Tau Zero Leonora Christine

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BigMacDaddy

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I posted about this in the Half Baked thread as well as the cluster thread but started to make progress tonight so decided it deserved its own thread.

I am going to try to make the Leonora Christine from the book Tau Zero (well an artists rendition of the spaceship from that book). https://en.wikipedia.org/wiki/Tau_Zero

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There was actually a 3D design out there but I decided to redesign from scratch and use that design as well as the pictures as inspiration. As mentioned elsewhere, I set this up to allow for an 8x mini-engine cluster + 24mm/18mm engine in the rear. Planning to use A10-0T engines for the cluster and made rear engine mount to handle 24mm or 18mm engines. That is a BT60 tube in the rear and a BT50 tube inside the big cone giving it structure (w/ 3D printed centering rings). I am pretty happy with the 3D design I came up with for the cluster setup but not as pleased with the rear engine design - may redo that.

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I also realized this was something I could actually simulate (more or less) in Open Rocket - been doing lots of ring tails lately so have not even bothered. None of the weights are accurate but it is great to get a sanity check on where CP is with that massive nose cone and other oddball elements. I was really surprised that OR puts the CP so far back in this design. Also nice to see what that mini engine cluster does to this. Those mini engines have a ton of power for a short duration so with 6 of them (it seems like OR maxes out at 6 engines in a cluster) it was going insanely fast off the rail. I dropped down to 4 engines (my thinking is that I can put 4 engines in bays and leave 4 empty bays to eject gas on engine burnout (so my cardstock nose cone does not explode). Still pretty fast off the rod -- 24.5m/s and going to a respectable 114m. Finally, found out is that a C6-3 seems like it will work well in the rear (double the thrust duration + 3 sec delay deploys chute around apogee).

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I will mess with OR more once I build this thing and see how much it really weighs.
 

Funkworks

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How will you make the nose cone? Can 3D printing make something so sharp and thin? I'm not a frequent flyer, but that's the thinnest I've seen. Awesome to see someone push that limit.
 
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BigMacDaddy

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How will you make the nose cone? Can 3D printing make something so sharp and thin? I'm not a frequent flyer, but that's the thinnest I've seen. Awesome to see someone push that limit.
You can print things quite sharp -- question is how durable they are. 3D prints are somewhat weak in the Z-axis direction so there would be a risk that this nose cone would break where it is narrow. Most of my nose cones are too sharp but I usually sand the tip off (or sometimes the pointed tip breaks off the first time the nose cone falls on the floor off my bench).

I am planning to make the main part of the cone out of 3D printed beveled / angled centering rings around a BT50 tube with card stock wrapped around it. The last foot or so would be 3D printed as a typical hollow long/thin nose cone. I may wrap the whole thing in paper with spaceship looking details on it. This would give a bit more strength to the tip but it still might break if it takes a hard landing.

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jqavins

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OK, I have four, no, make that five comments.
  1. Cool
  2. To my decidedly uncalibrated eyeball, your fins look a lot shorter than scale compared to the artist rendition.
  3. Would OR allow you to place two clusters? Two four-engine clusters with a 45° offset would be equivalent to the eight engines. I don't know if OR will do it.
  4. I know that some people use filler on their 3D printed parts to get a better smooth surface. Is there an epoxy that adheres to whichever plastic you'll be using? If so, using that as filler might also add considerable Z-axis strength by gluing the layers together.
  5. Cool!
 

BigMacDaddy

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OK, I have four, no, make that five comments.
  1. Cool
  2. To my decidedly uncalibrated eyeball, your fins look a lot shorter than scale compared to the artist rendition.
  3. Would OR allow you to place two clusters? Two four-engine clusters with a 45° offset would be equivalent to the eight engines. I don't know if OR will do it.
  4. I know that some people use filler on their 3D printed parts to get a better smooth surface. Is there an epoxy that adheres to whichever plastic you'll be using? If so, using that as filler might also add considerable Z-axis strength by gluing the layers together.
  5. Cool!
1. Thanks.
2. Depends on which picture you measure from. I measured from the top illustration (not the 3D rendering) since it was a 90 degree profile. I scaled everything to the rear cone being a BT60 at 41.655mm and got a total fin diameter of 162.5 and width of fins of 17. I will likely upscale to 100mm x 30mm per fin (around 240mm total diameter) to help make this stable (should not interfere with the look). The measurements scale the cone to about 773mm x 75mm (I setup close to that).
3. Yes, I think so - good idea.
4. Yes this is possible - also possible to put wood skewers inside or do other reinforcing tricks. Also possible to just glue the parts back together if they break on a hard landing.
5. Thanks!!!
 

BigMacDaddy

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Joe -- thanks for advice on two 4x clusters... It worked - and modeled an insane 434m/s max accelerator and over 32m/s off launch rod.

Need to get accurate final weight on this rocket but the combination of the 8x mini engines + 24mm motor mount in rear seems to create a bunch of interesting options. For example, I bet 2x mini engines + D engine would be a nice configuration (at least given the somewhat random weight estimated here).

Have not launched this obviously but, at least on paper, the mini engines seem to work as nice boosters to help get a rocket up to speed quickly and let a main engine carry it through launch.

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BigMacDaddy

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This is more or less what I have so far... I started printing -- the 8 mini-engine cluster / cone base and the centering rings to make the cone so far... I simplified the cluster mount portion from my original designs to keep weight down. I forgot the darn launch lug which needs to attach here since it is the fattest spot on rocket -- it is a 6 hour print so I do not think I will do it over, crazy glue it is.

I need to decide on how big to make the fins. In this 3D rending they are closer to scale from the 1st illustration I shared. I originally thought of making them larger but I think that may make it look less unique (looks obviously stable I guess).

I also need to decide where to split the rocket for ejection / recovery deploment. The BT60 tube is a bit too short. The model has a more or less continuous BT50 tube from the front of BT60 tube to about 2/3rds of way down the nose cone (this is isolated from the cluster mount in the middle). The rear engine is what will handle the ejection (I am sizing the mount for an E-engine but not sure if I will use 24mm or 18mm for launch).

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dhbarr

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That many a10's around a d12 are a kick in the pants. Note that if you have any ignition delays you're going to rock the launch rod pretty hard.
 

jqavins

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How are you venting the mini motors' ignition charges? Seems to me that the best way to fly this would be by pouring epoxy into the tops of the mini motors, but that violates the safety code, so no club launches. (Personally, I'm happily satisfied that plugging a motor this way is perfectly safe, but the code is the code.)

To dhbar's point, this would be a good rocket for rail buttons, but I can't imagine where you'd put them. This sounds whacky, but you might be best off with a custom shape fly-away rail guide. Perhaps this ridiculously crude sketch shows adequately what I mean.
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For recovery, I have only one idea and it may not be a good one. Whacky Wiggler style recovery. Use the ejection charge to separate at at least three places, with the pieces strung together. Separate at the bottom of the BT-60, the top of the BT-60 and/or the top of that ball below the cluster mounts, at the base or the printed cone, and perhaps between the cluster and the base of the hollow cone. That's three to five breaks, so you get four to six pieces. Just how you would pull this off in combination with venting the mini motors' ignition charges I have no clue.
 

BigMacDaddy

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Here are the rail buttons - one at bottom of cone and one at start of engine mount area (accidentally lined up with the fins but fixed that in a revision)... CG will be a bit forward of this but those are spots I could readily incorporate them into the design.

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For the mini engine venting my plan is to launch with just 2 or 4 engines in place. I have basically sealed off the area that the engines vent into with a PVC printed dome. So this should let the included engines vent out of the other engine holes that are unoccupied. If I was ever going to try to launch with all 8 mini engines I would maybe purchase the plugged A10-PT engines.
 

neil_w

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This whole thing looks great, awesome use of 3D-printing. Ring placement for the conical section needs to be quite precise, I imagine. Hope to see some good build pics as you apply the skins.

If you're going to fly without the plugged engines, you can consider using A3-4Ts, which will give a bit less of a spikey thrust curve (unless you need the thrust to get that whole thing moving, of course). Also the A10s lately *seem* to be a bit CATO-prone, although I don't know what that would affect the plugged motors equally.
 

jqavins

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Excellent plans, both on the venting and the rail buttons. Oh, and I forgot that there are A10-PT engines. I think you wrote that you'd use A10-0s, and I was just going from that. I clearly was overthinking things (again). Just one more overthought caution: check for clearance between the fins and the launch rail. With a three of four fin design there's be no issue. But with eight, check. It's a lot easier to make those rail button stand-offs longer now than later.

Since the A10s vent through unused motor mounts, you might consider using A10-3s to get a little smoke.
 

BigMacDaddy

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Here is current progress...

No card-stock nosecone yet and no fins but have dry-fit everything and looks like it will work well (assuming I can get my NC straight). I need to practice rolling this nose cone to see if I can get the centering rings perfectly positioned before gluing them to the center body tube. I saw someone else's post recently and realized I have not used fin mounting jigs in a long time since I am always slotting 3D printed parts for fins.

This looks like a lance and I might sword fight with it if it does not fly. It is frighteningly sharp but I will bet the point breaks off of before I finish the build so not too worried about getting stabbed by it if parachute does not deploy.

I decided to have the rear engine eject the entire nose cone so hope this works for the chute deployment. CG is a bit forward of the bottom of nose cone (above the cluster engine setup) w/ 4 mini engines in but no rear engine. This makes me optimistic that I can get this stable without too much nose weight.

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BigMacDaddy

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Ok, finally had the courage to approach this nose cone and build the rocket. I cut a piece of BT50 tube that was the distance that should be between each of the cone support centering rings and used that to help with spacing. Made things pretty easy but needed to be sure the spacer did not get glued to my rocket.

I need advice about how to smooth out / finish off the nose cone. Poster-board got a bit bent / squished here and there as I was mounting it, there is also the area where the poster-board overlaps itself, and variation at transition of poster-board to 3D printed nose cone (also a place where I had to cut and re-glue a part of the cone since poster board did not mount to rings perfectly. I was thinking I would prime, wood fill, sand, etc.. to try to smooth things out as best I can and then wrap the whole thing with one more layer of paper (ideally something pre-printed with space ship design). Instead should I just wrap the whole thing with another layer of poster-board (might cover imperfections a bit better but would be heavier)?

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p.s., tested this and it fits without fins rubbing on my 2020 rail.
 

neil_w

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That is a thing of beauty.

I had hoped for some more build pics and/or written details showing how you skinned the body. Looks like it came out great.
 

BigMacDaddy

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That is a thing of beauty.

I had hoped for some more build pics and/or written details showing how you skinned the body. Looks like it came out great.
Thanks very much!

I actually had no clue what I was doing when making the poster board nose cone so did not think to document it. I found a template online that let me create a cone with top and bottom of certain radius (however, it was too large for my project -- maybe I printed it wrong or something). I glued the edge of that funnel-shaped poster board cut-out to each of the centering rings with CA glue. Let it dry, then put some glue around 1/4 of the way further around and tried to roll the cone around the poster board to that point, let it dry, repeat. Somehow the poster board wound up being loose on the smaller end so I had to slice it and reapply glue to fix it down better.

Not sure how to smooth things out now (or how to do it better if I re-printed the 3D parts and built a new nose cone).
 

neil_w

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So you ended up doing it with just the one wrap piece? Rolling a long skinny piece like that is (in my experience) miserably difficult.
 

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I have used CWF on boat tails made out of poster board

Rocket does look phenomenal!

-Bob
 

jqavins

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Carpenters' Wood Filler. From Elmers. Lots of people swear by it, and for good reason. Thin it just a little bit with water. How much? People "to the consistency of peanut butter" but I think they must have different peanut butter than I do, 'cause I think it matches that description right out of the tube. So, well, a little. Just a little.
 

BigMacDaddy

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I went ahead and bought some plugged mini engines. I was worried about the mini engine cluster popping my nose cone off. I think I will try launching with just a D12-3 engine first so all I have to worry about is the total rocket stability. Then will try with 4x A10-PT engine cluster + C6-3 maybe...
 

Bruiser

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Like Joe wrote, carpenter's wood filler. I use Elmer's and it's the color changing type. Very useful stuff for rocket building. Here's a pic of some on the boat tail of my Lockheed Peregrine build

Peregrine Boat Tail.jpg


-Bob
 

BigMacDaddy

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Thanks everyone -- will definitely try wood filler, I have used it with good results on lots of other projects just never anything as large or flexible as this. I will try to prime, fill, sand, and then cover the whole thing with a final coat of pre-printed standard weight office paper (using spray mount to mount final coat of paper to hopefully smooth rocket tube). Wish me luck!
 

neil_w

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I look forward to seeing this thing in paint (or whatever finish).

I have one more question that's been bugging me: do you have any plans to ensure that those fins survive a landing? They seem... vulnerable.
 

BigMacDaddy

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I look forward to seeing this thing in paint (or whatever finish).

I have one more question that's been bugging me: do you have any plans to ensure that those fins survive a landing? They seem... vulnerable.
I am planning to load a parachute in there -- maybe even a pilot chute + main chute since it will need to be pulled from the nose cone. However, had not planned on additional protection beyond that. The fins are 2mm plywood so pretty sturdy but if one breaks I can replace.
 

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Try hardening up the shell with CA before using the CWF filler. That should stiffen it up quite a bit.
Looks beautiful!
-Ken
 
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