[TowerTalk] HF winch

[Mike Reublin NF4L]

Great Jim, thanks!

Lets say 1200 lbs., length of 32' including mast.

So 1200 x 32 / 10 = 3840.

Cos(0) = 1, sin(45) = .707

3840 x 1/.707 = 5430 lbs. initial pull, correct?

Halving that with a 2:1 pulley system = 2715 lbs., a bit over the winch rating. A 3:1 pulley arrangement drops it to 1810. Do-able but close to the edge.

Mike NF4L

On Feb 3, 2014, at 9:48 AM, Jim Lux <jimlux at earthlink.net> wrote:

> On 2/3/14 6:26 AM, Mike Reublin NF4L wrote:
>> Thanks David,
>> 
>> The plan is to have a 10' tall mast, and attach the cable 10' from
>> the bottom of the tower, giving a circa 45 degree pull when the tower
>> is horizontal.
>> 
> 
> How tall is the tower?
> The "down" force at your 10 foot pick point is tower weight* length/10
> 
> As an example, say you've got 50 feet of Rohn25, which weighs about 200 pounds.
> 
> So, if you had a scale and were lifting straight up on the horizontal tower at the 10 foot mark, it would be about 1000 pounds (= 200 lbs * 50 ft/10ft)
> 
> But you're not picking straight up, you're pulling at a 45 degree angle, so the actual pulling force is more like 1400 lbs.  (= 1000lbs/sin(45))
> 
> When you're half way up (tower at 45 degrees) the angle for the pull is better (22.5 degrees) and the load is less (because some of the weight is being carried by the base of the tower).  The pull is now
> 
> 1000lb*cos(45)/sin(67.5) = 1000 * 0.707/0.924 = about 770 lbs
> 
> And then it rapidly gets better.
> 
> 
> For your specific case of a pick point at 10 ft and a 10ft high pole with the winch, the formula is:
> 
> load in lbs = weight of tower * length of tower/10 ft * cos(angle of tower with respect to ground) / sin(angle of cable with respect to tower)
> 
> At the beginning, with tower flat on ground:
> angle of tower = 0
> angle of cable = 45
> 
> At the end, with tower vertical
> angle of tower = 90
> angle of cable = 90
> 
> 
> 
> 
> 
>> Do you know a formula a non-engineer could use to calculate the pull?
>> The ones I find are all based on Newtons, And not the one I know,
>> Fig.
>> 
> 
> 
> 4.5 Newtons = 1 pound  (approximately)
> 
> 
> 
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