What can you cook from squid: quick and tasty

Did you know that if you put dry alcohol in a pipe bent by an arc, blow air from a compressor and supply gas from a cylinder, it will go berserk, yell louder than a fighter taking off and blush with anger? This is a figurative, but very close to the truth, description of the operation of a valveless pulsating air-jet engine - a real jet engine that everyone can build.

Schematic diagram The valveless PUVRD does not contain any moving parts. The front of chemical transformations formed during the combustion of fuel serves as a valve for it.

Sergey Apresov Dmitry Goryachkin

The valveless PUVRD is an amazing design. It has no moving parts, compressor, turbine, valves. The simplest PUVRD can do without even an ignition system. This engine can run on almost anything: replace the propane tank with a can of gasoline and it will continue to pulsate and create thrust. Unfortunately, PUVRDs turned out to be untenable in aviation, but recently they have been seriously considered as a source of heat in the production of biofuels. And in this case, the engine runs on graphite dust, that is, on solid fuel.

Finally, the rudimentary principle of operation of the pulsating motor makes it relatively indifferent to precision manufacturing. Therefore, the manufacture of PUVRD has become a favorite pastime for people who are not indifferent to technical hobbies, including model aircraft and novice welders.

Despite all the simplicity, PuVRD is still jet engine... It is very difficult to assemble it in a home workshop, and in this process there are many nuances and pitfalls. Therefore, we decided to make our master class a multi-part series: in this article we will talk about the principles of operation of the PUVRD and tell you how to make an engine case. The material in the next issue will be devoted to the ignition system and the starting procedure. Finally, in one of the following issues, we will definitely install our motor on a self-propelled chassis to demonstrate that it is really capable of generating serious thrust.

From a Russian idea to a German rocket

It is especially pleasant to assemble a pulsating jet engine, knowing that the principle of operation of the PUVRD was first patented by the Russian inventor Nikolai Teleshov back in 1864. The authorship of the first operating engine is also attributed to a Russian - Vladimir Karavodin. The high point in the development of PUVRD is rightfully considered the famous cruise missile "V-1", which was in service with the German army during the Second World War.

To work pleasantly and safely, we pre-clean the sheet metal from dust and rust using a grinder. The edges of sheets and parts are, as a rule, very sharp and full of burrs, so you only need to work with metal with gloves.

Of course, it comes about valve pulsating motors, the principle of operation of which is clear from the figure. The valve at the entrance to the combustion chamber allows air to flow into it unhindered. Fuel is supplied to the chamber, a combustible mixture is formed. When the spark plug ignites the mixture, excess pressure in the combustion chamber closes the valve. Expanding gases are directed into the nozzle, creating jet thrust. The movement of combustion products creates a technical vacuum in the chamber, due to which the valve opens and air is sucked into the chamber.

Unlike a turbojet engine, in a PUVRD the mixture does not burn continuously, but in a pulsed mode. This explains the characteristic low-frequency noise of pulsating motors, which makes them inapplicable in civil aviation. From the point of view of efficiency, PuVRDs also lose to turbojet engines: despite the impressive thrust-to-weight ratio (after all, PuVRDs have a minimum of parts), the compression ratio in them reaches at least 1.2: 1, so the fuel burns ineffectively.

Before heading to the workshop, we drew on paper and cut out templates for unfolded parts in full size. The only thing left to do is to circle them with a permanent marker to get the markings for cutting.

But PUVRDs are invaluable as a hobby: after all, they can do without valves at all. In principle, the design of such an engine is a combustion chamber with inlet and outlet pipes connected to it. The inlet pipe is much shorter than the outlet pipe. The valve in such an engine is nothing more than a front of chemical transformations.

The combustible mixture in the PUVRD burns at a subsonic speed. Such combustion is called deflagration (as opposed to supersonic - detonation). When the mixture ignites, flammable gases are ejected from both pipes. That is why both the inlet and outlet pipes are directed in the same direction and together participate in the creation of jet thrust. But due to the difference in lengths at the moment when the pressure in the inlet pipe drops, exhaust gases still move along the outlet. They create a vacuum in the combustion chamber, and air is drawn into it through the inlet pipe. Some of the gases from the outlet pipe are also directed into the combustion chamber under the action of a vacuum. They squeeze a new portion of the combustible mixture and set it on fire.

When working with electric scissors, the main enemy is vibration. Therefore, the workpiece must be securely fixed with a clamp. If necessary, you can very carefully dampen the vibrations by hand.

The valveless pulsating engine is unpretentious and stable. It does not need an ignition system to keep it running. Due to the vacuum, it sucks in atmospheric air without requiring additional pressurization. If we build a motor on liquid fuel (for simplicity, we preferred propane gas), then the inlet pipe regularly performs the functions of a carburetor, spraying a mixture of gasoline and air into the combustion chamber. The only time an ignition and boost system is needed is at start-up.

Chinese design, Russian assembly

There are several common designs of pulsating jet engines. In addition to the classic "U-shaped pipe", which is very difficult to manufacture, there is often a "Chinese engine" with a conical combustion chamber, to which a small inlet pipe is welded at an angle, and a "Russian engine" resembling an automobile muffler.

Fixed diameter pipes are easily molded around the pipe. This is mainly done by hand due to the lever effect, and the edges of the workpiece are rounded off with a mallet. It is better to shape the edges so that when they are joined they form a plane - this makes it easier to put a weld seam.

Before experimenting with your own PUVRD designs, it is strongly recommended to build an engine according to ready-made drawings: after all, the sections and volumes of the combustion chamber, inlet and outlet pipes completely determine the frequency of resonant pulsations. If the proportions are not observed, the engine may not start. A variety of PUVRD drawings are available on the Internet. We have chosen a model called "Giant Chinese Engine", the dimensions of which are shown in the sidebar.

Amateur PUVRDs are made of sheet metal. It is permissible to use finished pipes in construction, but not recommended for several reasons. Firstly, it is almost impossible to select pipes of exactly the required diameter. It is all the more difficult to find the necessary tapered sections.

The bending of the tapered sections is purely manual labor. The key to success is to squeeze the narrow end of the cone around the small diameter pipe, giving it more stress than the wider end.

Secondly, pipes tend to have thick walls and a corresponding weight. For an engine that needs to have a good thrust-to-weight ratio, this is unacceptable. Finally, the engine glows red hot during operation. If pipes and fittings made of different metals with different coefficients of expansion are used in the construction, the motor will not live long.

So, we have chosen the path that most PUVRD fans choose - to make a case from sheet metal. And they immediately faced a dilemma: turn to professionals with special equipment (CNC water-abrasive cutting machines, rolls for rolling pipes, special welding) or, armed with the simplest tools and the most common welding machine, go through the difficult path of a novice engine builder from the beginning to end. We preferred the second option.

Back to school

The first thing to do is to draw the unfolded details of the future. To do this, you need to remember school geometry and quite a bit of university drawing. It is as easy as shelling pears to make reamers of cylindrical pipes - these are rectangles, one side of which is equal to the length of the pipe, and the other - to the diameter multiplied by pi. Calculating the unfolding of a truncated cone or truncated cylinder is a slightly more difficult task, for the solution of which we had to look in a drawing tutorial.

Welding thin sheet metal is a delicate job, especially if you use manual arc welding like we do. Perhaps welding with a non-consumable tungsten electrode in an argon atmosphere is better suited for this task, but the equipment for it is rare and requires specific skills.

The choice of metal is a very delicate matter. From the point of view of heat resistance, stainless steel is best for our purposes, but for the first time it is better to use black low carbon steel: it is easier to mold and weld. The minimum sheet thickness that can withstand the combustion temperature of the fuel is 0.6 mm. The thinner the steel, the easier it is to mold and the harder it is to weld. We chose a sheet with a thickness of 1 mm and, it seems, did not lose.

Even if your welding machine can work in plasma cutting mode, do not use it for cutting reamers: the edges of parts processed in this way do not weld well. Manual scissors for metal are also not the best choice, as they fold over the edges of the workpieces. The ideal tool is electric scissors, which cut a millimeter sheet like clockwork.

To bend the sheet into a tube, there is a special tool - rollers, or listogib. It belongs to professional production equipment and therefore is unlikely to be found in your garage. A vise will help to bend a worthy pipe.

Welding millimeter-gauge metal with a full-size welder requires some experience. Having slightly overexposed the electrode in one place, it is easy to burn a hole in the workpiece. When welding, air bubbles can enter the seam and then leak. Therefore, it makes sense to grind the seam with a grinder to a minimum thickness so that the bubbles do not remain inside the seam, but become visible.

In the next episodes

Unfortunately, within the framework of one article it is impossible to describe all the nuances of the work. It is generally accepted that these jobs require professional qualifications, but with due diligence, all of them are available to the amateur. We, journalists, ourselves were interested in mastering new working specialties, and for this we read textbooks, consulted with professionals and made mistakes.

We liked the body that we welded. It is pleasant to look at it, it is pleasant to hold it in your hands. So we sincerely advise you to take up such a thing. In the next issue of the magazine, we will tell you how to make an ignition system and start a valveless pulsating air-jet engine.

From the received e-mail (copy of the original):

"Dear Vitaly! Neither Magli would you tell us a little more

about model turbojet engines, what is it all about and with what they are eaten? "

Let's start with gastronomy, turbines do not eat with anything, they are admired! Or, to paraphrase Gogol in a modern way: "Well, what model aircraft does not dream of building a jet fighter ?!"

Many dream, but do not dare. There are many new, even more incomprehensible, many questions. You often read in various forums how representatives of respectable research institutes and research institutes with a clever look are catching up with fear and trying to prove how difficult it is! Hard? Yes, maybe, but not impossible! And proof of this - hundreds of home-made and thousands of industrial samples of microturbines for modeling! You just need to approach this issue philosophically: everything ingenious is simple. Therefore, this article was written in the hope of reducing fears, lifting the veil of uncertainty and giving you more optimism!

What is a turbojet engine?

A turbojet engine (TJE) or gas turbine drive is based on the work of expanding gas. In the mid-thirties, an intelligent English engineer came up with the idea of ​​creating an aircraft engine without a propeller. At that time, it was just a sign of madness, but all modern turbojet engines still work according to this principle.

At one end of the rotating shaft is a compressor that pumps and compresses air. Escaping from the compressor stator, the air expands, and then, entering the combustion chamber, it is heated there by the burning fuel and expands even more. Since this air has nowhere else to go, it strives to leave the confined space with great speed, while squeezing through the turbine impeller located at the other end of the shaft and driving it into rotation. Since the energy of this heated air stream is much more than the compressor requires for its operation, its remainder is released in the engine nozzle in the form of a powerful impulse directed backward. And the more air heats up in the combustion chamber, the faster it seeks to leave it, further accelerating the turbine, and hence the compressor located at the other end of the shaft.

All turbochargers for gasoline and diesel engines, both two and four-stroke, are based on the same principle. The exhaust gases accelerate the turbine impeller, rotating the shaft, at the other end of which there is a compressor impeller that supplies the engine with fresh air.

The principle of work - you can not imagine any easier. But if only it were that simple!

The turbojet engine can be clearly divided into three parts.

• A. Compressor stage
• B. The combustion chamber
• V. Turbine stage

The power of a turbine largely depends on the reliability and performance of its compressor. In principle, there are three types of compressors:

• A. Axial or Linear
• B. Radial or centrifugal
• V. Diagonal

A. Multistage linear compressors became widespread only in modern aircraft and industrial turbines. The fact is that it is possible to achieve acceptable results with a linear compressor only if several compression stages are put in series one after the other, and this greatly complicates the design. In addition, a number of requirements for the design of the diffuser and the walls of the air duct must be met in order to avoid stalling and surging. There were attempts to create model turbines on this principle, but due to the complexity of manufacturing, everything remained at the stage of experiments and trials.

B. Radial or centrifugal compressors... In them, the air is accelerated by the impeller and, under the action of centrifugal forces, is compressed - compressed in a rectifier system-stator. It was with them that the development of the first operating turbojet engines began.

Simplicity of design, less susceptibility to air stalls and the relatively high efficiency of just one stage were the advantages that previously pushed engineers to start their development with this type of compressor. It is currently the main type of compressor in microturbines, but more on that later.

B. Diagonal, or a mixed type of compressor, usually a single-stage, in principle of operation is similar to a radial, but is rather rare, usually in turbocharging devices of piston internal combustion engines.

Development of turbojet engine in aircraft modeling

There is a lot of controversy among aircraft modelers about which turbine was the first in aircraft modeling. For me, the first model aircraft turbine is the American TJD-76. The first time I saw this device was in 1973, when two half-drunk midshipmen tried to connect gas bottle to a round thing, about 150 mm in diameter and 400 mm long, tied with ordinary knitting wire to a radio-controlled boat, a target set for the Marine Corps. To the question: "What is it?" they replied, “This is a mini mom! American ... her mother does not start ... ".

Much later, I found out that this is a Mini Mamba, weighing 6.5 kg and with a thrust of about 240 N at 96,000 rpm. It was developed back in the 50s as an auxiliary engine for light gliders and military drones. The peculiarity of this turbine is that it used a diagonal compressor. But it has not found wide application in aircraft modeling.

The first "popular" flying engine was developed by the forefather of all microturbines Kurt Schreckling in Germany. Having begun more than twenty years ago to work on the creation of a simple, technologically advanced and cheap turbojet engine in production, he created several samples that were constantly being improved. By repeating, supplementing and improving its developments, small-scale manufacturers have formed the modern look and design of the model turbojet engine.

But back to the Kurt Schreckling turbine. Outstanding design with carbon fiber reinforced wooden compressor impeller. An annular combustion chamber with an evaporative injection system, where fuel was supplied through a coil approximately 1 m long. Homemade wheel turbines made of 2.5 mm sheet metal! With a length of only 260 mm and a diameter of 110 mm, the engine weighed 700 grams and produced 30 Newtons of thrust! It is still the quietest turbojet engine in the world. Because the speed of leaving the gas in the engine nozzle was only 200 m / s.

Based on this engine, several variants of self-assembly kits were created. The most famous was the FD-3 of the Austrian company Schneider-Sanchez.

10 years ago, the model aircraft designer faced a serious choice - an impeller or a turbine?

The traction and acceleration characteristics of the first model aircraft turbines left much to be desired, but they had an incomparable superiority over the impeller - they did not lose thrust with increasing model speed. And the sound of such a drive was already a real "turbine" one, which was immediately appreciated by the copyists, and most of all by the audience, which is by all means present on all flights. The first Schreckling turbines quietly lifted 5-6 kg of the model's weight into the air. The start was the most critical moment, but in the air all other models fade into the background!

An aircraft model with a microturbine could then be compared to a car constantly moving in fourth gear: it was difficult to accelerate, but then such a model was no longer equal either among the impellers or among the propellers.

I must say that the theory and development of Kurt Schreckling contributed to the fact that the development of industrial designs, after the publication of his books, followed the path of simplifying the design and technology of engines. What, in general, is what led to the fact that this type of engine became available for large circle model aircraft with an average wallet and family budget!

The first examples of serial model aircraft turbines were the JPX-T240 of the French company Vibraye and the Japanese J-450 Sophia Precision. They were very similar both in design and in outward appearance, had a centrifugal compressor stage, an annular combustion chamber and a radial turbine stage. The French JPX-T240 was gas powered and had a built-in gas regulator. She developed a thrust of up to 50 N, at 120,000 rpm, and the weight of the apparatus was 1700 grams. Subsequent samples, T250 and T260, had a thrust of up to 60 N. The Japanese Sofia worked, in contrast to the Frenchwoman, on liquid fuel. At the end of its combustion chamber there was a ring with spray nozzles, it was the first industrial turbine that found a place in my models.

These turbines were very reliable and easy to operate. The only drawback was their overclocking characteristics. The fact is that a radial compressor and a radial turbine are relatively heavy, that is, they have a large mass in comparison with axial impellers and, therefore, a larger moment of inertia. Therefore, they accelerated from idle to full slowly, about 3-4 seconds. The model reacted to the gas correspondingly even longer, and this had to be taken into account when flying.

The pleasure was not cheap, Sofia alone cost in 1995 6,600 German marks or 5,800 “forever green presidents”. And you had to have very good arguments in order to prove to your wife that the turbine for the model is much more important than new kitchen, and that an old family car can last a couple of years, but you can't wait with a turbine.

A further development of these turbines is the P-15 turbine sold by Thunder Tiger.

Its difference is that the turbine impeller is now axial instead of radial. But the thrust remained within 60 N, since the entire structure, compressor stage and combustion chamber remained at the level of the day before yesterday. Although at its price, it is a real alternative to many other samples.

In 1991, two Dutchmen, Benny van de Goor and Hahn Enniskens, founded AMT and in 1994 produced the first 70N turbine, the Pegasus. The turbine had a Garret turbocharged radial compressor stage, 76 mm in diameter, as well as a very well thought out annular combustion chamber and axial turbine stage.

After two years of careful study of Kurt Schreckling's work and numerous experiments, they achieved optimal engine performance, tested the size and shape of the combustion chamber, and the optimal design of the turbine wheel. At the end of 1994, at one of the friendly meetings, after the flights, in the evening in a tent over a glass of beer, Benny sly winked in conversation and confidentially said that the next production model of the Pegasus Mk-3 "blows" already 10 kg, has a maximum speed of 105,000 and a degree compression 3.5 with an air flow rate of 0.28 kg / s and a gas outlet velocity of 360 m / s. The mass of the engine with all units was 2300 g, the turbine was 120 mm in diameter and 270 mm in length. Then these figures seemed fantastic.

In fact, all today's samples copy and repeat to one degree or another the units incorporated in this turbine.

In 1995, Thomas Kamps's book "Modellstrahltriebwerk" (Model Jet Engine) was published, with calculations (more borrowed in abbreviated form from K. Schreckling's books) and detailed drawings of the turbine for self-made... From that moment on, the monopoly of manufacturing firms on the manufacturing technology of model turbojet engines ended completely. Although many small manufacturers simply mindlessly copy the Kamps turbine units.

Thomas Camps, through experiments and trials, starting with the Schreckling turbine, created a microturbine, in which he combined all the achievements in this area at that time and, willingly or unwittingly, introduced a standard for these engines. Its turbine, better known as KJ-66 (KampsJetеngine-66mm). 66 mm - compressor impeller diameter. Today you can see various names of turbines, which almost always indicate either the size of the compressor impeller 66, 76, 88, 90, etc., or the thrust - 70, 80, 90, 100, 120, 160 N.

Somewhere I read a very good interpretation of the magnitude of one Newton: 1 Newton is a 100 gram chocolate bar plus packaging for it. In practice, the indicator in Newtons is often rounded up to 100 grams and the engine thrust is conventionally determined in kilograms.

The design of the model turbojet engine

1. Compressor impeller (radial)
2. Compressor rectifier system (stator)
3. The combustion chamber
4. Turbine rectifier system
5. Turbine wheel (axial)
6. Bearings
7. Shaft tunnel
8. Nozzle
9. Nozzle cone
10. Compressor front cover (diffuser)

Where to begin?

Naturally, the modeler immediately has questions: Where to begin? Where to get? How much is?

1. You can start with kits. Almost all manufacturers today offer a full range of spare parts and kits for the construction of turbines. The most common are KJ-66 repetition sets. The prices of the sets, depending on the configuration and quality of workmanship, range from 450 to 1800 Euro.
2. You can buy a ready-made turbine if you can afford it, and you manage to convince your spouse of the importance of such a purchase, without bringing the matter to a divorce. Prices for finished engines start from 1500 Euros for turbines without autostart.
3. You can do it yourself. I will not say that this is the most ideal way, it is not always the fastest and cheapest, as it might seem at first glance. But for home-builders, the most interesting, provided that there is a workshop, a good turning and milling base and a device for resistance welding are also available. The most difficult thing in artisanal manufacturing conditions is the alignment of the shaft with the compressor wheel and turbine.

I started with self-construction, but in the early 90s there was simply no such choice of turbines and kits for their construction as today, and it is more convenient to understand the operation and subtleties of such a unit when making it yourself.

Here are photos of self-made parts for a model aircraft turbine:

Whoever wants to get acquainted with the device and theory of the Micro-TRD, I can only advise the following books, with drawings and calculations:

• Kurt Schreckling. Strahlturbine fur Flugmodelle im Selbstbau. ISDN 3-88180-120-0
• Kurt Schreckling. Modellturbinen im Eigenbau. ISDN 3-88180-131-6
• Kurt Schreckling. Turboprop-Triebwerk. ISDN 3-88180-127-8
• Thomas Kamps Modellstrahltriebwerk ISDN 3-88180-071-9

Today I know the following firms that produce model aircraft turbines, but there are more and more of them: AMT, Artes Jet, Behotec, Digitech Turbines, Funsonic, FrankTurbinen, Jakadofsky, JetCat, Jet-Central, A.Kittelberger, K.Koch, PST-Jets, RAM, Raketeturbine, Trefz, SimJet, Simon Packham, F. Walluschnig, Wren-Turbines. All of their addresses can be found on the Internet.

Practice of use in aircraft modeling

Let's start with the fact that you already have a turbine, the simplest one, how to operate it now?

There are several ways to make your turbine engine work in a model, but it is best to build a small test bench like this first:

Manual start (Manualstart) - the easiest way to control a turbine.

1. The turbine is accelerated by compressed air, hairdryer, electric starter to a minimum operating speed of 3000 rpm.
2. Gas is supplied to the combustion chamber, and voltage is supplied to the glow plug, gas is ignited and the turbine enters a mode within 5000-6000 rpm. Previously, we simply set fire to the air-gas mixture at the nozzle and the flame "shot through" into the combustion chamber.
3. At the operating speed, the travel regulator is switched on, which controls the speed of the fuel pump, which in turn supplies fuel to the combustion chamber - kerosene, diesel fuel or heating oil.
4. When stable operation occurs, the gas supply stops and the turbine runs on liquid fuel only!

Bearings are usually lubricated with fuel, to which turbine oil is added, about 5%. If the bearing lubrication system is separate (with an oil pump), then it is better to turn on the pump power before gas supply. It is better to turn it off last, but DO NOT FORGET to turn it off! If you think women are the weaker sex, then look at what they turn into when they see the jet of oil flowing out of the model nozzle onto the upholstery of the rear seat of a family car.

The disadvantage of this very easy way control - almost complete lack of information about the operation of the engine. To measure temperature and speed, separate instruments are needed, at least an electronic thermometer and a tachometer. Purely visually, you can only approximately determine the temperature, by the color of the heating of the turbine impeller. The alignment, as with all rotating mechanisms, is checked on the surface of the casing with a coin or fingernail. By placing your fingernail on the surface of the turbine, even the smallest vibrations can be felt.

In the passport data of motors, their maximum speed is always given, for example 120,000 rpm. This is the maximum permissible value during operation, which should not be neglected! After in 1996, my homemade unit flew right on the stand and the turbine wheel, tearing the engine casing, punched through the 15-millimeter plywood wall of the container, standing three meters from the stand, I made a conclusion for myself that without control devices to accelerate Self-made turbines are life-threatening! Strength calculations later showed that the shaft speed should have been within 150,000. So it was better to limit the full throttle operating speed to 110,000 - 115,000 rpm.

Another important point. To the fuel control circuit NECESSARILY the emergency shut-off valve must be switched on, controlled via separate channel! This is done so that in the event of a forced landing, carrot-unscheduled landing and other troubles, stop the fuel supply to the engine in order to avoid a fire.

Start control(Semi-automatic start).

Whatever the troubles described above happen on the field, where (God forbid!) Even the audience around, they use a fairly well-proven Start control... Here, the start control is the opening of gas and the supply of kerosene, the electronic unit monitors the engine temperature and rpm ECU (E lectronic- U nit- C ontrol) . The container for gas, for convenience, can already be placed inside the model.

For this, a temperature sensor and a speed sensor are connected to the ECU, usually optical or magnetic. In addition, the ECU can give readings on fuel consumption, save the parameters of the last start, readings of the fuel pump supply voltage, battery voltage, etc. All this can then be viewed on a computer. The Manual Terminal (control terminal) is used to program the ECU and read the accumulated data.

To date, the two competing products in this area, Jet-tronics and ProJet, are the most widely used. Which of them to give preference - everyone decides for himself, since it is hard to argue about which is better: Mercedes or BMW?

It all works as follows:

1. When the turbine shaft is spun (compressed air / hairdryer / electric starter) up to operating speed, the ECU automatically controls the gas supply to the combustion chamber, ignition and kerosene supply.
2. When you move the throttle handle on your console, the turbine is automatically brought to operating mode, followed by monitoring the most important parameters of the entire system, from battery voltage to engine temperature and rpm.

Autostart(Automatic start)

For especially lazy people, the startup procedure is simplified to the limit. The turbine is started from the control panel also through ECU one switch. No compressed air, no starter, no hair dryer are needed here!

1. You flip a toggle switch on your radio remote control.
2. The electric starter spins the turbine shaft up to operating speed.
3. ECU controls the start, ignition and output of the turbine to the operating mode, followed by control of all indicators.
4. After turning off the turbine ECU a few more times automatically scrolls the turbine shaft with an electric starter to reduce the engine temperature!

The most recent advancement in automatic start-up is Kerostart. Start on kerosene, without preheating on gas. By installing a different type of glow plug (larger and more powerful) and minimally changing the fuel supply in the system, it was possible to completely abandon gas! Such a system works on the principle of an automobile heater, as in the Zaporozhets. In Europe, so far only one company is converting turbines from gas to kerosene start, regardless of the manufacturer.

As you have already noticed, in my drawings, two more units are included in the diagram, these are the brake control valve and the landing gear retraction control valve. These options are optional, but very useful. The fact is that in "normal" models, when landing, the propeller at low speeds is a kind of brake, while jet models do not have such a brake. In addition, the turbine always has a residual thrust even at "idle" speed and the landing speed of jet models can be much higher than that of "propeller" models. Therefore, the brakes of the main wheels help a lot to reduce the model's mileage, especially on short grounds.

Fuel system

The second strange attribute in the pictures is the fuel tank. Reminds me of a bottle of Coca-Cola, doesn't it? The way it is!

This is the cheapest and most reliable tank provided that reusable, thick bottles are used, and not crinkling disposable ones. The second important point is the filter at the end of the suction pipe. Required element! The filter does not serve to filter the fuel, but to prevent air from entering the fuel system! More than one model has already been lost due to the spontaneous shutdown of the turbine in the air! Best of all, filters from Stihl chainsaws or the like made of porous bronze have proven themselves here. But ordinary felt ones will do as well.

Speaking of fuel, you can immediately add that the turbines are thirsty, and the fuel consumption is on average at the level of 150-250 grams per minute. The largest consumption, of course, falls on the start, but then the throttle lever rarely goes forward beyond 1/3 of its position. From experience we can say that with a moderate style of flight, three liters of fuel is enough for 15 minutes. flight time, while there is still a margin in the tanks for a couple of landing approaches.

The fuel itself is usually aviation kerosene, known in the west as Jet A-1.

You can, of course, use diesel or lamp oil, but some turbines, such as the JetCat family, do not tolerate it well. Also turbojet engines do not like poorly purified fuel. The disadvantage of kerosene substitutes is the high formation of soot. Engines have to be disassembled more often for cleaning and inspection. There are cases of turbines operating on methanol, but I know only two such enthusiasts, they produce methanol themselves, so they can afford such a luxury. The use of gasoline, in any form, should be categorically abandoned, no matter how attractive the price and availability of this fuel may seem! This is literally a game with fire!

Service and motor life

So the next question has ripened by itself - service and resource.

Service is more about keeping the engine clean, visually inspecting and checking for vibration at start. Most model aircrafts equip turbines of some kind air filter... Ordinary metal sieve in front of the suction diffuser. In my opinion, it is an integral part of the turbine.

Motors that are kept clean, with a good bearing lubrication system, serve 100 or more working hours without failure. Although many manufacturers advise, after 50 working hours, send turbines for inspection Maintenance but it's more to clear your conscience.

First reactive model

More shortly about the first model. Best of all, it should be a "trainer"! There are many turbine trainers on the market today, most of them are delta wing models.

Why delta? Because these are very stable models in themselves, and if the so-called S-shaped profile is used in the wing, then both the landing speed and the stall speed are minimal. The coach must, so to speak, fly himself. And you should concentrate on a new type of engine and control features for you.

The coach must be of decent size. Since speeds on jet models of 180-200 km / h are a matter of course, your model will very quickly move away at decent distances. Therefore, a good visual control must be provided for the model. It is better if the turbine on the trainer is mounted openly and sits not very high in relation to the wing.

A good example of which trainer SHOULD NOT be is the most common trainer - "Kangaroo". When FiberClassics (today Composite-ARF) ordered this model, the concept was based primarily on the sale of the Sofia turbines, and as an important argument for modelers that by removing the wings from the model, it can be used as a test bench. So, in general, it is, but the manufacturer wanted to show the turbine, as in a showcase, and therefore the turbine is mounted on a kind of "podium". But since the thrust vector was applied much higher than the CG of the model, the turbine nozzle had to be lifted up. The bearing qualities of the fuselage were almost completely eaten away by this, plus the small wingspan, which gave a large load on the wing. The customer refused other layout solutions proposed at that time. Only the use of the TsAGI-8 Profile, reduced to 5%, gave more or less acceptable results. Those who have already flown a Kangaroo know that this model is for very experienced pilots.

Taking into account the shortcomings of the Kangaroo, a sports trainer for the more dynamic HotSpot flights was created. This model is distinguished by more thought-out aerodynamics, and "Ogonyok" flies much better.

The further development of these models was the "BlackShark". It was designed for quiet flights, with a large turning radius. With the possibility of a wide range of aerobatics, and at the same time, with good steaming qualities. If the turbine fails, this model can be planted like a glider, without nerves.

As you can see, the development of trainers has gone along the path of increasing sizes (within reasonable limits) and decreasing the load on the wing!

An Austrian set of balsa and foam, Super Reaper, can also serve as an excellent trainer. It costs 398 Euros. The model looks very good in the air. Here is my all-time favorite Super Reaper video: http://www.paf-flugmodelle.de/spunki.wmv

But the champion at a low price today is "Spunkaroo". 249 Euro! Very simple construction made of balsa covered with fiberglass. Only two servos are enough to control the model in the air!

Since we are talking about servos, I must say right away that there is nothing to do with standard three-kilogram servos in such models! The loads on the steering wheels are huge, so they need to put cars with an effort of at least 8 kg!

Summarize

Naturally, everyone has their own priorities, for someone it is a price, for someone a finished product and time savings.

The most fast way to take possession of a turbine, it's just to buy it! Today prices for ready-made turbines of the 8 kg thrust class with electronics start from 1525 Euro. Considering that such an engine can be taken into operation immediately without any problems, then this is not a bad result at all.

Sets, Kits. Depending on the configuration, usually a set of a compressor straightening system, a compressor impeller, a non-drilled turbine wheel and a turbine straightening stage costs an average of 400-450 Euro. To this we must add that everything else must either be bought or made by yourself. Plus electronics. The final price may be even higher than the finished turbine!

What you need to pay attention to when buying a turbine or kits - it is better if it is a version of the KJ-66. Such turbines have proven to be very reliable, and their capacity to increase power has not yet been exhausted. So, often replacing the combustion chamber with a more modern one, or changing bearings and installing straightening systems of a different type, it is possible to achieve an increase in power from several hundred grams to 2 kg, and the acceleration characteristics are often much improved. In addition, this type of turbine is very easy to operate and repair.

Let's summarize what size pocket is needed to build a modern jet model at the lowest European prices:

• Turbine complete with electronics and small items - 1525 Euro
• A trainer with good flying qualities - 222 Euro
• 2 servos 8/12 kg - 80 Euro
• Receiver 6 channels - 80 Euro

Total, your dream: about 1900 Euro or about 2500 green presidents!

In the vastness of the world wide web, you can find many forums and discussions that relate to this type of engine. However, before that it was impossible to find a Russian-language instruction for the manufacture of a pulsating air-jet engine, since only all videos and text materials were in English. Fortunately, our long search was crowned with success, and we present you with a review of the Russian-language video on the manufacture of the Reinst engine.

We present to your attention a video from the author

What we need to build:
- glass jar 400 ml;
- a can of condensed milk;
- copper wire;
- alcohol;
- scissors;
- compasses;
- pliers;
- dremel;
- paper;
- pencil.

Immediately, we note that from a can of condensed milk we only need a side tin. We also clarify that if there is no dremel at hand, then you can use an ordinary awl, since we need a small diameter hole. You can start assembling the engine.

First, we make a hole with a diameter of approximately 12 mm in the lid of the glass jar. Why approximately? The fact is that there are simply no exact formulas for assembling such an engine.

After that we need to roll up the diffuser. To do this, take paper and draw a template on it, as shown in the picture below. You need to draw the template with a compass. The measurements are as follows: the near radius from the middle is about 6 cm, the far one is 10.5 cm. After that, we measure 6 cm from the resulting sector. At the near radius and cut it off.

We apply the resulting template to a tin from a can of condensed milk and circle it.

After that, we cut out the resulting part with scissors.

Bend one millimeter away from the two edges in different directions.

Now we form a cone and hook the bent parts together.

Our diffuser is ready.

Now we drill holes from four sides on the narrow part of the diffuser.

We do the same on the lid around the center hole.

Now, using a wire, we suspend our diffuser under the hole on the cover. The distance from the top edge should be approximately 5-7 mm.

After the Wings of the Motherland magazine (it was a long time ago) appeared the drawings of the PUVRD of the design of the world champion in high-speed models with such an Ivannikov engine, I had a passionate desire to make one. True, I did not have sheet heat-resistant iron. I decided to make it out of a tin can. Reeled up welding transformer for spot welding, made the appropriate electrodes and set to work. He was trained in turning and plumbing from his youth. The valve lattice was made of duralumin, the tank was glued from fiberglass, the valves and "springs" for them were made of sheet spring steel with a thickness of 0.15 mm. To cool the valves, I decided to make a tank for methanol or water with its own spray pipe and dosing needle. We started (with friends) the engine in the locksmith's area. The roar was such that one of the guys noticed how the glass on the windows buckled. The engine ran for less than a minute, because. a pipe made from a tin can burned out. But the adrenaline was there. Now I can only imagine in the photo the "head" of the PUVRD: a tank and a valve grid assembled with valves.
After a certain time, I got a small sheet of heat-resistant steel with a thickness of 0.15 mm. I decided to weld a small PUVRD out of it. It started several times. It was not used on models, although with a weight of 90g. gave traction 600g. Once it made a "splash" when, during a break in the regional meeting of the chairmen of the DOSAAF committees, to distract from the boredom of the meeting, it was launched with the help of a bicycle pump and a homemade high-voltage unit on the office desk. It was funny to watch as the crowd of chairmen, having thrown a smoke break, rushed to the table to look at the "curiosity". The spark plug is homemade. The high-voltage unit was powered by a KBS battery. The power supply was interrupted by a bell-type breaker. The unit uses a motorcycle ignition coil
.
I also have one more PUVRD, though not completed yet, there is no diffuser. Maybe I'll finish it. The peculiarity of this engine is that there are transverse rings on the exhaust pipe. This is done so that the pipe does not swell, because. metal thickness 0.15mm. Here are some photos:

:
Now this technique reminds me of the good old days. Generally, nostalgia.

The most difficult to manufacture and the most important for the operation of the turbine is the compressor stage. It usually requires a precision CNC or hand-driven machining tool to assemble it. Fortunately, the compressor runs at low temperatures and can be 3D printed.

Another thing that is usually very difficult to reproduce at home is the so-called "nozzle vane" or simply NGV. Through trial and error, the author found a way to do this without using a welding machine or other exotic tools.

What you need:
1) 3D printer capable of handling PLA filament. If you have an expensive one like the Ultimaker that's great, but a cheaper one like the Prusa Anet will do too;
2) You must have enough PLA to print all parts. ABS will not work for this project as it is too soft. You can probably use PETG, but this has not been tested, so do so at your own risk;
3) Tin can of the appropriate size (diameter 100 mm, length 145 mm). The jar should preferably have a removable lid. You can take a regular jar (say, from pineapple pieces), but then you will need to make a metal lid for it;
4) Galvanized iron sheet. A thickness of 0.5 mm is optimal. You can choose a different thickness, but you may have difficulty bending or sanding, so be prepared. In any case, you will need at least a short 0.5 mm thick galvanized iron strip to make the spacer for the turbine shroud. 2 pieces will do. The size is 200 x 30 mm;
5) Sheet of stainless steel for the manufacture of turbine wheel, NGV wheel and turbine casing. Again a thickness of 0.5mm is optimal.
6) Solid steel rod for making the turbine shaft. Beware: mild steel just doesn't work here. You will need at least some carbon steel. Carbide will be even better. The shaft diameter is 6 mm. You can choose a different diameter, but then you will need to find suitable materials for the manufacture of the hub;
7) 2 pcs. 6x22 bearings 626zz;
8) 1/2 "nipples, 150 mm long and two end fittings;
9) drilling machine;
10) Sharpener
11) dremel (or something similar)
12) Hacksaw for metal, pliers, screwdriver, M6 die, scissors, vice, etc .;
13) a piece of copper or stainless steel pipe for fuel atomization;
14) A set of bolts, nuts, clamps, vinyl tubes and more;
15) propane or butane burner

If you want to start the engine, you will also need:

16) Propane tank. There are gasoline or kerosene engines, but getting them to run on these fuels is a little tricky. Better to start with propane and then decide if you want to switch to liquid fuel or are you already happy with gas;
17) Manometer capable of measuring pressure in a few mm of water column.
18) Digital tachometer for measuring the speed of the turbine
19) Starter. To start a jet engine, you can use:
Fan (100 W or more). Better centrifugal)
electric motor (100 watts or more, 15,000 rpm; you can use your dremel here).

Making a hub

The hub will be made from:
1/2 "branch pipe 150 mm long;
two 1/2 "hose fittings;
and two bearings 626zz;
With a hacksaw, cut off the herringbones from the fittings, and use a drill to enlarge the remaining holes. Insert the bearings into the nuts and screw the nuts onto the nipple. The hub is ready.

We make a shaft

Theory (and experience to some extent) says that it makes no difference whether you make a shaft from mild steel, hard steel, or stainless steel. So choose the one that is more accessible to you.

If you expect to get decent thrust from the turbine, a 10mm (or larger) steel rod is better. However, at the time of writing, the shaft was only 6mm.

Cut M6 threads, one side, 35mm long. Next, you need to cut the threads from the other end of the rod in such a way that when the rod is inserted into the hub (the bearings rest against the end of the pipe are tightened with the nuts that you made from the hose connectors) and when the lock nuts are screwed to the end of the thread on both sides, between there is a small gap left in the nuts and bearings. This is a very complicated procedure. If the threads are too short and the longitudinal play is too great, you can cut the threads a little further. But if the thread seems too long (and there is no longitudinal gap at all), it will be impossible to fix it.

As an option, shafts from laser printer, they are exactly 6mm in diameter. Their disadvantage is that their limit is 20-25000 rpm. If you want higher RPM, use thicker rods.

3D printing of turbine wheel and NGV matrices

For the manufacture of the turbine wheel, or rather its blades, press dies are used.
The shape of the blade becomes smoother if the blade is pressed not to the final shape in one step (pass), but to some intermediate shape (1st pass) and only then to the final shape (2nd pass). Therefore, there is STL for both types of press dies. For the 1st pass and for the second.

Here are the STL files for the matrices for the NGV wheel and the STL files for the matrices for the turbine wheel:

Manufacturing of impellers

This design uses 2 kinds of steel wheels. Namely: turbine wheel and NGV wheel. For their manufacture, stainless steel is used. If they were made of lightweight or galvanized material, they would barely be enough to show how the engine works.

You can cut discs from sheet metal and then drill a hole in the center, but most likely you will not hit the center. Therefore, drill a hole in the sheet of metal, and then glue the paper template so that the hole in the metal and the hole in the paper template match up. Cut the metal to a template.

Drill auxiliary holes. (Note that the center holes must already be drilled. Also note that the turbine wheel has only a center hole.)

It is also a good idea to leave some allowance when cutting metal, and then grind the edge of the discs using a drill and sharpener.
At this point, it may be better to make multiple spare disks. It will be clear why later.

Blade formation

The cut discs are difficult to fit into the forming die. Use pliers to turn the blades slightly. Discs with pre-twisted blades are much easier to mold with dies. Clamp the disc between the press halves and squeeze in a vise. If the matrices were pre-lubricated with machine oil, everything will go much easier.

The vise is a fairly weak press, so you will most likely need to hit the knot with a hammer to squeeze it further. Use a few wooden cushions to avoid breaking the plastic matrices.

Two-stage shaping (using 1st pass matrices and 2nd pass matrices to finalize the shape) gives definitely better results.

We make a support

The document file with the template for the support is located here:

Cut the piece out of the stainless steel sheet, drill the required holes and bend the piece as shown in the photos.

We make a set of metal spacers

Use here a sheet of mild (or galvanized) steel with a thickness of 1 mm.

The template documents for the spacers are here:

You will need 2 small discs and 12 large ones. The quantity is given for a sheet of metal with a thickness of 1 mm. If you are using a thinner or thicker one, you will need to adjust the number of discs to get the correct overall thickness.
Cut the discs and drill the holes. Grind discs of the same diameter as described above.

Support washer

Since the support washer holds the entire NGV assembly, you must use a thicker material here. You can use a suitable steel washer or sheet (black) at least 2mm thick.

Support washer template:

Assembling the inside of the NGV

You now have all the parts for assembling the NGV. Install them on the hub as shown in the photos.

The turbine needs some pressure to function properly. And in order to prevent the free spread of hot gases, we need a so-called "turbine jacket". Otherwise, the gases will lose pressure immediately after passing through the NGV. For proper functioning, the casing must match the turbine + small clearance. Since our turbine wheel and NGV wheel have the same diameter, we need something to provide the required clearance. This is something - a turbine casing spacer. It's just a strip of metal that's wrapped around the NGV wheel. The thickness of this sheet determines the size of the gap. Use 0.5mm here.

Just cut a strip 10 mm wide and 214 mm long from any steel sheet with a thickness of 0.5 mm.

The turbine shroud itself will be a piece of metal, the diameter of the NGV wheel. Or a couple is better. Here you have more freedom to choose the thickness. The shroud is not just a strip, as it has attachment ears.

The documentation file with the template for the turbine shroud is located here:

Then remove the wire and screw the turbine shroud onto the spacer. Use wire again to wrap tightly.

Do as shown in the photos. The only connection between NGV and hub is three M3 screws. This limits the heat flow from the hot NGV to the cold hub and prevents the bearings from overheating.

Check if the turbine can rotate freely. If not, align the NGV shroud by repositioning the adjusting nuts on the three M3 screws. Vary the inclination of the NGV until the turbine can rotate freely.

Making a combustion chamber

Stick this template over the metal sheet. Drill holes and cut the shape. There is no need to use stainless steel here. Roll up the cone. To prevent it from unfolding, bend it.
The front of the camera is here:

Use this pattern again to make the cone. Use a chisel to make the wedge slots and then roll into a taper. Secure the cone with a fold. Both parts are held together only by the friction of the engine. Therefore, you do not need to think about how to fix them at this stage.

Working wheel

The impeller consists of two parts:
blade disc and casing

This is a Kurt Schreckling impeller that has been heavily modified by me to be more tolerant of longitudinal displacement. Note the labyrite to prevent air return due to back pressure. Print both pieces and glue the cover onto the paddle disc. Good results can be obtained using acrylic epoxy.

Compressor stator (diffuser)

This detail is very complex in shape. And when other parts can be (at least in theory) made without the use of precision equipment, this is not possible. To make matters worse, this part has the greatest impact on the efficiency of the compressor. This means that whether the entire engine will run or not is highly dependent on the quality and accuracy of the diffuser. That's why don't even try to do it manually. Do it on your printer.

For the convenience of 3D printing, the compressor stator is divided into several parts. Here are the STL files:

3D print and assemble as shown in the photos. Note that a 1/2 "pipe nut must be attached to the center stator housing of the compressor. This is used to hold the sleeve in place. The nut is secured with 3 x M3 screws.
Template where to drill holes in the nut:

Also note the aluminum foil heat-shielding cone. It is used to prevent the PLA parts from softening due to heat radiation from the combustion liner. Any beer can can be used here as a source of aluminum foil.

You will need a tin can with a length of 145 mm and a diameter of 100 mm. It's best if you can use a jar with a lid. Otherwise, you will need to mount the NGV with the hub to the bottom of the tin can and you will have additional problems rebuilding the engine for servicing.

Cut off one bottom of the can. On the other bottom (or better in the lid) cut a 52mm round hole. Then cut its edge into sectors as shown in the photos.

Insert the NGV assembly into the hole. Wrap the sectors with steel wire tightly.

Make a ring of copper tubing (outer diameter 6mm, inner diameter 3.7mm). Or better, you can use stainless steel tubing. The fuel ring should fit snugly against the inside of your tin can. Solder it.
Drill the fuel injectors. This is just 16 pieces of 0.5 mm holes evenly spaced around the ring. The direction of the holes must be perpendicular to the air flow. Those. you need to drill holes on the inside of the ring.

Check the quality of the fuel spray by igniting it. Flames should be equal to each other.

When finished, install the fuel nozzle into the can body.

All you have to do in this step is to put all the pieces together. If things go well, there will be no problem with this.

Cover the lid of the can with heat-resistant sealant, you can use silicate glue with heat-resistant filler. Graphite dust, steel powder and so on can be used.

After the motor is assembled, check if its rotor rotates freely. If so, do a preliminary fire test. Use a fan powerful enough to blow through the air intake, or simply rotate the shaft with your dremel. Turn on the fuel lightly and light the flow at the back of the engine. Adjust the rotation to allow the flame to enter the combustion chamber.

NOTE: at this point you are not trying to start the engine! The sole purpose of a fire test is to heat it up and see if it behaves well or not. At this point, you can use a butane cylinder that is commonly used for hand torches. If everything is ok, you can proceed to the next step. However, it is best to seal the motor with oven sealant (or silicate glue filled with a small amount of heat-resistant powder).

You can start the engine either by blowing air into it or by rotating its shaft with some kind of starter.
Expect to burn a few NGV discs (and possibly turbines) when trying to start. (This is why it was recommended that you make a few backups in step 4.) Once you are comfortable with the engine, you can start it anytime without any problems.

Please note that the engine can be used primarily for educational and entertainment purposes at this time. But this is a fully functional turbojet engine, capable of rotating to any desired speed (including self-destructing). Feel free to improve and modify the design to meet your goals. First of all, you will need a thicker shaft in order to achieve higher rpm and therefore thrust. The second thing to try is wrapping the outside of the engine metal pipe- the fuel line and use it as an evaporator for liquid fuel. This is where the hot outer wall motor design comes in handy. Another thing to think about is the lubrication system. In the simplest case, this can be in the form of a small bottle with a small amount of oil and two pipes - one pipe to relieve pressure from the compressor and direct it to the cylinder, and another pipe to direct oil from the cylinder under pressure and direct it to the rear beam. The engine can only run without lubrication for 1 to 5 minutes, depending on the NGV temperature (the higher the temperature, the shorter the running time). After that, you need to lubricate the bearings yourself. And with the added lubrication system, the engine can run for a long time.