What is VTOL System?
Many countries have worked on high cruising speed aircraft with vertical/short take-off and landing (V/STOL) systems for more than 25 years, and designs and prototypes with approximately 60 V/STOL systems have been tried. However, very few prototypes made it to the flight stage. Prototypes that can progress in line with field and operational needs and their incompatible qualities were made suitable and further developed, and new types were created. In our article, we will examine such a complex and costly system. Details are in our article.
VTOL ( Vertical Take-Off and Landing ) is an abbreviation for vertical take-off and landing. Today, CTOL ( Conventional Take-off and Landing | Conventional Take-off and Landing ), STOVL ( Short Take-off and Vertical Landing | Short Take-Off and Vertical Landing ) and V/STOL ( Vertical or Short Take-off and Landing | Vertical or Short Take -Off and Landing ) systems are also available. CTOL is the most used landing and take-off system today. The main reason for the use of other types is to allow the aircraft to land in narrow and congested areas.
The Birth of the Need for VTOL
At the end of the First World War, it was clear that aviation technology greatly influenced the outcome of the war. The side that could dominate the airspace was also mostly successful in land and sea operations. This situation continued as expected during the Second World War. The side, which showed superiority in the airspace, was extremely successful in sending troops to the front and splitting by making tactical observation flights. In addition, the planes could perform movements that would provide superiority on the battlefield, such as notifying the artillery of ground targets, bombing strategic positions, providing infantry and supply support to the battlefield, and giving intelligence to the soldiers who were on the move.
In 1942, the world's first mass-produced helicopter, the Sikorsky R-4, began to be produced. R-4, which has the capacity to carry only one passenger, was used as a rescue helicopter at sea and on land. By 1943, the H-5 model with a much higher carrying capacity was developed. This model, which is much more useful than the R-4 model, played an important role in the logistics of supplies and equipment. Studies on this system, which attracted the attention of countries thanks to its ability to position on the battlefield, accelerated. In 1957, the Hawker Siddeley P.1127 prototype, the world's first V/STOL aircraft, was produced by two aerospace engineers, Ralph Hooper and Sydney Camm. The Hawker P.1127 used a Rolls-Royce Pegasus/F402 turbofan engine with rotating nozzles. The nozzles gave the aircraft the maneuverability to all sides on the down axis, and thus the P.
Design Principle of Engine
The Pegasus directional-controlled turbofan engine has a dual-shaft design with three low-pressure and eight high-pressure compressor stages driven by two low pressure (AB) and two high pressure (HP) turbine stages. One of the double shafts connects the AB turbine and the fan, while the other connects the HP turbine and the compressor, ensuring optimal speed in both shafts. However, unlike other twin-shaft turbofan engines, Pegasus is a double-shaft engine that works in the opposite direction. The aim here is to minimize the gyroscopic effects of the engine on the aircraft when the aircraft is in VTOL or cruising at low speeds.
Design Principle of Nozzle
The direction of the thrust is adjusted by the nozzle that can move between the determined angle and axis limits. This nozzle system was initially produced for maneuverability on the vertical axis, and since it provides much higher maneuverability to the aircraft in flight, it has also started to be applied to engines with take-off system other than the VTOL system. The front two nozzles of Pegasus made of steel are fed with air from the AB compressor. The rear nozzles are jet exhausts made of Nimonic material. The temperature of the air coming out of the rear nozzles is around 650°C. Since the steel will deform at high temperatures, Nimonic alloy is used, which has very little metal deformation at high temperatures.
Comparison of the System
The advantages of the VTOL system vary depending on where it is used. Features such as landing and take-off capability without the need for a runway, hovering, fast positioning, and flexible maneuvering capabilities are features that conventional aircraft generally cannot reach. However, these advantages greatly limit the system. It limits capabilities such as weight, range, altitude, maximum cruising speed, efficiency and endurance. Speaking of VTOL aircraft, a lot of thrust will be required to lift the fuselage during vertical takeoff. Therefore, fuel consumption increases significantly. In addition, maintenance costs are quite expensive compared to conventional systems. V/STOL and STOVL systems are more commonly used, except for specific operations and applications, as they are highly negative factors.
Bell Boeing V-22 Osprey is also used today, apart from Harrier and F35B aircraft. The Osprey is an aircraft with a transitional form between an airplane and a helicopter. It uses two Rolls-Royce T406 turboshaft engines feeding the rotors. The main reason for the existence of such an aircraft is the desire to combine the capabilities of the aircraft and helicopter. It has greater range, payload and top speed than conventional helicopters. While using the V/STOL system, it also carries the capabilities of helicopters, making it a good aircraft to play a key role in the operation areas.
