Hi Roger, your points are well taken:
In a message dated 97-11-11 00:07:08 EST, you write:
<< I'll try once more to clarify by restating my
question.... Is it preferable to turn or park one's beam into the wind
[elements
taking the brunt of the blow] or 90° to it [boom taking the brunt of
the blow]? >>
Yes, vis a vis, my "bather in the surf" simplification. However, in some
cases, the answer can be no (discussed further on).
<<Wouldn't it be prudent to turn the beam perpendicular to the prevailing
wind to minimize the stress on both the beam and the tower.>>
Yes, in most cases (discussed further on).
Ref my "Einstein's theories correlated with vector analysis and basic wind
loading computations.":
<"I take it you are kidding about Einstein who worked in areas of physics
Newton rarely dreamed of. Newtonian physics coupled with vector
analysis are all that are needed here.... methinks.">
Actually, I wasn't kidding. I was trying to keep the empirical dissertation
out of it to conserve time on TT; hence, the "bather in surf" example. Not
to belabor this side issue, I agree with you, not that I am judging Newton's
dreaming abilities, that he probably didn't dream of Einstein's realm of
capacities. Newton preceeded Einstein by 300 years, I believe that, given
Newton's various theories; principles; law, and Newton himself, in HIS time,
would have a little difficulty with the concept we are contemplating here
some 350 years later (and I would have had difficulty with his concepts had I
been there-I'm no Newton!!!)
<Some have mentioned the "weather-cocking" tendency of
"freewheeling" beams as evidence that a weather-cocked beam experiences
the "least wind resistance" and therefore the least wind load. That
concept... I fear, is in grave error... simply because it is in this
position that the beam is measured to derive it's MAXIMUM WIND LOAD
SPECIFICATION! >
I agree. If one mounts members (i.e. elements) that aggragate MORE physical
area as comparred to the member that is at right angles to these elements
(i.e. the boom), the result is a max wind load will be effected upon the
antenna. If the antenna is freewheeling, it will equalize in the position of
most surface area, hence the most resistance, 90 degrees to the wind
direction. Thus, if one wants to reduce or minimize wind load, the boom
should be 90 degrees to the prevailing wind direction which will require
adequate breaking restraint force, which also results in issues of torque
through the mast, rotator, and tower. This then raises the consideration as
to the particular installation's ability to handle such torques, in given
wind condtions, as compared to its ability to handle forces associated with
a freewheeling antenna under the same wind velocity factors, i.e. the
antenna experiencing max load, which imposes DIFFERENT loading concerns to
mast, rotar and tower. Thus my qualified earlier answer of "yes" to
agreeing with your conclusions.
One could go on and on with this, i.e, the significance of pneumatic flows
in measuring load resistance and the resultant comparison of actual loads,
free wheeling vs. fixed or braked, to the extent that, again, the
considerations as to the ability of the associated structural parts to
handle these two altenatives. There are thus cases where the freewheeling
approach may be the best vs. fixed, and vice versa. Enough said and again,
these are obviously my opinions (I won't print the disclaimer here-HI)
thanks, 73, Steve Davis, K1PEK
DAVIS RF Co., Commercial wire/cable, RF connectors, custom cable design. BURY
-FLEX ? low loss HF-microwave coax; FLEX-WEAVE ? aerial wire. Registered
trademarks of Davis Associates, Inc.
P.S. <And therein lies the confusion! > Jim, I would suspect that Einstein
and Newton made the same remarks, thus, you are a learned man as well, I'm
sure!!
--
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