TRF Summer Build Off: The Ellipse

Some random thoughts just popped into my head for making a mandrel so you could roll your own elliptical tubes, should you desire to. I don't know why I'm sort of infatuated with the idea of rolling elliptical tubes, despite the fact that I've never (and probably never will) roll a tube of my own. Feel free to disregard.

Bottom line: build the mandrel yourself, using known techniques.

1) 3D-print. You'd probably have to make a small-ish piece (a few inches long) and then glue a bunch of them together. Could work.

2) Build the mandrel the same way you build your airframe, except with heavier wood (laser printed of course), and all stringers. Hardest part would be sanding the whole thing down to make the surface a really smooth curve, but quite doable.

3) I don't know the cost of CNC milling, but you could get a bunch of elliptical pieces of plywood and just stack them all together, no stringers even needed.

Probably not worth the effort to build one rocket, but if you had designs on building multiple of them in the future, it could be worth it. In any of the above approaches, you could build a short-ish mandrel (to save cost) and just join multiple segments of tubing to make longer ones. Although then you might need to roll some couplers.

Thanks for all the condolences.

Cabernut said:

With 3 weeks left until Labor Day, would it be considered a "repair" if you rebuilt it using the same fins? Either way, I look forward to seeing the rebuild.

Click to expand...

There's no way I'm rebuilding before labor day; I just don't work that quickly and I'd have to get new parts cut and printed first. I may rebuild, but I dont plan to until I've researched getting a mandrel, or some other improvement in the construction technique.

neil_w said:

Some random thoughts just popped into my head for making a mandrel so you could roll your own elliptical tubes, should you desire to. I don't know why I'm sort of infatuated with the idea of rolling elliptical tubes, despite the fact that I've never (and probably never will) roll a tube of my own. Feel free to disregard.

Click to expand...

Because round tubes we can buy in lots of sizes so it's rare that you've just gotta have a particular one that you can't buy (unless scale is your thing.) But if you want elliptical of particular size(s) even approximately then making your own is pretty much the only way.

Bottom line: build the mandrel yourself, using known techniques.

1) 3D-print...
2) Build the mandrel the same way you build...
3) I don't know the cost of CNC milling...

Click to expand...

Number one I've thought about. There are some 3D printers that can go better than six inches high. I would find someone with one of those and make sections with shoulders at one end so they stack.

I don't think number two would work. One thing I've learned from this build is that getting it really straight and smooth is next to impossible, but a mandrell has to be that way or you can't get the tube off.

I'm not sure I follow number three. If CNC milling is affordable, I'll get a whole alluminum mandrell. Plywood I'd get laser cut. But yes, a solid stack of wafers might be a way to go. I'd get each wafer cut with two square holes so I can stack them on a pair of square stock bars to ensure they are aligned, then sand, seal, and wax the surface.

And I agree that most of these would not be worth it for a single build. On the other hand, if there's an effective and affordable way to make a good mandrel then one might be able to produce a product, with tubes sized for 2x24mm, 2x18mm, and 2x13mm, and couplers for each. Transitions between those sizes and transitions between elliptical and circular could all be 3D printed like the nose cones, and you've got something. Add a few kits that use the tubes, starting with the one I just destroyed, and what you've got is a product line.

Next someone's going to try elliptical motor casings. The resulting thrust curves might be very interesting and/or useful, but that begins getting into a restricted subject.

jqavins said:

I'm not sure I follow number three. If CNC milling is affordable, I'll get a whole alluminum mandrell. Plywood I'd get laser cut. But yes, a solid stack of wafers might be a way to go. I'd get each wafer cut with two square holes so I can stack them on a pair of square stock bars to ensure they are aligned, then sand, seal, and wax the surface.

Click to expand...

Yeah, that's what I was thinking. I was thinking that when dealing with thicker plywood, CNC would ultimately be more cost effective than laser cutting, but I'm just wild guessing. Stack of wafers is the main idea.

Next someone's going to try elliptical motor casings. The resulting thrust curves might be very interesting and/or useful, but that begins getting into a restricted subject.

Click to expand...

Now that right there is above my pay grade.

jqavins said:

There's no way I'm rebuilding before labor day...

Click to expand...

Um, well, I take it back. I rechecked the contest rules, and the crash is definitely a DQ. I ordered a new set of parts for a slightly modified build (to fix the chute jamming.) If the parts arrive in time, I'll throw it together with no paint job and launch it in a park somewhere on C11s. I don't know if I'll make it in time, but I'm going for it.

GO YOU Joe! You can do this.

Right on! Now that you know how to build it, doing so a second time should go much faster. Get er done!

Did you ever end up rebuilding this?

I started to, but failed to meet the deadline. So count me out. (Dang!)

jqavins said:

I started to, but failed to meet the deadline. So count me out. (Dang!)

Click to expand...

Well, I was going to let the build go till labor day..however..to keep it fair..I cant do that seeing you gave up (because you missed the deadline) on your build.

Also see...Contest thread