[Towertalk] Quad question for mechnical enginners

[Vaclav Sal]

Being ignorant in the subject I need some professional opinion on this
mechanical problem. 

I am building 4 element 20 meters quad with the following physical
characteristics:
Boom length  - 40 feet
Boom diameter  4 inches 
Elements - spreader made from two 2 feet long aluminum angle ( ¾ by ¾ inch)
Elements - bamboo 
Wire - 20 gauge stranded plastic coated ( surplus )

Each element weight is approximately 10 pounds - this is educated guess on
my part.


I have a crank up tower ( two sections approximately 35 feet high extended)
with two guy wires sets - one attached to the stationary part which I assume
will be the main ones to keep the thing from falling over. The top guy wires
are just to keep the top section in place.

Since my element spacing is approximately 10 feet, I will need some
clearance for the top guy wires and the boom must be mounted some distance
above the top guy wires. 

The question is :
If I use thrust bearing on the 2 inch aluminum conduit mast ( two coupled 10
foot sections) - what should be the SAFE height of the mast above the top of
the tower?
I am guessing that the mast could act as a spring and the section inside the
tower should be as long as feasible. I just do not want to bend the section
above the bearing if it is made too long. 

My rotator is garden variety Ham rotator - no brake. I am not too concerned
if the rotator cannot handle the start/ stop . My main concern is not to
bend the mast above the bearing.

I  am no looking for detailed analysis, that would be waste of time. I just
need some expert opinion.

PS The monster is in the back yard with plenty of clearance to land "safely"
if necessary. Hi Hi.

73 Vaclav AA7EJ