Design Group, April 1992

Vernon Blomquist

Originally published April 1992

Two months ago I promised to review a program called DesignCAD 3-D. Last month I saw that aluminum block V-12 and just had to write about it first. Anyway, the program is what it says, a 3D Computer Aided Design package. I have mixed feelings about it, so I'll just tell you the things I liked and didn't like and let you decide if this is a program you want to have.

First of all, the price at $190 mail order isn't bad, especially compared to AutoCad at $2500 or so. The documentation is reasonable but not great. It does explain all of the features, but in many cases not well enough to really understand how to use it. As an example, there is a function to change the working plane in the drawing so that the plane of the screen that you are drawing on is any arbitrary plane in space. This makes it convenient to draw objects that are not in the x, y, or z plane. When I try to use it I always end up with an upside down view of what I'm trying to draw. That isn't very useful and I can't figure out why it's happening. I spent about a week of running the program every evening before I could reasonably draw what I wanted. That's about how long it took to try all of the functions and learn the details that aren't included in the books.

Before I start to sound too negative about the program, let me tell you some of the good points. There are some things you can do with this that would be difficult or much more time consuming to do any other way. One of the most useful to us is the ability to specify a root rib and a tip rib and have the program draw the wing in between them. You can then take cross sections through the drawn wing to get ribs or section templates very easily. The other similar use is for a fuselage. The program will let you define the outline at various fuselage stations, then do a cubic spline curve fit between those stations to create a solid body. The same routine for a wing could also apply to a propeller. Another good capability is to tell you the area of a plane surface or the volume of a solid as well as locating the center of either of those. The bad news on this one is that it is not very accurate. On known shapes I've had it be as much as 8% off. Fortunately, that is supposed to be reduced to .1% in the next upgrade. The version I'm using is 3.1, so wait for 3.2 or whatever they call it if you are going to buy the program.

Back on the negative side, there are some quirks and outright bugs in the program that I really don't like. One of the strangest things that it does is when you join two separate lines together, sometimes a portion of one of the lines will move. This doesn't happen all the time, and only on curved lines. The bad thing about it is that the program is not very good at modifying curved lines after they are already drawn, so when this happens you just about have to start over. In general, already drawn objects are fairly difficult to manipulate. Part of this is just the usual problem of handling a 3D object on a 2D screen, but I have seen other programs that were easier to use when it came to modifying things that were already drawn. Those were the 2D programs such as Aldus Freehand on the MacIntosh and Windows Draw or Corel Draw on a PC.

The other comment I have to make is that you should have a fairly fast computer if you want to do 3D CAD. I have a 40 Mhz 386 without a math coprocessor (yet). It will take 5 to 10 minutes to connect fuselage stations into a solid body and up to 30 minutes to do hidden line removal from a drawing that I did of a delta winged aircraft with drop tanks. You can run the program on a slower machine but it will take longer.

My recommendation would be to get a 2D drawing program unless you really want the 3D capability and are willing to spend a good amount of time learning to use it. There is a DesignCAD 2-D program that is compatible with 3-D and supposed to be optimized for 2-D drawing, but I haven't used it, so can't really comment. If you are interested in getting a drawing program, please feel free to talk to me after the meeting and I'll tell you more about the ones I've used. Also, don't be too put off by my negative comments. I don't like a lot of things about AutoCad either and it is the industry standard.

See you at Burger King after the chapter meeting for some more interesting design discussions.

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