Fighter Trio from drawings of Podešva family
Second Yak-3 in our country
The latest Yak aircraft was brought into the air by Milan Bábovka. The anabasis, as he succeeded in it, is illustrated in his article on the following pages.
First Yak-3 in our country
The first Yak 3 in the Czech sky is also an 82% replica, namely OK SAL-12 of Ladislav Ábel from Trutnov. "I originally wanted Mustang P-51, but the manufacturer did not even respond to me," Mr. Ábel explained how he found himself at the Podešva family, through whom he bought the plans for a scaled-down replica of this famous Russian fighter which he built by himself. The work went quickly and the following year the aircraft was ready. Due to the slightly higher empty weight (460 kg), a trouble occurred in the approval for the operation, which was solved by granting an exemption to this aircraft as a single one in the ELSA category, which was possible due to the sizing of the airframe and the quality of processing. The wing is all-metal and the fuselage consists of a welded truss with a metal coating. The aircraft is powered by a Suzuki Grand Vitara fork type six-cylinder car engine with a belt reducer through which it spins in flight electrically adjustable propeller of constant speed from MT Propeller (originally, on the ground adjustable propeller was used). The landing gear unit retraction (including the spur wheel) is solved pneumatically. It was necessary to manufacture various moulds for the construction (for the cabin, transition and end arches, etc.), which were also used in the construction of Milan Bábovka’s replica described in his article.
Until present Mr. Ábel has flown the aircraft for about 400 hours during which he enjoys its comfortable features, including an almost authentic sound which is due to a six-cylinder engine with its exhausts on both sides. "There exists no such aircraft anywhere. They don't even have a flying Yak 3 in Russia so they called me for the purpose of shooting. But for comprehensible reasons it did not take place", Mr. Ábel told the editorial office. In addition to dozens of flight demonstrations on air days his Yak 3 also appeared in the award-winning Czech film Painted bird.
Messerschmitt Bf 109 UL
The ultralight all-metal replica of the "Mule" comes - as well as the replica of Jak 3 - from the construction board of Petr Podešva, a well-known builder of UL replicas of classic sports aircrafts (e.g. Trenér (Coach), Brigadier, Bücker 131, etc.), but also a very popular Tulák (Rogue) and other types. He designed the replica of "Mule" and he built it to order around 2005/2006, but by fate interference it was sold to Germany where the new owner crashed with it due to an engine failure. The significantly damaged aircraft was then bought by Pavel Kouřil who repaired it, replaced the power unit and made further modifications, mainly on the undercarriage. Since then Mr. Kouřil has been flying with his aircraft in the Czech Republic, where - like both Yaks – his “Mule” goes around the aviation days and makes the fans of war aircrafts happy. We will return to the "Mule" in a separate article.
“Ultralight” Yak – 3
Yak 3 was a top Russian frontline fighter. Its origin is dated in the early 1940s when by gradual modernization, lightening and downsizing of the previous version of Yak 1 the designers of Yakovlev design office created an aircraft well suiting to the method of warfare on the Eastern Front – i.e. fighting mostly above the front at altitudes up to 4000 meters. It did not need a long range, it was very small and had an excellent weight to power ratio of the power unit used (Klimov VK 105 PF-2 engine had 1290 hp and the empty weight of the aircraft was 2105 kg). Its prototype took off in February 1943 and was deployed to combat in the summer of that year. According to the data in the book from the Soviet pilot A. Pokryškin, however, the first serial Yak 3 was not received by the front regiments sooner than in summer of 1944. Tests of the Yak 3 were carried out under combat conditions at 91st IAP of 2nd Air Force, under the command of Lt. Col. Kovalev from June to July 1944. During 431 combat flights 20 Luftwaffe fighters and three Junkers Ju 87s were shot down, while Soviet losses amounted to two shot down Yaks. On June 16, 1944, a great combat took place when 18 Yaks clashed with 24 German aircrafts. Soviet fighters shot down 15 German planes while the loss on the side of the Yaks was one destroyed and one damaged Yak. The next day Luftwaffe's activities over this part of the front practically ceased. A month later, on July 17, 1944 eight Yaks attacked a formation of sixty German aircrafts, including escort fighters. In the following battle the Luftwaffe lost three Ju 87 and four Bf 109G without any loss on the Russian side. At that time the Luftwaffe issued an order to "avoid fighting under five thousand meters with the Yaks without an oil radiator under their nose"…
Naturally, Yak 3 had its problems. These included, in part, plywood coating which was torn off when turning a fast dive flight, as well as a short flight range, and low engine reliability. The ailments also included a pneumatic system for controlling the retraction of the landing gear, flaps and brakes, which, however, was preferred for all fighter types of Yakovlev's design at that time due to weight savings also at the cost of greater failure rates.
Despite the aforementioned ailments, however, in the hands of Soviet pilots on the Eastern Front, Yak 3 caused the Nazis a lot of worries and damage. And not just the Soviet pilots as, in addition to the Soviets, the Yaks were also used by the French and later on by the Poles and Yugoslavs. It is worth reading, for example, the assessment of the German test pilot H. W. Lerch who, in addition to German aircrafts, performed also test flights on captured enemy aircrafts. In the book "On Foreign Wings" he states about Yak 3 that due to the small weight of the aircraft with its aerodynamic cleanliness and engine power an excellent climb can be expected, as well as better properties when manoeuvring at low altitudes compared to the Bf 109 and Fw 190. He also praised that flying this aircraft was a very pleasant flight…
No wonder then that Yak 3 found its place among the fans of World War II fighters, and since the 1990s there have been even produced (in Russia according to the original documentation) several "new" pieces for those more affluent, but with American engines.
The admirers of Yak 3 can also be found in the Czech Republic. However, with the difference that instead of astronomical sums for the acquisition of such an aircraft, they dispose of more skilfulness and technical and organizational skills. A few years ago Ladislav Ábel from Trutnov built a scaled-down replica of this famous fighter (designed by Petr Podešva in the ELSA category). Last year there was added to his replica another equally large ultralight replica built by Ing. Milan Bábovka residing in Liberec.
Milan is not unknown to our readers - his company Galaxy GRS manufactures rescue systems which are used by a large part of pilots in their UL aircrafts (to date over 100 pilots have been rescued on them). He was a skilled modeller, he started with hang gliders which he then built (both for free and motorized flying); he also made paragliders. He also built a Cora UL aircraft under amateur conditions. Since the time he is engaged in the production of rescue systems, he has been flying mainly with the UL aircraft KP 2 Sova (Owl) which he built from the kit. The following article illustrates how he built a replica of Yak 3 in his old days.
Ing. V. Chvála
I first saw the replica of Yak 3 in Trutnov in 2016. There Láďa Ábel demonstrated his 82% miniature with a two-and-a-half-litre Suzuki engine and a Volner-on the ground adjustable propeller. From a larger distance the aircraft was simply almost indistinguishable from the original because as a matter of fact the actual Yak 3 was very small compared to Spitfire or Mustang, just an interceptor to defend the front.
So I arrived at the decision to build such a fighter as well. I bought the plans from Petr Podešva having in mind that the AMC workshop of Míra Drahoš would manufacture the landing gear and fuselage weldment with an oxy-acetylene welder, and Ruda Starý from Mělník the wings as in the case of the construction of Láďa Ábel’s Yak. The rest will be the matter of our company Galaxy GRS, s. r. o., i.e. my person and Martin Dorotka, our young designer. At that time we were still living in the foolish hope that the work would be finished within a year…
The first spanner thrown in our works was when Míra Drahoš informed us that due to the onslaught of work on his company a welded fuselage could be manufactured not sooner than in a year, and that he would be happy if he could only make the landing gear for us.
So we started creating the work by ourselves and here a field of new ideas has developed how to improve the existing structure and the airframe and to transform the whole building into our own image. I didn't like how the engine of Láďa’s Yak was turning off by a speed limiter at a high speed in the course of the raid, and so I had a discussion with Láďa on how to prevent this and the idea was born: We would order two adjustable propellers from MT Propeller from Germany and I would build the same Yak, but with the Rotax 915 iS engine which was just a novelty on offer. At full power of 141 horsepower this engine is 50 kg lighter than Láďa's engine.
Yak is not like Yak, or one change after another…
Our assignment, which we set compared to the first flying replica, was demanding both on the calculations of the structure itself and on the manufacture. In contrast to Láďa's replica (even to the original which had an undivided wing) we decided to divide the wings on the outer parts of the wing outside the landing gear. Partly, since it was not clear where the aircraft would be assembled. And also due to possible emergency landing in the terrain when divided wings facilitate the transport of the aircraft if it is not possible to take off again. Láďa has the advantage that the workshop of Míra Drahoš in which the replica was made is situated directly below the airport, while our conditions were completely different.
Next, we had to lay out the position of all components relative to the centre of gravity of the aircraft. Because the selected engine was lighter by 50 kg, we had to extend the engine bed by 64 mm to maintain the centre of gravity. The remaining equipment as well, such as a rescue parachute system, pressure cylinders for closing the landing gear with a compressor and battery, hot water cockpit heating and two oil radiators, we therefore had to place as far forward as possible so as not to disturb the original beautiful line of the bow of the aircraft.
There is also "armament" located in the aircraft bow. We originally considered installing a loudspeaker system weighing about 8 kg (this was removed after testing in flight for a small effect). Instead, we mounted a Humbuk machine gun from Mr. Pick's company with 60 pieces of blind ammunition type Kraken under the turbo compressor (similarly to the arrangement of a 37 mm cannon which I saw on the Yak prototype in the Technical Museum in Moscow) On the back of the bow there is another pair of "machine guns" with LED lamps with which the effect of shooting is perfect in all respects. The black propeller of MT Propeller with a relatively large diameter of 2.05 m also contributes to this.
We decided to make the bow of the aircraft of glass laminate on the basis of 3D data created by us according to the shapes of the original aircraft. The radiator cover under the fuselage and all wing and rudder end archers are made in the same way.
Another important decision was to preserve the original concept of removable covers on the side of the fuselage for easy access to all parts of the equipment. This opened up the possibility of installing the components and final assembly in a different place from that where the wing was riveted and the fuselage coated: The construction of the wing, fuselage coating and tail surfaces were manufactured at Ruda Starý in Mělník where we commuted and coordinated the manufacture. Thanks to his workshop equipped with an American technology and his experience from Aero Vodochody, where he served his time of apprenticeship and worked, we were able to fulfil our ideas of what a new fighter should look like. He and his team also deserve our praise, as well as all my friends who have helped us put Yak in flight condition.
Painting and transport of the largest parts from Mělník was provided by the friendly company of Honza Perner from Český Dub who has a modern metal production near to our airport. There the entire aircraft was painted and the phenomenal pro “sprayer” Luděk Třešňák saved another 5.6 kg of the weight on the paint.
In the end we decided to carry out the final assembly at the airport in Český Dub where the individual components were imported.
All chrome-molybdenum tubes for the fuselage truss were computer designed with the help of Jihlavan design office and laser cut, including the design of the engine bed for which a new jig had to be made. The engine axis is tilted 2.5 ° to the right and 1.5 ° downwards. Then, Pepa Heřman welded the parts with millimetre precision by means of el. arch in the argon protective atmosphere in his prototype and production workshop in Benešov.
During the designing we took into account that the original construction of the replica made of metal, canvas and wood would be changed to an all-metal construction and its modifications would be made for a higher designed speed.
This "hard nut to crack" was helped by friendly companies and our "friends at arms". I would also like to thank to Ing. Mirek Kábrt and Peter Kábrt, Ing. Marek Ivanov, Ing. Martin Kotačka, Dr. Popel and his team at the Faculty of Mechanical Engineering - Aviation Institute of VUT Brno, but mainly to Ing. Radek Filip, the director of Jihlavan, and his team of great designers who helped us solve the preparation for the truss structure of the fuselage and engine bed. At the same time we are obliged to them for significant help after the accident in autumn last year when they helped us repair the aircraft in a relatively short time to serviceable condition, including the manufacture of the right third of the wing. I must also commend Ing. Václav Chvála and Ing. Petr Chvojka from the Amateur Aviation Association of the Czech Republic (LAA CR) for a great and helpful approach to the entire construction of our new prototype.
The frame of the cockpit cover was redesigned so that it could withstand the impact when the aircraft flips to avoid pilot’s injury. The 10 mm diameter tubes were replaced by 16 and 18 mm tubes and the entire cockpit weldment structure was reinforced.
Dividing the wing and cockpit reinforcement required a new calculation and a new design of the wing in the parts on both sides behind the landing gear. Two ribs made of duralumin sheet with the thickness of 0.8 mm were added to each joint, new H-fittings made of duralumin with the thickness of 0.10 mm that were attached to the web, and in the place of screws the flange was reinforced. The connection of the main beam is provided by 8 high-strength M12 screws, four on each side at the top and bottom, and the same on the other side of the wing. The auxiliary beam is fastened by eight M6 screws on each side and duralumin fittings with the thickness of 10 mm on the "H" web. We had to save the weight of the joints elsewhere, so the whole instrument panel was equipped with round instruments of the original design, but in a digital execution from the company Kanardia. This saved about 9 to 10 kg, which is the weight of the split wing fittings and added ribs, but at the same time it cost a lot of extra money.
The ailerons are materially balanced, but not as with the original (with the weight in front of the hinge in the middle of the leading edge inside the aileron), but with the weight on the lever, similar to the Bf 109, which saved 2.5 kg.
The elevator is balanced in the same way as the original with the weight on the lever in the keel of the rudder. It was also not easy to make all the trailing edges of the ailerons, rudder and elevator - compared to the replica of Láďa Ábel - of duralumin.
The landing gear retraction is done pneumatically and controlled by a lever with a lock releasing device from the Sova (Owl) aircraft. The two air reservoirs of the pneumatic system are filled by the compressor and automatically replenished when the pressure drops below the specified minimum pressure which is maintained in the range of 10 - 11 bar.
When retracting and lowering the landing gear, the sensor on its control lever releases the air pressure from the air reservoirs through the solenoid valve into the pressure cylinders which move the system of the undercarriage drawbars.
Position inductive sensors are installed in the landing gear system of which one sensor controls the position of flaps signalling their lowering before the landing gear is lowered, and 4 sensors for lowering the wheels. Two of them signal (in green) the lowering of landing gear and two signal the compression of landing gear shock absorber (in red). The red warning lights must not be on before the landing gear retraction as the wheel would not fit into the landing gear shaft when the shock absorber is compressed.
The emergency opening of the landing gear takes place mechanically - by unlocking the locks of the undercarriage legs and by means of the emergency air release lever from the main manifold. The system is equipped with a safety valve and a central cock to release the air. The wheels of the landing gear fall out under their own weight ensuring the gas shock absorber locking.
The wiring of complete electrical installation and the installation of Rotax 915iS engine with a turbocharger with two independent injection units controlled by a computer is so complicated that the professional aviation electrician David Novák took a total of about six week-ends to finish it.
The Rotax 915iS engine works with a lean fuel mixture and is therefore difficult to cool. It did forgive us nothing in this respect, so we had to install a second, auxiliary liquid radiator behind and above the existing one, and place it in the fuselage with a firmly set flap at the top of the air inlet where the air enters an additional radiator through a bypass with a diameter of 100 mm which is located in the vacuum part of the cooling cover and it is fitted with a dovetail for a better cooling air discharge. The engine main radiator cover flap is tilting and this was confirmed as a necessary detail during testing the aircraft at temperatures around 31 - 33 ° C. The advantage is that all motor telemetry can be downloaded immediately using a PC and you can quickly react to the current data from the operation. This helped us a lot in monitoring and comparing individual flight modes and their influence on the course of temperature. Thanks to Mr. Ing. Šámal and the development team in Rotax, Austria, we were able to put this complex engine into operation condition after four months.
The air flow to the intercooler is ensured by a deflector on the upper side of the bonnet, thus cooling the air coming from the turbocharger to the cylinders. The air supply to the turbocharger is through the inlet in the root of the wing from where it is led through the intercooler to the air-box by means of a hose with a diameter of 100 mm.
Oil cooling is partially controlled by manual closing the flap on the radiator from the breaths in the wing roots for one radiator and the other is fully open and blown through the NACA inlet under the engine. For oil system it was necessary to increase the diameter of the oil line pipes. Engine fluid cooling is regulated automatically by a thermostat and a manually operated air outlet flap from the main radiator under the fuselage of the aircraft. Ing. Petr Lonský’s and Tonda Brůna’s experience was of great assistance to us to properly install the second smaller fluid radiator under the aircraft fuselage. We installed it with the help of Tomáš Souček who made the transition parts for the auxiliary radiator. We also appreciate the approach and experience of Leon Likovský who tuned the aircraft and advised us with various details so we could put the aircraft into operation without the risk of overheating or seizing the engine.
The construction of Yak took 2.5 years and with the repair (after leaving the taxiway and closing one leg of the landing gear) for 3 years, and it was not easy to deal with such a challenge and the new parameters set in this way. For example, the landing gear closing system had to be modified several times because the limited space did not allow the landing gear shaft door to be locked when it was opened. But even that worked in the end.
I will also mention other equipment. The landing gear is equipped with Beringer hydraulic disc brakes with a differentiated control by the toes on the pedals (for controlling the rudder by means of cables). On the control stick (which controls the ailerons and the elevator by means of drawbars) there is also located an electric longitudinal balance control. Three-bladed propeller of constant speed from MT Propeller has a hydraulic regulator operated by a lever next to the throttle, identically as with the original. In addition to the basic instrument equipment (Kanardia brand) and the associated engine instrument, the g-meter is also installed. Of course, there is a radio station (KRT brand), but there is also a transponder and GPS navigation located on the bracket. In front part of the cockpit there is a hot water heater with an electric fan. The Galaxy GRS rescue system 6/600 SD Speedy FF which works up to the speed of 370 km/hour is located just behind the engine bulkhead.
Finally in the air…
The first flight was carried out at our one-way airport in Český Dub by Leon Likovský who has already flown 1000 hours on "spur" types Z-226 to Z-526. Láďa Abel arranged for him as he also made the first flight with his Yak. He was taxiing around the airport for a while and then he started uphill "on full blast". Uphill by the road we put the fence away and adjusted the terrain across the road. This stretched the airport by another 70 m, for a total of 450 m. He raised the plane 10-20 cm above the ground, crossed the road and said: "It's good, it will fly”, he turned on the extended section of the runway behind the road and took off normally. When he landed, he said, "Don't do anything about it, it's all as it should be." And so except for dealing with the temperature of water and oil and other things around the installation, the control and airframe of the aircraft have not been touched to this day.
Gradual debugging of "trifles" continues to this day. At first, their list was as long as a buying memo list for the Globus shopping centre, but it has already diminished and now it is like a tram ticket.
Up to the saddle!
During my life I have commissioned a lot of paragliders and hang gliders designed by me and manufactured by my company, including motorized hang gliders. I have always treated every flight, no matter what machine it was, with a great respect. I would never get into the machine if I didn't trust it. I trusted the machine, so I had to mentally prepare myself. I have flown hundreds of hours with ultralights, most in the recent years with the Owl which has a retractable landing gear and an adjustable propeller. And because besides the basic training with Coyote in Mladá Boleslav all it was with the bow undercarriage until now, I needed to train and experience the coordination of the spur landing gear in combination with a powerful engine. I had an offer and a recommendation to fly a few hours in two on the Z-226 which resembles Yak in inertia and properties, but the propeller turns anti-clockwise (to the left), which is just in opposite as it is on my Yak, which I didn't want to get used to. Another option was a simulator called IL–2 Sturmovik that I have next to my desk, including pedals and a joystick on a pedestal at the level of a real control stick. On this simulator Yak 3 caught my eye; however, Sturmovik had the same problem - a propeller turning anti-clockwise. So I reached for the Messerschitt Bf-109 on which the propeller rotates in the "right" direction, and I was training. The first take-offs were catastrophic, but later I started to succeed and I was able to take off and land with the Bf 109E. Even with shooting at enemies I spent about 230 hours on it within those three years. I dared to carry out the first take-offs with my Yak 3 - after Leon's proper instruction - on a large runway in Hradčany airport near Mimoň.
The replica is easier to take off, but worse to land than the computer simulated Bf 109. I soon found out this at the airport in Hradčany where I pierced the tire on the spur in the crosswind. Under Leon's supervision I flew the entire retraining according to the syllabus on the large concrete runway there. Leon examined me and then he assisted me remotely via radio. To Hradčany airport Leon always flew with Yak and I flew after him with the Owl. He turned the Owl into a control tower from which he controlled and directed me. Only after seven take-offs and landings in Hradčany we did go flying to Český Dub…
How is it to fly Yak
Now I have 49 hours of flying with Yak and 109 take-offs and landings. I have a lot of respect for this aircraft - it's a real fighter in its appearance and features. The speed is not so crucial, but the amazing dexterity of Yak is fascinating. One must always be alert when manoeuvring, especially before getting used to the deflections and effects of tilting ailerons. Horizontally Yak flies by itself, like a cruise liner.
Flying Yak is like flying a good plane if one knows what one must not neglect and to behave accordingly. It holds its direction perfectly, but it is sensitive to any movements of the control stick and pedals. Yak is reliable, not insidious. When the speed goes below 90 km/hour, it is warning me, so that the sheets on the fuselage are rattling - great sound!
It is taking off from the ground at the speed of 85 - 90 km/hour and thanks to a well-designed engine bed no great force is needed to exercise on the right pedal (half compared to my Owl which is equipped with a 100k Rotax 912). After take-off it is necessary to retract the landing gear before reaching 120 km/hour, which must be practiced because with full thrust (at 5760 rpm) the aircraft climbs 8 - 9 m/s and quickly increases the speed to 135 - 140 km/hour even when climbing. After practicing I manage to quickly retract the landing gear just after the take-off before the speed ramps up to the full climb speed. As soon as the red lights go out that indicate the correct length of the unloaded landing gear, it can be retracted immediately.
Large flaps can also be extended only below the speed of 120 km/hour and this is a bit of a complication on the circuit because at a normal circuit speed of 140 km/hour the aircraft must slow down, better with the thrust, below 120 km/hour and you need to change the grip of the right hand from the control stick to the flap lever and put your left hand on the control stick and after extending the flaps back again, and by adding the thrust and suppressing the speed to increase the speed again to 130 - 140 km/hour. Without thrust the drop is 5.5 m/s. Therefore a great care must be taken to a rapid loss of height which does not decrease so quickly with other ultralights. So keeping the aircraft to the right point in front of the RWY approx. 50 m in the fore-field in Český Dub airport and the correct approach speed is accurate work with the thrust and it must be practiced. Available for landing is 370 m slightly sloping (5%) and it is not possible to land in the downwind blowing more than 4 m/s. Then you must wait at another airport until the wind weakens.
Let me remind you that the beautiful blue "Baltic" colour of the aircraft represents the appearance of Yak 3 of General Grigory Zacharov, commander of the 303rd Air Division which consisted of 5 regiments that were equipped with these machines. Before Zacharov, as a valuable war expert, was "withdrawn" from the active air service, he achieved 27 shot downs…
Small comparison at the end
The original Yak 3 had at that time, perhaps, the most advantageous weight to engine power ratio, i.e. 2.08 kg/hp. This ratio for a replica with the quarter take-off weight and the engine with one-ninth of the original Yak’s engine power comes out to be double: 4.4. Interestingly, the ultralight Yak performances are about half of those of the original (for example, the climb was measured from 8 to 9 m/s up to 3000 m). But the effect is, at least according to the responses of spectators on all flight demonstrations, one hundred percent. And that's what this is about!