As mentioned, long before you get into the actual development of parts, it is find the errors time and develop a set of rudimentary three view plans. This is not to berate the designer, but a later set of plans will bring the CAD draftsman into a near "measurements not required" basis. You basically begin by recreating a sideview, a top view, the stabilizers, one of the wing halves or the whole wing. The rudimentary views are the key to beginning a project, maintaining correct fit, and to resolving discrepancies on the plans.

To begin such, a constant chord wing will be used as an example. That like for a Taylorcraft, a Piper Cub, a DeHaviland Beaver or many of the popular non-prototype model aircraft. A Hellcat, with double tapered wings, or a Spitfire with double elliptical edged wings becomes a poor choice for first try unless you are an experienced draftsman. The constant chord wing generally has enough variables for the first time draftsman to make the whole process enjoyable and make him aware of situations in what otherwise was a seemingly simple exercise.

When you turn on the computer and begin the CAD program, you are initially going to construct a single line horizontal across your screen to a 36, 48 or whatever random length, but longer than need be for one winghalf by at least 6 units.

Now, why was the term "Units" used? Let us digress here for a few paragraphs, to explain CAD drafting in a few simple terms.

CAD drafting is such that the operator is always considered to be smarter than the computer. He may not know all the operations of the buttons, and what goes on inside the CPU, but he knows what he wants as an end product. AND, if he sees the end product is not as envisioned, he is the one who calls the work incorrect, not the computer. As such, when we create a line of a certain length, the CAD program is thinking in UNITS, not inches, millimeters nor feet, or portions thereof. It can only divide and multiply units of a constant. Inches are only in our heads. Thus we always consider the end product to be in inches when we punch that print-out button. As an example, you cannot multiply a length given in feet/inches/fractions by another unit of measure without going into some sort of a conversion process. You have to do the math in either fractions, feet or inches. With metric units you have to convert over to millimeters, centimeters or meters also, or your computation will be of mixed results.

In CAD too, the operator has to make the initial decision as to units. For the domestic modeler, most of this is settled. He creates the project in inches, and the plotted, printed, or laser cut parts will be spoken of in terms of whole inches. Your printer, plotter and the laser cutting firm is set up in inches and will further communicate in inches hopefully. If your dream is to take an develop a set of plans from the real object or prototype, then at some point along the line you are going to have to proportion down your work to the correct model size. However, if you are beginning with a set of model plans as here, there is no proportioning to be done (hopefully). That note in the corner stating the plans are 1-1/2" equals 12" is nice for reference, but we will continue on at one-to-one. Your end result model will be one-to-one on the basis that one inch on the plan equals one inch on the model.

There is another CAD situation out there for the computer genius, and that is described in Autocad as paper space versus model space. If you know nothing about this, lets not dig into it, as it is in a world of itself. Although you may think the world of this feature, it just gets into the way down the road. Most CAD programs, including Autocad, when initially entering the drawing development stage start you at model space measurements. AND that is where we want to remain. We do not want to consider going into scale factors of drawings created outside the immediate need. Imagine handing your first disk to the laser cutting firm and letting him know it was done in paper space with a 1:7 scale ratio. He'll hand it back to you two weeks later and let you know that it doesn't compute in his computer. The same being in that several of the CAD programs out there have the option to change the scale ratio before you punch the button to print out or plot out some of your work. Make sure this feature is turned off, and your results become one-to-one or one unit equals one inch.

OK, got that? Scale ratio, paper space drawings, constant units. We need to give the firm something his computer will pull up quickly and he is able to understand equally as fast.

There are options available in the popular CAD programs which you may or may not get screwy results with. I cannot say if it was the fault of the program or the end user, but it did happen here a time or two. Often times there is an option called "Ortho" which enables the draftsman to lay out lines perfectly horizontal or vertical on an imaginary grid which has dots to a precise interval. As you move the cursor across the screen, it cogs from one dot to another. This is fine in the architectural world where a house is to be layed out with everything perpendicular, however an airplane is full of rounded shapes. I also got a very noticeable stepped leading edge for ribs once as the laser picked up the snap-to attributes still left on the disk. To be safe, you really won't need it, so keep the function turned off.

I use an engineer's scale in developing or measuring plans, as it is much faster reading an inch and proportion, than to stop and figure out what the length is in fractions. It is faster to input 1.25 inches than one and a quarter inches on the keyboard. In actually, you are going to find that perhaps the original designer laid out the plan in fractions of an inch. Thus the architectural scale isn't always that far away, it is used when you suspect an area of the model on the plans was done at a fractional scale. Let the UNITS command in your CAD system remain at decimals of one, not fractions of one.

Lets go into developing a rudimentary set of 3-view drawings. Perhaps the best place to begin is with a TOPVIEW. Open up a new file and SAVE AS a drawing named TOPVIEW. Lay a line on the screen beginning at about the middle, and straight to the right border about 50 units. For initial reference, this line will become the centerline or datum line as mentioned in the last chapter. Lay on a line about 6 units long and perpendicular to the initial datum line. Move the 6 line from the mid-point to the endpoint of the long one. This 6 line will be about where the forward face of the firewall is noted on your original plan. With your scale, go over to the original plan and measure from the face to the front face of one of the interior bulkheads. Offset the 6 line to the right this distance. You now have located positions for the firewall, a bulkhead. Do this again for another bulkhead until the front face of all bulkheads are on the plan. If any of the bulkheads are not perpendicular to the centerline in all three views, do not show it for now.

Next, measure across the width of the fuselage at a particular bulkhead. Make the measurement to the outside face of the model, even if the plans call out for 1/16 or 3/32 balsa sides. Take that distance, halve it, and offset the centerline that amount. Trim off all portions of the 6 line beyond these two parallel lines which represent the overall width of the model at the face of the bulkhead. Then erase the two offsetted lines. This will represent the overall width of the fuselage at that particular bulkhead.

Again, take on a different bulkhead line. Measure the overall width of the fuselage, halve this distance, then offset the centerline this amount to top and bottom. Trim the excess, and remove the offsetted lines. In Autocad, instead of manually figuring out what half the distance may be, just insert the bulkhead width divided by two. Or, when the question comes up as to the offset distance, enter something like 4.55/2. This will be read as 4.55 inches divided by two, or 2.275 inches.

After you get all the bulkhead lines on and to the correct length, go back to your plan and then offset the correct amount equal to the thickness of the wood to be used. i.e. offset the forward bulkheads 3/16, those to the rear maybe 3/32. These distances should equal the noted thicknesses on the original plans.

Then, taking yet another line, connect the ends of those 6 lines at each bulkhead line. This forms an outline of what the fuselage should look like overall. If your model is to be sheathed with film or paper, you are effectively done here. If your model is to be sheathed in 1/16th or 3/32nds balsa, then offset the fuselage edge inwards by this amount. If the exterior looks a bit lumpy bumpy, figure out where there may be any straight, slab sided features and adjust the overall length of the bulkhead lines accordingly. Use large radius curves to bend in the sides to the tail and nose.