Flight certification tests of the MC-21 passenger airliner continue in Zhukovsky. In March, after a two-month break due to the replacement of the engines PD-14, the prototype aircraft with the number plate 73055 resumed its flights. Intensive flights were performed by aircraft 73053, which for less than a month made 13 flights, and the sky took off one more prototype aircraft with Russian engines – aircraft 73051.
For one of the test pilots of Yakovlev Design Bureau, Vasiliy Sevastyanov, the year 2022 was marked with an important event – by the Decree of Russian President Vladimir Putin No. 713 of 7 October 2022 the Deputy Head of Flight Services of Yakovlev Design Bureau was awarded the title of the Hero of the Russian Federation for his courage, heroism and high professionalism shown during the testing and development of new aviation technology.
United Aircraft Corporation interviewed Vasily Sevastyanov, in which he talked about how the MC-21 is being tested.
– What are the differences between the certification tests of the MC-21-300 and MC-21-310? What was tested other than the propulsion system?
– The MC-21-300 was tested in full, in accordance with FAP-25. The MC-21-310 – only in the part of the main change – the installation of PD-14 engines.
The propulsion system is the key system of the aircraft. Its main characteristics are a derivative of the engine’s capabilities and economic indicators.
Certification with a new type of engine requires tests of the systems with which it interacts. These are hydraulics, electrics, air conditioning system and a number of others. In addition, engine replacement requires studies in aerodynamics, aeroelasticity, strength.
I note that the tests were not completed with the approval. We need to fly with PD-14 engines in the cold, in the heat, in the highlands. There’s still quite a lot of work to do.
– How is the scope of the tests for approval of the major change determined?
– The certification test program is prepared on the basis of calculations and mathematical modeling, which were conducted jointly by Irkut and UEC designers, scientists from TsAGI* and CIAM** and LII*** specialists.
– Which of the test programs were the most labor-intensive?
– This question should rather be asked to flight test engineers. The test pilot, of course, understands the big picture, but concentrates on the performance of individual flight tasks and programs.
The most voluminous flights are related to determining economic performance. It is necessary to collect a huge amount of data on the behavior of the aircraft at different speeds and altitudes in a wide range of masses.
This test program has no clear boundaries. The more characteristics that are captured, the more accurate the mathematical model will be. Accordingly, flight calculations will be more accurate for further tests and in operation.
– What is the typical composition of the crew in a certification flight? Who occupies the commander’s seat?
– The crew consists of three people: a certification center pilot, a test pilot and the flight operator of the Yakovlev design bureau.
The aircraft belongs to the Design Bureau, so our pilot is responsible for the outcome of the flight and the execution of the flight mission. The seat – left or right – does not matter.
– The certification center pilot: where is he from? Is he flying the aircraft?
– We work on the MS-21-310 with two certification centers, GosNII GA and LII. If the flight task is a certification task and an independent expert’s assessment is required, then the flight modes stipulated by the program are performed by the center’s pilot.
– Did the UEC (United Engine Corporation) flight operators take part in the flights?
– No. The engine tests as part of the aircraft are performed by the ground crew. Our on-board measurement systems ensure that a sufficient number of aircraft and engine parameters are recorded and analyzed on the ground during and after the flight.
– How do you start a test flight?
– By studying the flight test program, which defines what needs to be done and what results to be obtained. The task for a particular flight is developed by our lead test engineer. He includes in the task the modes that need to be performed.
The next step is to study the flight test methodology that is developed for each specific mode. If the mode is being prepared for the first time, we discuss with the flight crew how similar tests were conducted on other planes, in other conditions, with other crews.
If necessary, adjustments are made to the flight task. In particular, they may be related to optimizing the sequence of modes – the pilot often understands these issues better than the engineer. The “denser” the task, the more materials we bring from each flight, the lower the costs will be, the higher the efficiency of our work. Given the high cost of flight testing, this is basic.
– Who makes the decision in flight – is the regime completed or not?
– Often the pilot himself. For example, when you take off the expendable pads, the accuracy of holding speed should be within three knots. If I was within that accuracy after holding the pad for a few minutes, then the mode is considered to be a valid mode. More detailed information on the individual modes and systems is seen by the onboard operator on his console.
At the flight control point the flight experiment is monitored by specialists – leading engineers and designers of the aircraft. A large volume of data is sent continuously from the onboard telemetry system which is analysed in real time. In the circuit “pilot – flight operator – flight control system” a complex evaluation of flight performance is conducted promptly. If necessary, the mode is repeated.
If it fails, which is rare, but does happen, a post-flight analysis is performed. Based on its results, corrections are made to the task, to the experiment methodology, and to the systems software. In any case, the procedure required for certification will be completed.
– A lot of data is brought back from the flight, which is not analyzed in real time. What, from the pilot’s point of view, does studying them yield?
– In the interest of certification, it is necessary to analyze the fine details of aerodynamics, stability, and controllability. Based on the results, adjustments are made to the integrated airplane control system program. It has to be fine-tuned so that any airline pilot who has been trained can control the machine.
It’s a very subtle point that sometimes forces us test pilots to argue amongst ourselves. This or that phenomenon is perceived by everyone individually. For some, the reaction of the airplane to the pilot’s actions seems very sharp, for others, on the contrary, slowed down.
Our job is to make sure the airplane meets the regulatory requirements. Based on the test results, we have to make adjustments to the control system to make it comfortable for the pilot and ensure safe piloting.
If an error is found in the algorithms or software, we work with the designers to map out ways to fix it. As a result, new versions of the software appear, which are tested again in flights. And so on – until we get the certificate.
– How often does a given mode fail in flight?
– It’s rare. Today our understanding of the aircraft and the level of mathematical modeling is sufficient to understand, at the stage of preparing the flight task, whether it is feasible or not.
At the same time, it is possible to “fly over” part of the program in order to expand the operating range or improve the characteristics on which the designers consider it necessary to move forward.
– Do you divide test flights into simple and complex?
– For each flight a difficulty coefficient is determined, which has three degrees.
– What is the most difficult flight?
– The most difficult is a flight for which the pilot was not prepared (laughs – Ed.).
Actually, it’s not quite correct to say that one flight is difficult and another one is easy. Any simple flight can become very complicated and dangerous overnight. And not just in testing. An airplane is not a car. You can’t get out, fix it up and keep flying. You have to be ready not only for the flight mission, but also for the localization of all sorts of situations that can happen along the way.
There are flights that are difficult to perform. For example, when you have to get to a certain point with preset values of speed and g-load.
There are emotionally tense flights that require increased concentration and quick action, and there are fast-moving modes.
– Are there dangerous flights?
– There are flights that are assessed as dangerous in terms of possible consequences, to the limits of which you need to approach.
In civil aircraft, these boundaries are laid down in the operating range, which we have to close. But we also have to go slightly over the range to show that there is nothing dangerous going on there. There are quite a few such tests. For example, overcritical angles of attack, flutter tests, flights with engine shutdowns, and many other things.
When flying to determine evolutionary speeds on one engine, you slow down to a speed where the airplane can still be balanced by the rudders. When determining landing characteristics, this is done low to the ground. You slow down and get to a point where the airplane starts to “roll”. The rudders are gone and you have to come off the corners, but the ground is close by… These things are interesting, fleeting, and emotional.
But, again, they are understandable. Because you understand: approximately at what speed and where the car “will fall”. You get ready for that, you think how you are going to get out of the situation, you develop the separate actions to automatism. That is why, as a rule, everything goes well.
In addition, if you’re going to be in charge and complicated situations, you have to go through a series of so-called “approach regimes”. When approaching the borders, you might get to a point where you realize you should not go any further. After that, either the program is revised, or the range of characterization is reduced, or some restrictions are imposed. So, we are gradually approaching the limits, no one is jumping in headlong, because the aircraft is an expensive object and the responsibility is very high…
There’s another aspect that didn’t exist at the dawn of aviation. Aviation science is making rapid progress. Like it used to happen in the past: they built an airplane, nobody knew anything about it, and then a hero pilot walked by, sat in it, and flew. This is not the case today. Even before flights, the main characteristics are determined, test benches work, and mathematical modeling takes place. When an airplane takes off, it’s already a fairly well-studied object. Everyone understands what to expect from it. Some deviations from predictions are possible, but the airplane’s properties will not be diametrically opposed.
And the first pilots were heroes. They really faced the unknown.
– Was your first flight on MS-21-310 with Andrei Voropaev dangerous?
– It had its own peculiarities. The degree of integration of the engines into the control system and the readiness of the other systems was relatively low. We flew on a backup control law, and in it, the Three
Hundred and the MS-21-310 are not much different. So in terms of controlling the aircraft, we didn’t expect or receive any difficulties.
At the same time, lifting an airplane with a completely new power plant is both responsible and exciting. Emotional stress left its mark.
– You flew the MC-21-310 on scheduled routes. Is there any interest from air traffic controllers, pilots of neighboring planes?
– Lately, people often ask: what engines are you flying on, when will you fly with passengers? Everyone’s waiting for the plane and wants to see it on the roads as soon as possible.
– What will be the volume of tests in connection with the transition to Russian systems?
– The volume of tests seems quite large. We won’t be flying just the aerodynamics part.
TsAGI – Central Aerohydrodynamic Institute
CIAM – Central Institute of Aviation Motors
LII – Gromov Flight Research Institute