BT-60 / C11 / Ring Fin: How High?

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Dotini

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Many people building typical 3FNC and 4FNC rockets have found sim programs helpful. As we get further from simple rocket designs, the sim programs, which are guesstimates to begin with, become less accurate. I never would have guessed that a launch lug is a MAJOR cause of drag, and while I may have guessed that an elliptical fin may be lowest drag in the subsonic speed range, a clipped delta is pretty close.

two possible questions here.

The first is whether your rockets outperform the expected altitudes from the simulation programs? Quite possibly true. I did not find that all together amazing.

however, if you are suggesting that ring fins are more efficient than planar fins I think that is something that would be great if it’s true, but it is not currently obvious. Then as I have mentioned many facts of rocket aerodynamics are not intuitively obvious to many of us mortal minded amateurs .

I am currently working on “Go With The Flow”, an air brake recovery rocket that theoretically should have infallible deployment, no pull bands, and self corrects with elastic brake/blade retention for early or late ejections .

but how about this? I will build a ring rocket to your specs, except I will initially build it with fins long enough to be stable without the ring. I will fly it 3 times with altimeter. I will round but not taper the forward and leading edges.

I will then cut off the excess outer hemispan of the fins and add the ring, so final rocket should be at your specs. Then weight the rocket, adjust if possible for any changes, and fly it again

would this be an acceptable test of your conjecture?


love to see you having fun, even cooler if you can turn rocket science on its ear!
I agree that sims are very valuable for many people. But it would seem that at least on one flight one of my rockets has grossly outperformed what the sim forecast. This possibly could be a freak motor, so I will need to do more tests to confirm that. But in no way am I claiming that ring fins are more efficient than planar fins - although they may be more durable and can fit into a smaller box. I do suggest that the present understanding and implementation of the ring fin and its performance envelope has not been sufficiently defined. I would greatly enjoy being a part of that conversation. But it takes two to have a conversation. Who else is building/testing ring fins on a rocket with ridiculously tiny support fins?

Regarding the clipped delta; that is my favorite "normal" fin. Question: is the reversed clipped delta just as good at those subsonic speed?

Regarding your building a rocket to my specs and testing it: Yes! This makes me very happy. At last somebody takes this seriously. And I have no stake in my conjecture. Most likely, the sim program is defective when it comes to ring fins. Eventually, some one will fix it. In the meantime, I will try to make improved iterations of the concept. As you know, I have made some ring tails combined with boat tails, which seemed to be high flyers themselves. So one path of testing will be down the boat tail or "torpedo" approach, and another will be the simpler one with no heavy and complex boat tail to deal with.
 

lakeroadster

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This much I have bolded may well be true. But it would be no fun me. I greatly enjoyed building and flying the rocket the way it is, which is unique. Nobody on Earth has one like it. That it makes the RockSim look silly is merely a bauble, a bonus pleasure. RockSim said my rocket would go up 131'. Yet, in the real world, it went up almost 500'.
I'm aware of that. Who ran the RockSim? Was the model accurate?

I know nothing about RockSim... but I am a novice with Open Rocket. I attempted to work with you to determine a good way to simulate ring fins in Open Rocket. And then you responded with...

You are saying that one anomalous launch doesn't mean anything. Especially if it violates a computer sim. Agreed! Now, what does your sim say is the altitude my model should reach with the ring installed?

How many flights significantly above that figure would it take to convince you and @neil_w that the cause is not an anomalous Estes motor? Would three suffice?

To paraphrase Ian Fleming; "Once is happenstance. Twice is coincidence. The third time it's enemy action."
In other words, if I can prove to you it's not defective motors, then you'll know there are bugs running loose on your sim.
So now we are trying to determine if your "conjecture that ring fins may reduce base drag" has any merit by building a rocket that proves that is correct / incorrect and your now saying you enjoy building a unique rocket and your back to bashing simulation software.

I think your rockets are unique and they look amazing, but in regard to the topic at hand... you keep moving the goal posts.

Good luck to you sir.
 

Dotini

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I'm aware of that. Who ran the RockSim? Was the model accurate?

I know nothing about RockSim... but I am a novice with Open Rocket. I attempted to work with you to determine a good way to simulate ring fins in Open Rocket. And then you responded with...



So now we are trying to determine if your "conjecture that ring fins may reduce base drag" has any merit by building a rocket that proves that is correct / incorrect and your now saying you enjoy building a unique rocket and your back to bashing simulation software.

I think your rockets are unique and they look amazing, but in regard to the topic at hand... you keep moving the goal posts.

Good luck to you sir.
I apologize for moving the goalposts. Yesterday was bit stressful for me, and I reacted defensively. I think you are a good guy and want to continue working with you. I, on the other hand, am an old Neo-Luddite with one foot in the grave and the other on a banana peel. If you choose to exit the conversation, I cannot blame you.
 

lakeroadster

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I apologize for moving the goalposts. Yesterday was bit stressful for me, and I reacted defensively. I think you are a good guy and want to continue working with you. I, on the other hand, am an old Neo-Luddite with one foot in the grave and the other on a banana peel. If you choose to exit the conversation, I cannot blame you.
No worries... Thanks for the reply. Now that I know your mettle...... we can continue. I tend to lead with my chin... and respond as if we were standing face to face.
 
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hcmbanjo

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I can’t recall the name of ANOTHER rocket at the moment (probably something from Odd’L rockets, maybe @hcmbanjo or @jadebox can correct me), but I think there was a tube fin rocket where the tubes were intentionally canted off kilter to induce spin on ascent. Why? Simply because it looked cool, it certainly did nothing to improve speed or altitude.
That Odd'l Rockets kit name was the PIPELINE. Three slightly canted tube fins at the base of the model.
The first test model I made had too much cant on the tubes. I had quickly glued the model together with CA.
I did spin at boost, maybe too fast and tore itself apart. The CA was brittle.
The next prototypes were assembled with wood glue with less cant angle on the tubes.

oddl-rockets-pipeline.jpg
 
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BABAR

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Let’s go with glass half full.

differences of opinion are often a good thing as it forces us to think inside the box, outside the box, and sometimes even reshape or even discard the box .

breaking new ground is also fun, although preferably not with the pointy end of the nose cone!
 

Dotini

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In breaking news, the Swedish Ghost Rocket has conclusively FAILED its swing test! No matter how I started the rocket out swinging, it either flew sideways or backwards. Whoopee, just what I intended. Those 4 little 0.7 high x 1" fins are insanely small. Later this afternoon, after the epoxy has set up on the ring tail I just installed, I will try it again.

DSC00322.jpg

Swedish Ghost Rocket
 
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lakeroadster

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In breaking news, the Swedish Ghost Rocket has conclusively FAILED its swing test! No matter how I started the rocket out swinging, it either flew sideways or backwards. Whoopee, just what I intended. Later this afternoon, after the epoxy has set up on the ring tail I just installed, I will try it again.

View attachment 4746586
Any chance of getting a video of the next swing test?
 

Dotini

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The morning launch session at Dahl field is concluded. Video, altimeter and Alti-Trak data were acquired on the 6th Observable and the new Swedish Ghost Rocket. All of that is being edited and transcribed onto a spreadsheet by my assistant, and will be available reasonably soon. Generally things were a strong success, but some problems and damage were encountered during a preliminary swing test of SGR at the field. These were overcome for the purposes of these early flights. Both rockets are stable in flight and descend safely.

Magnus X-4 was flown on its most powerful motor yet, and new records were set for altitude and descent duration. This will be reported in greater detail in the Horizontal Spin Recovery thread.
 
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Dotini

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Ring bent, cracked and split, broken off, slobbered over with black tape. Then flown.
DSC00323.jpg


DSC00324.jpg

SGR flew in this deplorable condition on its 2nd flight. The first flight had four 1x1 fins CA'd to the exterior of the ring to ensure stability after an aborted swing test broke the ring off entirely. The rocket also had its length increased and ballasted up to 6 full ounces all in the cause of stability. All these measure were likely unnecessary. I should have read this beforehand:
Despite all this butchery, the rocket still managed ~340'. More details to come after the video and altimeter data get in.
 
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jadebox

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That Odd'l Rockets kit name was the PIPELINE. Three slightly canted tube fins at the base of the model.
As you probably know, Odd'l Rockets also produced the Corkscrew which was also a tube-finned rocket with a unique flight pattern.
 

BABAR

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Ring bent, cracked and split, broken off, slobbered over with black tape. Then flown.
View attachment 474772

View attachment 474773
SGR flew in this deplorable condition on its 2nd flight. The first flight had four 1x1 fins CA'd to the exterior of the ring to ensure stability after an aborted swing test broke the ring off entirely. The rocket also had its length increased and ballasted up to 6 full ounces all in the cause of stability. All these measure were likely unnecessary. I should have read this beforehand:
Despite all this butchery, the rocket still managed ~340'. More details to come after the video and altimeter data get in.
Durability on these plastic rings may be a recurring issue.
Rear ejection may help.

the challenges with rear ejection are that space is at a premium.

as a trick, you can use a BT-5 as a chimney forward of your motor mount, go all the way to the nose cone,

stick a rolled up piece of aluminum can about four or five inches long inside the BT-5 just forward of the BT-20, otherwise the ejection charge will “roast” the smaller tube, yes, aluminum is flammable, but not in the amount of time it will get exposed to an ejection charge.

add a second centering ring at the forward end of the BT-5, fixed only to the BT-5 chimney. As a plus, if you need nose weight, add it to the BT-5 forward end and it will put less stress on the main airframe.

now instead of trying to stuff your chute between the BT-20 and the outer tube, you have a BT-5. It gives you much more space than you would think.

bonus: no wadding needed.

Warning: make sure nose cone is firmly taped, glued, screwed, or otherwise firmly fixed to body tube. Don’t ask me how I know this,

rocket comes down nose first, so saves your fin can. It’s less stress on the nose than you might think, because the motor, motor mount, chimney, and nose weight (if attached to chimney) are separated from the fin can, body, and nose cone by the shock cord. Rigged correctly, the motor pod lands first, with a reasonably long shock cord connecting them, the chute will slow down the rest of the rocket even more.
 

Dotini

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I flew the following birds this morning at a fun launch reunion session with 3 classmates from Roosevelt High School, class of 1967.
DSC00327.jpg

Left to right:
1) Rebuilt and revised Swedish Ghost Rocket, C11-3, guesstimated 500' altitude. Drifted 500' downrange in a 9 mph wind with a 15" chute with big center cutout. Pure vertical flight cut the sky in half.

2) Monogamist, C5-3, beautiful straight flight.

3) Kitbashed Bertha, C6-3, weathercocked noticeably. This underrated motor rated for 4.0 oz performed well on a 5.0 oz model.

4) Bigamist, B4-2, weathercocked noticeably.

Next week I will do more instrumented flights on the Swedish Ghost Rocket
 

BABAR

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I flew the following birds this morning at a fun launch reunion session with 3 classmates from Roosevelt High School, class of 1967.
View attachment 475088
Left to right:
1) Rebuilt and revised Swedish Ghost Rocket, C11-3, guesstimated 500' altitude. Drifted 500' downrange in a 9 mph wind with a 15" chute with big center cutout. Pure vertical flight cut the sky in half.

2) Monogamist, C5-3, beautiful straight flight.

3) Kitbashed Bertha, C6-3, weathercocked noticeably. This underrated motor rated for 4.0 oz performed well on a 5.0 oz model.

4) Bigamist, B4-2, weathercocked noticeably.

Next week I will do more instrumented flights on the Swedish Ghost Rocket
Congrats on the flights, especially the Ghost.

I am curious, if the C6-3 “weathercocked noticeably” why would you describe the motor as having “performed well”? I only say this because Estes, as demonstrated by “exceptions that prove the rule” that Estes does indeed produce great rockets, historically and also (although rarely) currently, haphazardly throws out designs recommended for C6-3 motors that are over their own recommended maximum weight for the motor and frequently weathercock severely in the lightest breeze.

I think the re-release of the C5-3 will fix most of these problems. Don’t get me wrong, the C6-3 is a great motor for rockets that ARE under the recommend maximum lift off weight and not extremely draggy. But while apparently Estes does think it is fine for THEM to build and sell rockets over their OWN recommended weight limits and still recommend the C6, I think it is a poor choice for scratch builds and mods to use the C6 for rockets over 4 oz (113 grams for the Aussies and Kiwis out there). People obviously DO get away with it, but Estes itself says it’s a no no.


sorrry, pet peeve of mine for the number of Estes designs that SHOULD have had a 24 mm mount with option to downsize, and instead were sold with 18mm mounts when Estes had no 18mm motors that could consistently and safely loft them (Venus Probe, Exoskell, MIRV, PortaPot Shot…….)

quoted from Estes CURRENT motor chart (attached)

Do not fly a rocket/engine combination whose lift-off weight exceeds the recommended maximum lift-off weight.
 

Dotini

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Weather permitting, we will be launching these three ring tail rockets at least three times each later this morning. We will carefully collect altimeter data on two of them, and get calculated altitude on the small one.
DSC00333.jpg

Left to right, Animist 2, Swedish Ghost Rocket, and 6th Observable.

Edit:
All nine flights successful, no damage, Data and video currently being analyzed. Report to come.
 
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Dotini

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Animist 2 made the following flights:
1) A8-3, height 146', descent rate 15 fps, weight 2.31 oz
2) B4-2, height 241' descent 12 fps, weight 2.48 oz
3) B6-4, height 309' descent rate 9 fps, weight 2.45 oz

Swedish Ghost Rocket made the following flights, all on C11-3, weight 5.48 oz:
1) height 296', descent rate 21 fps
2) height 300', descent rate 20 fps
3) height 307', descent rate 22 fps

6th Observable made the following flights, all on C11-3, weight 5.15 oz:
1) height 321', descent rate 15 fps
2) height 324', descent rate 16 fps
3) height 335', descent rate 13 fps
 

BABAR

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I have read that ring finned rockets tend to weathercock less. What were the winds at launch and did you notice anything? Did your friend have some more conventional rockets for comparison?
 

Dotini

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I have read that ring finned rockets tend to weathercock less. What were the winds at launch and did you notice anything? Did your friend have some more conventional rockets for comparison?
We have launched ring finned rockets in winds of 10 mph, winds in which conventionally finned rockets like the Big Bertha will weathercock. None of my ring finned rockets have shown the slightest interest in turning into the wind. They go straight up. My friend has an Estes Patriot kit, but he hasn't started it. I have the Monogamist, shown below, which is of roughly similar size and weight to my larger ringtails. I can launch it next week. But it has no payload bay, so altitude will be by calculation. And there is the almost-completed "BoxFin", also shown, which has a payload bay.
DSC00336.jpg

Left to right: Monogamist, Swedish Ghost Rocket, uncompleted Box Fin

DSC00338.jpg


I also have this kit bashed Estes E2X with payload bay.

DSC00339.jpg
 
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Dotini

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Another attempt at pushing the ring fin boundaries, the third in my Animist series.

DSC00345.jpg

Temporarily assembled, length 20". Weight currently 1.69 oz less recovery system, altimeter and motor. Goal is well under 4 oz at launch, so can use a variety of 18mm motors.
DSC00343.jpg

I tried to make the total fin area equivalent to a 3 fin BT-55 rocket with square fins 1.5x body diameter.

DSC00347.jpg

Components
 
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Dotini

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Hopefully, later this morning I will be flying these finned models in a comparison to the ringtails I documented in post #47 above. Though far from an exacting comparison, these have more or less similar weights and sizes. All are 18mm powered.

DSC00348.jpg

From left, "BoxFin", Monogamist, bashed E2XL, Bigamist.
 
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Dotini

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Results from today's test flights (all heights as determined by altimeter unless otherwise noted);
Conditions: gusty, 4-10 mph
Calculation baseline: 300'


"BoxFin"
1) B6-2, height 219', weight 4.01 oz
2) C6-3, height 418', weight 4.23 oz
3) scrubbed due to rough landing and fin damage on flight #2, landed on concrete skateboard facility on edge of field.

Monogamist
1) C5-3, height 345' calc, weight 5.13 oz
2) C5-3, height 357' calc, weight 5.13 oz; This rocket has a good finish but square fin edges.
3) scrubbed due to high wind gusts

Estes E2X(L)
1) B4-4, height 187', weight 2.78 oz
2) scrubbed due to body tube crumpling sustained weeks ago. Today's flight exhibited faulty behavior. Rocket to be rebuilt.

Bigamist
1) B4-4, height n/a, weathercocking due to not enough power and high wind.
2) B6-4, height 234' calc, weight 3.54 oz
3) C6-3, height 824' calc; weight 3.69 oz; This rocket has a very smooth finish, rounded fin edges but an oddly shaped nose cone, thought to be high drag.

Next week we can hopefully have a direct runoff between ringtails and finned rockets, hopefully including the new Animist 3.

Edit:
On a humorous and heartwarming note, we had a supervised group of about 20 toddlers intently watching our session. We ended up answering and explaining things to them during the session, and having them come up to the pad, see the rockets close-up afterwards, and more Q&A. On the way back to Ballard, Blair and I discussed the meaning and purpose of life, amongst climate change issues, etc.
 
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Mike Haberer

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Question: Currently a Jolly Logic Altimeter 2 is carried in an aftermarket pouch loosely located in the payload section. Does this device require additional cushioning, or could it do with less?
If the ALT2 is in a payload section not subjected to ejection gasses, the pouch likely isn't needed. You could likely get by with lightly crumpled wadding fore and aft of the ALT2. Don't forget to put vent holes in a location where the ALT2 can utilize them.
 

Dotini

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If the ALT2 is in a payload section not subjected to ejection gasses, the pouch likely isn't needed. You could likely get by with lightly crumpled wadding fore and aft of the ALT2. Don't forget to put vent holes in a location where the ALT2 can utilize them.
Thanks for that information. Currently I have a 1/4" vent hole somewhere in a ~3.5" payload section tube wherein the ALT2 is located. I'm assuming the vent hole anywhere in the chamber is sufficient, that the hole does not need to be located directly adjacent to the device, and that the pouch with its gaps does not interfere in any way.
 

Dotini

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Two new rockets for my testing fleet, Animist 3 and Mongoose Bash. Both include an altimeter section.
Final finish details are incomplete, but the models will hopefully fly tomorrow at Dahl field. (No booster will be used there.)
DSC00350.jpg

Mongoose Bash has only one component from the Estes Mongoose kit - the fin unit - which is installed backwards, such that the fins now become reversed clipped delta. Other advantages include fins now tapering in thickness from front to rear, and lower drag boat tail. I have gone ahead and rounded the front and rear edges of the fins. Booster section weighs only 0.25 oz. Estes literature suggests their Mongoose kit can attain an altitude of 1600'. With development, I expect my model to perhaps do better.
 
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lakeroadster

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Being a student of WWII.. that fin configuration... looks familiar... 🤔

Cool looking rocket.

Der Fuher Fin Configuration.png
 
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lakeroadster

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Swedish Ghost Rocket made the following flights, all on C11-3, weight 5.48 oz:
1) height 296', descent rate 21 fps
2) height 300', descent rate 20 fps
3) height 307', descent rate 22 fps
So I guess the Open Rocket analysis we worked together to develop in the end of July, using Bruce Levision's instructions, was pretty close after all? I mean, your recorded average apogee was 301 ft.... so within 5 feet is pretty darn great, right? And if I shave off 0.5 ounce off the rocket in the OR simulation, I'm betting we're spot on.

Very interesting... thanks for posting the data.

Modeled in Open Rocket using an Estes C11-3, BT-55, ring fin simulated per Bruce Levision's instructions, overall weight of 6 ounces and overall length of 30 inches. Surfaces specified as smooth.

Simulation shows an apogee of 296 feet with the ring fin. ( 780 ft on a D12-5 )
 
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Dotini

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So I guess the Open Rocket analysis we worked together to develop in the end of July, using Bruce Levision's instructions, was pretty close after all? I mean, your recorded average apogee was 301 ft.... so within 5 feet is pretty darn great, right? And if I shave off 0.5 ounce off the rocket in the OR simulation, I'm betting we're spot on.

Very interesting... thanks for posting the data.
Correct. Although the finish on the SGR is nothing more than Sharpie. No effort has been made to fill the spirals, smooth the surface or round the edges of the support fins.

Could I ask you to run your program on the Animist 3, please? Let me know what additional data you need.
 
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