This is one of those odd-ball designs that has been stuck in my brain for several years. I keep revisiting it to see if I can work out the details of mass balancing and general stability. The design is asymmetrical, with more mass on the "bottom" (ahem...), and requiring some sort of compensation on the top. In this design, I'm hoping I can create an equalling "drag force" to keep the nose pointed in the right direction.

This may require more tinkering to get it right, so consider this version as a Mk I...

Length: 37.00"
Diameter: 1.04" (ST-10 largest tube)
Fin Span: 14.45"
Weight: 2.23 oz


B6-4......AVG 325'......Dv AVG 14-15 FPS......3/16" x 48" launch rod


Enjoy!

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Attached Files

Exoteria.rkt (170.9 KB, 182 views)

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Craig McGraw

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I absolutely love these types of rockets......very cool design.

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Thanks!

This offset design is an interesting challenge just to work up in RockSim. Getting the design to balance out in flight is another matter. I need to break down and order some parts...

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Here's a set of templates for the wings, vertical fins, and the three pylons. I'm supplying both a JPG and a CDR file (for those of you with Corel Draw 12 or better). The fins are cut from 3/32" sheet balsa.

Keep in mind the tube pylons are not solid balsa blobs, but rather are hollow gas passages. My design calls out balsa (a RS limitation), but actually uses 3/16" launch lugs as the central structure, with 0.02" matteboard skins and square balsa strips for the leading and trailing edges.

The nose cone for the rear pod should be hollowed out, and the lugs from the rear pylons should extend through the balsa to the opening.

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Attached Files

Patterns.zip (11.1 KB, 80 views)

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Craig McGraw

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Craig,

Can you output the file as Corel Version 10? That is the version we use on the laser cutter. I had 13 but it was not as stable.

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Carl McLawhorn
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Funny you should mention 13, I just DL'd the 15-day demo of X3...

Attached below is a zip with a V10 CDR. Let me know if I need to do something else to it. I've cleaned up the lines manually to remove the "cut throughs", but still being a novice with Draw I may have missed something.

Attached Files

Exoteria Patterns V10.zip (11.0 KB, 87 views)

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Craig McGraw

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Craig,
If I understand the Rocksim file, here are the three cdr files ready for laser cutting. They should give you a better idea of how the files have to look for sending to the laser cutter. Give me a call later today if you have questions.

Attached Files

Exoteria Patterns V10.zip (26.5 KB, 77 views)

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Carl McLawhorn
NAR#4717 L2
semroc.com

Carl,

I made some adjustments to the files based on text comments I made on the RS design. Attached below are both CDR 10 and 13 files (zipped).

• Sheet A -- Only one part, the Dish Pylon. I've modified the cutting pattern to get 4 kit sheets from a 4" x 9" blank.
• Sheet B -- This represents the biggest change. The pylons are hollow gas passages, with the inner cores made from 3/16" launch lugs. What I needed were some thin skins to overlay those lugs, with balsa strips for the LE and TE. Can we do this with 1/64" ply, or is this asking a bit much of the death ray?
• Sheet C -- No major change from your pattern.
• Sheet D -- Only change was to adjust the center line of the slot with the center line of the LE point. Otherwise, no major change to the outline.

Let me know how these alterations affect your setup.

Attached Files

Laser Patterns.zip (62.7 KB, 78 views)

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Craig,

I was going to cut a set, but it is going to take more work than I have time for right now.

The sheet size for the laser cutter is 11.811" x 8.268". If it is different from that, it cuts off some good stuff.

The lines to cut must not have any fill and must be hairline. The fill goes into slow raster mode and could take 10 or 15 minutes to try to burn an image. Black does a 30% power cut that burns names without going all the way through. Red cuts with 100% power. If it is hairline, the laser beam just follows the vector lines and cuts fast.

The other 14 basic colors are used for special power and speed levels for different canned settings for the Venus.

I use the Microgamma font because it shows up well on most balsa densities. The thinner fonts wash out.

The grain for balsa is left to right and plywood is (usually) up and down. Fiber has no "grain and can be cut in any orientation. We insert the sheets with the widest length from left to right.

We use balsa in widths of 8" (6 per sheet), 9.6" (5 per sheet) and 12" (4 per sheet) for different patterns. Plywwod is usually in 8" x 12" sheets and fiber is 8" x 10" sheets.

We use a .011" wide hold-in tab on 3/32" and 1/8". We sometimes use a .008" tab on 3/16" balsa, but it is preferable to just cut it into individual pieces since it is at the limit of the beams focus. 1/16" balsa is also .011" unless it is light, in which case we sometimes have to adjust the pieces to .013".

The colors (black and red) have to be set to RGB. If they are set to CYMK, they are selectively and sometimes arbitrarily ignored and nothing cuts in some areas.

We get the balsa sheets in 3" wide and 4" wide, but we try to avoid 4" wide since it costs almost twice as much.

Iknow it is minor, but I use 72 point for the title over the top of the page. This allows me to check the balsa size before I load the file by looking at the thumbnail. Saves a few seconds and it lets me manage many widths and lengths and thicknesses that are cut in a typical day.

Balsa is not always 3" or 4" so I try to keep the cutting area at least .10" from the top and bottom edges.

Whew!! That is about 5% of what you need to know to cut fins. Tomorrow's lesson will handle tab placement, smoothing, inter-object distance, optimizing order, grouping, cutting direction, object starting point, over-cut, handling raster scan early termination, and determining optimum balsa density and adjusting on the fly for different weights.

This is not nearly as boring as it sounds!

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Carl McLawhorn
NAR#4717 L2
semroc.com

Not boring at all! Thanks for the info, Carl. It'll be a big help for both this and future projects. I'm printing out your post to keep as a handy reference.

Getting a burn of the set is not time-critical, and I may need to readjust the images before you do, anyway. I wondered how you set the burn power. Never thought about the "color" being used to control it. Did you mean black represents 30% power, or 70% (30% off the top)?

My computer doesn't have the Microgramma font. Is there a substitute I can use instead which doesn't require me to buy or download a new font?

I'll remember the 72 pt headers...

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