This is a nice paper though I think for me quite worthless.
It does not go into enough detail around the aerodynamics of yawing the kite. It is clear that a kite can only yaw so much before performance degrades. Also, how much control input on rudder, aileron and flaps, and which associated drag and design constraints (how big flaps?)
If you want to optimize the trajectory before settling these details, you end up with very tight turns, because these are zero cost.
I think the better path forward is to gather real life data first, before trying to tackle this problem. Because I donât think the analysis at the current state will give a useful answer.
The performance of the wing, but also those of the turbine(s) at altitude because they take less front wind because of a too low radius of turn (by yaw or/and roll).
Its a matter of knowing where to focus your energy. The analysis in the paper seems a good initial guess, but I donât think this is the time to jump into that rabbit hole. First make some real energy flying any [sensible] pattern, then when you have more data, optimize the path.
It can make sense to decide circles vs fig eight early though, as that affects the build potentially a lot. But maybe start with fig eight first anyway, if you need a complicated slipring without it.
I have not found small wind turbines working at their maximum in very strong winds, e.g. 25 to 50 m/s. They peak at 15 m/s at the best, and stop at 25 m/s.
The Makani turbines are designed for apparent winds of around 50 m/s. But we do not know their lifespan.
So I tried to see if we could deduce anything from electric car motors. On the one hand they can run at a high rpm, then their lifespan is long (far much longer than that of a heat engine), and their power/mass ratio is high. I provide an example:
Teslaâs high-performance copper rotor motor generates 300 horsepower while weighing only 100 pounds, making it the worldâs lightest electric vehicle electric motor (45.4 kg).
The motor can spin at peak speeds of up to 14,000 revolutions per minute.
Now a blog (in French) about the lifespan of an electric motor:
I think this question is of less importance at this point other than to dismiss AWE altogether. The priority of any developer would be first to create power, then create cheap power, then make a machine to last 20+ years. So this discussion is definitively in the third bracket.
If we can already now say motor life itself is a showstopper, that is valuable information. But I donât think its easy to make a 100% convincing argument that you could not make a generator to last x years at any RPM you choose/need.
Now asking our beloved friend ChatGPT I get:
The life expectancy of an electrical motor depends on several factors including its type, usage, maintenance, and operating conditions. On average, a well-maintained electric motor can last anywhere from 15 to 20 years, but this can vary widely.
Type of Motor: Different types of motors, such as induction motors, synchronous motors, or DC motors, have different lifespans. For instance, brushless DC motors often last longer than brushed DC motors due to less wear and tear on components.
Usage: Motors used in continuous, high-load conditions will typically have a shorter lifespan compared to those used intermittently or under lighter loads.
Maintenance: Regular maintenance, including lubrication, cleaning, and checking for wear and tear, can significantly extend the life of an electric motor.
Operating Conditions: The environment in which the motor operates also plays a crucial role. Motors operating in harsh conditions, like extreme temperatures or dusty environments, may have a shorter lifespan.
Quality and Design: High-quality motors with robust designs tend to last longer than cheaper, lower-quality models.
Seems a generator/motor for a Makani style configuration would check off all the things that limit motor life. So that would be an indication that this is a hard issue to solve
Motor manufacturers choose what winding wire to use. The electrical insulation (varnish) on the wires is rated for how long it can withstand a certain temperature before losing its insulating ability. So they have tables of how hot you can get the insulation, for how long, before the windings short circuit. At some point, overheating get so extreme it will burn out almost any insulation. Iâve got a collection of charred stators, which you could only imagine were red-hot. Overheating increases wire resistance, which of course causes further overheating, like a runaway freight train. It starts at a hot spot and spreads outward. You can sometimes see from the pattern of overheating clues to how to address it for the next try. Small wind turbine manufacturers often think their machine is safe, due to some testing in strong winds. But then it encounters even stronger winds or sustained strong winds that go on for days, and thereâs another burned out turbine! Thatâs why they all go out of business.
Well Thanks Pierre for keeping the name Calnetix in our minds. The company is located here in Southern California. My impression is they are a boutiquey brand with probably very high prices and specialized customers such as aerospace. While there are various ways to fine-tune designs to optimize whatever characteristics are deemed important for a given application, Iâm not aware of any âmagic bulletâ or âsecret sauceâ that is going to change the basics of motor design and cooling, other than the recent article I posted about Iron Nitride as a new magnet material, stronger magnetization possible than present-day supermagnets, and able to withstand higher temps. I guess weâll see where THAT âpress-release breakthroughâ goes⊠(Often there are unstated showstopper problems remaining to be solved, such as with perovskites in solar panels - they donât last, quickly degrading - a decade of headlines, no panels available yet.)
I think Iâve seen some stators that use methods to create the copper windings other than just using wire, but do not have a lot of knowledge around that. I think some tesla motors do that. But you have to realize, Tesla motors are liquid-cooled, and coupled with sensors and a computer that prevents heat damage by limiting output as temps rise. I saw a video where they were trying to set a record lap time on a race course using an electric car, but after just one lap, they had to start over with a freshly-charged battery and a fresh, cool motor. Basically, by the time the tires were hot enough to get sticky, the motor was too hot for full performance.
Wind turbine design requires everything to go together to make a durable yet affordable package with high performance and the ability to survive sustained high winds. Everything has to be perfect, or close to perfect, for the application, to get there. Perfecting any design requires years of multiple units on various towers in multiple locations. Only then can you find out where the problems are, then fix the problems. Then get ready for another cycle of long-term testing. Thatâs why all small wind turbine companies go out of business.
With larger companies building larger turbines, they have a better chance of getting it right the first time, but then again, right now the entire wind energy industry is in a crisis due to making the turbines too big, too fast, and they are failing at an unexpectedly high rate, putting the manufacturers in financial danger.
Hi @dougselsam : an advantage of a crosswind flygen AWES is that it can go stationary quickly when winds are excessive, the turbines being designed to operate with an apparent wind of up to 50 m/s (like Makani M600) and more.
Hello Pierre: Thanks for reviewing a purported, theoretical advantage associated with a crosswind-traveling flygen generator configuration. I think it sounds great, but do not remember seeing a flygen system that works as you say. What I remember is flying figure-8 patterns, with the flight greatly slowed going upward, and accelerated going downward.
Hi Doug, you speak about the too heavy M600 flying by loops. Earlier smaller prototypes could fly correctly. And the advantage of being able to stop should be considered.
For example my old FlygenKite:
It remains stationary, undergoing a wind speed of 6 m/s (during tests) then flying crosswind at about 20 m/s. This means that with a wind of 20 m/s it only needs to be stationary.
The same for a rigid (and light) flygen system flying at 50 m/s.
