Nozzle and PVC questions

Advertise with us
madcow rocketry
the rocketry show
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Y

yoyo

Member
Joined
Mar 6, 2014
Messages
6
Reaction score
0
I've been reading about rocket propulsion and have a few questions.
1. If a PVC end cap with rounded ends with a hole drilled in the center were used as a nozzle, would it act as a plug nozzle or simply a regular convergent/divergent nozzle without the divergent part? Never mind whether it would be melted off.

2. Are there resources available for PVC pipe thickness versus heat tolerance? For instance, in a 1-inch PVC motor with ~3.5mm wall thickness, what would be the rate at which the heat would melt the insides of the pipe, also depending on whether there's a liner (tape/epoxy)?

3. If a burning grain does not exceed the maximum operating pressure of a PVC pipe at any time during the burn, will the pipe still degrade in tolerance just as it would if the operating pressure was exceeded, because of the heat to which the pipe is subjected to?
 
That's a "Research Section" kind of Question, so you won't be getting any Answers here.
 
Well... he is not asking for motor formulas...

All I am going to say is that you DO NOT WANT TO USE PVC. Aluminum will stay in 1 piece, and even if shrapnel does come off, it will show up in an X-ray. PVC will not show up in an X-Ray, and will turn to shrapnel if the motor over pressurizes.
 
yoyo said:
I've been reading about rocket propulsion and have a few questions.
1. If a PVC end cap with rounded ends with a hole drilled in the center were used as a nozzle, would it act as a plug nozzle or simply a regular convergent/divergent nozzle without the divergent part? Never mind whether it would be melted off.

2. Are there resources available for PVC pipe thickness versus heat tolerance? For instance, in a 1-inch PVC motor with ~3.5mm wall thickness, what would be the rate at which the heat would melt the insides of the pipe, also depending on whether there's a liner (tape/epoxy)?

3. If a burning grain does not exceed the maximum operating pressure of a PVC pipe at any time during the burn, will the pipe still degrade in tolerance just as it would if the operating pressure was exceeded, because of the heat to which the pipe is subjected to?
Click to expand...

1. It would melt off. Never mind what type of nozzle it'd be.

2. The thickness doesn't affect the rate of "melting the insides" very much. I don't know what said rate is. I don't want to try.

3. It'll blow up if the pressure is too high. It'll get weaker when you burn a motor in it even if it doesn't blow up.

Don't be foolish, and step awaaaaay from the PVC. Not a great idea.
 
CarVac said:
1. It would melt off. Never mind what type of nozzle it'd be.
Click to expand...

BAHAHAHAHAHAHAHAHAHAHAHAHAHA

But yes, in all seriousness, no one serious builds motors in PVC. Just don't. At best you'll make a crappy motor, probably you'll blow up a whole lot of motors, and possibly you'll get hurt in a bad way. Leave PVC for the youtubers and hillbillies.

If you're interested in making your own rocket motors, using sugar propellants or using APCP, there are many people on this form who can help. To access them, and to be taken seriously, get your HPR Level 2 cert, and get access to the research section. Then, say you're a beginner and say where you are from, and say you want to learn.
 
CCotner said:
If you're interested in making your own rocket motors, using sugar propellants or using APCP, there are many people on this form who can help. To access them, and to be taken seriously, get your HPR Level 2 cert, and get access to the research section. Then, say you're a beginner and say where you are from, and say you want to learn.
Click to expand...

Thank you. I'll go use the PVC for the hydroponics setup out front.
 
CCotner said:
BAHAHAHAHAHAHAHAHAHAHAHAHAHA

But yes, in all seriousness, no one serious builds motors in PVC. Just don't. At best you'll make a crappy motor, probably you'll blow up a whole lot of motors, and possibly you'll get hurt in a bad way. Leave PVC for the youtubers and hillbillies.

If you're interested in making your own rocket motors, using sugar propellants or using APCP, there are many people on this form who can help. To access them, and to be taken seriously, get your HPR Level 2 cert, and get access to the research section. Then, say you're a beginner and say where you are from, and say you want to learn.
Click to expand...


A different opinion. https://www.space-rockets.com/
 
tmacklin said:
A different opinion. https://www.space-rockets.com/
Click to expand...

Interesting; that's the first time I've seen anyone work seriously on PVC cases. Also interesting, it's all with ANCP; I'm not well versed with ANCP, I just know a good ANCP isn't as high specific impulse as a good APCP.

I'd like to know why he/they decided to use PVC and ANCP; it seems like if performance was the goal (light weight being the only advantage I see in PVC cases, other than cheap), then they would have bought a filament winder and made filament-wound low-pressure APCP motors; there's a great optimum there with ultra thin case walls and high Isp.
 
Way back I tried a 1" diameter PVC motor case with a graphite nozzle. The motor fired, then the graphite was hot enough that the nozzle and business end of the motor melted through and fell off the spent case. Would have ruined the rocket if it was in one.
 
cavecentral said:
Way back I tried a 1" diameter PVC motor case with a graphite nozzle. The motor fired, then the graphite was hot enough that the nozzle and business end of the motor melted through and fell off the spent case. Would have ruined the rocket if it was in one.
Click to expand...
And that's only one of the problems......

For a one shot motor you can use a lot of common place materials if you understand how heat is transferred, but you can only delay the inevitable so long, and if the motor has any kind of performance, the casing will not be useful afterwards......

That's why the majority of research folks use Kosdon type motor casings......

Bob
 
CCotner said:
Interesting; that's the first time I've seen anyone work seriously on PVC cases. Also interesting, it's all with ANCP; I'm not well versed with ANCP, I just know a good ANCP isn't as high specific impulse as a good APCP.

I'd like to know why he/they decided to use PVC and ANCP; it seems like if performance was the goal (light weight being the only advantage I see in PVC cases, other than cheap), then they would have bought a filament winder and made filament-wound low-pressure APCP motors; there's a great optimum there with ultra thin case walls and high Isp.
Click to expand...
It is cheap and readily available, or at least it was......until legislation passed by Congress circa 2006 made AN highly regulated...... but the law was never implemented by the regulatory agencies because of the expense to the seller and the requirements imposed on the buyer......:kill:

Cost to performance is better for ANCP than APCP by a lot......but the cheap fertilizer grade of AN will not make a storable propellant due to several phase changes the occur near room temperature which have large volume changes and eventually crack the propellant grain. Phase stabilized AN is not readily available and is more expensive than AP AFAIK.......and ANCP is hygroscopic........:facepalm:

Performance is substantially better than KN/sugar but less than APCP. Performance is good enough if you use the motor within a few days of making it so it is the rocket propellant of choice for terrorist organizations because agricultural supplies are readily available world-wide inexpensively and steel pipe and steel plate are just as accessible......the most difficult component of the terrorist rocket it the TNT for the warhead as that is hard to get......:dark:

Bob
 
Ammonium Nitrate Prills are readily available in the "Instant Icepacks".
 
I bought John Wickman's book back in 2003-04 and have built, ground tested and flown a number of his ANCP motor designs, both in PVC casings and aluminum tubing. I've had no casing failures in either casing type except for the first ground test which had picked up moisture and refused to ignite readily. After a few false starts, the ingniter was positioned at the nozzle end of the motor instead of the head and it finally burned. It burned for over a minute! This long duration did cause the casing to soften and deform. I don't know but would imagine that aluminum would also melt if subjected to such stress as I believe ANCP burns a 3,500 degrees F.

Ammonium nitrate is most definitely hydgroscopic and must be dried before use. I found that coating the freshly finished grains with molten paraffin wax greatly extended the shelf life.

I can tell you this: John Wickman knows his craft and his designs work if they are followed.
 
Last edited:
tmacklin said:
I bought John Wickman's book back in 2003-04 and have built, ground tested and flown a number of his ANCP motor designs, both in PVC casings and aluminum tubing. I've had no casing failures in either casing type except for the first ground test which had picked up moisture and refused to ignite readily. After a few false starts, the ingniter was positioned at the nozzle end of the motor instead of the head and it finally burned. It burned for over a minute! This long duration did cause the casing to soften and deform. I don't know but would imagine that aluminum would also melt if subjected to such stress as I believe ANCP burns a 3,500 degrees F.

Ammonium nitrate is most definitely hydgroscopic and must be dried before use. I found that coating the freshly finished grains with molten paraffin wax greatly extended the shelf life.

I can tell you this: John Wickman knows his craft and his designs work if they are followed.
Click to expand...
John indeed know his craft, he's a propulsion professional.

ANCP is more difficult to process because of the hygroscopic nature of AN, but it has higher performance and is safer to process than KN/sugar because mixing is done at room temperature. Additionally AN is green and non-polluting where as AP ground water contamination is problematic and it produces hydrochloric acid when burned which is toxic, corrosive, contributes to acid rain.

The BATFE considers ANCP an explosive (under the same logic that they considered APCP an explosive) so you technically need an explosives permit to make and use it. Additionally because of the Oklahoma City court house bombing with fuel oil explosive, legislation has been passed by congress to highly regulate AN circa 2006. As the legislation was passed without funding to enforce the legislation, it has not been implemented by HSA however non-agricultural purchases of "larger than normal" quantities of AN are frequently monitored by the AHJ as AN explosive mixtures is on the BATF explosives list. Note that the 2013 list includes: Ammonium nitrate explosive mixtures (cap sensitive); *Ammonium nitrate explosive mixtures (non-cap sensitive); Ammonium perchlorate having particle size less than 15 microns; Ammonium perchlorate explosive mixtures (excluding ammonium perchlorate composite propellant (APCP)); *ANFO [ammonium nitrate-fuel oil]; Black powder; Black powder based explosive mixtures; Black powder substitutes; Potassium nitrate explosive mixtures; Pyrotechnic compositions; Smokeless powder. (* designates a blasting agent which is regulated as an explosive.).

Bob
 
Correct me if I'm wrong, but what I'm hearing is ANCP is nice because it's cheap and decent, just not great, performance? Which explains the desire for equally cheap single-use PVC cases, light weight but far easier than FWCF.
 
bobkrech said:
John indeed know his craft, he's a propulsion professional.

ANCP is more difficult to process because of the hygroscopic nature of AN, but it has higher performance and is safer to process than KN/sugar because mixing is done at room temperature. Additionally AN is green and non-polluting where as AP ground water contamination is problematic and it produces hydrochloric acid when burned which is toxic, corrosive, contributes to acid rain.

The BATFE considers ANCP an explosive (under the same logic that they considered APCP an explosive) so you technically need an explosives permit to make and use it. Additionally because of the Oklahoma City court house bombing with fuel oil explosive, legislation has been passed by congress to highly regulate AN circa 2006. As the legislation was passed without funding to enforce the legislation, it has not been implemented by HSA however non-agricultural purchases of "larger than normal" quantities of AN are frequently monitored by the AHJ as AN explosive mixtures is on the BATF explosives list. Note that the 2013 list includes: Ammonium nitrate explosive mixtures (cap sensitive); *Ammonium nitrate explosive mixtures (non-cap sensitive); Ammonium perchlorate having particle size less than 15 microns; Ammonium perchlorate explosive mixtures (excluding ammonium perchlorate composite propellant (APCP)); *ANFO [ammonium nitrate-fuel oil]; Black powder; Black powder based explosive mixtures; Black powder substitutes; Potassium nitrate explosive mixtures; Pyrotechnic compositions; Smokeless powder. (* designates a blasting agent which is regulated as an explosive.).

Bob
Click to expand...

Very interesting. I hadn't reviewed the official list of explosives for awhile. Ammonium nitrate explosive mixtures would be ammonium nitrate mixed with anything that would produce an explosion. Neither ammonium nitrate or magnesium by themselves are explosive nor are they listed as such. Ammonium Nitrate Composite Propellant (ANCP) does not appear on current list of explosives. I think there is a distinction between "ammonium nitrate explosive mixtures" and "ammonium nitrate composite propellant".

Judge Walton's ruling removed APCP from the list, much to the consternation of the BATFE.
 
tmacklin said:
Very interesting. I hadn't reviewed the official list of explosives for awhile. Ammonium nitrate explosive mixtures would be ammonium nitrate mixed with anything that would produce an explosion. Neither ammonium nitrate or magnesium by themselves are explosive nor are they listed as such. Ammonium Nitrate Composite Propellant (ANCP) does not appear on current list of explosives. I think there is a distinction between "ammonium nitrate explosive mixtures" and "ammonium nitrate composite propellant".

Judge Walton's ruling removed APCP from the list, much to the consternation of the BATFE.
Click to expand...
Your interpretation is different than BAFTE. Please note their exact wording and their specific court ordered exemption.

Ammonium nitrate explosive mixtures (cap sensitive).
*Ammonium nitrate explosive mixtures (non-cap sensitive).
Ammonium perchlorate having particle size less than 15 microns.
Ammonium perchlorate explosive mixtures (excluding ammonium perchlorate composite propellant (APCP)).

From the above wording, and their past actions, it is very clear that BATFE considered APCP an Ammonium Perchlorate explosive mixture until a Federal Court Judge ordered them to exclude it from the Explosives List. Why would BATFE consider ANCP different than any other Ammonium Nitrate explosive mixtures unless a Federal Court Judge orders them to exclude it from the Explosives List. If you have a spare $1,000,000 you can probably get a Federal Court to exclude ANCP for the Explosives List but it's just cheaper to pay $100 to obtain a Federal Explosives Permit and be done with it. And besides you can also legally purchase black powder, smokeless powder or black powder substitute that also requires a Federal Explosives Permit unless you are a "Rocket Hunter". :wink:

Bob
 
bobkrech said:
Your interpretation is different than BAFTE. Please note their exact wording and their specific court ordered exemption.

Ammonium nitrate explosive mixtures (cap sensitive).
*Ammonium nitrate explosive mixtures (non-cap sensitive).
Ammonium perchlorate having particle size less than 15 microns.
Ammonium perchlorate explosive mixtures (excluding ammonium perchlorate composite propellant (APCP)).

From the above wording, and their past actions, it is very clear that BATFE considered APCP an Ammonium Perchlorate explosive mixture until a Federal Court Judge ordered them to exclude it from the Explosives List. Why would BATFE consider ANCP different than any other Ammonium Nitrate explosive mixtures unless a Federal Court Judge orders them to exclude it from the Explosives List. If you have a spare $1,000,000 you can probably get a Federal Court to exclude ANCP for the Explosives List but it's just cheaper to pay $100 to obtain a Federal Explosives Permit and be done with it. And besides you can also legally purchase black powder, smokeless powder or black powder substitute that also requires a Federal Explosives Permit unless you are a "Rocket Hunter". :wink:

Bob
Click to expand...

Well, Bob, I still don't see ammonium nitrate composite propellant on their list. Are you telling me that ammonium nitrate explosive mixtures are synonymous with ANCP in the eyes of the BATFE? As for the million dollars, well, I'll have to check under the mattress. Last time I looked, I was about $999,999 short. As for the FEP I believe there there is an exemption for making explosives for one's own personal use. Of course I can't transport it anywhere and I must store it in a magazine meeting federal standards.

I'm sure you're aware of Tannerite exploding targets, a proprietary mixture of ammonium nitrate/ammonium perchlorate and an aluminum powder sensitizer being legally sold at sporting goods stores. It is legal to purchase and possess so long as it is only mixed on site where it will be used. After mixing it cannot be transported even though it can only be detonated with the impact of a high power rifle projectile or equivalent shock. When mixed, it is clearly an "explosive mixture". Ammonium nitrate composite propellant is not and was never on the ATF list, whereas ammonium perchlorate composite propellant was on that list until Judge Walton ordered it removed. Even a federal judge can't order the removal of something from a list which never appeared on such list in the first place.

I want a lawyer! :wink:
 
tmacklin said:
Well, Bob, I still don't see ammonium nitrate composite propellant on their list.
I want a lawyer! :wink:
Click to expand...

Shoot Wickman an email. Im sure he knows the rules and will be happy to tell you.

-->MCS

.
 
I've lost touch with John Wickman, but we had a number of conversations about ANCP.

John is a pro in the business, a great resource, and generous with his time. John opened his own company many years ago, working under an SBIR grant, to research low cost solid fuels for big-dumb-booster applications. John patented and produced a phase stabilized ammonium nitrate (PSAN), eliminating hygroscopicity and phase problems. I don't know what ultimately happened to his PSAN formulas. The patent is easy enough to find.

The books that John used to sell described a simple low cost amateur fuel comprised of PSAN, HTPB, and Mg. No other additives were necessary. No vacuum was needed. The fuel burned in a single-use low pressure PVC case. I think you could make an M motor for a mid double digit cost. Wickman and followers have fired hundreds if not thousands of PSAN motors in PVC.

TRA gave EX-ers a hard time about using PSAN. I think PSAN might be disallowed these days. (anyone know?) I also think 9/11 and Oklahoma City changed the perception of ammonium nitrate.

-->MCS

.
 
I've only now discovered John Wickman's site, and am thinking of registering for one of his three day classes; has anyone attended one of those? The science and engineering aspects of the hobby are what attracts me the most, but a J90 for $11 is interesting too!
 
At TRA research launches AN motors are OK. PVC motor cases are not OK.

In the early 90's I did AN prop with just enough AP to keep it burning. Burn rate of 0.05"/sec.

M
 
To get to what OP is asking, you can use an end capped welded steel tube with a washer and get something like the rocket boys in october sky if you know how to mix propellant well to keep your temps down.

SS2S uses a single piece steel nozzle for a lot of motors, and it works just fine.
 
Having successfully built and flown up to large "O class" ANCP motors (and holding the unofficial largest AN motor flight @ BALLS) I have some real-world experience with the WSPC PSAN and traditional fertilizer grade AN oxidizer composites.

To the OP... The best material throat material for PVC/Durham's nozzles in my experience was phenolic rod "disks" embedded in the end-caps. Convergence/Divergence in the putty sections works very well.

In regards to hygroscopic/phase change deterioration of ANCP, I've not experienced these issues in either PSAN or AN composites. I've flown ANCP motors that were garage stored with minimal protection (baggies masking taped over the nozzle end and Colorado temperature swings) at 5 years, and will be flying a 9 year old ANCP motor next month.

With regard to ANCP performance overall, in traditional formulations my total ISP runs typically 80%'ish to that of APCP... what's of note based on all the data collection and analysis I've done over the years is that delivered ISP hovers around the 200 second realm. The explanation for this from Wickman/Oberth has a lot to do with the phase change of the Mg in the exhaust product.

And to the regulatory side, the operative word is "explosive" vs. "propellant", "deflagration vs. conflagration", etc... There's 2 halves to this discussion as well, the BATFE and DOT. There's an overwhelming mountain of evidence to support the propellant side argument when describing these formulations, however as we've all seen over the years, the "gray areas" are where we wage our regulatory battles.
 
I know for a while after the laws were passed about AN they had the manufacturers add diatomaceous earth to the AN. It causes the AN to clump and like "weld" over, snuffing out the process. Diatomaceous earth is calcium carbonate mostly.

I think since then there have been two formulation of AN, with diatomaceous earth for fertilizer and that without for ANFO use.
 

Similar threads

S
Adam Laakmann's Rocket Facts LinkedIn posts #1 - #10
Replies
8
Views
921
John Kemker
John Kemker
eJar0k
Composite Nose Cone Mold from 3D-Printed Parts
Replies
0
Views
306
eJar0k
eJar0k
J
Building Avionic System
Replies
11
Views
2K
BigDeal4
BigDeal4
Ez2cDave
Senate puts NASA on notice over Mars mission
Replies
21
Views
1K
RocketPro
RocketPro
frogglicker
Doorknob Scratch Build
Replies
5
Views
1K
86mustang408w
86mustang408w

Latest posts

Back
Top