Let’s go fly a kit Up to the highest height! Let’s go fly a kite and send it soaring Up through the atmosphere Up where the air is clear Oh, let’s go fly a kite!
Actually, kites have been used as weather-sensing solutions for more than 250 years. During the first half of the 1900s, kites served as the principal tool for conducting atmospheric profiling, advancing both meteorology and operational forecasting. While other forms of atmospheric vehicles like balloons and small unmanned aircraft systems (UASs) are also used to conduct atmospheric research, kites offer some compelling reasons for their continued enthusiasm: the fact that they are simpler to operate and train on than alternative aerial systems, their ability to keep station—hold their position—at a fixed point, simplified altitude control, and the ease of retrieving their payload.
Research conducted in the atmospheric boundary layer (ABL) or lower troposphere is crucial to advancing the accuracy of weather forecasting. It is precisely in this region where researchers at Oklahoma State University (OSU)’s Unmanned System Research Institute as well as Toyota have dedicated tremendous time and technology to studying kite development and operations for high-altitude deployments. Their goal is to develop an inflatable kite capable of reaching high altitudes (up to 10,000 m, or 32,808 ft) for precise local weather predictions, wind energy harvesting, and enhanced telecommunication technology.
During the first half of the 1900s, kites served as the principal tool for conducting atmospheric profiling, advancing both meteorology and operational forecasting.
To that end, OSU and Toyota have successfully designed and deployed kites that incorporate lightweight inflatable structures capable of handling wind gusts and high-altitude conditions. The OSU/Toyota eighth-generation inflatable kite (Fig. 1) has performed up to 2,755 m (9,039 ft) AGL. By suspending sensors below the kite, it is possible to provide continuous sensing in an easily deployable, cost-effective platform. The use of kite-based profile systems with distributed or mobile sensors to collect data on the lower troposphere is predicated on the fact that this region of the atmosphere is where the majority of damaging weather occurs.
In their research, OSU is currently utilizing several kite-based solutions: RAVEN (Repositionable Aerial Vane Environmental Network), a distributed sensing solution that uses aerodynamically stabilized data acquisition units to concurrently collect data from a number of altitudes, an approach pioneered by NASA’s Geoff Bland, which he called AEROKATS (Advancing Earth Research Observations with Kites and Tethered/Atmospheric Sensors); and SWIFT (Sliding Weather Instrument Fixed to Tether, an OSU innovation), a lightweight alternative to RAVEN for smaller systems at the cost of concurrent data collection from multiple sensors.
RAVEN is a set of independent data acquisition units. Each unit is composed of an aerodynamically stabilized body with sensors for temperature, pressure, humidity, wind speed, wind direction, and position. RAVEN’s design places sensors, controllers, a radio, and batteries on the nose and an aerodynamic tail on the back, similar in design to that of NASA’s AeroPod2 (Fig. 2).
SWIFT, on the other hand, uses a radio-controlled sail designed to slide up and down along the tether line from the ground to the kite (Fig. 3). Wind-driven instrumentation platforms have demonstrated their effectiveness in prior kite-borne research, such as by Balsley and colleagues in 1998, yet advances in miniaturized sensor technology are proving to be pivotal in expanding their functionality and usage.
Basic operation for weather research kites is fairly straightforward: You launch the kite, attach your data acquisition units as the kite climbs, and then stop when the target altitude is reached. OSU’s RAVEN system transmits data to the ground station as the kite is in flight, providing real-time data profiling of the atmosphere for immediate analysis while the kite continues to fly. When you have captured the desired data, the kite is retrieved.
Expanding flight envelopes for kites and operating in the National Airspace Systems (NAS) remain challenging. Typically, flight in the NAS follows compliance with 14CRF Part 101,3 including notifications to airports and the FAA as necessary, or arranging for restricted airspace.
Basic operation for weather research kites is fairly straightforward: You launch the kite, attach your data acquisition units as the kite climbs, and then stop when the target altitude is reached.
Jacob adds, “While current kite systems are limited to a small range of atmospheric conditions, as control systems are improved these enhancements will allow a larger range of operation conditions, particularly winds.”
Research has demonstrated that smart winches can launch kites with little to no wind controlling the ascent profile. Additionally, feedback on winds aloft can allow the kite to change angle of attack through active control via the bridle or onboard effectors, increasing the upper limit of maximum winds. Both of these concepts have been tested on OSU’s high-attitude kite demonstrator.
“Kites are not intended to be a replacement for other unmanned technology,” says Geoff Bland, a research engineer in the Earth Science Field Support Office at the NASA Goddard Space Flight Center’s Wallops Flight Facility. “Kites are an alternative unmanned aircraft system that can augment and bring a threshold for utilization that requires less training and, because it’s on a string, some inherent safety features associated with it.”
While kites are used predominantly in the lower troposphere, advanced aerodynamics and structural design of both kites and associated advancements in line handling systems are enabling flight into higher altitudes and higher winds. Bland is quick to point out that his sights are set well beyond the atmospheric boundary layer: “My goal is ultimately the stratosphere, but we’ve got a long way to go before we get to do that.”
To ultimately achieve stratospheric altitudes, work continues to make sensors, probes, and related componentry smaller, lighter, and less expensive. One firm on the forefront of these initiatives is Black Swift Technologies (BST) in Boulder, Colorado. “NASA has partnered with Black Swift Technologies as part of our Small Business Innovation Research (SBIR) Awards beginning in 2012,” Bland states. “The most important result of the company’s work with NASA is a fully integrated set of miniaturized instrumentation that delivers usable data under extreme conditions.”
SwiftFlow, a 3D wind dynamics probe (Fig. 4) that BST developed as part of NASA’s SBIR award work, addressed the need for a highly accurate atmospheric measurement device capable of being deployed on a small UAS or UAV, like a kite. “What sets this probe apart, in my mind, was that it was developed by a company that really understands the scientific requirements for this type of product,” emphasizes Bland.
SwiftFlow, a multihole wind probe, is engineered to be a tightly integrated wind vector measurement device able to accurately record airspeed, altitude, angle of attack, side slip, ambient temperature, and relative humidity.
“BST’s 3D wind probe allows us to look at the three-dimensional wind field as it changes in the atmosphere,” Bland states. “I see it as the ‘go-to’ or destination instrument package for those using kites to make these types of atmospheric measurements and employ them in a research field.”
Bland goes on to say, “What we’re after is really where is the wind coming from relative to the Earth, which means you also have to have the information of where is your instrument relative to the Earth, and where is it pointing? And that’s what Black Swift does in a very nice package. They provide all of that information: the attitude, the position, and the wind vector, all in a package that outputs the data such that we can get that wind vector, which is otherwise a very difficult measurement to obtain, especially if you want the vertical component. The beauty is that this is a device that you can take in a backpack somewhere and get that measurement.”
While kites are used predominantly in the lower troposphere, advanced aerodynamics and structural design of both kites and associated advancements in line handling systems are enabling flight into higher altitudes and higher winds.
While vertical profiles have traditionally been conducted using towers, such an approach results in a fixed-point source as opposed to being able to make that source portable to go to a particular site and take those measurements, or in the case of an unmanned aircraft flying a transect. Vertical profiling in the boundary layer can be done through remote sensing (lidar, radar, microwave profiling, sodar, etc.), yet key to kite-centric research is the ability to sample sites on demand as a result of its easy portability.
“What we’re after is really where is the wind coming from relative to the Earth, which means you also have to have the information of where is your instrument relative to the Earth, and where is it pointing?”
Let’s Go Fly a Kite from MARY POPPINS Words and Music by Richard M. Sherman and Robert B. Sherman
AeroPod is protected by U.S. Patent 8.196.853 and is available for licensing. More information is available at https://technology.nasa.gov/patent/GSC-TOPS-10.
Acknowledgments.
Kathleen McNamara (OSU) was the research engineer actively involved in the kite research that I showcased. She secured and provided the photographs of the experiments and provided content review for relevancy and accuracy. Geoff Bland (NASA) developed some of the methodology and sensors used in this research. He advised the team at OSU and provided content review for relevancy and accuracy. Dr. Jamey Jacob (OSU) is the director of the Unmanned Systems Research Institute at OSU. His team conducted all of the research showcased in the article. He encouraged McNamara’s involvement, and to that extent I am grateful. Dr. Jack Elston (BST) funded the writing of this manuscript and paid to secure photography rights for an image of the kites used in the research. His sensor was part of the research project, and he provided renderings of that sensor for publication. He provided content review for relevancy and accuracy. ●
FOR FURTHER READING
Balsley, B. B., M. L. Jensen, and R. G. Frehlich, 1998: The use of state-of-the-art kites for profiling the lower atmosphere. Bound.-Layer Meteor., 87, 1–25, https://doi.org/10.1023/A:1000812511429.