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Minimal Length for Spool Rocket

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mkmilion

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I'm deciding to construct a spool rocket; a 13mm to be exact.
I'm wondering if there is a minimal (or maxium) length for this type of rocket for optimum stability.
So any experts please chime in.
 

Fore Check

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When I read your post, I was certainly intrigued.....

This subject has been broached before with no clear answer.

The simulation programs that are popularly used don't predict much stability at all in spools - yet their performance is quite to the contrary.

Perhaps a first question before I say more than I know is to ask what diameter the discs on your spool are? Are they standard CD's or something else?
 

Fore Check

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I suppose the next question is why you'd go for a 13mm spool? Novelty? 18mm spools, let alone 24mm ones, don't acheive any significant height....
 

mkmilion

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I've chosen 13mm because I'm going for a backyard flyer type and yes I'm using standard CDs I believe they measure 4 3/4". I might actually trim them down accordingly depending on preformance. Seeing how preformance has no standard on these I guess trial and error is the only way to find out.
 

Fore Check

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Originally posted by mkmilion
I've chosen 13mm because I'm going for a backyard flyer type and yes I'm using standard CDs I believe they measure 4 3/4". I might actually trim them down accordingly depending on preformance. Seeing how preformance has no standard on these I guess trial and error is the only way to find out.
Hmmm...

I'm sure that an A series 18mm spool would barely clear your roof....

Anyway, to each their own. Certainly their is a minimum distance between the forward and aft discs on the spool that is proportional to the disc diameter to ensure stability.

We know that 2.75" works.

Why not build it at that length with an appropriate engine block to hold the 1.75" long 13mm motor where it needs to be? I'm certain that you would never realize the difference in altitude performance....

Just a suggestion.
 

teflonrocketry1

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John Cipolla is working on wind tunnel tests of spool rockets.

Visit: http://www.aerorocket.com/

You might ask him for a preprint of the article he is working on.

Based on what has been discussed on this forum before, as long as the plate diameter to body diameter ratio is large (>5) you should get a stable flight even with only one plate. I don't know if there is a minimum separation between two plates that is unstable. However, if one plate at either end of a motor tube is stable, I doubt there is an unstable configuration. Keep in mind that none of this has been proven by experiment.

Bruce S. Levison, NAR #69055
 

wwattles

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Hmmm... maybe a micro-maxx spool? Made with tiny cardboard rings? :rolleyes:

WW
 

mkmilion

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Originally posted by wwattles
Hmmm... maybe a micro-maxx spool? Made with tiny cardboard rings? :rolleyes:

WW
That's my next project if I can get what I want out of the 13mm.


Forecheck,
I do relize the semi-idiocy of this project, but if I can make it work on the current 'A' powered 13mm motors then it is a commendable feat. If not then oh well back to the 18mm and up. I just figured I'd give it a shot for all those shoe-string rocketeers that are strapped for cash.
What I do know if it doesn't work, it's a mistake I can learn from.
 

lalligood

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I've built a 13mm spool rocket using a pair of standard sized CDs. The body tube was just long enough to have a tiny rolled up strip of paper acting as a motor block with a 1/4" of motor sticking out the back. I had to concoct a way to "thicken up" the body tube because the center hole of a CD is closer to 15mm in diameter. After I flew it on a A10-PT & it struggled to reach 30ft (& that is a generous guesstimate), i considered it a failure & moved on. The only way I would ever consider building one again is if I came into any more of the mini-CDs (closer to 3" diameter vs standard CD's 4.75" diameter). I wouldn't expect the peak altitude to change that much though...

My advice: build an 18mm spool & only fly it on A8-3s. Easier to build & you can always put a C6 in it when you have a larger field.

My advice part II: After building & flying Art Applewhite's free 13mm Qubit, maybe explore other draggy designs that could be made with cardstock. Doesn't get any cheaper than a piece of paper!

Keep us up to date on your progress.
 

Fore Check

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Hmmm...

I can't think of *any* rocketry project that would involve "sem-idiocy." No matter the end result, I'm sure it will be fun! ;)

I am curious to read your results when you flight test your spool. I am certainly intrigued....
 

lalligood

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Originally posted by lalligood
The only way I would ever consider building one again is if I came into any more of the mini-CDs (closer to 3" diameter vs standard CD's 4.75" diameter). I wouldn't expect the peak altitude to change that much though...
I forgot to mention that if your local mall has a Sbarro's, they have those mini-CD's in the lids of their larges soft drinks. Just thought I'd pass the information along...
 

dvldrmmr

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This sounds like fun. I think I finally found a use for those old cd's I have lying around. I could even fly them in my backyard. Awesome... Anyone have links to pictures?

dvldrmmr
 

wscarvie

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Originally posted by lalligood
My advice: build an 18mm spool & only fly it on A8-3s. Easier to build & you can always put a C6 in it when you have a larger field.
Hi there,

Any chance you have a link to a set of plans or instructions for an 18mm spool rocket? In particular, I'm wondering how to widen the holes in a CD safely, and keep them centered.

Thanks much.
 

crashinj

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I experimented with spool rockets awhile back using 18mm motors. They were lots of fun and went up about 250ft or so, lots of fun. Do a search here on TRF for spool rockets, there was alot of discussion on the thread here about 6-8 months ago or so.

The spacing on mine was 3 3/4" using AOL CD's, I found a good use for them. I just took a piece of sandpaper coiled it up put it thru the center of the CD and turned it till it took off enough to fit my body tube.

Good luck with your Spool's

CrashinJ
 

mkmilion

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I have assembiled the spool. I will not yet show pics until. At least paint is done. BTW it turned out better than I planned.
 

lalligood

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Originally posted by mkmilion
I have assembiled the spool. I will not yet show pics until. At least paint is done. BTW it turned out better than I planned.
OK, first you want to make a 13mm spool & now you're painting one?!?

One thing about spools you've got to understand: They are ugly. More importantly, THEY ARE *MEANT* TO BE UGLY! :rolleyes:

If you make them pretty, people won't look at them so funny anymore & they'll be disappointed that it doesn't fly well... (People are always more impressed when you successfully fly something that's ugly & doesn't look like it should fly!) ;)
 

fehskens

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I'll echo everything that 's been said. I built an 18mm spool out of a 5" length of BT-20 and two AOL CDs. I enlarged the center hole with a Dremel, and used two cardboard 2060 centering rings on each side of each CD to center the body tube. Epoxy held everything together. I drilled a hole in each CD for 1/8" launch lug that ran the full length of the body. I put a short conical nose cone on it "to improve the aerodynamics". I flew it on a B, IIRC, and it got maybe 30 feet up. Spools are fun to watch, they fly ok under thrust, then go unstable at burnout and pretty much stop dead in their tracks. So if you bother with a recovery system, use the shortest delay motor possible.

I've got a picture of it around somwhere, both static and in flight, which I'll post as soon as I find them.

len.
 

lalligood

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I know that many TRFers have contacted me for my CD spool rocket instructions. I haven't modified them just yet (partially because I have recently decided to focus more on HPR) but I would like to include an alternate set of instructions for those folks out there without a drill press but happen to have a Dremel. (I *finally* got one for my b-day last month...HOW DID I EVER WORK WITHOUT ONE?!? :eek: )

Also, for anyone new to this thread that is interested in building your own CD spool rocket, send me a PM with you email address & I'd be glad to send you the PDF file.

The Dremel was a godsend when I experimented recently with a few old laserdiscs (because drilling out the center of those behemoths was looking pretty grim...) One of these days when I have some leftover 38mm tubing laying around, I'm going to upscale the CD spool design with laserdiscs powered by a Pro38 H153 :D :eek:
 

mkmilion

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I know they are supposed to be ugly. If it's any conselation I'm painting it copper. I should have pics later on tonight. I just waiting for the paint to dry. As for my unorthodoxism I appoligize.
 

mkmilion

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I hope to hear from you guys soon. Comments, questions, etc., etc. I also hope lalligood repeals my sacralege.
 

mkmilion

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I thought I'd also mention that when I fly it I'll posted estimated altitude. I do have an Alti-Tracker so it should be fairly accurate.
 

lalligood

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Originally posted by mkmilion
I hope to hear from you guys soon. Comments, questions, etc., etc. I also hope lalligood repeals my sacralege.
HAHAHA Glad to see we both have a sense of humor about this!

Now get out there & fly it so you can prove me wrong ;)
 

wwattles

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Following Lance's instructions, I built an AOL CD-ROM spool last night. Very easy to do. I've decided to call it (drum roll please)...

"AOL... Optimized."

:cool:
WW
 

fehskens

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See, the thing about using AOL CDs for spool rockets is you don't need to paint them and they still look garish.

len.
 

fehskens

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Oh, yeah, this one was obviously named "1050 Hours".

len.
 
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