Thinking about some tube-y and ring-y designs...

An after-the-fact index of all designs shown in this thread:
Tubular Warrior: (ORK file; from this post)


Tubular Warrior 2 (ORK file; from this post)


Ring Warrior 2 (ORK file; from post 27)


Ring Warrior 3 (ORK file; from post 27)


Ring Warrior 4 (ORK file; from post 36)


Ring Warrior 5 (ORK file; from post 40)


Ring Warrior 6 (ORK file; from post 40)


Tubular Warrior 4 (ORK file; from post 58)


New Ringer (ORK file; posts 55 and 58)


Biohazard (ORK file; "final" version from post 94) (this is the "winner", i.e. the one I'm gonna build first)


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I was considering doing something with tubes for my next scratch build, so I threw a couple of variations into OpenRocket. They differ only by the rear fin treatment. It seems like almost everything has been done with regard to tubes, so I'm not worrying too much how original it is, just trying to do something pleasing to me.

Here's my first attempt:

View attachment tubular_warrior.ork

The center of pressure is way far back on this one, and the design ends up ridiculously overstable (over 3 calibers). Is this correct? I know tube fins have weird properties, but would this really behave like a normal overstable rocket?

Slotting the tube fins and the rear ring together would be fun. I was thinking about angling the leading edge of the tube fins, but OR can't do that so I haven't bothered to fiddle with that yet.

So I next tried getting rid of the tube fins and just keeping the rings:

View attachment tubular_warrior_2.ork

Without the tube fins this one sims much more normally.

Both designs are quite light, and would fly out of sight on an E engine (they sim to ~2000ft), so I included a payload bay for an altimeter. That sounds fun, except that it's a BT55 and wouldn't fit a Chute Release or anything like that, so I don't know if I'd ever have the nerve to try it. It would do great on a C11 or D12. I could upscale it to a BT60 to enable it to fit a Chute Release, but I've been doing a lot of BT60 and wanted to do something (a little) different.

Anyway, I like these designs so far, but what really would hold me back is finishing. Painting is enough of a chore for me under normal circumstances, but I'm befuddled how you go about getting in all the nooks and crannies of designs like this (especially the first version, but the second one presents issues as well), and dealing with the masking. How do you paint these things? I know there are plenty of commercial models that present similar challenges, but I haven't done one yet. I don't want to bury myself in painting misery.

Any feedback on these designs welcome.

Loving the first one!!!

I have read that tube fins don't have as much tendency to weathercock as standard fins, which makes sense as they don't stick out from the rocket as much and therefore have less lateral surface area for the wind to impact. Thus over stability may not be as much of an issue. I like your first design.

BABAR said:

I have read that tube fins don't have as much tendency to weathercock as standard fins, which makes sense as they don't stick out from the rocket as much and therefore have less lateral surface area for the wind to impact. Thus over stability may not be as much of an issue.

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Having read around a bit more, I've seen that as well. I'm inclined not to worry too much about that at this point...

I like your first design.

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...however, I am worried as heck about painting that first one. I would have no idea how to do even a 1-color paint job on it, and of course I would want to do something a little more interesting than that.

I tried replacing the tube fins in design #1 with regular fins with the same cross section, and the stability margin came way down into a normal zone. So it seems like that design should be a good proxy for how it will behave in the wind, which is not bad.

I surveyed around and it appears unlikely I would be able to get that exact nose cone, so I'll need to swap out for a different one. I'm also gonna noodle around with scaling it up or down.

I realized that I don't have any tube cutting guides for BT-80. If I wanted to be lazy I could use pre-cut tail rings (such as these). For the 2" ring in the rear, I could use two of them and paper over the outside to hide the seam. Or I could just figure out how to do the cutting.

I'll probably have to start a thread in the Techniques section on how to paint these things, because the more I look at it the more I despair.

I like the second one, but encourage you to go with what you like!

The one real tube fin I built, I had sort of a graffiti wall punk look, and did not worry about getting the insides painted perfectly. A decent effort was good enough for the style. The only other time I used tube fins they were partial tubes split open, easier to paint.

I suspect that the use of any forward or mid-body tube will potentially be a stability disaster that is not properly modeled by your simulation.

In the real world, if there is any deflection of the rocket or angle of attack of the oncoming airflow, the upper tube will catch air and generate a huge deflecting force that will not be overcome by the rear tube. The reason is simple: the forward tube has a MUCH longer moment arm from the center of gravity than the rear tube.

Just like with regular fins, the use of "decorative" forward or mid-body fins requires that they be very small relative to the rear fins or they will 'steer' the rocket wildly or make it completely unstable.

I have seen perfectly normal rockets (long with only rear fins), where there was a large launch lug placed at the very top of the body tube along with another at the bottom. The upper lug catches the air and creates a huge drag/deflecting force. If the fins at the back are not huge and do not stick far out into the clear airstream, the rocket will gyrate around on the way up and some even go unstable.

watermelonman said:

I like the second one, but encourage you to go with what you like!

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I'm not close to finalizing at this point, still have many more design iterations to go. I'll post 'em all here, so both people reading this thread can comment further.

The one real tube fin I built, I had sort of a graffiti wall punk look, and did not worry about getting the insides painted perfectly. A decent effort was good enough for the style. The only other time I used tube fins they were partial tubes split open, easier to paint.

Click to expand...

Got any pics?

That gave me the ridiculous thought of making all the tubes hinge open for painting, and than latch back down for flight. No, not serious. But I could easily imagine some sort of strategy where you paint as you assemble (blech, had to do that a little for the Diamond Cutter and it's a real drag), but then keeping paint off the places where glue will go becomes and issue. Blech again.

I also experimented just a bit with paint schemes for the first design in OR, and the results were so bad that went back and reset all the components to default appearance, lest my retinas be scarred forever. Lotsa work to do here before this one gets going.

What about going to MD and making the FWD ring fin a BT-60 size while keeping the tail feathers the same size?

Screaminhelo said:

What about going to MD and making the FWD ring fin a BT-60 size while keeping the tail feathers the same size?

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Can you clarify what you mean by that? Do you mean going to BT50 for the main BT and keeping the 24mm mount?

neil_w said:

Can you clarify what you mean by that? Do you mean going to BT50 for the main BT and keeping the 24mm mount?

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That's exactly what I was thinking. That would allow you to reduce the size or the forward ring while keeping the aft ring and fins the same size, thus reducing the relative influence of the forward structure on the stability of the rocket. I also like the asthetic of going from smaller to larger as you move aft on the airframe.

This may even allow more motor choices and flying field options by reducing weight slightly, allowing lower power motors that would have been marginal before. Of course, you can now go even higher on the upper end:grin:

Almost missed this reply somehow, just noticed it now.

shreadvector said:

I suspect that the use of any forward or mid-body tube will potentially be a stability disaster that is not properly modeled by your simulation.

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Lack of confidence in the simulation is definitely a problem for me here. It is probably not a coincidence that I've never seen a design with a forward ring like this (although to be fair I've seen a lot of crazy stuff).

In the real world, if there is any deflection of the rocket or angle of attack of the oncoming airflow, the upper tube will catch air and generate a huge deflecting force that will not be overcome by the rear tube. The reason is simple: the forward tube has a MUCH longer moment arm from the center of gravity than the rear tube.

Just like with regular fins, the use of "decorative" forward or mid-body fins requires that they be very small relative to the rear fins or they will 'steer' the rocket wildly or make it completely unstable.

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Noted.

However, in the first design (for example) there's a lot of tube fin in the back, which I would think could be enough to offset the front ring. However, I don't trust my mind-simming any more than I do OR when it comes to this. I could imagine it being more of a problem in the second design.

I do like the look of the front ring, but I clearly have to think more about this.

neil_w said:

Lack of confidence in the simulation is definitely a problem for me here. It is probably not a coincidence that I've never seen a design with a forward ring like this (although to be fair I've seen a lot of crazy stuff).

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Not unlike a spool...
[YOUTUBE]Ct3PWoPQPb0[/YOUTUBE]

This one follows (sort of) Screaminhelo's suggestion: BT50, with BT60 and BT80 rings. Simulates to 1000 ft with a C6-5, dunno if there's real reason to go 24mm unless I never want to see it again. Also quite overstable (2.69 cal according to OR), which I haven't figure out how to fix without ruining the design. But I'm not sure I particularly trust the simulation. Maybe I'll get a trial of Rocksim and create this there, just for comparison. Hmm.

I like the look, though this variation is starting to drift similar in some ways to the Diamond Cutter, so I might want to change it some just to be more different. Anyway.

View attachment ringwarrior.ork

Of the ones you've posted thus far, I like the looks of this one best. In fact this may be my first scratch build, when I get that far. I played with your file and did some hacking. Just some minor tweeks like a single 18" body tube, added centering rings, engine hook and launch lugs. Adjusted position of the chute and shock cord, and added .125 ounces of weight to the nose cone. Also reduced the diameter of the chute to 6 inches.

Stability seems to be just slightly over 2 cal and altitude on the D engine is coming in at just short of 1500 ft. in calm air. This is what it would look like as I would paint it. OR file attached if you want to look at it.


Thanks for the ideas.

Diggr
View attachment Ringwarrior II.ork

Cool, by all means post some pictures (or build thread) if you go ahead with it.

In your ORK file, the shock cord should be further back, it'l fall back toward the motor mount when the rocket gets going. One other thing I noticed from your file is that because this rocket is so light, small changes (engine hook, launch lugs, etc.) make a noticeable difference in stability. I'll have to be a bit more thorough before drawing conclusions when working with light rockets like this.

I would like to see you build the first design. very cool

Neil,

You need to know that I'm just now getting back into rocketry, after a 30+ year "break". So to a large degree, the design presented, is my read of theory rather than documented experience. But a couple of questions?

As I understand (and remember things back then), the chute and shock cord assembly packed as a single unit, forward of the "recovery wadding". While you are correct (in my opinion) in your concern about the setback at launch, I wonder if there might be some some way to stop the chute/shock cord from standing still at launch? Perhaps a way to eliminate the nose weight and instead use a bulkhead of sorts, to keep the chute assembly in place on launch?

In any case, thanks for your reply. Have a good rest of the day!!

Diggr

I like to put a centering ring roughly 7 - 8" from the forward end of the BT to act as a parachute shelf. inner radius of 19mm (bt20 size) works for me.
Rex

Diggr said:

As I understand (and remember things back then), the chute and shock cord assembly packed as a single unit, forward of the "recovery wadding". While you are correct (in my opinion) in your concern about the setback at launch, I wonder if there might be some some way to stop the chute/shock cord from standing still at launch? Perhaps a way to eliminate the nose weight and instead use a bulkhead of sorts, to keep the chute assembly in place on launch?

Click to expand...

The chute is generally wrapped in the shroud lines (techniques vary) and should stay close to the nose cone. The shock cord, however, usually falls down toward the motor mount. That pushes a bit of weight backwards, but it's not something I would typically worry about, just want to account for it correctly in the OR file (especially for a very light rocket such as this where the weight of the shock cord is significant).

Rex R said:

I like to put a centering ring roughly 7 - 8" from the forward end of the BT to act as a parachute shelf. inner radius of 19mm (bt20 size) works for me.

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That's a nice simple approach, but is it really needed? With a very light chute wrapped in it's shroud lines, isn't it gonna pretty much stay put by the nose cone?

I agree with Diggr, you have a nice look there. Heck, I think that I have everything I need but the nose cone for that one, I am tempted!

Neil

This is my last hijack of your thread! I'm thinking that Rex R has a pretty reasonable idea with the centering ring/ shelf idea. It allows one to essentially move the .125 oz nose weight, or at least some of it, aft and have it serve some useful purpose. It would be easier to build, and there doesn't seem to make much reason to fly more weight than required. I've crunched the numbers and OR is showing stability at 1.57 cal on the big motor.

Please keep us informed of your progress with this design. It's been fun thus far.

Diggr

I am a firm believer in Murphy & Finnagle...if it can happen it will, at the worst possible time. a fiber/cardboard cr glued in w/ white glue doesn't add much weight and it keeps the dog barf from falling creating gaps for bad stuff to pass through.
Rex

Hmm, I hadn't thought of it as a dog barf shelf. Interesting. Maybe not a bad idea...

I've only built one rocket with tube fins, I think it was a gravity wave. Lost it first flight to the corn field due to weather cocking and late deployment Best thing about that build was that I painted the internal fins and smaller body tube yellow, orange and red. When the outer tube was added it looked like it was a running engine. I don't think I ended up painting the inside of the outer tube.

Got any pictures of that one?

A variation with the tail rings reversed. I think I could do better than this, but it's my first try:

View attachment ringwarrior3.ork

And a more accurate sim of a previous design, seems like it'd work OK. I do like this one:

View attachment ringwarrior2.ork

flew my ring fin bird last Saturday.
Rex

I'm liking the RW2; although, RW3 does get the mind sim wheels turning.

Screaminhelo said:

I'm liking the RW2; although, RW3 does get the mind sim wheels turning.

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I like the idea of the larger ring in front, but don't feel like I have it nailed yet. Will probably do a few more iterations before settling on something.

I think I have a decent idea how to sequence the painting and building. I'll be a pain but doable. I'm hoping someone else will build thread one of these first so I can learn from their mistakes.