Experimental turboprop fighter-bomber Republic XF-84H
The Republic XF-84H is an experimental turboprop fighter-bomber that was created in the USA in the first half of the 1950-s. The aircraft was designed by the Republic Aviation Corporation. In total, two experimental aircraft of this type were built. The first flight took place on July 22 1955. When creating the aircraft, the aerodynamic concept and some elements of the design of the mass-produced Republic F-84F Thunderstreak were used.
The Republic XF-84H was the fastest single-engine propeller aircraft in the world, but it remained only an experimental design. In addition to the high speed of the flight, which, however, did not become supersonic, the plane was distinguished by another feature - it was extremely loud in the literal sense of the word. The noise created by the plane taking off had a strong negative impact on the human body, it was difficult to be close to the plane even in special noise-protection headphones.
This is a marvel of engineering that went into history also not the most common look, was created by Republic Aviation Corporation, founded in 1931 year. The company's headquarters was located in Farmingdale, Long Island, New York. The company was originally called the Seversky Aircraft Company. It was opened by an emigrant from Russia, the famous pilot Alexander Nikolaevich Prokofiev-Seversky. From Russia, he was forced to emigrate in 1918. In 1939, the company was reorganized, called the Republic Aviation Corporation. At the same time, many Russian and Georgian émigrés traditionally worked there, including the leading designer Alexander Mikhailovich Kartveli. The company's most famous aircraft were the P-47 Thunderbolt, the F-84 Thunderjet and the F-105 Thunderchief, which were created by Kartwell. As it is easy to see, the word thunder - “thunder” was present in the name of the company's airplanes. Republic Aviation's experimental XF-84H aircraft would be the best word in the world.
In 1965, Republic Aviation Corporation was finally absorbed by another American company, Fairchild Aircraft. But the tradition with the name of the aircraft remained the same and continues to live today. It is reflected in the famous attack aircraft Fairchild Republic A-10 Thunderbolt II.
But back to the beginning of the 1950 of the last century, when most of the combat aircraft of the US Air Force was already reactive. It is worth noting that the turbojet engines of the mid-XX century already provided the aircraft with a fairly decent maximum speed and altitude, but they were obviously not economical. The turbojet engines of those years had a very large specific fuel consumption, so combat jets could not boast of a long range. At the same time, the tactical and technical requirements of the US military for new combat aircraft only increased.
The existing problem could be solved in two main ways - using PTB - outboard fuel tanks or refueling aircraft in the air. At the same time, refueling in the sky was suitable only for strategic bombers, while for tactical aviation such refueling was usually used only for ferry flights and then on a very limited scale. PTB really allowed to reduce the severity of the problem, for example, for fighter interceptors. But such a solution was not suitable for fighter-bombers, since the outboard fuel tanks occupied a place on the external suspension nodes, reducing the combat load, and hence the combat capabilities of the aircraft.
At the same time, aircraft equipped with piston engines dominated US naval aviation. The only aircraft with jet engines here were fighters. Deck attack planes and coast-based patrol vehicles were equipped with piston power plants, since the range and duration of flight were of key importance for aircraft operating over the sea. For carrier-based aviation a very important criterion was the lower landing speed of the screw aircraft in comparison with the jet ones.
In these realities in the United States, in an effort to increase the combat radius and combat load of aviation, the Navy and Air Force jointly initiated work on the development of a new turboprop fighter-bomber. In total, it was planned to build 4 prototypes: 3 for the Air Force and one for fleet. Turboprop engines (TVD) were not chosen by chance. They had lower fuel consumption compared with the turbojet engines available at that time and at the same time developed more power than ordinary piston engines. The Air Force considered the theater of operations ideal for fighter-bombers, for which high flight speed was not the determining quality of their effectiveness. Much more important was the flight range and its duration, and therefore the possible time spent on the target.
At that time, the most promising was the Allison XT40 engine, which developed power on the order of 6000 HP. It was this engine that was planned to be installed on the most promising naval aviation aircraft: deck attack aircraft, flying boat patrols, vertical take-off and landing aircraft. Interest in this engine showed in the Air Force.
The development of the aircraft, which would satisfy all customers, took the company Republic Aviation Corporation. The design team of the company was headed by Joseph Freeman. Initially, the aircraft received the designation AP-46. The project of the new aircraft was presented to the customer and received approval in May 1952. However, by this time, the US Navy lost interest in the project. This happened after the American aircraft carriers received powerful steam catapults, and also began the introduction of the corner take-off decks. This made it possible to operate heavier jet aircraft from aircraft carriers. The order for the new experimental aircraft was cut to two copies. The contract for their construction was concluded on December 15 of the year 1952. For the new model, Republic Aviation had reserved the designation XF-106, but it was decided to change it to XF-84H. Replacement was necessary, as it was much easier to obtain financing for the modernization of an existing machine than for a new model of the aircraft. In total, we managed to assemble two prototypes that received the 51-17059 and 51-17060 serial numbers. The new fighter-bomber was supposed to combine the speed of a jet with the efficiency and range of a turboprop aircraft.
The XF-84H was a single free-carrying monoplane with a swept-shaped forward wing. At the same time, the wing, landing gear, and cockpit were taken unchanged from the Republic F-84F Thunderstreak serial fighter-bomber. The wing was equipped with slotted flaps, aileron and slats. In the root part of the engine air inlets were located. The fuselage had to be re-designed, it was noticeably longer than the fuselage of the production aircraft F-84F. Immediately behind the cockpit was a triangular aerodynamic crest.
The experimental aircraft engine was located in the rear fuselage. Therefore, the rotating moment was transmitted to the propeller located in the front part by means of a shaft with a length of 6 meters. This shaft passed directly under the cockpit. Additional thrust was created by jet from the theater. An interesting feature of the selected theater was the presence of an afterburner. It was the only propeller aircraft in the world equipped with such a device, which, however, was not used in any of the flights.
The propeller had a diameter of 3,66 meters, while the width of its blades reached 1 / 3 from their length. The speed of their rotation was such that the tips of the blades exceeded the speed of sound, reaching the speed of M = 1,18. Most likely, the Allison XT40 was the world's first engine with a supersonic propeller.
The keel of the experimental aircraft XF-84H was higher and had a slightly different shape compared to the production model. The full turning stabilizer was placed in the upper part of the keel, since here it did not fall into the airflow zone from the working screw. The landing gear was a three-point, with a front desk.
The first flight of an experimental aircraft XF-84H made 22 July 1955, the machine was lifted into the air by test pilot of Republic Aviation Company Henry J. Beard. The takeoff was from Edwards Air Base. As part of a short test program, the entire 12 flight was performed. However, only one of them was recognized as completely successful, while the remaining 11 ended in an emergency landing. On the first prototype of an experimental fighter-bomber, 8 flights were made (including the only successful one), on the second - 4 flights.
Aircraft caused a large number of complaints, their pursuers various technical problems associated mainly with the propeller assembly. So very often the system failed to change the pitch of the propeller, which made the flight very difficult or impossible. A very strong vibration of a six-meter shaft, which went from the engine to the screw, was recorded. Another problem was a very strong noise. The propeller's rotational speed was so high that the tips of the blades overcame the speed of sound, and this created a noise that could be heard over 35 kilometers. And the HT40 turboprop engine itself, according to Allison engineers, was just a mechanic's nightmare. Suffice it to say that it took about 30 minutes to carry out all the necessary pre-launch procedures, including checking electrical and hydraulic systems, as well as warming up the engine.
But still, the brightest of the aircraft’s drawbacks was the incredible noise produced by its propeller-driven installation, primarily with screws. It was impossible to be close to the aircraft even in antinoise headphones. The aerodrome staff even at a distance of hundreds of meters from the plane could feel unwell, dizzy, there were cases of fainting and even an epileptic episode. One of the pilots of the company Republic Aviation flatly refused to fly on this machine, having made only one flight.
There is a high probability that the experimental aircraft XF-84H was the noisiest in history. According to some reports, in flight, he gave out whole 135 dB, despite the fact that the noise level above 120 dB is already considered dangerous for humans. The plane was nicknamed “screaming thunder”, and mechanics, who fully felt its acoustic impact on themselves, sarcastically pointed out that even if it did not overcome the sound barrier, it certainly overcame “noise”. It should be noted that the estimated speed of the experimental aircraft should have been 1080 km / h, but in practice it was possible to develop the maximum speed in 837 km / h, which in itself was a fairly good indicator.
Three months had not passed since the first flight until the program was closed, work on the experimental XF-84H aircraft was completely stopped on October 9 of the 1956 year. After the program was closed, the prototype with the number 51-17060 went for scrapping, and the aircraft with the number 51-17059 remained to this day. In 1999, this aircraft was transferred to the National Museum of the United States Air Force, located at Wright-Patterson Air Force Base in Ohio, where it can be seen today.
Flight performance XF-84H:
Overall dimensions: length - 15,69 m, height - 4,69 m, wing span - 10,21 m, wing area - 30,75 m2.
Empty weight - 7888 kg.
Normal take-off weight - 10 433 kg.
Maximum take-off weight - 13 432 kg.
Powerplant - Allison XT-40-A-1 HDD 6000 HP
The maximum flight speed is 837 km / h.
Practical range - 1650 km.
Practical ceiling - 10 700 m.
Crew - 1 man.
Information sources:
http://www.airwar.ru/enc/xplane/xf84h.html
http://aviadejavu.ru/Site/Crafts/Craft30789.htm
http://alternathistory.com/repablik-xf-84h-vopyashchii-grom-ssha-1952-g
http://ru.rfwiki.org/wiki/Republic_Aviation
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