Potato Posted June 29, 2017 Share Posted June 29, 2017 Hello, I'm from Germany and I made a lot of smaller rockets the last 10 years.But now I wanna built a bigger one The plan is a rocket engine with a ID of 45mm(1,77inch) and a length of 400mm(15,748").I wanna use Rocket Candy with Sorbitol instead of regular sugar due to the higher viscosity of the Kno3/Sorbitol mixture.Which ratio do you reccomend? 65:35 or better 60:40?And how much fuel do I need? Do you think that one kg(2,2lbs) is enough?I will cast it straight into the tube in one solid block. No separate grains.And the most important question: Which nozzle size do you think will make the job well? I would say a diameter of 15mm(0,590inch), because that is 1/3 of the internal diameter.The nozzle itself is casted out of plaster(gypsum) and is screwed in the tube.Thank you for your support! Kind regardsDokami 1 Link to comment Share on other sites More sharing options...
dangerousamateur Posted June 29, 2017 Share Posted June 29, 2017 In my opinion you should start smaller and learn.Because the questions you ask should not be asked when somebody moves to such monsters. Just my opinion 1 Link to comment Share on other sites More sharing options...
nils Posted February 22, 2018 Share Posted February 22, 2018 (edited) I have recently made similar size rockets with good results. Outer diameter of my PE plastic tubes were 50mm and thickness of the wall 1,8mm.Nozzle results were:15 mm - no thrust14 mm - little thrust13 mm - more thrust12 mm - ideal thrust, 2,5 kg on kitchen scale.11 mm - over 5 kg of thrust or explosion10 mm - mostly explosions, rarely ultimate acceleration. 12 mm nozzle version testing video: If you use plastic tube - then I recommend hot bending and no screws: Edited February 22, 2018 by nils Link to comment Share on other sites More sharing options...
stix Posted February 24, 2018 Share Posted February 24, 2018 (edited) I'm assuming we are talking about internal/core burner motors. Nils, what you have neglected to tell us is the length of your fuel grain (I'd guess around 100mm). This is important and will help determine what throat diameter of the nozzle to use. In your case 12mm works fine, but if you doubled the length of the fuel it would likely cato. Potato's planned motor is 400 in length which is 4 x the length of yours, and in my opinion too long compared to the width. What's important to work out is the Kn Ratios. This is the amount of fuel burning (surface area) in relation to the nozzle throat area. Therefore the longer the fuel, the higher the ratio until it over-pressurizes - boom!! There comes a point where you wouldn't be able to make the nozzle throat wide enough. The original post was from June last year. I hope Potato is ok because what he was planning was never going to work for many reasons. One thing he did get right was the amount of fuel required would be around 1 kilo (@ a density of 1.7 grams per cubic centimeter would equal 961.33 grams of fuel), providing that it was a core burner with the core running all the way through and the same diam. as the nozzle throat. But it would have cato'd anyway. Cheers. Edited February 25, 2018 by stix Link to comment Share on other sites More sharing options...
JMan Posted March 4, 2018 Share Posted March 4, 2018 (edited) https://www.youtube.com/watch?v=R93_4BWrC0AI have used laser cut wooden nozzles but I would recommend cutting 4 or 8 notches (about 1/8 the diameter of the circle) around the circumference of the nozzle and press it into the fuel. This lets the fuel grip the nozzle and instead of blowing plastic shrapnel (espicaly if youre using pvc) your nozzle will act as a burst diaphragm to help build pressure for a (now) nozzleless motor. This is almost a hybrid by starting with a nozzle to get that high pressure for take off and lower pressure for sustaining flight. As for the muxture I would recommend dry cooking a fuel consisting of sorbitol sucrose and kno3 in a 3:2:13 mix. Ive noticed this has many many benifits. The sorbitol will bind everything at a low temp and will flow to fill all gaps and air bubbles when directly filling a casing. Once dry the surcose causes the fuel to be very strong and solid but the sorbitol will keep it from cracking. I would not recommend only surcose because it does not bind to caseings well and is prone to cracking and air bubbles. I would also not recommend only sorbitol for such long burning motors. The fuel will get hot and will DRIP out of the motor unless it has a repetitively small nozzle. If your motor is long this mix will also allows the spindle to come out very very nice. You must insert the spindle while it is hot and spin it until it cools. It will become harder and harder to spin until the core solidifies and your spindle will spin with no resistance. I would recommend using a NON WATER ice pack to help cool it faster so you do t have to spin the spindle for so long. Im not sure how long youve been using sugar rockets but Im going on about 5 years and Id love to see you make a wonderful reliable rocket. Just be careful and if ever in doubt, dont. You are taking the risk and it is rocket science if you mess up its a bomb squad/ fire department/ paramedics. Post some pics/vids of your motors wed all love to see them! Edited March 4, 2018 by JMan Link to comment Share on other sites More sharing options...
stix Posted March 4, 2018 Share Posted March 4, 2018 Have to say I did like Nils video with his method for heating and folding over the pvc tube. @ JMan Your sorbitol/sucrose/kno3 mix is similar to my current standard mix. Are you melting the sucrose (ie. 186°C) or melting just the Sorbitol and leaving the sucrose as a filler? I wouldn't recommend "case-bonding" as it's too easy for the flame to propagate up the sides. Link to comment Share on other sites More sharing options...
JMan Posted March 4, 2018 Share Posted March 4, 2018 Stix, I am cooking at 100-110 c and using the sucrose as a filler. Ive never had a problem with the flames traveling up the sides when using sorbitol, however, with sucrose only it has happened (although its been the least of my catos) the sorbitol should really bind with the pvc if youve heated it up enough 1 Link to comment Share on other sites More sharing options...
stix Posted March 7, 2018 Share Posted March 7, 2018 (edited) Ah yes. Similar to my composition KNSUSB18+C, which I think we discussed a while back. Glad you've got some real results - I've got a few cast grains ready to go but have never tested in an actual motor. I'm interest to know how you made it "pourable" and what was the composition that worked for you? Cheers. Oh yeah, I guess this thread has been hijacked, Nils first, then me, then you. Might be better to start a new thread? Edited March 7, 2018 by stix Link to comment Share on other sites More sharing options...
JMan Posted March 8, 2018 Share Posted March 8, 2018 Yes it was your post which inspired me to try the sucrose sorb mix and the way I insert it into the motor isnt really pouring. Ive tried that but it cools too quick so I roll them a little smaller than the tube and let them cool on a heat sink then drop them in and let the motor caseing sit on the hot plate (its really cus its such a small motor) and once its up to temp I tap it on the ground a dozen times and repeat. The right mixture might not be the same for larger motors but I think its really the consistency. The added sucrose adds so much strength to sorb grains (or sorb adds so much malaubility and workable temps to sucrose grains) Once I get it 100% repeatable with common materials Ill post a thread so hopefully this weekend (and hopefully it will help potato with his/her motor 1 Link to comment Share on other sites More sharing options...
stix Posted March 12, 2018 Share Posted March 12, 2018 (edited) I'm glad you have done some tests with that formula. Seems like it works well. I ended up slightly heating the fuel in the forming apparatus in the oven then pressing again. Sorbitol makes that part much easier as in a final pressing to consolidate the mix (no voids). After a few months of testing, the "best" formula that I came up with was: KNO3 62% (fine powder)SURCOSE 20% (fine powder)SORBITOL 18% (doesn't matter because it melts) + a tiny amount of carbon black. The tests were based on "castability" that is, not necessarily pourable, but formable. The tests also rated "strength", "flexibility", "Set-Up time" etc....I'm interested to know what final mix worked for you? In the end, I got "testers block" similar to writers block. I couldn't test simply for the reason that I can't test at home, and going out somewhere to test, becomes a drag. All the testing became overwhelming and I went on to something else to give my brain a rest. Never tested in an actual motor, but I have made grains ready to go. I may do so - your post has inspired me to finish what I started. Edited March 12, 2018 by stix Link to comment Share on other sites More sharing options...
JMan Posted March 13, 2018 Share Posted March 13, 2018 (edited) I havent tested much different amounts as much Ive ive been trying to get an easy made motor. My mix is 14-21-65 I like sticking to the exact chemicle mx if 7-13 (35-65). But give me a weekend or two more and Ill have a new post explaining all about it. My biggest problem has always been voids and coreing the rocket this solves both Edited March 13, 2018 by JMan 1 Link to comment Share on other sites More sharing options...
stix Posted March 14, 2018 Share Posted March 14, 2018 Sounds good. Link to comment Share on other sites More sharing options...
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