Sail faster than the wind
Sailing vehicles ( sailing boats , ice sailors and land sailors ) can reach speeds that are greater than the speed of the true wind . The prerequisite for this is a high cornering force with low resistance along the direction of movement of the vehicle and a sail with a sufficiently high glide ratio .
physics
The apparent wind generates a force on the wing (sail) which (depending on the glide ratio of the wing) can have an angle of almost 90 ° to the apparent wind. As long as the apparent wind on the wing does not come directly from the front, this force can have a forward component that drives the glider. The physical effect occurring here is the Venturi effect , which describes that the air on the curved side of the sail has a higher speed and according to the Bernoulli equation also has a lower pressure. As a result, there is suction or force in the direction of the curvature of the sail, which pulls the sailor. So a sailor can accelerate or keep going, even if the apparent wind comes diagonally from the front, as is the case when one is going faster than the wind.
On close wind courses , sailors can develop a speed component that is parallel to the true wind and which is greater than the true wind speed. By crossing in front of the wind they can overtake the air mass in the direction of the wind. This somewhat counter-intuitive fact can best be illustrated with a vector diagram .
However, a classic sailor cannot:
- Sail directly against the wind
- Sail faster than the wind directly in front of the wind
In both cases the apparent wind on the wing comes directly from the front. However, if the design allows the wings to move relative to the vehicle, the above restrictions for the courses to the wind no longer apply. This is the case with the rotor glider . Classic sailors can, however, achieve a VMG that is greater than the true wind speed (see below). It follows that, although they cannot sail faster than the wind directly in front of the wind, they can reach a destination in this direction faster than the wind speed would suggest by crossing .
Classic sailors
Sailing boats
Sailboats with a displacement hull hardly manage to sail faster than the wind due to the high water resistance. Gliders, on the other hand, reach significantly higher speeds. In 2009 the trimaran Hydroptère set a world speed record of 95 km / h with a wind of 55 km / h. All sailboats need a lateral drag surface in order to minimize the displacement caused by the leeward force in sideways wind; In other words: a large lateral resistance area means that the boat can be pushed forward much more easily than to the side. The shape of the hull, a ballast keel or the crew weight prevent the wind from simply turning the ship on its side. That a force is at work can be seen from the sometimes quite significant heeling of the ship.
Kitesurfers and windsurfers reach similar maximum speeds, but mostly a lower multiple of the wind speed. Rob Douglas set a record in 2010 with a wind of around 80 km / h with a kiteboard of 103 km / h.
The most efficient sailboats reach a leeward speed (downwind VMG) that is more than twice the wind speed. At the America's Cup 2010 , the winning yacht sailed 37 km with the wind in 1 hour 3 minutes. So their downwind VMG was 2.5 times the wind speed. Hydrofoil sailboats can lift their hull completely out of the water using wings, which significantly reduces water resistance. Nevertheless, these boats also have a large lateral resistance area.
Contrary to intuition, sailing faster than the wind does not violate the principle of energy conservation , because the energy used for movement is withdrawn from an increasing amount of air with increasing apparent wind speed (wind speed on the boat).
Ice sailors
Because of the low friction between the runners and the ice, ice sailors routinely achieve a multiple of the wind speed. Although speeds over 200 km / h have been reported, measurements with GPS have reliably confirmed 135 km / h.
Land sailor
The land sailor Greenbird set a world record for wind-powered land vehicles of 203 km / h in 2009, with a wind speed of 50–65 km / h.
Rotor glider
The wings of the rotor glider rotate around a horizontal axis, so they experience a different apparent wind than the vehicle. Their rotation is linked to the movement of the vehicle, e.g. B. on wheels on land or a second rotor in the water. In contrast to the classic sailor, rotor sailors can theoretically go faster than the wind both directly against the wind and directly in front of the wind . While the rotor has a braking effect on the true wind in both cases, the direction of the power flow to or from the wheels (or the propeller) differs:
- Directly against the wind : The air rotor acts as a turbine that drives the wheels (or the water propeller).
- Directly in front of the wind, faster than the wind : the air rotor acts as a propeller that is driven by the wheels (or by the water turbine).
The energy required to drive or accelerate the vehicle is obtained by the fact that the real wind is slowed down by the air rotor.
The maximum speed in both directions is only limited by efficiency, not by wind speed. In practice, boats with a rotor can drive directly against the wind , but so far they have not been faster than the wind in either direction. Land vehicles other hand, have both directly downwind faster than the wind , and just faster than the wind against the wind practically demonstrated.
In 1969 Andrew Bauer built a rotor wagon that reached 1.2 times the wind speed directly in front of the wind. This result was clearly exceeded on July 2, 2010, when the Blackbird propeller car drove 2.8 times faster than the direct tail wind, setting the first certified world record in this category. On June 16, 2012, a turbine version of the Blackbird set another world record with 2.1 times the wind speed directly against the wind.
See also
Individual evidence
- ↑ Sailboats can sail faster than the wind . Retrieved February 11, 2011.
- ↑ YACHT readers ask, Bobby Schenk answers . Retrieved February 11, 2011.
- ↑ The aerodynamics on the sail . Archived from the original on October 20, 2009. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved February 11, 2011.
- ↑ Explanations and diagrams (in English): The physics of sailing . Retrieved February 11, 2011., Physics for Architects: Can Sailboats Sail Faster than the Wind? . Retrieved February 11, 2011.
- ↑ downwind VMG (English WP)
- ↑ Frequently Asked Questions (video) North American Land Sailing Association. Retrieved February 11, 2011.
- ↑ a b Bob Dill: Putting Numbers on Iceboat Performance (PDF; 177 kB) North American Land Sailing Association. Retrieved February 11, 2011.
- ↑ http://www.sailspeedrecords.com/wssr-newsletter-no-177.-hydroptere-world-records.-23/09/09.html
- ↑ 500 Meter Records , World Sailing Speed Record Council, accessed November 26, 2015
- ↑ Pierre Nussle: La démonstration de puissance d'Oracle breeze le rêve d'Alinghi . Tribune de Genève. February 13, 2010. Retrieved August 25, 2010.
- ^ First blood to USA - News - 33rd America's Cup . Consorsio Valencia. June 25, 2007. Archived from the original on May 31, 2012. Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved August 25, 2010.
- ↑ America's Cup: Velocity Made Good . BMW ORACLE Racing. September 30, 2003. Archived from the original on March 5, 2016. Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved August 25, 2010.
- ^ America's Cup, the numbers of a victory . Yacht Online. Archived from the original on July 22, 2011. Info: The archive link was automatically inserted and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved March 9, 2010.
- ↑ website of the Green Bird .
- ↑ "Measurement Report" of March 26, 2009.
- ↑ Mac Gaunaa, Stig Øye, Robert Mikkelsen: Theory and Design of Flow Driven Vehicles Using Rotors for Energy Conversion . Retrieved April 10, 2020. Presentation on Rotor Carriages
- ↑ Mark Drela: Dead-Downwind Faster Than The Wind (DFTTW) Analysis (PDF; 61 kB) Archived from the original on November 16, 2010. Information: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved February 11, 2011.
- ↑ Andrew Bauer: Faster Than The Wind (PDF; 4.9 MB) Retrieved on February 11, 2011., Photo of Bauer with his rotor car
- ↑ a b Direct Downwind Record Attempts . NALSA. Retrieved February 11, 2011.
- ↑ Kimball Livingstone: Downwind Noir . Blue Planet Times. Archived from the original on January 12, 2011. Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved February 11, 2011.
