More Half-Baked Designs Thread

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BigMacDaddy

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One remedy I've contemplated is to use a much longer, more gradual boat tail that is also smaller at the aft end. But making swept pylons will be easier, I think.
I read that as "go big or go home" ;)

I decided to do longer boat tail and nose cone. Cut 7.5cm off the bottom of an 18" tube and used that as the boat tail. Put 1oz of weight in nose cone. Result comes in at 31" long (CG 14" from front) and 120 grams w/ engine but no chute / shock chord (will try to keep those mounted forward to push CG up a bit more).

Think it will fly stable? Swing test was stable...

1634781381321.jpeg


Can almost guarantee that the ring tail will get some charring... Any flame resistant paint? Other options to protect interior of ring tail?

1634781396569.jpeg
 
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neil_w

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I decided to do longer boat tail and nose cone. Cut 7.5cm off the bottom of an 18" tube and used that as the boat tail. Put 1oz of weight in nose cone. Result comes in at 31" long (CG 14" from front) and 120 grams w/ engine but no chute / shock chord (will try to keep those mounted forward to push CG up a bit more). Think it will fly stable?
My guess is no, although it's truly a guess; I really don't know.

I'm a little curious if the ring is going to constrain the exhaust plume and reduce thrust, in a Krushnic-like way. But the open area between the motor nozzle and the ring means that... well once again I really don't know. Might be totally off base with this one.

Can almost guarantee that the ring tail will get some charring... Any flame resistant paint? Other options to protect interior of ring tail?
Well, you can get heat-resistant paint, which I used once to paint a fireplace grate with. Getting the spray into the tube would be interesting. Line it with foil, or foil tape? That will add some weight to the tail...

I suspect no matter what you do you're going to get some charring in there.
 

BigMacDaddy

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My guess is no, although it's truly a guess; I really don't know.

I'm a little curious if the ring is going to constrain the exhaust plume and reduce thrust, in a Krushnic-like way. But the open area between the motor nozzle and the ring means that... well once again I really don't know. Might be totally off base with this one.


Well, you can get heat-resistant paint, which I used once to paint a fireplace grate with. Getting the spray into the tube would be interesting. Line it with foil, or foil tape? That will add some weight to the tail...

I suspect no matter what you do you're going to get some charring in there.
I cheated and edited last comment while you were posting...

I did do a swing test and it was stable (as best I can swing this relatively large rocket around my living room).

I am fine with some charring but do not want to ring tail to catch on fire (partly since that would not help the stability but also because of the fire hazard of burning rocket coming down. Might need to do a static test or be sure to launch in a really swampy field after a rain storm...
 
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Dotini

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I have built and flown a very few models that have the motor in the front and a long ring or aft body tube closely behind the motor. Using the regular Estes starter kit igniter and launch controller, it becomes a fiddly and annoying matter to actually get the rocket wired up and launched.
 

jqavins

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I flat out don't know if it will be stable. I won't even guess. I really, really want it to be stable, because I want to build one.

Remember that I swing tested mine pretty hard, and it passed, and still was not stable off the rail. So launch it from a greater distance than you otherwise would for the engine size.

Static testing for fire risk sounds like a good idea. Your two reasons for being concerned about it are synergistic. It would come down on fire all the sooner if it's also unstable due to losing it tail.

Is there a launch lug that I don't see, or will you be using FARGs?

I think mine along these lines will have a shorter tube for the ring. I'll try the trailing edge of the ring about where your is, but the length of the ring about a third to a half of what you've got.
 

BigMacDaddy

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I have built and flown a very few models that have the motor in the front and a long ring or aft body tube closely behind the motor. Using the regular Estes starter kit igniter and launch controller, it becomes a fiddly and annoying matter to actually get the rocket wired up and launched.
Yeah, I was thinking about the annoyance of loading engine and igniter - likely more of an experiment and less of a common flyer.

Is there a launch lug that I don't see, or will you be using FARGs?
Thanks for reminding me to put one on before I prime it. I might use a Makerbeam rail lug to give it 1.5m of stable rail to get up to speed before release.
 

6inchmonster

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gotta get the big plastic fins and stick-like "airframe" onto this lawn statue someday..
 

BigMacDaddy

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I will post updates on the finless BT60 ringtail rocket once I do more testing and/or launch it... Moving on to next half-baked concept / build...

Tau Zero Leonora Christine - https://en.wikipedia.org/wiki/Tau_Zero

I saw someone post a picture of this somewhere, could not remember the name, then randomly came across the picture, which I had saved, in my rocket folder (not sure I should be impressed that I saved the picture or skeptical of my own sanity since I did not trust myself to have saved it so instead spent time looking around the internet for cone shaped space ships)...

Considering scaling this for 8x mini A10-3T engine cluster (inspired by the discussion of "Why clusters?") at the Ion Drive location in the pictures. That would make the rear tube portion a BT60 tube w/ the whole rocket coming in at just over 1 meter.

So my questions - How to make that massive cone??? If I 3D print the whole thing the cone will weigh around 150-200grams on its own.

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jqavins

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For the nose cone: card stock. Place multiple centering rings in graduated sizes along the length of a central body tube, BT-20 or even BT-5. Wrap the rings with card stock that's precut to the needed flattened shape (concentric circular arcs). That only makes a transition section, getting you most of the way up to the tip. Finish it off with a 3D printed cone that fits into that central tube. I've never done these, but have read through the procedure several time in other people's build threads, and I'll probably need to do it sooner or later. @neil_w does it a lot

Cluster: I trust you are aware of the issue that arises when clustered motors are spread apart from one another. 'Nuff said.

Oh, and one more thing: Cool rocket!
 

BigMacDaddy

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For the nose cone: card stock. Place multiple centering rings in graduated sizes along the length of a central body tube, BT-20 or even BT-5. Wrap the rings with card stock that's precut to the needed flattened shape (concentric circular arcs). That only makes a transition section, getting you most of the way up to the tip. Finish it off with a 3D printed cone that fits into that central tube. I've never done these, but have read through the procedure several time in other people's build threads, and I'll probably need to do it sooner or later. @neil_w does it a lot

Cluster: I trust you are aware of the issue that arises when clustered motors are spread apart from one another. 'Nuff said.

Oh, and one more thing: Cool rocket!
Thank you!

I have never done a cluster with more than 2 engine so I may not be conscious of all the issues or appreciate the difficulties doing this. I was planning to angle the mini engines out from rocket around 5 degrees and was hoping that since these are up on the body of rocket that this would help with stability and maybe correct some inconsistencies in thrust / firing.

My first sanity check was to calculate that this would cost $12.34 per launch and would have 680 grams of maximum lift. The mini engines have a short thrust duration which may not be ideal but 18mm engines would look too big I think. Maybe I could play with doing 4x18mm engines instead or, as I think about this more, maybe I can put a C5-3 engine in the rear (labeled "Gas Laser" in picture) to almost work like a sustainer since it would have more than 2x the thrust duration of the mini engines.

Do you think I need vertical frame elements to hold the card stock or are rings every few inches with center BT50 tube sufficient?
1634909989633.png

Ok back to student feedback...
 

Bill S

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Can almost guarantee that the ring tail will get some charring... Any flame resistant paint? Other options to protect interior of ring tail?
I've used some actual aluminum duct tape (basically thick aluminum foil with a good adhesive on it) in front of certain motor mounts to minimize the chances of the Hibachi Effect. So far, it seems to have worked out well. Maybe attach some of that tape on the inside of the rear ring and see if it helps? It does add some weight so be aware of that.
 

BigMacDaddy

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I've used some actual aluminum duct tape (basically thick aluminum foil with a good adhesive on it) in front of certain motor mounts to minimize the chances of the Hibachi Effect. So far, it seems to have worked out well. Maybe attach some of that tape on the inside of the rear ring and see if it helps? It does add some weight so be aware of that.
Thank you, good idea -- I have a roll of that tape for doing HVAC work...
 

jqavins

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OK, on multiple engines: each engine exerts some pitch/yaw torque, and those torques are supposed to cancel out due to the symmetry of the cluster. But engines differ from one to the next, even if they light exactly simultaneously, so the torques don't cancel perfectly; there is a little residual torque. The further each engine is from the rocket's center line the greater the torque is that it exerts. And thus, the greater the residual torque when they are all added together.

These are not very far apart and may very well be OK. Fin tip engine pods look really cool, but are a very bad idea. Your design is not that radical.

Canting the engines helps because each one's thrust line comes closer to the rocket's CG, and that reduced each one's torque. Aiming them right at the CG isn't really possible since the CG moves as the propellant burns away, and it would likely mean a whole lot of can't angle. Every little bit helps, a little bit.

As for the stringers on the long cone, all I can say is that it's not what I've seen done by others. The card stock should be stiff enough not to need them, as I understand it. And I'd recommend getting better qualified advice than mine, both on that question and on the number of rings needed along the way. I think your picture has more than you'll need.
 
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jqavins

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There's a whole forum section devoted to card stock models that you might go to looking for advice.
 

Jeff Lassahn

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You don't need stringers or other complicated stuff for strength.
A good way of thinking about it is that a cone or tube made by gluing a couple of layers of cardstock together is almost but not quite as strong as a professionally made spiral wound paper tube. So any construction techniques you'd be comfortable with if you were using a body tube of that size are probably OK for a cardstock cone.

About protecting the tail from charring, I don't know exactly what the limits are but you probably need less protection than you think you do. Boost gliders routinely have large fragile structures behind the engine really close to the thrust line, and they don't cover the whole thing with armor plating and asbestos.
 

BigMacDaddy

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You don't need stringers or other complicated stuff for strength.
A good way of thinking about it is that a cone or tube made by gluing a couple of layers of cardstock together is almost but not quite as strong as a professionally made spiral wound paper tube. So any construction techniques you'd be comfortable with if you were using a body tube of that size are probably OK for a cardstock cone.

About protecting the tail from charring, I don't know exactly what the limits are but you probably need less protection than you think you do. Boost gliders routinely have large fragile structures behind the engine really close to the thrust line, and they don't cover the whole thing with armor plating and asbestos.
Thanks very much... Good points... I was contemplating doing a cardstock layer and then a final paper layer pre-printed with spaceship details using spray mount to hold things together.

I will stop stripping the pipes in my basement for useful asbestos...

I did find some interesting how-to guides about making fire-resistant paper (basically soaking it with hot water w/ lots of dissolved borax if I recall correctly). I was thinking that it might be possible to make a fire-resistant body tubes for this type of application if you treated the paper and then wrapped your own tube.

p.s., while trying to spin test this rocket the nose cone popped off and hit a lamp and the tip full of weight broke off and shot off to space all on its own... spent some time this morning looking for the loose nose cone piece among my wife's knitting supplies and then gluing it back on the nose cone.
 

BigMacDaddy

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I decided to include a centering ring to keep the parachute forward on the minimalistic finless rocket above. It seems stable when parachute is forward so wanted to be sure to keep it that way... (what are these called?)

Not sure there are any better or worse designs for these but this is what I came up with... I assume I can stuff the dog barf through that with a long dowel....

1635164296988.png
 
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jqavins

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Is that for the monodiameter ring tail? Whatever it's for, I would not put dog barf under it. I think the barf would most likely jam up below the wheel and block the ejection gas. I'd coat the wheel with stove paint or engine paint (except on the gluing edge, of course) and keep the dog barf above it.
 

neil_w

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Not sure there are any better or worse designs for these but this is what I came up with... I assume I can stuff the dog barf through that with a long dowel....
There is no reason to stuff the dog barf through, and I would say that you don't want to do it. It can very happily sit on top of the ring. Leave room accordingly. Oh, and coat the hell out of that thing with epoxy so it doesn't melt. Or do it in wood instead, which I think would be safer.
I think the barf would most likely jam up below the wheel and block the ejection gas.
FWIW: I have had flights (admittedly not many) where the dog barf has stayed in the BT but ejection worked just fine. I'm not sure that the barf really blocks the ejection gas.

Anyway, I wholeheartedly agree that you do not want the barf below that ring.
 

BigMacDaddy

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Is that for the monodiameter ring tail? Whatever it's for, I would not put dog barf under it. I think the barf would most likely jam up below the wheel and block the ejection gas. I'd coat the wheel with stove paint or engine paint (except on the gluing edge, of course) and keep the dog barf above it.
Wow -- "monodiameter ring tail" makes the rocket sound so much cooler ;)

Yes, this is an internal block to keep the parachute forward in that model. This is around 8-10" below the nose cone since that leaves plenty of room to pack an 18" parachute in the BT60 tube and keep CG forward. I have never worried much about parachutes placement so this is my first time doing this so totally open to feedback (actually I rarely really know what I am doing, so even if my posts sound confident I am always open to feedback).

If I drop some dog barf down below this would that stop the ejection from pushing the nose cone off? It would keep the dog barf inside the rocket I guess but should still have plenty of room for air to move forward, push the heavy nose off, and pull the parachute out along with shock chord. I have often still had dog barf remaining in longer models in the past so did not think this would be too bad (and once I remove engine I can just shake it out the bottom or pull out with long tweezers).
 

BigMacDaddy

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There is no reason to stuff the dog barf through, and I would say that you don't want to do it. It can very happily sit on top of the ring. Leave room accordingly. Oh, and coat the hell out of that thing with epoxy so it doesn't melt. Or do it in wood instead, which I think would be safer.

FWIW: I have had flights (admittedly not many) where the dog barf has stayed in the BT but ejection worked just fine. I'm not sure that the barf really blocks the ejection gas.

Anyway, I wholeheartedly agree that you do not want the barf below that ring.
I may not have left enough room but if I can I will put dog barf on top of the ring...

It is printed in ABS so should do ok with the ejection gasses (it is almost a foot away from the engine).
 

neil_w

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I may not have left enough room but if I can I will put dog barf on top of the ring...

It is printed in ABS so should do ok with the ejection gasses (it is almost a foot away from the engine).
Let us know how it goes!
 

jqavins

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I too have had dog bark left in after a successful deployment. I suspect that the wad of barf is acting like a piston, and if it is blocked too soon by the wagon wheel that it won't do that either. And I could be all wet. But since there doesn't seem to be a reason to find out (i.e. to put the dog barf below) let's not find out.

Unless you really want to. In which case, I offer the following for consideration: add a coupler joint below the wagon wheel, one you can keep closed with removable plastic rivets. Take the rivets out and open the lower section, load dog bark, close it up and rivet it. Prep the parachute above as usual.

Let us know how it goes!
Yeah, that.
 

boatgeek

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I too have had dog bark left in after a successful deployment. I suspect that the wad of barf is acting like a piston, and if it is blocked too soon by the wagon wheel that it won't do that either. And I could be all wet. But since there doesn't seem to be a reason to find out (i.e. to put the dog barf below) let's not find out.

Unless you really want to. In which case, I offer the following for consideration: add a coupler joint below the wagon wheel, one you can keep closed with removable plastic rivets. Take the rivets out and open the lower section, load dog bark, close it up and rivet it. Prep the parachute above as usual.

Yeah, that.
I've definitely had dog barf not eject. A couple of my rockets have had a steady buildup of dog barf in the bottom. I suspect that whether it forms a piston or not depends on how big the body tube is relative to the motor mount and how much (if at all) you pack the dog barf. Personally, I wouldn't worry about the wagon wheel with loose dog barf just laid in the bottom of the tube. YMMV, of course.
 

BigMacDaddy

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I really need to get out there and test launch some of these rockets... But this weekend is Halloween so kids will not want to spend time away from candy gathering to launch rockets (and I really need help to carry all the gear and take pictures / videos)... Anyway, on to next half-baked idea...

Rob Goring posted this inspirational picture in FB and called my attention to it. Someone modeled a version of it in OR and it seemed close to stable. Not sure is motors etc.. were in there but I figured I would play with a bit late last night before going to bed and a bit early this morning. I re-interpreted the picture a bit with the rear wings as ring-wings. My [likely aerodynamically naïve] thought it that this would make this more stable since there was a shortage of fins in one dimension. I also expanded the top pod and added a bottom pod to try to help a bit with yaw stability. I jammed 8x mini engines and a 24mm center engine in there for good measure (looks like there are actually 12 smaller shrouds in the back but 8 was the most I could fit). What do you guys think? Viable with a boat-load of nose weight and maybe rear-ejection pod?

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jqavins

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Yeah, what he said. To be a little more specific, I think making the aft part of the wings into that "squashed ring tail" was a good move, but the forward part that remains flat constitutes large canards on a short rocket; that's going to be really tough. And that on top of the fact that flying cones are not stable to begin with unless they rely on base drag. (Put a nose cone alone into OR and look at where the CP is; it's not pretty.)

The yaw stability pods should probably be shorter, coming from the base up only as high as the front edge of the ring.

The first thing I would do in your shoes to get rid of the mini motor cluster. Just use faux nozzle bells. That'll take a lot of mass out of the bottom.

I hope you can make it work, 'cause it's definitely cool looking.
 
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