Second Attempt at Building & Testing a HUGE PVC Rocket Motor - Dan Pollino's K500 Motor
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- Опубліковано 8 чер 2024
- Rotary Rocketry Merch ➤ rotaryrocketry.myspreadshop.com/
Today will be my second attempt at building and testing Dan Pollino's K500 PVC rocket motor. This motor is filled with flexi-fuel sugar fuel. Our last build of this motor did not end well so we are back to correct our mistakes and see if we can finally get this motor to work.
If you are going to attempt building a PVC rocket motor, be sure you understand the possible dangers involved with using PVC as a motor casing. Take appropriate safety precautions when testing ANY type of experimental rocket motor.
How to build our Dart Monkey rocket motor:
• Class 1 Sugar Rocket M...
How to build our Super Monkey rocket motor:
• How to make a sugar ro...
Interview with Dan Pollino:
• Interview with Dan Pol...
Dan Pollino's UA-cam channel:
/ @danpollino
Some parts used in the K500 rocket motor:
Nozzle washer -
www.mcmaster.com/98029A037/
Motor mounting brass inserts -
www.mcmaster.com/92395A116/
Motion background:
• Habitación de nave esp...
Background music from UA-cam library:
TrackTribe - Busy City - Наука та технологія
amazing work , i regret that i did not know in the past . keep doing 🤩🤩🤩🤩
Well done for trying again! Love these videos❤
As always with you guys, an impressive build and video. Awaiting the rocket build!
Nice video. Good job addressing a lot of the safety issues, and congratulations on the successful test fire
Oooh excited 👍
I am very excited for the next video 😊
Me too :)
However, there's likely to be a few videos about design and preparation before I actually get to building the new rocket. Glad you're enjoying our content!
Definitely an improvement from the previous test. Thrust test stand and tune that Scooby to get 400Nm-sec. Shorter burn time was from a loss of oxygen and increased dissolved water. There's a slight a color change in the melt at 170° and gets more yellow up to 200°. Stop at 160° if it's melted just mix, less heat, more impulse and burn time. Don't catalyze until you reflect thermal away from the PVC. Maybe seperate grains, with wrapped Aluminum duct tape thermal blankets on the cheap, hey❤ At terminal velocity the partially melted tube would go unstable.
Me and my friends used to make these as teenagers back when the internet sucked lol.
This is really large though. I rrslly sugest an RCandy approach. Its a lot harder to make, but burns for longer 🙃
The best thing to do is improve the process as much as you can, and to heck with exact duplication of the past.
I can imagine making a little dinky hobby rocket motor but I couldn't fathom being near, or anyone being near, a big giant rocket that could potentially blow into bits if the nozzle is obstructed and it accidentally ignites somehow. SUPER SCARY! Thanks for sharing this so we can live vicariously from behind the safety of our screens! :]
When I first started building small homemade motors a few years ago, I NEVER expected to EVER EVER EVER build something this big. And YES, this motor scares the crap out of me too. The thing is a monster and weighs over 8 pounds.
Great job! WooWho! It worked great! I'm so glad you implemented my suggestions regarding the motor mounts and testing stand (missile silo). I think your careful prep of the fuel made a big difference. Is it possible you introduced air bubbles into the mixture by stirring it so long? Maybe that's why it came out to a larger volume. It happens with certain food recipes. I can't wait to see the first flight! Congrats!
You know, when you left the comment in the previous video about motor compression, I initially didn't think it was an issue, but after giving it some thought, I realized you might have a good point. Glad I implemented the new mounting stand as well.
There have been a few comments about the possibility of micro bubbles due to stirring. I really think the issue was cooking temp. A higher temp would result in harder, denser fuel. It would make sense that a denser fuel would take up less space. So this "less dense" fuel took up more space.
What about HDPE tubing instead of PVC? It's used for mortars/fireworks- just in case they explode instead of launching. Doesn't shatter.
It's something that has been suggested and I will be looking into it.
My wife would really give me trouble for over-stirring the mix, so maybe the conceot of adding bubbles while stirring was correct, or, the actual density changed with a slightly different temperature during the pour.
I really think it came down to density to be honest. Higher cooking temperature would result in a harder, denser fuel... Which then should take up less space.
Why is the epoxy end of the igniter aimed at the fuel? Surely the taped end should point towards the fuel.
I see where you would think that. The epoxy ensures a tight and air-tight seal on the ignitor powder. The epoxy gets blown out when the ignitor is ignited.
Great channel. I am still concerned about safety. I made a 3/4 inch pvc motor, sugar+kno3, the standard 35% 65%+1% ferric oxide. I finely milled and mixed the components(no cooking). My core was 8 mm, and 7/32 washer for the nozzle, 24 - 60degree divergent- convergent (anchoring cement, as you suggested.. I filled 8 mm in length of fuel. When tested , it exploded violently. I have read the busting pressure of pvc this size is 1500 psi, so I do not know what happened, since according to the software the chamber inner pressure should have been around 900 psi. What maximum pressure do you think would be the upper,limit for this type of design? Thanks very much for such a wonderful and instructive channel. By far, one of the very best in the web.
I have found software estimates difficult to work when developing sugar motors. I've made plenty of them that I "expected" to work and then they explode. I've found the best process is trial and error... If I have a size motor I like, I just keep testing different size nozzles until it finally doesn't explode.
If you are looking for a small, simple, dependable, PVC sugar motor I would recommend you check out our video on how to build our Dart Monkey motor here:
ua-cam.com/video/pzK8RQdJTSE/v-deo.html
You need to degas the fuel - bubbles in the fuel are taking up space.
A vacuum pump and vacuum lid on the wok will do it.
That's actually pretty short burn time ...
I also have the same problem very short burn time around 1.5sec with sugar propellant. Is there any way that i can increase the burn time probably 3-4 sec. What types of grain configuration should I use? BTW I am using BATES neutral grain...And also I am planning to use dextrose propellant. Do anyone here have tried firing the KNDX propellant?
I would recommend staying with a BATES neutral grain configuration. Going "progressive" or "regressive" will not really help with burn time, it will just make the curve less efficient. I don't have much to offer for recommendation on decreasing the burn time though. Many videos I've seen show additives to increase the burn rate... That's one thing I've never understood because sugar fuel already has a ridiculously fast burn rate. In my experience, the burn rate can be adjusted slightly by adjusting the cooking temperature. Lower temp = slower fuel. I'm probably going to try this motor one more time with 190F fuel to see if I can get that burn to somewhere over 2 seconds.
I have not used dextrose so no experience on that one.
Where can I get the book of Dan Pollino?. Thanks
Oh, I knew this question would come up. I mentioned that in the first build video for this motor. Unfortunately, the book is no longer being printed. You might be able to find a used copy for sale somewhere online. I cannot distribute the documentation I have for two reasons... 1. It's copyrighted. 2. Dan asked me not to distribute it :)
Just put fins on it and send it! Maybe a nose cone and a go-pro.
That did seem like an incredibly short burn time.
One and a half seconds to be exact. That's how it goes with bates grain sugar fuel... Hard and fast.
I've been wondering how you would refurbish these motors after use
Oh no... Single used motor... No refurbish.
“Bought the wok” means a tax deduction for a “business expense.” Very smart.
I wish.
@@rotaryrocketry Come on! Claim it! (Love your channel)
looking for a sugar motor for 5 gallons of fos-check
I don't know what you mean???
Please ad Al to the fuel!!
Measured thrust?
Or, did you you not have a thrust gauge? 😢
I did not measure thrust. We have blown up so many scales during motor testing over the last few years. At this point, I don't really need to know the thrust because Dan Pollino already has is classified as a K500 and I know what size/weight of a rocket it is capable of launching.
Cam u eat the fuil ?
Technically... all the ingredients are edible. Not that I'm recommending you eat it.
Just me or was that a short burn....really short
One and a half seconds to be exact. That's how it goes with bates grain sugar fuel... Hard and fast.
I was curious about the extra volume of fuel this time. I know you decided to heat the fuel slower so you wouldn't pass the 210 degree mark. My hunch was that you may have inadvertently introduced micro air bubbles due to stirring for a longer time. I was concerned that these bubbles would get trapped once the fuel solidifies and cause the fuel to become less efficient -- with reduced energy density. It would also cause the fuel to burn faster while producing less energy, and have a shorter overall burn time. The amount of volume increase from introducing air while stirring a viscous mixture can be as small as a few percent to as high as 20% - 30% according to my research.
I was trying to think of a way to get all the air out of the mix before you pour it into the motor. You can stir very gently, but I think you'd still get some amount of air bubbles. You could use a vacuum chamber, but that's certainly overkill for this hobby/project. You could bring it to 210 degrees just as you did this time, then turn down the heat source to 200 and let it cook, unstirred, for a few minutes to let the air escape. But I don't know if this cooking period would affect the chemistry of the mix while you wait, and if it would get all the air bubbles out.
Here's what I would do. There's a cheap dental lab vibrator on Amazon for under $50. It's used to release air bubbles from various mixtures. As I was stirring and bringing the fuel mixture up to 210 degrees, I would take the bowl off the burner and vibrate it for some time starting about 180 degrees, then 190, then 200, then again at 210 just before I poured it into the motor.
Here's the link to the Amazon product: www.amazon.com/OIHYA-Oscillator%EF%BC%8C4-Vibrator-Machine-Bubbles/dp/B0C2P43DHT
Maybe I'm going too far for what you're willing to do for this hobby/project. It's not rocket science. Oh, wait, yes it is.
Well, I read everything you said... And I think you may be over-thinking it. You do have to stir non-stop or else the sugars will burn against the hot surface of the wok. You may be interested to know that between 180 and 190 the fuel actually gets really foamy. You can see it in the video although I didn't call it to the viewers attention because I didn't want to discuss it at that time. That has nothing to do with the stirring, it just happens. At that point it would appear that there is a huge amount of air in the mix. But after 190F that goes away and you get a pancake batter consistency.
In the end, this technique was obviously successful. If there are micro bubbles in the fuel then they were insignificant to the project.
@@rotaryrocketry - Me? Overthinking it? Hell yes, that's entirely possible. I appreciate your open mind and your explanations as you figure this out. And I wanted to say, you're very good on your videos. Sort of a natural teacher I think. Thanks for taking the time to do them. It takes me back to the 10 year old kid in me, messing around with a couple of neighborhood friends, inventing a new way to blow something up. Lucky to have "all my fingers".
@@rotaryrocketry Just out of curiosity, it seems the K500 motor Dan was making 14 years ago had a burn time that was longer, at about 2.7 seconds I think? I don't want to diminish what you've done so far, I think it's excellent. But just wondering, what are your thoughts about extending the burn time as you continue your efforts? What could extend it?
So mine was burning for 1.5 seconds. I just downloaded a few of his videos and examined some launches frame by frame. You are correct that it appears his motor was providing thrust for somewhere around 2.75 seconds. That would also offer a higher safety margin for the motor since it would indicate that the burn rate is slower than mine. I don't have any really good answer for why there is such a significant difference. My fuel ingredient ratios were exactly the same as his. Possibly a slight difference with the potassium nitrate? Possibly if I cooked the fuel to an even lower temperature like 190F or so, it would further reduce the burn rate. Not sure if that would get me to 2.75 seconds though. But that might be something to try before putting this motor into a really fancy rocket.
@@rotaryrocketry Yes, I saw that your ratios are exactly the same as in Dan's builds.
His performance data shows his fuel mixture temperature was cooked to a full 210 degrees. About the temperature - I'm a little confused. Speaking of just the sugars, there are about 7 known phases when heating for candy making, but there isn't a significant phase change until 230 degrees (thread stage). Until then the sugars are just losing their water and the very beginnings of caramelization are starting to occur, hence the slightly darker brown hue. But full soft caramelization doesn't occur until 245-250. For potassium nitrate there isn't any change until well over 400 degrees. So it really appears heating it slowly and stopping at 210 is mainly removing the water which gets the sugar concentration higher - maybe ending with almost all the water gone. So, by stopping at 190 degrees, it seem you would just be leaving more water in the fuel? When you mentioned a "foamy" phase at 180 to 190 I'm trying to understand what causes that other than rapid evaporation of the remaining water.
Is it possible you are using 95% potassium nitrate (agricultural grade)? Of course it contains more impurities than the 99% high grade used in pyrotechnics.
I'm kind of thinking your first batch was actually just fine. There was no chemical reaction caused by possibly overheating by 5 -10 degrees, as far as I can tell. Maybe it really was just the testing stand causing compression that made it explode?
Hmmm - interesting problem. I'd like to hear what you think as you work it out.
Heat source should be an induction hot plate, better than double boiler
I agree that an induction plate would work well... I purchased that wok just because it was the way Dan Pollino was doing it and I really wanted to duplicate his technique.
@rotaryrocketry
I only mentioned it, as, to avoid a double boiler so you can keep the mixture dry
@@Freedom1man Yeah, I was a bit concerned about the double boiler producing a lot of humidity around the fuel. That was one reasons I was hesitant to use that technique.
A double boiler sounds like a really bad idea actually. The enemy of sugar based rockets is moisture and a double boiler is just going to raise the humidity whilts your combining the fuel and oxidiser.
True, but if I made a double boiler for fuel, I would design a way to direct the steam away from the cooking area. Thankfully, it's looking like that will not be necessary.
Some comments as I watched. I generally like your videos but right from the start you are holding the completed motor that has the igniter built into it. It would be less work and safer if you left the IGNITER out of the motor build. Insert the igniter through the nozzle and up into the motor at the test stand or launch pad...imagine driving around with sticks of dynamite with the blasting caps installed. And the ematch you are using for the igniter is a low current/voltage device, doesn't take much to set them off. An experienced 'Level-3 certified' flyer friend of mine once accidentally set off his ematch igniters. Fortunately, they WERE NOT installed in his motor and I've seen this happen a few other times during my 65 years of doing rocketry.
Secondly, you are preparing the propellant in what looks like your garage. The two most hazardous times for making 'sugar' motors are during the melting and later when igniting at the test stand/launch pad (explosion risk as with any rocket motor). And as mentioned above with this design, is during transport with the ends sealed and igniter installed; you mention you thought the motor would fail and yet you drive around with what could be considered a 'bomb'.
I realize you are attempting to follow what Dan did years ago but if you want to really do motor testing, you will test the motors in flight orientation...nozzle down. This way the slag formed by the burning propellant is blown out of the nozzle. People test 'sugar' and other solid propellant motors nozzle up because it's easy to do it that way.
Smooth mandrels are always easier to remove. Sometimes people have also told me they sometimes come out easy and other times difficult. I've occasionally experienced that myself with some of my mandrels. That could be attributed to having an ever-so-slight taper, pulling one direction will be easy, and the other direction is sometimes next to impossible and I once had a slightly hourglass-shaped mandrel that was always hard to remove either direction.
At 16:45 when you add the dry ingredients, the spaces between each of those tiny particles are air and this process incorporates tiny air pockets into the propellant lowering its density and increasing the burn rate. Lots of stirring can add larger 'bubbles' that also lowers the density. Heating the mix hotter lowers the viscosity allowing these larger bubbles to escape, allows easier pouring, but also drives off more water from the corn syrup (24% water at the beginning) and also causes the melted mix to increase it's volume when hot but will contract back as it cools down sometimes pulling away from the liner/casting tube/motor case depending on construction design.
Most 'sugar' type propellants will be flexible soon after it's melted and will harden as time goes by, the amount of hardening depends on the type of 'sugar' and processing used. When to pull the mandrel is often time crucial... too soon and you can tear the propellant and too late can make it difficult.
You now have a 50% success with this particular motor. We had 100% success with our first two 12" diameter sugar motors but blew the nozzle out of our third one.
ua-cam.com/video/eeOVhQKnTfg/v-deo.html
I've had better success with my 6" motors (100%) but only 92% with my hundred or so 4" sugar motors and less than 50% with my 8" motors. Just when you think you are on a roll, bam.
Wishing you success in your future motors.
All great stuff... As usual :)
I will note that for this particular ignition design, you must have the ignitor pre-installed. The ignitor ignites a small amount of powdered fuel built into the top of the motor that blows down the core to assist with fast ignition. So the ignitor needs to be built-in.
You are correct that I make the fuel in the garage. I realize that nothing is fool proof but the wok system is very safe. The heating element is in a protected space at the bottom and you would have to have some kind of catastrophic mess to get any fuel into that area.
I do realize the success rate is only 50% but I was tickled pink to actually have it not explode. I'll definitely be doing more testing before putting it into a fancy rocket. Next test will probably be cooking to an even lower temperature to reduce the burn rate. My motor appeared to have a shorter burn time than Dan's but I'm not entirely sure why... Which actually makes it amazing that it didn't explode.
@@rotaryrocketry I've done 'igniter lighting powder for fast ignition' using 1/8" long dowel up the nozzle and through the core for launching. If doing nozzle-up static testing it is simple to simply lower the igniter powder package (powdered sugar propellant, or black powder, or copper thermite, etc) down the nozzle without the dowel and through the core to the bottom, gravity is a wonderful thing for that.
As you say, "nothing is fool proof". It's not just getting something in that space beneath the woke. Nearly all of my propellant melting is done under a cover. I don't know if you've experienced ignition of melted propellant, it makes a large fast fireball with flaming splatter, something not nice to be standing near. You may have confidence in what you are doing but you have to realize many young people watching your videos don't have that experience.
What is your Kn? If you want a slower burn rate you can simply open up the nozzle throat. I have three motor cases that use the same steel nozzle. A single grain is a low-pressure long-burn J-impulse. Two grains is a higher pressure mid-burn rate K-impulse and the 'long case' is a high-pressure fast-burning three-grain 50% L-impulse motor. So the shorter burn time than Dan's doesn't mean it should have exploded...it depends on how much of a margin of safety Dan's motors had.
I've never had one of my two-grain K-impulse motors explode because the Kn and resulting pressure were relatively 'low'. I've also made motors that were within 10% of the case bursting pressure and had several failures.
I have no Kn or thrust data since I'm simply duplicating Dan's work at this point. I've been hesitant to use tools like Richard Nakka's SRM spreadsheet for calculating Kn. I know it's a good tool but because I've seen varying burn rates based solely on cooking temperature, I feel that tools that attempt to calculate Kn just will not be accurate because they do not account for this varying burn rate.
I know I could simply increase the nozzle to reduce Kn, reduce burn rate and therefore increase burn time BUT... Again, since I'm trying to remain as true as possible to Dan's work, I really don't want to adjust the nozzle... yet...
didn~t leave the ground
Ummm... It was a ground test.
He looks a bit like George Bush jr.
I don't know why Americans like to use Fahrenheit when doing thermodynamic applications.
I admit that Celsius and the entire metric system is simpler but... We just use Fahrenheit for temperature here. I don't make the rules.
Because the metric system hasn't put anyone on the moon.
As if it makes a difference as long as you are familiar with the unit of measure…
If TRA doesn’t allow PVC cases on EX motors at club launches (assuming you are L2 certified via TRA), what are your plans to fly this level 2 HP EX motor? Have you filed our own FAA class 2 Waiver/Cert of Authorization at your location or is that uncontrolled airspace out there (which would be awesome)?
If I ever get this one to the point where it gets to fly, I can certainly file for FAA permission. There is already a rocketry club that flies where I go so there is already a set ceiling at that location. I can't remember how high it is, but it's higher that I expect to ever go.