Quadrotor
From Wikipedia, the free encyclopedia
 |
This article or section may require cleanup to meet Wikipedia's quality standards. Please help improve this article or replace this tag with a more specific message. This article has been tagged since July 2006. (help, talk) |
A Quadrotor is an aircraft that is lifted and propelled by four rotors. Quadrotors are classified as rotary-wing aircraft, as opposed to fixed-wing aircraft. Unlike the pure (as opposed to compound) helicopter, quadrotor craft can use fixed-pitch blades, as control of the vehicles motion can be achieved by varying the thrust and torque produced by each of the four rotors.
Contents |
[edit] Flight Control
Each rotor produces both a thrust and moment about its center of rotation, as well as a drag force opposite to the vehicle's direction of flight. If all rotors are spinning at the same angular velocity, with rotors one and three rotating clockwise and rotors two and four counterclockwise, the net aerodynamic torque, and hence the angular acceleration about the yaw axis is exactly zero, which implies that the yaw stabilizing rotor of conventional helicopters is not needed. Yaw is induced by mismatching the balance in aerodynamic torques (ie. by offsetting the cumulative thrust commands between the counter-rotating blade pairs).
Angular accelerations about the pitch and roll axes can be caused separately without impacting the yaw axis. Each pair of blades rotating in the same direction controls one axis, either roll or pitch, and increasing thrust for one rotor while decreasing thrust for the other will maintain the torque balance needed for yaw stability and induce a net torque about the roll or pitch axes. This way, fixed rotor blades can be made to maneuver the quad rotor vehicle in all dimensions. Translational acceleration is achieved by maintaining a non-zero pitch or roll angle.
[edit] History
[edit] Etienne Oemichen, Peugeot, 1920
Etienne Oemichen, a young engineer with the Peugeot motor car company, began to experiment with rotating-wing designs in 1920, and in all designed and built six different vertical take-off machines. When the first of these failed to develop enough lift from its twin rotors and 25 hp engine to rise off the ground, he added a hydrogen-filled balloon on top of it to give it added stability and lift. The most noteworthy - and most striking - of his aircraft was the helicopter No.2, which had no less than 4 rotors and 8 propellers, all driven by a single 120 hp Le Rhone rotary engine when it flew for the first time on 11 November 1932. A 180 hp Gnome engine was substituted later. The Oemichen No.2 was basically a steel-tube framework of cruciform layout, with 2-blade paddle-shaped rotors at the extremities of the four arms. The angle of these blades could be varied by warping. Five of the propellers, turning in a horizontal plane, served to stabilise the machine laterally; another propeller mounted at the nose was for steering the helicopter; and the remaining pair acted as pusher propellers for forward propulsion. The opposing pairs of rotors were of slightly different diameters. The Oemichen No.2 exhibited, for its time, a considerable degree of stability and controllability, and in all made more than a thousand test flights during the middle 1920s. By 1923 it was able to remain airborne for several minutes at a time, and on 14 April 1924 it established the first-ever FAI distance record for helicopters of 360m. Three days later it increased this to 525m and on 4 May was airborne for 14 min, flying more than a mile and completing in the process the first 1km closed-circuit flight by a helicopter in 7 min. 40 sec. Oemichen was, however, dissatisfied with the modest heights to which No.2 was able to fly, and from the third machine onward he adopted a single main rotor layout, accompanied by two smaller anti-torque rotors. His last design, in 1938, reverted to the balloon-assisted principle of his first aircraft.
[edit] George de Bothezat, Dayton, Ohio, 1922
In January 1921, the US Army Air Corps awarded a contract to Dr. George de Bothezat and Ivan Jerome to develop a vertical flight machine. The 1678kg "X"-shaped structure supported a 8.1m diameter six-blade rotor at each end of the 9m arms. At the ends of the lateral arms, two small propellers with variable pitch were used for thrusting and yaw control. A small lifting rotor was also mounted above the 180hp Le Rhone radial engine (which it also cooled) at the junction of the frames, but was later removed as unnecessary. Each rotor had individual collective pitch control to produce differential thrust through vehicle inclination for translation. The aircraft weighed 1700kg at take-off and made its first flight in October 1922. The engine was soon upgraded to a 220hp Bentley BR-2 rotary. About 100 flights were made by the end of 1923 at what would eventually be known as Wright Field near Dayton, Ohio, including one with three "passengers" hanging onto the airframe. Although the contract called for a 100m hover, the highest it ever reached was about 5m. After expending $200,000, de Bothezat demonstrated that his vehicle could be quite stable and that the practical helicopter was theoretically possible. It was, however, underpowered, unresponsive, mechanically complex and susceptible to reliability problems. Pilot workload was too high during hover to attempt lateral motion.
[edit] Convertawings Model "A" Quadrotor , Amityville, 1956
This unique helicopter was intended to be the prototype for a line of much larger civil and military quadrotor helicopters. The design featured two engines driving four rotors with wings added for additional lift in forward flight. No tailrotor was needed and control was obtained by varying the thrust between rotors. Flown successfully many times in the mid 1950's, this helicopter proved the quadrotor design and it was also the first four-rotor helicopter to demonstrate successful forward flight. Due to a lack of orders for commercial or military versions however, the project was terminated. Specifications: Rotor Diameter: 19'4", Length: 26', Engines: Two 90 hp Continental, Top Speed: 80 mph, Weight: 2200 lbs.
[edit] Bell Quad Tiltrotor Concept
With the Quad Tiltrotor concept, Bell seeks to capitalize on V-22 Osprey investments to develop a large payload, high speed, Vertical and/or Short Take Off and Landing (VSTOL) capability for the military within 10 years. The QTR would use V-22 propulsion and support systems: engines, rotor systems, drive train, transmission, hydraulics, electronics, and generators, except that QTR would have four engines, instead of two, mounted on fore and aft wings. The wing structure outboard of the flaperons would also be common; however the front wing would have a slightly longer span than the V-22 to accommodate the wider fuselage The rear wing would be longer than the front wing, putting the rear rotors outboard of the front rotors for higher performance and fuel economy in cruise. The front and rear propulsion systems could be interconnected for additional reliability. The glass cockpit, avionics, instruments, and threat warning systems could also be adapted directly from the V-22.
The QTR fuselage would be the size of a Lockheed Martin C-130-30 Hercules transport, and could transport a wide assortment of loads: eight 463L pallets, 90 passengers, 70 stretchers, a helicopter as large as an AH-64 Apache, a 155mm howitzer, or three HMMWVs. A rear ramp, rollers and rails would facilitate common logistics equipment used for the C-5, C-17, C-130 and C-141 loading. According to Bell, an advanced concept technology demonstrator (ACTD) could fly by 2005, with production deliveries beginning in 2010. Although it would be possible to use a modified C-130 fuselage for a demonstrator, there are very different structural requirements since the QTR has two wings versus the single wing of the Hercules. For production, lower weight and a better match for the expected payloads would be possible with a new fuselage. Although Boeing builds the V-22 fuselage, Dick Spivey, Bell's Director of Advanced Concepts, said Boeing would not necessarily be a partner on the QTR; either Bell or a subcontractor could build the fuselage. Bell has recently determined that it can eliminate the vertical tail entirely, and provide directional stability via differential rotor thrust.
The QTR would be able to deliver cargo from airfields and port facilities directly to ground maneuver units and to ships at sea, needing as little as 1/2 acre to land. The QTR would allow a practical means to transport up to 13500kg externally or 18000kg internally far from shore bases (due to its size, however, it would obviously not be able to be stowed below deck). With twice the propulsion system of the V-22, the QTR could hover at 45000kg and have a maximum weight of 63000kg; internal volume would be 6-8 times that of the V-22. Maximum unrefueled range would be 3700km and it could cruise at 520km/h. According to Spivey, Bell has flown two V-22s in close proximity to each other, approaching the distance between the fore and aft rotor system, with no difficulties. Water tunnel tests indicate that the rotor wake from the front rotors in forward flight flow down and inboard, below and inboard the rear rotors. It should also be noted that from 1966 to 1980, some 200 flight test hours were conducted on two Bell X-22 quad tilt duct demonstrators. Using common parts with the V-22 would not only reduce the cost of the QTR, but also that of the V-22. It would allow existing support equipment, test equipment and spares pipeline to be used for both aircraft, reducing the logistics footprint. Efficiencies in maintenance and training could also be realized.
Bell is discussing the Quad Tiltrotor with the Services to define potential requirements (e.g., the Joint Transport Rotorcraft/Joint Common Lift mission), and is pursuing possible risk reduction activities with DARPA. With the QTR, the Marine Corps could deliver thousands of tons of supplies per day to forward troops without having to depend on land supply routes. The Navy could deliver of tons of supplies to carriers and even non-aviation ships while underway, without the need for a catapult or arresting gear. The Army is seeking to replace the heavy lift CH-47 Chinook helicopters it uses today with much greater capability, and is currently funding advanced rotors, transmissions and structures science and technology programs. The Air Force could supply its aerospace expeditionary forces directly from forward operating bases. Humanitarian relief, such as was needed for Central America in October 1998 after hurricane Mitch, could be greatly improved with a large heavy lift V/STOL transport. And non-combatant evacuations could be conducted from the continental US to anywhere in the world using the QTR's aerial refueling capability. For example, in a hypothetical rescue mission, a QTR could take off from Quantico Marine Corps Base in Virginia and fly to the American Embassy in Moscow with two refuelings over the North Atlantic. The QTR could then take up to 80 passengers out to a vertical recovery on an American ship in the Baltic.
