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@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)
>
>
>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|