The elevation of a geographic location is its height above or below a fixed reference point, most a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface. The term elevation is used when referring to points on the Earth's surface, while altitude or geopotential height is used for points above the surface, such as an aircraft in flight or a spacecraft in orbit, depth is used for points below the surface. Elevation is not to be confused with the distance from the center of the Earth. Due to the equatorial bulge, the summits of Mount Everest and Chimborazo have the largest elevation and the largest geocentric distance. GIS or geographic information system is a computer system that allows for visualizing, manipulating and storage of data with associated attributes. GIS offers better understanding of relationships of the landscape at different scales. Tools inside the GIS allow for manipulation of data for spatial cartography. A topographical map is the main type of map used to depict elevation through use of contour lines.
In a Geographic Information System, digital elevation models are used to represent the surface of a place, through a raster dataset of elevations. Digital terrain models are another way to represent terrain in GIS. USGS is developing a 3D Elevation Program to keep up with growing needs for high quality topographic data. 3DEP is a collection of enhanced elevation data in the form of high quality LiDAR data over the conterminous United States and the U. S. territories. There are three bare earth DEM layers in 3DEP which are nationally seamless at the resolution of 1/3, 1, 2 arcseconds; this map is derived from GTOPO30 data that describes the elevation of Earth's terrain at intervals of 30 arcseconds. It uses shading instead of contour lines to indicate elevation. Height Orthometric height Hypsography Geodesy Geodesy of North America Sea Level Datum of 1929 National Geodetic Vertical Datum of 1929 North American Vertical Datum of 1988 List of European cities by elevation List of highest mountains List of highest towns by country Normaal Amsterdams Peil Normalhöhennull Physical geography Table of the highest major summits of North America Temperature lapse rate Topographic isolation Topographic prominence Topography Vertical pressure variation U.
S. National Geodetic Survey website Geodetic Glossary @ NGS NGVD 29 to NAVD 88 online elevation converter @ NGS United States Geological Survey website Geographical Survey Institute Downloadable ETOPO2 Raw Data Database Downloadable ETOPO5 Raw Data Database Find the elevation of any place
Puerto Rico the Commonwealth of Puerto Rico and called Porto Rico, is an unincorporated territory of the United States located in the northeast Caribbean Sea 1,000 miles southeast of Miami, Florida. An archipelago among the Greater Antilles, Puerto Rico includes the eponymous main island and several smaller islands, such as Mona and Vieques; the capital and most populous city is San Juan. The territory's total population is 3.4 million. Spanish and English are the official languages. Populated by the indigenous Taíno people, Puerto Rico was colonized by Spain following the arrival of Christopher Columbus in 1493, it was contested by French and British, but remained a Spanish possession for the next four centuries. The island's cultural and demographic landscapes were shaped by the displacement and assimilation of the native population, the forced migration of African slaves, settlement from the Canary Islands and Andalusia. In the Spanish Empire, Puerto Rico played a secondary but strategic role compared to wealthier colonies like Peru and New Spain.
Spain's distant administrative control continued up to the end of the 19th century, producing a distinctive creole Hispanic culture and language that combined indigenous and European elements. In 1898, following the Spanish–American War, the United States acquired Puerto Rico under the terms of the Treaty of Paris. Puerto Ricans have been citizens of the United States since 1917, enjoy freedom of movement between the island and the mainland; as it is not a state, Puerto Rico does not have a vote in the United States Congress, which governs the territory with full jurisdiction under the Puerto Rico Federal Relations Act of 1950. However, Puerto Rico does have one non-voting member of the House called a Resident Commissioner; as residents of a U. S. territory, American citizens in Puerto Rico are disenfranchised at the national level and do not vote for president and vice president of the United States, nor pay federal income tax on Puerto Rican income. Like other territories and the District of Columbia, Puerto Rico does not have U.
S. senators. Congress approved a local constitution in 1952, allowing U. S. citizens on the territory to elect a governor. Puerto Rico's future political status has been a matter of significant debate. In early 2017, the Puerto Rican government-debt crisis posed serious problems for the government; the outstanding bond debt had climbed to $70 billion at a time with 12.4% unemployment. The debt had been increasing during a decade long recession; this was the second major financial crisis to affect the island after the Great Depression when the U. S. government, in 1935, provided relief efforts through the Puerto Rico Reconstruction Administration. On May 3, 2017, Puerto Rico's financial oversight board in the U. S. District Court for Puerto Rico filed the debt restructuring petition, made under Title III of PROMESA. By early August 2017, the debt was $72 billion with a 45% poverty rate. In late September 2017, Hurricane Maria made landfall in Puerto Rico; the island's electrical grid was destroyed, with repairs expected to take months to complete, provoking the largest power outage in American history.
Recovery efforts were somewhat slow in the first few months, over 200,000 residents had moved to the mainland State of Florida alone by late November 2017. Puerto Rico is Spanish for "rich port". Puerto Ricans call the island Borinquén – a derivation of Borikén, its indigenous Taíno name, which means "Land of the Valiant Lord"; the terms boricua and borincano derive from Borikén and Borinquen and are used to identify someone of Puerto Rican heritage. The island is popularly known in Spanish as la isla del encanto, meaning "the island of enchantment". Columbus named the island San Juan Bautista, in honor of Saint John the Baptist, while the capital city was named Ciudad de Puerto Rico. Traders and other maritime visitors came to refer to the entire island as Puerto Rico, while San Juan became the name used for the main trading/shipping port and the capital city; the island's name was changed to "Porto Rico" by the United States after the Treaty of Paris of 1898. The anglicized name was used by the U.
S. government and private enterprises. The name was changed back to Puerto Rico by a joint resolution in Congress introduced by Félix Córdova Dávila in 1931; the official name of the entity in Spanish is Estado Libre Asociado de Puerto Rico, while its official English name is Commonwealth of Puerto Rico. The ancient history of the archipelago, now Puerto Rico is not well known. Unlike other indigenous cultures in the New World which left behind abundant archeological and physical evidence of their societies, scant artifacts and evidence remain of the Puerto Rico's indigenous population. Scarce archaeological findings and early Spanish accounts from the colonial era constitute all, known about them; the first comprehensive book on the history of Puerto Rico was written by Fray Íñigo Abbad y Lasierra in 1786, nearly three centuries after the first Spaniards landed on the island. The first known settlers were the Ortoiroid people, an Archaic Period culture of Amerindian hunters and fishermen who migrated from the South American mainland.
Some scholars suggest their settlement dates back about 4,000 years. An archeological dig in 1990 on the island of Vieques found the remains of a man, designated as the "Puerto Ferro Man", dated to around 2000 BC; the Ortoiroid were displaced
Airport reference point
An airport reference point is the centre point of an airport, located at the geometric centre of all the usable runways. The ARP is computed. Internationally, the rules governing the establishment of an Airport reference point are defined by ICAO Annex 14, include: 2.2.1 An aerodrome reference point shall be established for an aerodrome. 2.2.2 The aerodrome reference point shall be located near the initial or planned geometric centre of the aerodrome and shall remain where first established. 2.2.3 The position of the aerodrome reference point shall be measured and reported to the aeronautical information services authority in degrees and seconds. National Geodetic Survey ARP Calculator
An octane rating, or octane number, is a standard measure of the performance of an engine or aviation fuel. The higher the octane number, the more compression the fuel can withstand before detonating. In broad terms, fuels with a higher octane rating are used in high performance gasoline engines that require higher compression ratios. In contrast, fuels with lower octane numbers are ideal for diesel engines, because diesel engines do not compress the fuel, but rather compress only air and inject fuel into the air, heated by compression. Gasoline engines rely on ignition of air and fuel compressed together as a mixture, ignited at the end of the compression stroke using spark plugs. Therefore, high compressibility of the fuel matters for gasoline engines. Use of gasoline with lower octane numbers may lead to the problem of engine knocking. In a normal spark-ignition engine, the air-fuel mixture is heated because of being compressed and is triggered to burn by the spark plug. During the combustion process, if the unburnt portion of the fuel in the combustion chamber is heated too much, pockets of unburnt fuel may self-ignite before the main flame front reaches them.
Shockwaves produced by detonation can cause much higher pressures than engine components are designed for, can cause a "knocking" or "pinging" sound. Knocking can cause major engine damage; the most used engine management systems found in automobiles today have a knock sensor that monitors if knock is being produced by the fuel being used. In modern computer-controlled engines, the ignition timing will be automatically altered by the engine management system to reduce the knock to an acceptable level. Octanes are a family of hydrocarbons, they are colorless liquids that boil around 125 °C. One member of the octane family, isooctane, is used as a reference standard to benchmark the tendency of gasoline or LPG fuels to resist self-ignition; the octane rating of gasoline is measured in a test engine and is defined by comparison with the mixture of 2,2,4-trimethylpentane and heptane that would have the same anti-knocking capacity as the fuel under test: the percentage, by volume, of 2,2,4-trimethylpentane in that mixture is the octane number of the fuel.
For example, gasoline with the same knocking characteristics as a mixture of 90% iso-octane and 10% heptane would have an octane rating of 90. A rating of 90 does not mean that the gasoline contains just iso-octane and heptane in these proportions but that it has the same detonation resistance properties; because some fuels are more knock-resistant than pure iso-octane, the definition has been extended to allow for octane numbers greater than 100. Octane ratings are not indicators of the energy content of fuels.. They are only a measure of the fuel's tendency to burn in a controlled manner, rather than exploding in an uncontrolled manner. Where the octane number is raised by blending in ethanol, energy content per volume is reduced. Ethanol BTUs can be compared with gasoline BTUs in heat of combustion tables, it is possible for a fuel to have a Research Octane Number more than 100, because iso-octane is not the most knock-resistant substance available. Racing fuels, avgas, LPG and alcohol fuels such as methanol may have octane ratings of 110 or higher.
Typical "octane booster" gasoline additives include ETBE, isooctane and toluene. Lead in the form of tetraethyllead was once a common additive, but its use for fuels for road vehicles has been progressively phased-out worldwide, beginning in the 1970s; the most common type of octane rating worldwide is the Research Octane Number. RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, comparing the results with those for mixtures of iso-octane and n-heptane. Another type of octane rating, called Motor Octane Number, is determined at 900 rpm engine speed instead of the 600 rpm for RON. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON.
Pump gasoline specifications require both a minimum RON and a minimum MON. In most countries in Europe the "headline" octane rating shown on the pump is the RON, but in Canada, the United States and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index, written on pumps as /2, it may sometimes be called the Posted Octane Number. Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel; this difference between RON and MON is known as the fuel's Sensitivity, is not published for those countries that use the Anti-Knock Index labelling system. See the table in the following section for a comparison. Another type of octane rating, called Observed Road Octane Number, is derived from testing gasolines in real world multi-cylinder engines at wide open throttle, it is still reliable today. The ori
Landing gear is the undercarriage of an aircraft or spacecraft and may be used for either takeoff or landing. For aircraft it is both, it was formerly called alighting gear by some manufacturers, such as the Glenn L. Martin Company. For aircraft, the landing gear supports the craft when it is not flying, allowing it to take off and taxi without damage. Wheels are used but skids, floats or a combination of these and other elements can be deployed depending both on the surface and on whether the craft only operates vertically or is able to taxi along the surface. Faster aircraft have retractable undercarriages, which fold away during flight to reduce air resistance or drag. For launch vehicles and spacecraft landers, the landing gear is designed to support the vehicle only post-flight, are not used for takeoff or surface movement. Aircraft landing gear includes wheels equipped with simple shock absorbers, or more advanced air/oil oleo struts, for runway and rough terrain landing; some aircraft floats for water, and/or skids or pontoons.
It represents 2.5 to 5% of the MTOW and 1.5 to 1.75% of the aircraft cost but 20% of the airframe direct maintenance cost. The undercarriage is 4–5% of the takeoff mass and can reach 7%. Wheeled undercarriages come in two types: conventional or "taildragger" undercarriage, where there are two main wheels towards the front of the aircraft and a single, much smaller, wheel or skid at the rear; the taildragger arrangement was common during the early propeller era, as it allows more room for propeller clearance. Most modern aircraft have tricycle undercarriages. Taildraggers are considered harder to land and take off, require special pilot training. Sometimes a small tail wheel or skid is added to aircraft with tricycle undercarriage, in case of tail strikes during take-off; the Concorde, for instance, had a retractable tail "bumper" wheel, as delta winged aircraft need a high angle when taking off. Both Boeing's largest WWII bomber, the B-29 Superfortress, the 1960s-introduced Boeing 727 trijet airliner each have a retractable tail bumper.
Some aircraft with retractable conventional landing gear have a fixed tailwheel, which generates minimal drag and improves yaw stability in some cases. Another arrangement sometimes used is central nose gear with outriggers on the wings; this may be done where there is no convenient location on either side to attach the main undercarriage or to store it when retracted. Examples include the Harrier Jump Jet; the B-52 bomber uses a similar arrangement, except that each end of the fuselage has two sets of wheels side by side. To decrease drag in flight some undercarriages retract into the wings and/or fuselage with wheels flush against the surface or concealed behind doors. If the wheels rest protruding and exposed to the airstream after being retracted, the system is called semi-retractable. Most retraction systems are hydraulically operated, though some are electrically operated or manually operated; this adds complexity to the design. In retractable gear systems, the compartment where the wheels are stowed are called wheel wells, which may diminish valuable cargo or fuel space.
] Pilots confirming that their landing gear is down and locked refer to "three greens" or "three in the green.", a reference to the electrical indicator lights from the nosewheel/tailwheel and the two main gears. Blinking green lights or red lights indicate the gear is in transit and neither up and locked or down and locked; when the gear is stowed up with the up-locks secure, the lights extinguish to follow the dark cockpit philosophy. Multiple redundancies are provided to prevent a single failure from failing the entire landing gear extension process. Whether electrically or hydraulically operated, the landing gear can be powered from multiple sources. In case the power system fails, an emergency extension system is always available; this may take the form of a manually operated crank or pump, or a mechanical free-fall mechanism which disengages the uplocks and allows the landing gear to fall due to gravity. Some high-performance aircraft may feature a pressurized-nitrogen back-up system; as aircraft grow larger, they employ more wheels to cope with the increasing weights.
The earliest "giant" aircraft placed in quantity production, the Zeppelin-Staaken R. VI German World War I long-range bomber of 1916, used a total of eighteen wheels for its undercarriage, split between two wheels on its nose gear struts, a total of sixteen wheels on its main gear units — split into four side-by-side quartets each, two quartets of wheels per side — under each tandem engine nacelle, to support its loaded weight of 12 metric tons. Multiple "tandem wheels" on an aircraft — for cargo aircraft, mounted to the fuselage lower sides as retractable main gear units on modern designs — were first seen during World War II, on the experimental German Arado Ar 232 cargo aircraft, which used a row of elev
VHF omnidirectional range
High Frequency Omni-Directional Range is a type of short-range radio navigation system for aircraft, enabling aircraft with a receiving unit to determine its position and stay on course by receiving radio signals transmitted by a network of fixed ground radio beacons. It uses frequencies in the high frequency band from 108.00 to 117.95 MHz. Developed in the United States beginning in 1937 and deployed by 1946, VOR is the standard air navigational system in the world, used by both commercial and general aviation. By 2000 there were about 3,000 VOR stations around the world including 1,033 in the US, reduced to 967 by 2013 with more stations being decommissioned with the widespread adoption of GPS. A VOR ground station sends out an omnidirectional master signal, a directional second signal is propagated by a phased antenna array and rotates clockwise in space 30 times a second; this signal is timed so that its phase varies as the secondary signal rotates, this phase difference is the same as the angular direction of the'spinning' signal.
By comparing the phase of the secondary signal with the master, the angle to the aircraft from the station can be determined. This line of position is called the "radial" from the VOR; the intersection of radials from two different VOR stations can be used to fix the position of the aircraft, as in earlier radio direction finding systems. VOR stations are short range: the signals are line of sight between transmitter and receiver and are useful for up to 200 miles; each station broadcasts a VHF radio composite signal including the navigation signal, station's identifier and voice, if so equipped. The navigation signal allows the airborne receiving equipment to determine a bearing from the station to the aircraft; the station's identifier is a three-letter string in Morse code. The voice signal, if used, is the station name, in-flight recorded advisories, or live flight service broadcasts. At some locations, this voice signal is a continuous recorded broadcast of Hazardous Inflight Weather Advisory Service or HIWAS.
Developed from earlier Visual Aural Radio Range systems, the VOR was designed to provide 360 courses to and from the station, selectable by the pilot. Early vacuum tube transmitters with mechanically-rotated antennas were installed in the 1950s, began to be replaced with solid-state units in the early 1960s, they became the major radio navigation system in the 1960s, when they took over from the older radio beacon and four-course system. Some of the older range stations survived, with the four-course directional features removed, as non-directional low or medium frequency radiobeacons. A worldwide land-based network of "air highways", known in the US as Victor airways and "jetways", was set up linking VORs. An aircraft can follow a specific path from station to station by tuning into the successive stations on the VOR receiver, either following the desired course on a Radio Magnetic Indicator, or setting it on a course deviation indicator or a horizontal situation indicator and keeping a course pointer centred on the display.
As of 2005, due to advances in technology, many airports are replacing VOR and NDB approaches with RNAV approach procedures. VOR signals provide greater accuracy and reliability than NDBs due to a combination of factors. Most significant is that VOR provides a bearing from the station to the aircraft which does not vary with wind or orientation of the aircraft. VHF radio is less vulnerable to diffraction around terrain coastlines. Phase encoding suffers less interference from thunderstorms. VOR signals offer a predictable accuracy of 90 m, 2 sigma at 2 NM from a pair of VOR beacons. VOR stations rely on "line of sight" because they operate in the VHF band—if the transmitting antenna cannot be seen on a clear day from the receiving antenna, a useful signal cannot be received; this limits VOR range to the horizon -- or closer. Although the modern solid state transmitting equipment requires much less maintenance than the older units, an extensive network of stations, needed to provide reasonable coverage along main air routes, is a significant cost in operating current airway systems.
VORs are assigned radio channels between 117.95 MHz. The first 4 MHz is shared with the instrument landing system band. To leave channels for ILS, in the range 108.0 to 111.95 MHz, the 100 kHz digit is always so 108.00, 108.05, 108.20, 108.25, so on are VOR frequencies but 108.10, 108.15, 108.30, 108.35 and so on, are reserved for ILS in the US. The VOR encodes azimuth as the phase relationship between a variable signal; the omnidirectional signal contains a modulated continuous wave 7 wpm Morse code station identifier, contains an amplitude modulated voice channel. The conventional 30 Hz reference signal is frequency modulated on a 9,960 Hz subcarrier; the variable amplitude modulated signal is conven