Four-stroke engine and Margaret Corbin: Difference between pages
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'''Margaret Corbin''' ([[November 12]], [[1751]] – [[January 16]], [[1800]]) was a woman who fought in the [[United States|American]] [[American Revolutionary War|Revolutionary War]]. On [[November 16]], [[1776]] she and her husband, John Corbin, both from [[Philadelphia]], along with some 600 American soldiers, were defending [[Fort Washington (New York)|Fort Washington]] in northern [[Manhattan]] from 4,000 attacking [[Hessian (soldiers)|Hessian troops]] under British command. John and Margaret crewed one of two cannons the defenders possessed. After her husband was killed, Margaret took over firing his cannon until she was seriously wounded. Three years later, she became the first woman in the United States to receive pension from Congress.'' |
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{{Cleanup|date=May 2008}} |
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Today [[internal combustion engine]]s in [[automobile|cars]], [[truck]]s, motorcycles, aircraft, construction machinery and many others, most commonly use a '''four-stroke cycle'''. The four strokes refer to intake, compression, combustion (power) and exhaust strokes that occur during two crankshaft rotations per working cycle of Otto cycle and [[Diesel engine]]s. The four steps in this cycle are often informally referred to as "suck, squeeze (or squash), bang, blow." |
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Margaret Corbin was born in West Pennsylvania on November 12, 1751 in what is now [[Franklin County, Pennsylvania|Franklin County]]. Her father was Robert Cochran, a Scottish-Irish pioneer. In 1756, when she was five years old, Margaret’s parents were attacked by Native Americans. Her mother was kidnapped and her father was killed. At the time, Margaret and her brother John were not at home, and so escaped the raid. Margaret lived with her uncle for the rest of her childhood. |
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ting loves nighthawk |
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In 1772, at the age of 21, Margaret married a Virginia farmer named John Corbin. |
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== Valve train == |
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The valves are typically operated by a [[camshaft]] rotating at half the speed of the [[crankshaft]]. It has a series of [[cam]]s along its length, each designed to open a valve during the appropriate part of an intake or exhaust stroke. A [[tappet]] between valve and cam is a contact surface on which the cam slides to open the valve. The location of camshafts vary among engines, as does the quantity. Many engines use one or more camshafts “above” a row (or each row) of cylinders, as in the illustration, in which each cam directly actuates a valve through a flat tappet. In other engine designs the camshaft is in the [[crankcase]], in which case each cam contacts a ''push rod'', which contacts a ''rocker arm'' which opens a valve. The ''[[overhead cam]]'' design typically allows higher engine speeds because it provides the most direct path between cam and valve. |
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==American Revolutionary War== |
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<div style="font-style: italic; text-align: center;"> |
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When the war began, John enlisted in the First Company of Pennsylvania Artillery as a matross, someone who worked with loading and firing the canons. As was common at the time for wives of soldiers, Margaret became a [[camp follower]], accompanying John during his enlistment. She joined many other women in cooking, washing, and caring for the wounded soldiers. |
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[[Image:Four stroke cycle start.png|200px|Top dead center, before cycle begins]] |
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[[Image:Four stroke cycle intake.png|200px|1 – Intake stroke]] |
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[[Image:Four stroke cycle compression.png|200px|2 – Compression stroke]] |
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<br>Starting position, intake stroke, and compression stroke.<br/> |
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[[Image:Four stroke cycle spark.png|200px|Fuel ignites]] |
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[[Image:Four stroke cycle power.png|200px|3 – Power stroke]] |
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[[Image:Four stroke cycle exhaust.png|200px|4 – Exhaust stroke]] |
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<br>Ignition of fuel, power stroke, and exhaust stroke. |
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</div> |
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On November 16, 1776, Fort Washington, where John's company was stationed, was attacked by the British. John, an artilleryman, was in charge of firing a small cannon atop a ridge, today known as [[Fort Tryon Park|Fort Tryon]]. During an assault by the Hessians, John was killed, leaving his cannon unmanned. Margaret had been with her husband on the battlefield the entire time, and, after witnessing his death, she immediately took his place at the cannon. She fired away until her arm, chest, and jaw were hit by enemy fire. The British ultimately won the [[Battle of Fort Washington]], resulting in the surrender of Margaret and her comrades. As the equivalent of a wounded soldier, Margaret was released by the British on parole. |
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== Valve clearance adjustment == |
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{{howto}} |
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After the battle, Margaret went to Philadelphia, completely disabled from her wound, which would never fully heal. Life was difficult because of her injury, and in 1779 she received aid from the government. On June 29, the Executive Council of Pennsylvania granted her $30 to cover her present needs, and passed her case on to Congress’s Board of War. On July 6, 1779, the Board, sympathetic to Margaret’s injuries and impressed with her service and bravery, granted her half the monthly pay of a soldier in the Continental army and a new set of clothes or its equivalent in cash. With this act, Congress made Margaret the first woman in the United States to receive pension from Congress. |
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Valve clearance refers to the small gap between a valve ''lifter'' and a valve ''stem'' (or between a rocker arm and a valve stem) that ensures that the valve completely closes. On engines that require manual valve adjustment, excessive clearance will cause excessive noise from the valve train (“hammering”) during operation. Improper valve clearance reduces engine performance and increases wear and noise. |
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After Congress’s decision, Margaret was included on military rolls until the end of the war. She was enrolled in the Corps of Invalids, created by Congress for wounded soldiers. In 1781, the Corps of Invalids became part of the garrison at [[West Point, New York]]. She was discharged from the Continental Army in 1783. |
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Most engines have the valve clearance set by grinding the end of the valve stem during engine assembly, overhead cams not needing subsequent adjustment. All engines with poppet-type valves make some sort of allowance for maintaining this "expansion joint", while less sophisticated engines use solid, "non-adjustable” components which are simply ground off at the contact points to provide the correct clearance (though the low efficiency of this design may not be practical when the cost of labor is very high). Another method is to provide some method of manually changing the clearance with adjustable screws or shims, the implementation of which depends on and varies widely with the design of the engine. Manual valve lash adjustment is used in almost all very high performance engines because the hydraulic adjusters used in "automatic" systems are often affected by the extreme valve train accelerations of ultra high-speed engines. |
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==After War Years== |
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Most modern production engines use some form of automatic valve adjustment (usually hydraulic) to maintain a state known as "zero lash". In pushrod and some OHC engines this adjuster is incorporated into the tappet, lash adjuster or tip of the rocker. Many [[DOHC]] engines now employ tiny hydraulic lash adjusters in the top of the cam followers to maintain "zero lash". "Zero lash" is a desirable condition, since this allows for very quiet engine operation. Hydraulic lifters or lash adjusters also reduce required maintenance, reduce noise, help engines to perform at peak efficiency and minimize exhaust emissions by compensating for wear and expansion of various engine components. Earlier engines, mostly those with push rods and rocker arms, used adjustable tappets or [[hydraulic lifters]] to automatically compensate for valve train component and camshaft wear. Lack of valve clearance will prevent valve closure causing leakage and valve damage. |
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After being discharged, Margaret remained near West Point, known to officials and acquaintances as “Captain Molly”. She depended on the government and West Point officials for financial support. She died in Highland Falls, New York ,on January 16, 1800, at the age of forty-nine. In 1926, the [[Daughters of the American Revolution]] had Margaret’s remains reburied in the West Point military cemetery, becoming the only Revolutionary War soldeir to be buried there. |
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While living in the soldier's camp and after, Margaret was poor, rude, drank, swore, and smoked. She was equal to and respected the male soldiers. Her story is often confused and intertwined with that of [[Molly Pitcher]]. Though Margaret Corbin is certain to have lived and fired the cannon, much of the Molly Pitcher story is myth. |
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Valve clearance adjustment must be performed to manufacturer's specifications. It is normal that the exhaust valve will have a larger clearance. Adjustment is performed by either adjusting the rocker arm or placing shims between cam follower and valve stem. Most modern engines have [[hydraulic lifters]] and require only infrequent adjustment. {{Fact|date=September 2007}} |
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A tablet commemorating her heroism was erected in 1909 in [[Fort Tryon Park]], near the scene of her service, and the entrance to the park is named Margaret Corbin Circle in her honor.<ref>[http://www.nycgovparks.org/sub_your_park/historical_signs/hs_historical_sign.php?id=11275 Margaret Corbin Circle] in [[Fort Tryon Park]], [[New York City Department of Parks and Recreation]]. Accessed [[October 24]], [[2007]].</ref> A large [[art-deco]] mural depicting the battle scene decorates the lobby of nearby 720 [[Fort Washington Avenue (Manhattan)|Fort Washington Avenue]]. She is interred in [[West Point Cemetery]].<ref>[http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=231 Profile for Margaret Corbin], [[Find-A-Grave]]. Accessed [[October 24]], [[2007]].</ref> |
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=== Valve clearance measurement === |
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Valve clearance is measured with the valve closed, typically at [[top dead center]] between the compression and power strokes. The tappet will be resting on the heel of the cam lobe. A [[feeler gauge]] must pass through the clearance space. The feeler gauge should fit in and out with a slight drag. If the feeler gauge will not fit in, then the clearance is too small. If the blade of the feeler gauge fits in too loosely, the clearance is too large. |
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==Footnotes== |
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==== Valve clearance too wide ==== |
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{{Reflist}} |
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A too-wide valve clearance causes excessive wear of the [[camshaft]] and valve lifter contact areas, and noise. Should the clearance become wide enough, [[valve timing]] is significantly affected, resulting in poor performance. |
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==== Valve clearance too narrow ==== |
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A too-narrow valve clearance does not allow for heat expansion and results in the failure of the valve to fully close. The combustion chamber does not seal properly, resulting in poor compression, which reduces performance. The valve can also overheat and even melt. However heat expansion can have the opposite effect in overhead cam engines that use [[aluminum]] alloy cylinder heads. The coefficients of thermal expansion of aluminum alloys are approximately twice that of the steel used for the valve train and this expansion can increase the clearance. |
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==Port flow== |
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The output power of an engine is dependent on the ability of intake (air–fuel mixture) and exhaust matter to move quickly through valve ports, typically located in the [[cylinder head]]. To increase an engine’s output power, irregularities in the intake and exhaust paths, such as casting flaws, can be removed and, with the aid of an [[air flow bench]], the radii of valve port turns and [[valve seat]] configuration can be modified to reduce resistance. This process is called [[cylinder head porting|porting]], and it can be done by hand or with a [[CNC]] machine. |
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==Output limit== |
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The amount of power generated by a four-stroke engine is related to its speed. The speed is ultimately limited by material strength. Valves, pistons and connecting rods (where applicable) suffer severe forces and severe acceleration, and physical breakage and [[piston ring]] flutter can occur, resulting in power loss or even engine destruction. Piston ring flutter occurs are dislodged, resulting in a loss of cylinder seal and power. If an engine spins too quickly, valves cannot close quickly enough, and this can result in contact between a valve and a piston, severely damaging the engine. |
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Rod/stroke ratio, an important factor in engine design, is the ratio of the length of the [[connecting rod]] to the length of the crankshaft's (or piston's) stroke. An increase in the rod/stroke ratio (a longer rod, a shorter stroke or both) results in a lower piston speed. A longer rod (and consequently, higher rod/stroke ratio,) can potentially create more power, due to the fact that with a longer connecting rod, more force from the piston is delivered tangentially to the crankshaft's rotation, delivering more torque. A shorter rod/stroke ratio creates higher piston speeds, but this can be beneficial depending on other engine characteristics. Increased piston speeds can create ''tumble'' or ''swirl'' within the cylinder and reduce detonation. Increased piston speeds can also draw fuel-air mixture into the cylinder more quickly through a larger intake runner, promoting good cylinder filling. |
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Rod length and stroke length are independent variables. Rod length is expressed as center-to-center (c/c) length. An engine with a particular stroke can be fitted with rods of several c/c lengths by changing the piston pin location or block deck height. A rod that is longer in relation to stroke causes the piston to dwell a longer time at top dead center and causes the piston to move toward and away from TDC more slowly. Long rod engines with a particular stroke also build suction above the piston with less force, since the piston moves away from TDC more slowly. Consequently, long rod engines tend to produce a lower port air velocity, which also reduces low speed torque. Long rods place less thrust load on the cylinder walls, thus generate less parasitic drag and result in less frictional losses as engine revolutions rise. A "short rod" engine has the opposite characteristics. “The short rod exerts more force to the crank pin at any crank angle that counts i.e.--20° ATDC to 70° ATDC” (Jere Stahl [http://www.stahlheaders.com/Lit_Rod%20Length.htm]). Short rod engines tend develop more torque at lower engine speeds with torque and horsepower falling off quickly as engine RPM rises to high levels. Long rod engines generally produce more power due to reduced engine drag, especially as engine RPM increases. Regardless of rod length for a given stroke, the '''average''' piston speed (usually expressed in ft/s or m/s) remains the same. What changes as the rod length becomes shorter or longer in relation to the stroke, is the RATE of motion as the piston rises and falls in relation to the crankshaft. A long rod fitted to a given stroke generates less stress on the component parts due to the lower rate of acceleration away from and toward TDC. The average piston speed is the same; however, the peak piston speed is lower with long rods. |
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There is no "Ideal" rod to stroke ratio, however a ratio of about 2 to 1 seems to be the upper practical limit and 1.5 to 1 the lower limit in general practice. The Chevrolet 350 engine with a 3.48" stroke and a {{convert|5.7|in|mm|sing=on}} c/c rod has a rod/stroke ratio of 1.638 to 1. The durability and longevity of this engine seems to prove that this is a “acceptable” figure for a rod/stroke ratio number. The "small block 400" used a 3.75" stroke and a rod c/c of 5.565" for a ratio of 1.484. The SB 400 was known for torque and "running out of breath" at high engine speeds. Even with large port heads and high lift camshaft, the S/B 400 ran into a "wall" of friction when engine speeds climbed above 5000 rpm. S/B 400s we also know for wearing piston skirts and cylinder walls at a faster rate than their smaller brothers. Many people that race the S/B 400 convert the engine to 5.7 or 6.0 rods to reduce the effects of the long-stroke crankshaft and lower friction within the engine. The 1967–1969 Z-28 302 engine was fitted with a 3.0" stroke crank and in some racing applications used up to a 6.0" rod, resulting in a 2 to 1 rod/stroke. The 302 Chevrolet V-8 was famous for phenomenal power in the upper RPM range while it sacrificed low speed torque to gain the high RPM power and reliability. |
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Honda's B16A/B16B is considered ideal in high revolution and high durability applications and it is, not coincidentally, right in between the 1.5:1 and 2:1 ratios, with a 1.75:1 ratio. Although this gives it relative low power at lower engine speeds, it also gives it a rev-happy nature that is durable beyond its factory rev limit. Some sport bikes surpass the 1.75:1 ratio, but the lower torque at less engine speed becomes evident for practical applications such as cars(where power/weight ratio is important). |
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A "square engine" is an engine with a bore equal to its stroke. An engine where the bore dimension is larger than the stroke is commonly known as an [[oversquare]] engine; such engines have the ability to attain higher rotational speed since the pistons do not travel as far. Conversely, an engine with a bore that is smaller than its stroke is known as an [[undersquare]] engine; such engines cannot rotate as quickly, but are able to generate more torque at lower rotational speeds. |
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==Bibliography== |
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*Hardenberg, Horst O., ''The Middle Ages of the Internal combustion Engine'', Society of Automotive Engineers (SAE), 1999 |
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== See also == |
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*[[Poppet valve]] |
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*[[Atkinson cycle]] |
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*[[Desmodromic valve]] |
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* [[Six stroke engine]] |
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*[[Two-stroke engine]] |
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*[[History of the internal combustion engine]] |
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{{Machine configurations|state=uncollapsed}} |
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==External links== |
==External links== |
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*[http://www.cbsd.org/pennsylvaniapeople/level2_biographies/Level_2_biographies/margaret_corbin_level_2.htm Biography of Margaret Corbin] |
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{{Nofootnotes|date=February 2008}} |
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*[http://www.findagrave.com/cgi-bin/fg.cgi?page=gr&GRid=231 Profile for Margaret Corbin], [[Find-A-Grave]] |
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*[http://www.animatedpiston.com Detailed Engine Animations] |
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*[http://www.howcarswork.co.uk How Cars Work] – lots of general and specific car information, with forums |
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*{{US patent|194047}} |
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*[http://www.compgoparts.com/TechnicalResources/FourStrokeEngineBasics.asp How Four-stroke Small Engines Work] |
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*[http://auto.howstuffworks.com/engine.htm How Car Engines Work] |
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*[http://www.barsantiematteucci.it/Inglese/home_eng.htm Barsanti & Matteucci Foundation] – "fathers of the internal combustion engine" |
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*[http://www.keveney.com/otto.html Animated Engines:] another explanation of the four-stroke engine |
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*[http://www.new4stroke.com/New%204%20stroke.mpg New 4 Stroke] |
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*[http://www.carbibles.com/fuel_engine_bible.html The Fuel and Engine Bible] – A good resource for comparing different engine types, fuels, and engine components |
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*[http://www.cdxetextbook.com/video/video.html CDX ''e''Textbook] – some videos of car components in action |
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*[http://www.liveleak.com/view?i=73e_1192001762 View from a camera mounted inside a four-stroke engine cylinder]. |
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{{DEFAULTSORT:Corbin, Margaret}} |
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[[Category:Internal combustion piston engines]] |
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[[Category: |
[[Category:Women in the American Revolution]] |
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[[Category:Continental Army soldiers]] |
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[[Category:1751 births]] |
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[[Category:1800 deaths]] |
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[[Category:People of New York in the American Revolution]] |
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[[et:Neljataktiline sisepõlemismootor]] |
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[[es:Ciclo de cuatro tiempos]] |
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[[fr:Cycle de Beau de Rochas]] |
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[[hr:Četverotaktni motor]] |
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[[id:Putaran empat-tak]] |
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[[it:Motore a quattro tempi]] |
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[[he:מחזור ארבע פעימות]] |
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[[th:เครื่องยนต์ 4 จังหวะ]] |
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[[ur:اربع ضربہ چکر]] |
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[[zh:四冲程循环]] |
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Revision as of 15:46, 10 October 2008
Margaret Corbin (November 12, 1751 – January 16, 1800) was a woman who fought in the American Revolutionary War. On November 16, 1776 she and her husband, John Corbin, both from Philadelphia, along with some 600 American soldiers, were defending Fort Washington in northern Manhattan from 4,000 attacking Hessian troops under British command. John and Margaret crewed one of two cannons the defenders possessed. After her husband was killed, Margaret took over firing his cannon until she was seriously wounded. Three years later, she became the first woman in the United States to receive pension from Congress.
Margaret Corbin was born in West Pennsylvania on November 12, 1751 in what is now Franklin County. Her father was Robert Cochran, a Scottish-Irish pioneer. In 1756, when she was five years old, Margaret’s parents were attacked by Native Americans. Her mother was kidnapped and her father was killed. At the time, Margaret and her brother John were not at home, and so escaped the raid. Margaret lived with her uncle for the rest of her childhood.
In 1772, at the age of 21, Margaret married a Virginia farmer named John Corbin.
American Revolutionary War
When the war began, John enlisted in the First Company of Pennsylvania Artillery as a matross, someone who worked with loading and firing the canons. As was common at the time for wives of soldiers, Margaret became a camp follower, accompanying John during his enlistment. She joined many other women in cooking, washing, and caring for the wounded soldiers.
On November 16, 1776, Fort Washington, where John's company was stationed, was attacked by the British. John, an artilleryman, was in charge of firing a small cannon atop a ridge, today known as Fort Tryon. During an assault by the Hessians, John was killed, leaving his cannon unmanned. Margaret had been with her husband on the battlefield the entire time, and, after witnessing his death, she immediately took his place at the cannon. She fired away until her arm, chest, and jaw were hit by enemy fire. The British ultimately won the Battle of Fort Washington, resulting in the surrender of Margaret and her comrades. As the equivalent of a wounded soldier, Margaret was released by the British on parole.
After the battle, Margaret went to Philadelphia, completely disabled from her wound, which would never fully heal. Life was difficult because of her injury, and in 1779 she received aid from the government. On June 29, the Executive Council of Pennsylvania granted her $30 to cover her present needs, and passed her case on to Congress’s Board of War. On July 6, 1779, the Board, sympathetic to Margaret’s injuries and impressed with her service and bravery, granted her half the monthly pay of a soldier in the Continental army and a new set of clothes or its equivalent in cash. With this act, Congress made Margaret the first woman in the United States to receive pension from Congress.
After Congress’s decision, Margaret was included on military rolls until the end of the war. She was enrolled in the Corps of Invalids, created by Congress for wounded soldiers. In 1781, the Corps of Invalids became part of the garrison at West Point, New York. She was discharged from the Continental Army in 1783.
After War Years
After being discharged, Margaret remained near West Point, known to officials and acquaintances as “Captain Molly”. She depended on the government and West Point officials for financial support. She died in Highland Falls, New York ,on January 16, 1800, at the age of forty-nine. In 1926, the Daughters of the American Revolution had Margaret’s remains reburied in the West Point military cemetery, becoming the only Revolutionary War soldeir to be buried there.
While living in the soldier's camp and after, Margaret was poor, rude, drank, swore, and smoked. She was equal to and respected the male soldiers. Her story is often confused and intertwined with that of Molly Pitcher. Though Margaret Corbin is certain to have lived and fired the cannon, much of the Molly Pitcher story is myth.
A tablet commemorating her heroism was erected in 1909 in Fort Tryon Park, near the scene of her service, and the entrance to the park is named Margaret Corbin Circle in her honor.[1] A large art-deco mural depicting the battle scene decorates the lobby of nearby 720 Fort Washington Avenue. She is interred in West Point Cemetery.[2]
Footnotes
- ^ Margaret Corbin Circle in Fort Tryon Park, New York City Department of Parks and Recreation. Accessed October 24, 2007.
- ^ Profile for Margaret Corbin, Find-A-Grave. Accessed October 24, 2007.