ARTAGs -- Autonomous Reciprocating Tethered Airfoil Generators
 

I have a question at the end of this letter, but I think you need some background first. I sincerely appreciate your constructive support or criticism.

I want to see Tethered Flight (TF) resurrected and developed as fully as possible. I've been looking for grants to do the required basic research. Finally I have uncovered grants that are offered to people to develop new ways to generate electricity. So my initial focus is to develop Autonomous Reciprocating Tethered Airfoil Generators (ARTAGs).

This posting only has the description of the Single ARTAG, please see posting #7 below where I describe what I propose to be the Double, Triangle, and Arch ARTAGs. Then please vote for whichever you think is best -- with the exeception of the Arch ARTAG which is only intended for large commercial installations at sea.

(Why are my posts so wide? What can be done about it?)

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Single ARTAG

Each ARTAG would have a reciprocating kite in the sky attached by a tether and a radio link to a combination generator/winch on the ground that is attached to a power grid to alternately generate and consume electricity.

During each generation phase:

1. The kite would automatically fly downwind,
2. At the angle of attack that maximizes tension in the tether,
3. As it is being pulled from a spool that is attached to the generator/motor,
4. Causing it to spin and generate electricity into a power grid,
5. Until the kite is at a “far” preset distance from the generator/motor,
6. At which time the kite radios the generator/motor that it is time to be winched back in.

During each winch phase:

1. The motor winds the tether back on the spool,
2. Consuming electricity from the power grid,
3. While the kite flies at an angle of attack that reduces the tension in the tether as much as possible,
4. And yet ensures that the tether is always reasonably taut to avoid knots at the winch,
5. While at the same time ensuring that the kite arrives back at the position at which generation began,
6. Until the kite is at a “near” preset distance from the generator/motor,
7. At which time the kite radios the generator/winch that it is time to generate electricity again,
8. In which case the whole process repeats -- continuously.

ARTAGs are also probably the only wind power electrical power generators that could work from boats at sea – instead of the ground as was just mentioned – anchored in deep sea or otherwise.

It is expected that the maximum tension for generation will occur close to the angle of attack where the combined vector forces of both Lift and Drag are maximized:

Square Root of (Lift Squared + Drag Squared)

Likewise, it is expected that a reasonably low tension for winching will occur close to zero angle of attack, if not a negative angle of attack.

But these assumptions do not take into consideration the weight and drag of the tether and the position of the kite in the sky due to changing weather conditions. So the processor on the kite will have to have the intelligence to continually adjust the kite’s angle of attack (pitch). Yaw and roll should not need to be correct because the kite would be designed to automatically fly at zero yaw and roll with respect to the apparent wind which hopefully will not deviate exceptionally from the true wind for very long -- or an accident might occur – in which case a more complex kite will have to be developed that can control pitch, yaw, and roll.

I intend to use a delta radio control sailplane to make a small-scale model. The delta was chosen because it has a large wing area and yet is quite fast. The question I have is what servomechanism method should I use to change the angle of attack? A standard kite bridle would probably not work well at low angles of attack. But standard control surfaces would probably not work at the extreme angles of attack that these kites would be required to fly at.

In the future I intend to discuss more issues regarding Tethered Flight (TF) and Autonomous Reciprocating Tethered Airfoil Generators (ARTAGs) in this forum. So discussions that start with ARTAG and TF will correspond to Autonomous Reciprocating Tethered Airfoil Generators and Tethered Flight (the more general topic). I welcome any who are interested to respond to and initiate discussions with these headings. If you wish you can request a paper entitled "Tethered Airfoils: An Enabling Technology". This paper outlines many potential uses for Tethered Flight. Once you read it I believe that you will agree with me that Tethered Flight should once again become a major division of aeronautics. I would invite you to participate in the ARTAG group that is now forming. If you wish to participate please email me below.

Sincerely,
Wayne German
503-538-4132
[email protected]

RE: ARTAGs -- Autonomous Reciprocating Tethered Airfoil Generators
 

Wayne,

I don't want to throw cold water on a good idea, but I think that there are more efficient ways to generate electricity using the wind. Tethered flight doesn't seem to have any advantages that I can see.

banktoturn

RE: ARTAGs -- Autonomous Reciprocating Tethered Airfoil Generators
 

Apparantly when someone suggested that this lad " go fly a kite "
He took it literally

RE: ARTAGs -- Autonomous Reciprocating Tethered Airfoil Generators
 

You need hands-on experience with 2 and 4-stringed stunt kites.
Then bungee/hi-start launched gliders.
A combination of these will do the job -without- needing energy from the power grid.

RE: ARTAGs -- Autonomous Reciprocating Tethered Airfoil Generators
 

Banktoturn,

1) If we can throw away the big expensive wind towers,
2) then we can make inexpensive kites of considerable size to generate electricity,
3) anywhere on earth because the winds that are a half mile in the air are typically four times as powerful as at the top of towers,
4) but particularly anchored at sea where wind turbines would be prohibitively expensive if not impossible, and
5) perhaps eventually tapping into the jetstream where the power available can be as high as 40KW per square meter.

Tall Paul,

You may not want to be tied into the power grid, but then you would not generate revenue from the suplus electricity generated. No doubt it would be fun to manually fly a kite, but I think it would be even more fun to design an array of kites that can fly without intervention and generate considerable revenue in the process. But all that aside, the power is not required to get the kite in the air, a little power is required to wind the tether to keep it taut as the kite flies back down.

-- Wayne

RE: ARTAGs -- Autonomous Reciprocating Tethered Airfoil Generators
 

What we have here is a failure to communicate..
.
The designated purpose -IS- to generate electricity for the power grid.
The economics of the situation are such that taking as little out of the grid is a plus.
Using power from the grid to move the kite back to the beginning upwind position is a negative.
Flying the kite back, your "negative alpha" situation, reduces or eliminates the power need to pull/force the kite back to Square 1.
Some power will be needed to wind back the generating tether, but with the kite providing the least amount of drag, by flying a programmed sequence,
the negative penalty is diminished.
.
For model testing, get a deep-sea fishing reel with lots of fishing line capacity to simulate the ground based generator and cable drum.
The "drag"wheel on the reel can simulate the power generation portion of the flight sequence, or the power assist added to the reel for the rewind can be used to simulate the actual generator's output, in lieu of the star-drag.
For the rewind situation, run the motor on the reel and measure the power it requires, and test the kite attitudes that need the least amount of power without it plunging to the ground.
And the effects of a long tether on the airframe will be interesting,guaranteed! :)

RE: ARTAGs -- Autonomous Reciprocating Tethered Airfoil Generators
 

Tall Paul,

Thanks. I think we're on the same wavelength.

Everyone,

(Why are my posts so wide? What can be done about it?)

As many of you know, I'm dangerous when it comes to aeronautical concepts. But even if I were not, I really believe that a multitude of eyes are better than mine alone. I would appreciate if you would review and vote on the following and give me your opinions. I would really appreciate it. I am trying to go after a grant with new technology. I just want to make sure that I choose the best technology to go after it with. Thanks for your help.

Please vote for one of three: the description of an ARTAG at the beginning of this thread (which I am now calling a Single ARTAG), or the Double or Triangle ARTAGs described below. At the end of this paper I have also included the Arch ARTAG for completeness, but it should not be voted for now, although I would appreciate your comments.

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Double ARTAGs

In another thread entitled: “Any wind tunnel data for up to 90 degree angle of attack?”, Bruce Mathews wisely suggested that ARTAGs should get their power stroke more from traveling upward (crosswind) rather than downwind. When I thought about it I realized that he’s right. I was trying to maximize the initial force of a power stroke, rather than trying to maximize the energy that can be derived by the entire power stroke. By flying upwards, the kite would be flying crosswind. By flying crosswind the kite can fly at the speed of the wind times the lift-to-drag ratio. Numerous sources tell me that this is true, but it is hard to imagine. If the wind is 25 miles-per-hour, and an efficient kite has a lift-to-drag ratio of 50 (let’s be conservative), would a kite really fly crosswind at 1250 miles-per-hour if the tether had no drag?

In my previous simple-minded approach, a kite flying downwind at 15 miles-per-hour in a 25 mile-per-hour wind would only see 10 miles-per-hour of apparent wind so it would have little lift. And since wind power is related to the cube of the air velocity, it would have far less power. But Bruce’s preference to go up instead of out would increase both velocity and power.

Let’s call the ARTAG discussed previously the: “Single ARTAG” because it has only one tether. However, a “Double ARTAG” (one having two tethers) might be more efficient and generate more power. Let me explain.

Imagine if a kite on the ground has two tethers. The other end of one tether we run along level ground to a point directly up wind and stake it in the ground. Let's call this the Radius Tether. The other tether we wind on a spool on a generator/winch on the ground next to the kite. Let's call this the Power Tether. Imagine the wind is blowing at 25 miles-per-hour. After the kite is launched:


During the generation phase:

1. The wind continuously keeps the Radius Tether taut,
2. And as the kite goes up in an arc determined by the Radius Tether,
3. The kite pulls the Power Tether from the spool on the generator/winch,
4. Causing the generator to spin,
5. Generating electricity into the grid,
6. While the kite is continuously correcting the angle of attack,
7. To maximize the over-all energy generation,
8. Until the Radius tether makes about a 60 degree angle with respect to the horizontal,
9. At which time the generator/winch radios the kite to tell it that it is time to winch again.

During the winching phase:

1. Then the kite would reduce its angle of attack,
2. The generator/winch would quickly wind the tether onto the spool,
3. Pulling the kite down in a controlled descent,
4. That is designed to feed tether onto the spool no faster than it can accommodate,
5. consuming electricity,
6. Until the Radius Tether is nearly at an angle at which to generate electricity again,
7. At which time the generator/winch radios the kite to tell it that it is time to generate again.

The cycle then repeats, generating and consuming electricity, but generating more than is consumed.

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Triangle ARTAGs

ARTAGs could be configured in a third way that might generate significantly more power than in either the Single or Double configurations. I call this the Triangle configuration because instead of flying upwind, downwind, up, or down like Single or Double ARTAGs, the tether on these kites would form a triangle. Triangle ARTAGs would have no spool or winch. Instead of cycles of generation and winching as in the other configurations, they would fly in the air from a generator to a pulley and back – generating power both directions. The Triangle configuration is described below:

1. Imagine a tether loop that passes through a generator on the ground,
2. To a pulley that is also on the ground,
3. To a kite in the sky,
4. Back to the generator again,
5. Such that a straight line between the generator and the pulley,
6. Is perpendicular to the direction of the prevailing wind, and
7. The kite has a GPS, and
8. Automatically executes a roll,
9. Whenever the kite is too close to either the generator or the pulley,
10. So that the kite’s lift causes the tether to move in the opposite direction,
11. Generating electricity to feed into the power grid,
12. As the tether moves back and forth through the generator.

These Triangle ARTAGs could also be deployed between two anchored boats at sea.

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(For completeness sake I am including the following, but please just vote for one of the three above.)

Arch ARTAGs

Large commercial enterprises could attach numerous large kites on both sections of a tether loop that loops between a generator and a pulley. A generator would be in one anchored boat and a pulley would be in the other.

1. The tether would pass through a generator on one anchored boat,
2. Through a long arch in the sky,
3. To the pulley in another anchored boat,
4. Through another long arch in the sky,
5. Back to the generator again, and
6. The long arches in the sky would have numerous large kites equally spaced,
7. And the kites would be synchronized by radio,
8. To roll in directions that would cause the tether to pull in the same direction,
9. Such that the kites on one arch would roll one direction, and
10. The kites on the other arch would roll in the other direction, and
11. The kites on one arch would have a higher angle of attack, and
12. The kites on the other arch would have a lower angle of tack,
13. So that there would always be a safe distance between the two arches to avoid collisions, but
14. The kites would be inflatable,
15. So they would generally bounce rather than crash in the case of a collision, and
16. The arches are arranged perpendicular to the prevailing winds.

RE: ARTAGs -- Autonomous Reciprocating Tethered Airfoil Generators
 

I must say this is all very interesting!

I have a question: How are you going to keep the kite up for long periods of time? You need electricity in the kite to operate the radio and computer. If you use a battery it is going to discharge after a relatively short time, considering that kites can stay aloft for most of the day. You cannot use the teather unless you have something very light and strong that can conduct electricity and is insulated.

Also, what about lightning and storms?

RE: ARTAGs -- Autonomous Reciprocating Tethered Airfoil Generators
 

A smallish propellor driven generator could supply the power needs for the systems in the kite itself.
As for electrical storms, keep your keys in your pocket. :)