And of course Makani.

Some components as motors, RC and wings on

Looks like they’re still playing the “shell-game” of shifting “future activity” locations. “Where is the bean” at any given (future) moment? Under which shell? (Please excuse the pun.) Alameda? Hawaii? Norway? Hurray hurray, step right up and take your best guess!

A problem I see is the tip speed of the secondary turbines, leading to noise and perhaps a lower lifetime. There are also efficiency losses but they look to be not too significant (5-10%) as there is not a second Betz limit.

Betz is the wrong (2D) model for turbine-on-a-wing (3D) and other specific turbines. Power-to-weight is the best First-Order Factor to reveal FlyGen inferiority. There is no competitive kite sport where a flygen powering a traction-motor drive can rival the direct traction of a simple power kite, of equivalent mass.

"7.1. Effect of flying mass
In all AWESs, increasing the flying mass decreases the tension of the cables. Since Ground-Gen systems rely on cables tension to generate electricity, a higher mass of the aircraft and/or cables decreases the energy production [107] and should not be neglected when modelling [109]. On the contrary, increasing the flying mass in Fly-Gen systems does not affect the energy production even though it still reduces the tension of the cable. Indeed, as a first approximation, the basic equations of Fly-Gen power production do not change if the aircraft/cable mass is included and this is also supported by experimental data[108]. "

Dave, it is difficult to argue with such an irrelevant comment. Betz limit and power-to-weight ratio are two different things. Please read the quote about the “Effect of flying mass” I introduced. Arguing power-to-weight vs efficiency in regard to Betz limit doesn’t allow a clearer debate.

Concerning Betz limit it applies for all wind systems, possibly as a first approximation. When a 3D space system is analysed, like an AWES, Betz limit applies to the front airspace which is swept.

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Pierre, The question is which factor is more important, not how wildly different they are as First Order AWES choices. Betz is a very poor flight analytic compared to power-to-mass.

Given excess mass is known toxic to kite performance, what to make of claims that increasing flygen mass does not “affect the energy production”. Increased mass should increase production, not leave it the same.

Dave, the power-to-mass ratio per wing area is not the same as the power-to-mass ratio per swept area.
And the power-to-mass ratio can be measured with all components, or only with the components aloft.

The Betz limit is a mean to appreciate the power-to-mass ratio per swept area.

There is no flight-mass term in Betz. Swept area by itself does not predict highest power-to-mass. A more efficient AWES can beat a poorer AWES with a higher swept area. Highest power-to-mass best predicts lowest LCOE, in kPower’s standard aeronautical-engineering view, definitely not based on Betz or sweep (TSR) numbers.

Kite-reeling AWES can reach high altitude but have severe efficiency limits of which a discontinuous power with two phases.
Some torque systems are efficient but cannot reach high altitude.
Flygens can reach both high altitude and efficiency.

That’s such a cool page thanks @PierreB
Do you have a list of components that you used on flygenkite?
I’d really love to see what experiments have been done using remote control paramotors rigged as kites with turbine blades instead of prop for onboard power.
Anyone tried it yet?

Several propellers of which Master Airscrew 9x4, Graupner or Mabuchi DC motors used as generators, Ozone 1 m² or 1.5m² two lines kite, molded support in two parts (see on video below) containing the generator, adhesive led tape.

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A crosswind rigid flygen wing seems to be the most appropriate AWES for several reasons:

  • Flygen system is a natural design similar to the known design for planes with propellers.

  • Generators onboard are very light thanks to the high rotation speed and allow also take-off operation.The weight of Makani’ (flygen) and Ampyx’ (yoyo reeling) wings is similar for a given power. And the weight theoretically does not impact performance as shown on Flygen.

  • Flygen systems deliver a continuous power at high efficiency (no downwind swept area, no return phase) as shown on (3’15" from the beginning), and in the same time sweep a large area.

  • The most advanced AWES prototype for electricity production is Makani’s M600.

  • The maximization of the space can be achieved using several means, the main idea being sharing the swept disk to achieve a high level enough in Betz limit, taking account of safety requirements.

  • The research and development can be coupled with that of the electric plane like

When the flygen method will be selected as the probable AWES, companies will be focused on better flygen designs, accelerating possible implementation, that instead of scatter in directions leading most of the time to dead ends.

If it is true, the question would be if is it possible to do as well with a ground-based wind turbine. I think perhaps yes, by using the same method, putting light secondary turbines, avoiding a too massive generator as the wind turbine scales up. The weight of the flygen wing and the blades could be similar.

So we have a complex automated control, a higher land use due to the elevation angle of the tether, so difficult or not possible secondary use on a large area, or the requirement to implement AWES above forests or offshore or in deserts, all that against the mast and the heavier and less useful central part of the rotor. AWES could become a serious possibility.


Kite Scaling Laws and Aviation Regulations put severe limits on how much generator mass is practical. How big a Flygen do you predict is workable? The M600 is severely burdened to carry its mass and make high power in most-probable wind velocities. They are not proud of their tested power-curve, or they would share it.

kPower instead proposes the world’s largest existing generators, at GW scale, to be driven as Groundgens by power kite networks. This avoids Flygen mass scaling limits to exploit Utility Plant economy-of-scale and capital-legacy advantage.

Flygens work great up to about 5kW before issues like scaling laws, failure modes, safety factors, become critical. A formal aerospace scoring matrix would help better weigh positive against negative factors. The electrical tether is also problematic. Full M600 data made public would quickly settle all doubts.

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Really? How?

Scaling laws and aviation regulations are two different concerns.

M600 is far to be perfect but is the most advanced AWES for electricity production. As I mentioned several times (Flygen) some studies show there is no impact of the flying mass when the flygen method is used. Moreover the generators onboard are light thanks to the high apparent wind speed.

With scaling laws we have the A 380. And soft wings are also impacted with scaling laws: Is the modern Power Kite the answer to Kite Power?.

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Read Old Forum posts on how kite-driven cableways can be matched to existing generators.

Aviation regulations reflect scaling laws by accounting for mass and velocity. These are not “two different concerns”, but two views of the same physics.

M600 is “most advanced” only to anyone who thinks Google does advanced aerospace. Its at best an advanced failure, by Fort Felker’s own 2010 criteria.

It is not even sure that a rigid wing is heavier than a soft wing for the same power.

I am. A soft wing more efficiently distributes loads, so its easier to maintain max working load. The rigid wing also carries resin mass for compressive structure, and many extras, like maybe even back-up parachutes (DamonL, Makani).

It would be nice if you had followed this on the Old Forum, to no be so unsure still. At least consider the latest 1kg paraglider. A rigid glider must weigh far more for comparable power performance.