In the second half of the fifties, several projects of promising vertical or short take-off and landing aircraft were developed in the United States. Such a technique was of great interest from the point of view of practical operation, which is why several aircraft building companies began to study promising topics at once. Soon, various technical projects were created using different principles for increasing takeoff and landing characteristics. Parts of the projects managed to reach full-fledged tests, while others faced serious problems and were stopped early. One of the developments that did not progress beyond preliminary checks was the Robertson VTOL aircraft.
The Robertson VTOL project started in the fall of 1956. The Robertson Aircraft Corporation began developing a new aircraft with unusual capabilities. It is noteworthy that this organization was founded in October 56th specifically for work on a new project of a vertical or short takeoff aircraft. It should be noted that the Robertson company, which worked on the VTOL project, has nothing to do with the company of the same name, which built aviation equipment in the interwar period. The "old" Robertson Aircraft Corporation by that time managed to cease its activities.
In just a few months, the development company, not loaded with other orders, completed the design and then built a prototype of the aircraft. Thanks to this, already at the beginning of 1957, it was planned to conduct the first tests of the prototype aircraft. All these plans were successfully implemented, but further work was prevented by the results of checks of new equipment.
The only surviving photograph of a Robertson VTOL aircraft. Photo Vertipedia.vtol.org
In the fifties, several methods were proposed to improve the take-off and landing characteristics of aviation technology, which made it possible to sharply reduce the take-off run or provide a vertical take-off. All of these methods were different in terms of technique and implementation complexity. The designers of the Robertson company have chosen one of the simplest ways to improve performance - the technology of deflection of the air flow. In addition, in the new VTOL project, it was proposed to use some other ideas that made it possible to simplify the design of the aircraft in comparison with other similar samples of that time.
The Robertson Aircraft Corporation project received the simplest working title that fully reflected its goals. The car was named VTOL (Vertical Take-off and Landing). As far as is known, the US military did not show interest in this development, which is why it did not receive an army designation with the letters "VZ". In addition, the project simply did not reach the stages at which it could find application in the army.
It was proposed to work out new ideas using an aircraft of a relatively simple design. The experimental Robertson VTOL was supposed to be a twin-engine high-wing aircraft with an original wing design. At the same time, it was proposed to use the fuselage, power plant, chassis and tail of traditional schemes. An interesting feature of the project, which distinguished it from its modern counterparts, was to have a full-fledged closed cockpit for the pilot and several passengers or other payload.
For the aircraft of the new type, a fuselage was developed, similar to that used in other projects of light aircraft. There was an ogival nose cone, smoothly coupled with diverging sides. Behind the fairing there was an inclined cockpit windshield, above which the wing attachment means were located. Behind the passenger compartment, which was relatively long, the fuselage began to taper. In a narrow tail section, it housed a keel and a stabilizer with a large transverse V. Some features of the fuselage suggest that the Robertson Aircraft Corporation manufactured its aircraft by converting an existing production aircraft of another enterprise, but there is no exact data on this.
A significant part of the internal volume of the fuselage was given for the placement of the cockpit. Inside the existing volume, the authors of the project placed four seats for the pilot and passengers. Access to the cockpit was carried out using side doors. There was a large front and side glazing. An interesting feature of the vehicle layout was the absence of fuselage tanks for fuel and oil. The containers for the necessary fluids were placed in the wing and its assemblies. At the same time, it is likely that some devices that control the wing assemblies should have remained inside the fuselage.
The experimental Robertson VTOL aircraft received a high-positioned straight wing with advanced mechanization. To the upper part of the fuselage, it was proposed to mount a main wing unit rectangular in plan, which had a relatively thick profile. A pylon with a relatively large engine nacelle was placed in the middle of each plane. In other experimental projects of a similar nature, a single engine was located in the fuselage and was connected to the propellers using a complex transmission. The Robertson project involved the use of two full-fledged propeller-driven groups. The engines were inside their own streamlined nacelles.
Large wingtips were used to prevent air overflow. The basis of such a device was a trapezoidal plate. Additional flow control is provided by large teardrop tanks placed on the bottom of the tips.
Lycoming GSO-480 piston engine, top view. Photo Ranger08 / Southernairboat.com
It was proposed to install Lycoming GSO-480 gasoline engines in two underwing gondolas. The six-cylinder horizontal boxer engine was equipped with a supercharger and developed power up to 340 hp. The engine had a built-in gearbox to reduce the speed when using the propeller. The cylinder block was cooled by air entering through the windows in the nacelle nose cone. The Robertson VTOL aircraft was to be equipped with two three-bladed propellers of a relatively large diameter. To improve the airflow of the wing and, as a result, to increase its characteristics, the propeller's swept disk had to cover the wing almost completely.
The main way to improve takeoff and landing characteristics in the framework of the new project was to be developed wing mechanization. On the rear of the fixed plane, retractable double-slotted flaps of a large area were located, occupying the entire wing span. When deployed at low angles, such flaps could be used in the "traditional" quality. Greater deflection of these planes led to an additional increase in lift. At maximum extension, the wing, flaps, tips and sides of the fuselage formed a box-shaped structure directing the airflow from the propeller down and back, which could be used to improve takeoff and landing performance or even to gain new capabilities.
The exact information about the aircraft control systems has not been preserved. It is known that he had the classic elevators and rudders, placed on the tail. At the same time, the presence of large flaps located throughout the wingspan did not allow equipping the aircraft with ailerons. How exactly it was proposed to carry out roll control with the flaps extended is unknown. It is possible that it was proposed to control the roll by means of a differentiated change in the thrust of the engines, which affects the lift of the planes.
The experimental aircraft received a three-point landing gear with a nose strut. In the central part of the fuselage, near the cockpit, there were two main struts. To facilitate the design, they were made non-removable, and the wheel mounts were located on a relatively simple pipe structure. Under the nose cone there was a non-retractable strut with a shock absorber and a small-diameter wheel. The tail crutch was not used to protect the fuselage from strikes against the runway.
A curious feature of the Robertson VTOL aircraft, which was completely uncharacteristic for experimental aircraft of that time, was the presence of a multi-seat cockpit. In the general compartment, four seats for the pilot and passengers were located in two rows. The pilot seat had a set of all the necessary controls, both traditional for aircraft and new, the presence of which was associated with the use of certain devices and assemblies.
The development of the Robertson VTOL project was completed at the end of 1956, which made it possible to quickly start building a prototype. The first prototype, intended for testing, was completed in December of the same year. In the near future, it was planned to start ground checks, and then lift the plane into the air. The start of this stage of the project was scheduled for early January 57th.
Already on January 8, the prototype aircraft of the new model performed the first lift into the air using the technology of deflecting the air flow with the help of large flaps. Since there was still no information about the real capabilities of the machine, the first approach was carried out using tethered cables. For some time, the experimental aircraft was in the air, showing the real effectiveness of the power plant and wing used. They actually allowed the car to rise almost vertically into the air. After completing the entire program of the first tethered flight, the prototype landed on the ground.
Robertson VTOL advertises Lycoming engines in Flight Magazine
As it became clear later, Robertson VTOL took off for the first and last time. More flights of the experimental machine were not carried out. The exact reasons for this remain unknown, but the available information allows us to draw some conclusions and make it possible to determine a list of possible problems that put an end to the tests.
It makes sense to compare the development of the Robertson Aircraft Corporation with other similar projects of that time. This comparison shows that the Robertson VTOL aircraft, due to a number of characteristic features, was significantly heavier than its competitors, which could have a negative impact on its flight performance. He could also have a serious drawback in the form of the lack of special control systems designed for use when flying at low speeds. There is no information about the use of gas rudders or additional tail propellers: without such systems, the aircraft could not be properly controlled during vertical or short takeoff, which made it extremely dangerous for itself and for the crew. Another disadvantage is the placement of engines in underwing gondolas. Large units, despite their streamlined shape, could have a negative effect on the air flow, impairing the aerodynamics of the wing.
Unfortunately, the exact list of negative features of the Robertson VTOL project has not been preserved. However, the consequences of these shortcomings are well known. Experimental aircraft on January 8, 1957 made the first and only flight on a leash. More tests were not carried out, since in its current form the machine did not meet the existing requirements. Due to the lack of real prospects, the original project was closed without giving the expected results. The only built sample of the aircraft was later disassembled. Now it can only be seen in the only surviving photograph.
An interesting fact is that all work on the Roberton VTOL project was discontinued back in 1957-58, but the experimental aircraft was not immediately forgotten. For example, the February 1959 issue of Flying Magazine featured an advertisement for Lycoming engines. In support of the slogan "leading manufacturer of aircraft engines", more than six dozen samples of aircraft equipped with Lycoming engines were drawn on the entire spread of the magazine. Among serial aircraft and helicopters, as well as experimental aircraft, the Robertson VTOL machine was also present in such advertisements. Even after its completion, the original project helped the further development of aviation, even if in the role of a "participant" in the advertising of aircraft engines.
Not receiving the expected results, Robertson Aircraft Corporation was forced to discontinue work on the pilot project. The experience gained in the design and testing of the aircraft, apparently, was never used in new projects. The creation of the Robertson VTOL aircraft was carried out on an initiative basis and without the support of the military department, because of which the developments had no noticeable chance of getting to other aircraft building organizations. As a result, the original and unusual project did not receive the planned continuation, and also remained without further development. The study of the problems of vertical / short take-off and landing further proceeded without taking into account the experience of the Robertson firm.
