kpknd Posted April 8, 2013 Author Posted April 8, 2013 Stupid system for uploading photos! # $^&$@~! http://www.amateurpyro.com/forums/gallery/image/2110-meteor-ii/
kpknd Posted April 8, 2013 Author Posted April 8, 2013 That looks nice. How did it fly? UP!!! It went real nice on the 8oz. motor, although the 1# motor nozzel blew out and the model went almost horizontal most of its flight but the chute did deploy.
SekndAmendment Posted April 29, 2013 Posted April 29, 2013 Go nozzleless. In short: Make your motor without the clay nozzle. I have tried a few and they work surpisingly well with hot BP as fuel. I wouldn't go without a nozzle. Without a nozzle to focus and increase exhaust gas velocities you lose specific impulse and could develop regions on the aft end of your propellant grains that burn hotter and result in asymmetrical thrust profiles, which ruin the nice smooth trajectory that most hobbyists are looking for. Nozzles are easy to make if you shape yourself a mandrel and look elsewhere on this or other websites for information on bentonite clay forming.
psyco_1322 Posted April 29, 2013 Posted April 29, 2013 (edited) I wouldn't go without a nozzle. Without a nozzle to focus and increase exhaust gas velocities you lose specific impulse and could develop regions on the aft end of your propellant grains that burn hotter and result in asymmetrical thrust profiles, which ruin the nice smooth trajectory that most hobbyists are looking for. Nozzles are easy to make if you shape yourself a mandrel and look elsewhere on this or other websites for information on bentonite clay forming. You've never made a nozzleless rocket have you? Edited April 29, 2013 by psyco_1322
SekndAmendment Posted April 29, 2013 Posted April 29, 2013 You've never made a nozzleless rocket have you? Yes, I have. It's only practical on small diameter projects with relatively short burn times that result in low altitude flights. A larger diameter rocket, or one with a significantly longer propellant grain stack will exhibit compressible flow dynamics that are not conducive to uniform resultant impulse. The smaller rockets will as well, but as the flight times are shorter, these effects become less noticeable. The Reynolds Number associated with super sonic or high-end sub sonic flows when compared to the motor diameter creates an internal flow profile of extreme turbulence. Without a nozzle to mitigate the random motion of exhaust gasses and particulate, the pressure variations behind the rocket result in poor aerodynamic stability for the air frame as a whole, regardless of geometry. There is a real reason that aerospace engineers put nozzles on rocket motors. That reason is improved thrust (they accelerate exhaust gas), and decreased vibration caused by asymmetrical pressure variations behind the rocket. If you're building bottle rockets, don't waste your time on nozzles because they'll fly just great without them. You'll have a blast doing it too. If you're making something that's capable of flying a few thousand feet or more...a nozzle is essential. Will it fly without one? Perhaps, but very poorly for the amount of fuel grains you use. Rockets fly much better with divergent nozzles. I'm not trying to be snooty or argumentative here. I'm just sharing some experience to help my fellow hobbyists. If you're interested, check out a company called Raytheon Missile Systems in Tucson, AZ. That's where I work. 1
psyco_1322 Posted April 29, 2013 Posted April 29, 2013 I think you took that to a whole nother level. We are talking about pyro rockets here, made from black powder, or whistle maybe. Things that have only one fuel grain, since it's all pressed into a tube. I see you were referring to more composite motors, I see what you are getting at with those. There are regularly people making rockets up to 1.5", some even 2" and 3" ID, that are nozzleless. Using black powder and/or whistle fuel, and they are capable of reaching multiple thousands of feet. Nothing like the 10k+ stuff you are probably more accustomed to though.
SekndAmendment Posted April 29, 2013 Posted April 29, 2013 I think you took that to a whole nother level. We are talking about pyro rockets here, made from black powder, or whistle maybe. Things that have only one fuel grain, since it's all pressed into a tube. I see you were referring to more composite motors, I see what you are getting at with those. There are regularly people making rockets up to 1.5", some even 2" and 3" ID, that are nozzleless. Using black powder and/or whistle fuel, and they are capable of reaching multiple thousands of feet. Nothing like the 10k+ stuff you are probably more accustomed to though. I feel like people that launch a 3" ID rocket without a nozzle are missing a bit of the show! Even Estes sells their smallest motors with integral C-D nozzles in them. You lose quite a bit of thrust without it. But, to each hobbyist his own...right? I enjoy the technical aspect and the optimization process to make some seriously stellar (pun intended) flights. Others just like the sound and sparks, and others the fun is in the building. At the end of the day the most important thing is that we all have fun and are safe doing it. 1
kpknd Posted April 29, 2013 Author Posted April 29, 2013 That is a very good informative disertation on nozzeless motors by 2nd amndmt. My objective is to have a motor with good thrust to lift a model. A nozzeless design I guess would work good if you are just going to tape it to a stick, but I have done that plenty of times too. The weather is finaly straightning out and the fields are getting dry, so I am waiting to go out and do some flights of the model and post it here.
SekndAmendment Posted April 30, 2013 Posted April 30, 2013 That is a very good informative disertation on nozzeless motors by 2nd amndmt. My objective is to have a motor with good thrust to lift a model. A nozzeless design I guess would work good if you are just going to tape it to a stick, but I have done that plenty of times too. The weather is finaly straightning out and the fields are getting dry, so I am waiting to go out and do some flights of the model and post it here. Good luck on your flights! I'd like to see hear how it went.
Mumbles Posted April 30, 2013 Posted April 30, 2013 I've witnessed three or four 3" ID whistle rockets. It's less about the height and performance, and more about the effect. They certainly have a mighty roar and look pretty intimidating in person. They probably only get up to 500-700 feet depending on the header. It also makes you glad you're not the one financing the fuel.
kpknd Posted May 9, 2013 Author Posted May 9, 2013 Finaly got video of the rocket flights. All went real well. I will get it posted when the guy who does that for me has time. Yes, I am computer ilitterit. sorry.
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