Accession Number:



New Aerodynamic Design of the Fenestron for Improved Performance,

Descriptive Note:

Corporate Author:


Personal Author(s):

Report Date:


Pagination or Media Count:



Since the first Gazelle flight in 1968, Aerospatiale has developed the fenestron as an alternate solution to the conventional tail rotor for light or medium helicopters weighing less than 6 tons. This concept has widely evidenced its advantages on about 1100 Gazelle and 235 Dauphin helicopters equipped with this fenestron and totalizing more than 2 million flight hours, without any major accident. The paper first recalls the general definition of the fenestron and its advantages for civil or military applications. Recent research has shown new opportunities for improving the aerodynamic efficiency of this fenestron. A detailed airflow analysis through the fenestron has recently been achieved with extensive model and full scale tests on the tail rotor bench in hover. The research program was sponsored by the French Government Agencies DRET and STPA. This paper surveys the experimental technique and the flow measurements. It also presents the correlations that have been made with blade element theory as well as a more advanced analysis developed by METRAFLU and derived from a radial equilibrium code in use for compressors. The tests have authorized more thorough flow investigations which have shown potential benefits in recuperating the rotational energy. This has led to design stator blades located behind the rotor, inside the diffuser. Tests of this device have shown large improvements in the fenestrons figure of merit and maximum thrust, for a given rotor blade solidity. Furthermore, improving the diffusers performance, the stator blades permit reducing the diffusers length and thus the fenestrons width with drag savings as a final result. NATO.

Subject Categories:

  • Helicopters

Distribution Statement: