3lb nozzle-less coreburners and different delays

[nater]

I don't ball mill BP for rockets either, it is not necessary. Pressing small increments is essential to good rockets. I use increment sizes which press to 1/2 the ID of the motor I am pressing. I often use the same comp for the thrust and delay. I also like to use C6 with FeTi or Ti added. If you want a colored flame, the colored gerb comps published by John Glaswick in the PGI Anthology and written by Ned on Skylighter make a nice delay too.

[hindsight]

Nater,

Good to know. Have been making increments about that size. Over 20 aliquots of fuel in a 3lb rocket strains my patience a bit, but it is worth it if it contributes to success.

 

dagabu,

Followed your instructions as I understood them. 200 grams commercial FFG was spread thinly on a piece of paper. By weighing the can before and after, 2 grams (1%) aerosolized machine oil was sprayed over the surface of the BP, which was then mixed well. The increments were pressed to 13,500psi for 10 seconds. Interesting that the 200 grams barely made it over the top of the spindle this time! And your suggestion to oil the bolts was excellent-- they came off much easier!

 

 

There is a severe thunderstorm outside here now, so launch will have to wait.

[hindsight]

 

Hurrah! The 3lb rocket jumped into space faster than a cheetah with its tail on fire. Thanks, fellows, for the assist!

 

 

 

Perhaps the same result can be achieved by oiling the commercial BP and pressing at something less than 13,500psi. And how to oil large quantities of commercial BP at one time?

 

Then there's the screen/scratch mix BP...

[dagabu]

For consistency sake, you can coat large amounts of BP with oil but make sure you have your fuel dialed in first. You dont want to slow it down too much.

 

​Congrats on your successful launch! Ummmm, wheres the video?

[hindsight]

dagabu,

The success is largely yours. You could probably teach someone across the internet how to disarm a nuclear device or how to perform neurosurgery in the comfort of their livingroom .

You speak of slowing down the fuel by adding oil, and I understand what you said about the fuel not being too fast before, but...even though the purpose of the oil was to aid in consolidation of the grain, do you think perhaps it could have prevented CATO, (in part) by slowing down the fuel? Know what you are going to say, since you have already told me--just had to ask.

About the video...I was drawing testimonial pictures of the event until my crayon broke, sorry.

[Mumbles]

If I were going to try to oil a larger amount of commercial BP, I'd probably do it in a star roller. Add in your BP granules and spray on a predetermined amount. The tumbling action should both ensure equal spread, as well as distribute it around.

[mkn]

Hi Hindsight,

 

Just had to chime in a bit, as I read your posts , I felt your pain with cato. I had great hand rammed rockets, then I made my BP hotter and all my once great rockets were cato. I hung my head and shook it. Then I started gathering info like you on the issue, made some determinations, and presto, no more cato ( for me it was bottom light and stopped using my home rolled tubes) I read your posts and smiled to myself, I just went thru the same thing and had the same shout of joy when I concord it !! Now I laugh because soon I am going to start pressing instead of ramming, and I can't wait for all the learning curve joys that will bring ! I imagine it will be a much shorter testing phase with pressing..........I do ball mill my rocket fuel, I did not have much success screening, although I was not ball milling individually, just coffee milling. I like the simplicity of one fuel that I can granulate, rice, rocket mix or add 10% ti or coal to and be ready to go ! Of course the recent postings have me reconsidering this.

Anyway enjoy the testing and success, there are many of us in the same boat !!

Matt

[dagabu]

Agreed...

[hindsight]

Mkn, The old proverb (roughly translated), "Trouble never comes alone" applies to pyro endeavors and it is fun to share our successes and even our failures.

 

Mumbles, Good idea. Making a decent star roller is on the task list (right after building a drying box, more drying screens, a bunker for the ball mill....).

 

The alcohol granulated screen mix should be dry tomorrow and ready to press into a 3lb rocket motor.

[hindsight]

Used the alcohol granulated screen mix 75-15-10 to press a 3lb rocket at 12,700psi. It took a good 20% more fuel by weight to reach the top of the spindle compared to commercial FFG. The rocket flew in a grander (i.e., slower) manner than the oiled FFG. It was a costly success, because 1 of the 4 clamshell bolts snapped during the high pressure on the last increment. Rich Wolter does good work, so it was a bit of a surprise. Obviously the screen mixed BP does compress better than the commercial, confirming your collective opinions. Once the clamshell bolt is repaired, I will press at less extreme pressures. In the meanwhile, time to work on some other pyro activities.

[dagabu]

Used the alcohol granulated screen mix 75-15-10 to press a 3lb rocket at 12,700psi. It took a good 20% more fuel by weight to reach the top of the spindle compared to commercial FFG. The rocket flew in a grander (i.e., slower) manner than the oiled FFG. It was a costly success, because 1 of the 4 clamshell bolts snapped during the high pressure on the last increment. Rich Wolter does good work, so it was a bit of a surprise. Obviously the screen mixed BP does compress better than the commercial, confirming your collective opinions. Once the clamshell bolt is repaired, I will press at less extreme pressures. In the meanwhile, time to work on some other pyro activities.

 

Yupper, drop that pressure down to 10k max. No need to go superhero on the scratch mix. Nice flight? BTW- Scratch BP will hold a LOT more moisture than commercial grains, the weight difference can partially be water.

[hindsight]

dagabu,

 

Good point. It did not occur to me that the increased density could be due to water since no water was used in the granulation, but the water content of the apparently dry ingredients was not checked.

 

Pilots say any landing you can walk away from is a good landing. Launching rockets is analogous. And unlike you club members in the U.S., I have nothing to compare it to, being isolated in this hobby except via the internet. It was much more graceful than expected, and climbed more deliberately than the first 3 pounder. I'm inclined to use screen mix in the immediate future for unladen rockets. When it comes time to lift big shells who knows...

[dagabu]

You have many options for lifting shells. The poorest lifter but the best tail is using a nozzle. You can light the core further up until you CATO them and then just come down a 1/4" (5mm) and try again. the core lights faster,. more fuel to burn, will list more weight. The next is nozzleless. Top light them and they become the workhorse of BP rockets.

 

​Switch to whistle and you have Benzoate and Salicylate to choose from. benzo has less power but is cheaper and the sodium variety is less hygroscopic and doesn't stick to everything like Sali.

[hindsight]

Thanks dagabu. It would be nice to stay with the safest fuels available, so perhaps top-fused nozzleless are my goal.

Dropped the pressure to 10,500psi, and used an un-waxed NEPT with the same 200 grams 75-15-10 alcohol granulated screen-mix and a Bentonite bulkhead bottom fused. Perfect flight. Just need about a hundred more to get comfortable.

[dagabu]

Whoot! Good for you!

[alpinecb]

You have many options for lifting shells. The poorest lifter but the best tail is using a nozzle. You can light the core further up until you CATO them and then just come down a 1/4" (5mm) and try again. the core lights faster,. more fuel to burn, will list more weight. The next is nozzleless. Top light them and they become the workhorse of BP rockets.

 

​Switch to whistle and you have Benzoate and Salicylate to choose from. benzo has less power but is cheaper and the sodium variety is less hygroscopic and doesn't stick to everything like Sali.

Would you be so kind to explain to a new guy what you mean by "light the core further up"(and is this on a nozzle rocket?) and how you "top light" a nozzleless rocket.... please and thanks!

 

Charles

[nater]

By "top lighting" it means using piped match placed all the way up inside the core of the motor, with about an inch of black match exposed at the top of the core. Since the hot gasses are flowing down through the core, this lights the entire core at once, giving more thrust.

 

If you light the core at the bottom, just above the nozzle, it takes a little time for the flame front to travel up and light the rest of the core. The pressure builds gradually until there is enough thrust for lift off, and your total thrust to lift the rocket is reduced.

 

The difference in how the core lights is only a fraction of a second, but it is noticeable when you see the rockets fly (or flop on the ground). Neither method is right or wrong, and either one can be used for a desired effect or on certain motor / heading combinations.

 

Furthermore, some rockets are slow enough they will only fly if they are lit at the top of the core. Other motors, especially whistle, are hot enough they need to be lit at the bottom of the fuel grain or else they will CATO. Only trial and error can give you a sure answer with your motors. Generally BP motors (nozzled or nozzleless) can be top lit or bottom lit and whistles should be bottom lit.

Edited July 14, 2014 by nater

[alpinecb]

By "top lighting" it means using piped match placed all the way up inside the core of the motor, with about an inch of black match exposed at the top of the core. Since the hot gasses are flowing down through the core, this lights the entire core at once, giving more thrust.

 

If you light the core at the bottom, just above the nozzle, it takes a little time for the flame front to travel up and light the rest of the core. The pressure builds gradually until there is enough thrust for lift off, and your total thrust to lift the rocket is reduced.

 

The difference in how the core lights is only a fraction of a second, but it is noticeable when you see the rockets fly (or flop on the ground). Neither method is right or wrong, and either one can be used for a desired effect or on certain motor / heading combinations.

 

Furthermore, some rockets are slow enough they will only fly if they are lit at the top of the core. Other motors, especially whistle, are hot enough they need to be lit at the bottom of the fuel grain or else they will CATO. Only trial and error can give you a sure answer with your motors. Generally BP motors (nozzled or nozzleless) can be top lit or bottom lit and whistles should be bottom lit.

Thanks! This is the first I have heard of using piped match in rockets. I had only considered the issues using fuse in rockets as regards to obstructions in the nozzle.

Charles

Edited July 14, 2014 by alpinecb

[hindsight]

Yes, thanks for the suggestion of using quick match to top light these rockets.

 

Because pressing (10000psi) screen mixed ethanol-granulated 75-15-10 using milled KNO3 produced rockets that climbed too fast to see, I intentionally slowed down the fuel by skipping a step and using GG straight from the bag. Bottom fusing resulted in the 3lb rocket straining to get off the ground, assuming an attitude of 15 degrees off the horizontal, traveling 50 meters, then skidding across the roof of my work building and finally dying in the gutter. Fortunately, I only launch after it rains, so no damage done.

 

An identical rocket, top fused, gave the most spectacular flight l have seen so far. Using the slower BP may make the process of making these rockets safer anyway, so I will stay with this.

Mission accomplished, thanks chaps.

[schroedinger]

For top llighting, also visco wraped in tape can be used. Just let about 5mm of it exposed and they work fine.

[jessoman]

Anyone found a nozleless top-lit seems to go dead straight?

I have a theory because bottom fusing reaches max thrust a bit later, when it flexes it's muscles it can cause the thing to change course a bit.

?

Edited July 26, 2014 by jessoman

[dagabu]

From my videos, I haven't seen much of a difference with lighting types but a lot of difference with proper balancing or equalizing the air resistance.