Spindle Length / Width Correlation with performance (Nozzleless and Cored Rockets)

[scrmlw]

Is there a general rule of thumb pertaining to spindle length / width and performance?

Generally I'm thinking Nozzleless, because a nozzle adds a whole other can of worms (there's SO many variables to all of this!).

I know the standard numbers for spindle sizes, but I've been playing around with them a little.

What I've settled on so far, ID x .575 gives higher thrust, and possibly a little more forgiveness (RUDwise) than ID x .5 (not to mention use less comp).

It's been working well for whistle and strobes.

But from what I read (not tested), smaller widths give higher thrust as well.

 

*Bonus Question

Why is the U/H spindle wider than the standard BP spindle?

Why wouldn't you just take a U/H width spindle, and make it longer for a BP rocket?

Does BP work better with a thinner spindle, because of smart brain sciencey thrust curves?

Or is it as simple as "It's not as hot as whistle, so you can push it harder before you get a CATO"?

Or even "Whistle / Strobe sounds better with a wider core, but since a BP motor is not concerned with the audible aspect, it's optimized for performance" (I don't buy that, it's just an example of some lateral explanation )

[justvisiting]

OK, I'll bite since nobody else has

 

I don't see how a larger core using less propellant gives higher thrust. I do see how it would make a more forgiving whistle rocket, and probably a better strobe rocket too.

 

In my view, the UH spindle is wider than a standard BP spindle because it's a 'one size fits all' spindle. It's forgiving enough for whistle, and OK for BP rockets too. A standard BP spindle allows more propellant to be used, and the smaller choke allows more thrust to develop. I don't know if you are aware, but 'standard' nozzled BP rocket propellant is very weak and slow-burning compared to other propellants.

 

If you are thinking of nozzleless BP motors, then you are using hot BP to propel the motor, not 'standard' nozzled BP motor propellant. In that case, a UH spindle will give a motor with about half the thrust as a motor made with a standard BP spindle.

[Arthur]

There are too many variables, IMO most people either pick a comp and alter the tool, OR buy a tool and change the comp.

[scrmlw]

I don't see how a larger core using less propellant gives higher thrust. I do see how it would make a more forgiving whistle rocket, and probably a better strobe rocket too.

 

In my view, the UH spindle is wider than a standard BP spindle because it's a 'one size fits all' spindle. It's forgiving enough for whistle, and OK for BP rockets too. A standard BP spindle allows more propellant to be used, and the smaller choke allows more thrust to develop. I don't know if you are aware, but 'standard' nozzled BP rocket propellant is very weak and slow-burning compared to other propellants.

 

If you are thinking of nozzleless BP motors, then you are using hot BP to propel the motor, not 'standard' nozzled BP motor propellant. In that case, a UH spindle will give a motor with about half the thrust as a motor made with a standard BP spindle.

Thanks for the reply

I should have mentioned in the OP, I'm no expert. If I'm wrong, I'd like to know.

 

I don't know how either, but they seem to take off faster and lift higher. I don't have anything qualitative to back that up, but that's what it looks like to me.

 

On most of my previous nozzleless BP rockets (.575 width), I've had to mix in another 7parts Charcoal (from 75:15:10) to avoid a CATO, but I've very recently discovered it may have been my tube rolling technique, making the tube walls too thin (another variable).

Finally got some good tubes, and I'm working my way up to see when it starts to CATO again.

[scrmlw]

There are too many variables, IMO most people either pick a comp and alter the tool, OR buy a tool and change the comp.

Well yeah, but that's part of the fun, figuring out why this does that and that does this.

I change a little of each, but there's thresholds too. Too slow comp doesn't lift, and too hot goes Kapow.

Is it my tubes? Is it my spindle design? What's causing the CATOs? What's causing the Flops?

I'd like to increase the performance in the middle ground. The more I know, the more I know.

Edited January 23, 2023 by scrmlw

[justvisiting]

A very thin coat of paraffin wax on the inside of the tube is quite helpful in avoiding CATO. There's quite a long thread about it here somewhere.

[scrmlw]

I thought of an example

What I've settled on so far, ID x .575 gives higher thrust, and possibly a little more forgiveness (RUDwise) than ID x .5 (not to mention use less comp).

It's been working well for whistle and strobes.

 

I don't see how a larger core using less propellant gives higher thrust. I do see how it would make a more forgiving whistle rocket, and probably a better strobe rocket too.

 

In my view, the UH spindle is wider than a standard BP spindle because it's a 'one size fits all' spindle. It's forgiving enough for whistle, and OK for BP rockets too. A standard BP spindle allows more propellant to be used, and the smaller choke allows more thrust to develop. I don't know if you are aware, but 'standard' nozzled BP rocket propellant is very weak and slow-burning compared to other propellants.

 

I made 2 sets of adjustable height tooling. The 2 pieces of each set have a °33 and a °72 Divergent nozzle at the bottom. One set was .575" width, and the other was .5.

I won't even get in to diverging nozzle shape on a nozzleless rocket, because I don't understand the basics of the core yet, so both examples are with a °33 diverging nozzle (only to make it easier to remove the tube without crumbling).

I made whistle rockets, with the same mix (70:29:1 KBenz).

The .575" CATO'd with a shorter spindle than the .5", and flew higher.

Now that doesn't equate to thrust. I don't have the gear to measure that.

Maybe I'll go back and test that again, definitively, now that I have thicker tubes, but theoretically, that shouldn't make a difference.

[JAWChemist]

In Blogs, Redrocketman’s Blog "Correct core dia formula", in a comment by Mixer (not shown has to be viewed); there is a discussion and details about a Maurizio article on reducing trial and error on different spindle length and nozzle throat combinations for a specific fuel. It seems like it might be of interest. I mention it only because even searching the blogs for it did not seem to hit the discussion.’

[scrmlw]

In Blogs, Redrocketman’s Blog "Correct core dia formula", in a comment by Mixer (not shown has to be viewed); there is a discussion and details about a Maurizio article on reducing trial and error on different spindle length and nozzle throat combinations for a specific fuel. It seems like it might be of interest. I mention it only because even searching the blogs for it did not seem to hit the discussion.’

Awesome! Found it

That's super helpful. Now to just read it 10 times and decipher it

 

--------

 

Ok, I was wrong about the whistle test spindle height. Checked my numbers in my notebook.

The .5 and the .575 dia both flew at 1.7 ID Length. They both CATO'd at 1.8.

The .575 flew higher + faster though

This was all with tubes that weren't thick walled enough though (~.17 ID)

Still have yet to find the Redline with .25 ID walled tubes. Only tested the .575 dia. Up to 2 ID height and juiced up the mix to 71:28:1

[cmjlab]

OK, I'll bite since nobody else has

 

I don't see how a larger core using less propellant gives higher thrust. I do see how it would make a more forgiving whistle rocket, and probably a better strobe rocket too.

 

In my view, the UH spindle is wider than a standard BP spindle because it's a 'one size fits all' spindle......

JustVisiting,

 

I was reading your response about core size relative to thrust - is it true that a wider longer core doesn't produce more thrust? (I wouldn't doubt you if that's what you are saying, but I wanted to make sure I didn't misinterpret something).

 

I thought with nozzle less, core burn rockets, a slightly larger core would produce slightly more thrust (than a "normal" core), due to increased surface area? Specifically (like the OP) I would have thought a whistle rocket with a wider / longer core would produce more thrust (if it didn't CATO due to over-pressurizing when the core is to deep).

 

Again, you've done WAY more with rockets than I, so I don't doubt you if that's what you are saying. Thanks for bearing with me on this!

 

Charles

[justvisiting]

Charles, I don't claim to be an expert, but I do have opinions (and an Acme The way I see it (with nozzleless rockets) is that a larger core has more surface area, but the aperture is also larger. So there's more exhaust leaving through a larger (and enlarging) hole. And, there's less propellant in the rocket than if the core was smaller. End burn rockets lose thrust due to nozzle erosion. I see the nozzleless rocket aperture as being the same idea. A longer core would produce more thrust because there's more propellant in the motor. I have extra long BP spindles I use for nozzleless BP rockets so I can lift 6" ball shells way high on 1" ID motors. UH spindles are shorter than BP spindles, so I can't comment on whether a larger core AND a longer core would be better than a smaller core and shorter core. Maybe I misunderstood the OP's original questions.

 

Donald Josar, the originator of the nozzleless BP rockets, used a coat hanger as a spindle for his 1lb rockets. He used hot BP, but not a hot BP charcoal. I believe he used mesquite. He lifter 1lb bottles of water with those rockets.

[scrmlw]

UH spindles are shorter than BP spindles, so I can't comment on whether a larger core AND a longer core would be better than a smaller core and shorter core. Maybe I misunderstood the OP's original questions.

Right on, that's kind of what I'm wondering. I haven't been able to find a lot of info googling around.

2 nozzleless rockets, same fuel, same length, different diameters?

I've found conflicting info searching APC.

Then, to extrapolate from that, does the optimum diameter change with different fuels (for reasons I don't understand besides burns faster / slower) Whistle, BP, APbased fuels, Magnalium Chuffers....

[cmjlab]

Appreciate the explanation, it makes sense the way you explained it. I get confused thinking about thrust between end burners, nozzle less, core burners, and everything(s) in between.

 

Plus.... Expert or no, it's hard to argue against Acme data!

 

I also happen to have read enough of your topics and responses to at least figure out you know more than I do on the topic!

[justvisiting]

There are other guys around here that are more familiar with tooling differences, and they use a program called 'Rocket Sketcher', or something similar to predict thrust, chamber pressure, etc... That stuff is beyond me. I just use off the shelf tooling. The kind words are appreciated.

[JAWChemist]

I helped another member in APC Forum's Discord chat find the Rocket Sketcher at

https://drive.google.com/file/d/0BwXIGQD4ku3hZXNNd3FiM1R4aGc/view?resourcekey=0-wf-P85VuwodNRt1sOKqTuQ.

Just click on the download at the upper right. At that time, I scanned it for viruses and loaded it in an Oracle Virtual Machine. It seemed to work and nothing obnoxious occurred.

If there are issues, I have a copy. My involvement in both these cases is just an accidental coincidence.

[cmjlab]

I helped another member in APC Forum's Discord chat find the Rocket Sketcher at

https://drive.google.com/file/d/0BwXIGQD4ku3hZXNNd3FiM1R4aGc/view?resourcekey=0-wf-P85VuwodNRt1sOKqTuQ.

Just click on the download at the upper right. At that time, I scanned it for viruses and loaded it in an Oracle Virtual Machine. It seemed to work and nothing obnoxious occurred.

If there are issues, I have a copy. My involvement in both these cases is just an accidental coincidence.

Appreciate the link. I'll have to check it out for curiosity when I get home, I wish I owned a lathe and/or mill to make tooling for myself!

 

For my limited rocket activities I only have two sets in 3/4"(1#): a hybrid universal and standard B.P. tooling, with PVC sleeves and brass shim stock. So my experience is pretty limited.

 

Thanks

[scrmlw]

JAWChemist I'm not even gonna google anymore. I'm just gonna hit you up. You know where everything is archived!

I've never been able to make that work before.

Is it supposed to let me know how the rocket is going to work? Or it just sketches the spindle, and I have to do the math and the testing?

I just want to make sure I have it working properly.

[CountZero]

Rocket tool sketcher just gives the dimensions, testing you have to do yourself.

 

Anyone knows a program that lets you predict performance? I have seen some kind of program(but can't remeber the name), that was aimed at model rocketry with I think estes motors primarily. But I think you can enter your own data if you have it(or make some educated guesses)

[cmjlab]

Richard Nakka Rocketry site posts several software and references, maybe one of those?

 

https://www.nakka-rocketry.net/softw.html

Specifically "SOAR"

[JAWChemist]

JAWChemist I'm not even gonna google anymore. I'm just gonna hit you up. You know where everything is archived!

I've never been able to make that work before.

Is it supposed to let me know how the rocket is going to work? Or it just sketches the spindle, and I have to do the math and the testing?

I just want to make sure I have it working properly.

Hi scrmlw,

Thanks for the confidence. My career has involved a lot of finding information, but I am afraid that your questions are application specific to Rocket Sketcher. I have no experience with actually using it, other than to just start it, or even enough background with rocket design to get a quick understanding of what it does. I can only suggest that you rely on the forum's resources. There seems to be many familiar with the program. One post did seem to suggest that it might have a issue when used even if it starts up (killforfood on 09 January 2011 - 05:54 PM in Tools and Tooling).

A way to locate the posts is on the Home page, Gear to the right of the search box, in “Find Words” enter “Rocket Sketcher” , and in “Display Results” select the “As posts” radio button and then click the button “Search Now” at the bottom. The results (61) will give you a lot of commentary that might help and leads on those who might have a better understanding of the application and be able to answer your questions.

From cmjlab comments there seem to be a lot of other options to chose from.

[scrmlw]

Thanks CountZero. That's ok, Testing is part of the fun.

It gives me an excuse to get out and , well, Test my motors.

I guess if I knew they were just gonna work great, I wouldn't have as much of a justifiable excuse to get out and, well, TEST my rocket motors as often

 

Thanks cmjlab, I'll check them out. Nakka's site is intimidating to me a little. There's so many equations and graphs.

 

I realized why it never worked for me before. I just got a newer computer. My old one was running Win7 (I wish I could still run it safely and efficiently, honestly).

Didn't dare use Adobe Flash on that. The newer one is running Win10.

[cmjlab]

Yeah Nakka's website is mainly gears towards amateur Rocketry / model Rocketry, but the link I provide is just where he lists out the software he uses for testing with links (along with links to the high speed graphs/charts/spreadsheets he uses).