Ashes, ashes, you are powerful !: Is it dangerous to fly? In the wake of the volcano

Hot breathing of the engine To maintain combustion, the engine needs fuel and air in a ratio of about 1:14. Note that this is a mass rather than volumetric ratio. The more dust there is in the air, the less space is left for oxygen. At a certain concentration, the quality of the mixture is beyond acceptable limits and combustion stops

At the time of this writing, the number of flights canceled due to the volcanic eruption in Iceland is close to 100, 000. The losses of European airlines are estimated at $ 1.7 billion, at least five medium-sized carriers are balancing on the verge of bankruptcy.

As soon as Eurocontrol (the European Organization for Air Traffic Safety) reopened the skies over Europe, officials were bombarded with anger by airlines, European government transport ministers, and finally hundreds of thousands of passengers, including those who were stuck for a week away from home. Heavenly functionaries were accused of reinsurance and the desire to cover their own rear contrary to the interests of millions of citizens.

In the very first days of the “air blockade”, airplanes of KLM, British Airways, Lufthansa, Air Berlin took off without passengers. On board were senior officials of the companies, and the pilots did not report any deviations from the regular regimes. Airbus conducted a series of test flights over Europe with its A340 and A380, during which the crew and engineers carefully monitored the behavior of the aircraft and engine systems and did not detect any deviations (the post-flight inspection did not find them either). But in response to Eurocontrol, only one wording sounded: "We do not know how volcanic dust will affect the aircraft."

But there is an opposite point of view. Again, at the time of this writing, a new cloud of volcanic ash approached Europe. This time, the airports remain open. Meanwhile, the wording “we don’t know” is still valid. Eurocontrol did not boast of the results of the work of independent flying laboratories, and airlines get off with an avaricious wording: "No deviations from the norm were noted." Not a single pilot these days agreed to explain in detail how extensible the concept of “normal flight mode” can be. If you believe the press services of carriers, then every single pilot of civil aviation simultaneously flew up to the sky to eliminate the effects of the transport crisis without rest and sleep.

These days, editorial staff had to travel abroad. And we were scared to fly. Manufacturers of aircraft engines added fuel to the fire, which threatened carriers with the termination of warranty. We decided to find out exactly what threatens an airliner from getting into a cloud of volcanic dust, and we turned to the State Research Institute of Aviation Systems (GosNIIAS) and NPO Saturn (engine manufacturer).

Breathe deeper!

The most common phobia is associated with a possible engine failure associated with volcanic dust entering it. An example of such a failure is the flight accident that happened on KLM867 in 1989. After passing through a cloud of dust 300 km from the eruption site of the Redout volcano, the crew reported the failure of all four engines. Similarly, the events of the British Airways9 flight developed, during which the aircraft fell into the ash cloud of the Indonesian Galunggung volcano. In both cases, the engines were able to restart after exiting the ash suspension.

In numerous sources, there is a version that volcanic ash, which is microscopic pieces of volcanic glass, melted in the combustion chamber of the engine and formed a viscous mass that clogged the fuel supply channels. This is a common misconception.

In flight, the engine sucks in air at an enormous speed: air consumption is from 40 to 100 kg per second. In order for fuel to enter the combustion chamber, the pressure in the nozzles must be even greater than the air pressure created by the compressor. In addition, the nozzles are located along the air stream, and not against it. According to Roman Lyubimov, head of the test shop at NPO Saturn, under such conditions volcanic ash cannot enter the fuel line either in solid or in liquid form.

The flame outage (cessation of combustion in the combustion chamber), which was reported by the crews of the ill-fated KLM and British Airways flights, is attributed by Roman to the quality of the air-fuel mixture (see sidebar). This is possible only with a very high concentration of ash in the air - for example, 300 km from an erupting volcano, as is the case with KLM 867. Then the eruption was a complete surprise for pilots. If the presence of dust in the air is not a surprise to the crew, a sudden engine shutdown will not occur either. The combustion chamber of a modern aircraft engine contains at least 12 nozzles. Disruption of the flame on one or more of them does not entail negative consequences. The shutdown of part of the nozzles is used in normal flight modes in order to save fuel and reduce emissions of harmful emissions into the atmosphere. On the other hand, the failure of part of the nozzles will give the pilot an alarm signal about the need to leave the danger zone.

Sandblasting

Volcanic dust is a strong abrasive. What effect do microscopic glass particles have on engine parts rotating at speeds of over 6000 rpm when they collide with them at a speed of 800 km / h? The exact answer to this question is unknown, because the corresponding tests are not included in the engine certification program for civil aviation aircraft and, therefore, are not carried out. Some gas turbine engines for helicopters that are to operate in difficult climatic conditions pass through similar tests.

The closest conditions are modeled during hail casting tests. “In a collision with a fan, most hailstones are thrown from the center of the stream to the periphery and pass along the external circuit without falling into the high-pressure part, ” says Roman Lyubimov. “This is a fundamental principle in the design of civil aviation engines.”

The hardness of hailstones is not comparable with the surface hardness of rotating engine parts. The motor must fully preserve its characteristics when passing through a hail cloud. However, after such a flight, the engine is necessarily sorted out: the energy of a 1 g hail is large enough to cause bends or nicks to form on the fan edges in a collision. Of course, light suspended volcanic dust is not capable of causing such damage.

As applied to metals, it is customary to speak of surface cleanliness. This parameter takes into account the height and number of bumps on the surface of the part. In a turbojet engine, surface cleanliness is most important for compressor blades. Its openwork blades are surrounded by air at the highest speed, and the engine efficiency and thrust directly depend on their smoothness. The compressor blades are coated with an erosion-resistant material and ground. Due to the design of the fan, most of the volcanic dust bypasses the compressor. Nevertheless, long-term operation in dusty conditions can adversely affect the cleanliness of the surface of the blades and engine performance. This is partly due to the possible failure of manufacturers to warranty.

For a turbine, surface cleanliness is not as important as heat resistance - after all, it has to work literally in the combustion chamber. It is cast from a refractory alloy and is not even polished, so the abrasive is not afraid of it. In addition, ash particles are unlikely to overcome the combustion chamber without being melted. However, there are cooling air ducts inside the turbine. It is these that molten glass can clog, disrupting air circulation and cooling. This can lead to overheating, premature wear and even destruction of the assembly.

However, an increase in temperature does not occur instantly. The crew will receive an alarm long before the irreparable happens. As a result, according to Roman Lyubimov, when flying in a continuous cloud of dust, the probability of problems with navigation is many times higher than the probability of engine failure.

Five steps north

From contact with numerous particles of ash mixed with water vapor at high speed, the aircraft acquires an electric charge. The crew and passengers of the aircraft, who happened to fly through a dusty cloud, observed a bright glow on the windows, fuselage, wings. According to Oleg Titkov, senior researcher at GosNIIAS, with prolonged exposure, static electricity can lead to the destruction of some parts, such as antennas of radio receivers. Passing a charged plane can cause lightning. However, interference is more likely to occur in on-board electrical networks.

Each engine of a modern liner has its own generator and an onboard network. A powerful industrial computer installed directly inside the engine nacelle controls the engine automation, including regulates the quality of the air-fuel mixture. It is he who reduces the fuel supply as you climb (the higher, the more rarefied air) or if instead of a part of the air the engine swallows dust.

Volcanic ash will not be able to arrange an electric shock for the engine: the onboard electrical networks are too well shielded. But static electricity is quite capable of creating interference in radio receivers up to the complete cessation of communication. This means that, passing through a cloud of ash, the aircraft is likely to lose the main part of navigation systems.

To determine the current position in space, the FMS (Flight Management System) navigation system uses several sources at once. The most accurate of them is GPS. The next in accuracy is the VOR-DME ground beacon signal, which allows you to determine the direction and, depending on the design, the distance to a given point on the ground. NDB omnidirectional beacons are even less accurate. Finally, inertial navigation systems (ANNs) have the least accuracy. They are a set of gyroscopes and accelerometers. The error during a long flight by inertial navigation system can reach several hundred meters.

As you can see, during a riot of static electricity, pilots will be able to navigate in space only by ANN. In addition, the weather radar can become a victim of a charge. So, you will have to rely on getting into dangerous thunderclouds, relying on your own eagle eye. Fortunately, test flights have demonstrated that the transparency of cabin windows does not suffer from the abrasive effects of volcanic ash.

Volcanic ash cannot cripple an airplane. It only brings to the fore the human factor. If you believe in the professionalism of the crew commander, feel free to board. Personally, we will do just that.

The article was published in the journal Popular Mechanics (No. 6, June 2010).

Recommended

Challenger explosion: how they reacted to the disaster at the MCC
2019
10 motorcycles from Lego: like real
2019
The largest frogs in the world dig their own pools for posterity
2019