The "Venturi" Ring-Tail Thread

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Dotini

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The purpose of this thread is to post your designs, builds and flights of rockets with ring-tails entirely aft of the main tube and motor casing.

In my humble opinion, whether or not there is any Venturi effect possible with a ring tail rocket is open to question, and remains to be determined. I look forward to the investigations and answers, and will start by building two different ways (of many) to locate a ring behind the rocket while trying to eliminate as much conventional fin area as possible.

DSC00395.jpg

Left, BT-60 tube intended for 24mm motors fitted with beefy T-sections. On right, A BT-55 for 18mm motors with the beginnings of a filigree trapezoid trusswork of bamboo and birch.
 

lakeroadster

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The purpose of this thread is to post your designs, builds and flights of rockets with ring-tails entirely aft of the main tube and motor casing.

In my humble opinion, whether or not there is any Venturi effect possible with a ring tail rocket is open to question, and remains to be determined. I look forward to the investigations and answers, and will start by building two different ways (of many) to locate a ring behind the rocket while trying to eliminate as much conventional fin area as possible.

View attachment 481076
Left, BT-60 tube intended for 24mm motors fitted with beefy T-sections. On right, A BT-55 for 18mm motors with the beginnings of a filigree trapezoid trusswork of bamboo and birch.
Wooden Spars... Hmmm.... Maybe use some spar urethane to emphasize the wooden spars and do a WWI Spad XIII themed "Hat in the Ring" tribute?

Your innovative designs always spur my imagination.

1631280143455.png
1631280168333.png
 

Dotini

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Wooden Spars... Hmmm.... Maybe use some spar urethane to emphasize the wooden spars and do a WWI Spad XIII themed "Hat in the Ring" tribute?

Your innovative designs always spur my imagination.

View attachment 481176 View attachment 481177
Thanks for your generous comment! Although sometimes "innovation" feels like dancing on rotten ice.😰

DSC00398.jpg

Building model on left is slow and fussy, involving many tiny parts and slow drying glue.
Model on right builds quicker with a few big, simple parts assembled with CA. These basswood support fins probably could stand some more trimming, but not yet.
 

Dotini

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For both rockets, my plan is to locate the rings so that they will be well aligned to the tube when well aligned with the support members. I trimmed the length of the support members so the tips all touched a reference plane and a series of measurements determined that rotating the tube did not change its vertical relationship to the reference plane.
DSC00400.jpg

Next steps, additional finish operations to the fin units and manufacture the rings.
 
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Dotini

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A third way, perhaps my easiest and most straightforward way yet of locating a ring behind the motor.

DSC00401.jpg

These angles may yet be trimmed, and tabs will be added to space the ring out to the appropriate diameter.
In background, tube and cone in 2X Deep Blue and Marigold.
 

lakeroadster

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FWIW: Toe to Toe attachment to the cylindrical vessel (body tube) helps the angle tp resist torsion...

Toe to Toe Angle Legs.png
1631627345905.png
 
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lakeroadster

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A third way, perhaps my easiest and most straightforward way yet of locating a ring behind the motor.

View attachment 481735
These angles may yet be trimmed, and tabs will be added to space the ring out to the appropriate diameter.
In background, tube and cone in 2X Deep Blue and Marigold.
The struts really look classic 50's Sci-Fi.
 

Dotini

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FWIW: Toe to Toe attachment to the cylindrical vessel (body tube) helps the angle tp resist torsion...

View attachment 481752View attachment 481753
Past experience with D motors blowing the fins off of very light rockets has conditioned me to maximize the contact area between fin root and paper tube body. And I am actually considering "streamlining" one-side-only of the support tabs, inducing some torque (spin) into the rocket. The material properties of the angle stock I am using is actually quite springy (not at all brittle), but spin may rob some energy that may otherwise go towards altitude. So maybe not. However - if I do it - a high spin visibility paint scheme would be justified! :)

DSC00299.jpg

Experimental Magnus effect rocket spins at about 500 rpm - in descent only.
 
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Dotini

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Still slowly building 3 "Venturi" ring fin models. Change in the weather and attention to other matters has slowed me down somewhat. With rain and wind picking up, finding a launch window won't be any easier. I do have another hobby, classical fencing. I attend lessons, classes and occasional tournaments.

DSC00402.jpg
 

lakeroadster

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Still slowly building 3 "Venturi" ring fin models. Change in the weather and attention to other matters has slowed me down somewhat. With rain and wind picking up, finding a launch window won't be any easier. I do have another hobby, classical fencing. I attend lessons, classes and occasional tournaments.

View attachment 481952
A swashbuckler! One for all, all for one!
 

Dotini

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Finishing operations continue.
DSC00404.jpg

Model in front row has empennage reinforced with 3/32" Canadian birch dowels nested in the angles, and 24 lb linen skins on the basswood support fins. The life of a light rocket with D impulse is not an easy one.
 

Dotini

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The rockets need more work, but two have all their parts.
DSC00407.jpg

I will likely paint the rings in contrasting colors.
 

BABAR

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You may want to use a longer blast plate standoff to keep the nozzle and the (meltable) plastic ring away from the initial blow back exhaust plume.
 

Dotini

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Dotini's customary launch tower:
DSC00408.jpg


DSC00409.jpg

Launched numerous times (with device to support wires, not shown) and inside of ring remains pristine white.
Yes, those are lead weights around the rim of the ring. This is the most puzzling rocket I have ever built, and I don't understand it to this day.
 
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Dotini

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Not yet fully assembled, three new rockets show off their ring-tails, all behind the motor casing.

DSC00411.jpg

DSC00412.jpg

When completely finished and weather allows, I will launch, measure and compare the performance of these rockets to ringtails of similar size and weight which have their rings straddling the tube.
 

lakeroadster

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Not yet fully assembled, three new rockets show off their ring-tails, all behind the motor casing.

View attachment 482463
View attachment 482464
When completely finished and weather allows, I will launch, measure and compare the performance of these rockets to ringtails of similar size and weight which have their rings straddling the tube.
I don't want to be a Monday morning quarterback.... but do you think the rings are thick enough?
 

Dotini

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I don't want to be a Monday morning quarterback.... but do you think the rings are thick enough?
Sure, it's possible they are not thick enough.
But take a look at all the ring tail, tube fin and curvy fin rockets below that have made dozens of successful flights with the identical material. They may not be thick enough either. Still, they flew and came back.
DSC00414.jpg

Ring tail models front row, 5 on left have .020" PETG ring material.
Back row, all spinners. Four have curved fins of the same material, same thickness.
 
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Dotini

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If they flew and came back... undamaged... I'm pretty sure that is the definition of "thick enough".
None of my ring-tails have ever sustained damage to the empennage. But some of the horizontal recovery spinners have. They tend to land on the spinning (up to 500 rpm) fins. Sometimes a fin will shatter, sometimes it will come off at the root.
Also, I have have wondered about flutter. Never heard it. Never seen it. But it still may be there. So the science and engineering of ringtails - and ultra-thin plastic fins in general - is not at all settled, IMHO. So keep asking tough questions!
 

jqavins

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Hmm, flutter in ring tails. I've never heard of that. But I'm about as far from an expert as they come. I do know that 1. flutter is a high speed issue (where what "high" means depends on many factors) and B. ring tails are generally known to be high drag designs. So ring tails and high speed phenomena may not go together.
 

BABAR

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Part of the issue may be just how strong the struts are, and the number of struts. Normally I would think that four would be overkill, three would be enough. But with the thin material used for the rings, four struts instead of three is likely a significant boost in strength.

So have you come up with a consistently reliable (i.e., usually not broken) design for your Horizontal Spin birds?
 

Dotini

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So have you come up with a consistently reliable (i.e., usually not broken) design for your Horizontal Spin birds?
Yes, and very clearly so - and that would be Magnus X-4. It is the one with the smallest mass and smallest fins. It's had many flights and never had damage of any kind. And in terms of descent rate, it is the best performer in my fleet of horizontal spin recovery models. If I do say so myself, it is a great basic design that could do with more copies, better finish, and testing with a booster in the quest for a full one minute descent.
 

Dotini

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Hmm, flutter in ring tails. I've never heard of that. But I'm about as far from an expert as they come. I do know that 1. flutter is a high speed issue (where what "high" means depends on many factors) and B. ring tails are generally known to be high drag designs. So ring tails and high speed phenomena may not go together.
I fully intend (in due course) to use D motors on my latest ring tails. I haven't weighed them yet, but for sure they are fairly light for a BT-60 diameter. I expect my altimeter to report accelerations and speeds I've never measured before. I wonder, are there any established such records or reports for ring-tails?
 

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