Aircraft stopping distance during landing. How does a plane slow down when landing? Types of aircraft and methods of braking. Propeller engine

Reverse (aviation)

The flaps of the engine reversing device are activated and redirect the jet stream against the movement of the aircraft.

Reverse- a device for directing part of an air or jet stream against the direction of aircraft movement and thus creating reverse thrust. In addition, reverse is the applied mode of operation of an aircraft engine, involving a reversing device.

Reverse is used mainly on the run, after landing, or for emergency braking during aborted takeoff. Less often - taxiing, for reversing the aircraft without the help of a towing vehicle. A small number of aircraft allow the inclusion of reverse in the air. Reversing is most widely used in commercial and transport aviation. A characteristic noise can often be heard when the aircraft runs along the runway after landing.

The reverse is used in conjunction with the main (wheel) braking system of the aircraft. Its use allows to reduce the load on the main braking system of the aircraft and reduce the braking distance, especially with a low friction coefficient of the wheels on the runway, as well as at the beginning of the run, when the residual lift of the wing reduces the weight on the wheels, reducing the effectiveness of the brakes. The contribution of reverse thrust to the total braking force can vary greatly for different aircraft models.

Jet engine reverse

Using the reverse to slow down the aircraft during landing.

The reverse is realized by deflecting part or all of the jet emanating from the engine using a variety of shutters. In different engines, the reversing device is implemented in different ways. Special shutters can block the jet created only by the external circuit of the turbojet engine (for example, on the A320), or the jet of both circuits (for example, on the Tu-154M).

Depending on the design features of the aircraft, both all engines and some of them can be equipped with reverse. For example, on the three-engine Tu-154, only the outermost engines are equipped with a reversing device.

Restrictions

The disadvantages of the reverse system include the troubles associated with its use at low speeds (approximately<140 км/ч). Реверсивная струя может поднимать в воздух с поверхности взлётно-посадочной полосы мусор (например, мелкие камни), который, при пробеге самолёта по ВПП на относительно небольшой скорости, может попасть в воздухозаборник двигателя и стать причиной его повреждения . При высокой скорости движения самолёта поднятый мусор помех не создает, поскольку не успевает подняться до высоты воздухозаборника к моменту его приближения.

Propeller engine reverse

Rotation of propeller blades.

The reverse of propeller-driven aircraft is implemented by turning the propeller blades (the angle of attack of the blades changes from positive to negative) with the direction of rotation unchanged. Thus, the screw begins to create reverse thrust. This type of reversing device can be used both on aircraft with a piston engine and on turboprop aircraft, incl. and single-engine. Reverse is often provided on seaplanes and amphibians, because provides significant comfort when taxiing on the water.

Story

The first use of reverse thrust on propeller-driven aircraft can be traced back to the 1930s. So, passenger planes Boeing 247 and Douglas DC-2 were equipped with a reverse.

Aircraft without a reverser

A number of aircraft do not need reverse. For example, due to the peculiarities of the mechanization of the wing and the extremely effective air brakes in the tail of the BAe 146-200, it is not necessary to reverse when landing. Accordingly, all four engines do not work in reverse mode. For the same reason, the Yak-42 aircraft does not need a reverse device.

Using reverse in the air

Some aircraft (both propeller and jet, military and civil) allow the possibility of in-flight thrust reverse, while its use depends on the specific type of aircraft. In some cases, the reverse is turned on immediately before touching the strip; in other cases, on a descent, which makes it possible to reduce the vertical speed by braking (when approaching on a steep glide path) or to avoid exceeding the permissible speeds when diving (the latter applies to military aircraft); to perform combat maneuvers; for a quick emergency descent.

So, in the ATR 72 turboprop airliner, reverse can be used in flight (when the pilot removes the safety seal); the Trident turbojet also allows reverse in the air for a rapid descent at vertical speeds of up to 3 km / min (although this possibility was rarely used in practice); for the same purpose, the reverse of two internal engines of the Concorde supersonic liner could be turned on (only at subsonic speed and at an altitude below 10 km). The C-17A military transport aircraft also allows the inclusion of a reverse of all four engines in the air for a quick descent (up to 4600 m / min). The Saab 37 Wiggen fighter also had the ability to reverse in flight to reduce landing distances. The single-engine turboprop aircraft Pilatus PC-6 can also use reverse in the air when approaching on a steep glide path on short landing areas.

For an example of using reverse thrust in the air (immediately before touching the runway), we can cite an excerpt from the flight manual for the Yak-40 aircraft:

at a height of 6–4 m, reduce the operating mode of the side engines to idle and start leveling the aircraft by giving the command: Reverse.

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Notes

Links

If you want to read about aircraft engine thrust reverser, I recommend checking out a recent article on the subject. It was written on 03/30/13 and is located on this site in the same section under the title “Once again about thrust reverser ... A little more ... :-)”, that is. And this article (where you are now), in my opinion, no longer meets the exacting needs of both mine and my readers. However, it will remain on the site, so if you want, you can pay attention to it too ... Only for comparison :-) ...

The work of the reverse when landing A-321.

The problem of aircraft deceleration after landing on the run was insignificant, probably only at the dawn of aviation, when aircraft flew slower than modern cars and were much lighter than the latter :-). But in the future, this issue became more and more important, and for modern aviation with its speeds it is quite serious.

How can you slow down an airplane? Well, firstly, of course, with brakes mounted on a wheeled chassis. But the fact is that if the plane has a large mass and lands at a sufficiently high speed, then often these brakes are simply not enough. They are not able to absorb all the energy of the movement of a multi-ton colossus in a short period of time. In addition, if the contact (friction) conditions between the tires of the chassis wheels and the concrete strip are not very good (for example, if the strip is wet during rain), then braking will be even worse.

However, there are two more ways. The first one is drag parachute. The system is quite effective, but not always easy to use. Imagine what kind of parachute is needed to slow down, for example, a huge Boeing 747, and what kind of parachute service should be at a large airport, where planes land, one might say, in droves :-).

The work of the reverse (sash) on the Airbus A-319 of the company JeasyJet.

The second method is much more convenient in this regard. This thrust reverser aircraft engine. In principle, this is a fairly simple device that creates reverse thrust, that is, directed against the movement of the aircraft, and thereby slows it down.

Reverse device on turbojet engine. The hydraulic cylinders for controlling the reversible flaps are visible.

Reverse thrust can create propeller-driven aircraft with variable pitch (VISH). This is done by changing the angle of the propeller blades to a position where the propeller begins to "pull" back. And on jet engines, this is done by changing the direction of the outgoing jet stream using reverse devices, most often made in the form of flaps that redirect the jet stream. Since the loads there are multi-ton, these doors are controlled by a hydraulic system.

Reverse on a KLM Fokker F-100.

The main application of thrust reverser is braking during a run. But it can also be used for emergency braking if it is necessary to stop the takeoff. Less often and not on all aircraft, this mode can be used when taxiing at the airport for reversing, then there is no need for a towing vehicle. The Swedish fighter Saab-37 Viggen is very characteristic in this regard. His evolution can be seen in the video at the end of the article.

Fighter Saab 37 Viggen.

However, in fairness, it should be said that it is almost the only aircraft that so easily drives around in reverse :-). In general, reverse thrust on jet engines is rarely used on small aircraft (). It is mainly used on commercial and civil aviation liners and airplanes.

It is worth saying that some aircraft provide for the use of reverse thrust in flight (an example of this is the ATR-72 passenger aircraft). This is usually possible for an emergency descent. However, restrictions are imposed on such modes and they are practically not used in normal flight operation.

Aircraft ATR-72.

The aircraft has, however, with all its advantages and disadvantages. The first is the weight of the device itself. For aviation, weight plays a big role and often because of it (and also because of the dimensions) the reverse device is not used on military fighters. And the second is that the redirected jet stream, when it hits the runway and the surrounding soil, is capable of lifting dust and debris into the air, which can enter the engine and damage the compressor blades. Such a danger is more likely at low aircraft speeds (up to about 140 km / h), at high speeds, debris simply does not have time to reach the air intake. It's pretty hard to deal with this. The cleanliness of the runway (runway) and taxiways is generally an ongoing problem of airfields, and I will talk about it in one of the following articles.

Aircraft Yak-42

It is worth saying that there are aircraft that do not need jet thrust reversers. These are, for example, the Russian Yak-42 and the English BAe 146-200. Both have advanced wing mechanization, which significantly improves their takeoff and landing characteristics. The second aircraft is especially indicative in this regard. In addition to mechanization, it has tail air brakes (shields) that allow it to effectively dampen speed during descent and after landing on the run (together with the use of spoilers). There is no need to reverse, which makes this aircraft suitable for use at airports located within the city and therefore sensitive to noise, as well as having a steep landing pattern (for example, London City Airport).

Aircraft BAe 146-200. The open brake flaps in the tail are clearly visible.

However, there are still not so many such aircraft, but thrust reverser is already a fairly well-developed system, and without it, the work of airports is unthinkable today.

In conclusion, I suggest you watch videos in which the operation of the reverse mechanisms is clearly visible. It can be seen how the reversed jet lifts water from the concrete. And, of course, SAAB's "reverse" :-). Better to watch in full screen :-)..

Photos are clickable.

Yes, where I work now is a contractor. And not only Boeing, but also Airbus, Bombardier, ARZH-21, Augusta Westland, etc.

Fischer Advanced Composite Components. FACC for short.

Together with Goodrich, we are collaborating with Boeing on this project and may be collaborating on the A350.


, posted a few descriptions with pictures
I think, since not everyone here is connected with aviation, it will be useful to have a look.
And who is connected - it is interesting to see how it works on specifically 787

Thanks to an excellent occasion in the form of rolling out a new Boeing 787 Dreamliner model and the informational support of our dad Nestor, a number of comrades just now in general and on the B-787 Dreamplane in particular. I understand that LJ can be read by completely different people with very different levels of awareness and areas of interest, so I will break the answer into three parts.
For those who are "in the know", Translating Sleeve is the rear part of the engine nacelle with reverse elements.
For beginners and those who are more interested in knowing more, I will try to describe it in a simpler way. If something is not clear, ask, and if it is written too naively, then do not judge strictly. Well, for those who do not need to talk about the plane, but just talk about the reverse, you can just read the final part of my opus.

What is a reverse?
The landing speed of modern liners is about 200-240 km / h, which is certainly much lower than cruising speed, but still quite a lot for multi-ton machines. At this speed, aerodynamic control rudders are still effective and ground-based traffic controls are still very ineffective. With a sharply applied brake at such a speed, the aircraft will not slow down, but simply “take off” - it will tear the tires of the landing gear wheels.



Such a situation is very dangerous for the loss of control of the aircraft's position, which threatens with fatal consequences (aircraft derailment, damage to fuel tanks, etc.). To prevent this from happening, at speeds up to 150-180 km / h, aerodynamic means of speed reduction are used. All of them either increase the drag of the aircraft (landing flaps, aerodynamic brakes, braking parachutes), or create reverse jet thrust (engine reverse), or combine these means.




In this case, we are talking about the development of a reverse for the Boeing 787 Dreamliner.
Reverse- This is a system that allows the engines to create a reverse jet thrust to decelerate the aircraft during the run along the runway.

Translating Sleeve Reverse Thrust on Boeing 787 Dreamliner. Part 3

How does reverse work?
In the 60-70s. the reverse was most often designed as the back of the engine nacelle, in the form of two "buckets", simply blocking the path of the jet stream of the engine and directing it in the opposite direction. A similar reverse was used in the design of aircraft until the 70s (Fokker-100, B737-200, Tu-154 and An-72/74). An obvious plus is the simplicity of the design. Minus - the need to develop "temperature-loaded" structures, additional protection of adjacent elements (wing or fuselage skins).



In the 80s, due to the emergence of a large number of engines with a high bypass ratio, such a design solution finally lost its appeal. The new concept of reverse does not imply shutting off the first "hot" circuit of the engine. Only the second - "cold" circuit is blocked. At the same time, the reverse system itself is now hidden inside the fairing, which significantly reduces the likelihood of damage to it by foreign objects. It is obvious that the jet stream in this case does not work on the reverse completely, but only by the "second circuit". However, the principle of such a reverse is not so much in the direct impact of a jet stream, but in creating a kind of air cushion in front of the aircraft, which greatly increases the aerodynamic drag of the aircraft and very effectively slows down the aircraft at speeds up to 130 km/h. This pillow is clearly visible in the photographs of the aircraft landing on a wet runway. Drops of water raised from the concrete perfectly visualize this effect.



Translating Sleeve Reverse Thrust on Boeing 787 Dreamliner. Part 4
How is reverse arranged?


The engine nacelle as a whole on modern liners consists of an air intake (Inlet Cowl), a fan fairing (Fan Cowl), and the rear of the engine nacelle, where the second engine circuit (Fan Duct) and the reverse (Reverse Thrust) are located. The latter, as well as the fan fairing, consists of two halves that can be moved apart for access to the engine during maintenance and repair work. The term Translating Sleeve in this case refers to the outer fairing of the second circuit, which includes the outer skin and the outer skin of the second circuit of the engine (Outer Cowl, Outer Duct).
S-17, Tu-334 and An-148 and many other aircraft, including the Dreamliner.

Directly Translating Sleeve aircraft Boeing 787 Dreamliner looks like this.

A passenger liner flying at an altitude of 10,000 meters and covering many hundreds of kilometers per hour must one day smoothly reduce its speed to zero, freezing on the airport platform. Only then can the flight be considered successful. Alas, sometimes it happens that applause so popular in Russia for pilots after the plane touches the ground can mean premature joy. Contingencies after landing are the scourge of civil aviation.

Just wheels There are no outstanding design features of the chassis wheels and their braking system. Almost everything is like in a good car: disc brakes and a system that prevents skidding.

Oleg Makarov

I would like to make a reservation right away that this article in no way aims to infect anyone with aerophobia. Serious aviation accidents, especially those with casualties, instantly hit the headlines of the world news, and this is the best evidence that air transport is characterized by a high degree of safety: an airplane crash is a rare and not ordinary event. It is all the more interesting to understand what is happening when neither modern aircraft stuffed with electronics, nor high qualification of the crews can save us from situations like the one that spoiled the New Year's mood for the inhabitants of our country a few years ago. We are talking about the death of the Tu-204 airliner - the one that on December 29, 2012 could not pay off speed after landing, rolled out of the runway, broke through the airfield fence and collapsed with partial removal of debris to the Kiev highway. Runway overrun is one of the world's most common causes of air crashes (that is, fatal accidents), sometimes called the "number one killer" in civil aviation. According to IATA (International Air Transport Association) statistics, approximately 24% of deaths occur in this type of accident.


Braking in the air

Before talking about the reasons for these unfortunate events, it is worth dwelling a little on the technical side of the issue, briefly talking about what capabilities a modern passenger liner has for timely and controlled deceleration. When the plane is in the air, there are only two main ways to reduce the speed of the liner: to remove the gas by reducing the power of the engines, and to increase drag. To solve the latter problem, there are several specialized devices. Experienced air travelers know that a wing has a large number of moving parts, which (with the exception of ailerons - air roll rudders) are combined into the concept of "wing mechanization". Panels deviating at different angles, which are responsible for increasing drag (as well as reducing wing lift), are called spoilers. In domestic aviation literature, they are usually divided into spoilers proper, spoilers and aileron spoilers, as a result of which confusion arises between these concepts. As one of the Russian airlines explained to us, the general term “spoilers” is considered more correct today, which operate in three modes on modern aircraft.

The first mode is the air brake mode (speed brakes). Used to decrease airspeed and/or increase vertical rate of descent. The pilot controls this mode by moving the steering wheel or handle to the desired angle, while not all spoilers are deflected, but only some of them.

The second mode is the joint work with the ailerons to improve the roll control characteristics (roll spoilers). Deflection occurs automatically at angles up to seven degrees with the corresponding movement of the steering wheel (control sticks) along the roll, and only external spoilers (those farther from the fuselage) or only internal spoilers (this depends on the design of a particular type of aircraft) are deflected.


There are no outstanding design features of the chassis wheels and their braking system. Almost everything is like in a good car: disc brakes and a system that prevents skidding.

Finally, the third mode - ground braking (ground spoilers) - is of greatest interest to us. In this mode, all spoilers are automatically deflected to the maximum angle, which leads to a sharp decrease in lift. After the machine actually ceases to hold air, there is an effective load on the brake wheels and braking begins with an automatic brake release. This machine, called anti-skid, is in fact nothing more than an anti-lock braking system, functionally similar to the one that is installed on cars today: ABS came from aviation.

Reverse? Is it possible without it

In addition to spoilers, the aircraft has two more speed damping systems. Firstly, these are the already mentioned wheel brakes. They are made according to the disk scheme, and in order to increase wear resistance, disks are often used not from steel, but from composite materials (carbon fiber). The brakes are hydraulically actuated, although options with electric actuators have already appeared.


This aircraft did not leave the runway and is still at serious risk. The front landing gear is jammed, and the wheels do not roll, but drag along the strip and, while being erased, burn. The main thing is that the stand does not break.

And finally, reverse is a word that was heard so often in connection with the disaster at Vnukovo. In the thrust reverser, part of the jet is deflected by means of hydraulically driven flaps. Thus, jet thrust no longer pushes the aircraft forward, but, on the contrary, slows it down. So could a faulty reverser be the culprit behind the crash?

The answer will be rather negative, because, as practice shows, there is no single “culprit” for serious accidents in civil aviation at all. A disaster is always an unfortunate combination of several circumstances, including both technical and human factors. The fact is that the thrust reverser is, in fact, an emergency, emergency braking system.


1. The wingtip reduces the drag created by the vortex shedding from the end of the wing, and thus increases the lift of the wing. Different manufacturers produce endings of different shapes and even give them special names: “winglets”, “sharklets”, etc. 2. Ailerons are aerodynamic rudders (roll control) and are not part of the wing mechanization. 3. High speed aileron. 4. The purpose of a number of nacelles located under the wing often raises questions from air passengers. It's simple - these are drive fairings that change the position of the flaps. 5. Kruger's slat (inner slat) looks like a drop-down shield. 6. The slats change the configuration of the wing in such a way as to increase the angle of attack allowed for the aircraft without stalling. 7. Extended flaps increase the lift of the wing, allowing the aircraft to stay in the air at low speeds (during takeoff and landing). 8. Flap. 9. External spoiler. 10. Internal spoiler.

Western types of aircraft, of course, are equipped with reverse devices, but they are certified as if they were not there. The main requirement is imposed on the energy consumption of the brakes of the main landing gear. This means that in the absence of pilot error and with all systems in good working order, the aircraft should, without resorting to reverse, land on a dry runway and stop speed without problems in order to turn onto the taxiway. Moreover, due to the increased noise level during jet deflection at all airports in the European Union, the use of reverse is not allowed during night flights (23:00 - 06:00) except for poor runway conditions and / or an emergency. Modern types of aircraft can be operated both with one reverse and without them at all, provided the runway is long enough, even if it is covered with precipitation. In other words, in the event of a combination of a number of unfavorable factors that contribute to the aircraft overrunning the runway, reverse may be the last hope for a successful outcome. But if he refuses, it is unlikely that he can be considered the only cause of the accident.


The spoiler not only increases the drag, but also organizes a stall when the air flows around the wing, which leads to a decrease in the lifting force of the latter. During the flight, spoilers are used, for example, to increase the vertical speed of the aircraft without changing the pitch. The automatic release of spoilers on the runway is ensured when they are “reinforced” - transferred to the ARMED position prepared for release. It's like cocking a gun, if you don't cock it, it won't fire. The release signal is a combination of data from the radio altimeter (height 0), sensors for the compression of the main racks, the position of the throttle is 0 (low throttle). Unarmored (by mistake or forgetfulness) spoilers quite often appear in the analysis of cases related to rolling out of the lane.

Don't rush to board!

One of the main reasons for aircraft overrunning the runway is the so-called unstabilized approach. This concept includes flying on the landing straight at high speeds, with the wrong position of the wing mechanization (we are talking primarily about the flaps), with a deviation from the course. Other reasons include the late application of the wheel brakes (the pilot's postulate is "don't leave the brakes at the end of the runway!"). There are also cases when pilots received inaccurate data on the state of the runway and landed on a slippery strip, hoping to land on a dry one.


According to Russian textbooks of aerodynamics, the landing distance with the use of reverse is reduced by 25-30%, however, modern types of aircraft are certified without taking into account the possibility of reverse. The start of the reverse is strictly tied to the operation of the rack compression sensor. This binding is caused by the bitter experience of several plane crashes, the cause of which was the operation of the reverse in the air. In one of these disasters, a mentally ill Japanese pilot was guilty, who turned on the reverse during the landing approach.

What happens when an aircraft is moving on a glide path that exceeds a predetermined (usually 220 km/h) speed? Usually this means a flight, touching the runway at an off-design point (especially if the plane is empty, as was the case with the Tu-204). This in itself constitutes an emergency situation, which involves the use of all means of braking, including reverse, - there is no longer a "reserve" of the strip. But the danger also lies in the fact that the liner, even after touching the runway, continues to move at an undesigned high speed, and the higher the speed, the higher the lift of the wing. It turns out that the car does not roll along the strip, leaning on it, but actually flies, touching the strip with its wheels. In this situation, the landing gear compression sensors, which in English are called the more understandable term weight-on-weels (weight on wheels), might not work. Thus, from the point of view of automation, the liner continues to fly and cannot perform such purely ground operations as turning on the reverse or releasing spoilers in ground braking mode. And if, after touching the strip, the spoilers are not released or removed, a catastrophe is almost inevitable. Moreover, in case of weak adhesion of the wheels to the lane, the automatic anti-skid will release the wheels, as it would do on a slippery surface, in order to avoid loss of wheel control. The brakes will work properly, but ... they will not slow down. Well, if the strip is still really slippery, then the chances of avoiding rolling out in the described case can be considered almost zero. The consequences of rolling out depend on the speed at which it occurs and what happened in the path of the aircraft. Thus, the circumstances leading to a catastrophe can grow like an avalanche, and the failure of, say, the reverse cannot be of decisive importance in this situation.


The frequency with which runway accidents occur around the world can be seen in an analysis report prepared by the Dutch National Aerospace Laboratory in 2005. Approximately 400 rollout cases worldwide over the past 35 years were analyzed for this report. It is easy to calculate that this is more than ten cases per year, although the study emphasized that the number of such accidents is rapidly declining due to the improvement of aviation and navigation technology. Fortunately, not all of these cases developed according to the worst-case scenario described in the article, however, of those that ended happily, there were quite remarkable. In 2005, a huge A340, landing at Toronto airport on a flight from Paris, touched the runway, skidded off the runway, partially collapsed and caught fire. Fortunately, all three hundred people on board survived.

As follows from the preliminary conclusions of the IAC, the disaster at Vnukovo developed according to a similar scenario, and the speed of the liner during the roll-out was 190 km / h, only 30 km / h less than the speed at which the plane was supposed to touch the runway. Hence the tragic ending.


There is something to strive for

Runway overrun incidents happen in different countries and on different continents, but still some socio-geographical dependence is visible. According to research, most of these incidents occur in Africa, followed by South and Central America, then Asia. In developed countries, such accidents occur in less than one in two million landings. The situation is best in North America, and this is with enormous air traffic in the sky over the USA. This, in fact, is not surprising: in developing countries there are more old aircraft, they are worse maintained, there are many poorly equipped airports and outdated navigation equipment, and the technological discipline is lower. To some extent, all this can be said about the aviation industry of Russia, and cases of rolling out, including with victims, are not so rare in our country. But I would rather leave this company of outsiders.

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