Newbe rocket test/fail

[jallafish]

Everything is the same as last, but now a shorter engine(8cm), bigger hole in the nozzle(8mm) and core. Will post a flying test when the wind has stopped.

[deer]

Congrats on success, but damn you like to risk it... I mean, I'm not judging you, just a friendly reminder to rise your awareness. No gloves and hand under nozzle during light up. Exhaust pointed at house. Backing up so little for PVC. Did you at least use safety goggles / glasses? Just try to keep these things in mind and abide by them. With PVC I run as far as fuse allows during manual start (prefer electronic though) and wear gloves and protective glasses. For better view I place shielded camera right next to test, or zoomed-in one on tripod. Free hands = more mobility = less clumsy and safer.

 

Several times gloves have saved me from burned fingers. While the KNO3/sugar seems like a tame composition, once in a while it happens to develop hot spots / voids causing pressure spikes that can eject the whole fuel grain out of case and (thanks to the Murphy), exactly in direction of you or nearest flammable object.

 

Now, for the performance - judging from the intensity of output, I'm not sure if it'll fly, but it looks worth trying - just keep in mind it might hover or start to randomly tumble and spin near ground. Mines make quite roaring sound and even then they seem to linger in "launchpad" for some time:

https://www.youtube.com/watch?v=Rc01MN0snRE

 

BTW, anyone got idea why my fuel goes brown (the video in post #21)?

 

 

[GMetcalf]

The fuel is going brown because the sugar is caramelising. I saw the temperature probe showed it reaching above 100^o (I'm assuming it's in ^oC here) which is well into the caramelisation range for fructose. As sugar (sucrose) is heated in the presence of water, it hydrolyses into glucose and fructose, allowing the fructose to begin the process of caramelisation (which occurs at lower temperatures than the caramelisation of glucose, hence starchy vegetables need to cook for longer than fruits to caramelise). I can't see it causing a drop in performance much, but you could always try cooking it at lower temperatures for longer to drive the water off. Maybe nothing above 80^oC for however long it takes? Can't say I'm an expert in cooking sugar but I do indulge occasionally when making sugar glass or caramel lattices for various desserts.

[stix]

Congrats on success, but damn you like to risk it... I mean, I'm not judging you....

 

I'm not having a go at you deer, that's fine that you don't wish to judge. I have no such concerns regarding the personal "feelings" of others when it comes to safety.

 

"Safety isn't a judgement call - it should be a standard". - stix 2015.

 

Hay again. Finaly the rain has stopped ☺. Soo bad wather the last week. Still too much wind to test my rockets, so I tested an engin instead. Successful this time ! Ty for the advice.

 

Video: https://m.youtube.com/watch?v=AnsfrUPmqa4

 

JF, I viewed your video.

 

Firstly, I agree with others regarding the safety aspects of making sugar rockets. PVC is not a great idea. Also lighting so close is potential for an accident. We should always look for the worst case scenario, ie. "What if.....".

 

I'll give you an alternate reality of the video you posted: You light the fuse, the sparks from the fuse ignite the motor prematurely, there are cracks in the fuel due to untested methods, the motor explodes, you get pvc shrapnel embedded in your face, the clamp holding the motor shatters and inserts itself into your eye socket and other on-lookers are also injured.

 

So, the positives:

• Find yourself an off-site area to do your testing, not close to buildings etc.
• You could supplement your fuse by using a sparkler tightly wrapped in aluminium foil - this at least would give you enough of time for a safe retreat. An e-match would be better.
• Get some good goggles
• Ditch the metal clamp - use a thinner piece of wood and wrap around with 5 to 6 layers of cloth tape.
• Don't approach the motor until well after it has seemingly finished - especially if it is still smoking (5mins)

It sounded like there were children in the background? I hope not. You would never forgive yourself if something terrible happened.

 

As for the motor performance in the video, my view is that it would be unlikely to take off - it burned too long. If you want to go for a launch then please do it in a large open space and with enough time to get away in case it flies sideways.

 

I imagine that this seems like a personal attack on yourself, but it's not just that. It's about people who expect to get results with careless and quick-fix methods. However, plus points to you for asking these questions on this forum - this is a good start. There are many people on this forum who will help you to improve your rocket motors, but at this stage, I'm unwilling to do that, as it could help improve a situation that could lead to an accident.

 

Rocketry is a very fulfilling hobby that I have enjoyed for many years, and I'm not without guilt for doing stupid and unsafe things - I now have the benefit of hindsight . I learned from library books pre-internet days. With forums like this, there is no excuse for recklessness.

 

If you are serious about rockets, then you will persist, Please heed the advice of not only myself, but others on this forum.

 

Be Safe - Cheers.

Edited May 13, 2015 by stix

[jallafish]

Stix, thanks! Your comment made me thinking. I can luckily say that the childs in the background was there, but far away and behind a wall. And I used safety glasses.

 

But yea, safety glasses wont help my face and fingers if it blows. I promise, no more stupid actions. And again, thanks for the comments.

I have now also purchased a e-match/ignitor with remote control.

 

Safety is number one priority from now.

[deer]

So, apparently baking paper isn't a suitable choice. Besides strength and heat resistance it has quite pronounced non-sticking and hygroscopic properties. I wonder if it's been treated with some grease already during manufacture:

 

Btw, this thing managed to get camera airborne:

Now I just have to figure out how to stop it from spinning:

https://www.youtube.com/watch?v=qSMOdLdhatc

 

[stix]

Good job getting a camera up.

 

To stop it spinning you could try and put some fins on the motor body - this might help, or maybe lose the stick altogether and attach some fins and use some sort of launch rail or tower similar to a model rocket.

 

Also if the nozzle hole isn't centered properly this can cause it to spin.

 

Cheers.

 

[EDIT] btw. I don't think you'll be able to stop it from spinning completely - but should be able to reduce it enough to get some good video.

Edited May 15, 2015 by stix

[chand]

Guys if ur rocket is exploding then first calculate pressure if it's excessive then just make nozzle bigerand decrease the burning area u and use this equation

P = Kn density of propellant r C*

 

P = maximum pressure

Kn = burning area/throat area

R = burn rate for sucrose based propellant r= 0.602

C* = characteristic exhaust velocity for sucrose C*= 3016

And all units are English units means inch

[FlaMtnBkr]

How do you know if your tube can handle whatever value you calculate? It's cool to approximate values with various equations but it doesn't really let you know if your rocket is going to blow up, and if it does blow up, why it happened.

 

If you use standard tooling for a certain size motor and fuel you should make a working motor. If not, then you should only have to make a small adjustment to your fuel and most likely an adjustment to your manufacturing process.

 

Just my opinion. Maybe others can do something with a calculated pressure number but it doesn't mean anything to me.

[stix]

In an ideal world we would have facilities where we could pump air into our proposed tubes to see how much pressure they can take before failure. We could work the math from there - if we had the inclination.

 

A procedural approach (ie. trial and error) can also yield satisfactory results. As FlaMtnBrr pointed out - small and incremental steps is part of the scientific method.

 

Better to do small steps than pretend you understand the math. Just work it through and write down your steps and compare the results.

[Rocketier]

Calculating is for those intrested in de maths. But I think that the path with trail and error brings the fun and knowledge.

Offcoarse it's good to read yourself into the stuff this will put you on track but after that testing and building is half the fun.

If you don't want that just buy your rockets on store. What's more fun than running away from youre device and after loads of catoos your first rocket will go airborn.............whooooohieeeeee Fun I want to do more jjjjjjjjjjjjeeeeeeeeeeeeheeeeee. :D

 

 

And if you really want to do calculating visit Richard Nakka's page.

Edited June 13, 2015 by Rocketier

[deer]

Math is a good way to obtain initial values for custom design. So instead of e.g. trying 100 faulty nozzle sizes, you do 10 working ones where you just fine tune the performance.

 

If you use any well known configuration, the numbers are out there and you just have to fine tune them to match your circumstances, such as actual ingredients (e.g. specific sugar brand) and manufacturing process. E.g. in my specific case it seems that the caramelizing is caused by too small pot filled too high. Large area skillet allows water vapour escape faster, cooling the mixture. In my case the mixture develops hotspots much more easily, since the hot steam cant escape.

 

P.S. I recall reading tube strength test with bentonite, basic diy hydraulic press and heavy weight gauge... ahh, here it was: http://www.skylighter.com/fireworks/how-to-make/Fireworks-tubes.asp(scroll slightly past middle).

Edited June 13, 2015 by deer

[chand]

In an ideal world we would have facilities where we could pump air into our proposed tubes to see how much pressure they can take before failure. We could work the math from there - if we had the inclination.

 

A procedural approach (ie. trial and error) can also yield satisfactory results. As FlaMtnBrr pointed out - small and incremental steps is part of the scientific method.

 

Better to do small steps than pretend you understand the math. Just work it through and write down your steps and compare the results.

Stix I do know math better than u okay that's why I told u read the theory solid rocket motor theory okay

[FlaMtnBkr]

That is a fairly simple equation. I'm sure any of us can use it correctly and it doesn't take a math wizard to pull it off.

 

My calculator knows math better than any of us. But he doesn't go around bragging about it okay. Unless he has been getting on the internet again. Oh crap.