THEONE Posted June 17, 2011 Posted June 17, 2011 Hi boys, i want to ask something about the core rockets....The think that i want to ask is what is the difference between two exactly the same rockets witch the one have a bigger nozzle/core....Thanks
dagabu Posted June 17, 2011 Posted June 17, 2011 The difference is that one has a bigger hole then the other... Is that what you wanted to know? -dag
pillyg Posted June 17, 2011 Posted June 17, 2011 The bigger the nozzle, the lower the thrust. The bigger the core the faster it burns so the higher the thrust.
THEONE Posted June 17, 2011 Author Posted June 17, 2011 (edited) OKLets say that i have a rocket with 5mm nozzle and 5cm (for example) core length with max thrust xxxx gramsand i have the same rocket with 7mm nozzle and 8cm (for example) core length with the same thrust....So what is the advantages and the disadvantages and the difference (except the nozzle-core) between them... Edited June 17, 2011 by THEONE
shockie Posted June 17, 2011 Posted June 17, 2011 The nozzle throat size and mandrel greatly affect the performance of your rocket and in small rockets this can only be found by trial and error. The quality of your black powder also has an enormous impact on nozzle and mandrel design. Some powders have a very fast burn rate creating more pressure quicker requiring a larger nozzle opening and some powders have a slower burn rate requiring a smaller opening. A deeper mandrel will also generate more thrust as this creates a larger surface area for the burn resulting in more powder being burnt at ignition time. Too deep, and the rocket will explode on the launch pad, too shallow and take-off will be very slow which will not allow the rocket to reach a proper altitude (having burnt most of its propellant even before it gains sufficient thrust to take off). So as you can see there are many factors that will affect the performance of your rocket, just keep experimenting and eventually your rocket will fly fast and high. from: http://www.pyroguide.com/index.php?title=Black_powder_rocket What the above leaves off is ignition location. For example, you will two completely different thrust-time curves which correlate to chamber pressure depending on where you ignite the core. For example, you can ignite the cored at the bottom or the top.....Igniting at the bottom will result in a lowerchamber pressure while conversely igniting the core at the top will generate higher chamber pressures. Why is this so? Because where you ignite in the core will result in differning burn patterns in the core itself. more surface area, more thrust...less surface area less thrust. If you want to simulate nozzle shape/size consider a sim program like nozzle at aerorrocketor its AeroISP program; or Burnsim or similar products.... Here's a Rocket Tool Sketcher program that will help with core design: http://www.flashnet.dk/rts/ Most BP cored rockets basically just have a cylindrical hole for a nozzle.......it can be slightly tapered for better efficiency. End Burners require a DeLaval type nozzle to be most efficient. Your best bet is to just purchase some tooling as much of the work has been done for you. The tooling is based on hundreds of years of experimentation..all you have to add is the BP...... HTH Terry
Mumbles Posted June 17, 2011 Posted June 17, 2011 It's generally accepted as much easier to tune a fuel to a specific set of tooling, than tune your tooling to the fuel. That of course does not mean experimental spindles or tooling are not any fun. TheOne, as for your question, what are you calling the "thrust curve"? Nearly all rockets, especially that with a core has some sort of initial thrust peak as the core burns away, and then it tends to taper off as it becomes essentially a functional end burner. If you assuming the entire burn is identical then it doesn't matter, both are the same and neither has an advantage over the other. However, it sounds more like you're describing a situation in which they both generate the same amount of peak thrust, during the core burning stage. I'd think that the smaller nozzle would be better as it (in theory) should have a higher sustained thrust through the rest of the fuel burn.
dagabu Posted June 17, 2011 Posted June 17, 2011 The bigger the nozzle, the lower the thrust. The bigger the core the faster it burns so the higher the thrust. Not quite so, the bigger the core the more fuel is consumed in the same time but the thrust is lessened due to the larger nozzle. I think you meant the LONGER the core maybe? -dag
dagabu Posted June 17, 2011 Posted June 17, 2011 Most BP cored rockets basically just have a cylindrical hole for a nozzle.......it can be slightly tapered for better efficiency. End Burners require a DeLaval type nozzle to be most efficient.Terry Only if the resulting exhaust is traveling faster them mach. Speeds lower then mach will actually hinder the efficiency and cause less thrust. -dag
THEONE Posted June 18, 2011 Author Posted June 18, 2011 Guys i still haven't understand the differences between them, can somebody explain to me with two simple words please ?
THEONE Posted June 18, 2011 Author Posted June 18, 2011 (edited) Can i ask something else, if i have a 3mm-6cm core and 5mm nozzle (for example ) and is works fine, if i will make the core from 3mm to 5mm it is possible that way i would have CATO ? I have put on you tube a video with a test...http://www.youtube.com/watch?v=8BQQSG_GkxI Edited June 18, 2011 by THEONE
dagabu Posted June 18, 2011 Posted June 18, 2011 Can i ask something else, if i have a 3mm-6cm core and 5mm nozzle (for example ) and is works fine, if i will make the core from 3mm to 5mm it is possible that way i would have CATO ? I dont know what that means but it sounds like you are making the core shorter, if that is the case, no, it would be less likely to CATO. The longer (deeper the hole) the core the more pressure it will create. -dag
Mumbles Posted June 18, 2011 Posted June 18, 2011 With your successful rocket, if you make the core wider (from 3mm to 5mm), yes it is possible to have a CATO. You wont know for sure unless you try though.
THEONE Posted June 18, 2011 Author Posted June 18, 2011 0With your successful rocket, if you make the core wider (from 3mm to 5mm), yes it is possible to have a CATO. You wont know for sure unless you try though. OK my friend thank you i will try itWhat about the video ? It is good ?
dagabu Posted June 18, 2011 Posted June 18, 2011 0 OK my friend thank you i will try itWhat about the video ? It is good ? Please edit out the time waiting for it to fire and film it horizontally and it will be fine. It sure is good to see the thrust made from the little motor on that scale though -dag
THEONE Posted June 19, 2011 Author Posted June 19, 2011 Please edit out the time waiting for it to fire and film it horizontally and it will be fine. It sure is good to see the thrust made from the little motor on that scale though -dag I am sorry dagabu but i didn't understand you, my English are not the best
THEONE Posted June 19, 2011 Author Posted June 19, 2011 (edited) Guys i tried the engine at the video, it works well but it does not go strain, it flies and after it falls down after some meters... I tried before with the same engine with a small core but it flies well...I notice that it had a slow lift up but i do not know if this is the problen, the previus one worked well I use two iron welding electrodes for stick and i have take out this white thing around the electrode (i dont know how it calls ) Edited June 19, 2011 by THEONE
THEONE Posted June 19, 2011 Author Posted June 19, 2011 (edited) Here a test were i increase the core dimension from 3mm to 5mm and i decrace the length from 7cm to 6 cm 2.avi Edited June 19, 2011 by THEONE
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