Supersonic 3D printed nosecone?

Building a cirrus dart type rocket. 38mm min diameter.

I was thinking about 3D printing the nosecone in PLA. Would anyone know how hot the nosecone tip would get if it momentarily reached Mach 2? 38mm min diameter on a I or J should reach 10-12K ft at Mach 1.5-2

Is this a good idea. I'd prefer not to recover a melted blob...

Thanks

At that speed it's not just heat, it's aero-erosion to some degree as well along with the usual aero-loading.

That said, I don't know enough about the physical properties of PLA to make the call.

My guess is that would be a poor material choice for that velocity. Especially if it is hollow and not reinforced.

Greg

Sport Rocketry May/June has an article on trying to go 2000mph with 38mm and 54mm rockets. Used LOC tubing for the 38 and
un-reinforced bluetube for the 54. Failed both times. Nice article explaining the problems and my hats off to Mike Caplinger for making the attempts and documenting them. Probably needs carbon fiber and lamination of the fins. Don't know how a PLA nosecone would hold
up as I don't know what that material is. Kurt

I just looked up high temp plastic filaments on google and got a site called proto-pasta. They have a whole bunch of different PLA filaments that are infused with different metals and materials. They've got one with stainless steel dust and one with carbon fiber too. I don't have a 3d printer but if I did I'd look into one of those for making a NC out of...

PLA melts at 185C or so. It can start to deform as low as 165C. It doesn't matter what's in it - whether stainless steel or carbon dust. It still melts at that temp because that's how 3D printers work.

I can make it hollow or solid or any wall thickness. Don't want to waste time if someone knows it will exceed that fixed temperature.

amell said:

PLA melts at 185C or so. It can start to deform as low as 165C. It doesn't matter what's in it - whether stainless steel or carbon dust. It still melts at that temp because that's how 3D printers work.

I can make it hollow or solid or any wall thickness. Don't want to waste time if someone knows it will exceed that fixed temperature.

Click to expand...

Yeah that makes sense. But a plastic infused with steel or carbon fiber would probably be better strength wise if you could keep it under 165C. That was my main point.

amell said:

PLA melts at 185C or so. It can start to deform as low as 165C. It doesn't matter what's in it - whether stainless steel or carbon dust. It still melts at that temp because that's how 3D printers work.

I can make it hollow or solid or any wall thickness. Don't want to waste time if someone knows it will exceed that fixed temperature.

Click to expand...

This is only part of the story though. The softening temperature of the base plastic won't change with fillers but the bulk thermal properties will. That means it may take more or less thermal energy to get the same temperature change. It may also make the material absorb energy at a different rate from the hot air flow around it, or it may make the material more thermally conductive and allow the energy to spread out through the cone away from the surface, keeping it cooler.

I don't think heat should be your number one concern. My concern is that the plastic would begin deform due to the aero-loads, and that the deformation would continue and become so great that it would disintegrate, with the Mach 2 airstream then filling the airframe resulting in the loss of the rocket.

I would think that you would want a fairly stiff material, one with a high elastic modulus.

Aluminum has a elastic modulus of about 70 GPa, and FR-4 (flame resistant G-10) has one of about 21-24 GPa. I would think you would at least try to shoot for a 3D plastic that approximates G-10/FR-4. Once that's done, you can start to calculate the thermal loads to the nose cone.

Anyway, my :2:.

Greg

amell said:

PLA melts at 185C or so. It can start to deform as low as 165C. It doesn't matter what's in it - whether stainless steel or carbon dust. It still melts at that temp because that's how 3D printers work.

I can make it hollow or solid or any wall thickness. Don't want to waste time if someone knows it will exceed that fixed temperature.

Click to expand...

There is only one sure way to find out. Make one, fly it, and share the results with the community. Its not a waste of time even if it fails because something was learned and shared.

You could make it out of PLA or ABS and put a metal tip on it...

Here's a good comparison: https://www.matterhackers.com/3d-printer-filament-compare

I'd suggest polycarbonate for the best chance of survival. However it extrudes at 265C, and probably requires a heated bed (~100C) and chamber (~50-80C). I've got a job to do some PC parts right now and I'm making some changes to the printer so I hopefully don't melt it down.

I am just starting to ramp up some large scale 3D printed fins in high performance vehicles. So far I have done M.9 (dwell) and 1.3 (push) and have plans on the table for a 1.9 flight in June.

vcp said:

Here's a good comparison: https://www.matterhackers.com/3d-printer-filament-compare

I'd suggest polycarbonate for the best chance of survival. However it extrudes at 265C, and probably requires a heated bed (~100C) and chamber (~50-80C). I've got a job to do some PC parts right now and I'm making some changes to the printer so I hopefully don't melt it down.

Click to expand...

Polycarbonate is a terrible choice unless you have an extremely high temperature 3D Printer. The only ones I'm aware of which actually makes decently strong parts are the Fortus machines from Stratasys. Lots of cheap printers claim they can print polycarbonate, but they can only print very thin walled objects and/or parts far below the actual strength of molded PC.

For PC, to actually get parts with good bonding you need to keep ambient air above 100C. 150-185C is preferred for maximum strength. It doesn't matter how strong the material is in theory if the paths aren't bonding together at that strength.



PLA is more than sufficient structurally speaking. I've tested my PLA cones to M1.6 and they have a 1.6mm wall thickness. I'm very confident they can do M2 on a lightweight 38mm rocket which is only briefly above mach.

If you want more strength, just make thicker walls or do something else to add material and stiffen the design.

Great stuff Landru. Just what I needed to know thanks. Going to try printing one in one piece 8" tall, hope it stays stuck to the bed...