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 ```How does this wind loading information apply to a bertical antenna which is rigidly mounted at the base and flexes in the wind? In addition, if the vertical antenna is mounted on top of a 22 ft tower, which is anchored in concrete, how does this info apply? 22 ft tower is short in comparison and maybe can be considered non-movable and then the vertical can be seen as the same as if it were mounted on the ground. Dan Schaaf K3ZXL "In the Beginning there was Spark Gap" www.k3zxl.com ----- Original Message ----- From: "Charles Coldwell" To: "Tower and HF antenna construction topics." Sent: Thursday, February 18, 2010 2:55 PM Subject: Re: [TowerTalk] wind load On Thu, Feb 18, 2010 at 2:02 PM, Gene Smar wrote: > > To get these figures into engineering terms, you'd have to convert the > wind speed into pounds-per-square-foot > http://www.arraysolutions.com/Products/windloads.htm and multiply by the > EFFECTIVE area of the antenna. Then this force is applied to the top of > the > tower; let's say the tower is 100 feet tall. In the example, the force of > a > 70 mph wind is 12.54 psf. The total forced applied to the tower at 100 > feet > AGL would be 12.54 X 15 = 188 pounds. Well, that is substantially less than the 450 pounds I came up with from the "30 pounds per square foot in a 70 MPH wind" rule mentioned upthread. > The trick comes in determining what the effective area (sqft) of the > antenna really is. Manufacturers are unclear in their literature in how > they calculate the advertised areas of their antennas. I suppose this is due to uncertainty in the drag coefficient since the geometric cross-section should be unambiguous. Rewriting the Array Solutions formula as F = A * 0.00256 * W * W * Cd the effective cross-section is the product A * Cd, where A is the geometric cross-section, and Cd is 1.2 for long cylinders and 2.0 for flat plates. > That calculation showed that my D40 rotatable dipole had a spec from > Cushcraft of 1.3 sqft, whereas the "shadow area" of the elements > calculated > out to be 3.55 sqft. Go figure. Yeah, I can't make up that difference no matter how I play around with drag coefficients. -- Charles M. Coldwell, W1CMC "Turn on, log in, tune out" Winchester, Massachusetts, New England (FN42kk) GPG ID: 852E052F GPG FPR: 77E5 2B51 4907 F08A 7E92 DE80 AFA9 9A8F 852E 052F _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```