1lb Rockets Failing - I Need Help

[NeighborJ]

Dag and DavidF have a way of explaining things which is clear and decisive. I tried explaining this concept earlier in the thread but It went largely unnoticed. I was hoping Dag would step in and clarify the concept so it could be ruled out as the probable cause of the blowout. It may not have been the reason for the Cato but is still an unknown factor. The diagrams really help.

[joeyz]

no, i remember but what led me off to assume something different was the fuel, press and talk and putt, putt strobe effect. you too have been very helpful and learning alot from you as well with excellent comments and really appreciate it. i love ya too brother

[NeighborJ]

Haha I was not fishing for a compliment. This information was freely given away to all who wish to read it. I enjoy everything about this hobby and the people who participate in it. And if I can help any one of them, I will because lord knows I have so much more to learn and will need your help. Love all of you.

[calebkessinger]

I sent him a smaller gauge today. It does take quite a pull to get to 4k on one of those presses. Who knows what's up with that other one.. One little piece of anything over the hole on the gauge and it wouldn't let it work correctly. The 10k gauges have a very tiny hole going into them.

 

I was thinking the chuffing could be from extra oil or thinner in the fuel. either one will make a nice chuff. Poor consolidation just makes a faster burning rocket most of the time.

 

 

 

 

 

 

Edit,

I guess I posted this without updating the thread.. oops you guys jumped ahead quite a bit.

Edited August 22, 2016 by calebkessinger

[calebkessinger]

I tend to lean towards using the shortest choke possible on any rocket. If a guy looks at Duke's endburners you will see why. He uses a very hard nozzle mix with hawthorn clay, and crushed pots. It has very little erosion and shows in the rocket flight. I'm betting that it's under 1/8in. thick at the choke.

 

I make my endburner tooling real close to what he uses with the exception of making the nipple a little longer so folks can use a little more nozzle with softer clay.

[NeighborJ]

I've had several issues in the past using a short throat. In coreburners I've noticed they have a tendency to ignite one side of the core before the other, so at liftoff it had a high likelihood of shifting directions until the entire core lights. The longer throat fixed this problem by ensuring any gases are forced directly down. The thin throats also had a tendency of chipping off little flakes which also changed its direction in flight. And finally the endburners would produce weird cavitations and turbulence which sounded similar to chuffing and had pretty much the same effect as a fuel rich mixture. Long story short I need at least 1.5- 2x the nozzle dia to get proper performance.

[calebkessinger]

Whaaaaatttt?

2 X the choke diameter in a coreburner in a 1lb rocket would be 3/4in. on the spindle? That would leave a guy with almost 1.5in of clay in the bottom of the rocket. That's a BUNCH! That's gonna be one hard spindle to pull.

 

hmmmm... I got some research to do I guess.

 

I'd love to see some examples. I've never put that much nozzle in one except by accident maybe.

 

I've never heard anyone say variations in the nozzle would cause different flight paths of a rocket. learn something new everyday. What size rockets did that? You have my attention.

[NeighborJ]

OK the end burners get the 1.5-2x dia. The core burners get about 1to1. The motors I first noticed this on was a 4# shorty coreburner and was not a standard motor. The core was about 3" long and the nozzle was aprox 5/16, so it only needed a 1/2-5/8" throat. This motor sucked before I lengthened the throat but now it is quite impressive. I also have one coreburn motor which is designed for the short 1# stinger tubes also impressive. The thrust is intense near the end of the burn and it certainly needs that long throat to hold back the pressure.

Edited August 23, 2016 by NeighborJ

[calebkessinger]

AKA Skinny spindle rockets !!!!

 

:D

 

Lots of guys out there loving their sets of tooling for those. I love my sets in every size rocket. From straight Sali to nozzled bp. what fun they are. I use the same spindle for my stinger kits also.

 

http://www.woodysrocks.com/store/p8/STINGER_%2F_ZIPS.html

 

 

 

 

I completely understand your use of more clay now. That's a heck of a choke on them.

Edited August 23, 2016 by calebkessinger

[dagabu]

I've had several issues in the past using a short throat. In coreburners I've noticed they have a tendency to ignite one side of the core before the other, so at liftoff it had a high likelihood of shifting directions until the entire core lights. The longer throat fixed this problem by ensuring any gases are forced directly down. The thin throats also had a tendency of chipping off little flakes which also changed its direction in flight. And finally the endburners would produce weird cavitations and turbulence which sounded similar to chuffing and had pretty much the same effect as a fuel rich mixture. Long story short I need at least 1.5- 2x the nozzle dia to get proper performance.

 

The question of the day is how you would determine the one side of the cavity lighting before the other? Sadly, you are stealing lift, impulse and thrust and have to use a cooler propellant due to the longer throat (choke). Like all of the sciences, you cannot take from one place without paying for another, every action has an equal and opposite reaction, etc.

 

Especially with the skinny spindle, that is a lot of pressure stealing throat to overcome the resistance the walls of the throat inflict.

 

Solutions: Change the lighting method if you suspect side lighting, only a high speed camera watching the nozzle can determine that and the small nozzle would have a hard time overcoming the mass of the rocket as a whole and make it oscillate like that. It is likely the guidance stick. Shorten the nozzle and try 2 sticks and see if you get straight flight.

 

Change your nozzle clay by adding a small amount of wax and heat it up to get a homogeneous mixture and when pressing, allow the nozzle time to dwell. Flakes should not change the laminar flow of the gasses much but rutting will. Rutting is a channel that the high speed gasses make in a nozzle grain when random sized particles are used to press form or cast form the grain.

[dagabu]

Thanks Caleb for using the term "choke". This is probably the most important part of the nozzle construction to consider. We want to choke but NOT pipe the gasses, the idea is to speed the gasses up to supersonic speeds and then allow them to expand at a rate that takes the most advantage of the gas speed and volume. We try to do this with our tooling bases but clay is a poor media for creating the proper "Bell" shape needed as determined by De Lavalle.

 

http://www.jacobsrocketry.com/general/graphics/de_leval.JPG

 

The gasses then should be choked for as short a time as practical and expelled into clean air, i.e. no obstacles. In end burners, the convergence and divergence mean even less since the gas flow in black powder rockets is so much less and therefore do not use the De Lavalle concepts to their favor.

 

http://www.wichitabuggywhip.com/fireworks/rockets/endburner1.jpg

[NeighborJ]

Thanks Dave for the info. When I first designed my skinny spindle I had only begun to experiment with nozzle geometry. So with this short core I had encountered issues which I haven't seen in the normal bp motors. I do not regret all the problems I had because it forced me to gain a much better understanding of why they need to be the shape they are. All suggestions you've made were learned the hard way, which is sometimes the way I need it to be done to gain that complete understanding. These issues with the nozzle did not effect the long cores quite as dramatically but when I applied these principals to all motors, their little quarks seemed to disappear. Nozzles are only one part of the motor and certain symptoms can be resolved with different guidance or nozzle comp but if I can fix the problem first then I won't need to address the symptoms. I am finally making that new skinny spindle today and am correcting several issues it had by doing so. I should have clarified a few things in the previous post but I don't feel like writing a book.

Edited August 23, 2016 by NeighborJ

[dagabu]

I think the spindle is sound, I would not change that first off but reshape the nozzle rammer and the base, a ring can be made to form the divergence if need be without changing the base or spindle.

 

The reason that I posted this long winded tome is because new people come on here looking for guidance and read about a particular "fix" for a certain problem that in turn will introduce all sorts of problems if followed so i want to make sure anybody reading this will understand the issues behind your fix and the actual science behind good nozzle structure.

 

One should not be mistaken for the other.

[NeighborJ]

I suppose then if it's not a simple solution to a problem which I have the answer to I could just let them struggle so as not to confuse people who don't want to read the entire thread.

[dagabu]

No, J, a wrong answer is not a good answer and you cannot take on the persona of one leading the masses if you found a "fix" that does not keep in sync with good science. These answers are NOT mine, they have been beat into my overly thick skull for the past decade by rocketeers much smarter than I.

 

The point being, correct the issues to a known working and scientific model, stop cutting the ends of the ham off...

[NeighborJ]

OK OK I love poking a sleeping bear. For some reason my imogies are not working so I can't add satire properly. But all joking aside the fix worked and later it was you who suggested the exact same fix in a different thread on an endburner which also worked. Your description of the fix was different but the math equates to the same description I gave. I'm not trying to prove you wrong but I believe it should be expressed by a ratio of the choke rather than ratio of the tube size because not all tooling is a 1-4 ratio. Edited August 23, 2016 by NeighborJ

[dagabu]

I'm all jiggy wid that!

 

I like ratios a lot. Yes, I gave advice but it was to place a band-aid on a problem, it did not really solve it. The hope was that once the motor worked, the issue would be isolated, removing the fuel, tube etc. from the equation.

[NeighborJ]

I think I will start another topic to address the problems with this skinny spindle motor. I'd rather not make any more posts which are irrelevant to this topic.

[stix]

 

The question of the day is how you would determine the one side of the cavity lighting before the other? Sadly, you are stealing lift, impulse and thrust and have to use a cooler propellant due to the longer throat (choke). Like all of the sciences, you cannot take from one place without paying for another, every action has an equal and opposite reaction, etc.

 

Especially with the skinny spindle, that is a lot of pressure stealing throat to overcome the resistance the walls of the throat inflict.

 

Solutions: Change the lighting method if you suspect side lighting, only a high speed camera watching the nozzle can determine that and the small nozzle would have a hard time overcoming the mass of the rocket as a whole and make it oscillate like that. It is likely the guidance stick. Shorten the nozzle and try 2 sticks and see if you get straight flight.

 

Change your nozzle clay by adding a small amount of wax and heat it up to get a homogeneous mixture and when pressing, allow the nozzle time to dwell. Flakes should not change the laminar flow of the gasses much but rutting will. Rutting is a channel that the high speed gasses make in a nozzle grain when random sized particles are used to press form or cast form the grain.

 

Yes you're right Dags, that IS the question.

 

I wonder what would happen if you had a bates grain - and in the vertical direction, half with fuel and the other an inert substance. How much would that affect the effeciency of the nozzle? I'd think that the shifting of weight would play a role in trajectory but to what extent I don't know.

 

Yep, not igniting the fuel core at the same time will degrade the measured performance. It's probably more important with larger motors than smaller ones.

[NeighborJ]

Stix thanks for the response, to answer some of your concerns, the double sticks helped but did not fix the problem. The side light issue was determined from watching slow mo vid but is still open for debate. And I do understand that this motor is not operating at peak performance and that is one of the issues. As far as creating a Bates grain design, it would be of a different design and may behave differently then this motor making the inert grain idea unnecessary.

I've created a proper topic for this design under "skinny spindle issues".

[joeyz]

AKA Skinny spindle rockets !!!!

 

:D

 

Lots of guys out there loving their sets of tooling for those. I love my sets in every size rocket. From straight Sali to nozzled bp. what fun they are. I use the same spindle for my stinger kits also.

 

http://www.woodysrocks.com/store/p8/STINGER_%2F_ZIPS.html

 

I completely understand your use of more clay now. That's a heck of a choke on them.

 

hmm, i may want to visit the caleb store again sooner than later for end burner with thicker spindle. but i thought end burner is suppose to have short spindle. i say this because examining all the estes rocket motors have a very short spindle, just enough to pass the clay nozzle and touch the fuel for lighting. thats why i bought the end burner spindle you see in below photo. wouldnt a longer spindle be considered a core burner? again, im just a new person to rocketry attending wizard univeriaty, learning and improving my knowledge from you master wizards. did i buy some cheap junk and hurt performance? here are all the sets i currently have. i surely wished i bought caleb's entire set like dag, dave and neighbor suggested, dang!

 

Edited August 24, 2016 by joeyz

[dagabu]

Yes, the end burner set in on the right and the core burner set is on the left in your picture.

 

Nothing 'wrong' with your sets but I would ask Caleb to make new spindles for you. The #1 end burner set he made for me recently has the "perfect" shape and size, it makes outstanding rockets!!

Edited August 24, 2016 by dagabu

[joeyz]

FAILING ROCKET SANITY CHECK and FOLLOW UP

 

team, thank you so much for your help in my failing rockets which were numerous issues (fuel mixture, clay nozzles, pressing, tool kits, clamping and tubes. i think im off on the right track. im simply just trying to reverse engineer estes rockets to reduce cost and make bigger and better ones like all you guys are doing. some feedback...

 

- fuel & compaction: learned from you guys that fuel is not the same for all rockets and cant be powdery moon dust. i have corrected this which was causing problems.

1lb end burner: 75/15/10

1lb core burner: 70/20/10

enough moisture added/dried to eliminate moon dust, compacts harder like a rock oppose to wood like density.

 

- tubes: learned from you guys that tubes are also key, corrected by getting new tubes, im loving these tubes from phil. they fit EXACTLY into the 1" PVC pipe exactly (new pvc clamp cut with jig saw). SEE PHOTO. the other tubes i bought from pyro sites didnt fit right in pvc clamp, causing an oval egg diameter that probably caused air cracks to slip fire along inside walls. my next step is coat inside tube wall with wax to fill in swirl seams to fill in tube anomalies that prevents pass fire catos and chuffle (mini strob rocket effect, puff, puff car engine back fire sound).

 

- clay nozzle: learned from you guys that my end nozzle (1") with 1/2" choke was too thick (straw tube chamber effect) causing too much back pressure and heat, forcing blowing hole through side, plus the crappy tubes added risk factor. corrected, now using less clay, washer line and my nozzles don't exceed a total of 1/2".

 

- rocket press pressure: learned from you guys that your not sure what im pressing or consistent in each increment press even though presser is sufficient. i corrected this by ordering a pressure gauge from caleb to stay consistent throughout the press process.

 

again, thanks so much, cant wait to test these new rockets, any other tips on what im doing wrong is always appreciated. i hope i havent been a pain and a good student wizard this semester at your rocket rocket wizard university for i have learned so much from you professional professors in such a short time and you didnt dog me out. truly a great website/forum, keep up the awesome site. - joe

 

 

 

 

PS: i think i got a crappy end burner, should i buy a new one?

Edited August 24, 2016 by joeyz

[joeyz]

Yes, the end burner set in on the right and the core burner set is on the left in your picture.

 

Nothing 'wrong' with your sets but I would ask Caleb to make new spindles for you. The #1 end burner set he made for me recently has the "perfect" shape and size, it makes outstanding rockets!!

the one on the left, core burner, is the one i bought from him a couple weeks ago that you recommended. its the unviersal one that allows me to make a variety of things.

[dagabu]

AHHH! The stainless steel style! Awesome.