How does reverse work on an airplane? Why engine reversal is dangerous for certain aircraft

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. Abbreviated FACC.

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

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

Thanks to the excellent occasion in the form of the rollout of the new Boeing 787 Dreamliner model and the information support of our dad Nestor, a number of comrades just now in general and on the B-787 Dreamliner in particular. I understand that LiveJournal can be read by completely different people with very different levels of awareness and areas of interest, so I will divide 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 more simply. 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 tell about the plane, but enough to tell about the reverse, you can just read the final part of my opus.

What is reverse?
The landing speed of modern airliners is about 200-240 km/h, which is of course much lower than cruising speed, but still quite high for multi-ton aircraft. At this speed, aerodynamic control surfaces are still effective and ground-based motion control devices are still very ineffective. If the brake is sharply applied at such a speed, the plane will not slow down, but will simply “take off its shoes” and tear the tires of the landing gear wheels.

This situation is very dangerous for loss of control of the aircraft’s position, which can lead to fatal consequences (aircraft leaving the runway, damage to fuel tanks, etc.). To prevent this from happening, aerodynamic speed reduction means are used at speeds up to 150-180 km/h. All of them either increase the drag of the aircraft (landing flaps, aerodynamic brakes, braking parachutes), or create reverse jet thrust (reverse engines), 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 engines to create reverse jet thrust to slow down the aircraft while running 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 rear part of the engine nacelle, in the form of two “buckets”, simply blocking the path of the engine jet stream and directing it in the opposite direction. A similar reverse was used in aircraft design until the 70s (Fokker-100, B737-200, Tu-154 and An-72/74). An obvious advantage is the simplicity of the design. The downside is the need to develop “temperature-loaded” structures and additional protection of adjacent elements (wing or fuselage skins).

In the 80s, due to the emergence large quantity engines with a high bypass ratio, such a design solution has finally lost its attractiveness. The new reverse concept does not involve shutting off the first “hot” circuit of the engine. Only the second – “cold” circuit – is closed. 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 in reverse, but only as a “second circuit”. However, the principle of such a reverse is not so much the direct impact of the jet stream, but rather the creation of a kind of air cushion in front of the aircraft, which greatly increases the aerodynamic drag of the aircraft and very effectively brakes the aircraft at speeds of up to 130 km/h. This pillow is clearly visible in photographs of the plane landing on wet strip. Drops of water lifted from the concrete perfectly visualize this effect.

Translating Sleeve Reverse Thrust on Boeing 787 Dreamliner. Part 4.
How does reverse work?

The engine nacelle as a whole on modern airliners consists of an air intake (Inlet Cowl), a fan fairing (Fan Cowl), and the rear part 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 to provide access to the engine during maintenance and repair work. The term Translating Sleeve in this case refers to the outer fairing of the secondary circuit, which includes the outer casing and the outer casing of the secondary circuit of the engine (Outer Cowl, Outer Duct).
S-17, Tu-334 and An-148 and many other aircraft, including the Dreamliner.

The Translating Sleeve of the Boeing 787 Dreamliner looks like this.

A passenger airliner, racing 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 for pilots, so popular in Russia, after the plane touches the ground can mean premature joy. Emergency situations after landing are a scourge civil aviation.

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

Oleg Makarov

I would like to immediately make a reservation that this article in no way intends to infect anyone with aerophobia. Serious aviation accidents, especially with casualties, instantly hit the headlines of world news, and this is the best evidence that air transport has a high degree of safety: an airplane crash is a rare and not an ordinary event. It is all the more interesting to understand what happens when neither modern aircraft stuffed with electronics nor highly qualified crews can save us from situations like the one that ruined the pre-New Year mood of the residents of our country several years ago. We are talking about the death of the Tu-204 airliner - the one that on December 29, 2012, was unable to reduce speed after landing, rolled out of the runway, broke through the airfield fence and collapsed with partial removal of debris onto the Kievskoye Highway. Aircraft running off the runway is one of the most common causes of air crashes in the world (that is, accidents involving human casualties), sometimes called the “number one killer” in civil aviation. According to IATA (International Air Transport Association) statistics, approximately 24% of fatalities 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 modern passenger airliner there are opportunities for timely and controlled speed reduction. When a plane is in the air, there are only two main ways to reduce the speed of the airliner: remove the throttle, reducing engine power, and increase drag. To solve the latter problem, there are several specialized devices. Experienced air travelers know that the 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 that deviate at different angles, which are responsible for increasing drag (as well as reducing the lift of the wing), are called spoilers. In domestic aviation literature, they are usually divided into spoilers themselves, spoilers and aileron spoilers, as a result of which confusion arises between these concepts. As we were explained in one of Russian airlines, today the general term “spoilers” is considered more correct, which on modern aircraft operate in three modes.

The first mode is the air brakes mode. Used to reduce 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 a collaboration with ailerons to improve roll control characteristics (roll spoilers). Deviation occurs automatically at angles of up to seven degrees with appropriate movement of the steering wheel (control stick) along the roll, and only external spoilers (those further from the fuselage) or only internal spoilers (this depends on the design of the specific type of aircraft) are deflected.

The landing gear wheels and their braking system do not have any outstanding design features. Almost everything is like in a good car: disc brakes and a system that prevents skidding.

Finally, the third mode - 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 reduction in lift. After the car actually stops holding air, an effective load appears on the brake wheels and braking begins with automatic brake release. This machine, called anti-skid, is actually nothing more than an anti-lock braking system, functionally similar to the one installed on cars these days: ABS came from aviation.

Reverse? It's possible without it

In addition to spoilers, the aircraft has two more speed reduction systems. Firstly, these are the already mentioned wheel brakes. They are made according to a disk design, and to increase wear resistance, they often use disks not made of steel, but of 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, as they wear out, 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 a thrust reverser device, part of the jet stream is deflected using valves driven by hydraulics. Thus, jet thrust no longer pushes the plane forward, but, on the contrary, slows it down. So could a faulty reverse be the culprit of the disaster?

The answer will most likely be negative, because, as practice shows, there is no single “culprit” for serious aviation accidents in civil aviation. 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 breaking off from the end of the wing, and thus increases the lift of the wing. Different manufacturers produce winglets of different shapes and even assign special names to them: “winglets”, “sharklets”, etc. 2. Ailerons are aerodynamic rudders (they control roll) 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 among air passengers. It's simple - these are drive fairings that change the position of the flaps. 5. The Krueger slat (inner slat) has the appearance of a drop-out flap. 6. Slats change the configuration of the wing in such a way as to increase the angle of attack permissible 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 are certified as if they do not have one. The main requirement is for the energy capacity of the main landing gear brakes. This means that in the absence of a piloting error and with all the systems working properly, the aircraft should, without resorting to reverse, land on a dry runway and without any problems reduce speed in order to turn onto the taxiway. Moreover, due to the increased noise level when the jet is diverted at all airports in the European Union, the use of reverse is not permitted for night flights (23:00 - 06:00) except in poor condition of the runway and/or emergency situation. Modern types of aircraft can be operated either with one reverse or without them at all, provided the runway is of sufficient length, even if it is covered with precipitation. In other words, if a number of unfavorable factors conspire to cause the aircraft to roll off the runway, the reverse may turn out to be last hope for a successful outcome. But if he also refuses, he can hardly be considered the sole cause of the accident.

The spoiler not only increases drag, but also organizes stalling when air flows around the wing, which leads to a decrease in the lift of the latter. During flight, spoilers are used, for example, to increase the aircraft's vertical speed without changing 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 signal for release is a combination of data from the radio altimeter (altitude 0), compression sensors of the main struts, throttle position - 0 (idle throttle). Unreinforced (by mistake or forgetfulness) spoilers quite often appear in cases involving driving off the runway.

Don't rush to board!

One of the main reasons for aircraft rolling off the runway is the so-called unstabilized approach. This concept includes flying on the pre-landing straight line at elevated 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 use of wheel brakes (the pilot’s postulate is “don’t leave the brakes at the end of the runway!”). There are also cases where pilots received inaccurate data about the condition of the runway and landed on a slippery runway, expecting to land on a dry one.

According to domestic aerodynamics textbooks, the landing distance using reverse is reduced by 25-30%, however, modern types of aircraft are certified without taking into account the capabilities of reverse. The start of reverse is strictly tied to the activation of the strut compression sensor. This binding is caused by the bitter experience of several plane crashes, the cause of which was the activation of the reverse in the air. One of these accidents was caused by a mentally ill Japanese pilot who engaged the aircraft in reverse during landing.

What happens when an airplane moves on a glide path above a specified (usually 220 km/h) speed? Usually this means overflight, touching the runway at a non-designated point (especially if the plane is empty, as was the case with the Tu-204). This in itself constitutes emergency situation, which involves the use of all means of braking, including reverse, - there is no more “reserve” of the lane. But the danger also lies in the fact that the airliner, 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 by the more understandable term weight-on-wheels, may not have worked. Thus, from the point of view of automation, the airliner 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 stripe, the spoilers do not release or are removed, a disaster is almost inevitable. Moreover, if the wheels have weak adhesion to the strip, the automatic anti-skid system 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 won't 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 the rollout depend on the speed at which it happens and what happens to be in the plane’s path. Thus, the circumstances leading to a catastrophe can grow like an avalanche, and the failure of, say, the reverse cannot be decisive in this situation.

The frequency with which runway runaway incidents occur around the world can be imagined from an analytical report prepared by the Dutch National Aerospace Laboratory in 2005. To prepare the report, about 400 cases of rolling out that occurred in the world over the previous 35 years were analyzed. It is easy to calculate that this is more than ten cases per year, although the study emphasized that the number of such aircraft accidents is rapidly decreasing: the improvement of aviation and navigation technology is having an effect. Fortunately, not all of these cases developed according to the worst-case scenario described in the article, but some of those that ended well were quite remarkable. In 2005, a huge A340 landing at Toronto Airport on a flight from Paris touched down over 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 airliner during roll-out was 190 km/h, only 30 km/h less than the speed at which the plane should have touched down. runway. Hence the tragic ending.

There is room for improvement

Runway excursion incidents occur in different countries and on different continents, but still some socio-geographical dependence is visible. According to research, such incidents most often occur in Africa, followed by South and Central America, then Asia. In developed countries, such accidents occur in fewer than one in two million landings. It works best in North America, and this with colossal air traffic in the skies over the USA. This, in fact, is not surprising: in developing countries there is more old aircraft, it is poorly maintained, there are many poorly equipped airports and outdated navigation equipment, and technological discipline is lower. All this, to some extent, can be said about the Russian aviation industry, and cases of roll-outs, including casualties, are not so rare in our country. But I would rather leave this company of outsiders.

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. Abbreviated FACC.

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

Thanks to the excellent occasion in the form of the rollout of the new Boeing 787 Dreamliner model and the information support of our dad Nestor, a number of comrades just now in general and on the B-787 Dreamliner in particular. I understand that LiveJournal can be read by completely different people with very different levels of awareness and areas of interest, so I will divide 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 more simply. 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 tell about the plane, but enough to tell about the reverse, you can just read the final part of my opus.

Translating Sleeve Reverse Thrust on Boeing 787 Dreamliner. Part 3.

In the 80s, due to the advent of a large number of engines with a high bypass ratio, this design solution finally lost its attractiveness. The new reverse concept does not involve shutting off the first “hot” circuit of the engine. Only the second – “cold” circuit – is closed. 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 in reverse, but only as a “second circuit”. However, the principle of such a reverse is not so much the direct impact of the jet stream, but rather the creation of a kind of air cushion in front of the aircraft, which greatly increases the aerodynamic drag of the aircraft and very effectively brakes the aircraft at speeds of up to 130 km/h. This cushion is clearly visible in photographs of an airplane landing on a wet runway. Drops of water lifted from the concrete perfectly visualize this effect.

Translating Sleeve Reverse Thrust on Boeing 787 Dreamliner. Part 4.
How does reverse work?

The Translating Sleeve of the Boeing 787 Dreamliner looks like this.

Reverse is a mechanism for directing part of the jet or air stream in the direction of movement of the aircraft and creating reverse thrust. In addition, reverse is the name used for the operation mode of an aircraft engine, which uses a reversing device.

The device is mainly used after landing, during the run or for emergency braking. In addition, reverse is used for reversing without the help of a towing vehicle. Some planes turn on the reverse while in the air. Most often, the device is used in transport and commercial aviation. After landing, the reverse is characterized by noise. It is used in conjunction with a wheel braking system, which reduces the load on the main braking system of the aircraft and shortens the distance, especially when the runway friction coefficient is low, as well as at the very beginning of the run. The contribution of reverse thrust varies greatly in different situations and aircraft models.

Jet engine

Reverse is produced by deflecting all or part of the jet that comes from the engine using different shutters. In various power plants, the reversing device is implemented in different ways. Special shutters are capable of blocking the jet, which is created purely by the external circuit of a turbojet engine (as on the A320), or the jet of all circuits (Tu-154M). The design features of the aircraft affect the equipment of the reverse gear. This can be either all engines or a specific part. For example, on the three-engine Tu-154, only the outer engines can create reverse, while the Yak-40 aircraft can create reverse.

Bucket flaps are a special mechanism that redirects the air flow. There can be two or more similar valves on engines. Outwardly they look like buckets. For example, in an engine with a high bypass ratio with flow over the entire plane, like the D-30Ku-154 (Tu-154M).

The reverse method, in which a special metal profile is installed in the nozzle and the rear part of the engine, is called profiled grilles. The engine is operated in direct thrust, and the flaps in the grilles redirect the passage of exhaust gases. A similar design is used in many aircraft engines, in particular in power plants with a low bypass ratio with shutoff of the entire flow (Tu-154, Boeing 727).

Restrictions

But the reverse system has its drawbacks. Possible troubles include the use of reverse at low speeds (less than 140 km/h). The jet can lift debris from the runway surface, which, when the aircraft runs at low speeds, can enter the air intake and cause damage. At high speeds, raised debris does not create interference due to the fact that it does not reach the height of the air intake.

The reverse device is installed on four engines, but in practice the 2nd and 3rd engines do not use reverse, because the process can damage the fuselage skin.

Engine with propeller

Reverse in propeller-driven aircraft is realized by turning the propeller blades (the angle of attack of the blades changes to negative), namely, with the direction of rotation unchanged. Therefore, the propeller creates reverse thrust. This type of reversing device can be used on piston and turboprop engines. Reverse is often provided on amphibians and seaplanes.

The first use of reverse began in the 30s. Equipped with reverse passenger aircraft Douglas DK-2 and Boeing 247.

Airplanes without reverse gear

A huge number of aircraft do not use reverse due to its uselessness or technical complexity. For example, due to some wing mechanization capabilities and the high efficiency of air brakes in the tail of the BAe 146-200, turning on the reverse is not required. Accordingly, all 4 engines do not work in reverse mode. For the same reason, the Yak-42 aircraft does not need a reverse device.

Majority aircraft with afterburners does not have reverse due to the magnitude after the landing run. This circumstance forces the construction of long runways, at the end of which emergency braking devices should be installed. In this case, aircraft are equipped with effective wheel brakes and parachutes. It should be noted that the pneumatics and brakes of such aircraft are subject to severe wear and tear and often require replacement.

Application of reverse in the air

Some aircraft allow the possibility of using thrust reverser directly in the air, but such inclusion depends on the type of aircraft. In some situations, the reverse is turned on before landing, and in others - at the time of descent, which significantly reduces the vertical braking speed or makes it possible to avoid permissible excess speeds during a dive, emergency descent or combat maneuvers.

The ATR 72 is a turboprop airliner, a prime example of the use of reverse in the air. In addition, the air reverse can be used by the Trident turbojet airliner, the Concorde supersonic airliner, the C-17A military transport aircraft, the Saab 37 Wiggen fighter, the Pilatus RS-6 turboprop and others.