[Towertalk] Mast placement in tower top

[JBaumgarte@aol.com]

In a message dated 4/12/02 3:03:33 PM Central Daylight Time, w9ac@arrl.net 
writes:

<< 
 Is there any documented work relating to the optimal mast position within a 
tower?  For example, if one contemplates using a 20-foot
 steel mast with a Force12 C31 on one end, inserted into Rohn 55, what length 
of mast should rise above the tower's thrust bearing?
 
 -Paul, W9AC
  >>
I have a 20' chromolly mast with 1/2" wall 4' in the Rohn 55 tower and 16' 
out with a C31XR at 1', F12 180C up 8', and Mosely 2 el 40 at 15' (boom guy 
for Mosely at 16').  It's been there several years, survived storms that blew 
down 100 yr old trees, etc.  I do have two thrust bearings--one on top plate 
and one between rotor and top plate.  I've watched it in a 80 MPH wind and 
the mast bends about a foot.  Kinda tricky getting the 180# mast into the 
tower top  :-)    Next time it goes in the tower first!

K5RC (now a 7 in NV), who sold me the mast, has a nice program relating to 
the stress loading on the mast with installations like this.  Don't know 
about documentation regarding exactly how much the Rohn 55 tower can stand.

John, N0IJ
Duluth, MN