Yet another 3D printed fin can

A fellow club member designed and printed a fin can, and I think the results are worth sharing. While using a 3D printer is quite nice in its own right, it also allows to easily incorporate features that might be impossible or at least difficult to manufacture with other methods.
In this case, the fin can has two notable details. The fins have a defined airfoil (von Karman profile) and they contain an internal structure to reinforce the fins while keeping them lightweight. The internal surface of the fins is similar to an isogrid, but the ribs that are parallel to the leading edge have been extended to form spars. The angles differ a bit from a traditional 0, +/- 60° isogrid, because of the design constraints of the 3D printer.





(It doesn’t hurt to spice up the pictures a bit with creative lighting. The internals are usually less visible)

A cut model of an earlier revision shows the details a bit better.
https://sketchfab.com/models/61e83d5806c74a68a13f56526734223d

The next step is to find out if the result can be improved by smoothing it with aceton vapor and/or glassing it. I’m a bit skeptical about the adhesion of epoxy on ABS, but at least it should be an educational exercise.

Reinhard

Very nice! I assume it is 54mm? Will these be available for sale?

NikeMikey

Yes, this one is 54mm. It fits snuggly over a 54mm casing, but this was only a test.



There are no plans to fly it in this configuration. The glass transition temperature of ABS is 105°C while the casing might reach up to 200°C and still be NFPA1125 compliant. Besides, it is hard to find a waiver in central Europe that supports 54mm minimum diameter flights and we have no idea how much it can handle structurally.

The fin can is not for sale, but I can send you a STL file if you tell me the intended tubing diameter. You could have it print at a local fablab or use contractors like Shapeways, Ponoko or i.materialise.

Reinhard

Reinhard said:

Yes, this one is 54mm. It fits snuggly over a 54mm casing, but this was only a test.

View attachment 258535

There are no plans to fly it in this configuration. The glass transition temperature of ABS is 105°C while the casing might reach up to 200°C and still be NFPA1125 compliant. Besides, it is hard to find a waiver in central Europe that supports 54mm minimum diameter flights and we have no idea how much it can handle structurally.

The fin can is not for sale, but I can send you a STL file if you tell me the intended tubing diameter. You could have it print at a local fablab or use contractors like Shapeways, Ponoko or i.materialise.

Reinhard

Click to expand...

Can you please email me a 38mm and 54mm version still file. Thanks [email protected]

It starts to look like a family. From left to right:

1. 54mm, ABS, FDM, the one from my last posts. Test piece that won't fly.

2. 75mm, Aluminum, DMLS, should by flyable (not sure if appropriate for a nasty motor). Some grinding and polishing of the outer surface would be nice. In contrast to the plastic fin cans, this one contain an internal thrust ring on the rear end (second image), so it can be slipped over the casing and held in place with the aft closure. For a perfect fit, the aft closure requires a bit of machining of the thrust ring portion.

3. 75mm, Aluminum, DMLS. Probably won't fly, certainly not minimum diameter. A further development from #2, it was a little bit over-optimized (thinner walls to reduce weight) and ran into minimum gauge issues during post machining. While the FEM simulation indicated that it should handle supersonic flight, this was only based an static loads derived from a guesstimate based on dynamic pressure and angle of attack. The fin can oscillates "nicely" after it getting tipped with a finger, so it is not reasonable to assume it will survive the dynamic loads during flight. Because of the minimum gauge issues encountered during manufacturing, one can also assume that the realized geometry differs significantly from the CAD model.

4. 98mm, same issues as with #3.

5. 104mm, glassed PLA, FDM. This one was printed in two parts, because of build volume limitations. The parts were fitted on a CF tube (ID 100mm, OD 104mm) and then glassed. 2 or 3 layers of 160g/m^2 (~4.7 oz/sq-yd) if I remember correctly. A similarly constructed one flew on a K570 to about 9kft 2 weeks ago.

Reinhard