Bluefin Tuba 3"

With paint and decals on, next to its little brother.

Ari.

That looks neat. Nice job!!!

iter said:

Thank you for your encouragement Kit.My approach to landing damage control is right-sizing chutes :=)

As far as Mach, I doubt a tube fin can punch though. OTOH, it's unclear to me that one must disintegrate when it gets close. The 1.5" BFT survived a J510 which simmed to Mach 1.33.

Ari.

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I read somewhere that speeds approaching mach, the tube fins start acting like closed cylinders rather than open ended tubes. The tube fin fragments usually stay attached to the body tube but the tubes themselves basically explode.

o1d_dude said:

I read somewhere that speeds approaching mach, the tube fins start acting like closed cylinders rather than open ended tubes. The tube fin fragments usually stay attached to the body tube but the tubes themselves basically explode.

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Closed cylinders don't explode. Tube fins that explode don't behave like closed cylinders, they behave like fins that explode.

Ari.

iter said:

Closed cylinders don't explode. Tube fins that explode don't behave like closed cylinders, they behave like fins that explode.

Ari.

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You're probably right about my faulty description. I am only a certified rocket monkey (monkey see/monkey do LOL!) and not well versed in aerodynamic theory. The tube fins definitely appear to explode. Over pressure condition inside the tube? I don't know.

I don't understand the aerodynamics of tube fins, but for my money their practicality has been demonstrated in a spectacular way with Ari's flights this weekend. G through M motors in the same airframe is an elegant and conclusive proof!

I would say that "appears" to act like a closed cylinder is partly correct. Looking at drag patterns, etc, you get a shock wave in a V formation going back from the leading edge. In tube fins, this shock wave does not seem to have a chance to collapse and as speeds get higher, it seems that the pressure inside the tube fin increases. I believe that this is due to the fact that, on a tube fin, draw the V around the whole of the leading edge and you get a point in the center of the tube fin where all these meet. I am tending to lean towards a theory where that point in the middle starts to form a static high pressure zone. As the speed increases, the pressure gets higher and higher, and airflow starts to stack in front of the zone. At some point, the tube will explode outwards (in theory). This 'theory' does seem to fit the aftermath damage we see.


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EDIT

"shock wave" may not be the best of descriptions, but i think you get my idea

Salvage-1 said:

This 'theory' does seem to fit the aftermath damage we see.

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I have seen exactly one tube fin rocket with exploding fins, in real life or on the internet. You seem to be drawing on a wider body of knowledge. If you can share it with us, I feel we would all benefit.

There is no doubt that fins (tubular or otherwise) experience aerodynamic forces that can lead to structural failure. The subject of my experimentation with this rocket is to find how well can tube fins withstand these forces. Even in this thread, a number of posters recommend that I reinforce fins with internal couplers, employ different adhesives (or in larger amounts) and otherwise encourage me to beef up the fins. Literature is very sparse on people's experience with tube fins on larger-impulse motors. So I set out to make some.

Ari.

Saturday, August 2 2014 my girlfriend Amy and I roll onto the Black Rock playa with BFT3 and a trunk full of motors. When people ask me about my plans for the day, I tell the truth: I plan to fly the alphabet. I'm starting at G and going up a letter every flight, until I either run out of motors or break the rocket.

The almost completely calm winds are encouraging.

Time: 09:58
Motor: G80
Altitude: 536'
Result: successful flight and safe recovery.

View attachment g80.txt

I notice people smiling amicably. Ari schlepped all the way out to the desert to fly toy rockets on G's and H's.

Time: 10:45
Motor: H115 Dark Matter
Altitude: 887'
Result: successful flight and safe recovery







View attachment h115.txt

I discover that 5G38mm case I have prepped for the I flight refuses to fit in my 38mm adapter. Adapter tube is long enough, but something interferes with the motor in the last 5/16" of the way and makes it impossible to screw on the retainer cap. Excess glue from anchor point installation had dripped on the inside of the adapter BT. I borrow a 1/4" rod from the low-power pad stash and scrape the inside of the adapter. It feels embarrassing not to have tested the fit at home, seeing especially as quick turnarounds are a design goal on this rocket.

Time: 11:39
Motor: I350 Smoky Sam
Altitude: 3004'
Result: successful flight and safe recovery







View attachment i350.txt

Reloading a full I for a baby J in the same 5g38mm case is a breeze now that adapter is clear of extra glue. Another problem pops up however. Actual altitudes from my flights exceed sims by a fairly consistent factor of 1.5x. This makes visual tracking more of a challenge and recoveries longer as we move into driving, rather than walking, distances.

Time: 12:32
Motor: J316 Pink
Altitude: 3357'
Result: successful flight and safe recovery







View attachment j316.txt

I figure out the sim discrepancy. I had assumed standard meteorological conditions, but density altitude is lower in the desert. Air is thinner, drag is lower. I'm looking uncomfortably at sim altitudes of upcoming flights, multiplying them by 1.5x in my mind. I had experimented with a GPS tracker on BFT3's nose cone, but left it out to fit a larger altimeter battery. I regret this decision now. Suddenly, I realize a third outcome is possible: I can run out of motors, I can break the rocket, or I can lose it.

Amy is getting tired, and we rush through recovery without a photo.

People jokingly ask if I plan to fly an L in BFT. I point to the prepped 75mm 3G case sitting on my table. Their faces turn serious. A gentleman tells me he had planed to build a rocket like this all along, but never got around to it.

Time: 13:19
Motor: K695 Red
Altitude: 5741'
Result: successful flight and safe recovery





View attachment k695.txt

RSO moves my flights to the away pads now. L motor exceeds 200' distance from "midpower" pads. Because K motors are midpower at Black Rock.

Time: 14:43
Motor: L645 Green
Altitude: 10,040'
Result: successful flight and safe recovery







View attachment l645.txt

The big one: 75mm 5-grain moonburner M. Extrapolating from existing sims and previous flights of the day, it is clear that in case of a successful flight I am going to lose the rocket without some kind of radio tracking. Tony Alcocer generously lends me his tracker and offers to operate the receiver.

Time: 16:55
Motor: M650 White
Altitude: 14,273'
Result: successful flight and safe recovery







View attachment m650.txt

So there you have it. A rocket that has flown on 7 impulse classes, G to M. It burned a total of 12,467 Ns in one day. This is a rocket that flies on L0, L1, L2 and L3 motors. This is a rocket I can fly at Moffett with a 160 Ns impulse limit, and and one that I can fly on an M in the desert. This is a rocket that you can build for the cost of 2, 3"x48" blue tubes (2x $30) and a LOC plastic nose cone ($20).

All together now, just the liftoff photos.

A beautiful presentation to cap off a fantastic achievement; bravo!

Iter, I'm building another 4" tube fin . What length fins do you do ? I have seen 1-1.5 times diameter is best . Mine is 36" tall 4" air frame with one caliber for fins 4", Will go with 54mm and be able to adapt down also I built the nose cone out of foam and glassed .

JohnCoker said:

A beautiful presentation to cap off a fantastic achievement; bravo!

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Thank you John. I was hoping to make it a cliffhanger, but you beat me to a spoiler in post #36!

Thank you for your support in the desert, including letting me share your ez-up. Prepping all this stuff in the sun would have been that much more grueling. Thank you again!

Ari.

chris m said:

Iter, I'm building another 4" tube fin . What length fins do you do ? I have seen 1-1.5 times diameter is best . Mine is 36" tall 4" air frame with one caliber for fins 4", Will go with 54mm and be able to adapt down also I built the nose cone out of foam and glassed .

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I usually make mine "a little longer than their diameter," basically same as your "1-1.5 diameter," not very scientific. I have no intuition and have done no experiments on how fin length affects flight characteristics. I imagine that making them too short would make them fragile, but have little concrete knowledge beyond that.

Ari.

Just fantastic.

Could you give some details on your motor retention and adapters?

Yes but don't go wild like I did " super evil minion " was a 4" air frame and mis reading but 14" tube fins it was a 5.5 ' rocket weight was 6lbs with I 280 DM after 300-400 feet it hit it's wall and came back down. Rebuilding those fins were like air breaks .

That M flight was beautiful! I really wish i had my camera out for that. Easily one of the prettiest flights of Aeronaut.

Congrats! Flying the alphabet in one launch is no small feat.

Alex

Congrats Ari! That's quite the sequence of flights and a very difficult thing to pull off in one day. Fantastic!

iter said:

So there you have it. A rocket that has flown on 7 impulse classes, G to M. It burned a total of 12,467 Ns in one day. This is a rocket that flies on L0, L1, L2 and L3 motors. This is a rocket I can fly at Moffett with a 160 Ns impulse limit, and and one that I can fly on an M in the desert. This is a rocket that you can build for the cost of 2, 3"x48" blue tubes (2x $30) and a LOC plastic nose cone ($20).

All together now, just the liftoff photos.

Click to expand...

Very impressive, from the materials used, to the style of rocket, to launching 1 rocket on such a wide variety of engines. The only thing I noticed missing was your little helper.

WOW congrats, , do you used TieBond to glue the fins with this one ?

Awesome job on the rocket/flights, and a very enjoyable thread too! *Sigh* I guess I have ANOTHER project that I will need to start planning. Tube fins are really cool, and bluetube does sound like the proper material for such a build. Threads like this are probably responsible for at least 50% of most rocketry companies' profits.

That is amazing on a number of levels. Congrats.

Rrwjr said:

Very impressive, from the materials used, to the style of rocket, to launching 1 rocket on such a wide variety of engines. The only thing I noticed missing was your little helper.

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It might be a couple of years before Leah is old enough to enjoy the desert. It's a long drive, and once you get there, if you get bored of rockets there are few distractions.

Area66 said:

WOW congrats, , do you used TieBond to glue the fins with this one ?

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Yes. Yellow glue throughout. I use crown and molding glue for fillets between tube fins, though I'm unclear on how necessary it is. The thing to do would be to build another one jut like this but without the fillets and see how it does on the same motors.

Ari.

Glad I was able to witness the M flight in person. Honestly one of the most impressive flights of the event.