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 Post subject: Tools of the Trade
PostPosted: Mon Apr 21, 2008 5:29 pm 
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FG Cutter

Joined: Sat Nov 03, 2007 11:41 am
Posts: 60
Location: Middle GA
Ok guys, here's a cry of desperation.

I broke out the ol' BUFF again, working on the D->H conversion. (actually started making a "D" and talked myself into revisiting the"H") I used GIMP last time to shorten and remark the tail, but my plans for a re-engining seem to get bogged down (art imitating life?). Not to mention that I also want to:

- draw and color whiskers, fangs & antennas (I know the shape, but I free-cut them last time)
- recolor to modern paint scheme (as boring as it might be)
- improve on the "H" turret-less tail
- put together a "small" format model(regular is 2 large/page, small would be 4/page) that would combine some split pieces into one piece(center fuse, tail, main wings).

those are some of my plans, my problem is this:

What software do I use and how do I go about it?

I saw chip's (I think it was chip) suggestion for corel draw, but I'm trying to reshape an arc. My formal training is by drafting or in the OLD Aucotcad (running command line and everything) and freehanding a conic section seems like a nightmare to me.


So:

A. Does anyone know of some program with the precision of the vector CAD program that draws to raster? all the precision of a CAD in a "paint" program. (oh, did I mention I'm a cheepskate? I am using GIMP after all)

B. The alternative question- what do you use and if you had to draw a random conic section and how would you go about it? (maybe I'm going about this wrong -- substituting too much software for technique)

Waddya think?

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 Post subject:
PostPosted: Mon Apr 21, 2008 6:15 pm 
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Joined: Tue Sep 14, 2004 5:01 pm
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Location: Phoenix
This is what I used to use before I got Rhino3D

http://www.pulserate.com/

$29 fir the fullware, and it saves to raster. Plus it will export the cone shape to .dxf so it can be imported to Autocad.

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 Post subject:
PostPosted: Tue Apr 22, 2008 2:39 am 
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Location: Cape Town, South Africa
For some "old school" design techniques, you might want to check out Rob Carleen's guide. You can find it on the main FG page here: http://www.worlds-smallest-air-museum.com/TUTORIALS

Niki


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 Post subject:
PostPosted: Tue Apr 22, 2008 5:41 pm 
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FG Cutter

Joined: Sat Nov 03, 2007 11:41 am
Posts: 60
Location: Middle GA
Murphy,

Thanks for the suggestion. I tried it out and it *Might* do for the turbofan cowlings. I'll have to take some measurements and crunch some numbers to get tangible results.

I'm still not thrilled with it. It only does a planar slice conic section and the planes must be parallel in one axis. if you wanted to twist the planes relitive to each other, it wouldn't cut it (no pun intended). It also pre-selects where the seam is. If you want it anywhere else, you've got edit the final image. Overall, it''s a neat toy, but it's still a toy.

So did you really pony up a Grand for Rhino?!?!? I mean, it's pretty and all, but it seems a bit much for a hobby. They're only paper airplanes, after all :wink:


Niki,

Thanks -- I've seen those before, but it's still a good suggestion.

I could run the math pull out my drafting tools and go to town, but: A. I'd like to avoid the Draw-and-Scan method, B. It's been a really long time since I've drafted (and I never was very good) and C. that's WAY too much like real work :lol:



I have seen suggested on another site Metasequioa 3d paired with Pepakura Designer. Anyone have any experience good or bad with these?

any different suggestions?

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 Post subject:
PostPosted: Wed Apr 23, 2008 3:13 am 
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Nah, I'm still using the demo version. I can't save anymore, but as long as I get the model finished in a day, then unroll it and get screenshots of the parts, I'm good.


Notice I haven't had a new model in a while.

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 Post subject:
PostPosted: Wed Apr 23, 2008 6:57 am 
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Paper Model CINC
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Joined: Thu Oct 21, 2004 9:34 am
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Location: Pensacola
AS you've probably figured out--there's no "Easy" button for designing a model. A lot of it is intuitive, some math is involved, as well as some art. It's actually a lot like sculpting, with a bit of spacial perception involved. Having said that--a program I've used with some success is called CONE LAYOUT, by Pulse Rate Software. It's not an expensive program, and was first created to lay out exhaust systems for motorcycles. You can only go so far using freebies and trial ware--but this program does offer a free 30 day trial period. I liked it enough that I shelled out the $30 or so bucks it cost for the software. It does allow you to put the seam where you want it, and gives you the option of deciding what angle the top and bottom of the cone are cut. I've used it to create tip tanks and other circular cross sectioned objects. The out put gives you an unfolded version as either a CAD or EPS file, and ther is also an option that gives you a 3d picture of your conical projection. I have played with this progam a bit, and it might have potential beyond it's original intent, with a bit of intuitive tinkering with the output.

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 Post subject:
PostPosted: Thu Apr 24, 2008 5:49 pm 
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FG Cutter

Joined: Sat Nov 03, 2007 11:41 am
Posts: 60
Location: Middle GA
Thanks Rob, I do stand corrected: Cone Layout will allow you to place the seam.

After you mentioned it, I noticed the auto minimize option locks it out.

Conic sections are a primary primitive shape used in modeling, but this program is a bit of a one trick pony. It's a neat enough trick to keep it in a back pocket, but not sure I'm giving up on looking for alternatives yet

I didn't particularly expect an "easy" button, but a "not extremely difficult" button would have been nice. I'm playing around with the Metasequioa I mentioned earlier and it appears I've got a learning curve to climb (I guess it doesn't help that the instructions are in Japanese. maybe I need to pick another 3d package :? ).

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 Post subject:
PostPosted: Fri Apr 25, 2008 3:29 pm 
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Paper Model CINC
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Using aforementioned software--to get the cuts into different planes: I just make two separate projections, joined with a (0 degree) straight base. You can then splice the two together as a single unit on paper, or, just continue using a two piece approach to you model. takes a bit of elementaqry math to calculate the cones--but nothing an elementary school grad couldn't handle.

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 Post subject:
PostPosted: Fri Apr 25, 2008 5:51 pm 
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FG Cutter

Joined: Sat Nov 03, 2007 11:41 am
Posts: 60
Location: Middle GA
Ah, I see your point:

mentally cut the "desired" cone in half (roughly), calc the diameter and hight of each half, and offset the seam angle between each half to the desired angle between the cutting planes. The circular arc on the bottom of the top and the top of the bottom should nest (and set the angle between the cuts). Stitch the two halves together for a genuinely arbitrary conic section.

I wouldn't call this elementary -- I didn't hit this kind of stuff 'till high school -- but I can see your earlier point about a little tinkering can bend this program to your will.

Ok, I suppose I should switch back to fishing. I'll cut more bait later on the 3D CADs when I feel up to learning a new program.

now where'd I put those engine files . . .

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 Post subject:
PostPosted: Sat Apr 26, 2008 5:23 am 
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Paper Model CINC
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Location: Waterlooville, Hampshire, England
This all sounds very informative, I just wish I knew what it meant! :lol:


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 Post subject:
PostPosted: Sat Apr 26, 2008 1:22 pm 
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FG Cutter

Joined: Sat Nov 03, 2007 11:41 am
Posts: 60
Location: Middle GA
Sorry 'bout that CD. A picture = 1000 words, but the picture is in my head. It isn't hard to get a poor translation.

my goal for the final shape is a cone set on it's side that will flare away from the main engine body on outer edge and glue flush to the engine and the opposite cowling at the middle the nacelle. This I see is the 75% solution -- a fair approximation.

A quick look at the intake shows isn't flat nor does it meet on the mid-line, as seen from this picture*:
Image

setting the cone on the side requires the cone's base to be cut by 1/2 the cone's angle. If I were to cut the top by the same angle, the intake would also be flat. If I steepen the cutting angle a bit, I'll start to get the right look for the intake, but they'll meet at the midline.

Ok, that's up to 80-85% solution, and that can be completely done in Cone Layout. What Cone Layout won't do directly is allowing the cuts to be twisted relative to each other, allowing the matching edge to meet above the midline. If I could twist the top cutting plane ~20 degrees, I'd be up at 90% -- where I usually stop :)

That's the why.

How? The limitation is the software won't rotate the two cutting planes. Thanks to Rob's astute observation, that's not a problem.

Cut the planned cone in half. build the top half, then build the bottom half. The only requirements are that the meeting surface is circular (0 degree tilt, same diameter) and the total cone angle is the same in both halves (a little trickier) . I can then build them separately and twist the two halves to my heart's content.

The beauty of it is once both sets of parameters are gathered, I can use the seams to align and stitch the two rendered projections into one part. I just need to set the seam angles differently between the two parts. the difference is the desired angle between the two cutting planes -- in this example 20 degrees.

I'll set one seam to 180 degrees and the other to 160 degrees. render and combine.

The only thing left to add is this will generate left and right hand engines. until I twisted the cones, each engine was symmetric. Now mirrored pairs will need to be generated for each nacelle.

I've run through some "simple" calculations and slapped together a 1st prototype(untwisted, but enough to see where I need to readjust). Once I find where I've laid down my camera, I'll snap a few shots of it and drop them in the "built" forum.

* - No, that isn't me. I admit it. I stole this image from a free republic post -- but it's the best image of an H-model intake I've seen , and a lot of models don't get this detail right.

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 Post subject:
PostPosted: Sat Apr 26, 2008 2:35 pm 
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Paper Model CINC
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Location: Waterlooville, Hampshire, England
Oops, sorry Dan, I think you misunderstood my attempted levity :oops:.

It wasn't your previous post that I found puzzling, but the whole topic. All that designer-speak was way over my head - I was trying to be humourous but it didn't work out, sorry. Course, now I feel guilty for making you post a lengthy but unnecessary (for me, anyway) explanation because of it......:oops:.

I think in future I'll stick to just building card models and leave the designing bit to those much more qualified than I am i.e. you, Rob, murph etc!


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 Post subject:
PostPosted: Sat Apr 26, 2008 2:48 pm 
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Paper Model CINC
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Location: Pensacola
Dan--excellent expansion on the solution to my suggested solution. I couldn't have done it as well--so I din't expound much--figured you'd get the gist right off. But, now any and all can use the same technique, as you've quite elegantly explained it clearly.

If this helps just one person--it was well worth your effort.

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 Post subject:
PostPosted: Sat Apr 26, 2008 4:46 pm 
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FG Cutter

Joined: Sat Nov 03, 2007 11:41 am
Posts: 60
Location: Middle GA
Hey CD, no sweat.

My wife long since has learned not to ask "why" about something technical if she didn't have the time for the answer. On the positive side, she's helped me learn some ways to explain the unexplainable . . . Or she's doing a good job faking interest (women wouldn't fake it . . . would they :shock: ) :lol:

Rob,

I'm giving the twisting a go, and this .eps format is killing me! GIMP refuses to suck it in (throws an error) and I can get ghostScript to open and export but it's got a one track mind and is "scaling to fit" to it's preferred size. That means top and bottom come out the same length in pixels. Grrr :evil:

Is this a unique experience, or have you run into this before?

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 Post subject:
PostPosted: Sun Apr 27, 2008 5:58 pm 
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Paper Model Overlord
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Joined: Fri Oct 06, 2006 1:15 pm
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Location: Alameda CA
craftyDan wrote:
A quick look at the intake shows isn't flat nor does it meet on the mid-line

I've been trying to follow this discussion and envision the paper nacelle design but I can't picture it. First, I'm not convinced the actual aircraft intakes don't meet at the midline, if the midline is what I think it is. If one were to draw a line connecting the midpoints of the compressor cones in the photo, yes, the line would fall below the point of intersection of the intake rims, but does NOT mean that intersection isn't at the midline, it only means that the camera angle is from BELOW the midline, so points on the midline further aft will appear lower than points on the midline further forward. The only way to be certain is Boeing's drawings (or at least a photo taken with the camera parallel to and exactly between the extended centerlines of the engines), but the photo shown certainly makes it appear that the intersection is at midline. The camera is below the engine centerlines because the nacelle bottom is visible while the nacelle top is out of sight.

It sounds like the finished paper nacelle will have both interior and external surfaces foward of the compressor (just as the real aircraft does) - I cannot picture what you're trying to accomplish with just a single cone surface. With that kind of fidelity, you may want to take into account that the intake interior surface extending out to the point of intersection is a compound curve in the shape of a saddle, and not easily replicated with just a conic section.

However you accomplish it, my best wishes for your success, and I can't wait for your pictures so I can finally see what is still a vague vision in my own mind.

Mark Baird
Alameda CA


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