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Modern ship rudder
Aircraft rudder


A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft,or other conveyance that moves through a fluid (generally air or water). On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane. A rudder operates by redirecting the fluid past the hull or fuselage, thus imparting a turning or yawing motion to the craft. In basic form, a rudder is a flat plane or sheet of material attached with hinges to the craft's stern, tail or after end. Often rudders are shaped so as to minimize hydrodynamic or aerodynamic drag. On simple watercraft, a tiller -- essentially, a stick or pole acting as a lever arm -- may be attached to the top of the rudder to allow it to be turned by a helmsman. In larger vessels, cables, pushrods, or hydraulics may be used to link rudders to steering wheels. In typical aircraft, the rudder is operated by pedals via mechanical linkages or hydraulics.

History of the rudder

Terminology



Generally, a rudder is "part of the steering apparatus of a boat or ship that is fastened outside the hull", that is denoting all different types of oars, paddles and rudders. More specifically, the steering gear of ancient vessels can be classified into side-rudders and stern-mounted rudders, depending on their location on the ship. A third term, steering oar, can denote both types. In a Mediterraneanmarker context, side-rudders are more specifically called quarter-rudders as the later term designates more exactly the place where the rudder was mounted. Stern-mounted rudders are uniformly suspended at the back of the ship in a central position, but the term has historically been found wanting because it does not take into account that the stern rudders were attached to the ship hull in quite a different way: While the European pintle-and-gudgeon rudder was attached to the sternpost by pivoting iron fastenings, the Arabs used instead a system of lashings. Chinesemarker stern rudders also featured tackles, but, unlike their medieval and Arab counterparts, had no sternpost to which to attach them. Roman and particularly ancient Egyptian stern rudders featured again a different method of fastening where the stock, having a single point of contact with the stern, was additionally secured to the ship body by an upright rudderpost or braced ropes.

Although Lawrence Mott in his comprehensive treatment of the history of the rudder, Timothy Runyan, the Propyläen History of Technology, the Encyclopedia Britannica, and The Concise Oxford Dictionary of English Etymology classify a steering oar as a rudder, Joseph Needham, Lefèbre des Noëttes, K.S. Tom, Chung Chee Kit, S.A.M. Adshead, John K. Fairbank, Merle Goldman, Frank Ross, and Leo Block state that the steering oar used in ancient Egypt and Rome (and even ancient China) was not a true rudder; the steering oar has the capacity to interfere with handling of the sails (limiting any potential for long ocean-going voyages) while it was fit more for small vessels on narrow, rapid-water transport; the rudder did not disturb the handling of the sails, took less energy to operate by its helmsman, was better fit for larger vessels on ocean-going travel, and first appeared in ancient China during the 1st century AD. In regards to the ancient Phoenicianmarker (1550–300 BC) use of the steering oar without a rudder in the Mediterranean, Leo Block (2003) writes:

A single sail tends to turn a vessel in an upwind or downwind direction, and rudder action is required to steer a straight course.

A steering oar was used at this time because the rudder had not yet been invented.

With a single sail, a frequent movement of the steering oar was required to steer a straight course; this slowed down the vessel because a steering oar (or rudder) course correction acts like a brake.

The second sail, located forward, could be trimmed to offset the turning tendency of the main sail and minimize the need for course corrections by the steering oar, which would have substantially improved sail performance.



Ancient Egypt

Stern-mounted steering oar of an Egyptian riverboat depicted in the Tomb of Menna (c.
1422-1411 BC)


Rowing oars set aside for steering appeared on large Egyptian vessels long before the time of Menes (3100 BC). In the Old Kingdom (2686 BC-2134 BC) as much as five steering oars are found on each side of passenger boats. The tiller, at first a small pin run through the stock of the steering oar, can be traced to the fifth dynasty (2504–2347 BC). Both the tiller and the introduction of an upright steering post abaft reduced the usual number of necessary steering oars to one each side. Apart from side-rudders, single rudders put on the stern can be found in a number of tomb models of the time, particularly during the Middle Kingdom when tomb reliefs suggests them commonly employed in Nile navigation. The first literary reference appears in the works of the Greek historian Herodot (484-424 BC), who had spent several month in Egyptmarker: "They make one rudder, and this is thrust through the keel", probably meaning the crotch at the end of the keel (see right pic "Tomb of Menna").

In Iranmarker, oars mounted on the side of ships for steering are documented from the 3rd millennium BCE in artwork, wooden models, and even remnants of actual boats.

China



In China, miniature models of ships that feature steering oars have been dated to the Zhou Dynasty (c. 1050 BC – 256 BC). Stern mounted rudders started to appear on Chinese ship models starting in the 1st century AD. However, the Chinese continued to use the steering oar long after they invented the rudder, since the steering oar still had limited practical use for inland rapid-river travel. One of oldest known depiction of a stern-mounted rudder in Chinamarker can be seen on a 2 ft. long tomb pottery model of a junk dating from the 1st century AD, during the Han Dynasty (202 BC-220 AD). It was discovered in Guangzhoumarker in an archeological excavation carried out by the Guangdong Provincial Museummarker and Academia Sinica of Taiwanmarker in 1958. Within decades, several other Han Dynasty ship models featuring rudders were found in archaeological excavations. The first solid written reference to the use of a rudder without a steering oar dates to the 5th century.

Chinese rudders were not supported by pintle-and-gudgeon as in the Western tradition; rather, they were attached to the hull by means of wooden jaws or sockets, while typically larger ones were suspended from above by a rope tackle system so that they could be raised or lowered into the water. Also, many junks incorporated "fenestrated rudders" (rudders with holes in them, allowing for better control), an innovation adopted in the West in 1901 to increase the manoeuvrability of torpedo boats. Detailed descriptions of Chinese junks during the Middle Ages are known from various travellers to Chinamarker, such as Ibn Battuta of Tangiermarker, Moroccomarker and Marco Polo of Venicemarker, Italymarker. The later Chinese encyclopedist Song Yingxing (1587-1666) and the 17th century European traveler Louis Lecomte would write of the junk design and its use of the rudder with enthusiasm and admiration.

Paul Johnstone and Sean McGrail state that the Chinese invented the "median, vertical and axial" stern-mounted rudder, and that such a kind of rudder preceded the pintle-and-gudgeon rudder found in the West by roughly a millennium. However, Mott points out that the Chinese rudder worked by a very different suspension system, and that it was not permanently attached to a sternpost, leaving little point in comparing two such different types of rudder. The method of mounting steering gear from the stern was well known in Mediterraneanmarker navigation by the time the practice appeared in Chinese ships.

Ancient Rome

Stern-mounted rudder of a Roman boat, 1st century AD (RG-Museum, Cologne).


Roman navigation used sexillie quarter rudders which went in the Mediterranean through a long period of constant refinement and improvement, so that by Roman times ancient vessels reached extraordinary sizes. The strength of quarter rudder lay in its combination of effectiveness, adaptability and simpleness. Roman quarter rudder mounting systems survived mostly intact through the medieval period.

By the first half of the 1st century AD, rudders mounted on the stern were also quite common in Roman river and harbour craft as proved from reliefs and archaeological finds (Zwammderdam, Woerden 7). A tomb plaque of Hadrianic age shows a harbour tug boat in Ostia with a long stern-mounted oar for better leverage. Interestingly, the boat already featured a spritsail, adding to the mobility of the harbour vessel. Further attested Roman uses of stern-mounted rudders includes barges under tow, transport ships for wine casks, and diverse other ship types. Also, the well-known Zwammerdam find, a large river barge at the mouth of the Rhine, featured a large rudder mounted on the stern. According to new research, the advanced Nemi shipsmarker, the palace barges of emperor Caligula (37-41 AD), may have featured 14 m long stern-mounted rudders.

Medieval Near East

Arab ships also used a sternpost-mounted rudder, but which differed technically from both its European and Chinese counterparts, indicating an indepentent invention. On their ships "the rudder is controlled by two lines, each attached to a crosspiece mounted on the rudder head perpendicular to the plane of the rudder blade."Lawrence V. Mott, p.93 The earliest evidence comes from the Ahsan al-Taqasim fi Marifat al-Aqalim ('The Best Divisions for the Classification of Regions') written by al-Muqaddasi in 985:

The captain from the crow's nest carefully observes the sea. When a rock is espied, he shouts: "Starboard!" or 'Port!" Two youths, posted there, repeat the cry. The helmsman, with two ropes in his hand, when he hears the calls tugs one or the other to the right or left. If great care is not taken, the ship strikes the rocks and is wrecked.


Arabs used instead a system of lashings. Chinesemarker stern rudders also featured tackles, but, unlike their medieval and Arab counterparts, had no sternpost to which to attach them. According to Lawrence V. Mott, the "idea of attaching the rudder to the sternpost in a relatively permanent fashion, therefore, must have been an Arab invention independent of the Chinese."

Medieval Europe



Oars mounted on the side of ships evolved into quarter rudders, which were used from antiquity until the end of the Middle Ages in Europe. As the size of ships and the height of the freeboards increased, quarter-rudders became unwieldy and were replaced by the more sturdy stern-mounted rudders with pintle and gudgeon attachment. While stern-mounted rudders were found in Europe on a wide range of vessels since Roman times, including light war galleys in Mediterranean, the oldest known depiction of a pintle-and-gudgeon rudder can be found on church carvings of Zedelgemmarker and Winchestermarker dating to around 1180.. The invention of the rudder in Medieval Europe is attributed to Somerled in 1156, when it was the decisive factor in his defeat of Gofraidh mac Amhlaibh during the formation of the Lordship of the Isles.

Historically, the radical concept of the medieval pintle-and-gudgeon rudder did not come as a single invention into being. It presented rather a combination of ideas which each had been long around before: rudders mounted on the stern, iron hinges and the straight sternpost of northern European ships. While earlier rudders were mounted on the stern by the way of rudderposts or tackles, the iron hinges allowed for the first time to attach the rudder to the entire length of the sternpost in a really permanent fashion. However, its full potential could only to be realized after the introduction of the vertical sternpost and the full-rigged ship in the 14th century. From the age of discovery onwards, European ships with pintle-and-gudgeon rudders sailed successfully on all seven seas.

Contrary to an older hypothesis, all evidence indicates that the European hinged stern-mounted rudder, whose technical specifications considerably differ from the Chinese one, was invented independently:

The only actual concept which can be claimed to have been transmitted from the Chinese is the idea of a stern-mounted rudder, and not its method of attachment nor the manner in which it was controlled. Since that idea of putting a rudder on the stern can be traced back to the models found in Egyptian tombs, the need to have the concept brought into the Middle East is questionable at best. There is no evidence to support the contention that the sternpost-mounted rudder came from China, and no need to call on exterior sources for its introduction into the Mediterranean.


Boat rudders details

Boat rudders may be either outboard or inboard. Outboard rudders are hung on the stern or transom. Inboard rudders are hung from a keel or skeg and are thus fully submerged beneath the hull, connected to the steering mechanism by a rudder post which comes up through the hull to deck level, often into a cockpit.

Rudder post and mast placement defines the difference between a ketch and a yawl, as these two-masted vessels are similar. Yawls are defined as having the mizzen mast abaft (ie. "aft of") the rudder post; ketches are defined as having the mizzen mast forward of the rudder post.

Small boat rudders that can be steered more or less perpendicular to the hull's longitudinal axis make effective brakes when pushed "hard over." However, terms such as "hard over," "hard to starboard," etc. signify a maximum-rate turn for larger vessels.

Aircraft rudders



On an aircraft, the rudder is called a "control surface" along with the rudder-like elevator (attached to horizontal tail structure) and ailerons (attached to the wings) that control pitch and roll. The rudder is usually attached to the fin (or vertical stabilizer) which allows the pilot to control yaw in the vertical axis, i.e. change the horizontal direction in which the nose is pointing. The rudder's direction is manipulated with the movement of foot pedals by the pilot.

In practice, both aileron and rudder control input are used together to turn an aircraft, the ailerons imparting roll, the rudder imparting yaw, and also compensating for a phenomenon called adverse yaw. Adverse yaw is readily seen if the most simple type of ailerons alone are used for a turn. The downward moving aileron acts like a flap, generating more lift for one wing, and therefore more drag (though since the 1930s, many aircraft have used frise ailerons or differential ailerons, which compensate for the adverse yaw and require little or no rudder input in regular turns). Initially, this drag yaws the aircraft in the direction opposite to the desired course. A rudder alone will turn a conventional fixed wing aircraft, but much more slowly than if ailerons are also used in conjunction. Use of rudder and ailerons together produces co-ordinated turns, in which the longitudinal axis of the aircraft is in line with the arc of the turn, neither slip (under-ruddered), nor skidding (over-ruddered). Improperly ruddered turns at low speed can precipitate a spin which can be dangerous at low altitudes. This can be clearly seen in the crash of United Airlines Flight 585marker and USAir Flight 427, where the aircraft experienced a rudder hard-over at a low altitude.

Sometimes pilots may intentionally operate the rudder and ailerons in opposite directions in a maneuver called a forward slip. This may be done to overcome crosswinds and keep the fuselage in line with the runway, or to more rapidly lose altitude by increasing drag, or both. The pilots of the Air Canada Flight 143marker used a similar technique to land the plane as it was too high above the glideslope.

Any aircraft rudder is subject to considerable forces that determine its position via a force or torque balance equation. In extreme cases these forces can lead to loss of rudder control or even destruction of the rudder. (The same principles also apply to water vessels, of course, but it is more important for aircraft because they have lower engineering margins.) The largest achievable angle of a rudder in flight is called its blowdown limit; it is achieved when the force from the air or blowdown equals the maximum available hydraulic pressure.

Footnotes

  1. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, p.2f., 92-95
  2. rudder.Encyclopædia Britannica. Retrieved August 8, 2008, from Encyclopædia Britannica 2006 Ultimate Reference Suite DVD
  3. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, p.2f., 92
  4. William F. Edgerton: “Ancient Egyptian Steering Gear”, The American Journal of Semitic Languages and Literatures, Vol. 43, No. 4. (1927), pp. 255-265
  5. R. O. Faulkner: Egyptian Seagoing Ships, The Journal of Egyptian Archaeology, Vol. 26. (1941), pp. 3-9
  6. Timothy J. Runyan: “Review of The Development of the Rudder: A Technological Tale“, Speculum, Vol. 74, No. 4, (1999), pp. 1096-1098 (1098)
  7. Wolfgang König: Propyläen Technikgeschichte: Landbau und Handwerk 750 v. Chr. bis 1000 n. Chr., Berlin 1990, p.260
  8. The Concise Oxford Dictionary of English Etymology
  9. Needham, Joseph. (1986). Science and Civilization in China: Volume 4, Physics and Physical Technology, Part 3, Civil Engineering and Nautics. Taipei: Caves Books Ltd. Pages 627–628.
  10. Chung, Chee Kit. (2005). "Longyamen is Singapore: The Final Proof?," in Admiral Zheng He & Southeast Asia. Singapore: Institute of Southeast Asian Studies. ISBN 9812303294. Page 152.
  11. Tom, K.S. (1989). Echoes from Old China: Life, Legends, and Lore of the Middle Kingdom. Honolulu: The Hawaii Chinese History Center of the University of Hawaii Press. ISBN 0824812859. Page 103–104.
  12. Adshead, Samuel Adrian Miles. (2000). China in World History. London: MacMillan Press Ltd. New York: St. Martin's Press. ISBN 0312225652. Page 156.
  13. Fairbank, John K. and Merle Goldman. (1998). China: A New History, Enlarged Edition. Cambridge: Harvard University Press. ISBN 0674116739. Page 93.
  14. Ross, Frank. (1982). Oracle Bones, Stars, and Wheelbarrows: Ancient Chinese Science and Technology. New York: Houghton Mifflin. ISBN 0395549671.
  15. Block, Leo. (2003). To Harness the Wind: A Short History of the Development of Sails. Annapolis: Naval Institute Press. ISBN 1557502099. Page 123.
  16. Block, Leo. (2003). To Harness the Wind: A Short History of the Development of Sails. Annapolis: Naval Institute Press. ISBN 1557502099. 8–9.
  17. William F. Edgerton: "Ancient Egyptian Steering Gear", The American Journal of Semitic Languages and Literatures, Vol. 43, No. 4. (1927), pp. 255
  18. William F. Edgerton: "Ancient Egyptian Steering Gear", The American Journal of Semitic Languages and Literatures, Vol. 43, No. 4. (1927), pp. 257
  19. William F. Edgerton: "Ancient Egyptian Steering Gear", The American Journal of Semitic Languages and Literatures, Vol. 43, No. 4. (1927), pp. 260
  20. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, p.84, 92
  21. Francesco Tiradritti (ed.): “The Treasures of the Egyptian Museum”, The American University in Cairo Press, Cairo 1999, ISBN 978 977 424 504 6, p.92f.
  22. Mohamed Ata: “Egypt from Past to Present. Through the Eyes of an Egyptian”, Cairo 2007, p.68
  23. Herodot: Histories, 2.96
  24. William F. Edgerton: “Ancient Egyptian Steering Gear”, The American Journal of Semitic Languages and Literatures, Vol. 43, No. 4. (1927), pp. 263
  25. Needham, Volume 4, Part 3, 649-650.
  26. Fairbank, 192.
  27. Deng, Gang. (1997). Chinese Maritime Activities and Socioeconomic Development, c. 2100 B.C.-1900 A.D. Westport: Greenwood Press. ISBN 0313292124. Page 42.
  28. Johnstone, Paul and Sean McGrail. (1988). The Sea-craft of Prehistory. New York: Routledge. ISBN 0415026350. Page 191.
  29. Needham, Volume 4, Part 3, 362.
  30. Needham, Volume 4, Par634.
  31. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, p.1
  32. Lionel Casson: Harbour and River Boats of Ancient Rome, The Journal of Roman Studies, Vol. 55, No. 1/2, Parts 1 and 2 (1965), pp. 31-39 (plate 1)
  33. Lionel Casson, Harbour and River Boats of Ancient Rome, The Journal of Roman Studies, Vol. 55, No. ½, Parts 1 and 2. (1965), pp. 35 (Pl. I); 36, Fn.43 (Pl.II,1)
  34. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, p.84, 95f.
  35. Lionel Casson: “Ships and Seamanship in the Ancient World”, ISBN 0801851300, S.XXVIII, 336f.; Fig.193
  36. Tilmann Bechert: Römisches Germanien zwischen Rhein und Maas. Die Provinz Germania inferior, Hirmer, München 1982, ISBN 3-7774-3440-X, p.183, 203 (Fig.266)
  37. M. D. de Weerd: Ships of the Roman Period at Zwammerdam / Nigrum Pullum, Germania Inferior, in: Roman Shipping and Trade: Britain and the Rhine Provinces. (The Council for) British Archaeology, Research Report 24, 1978, 15ff.
  38. M. D. de Weerd: Römerzeitliche Transportschiffe und Einbäume aus Nigrum Pullum / Zwammerdam, in: Studien zu den Militärgrenzen Roms II (1977), 187ff.
  39. Deutschlandfunk: Römische Schiffsversuchsanstalt in den Albaner Bergen
  40. Lawrence V. Mott, p.92f.
  41. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, p.2f., 92
  42. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, S.2, 95f.
  43. Kathleen Macphee, Somerled: Hammer of the Norse, Vital Spark, 2004, ISBN-13 9781903238240
  44. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, S.118f.
  45. Lawrence V. Mott, The Development of the Rudder, A.D. 100-1337: A Technological Tale, Thesis May 1991, Texas A&M University, S.2, 92f.
  46. Lawrence V. Mott, p.92


References



See also



Conventional ship and boat rudders



Specialist ship and boat rudders




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