[TowerTalk] Yagi torque balance

[Steve Maki]

K6MR was kind enough to send me an article by K5IU that sheds some light 
on this issue. It's not intuitive (at least for me), but when you look 
at his drawings of the vectors and accept the formulas, you can see that 
the boom does NOT go in-line with the wind even in the case of a one 
element yagi with the element at one end of the boom.

K5IU shows, in the course of debunking commonly accepted methods of 
determining wind area of a yagi, that when you have crossed tubes, the 
minimum wind force occurs when NONE of the tubes are either in-line with 
or perpendicular with the wind. It doesn't matter how the elements are 
distributed. Only the relative areas of the boom vs the elements. If the 
areas are the same, than minimum wind force occurs at 45° offset. If one 
or the other has more area, than it's some other angle, but always 
oblique from the wind direction.

By extension (my take from the article) is that if allowed to, the 
assembly WILL rotate to the minimum wind force position. It may be that 
the torque for a given wind speed is not all that great, but the torque 
must be there.

So it still seems to me that the assertion that yagis are automatically 
torque balanced just by mounting them at the boom center is not true.

I hope Dick Weber won't mind if I post a url to his article.

https://app.box.com/s/40l9icahrtlpqoyd0zppp9vdxn5ck1xc

-Steve K8LX


On 9/3/2019 10:59 AM, dj7ww at t-online.de wrote:

> No, the wind aerea at the boom side with the element on is much larger then on the opposite side and turns the boom into the direction of the wind, always!
> 
> 73
> Peter
> 
> 
> 
> 
> -----Original-Nachricht-----
> Betreff: Re: [TowerTalk] High VSWR
> Datum: 2019-09-03T14:21:19+0200
> Von: "Steve Maki" <lists at oakcom.org>
> An: "towertalk" <towertalk at contesting.com>
> 
> I can't wrap my head around this.
> 
> Yes, the element is "torque balanced" at it's own center, but at the
> boom center? I think not.
> 
> -Steve K8LX
> 
> On 09/02/19 12:41 PM, Jim Thomson wrote:
> 
>> ##  vane NOT  required if boom  mounted at  center.   Counterweight  IS  required....at  light end.
>> ##  Longer  eles... and  number  of  eles  has  nothing to  do with with it.    Each  ele  is  symetrical...so  the  eles  are  already tq  balanced .    If  wind  hits the  eles  at  an angle......  and  viewed from above...  left  side  of  eles  bends CW.....
>> meanwhile right  side of  ele  bends  CCW...... they  cancel out...... or  vice versa.   The  eles  are  still  tq  balanced.
>>
>> ##  I tried  this  experiment.   40  ft  boom.....  mounted   at  exact center  of  boom....to  mast.  Only  ONE  20m  ELE USED...THE REF..... mounted   of course, at extreme  end of  boom.   no  counterweight used for  this  test.   No  coax,  no  rotor.
>> Does  not  rotate,  nor ....weathervane,  etc.   Stays  put,  regardless  of  windspeed,  or  where boom  was oriented by  hand.