Guest Mark_the_pyro Posted February 24, 2006 Posted February 24, 2006 Regarding stick rockets, is there a general equation on how long it should be? Or is it enough to know that the stick should weigh more than the motor and payload?Thanks
Mumbles Posted February 24, 2006 Posted February 24, 2006 Usually I just balance it. After you make one, you can just remember the length, and keep using it. It all depends on the wood type and thickness really.
Frozentech Posted February 24, 2006 Posted February 24, 2006 Regarding stick rockets, is there a general equation on how long it should be? Or is it enough to know that the stick should weigh more than the motor and payload?Thanks From experience, 4oz BP rockets need a 24" stick, and 1lb rockets need a 36" stick. I don't know of a specific formula for the length. It is commonly said that the rocket needs to balance on the stick just behind the nozzle. I don't believe I have ever had a rocket that did ! The actual weight of the stick is less of a factor than the drag which is imparted behind the center of mass. If the stick weighed more than the motor and payload it would result in a massive decrease in lifting capacity. I don't have access here to my logbook, to give you some specific weight examples, I am sure others will though.
teknix Posted February 24, 2006 Posted February 24, 2006 I can usually get my rockets to balance on the stick. I just take the diameter of the rocket engine and measure that far back on the stick behind the nozzle and balance it there. I can usually get it balanced in the matter of seconds and they flight pretty straight.
shadopyro Posted March 28, 2006 Posted March 28, 2006 Hello, i know this is probably very old topic, most likely closed by now. i know how to stabilise rockets with stick or bamboo canes etc, but what would be the "rule of thumb" for a finned rocket? as in where should it balance where the engine should be placed etc. i tried making a finned rocket, made it as long as possible but it was very unstable and flew all over the garden instead of into the air lol!
Swany Posted March 28, 2006 Posted March 28, 2006 The center of gravity may be too high, I dont remember where it is supposed to balance to, but you could seach it, and then balance it before you fly. Make sure everything is mostly symmetric. I made a finned rocket using all pop cans, and it went sort of up, then took a sharp split S turn to try and decapitate my brother. It was an interesting rocket. I belive I killed it after that run....
TheSidewinder Posted March 28, 2006 Posted March 28, 2006 For BP rockets, a certain rocketeer named Steve says to just balance it at the nozzle or slightly further down, payload or not. However, he says his hybrid (whistle/BP) rockets lift so hard and fast that they MUST have a payload on them or they fly just as you described, shadopyro. Perhaps you have too much thrust for the total weight? Try adding a sand-filled header and see if that helps. Or balance a lot more carefully? As to finning.... I've seen pyrotechnic rockets with fins. Some people glued them to the rocket motor body, some to the sticks. One design that looked nice and relatively simple was to take a launching TUBE (not rail), and find a 2" long cardboard tube with a very thin wall (use Estes rocket body building tubes, if nothing else) that just fits inside the lauch tube, but is the right outside diameter to fall through the tube without "catching" anywhere. Cut and glue rectangular (or leading-edge-tapered) wooden fins on the end of the rocket stick (NOTE: Stick MUST be straight, warped ones will NOT work, and should be square although round ones will work) in a cross pattern, then slip the 2" tube over the fins, glue everything and square it up then let dry. You can do this on the sticks alone to make a batch ahead of time, and a building jig would help a LOT. You end up with an "X" or "cross" inside a circle if viewed end-on. I'm sure you can visualize the rest. Cut the stick and attach it so that it balances as above. The added weight will change the balance, so you end up using a shorter stick. I'm going to try this on a small batch of rockets this summer and see if it's all that it's cracked up to be.... M
BigBang Posted March 28, 2006 Posted March 28, 2006 The center of gravity, CG, must be on top of the center of pressure, CP. That is, the closer it balances to the nose, the better. You have to calculate the CP yourself though, but it is very simple. You can do it with a cheat sheet I came across, or use a computer program like space cad or rocsim. I'll just post the sheet because I think it is better to work it out yourself. http://www.mdra-archive.org/newsletter/SPECIADB.PDF Hope this helps.
shadopyro Posted March 29, 2006 Posted March 29, 2006 Ah yes i see, i further maths at sixth form at the moment, maybe my mecanics teacher will be able to help in some way...I guess in a way i just have add weights of some sort to the nose cone until it balances... Seems logical as the first few all i did was stick an A4 sheet of paper around the engine to make a tube, added some cardbord fins and a nose cone. think i'll have try at putting on some extra weight to the nose cone when i get some time (easter holidays).thanks for all your help!
psyco_1322 Posted January 12, 2009 Posted January 12, 2009 Its a bit of both. With a stick, its a lot about being a long counter balance. It you chop your sticks down, or are using fins, it becomes more about a balance of weight. Para flare rockets have about zero stabilization devices, rather they operate and stay flying straight being carefully weighted down to make them balanced. If you tie about 6 feet of string around your rocket at its center of gravity, and swing it around in a cirlce above your head you can visibly see if it will stabalize. It it lays flat and spins fine, it should "theoretically" fly like that. If it tumbles and flops around, its off ballance and will fly just about how you see it. I'm pretty sure the above is correct, if not, someone correct me.
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