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

MATERIALS DATA:

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)                                 

Wind Turbine Guyed Tower Raising with 300w Air-X

 

So what you see here is a 300w Air-X 12 volt DC generator mounted on a 6 meter guyed tower with an NRG micro site Wind Explorer Data Retriever attached to the tower.

Now if you are involved with KidWind or interested in learning the process and just what is involved in designing, rigging and raising a guyed tower like this then read on...

The goal in this posting is to show you the process and give you the leads for more research into the details that are required to have a SAFE and SUCCESSFUL project resulting in a raised wind turbine tower that produces electricity. 

First assignment is to get Hugh Piggott's Windpower Workshop book and read chapter 8 on Towers. Here is one of the diagrams that show just how the tower, gin pole and anchors are arranged.

And if you are going to try raising a tower of your (THIS IS A MUST for SAFEY REASONS) own go to the NRG web site and down load their 10 m TallTower Installation Manual and specifications document. 

NOTE: Newton learned a lot by having an apple fall on this head. If you live, having a 50 to 500 pound turbine fall on your head or crew member will be a lesson that could be better learned by prevention. THINK - What is the worst that could happen?

In this application screw in anchors will be used. An attachment that is driven by a Milwaukee Hole Hawg did the trick.

TBA (TO BE ANSWERED) Size of anchor needed for load capacity required and soil class (NRG booklet page 37) to handle that load?

Selecting the tower height will impact the diameter and gin pole size. Then of course the weight of the turbine that will be sitting on top has to be factored in. Then there is the construction of the base where the gin pole and tower are going to be hinged to. This picture shows using the 3,4,5 rule to layout the right angle to the tower hinge line. Two of the tower screw in anchors will be located on this line. TBA - What is the weight of the turbine?

Now about those screw in anchors. First when they are drilled in they must be drilled in at an angle that lines up with the anchor line it is being attached to. You want any pulling forces to be placed on the disc on the bottom of the anchor not on the small diameter rod that will cut into the soil easily. TBA - Where will these screw in anchors be places?

One of the anchor lines being formed around a thimble and the aluminum sleeve being crimped. Wire rope is used to make the anchor lines. I have done this for you. They must be of the right strength to handle the loads that will be placed on them and correct length so attachments can be made between the tower and the screw in anchors. TBA - What diameter wire rope is needed to handle the loads? How many and what lengths of each will be needed? What will be used to take up the slack in the guy wires and plumb the tower?

Sometimes it is the smallest of things that will cause you problems. Look at the way the connectors have been placed. The one on the left and middle one is wrong. Placed like this the threaded nut hits the tower when turned. Putting them in like the one on the right gives the wrench free access to the nut without interference.

Thimbles protect the wire rope from friction wear when being attached to other points. In this case the thimble is being attached to a turnbuckle. Notice how the thimble has been twisted so it will allow the closed end of the turnbuckle in. Then the thimble is twisted back into alignment and the cable ran. Never pry the thimble legs apart it will distort the groove and cause damage. TBA - What size, length and how many turnbuckles will be needed?

Here is the base that will be used to hold and hinge the tower and gin pole. For a guyed tower the base needs minimal support as compared to a free standing tower. So here the two rods will be driven into the ground to hold the base in place while the tower is being raised. A punch is being used to start the holes for the two rods. This make the process easier and more accurate.

The base is in and the gin pole and tower have been attached. Each by a single hinge pin. TBA - What size diameter and length of gin pole is needed? Answering this question has a lot to do with what the load will be on the raising cable that goes over the top of the gin pole and attaches to the top of the tower with the generator on it.

The winch I selected is a 1 ton worm screw drive unit with a 3/16" wire rope cable. It is anchored in place with four 12" long 2" diameter screw in anchors. 1/2" diameter steel rods are slid through the eyes of each anchor and over the top of the mounting board the winch is on. As a recommended safety precaution the hand crank will be used for the first test raising so the resistance in the (anchor and lifting) cable lines to the lift can be felt and adjusted if needed. A power drill can be used after the system is proved out and safe. 

This shows the hinge line for the tower. The location of the anchor points have been chosen and calculated. I say chosen because several factors come into play here. The idea distance would be so that the anchor cables were at 45 degree angles to the tower but that takes up a lot of area. So by doing some Force and Tension In A Rope Due To Angle calculations found on the www.EngineeringToolBox.com web site I came up with this distance. Also for my application these anchor points are also used as lifting anchors to stabilize the gin pole. Lets me get by with two anchors instead of four along this hinge line.

Here we are all rigged and ready for the test lift. This is done without the generator being mounted so that if anything should be wrong or goes wrong you don't have all the weight to deal with. Also dropping the generator would most certainly wreck the blades and damage the Nacelle at the very least. A well designed and rigged system should be easy to raise and lower. This will need to be done for annual maintenance anyway.

Going up nicely. This project is way over engineered I am using a scrap 6 m aluminum light pole for the tower. Plenty of strength of the weight of my 15 pound 300 w Air-X generator. I used a 2.35 m gin pole as that is another scrap I had laying around. 

With the success of the test run and some minor tweaking of the anchor and lifting cables it is time to attach the generator and run the power lines. Just noticed that I have left the nose cone off. No problem and the tower can easily be raised and lowered.

In 2001 The NRG company came out with a nifty wind analyzer unit call the Wind Explorer. I reached out to them to see they might send me a unit to use in teaching my students. They said yes! So I think this is the perfect time to dust the unit off and add it to this project for the KidWind teams to learn from. I set it up to bench test it and get familiar with the unit. This will give a team the chance to analyze the wind potential for an area and collect a few months worth of real time data.

I welded up a mounting bracket for the anemometer and direction sensor and attached it to the tower.

I wonder just how important knowing the direction the wind comes from is since all the turbines can yaw at will?

"The Wind Explorer writes Raw data into a DataPlug in 10 minute averages. This data will require scaling and offset at a later time. The scaling, offsets and other important information for each Site are stored in a Site File on your computer..." Lets just say this is no toy but the real deal for wind data and site analysis. If a KidWinder wants to get into it.

In all it's glory up goes the tower and MET station.

So here is the wind data collector. The nice thing is that this unit will also collect a years worth of wind, month by month and can be looked at to see average wind speed, peak, and day by day results.

The Air-X unit is a self regulating generator that requires a 12 volt battery wired into the system that it will charge when the wind is blowing. The charge controller in the unit prevents over charging of the battery when it is full. It would be interesting to get a unit like the Lab Quest to measure the generators output over time along with the wind.

Want to try laying out, rigging and raising this tower with your students? It will take about four hours. The "kit" has everything needed. Great hands on learning experience. Contact me if you are interested.

I wonder if he called Diggers Hotline before drilling in all those screw anchors?