Reduced drag of airframe & non lifting rotating parts (GRC2)

Challenge

The power required to fly a helicopter in forward flight, and consequently the fuel burn and CO2 emissions are strongly dependent on the design of its airframe and of non-lifting rotating parts such as the main and tail rotor shaft, control system and hub. These components determine the aerodynamic drag and also the download in the nose-down flight attitude typical for helicopers  in cruise flight. A preliminary review confirmed that significant  aerodynamic gains could possibly be obtained by:

  • Reducing the main rotor hub drag e.g. by means of optimised hub caps and pylon fairings;
  • Delaying flow separation on the aft part of blunt fuselage for helicopters equipped with rear access doors, by means of passive or active flow control devices;
  • Reducing the tail unit size thanks to optimised design and additional control surfaces.

In addition to conventional helicopter configurations, similar design challenges are adressing tilt-rotor aircraft, especially the ERICA concept investigated in earlier FP5 and FP6 projects including NICETRIP.
The fuel consumption of turboshaft engines depends not only on the output power but also on the aerodynamic performance of air inlets and to a lesser extent, of exhaust nozzles. Engine performance loss as compared to the ground bench reference may be quite substantial, in the order of 5% or more on some  helicopters. Some earlier research on the subject was conducted as part of the FP6 Friendcopter which included a re-design of EC135 air inlets. The engine noise could be reduced by 10 dB but the installation loss remained high. Within the GRC2 subproject, this research is further pursued for the twin engine light helicopter and extended to heavy helicopters which feature a different architecture with engines located ahead of the main gearbox. Engine integration in a tilt rotor nacelle is also addressed. 

Expected benefits

Depending on the rotorcraft configuration and weight class the aerodynamic cumulated drag benefits are currently estimated in the range 10-15% which would translate into a 4 to 5% fuel consumption reduction for the same payload and mission. The activity performed in GRC2 is supporting the derivation of conceptual rotorcraft helicopter models that will be used by TE for environmental assessment. The airframe aerodynamic data included in these models will be regularly updated by using test results in order to reduce the uncertainty range. 

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