-T / T / +T | Comment(s)

Saturday, February 1, 2003

The All-Digital, All-Weather Helicopter

Eurocopter claims that, with its LCD smart displays, the EC-155B1 is the world’s first all-digital helicopter. In a demonstration program, the medium twin may become the first true all-weather helicopter, as well.

David Jensen

The European rotorcraft manufacturer, Eurocopter, has employed the first all-digital helicopter for a program it calls the All-Weather Helicopter (AWH). Expanding the capabilities of a highly sophisticated EC-155B1, Eurocopter is evaluating the use of GPS, differential GPS (DGPS), a stored terrain database, the SAGEM (formerly SFIM) Model 155, 4-axis autopilot, and a full three-dimensional flight management computer to ensure point-to-point helicopter operations in zero-visibility conditions.

Helicopters have long been able to fly in instrument flight rule (IFR) conditions, but when doing so, they often have had to adhere to flight movements and regulations tailored to fixed-wing aircraft. Eurocopter’s goal is to reduce the operational minima and expand the envelope of helicopter IFR operations, to take advantage of rotary-wing technology’s unique flying capabilities and flying environment.

To achieve this goal, Eurocopter is pursuing five technological areas:

  • Navigation in zero visibility down to the descent initiation (final approach) point;

  • Enhanced pilot information through the flight management systems (FMS);

  • Takeoff/landing aids for steep climb and descent gradients;

  • Ground obstacle collision avoidance in zero visibility; and

  • Economical de-icing equipment.

Partnered with Thales Avionics, Eurocopter is advancing these technological areas simultaneously, according to a Eurocopter official. "We have to develop each of them consistently with the others," he explains.

In advancing the five technological areas, Eurocopter intends to "improve the usage rate of helicopters, [to] make them fly in conditions in which they cannot fly today," says the official. Recognizing that such capabilities come with a price, he adds that "estimations of cost and benefit for operators have to be confirmed by the completion of our research program." (Costs, along with the constraints imposed on rotary-wing IFR operations, have thus far precluded the proliferation of IFR-equipped helicopters.)

Eurocopter and Thales began by testing AWH avionics in a simulator, and then started flying a fully equipped demonstrator EC-155B1 on Oct. 15, 2002, when the helicopter made its initial flight to confirm the operation of its on-board systems. The 50-minute flight took place at Eurocopter’s Marignane facility, near Marseilles, France. Systems and procedures testing is to proceed until 2004, when Eurocopter plans to incorporate the AWH avionics in production helicopters.

Precise Positioning

At Marignane, Eurocopter installed a DGPS ground station developed by France’s Service Technique de la Navigation Aerienne (STNA). It includes a stationary GPS receiver and a VHF transmitter that transmits differential corrections to the range errors from satellite signals as the helicopter makes its approach to land. The EC-155B1’s differential beacon receiver, made by Thales, receives data that pinpoints the aircraft’s position to within 1.5 feet (5 meters). The DGPS guidance coupled to the 4-axis (roll, pitch, yaw and altitude) autopilot allows the steep approaches (unique to helicopter performance capabilities) in zero-visibility conditions.

This precise positioning information is combined in the EC-155B1’s mission computer with three-dimensional flight plans and a terrain database, produced by the French government, to present the aircraft’s location geographically and in relation to terrain. Coupling the terrain data with a terrain awareness warning system (TAWS), provided by Thales, ensures safe navigation over all terrain and in virtually any weather condition.

The demonstrator EC-155B1 has two SMD68 6-by-8-inch displays that present the AWH-specific symbology that allows the pilot to follow accurately the steep approach path. The displays also show the mission information on a 3D map background. The flight route imagery from the FMS is overlayed on the map display, and a helicopter symbol indicates the aircraft’s position on the map.The TAWS imagery–with its red, yellow and green colors–is presented on either the map display or on either or both of the EC-155B1’s two navigational displays.

Evolutionary Process

The AWH program is part of a lengthy evolution of Eurocopter helicopters in general, and the EC-155B1 in particular (see sidebar below). The medium, twin-engined helicopter already has broken new ground with its digital Avionique Nouvelle avionics suite. Its cockpit design employs integrated modular displays and highly integrated symbology, which now are installed in all Eurocopter models–from the light 3,800-pound EC-120B Colibiri to the brawny 20,000-pound AS-332L-2 Super Puma. This display standardization indicates Eurocopter’s desire to mimic Airbus, its European fixed-wing counterpart, which installs comparable avionics suites in all of its models to facilitate transitional training, among other advantages.

Introduced with single-pilot IFR certification at the 2000 Heli-Expo show, the EC-155B1 was first delivered to the German border guard, which ordered 13 aircraft. More than 60 EC-155B1s have been sold, largely to offshore support operators, taking advantage of 13-passenger seating, corporate flight departments and parapublic (air medical and police operations) units.

For all operators, a fully digital helicopter provides important advantages: weight savings (thus better fuel economy) and reduced maintenance cost. It gives pilots more information than is provided by helicopters equipped with electromechanical or cathode ray tube (CRT) displays. And it allows for the incorporation of features, such as a TAWS, weather radar and traffic alert collision avoidance system (TCAS).

"Eurocopter has gone the step of making everything digital," says Jeff Warner, senior manager-commercial sales at Grand Prairie, Texas-based American Eurocopter. "This is not a digital display system that shows analog data."

To develop the Avionique Nouvelle suite, Eurocopter drew up the specifications for the display functionality, and Thales Avionics produced the systems hardware and software. "Eurocopter has taken the digital development from fellow EADS [European Aeronautic Defence and Space] companies and expanded that technology into the rotorcraft market," says a Eurocopter spokesman.

All Glass

The EC-155B1 cockpit panel typically includes no fewer than seven active matrix liquid crystal displays (AMLCDs). It has four SMD45 landscape-format 4-by-5-inch displays for flight control. Two of the displays (one on each side of the panel) serve as primary flight displays, showing an electronic artificial horizon, electronic attitude director indicator (ADI), altitude, vertical speed, autopilot mode and instrument landing system (ILS) with heading scale. The other two displays serve as navigational displays–showing radio navigation sources, automatic bearing, ILS, DME, map and route data.

In the central panel display system (CPDS) is a vehicle engine multifunction display (VEMD) with two 3-by-4-inch screens, and a 3-by-4-inch caution advisory display (CAD). Schematics on the CAD "tell you everything from whether a door is open to an engine going out or if there’s a fire," says Warner. "It will always give a visual warning but also could include an audio warning, depending on the seriousness of the alert," he adds. Optional on the EC-155B1 is one or two portrait-format 6-by-8-inch SMD68 displays, which can serve as enhanced nav display or a mission display presenting, for example, infrared imagery.

All are "smart" displays that house individual processors, according to Gil Michielin, Thales Avionics’ vice president in charge of helicopter systems. The displays receive navigation and flight data from dual-redundant processors located in the aircraft’s nose and linked to the panel by ARINC 429 data buses. The processors collect and prepare data from the sensors or computer (VOR, DME, FMS, air data, etc.) for transmission to the smart displays, which create the imagery.

The CPDS displays are controlled by buttons along the side of the screen. Two central console-mounted instrument control panels (ICPs)–one for each pilot–control the primary flight display and nav display. The center console also includes a control box for the aircraft’s attitude heading reference system (AHRS).

The integrated display system allows pilots to transfer data from one display to another, should there be a display failure. The system includes automatic transition modes, for example, between the navigation display and primary flight display on each side of the panel and among the VEMD and CAD displays, according to Michielin.

"PFD [information] and navigational display information appear on the remaining screen on the ‘faulty’ side of the cockpit panel, in what we call the ‘composite mode,’" says the Eurocopter official. "Some information may be sacrificed, but the essential information is on the remaining screen."

Pilots use the flight management system to input the waypoints, which appear on the nav display, dedicated to the FMS. (The standard FMS on the EC-155B1 is the Universal Avionics System UNS-1D, which can manage typical sensors, such GPS, VOR and DME.) The route can be overlayed on a Jeppesen map database or on a scanned paper map.

Standard on the EC-155B1 are Rockwell Collins Pro Line radios. Eurocopter suggests three avionics packages, tailored to three missions: corporate/VIP, offshore support and parapublic.

Within Limits

Perhaps a godsend for helicopter pilots–who must continually scan various instruments to monitor, for example, engine and transmission torque, gearbox and engine oil temperatures, and outside air temperature–is the EC-155B1’s "first-limit indicator," which is part of the VEMD. The flight control display module in the VEMD processor takes in the engine, aircraft and atomospheric parameters, fuses the data and then automatically indicates to the pilot the first limit he or she will reach during a period of flight. If it is a cold day, the transmission torque may be the first limit; on hot days, engine N1 speed would probably be the first limit. Regardless, the pilot looks at just one needle. If he or she does not "red line" the single needle, all systems are within their limits.

What also makes operating the EC-155B1 easier is the full authority digital electronic control (FADEC), managing the aircraft’s two Turbomeca Arriel 2C2 turboshaft engines. To start the engines, the pilot merely places the throttle controls in the "IDLE" position. He or she then places the controls in the "FLT" position, and the FADEC does the rest throughout the flight.

Eurocopter is considering the installation of a health and usage monitoring system (HUMS) in the EC-155B1. It would record anomalies, as well as data to optimize the track and balancing of the main and tail rotors, but would do so for the maintenance crew only, says a Eurocopter official. No warning would be displayed in flight. The HUMS would be activated automatically when the first engine starts, he adds.

A Long Lineage

The Eurocopter EC-155B1 may be a state-of-the-art helicopter, but its lineage dates back three decades. In June 1970, Aerospatiale Helicopter Division (later Eurocopter) initiated the development of the single-engine SA-360 Dauphin, which made its maiden flight June 1, 1972. Except for the finestron, an anti-torque rotor incorporated in the aircraft’s tail, the SA-360 bears only marginal resemblence to today’s EC-155B1.

It wasn’t long before Aerospatiale decided to develop a twin-engine Dauphin, the SA-365C, which was first flown in January 1975. Military versions of the Dauphin were developed, as was a variant for the U.S. Coast Guard, designated SA-366G1 (HH-65) Dolphin.

One special Dauphin was modified to incorporate an experimental fly-by-wire (FBW) system. Instead of the traditional cyclic control for pitch and yaw, the aircraft was fitted with a sidestick controller. Trials funded by France’s Service Francais Techique des Telecommunications et des Equipement Aeronautiques (STTE) determined pilot workload and the helicopter’s response time when pilots made command inputs to the FBW computer. The trials led to the development of a FBW system for the multirole NH-90 helicopter.

Another special variant, the AS-365X "Super Dauphin," was outfitted with five-bladed main rotor system and went on to set three world speed records with speeds exceeding 230 knots.

The latest Dauphin is the EC-155B1, with its larger fuselage, five-bladed main rotor and new-version Arriel engines. It first flew in June 1997, 20 years after development of the SA-360 was launched. Employed for Eurocopter’s All-Weather Helicopter program as a demonstrator aircraft, the EC-155B1 would appear to extend the Dauphin lineage still further into the future.

Live chat by BoldChat