Last time we looked at the projects of disc-shaped aircraft created in Nazi Germany. None of them reached a more or less refined state. The most successful design, the AS-6 aircraft, managed to enter flight tests and even made an attempt to take off. Nevertheless, all this was achieved at the cost of several accidents. As a result, Germany, having invested a lot of money, never received a single aircraft with a non-standard round shape. A few years before the Germans, similar projects were started by American engineers. And for various reasons, the "discs" from the United States turned out to be much more successful than the German ones, although they also did not go into mass production.
"Pancakes" by Zimmermann
Of all American engineers, Charles Zimmerman achieved the first success in the field of disc-shaped aircraft. It should be noted that the idea to make the wing round in plan existed before. Only the previous ideas remained at the stages of ideas or preliminary sketches of the appearance of the aircraft. In 1933, Zimmerman got a job at Chance Vought and was able to begin research on ultra-low aspect ratio wings. The purpose of his work was to study the properties of a wing with an aspect ratio of about unity, as well as various forms of the leading and trailing edges of the wing. Over the course of several years, Zimmermann tested various aerodynamic configurations until he came to the conclusion that the bearing surface, which had a round shape, was good.
Vought V-173 "Flying Pancake"
Studies have shown that a disc-shaped wing, despite the relatively high air resistance, has very good lift. In addition, it was found on test models that it was possible to improve the aerodynamic characteristics of an aircraft with such a wing only by the correct arrangement of engines and propellers. To do this, the latter should be placed so that the flow created by them washes the upper and lower surfaces of the wing. By 1939, Zimmermann's project had reached the stage where it was possible to stop experimenting on models and start designing a full-fledged aircraft.
The aircraft with the index V-173 and the unofficial name Flying Pancake ("Flying Pancake") has incorporated all the new ideas of Zimmermann. The main unit of the structure was a wing-hull, close in shape to a circle. In this case, the wing profile was symmetrical. Two propellers of the aircraft were carried forward of the wing and each had a diameter of more than five meters. Thanks to this, as well as the specially selected rotational speed of the propellers, the lift of the wing was several times higher than that of aircraft with a straight wing of the same span. In addition, the propellers rotated so that the vortices coming off the blades swirled in the direction opposite to the motion of the wake vortices at the ends of the wing. This design feature increased the effective bearing plane extension from one to four. At the same time, no changes in the size of the aircraft were required.
Inside the wing hull were placed two Continental A80 piston engines with only 80 horsepower each. Each of them was connected to its own propeller and synchronized with the other motor through an additional shaft. It is worth noting that in order to ensure effective flow around the wing, a separate gearbox had to be introduced into the synchronization mechanism: one motor rotated its propeller clockwise, and the other counterclockwise. Nevertheless, even with such a complex and unusual power plant, the V-173 weighed no more than 1400 kg. In the center of the front part of the wing-hull, a cockpit with a drop-shaped canopy was placed. For the convenience of the pilot, the underside of the front wing was made of glass. The fact is that when this part of the plane was sealed with a canvas or plywood, the pilot could not normally look forward and down, which could have an extremely deplorable effect on the landing of the aircraft. Landing and takeoff were planned to be carried out in the traditional way, using the runway. The V-173 was equipped with a simple strut-braced non-retractable landing gear. For a purely experimental aircraft, this was considered sufficient. The flight control was to be carried out using two keels with rudders and two stabilizers with rudders, called "elevators". As conceived by Zimmermann, they simultaneously played the role of both ailerons and elevators. A little later, such a governing body will be called the term "Elevon".
By the beginning of the assembly of the prototype, the US Navy Bureau of Aeronautics became interested in the project. Soon after that, they changed their interest to close attention and demanded that the V-173 be further developed taking into account the possible operation on aircraft carriers. However, the appearance of the machine was so unusual that the naval authorities first demanded that the full-scale model of the "Pancake" be blown in a wind tunnel. It got to the point that one of the admirals asked a question like "can this thing fly?" On September 15, 1941, the experiments in the wind tunnel were completed and no one from the high authorities any longer doubted the potential of the new aircraft. The day after the end of the tests of the full-scale model, the Navy offered Chance Vought a contract to develop a full-fledged carrier-based fighter.
During the purging, several design flaws were identified, which were soon corrected. In the summer of 42, an experienced V-173 went for testing. At first, test pilots were limited only to taxiing and jogging. The first flight of the aircraft took place only on November 23. At the same time, already in the first flights "Flying Pancake" showed excellent characteristics and fully confirmed the correctness of its designer. For example, the takeoff speed during takeoff did not exceed 45-50 km / h, and two engines only 80 hp each. accelerated it to 240 kilometers per hour. For such a weak power plant, this was more than good. Not without accidents. At the beginning of 1943, both engines were switched off on the prototype aircraft during the flight. The pilot had to glide to the nearest beach and make an emergency landing. Due to the insufficient strength of the sandy "coating" the aircraft turned over through the nose and damaged the propellers. However, the repair took only a few days.
By the time the prototype V-173 was rebuilt, Zimmerman, in collaboration with the Chance Vout designers under the direction of Y. Greenwood, had completed the development of a new version of the Flying Pancake. This time, the design was intended for military use. Only the military, let's face it, did not show much interest in the original aircraft. Yes, takeoff and landing performance looked promising, but the need to restructure production, introduce new technologies, etc. clearly did not add optimism. Therefore, the layout of the new aircraft with the XF5U index was adopted only in July 1943, and the contract for the construction of two prototypes was signed a year later. The new fighter received the nickname Skimmer - "Skimmer".
The general design of the XF5U was similar to the V-173. However, unlike the wooden structure of the older aircraft, it was proposed to make the new one from metal. This material was a composite of balsa parts covered with aluminum sheet. Metalite had good strength values and was very lightweight. In addition, there was the possibility of manufacturing metal parts by stamping, which promised to significantly reduce the cost of production. The XF5U is larger than its predecessor, which, however, has no effect on load capacity. The control system as a whole remained the same, but the cockpit was significantly altered. Thanks to a new, strong metalite frame, the cockpit was moved upward, which also made it possible to remove the window on the underside of the front of the wing. Six Browning M2 12.7 mm machine guns were placed on the sides of the cockpit. On the sides of the pilot's workplace there were two installations of three machine guns. For the mid-40s, such weapons were considered sufficient, but in the future it was planned to replace machine guns with 20-mm cannons. In addition to barrel armament, the aircraft could carry unguided missiles, bombs, etc. For them, there were six pylons under the middle part of the aircraft.
Separately, it is worth talking about the new power plant XF5U. A full-fledged carrier-based fighter was to be equipped with Pratt & Whitney R2000-7 piston engines with a capacity of 1350 hp. Together with the new motors, the updated "Pancake" received new propellers. For the XF5U, Hamilton Standard has developed an original blade propeller shape. Compared to the old ones, they were more efficient at low and medium speeds. In addition, the new four-blade propellers have been optimized for relatively low RPM performance. The total power of the power plant exceeded two and a half thousand horsepower. Combined with efficient propellers and a maximum take-off weight of 7600 kg, this even made it possible to take off vertically. Only for this it was necessary to install the plane on a special ramp.
In mid-June 1945, the first prototype of the Shumovka was ready. The novelty of the design and even of its very concept for a long time prevented the start of testing. The leadership of the US Navy every now and then issued new bans on flights. Because of this, the first taxiing was possible only at the end of the 46th. In turn, the first flight took place on January 12, 1947. As luck would have it, there were few problems with supporting the military. By the beginning of the 47th, the Navy also cut funding. For this reason, the flight test program had to be shortened. Nevertheless, while maintaining the takeoff and landing performance, it was possible to accelerate the aircraft to more than 800 kilometers per hour. For 1945, this was a very good indicator, but not for the 48th. By that time, jet fighters began to enter the troops and "Shumovka" simply did not find a place in the nomenclature of naval aircraft. At the beginning of 1948, the program was frozen, and a little later, both prototypes were disassembled.
XF5U-1
Theoretically, the aerodynamics of the "Flying Pancake" and "Skimmer" made it possible to perform such maneuvers that other aircraft were simply not capable of. In addition, the layout of the XF5U Skimmer could make life much easier for the crews of aircraft carriers. However, the revolutionary novelty of the design was the factor that put an end to the entire project. Of all the Zimmermann disc-shaped aircraft produced, only one prototype V-173, which is kept in the Smithsonian Museum, has survived to this day.
The flying saucer that didn't fly
For several years after the closure of Zimmermann's projects, the ideas of non-standard layouts returned only in a scientific manner. It didn’t come to the construction of prototypes. That changed in 1952 when Avro Canada employee John "Jack" Frost initiated the Avro VZ-9 Avrocar project. It is worth noting that, unlike the previously described designs, Frost's idea fully corresponded to what most people imagine when they say "disc-shaped aircraft." The Canadian designer decided not to make the wing in the form of a disc, but to swing at another original idea.
The Avrocar S / N 58-7055 (marked AV-7055)
Frost decided to use the jet thrust already familiar for that time in combination with the so-called. the Coanda effect. The essence of this phenomenon lies in the fact that a stream of liquid or gas, moving next to any object, tends to approach it or even "stick". According to Frost's idea, this air behavior was supposed to facilitate the maneuvering of the apparatus. First, Avro Canada engineers made a small apparatus to demonstrate their ideas. The model with a diameter of only 11 centimeters could rise into the air to a small height, but any maneuvering mechanisms did not fit into it. Nevertheless, the Canadian military department became interested in the idea and allocated about 400 thousand US dollars to continue the work. Shortly thereafter, the project received the Y2 index.
At this stage, the future Avrocar became the target of a spy drama. Since 1952, the CIA has been trying to find out if some countries have new aircraft designs. In the 53rd, the scouts learned about the existence of the Y2 project and reported this to their superiors. Soon after the transfer of documents to the "upstairs" gentlemen from the Pentagon contacted the Canadian military and invited them to continue the creation of Y2 jointly. Canada accepted the offer. Among other things, this had pleasant financial implications. The head of the US Air Force Research Division, Lt. Gen. D. Putt, has raised $ 2 million in funding a year. Very bold for a revolutionary new project. However, the money was allocated and Avro continued its research. By the middle of the decade, the VZ-9 project was ready, which, in fact, became the "swan song" of the Y2 program.
The fifteen-meter disc with six turbojets, which ejected gases through their own nozzles, and also powered a large turbine, could theoretically climb to any height and fly in any direction. The customer, in the person of the American and Canadian military, approved the project, but demanded first to test the new technology on a smaller manned vehicle. Because of this, the "plate" was squeezed to a diameter of about six meters. The power plant was also changed accordingly: now only three engines were placed around the central turbine. The flight control system is interesting. For ascent or descent, it was supposed to change the thrust of all engines at once, which affected the speed of the lifting turbine. To tilt in one direction or another, Avrocar had a special system that changed the thrust of individual engines so that the body of the device, due to its difference, tilted in the right direction. I had to tinker a lot with this system: it was necessary to take into account the throttle response of the engines, the stability of the entire apparatus and a lot of other parameters.
A few photographs in flight
In mid-1959, the first prototype of the Avrocar was ready. The time has come for testing. The first weeks were spent working out the interaction of the engines and their control systems. It was a tough business, but the Canadians and Americans did it. By November of the same year, the VZ-9 was ready for its maiden flight. On November 12, the "flying saucer" took off from the ground and hovered at a low altitude. Over time, they began to add traction and take the device to slightly higher altitudes. At a distance of about a meter from the ground, Avrocar hung freely, maneuvered and could move in any direction. But when it came to climbing to a height of at least a few meters, one very unpleasant feature of the project suddenly emerged. The relatively weak power plant of the prototype could provide satisfactory stability and controllability only at a height of up to one and a half meters. With the further rise of "Avrocar" had to rely only on the Coanda effect. The screen effect, in turn, disappeared and the aircraft lost its former stability. After a series of test flights, Avro Canada engineers had to return behind the drawers. Meanwhile, the Canadian military, dissatisfied with the results, came to the conclusion that the project was useless and refused to continue giving out money.
Over the next months, a team of designers led by J. Frost tried to find a solution to the discovered problem and ensure proper stability. At this stage of the work, several more models were collected, on which new ideas were worked out. However, none of the models was able to climb to a tolerable height and still not roll over. Among the reasons for this behavior of the vehicles were the lack of additional air support (the same ground effect), and the design requirements for accurate and accurate balancing, and the need to synchronize the operation of the engines. All this could be corrected only with the help of a radical design change. At the end of 1960, Frost began redesigning the project in accordance with the experience he had gathered. Since 1959, the Y2 project has been funded only by the United States. Over time, the American officials responsible for the program began to doubt its expediency. Therefore, shortly after the start of the cardinal modernization, funding for Avrokar ceased. The Pentagon staff were tough and laconic. The document on the termination of work indicated the futility of the project, as well as the absence of any satisfactory result at a cost of about twelve million dollars.
The flightless "saucer" was nevertheless taken to the aerospace museum
Both built prototypes of Avrocar, which are kept in the aviation museums of the United States, have survived to our time. About ten years ago, a number of Canadian historians advocated the transfer of one of the "Avrokars" into the hands of Canada. They motivated this by the need to recognize the merits of their country in the creation of the project. At the same time, the topic of financing shares was somehow bypassed, although the United States spent more than ten times more money on the Y2 program than its northern neighbor. In particular, and therefore, the conversations of the beginning of the 2000s have remained just conversations, and both built VZ-9s are still in American museums.
