image

Wind Load (lb/ft)
MPH Plate Sphere/Tube Airfoil
10 .30 .10 .01
25 1.9 .60 .07
50 7.6 2.4 .27
75 17 5.4 .60
100 31 10 1.1
125 48 15 1.7
150 69 22 2.4
175 93 29 3.3
200 122 38 4.3
225 154 48 5.4
250 190 60 6.7

Wind Load


F = a * cd * [d * v2]

  Wind speed (mph)
  Area (ft2)
 Air density (slugs)
Shape (Cd)

  Total force (lbs)  

Introduction

This formula determines the force on an object in a wind. I.E. A length of tubing or flat surface that is part of a structure. The force per unit area would be found by setting the area to 1. The results are based on standard temp and atmospheric pressure. A safety factor should be included in any design using this formula.

The Generic Formula

      
      Force: f = a * cd * [d * v2]  brackets denote air pressure (standard atmosphere)
      Where:
        f   = force (lbs)
        a   = frontal area (ft2)
        cd  = coefficient of drag
        d   = air density (slugs)
        v   = wind speed(mph)
      
      Cd: Drag coefficient of shape
        1.5  for flat plates
        1.2  flat faced triangle
         .3  bullet 
         .4  sphere or tube
         .1  airfoil 
 
      Example: What is the pressure on the rudder of an airplane spinning 2 
               rotation per second with a vertical tail volume of 10sq/ft and
               a rotation arm from the cg of 12ft?

        preparation: The tail speed can be determined using...
          v(ft/sec)   = 2pi * r / t 
                      = 6.28 * r / t
            r = radius, t = time(sec) for one rotation
        so:  
          151(ft/sec) = 6.28 * 12(ft) / .5(sec) ...1/2 sec per rotation
          102(mph)    = 151(ft/sec) * .68       ...since 1ft/sec = .68(mph)
        
        using: f = a * cd * [d * v2]
        
        given:
          f   = (lbs)
          a   = 10(ft2)
          cd  = 1.3(flat)
          d   = .00237(slugs@sea level)
          v   = 102(mph)
          v2  = 10404(mph2)
          
        solution:
          f = a * cd * [d * v2]  
            = 10 * 1.3 [.00237 * 10404]
            = 321(lbs) total wind pressure