usapyro Posted June 22, 2017 Share Posted June 22, 2017 (edited) I am having a interesting issue with my new high power BP rockets with my new quality hand rolled tubes. I am able to use a smaller nozzle and much higher pressure... Which is causing a problem. I recently launched a BP rocket with +10% magnalium, and didn't see any tail effect. I assumed the MgAl was being burned up or something... Then tonight I launched a rocket with +20% pine charcoal BP... Only saw a few "puffs" of charcoal tail effect. Then, I realized whats going on... Most all the sparks are getting trapped against the flat face on the back of the nozzle. I had a similar issue with my "Flying Fountain" rockets. The centrifugal force of the rotation speed was preventing any metal sparks exiting the rocket. What angle do I need to make the internal nozzle to get all the sparks out of a end burner? About 20 degrees? 30? Maybe even 40 to get all the sparks out fast for maximum effect? Edited June 22, 2017 by usapyro Link to comment Share on other sites More sharing options...
EliTheClasher Posted June 22, 2017 Share Posted June 22, 2017 (edited) I don't know much about nozzles, but I thought I would just be annoying and point out centrifugal force should be centripetal force. (I gotta make myself feel better because I cant even get my KN03-sugar fuel to ignite...) Edited June 22, 2017 by EliTheClasher Link to comment Share on other sites More sharing options...
lloyd Posted June 22, 2017 Share Posted June 22, 2017 USA,We always used a 60-degree convergent cone, and a 30-degree divergent cone. It's the same angles as the 'classic' DeLaval, but modified in length, such that the divergent cone isn't long enough to fully-expand the gasses to atmospheric pressure. Were it that long, it would also end up larger than the tube i.d. Our whole nozzle fits inside the tube (as do most gerb nozzles). L Link to comment Share on other sites More sharing options...
dagabu Posted June 22, 2017 Share Posted June 22, 2017 (edited) A long time back now, I did experimentation on the de Laval nozzle design on BP rockets and with a cheap-o chi-com metal lathe, I formed a base and rammer that left me with this design: http://www.pyrobin.com/files/de_leval.jpg Yes, pretty elementary and I had to remove the white space between the bells since I was using R-candy at the time, I didn't use spindles but drilled the hole afterward. I was unable to use a spindled base with this design since I couldn't get the compaction I was looking for. Durhams water putty and two steel washers (where the solid white part is) did a great job making nozzles too as long as the tube has a rough texture inside. Since then, I settled on a 45° convergence and a 70° divergence to mimic the de Laval but with straight lines. This is an example of a 77.5° divergence with the 45° convergence angles. Very close to what I use now . http://pyrobin.com/files/new%20nozzle%20mix_1.jpg Edited June 22, 2017 by dagabu Link to comment Share on other sites More sharing options...
lloyd Posted June 22, 2017 Share Posted June 22, 2017 Huh? Dag, do you have the terms "divergent" and "convergent" swapped? A better acceleration of the gasses is provided with a wider angle convergent cone, and a narrower divergent cone. LLoyd Link to comment Share on other sites More sharing options...
usapyro Posted June 23, 2017 Author Share Posted June 23, 2017 (edited) Here we go... Internal nozzle former rammer. Made with first a angle grinder, then spinning it fast against a file with a drill for a while, and finishing with steel wool. Not perfect, but should work! Edited June 23, 2017 by usapyro Link to comment Share on other sites More sharing options...
lloyd Posted June 23, 2017 Share Posted June 23, 2017 USA, that should work fine, but make the divergent part (the nozzle-former, proper) a LITTLE straighter. That's not for performance so much as ease of manufacture. Doing a "true" DeLaval with the paraboloid convergent and divergent sections makes almost no difference on gerbs... flat-sided cones work as well. What you did might improve rockets some, though. Lloyd Link to comment Share on other sites More sharing options...
usapyro Posted June 23, 2017 Author Share Posted June 23, 2017 (edited) USA, that should work fine, but make the divergent part (the nozzle-former, proper) a LITTLE straighter. That's not for performance so much as ease of manufacture. Doing a "true" DeLaval with the paraboloid convergent and divergent sections makes almost no difference on gerbs... flat-sided cones work as well. What you did might improve rockets some, though. Lloyd It grips slightly after ramming the nozzle, but nothing significant. It's fine for 1# rockets. For bigger rockets, I can see how it would be an issue. I switch to a flat faced rammer immediately afterward for the first big BP increment. Edited June 23, 2017 by usapyro Link to comment Share on other sites More sharing options...
dagabu Posted June 27, 2017 Share Posted June 27, 2017 Huh? Dag, do you have the terms "divergent" and "convergent" swapped? A better acceleration of the gasses is provided with a wider angle convergent cone, and a narrower divergent cone. LLoyd Depends on where the angle is measured, the convergence is 45°, the divergence is 77.5°. Both measure from the width of the tube (or 12.5° along the dominant, straight length of the tube). I measure the width due to the way I see the base as the rocket is pressed being the horizontal or the width. Link to comment Share on other sites More sharing options...
lloyd Posted June 27, 2017 Share Posted June 27, 2017 (edited) Ordinarily (at least in 'rocket terms') the angle is measured along or about the centerline of the nozzle. The angles I quoted are the angles of the nozzle's, not 'relative' to anything else but the nozzle itself. The convergent angle should be 'wider' than the divergent angle. Sometimes, they're expressed in 'half-angle' from the centerline of the nozzle... but it's still relative to the centerline of the nozzle's bore, not to the sidewall of the tube. This isn't 'my choice' of expression. It's the way rocketeers have been doing it since day-one. We just borrowed the parlance from them, since we didn't have any specific terms to describe our nozzles until those guys quantified the method. Lloyd (PS... what you SHOWED is correct in its configuration, so long as the gasses are flowing right-to-left... which I assume they are, or that nozzle wouldn't have worked worth a darn.) Edited June 27, 2017 by lloyd Link to comment Share on other sites More sharing options...
dagabu Posted June 27, 2017 Share Posted June 27, 2017 Ordinarily (at least in 'rocket terms') the angle is measured along or about the centerline of the nozzle. The angles I quoted are the angles of the nozzle's, not 'relative' to anything else but the nozzle itself. The convergent angle should be 'wider' than the divergent angle. Sometimes, they're expressed in 'half-angle' from the centerline of the nozzle... but it's still relative to the centerline of the nozzle's bore, not to the sidewall of the tube. This isn't 'my choice' of expression. It's the way rocketeers have been doing it since day-one. We just borrowed the parlance from them, since we didn't have any specific terms to describe our nozzles until those guys quantified the method. Lloyd (PS... what you SHOWED is correct in its configuration, so long as the gasses are flowing right-to-left... which I assume they are, or that nozzle wouldn't have worked worth a darn.) Uh, yep. What YOU said... The long and short of it is that I do what you say and it works, I was just showing some of my trials. Link to comment Share on other sites More sharing options...
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