pyro159 Posted June 25, 2016 Posted June 25, 2016 So I had this crazy idea one day to make a 6 foot tall rocket. I had already made a couple rockets and one that was 2 foot tall and they flew well. Except for the 2 foot tall one. I made the center of gravity too high and flipped mid-air and crashed. Learning from my mistakes I want to build a bigger and better one than the previous 2 foot tall rocket . So far I have bought a 2 foot segment of 3 inch wide schedule 40 PVC tubing and I also have a 6 foot tall schedule 20 PVC tubing for the rocket body. I made a wooden nozzle copy 3 inch wide for the rocket motor and I'm going to take it to machine shop and have them copy it and aluminum. I'm either going to use the ammonium nitrate based fuel or potassium nitrate based fuel. One of the questions I have is should I use an aluminum nozzle or should I use a steel nozzle? My other question is what should I use for the rocket motor body? At the moment I'm using a 3 inch wide PVC tubing that's 2 foot long and I've been suggested to use a steel or aluminum based rocket motor housing instead. Another question I have is should I cast the potassium nitrate and sugar fuel directly into the rocket motor or should I cast into grains and then put in the rocket motor? Also if anybody has any formulas for ammonium nitrate fuels or know where I can get a program to design nozzles, it'd be very helpful.
pyro159 Posted June 25, 2016 Author Posted June 25, 2016 The second picture is of the converging side of the nozzle. The first one is the diverging side.
pyro159 Posted June 25, 2016 Author Posted June 25, 2016 If you want to look at the video of my previous rocket, you can see where I made the mistake of putting the fin too high. https://m.youtube.com/watch?v=1LjsKP9VY3k
dagabu Posted June 25, 2016 Posted June 25, 2016 (edited) While I love your enthusiasm, you have a lot of reading to do first as you seem to be working to reinvent the wheel, so to speak. The whole nozzle debate was fully hashed out with the de Laval nozzle design, long ago and gives you the design profile based on approximate flow velocity (v), together with the effect on temperature (T) and pressure (p). And while your wood blocks are very pretty, the bell ends up facing the outside and not inside, which will reduce the efficiency dramatically. I no longer do any high power rocketry so Ill hand this off to the HP guys for further discussion. NOTE: In your video, I notice schedule 40 PVC pipe used for the body? WAY too heavy, use paper or cardboard, roll it your self if you are able. It will take off a good 500g of weight. I would try that same motor again with a hand rolled tube and see what you get out of it, fins angle back further will help too. Edited June 25, 2016 by dagabu
pyro159 Posted June 25, 2016 Author Posted June 25, 2016 Thanks for the reply. I have just re-lathed my model nozzle so that it has more of a bell shape rather than a straight cone shape. I was also researching viable fuels I could use for my motor and was looking at APCP. Do y'all think that would be a good propellant for a six foot tall rocket?
pyro159 Posted June 25, 2016 Author Posted June 25, 2016 Oh and here's the picture of my re-lathed model nozzle.
pyro159 Posted June 25, 2016 Author Posted June 25, 2016 Oh, and I mixed up the sides of the nozzle. The picture shown is the side that is facing down when the rocket is vertical.
dagabu Posted June 25, 2016 Posted June 25, 2016 The nozzle is pretty, nice job on the lathe. I would pass on making from aluminum, raw aluminum has a melting temp of 1,221°F while Black Powder tends to burn at or about 3,000°F. I don't know the burning temp of R-candy or APCP, I am sure others here know what it is but I cannot see anything below 2,500°F. That means that your aluminum nozzle will vaporize and extreme erosion will happen. I suggest (with your fantastic lathe skills) that you think about making some graphite nozzles. Use a shop vac, trust me...
pyro159 Posted June 25, 2016 Author Posted June 25, 2016 Haha yeah. Problem is, I don't have a metal lathe. Do you know if graphite can be cut with wood lathe tools?
dagabu Posted June 26, 2016 Posted June 26, 2016 Yes, it is "soft" to the tool, like a good hard, tight grained wood is. Go slow and use a low speed with hand tools. Carbide holds up better but even tool steel ground to a shallow angle will work as well.
AzoMittle Posted June 26, 2016 Posted June 26, 2016 Most large rockets (in the range of the 6' you mentioned) are fiberglass, sometimes they use a metallic casing but usually fiberglass. At those sizes they can go trans or super sonic, that brings in all kinds of new challenges, most of them related to stability and fins. You also need to think about recovery systems, the parachute ejection, the parachute itself, finding the rocket when it lands, etc. Rockets of that size often are flown out on the dry salt lake beds and require a GPS tracker to find, they also usually require notifying the local airports in order to get clearance. Use a de Laval nozzle, graphite. You can mill it yourself or buy it online. I can give you APCP formulas but I'm not going to. APCP is whoooooole other ballpark, it requires oven or vacuum curing. I'm not sure how a sugar rocket would perform at that size but I would use a black powder based propellant, here is an example of one from Alan Yates: http://www.vk2zay.net/composition/4 I would HIGHLY recommend starting with a kit for your first large build. The Darkstar Extreme has always been a popular choice: https://www.wildmanrocketry.com/ProductDetail.aspx?product=2902 Wildman Rocketry also has plenty of components, you should also check out Apogee Rockets, they have a great store and LOTS of very informative videos and articles, I believe they publish a new one every week. 1
pyro159 Posted June 27, 2016 Author Posted June 27, 2016 Thank you for the information. Do you happen to know of a site where i can get a lot of potassium nitrate for cheap? I think i'll go with the black powder based propellant you suggested. Also, do you know of where i can get instructions to make said 3 inch black powder rocket motor?
dagabu Posted June 27, 2016 Posted June 27, 2016 Thank you for the information. Do you happen to know of a site where i can get a lot of potassium nitrate for cheap? I think i'll go with the black powder based propellant you suggested. Also, do you know of where i can get instructions to make said 3 inch black powder rocket motor? Sorry, little steps grasshopper!! Don't rush this, BP has a lot of thermal mass to it and you can get hurt badly or even die, or worse, you can lose parts of your body and be a burden to others for the rest of your life. http://www.amateurpyro.com/forums/topic/11642-my-thumb-was-blown-off-half-a-section/ Me, 6 weeks after my ball mill went up in flames: 1
pyro159 Posted June 28, 2016 Author Posted June 28, 2016 Dang man. How? I realize how dangerous a ball mill is. I remember reading about how in aluminum powder manufacture, there's only one person allowed in the building when they open up the ball mills, or something to that extent. I also heard that you should never use steel bearings for a grinding media due to the high chance of a spark.
AzoMittle Posted June 28, 2016 Posted June 28, 2016 Thank you for the information. Do you happen to know of a site where i can get a lot of potassium nitrate for cheap? I think i'll go with the black powder based propellant you suggested. Also, do you know of where i can get instructions to make said 3 inch black powder rocket motor? Google it. Potassium nitrate is used in several industries and is not hard to find at all. It should cost around $1-5 per pound depending on sources, amount you're purchasing, etc. Shipping will be the most expensive component. Making a black powder rocket motor could be a whole forum unto itself, I'm afraid I have no quick and simple answer, you'll have to research. For starters, you'll want to look at ramming vs pressing vs castable, bates grains, grain geometry (you'll probably want to use a combination of simple cylinder core and solid grain, probably), progressive vs neutral vs regressive burns, motor liners/insulation, ejection charges/computers and baffles, parachutes and recovery, and motor mounting methods (I'm sure I'm forgetting things but plug those into google and it will lead you down the rabbit hole). At that size the engine can easily tear your airframe apart (usually at the fins or motor mount) if you aren't careful. Like Dagabu said, start small and work your way up. I know the big ol' rockets look exciting, and they are, but they also come with a buttload of research, expense, and hazards. Spending a year building a 6' rocket only to have it cato on the launch pad is heart breaking. Build small and work your way up, each step is an achievement (instead of a hurdle), plus you can mess around with different methods and see what works for you. No one lays fiberglass perfectly the first time, let alone rolling a paper tube, take the time to invest in yourself. Stay safe, have fun!
MrB Posted June 28, 2016 Posted June 28, 2016 I wish! You really should warn us before posting them pictures. I still react quite violently, thinking about the horror and pains you must have been in. Damn dude.
Redrocketman Posted June 28, 2016 Posted June 28, 2016 Holy s@#t. Lucky.... Casting grains I believe is the way to go. With the correct tooling you should cast each grain slightly recessed at one end. When loaded in the motor casing & ignition takes place, the grains will burn both the surface area of the core, and the ends of the grains, due to the grain spacing caused by the recession on one end of each grain - hence more surface area = more burn. I have focused on r candy motor design, as recently I nearly took your path of attempting a full scratch build, before joining this forum & talking to people who know their stuff. As said, when u take into account launch, recovery deployment timing, fin design, Ardunio, etc etc, it really gets full on!! I have brought a Tempest 2.5" kit to hone my skills, focusing 1st on motor design, & will move on with time, research, study & a lot of patience!! Good luck 🚀🚀🚀
stix Posted June 28, 2016 Posted June 28, 2016 Well, a picture certainly tells a thousand words Dave. Thanks for having the courage to post it. The link to benrenyi4's half blown off thumb also says a lot. I've done some pretty unsafe things in the past, so I'm not without fault - luck was on my side. @ pyro159: As already suggested, it's best to start off with smaller one's then work your way up and forget about black powder for now. The fact that your rocket in the video was heavy was probably a good thing. At least it gave people a chance to get out of the way. Imagine if it was lighter and/or had more thrust? Unpredictably, quickly ending up who knows where. The little girl running away at the end of the video seemed to have more sense that anyone. If you want to have an accident, do it by yourself. Please don't have your family and friends around when doing 'unproven' testing. If you really ARE interested in rocketry, then there's lots of good advice on this forum - listen to it.
Redrocketman Posted June 28, 2016 Posted June 28, 2016 Make a test chamber, design & test your motors in the chamber. When they are reliable & pushing regular, consistent thrust, Then move onto the next stage. Mine is set up so the only way in is though a 1/4" steel plate door, has ONE small hole for video recorder lens & an exhaust outlet. I could have a " J" class motor C.A.T.O. and know it will all be contained ( never happened with 1 that big!! ) I have three kids & a beautiful wife - & I want to grow old with them. Safety 1st.
dagabu Posted June 28, 2016 Posted June 28, 2016 You really should warn us before posting them pictures. I still react quite violently, thinking about the horror and pains you must have been in. Damn dude. B, that was the only nice one, I have surgical pictures that still make me go weak at the knees.
dagabu Posted June 28, 2016 Posted June 28, 2016 Make a test chamber, design & test your motors in the chamber. When they are reliable & pushing regular, consistent thrust, Then move onto the next stage. Mine is set up so the only way in is though a 1/4" steel plate door, has ONE small hole for video recorder lens & an exhaust outlet. I could have a " J" class motor C.A.T.O. and know it will all be contained ( never happened with 1 that big!! ) I have three kids & a beautiful wife - & I want to grow old with them. Safety 1st. I respectfully disagree with the test chamber idea. Unless one is an engineer with the data to build a containment vessel (chamber) correctly, you are instead making a very large shell casing. All large scale motor testing is done outside just for that reason, distance is the best test chamber there is.
Redrocketman Posted June 29, 2016 Posted June 29, 2016 Sorry Dave, have to disagree. The vessel is not sealed, therefore pressure buildup can't be obtained. 1/4" steel plate can withstand a phenomenal amount of torture, as I have found through long range high calibre target shooting, tho I am totally open to your and anyone else's opinion, experiences or thoughts. The chamber is triple run welded, with 10 layers of h duty tarp lining the inside walls to catch any debris, tho it's not Kevlar, and most likely wouldn't do much!!! Please gone me your thoughts cause will all be taken seriously 🚀🚀🚀
MrB Posted June 29, 2016 Posted June 29, 2016 B, that was the only nice one, I have surgical pictures that still make me go weak at the knees. Yeah i know. Your thread was a complete horror-show. I cant even fathom how you are still in to pyro, and your kids... I said it before, i'll say it again. I don't think i could "deal" with it as well as you have had. In my book you remain a rockstar.B!
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