by Paul Gale
The method of drawing a car body plan described in this article is a basic guideline. Although most car bodies are designed using a combination of two or more airfoils, the example uses all 50% airfoils in order to simplify the explanation. A 50% airfoil has its maximum width at 50% of the cars length.
The following instructions outline how to draw formers for a 14 inch wide by 12 inch high car. All formers will be to the outside of the car body.
STEP 1 - Determine the plan view (looking down at the top of the car) airfoil(s) to be used. 50% for this example.
STEP 2 - Draw vertical and horizontal centerlines (see example sheet, page 6
STEP 3 - Using "Y" dimensions taken from the 7.00 inch column of the 50% Airfoil Data Sheet, plot Former 1 through 10 ordinates onto the horizontal centerline (side of car).
STEP 4 - Using "Y" dimensions taken from the 7.00 inch column of the 50% Airfoil Data Sheet, plot Former 1 through 10 ordinates onto the vertical centerline above the horizontal centerline (top of car).
STEP 5 - Using "Y" dimensions taken from the 5.00 inch column of the 50% Airfoil Data Sheet, plot Former 1 through 10 ordinates onto the vertical centerline below the horizontal centerline (bottom of car).
Step 6 - Draw Former at maximum width/height (Former 10 in this example). The shape of the maximum Former will establish the "LOOK" of the car. It can be drawn freehand or with basic drafting equipment: Compass, Triangle, and French Curves.
STEP 7 - Draw a minimum of four radial lines.
STEP 8 - Measure distance from intersection of horizontal and vertical centerlines to Former 10 along each of the radial lines.
STEP 9 - Calculate Former 1 through 10 ordinates for first radial. Using 7.00 inch column from 50% Airfoil Data Sheet, divide length of radial (a) by 7.00: (a) divided by 7.00 = (b). (Example: If radial measured 5.25, 5.25 divided by 7.00 = .75). Multiply each ordinate ("Y" Dim) in the 7.00 inch column by (b). (Example: Former 6; 6.233 x .75 = 4.675). This will establish the radial's ordinates.
STEP 10 -Repeat STEP 9 for each radial drawn.
STEP 11 -Draw Former 1 through 9 by connecting the ordinates for each Former. (Just like drawing a picture by connecting the dots).
STEP 12 -Draw a second vertical and horizontal centerline.
STEP 13 -Redraw maximum Former onto new centerlines.
STEP 14 -Using "Y" dimensions taken from the 7.00 inch column of the 50% Airfoil Data Sheet, plot Former 11 through 15 ordinates onto the horizontal centerline (side of car).
STEP 15 -Draw a minimum of four horizontal lines. Two above the horizontal cent6rline and two below.
STEP 16 -Measure distance from vertical centerline to Former 10 along .each horizontal line.
STEP 17 -Calculate Former 11 through 15 ordinates for first horizontal line. Using 7.00 inch column from 50% Airfoil Data Sheet, divide length of horizontal (c) by 7.00: (c) divided by 7.00 (d). (Example: If horizontal line measured 6.12, 6.12 divided by 7.00 = .874). Multiply each ordinate ("Y" Dim) in the 7.00 inch column by (d). (Example: Former 14; 2.937 x .874 = 2.567). This will establish the horizontal line's ordinates.
STEP 18 - Repeat STEP 17 for each horizontal line drawn.
STEP 19 - Draw Formers 11 through 15 by connecting ordinates for each Former.
NOTICE: Full size Senior Division car body. plans are now available for purchase - $3.00 postpaid. Contact your NDR Regional Manager or obtain a copy of the latest NDR Racing Report for additional information.
* Most people do not have easy access to NACA Airfoil Data Sheets. DERBY TECH will be publishing these Data Sheets - one per issue. -- ED.
