Blackbird is an experimental wind-powered vehicle, built in 2010 to demonstrate that it is possible for such a vehicle to go directly downwind faster than the wind (sometimes abbreviated as DDWFTTW). Blackbird employs a rotor connected to the wheels and does not have a motor, battery, or flywheel. [1] It was constructed by Rick Cavallaro and John Borton of Sportvision, sponsored by Google and Joby Energy in association with the San Jose State University aeronautics department.
In a test supervised and recognized by the North American Land Sailing Association in July 2010, Cavallaro achieved a speed of 27.7 mph (44.6 km/h) sailing directly downwind in 10 mph (16 km/h) winds: almost three times the speed of the wind. [2] [3] [4] [5] In 2012, Blackbird also demonstrated sailing directly upwind with twice the speed of the wind.
Rotor-powered vehicles are wind-powered vehicles that use rotors—instead of sails—which may have a shroud around them (ducted fan) or constitute an unducted propeller, and which may adjust orientation to face the apparent wind. The rotor may be connected via a drive train to wheels or to a generator that provides electrical power to electric motors that drive the wheels. [6]
A vehicle with a bladed rotor mechanically connected to the wheels can be designed to go at a speed faster than that of the wind, both directly into the wind and directly downwind. Upwind, the rotor works as a wind turbine driving the wheels. Downwind, it works as a propeller, driven by the wheels. In both cases, power comes from the difference in velocity between the air mass and the ground, as received by the vehicle's rotor or wheels. [7]
Relative to the vehicle, both the air and the ground are passing backwards. However, travelling upwind, the air is coming at the vehicle faster than the ground, whereas travelling downwind faster than the wind speed, the air is coming at the vehicle more slowly than the ground. The vehicle draws power from the faster of the two media in each case and imparts it to the slower of the two: upwind, drawing power from the wind and imparting it to the wheels and, downwind, drawing power from the wheels and imparting it to the rotor: in each case in proportion to the velocity of the medium, relative to the vehicle. [7]
In summary: [7]
How fast a given wind speed can propel a vehicle in either direction is limited only by the efficiency of the turbine blades, losses in the drive train, and the vehicle's aerodynamic drag, apart from the drag of the turbine. [7]
In 2006, following a viral internet debate started by Rick Cavallaro as a brain teaser, [2] a wind-powered, propeller-driven vehicle was built and filmed, demonstrating that it is possible to sail 'dead' downwind faster than the wind by the power of the available wind only. [9]
In 2009, professor Drela of MIT worked out the equations for such a device and concluded that one could be built "without too much difficulty". [10] Other researchers arrived at similar conclusions. [7]
The same year, team members Rick Cavallaro and John Borton of Sportvision, sponsored by Google and in association with the San Jose State University aeronautics department, built a test vehicle nicknamed Blackbird. A year later, in 2010, Cavallaro successfully tested the vehicle, achieving more than twice the speed of wind, [2] definitively demonstrating that it is possible to build a vehicle which can achieve the claim. [11] [4] A second test with an improved vehicle in 2011 reached close to three times the speed of wind. [5]
After proposing the vehicle's design, and presenting the analysis to demonstrate its viability, the Blackbird team learned that others had previously conceived and built similar designs: most notably, aerodynamics engineer Andrew B. Bauer, later with the Douglas Aircraft Company, built and demonstrated such a vehicle in 1969, based on an analysis presented in a student's paper from some twenty years earlier. [12] [13]
Bauer reported "a rearward deflection of a foot-long tuft located about 12 feet forward of the propeller plane," indicating that his vehicle went faster than the true wind (the strand would have streamed forward, if the apparent wind was from behind). Several sources of engineering and scientific articles explain the theory and physics of such a device. [10] [7] Besides still photography, a film has been found showing it in operation. [14]
On 7 and 8 March 2010, the team reported testing their vehicle on a motor-driven moving belt (treadmill), showing that it would advance against the belt, which means that it can progress dead downwind faster than the wind.
On 24 March 2010, the team ran the vehicle on the Ivanpah dry lake bed south of Las Vegas, Nevada, showing that it could accelerate dead downwind from a standstill and reach velocities well in excess of wind speed. [3] [15] [16] That is, the vehicle was progressing dead downwind faster than the wind. Officials of the North American Land Sailing Association (NALSA) were in attendance and one NALSA Board of Directors member (Bob Dill) was there for every run and collected his own rough wind and GPS data. [17]
On July 2, 2010, Blackbird set the world's first certified record for going directly downwind, faster than the wind, using only power from the available wind during its run on El Mirage Dry Lake. The yacht achieved a dead downwind speed of about 2.8 times the speed of the wind. [1] [18]
On June 16, 2012, Blackbird set the world's first certified record for going directly upwind, without tacking, using only power from the wind. The yacht achieved a dead upwind speed of about 2.1 times the speed of the wind. [1]
In 2021, University of California, Los Angeles physics professor Alexander Kusenko disputed the claim citing the role of possible wind gusts and other factors in the apparent accomplishment, having seen a YouTube video on the Veritasium channel by Derek Muller. Kusenko and Muller entered into a $10,000 bet that required Muller to prove the validity of the claim, which was witnessed by noted scientists, Neil deGrasse Tyson and Bill Nye. Muller won the bet to Kusenko's satisfaction with a series of model experiments, investigation of the original supporting data of the Blackbird run, and exploration of the supporting equations. [19]
Although Kusenko conceded the bet on a technicality, he stated that he saw no evidence that Blackbird exceeded the speed of the wind, following the given constraints of the experiment. [20]
In July 2013, Cavallaro sold Blackbird in an eBay auction. It was purchased by Neil Cutcliffe. In May 2023, Cutcliffe donated it to the Castle Air Museum [21] in Atwater, California. Museum curators plan to restore and preserve it as a static display.
Sailing employs the wind—acting on sails, wingsails or kites—to propel a craft on the surface of the water, on ice (iceboat) or on land over a chosen course, which is often part of a larger plan of navigation.
Apparent wind is the wind experienced by a moving object.
A point of sail is a sailing craft's direction of travel under sail in relation to the true wind direction over the surface.
A scientific wager is a wager whose outcome is settled by scientific method. It typically consists of an offer to pay a certain sum of money on the scientific proof or disproof of some currently-uncertain statement. Some wagers have specific date restrictions for collection, but many are open. Wagers occasionally exert a powerful galvanizing effect on society and the scientific community.
Tacking or coming about is a sailing maneuver by which a sailing craft, whose next destination is into the wind, turns its bow toward and through the wind so that the direction from which the wind blows changes from one side of the boat to the other, allowing progress in the desired direction. Sailing vessels are unable to sail higher than a certain angle towards the wind, so "beating to windward" in a zig-zag fashion with a series of tacking maneuvers, allows a vessel to sail towards a destination that is closer to the wind that the vessel can sail directly.
Land sailing, also known as sand yachting, land yachting or dirtboating, entails overland travel with a sail-powered vehicle, similar to sailing on water. Originally, a form of transportation or recreation, it has evolved primarily into a racing sport since the 1950s.
Unconventional wind turbines are those that differ significantly from the most common types in use.
Wind-powered vehicles derive their power from sails, kites or rotors and ride on wheels—which may be linked to a wind-powered rotor—or runners. Whether powered by sail, kite or rotor, these vehicles share a common trait: As the vehicle increases in speed, the advancing airfoil encounters an increasing apparent wind at an angle of attack that is increasingly smaller. At the same time, such vehicles are subject to relatively low forward resistance, compared with traditional sailing craft. As a result, such vehicles are often capable of speeds exceeding that of the wind.
A wind turbine is a device that converts the kinetic energy of wind into electrical energy. As of 2020, hundreds of thousands of large turbines, in installations known as wind farms, were generating over 650 gigawatts of power, with 60 GW added each year. Wind turbines are an increasingly important source of intermittent renewable energy, and are used in many countries to lower energy costs and reduce reliance on fossil fuels. One study claimed that, as of 2009, wind had the "lowest relative greenhouse gas emissions, the least water consumption demands and the most favorable social impacts" compared to photovoltaic, hydro, geothermal, coal and gas energy sources.
USA-17 is a sloop rigged racing trimaran built by the American sailing team BMW Oracle Racing to challenge for the 2010 America's Cup. Designed by VPLP Yacht Design with consultation from Franck Cammas and his Groupama multi-hull sailing team, BOR90 is very light for her size being constructed almost entirely out of carbon fiber and epoxy resin, and exhibits very high performance being able to sail at 2.0 to 2.5 times the true wind speed. From the actual performance of the boat during the 2010 America's Cup races, it can be seen that she could achieve a velocity made good upwind of over twice the wind speed and downwind of over 2.5 times the wind speed. She can apparently sail at 20 degrees off the apparent wind. The boat sails so fast downwind that the apparent wind she generates is only 5-6 degrees different from that when she is racing upwind; that is, the boat is always sailing upwind with respect to the apparent wind. An explanation of this phenomenon can be found in the article on sailing faster than the wind.
Richard Jenkins is a 47 year old engineer from Lymington, UK. He is known for engineering and sailing wind-driven vessels on land, ice, and water. In 1999, he founded the Windjet Project while studying mechanical engineering at Imperial College. Since then he has designed, built, and tested four separate speed record craft. Jenkins is currently the founder and CEO of Saildrone, a company that designs, manufacturers, and manages unmanned surface vehicles that sail the world's oceans collecting science data. In 2019, SD 1020 became the first unmanned vehicle to complete a circumnavigation of Antarctica, crossing every longitude line in the Southern Ocean.
Alinghi 5 is a 90 ft (27 m) (LWL), 90 ft (27 m) beam sloop-rigged catamaran built by Alinghi for the 33rd America's Cup.
High-performance sailing is achieved with low forward surface resistance—encountered by catamarans, sailing hydrofoils, iceboats or land sailing craft—as the sailing craft obtains motive power with its sails or aerofoils at speeds that are often faster than the wind on both upwind and downwind points of sail. Faster-than-the-wind sailing means that the apparent wind angle experienced on the moving craft is always ahead of the sail. This has generated a new concept of sailing, called "apparent wind sailing", which entails a new skill set for its practitioners, including tacking on downwind points of sail.
A windmill ship, wind energy conversion system ship or wind energy harvester ship propels itself by use of a wind turbine to drive a propeller.
Forces on sails result from movement of air that interacts with sails and gives them motive power for sailing craft, including sailing ships, sailboats, windsurfers, ice boats, and sail-powered land vehicles. Similar principles in a rotating frame of reference apply to windmill sails and wind turbine blades, which are also wind-driven. They are differentiated from forces on wings, and propeller blades, the actions of which are not adjusted to the wind. Kites also power certain sailing craft, but do not employ a mast to support the airfoil and are beyond the scope of this article.
Starting in 1975, NASA managed a program for the United States Department of Energy and the United States Department of Interior to develop utility-scale wind turbines for electric power, in response to the increase in oil prices. A number of the world's largest wind turbines were developed and tested under this pioneering program. The program was an attempt to leap well beyond the then-current state of the art of wind turbine generators, and developed a number of technologies later adopted by the wind turbine industry. The development of the commercial industry however was delayed by a significant decrease in competing energy prices during the 1980s.
The RS100, first launched in 2009 by RS Sailing, is a singlehanded skiff. Possessing an asymmetric spinnaker the boat has two PY numbers of 981 for the 10.2 rig and 1004 for the 8.4 rig. The RS100 has a racing event circuit in the United Kingdom and in Europe, with the Eurotour beginning in 2011.
Rhett Allain is an American associate professor of physics at Southeastern Louisiana University and the author of the Wired magazine science blog Dot Physics. He received his Ph.D. from North Carolina State University in 2001 and works in the field of physics education research.
Crosswind kite power is power derived from airborne wind-energy conversion systems or crosswind kite power systems (CWKPS). The kite system is characterized by energy-harvesting parts flying transversely to the direction of the ambient wind, i.e., to crosswind mode; sometimes the entire wing set and tether set are flown in crosswind mode. From toy to power-grid-feeding sizes, these systems may be used as high-altitude wind power (HAWP) devices or low-altitude wind power (LAWP) devices without having to use towers. Flexible wings or rigid wings may be used in the kite system. A tethered wing, flying in crosswind at many times wind speed, harvests wind power from an area that exceeds the wing's total area by many times.
Alexander Kusenko is a theoretical physicist, astrophysicist, and cosmologist who is currently a Professor of Physics and Astronomy at the University of California, Los Angeles (UCLA). In addition, Kusenko holds an appointment of Senior Scientist at the Kavli Institute for the Physics and Mathematics of the Universe (IPMU) since February 2008. He has served as a general member of the board of Aspen Center for Physics 2004-2019. Kusenko was awarded the status of Fellow of the American Physical Society in 2008 for original and seminal contributions to particle physics, astrophysics, and cosmology. In 2021, Kusenko was awarded a Simons Fellowship in Theoretical Physics. In 2021, he entered a $10,000 wager with Derek Muller over the possibility of sailing straight downwind faster than the wind, which he later conceded.
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