In the course of the development of aviation technology, bold and unusual ideas were often proposed, implying the rejection of the usual schemes of aircraft. At the beginning of the fifties, attempts to create technology with vertical take-off and landing led to the emergence of aircraft of the Tailsitter class. Testing the unusual ideas behind this concept was planned through two pilot projects from Lockheed and Convair. The latter presented the Convair XFY-1 Pogo aircraft for testing.
The idea of an aircraft of the Tailsitter type ("Sitting on the tail") emerged from the analysis of the experience of using carrier-based aircraft and a number of new studies. For all its advantages, carrier-based fighters and bombers needed a large aircraft carrier ship and, by definition, could not work without it. Back in the late forties, an original idea was proposed that made it possible to place a fighter on almost any ship or vessel. It was proposed to develop and build a vertical take-off combat aircraft.
Prototype Convair XFY-1 during testing. Photo 456fis.org
As conceived by the authors of the new concept, on the ground or on the deck of the carrier ship, the promising "tailsitter" was to be placed vertically. This allowed him to take off without a run, and then switch to horizontal flight "like an airplane." Before landing, accordingly, it was necessary to return to vertical flight again. Without the need for a large runway or flight deck, such an aircraft could be based on a wide variety of ships with sufficient free space. As a consequence, it was of great interest to the naval forces.
The program for creating a promising combat "tailsitter" was launched in 1948. At its first stages, research organizations were engaged in theoretical calculations and experiments, the results of which soon made it possible to start creating full-fledged projects. The development of new technology was entrusted to two leading aircraft manufacturers - Lockheed and Convair. They had extensive experience in the creation of aviation technology, including unusual schemes. Together with their experience, the contractor companies had to use the data collected from the recent research.
Machine diagram. Figure Airwar.ru
Initially, the contractors were faced with a rather difficult task. They had to develop tail-sitter aircraft suitable for practical use in the armed forces. Further, the command of the Navy was going to compare the two samples received and choose the most successful one. This car was planned to be put into production and sent to the troops. Nevertheless, it soon became clear that such an approach to the creation of new military equipment could not be put into practice. First, it was required to test new original ideas during tests, assess their prospects and only after that take on the creation of a full-fledged combat vehicle.
In this regard, in 1950, Lockheed and Convair received a new assignment. Now they were required to create experimental aircraft that could be used to test the Tailsitter concept. With a favorable completion of this stage of the project, it was possible to take on the creation of combat aircraft.
Preparation for tests in the hangar. Photo 456fis.org
On April 19, 1951, the US Navy signed contracts for the construction of prototypes. In accordance with the agreement concluded, Convair was to build and submit for testing two prototypes. Subsequently, the company proactively decided to build three machines, which were to take on different types of tests. The Convair project at this stage received the official designation XFY-1, formed in accordance with the naming rules of the fleet's aviation equipment. The first letter of the designation indicated the experimental nature of the project, the letter "F" related the aircraft to fighters, and the letter "Y" designated the Convair company. The unit, accordingly, showed that this was the first project in its line.
The proposed operation on ships of the naval forces and other requirements led to the formation of an unusual design of the aircraft. "Tailsitter" Convair XFV-1, in general, was supposed to resemble existing aircraft, but the main technical solutions gave it an unusual appearance. The project proposed the construction of a midplane turboprop with a large swept wing, devoid of horizontal tail. At the same time, a large keel and ventral ridge were to be used. To obtain the required thrust, two large-diameter propellers were used. As a result, the car had a recognizable appearance.
Flight on a leash. Photo 456fis.org
The tailless aircraft received an original fuselage design. This unit had a streamlined shape with a variable cross-sectional area. Immediately behind the spinner and the propeller hub, the fuselage increased significantly in height, maintaining its original width. The upper part of the fuselage formed a pronounced "hump" necessary to accommodate the pilot's cabin. Behind the lantern was a gargrot of short length, on which the keel mounts were located. A very original fuselage layout was used. The nose part was given under the engine gearbox and the hub of the coaxial screws. The engine was located behind the gearbox above the bottom. The pilot's cabin was located above it. The tail compartments of the fuselage housed part of the fuel tanks, as well as the long exhaust pipe of the engine. The latter was displayed on the tail section of the fuselage.
A new wing with a large sweep was developed for the aircraft, the root part of which occupied most of the sides of the fuselage. Elevons were placed on the trailing edge of a small sweep. The wing received container endings, in which there were additional fuel tanks. The wing shape used made it possible to obtain the maximum possible area with limited dimensions.
Experienced aircraft on a transport trolley. Photo Airwar.ru
A characteristic feature of the Convair Tailsitter is its large keel and ventral ridge. Thanks to the use of a large wing, it was possible to abandon the stabilizers of the classical design. Stability and controllability in the vertical take-off mode and directional stability in horizontal flight were to be ensured, first of all, by the vertical tail. Two vertical planes with a swept leading edge and a rounded tip were used. On the trailing edge of the keel and crest were rudders. Both planes were symmetrical about the longitudinal axis of the machine. In this case, however, due to the asymmetric design of the fuselage, the keel protruding above it had a smaller area and a different shape of the root part.
Due to its characteristic position in the parking lot or during takeoff, the aircraft "sitting on its tail" received an original landing gear. Near the wingtips-containers of the wing and near the tips of the vertical tail there were tubular casings in which there were fixed landing gear legs. The tailsitter aircraft received a four-point landing gear with shock absorbers and small wheels. Racks with caster wheels allowed the aircraft to take a vertical position, as well as maneuver when towing.
Cabin interior. Photo Airwar.ru
In the central part of the fuselage, directly under the cockpit, there was an Allison YT40-A-6 turboprop engine with a power of 5100 hp. The supply of atmospheric air to the engine was carried out using two intake devices placed on the sides in front of the wing edge. An air intake for radiators was provided on the bottom. A pipe was attached to the nozzle apparatus of the engine, which reached the tail of the fuselage and removed the reactive gases outside. The aircraft was equipped with two coaxial three-bladed propellers with a diameter of 4.88 m, developed by Curtiss-Wright. The blades were mounted on a common bushing of a relatively complex design. The propeller drive was equipped with a hydraulic brake.
One pilot, who was in the cockpit, was supposed to control the machine. His workplace was equipped with a large instrument panel with dial gauges and several panels with a variety of equipment. Control was to be carried out using standard "fighter" systems: aircraft and engine control sticks, as well as two pedals. The cockpit received an ejection seat with unusual mounting means. For more convenience in working in different modes, the chair could swing within a wide sector. In case of an unsuccessful landing, the pilot could leave the plane and descend to the ground using a 25-foot (7.6 m) rope fixed in the cockpit. A large area lantern protected the pilot from the incoming stream. In its composition there was a fixed visor and the main part, sliding back.
Test pilot James F. Coleman. Photo by US Navy
The experimental aircraft did not need a weapon, but this issue was still being worked out at the design stage. While maintaining the existing dimensions and weight parameters, the Convair XFY-1 could carry up to four 20-mm automatic cannons or several dozen unguided missiles. Due to the lack of other free volumes, it was proposed to mount them in containers at the ends of the wing.
Despite all efforts to reduce the size, the promising tailsitter aircraft turned out to be quite large. The length of the vehicle reached 10, 66 m, the wingspan was 8, 43 m. The vertical tail span was about 7 m. The empty aircraft had a mass of 5.33 tons, the maximum takeoff was determined at the level of 7, 37 tons. level flight was supposed to exceed 980 km / h. It was planned to obtain high rate of climb characteristics: for this, the screws had to perform the functions of carriers.
Test pilot John Knebel. Photo Thetartanterror.blogspot.fr
For the transportation of an aircraft with a specific chassis, a special towed bogie has been developed. On a frame with four wheels were placed two swinging beams with hydraulic cylinders. At the free ends of the beams, using their own hinges and separate drives, smaller holding devices were fixed. When loading the aircraft, the latter were brought under its center section and connected to it with locks. The hydraulics made it possible to transfer the machine to a horizontal position and, using a separate tractor, move the cart to the desired position. In preparation for takeoff, the aircraft was transferred to an upright position, after which it uncoupled and stood on its own wheels.
At the end of 1953, Convair began building experimental equipment. It was decided to build three identical machines, designed to solve different problems as part of an extensive testing program. The first glider should have been equipped with a propeller-driven group, a fuel system and controls. Such a prototype was intended for preliminary checks of the power plant. The third sample was sent for static tests. Checked on the ground, leashed into the air, and free-flying was followed by a second experienced Tailsitter.
Preparing for takeoff, engine running. Photo Airwar.ru
After checking the operation of the engine on the first prototype, permission was obtained to conduct subsequent tests with ground testing of equipment and subsequent ascent into the air. As a site for these checks, Moffett airfield (California) was chosen, namely one of its slipways, at one time built for airships. Under the roof of the boathouse, almost 60 m high, there was a crane-beam, which was to become a safety device. Preparing the experienced XFY-1 for flights, the specialists of the developer company dismantled the fairing of the propeller hub, under which there was a special fastening structure. With the help of the latter, the aircraft should be hung on the hook of a crane-beam. By selecting and releasing the rope, the crane operator could prevent the aircraft from falling.
On April 29, 1954, the aircraft was to take off for the first time using belay. Pilot James F. Coleman was in charge of operating the prototype. Engineer Bob McGreary operated the jib crane and monitored the length of the free cable. Having brought the engine to the required power, the test pilot was able to lift the car off the ground, but immediately after that, problems began. Once in the air, the aircraft began to rotate uncontrollably around the longitudinal axis. Thanks to the timely response of the crane operator, the machine was saved from falling. After the completion of the first test flight, the car sat down with some difficulty.
The car is in the parking lot. Photo Airwar.ru
Probably, it was at this stage, due to the peculiarities of the chassis spring damping, that the aircraft received the nickname Pogo (from Pogo-stick - the "Grasshopper" sports equipment). Subsequently, the unofficial name of the project became widely known and is now used as often as the official designation assigned by the customer.
The aircraft showed its ability to take off and land vertically, but uncontrolled rotation in these modes did not allow to realize all the advantages of the original scheme. It was necessary to find out the causes of such problems and eliminate them. For this, the outer surfaces of the airframe were pasted over with "silk threads", the observation of which made it possible to identify problems of an aerodynamic nature. Such tests quickly gave results. It turned out that even the existing large boathouse was not large enough for an experimental vehicle. The air flow from the propellers hit the floor of the structure, moved to the sides, reflected from the walls and returned back. It was the numerous vortices that prevented the tailsitter plane from maintaining the required position.
Convair XFY-1 Pogo makes vertical takeoff, November 30, 1954. Photo by US Navy
The testers took this fact into account, but still were forced to continue testing in a closed structure. The prototype machine still needed insurance, which could only be carried out by a boathouse crane. Installation of such equipment in an open area was not possible. In such difficult conditions, J. F. Coleman completed several dozen test flights with a total duration of about 60 hours. Due to the unstable behavior of the machine during the first tests and subsequent flights, the test pilot never closed the lamp. This caused some inconvenience, but Coleman considered them an acceptable price for the ability to quickly leave the aircraft.
In the middle of 1954, the prototype was taken to an open area for free flights. On the very first day of such tests, the test pilot was able to climb to a height of 6 m, and then overcome the bar of 45 m. The control of the machine was not very simple, but the absence of walls and a roof had a positive effect on the characteristics of the equipment. Taking advantage of this, J. F. Coleman continued vertical flights with numerous take-offs, helicopter maneuvers and subsequent landing.
Helicopter flight. Photo by US Navy
Soon the experienced "tailsitter" was transferred to Brown Field (California), where the tests were to continue under the supervision of representatives of the military department. At the new location, 70 more vertical flights were performed, after which it was decided to test the prototype in transient modes and in horizontal flight.
On November 2, 1954, the experienced XFY-1 took off vertically for the first time and after climb switched to horizontal flight. After that, the car was returned to an upright position and seated. The flight lasted 21 minutes, of which 7 were airplane flights. The beginning of such checks made it possible to determine the real characteristics of horizontal flight. So, it was found that even with the minimum engine thrust, the tailsitter aircraft develops a speed of more than 480 km / h. The aircraft was not equipped with air brakes, which made speed control difficult. Because of this, he repeatedly involuntarily overtook the backup aircraft accompanying him.
Level flight. Photo Airwar.ru
Having confirmed the calculated characteristics, the prototype showed certain drawbacks. First of all, it was found that the XFY-1 is difficult to control, especially in transient conditions. For a safe landing, experienced pilot J. F. Coleman had to move the car to an upright position at an altitude of about 300 m, and then gently lower it to the ground. The last meters of the descent were associated with special difficulties, since numerous vortices interfered with the landing, and in addition, the pilot from his cockpit could not properly monitor the situation. To partially solve this problem, at one of the test stages, the prototype received a radio altimeter with light alarms: green and orange lamps indicated normal descent, and red indicated an excess of the safe vertical speed.
J. F. Coleman flew a single Pogo until mid-1955. An experienced pilot managed to master all the subtleties of controlling such a machine in difficult modes. At the same time, it became clear that ordinary pilots from combat units are unlikely to be able to learn how to pilot such a technique. Moreover, such tasks were beyond the power of even professional testers. So, in mid-May 1955, pilot John Knebel was supposed to join the tests. On his first flight without belay, he was unable to keep the car in position and nearly crashed it. After that, all new flights were assigned only to Coleman.
Back-top view. Photo Airwar.ru
June 16, 1955 J. F. Coleman sent the experienced Tailsitter into free flight for the last time. After that, the car was sent to the hangar while studying the test results, finalizing the project, etc. In the spring of the next year, it was decided to conduct new tests by the naval forces, for which two pilots of naval aviation went for training. However, they were never able to join the work.
During the test flights, the only flight model Convair XFY-1 Pogo managed to develop most of the resource. During the next check, chips were found in the oil from the gearbox. The car needed repair and restoration before new tests. However, the customer considered the overhaul of the aircraft unnecessary. The original project was no longer of interest to him, which made restoring the prototype readily meaningless.
"Pogo" in color. Photo Airwar.ru
After examining the successes of two pilot projects from Lockheed and Convair, the command of the US naval forces has drawn conclusions about the practical benefits of tail-sitting aircraft. This technique had noticeable advantages over both airplanes and helicopters, but at the same time it was not devoid of characteristic disadvantages. Tests of the prototype "Pogo" showed that such a machine is very difficult to fly and demanding on the landing sites. The control of such a technique could hardly be mastered by an average pilot. In addition, landing on the rocking deck of the ship was virtually impossible.
The unusual projects were of technical and scientific interest. They showed the fundamental possibility of creating non-standard vertical take-off aircraft. At the same time, these developments had a specific ratio of positive and negative features. Serial production, operation and mass development of such equipment did not make sense.
Experimental machine as an exhibit, August 1957 Photo Wikimedia Commons
In 1956, the XFY-1 project was closed due to the lack of real prospects. The first and third prototypes, intended for ground and static tests, were disassembled as unnecessary. The only flying Pogo was for some time at the Norfolk Air Force Base (California). It was later donated to the Smithsonian Institution's National Air and Space Museum. A unique piece of equipment is kept in the branch of the museum in the city of Suiteland (Maryland).
The closure of the Convair XFY-1 pilot project led to the completion of work on the Tailsitter aircraft, carried out since the late forties by order of the United States Navy. Two projects showed the fundamental possibility of developing and building equipment of an unusual appearance, but at the same time demonstrated the excessive complexity of its operation. It was originally planned that the result of two projects would be the emergence of a carrier-based fighter, but later these developments became experimental. Two projects successfully solved a similar problem.
