Thrust vengeance , also called push back , is a temporary diversion thrust the engine of an aircraft so that it is directed forward rather than backward. The push action is reversed on the way to the front of the plane, giving it a slowdown. The thrust reversing system is shown in many jet planes to help slow down only after landing, reducing wear on the brakes and allowing shorter landing spacing. The device significantly affects the aircraft and is considered essential for safe operations by airlines. There are accidents involving thrust reversal systems, including fatal ones.
Push back is also available on many propelled-propelled aircraft by reversing the controllable blades to the negative angle. The equivalent concept for a boat is called astern propulsion.
Video Thrust reversal
The principle and usage
The landing roll consists of touchdowns, bringing the plane to the speed of a taxi, and finally stopping completely. However, most commercial jet engines continue to generate forward impulse, even when silent, acting against the slowdown of the aircraft. The landing gear lever of the most modern aircraft is sufficient under normal circumstances to stop the aircraft itself, but for safety purposes, and to reduce the pressure on the brakes, another slowing method is required. In scenarios involving bad weather, where factors such as snow or rain on the runway reduce the effectiveness of the brakes, and in emergencies such as rejected takeoff, this need is more pronounced.
A simple and effective method is to reverse the direction of jet engine discharge flow and use the power of the engine itself to reduce speed. Ideally, the reverse drain flow will be directed straight ahead. However, for aerodynamic reasons, this is not possible, and 135 Â ° angles are taken, making it less effective than it should be possible. Thrust retaliation can also be used in aviation to reduce airspeed, although this is not common with modern aircraft. There are three types of general pushover systems used on jet engines: targets, clam-shells, and cold-flow systems. Some propeller-driven aircraft equipped with variable-pitch propellers can reverse the thrust by changing the pitch of their blades. Most commercial jet aircraft have such devices, and it also has applications in military aviation.
Maps Thrust reversal
The type of thrust reversal system
Small aircraft usually do not have a thrust reversal system, except in special applications. On the other hand, large aircraft (weighing more than 12,500 pounds) almost always have the ability to reverse the thrust. Reciprocating engines, turboprops and jet planes can all be designed to include a pushover reversal system.
Aircraft driven by propeller
The propelled aircraft produces a back impulse by changing the angle of the controlled propeller so that the propeller directs the pusher forward. This retractable feature becomes available with the development of controlled propellers, which convert the angle of the propeller blades to make efficient use of the engine power under various conditions. Single-engine aircraft tends to have no backlash. However, single turboprop engines such as PAC P-750 XSTOL, Cessna 208 Caravan, and Pilatus PC-6 Porter do have this feature.
One specific application of counterattack comes in its use on multi-engine amphibians and aircraft carriers. This aircraft, when landing on water, does not have conventional braking methods and must rely on slaloming and/or backpressure, and drag water to slow or stop. In addition, a backlash is often necessary to maneuver over water, where it is used to make narrow turns or even push the plane in reverse, maneuvering that may prove necessary to leave the dock or beach.
Airplane jet
On aircraft using jet engines, thrust reversals are made by causing a jet burst to flow forward. The machine does not rotate or rotate upside down; instead, a thrust reversing device is used to block the blast and direct it forward. High bypass ratio engines usually reverse the thrust by changing the direction of only the fan airflow, since the majority of thrust is generated by this part, as opposed to the core. There are three commonly used jet engine thrust reversing systems:
Target type
The inverting thrust target uses a hydraulically operated 'bucket' type door to reverse the flow of hot gas. To push forward, these doors form the engine thrust nozzle. In the original implementation of this system on Boeing 707, and still common today, two bucket reversers are hung so that when placed they block out the rear exhaust flow and divert it with the forward component. This inverting type is visible on the back of the machine during installation.
Clam-shell type
Clam-shell doors, or cascades, are pneumatically operated systems. When activated, the door rotates to open the channel and closes the normal exit, causing the drive to be directed forward. Inverted thrust cascades are commonly used on turbofan engines. On a turbojet engine, the system will be less effective than the target system, since the cascade system only utilizes the fan airflow and does not affect the main engine core, which continues to generate a boost.
Cold stream type
In addition to the two types used on turbojets and low-bypass turbofan engines, a third type of thrust reverser is found on some high-bypass turbofan engines. The door in the bypass channel is used to direct air accelerated by the engine fan parts but not through the combustion chamber (called the water bypass) in such a way as to provide a back impulse. The cold-flow inverting system is powered by an air motor. During normal operation, the propeller thrust is otherwise blocked. At the election, the system folds the door to block the final nozzle of cold flow and directs this air flow to the cascade propeller. This system can direct the flow of exhaust fan and core.
The cold flow system is known for its structural integrity, reliability, and flexibility. During activation of the inverting thrust, the arm mounted around the perimeter of the nacelle aircraft engine moves backwards to expose the cascade propellers acting to direct the flow of the engine fan. This pushover system can be heavy and difficult to integrate into large nacelles housing machines.
Operation
In most cockpit settings, the push back is adjusted when the thrust lever is still by pulling it further back. The push back is usually applied immediately after the touchdown, often along with the spoiler, to increase the deceleration at the start of the landing roll when the residual and high-speed aerodynamic elevators limit the effectiveness of the brakes located in the landing gear. The push back is always selected manually, either using a lever attached to the thrust lever or moving the thrust lever into the 'door' thrust upside down.
The initial deceleration provided by the back pressure can reduce the landing roll to a quarter or more. The regulations require, however, that aircraft should be able to land on the runway without using a thrust reversal to be certified to land there as part of a scheduled flight service.
After the speed of the aircraft slows down, push the backwards closed to prevent the inverted airflow from disposing of debris in front of the machine intake where it can be swallowed, causing damage to foreign matter. If circumstances require, the back impulse may be used until it stops, or even encourages to push the plane backwards, even though tugboats or towbars are used more often for that purpose. When the back impulse is used to push the plane back from the gate, the maneuver is called powerback. Some manufacturers warn against the use of this procedure during cold conditions because using thrust back on snow-covered ground or mud can cause mud sprays, water, and runways to become airborne and attached to the wing surface.
If the full throttle is undesirable, the retractable power can be operated with the throttle set less than full power, even down to idle power, which reduces stress and wear on the engine components. The push back is sometimes selected on the idling engine to remove residual impulses, especially in cold or slippery conditions, or when an engine jet blast can cause damage.
In-flight operation
Some aircraft, particularly some Russian and Soviet planes, can safely use push-backs in flight, although most are driven by propellers. Many commercial aircraft, however, can not. The use of backlash in flight has several advantages. This allows rapid deceleration, allowing rapid speed changes. It also prevents the increase in speed normally associated with steep dives, allowing for rapid loss of altitude, which can be very useful in hostile environments such as combat zones, and when making a steep approach to land.
The Douglas DC-8 series aircraft has been certified for backfill in flight since the inception of the service in 1959. Safe and effective to facilitate fast landing at acceptable speeds, it still resulted in significant airplane slowdown, resulting in actual use less common on passenger flights. and more commonly on cargo and ferry flights, where passenger comfort is not a concern.
The Hawker Siddeley Trident, a 120-180 seat aircraft, is capable of down to 10,000 ft/min (3.050 m/min) using a back impulse, although this capability is rarely used.
Concorde supersonic aircraft could use an upside-down push in the air to increase the rate of decline. Only the inboard engine is used, and the machine is placed in a vacant position only in subsonic flight and when the plane is below 30,000 feet altitude. This will increase the rate of decline to about 10,000 ft/min.
Boeing C-17 Globemaster III is one of the few modern aircraft that uses in-flight thrust. The Boeing aircraft is capable of deploying a direct counter-attack on all four engines to facilitate a tactical tactical slope of up to 15,000 feet/min (4,600 m/min) into combat environments (drop rates greater than 170 mph, or 274 km/h). The Lockheed C-5 Galaxy, introduced in 1969, also has reverse capability in the aircraft, albeit only on the inside machine.
Saab 37 Viggen (retired in November 2005) also has the ability to use backlash either before landing, to shorten the required runway, and glide after landing, allowing many Swedish roads to double as the basis of war.
Shuttle Shuttle Shuttle, the highly modified Grumman Gulfstream II, uses a reverse push in flight to help simulate Space Shuttle aerodynamics so astronauts can practice the landing. A similar technique is used on the modified Tupolev Tu-154 that simulates the Russian Buran shuttle.
Effectiveness
The amount of thrust and power generated is proportional to the speed of the aircraft, making the impulse more effective at high speeds. For maximum effectiveness, it should be applied quickly after touchdown. If activated at low speed, foreign object damage is possible. There is some danger of an airplane with an inverting thrust applied to temporarily leaving the ground again due to the thrust effect and the shock effects of the spoiler. For aircraft susceptible to such occurrences, the pilot must be careful to achieve a strong position on the ground before applying back pressure. If applied before the nose-wheels come into contact with the ground, there is the possibility of asymmetric deployment causing uncontrolled jaws to the higher impulse side, such as directing the aircraft with the nose wheel is the only way to maintain control over the direction of travel in this situation.
Inverted thrust mode is only used for a fraction of the aircraft's operating time but is greatly affected in terms of design, weight, maintenance, performance, and cost. Penalties are significant but necessary because they provide relentlessness to increase safety limits, directional control during landing rolls, and assistance in rejected takeoffs and ground operations on contaminated runways in which the effectiveness of normal braking is reduced. Airlines considers a thrust reversal system as a vital part of achieving the maximum level of safety of aircraft operations.
The flight deployment of a direct counterattack has contributed to the collision of several types of transport aircraft:
- On February 11, 1978 Pacific Western Airlines Flight 314, a Boeing 737-200, crashed while landing rejected at Cranbrook Airport. Left thrust reversal is not stored properly; it was deployed during the ascent, causing the plane to roll over to the left and attack the ground. Of the 5 crew members and 44 passengers, only 6 passengers and a flight attendant survived. On 9 February 1982, Japan Airlines Flight 350 crashed 1,000 feet (300 m) below the runway at Tokyo's Haneda Airport after the imposition of involuntary thrust on two of Douglas DC-8's four engines by a mentally unstable captain, in 24 passenger deaths.
- On August 29, 1990, the US Air Force C-5 Galaxy crashed shortly after takeoff from Ramstein Air Base in Germany. As the plane started up the runway, one of the thrusters was suddenly lowered. This results in a loss of control over the plane and subsequent accidents. Of the 17 people in it, 4 survived the accident.
- On May 26, 1991, Lauda Air Flight 004, a Boeing 767-300ER, had an unintentional placement of a reversal of the engine's thrust on the left, causing the aircraft to dive rapidly and break up in the air. All 213 passengers and 10 crew were killed.
- On October 31, 1996, TAM Linhas AÃÆ' Â © reas Flight 402, Fokker 100, crashed shortly after takeoff from Congonhas International Airport-SÃÆ'Â £ o Paulo, SÃÆ'Â £ Paulo, Brazil, attacked two apartment buildings and some houses. All 90 passengers and 6 crew members as well as 3 people on the ground were killed in the accident. The accident was caused by an unauthorized inversion thrust on the right engine shortly after takeoff.
- On February 10, 2004, Kish Air Flight 7170, Fokker 50, crashed while on a trip to Sharjah International Airport. A total of 43 out of 46 passengers and crew were killed. The researchers determined that the pilot had prematurely set the propellers to reverse the thrust mode, causing them to lose control of the aircraft.
See also
- Afterburner
- Thrust images
- Vertical pickup and landing
References
External links
- Reduce Landing Distance
- "Power Jets push spoilers that can give a negative boost to braking" - a Flight article on the development of a new machine showing reverse Power Jets devices
Source of the article : Wikipedia
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