Makani M600 Airframe Structure
In 2014 I joined a small company in Alameda, CA called Makani developing an airborne wind turbine. This type of wind power is known as an Airborne Wind Energy (AWE), and makes use of the principle of crosswind kite power, explained very well by the slide presentation and Wikipedia page below.
Airborne Wind Energy Technology Overview
I put together this presentation to explain airborne wind energy to employees at Astra after it became apparent this was not an easily-understood technology and a lot of folks were very interested in it. The slides accompanied an oral presentation so it lacks context in a few areas, but the rest of the Wikipedia page below and film documentary at the bottom of the page should help fill in any blanks.
Airborne Wind Energy (AWE).pdfMy Work at Makani
I initially worked on the composite and metallic primary structure of the vehicle (hardpoints, wing spar & skin laminate, etc.) and later lead the development of the next generation vehicle through collaboration with an outside design firm called TLG Aerosapce, an extremely professional and capable group of engineers.
Other work I performed during my nearly 6 years at Makani:
Developed bottoms-up wing designer tool employing lifting line theory to auto-size wing structures for system level trades, details in the section below.
Developed multiple airframe configurations, downselecting through multi-disciplinary system-level evaluation
Moved production of 85 ft span energy kite wings to an outside vendor, completing handoff through on-site visits, engineering and troubleshooting support, drawing revisions, and issue dispositions
Developed specification handbook for the manufacture and assembly of composite structures
Developed primary and secondary composite and metallic structural components
Designed and lead onsite & offsite repairs of primary and secondary composite structures on short timelines
Developed spreadsheet-based analysis tools with automatic margin reporting to allow engineers to quickly perform common structural analyses (Lug sizing based on Bruhn / A- and B-basis statistical material allowables / interlaminar tension in radii / Load distribution in arbitrary bolt patterns)
A Makani M600 energy kite in crosswind flight through the clouds at the Parker Ranch test site in Hawaii.
Wing Designer Spreadsheet Tool
The wind designer spreadsheet tool I created is designed to rapidly explore different energy kite configurations and output vehicle mass and stiffness for use in other analysis tools such as ASWING and Makani's in-house developed system optimization tools. The spreadsheet has since been open-sourced and is attached below.
The sheet’s primary function is to size a wing structure based on a given tether load which is assumed to be generated by aerodynamic lift of a specified distribution at a specified airspeed. Additionally, a tail is sized based on required pitch and yaw authority from the Force Balance Loop (FBL) runs, as well as stability requirements. Given the hand-calc nature of this spreadsheet tool, it is only suitable for preliminary sizing, providing planform geometry that can be achieved with a specified mass budget. Final sizing and analysis should be performed with more sophisticated tools.
The below dashboard screenshot shows a number of inputs and plots that depict the defined configuration and some of its properties. Click the image to take you to the full report I wrote while employed at Makani.
I also wrote a complete guide on how the sizer works and how to use it which is available starting on page 273 of The Energy Kite Report Part II.
Deep Water Offshore Capability
While Makani saw little promise in being able to compete with traditional wind turbine design on land and in shallow waters where the towers could be afixed to a sturdy foundation, there was great promise for installation in deep water offshore locations:
Stability of the base station was not a requirement, as such the spar buoy could be significantly smaller.
A smaller spar buoy requires less heavy catenary chain and smaller anchors, a supply constraint for traditional wind turbine-based deep water installations.
A smaller spar buoy meant the system could be assembled using land-based cranes at deep water ports rather than offshore with massive bespoke floating cranes, making installation and deployment costs relatively very low.
These advantages over traditional wind made for a compelling business case, so in 2019 Makani set out to install the M600 system on a custom spar buoy in the North Sea and show that it can be done, in the hopes of attracting additional investment.
A Makani M600 energy kite in hover off a bespoke spar buoy over the North Sea off the coast of Norway.
In the fall of 2019, Makani indeed demonstrated deep water offshore airborne wind energy is possible in a world first flight over the North Sea. The liftoff, unreeling of the tether, crosswind flight, and transition back into hover were all successfully demonstrated. Unfortunately the vehicle experienced a roll instability in hover following the crosswind flight and crashed into the water below.
This is me on a boom lift installing the remotely operable kite restraint system at the test site in Parker Ranch in Hawaii. This restraint system would permit safe offshore operations where personnel could not access the vehicle to release it before or restrain it after flight.
Makani's Unfortunate End
While Makani made huge strides in the development of rigid kite airborne wind turbine design and operation, the company unfortunately shut down in early 2020, due to lack of foreseeable cost competitiveness of the product. It became evident that the traditional Horizontal Axis Wind Turbine (HAWT) industry grew into deep water off-shore market faster and at a lower cost than the market anticipated, and the additional investment required to develop the M600 successor and make the technology profitable was more risk than investors were willing to take on. However, due to having demonstrated a new way to extract wind energy at commercial power ratings, and Makani being nearly a decade ahead of most other airborne wind energy companies/efforts, X, and Alphabet supported an extensive open-sourcing effort to not let all the years of learnings and technology development go to waste. This is now all accessible at The Energy Kite Collection.
The Energy Kite Report
Other open-sourced media
As part of the open-sourcing effort, a beautiful full length film documentary was put together to showcase Makani's journey from its humble beginnings till its unfortunate end.