Building a 2 stage ringtail

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Dotini

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The purpose of this project is to fly a two stage model with a loud and smokey D motor booster on a small field, yet limit the altitude to a modest height. Since ringtails are known to be draggy and/or inefficient compared to conventional fins, these will be ideal for this purpose.

DSC00447.jpg

Raw materials, tools, and semi-finished components laid out. Tube is BT-60, support fins are 1/8" balsa, rings are 3" PETG shipping tube cut down to 1.3". Length is projected at 28". The finish is planned to be a lurid pink, purple and lime green.
 
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Sandy H.

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The Fliskits Corona with Corona2 booster was used this way at many Boyscout launches. Plus it looks cool. A lot smaller in diameter than your plan, so low and slow should be even better for small fields for you.

Sandy.
 

Dotini

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Rain and wind currently prohibit my backlog of test flights on three Venturi ringtails, a two-stage kit bash and a CHAD device. Painting and finish operations in the shop are also restricted. Even so, work continues on my most outrageous scratch rocket yet.
DSC00449.jpg

Support fins have just been glued on. Next comes more trimming, sanding and finish, fitment of rings, etc. There will be surprises.
 

Rktman

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The purpose of this project is to fly a two stage model with a loud and smokey D motor booster on a small field, yet limit the altitude to a modest height. Since ringtails are known to be draggy and/or inefficient compared to conventional fins, these will be ideal for this purpose.

View attachment 484265
Raw materials, tools, and semi-finished components laid out. Tube is BT-60, support fins are 1/8" balsa, rings are 3" PETG shipping tube cut down to 1.3". Length is projected at 28". The finish is planned to be a lurid pink, purple and lime green.
Just curious: how do you cut out your rings so cleanly and evenly? Hobby knife and steady hand, or some other method? Looking forward to this build!
 

Dotini

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Just curious: how do you cut out your rings so cleanly and evenly? Hobby knife and steady hand, or some other method? Looking forward to this build!
Thanks for your excellent question!

The method is sort of hinted at in the OP photo. First, I wrap a piece of paper around the tube, align the edges and tape it tightly around the tube. I happen to use 24 lb linen stationary. Using the edge of the paper as a guide, a line is drawn around the tube with an ultra fine point Sharpie. I then stab the line with my hobby knife and slice off the section. This leaves a somewhat rough ring a fraction - 1/4" or so - wider than what I want. I then tape another piece of paper of the finish dimension around the workpiece, again carefully aligning the edges, and draw the two finish lines around the ring. Using special scissors, shown below, I cut carefully along the lines. Almost done. Using a sanding block or Apogee sanding tee, I sand off any irregularities remaining. The edges are deburred with sandpaper, and the surfaces abraded with 400 to encourage paint to stick.
DSC00450.jpg

These are embossed with "Fiskars Finland". Accept no substitute from China.
 

Aeronerd

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Thanks for your excellent question!

The method is sort of hinted at in the OP photo. First, I wrap a piece of paper around the tube, align the edges and tape it tightly around the tube. I happen to use 24 lb linen stationary. Using the edge of the paper as a guide, a line is drawn around the tube with an ultra fine point Sharpie. I then stab the line with my hobby knife and slice off the section. This leaves a somewhat rough ring a fraction - 1/4" or so - wider than what I want. I then tape another piece of paper of the finish dimension around the workpiece, again carefully aligning the edges, and draw the two finish lines around the ring. Using special scissors, shown below, I cut carefully along the lines. Almost done. Using a sanding block or Apogee sanding tee, I sand off any irregularities remaining. The edges are deburred with sandpaper, and the surfaces abraded with 400 to encourage paint to stick.
View attachment 484500
These are embossed with "Fiskars Finland". Accept no substitute from China.
Cool!
 

Rktman

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Thanks for your excellent question!

The method is sort of hinted at in the OP photo. First, I wrap a piece of paper around the tube, align the edges and tape it tightly around the tube. I happen to use 24 lb linen stationary. Using the edge of the paper as a guide, a line is drawn around the tube with an ultra fine point Sharpie. I then stab the line with my hobby knife and slice off the section. This leaves a somewhat rough ring a fraction - 1/4" or so - wider than what I want. I then tape another piece of paper of the finish dimension around the workpiece, again carefully aligning the edges, and draw the two finish lines around the ring. Using special scissors, shown below, I cut carefully along the lines. Almost done. Using a sanding block or Apogee sanding tee, I sand off any irregularities remaining. The edges are deburred with sandpaper, and the surfaces abraded with 400 to encourage paint to stick.
View attachment 484500
These are embossed with "Fiskars Finland". Accept no substitute from China.
Thanks, really appreciate the step-by-step description.
I never thought to do a rough-cut first then finalize things with a pair of (sharp) shears and sandpaper. I'll definitely use your method the next time I do a ring-tail or need a ring for decorative/design reasons. It's so much faster and easier than using a hobby knife on thick-walled tubes, even paper ones.
 

jqavins

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The Fliskits Corona with Corona2 booster was used this way at many Boyscout launches. Plus it looks cool. A lot smaller in diameter than your plan, so low and slow should be even better for small fields for you.
One of my favorite designs is a two stage ring tail, the Estes Solar Flare.
1633537255827.png
Those pylons/fins are so big that it probably doesn't really need the rings.
 

jqavins

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Different phraseology because those objects are holding the rings, so they are serving as pylons, and are also so big that they could serve as fins on their own. Dual purpose, dual term.

But you knew that. :)
 

Dotini

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One of my favorite designs is a two stage ring tail, the Estes Solar Flare.
View attachment 484547
Those pylons/fins are so big that it probably doesn't really need the rings.
That is an interesting design I'd not seen. I suppose it's been discontinued for awhile?

Since my current model does have four small true fins supporting the ring(s), I will set them to additional work spinning the rocket on ascent, a trick that my rings cannot perform. This will be yet another measure to hold down altitude.
 

jqavins

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Since it's spinning, you could cut saw teeth into the leading edge of the sustainer ring and call the rocket Hole Saw.
 

BABAR

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That is an interesting design I'd not seen. I suppose it's been discontinued for awhile?

Since my current model does have four small true fins supporting the ring(s), I will set them to additional work spinning the rocket on ascent, a trick that my rings cannot perform. This will be yet another measure to hold down altitude.
you have already probably planned this, but since they are already attached you could put a clockwise airfoil on each of the fins (or counterclockwise, doesn’t matter as long as all are the same).

I think this was the technique used to obtain long axial rotation on the StovePipe.

 

Dotini

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Since it's spinning, you could cut saw teeth into the leading edge of the sustainer ring and call the rocket Hole Saw.
Hah hah! True. But then I'd have to recalculate my stability equations. So I'll leave the Hole Saw in the wind at this time.

you have already probably planned this, but since they are already attached you could put a clockwise airfoil on each of the fins (or counterclockwise, doesn’t matter as long as all are the same).

I think this was the technique used to obtain long axial rotation on the StovePipe.

Yes this was my plan: Sand a rudimentary Clark Y profile - a rounded leading edge with an airfoil section on the port side and the starboard side flat, but with a Gurney flap added at the trailing edge. Even though the fins (and the flaps) are quite small, this should get them going counterclockwise.
 

jqavins

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Hah hah! True. But then I'd have to recalculate my stability equations. So I'll leave the Hole Saw in the wind at this time.
Nah. If you just cut small teeth, like making a cut with pinking sheers, it shouldn't change the stability noticeably at all. But then, it was a joke to start with.
 

Dotini

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You might find this blast from the past interesting:
dom0976.pdf (spacemodeling.org)
Very cool design for the time. Any information on altitude, and the reason for the upper fins? A few years after your Dinsmore 3 stage ringtail design, around 1981, I was launching, recovering and launching again this insane four stage rocket. All that remains now are stages1, 3 and 4, and the fins from the 2nd stage.
DSC00451.jpg

All 4 motors 18mm.
 

BigMacDaddy

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I saw your comments about your hobby shears / scissors....

FWIW - I love these shears from Harbor Freight. They look incredibly cheap (with price to match) but cut everything up to fairly-thick sheet metal really cleanly. Anyway, just a recommendation for a dirt cheap backup pair of shears for your hobby tool box...

 

Dotini

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Slow progress to report on the 2 stage ringtail model. Fins have been configured to induce spin. Rings and motor mounts are ready to install. Im still pondering the livery.
DSC00453.jpg

DSC00454.jpg
 

Dotini

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Motor mounts, baffle and shock cord, coupler, all are glued in. A fresh coat of white primer reveals additional places to sand. No hurry to fly this little monster, so finish will be a lengthier process than for most of my projects. Goals for the finish: Easy to spot booster in yon grassy field, easy to see spin on the sustainer in flight, different colors than those I've used previously.

DSC00455.jpg

2 stage D motor ringtail, lacking only finish, lug(s) and ring installation.
 
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Dotini

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A brief spike in temperatures and reduction of humidity allowed me to spray a first coat of paint on some of my parts.
DSC00457.jpg


DSC00458.jpg

A bit more assembly, sanding and painting is needed, including a roll pattern of some kind on the main tube. Weight of this model currently stands at 4.35 oz.
 

Aeronerd

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A brief spike in temperatures and reduction of humidity allowed me to spray a first coat of paint on some of my parts.
View attachment 486041

View attachment 486042
A bit more assembly, sanding and painting is needed, including a roll pattern of some kind on the main tube. Weight of this model currently stands at 4.35 oz.
Looking really great! Just wondering what are the little holes in the end CR for?
 

Dotini

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Looking really great! Just wondering what are the little holes in the end CR for?
Thanks for your kind remark and your question.

I don't think those holes (in both fore and aft booster centering rings) are really totally mandatory, based on my limited experience with gapped staging. But they are found on the Estes Savage (IMO a very well designed rocket), and referred to by others as relieving ejection charge pressures that might separate the stages before ignition of the sustainer motor was achieved. I used a punch. Two or more larger holes in the side of the tube between the two motors might achieve the same purpose - at the cost of weakening the tube.
 
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Aeronerd

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Thanks for your kind remark and your question.

I don't think those holes (in both fore and aft booster centering rings) are really totally mandatory, based on my limited experience with gapped staging. But they are found on the Estes Savage (IMO a very well designed rocket), and referred to by others as relieving ejection charge pressures that might separate the stages before ignition of the sustainer motor was achieved. I used a punch. Two or more larger holes in the side of the tube between the two motors might achieve the same purpose - at the cost of weakening the tube.
This sounds like a better solution. Doesn't weaken the body tube.👍
 

BABAR

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Looking great as usual.

IMO gap staging should always include vents. Venting out the back is certainly more elegant, cosmetic, and aerodynamic.

HOWEVER if you vent out the back you need holes in both the forward and rear centering rings (I suspect you have forward holes, just not pictured) AND the booster motor mount needs to extend forward to with 1/8 to 1/4 inch from nozzle of the sustainer motor in launch config.

the extended motor mount guides the flame to the sustainer, the holes vent the pressure to prevent premature separation prior to sustainer ignition.

with your airfoiled PYLONS (@neil_w) should have an entertaining flight.
 
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