thing I wanted to try though but wanted opinions and advice on are nozzleless rockets but using tooling designed for a nozzled coreburner. From what I understand I could achieve this by using as hot a BP fuel mix as I can and ramming them just the same but without the clay nozzle.

Is that really all there is to it? I was going to give it a go and I wondered if this method might be more forgiving and reliable for someone who clearly needs to work on their nozzled core burners lol.

p.s. I would like to make a press but until I have more workshop space it's the one thing I am going to have to wait a bit longer for unfortunately.
 

[Vic]

I doubt your tubes were at fault or your method, what mix and tooling are you using.

After rereading your post why are your tubes splitting if you are hand ramming

Edited by Vic, 26 July 2015 - 10:45 PM.

[dr thrust]

Hi, long time since I made them, started back in 2008
You can ram them but I found pressing better well at least the 3lb motors preferred it lol
They were and still are one of my favs, I had a thread on it, I was pretty new to pyro when I started it, but it snowballed into exotic (to me) fuels and adding metals to aid heat of reaction for extra " juice"
There's still a lot of work to do on these motors re tooling design, Standard bp tooling works fine or slightly narrower
The best fuel I found was willow bp milled for four hours( ballmill on a timer) riced with 2-3% Vaseline/ mineral oil dissolved in warm cellulose thinners to get a very nice fuel grain when pressed.
One disadvantage of this fuel was no " tail" the oiled fuel really gobbled up the orange sparks
There was talk of using this mix at the bottom of the fuel grain as a kind of eroding nozzle with the rest of the propellant being straight bp meal .
Anyways I'm yakking on http://www.pyrosocie...?hl=nozzle-less

[Sparky]

I doubt your tubes were at fault or your method, what mix and tooling are you using.

 

After rereading your post why are your tubes splitting if you are hand ramming

 

I experimented with various mixes from as much as 65% KNO3 25% Willow C,10% Sulfur and others reducing down to about 55% KNO3. I wouldn't mill them but they were very fine and well integrated plus I'd rice the BP to reduce duct when I ram. I have got the ramming force just right as I know any harder and the tubes buckle. Occasionally they would CATO, sometimes it would be the bulkhead failed but never the nozzle.

One thing I haven't tried is using mineral oil in the BP and I'd like to try a nozzleless version with a 75:15:10 ratio of green just to see if it has much lifting capability. To be frank I would rather a slightly poor power than a CATO as I hate pissing off my neighbours with loud bangs as I test them.

The tooling is one I bought of Oliver Brown ages ago, it's a nice design, long spindle with appropriate sized nozzle etc. Not sure what more info to provide on that.

It's been a while since I made some so I'm going to hide away in my workshop and try again and give it all some more thought.

[Sparky]

I doubt your tubes were at fault or your method, what mix and tooling are you using.

 

After rereading your post why are your tubes splitting if you are hand ramming

 

I experimented with various mixes from as much as 65% KNO3 25% Willow C,10% Sulfur and others reducing down to about 55% KNO3. I wouldn't mill them but they were very fine and well integrated plus I'd rice the BP to reduce duct when I ram. I have got the ramming force just right as I know any harder and the tubes buckle. Occasionally they would CATO, sometimes it would be the bulkhead failed but never the nozzle.

One thing I haven't tried is using mineral oil in the BP and I'd like to try a nozzleless version with a 75:15:10 ratio of green just to see if it has much lifting capability. To be frank I would rather a slightly poor power than a CATO as I hate pissing off my neighbours with loud bangs as I test them.

The tooling is one I bought of Oliver Brown ages ago, it's a nice design, long spindle with appropriate sized nozzle etc. Not sure what more info to provide on that.

It's been a while since I made some so I'm going to hide away in my workshop and try again and give it all some more thought.

[starseeker]

From my experience, using just willow charcoal made my 1lbers cato , have you tried a slower charcoal ,and /or try adding a percentage of 80 mesh to slow it down and give a nice tail ?

[samboradford]

Hi Sparky,

 

I'm sure I can help you.  Can you just confirm where you got your tubes from, you said they are concentric ( do you mean parallel wound and not spiral ) - it's usually quite difficult to properly buckle a good tube with hand ramming, they will flare at the bottom though.  Can you also confirm the following :

 

a) how are you ricing ?  with alcohol / water and NO binder

what are you using to ram them - what is the mallet made from, does it bounce ?

c) are you using a ramming post

d) is your fuel completely dry ( how long after making them do you fire them )

e) how are you fusing them

f) do they CATO immediately or after a short delay

 

+1% mineral oil reduces thrust by around 6 - 8% but it also significantly aids compaction which if your rammers are bouncing will reduce grain flaking and cracking and lower your CATO incidence. I dissolve 1% mineral oil in coleman naphtha fuel ( others use zippo fuel ) - add to pre-milled mix until tomato soup consistency, stir until comes together in a ball then rice as is through 4-mesh screen and dry.

[Sparky]

Sam

 

I think your questions have precisely mirrored the point I've reached with my next tests!
 

a) how are you ricing ?  with alcohol / water and NO binder - no binder, I use methylated spirits 

what are you using to ram them - what is the mallet made from, does it bounce ? - Wood but I have noticed it bounces a bit.

c) are you using a ramming post - No I need to put one in my shed workshop..it is next on the list of to do's

d) is your fuel completely dry ( how long after making them do you fire them ) - definitely dry before I make them and I usually test very soon after making one.

e) how are you fusing them - I've tried a variety of ways. I've used green visco folded into a hook just inside, I've used blackmatch strands all the way up the core, just into the end etc etc.

f) do they CATO immediately or after a short delay - I'd say within .2 of a second. They often get some lift but then go instantly. It is hard to be precise though.

 

[Sparky]

From my experience, using just willow charcoal made my 1lbers cato , have you tried a slower charcoal ,and /or try adding a percentage of 80 mesh to slow it down and give a nice tail ?

To be frank I've not tried enough combinations of the compositions but I've tried pine charcoal (air float) and this cato's as well I believe but I may need to revisit that. I gave up making them as I was worried about pissing the neighbours off.

[cooperman435]

I apreciate this is very simplistic but if your getting Cato after Cato surely the speed of your powder is to blame? If you've good tubes and methods have you tried dialling back the speed to the point you get no Cato but no lift and then tried to find the sweet spot?

Back int t day when I did rockets I had good success simply adding more and more charcoal of a given mesh size pre milling to slow it down in a very controlled way and it resulted in very nice fine tails with lots of thrust from relatively slow burning powder.

It does however make compacting it well harder if you don't mill it plenty as the excess charcoal gives it a springy nature in larger particles

[dr thrust]

Hi sparky, if you want your rockets to launch, launch the wooden mallet as far as you can , it's not ideal, go for a rawhide,brass, or copper hammer , I had the same prob when I swapped to a rubber mallet Cato after Cato , look at a tube support as well, you can go to town on the ramming

[samboradford]

Phil is spot on - the CATO occurs when the pressure exceeds the containment strength of the tube which, broadly speaking, can only be solved by 1 of 5 ways :

 

1. Increasing the strength of the tube

2. Reducing the power of the mix

3. Increasing the size of the nozzle

4. reducing the length of the core

5. Improving the stability of the mix during burning so that oscillations in pressure don't exceed that which is containable by the vessel

 

1.

Wood hardener in my experience makes little difference.  Most UK parallel wound tubes are fairly comparable in strength. I have some NEPT tubes I have yet to test.

 

2.

Can be done with charcoal or other additives. For a really hot mix sometimes quite a large amount of charcoal needs to be added and can be tedious as you need to mix, rice and dry each time.  My preference is vaseline or mineral oil dissolved in naptha add 1 - 3% ( I can't tell much difference between vaseline vs baby oil personally )

 

3.

not feasible with O.B. tooling unless you go nozzless

 

4.

not feasible with O.B. tooling

 

5.

Only really relevant if your fuel is on the edge, you will only know this from starting slow and titrating up.  Greater burn stability is achieved by :

a) better compaction - ie a press or using a wooden mallet on a wooden post to reduce bounce and whacking it really hard, you can tell if it's bouncing on your O.B. tooling as you will find it tedious to switch to your final rammer after the spindle is passed as it will keep flaking at you and seem to take ages to switch up rammers - add mineral oil ( baby oil ) or vaseline as above and you won't look back

igniting the core in one single go - ie BM up to the tip of the core

c) good mixing of your ingredients - Ball mill, add mineral oil and rice.

d) preventing cracking of the grain during storage which allows the flame front momentary access to a greater surface area which causes a pressure spike and CATO - mineral oil helps reduce this, as does having completely dry KNO3 and charcoal ( yep, check your charcoal is dry )

e) there is a relatively new wave of tube waxers - it does work, you have to dissolve paraffin wax in naphtha and coat the inside of your tube, this is believed by LLoyd S. over the pond and others to lubricate the wall which prevents distortions in the grain due to binding with it and also to prevent the flame front leaching up between the grain and the tube.  Again, only relevant if aiming for super hot fuels.

 

I have your tooling and this will work for you for that tooling.

 

ball mill 4 hours 60:30:10 pine or willow.

 

Make 3 batches, + 3% mineral oil, + 2% mineral oil and + 1% mineral oil, all dissolved in naphtha then riced with acetone or IPA to dilute and dried.  Start with your +3% mix and test that rocket, then gradually test +2%, then +1% until CATO.

 

In fact, if I press my motors I can easily run 60:30:10 + 1% mineral oil on the O.B. Set.

 

This should work.

 

Let me know.

[samboradford]

So basically ken you agree - add the baby oil and everyone's happy.

 

A fish hooked visco makes no difference to the CATO. But I do disagree on fusing the core and I have the thrust tests to prove it, on your tooling - if you fuse the core with BM up to the tip then peak thrust is achieved near immediately. This means liftoff is instantaneous and if you have a heavy heading can be the difference between a decent height and a low break.

 

Sorry if my posting wasn't helpful.  Seems like a case of too many cooks and all that so I'll duck out of this thread then.

 

Good luck Sparky.

[Sparky]

Thanks to you all for the words of advice. You've all got me thinking about what it could be and I think a number of you are probably right as I doubt it is one issue.

 

I've 2 weeks holiday coming up where I can just potter about at home and do some tests. I've a short list of likely causes and things I'm reasonably sure are not the cause. i will follow up with the results so anyone else having trouble can possibly learn from my experiences.

Things I won't yet rule out but I am fairly sure are not the issue.

 

1. BP mix being too hot - There is no way the various comps I've tried are all too fast for the purpose. I've tried a number of variations and none as hot a composition as I know I should be able to use.

2. Tubes - I have cheaper and more expensive makes. They are both easily strong enough, the netter ones should not fail with the composition I've tested them with.
3. Bulkhead - I am using a very thin bulkhead and when I drill through it Im not compromising the grain. I may try not using a bulkhead but given how thin mine have been and the fact I hand whittle a hole to the edge that only just touches the fuel, I am sure it is not this.....well almost sure ;-)

4. Fusing - I have tried all manner of fusing positions and for now am sticking with visco to the nozzle end only. Once I get a reliable design I can then go for the QM right up the core, especially if the initial impulse seems low.
 

Things I'm definitely going to try and I think could be an issue. 

 

1. New ramming post in the shed. My ramming surface is simply not solid enough so I have a large post I need to pile drive into the ground in my shed!

2. Get a leather faced mallet. Can anyone recommend how heavy / the size of these? Remember I have arms like Popeye the sailor and have been known to break a man's arm just shaking hands ;-)

3. Try some mineral oil in the mix to help it consolidate.

As you can see I'm reasonably sure now that I have problems with my grain not consolidating well enough. I've made enough motors that flew well and enough that failed to know that I can get it right with existing compositions and tubes etc. I also know what definitely doesn't work. The one thing I now realise was that the variability could well have been due to the ramming action.

 

We shall soon see!!!



 

[cooperman435]

Would a hydraulic press not be an idea then as it would immediately remove the consolidation variant?