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## [TowerTalk] Antenna surface area

 To: [TowerTalk] Antenna surface area SPELUNK.SUENO@prodigy.net (EUGENE SMAR) Sun, 10 Jun 2001 00:11:36 -0400
 ```Mike, Bill, et al: Hold everything! Multiplying by 0.6 or 0.67 as a shape factor is NOT the correct number. It's 1.2 - at least according to Mechanical Engineering in Radar and Communications, one of K5IU's references. Let me go through this again. A long, thin cylinder's drag coefficient is 1.2 (above) or the book's wrong! A flat plate's drag coefficient is 2.0 according to the same book. Therefore, 1.2 is 60% of 2.0. In other words, the effective area (taking shape into account) of a Yagi tube is 1.2 times GREATER than the projected area (simply L X diameter), not 40% LESS. Big difference and the reason I've begun questioning manufacturers' spec sheets. (Jump in here anytime, Dick.) 73 de Gene Smar AD3F -----Original Message----- From: Michael Tope To: Bill Hider ; EUGENE SMAR ; towertalk@contesting.com ; Stu Greene To: Date: Saturday, June 09, 2001 11:08 PM Subject: Re: [TowerTalk] Antenna surface area >Bill, > >Gene specifically said that he was calculating projected area without any shape >factors. The projected surface area at right angles to a cylindrical tube is simply >diameter x length. The effective area is computed by including the drag coefficient >of the object. For a cylinder, the drag coefficient is around 0.6. Thus the effective >area of an antenna with round members is about 40% smaller than the projected >area (a round tube of length, L and diameter D, is more aerodynamic than a flat >plate length L and width, D). > >73 de Mike, W4EF.................... > > >----- Original Message ----- >From: "Bill Hider" >To: "EUGENE SMAR" ; ; "Stu Greene" >Sent: Saturday, June 09, 2001 6:13 PM >Subject: Re: [TowerTalk] Antenna surface area > > >> The formula Gene proposed is not exactly correct, nor does he precisely >> state what to do with the taper. >> >> Regarding the formula, Gene's thinking is: If you think of the wind as >> hitting the tube broadside (at 90 Deg to the tube), the exposed surface area >> as seen by the wind looks like a rectangle whose length is the length of the >> tube and whose height is the full OUTSIDE diameter of the tube. Hence, L x >> Dia. Unfortunately, it is not that simple. >> >> The tube is a cylinder as seen by the wind, hence the angle that the wind >> *hits* the tube, even if it is perpendicular to the tube, hits at 0 Deg on >> the centerline and then the angle increases to 90 Deg as the wind hits the >> tube away from the centerline (above and below the centerline of the tube >> for a horizontal element). This assumes the wind-front is wider than the >> outside diameter of the tube, which is probably a very good assumption. So, >> the surface area exposed to the wind by the tube is not simply L x Dia. >> It's the exposed tube length times the integral from 0 to Dia of the surface >> area of each tube (Pi x Dia), where Dia is the Outside diameter of the tube. >> Gene, this is why the manufacturer's wind area is less than what you >> calculated, and theirs is correct. [If anyone has trouble picturing this, >> let me know and I'll try to explain it in more detail.] >> >> But, I question the correctness of adding all of these calculations up and >> saying that's the *wind area*. It certainly is the 1/2 of the *surface >> area* if it's done this way, but the wind cannot be simultaneously hitting >> the elements at 90 Deg and the boom at 90 Deg, so it should take that into >> account by specifying the *larger* of both calculations, but not the sum of >> both. >> >> Regarding the taper: each tube should be calculated separately for the >> *exposed* length of the tube *only*. Remember, some tubes are *inside* >> other tubes, causing the taper. >> >> Bill, N3RR >> >> >> ----- Original Message ----- >> From: Stu Greene >> To: EUGENE SMAR ; >> Sent: Sunday, June 10, 2001 2:42 AM >> Subject: Re: [TowerTalk] Antenna surface area >> >> >> > At 09:06 PM 6/9/01 -0400, you wrote: >> > >> > > Area = L X diameter for the exposed surface of each piece of aluminum, >> > > simple as that. >> > >> > >> > >> > Shouldn't the calculation be L X (Diameter X pi) ? Or length times >> > circumference? >> > >> > And this doesn't reflect tapering of the elements. >> > >> > >> > List Sponsor: Are you thinking about installing a tower this summer? Call >> us >> > for information on our fabulous Trylon Titan self-supporting towers - up >> to >> > 96-feet for less than \$2000! at 888-833-3104 > HREF="http://www.ChampionRadio.com";> >> > www.ChampionRadio.com >> > >> > ----- >> > FAQ on WWW: http://www.contesting.com/FAQ/towertalk >> > Submissions: towertalk@contesting.com >> > Administrative requests: towertalk-REQUEST@contesting.com >> > Problems: owner-towertalk@contesting.com >> > >> >> >> List Sponsor: Are you thinking about installing a tower this summer? Call us >> for information on our fabulous Trylon Titan self-supporting towers - up to >> 96-feet for less than \$2000! at 888-833-3104 >> www.ChampionRadio.com >> >> ----- >> FAQ on WWW: http://www.contesting.com/FAQ/towertalk >> Submissions: towertalk@contesting.com >> Administrative requests: towertalk-REQUEST@contesting.com >> Problems: owner-towertalk@contesting.com >> > List Sponsor: Are you thinking about installing a tower this summer? Call us for information on our fabulous Trylon Titan self-supporting towers - up to 96-feet for less than \$2000! at 888-833-3104 www.ChampionRadio.com ----- FAQ on WWW: http://www.contesting.com/FAQ/towertalk Submissions: towertalk@contesting.com Administrative requests: towertalk-REQUEST@contesting.com Problems: owner-towertalk@contesting.com ```
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