The EC-135 light twin was intended as a replacement for Eurocopter’s successful Bo.105. The combination of the Bo.108 and the fenestron (shrouded tail rotor) led to the definitive EC-135 which had its first flight on 15 February 1994 at Ottobrun, Munich.
Built using composite materials, the EC-135 is a modern technology helicopter incorporating the latest in modular cockpit design and Anti-Resonance Isolation Systems etc. The tail-rotor has been replaced with a 10-blade advanced Fenestron and the helicopter incorporates the latest bearingless main rotor system. It can be powered with either Pratt & Whitney 206B, or Turbomeca Arrius 1B1 powerplants managed through a FADEC control system. With an all-up-weight of 2485kg, the EC-135 has a larger cabin area than the Bo.108 and has been designed to accommodate seven adults or five in luxury club seats. Intended to replace the successful Bo.105 series, the EC-135 has been designed for reduced operator costs and to provide ease of maintenance.
First flight on 15 October 1988 as a technology prototype, D-HBOX, previously known as BO 108, powered by two Rolls-Royce 250-C20R turboshafts with conventional tail rotor. A new all-composites bearingless tail rotor was tested during 1990. Eurocopter announced in January 1991 that BO 108 was to succeed BO 105. The first flight of the second prototype (D-HBEC) powered by two Turbomeca TM 319-1B Arrius was on 5 June 1991, and production main and tail rotors were flight tested during 1992 in preparation for certification programme. The design was revised late 1992 to increase maximum seating to seven; advanced Fenestron adopted.
Two preproduction prototypes D-HECX and D-HECY made first flights respectively on 15 February and 16 April 1994 powered by Turbomeca Arrius 2B and P&WC PW206B intended as production alternatives. The third preproduction prototype (D-HECZ) made its first flight on 28 November 1994, powered by Arrius 2B, and subsequently made the type's US debut at HeliExpo '95 in Las Vegas in January 1995. Total flight time of first three preproduction EC 135s was nearly 1,600 hours by the end of 1996, by which time all three preproduction prototypes had been retired. VFR certification to JAR 27 was achieved on 16 June 1996 and to FAR Pt 27 with Category A provisions and for both engine options, on 31 July 1996. IFR certification was awarded jointly by DGAC (France) and LBA (Germany) on 9 December 1998, while that for CAA was attained late 2000. LBA (JAA) single pilot TFR certification was achieved on 2 December 1999, and certified in 17 countries by June 2000. The first two production aircraft were delivered to Deutsche Rettungsflugwacht on 31 July 1996.
More than 300 were on order by 92 customers in 25 countries by January 2003. The 100th was delivered (to Bavarian Police) on 16 June 1999, and 250th to Spanish operator CoyotAir on 25 October 2002, some two-thirds with Turbomeca engines. Thirty were ordered in 1999, 40 in 2000 and 38 in 2001. Deliveries totalled 37 in 1999 and 31 in 2000.
The development programme was funded by Eurocopter Deutschland and Eurocopter Canada, suppliers, and German Ministries of Economics and Research and Technology. Flyaway cost was US$2.39 million (1996). Designed to FAR Pt 27 including Category A and European JAR 27, of pod-and-boom configuration, with Fenestron. Forward flight stability is by two horizontal and four vertical (fin, underfin and two endplates) surfaces. Equipped with a four-blade FVW bearingless main rotor, single-piece rotor head/mast, rotor rpm are variable. Composites blades are mounted on controlled flexibility composites arms giving flap, lag and pitch-change freedom. Control demands are transmitted from rods to root of blade by rigid CFRP pitch cuffs. The main rotor blades have DM-H3 and -4 aerofoils with non-linear twist and tapered transonic tips, and the main rotor axis is tilted forward 5 deg. The Fenestron has 10 asymmetrically spaced blades.
Airframe drag 30% lower than BO 105 by clean and compact external shape; cabin height retained by shallow two-stage transmission; vibration reduced by ARIS mounting between transmission and fuselage; all dynamically loaded components to have 3,500 hours MTBR or be maintained on-condition.
The second BO 108 prototype had EFIS-based IFR system; fuselage stretched 15cm and interior cabin width extended by 10cm; main rotor diameter extended to 10.20m; for EC 135, tail rotor replaced in 1992 by New Generation Fenestron with 11 fixed flow-straightening vanes in fan efflux designed to avoid momentum losses and improve fan figure of merit; vanes are swept relative to radius and fan has different number of blades to avoid shocks and reduce noise; fan blade tip speed is only 185m/s; maximum T-O weight increased to 2,720kg.
Conventional hydraulic fully powered controls with integrated electrical SAS servos; objective is single-pilot IFR with cost-effective stability augmentation. Electric cyclic trim system.
The airframe mainly Kevlar/CFRP sandwich composites, except aluminium alloy sidewalls, pod lower module and cabin floor, tailboom and around cargo area; some titanium in engine bay; composites tailplane. Landing gear is skid type; ground handling wheels can be fitted.
Power is a choice of turboshaft engines. Turbomeca-engined aircraft have two Arrius 2B2s, each giving 452kW at T-O, 426kW maximum continuous, 528kW OEI continuous, 580kW for 2 minutes with OEI and 609kW for 30 seconds. Alternative power plant is two Pratt & Whitney Canada PW206B2s, each giving 463kW at T-O, 419kW maximum continuous, 528kW OEI continuous, 580kW for 2 minutes with OEI and 609kW for 30 seconds. Both types of engine have FADEC. Transmission rating 616kW maximum T-O, 567êW maximum continuous, 353kW OEI continuous, 513kW for 2 minutes with OEI and 526kW for 30 seconds.
Fuel capacity of first 249 aircraft 673 litres of which 663 litres are usable. Capacity 700 litres from No. 250. Additional long-range tank optional, usable capacity 198.5 litres. Optional self-sealing fuel tanks. Oil capacity 8 litres.
Accommodation is for seven persons, including one or two pilots, in standard version, or six persons in VIP version; optional max capacity of eight. Four-point harnesses for front seats; three-point harnesses for remaining seats. Forward-hinged doors for two front occupants; sliding doors for five persons in cabin. Rear of pod has clamshell doors for bulky items/cargo; flights permissible with clamshell doors removed; optional window in each rear door. Unobstructed cabin interior. EMS variant can accommodate one pilot with two stretcher cases and two seated medical staff/ attendants; alternative layouts for one, one, three, or two, one, three, or two, two, two.
A redundant 28V DC electrical supply systems to JAR/FAR 27 standards; two 160A 28V starter/generators and 24V 17Ah Ni/Cd batteries in Arrius 2B variant, two 200A 28V starter/generators and 24V 25Ah Ni/Cd batteries in PW206B variant. Fully redundant dual hydraulic systems. NATO standard external power connector.
Instrumentation includes Liquid crystal dual-screen (Thales SMD45) vehicle and engine management displays with AN equipment.
EC 135P1: Pratt & Whitney engine version (PW206B). First two (D-HQQQ and D-HYYY; c/ns 0005 and 0006) delivered on 31 July 1996 to Deutsche Rettungsflugwacht.
EC 135P2: Introduced August 2001. FW206B2 engine with improved contingency ratings.
EC 135T1: Turbomeca engine version. First (0010/ N4037A) delivered to USA in November 1996. Early helicopters had 435kW Arrius 2B engines, later replaced by 500kW Arrius 2B1. Uprated Arrius 2B1A engine certified April 2001.
EC 135T2: Deliveries from September 2002. Arrius 2B2 engines.
EC 135 ACT/FHS: Active control technology and flying helicopter simulator; German fly-by-light trials programme; first flight of modified production EC 135 (D-HECV) from Eurocopter's Ottobrunn facility 28 January 2002.
EC 135 APH: Advanced Police Helicopter. Unified mission fit offered by McAlpine Helicopters of UK, 1997; allows simple outfitting with sensors and equipment, according to tasking, using underfuselage pod; typical equipment, including loudspeakers, searchlights, microwave downlink and multisensor turret, can be fitted externally; TV and video equipment earned internally. Pod reduces maximum speed by 9km/h.
Main rotor diameter: 10.2m