A question about my bp rockets

[ballmill]

I fired a 1# core burner made with slow 75/15/10 that I had which wasn't hot enough for lift. The past few times I tried this fuel, they flew great but this time the rocket didn't fly as high. I added a small 1" heading filled with 2FA to observe when my heading would burst but it didn't go very high at all and the heading fell off in flight. I only hot glued it on.

 

Could my fuel be burning too fast where it burns out before getting any good altitudes? I think I'm going to mill some correct fuel and try another one.

[dan999ification]

I fired a 1# core burner made with slow 75/15/10 that I had which wasn't hot enough for lift. The past few times I tried this fuel, they flew great but this time the rocket didn't fly as high. I added a small 1" heading filled with 2FA to observe when my heading would burst but it didn't go very high at all and the heading fell off in flight. I only hot glued it on.

 

Could my fuel be burning too fast where it burns out before getting any good altitudes? I think I'm going to mill some correct fuel and try another one.

 

 

how are the headers fused?. for extra stabillity i use a passfire tube filled with bm that sticks out of the shell about an inch this fits into the top of the motor i dont fill mine all the way for this reason the motor tubes are longer than needed this gives a nice "collar" for the tube to sit in, its less likely to come off in any direction other than pulling it up, a small bead of hot glue usually does it

i use the standard bp fuel and find that compressing it as much as possible optimises the burn time. the only thing i can think is that the grain is too soft[burning fast], the nozzle a bit bigger than before [not going up] or the header coming off affecting the flight path and altitude. ive seen small cored rockets burn out in less than a second but getting good height if they're pokey enough

dan

Edited April 10, 2011 by dan999ification

[mabuse00]

Could my fuel be burning too fast where it burns out before getting any good altitudes?

If your Motor is overloaded or it simply sucks, yes.

 

I think it's necessary to know the dimensions of your motor and especially the core.

 

slow 75/15/10

If your fuel is to slow you can rice it. To me the difference to green mix is enormous...

[dagabu]

If your fuel is to slow you can rice it. To me the difference to green mix is enormous...

 

Just ricing will not increase the power *at all. Green mix is just unmilled BP, ricing BP will just make it riced green mix. The enormous part is ball milling the meal, that gives the highest boost of any other operation.

 

*Ricing a ball milled green mix with boiling water 1% red gum has shown improvement over just whetting it and passing it through a screen but green mix with cold water add little if any power to the meal.

[dagabu]

I fired a 1# core burner made with slow 75/15/10 that I had which wasn't hot enough for lift. The past few times I tried this fuel, they flew great but this time the rocket didn't fly as high. I added a small 1" heading filled with 2FA to observe when my heading would burst but it didn't go very high at all and the heading fell off in flight. I only hot glued it on.

 

Could my fuel be burning too fast where it burns out before getting any good altitudes? I think I'm going to mill some correct fuel and try another one.

 

Show us your tooling, your tubes, how do you make your BP? I bet my money on your nozzle eroding and releasing the pressure but even so, with just 60:30:10 BP, it should still take off pretty good even with a nozzleless motor.

[Mumbles]

It's also very possible you just need more of a delay portion above your spindle. The core burns out pretty quickly, within a second or two, but the height is created during the coasting stage of the rocket while the delay is burning. This is where you can get creative and use various compositions. Charcoal streamers are pretty common as are glitters. They will give more time for the same height of fuel.

[ballmill]

Dagabu, the BP I was using was that leftover BP that was made during my first try out batches. It worked great for the first rocket I rammed with it, but not so good with this one. The tubes are the best type from pyro direct and my tooling is homemade pictured below. The dimensions were off the rocket sketcher for 1# rockets.

 

I did not add delay fuel. I have been using the same fuel throughout the rocket so that's probably my problem. I have some tigertail made so I'll try adding that for my next one.

 

http://i52.tinypic.com/2heiis7.jpg

[mabuse00]

but green mix with cold water add little if any power to the meal.

I used 50/50 cold alcohol/water and no dextrin, and it was definitely faster.

Several rockets with green mix went fine, every rocket i did with exactly the same ratios, tooling and riced fuel exploded and I had to use +5% charcoal...

 

I don't have a ball mill, the KNO3 was ground in the kitchen blender and all ingredients where screened together several times. The dealer I bought the charcoal from claims it to be <40µm.

Edited April 11, 2011 by mabuse00

[dagabu]

Dagabu, the BP I was using was that leftover BP that was made during my first try out batches. It worked great for the first rocket I rammed with it, but not so good with this one. The tubes are the best type from pyro direct and my tooling is homemade pictured below. The dimensions were off the rocket sketcher for 1# rockets.

 

I did not add delay fuel. I have been using the same fuel throughout the rocket so that's probably my problem. I have some tigertail made so I'll try adding that for my next one.

 

 

If you use TT, go easy and only add a little then add a clay bulkhead. I have had a few do a round trip (up 800', tip over and come back down 800') using 1 ID of TT as the delay.

[dagabu]

I used 50/50 cold alcohol/water and no dextrin, and it was definitely faster.

Several rockets with green mix went fine, every rocket i did with exactly the same ratios, tooling and riced fuel exploded and I had to use +5% charcoal...

 

I don't have a ball mill, the KNO3 was ground in the kitchen blender and all ingredients where screened together several times. The dealer I bought the charcoal from claims it to be <40µm.

 

I can only guess that you are getting a little nitrating of the charcoal from the water.

[ballmill]

I might add that this rocket balanced but didn't have a square stick. It was about 3/4" by 3/16" with a weight on the end for balancing.

[dan999ification]

you know square sticks are better then, how big was the weight? in size[not weight] this could have made a bit too much drag slowing it down, i think a longer sqare stick no weight and a delay as mumbles said will get em up

dan

[dagabu]

There are so many theories on guidance sticks that it is largely irrelevant now. The whole balancing the rocket at the the stick is flawed at best, take this rocket for example, it has three small fins glued right to the 3# rocket motor with a dummy kitty litter shell on top just to give it MORE forward weight. There was an 8" brass rod holding it up but only offering about 3" of guidance.

 

If one is to use a guidance stick, an accepted rule of thumb has been to use a square stick 1/2 ID of the motor and x6 the length of the motor casing. Rectangular sticks wind-vane horribly and should not be used in windy conditions.

 

I strongly suggest that you never add weight to a rocket stick.

 

This rocket flies in a straight line with no stick at all.

 

http://www.pyrobin.com/files/3%20pound%20finned%20rocket.wmv

Edited April 12, 2011 by dagabu

[ballmill]

Thanks for the info. One final question for the master rocket guy.. when I add enough propellant to cover the spindle and begin my delay fuel, there isn't much room left in the tube for an ID worth of delay plus a clay bulkhead. Could I get away with trimming down my spindle a quarter inch to provide more room? The tip of the spindle is a bit under 3/16" I think. The tubes I'm using are standard 3/4" ID 7.5" long. It will probably be OK but I figured I'd ask to make sure.. wouldn't want to ruin my tooling.

[dagabu]

I would have a new spindle made for your tubes if it were me. Perhaps a Universal Rocket Tooling spindle? They are about 1.5" shorter then the standard BP rocket spindle.

[ballmill]

I've also been fusing my motors by sticking quick fuse all the way up the core until it stops essentially at the top point of the core. I've heard of doing it this way, however I've also seen it done by sticking the fuse halfway up the core.

 

How do you fuse your rockets? Thankyou for your patience

.

[ballmill]

Ill probably consider a universal set if all else fails. I've got the rockets flying at least

[Algenco]

Dan T will tell you it should be lit on the edge, he tapes the fuse to the inside of the tube with the end touching the fuel at the edge

 

I don't argue with Dan

Edited April 12, 2011 by Algenco

[dagabu]

Dan T will tell you it should be lit on the edge, he tapes the fuse to the inside of the tube with the end touching the fuel at the edge

 

I don't argue with Dan

 

That's just his whistle Al, a J hook is used on BP rockets, it is placed just past the nozzle on most motors.

 

Nski drills a hole in the side of the casing right below the whistle fuel, that is the method I use too. The hole is drilled before the motor is made and a brass pick is used to open it up enough to slip the visco in.

[Algenco]

That's just his whistle Al, a J hook is used on BP rockets, it is placed just past the nozzle on most motors.

 

Nski drills a hole in the side of the casing right below the whistle fuel, that is the method I use too. The hole is drilled before the motor is made and a brass pick is used to open it up enough to slip the visco in.

 

 

Nope, that how he showed me to fuse BP rockets we made/shot at Tri-State he mentioned the J hook but said he wanted every bit of thrust available and preferred lighting the edge

Edited April 13, 2011 by Algenco

[donperry]

Your rocket design and payload weight.

End of discussion

[dagabu]

Nope, that how he showed me to fuse BP rockets we made/shot at Tri-State he mentioned the J hook but said he wanted every bit of thrust available and preferred lighting the edge

 

That will be the first time I have disagreed with Dan then. Edge lighting on a BP rocket wastes fuel, the point is to light the fuel in a way that will get the grain burning fast enough for lift but not create a pressure spike, edge lighting starts the grain burning all to one side delaying the lift thrust.

 

Nakka and Yawn have both published on the phenomenon.

[ballmill]

I willing to take a guess as to why I see two different ways of fusing. In Neds article he pushes the fuse up in the core until it won't go any further, and Kyle's article on passfire uses the hooked method where the fuse only goes half way in.

 

Would it make sense that the top of the core being lit first would provide more thrust but shorter burn time? And would the hook method lengthen the burn time because the fuel above the ignition point is not being burned right away?

[dagabu]

Kyles is a third method, most of the rocketeers will J hook just above the nozzle, not half way up the core. Ned and others that fuse to the top run tamer fuels then others like me do. If I were to fuse to the top, I would CATO every time but with the J hook, I can use a hotter fuel and still fly the rockets.

[ballmill]

I'm going to try a straight 75/15/10 black willow mix with 10% 80 mesh hardwood added, and light just above the nozzle. Edited April 14, 2011 by ballmill