8.
USE OF AIDES: AIRFOIL PROGRAMS
One of the aides as to putting together a model of an airplane is the use of an airfoil generating program. Equally, perhaps on the mind of readers is what airfoil is the best or recommended? That's a hard question to answer, as I use three different programs at this time. One being quick to enter, and obtain your results, but having limitations. The others giving somewhat the same results, but more involved to set up and get your first generated airfoil and their output is a bit different too.
The thing with airfoil generating programs, is that they initially take a bunch of fiddling around before you get any results resembling what you may envision. As most plans for a model airplane have at least one rib or initial airfoil shown, you then need to decide if it is simpler to:
1: Copy the rib using a scanner and trace it within the CAD programing
2: Scan the rib into BMP format, and then convert the lines to vectors
3: Digitize, then interpret with rounding etc.
4: Develop a profile in CAD and then use Compufoil Convert to generate templates for additional ribs
5: Measure using published numeric offsets or coordinates to make up the series of endpoints to derive a rib
6: Use an airfoil generated by one of the popular programs and match the hand drawn airfoil to one of those shown in a catalogue to what you may need.
It is probably best to use the program generated airfoil, as it is a much smoother representation than what can be obtained by and of the hand interpretations. However, just getting to the general shape of the airfoil shown on the plans may take quite some time, as determining the airfoil may take longer than doing via hand. Airfoil programs use templates or coordinates to calculate the exact shape in your computer and then print out graphically or convert to CAD line output formats. These output formats are then brought into your CAD software and used to develop parts or whole ribs for laser cutting.
Using an airfoil building program allows the draughtsman to so quickly alter the thickness, chord length and on occasion camber to match the ribs on your plan set. As the percentage of thickness is not always constant from wing root to tip, the option of altering this thickness by simply inserting a new number outweighs not using a program.
A couple of the available programs have little preview screens of what the airfoil number or file will look like. In lieu of such, I bring home a big handful of tossed away Xerox copies. I then print out one by one all the airfoils available and within a program to a chord of ten inches. The printer plotted out airfoil examples are then bound into book which I can flip through quickly to determine which comes closest to the one on the plan. This length of chord will enable you to much quicker determine thickness or camber.
If you are a bit unfamiliar with the terms chord length, camber, max thickness and other terms used in describing airfoils, it is perhaps best for you to visit the local library and locate a text book on airplane design. Within such should be definitions, and examples as to the terms, and how you can use them to obtain the airfoils designed for your model.
EXAMPLES OF AIRFOIL OUTPUT FORMATS
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