Gregg:
The 87,000 is the stress in pounds per square inch required for the metal to
yield. You need to know the cross sectional configuration of your mast, (OD
and wall thickness) and calculate what is known as the "section Modulus".
You then divide the bending force in inch-pounds by the section modulus to
determine the actual stress for your assumed conditions. Then divide the
answer into 87,000 to determine your safety factor.
You should have a 2:1 safety factor for good, safe design.
If you want I can send you an Excel file with various size mast
configurations with section modulus figures and you can figure what is best
for you.
73s
Bob, W5LT
-----Original Message-----
From: Gregg Seidl [mailto:k9kl@centurytel.net]
Sent: Saturday, November 18, 2006 4:48 PM
To: TowerTalk@contesting.com
Subject: [TowerTalk] mast strength
I'm considering stacking a Cushcraft XM-240 and 10 feet below that per
Cushcrafts recommendations an X-7.I want to make sure that I get a
strongenough mast so it doesn't go horizontal on me.The windload @ 80 MPH
is142 pounds for the XM-240 times 10 feet is 1420 plus 202 for the X-7 comes
to 1622 pounds of bending force.Is this right?I see masts being rated at
87,000,what does that mean,it takes 87 kpounds to bend it???Doesn't seem
right.Thats a LOT of force,thats like driving our big John Deere on it and
it wouldn't bend until the 4 foot level 20000 pound tractor times 4
equals 80000.......I think I'm missing something here. Gregg K9KL
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|