SIM Modelers - Post Your Designs

Here's an update on this guy. Not radically different, but a bunch of small changes that add up. Most interesting (maybe) I offset the tail ring upward, and added a proper cockpit and some decals. And I shortened it up a bit. It desperately needs some more decal work towards the front and some text and other markings, but I have zero clue how to do that stuff (anyone?). And it needs a name. OR is not happy with the stability, although I don't particularly trust it on a design like this with.

I'm liking it more and more, might even build it one day if I can finish the decor in a satisfactory way.

That's cool, though I'm not sure about the canopy. Maybe its the way that OR renders it. It reminds me of an Estes Starship Nova.

Kinda sorta copied it from this, which popped up on another thread earlier:


Not sure what I'd actually do on the model, might even use an Interceptor nose cone, or I could go back to the way it was, with a simple ogive with a canopy decal. Wanted to try this anyway.

It reminds me of an Estes Starship Nova.

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Good grief, it sure does (color scheme and decor, anyway). I wasn't familiar with that one.

If you made a paper canopy, you probably would have a lot of options. What size tube is it anyway? The neat thing about adding a cockpit is that they sort of define the scale of the model. Is it a big, luxury space liner? Small rows of windows. Or maybe an interstellar strike fighter? A larger canopy then. Another option would be to add an upper deck that's a section of tube sliced longitudinally, capped off fore & aft by a balsa cone that's cut in half and sanded to fit, sort of like my Fast Burn Rocket Shuttle design posted previously. But I'm not sure how you'd do that without pods in OR...

neil_w said:

OR is not happy with the stability, although I don't particularly trust it on a design like this.

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I don't have enough OR experience to know what it handles well or doesn't, but I have my doubts too. I'm sure everyone was right about eliminating the ventral fin and would have said so myself if I hadn't been late to the party. What gives me doubt is that it looks a little short to me, and has those canards as well. Either one wouldn't really trouble me, but both short and canards on the same rocket... Lots of people's mind sims are better than mine, but for my two cents it looks questionable.

I'll futz with it some more, maybe try it in Rocksim.

It's a BT55, BTW.

I think that the ring tail adds a lot more drag than people think. Models in Rocksim that I've applied one to slow down very quickly after burn out. Is there a way that you can open the OR file in Rocksim to rerun it and get a second opinion?

Rocksim likes it:


Two things I noticed:
1) The ring tail cuts the sim altitude in half. I suppose that's *possible*, but it seems awfully pessimistic to me.
2) I couldn't get the "stability analysis to output anything useful. Is that a limitation of the trial version?

FYI - you're using the Barrowman Equations setting for calculating CP (CP symbol is gray). That uses the "standard" set of equations, which modelers have been using for decades. But in reality (Tim explains this in one of the newsletter articles) that this a sweetened-condensed version, which makes several assumptions in order to make the hand calculations somewhat simpler. However, those assumptions will steer you wrong once you start getting away from the standard 3FNC type of rocket - especially when you attempt something along the lines of what we're doing here. Use the Rocksim Calculations (CP symbol turns red), which basically makes use of the full Barrowman equations without baseline assumptions. You'll find that often, the "gray" CP is a bit more conservative than the "red" CP, and there's really no reason to settle for that. Apogee includes both options - and the 2D cutout approximation - for the sake of comparing to previously calculated or approximated results. But there's no reason not to use the full equation set in the Rocksim calculation mode.

I'm not sure about the Stability Analysis tool, I'll have to look at the when I get home. Anyway, the real fun begins when start to see what the pod feature allows you to do...

Thanks for that pointer. I selected Rocksim Calculations and it moved the CP up just a bit, not enough to cause problems. Still in comfortable stability range. Still no joy on the radial stability.

I'm confused on the radial stability as well. I haven't used that feature before, but I'm at a loss as to how to make it do something. All I get is base view against a turquoise background, and nothing changes when I play with the velocity slider. There doesn't seem to be anything to click to make it do anything else...

The radial stabilty analysis in my up to date instance of Rsim is hosed. The analysis page that worked at one time now does not. I can get a display on the base view but I don't at all trust what I have seen in some test cases.

Mucking around with a new idea, no clue what to do with it. Since this thread has gone quiet I'll toss it out here.


Obviously the full length ribs that extend all the way around the nose cone are the main concept, but I have no good idea what else to do with it yet. Anyone?

That's pretty neat, but I have to imagine that it pulls the CP up a bit. Its slightly reminicent of the old Astron Starlight, though without the rings and strakes. And, of course, the fins tapered down short of the cone on that one. If it were me, I'd probably add some manner of pods to the fin tips. Or maybe a ring around them. Or both...

CP can be managed. I'll have to see what I can do with pods and rings and whatever to make the whole thing interesting.

I just figured out what it reminds me of - the Disney version of the Nautilus. Which is kind of cool in and of itself. Maybe you can work that angle...

Hmm...

I was thinking of a Quadracant design that would be nice for the Nautilis. Would be a challenging build either totally scratch or maybe utilizing pieces of a resized card stock model. The mind sim would have to go through a steam punk calculation machine.

There was a ribbed, 3D printed rocket st NARAM which did not fly so well. The flier is experienced enough that I would assume he did the normal checks. May not apply here but it is a fuzzy data point.

I would taper the ribs starting at the bottom of the nose so they go to zero at the tip.

Often, I like to see or do one novel thing at a time, so to me it looks pretty good as is. Twin skinny pods bracketing each fin (six pods total) would look good. Or strakes that look just like the fin extensions half way between the fins, but tapering off half way up (which would help a little with the CP as well as looking good.)

I suppose I should make my own contribution to the thread here. This is a design I call Astraeus, and was the first design in the "Constellation Series" that I've been working on since. This was really my first attempt at a Starship Vega / Laser-X type rocket, done shortly after I started getting the hang of Rocksim:



I think as designs go, its OK. But not above that. With a bit of work and messing around, it eventually evolved into Perseus:


This is a design I like much better. It's a full 3' tall, has pods and strakes, and a long boat tail that leads down to a 24mm mount. It's also large enough to accommodate a Chute Release in the chute bay and an altimeter in the nose. This one is on my to-do list, just not sure when.

I'm not inclined to build another elliptical tube soon unless I find a better way (and I have one in mind to research) but when I do, a wide body plane is the next thing. This is from OpenSCAD, not RockSim, since the latter can't do such tubes.

The half tube on the bottom is meant to resemble an air scoop while at the same time functioning as a fourth fin.

I have an RS file for it, using the ellipse's major diameter for the body tube diameter, and with the wings at 90 degrees rather than raised up. (I should be able to raise them with a separate pod for each, but it misbehaves.) The result, with a pair of E9's, is nicely stable and reaches 186 meters altitude.

EXPjawa said:

This is a design I like much better. It's a full 3' tall, has pods and strakes, and a long boat tail that leads down to a 24mm mount.

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Very nice, I like the second one better as well. And it has not one but *2* sets of your signature strakes. You should get like a hundred of those things laser cut and just keep a bin of them handy.

I'm really enjoying this thread...

neil_w said:

You should get like a hundred of those things laser cut and just keep a bin of them handy.

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I probably should. I have down to two standard sizes, though might add a third. But they're in my Rocksim parts library as JawaParts FS-1 & -2 (for Fin Strake). That leads to another thought - it would be nice if we could keep a standard parts library somewhere for parts that are developed for specific models. For example, I've got fins specific to several vintage Estes kits that I've drawn up - and occasionally applied to other designs. Its nice having that sort of thing available.

Calculate ID of tube. Calculate appropriate ellipse using standard formula. Cut thick foam using regular woodworking elliptical jig. Repeat a bunch. Glue stack. Slit BT. Wrap, glue, shrinktape.

Maybe?

jqavins said:

I'm not inclined to build another elliptical tube soon unless I find a better way (and I have one in mind to research) but when I do, a wide body plane is the next thing.

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The elliptical body should look really good in a plane-type configuration. Wish I had even a single good suggestion about how best to fabricate the tube...

Well, people make their own tubes, the how-to on that isn't hard to find. So, the key is the mandrel, right? Since its elliptical, standard sizes go out the window anyway. You can buy various shaped elliptical tubes that are steel, carbon fiber, etc. commercially. So, pick a suitable tube as a mandrel and wrap the tube. Kind of like how New-Way uses square tube mandrels, just different. Then the next challenge is centering rings that fit well. Its relatively easy to make circular rings that are concentric. This would be trickier, but I'm sure anyone that has access to laser cutting or CNC mills or routers could lick that issue. Then its a matter of nose cones and tube couplers, which maybe resort to 3D printing.

Sorry for the silliness, but this is the first thing that came to mind from the picture of the Nautilus:

Two words: laser cutter.

Anyway, I should probably move onto something more productive...

For the elliptical I'm building, I got laser cut centering rings and a 3D printed nose. That part's easy. I used skin over frame for the tube, using laser cut ribs and it worked out OK, but not really well. I have looked for elliptical objects that could be used as mandrels but have found only a few sizes, and not the size(s) that I want. However, it shouldn't be hard to turn the required mandrel(s) on a CNC mill or lathe; the question is what it would cost.

I don't think that you even have to do that. You can buy oval and elliptical tubing off the shelf if you know where to look. A 3' segment would be a fine mandrel for 30" or so kraft paper tubes. I might have to give it a shot. By the same token, you can buy square tubes that are 2.5, 3, & 4 inch "diameter". That would be a neat way to upscale some of the New-Way kits.