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Model Forum / General / Rockets / June 2007The new K450 PVC Rocket Engine Manual is now available on my site.
The new K450 PVC Rocket Engine Manual is now available on my site. The manual details step by step instructions on the design and construction of a 2" PVC K class engine. Only common materials are used and no special tooling is required. Build the engine start to finish in a few hours and get 300 pounds of thrust for about $10! www.inverseengineering.com Dan www.inverseengineering.com It's always good to keep in mind that PVC does not show up easily on XRAYs. On Jun 14, 2:48 pm, danpoll...@gmail.com wrote: > The new K450 PVC Rocket Engine Manual is now available on my site. The > manual details step by step instructions on the design and [quoted text clipped - 3 lines] > > Danwww.inverseengineering.com It shows up just fine on x-rays actually and PVC shrapnel tends to be significant in size, leaving a substantial entry wound. Exploratory surgery is generally not required. You're probably refering to materials such as glass or when HE is employed. PVC dust even shows up on chest x-rays. Research PVC-induced pneumoconiosis Be safe and It's not a problem. :-) Anthony J. Cesaroni President/CEO Cesaroni Technology/Cesaroni Aerospace http://www.cesaronitech.com/ (941) 360-3100 x101 Sarasota (905) 887-2370 x222 Toronto > It's always good to keep in mind that PVC does not show up easily > on XRAYs. [quoted text clipped - 8 lines] >> >> Danwww.inverseengineering.com Many surgical plastics have additives to help with x-ray visibility. If the equipment isn't tuned for generic PVC, you'll never see it unless it's big enough to displace a significant amount of tissue. ;-) Specially tuned x-ray detectors will look for the chlorine if PVC dust exposure is expected. Similar equipment is used to sort plastics for recyling. Back to the subject at hand.... safe distances for fragmenting cases are larger than the one's in the NAR/TRA/NFPA safety codes. After a piece of PVC buzzed by me from someone's J-sized motor, I have a much different attitude! > It shows up just fine on x-rays actually and PVC shrapnel tends to be > significant in size, leaving a substantial entry wound. Exploratory surgery [quoted text clipped - 24 lines] > > - Show quoted text - There is vinyl and there is vinyl. Medical is not necessarily generic. Chlorine absorbs x-rays and in the case of PVC, it makes up a considerable amount of the mass in the polymer molecule. This is one of the attractions of PVC actually as it requires much less hydrocarbon to produce. It does however have a propensity for corroding equipment in manufacturing plants hence the term "polymer from hell". Medical articles made from PVC are generally small, thin and highly plasticized with materials such as phthalates to make them flexible ("Neat" PVC is hard and rigid and can be brittle). These plasticizer additives have also fallen under scrutiny as they have been shown to leach from the composition over time. In any event these particular properties result in reduced x-ray absorption in some medical articles so the polymer is typically "doped" in order to opacify it for x-ray radiation if required in the procedure. Now let's take the PVC pipe proposed into consideration. Not only does it generally have a much lower percentage of plasticizer to keep it hard and rigid but it's also often compounded with metal based heat stabilizers. You be surprised what metals BTW. In addition, titanium dioxide is used to give the pipe it's white color and improve weathering resistance. Flame retardants, biocides and blowing agents etc. are also routinely used. The formulation combined with the physical characteristics typical in the case of the expected shrapnel produced would be a identifiable target for an experienced radiologist, especially when one considers the associated trauma. This is all moot and I'm not suggesting that PVC is a good choice for a rocket motor case. The real issue has more to do with the ballistic characteristics of the material in the event of a case failure. Ballistic coefficients of the various materials notwithstanding and I wont get into that here, I don't see why PVC would present any greater hazard than aluminum if accepted safe distances or appropriate ballistic shielding is employed. These are experimental motors after all. You say you got buzzed. Can you be more specific? We have seen polymer monolithic hybrid grains fail under high pressure on rare occasions but have never had reports of safe distances being compromised. Anthony J. Cesaroni President/CEO Cesaroni Technology/Cesaroni Aerospace http://www.cesaronitech.com/ (941) 360-3100 x101 Sarasota (905) 887-2370 x222 Toronto > Many surgical plastics have additives to help with x-ray visibility. > If the equipment isn't tuned for generic PVC, you'll never see it [quoted text clipped - 38 lines] >> >> - Show quoted text - > In addition, titanium dioxide is used to give > the pipe it's white color and improve weathering resistance. I hadn't thought about the titanium dioxide, but that would certainly make it quite visible for a wide range of xray technologies. My experience is with a range of surgical plastics, most of which are difficult to detect without doping. (I designed medical image processing software for high-end xray machines in the early 90's). But, I should have known better and deferred to you in all matters involving physical chemistry and material science! > This is all moot and I'm not suggesting that PVC is a good choice for a > rocket motor case. The real issue has more to do with the ballistic [quoted text clipped - 6 lines] > under high pressure on rare occasions but have never had reports of safe > distances being compromised. It was motor build using Wickman's instructions and chemicals. A PVC ANCP J-motor in a rocket on the pad, >NAR/TRA safe distances. It cato'd and sent piece of plastic 2x that distance. Not an axial failure, as the closure design should have had. With reasonable procedures, barriers, and distances, any material may be used for motor experimentation without a safety hazard. I'm sure you know this better than anyone else here. :) But, what you may not be aware of is the level of complacency and blind faith with which some amateur rocketeers conduct themselves. I'm not a scientist, I just slept at a Holiday Inn last night. :-) Take care. Anthony J. Cesaroni President/CEO Cesaroni Technology/Cesaroni Aerospace http://www.cesaronitech.com/ (941) 360-3100 x101 Sarasota (905) 887-2370 x222 Toronto >> In addition, titanium dioxide is used to give >> the pipe it's white color and improve weathering resistance. [quoted text clipped - 30 lines] > not be aware of is the level of complacency and blind faith with which > some amateur rocketeers conduct themselves. > > In addition, titanium dioxide is used to give > > the pipe it's white color and improve weathering resistance. [quoted text clipped - 22 lines] > cato'd and sent piece of plastic 2x that distance. Not an axial > failure, as the closure design should have had. Ah, excuse me, but if it was built using Wickman's instructions, it would not have failed. The builder would know the burn rate parameters, C* and using the provided software would have calculated the correct chamber pressure for your grain pattern. A PVC motor that blows out the sidewalls is not even close to a reasonable chamber pressure for PVC. These types of failures happen for three reasons, (1) the throat gets plugged during the burn, (2) the chamber pressure is in terms of thousands of psi and raising so fast the sidewalls fail and (3) igniter is essentially a blasting cap. Believe it or not, I actually was sent video of someone doing number 3 on the list. We have people go through our motor classes and hit their designated chamber pressure everytime. No failures in four years of classes. Hundreds if not thousands have had success with the bookset as well. Link below to the last class web page. http://www.space-rockets.com/ae101-042007.html John Wickman > Ah, excuse me, but if it was built using Wickman's instructions, it > would not have failed. The best judge of a system (design, materials, and methodology) is what happen when something goes wrong. Is it robust? Does is fail gracefully? How much safety margin is there if someone's learning curve, or a defective material, isn't perfect? > Believe it or not, I actually was sent video of someone doing number 3 on the list. Isn't that outlawed is the lower 48 states? ;) Oversizing an igniter is a common mistake, and a system designed for amateurs should take that into account, in my opinion. The preferred result is to have the closures fail before the casing. PVC does not have that margin of error. > We have people go through our motor classes and hit their designated > chamber pressure everytime. No failures in four years of classes. > Hundreds if not thousands have had success with the bookset as well. This is a good example of the "blind faith" I was referring to. You say it's so, therefore it must be so. Your omnipresence has witnessed all who have purchased your book? Not everyone who follows the Wickman Way stayed at a Holiday Inn last night. 8-] > The preferred result is to > have the closures fail before the casing. PVC does not have that > margin of error. By necking down the wall thickness at the closure you can ensure that it fails there as you desire. I have the Wickman books and they are great. Never had a cato. I am also a structural analyst so I can make my case fail any where I wish to. People who don't know what they are doing should avoid experimental motor making. They might as well play Russian roulette. KT On Jun 18, 8:44 pm, kimba...@pacbell.net wrote: > By necking down the wall thickness at the closure you can ensure that it > fails there as you desire. I have the Wickman books and they are great. > Never had a cato. I see a couple "blow up" videos on your website: http://www.inverseengineering.com/Pages/Elements/Archives.html And from your archives: http://www.inverseengineering.com/Pages/2003/1025/1025%20Flight.html "Something is seriously wrong with the engines. All of the engines shattered. In the past, I've had end caps blow out and nozzles blow out, but rupturing the PVC casing without a blockage in the throat, in my experience, is very rare." > I am also a structural analyst so I can make my case fail > any where I wish to. People who don't know what they are doing should avoid > experimental motor making. They might as well play Russian roulette. I think you've made my point for better than I could have. Even if someone knows what they're doing (a structural analyst?) then you're still playing Russian roulette with PVC casings. > I see a couple "blow up" videos on your website: My apologies to t.kimball. I thought I was directing those comments to the original poster who is selling the PVC pipe bomb books. > I think you've made my point for better than I could have. Even if > someone knows what they're doing (a structural analyst?) then you're > still playing Russian roulette with PVC casings. That statement is simply untrue. You keep stating that a sidwall rupture of a PVC case is a common or normal failure mode for PVC. It is not. The normal failure mode is the end cap coming off or the nozzle fitting. If water putty is being used in the nozzle, the putty will blow out and the fitting will remain. For example, 2" pvc is rated for 280 psi. It is good for twice that amount or 560 psi. I would not push it above 450 psi, but I have seen motors work on the test stand up to 620 psi. Now, if I were to design a 2" pvc motor for 800 psi and put it on the test stand. The failure mode would be a blown end cap, blown nozzle fitting or blown out water putty and nozzle. We have done extensive testing on this including propellant cartridges where the entire outside of the propellant grain was debonded from the cartridge. Even in those cases, the failure mode was never a blown sidewall. The sidewall failure occurs because the pressure inside the case is building so rapidly past the failure point that even after the end cap lets go, the pressure relief is inadequate to prevent the sidewalls from failing. We have only been able to duplicate this rapid pressure raise by throat blockage, essentially creating a pipe bomb, or high burn rate propellants coupled with a chamber pressure way beyond the limits of PVC or with smokeless powder igniters. One of the great myths of consumer rocketry is that aluminum cases do not fragment. That is usually true, but it can and does happen. I have an aluminum case fragment from an 18 inch diameter motor. The fragment is about a 18 inches on each side. I would be much more worried about that aluminum fragment than a PVC fragment of the same size. Why? Because that aluminum fragment will travel through the air much farther and faster than the PVC fragment. The same is true for the smaller pieces. I have yet to see PVC fragments even come close to traveling the distance of aluminum case fragments. I have never seen any PVC fragments travel beyond the standard safety distance for launching a rocket or testing a motor. John Wickman > One of the great myths of consumer rocketry is that aluminum cases do > not fragment. That is usually true, but it can and does happen. I [quoted text clipped - 7 lines] > never seen any PVC fragments travel beyond the standard safety > distance for launching a rocket or testing a motor. I have seen up to 8" aluminum-cased APCP motors rupture the case. I've seen hybrids pop their pressure vessels. 6061-T6 splits and does not fragment. With the energy and circumference of an 18" motor, I can image that a large piece would rip and fly off. But that is an extreme example that does nothing to support your argument. For the up to 6" casings, made from 6061-T6, all the pieces were within 50 ft of the rocket or test stand. In most case, there was a single flattened piece of metal with no pieces. Your quoted (already slim) margins for PVC's rated pressures are misleading. It is not a material made with a qualified process. It's meant for zero-pressure relatively cool fluids. And feces! The yield pressure has a significant negative temperature coefficient. The longer the motor burns, the more likely you will have heat transfer to the case, and reduce the burst pressure to <100#'s. It is outright unethical, in my opinion, for anyone to condone the use of PVC for amateur rocket motors. Making money off of it is something even lower than that. On Jun 19, 11:47 pm, wildbluerocket <wildbluerocke...@gmail.com> wrote: > > One of the great myths of consumer rocketry is that aluminum cases do > > not fragment. That is usually true, but it can and does happen. I [quoted text clipped - 26 lines] > amateur rocket motors. Making money off of it is something even lower > than that. I was talking about 6061-t6 and it does fragment even in small diameters, if the pressure raise is rapid enough. It is all about the transient stress distribution. I know all about the heat transfer aspect. Solid rocket motors are all about transient heating analysis. Every solid rocket motor is overheating to the point of failure as there is no cooling. The trick is to consume the propellant before the motor overheats and the case fails. Liquids are the only steady state system. As for being unethical, that is a hot one from a person who does not even have the courage to post under his name. I had DoD safety people at our lab. yesterday and they really like the idea of using PVC pipe motors for testing on DoD contracts. Since we all are getting paid for this, we must all be lower than unethical, too. John Wickman > The trick is to consume the > propellant before the motor overheats and the case fails. Liquids are > the only steady state system. A trick which is trickier when the casing has a low melting point and lower heat capacity. Consider this: you advocate using the same material for a case that some people use as a hybrid motor fuel, and in the same physical form. ;-) You should qualify your other statement: only liquids motor designs with sufficient cooling capacity are steady state. > I had DoD safety people > at our lab. yesterday and they really like the idea of using PVC pipe > motors for testing on DoD contracts. Since we all are getting paid > for this, we must all be lower than unethical, too. The "getting paid" part is not unethical. Using non-qualified, cost-saving materials for special testing is not unethical. Both of these are quite admirable! As I've continued to say, any material can be used 'safely' (not to be confused with 'successfully') with the correct methods and safe distances. Assuming that the average amateur will do the same is just plain ignorant. Making money from this is arguably unethical. > > I had DoD safety people > > at our lab. yesterday and they really like the idea of using PVC pipe [quoted text clipped - 9 lines] > distances. Assuming that the average amateur will do the same is just > plain ignorant. Making money from this is arguably unethical. By comparison; would you consider car and motorcycle manufacturers making money from vehicles that are capable of exceeding reasonable speed limits by quantum amounts as, "arguably unethical"? I guess, " assuming the average driver will operate such a vehicle in a sane manner is also plain ignorant ". (:-) Every ski manufacture is unethical for selling a product that if pointed straight down the mountain by an ignorant amateur, could result in damaged limbs or possible death. Whatever happened to personal responsibility?? This is a pointless debate, with your perspective supporting furtherance of the nanny state. (:-( Fred > By comparison; would you consider car and motorcycle manufacturers > making money from vehicles that are capable of exceeding reasonable [quoted text clipped - 6 lines] > debate, with your perspective supporting furtherance of the nanny state. > (:-( Bad analogy. The motorcycle example would apply if the manufacturer required the owner to build his own gas tank and glue on the hoses and fuel injector. "You can get the parts at any plumbing supply store". This would be unethical because the manufacturer knows there is a quality issue with the components. He also tells them that "we've never had a problem making the fuel systems ourselves, so go ahead and ride that motorcycle like you would any other one!". The ski analogy doesn't apply either. Maybe if the manufacturer told the buyer: "we're saving you money by selling you these instruction on how to use PVC planks instead of engineered fiberglass skis. We've never had a problem when we ski on them!". I don't get your 'nanny state' reference. I'm not asking for new government-based rules against plastic rocket motors. People should just be aware of the added risks. And especially, use safe distances that are much farther than the NPFA 1127 safety codes. The NAR/TRA safe distances are based on those codes, which require non-fragmenting casings, designed to keep all parts within a 50ft radius for H/I/J (NFPA1125-7.4.3). I've personally seen a cato'd PVC 'J' motor (in a rocket on a pad) throw fragments further than 3x that distance. Not far from where my son and I were standing. > Snipped > [quoted text clipped - 7 lines] > rocket on a pad) throw fragments further than 3x that distance. Not > far from where my son and I were standing. How can I debate your logic, you win. As for as the distance of, "3x that distance", I suspect the individual who made that motor, screwed up during the processing of his chemical formulation and/or motor construction. However, as I have witnessed several PVC motor flights and made and launched a few myself, with none of the results you describe, I still question the fragment dispersal distances you describe, as I have never experienced or observed a PVC cato, such as you describe; experience a nozzle blow out once. Wish I could say the same for some of the aluminum case, AP based, motor cato's I have experienced and observed. I know of a Prefect, "down south", who at one time would not allow PVC motors at his launches, for the reasons you have described. However, he is a EX component dealer, and while there may be an appearance of, "conflict of interest", I have never made the individuals acquaintance and I'll leave the reality of that for others who know the individual to judge. I will agree with you on one thing, (slightly modified): NFPA 1127, safe distances are not adequate for any type of non commercial, EX, and amateur rocket motor usage, especially where the activity is open to the public. > I see a couple "blow up" videos on your website: > http://www.inverseengineering.com/Pages/Elements/Archives.html > > And from your archives: > http://www.inverseengineering.com/Pages/2003/1025/1025%20Flight.html I don't have a web site or videos on the web. Your seeing someone else. > I don't have a web site or videos on the web. Your seeing someone else. Yes, I apologed to you for that a couple messages ago in this thread. I was referring to the original person who started this thread: danpollino@gmail.com The bottom line is: please use extra caution when firing motors with fragmenting casings and low yield pressures, such as PVC. Extra distance, especially. NFPA1127 distances are not enough. |
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