BP rocket problem

[superspike23]

hi all

I have a problem with my test rockets with black powder. I use a brown paper rolled tube of 10 cm long internal diameter is 1.5 cm bentonite is the nozzle 4 mm in diameter and 2 cm height. I drilled 2 cm in the black powder. Here are two videos.

 

http://www.youtube.com/watch?v=ubc_hfRNgyU

 

http://www.youtube.com/watch?v=peBGO797wew

 

http://www.youtube.com/watch?v=_mf2h1mUqyg

Edited July 12, 2012 by superspike23

[The504]

The core needs to be longer. If you only drilled a little ways into the BP anything above the core you drilled will act like a Delay charge and blow up. What's the ratio of the BP you're using? Edited July 12, 2012 by The504

[thechewy]

well i cant really watch videos on this damned phone.also im not the smartest wih stars and all that other good stuff.but i have been making rockets for a few years lol. Could u please explain to me whats going on?like are they blowing up,not flying straight,or not lifting off as fast or slow as you would like?i think i may beable to help u out on this..also are you using meal powder or granulated black powder?it makes a difference fro my experience

[californiapyro]

well a larger core certainly won't fix CATOs... try a longer bentonite nozzle, widen the aperture a little. you're ramming in increments, right?

[superspike23]

I press the black powder using a hammer and a round piece of wood. I make black powder in my ball mill. per 200 grams of black powder, I use 150 g KNO3, 30 g of charcoal for bbq and 20 grams of sulfur. I let run the ball mill 5 hours. All my rockets explode. The nozzle bentonite does not support the pressure.

[pyrokid]

Traditional core burners use a formula closer to 60 KNO3 30 Charcoal 10 Sulfur. It sounds like your fuel is too fast.

 

With your remaining fast milled fuel, drill a shorter core into the rocket, and see if that reduces CATOs.

[dagabu]

The core needs to be longer. If you only drilled a little ways into the BP anything above the core you drilled will act like a Delay charge and blow up. What's the ratio of the BP you're using?

 

Could you explain your hypothesis a little more? What you seem to be saying is that a shorter core causes more pressure? With a short core, the rocket becomes an end burner, they have significantly less pressure and are much less likely to CATO.

 

also are you using meal powder or granulated black powder?it makes a difference fro my experience

 

Only in consolidating the fuel grain but the pressures are identical if all the chems are the same.

 

well a larger core certainly won't fix CATOs... try a longer bentonite nozzle, widen the aperture a little. you're ramming in increments, right?

 

A longer nozzle will create more pressure due to the spindle taper (if there is any) and the extra weight isn't helpful. Are you saying a thicker nozzle throat so that the nozzle doesn't eject?

 

I press the black powder using a hammer and a round piece of wood. I make black powder in my ball mill. per 200 grams of black powder, I use 150 g KNO3, 30 g of charcoal for bbq and 20 grams of sulfur. I let run the ball mill 5 hours. All my rockets explode. The nozzle bentonite does not support the pressure.

 

Ejecting nozzles is a sign that the tube is not being supported or the clay is not consolidating. Properly rammed, no nozzle will eject but will make the casing split causing the rocket to CATO. A proper nozzle throat should be at least 1/2 the ID long and the clay plug that the nozzle is pressed into should not exceed 1 ID.

 

Traditional core burners use a formula closer to 60 KNO3 30 Charcoal 10 Sulfur. It sounds like your fuel is too fast.

 

With your remaining fast milled fuel, drill a shorter core into the rocket, and see if that reduces CATOs.

 

Or add another 5% charcoal until you stop blowing them up but first, lets get that nozzle fixed. You NEED a tube support to get these to fly the same way every time. Schedule 40 PVC pipe is available world wide and works well for a support. All you need is a hacksaw and some hose clamps. Bring a tube with you to a hardware store and see what is the smallest PVC tube your tube will fit in. Cut the tube off as close to 90° as you can, use a chop saw if available. Hold the tube in a vice with the jaws holding the ends and leaving enough tube exposed above the chuck to split with the saw.

 

Split the tube, check with your rocket tube and clamps to see how close you are to a tight but not crushing fit. Keep cutting tiny amounts off the tube lengthwise until the support fits tightly without crushing the your motor tube. Now wrap a sheet of writing paper around your rocket tube twice, only twice, clam on the PVC support snugly but not too tightly, turn Mom's oven on to 200° F and place the support on its end for 20 minutes. Pull it out of the over and let it cool standing on its end.

 

The PVC will now be round instead of oblong and will fit your tubes perfectly. the paper you wrapped around the rocket tube allows the support to be opened slightly when the clamps are relaxed and the clamps will have dug in slightly keeping them in place when you loosen them up to remove your motors.

 

 

This method is not mine but has been passed down from one generation to another and so on...

 

-dag

Edited July 12, 2012 by dagabu

[californiapyro]

dag,

I was saying a thicker nozzle throat to prevent ejection. and since he's drilling them, the nozzle won't be any smaller but, have at it rocket man! i'm by no means an expert.

 

-Hunter

[dagabu]

dag,

I was saying a thicker nozzle throat to prevent ejection. and since he's drilling them, the nozzle won't be any smaller but, have at it rocket man! i'm by no means an expert.

 

-Hunter

 

Gotcha! There is something called the theory of diminishing returns. This is especially true for end burners and small rockets like bottle rockets, cored or not. The addition of 1-2g of clay for bulkheads or thicker nozzles can easily overwhelm the lift and case the rocket to not even lift off the rack. I have had lost of experience with inverted gerbs to ground flowers.

 

-dag

[californiapyro]

i'm familiar with it i just thought thrust didn't seem to be a problem, since he was getting mid-air CATOs.

[thechewy]

i always use kitter litter"all natural clay". I make my nozzels no smaller than 1/3 th id of the tube i use and mineees never go cato. I use meal powder for rocket because i find that granulated burns faster and gives more pressure. Therefore when i tried granulated bp,it usually goes cato. If you mke the core to long itll ignite more of the fuel,in turn thatll give a faster rocket but a shit load of more pressue build up. If they go cato everytime i reccomend you try to make end burners. Basically try to drill the nozzel to where you start to see the fuel and see what happens. Or simply try to use ungranulated bp,end burner first and if its to slow and not enough thrust. Then you can try coring it a little but not to much until you see if your nozzles/plugs will hold better. Also try what the others are saying and make your plug a little larger. To ensure a nice solid plug always ram in small increments:) . Its tricky getting the rocket to work the way you want them to. Trial and error

[dagabu]

i always use kitter litter"all natural clay". I make my nozzels no smaller than 1/3 th id of the tube i use and mineees never go cato. I use meal powder for rocket because i find that granulated burns faster and gives more pressure. Therefore when i tried granulated bp,it usually goes cato. If you mke the core to long itll ignite more of the fuel,in turn thatll give a faster rocket but a shit load of more pressue build up. If they go cato everytime i reccomend you try to make end burners. Basically try to drill the nozzel to where you start to see the fuel and see what happens. Or simply try to use ungranulated bp,end burner first and if its to slow and not enough thrust. Then you can try coring it a little but not to much until you see if your nozzles/plugs will hold better. Also try what the others are saying and make your plug a little larger. To ensure a nice solid plug always ram in small increments:) . Its tricky getting the rocket to work the way you want them to. Trial and error

 

Also, the diameter of the nozzle throat is not static, it is dynamic, meaning that you can open it up to any diameter you want, this allows you to use hotter and hotter fuels. I had a few dozen nozzled BP #1 rockets I brought to PGI last year to lift commercial shells with. Six CATO'd in the rack (those watching them and getting showered with stars kept yelling at me to bring them closer! Rocket nuts!!) so I took the rest back to manufacturing, took a drill bit 1/8" larger then the nozzle hole and reamed the nozzles open.

 

Each and every rocket worked beautifully and lifted the shells to a pleasing height. The crowd was disappointed though.

 

The moral is, if you still CATO your rockets, open up the nozzle.

 

-dag

[superspike23]

hi Here's my last try with a larger nozzle and more clay. always the same.

 

http://www.youtube.com/watch?v=QJi24IHBpOI

[LehighValleyPyro]

Skip the nozzle entirely. I don't use nozzles on any of my rockets. Several real pyro experts (not me) found that nozzles aren't required with hot fuel core-burners.

 

 

If it still blows up after that then you're not ramming it hard enough.

[dagabu]

Skip the nozzle entirely. I don't use nozzles on any of my rockets. Several real pyro experts (not me) found that nozzles aren't required with hot fuel core-burners.

 

 

If it still blows up after that then you're not ramming it hard enough.

 

Looking at the video, I didn't see the tell tail signs (or hear them) of an over-pressure so I am leaning toward a weak tube. The sound and the tail show a high charcoal content, not a whole lot of thrust so I don't think it is a matter of the nozzle at this point. You may have to go nozzleless on this one to get successful flights.

 

Good luck!

 

-dag

[Col]

Hi Guys

Looks like the tube gave way as the thrust kicked in, SS didnt mention if the tube was dry rolled or fully glued which could make all the difference to the burst strength.

The first test vid shows a definite open flap of paper which doesnt bode too well.

Only other thing i can think of is the cat litter may be overly coarse so its not consolidating well enough ..in which case chucking it in the blender for a few minutes and adding a little candle wax should help

I use a 6mm core x 50mm long (including the 1/2" nozzle) on my 1/2" coreburners with hot fuel.

Edited July 24, 2012 by Col

[californiapyro]

welcome back col! haven't heard from you since the saxon contest

 

yeah, that seems likely. nozzleless are a lot easier

[Col]

cheers mate, been real busy with work and other stuff.

I still havent got around to trying a nozzleless, it`d be bit less weight. coming back down

[dagabu]

cheers mate, been real busy with work and other stuff.

I still havent got around to trying a nozzleless, it`d be bit less weight. coming back down

 

AND... More fuel going up!

 

-dag

[Col]

Hi Dag,

I hadnt thought of it that way..i`ll have to give it a go now