Jet propulsion
Текст: Ekaterina Hvorova, Aydar Fahrutdinov | 2015-01-19 | Фото: RUSJET, | 29659
Aircraft modeling: hobby of millions. Most model plane enthusiasts use inexpensive and easy-to-master aircraft – technical progress has led to the appearance of a large number of manufacturers of components for aircraft modelers; one can even acquire pre-assembled radio-controlled models. And then there’s aircraft modeling, which presupposes not only the independent construction and preparation of flying model aircraft, but also competition for airspeed, range, flight endurance, and aerobatics. This places certain demands on the models as well as on training of their constructors.

Today European and world championships in aircraft modeling are regularly held under the management of international organizations. Aircraft modeling includes, within its scope, sixty disciplines divided into five categories, each of which contains fundamental and supplementary classes. The elite of aircraft modeling are sportsmen competing in the class of radio-controlled jet models, and the primary organization uniting jet modelers is the International Jet Model Committee, which holds a world championship once every two years.

At the first stage of competition the radio-controlled jet models are evaluated for their fidelity to the original in scale, detailing, and color scheme; together these constitute fifty percent of the points. A panel of three to five judges compares the model with a set of documents presented by the participant (blueprints of the original and around fifty high-quality large-format photographs of the original aircraft from different angles, with all its characteristic details). The judges take into account the smallest details: skin paneling, hatches, rivets, latches, the exactness of the color scheme, insignia, markings, and even wear and tear noted on the prototype aircraft. Jumping ahead a little, we can tell you that in the Yak-130 model belonging to the current world champion in this category, Vitaliy Robertus from Russia, even the miniature liquid-crystal displays of the instruments show the same figures in flight that the screens of a real aircraft would. 

 The other fifty per cent of the points are awarded after the second stage, in which the participants make three flights, of which the two best make up the final score. The flight plan contains aerobatic maneuvers, chosen by the participant from the standard selection as most suiting the flight capability of the prototype aircraft. However, some aerobatic maneuvers can be even more difficult – some models are capable of withstanding load factors of up to 20 G, whereas a trained pilot can maintain control of an aircraft only up 10 G. At this stage the main mission of the pilot is to control the model during taxiing, takeoff, and the flight itself, so that it behaves as much as possible like the original. The judges evaluate not only the speed and smoothness of the flight, the angular velocities of the model while maneuvering, but even the sound of the engine as well.

When building a model it’s important to keep to the external proportions of the original, as well as its aerodynamic characteristics. When you take into account air viscosity and other factors, it turns out that the larger a model is, the better it flies. It’s best to make the model as large as possible. Although the competition’s rules state that the model’s unfueled weight cannot exceed 20 kilograms, the scale of the model and its dimensions are not regulated.

As a rule, airworthy aircraft are taken as the original and recreated at a scale of from 1:3 to 1:9. The resulting model is two to three meters long. After deciding on the scale of the model, the modelers begin building it independently. The process takes several years, requiring painstaking work and considerable financial expenditure. The first stage is one of drafting and calculation. The model must replicate the original externally and be able to fly at high speeds. Since in aerodynamics giving a model the same proportions as the original does not mean it maintains the same aerodynamic characteristics as the original, larger aircraft, the modelers have to completely recalculate control surface deflection, the center of gravity, and other important figures. It is also essential to distribute the aircraft’s weight correctly. During construction essential statistical and flight trials are carried out. At this stage crash landings and the complete loss of the experimental model sometimes occur. It is little different from the creation of a real aircraft with blueprints, wind tunnels, and experimental prototypes.

World championships in aircraft modeling are incredible sights. They always draw in audiences of all ages.

Jet aircraft modeling hasn’t been around for very long. Aircraft with jet engines were first built in the 1940s, but it took another fifty years to create miniature jet engines. At one point it was even considered to be impossible, since the square-cube law states that when one changes the dimensions of the engine, its energy conversion efficiency changes as well, along with other characteristics. For example, if you made a matchbox-sized exact copy of an automotive engine, it would not work. Model turbojet engines appeared thanks to German engineer Kurt Schreckling, who was able to build a simple, easy-to-assemble, and cheap-to-produce engine, which in many ways copied the HeS 3, the first German turbojet engine, created in 1939 by Pabst von Ohaim. This was a true technical breakthrough. The small and cold radial-flow centrifugal compressor was planted on one shaft with a single-contour hot turbine. Schreckling chose a centrifugal compressor because it was simpler to make and had fewer demands in tolerance; it also increased pressure by 2.4 to 2.7 times.  The wooden impeller of the compressor was strengthened with carbon fiber, while the turbine wheel was made of 2.5 millimeter tin. A true engineering revelation was the annular combustion chamber with its evaporative injection system, where a coiled pipe approximately one meter in length transports the fuel. With a length of only 260 mm and a diameter of only 110 mm, Schreckling’s engine weighed 700 g and gave 22 Н of thrust. The exit velocity of the gas in the jet nozzle was 200 meters / second. The engine is to this day the quietest in the world.

Kurt Schreckling’s deve­lopments contributed to the construction of industrial prototypes of the engine. Various companies created several sets for self-assembly as well, the most famous of which was the FD-3 from the Austrian firm Schneider-Sanchez.

The first completely assembled serially-produced aircraft modeling turbines were the JPX-Т240 from the French firm Vibraye and the Japanese J-450 Sophia Precision. They were very reliable and easy-to-operate, but had poor acceleration. Plus, they weren’t all that cheap – one Sophia cost $5800 in 1995 – almost as much as a new car. Later the construction and technology proposed by Schreckling were simplified, and the cost of the engine fell.

In 1994 the Pegasus turbine was released, with performance figures that were incredible for the time: an output of 10 kg of thrust, a maximum engine speed of 105000 rpm, a compression ratio of 3.5 at a rate of airflow of 0.28 kg / second, a gas discharge velocity of 360 meters / second. The mass of the engine with all of its units was 2300 g, while the turbine itself was 120 mm in diameter and 270 mm in length. 

In 1995 Thomas Kamps’ book ”Model Jet Engines” was published, featuring calculations and detailed blueprints of a turbine for home assembly. By experimenting with Schreckling’s turbine, Thomas Kamps created the microturbine KJ-66, in which he combined all that the field had hitherto accomplished. In effect all of today’s examples copy or reproduce to a greater or lesser degree the units put into this turbine. With the publishing of this book an engine of this type became attainable and could be built by any technically-minded person with the aid of basic engineering devices, such as a lathe.

The next revolution in the construction of mini-turbines took place thanks to German company JetCat. Its main innovation was the electronic control unit of the turbine, developed by Horst Lehnertz. JetCat added an electric starter, to the turbine a temperature transmitter, an optical tachometer, a fuel control unit, and an electronic “brain” that made everything work together. After the command to start, the electric starter turns on first, which takes the turbine up to 5000 rpm. Later, through six injectors (steel tubes 0.7 mm in diameter), the combustion chamber starts to receive a gas mixture (propane and butane), which is ignited by an aircraft modeling glow-plug. After the initiation of sustained combustion, kerosene begins to be passed through the neighboring injectors. Once the engine has reached 45000 – 55000 rpm the engine switches to kerosene, then reduces to idle revolutions (33000 − 35000 rpm). A green light flashes – that means that the onboard electronics have passed control of the turbine on to the radio control unit. Now the plane can take off.

Comparison: to launch the first models of the turbojet engine it was necessary to have at least four people – one pilot, one person with a container of compressed air, one with a fire extinguisher, and another with gas for ignition. The start sequence was as follows. First compressed air was blown onto the compressor impeller, bringing it up to 3000 rpm. After that gas was injected and ignited, trying to achieve sustained combustion in the combustion chambers. After this it was necessary to somehow switch transmission over to kerosene. As a rule, three-quarters of these attempts ended in failure, and often in flames – in such cases someone with a fire extinguisher was needed.

While in a French aircraft modeling store in 2001, Russian Vitaliy Robertus saw a Graupner catalog with a description of the JetCat P-80 – a turbine with an automatic start. The catalog stated that 45 seconds after ignition the turbine starts, revs, and passes control over to the transmitter. Such a wonder of technology with a completely automatic start then cost $2500. Not believing the unit’s incredible possibilities, but nevertheless having gathered the necessary funds, Robertus returned to Russia the happy owner of the country’s first model turbojet engine. In his words, his happiness could only be compared with buying one’s own satellite orbiting the Earth. The most striking thing was that the catalog didn’t lie, and the turbine really did start with the push of a single button. This purchase laid the foundation for the birth of jet aircraft modeling in Russia, and after ten years made Vitaliy Robertus the world champion in jet aircraft modeling.

World champion Vitaliy Robertus and executive director of the air sport club RUSJET, Pavel Lapshov, spoke to us about the creation of this championship-winning model of the Yakovlev Yak-130.


– What is the story behind the creation of your championship-winning jet copy of the Yak-130?

Vitaliy Robertus (V.R.): The Yak-130 is only part of what we’re doing, though it is our most impressive accomplishment. The path of the RUSJET team began ten years ago with the appearance of the first model jet engine in Russia. At that point we had already built up a fair amount of experience, knowledge, and education. We are all graduates of aviation institutes, and all of us have been involved in aircraft modeling in the traditional sense.

Pavel Lapshov (P.L): Now technical creativity among children is dying out. When we were kids we could build a dream out of a piece of plywood we found in a dump. Now a mother takes her children to an aircraft modeling club, and a month later she comes in and asks: “And where’s the plane my son has made?” They start explaining to her that first you need to make a Mokhov helicopter – it’s this propeller on a stick – and then you need to teach the child to use a fret saw… And then mom brings in a box with Chinese-made parts, and the modeling ends there.

But our childhood hobby, plus experience and knowledge, went onto serious competition and work. Before Vitaliy brought the first model jet engine from France in 2001, we had already been very involved with flying piston-engined models. Buying that jet engine was a turning point and predestined the formation of the RUSJET club in the future.

V.R.: The first flight of our own jet model took place in the summer of 2002 at Khodynskoe Polye. Unfortunately, you could hardly call it successful. Only by 2007 did we have enough technical experience under our belts to use the technology without accidents. This is what that means – you get a turbine, put it on the cheapest Chinese-made glider you can find, try to get it to start. At first it won’t start; then it starts, but it catches fire. You learn how to avoid it catching fire and, finally, how to make it take off. 

By the way, now we’ve created a “school for jet modelers” by recording over a dozen training clips for newcomers, because today they are taking the exact same hard knocks that we once took. There are some very interesting locations in the videos – take, for example, one from our first world championship in South Africa, where our plane (a model of an L-39) caught fire in the very first round and crashed into the savannah. The organizers of the championship allowed us to fly the rest of the rounds using a duplicate model, but outside the competition, which allowed us to get the first kernels of competition experience. This gave us a powerful jumpstart in understanding how important a systematic approach to flight preparation is, as well as how to build a model that can stand the test of competition. That same year I had an important conversation with Pavel, after which it became clear that our positions were very similar, and that combining our efforts would give us significant advantages. Pavel expressed his interest in taking direct participation in the building and preparation of jet models to participate in competitions at the highest level. And that was pretty much how the club started. 

Vitaliy Robertus’ first world championship (South Africa 2003) ended in failure: all that remained of the L-39 (above) was burning wreckage (below). Nevertheless, the first kernels of competition experience had been gathered.

In early 2004 we rented premises on the edge of Moscow, bought the necessary instruments, and got down to building models. And we made a lot of them. We flew them, built up our experience, and we got a very clear understanding of the current possibilities and of what still needed to be done. We met Aleksey Prokhorov – one of the pilots from the Strizhi aerial demonstration team. Thanks to his support and his telling the command of the Kubinka Airbase that aircraft modelers love the sky just as much as real pilots, we got the rare opportunity to occasionally carry out training flights on the airbase’s runway. The majority of the accidents with engine failures ended with minimal damage to the models thanks to the airbase’s long concrete runway. 

Back then RUSJET already existed in practically the same form as it does now. The name RUSJET best expresses the meaning of our club – the Russian Jet Movement.

P.L.: The beginning of the 2005 World Championship in Hungary went well: we achieved third place in the static grading, but in the second round our plane crashed again – it exploded and caught fire. Only two years later in Northern Ireland did we get our first serious result, taking second place, thanks to our reaching the right conclusions from our previous performances.

After this success we were invited to put up a stand at the Moscow International Aviation and Space Show, where we saw one of the first pre-production Yak-130s. We took a fancy to it and decided to choose it as the prototype for our next model. The Yak-130, like all training aircraft, is small in size, so it can be made in 1:4 scale. We were also influenced in our choice by it being subsonic, having wings swept-back at a low angle, a moderate thickness of profile, and a promising aerodynamic layout – all of which influenced the construction of the model.

Looking back we see that our decision was 100% correct. However, at that time we had two very serious challenges. The first was connected to the fact that everyone was flying with only one engine back then, and the Yak-130 has two engines.  While using this model we’ve had 20 or so landings with only one engine, so there’s still the risk of an engine giving out. The second challenge was that earlier we had used models that we had bought. This means that the model was made out of components from a box. Later on we started modernizing them, taking them up to the highest level of modeling – the copying of everything, right down to the smallest details. We make a copy of everything that’s visible externally, and no one would ever be able to tell the model from the real aircraft. Even we can’t tell the photographs apart. Then the world championship changed the rules and added an additional bonus for those who make their own models. In 2008 we understood that we weren’t going to get anything else by flying someone else’s planes. That was a pivotal moment – we needed to gather up the courage and decide to make the plane ourselves.

It’s hard to believe, but this isn’t a real Yak-130 on the runway – it’s a very skillfully-made copy. It looks and flies, however, just like the real thing.

– How did you begin your work on the model?

V.R.: One of the most crucial steps is the gathering of documentation and information. At the moment we have something like 9,000 photographs of one example of the Yak. That was the result of a week spent at an airfield with all sorts of cameras, measuring tapes, and rulers. We measured everything – every little feature, every little star, every label. And that was only the visual part. As for the engineering part, then the Yakovlev design bureau was very generous with us.  The management gave the green light, and we were given information not only on paper, but in electronic form? The theoretical contour of the aircraft was cut up into the number of sections that we needed; they gave us blueprints from all the general angles and gave us kinetic diagrams. That got rid of our need to guess some details. For instance, the landing gear strut has complicated kinetic characteristics, and trying to place the suspension point by trial and error would have been useless.

After nearly two and a half years we were at the physical reproduction stage. We drew 3D models of all the details. By the standards of aircraft modeling we used some high technology, spending as little time as possible on manual work – when this was possible, of course. Large components were milled. For instance, the core of the master-model of the fuselage was milled on a CNC system based on a 3D model. It’s a 3x5 meter five-axis machine that makes actual components for real yachts and trains.

After this came the most painstaking moment – imitation. Most models in the best case copy only the exterior, but our plane copies every rivet, every pucker of the metal. Another thing that we surprised people with was the absolutely realistic texture of the surface. It’s pretty hard getting to that level. Every pucker, every dent is sanded and covered with foil on the master-model.  That’s a tremendous amount of work – every sheet of metal is cut to size out of thin foil and glued to the master-model.  Later something called matrices are made out of composite materials based on the master-model – they are basically the same thing as a mold. And we use the molds to make the components. The master-model is made out of dense plastic, weighs dozens of kilograms, and it’s heavy even with three people carrying it. According to the competition rules, the weight limit for the final model is 20 kilograms.

Two or three years go into the design and preparation of the model alone. Then the flight trials and finishing begin.

– What difficulties did you have in creating the model?

 P.L.: The most interesting part begins when you do the inside of the plane. The challenge is to make a high-tech item with the maximum number of options within the regulation weight. We weren’t afraid to use new composite materials that are used in real-life aviation and not in aircraft modeling. The internal diagonal bracing is usually plywood; we used sandwich panels made from foam plastic and carbon fiber-reinforced polymer.

Another example is the landing gear. In aircraft modeling thick rubber tires are used, which keep their form thanks to the thickness of the rubber. But they’re very heavy. With small dimensions inflatable constructions are used, but then there are technical problems with compression, pressure, hermetic seal, and stuff like that. In our case the enormous (by our standards) wheels had to be made light. We had to put in an internal hard spatial frame that is put on over a thin aluminum disk. We then put on a layer of air-foam rubber and a thin covering of normal rubber. That combination gives light weight and durability – not a single wheel has worn out yet. And no one else has done that.

– Did you develop that yourselves?

P.L.: Yes, we did. At competitions level they appreciate it when the model stands on display and its wheels “give” a little, just like with a real aircraft’s.  That’s also thanks to the layering. We introduced a lot of new things like that.

Commercial companies started making clones of our developments, using many of our systems. For example, we have an interesting tailplane actuator – there are two, and they work like a two-headed horse. Or there’s the flap suspension system, which duplicates the parallelogram mechanism of a real aircraft, but on a completely different scale.

– You were able to win the world championship twice with the Yak-130. Was it the same aircraft both times?

V.R.: No, they were different models. The first we made in 2011. Looking at it now, it was an ugly duckling, but that was enough to beat everyone else by a wide margin. By 2013 we had made a second, perfected version. It was lighter and had many new systems.  The entire cockpit lights up – the little lights and monitors work, the control sticks move in sync with the commands from the ground. The dummy of the pilot moves; every nook is worked out in detail; the valves on the auxiliary power plant (a little turbine in the tail) open up, it revs, a sound-imitator goes… Besides the mock-up work, the model had a lot of new construction work.

– What is there more of in creating a model – practical construction or the theoretical part?

V.R.: As a rule, traditional aircraft modeling has a small theoretical component and a lot of practical experience. In our case there are a lot of calculations. For instance, the landing strut loads, the loads on the control surfaces, the stress diagrams for the retracting cylinders – all of those get calculated. But then doing calculations with composite materials is hard: if the pressure in the vacuum changes slightly or the resin doesn’t properly dissolve, the composite is already something completely different.

There’s also a practical part – we did high-speed runs for control surface disturbance. They looked pretty funny. We made special mounts on the roof of a car. We fastened everything to the trunk of the car – for example, the tail unit, the fin, the tailplane with actuators. The car drove at a speed of 180 km/h. That’s how we tested the control elements and wing’s high-lift device for deflection at extreme loads. But even during flight trials we were perfecting the aircraft.

P.L.: Once, after some flights at Kubinka, we had an open house and many of the leading pilots came. The Yak-130 test pilot Roman Taskaev was invited to take a look at our model, and we told him about our tests, in particular about one thing – the aircraft has deflecting leading wing edges. For a real Yak-130 the deflection of the leading edges on landing is 20 degrees, and after the first two weeks of test flights we realized that that was too much: the model was unstable, so we reduced the deflection to 10 degrees. He looked at me and said: “It took us three years of flying to realize that.” It turned out that on the real aircraft they changed the figures too; it’s just that this didn’t make it into the general flight characteristics.

We stay on very good terms with the pilots. Oleg Olegovich Kononenko, who is a recipient of the Hero of Russia award, for instance, invited us and our model to his fiftieth birthday party, where among the guests were leading pilots and engineers of the major aircraft design bureaus and the M.M. Gromov Flight Research Institute. They were shocked by what we were able to do on such a small scale.


– Besides competitive victories, what goals have you set for the club?

V.R.: Our club is a nonprofit organization whose main mission is getting the word out about aircraft modeling, and reviving the Soviet-era tradition when it was the basis for the development of aviation. Back then many aircraft modelers devoted their lives to the sky. It would be great if the incredible things that we learned to make with our own hands existed today as well. Despite the wealth of technologies that are used today, a person needs to do everything with his own hands, feeling every detail. There are things that develop spatial perception, thinking, and motor skills. The development of technology today is leading, unfortunately, to the degradation of humanity – we’re going back to monkeys. I often see how children are given iPads so they won’t bother anyone. Children get addicted to them because they’re a very neat toy. You shouldn’t ignore electronics like that, but you need to use them in a different way. The most important thing is to try to immerse children in reality: construction sets, toys, books. Today’s children aren’t reading anymore because there’s so much video content. This is how children lose their imagination – here’s one picture, there’s another. There’s everything in front of you, and you don’t need to imagine anything.

I see the results of this even at my main job (Vitaliy is the manager of a department of a major company). People come in, they bring figures, but they don’t understand them or feel them. We can look at a component, for instance, and tell you right away if it will work or not, if it will withstand the necessary load or not. That’s because we touched everything with our own hands, beginning with a slide rule and ending with the lathes. We understand what works and how it works. When a person comes up to me and gives me some figures and says, “The computer came up with this,” I simply send him out of my office. “Go, turn off your computer, get a calculator, a pen, and do the math on paper.” That’s the sad thing. The means have started crowding out the content.

– So your club is also a personnel-development project?

V.R.: To a certain extent.  At first we just worked on our own, but later on we decided to create a society around us that nurtures and develops itself. It’s one thing to do something all on your own, but it’s three times as interesting when a lot of people do it. We’re getting more and more interested people every year.

– What drives your development and where do you get the enthusiasm to work in aircraft modeling?

V.R.: There’s competition – that’s the driver for all of our activities. To win you have to be the best in everything, beginning with the little things. For us this is a hobby – we’re all amateur aircraft modelers. We like it, and we do it. But we try to be professionals in our approach – we should do it the best we can in terms of materials, technologies, and the engineering of the model. Everything is the best in the world. We gather the best bit by bit at exhibitions, competitions, bringing something of our own to it. What we end up with is some kind of Mona Lisa of engineering.

But if you did this just out of love for pure art, it would be very difficult. Competition is a strong stimulus. The title of world champion, on the one hand, gives you obligations, and on the other allows you to widen your professional ties, including commercial ties. The meaning isn’t in the title, but in the movement. Rules and approaches to competition change; the goal is to keep up with all of it and win under any conditions.

– Aside from your participation in international competitions, is there any other way that you get the word out about what you’re working on?

P.L.: We try to participate in all the events that we can. Every year we have large shows, perform, run a whole series of programs, gather together like-minded people. The largest show in Rostov brings in nearly 10000 viewers every year. We have been near Moscow, in Kiev, in Borisoglebsk… We try to show as much as we can over the internet, on social media, and in professional associations. We use all of the latest technologies, especially if we need to spread information as fast as possible. And we’re always ready to help others.

V.R.: We launched a video course called Jet School. We also support the Krasnogorsk aircraft modeling club for children. When I was growing up every town and city had aircraft modeling laboratories and shipbuilding laboratories that children attended and where they built things. But today, talking with the head of a youth center, I’m very sad to find out that children are embarrassed that they go to the aircraft modeling club. That’s strange. I remember being proud that I could make things with my hands. Today that’s funny and bizarre – why should you do something yourself when your parents can buy it for you at a store?

When I was a kid we couldn’t even dream of doing what we do now. Many people, though, are realizing that it’s a dead-end, consumeristic path – and for their children as well. Something that you haven’t made with your own hands and haven’t felt doesn’t have any value. A store-bought model falls and breaks and the child forgets about it.

– Is your intention to change the world around you?

V.R.: Yes, we try to change the world around us as much as we can. After our past projects a huge number of interested people appeared. And for us that was a new challenge. We want to create something in Russia that exists elsewhere in the world. We Russians can do a lot, but we did go through a period of time when we stopped believing in ourselves, stopped being proud of our country.  When we were children watching hockey, our team always won, and we didn’t think about what was good or bad. The feeling you get when you stand on the winner’s stand and our national hymn plays – I’ll call it a Soviet feeling – is just amazing. We want to bring that feeling back to people. You can’t imagine how the people were cheering for us when we were performing.

I think this will bear fruit in our country – at some point it will go over into the next generation. We understand why officials send their children abroad to study. I want our children to study here. I understand that, maybe, we won’t solve this problem for everybody, but judging by the feedback we get, then we’re not doing all of this for nothing.

– How do you see your activity developing in the future?

V.R.: We think it would be inappropriate to perform with the Yak-130 after 2015, so we will be making other aircraft.  There are new prototypes that are more complicated and more interesting. We need to grow, and each new aircraft is a new set of aerodynamics, a new set of electronics, and an entirely new level of mock-up. It’s possible that we’ll do a MiG-29. It’s a supersonic aircraft and because of that there are two aerodynamics. There’s the possibility that we’ll make it super-maneuverable, with thrust-vectoring. Maybe we will try to make a Т-50, a fifth-generation aircraft. It’s a flying computer, and it has no traditional aerodynamics at all.

There’s also a desire to master vertical take-off aircraft. Here a lot of emphasis goes on piloting, handling, automation, construction of the swiveling jet nozzle. But that’s not a project for competition, and if it ever comes off, then it will definitely be a long time from now.

Drones are another direction we could take. On our own it might not happen, but then we would need to look for people in related fields. That’s a completely different topic.


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