The present invention relates to the field of aircraft propeller blades, such as those present on turboprops.
Propeller blades for turboprops are generally made of metal material. Although propeller blades made of metal material present good strength, they nevertheless present the drawback of being relatively heavy.
In order to obtain lighter blades, it is known to use propeller blades that are made of composite material, i.e. by making structural parts out of fiber reinforcement and a resin matrix.
Documents US 2013/0017093 and WO 2012/001279 describe making a propeller blade from a streamlined fiber structure into which a portion of a spar is inserted for the purpose of shaping the airfoil portion of the blade so as to form a propeller preform that is subsequently densified with a matrix. The fiber structure, which is made as a single piece by three-dimensional weaving, includes a non-interlinked zone serving to form a housing inside the fiber structure into which a shaping portion of the spar is inserted.
The propeller blade as obtained in that way presents both lower overall weight and considerable mechanical strength as a result of having a skin made of a composite material structure (i.e. fiber reinforcement densified by a matrix).
In order to impart good strength to the most exposed portion of the blade, i.e. its leading edge, the fiber structure does not include any opening or non-interlinked zone in those portions of the fiber structure that are to form the leading edge of the blade. The non-interlinked zone provided inside the fiber structure opens out both into the bottom edge and into the rear edge of the structure so as to form an opening that enables the shaping portion of the spar to be inserted into the inside of the fiber structure.
Nevertheless, in certain circumstances, such as for example when the blade is subjected to high levels of mechanical loading, to impacts, or to shocks, keeping the shaping portion in its reference position inside the densified fiber structure can be difficult, in particular at the rear edge of the fiber structure which is of reduced strength because of the presence of non-interlinking at this location in the fiber structure.