Vertical Takeoff and Landing Aircraft

Summary

Vertical takeoff and landing (VTOL) and short takeoff and landing (STOL) aircraft have emerged as integral segments of the aviation industry, particularly in terms of their military and civilian transport applications. The helicopter became vital to combat during the Vietnam War, as it was able to deploy troops quickly to a variety of areas that were previously only accessible by foot. The most important benefit was the development of medevac (medical evacuation) technology, a practice brought back to the United States by pilots and medical personnel.

Definition and Basic Principles

Vertical takeoff and landing (VTOL) aircraft have the capability to take off from a standstill, rise straight up, fly from one place to another, and then set down vertically again.

Short takeoff and landing (STOL) aircraft use a shorter runway for takeoffs and landings, often from unprepared or abnormal surfaces.

Hybrid aircraft can perform both functions to a considerable extent and have been outed as a way of the future in the development of new aircraft systems. The existing hybrid craft are used primarily by the military, and two iconic models showcase the two main technologies in use. The V-22 Osprey is a tilt-wing system developed by Bell Boeing, and the Harrier Jump Jet is a British creation that uses a variable nozzle system to redirect power. As of 2021, the fleet of V-22 Ospreys in use had recorded more than six hundred thousand hours of flight. Meanwhile, in 2015, a small fleet of hybrid fighter jets, Joint Strike Fighter F-35Bs, designed for the Marine Corps were declared ready for combat. The planes were made ready for combat for the Air Force in 2016 and for the Navy in 2019.

The autogiro (or autogyro), popular in Europe during the 1920s and 1930s, was a rotary-wing aircraft that had a very short roll distance. The United States even gave the autogiro a trial as an addition to the airmail fleet before determining that the cost far outweighed the benefits.

In the twenty-first century, uncrewed aerial vehicles (UAVs), or drones, became an important new branch in VTOL aircraft development.

Background and History

In 1907, French engineer Paul Cornu's "flying bicycle" was the first machine to take off vertically with a pilot and achieve a stabilized, controlled free flight. He is not well known within aviation circles because he was basically overshadowed by the Wright brothers and other aircraft pioneers.

Igor Sikorsky is most often associated with the development of the helicopter and is called the father of the modern helicopter. Sikorsky's VS-300, the first operational helicopter, made its first free flight in 1940. It introduced the practical use of the tail rotor to the helicopter airframe. Its purpose was to counteract the action of torque on the body of the aircraft and keep it from spinning wildly out of control in the opposite direction of the blades overhead.

The Sikorsky R-4 was the first helicopter to fly in combat. It was used for medical evacuation and resupply missions in the China-Burma-India theater of World War II beginning in 1943. The first widespread use of helicopters was during the Korean War. The Bell 47, the bubble cockpit helicopter used for transporting medical cases, is probably the best known. Less well-known models include the OH-23 Raven, Sikorsky's H-19 Chickasaw, and H-5, which was used mostly by the Navy for the recovery of pilots downed at sea.

The Vietnam War became known as the "helicopter war." The use of these machines in various roles changed military tactics as well as the public perception of future non-military use.

How It Works

Fixed-Wing Aircraft. A fixed-wing aircraft has wings extending from both sides of the aircraft with one, two, or more engines used to propel the aircraft forward. To accommodate a variety of tasks, both military and civilian, some are adapted to serve fast transportation needs into and out of small environments. The challenges of this goal have been approached from two directionsvariable wing and ducted variable thrust.

The concept of variable wing thrust is to vary the orientation of the wing relative to the ground and the direction of flight to achieve lift or thrust. Ducted variable thrust flight is achieved by manually changing the thrust direction of the engine in a fixed-wing jet aircraft from the rear to directly below the aircraft. The aircraft rises and can be controlled as a helicopter would until the thrust direction is changed for vertical flight or reversed for landing. The Harrier Jump Jet is the most common example of this.

Hybrid Aircraft. The V-22 Osprey has the ability to tilt its wings 90 degrees to surface. The overly large propellers act as rotor blades that turn in opposite directions to cancel out the torque effect. The craft can then act like a helicopter to rise into the air. After clearing ground obstacles and with some forward speed, the pilot engages a lever that causes the wing to tilt into a normal fixed-wing position. The large propellers and standard configuration then allow the plane to fly at speeds of about 300 miles per hour. Upon arrival, the pilot reverses the procedures and again lands as a helicopter would.

Autogiro Aircraft. Autogiros typically have a small body, a pulling or pushing engine, and either short, stubby wings or no wings except for a conventional tail surface and structure. The main distinguishing characteristic is the free-wheeling rotor, usually of three to five blades, that is attached to the body above what would be the wing center of gravity for the plane. This rotor generates the lift by reversing the operation of a rotor on a helicopter. The pushing or pulling engine will move the body along the ground or through the air. Instead of pushing air down as a helicopter rotor or airplane wing does, wind rises through the rotor on the autogiro, which is a free-wheeling device, and causes lift.

Rotary-Wing Aircraft. Helicopters use the same principles, with two exceptions. The engine in the helicopter is usually hooked directly to the propeller or rotor. It is also hooked in sync with the shaft that turns the rear or tail rotor. The tail rotor is necessary for the directional control of the aircraft. When the collective, the control system that governs lift, is pulled up, it sends directions for the rotor blades to change their pitch and take a larger bite out of the air to lift the machine. Without the tail rotor, torque takes effect, and this causes the aircraft body to rotate in the opposite direction of the rotor blades. The pitch (or amount of bite into the air of the blades) of the tail rotor is controlled by the foot pedals.

The other exception is in the control. To make an aircraft go in one direction or another, the pilot inputs the movements directly, and the aircraft follows those movements. In a helicopter, the movements are put into the control stick. The control stick is pushed forward, and the craft follows suit. Although the pilot is facing forward, the command actually goes to the rotor 90 degrees to the right. As the blade continues to turn, the pilot's command is fully completed, and the aircraft moves in the direction the pilot intended.

Applications and Products

Aviation and aviation technology constitute a multibillion-dollar business. Areas include conceptualization, design, manufacture, and sales of aircraft and aircraft-related components; commercial and private flight; and movement of freight and mail.

Fixed-Wing Aircraft. The most prevalent area of aviation is the fixed wing. However, the variable-duct technology has not yet been widely applied outside of specialized military applications. While some companies have shown interest in adapting such technology for civilian use, the expense involved means any market would likely be highly limited for the near future.

Helicopters. Since their general rise during the Vietnam War, helicopters have become indispensable in a number of fields. Air ambulances and mercy flights allow accident victims and the ill to reach emergency-care facilities within minutes. Air ambulances can be outfitted with the same trauma equipment as a ground ambulance, and they have the added benefit of conveying trained trauma personnel directly to the scene of the accident or injury, allowing for quicker diagnosis and treatment.

Originally, this trauma-care element was assigned to police departments, the Army National Guard, and military reserve units. As the use of helicopters expanded, law-enforcement air units could not keep up with the specialized requirements of trauma and continue to respond to calls for assistance from ground units. Police helicopters shed some of the lifesaving equipment but gained other specialized equipment for their duties. Forward-looking infrared radar (FLIR) allows the helicopter to track subjects at night. Powerful searchlights provide light equal in brightness to daylight, allowing officers on the ground to conduct searches without using flashlights.

Fire departments in many larger cities have added helicopters to their inventory of rescue equipment. In some cases, where law enforcement was shedding the medical jobs and the hospitals could not bear the loss of the service, the fire department stepped in to do the job. Fire departments have also found that in some cases, they can use a helicopter as a rescue vehicle for individuals who have become trapped or to carry hoses up above the flames where a truck's ladder could not reach. Similarly, specialized helicopters have been used to fight forest fires.

Heavy-lift helicopters are used to carry things to and from the tops of buildings, where they can hover in one position long enough for the item to be attached or removed from the top of the building without having to make multiple trips via crane. They are also used in logging to carry felled trees from one remote location to a central assembly point for collection or transportation to a mill.

Helicopters are still the best way for damage assessment to be done after, or in some cases, during an emergency. By placing evaluators near the scene or flying dignitaries over it, they can decide how best to respond to the emergency or even speed up the money flow from the government to the disaster site.

Helicopters have also impacted such diverse fields as fishing, crop dusting, intercity and short-range transportation, electricity, and broadcast journalism.

Autogiros. Autogiros have become more of an amusement on film and at air shows than a viable part of the transportation arena. However, there are still enthusiasts who fly these small aircraft for pleasure.

Hybrids. Primarily used by the military, hybrid VTOL aircraft have been considered as a possible replacement for helicopters and fixed wing aircraft for civilian transportation and other uses. The hybrids are able to land in small areas, like a helicopter, but they also have the speed of a fixed wing for level-distance flying.

Careers and Course Work

The most difficult skills to develop in flying are the coordination of movements between the feet, hands, eyes, and the controls. Being able to go seamlessly back and forth between all of these are the basics of a smooth, coordinated flight. In flying helicopters, it is called "finding the hover button." At first, developing these skills is difficult, but with time and experience, they become second nature.

Pilot is the first job that comes to most people's minds regarding VTOL aircraft. Many helicopter pilots have military backgrounds. The services are usually looking for people with strong math, science, computer, or engineering backgrounds. The Army has less stringent academic requirements because of the extensive use of warrant officers. Warrant officers become experts in a variety of areas within the aviation field, including airframe repair, mechanical and engine maintenance, and airfield operations. Upon graduation from a military flight school, one can take the written exam given by the Federal Aviation Administration (FAA) to qualify as a commercial pilot in fixed, rotary wing, or both classifications.

To become a pilot without military training, flying either fixed- or rotary-wing aircraft, one needs the followinga private pilot's license, commercial pilot's license, instrument rating, airline transport pilot certificate (ATP), and a rating for the type of aircraft one will be flying. Many pilots who will be flying for small charter services, product transport services, news agencies, or police agencies may need no more than a commercial pilot's license. For training in rotary-wing aircraft, individuals usually have to attend a private specialty company's ground school and follow up with the flight portion in a separate instruction.

Vocational schools and some two-year colleges train students with specialized skills in airframe construction, power-plant development and testing, maintenance, avionics, and other assorted disciplines applicable to both fixed- and rotary-wing aircraft. Four-year colleges and universities may also incorporate some aspects of these programs but often concentrate on the management side of the aviation industry.

Social Context and Future Prospects

Statistical studies from the FAA and the National Transportation Safety Board (NTSB) show that flying is usually safer than driving an automobile. Society has accepted flight as a standard way of commuting from place to place and will put up with the stress and hassles associated with using fixed- and rotary-wing aircraft.

Though not yet a widespread reality, several visionary inventors and companies are planning the replacement of existing automobiles with sky cars—hybrids that run on the ground and in the sky. Moller International SE created a mock-up of a sky car with four ducted engines (one on each fender) that it claims will be able to hover, translate to forward flight, and land to a hover again, just like the V-22 Osprey. Other companies working on these vehicles are testing long-held design concepts of the automobile as a fixed-wing. Alfa Romeo departed from even that concept by showing the Spix, a concept car, as an air-cushion vehicle. In 2017, the German company Lilium completed the first tests of an electric jet-powered VTOL air taxi, which it claimed would cut down travel times and operate efficiently. Two years later, Lilium announced that it had successfully flown a five-person version of its air taxi as a test and had briefly demonstrated its ability to go from vertical to level flight. The growing ride-sharing industry also began exploring the potential of VTOL aircraft systems, with the company Uber pledging to introduce electric vertical takeoff and landing (eVTOL) vehicles in the 2020s. By 2020, Uber partnered with several companies to meet this goal, including Hyundai, which displayed a prototype the same year.

Traditional helicopter companies are trying to develop single-design helicopters that can be versatile in many roles and configurations. The latest designs in small helicopters have varying interiors and are meant to be used in various situations.

The Defense Advanced Research Projects Agency continues partnering with private companies like Northrop Grumman and Piasecki Aircraft Corporation to advance vertical takeoff and landing aircraft capable of faster speeds than the V-22 Osprey. In May 2024, Northrop Grumman received a contract with the Department of Defense to continue developing an autonomous vertical takeoff and landing aircraft. The US Air Force also continues investigating electric vertical takeoff and landing aircraft.

Bibliography

"Aerospace Engineers." US Bureau of Labor Statistics, 17 Apr. 2024, www.bls.gov/ooh/architecture-and-engineering/aerospace-engineers.htm. Accessed 10 June 2024.

"Bell Boeing V-22 Osprey Soars Past 600,000 Fleet Flight-Hours." Vertical, 24 Mar. 2021, verticalmag.com/press-releases/bell-boeing-v-22-osprey-soars-past-600000-fleet-flight-hours. Accessed 15 Mar. 2022.

Crosby, Francis. The World Encyclopedia of Fighter Aircraft: An Illustrated History from the Early Planes of World War I to the Supersonic Jets of Today. Lorenz Books, 2020.

"NASA Electric Vertical Takeoff and Landing (eVTOL) Aircraft Technology for Public Services – A White Paper." NASA, 20 Aug. 2021, ntrs.nasa.gov/api/citations/20205000636/downloads/2021-08-20-eVTOL-White-Paper-Final‗V48.pdf. Accessed 20 May 2024.

Grossman, David. "A Brief History of Vertical Take-Off and Landing." Popular Mechanics, 12 Jan. 2018, www.popularmechanics.com/flight/a15072284/video-history-of-vtol. Accessed 24 Aug. 2018.

Insinn, Valerie. "Air Force Declares F-35A Ready for Combat." Defense News, 2 Aug. 2016, www.defensenews.com/breaking-news/2016/08/02/air-force-declares-f-35a-ready-for-combat. Accessed 15 Mar. 2022.

Taylor, Derrick Bryson. "Humans Take a Step Closer to 'Flying Cars.'" The New York Times, 29 Aug. 2020, www.nytimes.com/2020/08/29/world/asia/japan-flying-car.html. Accessed 30 Nov. 2020.

Johnson, E. R. American Military Helicopters and Vertical/Short Landing and Takeoff Aircraft since 1941. McFarland & Company, Inc., Publishers, 2021.

Tresslar, Tim. "Air Force Pilots Reach New Program Milestones in Electric Vertical Takeoff and Landing Aircraft." Air Force Materiel Command, 25 Apr. 2023, www.afmc.af.mil/News/Article-Display/Article/3373134/air-force-pilots-reach-new-program-milestones-in-electric-vertical-takeoff-and. Accessed 10 June 2024.

Wang, Jie, and Baoli Ma. “Global Path Following Control for the Planar Vertical Takeoff and Landing Aircraft.” International Journal of Control, Automation and Systems, vol. 19, no. 12, 2021, pp. 4046–4055. doi.org/10.1007/s12555-020-0682-4.

Woodbridge, Ewan, et al. “Airborne Gamma-Ray Mapping Using Fixed-Wing Vertical Take-Off and Landing (VTOL) Uncrewed Aerial Vehicles.” Frontiers in Robotics and AI, vol. 10, 28 Jun. 2023. doi:10.3389/frobt.2023.1137763.