How to build a tail nozzle (other than 3D-print)

Wildman Rocketry
eggtimer rocketry
the rocketry show
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
neil_w

neil_w

OpenRocketeer
TRF Supporter
Joined
Jul 14, 2015
Messages
16,686
Reaction score
11,503
Location
Northern NJ
Consider the following rocket:
upload_2019-7-20_21-46-14.png

That tail nozzle goes from BT55 to BT60 size, 1.25" long. How would I fabricate such a thing? I'm comfortable doing transitions in cardstock, but that thing is going to take the brunt of landing, and I am not sure if I can imagine a cardstock shroud surviving. Or could, it with sufficient reinforcement? If so, what sort of reinforcement?

I can't think of any other way to fabricate that thing other than 3D printing. At least, no way that I'm reasonably capable of. It needs to be light, this is LPR.

My hesitation with 3D printing is that I don't have a printer, and getting it printed will either be difficult, expensive, or both. I used to have good result with 3D Hubs but they changed their business model and it doesn't work for me anymore.

Any thoughts?
 
I make some of mine from doubled up cardstock transitions made from posterboard. Then soak with CA after the epoxy or white glue has cured.
 
I think a paper transition would be fine as long as the MMT goes all the way to the aft and there is an aft centering ring.

3D printing will likely be too heavy for LPR, especially with the weight all the way at the aft end.
 
Any chance the ketchup cups at Wendy’s would work?

At least they would be easily replaceable.
 
You could try using a cardboard yarn spool, some of those are conical. You could cut out a section of the correct size and then soak it with epoxy or CA for reinforcement. For a data point on 3D printing if you change your mind, the nozzle on my 24mm LauncherOne was printed out of PETG, and it held up pretty well.
 

Attachments

  • DSC_3762.JPG
    DSC_3762.JPG
    199.6 KB · Views: 113
neil_w said:
Consider the following rocket:
View attachment 388983

That tail nozzle goes from BT55 to BT60 size, 1.25" long. How would I fabricate such a thing? I'm comfortable doing transitions in cardstock, but that thing is going to take the brunt of landing, and I am not sure if I can imagine a cardstock shroud surviving. Or could, it with sufficient reinforcement? If so, what sort of reinforcement?

I can't think of any other way to fabricate that thing other than 3D printing. At least, no way that I'm reasonably capable of. It needs to be light, this is LPR.

My hesitation with 3D printing is that I don't have a printer, and getting it printed will either be difficult, expensive, or both. I used to have good result with 3D Hubs but they changed their business model and it doesn't work for me anymore.

Any thoughts?
Click to expand...

Make two or three conical transitions from thin cardboard or heavy card stock and stack them, laminating between with long-cure epoxy. The resulting structure will be lightweight(ish) and strong.

stackingcups.png

Somewhere on the forum there is a report of an experiment comparing the lateral crush strength of Estes tubes that had been soaked in Minwax wood hardener to tubes that had been soaked in thin CA to untreated tubes. IIRC, the conclusion was that the Wood hardener was the winner according to the test criteria.

While repairing a Viking that we found in the park, I tried soaking a section of BT20 tube in Wood Hardener. It shrank enough that I couldn't get a motor all the way in -- so I haven't tried it again.
 
The best looking nozzle like this that I have seen is from TRF member Jumpjet.

This is from his X-34 concept scale build, he never mentioned exactly what it was made from, if I had to guess it is a portion of blow mold nosecone with a centering ring glued to the front.

-OR-

If he didn’t find a piece to MacGyver in, I’d wager it’s layered card stock and fiberglass

Both seem like viable/ durable options

x-33-jpg.172600
 
You could turn a mold plug on a drill press and lay up a fiberglass nozzle on it. It won't be much (if any) heavier than a cardstock+resin cone, and should be a lot stronger. No 3D printing required. For less work, go find a suitable blow-molded nose cone and cut a section from it. Or use it as a pre-shaped form to make a glass one.
 
Ah, yes the old price/weight/durability conundrum.
Cardstock: lighter, least expensive, least durable. Durability can be increased by doubling up with Chris' "Supershroud" technique.
or saturating with thin CA.
or reinforcing with balsa ribs.
Balsa or 3D print: Need either a lathe or 3D printer. Bit of a learning curve with both. Or you can order one from a shop, one offs can be expensive.

I've made V2 boat tails by using cut off plastic nose cones but your dimensions suggest that finding an off the shelf product might be difficult.
 
Had a 20 oz Diet Coke this morning. Looking at the top of the bottle, looks like could be cut to fit.

How “pure” are you regarding “shelf appearance” vs “launch rod appearance”?

If you aren’t a purist, make the nozzle removable for flight.

Also, moving motor mount back so that the motor protrudes through the nozzle enough so motor takes the impact rather than nozzle. Can your design accommodate the extra nose weight or fin surface to counter the CG shift?
 
jlabrasca said:
Make two or three conical transitions from thin cardboard or heavy card stock and stack them, laminating between with long-cure epoxy. The resulting structure will be lightweight(ish) and strong.

Did that on my 4" '260 space booster' upscale, but I also filled the space between MMT and transition with expanding foam, then added the centering ring. Haven't finished the rocket yet.
Click to expand...
 
Rig an external harness and have it recover horizontally?

Of course, then you will break a fin.....,
 
Thank you all for an impressively helpful (and quick!) set of suggestions. Just a couple of quick followups:
jlabrasca said:
Make two or three conical transitions from thin cardboard or heavy card stock and stack them, laminating between with long-cure epoxy.
Click to expand...
I have made double shrouds before but never thought of laminating them with epoxy. That sounds interesting and worth some experimentation.

JohnCoker said:
I think a paper transition would be fine as long as the MMT goes all the way to the aft and there is an aft centering ring.
Click to expand...
The problem there is that it would force the motor to stick out the back; I'd rather it stay within the nozzle.

What I *could* do, though, is put the aft centering ring about 3/8" in from the back, which would support *most* of the nozzle and leave me with only a small bit at the very rear needing reinforcement. Then I could apply a layer of epoxy to that interior surface. Seems like it could work; I'll need to see if the epoxy adds enough strength.

As for cutting a nose cone: I would be happy with that solution if I could find the appropriate plastic nose cone at a reasonable price. I haven't looked yet, but will do so. It's not the easiest geometry to match up with a cheap commercial part, but also my measurements are not sacred, and I could modify as necessary.

Thanks again, I got some 'sperimenting to do.
 
neil_w said:
The problem there is that it would force the motor to stick out the back; I'd rather it stay within the nozzle.
Click to expand...
If the nozzle needs to withstand heat from the motor as well as landing forces, you're going to be even more limited in materials. To allow the motor to be flush with the aft end of the MMT/nozzle, you will need to either include a slot so the motor hook can move aside or use friction fit.
 
jlabrasca said:
Plastic erlenmeyer flasks
Click to expand...
I dunno, pretty pricey! ;)

Here's an updated version of what I was thinking:
upload_2019-7-22_10-14-14.png
Basically, I would recess the rear centering ring 3/8" (or 1/4", depending on my mood). Then reinforce the last bit of nozzle on the inside with either a 3D-printed piece or a stack of 5560 plywood centering rings, sanded to shape. The weight in either case should be negligible. I'm already looking at about an ounce of nose weight, just checked in OR and the nozzle support makes almost no difference. In fact, 3D-printing the whole thing would probably not make much of a difference, weight-wise, but I generally prefer to fabricate out of wood and paper when possible, just more fun for me.
 
JohnCoker said:
If the nozzle needs to withstand heat from the motor as well as landing forces....
Click to expand...

My tail cones slope the other way, but I've direct evidence that both aluminum foil tape and Rustoleum high heat paints will stand up pretty well to the exhaust from B and C impulse BP motors. No data yet on what a Q-jet will do (If I ever get to a launch this summer, I will try to test this).

I think we really should be warning neil_w about the Krushnic Effect <smile>
 
Last edited:
JohnCoker said:
If the nozzle needs to withstand heat from the motor as well as landing forces, you're going to be even more limited in materials. To allow the motor to be flush with the aft end of the MMT/nozzle, you will need to either include a slot so the motor hook can move aside or use friction fit.
Click to expand...

jlabrasca said:
I think we really should be warning neil_w about the Krushnic Effect <smile>
Click to expand...

The motor won't be significantly recessed (if at all) within the nozzle. Rather, I need the *motor mount tube* to be recessed, because the motor needs to stick out a bit (either 1/4" or 3/8") to be able to grab hold of it, and I don't want the motor sticking out behind the nozzle. Actually I'd probably prefer it to be ever so slightly recessed (at most 1/8"), which should keep Mr. Krushnic away, and also give very, very little exposure of the interior of the tail nozzle support to the heat of the motor. If I use a stack of plywood centering rings for the interior support (my current preferred implementation), a protective layer of epoxy should have me good to go.

Haven't finalized any of this, but the approach shown in my diagram above seems to give me a very robust landing support with a straightforward construction.
 
neil_w said:
I dunno, pretty pricey! ;)
Click to expand...

Have you ever (knowingly) ordered anything from aliexpress or Banngood? A $5 purchase sometimes shows up in less than a week, shipped free. Thats the kind of nonsense that is killing the planet, of course, but the fact that it can happen is amazing.

neil_w said:
Here's an updated version of what I was thinking:
View attachment 389096
Basically, I would recess the rear centering ring 3/8" (or 1/4", depending on my mood). ...
Click to expand...

After all the HPR builder's advice to glass it, or mill it from highly oriented CF, this is where somebody is supposed to say "you are overbuilding, do it the way I would do it!"

Seriously, though, an unsupported paper nozzle isn't going to be more fragile than the long fins on the Drifter or Skyhook, or the tail cone on a Sprint (yes, I am old)

neil_w said:
Whoa, crazy site. Love it!
Click to expand...

Their print catalogs are infamous. Google "nugatory contrivances" (very old)
 
Last edited:
jlabrasca said:
After all the HPR builder's advice to glass it, or mill it from highly oriented CF, this is where somebody is supposed to say "you are overbuilding, do it the way I would do it!"
Click to expand...
Hey man, overbuilding is my thang.

Seriously, though, an unsupported paper nozzle isn't going to be more fragile than the long fins on the Drifter or Skyhook, or the tail cone on a Sprint (yes, I am old)
Click to expand...
Well, the Sprint cone is supported by the end of the BT, and those other rockets are way lighter than this one will be. Possible you're right, but I'd have a hard time trusting it. Double-shrouds with 65lb cardstock still feel pretty delicate to me; I need to try with heavier cardstock and laminate with epoxy, and see how it feels. Benefit of plywood ring reinforcement is that I pretty much wouldn't have to worry about it, right up to and including standing the rocket up on the tail cone for storage/display. If I had a 3D printer I would definitely print that little support piece, but failing that I'm liking the stacked CR solution.

Until I change my mind, of course. ;)
 
I like Babar's rear eject idea. but with a pop pod instead of an aft separation point. You don't mention if this is a 24 or 18 mm mount.
Would make a difference in space available to wrap the recovery gear around the pod.
Rocket comes down nose first, hopefully sparing the tail nozzle from damage.
In fact, the fins would also protect the tail nozzle at landing.
 
kuririn said:
I like Babar's rear eject idea. but with a pop pod instead of an aft separation point. You don't mention if this is a 24 or 18 mm mount.
Would make a difference in space available to wrap the recovery gear around the pod.
Rocket comes down nose first, hopefully sparing the tail nozzle from damage.
In fact, the fins would also protect the tail nozzle at landing.
Click to expand...
This will be 24mm for sure; it'll be upwards of 6 oz with no motors.

Rear-eject is certainly possible (and would indeed protect the tail nozzle) but I just don't love the look of this one with rear eject. It would be BT50 inside BT55, pretty tight, and it would also concentrate more weight toward the rear. For this I think I'd rather just reinforce the tail and go with standard front eject.
 
Bonus points for testing fit with actual specified body tubes! :)

I'll keep that one in mind. At the moment I seem to be hell-bent on figuring out a way to make it work with reinforced cardstock, but if that doesn't work out I have some good alternatives here.

I notice in @hcmbanjo 's blog that he used a double-110lb shroud as a tail cone on his Saros build, with no additional support... I'm gonna get some 110lb stock tomorrow at Wally World and see what it's like. Everything I've done so far has been 65lb, and even double-layered it's clearly not sturdy enough to survive a landing.

I have another idea how to further reinforce the shroud without resorting to centering rings. I'll check back here with progress (or lack thereof).
 

Similar threads

J
3D Printing New to 3D printing
Replies
9
Views
580
cwbullet
cwbullet
eJar0k
Composite Nose Cone Mold from 3D-Printed Parts
Replies
0
Views
313
eJar0k
eJar0k
ljwilley
3D Printing 3d printed glider for rockets
Replies
0
Views
580
ljwilley
ljwilley
frogglicker
Scratch Build - Upscaled 3-in "Menace-3D"
Replies
2
Views
290
frogglicker
frogglicker
Blast it Tom!
3D Printing Please forgive me... But perhaps a little guidance?
2
Replies
36
Views
2K
Blast it Tom!
Blast it Tom!

Latest posts

Back
Top