In a message dated 97-04-03 12:57:19 EST, alsopb@vance.net writes:
> K7> Thanks for the support of the latest TOWER TECH product, the MARC
> K7>Program. This Mast, Antenna and Rotator Calculator software program
> takes
> K7>wind speed, antenna load and spacing and calculates the bending moment
of
> th
> K7>system. It then specifies a mast size, wall thickness and tensile
> strength.
> 73, Steve K7LXC
> Does it do Quad's? I'm interested in seeing if my 4 el 5 band quad and
> rotatable 40 dipole are within mast limits.
>
> Since I know the mass of each quartet of "elements" and approximately
> the center of gravity of each, maybe I can model the quad as a beam?
> Alternatively, the manufacturer of the quad and dipole have supplied sq.
> ft of each and maybe all that's needed-- at least for the bending
> moment.
>
To calculate the mast bending moment, you're primarily looking at
antenna square foot wind load so the answer would be yes, it'll handle quads.
I'm not sure what you mean by 'modeling' the antenna. The
'fill-in-the-blank' parameters for mast calculations are wind speed, antenna
square footage and height above the tower. Other information such as weight
and turning radius are used for the Effective Moment rotator calculation.
> How is the thrust bearing modeled? Is the calculation done assuming the
> mast to be pinned at the thrust bearing? I guess the torque can be
> assumed to be directly passed through to the rotor? It seems one needs
> to know more than bending moment, doesn't one also have to worry about
> shear strength at the rotor caused by the torque and in the case of Hamm
> rotors brake (aka break) application? I'm assuming one needs to compute
> the torque requirments to specify a rotor.
The thrust bearing doesn't enter into it. We just want to know what
the bending moment of wind forces on the mast is. That is relative to the
top of the tower.
> Does the printout of recommended mast parameters have both separate
> edits for steel, chrome moly, aluminium etc?
>
The calculation tells you what the bending moment in inch/pounds is and
MARC tells you what tensile strength and wall thickness is required for THAT
figure. There is some information on relative tensile strengths of different
mast materials that's included in the program. MARC gives you enough
information so that you can call a tubing supplier and order a suitable mast.
Hope that answers your questions.
73, Steve K7LXC
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