3.
BEGIN THE PROCESS
As suggested, don't begin with a real miniature set of plans from some old aero magazine, nor plans which were "scaled up" to meet your needs. Try them on your second or third project. Begin with a straight forward project to the size and character for which you have an interest in. Don't come up with a whole set of changes you'd like to incorporate, unless you know what you are doing beforehand. If the plans are quite old, and the engine or radio system specified is now considered a collectible, then you ought to consider "upgrading" to more modern or available. However, the plans available on the market today generally have so much latitude designed into them, it may not be necessary.
At this point, you don't even need to have your computer turned on. Lay out those plans, and with your trusty architect's and engineer's scale, begin with some simple measurement checks. The fuselage and wing should have a centerline. Measure both ways and see if the original draftsman made everything symmetrical. I have come upon plans where one winghalf was about 1 inch longer than the other, or the fuselage was 1/4" wider to one side. A swing over the sheets with the scale now, and some cussing out the designer at this point will save you some cussing of your own in a week or two. See if the top view is the same length as the side view. If the initial rib at the wing root is just sketched in on the sideview, you will need to determine its ultimate fit. Are the spars shown in the outline of the wing root rib in the sideview the same as elsewhere on the plan for the number one rib? Compare, compare, compare. Some time ago, I was a plans checker. When one sheet tells the contractor to build an item to one configuration, and the match-up sheet tells another story, it was an instant red-flag and return to the engineer for correction. If the design engineer can't draft or figure out his intent, then it is useless to hand copies the plans out to others and create more confusion.
While you examine the top, side and front view, and maybe those extras for each wing and the stabilizers, begin your consideration as to datum. As most plans are drawn full size and you will be creating parts and rudimentary drawings to the same, you will need datum lines to use for offset purposes. As a self imposed rule here, I use the centerline of the fuselage in top views and if one is shown for the wing. Measurements will be made left and right from these datum lines. Usually the front face of the first fuselage former (the firewall?) will become yet another datum surface in that it is used as zero along the fuselage centerline. Thus the spinner or crankshaft nut so accurately shown is not a part of the datum, but is a variable. A simple pencil mark or arrow on the plan will remind you where all measurements are to be taken from. Don't create or use a perpendicular line near the center of the fuselage unless you are desperate, or have cock-eyed fitting fuselage formers. Then, compare the position of your datum line in the top view, to that in the sideview. Make sure they compare, and a measurement to a fuselage bulkhead in the top view can easily be corresponded to the same distance in the sideview along both datum lines.
As to a datum line in the sideview, there are a couple choices often available. So many times, I see plans with a centerline indicated in the sideview, thus there isn't a lot of choice available. Other times, the plan designer may have used the upper or lower edge of a longeron. If it is straight, and perpendicular to the top view centerline, it should be OK. A few plans show one across the bottom of the plan sheet, perhaps touching the bottom or the tire. However, again make sure the datum line in the sideview is to the same overall length as that in the top view. Otherwise, when you get to making up the rudimentary drawings, and then using them for measurements, your end result parts will not match those on the plans. They may only fit a model built cockeyed.
Not too often is there a defined or hard drawn reference line shown on plans
for which you can use for measurement and fit purposes like in the wing plan section. Many times a spar, even through laminations, is drawn perpendicular to the centerline of the fuselage. This reference datum line must be locatable in all three views. I have found sometimes the draftsman only indicates the position of the leading edge in the sideview. This becomes near useless on an airplane with tapered wings. You then need to establish a known 3-D distance from his indicated position to your perpendicular reference line.
To help confuse matters a bit more, if there is a higher than usual amount of wing incidence, you will need to determine if maybe the wing reference line is at the front face near the top, at the bottom, or midway or at yet some other intersection of line drawn on the plan. All this provided that the original draftsman made a good and accurate set of plans.
Depending upon the particular model or plan I am working with, I then establish a few more parameters for measurements. Generally all lengthwise measurements along the fuselage centerline (or datum line) are to the forward face. Regardless of the former thickness. Thus, up front it may be to the front face of 1/4" and 1/8" plywood, and towards the rear it is to the face of 1/8 or 1/16" balsa. This means you only have to offset one line to one side instead of zooming in and offsetting it two ways. About the same situation is used for the wing also. Measure from the centerline to the inside face of each rib. As to up and down from the datum line on the fuselage sideview, I measure to the outside face of the skin. This will make the end result and overall appearance of the model more exact as to contour. More on this later on.
Most times the wood sizes are noted in fractional dimensions. If the plans state wing spars to be 3/8" by 1/2" and they measure under or over, then get another cup of coffee and figure out what was intended. I have run upon model plans which state fuselage longerons to be 1/4" square at one end, and 3/8" square at the other, but measure 5/16" square over all. It's your choice here as to the intent of the draughtsman.
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