2.63" (formerly 3" Mailing) Tube Printed Rocket

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True enough... and yeah, I think its too flexible.

I used a profile generator tool for the NACA based shapes in OnShape.
 
It’s good to know I’m not the only one printing fins with too much flex. I changed to NylonX to try to fix the issue—still too flexible in my opinion.
 
Yeah, haven't tried NylonX yet... not sure my printer can handle it based on recommended temps.

I did just do another test print (well thats what I call it since I got a dimension wrong) where I printed with the layers parallel to the root chord. Came out really well.

I also switched from the NACA M1 to the M2 shape, so its a tad thicker.

Its definitely much more rigid

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That works! Can you put a big fillet at the base of it? My 3D printed fins are usually 10mm wide at the base, 5mm at the tip, and at LEAST a 10mm radius fillet at the root, so it's more like 30mm wide at the root. They come out stiffer than the .093" G10 fins I had on my L2 rocket.
 
That leading edge layer print looks good. The ribs can be puttied or epoxy filled and sanded for smoothness.

How fast is this going to go?
 
Well, that did not go well. Layer shift, had same thing happen on my first attempt at this. Upright and second shorter span attempts didn't layer shift. So something about when its moving to the edges of the x-axis - also apparently came unstuck. Might try it at along the z-axis.
 

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Ah, yeah, I think this one is like 8mm at the base/mount joint. Looks like its only a 5mm filet.

Thankfully its mostly parameter driven, so I can adjust the model pretty easily.

That works! Can you put a big fillet at the base of it? My 3D printed fins are usually 10mm wide at the base, 5mm at the tip, and at LEAST a 10mm radius fillet at the root, so it's more like 30mm wide at the root. They come out stiffer than the .093" G10 fins I had on my L2 rocket.
 
That leading edge layer print looks good. The ribs can be puttied or epoxy filled and sanded for smoothness.

How fast is this going to go?

No idea... figure its gonna have a high quotient of drag, kinda heavy. Shooting for Gs and Hs. So prelim sim model says around ~500ft/s^2 with a H128
 
No idea... figure its gonna have a high quotient of drag, kinda heavy. Shooting for Gs and Hs. So prelim sim model says around ~500ft/s^2 with a H128

That's not bad at all. Should see minimal aero deflection.

Ground hit forces will likely be your issue. Bring it down soft!
 
I've never had issues with 3D printed fins snapping on impact, but what I do is print a decently sized tail cone that also does motor retention. I had one come down on a rock....took a bite out of the tail cone, but the fins were fine.
 
And I "borrowed" Dustin's idea with the tail cone/motor retention too. :) 'sides if a fin break, print another one, unbolt the broken one, bolt in new one - fly again!
 
Well, worked.... Shot is a little weird, certainly not as grainy the lighting seem to make it. Pretty darn stiff, certainly can't flex it like could with the layers following the root.

PXL_20210130_043529764.jpgPXL_20210130_043542627.jpg
 
Decided to scale down slightly to a LOC 2.63" due to overall weight and wanting to meet certain performance envelope parameters (min. 50f/s off a 72" rail, between 1000-3000', and from G to I motors) due to field sizes, etc.

The motor and fin mount.

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And a shot with a fin.

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Screenshots from OpenRocket

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And the performance simulations...

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These may change as I had to approximate the weight of the nose cone.

Technically I have about 84" on the rail with the rail button being where it is, so speeds coming off my rail will be a tad higher. I prefer to shoot lower because if I launch at other events that have existing rails then that becomes an issue. It does impact motor selection a bit too, i.e. on shorter rails the Gs may be out.
 
This looks great! I really like method for fin mounting. My design for something similar is much more complex.

Do you have any tricks for knowing where to drill the holes for fin attachment through the airframe besides "measure really carefully?"
 
Thanks. Plan is to print a guide. Although I've also been trying to see how I can roll this out so I can just print it on paper as a wrap; haven't figured that one out.

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Here is the Onshape link... its constantly changing, so mileage may vary. :) And its public, so it can be used in the "free" OnShape version (which is what I use).

https://cad.onshape.com/documents/9...c62a6c867bece3d11f/e/dd0909b35cc525e5032c1046

I'm sure someone who is CAD expert could probably put these together much more efficiently, etc. but they are working for me now as a neophyte.
 
Hard to see, but I was able to figure out (with planes and geometry) how to angle the attachment holes so that they are perpendicular to the curved surface. Other than better sitting on the fit attachment without needing to flatten areas, it also should mean there is some more mechanical 'grip' as the bolts are angled in.

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Printed out motor mount, after some adjustments, prints, readjustments, etc. Decided to go with 3mm screw hardware; think it should be sufficient.

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Checking the inserts that they fit, align, etc.

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Applied some heat with a specific 3mm soldering tip for inserts. Turns out ok, but definitely have to pay attention as there really is no 'redo'

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Made some more progress.. was able to get a drill hole guide printed.

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Then it all lined up as it got tied down with 3mm bolts.

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From the top
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Now to get the other two fins printed, the brass inserts inserted, so the fins then can be mounted.
 
Have plans to just print the attachment blocks, and use plywood or fiberglass plates for the actual fins. This would work a bit different in that there would be a tab that would go through the tube into the motor mount, then the attachments mounts would be screwed into the fin and through the body tube to the motor mount.

Not really sure its a great replacement for just epoxing the fins in, but hey... no fun to only build rockets just one way!
 
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