Towertalk
[Top] [All Lists]

Re: [TowerTalk] Wind loading comment misdirected? W7VP

 To: "Michael Tope" , "Bill" ,, Re: [TowerTalk] Wind loading comment misdirected? W7VP Jim Lux Sun, 26 Mar 2006 20:43:20 -0800
 ```At 06:17 PM 3/26/2006, Michael Tope wrote: >----- Original Message ----- >From: "Jim Lux" > >Stated another way, what does the Cd value look >like as a function of wind speed for say the 6" diameter pipe that >has a Cd of 0.18 at 60 mi/hr? Such widely varying drag coefficients >might suggest large diameter thin-wall masts are better than small >diameter thick wall masts with the same section modulus due to >lower drag coefficients, but only if the lower drag coefficient were >valid over a fairly wide range of windspeeds. here's the data for a 3" pipe v (ft/sec) re Cd lb/ft mi/hr 40 61,900 1.01 0.47 27 50 77,400 1.01 0.73 34 60 92,900 1.00 1.05 41 70 108,400 1.00 1.42 48 80 124,000 0.98 1.82 55 90 139,000 0.94 2.22 61 100 155,000 0.89 2.59 68 110 170,000 0.82 2.89 75 120 186,000 0.73 3.07 82 130 201,000 0.63 3.08 89 140 217,000 0.50 2.87 95 150 232,000 0.36 2.37 102 160 248,000 0.20 1.52 109 170 263,000 0.18 1.51 116 180 278,000 0.18 1.70 123 190 294,000 0.18 1.89 130 200 309,000 0.18 2.10 136 the peak drag is around 80-90 mi/hr, where the Cd is about .6-.7, so Leeson's ballpark number of 0.67 is in the right ballpark, at least for 3" diameter cylinders. If you use that, it's conservative for higher speeds. You have to get up to around 160 mi/hr before the load (now at a Cd of 0.18) gets to be the same. There's another factor that's not included here, and that's the effect of roughness.. You might get low "form drag" from a large diameter tube, but now there's more "surface drag" because the length of the surface is bigger. Some more fiddling is needed, clearly. Jim _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread [TowerTalk] Wind loading comment misdirected? W7VP, NPAlex Re: [TowerTalk] Wind loading comment misdirected? W7VP, Jim Lux Re: [TowerTalk] Wind loading comment misdirected? W7VP, Bill Re: [TowerTalk] Wind loading comment misdirected? W7VP, Jim Lux Re: [TowerTalk] Wind loading comment misdirected? W7VP, Michael Tope Re: [TowerTalk] Wind loading comment misdirected? W7VP, Jim Lux [TowerTalk] Error correction: Re: Wind loading, Jim Lux Re: [TowerTalk] Wind loading comment misdirected? W7VP, Bill Re: [TowerTalk] Wind loading comment misdirected? W7VP, Jim Lux <= Re: [TowerTalk] Thanks everyone re Wind loading Question from K6XN, K6XN Re: [TowerTalk] Thanks everyone re Wind loading Question from K6XN, noddie