Tuesday, August 31, 2021

Gin Pole Calculations for Tilt Up Tower

This post is meant to be for the KidWind team that wants to go the extra mile and learn a bit more about the process and keep the engineering going. So what goes into designing and planning a tilt up tower for a 300 watt Air-X wind turbine? 

I hear or read, I forget.       I see or watch, I remember.        I do it, I understand!

This will be about a guyed "tilt-up" tower. The big question. How strong is strong enough?  Design and build your system to stand up to 50 m/s (110 mph) max force wind (worst case) with a safety factor of five and you will be able to sleep through any weather event!

Lets look at the F.A.T. (Frontal Area of the Tower) and swept area of the turbine. At 50 m/s you can count on a force of 250 kg/square meter of area to the wind.

We have a .1m wide by 6m tower = .6 sq/m and a .6m radius rotor on the Air-X = 1.13 sq/m 

Total FAT = 1.73 sq/m x 250 kg = 432.5 kg (951.5 lbs) force at 50 m/s (110 mph) wind velocity. Times the safety factor of 5 means designing it to withstand 2162 kg (4757 lbs) of force. 

This will help decide the rigging and anchor sizes needed for the tower guys.

Now the raising  of the tower is another story...

In our example with a 6m (19.5 ft.) tower weighing 17.27 kg (38 lbs) and 11.36 kg (25 lb) 300 watt turbine for a total weight of 28.63 kg (63 lbs) you could probably just "muscle" the tower up to vertical and tighten up the guys. However this will help prepare you for bigger projects.

Anyway you need to think about the forces at play when you try to lift a hinged tower, to vertical, with a weight at the end of tower by pulling on a rope. 

First, understand that lifting a 28.63 kg (63 lb) weight straight up with a rope would require a force of 28.63 kg (63 lbs)

Second, understand that lifting a weight by pulling at an angle is going to require more force than the weight of the object (the pole and turbine) you are lifting.

Third, the angles of the lifting rope to the weight determine the fore you will need to lift the tower and turbine.

The vertical line in the drawing represents the gin pole. The force will be brought down to the ground level (thick black horizontal line) forming another angle that will also impact the winching force needed to raise the tower and turbine from horizontal to vertical.

This graph shows the rapid increase in force needed the shorter the gin pole is compared to the length of the tower. 

This table shows the rope angles 'a' and 'B' in degrees and the Increased Force or Tension Factor when the gin pole is rigged. Remember a second set of angles from the top of the gin pole to the lifting winch also needs to be calculated.

So if you are ready lets now look at what should be in the "kit" to put all these calculations into practice and "do it!"

Hard hat
811 Diggers Hotline number
25 foot extension cord
Marking flags
Milwaukee drill
Screw Anchor Driver
4 Long screw in anchors 
6 meter tower
Metric measuring tape
Spring clamp
12 volt battery
Wind Data station (white box)
20 volt cordless drill

2 - 3/4" diameter hinge pins w/bolts
#1 Phillips screwdriver
3/8" hexagon wrench
5/16" nut driver for drill
3/8 drive 3/4" socket
3/8 drive 7/8" socket
3/8 driver for drill
7/16" - 1/2" open end wrench
5/8" by 6" long bolt
Wind Data Collection units w/hose clamps
Red weather station box w/hose clamps
1-1/4" by 2.3m long gin pole
4 lengths of 3/16" wire rope with end fittings
Air-X rotor blades
Air-X nose cone
Air-X turbine w/mount and wiring

2 - 3/16" wire rope stabilizer cables with end fittings
Tower base
4 - short screw anchors
40 : 1 worm screw drive winch
2 - winch mounting rods


Name                        Description                                        Load Capacity
Gin Pole                   1-1/4" Schedule 40                             255 kg     (562 lbs)
Anchor Cable            3/16" wire rope                                7.56 kg     (1700 lbs)
Schakel                     5/16"                                                   454 kg    (1000 lbs) 
Turnbuckle                3/8" closed end                                    545 kg    (1200 lbs)
Winch                        Worm Drive                                        454 kg    (1000 lbs)
Short Screw Anchors    12" by 3" diameter                        227 kg    (500 lbs)
Long Screw Anchors    30" by 4" dia                                 454 kg    (1000 lbs)                                 

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