I need to calculate power for M600 (Makani kite) for my project. can someone help me that how I can choose values of CL, CD and air density etc. The only thing that I know is 600KW is its output power.

# Makani Kite power calculations

http://www.energykitesystems.net/FAA/FAAfromMakani.pdf

This should provide some info. I would assume C_L \approx 2.0. The drag is difficult to find, you could calculate it backwards assuming a certain power delivery at a certain windspeed.

Alternatively choose a glide number based on the list at https://en.m.wikipedia.org/wiki/Gliding_flight

Welcome @Saqlain,

I made a rough and heavy calculation for M600 on Makani's presentation in AWEC2017, assuming a (already high) CL of 1.2, but by without knowing it. The CL of 2 such as given by Tallak looks to be very high, but possible: he might have some data I don’t have. It is also possible to change some variables to calculate it.

The reason I chose 2.0 is that Makani features a three-foil high lift wing design. I think Ampyx in their AWEC 19 talk were planning for even higher C_L, but I chose 2.0 as an improvement on normal lift coefficients (1.5) and not extremely high… Of course I have no idea what the real value is

I would expect Makani’s 600 kW unit to produce 600 kW on average in a loop. So the maximum power is likely a bit higher…

Now we are waiting for the real curves of power.

Thank you so much for your nice reply sir. I really appreciate it. I just want to ask that would it be wise to choose gliding ration=4? which is for helicopter (auto rotation) in the list that you shared with me. One more thing I want to ask about power calculation formula. did you use Loyd’s formula for calculation which is P= 2/27 x rho x Vw^3 x CL x (CL/CD)^2 ?

Thank you so much bro for your reply and welcoming me in this group. I have couple of questions regarding your calculations, I hope you will not mind it.

1- How you choose the value of air density as 1.2 though you do not know exact height? because as we know that air density will change as per height because temperature and pressure will change.

2- How you choose value of velocity as 10 m/s? I am just asking your logic of choosing this value. I read somewhere in their documents that Full rated power wind speed is 11.5 m/s so which value would you recommend e to use?

3- How you choose L/D ratio as 10.6 for wing alone and 7.066 with turbines? There are total 8 turbines in MAKANI kite but as per my understandings in your calculations you used only one.

4- I am wondering that which formula you used in verification part of your calculations?.

Once again thank you for your reply

Yes @Saqlain, Loyd’s formula is used. The gliding ratio can be defined as the lift-to-drag ratio. If L/D =

4, (CL/CD)² = 16. So this ratio is important to determine the efficiency of a crosswind kite.

The value obtained by this formula is multiplied with the cubed cosine. As an example if the elevation angle is 30°, the cubed cosine is 0.65.

I guess Makani would be using a glide ratio 8-20? This is pure guesswork of course. I would not use the energy formula, rather just calculate the power, speed etc. There are many ways to do this, differing in perspective…

You could read some paper which are quite detailed about this, eg. Kheir et al 2019, DOI: 10.1016/j.jweia.2019.04.010

Air density of I.2 is an average value at ground level. Of course the air density varies with altitude and temperature.

As full rated power wind speed, 10 m/s is an often used value. Other values can be chosen. http://www.energykitesystems.net/FAA/FAAfromMakani.pdf Makani provides a rather low value of 9 m/s.

Because the conversion system (the turbines aloft for a flygen like Makani, but also the reel-out phase for yoyo mode with the generator at ground) should slow down the device for 1/3 in a standardized calculation.

“Verification: 33 x 1.2/2 x 70.666666 x70.666666 x 70.666666 x 0.0857575 = roughly 600 kW.”

If I remember correctly I used the classic wind energy formula, multiplying the full area of the secondary turbines (33 m²) with air density/2, and with cubed apparent wind speed.

I added a coefficient of 0.0857575 to obtain 600 kW, because the turbines are very large in regard to the expected efficiency in regular flight, that due to vertical takeoff requirement. Indeed 33 m² of secondary turbines is a huge value compared to the wing area.

Some precision; I do not know what are all features of Makani M600, so I complete with hypothetical numbers in order to obtain 600 kW. If we consider the 9 m/s wind speed value as specified by Makani (instead of 10 m/s), some other variables should have a higher value.

How much value should I choose for density? what would you suggest. For height of flight only range is given from 110-310.

A little less, perhaps 1.1. There is a curve for air density below:

https://www.engineeringtoolbox.com/air-altitude-density-volume-d_195.html

Another point: there are losses due to the irregular power according to the place of the wing within the wind window. The sound varies during the figure as we can hear on the videos below.

Circular figure:

Figure-eight:

.

Hi Saqlain,

Welcome to this forum!

How much time do you have to complete your project? You have chosen a very complex question, and it will take some time to locate key references scattered in the domain literature.

Be sure to calculate square-cube and other parasitic up-scaling factors, which are predicted to be starkly evident between Makani’s 30kW Wing7 prototype and the M600 prototype. Its quite possible the M600 is netting very little power due to looping cycle phase losses, and high energetic cost of just maintaining its large mass in flight.

. Thank you for your help brother. I have another question related to this topic that why we can not use blade element momentum theory beyond induction factor of 0.5?

You’re most welcome, Saqlain. Given the short time frame, it will be very hard to produce a correct estimate. Blade element momentum theory as such omits many critical parameters, including the parasitic effect of maintaining high mass powered flight.

The 600kW claim has limited objective public data basis. Makani has not provided key data, like how much platform and tether weigh, nor the tested thermal limits of their larger motorgens, and other electrical losses. They likely would have shared power curves that met optimistic claims.

There is one source of good public data; Videogrammetric parameters, to derive flight pattern scale and time values. A sufficiently deep video analysis, including the audio track and wind-velocity clues, in principle suffices to derive close net power-out estimates.