60-497: The ascent propulsion system ( APS ) or lunar module ascent engine ( LMAE ) is a fixed- thrust hypergolic rocket engine developed by Bell Aerosystems for use in the Apollo Lunar Module ascent stage. It used Aerozine 50 fuel, and N 2 O 4 oxidizer. Rocketdyne provided the injector system, at the request of NASA, when Bell could not solve combustion instability problems. The LMAE traces its origin to
120-421: A bevel gear , whose overall shape is like a slice ( frustum ) of a cone whose apex is the meeting point of the two axes. Bevel gears with equal numbers of teeth and shaft axes at 90 degrees are called miter (US) or mitre (UK) gears. Independently of the angle between the axes, the larger of two unequal matching bevel gears may be internal or external, depending the desired relative sense of rotation. If
180-430: A constant rate, whether the aircraft is moving or not. Now, imagine the strong chain is broken, and the jet and the piston aircraft start to move. At low speeds: The piston engine will have constant 100% power, and the propeller's thrust will vary with speed The jet engine will have constant 100% thrust, and the engine's power will vary with speed If a powered aircraft is generating thrust T and experiencing drag D,
240-465: A few mm in watches and toys to over 10 metres in some mining equipment. Other types of parts that are somewhat similar in shape and function to gears include the sprocket , which is meant to engage with a link chain instead of another gear, and the timing pulley , meant to engage a timing belt . Most gears are round and have equal teeth, designed to operate as smoothly as possible; but there are several applications for non-circular gears , and
300-611: A geared astrolabe was built in Isfahan showing the position of the moon in the zodiac and its phase , and the number of days since new moon. The worm gear was invented in the Indian subcontinent , for use in roller cotton gins , some time during the 13th–14th centuries. A complex astronomical clock, called the Astrarium , was built between 1348 and 1364 by Giovanni Dondi dell'Orologio . It had seven faces and 107 moving parts; it showed
360-452: A length of 47 inches (120 cm) and diameter of 34 inches (86 cm). Rocketdyne brought the lunar module ascent engine out of its 36-year retirement in 2008 for NASA's Exploration Systems Architecture Study (ESAS) engine testing, re-designated it as RS-18 , and reconfigured the non-throttleable hypergolic engine to use LOX/methane. [REDACTED] This article incorporates public domain material from websites or documents of
420-517: A motor communicates motion' is from 1814; specifically of a vehicle (bicycle, automobile, etc.) by 1888. A cog is a tooth on a wheel. From Middle English cogge, from Old Norse (compare Norwegian kugg ('cog'), Swedish kugg , kugge ('cog, tooth')), from Proto-Germanic * kuggō (compare Dutch kogge (' cogboat '), German Kock ), from Proto-Indo-European * gugā ('hump, ball') (compare Lithuanian gugà ('pommel, hump, hill'), from PIE * gēw- ('to bend, arch'). First used c. 1300 in
480-682: A pointer on top of the chariot kept the direction of latter unchanged as the chariot turned. Another early surviving example of geared mechanism is a complex calendrical device showing the phase of the Moon, the day of the month and the places of the Sun and the Moon in the Zodiac was invented in the Byzantine empire in the early 6th century AD. Geared mechanical water clocks were built in China by 725 AD. Around 1221 AD,
540-418: A pressure-fed fuel system using hypergolic (self-igniting) propellants, the ascent engine was fixed-thrust and nongimbaled, capable of lifting the ascent stage off the Moon or aborting a landing if necessary. The engine developed about 3,500 pounds-force (16 kN) of thrust, which produced a velocity of 2,000 meters per second from lunar launch, to LOR, and CM docking. It weighed 180 pounds (82 kg), with
600-605: A series of wooden pegs or cogs around the rim of a wheel. The cogs were often made of maple wood. Wooden gears have been gradually replaced by ones made or metal, such as cast iron at first, then steel and aluminum . Steel is most commonly used because of its high strength-to-weight ratio and low cost. Aluminum is not as strong as steel for the same geometry, but is lighter and easier to machine. powder metallurgy may be used with alloys that cannot be easily cast or machined. Still, because of cost or other considerations, some early metal gears had wooden cogs, each tooth forming
660-400: A type of specialised 'through' mortise and tenon joint More recently engineering plastics and composite materials have been replacing metals in many applications, especially those with moderate speed and torque. They are not as strong as steel, but are cheaper, can be mass-manufactured by injection molding don't need lubrication. Plastic gears may even be intentionally designed to be
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#1732877339286720-425: Is not only acceptable but desirable. For basic analysis purposes, each gear can be idealized as a perfectly rigid body that, in normal operation, turns around a rotation axis that is fixed in space, without sliding along it. Thus, each point of the gear can move only along a circle that is perpendicular to its axis and centered on it. At any moment t , all points of the gear will be rotating around that axis with
780-512: Is produced by net shape molding. Molded gearing is usually powder metallurgy, plastic injection, or metal die casting. Gears produced by powder metallurgy often require a sintering step after they are removed from the mold. Cast gears require gear cutting or other machining to shape the teeth to the necessary precision. The most common form of gear cutting is hobbing , but gear shaping , milling , and broaching may be used instead. Metal gears intended for heavy duty operation, such as in
840-500: Is pushed in the direction opposite to flight. This can be done by different means such as the spinning blades of a propeller , the propelling jet of a jet engine , or by ejecting hot gases from a rocket engine . Reverse thrust can be generated to aid braking after landing by reversing the pitch of variable-pitch propeller blades, or using a thrust reverser on a jet engine. Rotary wing aircraft use rotors and thrust vectoring V/STOL aircraft use propellers or engine thrust to support
900-671: Is reversed when one gear wheel drives another gear wheel. Philon of Byzantium was one of the first who used gears in water raising devices. Gears appear in works connected to Hero of Alexandria , in Roman Egypt circa AD 50, but can be traced back to the mechanics of the Library of Alexandria in 3rd-century BC Ptolemaic Egypt , and were greatly developed by the Greek polymath Archimedes (287–212 BC). The earliest surviving gears in Europe were found in
960-468: Is the velocity at the actuator disc, and v f {\displaystyle v_{f}} is the final exit velocity: Solving for the velocity at the disc, v d {\displaystyle v_{d}} , we then have: When incoming air is accelerated from a standstill – for example when hovering – then v ∞ = 0 {\displaystyle v_{\infty }=0} , and we can find: From here we can see
1020-410: The P 2 ∝ T 3 {\displaystyle \mathbf {P} ^{2}\propto \mathbf {T} ^{3}} relationship, finding: The inverse of the proportionality constant, the "efficiency" of an otherwise-perfect thruster, is proportional to the area of the cross section of the propelled volume of fluid ( A {\displaystyle A} ) and the density of
1080-456: The Antikythera mechanism an example of a very early and intricate geared device, designed to calculate astronomical positions of the sun, moon, and planets, and predict eclipses . Its time of construction is now estimated between 150 and 100 BC. The Chinese engineer Ma Jun (c. 200–265 AD) described a south-pointing chariot . A set of differential gears connected to the wheels and to
1140-447: The Geneva drive has an extremely uneven operation, by design. Gears can be seen as instances of the basic lever "machine". When a small gear drives a larger one, the mechanical advantage of this ideal lever causes the torque T to increase but the rotational speed ω to decrease. The opposite effect is obtained when a large gear drives a small one. The changes are proportional to
1200-469: The National Aeronautics and Space Administration . Thrust Thrust is a reaction force described quantitatively by Newton's third law . When a system expels or accelerates mass in one direction, the accelerated mass will cause a force of equal magnitude but opposite direction to be applied to that system. The force applied on a surface in a direction perpendicular or normal to
1260-526: The Ranger and Lunar Orbiter lunar probes. The Lockheed Agena target vehicle using the Bell 8247 engine was qualified for 15 restarts for NASA's Project Gemini . A total of 365 Agena rockets were launched by NASA and the U.S. Air Force between February 28, 1959, and the last Agena D launched on 12 February 1987, configured as the upper stage of a Titan 34B . During the spring of 1963, Grumman hired Bell to develop
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#17328773392861320-435: The gear ratio r , the ratio of the tooth counts. namely, T 2 / T 1 = r = N 2 / N 1 , and ω 2 / ω 1 = 1/ r = N 1 / N 2 . Depending on the geometry of the pair, the sense of rotation may also be inverted (from clockwise to anti-clockwise , or vice-versa). Most vehicles have a transmission or "gearbox" containing a set of gears that can be meshed in multiple configurations. The gearbox lets
1380-431: The transmissions of cars and trucks, the teeth are heat treated to make them hard and more wear resistant while leaving the core soft but tough . For large gears that are prone to warp, a quench press is used. Gears can be made by 3D printing ; however, this alternative is typically used only for prototypes or very limited production quantities, because of its high cost, low accuracy, and relatively low strength of
1440-559: The Thompson Manufacturing Company of Lancaster, New Hampshire still had a very active business in supplying tens of thousands of maple gear teeth per year, mostly for use in paper mills and grist mills , some dating back over 100 years. The most common techniques for gear manufacturing are dies , sand , and investment casting ; injection molding ; powder metallurgy ; blanking ; and gear cutting . As of 2014, an estimated 80% of all gearing produced worldwide
1500-698: The air-breathing category, the AMT-USA AT-180 jet engine developed for radio-controlled aircraft produce 90 N (20 lbf ) of thrust. The GE90 -115B engine fitted on the Boeing 777 -300ER, recognized by the Guinness Book of World Records as the "World's Most Powerful Commercial Jet Engine," has a thrust of 569 kN (127,900 lbf) until it was surpassed by the GE9X , fitted on the upcoming Boeing 777X , at 609 kN (134,300 lbf). The power needed to generate thrust and
1560-442: The aircraft by itself (the propeller does that), so piston engines are usually rated by how much power they deliver to the propeller. Except for changes in temperature and air pressure, this quantity depends basically on the throttle setting. A jet engine has no propeller, so the propulsive power of a jet engine is determined from its thrust as follows. Power is the force (F) it takes to move something over some distance (d) divided by
1620-450: The axes, each section of one gear will interact only with the corresponding section of the other gear. Thus the three-dimensional gear train can be understood as a stack of gears that are flat and infinitesimally thin — that is, essentially two-dimensional. In a crossed arrangement, the axes of rotation of the two gears are not parallel but cross at an arbitrary angle except zero or 180 degrees. For best operation, each wheel then must be
1680-424: The axis of rotation and/or to invert the sense of rotation. A gear may also be used to transmit linear force and/or linear motion to a rack , a straight bar with a row of compatible teeth. Gears are among the most common mechanical parts. They come in a great variety of shapes and materials, and are used for many different functions and applications. Diameters may range from a few μm in micromachines , to
1740-438: The axis, meaning that it is congruent with itself when the gear rotates by 1/ N of a turn. If the gear is meant to transmit or receive torque with a definite sense only (clockwise or counterclockwise with respect to some reference viewpoint), the action surface consists of N separate patches, the tooth faces ; which have the same shape and are positioned in the same way relative to the axis, spaced 1/ N turn apart. If
1800-448: The best shape for each pitch surface is neither cylindrical nor conical but a portion of a hyperboloid of revolution. Such gears are called hypoid for short. Hypoid gears are most commonly found with shafts at 90 degrees. Contact between hypoid gear teeth may be even smoother and more gradual than with spiral bevel gear teeth, but also have a sliding action along the meshing teeth as it rotates and therefore usually require some of
1860-438: The difference between the two, T − D, is termed the excess thrust. The instantaneous performance of the aircraft is mostly dependent on the excess thrust. Excess thrust is a vector and is determined as the vector difference between the thrust vector and the drag vector. The thrust axis for an airplane is the line of action of the total thrust at any instant. It depends on the location, number, and characteristics of
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1920-526: The earlier Bell Aerosystems engines (8096, 8247) used in the RM-81 Agena , the rocket upper stage and satellite support bus developed by Lockheed initially for the canceled WS-117L reconnaissance satellite program. The Agena served as an upper stage for several defense, intelligence, and exploration programs: SAMOS-E , SAMOS-F (ELINT Ferret) and MIDAS (Missile Defense Alarm System) military early-warning satellites, Corona photo intelligence program, and
1980-408: The fluid ( ρ {\displaystyle \rho } ). This helps to explain why moving through water is easier and why aircraft have much larger propellers than watercraft. A very common question is how to compare the thrust rating of a jet engine with the power rating of a piston engine. Such comparison is difficult, as these quantities are not equivalent. A piston engine does not move
2040-454: The force of the thrust can be related in a non-linear way. In general, P 2 ∝ T 3 {\displaystyle \mathbf {P} ^{2}\propto \mathbf {T} ^{3}} . The proportionality constant varies, and can be solved for a uniform flow, where v ∞ {\displaystyle v_{\infty }} is the incoming air velocity, v d {\displaystyle v_{d}}
2100-407: The jet engines or propellers. It usually differs from the drag axis. If so, the distance between the thrust axis and the drag axis will cause a moment that must be resisted by a change in the aerodynamic force on the horizontal stabiliser. Notably, the Boeing 737 MAX , with larger, lower-slung engines than previous 737 models, had a greater distance between the thrust axis and the drag axis, causing
2160-599: The lunar module ascent engine, on the assumption that Bell's experience in development of the Air Force Agena engine would be transferable to the lunar module requirements. Grumman placed heavy emphasis upon high reliability through simplicity of design, and the ascent engine emerged as the least complicated of the three main engines in the Apollo space vehicle, including the LM descent and CSM service propulsion system engines. Embodying
2220-434: The most common configuration, the axes of rotation of the two gears are parallel, and usually their sizes are such that they contact near a point between the two axes. In this configuration, the two gears turn in opposite senses. Occasionally the axes are parallel but one gear is nested inside the other. In this configuration, both gears turn in the same sense. If the two gears are cut by an imaginary plane perpendicular to
2280-522: The most efficient and compact way of transmitting torque between two non-parallel axes. On the other hand, gears are more expensive to manufacture, may require periodic lubrication, and may have greater mass and rotational inertia than the equivalent pulleys. More importantly, the distance between the axes of matched gears is limited and cannot be changed once they are manufactured. There are also applications where slippage under overload or transients (as occurs with belts, hydraulics, and friction wheels)
2340-445: The most viscous types of gear oil to avoid it being extruded from the mating tooth faces, the oil is normally designated HP (for hypoid) followed by a number denoting the viscosity. Also, the pinion can be designed with fewer teeth than a spiral bevel pinion, with the result that gear ratios of 60:1 and higher are feasible using a single set of hypoid gears. This style of gear is most common in motor vehicle drive trains, in concert with
2400-536: The nose to rise up in some flight regimes, necessitating a pitch-control system, MCAS . Early versions of MCAS malfunctioned in flight with catastrophic consequences, leading to the deaths of over 300 people in 2018 and 2019. Helical gear A gear or gearwheel is a rotating machine part typically used to transmit rotational motion and/or torque by means of a series of teeth that engage with compatible teeth of another gear or other part. The teeth can be integral saliences or cavities machined on
2460-512: The nymphs of the planthopper insect Issus coleoptratus . The word gear is probably from Old Norse gørvi (plural gørvar ) 'apparel, gear,' related to gøra , gørva 'to make, construct, build; set in order, prepare,' a common verb in Old Norse, "used in a wide range of situations from writing a book to dressing meat". In this context, the meaning of 'toothed wheel in machinery' first attested 1520s; specific mechanical sense of 'parts by which
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2520-409: The operator vary the torque that is applied to the wheels without changing the engine's speed. Gearboxes are used also in many other machines, such as lathes and conveyor belts . In all those cases, terms like "first gear", "high gear", and "reverse gear" refer to the overall torque ratios of different meshing configurations, rather than to specific physical gears. These terms may be applied even when
2580-446: The part, or separate pegs inserted into it. In the latter case, the gear is usually called a cogwheel . A cog may be one of those pegs or the whole gear. Two or more meshing gears are called a gear train . The smaller member of a pair of meshing gears is often called pinion . Most commonly, gears and gear trains can be used to trade torque for rotational speed between two axles or other rotating parts and/or to change
2640-481: The points p and q are moving along different circles; therefore, the contact cannot last more than one instant, and p will then either slide across the other face, or stop contacting it altogether. On the other hand, at any given moment there is at least one such pair of contact points; usually more than one, even a whole line or surface of contact. Actual gears deviate from this model in many ways: they are not perfectly rigid, their mounting does not ensure that
2700-455: The positions of the sun, the moon and the five planets then known, as well as religious feast days. The Salisbury Cathedral clock , built in 1386, it is the world's oldest still working geared mechanical clock. Differential gears were used by the British clock maker Joseph Williamson in 1720. However, the oldest functioning gears by far were created by Nature, and are seen in the hind legs of
2760-672: The resulting part. Besides gear trains, other alternative methods of transmitting torque between non-coaxial parts include link chains driven by sprockets, friction drives , belts and pulleys , hydraulic couplings , and timing belts . One major advantage of gears is that their rigid body and the snug interlocking of the teeth ensure precise tracking of the rotation across the gear train, limited only by backlash and other mechanical defects. For this reason they are favored in precision applications such as watches. Gear trains also can have fewer separate parts (only two) and have minimal power loss, minimal wear, and long life. Gears are also often
2820-401: The rocket, times the time-rate at which the mass is expelled, or in mathematical terms: Where T is the thrust generated (force), d m d t {\displaystyle {\frac {\mathrm {d} m}{\mathrm {d} t}}} is the rate of change of mass with respect to time (mass flow rate of exhaust), and v is the velocity of the exhaust gases measured relative to
2880-611: The rocket. For vertical launch of a rocket the initial thrust at liftoff must be more than the weight. Each of the three Space Shuttle Main Engines could produce a thrust of 1.8 meganewton , and each of the Space Shuttle's two Solid Rocket Boosters 14.7 MN (3,300,000 lbf ), together 29.4 MN. By contrast, the Simplified Aid for EVA Rescue (SAFER) has 24 thrusters of 3.56 N (0.80 lbf) each. In
2940-425: The rotation axis will be perfectly fixed in space, the teeth may have slightly different shapes and spacing, the tooth faces are not perfectly smooth, and so on. Yet, these deviations from the ideal model can be ignored for a basic analysis of the operation of a gear set. One criterion for classifying gears is the relative position and direction of the axes or rotation of the gears that are to be meshed together. In
3000-456: The same angular speed ω ( t ), in the same sense. The speed need not be constant over time. The action surface of the gear consists of all points of its surface that, in normal operation, may contact the matching gear with positive pressure . All other parts of the surface are irrelevant (except that they cannot be crossed by any part of the matching gear). In a gear with N teeth, the working surface has N -fold rotational symmetry about
3060-524: The sense of 'a wheel having teeth or cogs; late 14c., 'tooth on a wheel'; cog-wheel, early 15c. The gears of the Antikythera mechanism are made of bronze , and the earliest surviving Chinese gears are made of iron, These metals, as well as tin , have been generally used for clocks and similar mechanisms to this day. Historically, large gears, such as used in flour mills , were commonly made of wood rather than metal. They were cogwheels, made by inserting
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#17328773392863120-457: The speed is zero, then the propulsive power is zero. If a jet aircraft is at full throttle but attached to a static test stand, then the jet engine produces no propulsive power, however thrust is still produced. The combination piston engine –propeller also has a propulsive power with exactly the same formula, and it will also be zero at zero speed – but that is for the engine–propeller set. The engine alone will continue to produce its rated power at
3180-536: The surface is also called thrust. Force, and thus thrust, is measured using the International System of Units (SI) in newtons (symbol: N), and represents the amount needed to accelerate 1 kilogram of mass at the rate of 1 meter per second per second . In mechanical engineering , force orthogonal to the main load (such as in parallel helical gears ) is referred to as static thrust . A fixed-wing aircraft propulsion system generates forward thrust when air
3240-437: The time (t) it takes to move that distance: In case of a rocket or a jet aircraft, the force is exactly the thrust (T) produced by the engine. If the rocket or aircraft is moving at about a constant speed, then distance divided by time is just speed, so power is thrust times speed: This formula looks very surprising, but it is correct: the propulsive power (or power available ) of a jet engine increases with its speed. If
3300-416: The torque on each gear may have both senses, the action surface will have two sets of N tooth faces; each set will be effective only while the torque has one specific sense, and the two sets can be analyzed independently of the other. However, in this case the gear usually has also "flip over" symmetry, so that the two sets of tooth faces are congruent after the gear is flipped. This arrangement ensures that
3360-416: The two gears are firmly locked together, at all times, with no backlash . During operation, each point p of each tooth face will at some moment contact a tooth face of the matching gear at some point q of one of its tooth faces. At that moment and at those points, the two faces must have the same perpendicular direction but opposite orientation. But since the two gears are rotating around different axes,
3420-533: The two gears are sliced by an imaginary sphere whose center is the point where the two axes cross, each section will remain on the surface of that sphere as the gear rotates, and the section of one gear will interact only with the corresponding section of the other gear. In this way, a pair of meshed 3D gears can be understood as a stack of nested infinitely thin cup-like gears. The gears in a matching pair are said to be skew if their axes of rotation are skew lines -- neither parallel nor intersecting. In this case,
3480-517: The vehicle does not actually contain gears, as in a continuously variable transmission . The earliest surviving gears date from the 4th century BC in China (Zhan Guo times – Late East Zhou dynasty ), which have been preserved at the Luoyang Museum of Henan Province, China . In Europe, Aristotle mentions gears around 330 BC, as wheel drives in windlasses. He observed that the direction of rotation
3540-467: The weakest part in a mechanism, so that in case of jamming they will fail first and thus avoid damage to more expensive parts. Such sacrificial gears may be a simpler alternative to other overload-protection devices such as clutches and torque- or current-limited motors. In spite of the advantages of metal and plastic, wood continued to be used for large gears until a couple of centuries ago, because of cost, weight, tradition, or other considerations. In 1967
3600-419: The weight of the aircraft and to provide forward propulsion. A motorboat propeller generates thrust when it rotates and forces water backwards. A rocket is propelled forward by a thrust equal in magnitude, but opposite in direction, to the time-rate of momentum change of the exhaust gas accelerated from the combustion chamber through the rocket engine nozzle. This is the exhaust velocity with respect to
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