Tilt-Over Mast Questions?

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pgnsucks

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I read the Wiki on the Tilt-Over Mast using 2" & 1 1/2" steel pipe to get a 40' working antenna mast.

I do not have the math or engineering skills however I found a 2" x 1" x 3/16th" twenty foot sections of Channel for at least half the cost of the lower section in the Wiki.

Then with a cantilever section of steel pipe probably 21' of 2" & an additional section 21' of 1 1/2" pipe bearing 3' into the lower 2" section. It seems the same height of 40' feet could be achieved.

Cutting the Steel Channel in half with 5' below ground for each half with the other 5' of both sides above ground. Using Flat steel as needed for strength is this a viable consideration?

I am not asking anyone to engineer or stake their legal opinion however what are member's opinions?

I really like the Wiki article as with a Winch added it makes the set-up safe. It also allows for raising and lowering the mast simpler for maintenance and addition or subtraction of an antenna much simpler.

Right now I am at 30' with a Diamond scanner antenna however the additional 10' that could easily be raised and lowered to the ground without guying sounds interesting. I would also like to leave open adding say a Dipole off a pulley mounted on the mast for future ham interests.

Again most members are much more experienced than I am and I am only asking for general opinions on whether you think this might work.

For clarity here is a link to the Tilt-Over mast on this sites Wiki;
Tilt-Over Mast - The RadioReference Wiki
 

LtDoc

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I'm not familiar with the 'pipe'/tubing you've quoted, so can't say much about it's 'strength'. I'm familiar with some of the 'oil field' pipe though, and have every reason to think it would do to make a tilt-over type mast as you are talking about. diameters range from 3 to 4", so even if there's some flexibility in that pipe, it ought'a work just dandy. Three 'sticks' of that stuff should get an antenna something like 30 - 60 feet in the air. (Two planted in the dirt, one section swinging between them, right?) Living in Oklahoma where the wind does go whipping across the plains, heavier than necessary is a very nice idea, you know? Your milage may vary, who knows, but bigger is better to some ridiculous extent.
Have fun...
- 'Doc

And just for grins... I've seen a beer keg bolted to the bottom of that swinging-arm. Fill it with water and the thing stand up straight. Drain the water out of that keg and down she comes. Ain't that a neat idea?!
 
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N0IU

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And just for grins... I've seen a beer keg bolted to the bottom of that swinging-arm. Fill it with water and the thing stand up straight. Drain the water out of that keg and down she comes. Ain't that a neat idea?!
But if you actually fill the beer keg with beer, you won't have any problems finding people to help you with your antenna work!
 

kc5uta

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But if you actually fill the beer keg with beer, you won't have any problems finding people to help you with your antenna work!
BEER???? I'm IN ...I'll bring the BBQ Pit and some Pecan wood...oh wait this a radio forum...sorry..in that case ...... I am looking into a falling derrick type of arrangement for my home QTH. I am way too lazy to climb that 65 footer with any regularity. When in doubt...overbuild!!!

beer???? : )
 

QDP2012

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Use caution when mixing pipe-diameters

...Then with a cantilever section of steel pipe probably 21' of 2" & an additional section 21' of 1 1/2" pipe bearing 3' into the lower 2" section. It seems the same height of 40' feet could be achieved.

Cutting the Steel Channel in half with 5' below ground for each half with the other 5' of both sides above ground. Using Flat steel as needed for strength is this a viable consideration?
You probably already considered each of these ideas, but the general-purpose cautions that stand-out to me are:
  • The physical differences between channel and pipe. (Links are for picture illustrations only.)
    • Round-pipe and U-Channel do not react to weight loads in the same manner.
    • Regardless of load-direction, round-pipe behaves uniformly.
      • A round-pipe vertically in the air can resist wind from direction-A just as well as from direction-B.
    • U-Channel is "weaker" depending on the load's-direction.
      • A U-Channel is "weaker" if the wind blows against the broad side of the Channel than if it blows against the narrow side.
      • And, under certain circumstances, the U-Channel will be "weaker" if the wind is blowing against the bottom of the U versus the top of the U.
        • This same stress situation is why off-road-vehicle builders will "box-in" the vehicle's frame, meaning the missing fourth side is welded-on to create a rectangular pipe, for added strength.

  • Joint-Weakness:
    • Joints that involve a diameter-change (like described above as 1.5" tubing inserted into the 2" tubing) can become failure-points, shear-points, or recurring-maintenance points. Avoid diameter-changing joints when possible.

  • Cross-sectional area of the 2" diameter round-pipe vs the 1.75" diameter round-pipe:
    • The cross-sectional area is what protects your equipment, while elevated and during raising-and-lowering of the mast.
    • The shear-strength of the round-pipe is what resists the wind, because the wind will try to snap that pipe (like a broken pencil).
    • The longer (or higher) your mast is, the more important its cross-sectional area becomes.
    • Area of a circle is calculated as A = Pi x R x R, where R is the circle-radius (half-of-diameter).
      • To calculate for a cross-sectional area of a pipe, subtract the inner circle's area from the outer circle's area.
        • For the 2" diameter x 3/16" thick pipe, this calculates to 1.067 square inches.
        • For the 1.75" diameter x 3/16" thick pipe, this calculates to 0.9199 square inches.
          • That is a 14% loss of cross-sectional material if you change from 2" to 1.75" diameter pipe.
        • For the 1.5" diameter x 3/16" thick pipe, this calculates to 0.7727 square inches.
          • That is a 27.5% loss of cross-sectional material if you change from 2" to 1.5" diameter pipe.

  • Recommendations:
    • Strictly from a natural-strength perspective (without any other design-information other than what you've described above), I would recommend:
      • use only pipe (not U-Channel)
      • do not use pipe smaller than 2-inch diameter

  • Disclaimer:
    • I have no affiliation with the linked-site wagnercompanies.com, and I am not a professional engineer.
    • Depending on the actual material used and the specific design, as they say, "your mileage may vary".
Hope this helps,
 
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tonsoffun

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Hi,

Using a U channel will be fine but certainly not the size you listed, way to small. You need some good strength down at your base, using a u channel I would not go smaller then 4"HX2"HX1/4 thick. You will find that your price for the channel is going to increased.

For the base, wind really is not going to move this one bit and not really an issue ( I know I have been at the base while a wind storm was upon us), you will notice that the mast has its flex not the base (But needs to be strong) Your 1 1/2" pipe going into the 2" has to be very snug, if its not then you have to worry about shearing and your bolts breaking.

My tilt over mast (The one in the wiki) has been up for about seven years and winds up to 70 MPH, nothing has broke,cracked etc It does sway about 5" in either direction in a good storm.
 
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