[TowerTalk] aircraft bearing

[Dino Darling]

Hello John,

I had the pleasure of getting a free tour of Alpha by you when I was living in Colorado.  I will never forget that!

On to bearings...

I've been reading this thread with great interest.  I wasn't getting it at first.  Sometimes the term, "thrust bearing" gets confused in the tower arena.  "Thrust Bearing", in my vocabulary, means taking on SIDE loads in one dimension, like a thrust bearing in an engine that prevents the crankshaft from moving fore and aft, but not responsible for supporting that crankshaft.  When we speak of tower masts, we take on loads in two dimensions; vertical and side.

So this is how I try to separate the two (your mileage may vary).

  The "bearing" used to take the side loads, I call, a "BUSHING".  I believe the majority of this thread was dealing with this type of bearing.  Simply, it's a 1" thick triangle plate, the size of, and bolted to, the top/rotor plate.  The center of this plate is drilled to accept the 2" mast and prevent it from touching the tower's metal parts.  We rub the bearing rather than the metal tower parts.  On the top of a "pointy" Rohn section, I've used a piece of PVC pipe, the length of the tower tube, as a bushing.  In both examples, they only provide support in one (side) dimension.

  The "bearing" used to take the vertical loads, I call the THRUST bearing.  It's just like the crankshaft, only flipped up vertical.  

(As a side note, it's my feeling that the majority of the bearings (fanfir) used to support the vertical load of the mast and antennas is used incorrectly.  They were designed to support horizontal shafts parallel (load) to the flange, not how we use them.  But, they seem to work OK.  A taper bearing would be a better option.  IMHO)

What I don't fully understand at this point, is how the UHMW (plastic) sheet is used to support the vertical load.  I'm assuming you are using 2 sheets.  How is the second sheet secured to the mast?  If possible, a picture is worth a thousand words!  :-)

Dino - K6RIX

-----Original Message-----
From: W0UN -- John Brosnahan <shr at swtexas.net>

If you end up using the UHMW to handle the vertical load as well, then
the large "washer" that sits on top of the UHMW to spread the weight
over a larger area will provide the UV protection needed.

--John   W0UN