Tubularity: 4" tube-fin breakapart rocket

[iter]

I'm building a 4" Blue Tube breakaway rocket with tube fins. We're having a lot of fun upscaling a 1" Breakaway to a 2.6" Castaway. The next obvious step is a 4-incher.

I apparently buy the last 3 of LOC's 4" Blue Tube deals. That's 12 feet of BT. I cut it up into 11" sections (the longer one is the fin can center). 6 sections for the fuselage, 6 sections for fins. All thiese bits of tube inspire the name Tubularity.

Breakaways consist of multiple sections that break away at deployment and descend as a train of sections. Tubularity is single-deploy, motor eject, and recovers without a parachute. The goal is a simple L2-capable design that can fly with a minimum of fuss. I choose tubular fins as most resilient to occasional hard landings.

One-before-last photo: 2.6" Castaway onboard view post-deployment.
Last photo, right to left: 1" Breakaway, 2.6" Castaway, 4" Tubularity, 1" Neon (with tube fins).

Ari.

 

[iter]

Of course I have help cutting the tubes.

Ari.

 

[CarVac]

Does it rely on momentum to pull all of the sections apart?

I imagined a hilarious rocket once which would break apart into ten segments, but none interconnected and all with parachutes tuned to provide precisely the same descent rates.

Also, what motor are you planning on using?

 

[MasonH]

I thought cert flights required active recovery?

 

[Pantherjon]

I thought cert flights required active recovery?

They do..Wouldn't be hard to put a small chute in the top or middle section to satisfy that requirement..

Estes used to make the Wacky Wiggler that did this sort of recovery..Flew nice on B6-4's but wasn't so good one a C6-5-too much power and it folded like an accordion!:rofl:

 

[jadebox]

I thought cert flights required active recovery?

Ari didn't say anything about certification, but "break-apart" is definitely a form of active recovery since it dramatically changes the aerodynamics of the rocket.

But ... I'm not sure that it's enough for a rocket this large. My YouBee is a 5 1/2" diameter upscale of the Odd'l Rockets Break Away. It uses "break-apart" recovery at apogee, but later deploys a parachute. The "break apart" part of the flight worked better than I had expected - with the rocket falling almost perfectly horizontal. But, I'm not sure it falls slow enough to be considered safe.

-- Roger

 

[MasonH]

Maybe make the coupler in the top section an av bay?

 

[jadebox]

Maybe make the coupler in the top section an av bay?

My YouBee has an electronics bay as part of the second section from the top. It contains the altimeter and a pod for holding a camera. The upper section holds the main parachute. The nose cone ejects to deploy the 'chute. I attached a small drogue 'chute near the top setion just in case the thing decided to fall nose-first and from a stable train. But, after three flights, I'm sure that the drogue isn't needed. The pieces flop each other around enough that no individual piece has a chance to fall stable.

-- Roger

 

[iter]

Does it rely on momentum to pull all of the sections apart?

I imagined a hilarious rocket once which would break apart into ten segments, but none interconnected and all with parachutes tuned to provide precisely the same descent rates.

Also, what motor are you planning on using?

BP charge ejects the nose cone, NC pulls the next section behind it, etc. I works very well in my 1" and 2.6" versions, and in Roger's 5.5". I o expect to test it on the ground and post slow motion video here.

The MIRV idea has occurred to me, but I have enough trouble finding one rocket after a flight :=) Unless I put a tracker on each segment, I can see the rocket getting shorter every flight!

That's a 38mm 6-grain case in that picture. I have an I297 waiting for Tubularity.

Ari.

 

[iter]

Ari didn't say anything about certification, but "break-apart" is definitely a form of active recovery since it dramatically changes the aerodynamics of the rocket.

But ... I'm not sure that it's enough for a rocket this large. My YouBee is a 5 1/2" diameter upscale of the Odd'l Rockets Break Away. It uses "break-apart" recovery at apogee, but later deploys a parachute. The "break apart" part of the flight worked better than I had expected - with the rocket falling almost perfectly horizontal. But, I'm not sure it falls slow enough to be considered safe.

-- Roger

Don't you love the lawyers, Roger? Of course breakapart satisfies the active recovery requirement. It even satisfies it with BP! On the Vulcan glider, I had to argue with my certification team's "but there's no explosion at deployment."

How large a rocket one can safely recover on breakapart alone is an open question. It works fine on my 2.6" version, but on your 5.5 YouBee, you clearly feel that it needs DD. There's one way to find out!

As you're noticing, even big breakaways stay very horizontal on their descent. Imagine you drop a 10" piece of 4" tube from a couple thousand feet and it lands horizontally. It probably survives without damage. Rockets break when they land nose-first, when they land on a pointy end of a fin, or when long fuselages fold. Tubularity avoids every one of these scenarios. I choose tube fins to make the impact softer. Also, zipper is unlikely :=)

It's a little hard for me to estimate descent rate--existing software neglects my use case :=) If I find that it lands too hot, the design's modularity make it very easy to add a main in one of the sections. I'm thinking of the bottom section rather then top, as the fin can is the heaviest section, and I prefer for it to land last, when the weight of all other sections is on the ground already.

Ari.

 

[iter]

They do..Wouldn't be hard to put a small chute in the top or middle section to satisfy that requirement..

Estes used to make the Wacky Wiggler that did this sort of recovery..Flew nice on B6-4's but wasn't so good one a C6-5-too much power and it folded like an accordion!:rofl:

I have no experience with the original, but in my experience the reproduction does phenomenally on C6: https://www.jonrocket.com/index.php...id=322&zenid=e34abab54576b8f6470412d5d117b477

Ari.

 

[iter]

Ready to fly, but without any paint or motor, the rocket comes in at 125 ounces and 85"

Ari.

 

[iter]

I have two redundant recovery harnesses running the length of the rocket. In addition to redundancy in case of breaks, it makes for a straighter pull with less sideways force--and lower probability of zipper.

I make 10 1"x5" attachment point anchors out of 3/4" plywood. I shape them to fit the inside radius of my BT and cut a shallow groove to increase glue surface area. Using #8 t-nuts and screw, I attach mirror-hanging loops to the anchors. I then glue the anchors in place using titebond. I'm doing this entire build with yellow glue. The only places where I use epoxy are where I'm attaching metal: eyebolts on the fincan and the AeroPac retainer on the bottom. After titebond dries, I add a another layer on the outside to form a kind of fillet. I'm curious to see how effective this technique is.

All 12 pieces of BT ready to go. "BT Overcast."

Ari.

 

[iter]

I assemble the fincan in two steps: First, I assemble the pieces I can assemble flat on the bench, two pairs of fins and the central trio. I also glue on the 1/2" launch lugs--they fit perfectly between the tubes. You know the 1/2" rod that every club has and no one ever uses? Well it's getting some use this time. I put in the MMT and CRS at this stage--it's easier to handle a single tube than a 7-tube bundle. Everything is yellow glue.

Once the pairs are dry, I dry-fit the sub-assemblies and mark tangent points to put glue lines on. Tubularity has a 38mm MMT. If I'm happy with how it flies and decide it needs bigger motors, I can build another fin can for it. I like modularity :=)

Ari.

 

[iter]

And now a word from our crazy-ideas department, with apologies to Boris Katan.

A 4" tube exactly fits a 12-cluster of 24mm motors--or one central 38mm AP and a ring of 9, 24mm BPs.

We resume our normal programming now.

Ari.

 

[iter]

Here are a couple of ground deployment tests. It's disconcerting how much BP it takes to separate these sections.

It's very humid here (I scrapped plans to launch this morning on account of the rain). I wonder if humidity is affecting blue tube's dimensional stability.

Ari.

[video=youtube;Gix9Ze3V_zE]https://www.youtube.com/watch?v=Gix9Ze3V_zE[/video]

 

[AHansom]

Here are a couple of ground deployment tests. It's disconcerting how much BP it takes to separate these sections.

It's very humid here (I scrapped plans to launch this morning on account of the rain). I wonder if humidity is affecting blue tube's dimensional stability.

Ari.

]

Cool looking rocket!!! I think ground testing this type of setup and compairng it to a real flight will be hard to do. In a real flight the rocket should be in a close to weightless state at apogee deployment and the nosecone and fincan will be able to accelrate away from each other. Maybe even a little extra weight in the nose and fincan to help pull the chain apart? Do you have a idea of when and where you think you will try again? Good luck.

 

[iter]

Thank you. I'm thinking the same thing about the difference about air and ground. But the amount of BP it takes is disconcerting--it's many times more than norm, and it's producing bruises and mini-zippers on the tubes.

Next launch around here is Dec 1, though the weather there is also uncertain.

Ari.

 

[AHansom]

Thank you. I'm thinking the same thing about the difference about air and ground. But the amount of BP it takes is disconcerting--it's many times more than norm, and it's producing bruises and mini-zippers on the tubes.

Next launch around here is Dec 1, though the weather there is also uncertain.

Ari.

I ran some guessing #'s through a ejection charge calculator. To presurize 65" inches of 4"tube to 15 PSI it takes 6.3 grams of BP. I think that once one section seperates the internal preasure is gone and the rest of the seperating will rely on the mass of the nosecone and fincan to pull them apart. I know what you mean about damaging your rocket, I think trasporting and ground testing can cause far more damage than flying.

 

[o1d_dude]

I think you've hit the nail on the head. Once the nose cone blows, there is no overpressure and unless the inertia of the nose cone is sufficient to pull out the remaining sections, nothing will happen.

All is not lost if this proves to be the case. Your fallback position can be to permanently join the tube sections and use standard parachute deploy.

I like tube fin rockets.

 

[jadebox]

Here are a couple of ground deployment tests. It's disconcerting how much BP it takes to separate these sections.

Oh, yeah. My YouBee requires about 9 grams. I make the charge by wrapping the BP in plastic wrap. It forms about a golf ball size bundle. And ... be careful, it makes quite a bang (and a mess) when it accidently goes off right beside you.

-- Roger

 

[jadebox]

I think you've hit the nail on the head. Once the nose cone blows, there is no overpressure and unless the inertia of the nose cone is sufficient to pull out the remaining sections, nothing will happen.

With my YouBee, all the sections appear to separate in the air without the shock cords becoming taught. The ejection charge sets all the pieces moving in relation to each other well enough and inertia keeps them moving so that the nose cone and fin sections don't have to pull the rest apart. During the ground test, the middle sections didn't completely separate, but came close. I think that's because it was laying on it's side.

-- Roger

 

[iter]

Your fallback position can be to permanently join the tube sections and use standard parachute deploy.

Now now Kit. What fun would that be.

After I discovered the ejection challenge, and before the weather rained me out of today's launch, I did consider tying a 36" parachute and letting gravity and drag work it out to pull remaining sections apart.

Now that today's launch didn't happen, I have two weeks until next Snow Ranch to work this out. You're coming, right?

Ari.

 

[iter]

Oh, yeah. My YouBee requires about 9 grams. I make the charge by wrapping the BP in plastic wrap. It forms about a golf ball size bundle. And ... be careful, it makes quite a bang (and a mess) when it accidently goes off right beside you.

-- Roger

But... but... yours is... bigger!

I did fire a 10g load, and it separated everything but the bottom section (no video on that one). It also tore one of the cords (I have two redundant trains). And boy is the rocket now full of soot and gunk! And it hasn't even flown yet.

Ari.

 

[iter]

In the other threads people are asking if I'm plugging the MMT. Why yes I am. I tend to build motor analogues for ground tests--a piece of dowel the same length and diameter as the motor, with a 1/4" piece of MMT as the thrust ring. I drill holes through the dowel and make a groove for igniter leads. In this photo, you can see the motor analog after a test, with remains of the BP container still on the igniter leads.

In addition to making a more realistic test, this dummy also allows me to test my motor retention (aeropac in this case). I'm happy to say that with the larger-than-usual charges and all the other challenges that are coming up, motor retention is functioning perfectly.

Ari.

 

[terryg]

I am not sure if you are going to be able to reliably ground test this deployment system anyway. Use a reasonable charge size and test fly it. Increase the charge as needed and test out if the parachute can be used to reliably pull the sections apart after it deploys.

 

[iter]

I'm unhappy about how this project is coming. The basic problem is that my sections have gone very far out of round and have extraordinary amount of friction. This is in stark contrast with my smaller breakaparts which work flawlessly. This may be a BT issue, or my build issue, or humidity issue. Whatever it is is making me unhappy. One solution is to redo the whole thing (maybe leave the fincan) in paper tube rather than Blue Tube and see if it makes a difference.

My stop-gap solution is to put a bulkhead in the middle of the middle section. I now plan to use two deployment charges, one on each side of the bulkhead. This decreases the volume each charge needs to pressurize and reduces the number of couplers each charge needs to separate. This bulkhead requires electronic ignition. Tubularity now has an A/V bay and electronic deploy. I have an altimeter in the mail, but it is unlikely to arrive in time for Snow Ranch this weekend. The current setup uses R/C deployment. Tubularity sims to 2,000' with largest motor that fits, which I expect to be visible form the ground.

The A/V bay is very simple and lacks a traditional sled. Since the diameter is large, I can lay everything flat on the bottom bulkhead. The bay is just over an inch tall. Top sections attach to original metal loops on the side of the BT. Bottom sections attach to the 3" eyebolt that holds two bulkheads together. To increase glue area to hold the bulkhead against the pull of lower sections, I glue in a section of tube under the top bulkhead (just visible in first photo). This tube defines the depth of A/V bay and serves as a stop against which lower bulkhead rests.

A 1/4" phono jack serves as an arming switch (and gratuitous static port) with the obligatory "remove before flight" keychain through the plug.

Ari.

 

[jadebox]

The A/V bay is very simple and lacks a traditional sled. Since the diameter is large, I can lay everything flat on the bottom bulkhead.

If the altimeter that you ordered uses an accelerometer, be sure to mount it in the correct orientation.

-- Roger

 

[jadebox]

Odd ... my previous reply (which I entered previously to my previous message) seems to have disappeared.

I commented that your out-of-round solution is similar to an upgrade I'm making to the YouBee to solve another problem. And, your fix might help you avoid a similar problem.

During one flight of the YouBee, one of the shock cords caught on something - most likely one of the shock cord mounts - and created, ironically, a big shock when the ejection charge fired. I caused a big mess.

After that, I tried to avoid the problem by accordian-folding the shock cords and holding the pleated sections together with masking tape. But, on the last flight, I think the tape came lose early and one of the shock cords caught again. This caused the main 'chute to deploy at apogee and it caused the 'chute and one of the shock cords to get tangled.

My fix is to add stuffer tubes in the middle sections. This will give the shock cords something to sit on (and nothing to catch on if they happen to fall down a stuffer tube). And, it will reduce the volume that needs to be pressurized by the ejection charge.

-- Roger

 

[iter]

Yes, stuffer tubes.

If you look at the first post in this thread, my original open-rocket file has them, and 2x centering rings per section. My shock cords are short (3' between sections) and tangling has yet to become as issue in any of my testing (of course Tobularity is yet to fly).

I have even discussed setting up separate charges, one per section. Difficulty is in sequencing them correctly, or wires disconnect before charges go off. One idea is to iniate a QM electronically, and have it run the length of the rocket, with BP charges in every section. This would be an interesting apogee event to see from the ground!

Thank you for your comment about orientation. The altimeter I'm waiting for is baro only, and in any case unlikely to arrive here in time. I plan to fly it this Saturday, and it either survives or doesn't, and may never fly again either way. R/C components care nothing about orientation, naturally. If I need to, I can extend the A/V bay to the coupler's full length, 6". All it takes is another "stuffer" tube to hold it off.

Ari.