Bombardier's Canadair CL-227 unmanned air-vehicle is finally being prepared for production.
Graham Warwick/MONTREAL
Unmanned air-vehicles (UAVs) come and go, but the Canadair CL-227 just keeps on going - or so it seems. Although similar externally, the production CL-227 now taking shape at Bombardier's Canadair Defence Systems division will be a very different machine to the original "Peanut" vertical take-off and landing (VTOL) UAV first flown in 1978.
After years of chasing requirements, Bombardier took the bold step in late 1994 of launching the design of a production CL-227, in the belief that customers would come forward once a definitive vehicle is available. Design of the production CL-227 will be completed by the middle of the year and the major improvements planned (a new engine and avionics) will be flight-tested later this year.
"We are looking at how to transition [the CL-227] to production," says vice-president, aviation services, Jean Girard. "We are looking at reliability, cost reduction, and at establishing a 'bogey' price for the vehicle," he says. Bombardier aims to have the production design ready to enable the company to compete for the US Army's Manoeuvre (formerly Close-Range) UAV contract, which could be awarded as early as September.
Bombardier also believes that a production-ready vehicle will give it a leading position in what it sees as an emerging market for "turn-key" UAV systems with paramilitary and commercial customers. The focus of current activity is the US Coast Guard, which has a near-term requirement for an off-the-shelf VTOL UAV able to be operated from small ships' decks, says US UAV-marketing director Michael Hughes.
"We need a launch customer," admits Girard, citing the Manoeuvre and Coast Guard requirements, both for "non-developmental" UAVs, as good prospects. The aim of the current production-design phase is to define a baseline configuration, "to put a stake in the ground...so that we can go to the customer with a real price [and guaranteed performance]," he says.
Design origins
The CL-227 has its design origins in the tail rotor of the Canadair CL-84 tilt-wing aircraft. The tail-rotor designer, Servotec (formerly Cierva Autogyro) of the UK, also designed for Canadian Westinghouse a tethered air-vehicle which was intended to provide over-the-horizon targeting for long-range wire-guided missiles. The 70kg vehicle had two 1.4m (4.6ft)-diameter contra-rotating two-blade rotors driven by 4.5kW electric motors, with power coming to the vehicle via its 2,400m-long "extension chord".
Canadair picked up the design when it was cancelled in 1968 and decided to unplug the Peanut and let it roam free to realise the flexibility of a VTOL UAV. The vehicle was extensively redesigned, re-engined with a Wankel rotary, and flown for the first time in 1978.
Two air-vehicles were flown tethered 300 times to prove the concept of the rotary-wing UAV. The vehicle was evaluated by the US Army, but the concept proved to be ahead of Army thinking and to need significant development, Hughes says. Lift had to be increased, reliability improved, and a "heavy-fuel" engine was required.
The Wankel rotary engine was replaced by a Williams WTS34 turboshaft, and four air-vehicles completed 13 free flights, as well as a further 100 tethered flights, in a technology-demonstration phase. Full-scale engineering development was launched in 1984, and in the process the vehicle was redesigned from the ground up for reliability.
The development phase, which included ten air-vehicles and 50 tethered flights, was followed by a series of demonstrations and evaluations which ran from 1988 to 1994 and included 168 free and 579 tethered flights with four air-vehicles.
Improvements incorporated in the production air-vehicle will reduce weight by 5.5kg, increase endurance by 15min, improve navigation accuracy and improve autonomous-flight capability. The design goal is to provide a flight endurance exceeding 3h, with an objective of 4h, while carrying a mission payload exceeding 22.5kg. The improved engine and avionics will be flight-tested in a CL-227, beginning in September, says Hughes.
Peanut shape
The Peanut earned its nickname because of its unusual shape. This stemmed from the decision to locate the rotors on the vehicle's centre of gravity, to provide direct control of airframe attitude. Mounting the rotors centrally meant that the payload had to be mounted below, for an unobstructed view, and the engine above, for balance. The resulting vehicle consists of three modules: powerplant, propeller and payload.
Mounting the engine above the rotor had the additional advantage of reducing infra-red (IR) signature. The 95kW (130hp) Williams WTS117 turboshaft is installed vertically, inside an annular fuel tank, breathing through slots in the rotor hub and exhausting upwards, away from the ground.
The turboshaft, derated to 45kW for the production CL-227, is of similar configuration to the original WTS34, with single centrifugal compressor and turbine stages, but is more powerful, less expensive and more reliable. Exhaust-gas temperature is lower, reducing IR signature. The annular fuel-tank - the engine will run on diesel or kerosene - has been increased in capacity and is now made from composites, rather than metal, to reduce weight.
Integrated with the engine is the differential gearbox ,which splits torque between the two rotors. The rotor system consists of two, 2.8m-diameter, contra-rotating, rigid rotors each with three quick-attach glassfibre reinforced plastic/Kevlar blades. The 975RPM rotor speed results in low noise, making the vehicle virtually undetectable, Hughes says.
The blades themselves are almost transparent to radar. The inlets were redesigned for the Maritime VTOL UAV System (MAVUS) programme to reduce radar returns. US Army measurements indicate that the air-vehicle signature is small enough to avoid shoulder-launched surface-to-air missiles, he says.
The structural backbone of the vehicle is a central tube to which the upper and lower rotor-hub centres are attached. These centres house the rotor drive-trains. Each hub consists of a titanium spool with upper and lower titanium plates. Aluminium blade-retention blocks clamped between these plates house the blade-pitch bearings: wound-wire tie bars attach the blade roots to the hub spool and carry the centripetal loads.
Blade pitch is controlled by a swashplate assembly mounted between the rotors and moved vertically (collective pitch) or tilted (cyclic pitch) by three linear actuators operating in unison or differentially. The centre, non-rotating, swashplate is mounted on the central tube and gimballed. Upper and lower swashplates rotate with the respective rotors and are connected to the blade roots by pitch links.
Blade pitch is used to control the vehicle in pitch and roll, and vertically. The contra-rotating rotors eliminate rolling moments caused by differences in lift on the advancing and retreating blades. Yaw control is by differential rotor torque. Magnetic-particle clutches in the upper hub-centre act on the drive shafts to the upper and lower hubs. Energising one clutch transfers torque to the other shaft, the unequal torque causing the vehicle to yaw.
The CL-227 is inherently unstable, and is controlled by an autopilot which provides pitch, roll and yaw stabilisation and altitude hold. The axisymmetric vehicle is tilted for horizontal flight, and flies in the direction of the tilt; "It doesn't care which way it is pointing," Hughes says. Steering is via waypoints preprogrammed into the autopilot or updated in flight via the payload datalink. If contact is lost, the vehicle remains upright and executes automatically a datalink re-acquisition pattern.
Avionics are housed in the upper part of the payload module, beneath the rotors. Two honeycomb discs separated by four honeycomb webs at 90¡ form quadrants in which are housed the electronics and power supplies, accessible via quick-release Kevlar panels. Sockets for the quick-attach glassfibre-reinforced-plastic landing legs, complete with shock absorbers, are an integral part of the module structure.
Upgraded avionics under development for the production CL-227 by risk-sharing partner Lear Astronics consist of a single line-replaceable unit housing a fibre-optic-gyro inertial sensor, global-positioning-system (GPS) receiver, and a computer. The 9kg unit is smaller and lighter than the avionics it replaces, with increased processing power, lower cost and increased reliability, Hughes says.
The functions of the new unit include:
attitude and heading reference;
multi-mode GPS/inertial navigation;
vehicle control and stabilisation;
optional air-data computation;
mission-data loading;
waypoint guidance.
Core avionics reliability is increased by more than 250% and life-cycle cost reduced by a factor of three, Bombardier says.
The company has succeeded consistently in training inexperienced soldiers to operate the CL-227 within four weeks, Hughes says. The bulk of training is accomplished using the actual air-vehicle, tethered top and bottom to a gantry, and ground station. The remaining tasks are taught with the vehicle in free flight on a safety tether.
Payload studies
Several payloads have been carried by the CL-227 over its life. Most recently, for the MAVUS demonstrations for the US UAV Joint Programme Office (JPO), the vehicle carried a gimballed television or forward-looking infra-red (FLIR) sensor, or communications-relay or electronic support-measures payloads.
Payloads now being studied include a low-volume spray system and a chemical/solvent-detection sensor. Missions being considered include psychological operations, using a loudspeaker, leaflet drops, or TV or radio broadcasts; and special-operations-force resupply, with a parachute-deployable payload.
Other missions under study include tactical communications-relay; near-shore mine detection; electronic-warfare deception (helicopter decoy); aerial dispensing of mines, unattended ground sensors and sonobuoys; and laser designation. Paramilitary and commercial uses identified include cross-border counter-narcotics operations; crowd control and monitoring; and surveillance of power-station emissions.
The US Army's Manoeuvre UAV requirement is for a vehicle with 3-4h endurance, providing 1.5h on station at a 50km (27nm) radius of action. Payloads include FLIR and meteorological sensors, and possibly a laser designator. A draft request for proposals (RFP) was issued in early 1995 and a final RFP is expected in May. Award of a low-rate initial-production contract could come as early as September.
Stringent tests provide valuable lessons
Canadair's CL-227 has been tested, demonstrated and evaluated more than any other vertical take-off and landing unmanned air vehicle (VTOL UAV). "There are a lot of VTOL concepts out there," says Hughes, "but the CL-227 is a mature, 'third-generation', UAV." The assessment of maturity is based on the results from two demonstrations conducted under the Maritime VTOL UAV System (MAVUS) programme.
Funded by the US UAV Joint Programme Office (JPO), the MAVUS trails evaluated the operational utility of a ship-based VTOL UAV. Bombardier received the first MAVUS contract in May 1990. The MAVUS was a system, not just an air-vehicle, and the Canadian company assembled a team to produce the total system, including: mission planning and control system (Loral); datalink (Loral); launch and recovery system (Indal); and payloads.
The demonstration system, including three air-vehicles, was installed in the helicopter hangar of the US Navy frigate USS Doyle for trials with a NATO task force operating in the North Atlantic. During the evaluation, the CL-227 was launched and recovered in 2-2.5m waves; underwent 2h-plus shore-reconnaissance missions, operating up to 60km (30nm) from the ship; and datalinked real-time imagery back to the Doyle for rebroadcast to other NATO ships.
The MAVUS trials produced "excellent results and valuable lessons," Hughes says. A second series was ordered, the MAVUS II, specifically to demonstrate an automatic-landing system developed for the JPO by Sierra Nevada. Despite problems with ship availability, which cut short the at-sea flying, these trials were completed successfully in May 1994.
With US Navy, NATO and French navy maritime VTOL-UAV requirements in mind, Bombardier is working on improvements to the MAVUS configuration. The launch and recovery equipment, based on Indal's RAST helicopter-recovery system, will be made lighter and more compact, Hughes says.
The launch and recovery system consists of a self-propelled traverser, complete with hydraulic arm for handling the UAV, and a landing grid. For launch, the CL-227 is moved from hangar to flightdeck on the back of the traverser, which is equipped to start, initialise and launch the UAV. For recovery, the traverser pushes out a landing grid. Locks on the vehicle's feet engage the grid and hold the UAV down after landing.
For the MAVUS II automatic-recovery trials, the CL-227 was acquired by a laser tracker mounted on the ship's aft datalink-antenna and guided automatically on to the grid. The vehicle can be recovered safely with only one leg locked to the grid. "It won't fall over," Hughes says. During the MAVUS II trials, the furthest from the centre of the 3.6m-wide grid that the CL-227 was landed was 200mm, he says.
The US Navy's requirement is now dormant, lacking funds, but efforts are under way to revitalise US VTOL UAV efforts, Hughes says, adding that France is planning a JPO-style technology demonstration. The Canadian company is talking to potential French-industry partners in the programme, he says.
Source: Flight International
