BO108
Looking Back at the BO 108, Forerunner for the Eurocopter EC135, today’s World Best Selling Light Twin Engine Helicopter
Today a best seller among the Eurocopter range, the EC135 has established itself as a leader on the light twin market, with operations spanning from emergency medical services to corporate transport , offshore, police missions and military operations. But let’s take a look back at the BO 108 and how this German predecessor became the EC135 as we know it today, with a little of the magic we like to call Franco-German cooperation.
The BO 108, manufactured by MBB, was initially designed to replace the BO 105, another highly successful helicopter produced by this manufacturer. The helicopter which made its maiden flight on October 15, 1988 was a technical demonstrator used to evaluate the new technologies in operation from technical and economic viewpoints. Several areas for improvement were identified over the course of extensive flight tests, and included rotor technology, development of new dynamic assemblies, anti-resonance systems, composite materials applied to the structure, and integration of a latest generation avionics system. The Bearingless Main Rotor (BMR) was certainly the most innovative of these systems. It does not have a rotor head in the traditional sense. It consists of four aerodynamically optimized composite rotor blades with an integrated fiberglass-composite flexbeam and control cuff, and the rotor shaft with blade attachment flange which is a one-piece forging. Hub elements used in conventional systems such as centrifugal force transmission elements, bearings, bearings sleeves etc. were eliminated and replaced by the elastic properties of the flexbeam. Therefore, the BMR does not require flap and lag hinges or any bearings, making it the simplest and easiest-to-maintain main rotor in the world today.
Less than three years after the first prototype, a second BO 108 took to the skies in June 1991. Powered by two Turbomeca Arrius 1B turbines, this helicopter was 15 cm longer and featured an avionics system to enable single pilot IFR flight. Following the excellent results demonstrated by this prototype, MBB announced the series production launch and key dates for the helicopter, with certification expected in 1994 and the first helicopters to be delivered to customers in 1995.
However these plans were modified to a certain extent following the creation of Eurocopter in January 1992. The BO 108 project was reworked slightly and renamed, and thus the EC135 was born. The modifications to the project mainly concerned the standard tail rotor, which was replaced by a Fenestron® shrouded rotor, a specific feature of the light helicopters manufactured by Aerospatiale. Market research among potential customers also led to some modifications to the internal architecture: the size of the cabin was increased to provide capacity for two pilots and six passengers, visibility was improved and space was freed up on the cabin floor in order to facilitate configuration changes and increase mission potential. These adjustments provided the new helicopter with heightened versatility, with excellent sales figures attesting to the success of the modifications.
By the end of 1992 the EC135 design had been finalized. The new helicopter achieved its maiden flight on February 15, 1994, and since then EC135 orders have reached the 700 mark
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100 Years of Vertical Flight
In 1907, Paul Cornu achieved the first vertical flight in history. Since then, technological advances, innovative ideas, but most of all a conquering spirit, have made the helicopter an indispensable instrument to save lives, protect citizens, and contribute to international economic development. In 2007, Eurocopter is proud to celebrate this centenary by sharing its passion for helicopters.
