Robinson R22
| R22 | |
|---|---|
| |
| Role | Light utility and trainer helicopter |
| Manufacturer | Robinson Helicopter (Torrance Airport, California) |
| Designer | Frank D. Robinson |
| First flight | 1975 |
| Introduction | 1979 |
| Number built | over 4,444 (2011) |
| Developed into | Robinson R44 |
The Robinson R22 is a two-bladed, single-engine light utility helicopter manufactured by Robinson Helicopter. The two-seat R22 was designed in 1973 by Frank Robinson and has been in production since 1979.
Development
Due to relatively low acquisition and operating costs, the R22 has been popular as a primary rotorcraft trainer around the world and as a livestock management tool on large ranches in North America and cattle stations in Australia. The R22 has a very low inertia rotor system and the control inputs are operated directly by push rods with no hydraulic assistance. Thus, the flight controls are very sensitive and require a light touch to avoid over correcting. A student that masters an R22 generally does not have a problem transitioning to a heavier helicopter. Due to the issues relating to a low inertia rotor-system and a teetering main rotor, operation by any pilot in the United States of the Robinson R-22 or R-44 requires a special endorsement by a certified flight instructor [1]. Tip weights were added to increase rotor inertia,[2] but the small rotor limits weight.[3]
Maverick and Renegade UAVs
The R22 is the basis for Boeing's Maverick military unmanned aerial vehicle helicopter, and its Renegade version. In 1999, Frontier Systems developed a remotely piloted R22, the Maverick. This aircraft, along with the company, was later acquired by Boeing Phantom Works. In 2003 the U.S. Navy purchased four aircraft, equipped with Wescam EO/IR (Electro-Optical/Infrared) systems.[4]
Boeing then modified one of the Mavericks further, calling it the Renegade, under contract with DARPA as a research testbed to develop software for its A160 Hummingbird.[4] The software system, known as the Software Enabled Control (SEC) program, was developed by Boeing and teams from the University of California Berkeley, Georgia Institute of Technology and Massachusetts Institute of Technology, and was first flown on May 26, 2005. During the flight, the SEC assumed control of the aircraft to "execute autonomous maneuvering algorithms".[5] The software allows the aircraft to autonomously select "optimal routes through a field of pop-up and already-known threats; flying low-level, terrain-hugging profiles to avoid detection; and determining safe landing zones by using vision-based algorithms to process landing site imagery and terrain height information."[6]
Design
The R-22 is a single-engined helicopter with a semi-rigid two-bladed main rotor and a two-bladed tail rotor. The main rotor provides a teetering hinge and two coning hinges. The tail rotor provides only a teetering hinge.
The normal production variant has skid landing gear. The Mariner version provided floats. Wheeled gear is not available.
The basic structure is welded chromoly steel tubing. The forward fuselage is made of fiberglass and aluminum with a Plexiglas canopy. The tailcone, vertical and horizontal stabilizers are aluminum. It has an enclosed cabin with side-by-side seating for a pilot and passenger. The doors may be removed for flight, and are often done so for photographic flights, interior cooling in high temperatures, or a 10.4 lb weight saving.
The first version was produced as the R22, followed by the R22 HP, R22 Alpha, R22 Beta and R22 Beta II. Superficially, the aircraft appear similar. The R22 HP was fitted with a 160 bhp Lycoming 0-320-B2C engine, an increase of 10 bhp (7.5 kW) over the original R22. The landing skid assembly on the R22 Alpha was modified by extending the rear struts, giving it a slightly nose-down attitude on the ground and better matching its attitude in a low altitude hover with two people onboard. The R22 Beta added an engine speed governor (optional), rotor brake and auxiliary fuel tank (optional). The battery was moved from below the instrument cluster to the engine compartment for better balance. It has been offered as an instrument trainer version, with optional fixed floats as the R22 Mariner, and other special configurations for police work, electronic news gathering, and so on. The R22 Beta II added a Lycoming 0-360 engine, remade of lightweight materials and derated for sealevel operation. It allows greater altitudes for hovering in and out of ground effect (HIGE/HOGE). The R22 Beta II also made the engine speed governor standard and included a "carb heat assist" which correlates adding carb heat with decrease in collective control. Only the basic skid style is currently being sold. The R44 is available as the Clipper with floats, and as police and electronics news configurations.
Controls
Instead of a floor-mounted cyclic stick between the pilot's knees, the R22 uses a unique teetering "T-Bar" control connected to a stick that emerges from the console between the seats. This makes it easier for occupants to enter and exit the cabin and reduces chances for injury in the event of a hard landing. The teeter bar has a hand grip on both sides that hangs down between the pilots' legs. Thus, if teetered to the right, the right side pilot would be flying and the left grip would be about 12 inches above the left pilot's lap. R22 flight instructors quickly learn how to fly with their hand in the air. The left part of the bar, left collective control, and left tail rotor pedals can be removed if the left seat occupant is not certificated to fly the R22 or needs the room for technical or observer duties. A floor-mounted foot activated push-to-talk switch facilitates intercom communications for the left seat occupant. The R22 has no artificial horizon indicator.
The helicopter rotor system consists of a two-bladed main rotor and two-bladed anti-torque rotor on the tail, each equipped with a teetering hinge. The main rotor is equipped with two coning hinges. Collective and cyclic pitch inputs to the main rotor are transmitted through pushrods and a conventional swashplate mechanism. Control inputs to the tail rotor are transmitted through a single pushrod inside the aluminum tail cone.
To ease the pilot's workload, a mechanical throttle correlator adjusts the throttle as the collective pitch control is raised or lowered. The pilot only needs to make small adjustments by twisting the throttle grip on the collective throughout the flight regime. Later models are also equipped with an electronic governor which works to maintain RPM within normal operating limits (between 97 and 104% RPM); the governor is only active when the engine is running above 80% RPM, and is most effective in normal flight conditions.[7]
Powerplant
The R22 uses a horizontally mounted Lycoming O-320 (O-360-J2A on the Beta II), four-cylinder, air-cooled, normally aspirated, carburetor-equipped piston engine. It is fueled with 100LL grade aviation gasoline. Cooling is provided through a direct drive squirrel-cage blower. At sea level it is capable of producing more power than the transmission and rotor system can safely handle, and to ensure maximum engine and transmission life the O-360 must be derated, or operated at less than maximum power. As the air becomes thinner with increasing altitude, maximum available horse power decreases, reaching a point where the throttle can be completely open and rotor RPM is controlled by collective position. By derating the engine at sea level, the R22 achieves acceptable high-altitude performance without use of supercharging or turbocharging, thus saving the weight, complexity, unreliability, and shortened engine life of a forced induction system.
A carburetor is used to provide the air-fuel mixture. Carbureted engines are susceptible to carburetor icing, a condition most likely to occur in conditions of low (11°C) difference between the outside air temperature and dew point (the "dew point spread"), as well as visible signs of moisture in the atmosphere. Icing can lead to loss of engine power, and if not corrected total shutdown of the engine. A carburetor heat control is available to supply heated air to the carburetor; this can prevent or cure icing, but also causes a reduction in engine power output because hot air is less dense. The R22 employs a carburetor air temperature gauge, marked to indicate temperatures conducive to icing. The Beta II version of the R22 also includes a "carburetor heat assist" which automatically applies carburetor heat when the collective is lowered below a certain point. When icing conditions are present carburetor heat is required to prevent icing around the butterfly valve from the pressure drop at that point. As the Carburetor Air Temperature (CAT) indicator does not read correctly below 18" of intake manifold pressure, icing conditions require applying full carburetor heat below 18" of manifold pressure. A placard indicating this requirement is located on the CAT indicator and in the Pilots Operating Handbook (POH).
Power is transmitted from the engine to the rotor system through drive belts. Originally, the R22 used four separate v-belts. This system proved problematic, as belt length variations due to manufacturing tolerances caused some belts to overstress and break. In 1982, R22 operators received a kit from Robinson that was installed in the cockpit and clutch worm-gear motor that isolated the tensioning circuits and locked the clutch/drive system at take-off tension, but this was only a stop-gap measure. The problem was solved by replacing the four individual belts with two dual-v belts, running on matching multi-groove sheaves. The upper driven sheave is mounted on the tail rotor drive shaft next to a flexible coupling and is raised and lowered relative to the engine-mounted driving sheave by means of a small electric gear motor. During shutdown, the gear motor is used to lower the top sheave to loosen the drive belts. For startup, the engine is started with the belts loose, allowing the engine to run without spinning the rotor system. Immediately after engine start, the clutch switch located in the cockpit is closed by the pilot, powering the gear motor to slowly move the top sheave up to flight position which tightens the belts. The gear motor is thereafter controlled by a pressure-sensing switch, automatically maintaining proper belt tension during flight as the belts warm up and stretch. The tail rotor drive shaft also turns the main transmission, delivering power to the main rotor shaft through a pair of spiral bevel gears.
The top sheave has an over-running clutch built in to the middle to allow the rotor system to continue to rotate in the event the engine stops. This allows the R22 to enter auto rotation and land in a controlled manner after loss of engine power. Because the main rotor has very little mass and resulting inertia, auto rotations in an R22 are exciting at best and require careful and proper execution to assure a successful outcome. Much time is spent in training practising various types of autorotation. Target speed in an auto rotation is 65 kn (120 km/h) and the glide angle is approximately 4:1 in max glide configuration.
Variants
- R22
- Initial production version powered by a Lycoming O-320-A2B or A2C piston engine.
- R22 HP
- Higher-powered version, powered by a 160-bhp Lycoming 0-320-B2C piston engine.
- R22 Alpha
- Improved version certified in 1983 powered by a Lycoming 0-320-B2C piston engine.
- R22 Beta
- Fitted with a more powerful engine, powered by a Lycoming 0-320-B2C piston engine.
- R22 Beta II
- Fitted with a more powerful engine, powered by a Lycoming O-360-J2A piston engine.
- R22 Beta II Police
- Police patrol version, equipped with searchlight and loudspeaker.
- R22 Mariner
- Designed for off-shore work, fitted with floats and wheels, powered by a Lycoming 0-320-B2C Beta piston engine. Limited to daylight operations when fitted with floats.
- R22 Mariner II
- Designed for off-shore work, fitted with floats and wheels, powered by a Lycoming O-360-J2A Beta II piston engine. Limited to daylight operations when fitted with floats.
- R22 Police
- Police version.
- R22 IFR
- Designed for IFR training with a larger 10-hole panel to accommodate additional instruments. Not IFR certified so training must be done with a safety pilot in VFR conditions.
- Maverick UAV
- Unmanned military version marketed by Boeing
- Renegade UAV
- Unmanned R&D version built for DARPA
Operators
The R-22 is operated by many private individuals, companies and flying clubs. In Australia, where there are 489 R22s registered as of mid-2011, a survey found that 62% of the fleet's flying time was in mustering operations, while 13% of hours were spent in training pilots. Many broadcasters used the R-22 until the mid-1990s when the financial landscape of radio broadcasting in the U.S. changed due to deregulation of the industry.[8]
Military
Accidents and incidents
The R22 has had 182 fatal accidents between December 1975 and June 2010 from a total of 1,230 incidents. [9] In late 1981, the R22 became the first (and, to date, only) US helicopter to have its type certificate (FAA #H-10-WE) revoked by the Federal Aviation Administration due to the agency's conclusion that the main rotor blades tended to suffer catastrophic failure in flight. An early fatal accident was traced to a blade delamination, which was, in turn, traced to the Robinson rotor blade sub-contractor. The blades were assembled using special adhesives which were applied, then "set-up" overnight. The sub-contractor's factory had a mosquito problem, and a gasseous "mosquito bomb" interacted with the blade adhesive and degraded its efficacy which led to downstream delamination.
Specifications (R22)
Data from Robinson R22 Pilot's Operating Handbook.[7] Current versions of the R22 vary slightly.
General characteristics
- Crew: 1Main tank total capacity: 19.8 US gallons (75 liters)
- Main tank usable capacity: 19.2 US gallons (73 liters)
- Optional aux tank total capacity: 10.9 US gallons (41 liters)
- Optional aux tank usable capacity: 10.5 US gallons (40 liters)
Performance
- Endurance: approx. 2 hours, with 30-minute reserve
See also
Related development
Aircraft of comparable role, configuration, and era
References
- ^ SFAR No. 73 to Part 61 in the Federal Aviation Regulations
- ^ http://www.unicopter.com/0385.html
- ^ Borrows, David A. Rotor RPM Flight Training, March 1998. Accessed: February 2011.
- ^ a b Boeing Maverick at Designation Systems
- ^ Boeing Team Demonstrates Advanced Autonomous Flight Control for UAVs "Boeing Team Demonstrates Advanced Autonomous Flight Control for UAVs" Boeing news release, June 21, 2005
- ^ "Boeing Completes Successful Autonomous Flight Control Technology Program", Space Daily, March 20, 2006
- ^ a b Robinson Helicopter Company (1996-10-22). R22 Pilot’s Operating Handbook and FAA Approved Rotorcraft Flight Manual. pp. 2–2, 7–17.
{{cite book}}: Cite has empty unknown parameter:|coauthors=(help) - ^ Marchbank, Margo, ed. (2011). "Stockhorse of the sky: the Robinson R22". Flight Safety Australia (81). Civil Aviation Safety Authority: 14–15. ISSN 1325-5002.
{{cite journal}}:|access-date=requires|url=(help); Unknown parameter|month=ignored (help) - ^ "R22 Accident Database". Griffin Helicopters. Retrieved 7 August 2011.