By the early thirties the autogiro had a relatively stable control system that used the rotating blades for control of vertical flight at very low speeds
. By the end of the decade, World War II was under way and the United States Military released a request for bids from aircraft manufacturers to design and build a helicopter. Contracts were given to Sikorsky Aircraft in Bridgeport and Platt-LePage in the Philadelphia, and from this the American helicopters were developed.
V. American Helicopters
There are four general helicopter designs which have been developed and produced in the United States: the most common being the tail rotor design, more popularly known as the single rotor design, which has one main rotor and a small tail rotor. Other rotor designs produced in America include the tandem rotor design, the syncropter design and the coaxial design
. The single main rotor and a small anti-torque rotor dominate modern helicopter design today.
By 1940, just after the start of WWII Sikorsky had developed a helicopter that could fly but it was impractical for military use because the system was too complicated for trainee pilots
. Within a few years of this early design, Sikorsky gained access to the Autogiro Company's patents and designs. Once the autogiro rotor system was added to Sikorsky's earlier designs he was able to deliver a simple and flyable helicopter to the United States Military.
Gyrodyne Company of America, Inc. began to occupy the field of design, development, testing, and production of coaxial helicopters starting in the late 1940s once Sikorsky's WWII contract with the military ended
. From the mid-fifties to the early seventies, Gyrodyne manufactured and sold approximately 800 coaxial helicopters. Gyrodyne ceased development on coaxial designs in the mid 1970s due to financial difficulties but it was at the forefront of numerous technological milestones that paved the path for the contemporary helicopter.
VI. Tilt Rotor Aircraft
A tiltrotor aircraft, unlike traditional helicopters combines the vertical raise and hover capabilities of a helicopter with the forward motion speed and range of a fixed-wing airplane. It gets its lift and propulsion through powered rotors mounted on rotating shafts at the end of a fixed wing
. For vertical flight, the rotors are angled maintain a helicopters horizontal plane of rotation. The rotors tilt forward as the aircraft gains speed to culminate in a vertical plane of rotation that provides propulsion for forward flight. In this mode the wing provides the lift, and the rotor provides thrust as a propeller
. The wing provide the lift and move at the same speed as the craft to help the tiltrotor reach speeds in excess of that achieved by traditional helicopters
. By combining a helicopter's operational flexibility with the greater speed, range, and efficiency of fixed-wing airplane, the tilt-rotor craft can perform such missions as troop/cargo transport, amphibious assault, special operations, and search and rescue operations.
For the past twenty years, the United States Army, Airforce and Marine Corps have been producing the V-22 tilt-rotor aircraft and Congress continues to support government funding for this aircraft in spite of critical testimony that the tilt-rotor technology is too risky as it has been the cause of several life-taking accidents
. The V-22 can carry much larger payloads than the traditional CH-46 helicopter that it replaced. Additionally it can fly five times the range, twice as fast and is twenty-one times less vulnerable to small arms fire than traditional helicopters
. It makes less than half the sound that traditional rotors and engines make and it is the only U.S. tactical transport aircraft with designed-in nuclear, biological and chemical warfare protection
. Further, the newest MV-22 Osprey unmanned aircraft increases ease on battlefield because of it's size. It folds up into a cargo container and can be taken out and put together in working order by a couple of troops in the field
The potential usefulness of the V-22 to the government and military however may shortly be made obsolete by developments in the mono-tiltrotor aircrafts. Currently in development by Aerocoper, a Boston-based aircraft facility, the mono-tiltrotor aircrafts combine the traditional usefulness of the helicopter/fixed wing airplane nature of the tilt-rotor craft with a large UFO type ring [see image below]. This new prototype has a single turbine that powers a ducted fan pusher propeller and an electromagnetically driven diameter ring circling the fuselage. The rotor blade of the right has counter-rotating upper and lower halves that generate lift. The encircling ring is turned by permanent magnets attached to the driveshaft and the circumference of the ring holds several magnets at short intervals. The ring is designed to turn by the magnets throughout lift off and then lock in place by the magnets when the craft reaches an altitude of 1000 feet
Aerocopter also stresses the usefulness of the mono-tiltrotor as a personal air vehicle that can replace traditional car use. The company also touts its environmental and societal benefits such as decreased emissions, increased safety resulting from fewer cars on the road and robotic navigation, decongestion due to increased capacity on highways and increased mobility due to faster transport
. However, one issue that is not addressed by Aerocopter is the availability and adaptability of current aviation airports to an influx of daily use personal aircraft. The congestion that such use could create at airports may be so extreme as to not warrant the public's use of such personal mobility aircraft.
Figure 3: Computer-generated image of the mono-tiltrotor prototype
Aside from military purposes, tiltrotor aircrafts have numerous commercial potential. The BA609 [see image below] is the world's first commercially available tiltrotor aircraft. It is currently in development by Bell Agusta Aerospace Company to fulfill a number of commercial roles including speedy corporate transport for routes between 90km and 900km; offshore utility, with an operational radius of around 450km; coast guard; emergency medical services, with capacity for two stretchers plus three medical staff; and search and rescue
. According to the aerospace technology website, "the BA609 has a composite fibre-placed fuselage with aluminum internal structure, a six to nine-seat pressurized composite cabin and two composite three-bladed proprotors on swiveling nacelles.
Figure 4: BA 609 commercial tiltrotor aircraft
VII. Future Rotorcraft Capability
Many engineers and aeromechanics believe, due to vague government projections for improvement of rotorcraft capability, that any advances in helicopter-type crafts will be made in the civilian sector
. The building social trend toward miniatures has extended into the designs of future rotorcrafts as many attempts have been made to reduce the rotorcrafts size and to realize fully autonomous ?ight. A multi-year, 35-million-U.S.-dollar launched by DARPA in 1997, directly aims to develop micro-air- vehicles such as the Fancopter UAV system, whose largest rotor span is no more than 15 cm. Unfortunately, results have exhibited that a 15 cm UAV is too small to be useful or workable
. However, significant strides have been made in the way of the Epson Tokyo micro-flying robot [see image below]. The mini rotorcraft has potential for providing unique combat support for battles in con-ned areas such as streets
Figure 5: The 2004 Epson Tokyo Micro Flying Robot
Attention has recently shifted to the development of larger miniature unmanned aerial rotorcraft vehicles with practical applications. One successful application of the rotorcraft unmanned aerial vehicles (UAV) is in the civil domain is the pesticide spraying in agriculture and forestry. As a result of the Japanese Ministry of Agriculture's 1983 request for crop dusting helicopters from Yamaha, the most representative examples of UAV's for this purpose are the Yamaha R50 and Rmax helicopters
. These UAV's reduced the labor and costs in the rice farming industry. The R50 and Rmax series have now emerged as the dominating force in the pesticide spraying service
The unmanned aerial vehicle also provides a platform for surveillance and reconnaissance in some crucial tasks such as range safety monitoring, arms transfer monitoring, and mine detecting
. As far as arts and entertainment are concerned, the miniature UAV'S are capable of providing a birds-eye view of stadiums or capturing aerial footage for special effects in movies
. Further applications include assisting workers and engineers to solve engineering and construction problems, which are dif-cult to resolve through conventional means. For instance, the Automatic Lab of Chiba University has successfully developed a rotorcraft UAV, called Sky Surveyor2 equipped with a vibration-free PTZ camera to help Chugoku Electric Power conduct inspection on power transmission lines between each conjoined high-voltage tower
The civilian sector however is not solely engaged in miniature aircraft, but is also focusing on improving the traditional manned helicopter. The current tilt-wing MV-22 Osprey, can hit speeds upward of 240 knots, but it's a hybrid machines, thus to reach heightened speeds it needs to fly like a fixed wing airplane. However, the X2 technology, currently in development by Sikorsky will allow a coaxial helicopter to reach speeds almost twice as fast…