[TowerTalk] Rohn HDBX48 failure

[Chuck Sudds]

OK.  Here are the dirty details, as I remember them from 7-9 years 
ago....  Put up the HDBX48 in 1993 with a huge concrete base.  I am in 
Western Iowa and out in the middle of 10,000 acres of corn fields.  At that 
time, I only had an old Mosley TA-33 mounted on top of it.  The rotor was 
mounted in the top section in the normal position.

After burning up the traps in the TA33 (literally!) I opted to go with a 
trapless antenna and chose the KT34XA.  SInce I already had the HDBX48 
mounted out back, I installed the KLM antenna up there about 6 inches above 
the tower with the rotor still in the normal position.

About a year later, I noticed some severe twisting in the tower and a 
closer inspection revealed quite a few rivets had popped our or loosened in 
the top two sections of the tower so we tilted the tower over and removed 
the KT34XA and the two top sections.  Jim Smith at Burghardt's sent me the 
two top sections and we replaced them.  At the same time, we decided to 
mount the T2X rotor lower in the tower, to help with the twisting, as 
several have indicated.  I went to a local machine shop and had them build 
me a rotor plate of the proper dimensions, so that it would mount inside 
the largest base section, about 6 feet off the ground level.  Worked great 
and they only charged me $35.  5 sections of 2 inch (approximately) HD 
electrical conduit from the local Menards store, along with 4 threaded 
couplers.  I installed the rotor and proceeded to install the 50ft mast one 
section at a time, using 4ft pipe wrenches to first tighten them together 
and then pinning them by drilling through 1/2 the mast and using 
self-tapping screws.  BTW, after the failure, none of these screws had come 
loose!

Everything was put up and it appeared that this tower was going to do the 
job A-OK.  Just to be sure that there would be little or no twisting, I 
installed three aircraft cable guys at about 46ft where the rotor would 
have normally mounted.  I simply looped the cable around each leg and guyed 
the ends to existing structures on my property.

The following May, we were hit with 100MPH straight-line winds which 
actually blew some rail cars off the tracks in this area!  I knew they were 
coming by listening to the local weather spotters net but could do nothing 
but point the beam(s) into the wind.  They hit the tower with so much force 
that the aircraft cable guys literally cut right through the legs of the 
HDBX48 metal on one leg!  This caused the tower to actually fold over at 
the 6ft level, right where the new rotor plate was mounted!   Had I mounted 
right at ground level, there is a chance, I guess, that it just might have 
survived ;)

As I said, thankfully there was no damage other than the total loss of the 
tower and antennas.  The rotor survived, as did the mast, except for the 
top piece.  I had alot of damage photos but can't seem to find them right 
now but if I do, I will put them out on my web-site for viewing.

Chuck KØTVD


>Chuck.  The devil is in the details.  Please share with us the details of
>your loss. Was your HDBX48 sensibly guyed?  Share how you had guyed the
>tower.  Did the guys break or pull out first?  Was the tower guyed at the top
>and also lower?  What was the wind speed?  Was it a hurricane or tornado?
>How long a mast did you use?  How far above the apex of the tower was the
>KT34XA mounted?  Did the mast collapse first?  Was the HDBX48 mechanically
>sound?...i.e all cross braces in place and secured.
>
>Doug/VA5DX