According to an aspect, a method of assembling a mandrel includes assembling a plurality of members via interlocking features arranged at opposing edges of each member of the plurality of members to form a compartment, the assembled members having a collective outer surface that conforms to an inner surface of the spar. A support member is inserted into the compartment formed radially inward from the assembled members, the support member making contact with a portion of each member of the plurality of members.

A double-blade tandem helicopter comprising a fuselage (10), a power system, a control system, and two rotor assemblies (30, 50). The rotor assemblies are longitudinally disposed relative to the fuselage. Each rotor assembly comprises a rotor shaft (31, 51), a rotor head (33, 53), and two blades (35, 37, 55, 57). The rotor shaft is connected to the power system, the rotor head is fixed to the rotor shaft, and the blades are attached to the rotor head. The double-blade tandem helicopter has a larger rotor disk area than that of a single-rotor helicopter while has a fuselage weight approaching that of the single-rotor helicopter, and thus has a take off weight approximately twice or more times of the single-rotor helicopter, and meanwhile has characteristics such as small volume, simple structure and high aerodynamic efficiency.

An assembly system includes a fixture configured to support a structure including at least one component to receive a malleable material, and a bladder system coupled to the fixture. The bladder system includes a hollowed frame having sidewalls that support a bladder disposed therein. The hollowed frame has an opening that exposes an outer portion of the bladder and is configured to guide the exposed outer portion externally from the hollowed frame toward a targeted area of the structure. In response to inflating the bladder, the outer portion of the bladder extends through the opening and applies a force against the at least one component so as to form a design feature element from the malleable material.

According to an aspect, a method of assembling a mandrel includes assembling a plurality of members via interlocking features arranged at opposing edges of each member of the plurality of members to form a compartment, the assembled members having a collective outer surface that conforms to an inner surface of the spar. A support member is inserted into the compartment formed radially inward from the assembled members, the support member making contact with a portion of each member of the plurality of members.

A rotor is described that comprises: a hub; a plurality of blades; each blade extends along an axis and comprises: a leading edge and a trailing edge; a top surface and a bottom surface, a chord joining points of the leading edge and the trailing edge; and a closed shell made of composite material and adapted to withstand the torque directed along a first axis of the blade; the shell comprises a first and a second element separate from each other, delimiting the respective shell on mutually opposite sides; a first connection element arranged on the side of the associated leading edge and interposed between the first ends of the respective first and second elements; and a third element connected to the associated first and second elements and arranged on the side of the leading edge; the first connection element is connected to respective first faces, and the third element is connected to respective second faces of the first and second elements; the blade comprises a fourth element interposed between the fourth element and the first connection element.

A rotor system is provided in one example embodiment and may include a rotor duct; at least one rotor blade, wherein the at least one rotor blade comprises a tip end; and a multi-material tip extension affixed at the tip end of the at least one rotor blade, wherein the multi-material tip extension comprises an inboard portion fabricated from a first material and an outboard portion fabricated from a second material, wherein the second material is different than the first material.

Systems and methods are provided for applying cold spray erosion protection to an airfoil. One embodiment is a method for applying an abrasion coating to a fiber-reinforced composite substrate. The method includes applying a bond layer to the fiber-reinforced composite substrate by emitting, with a supersonic nozzle of a High Pressure Cold Spray (HPCS) system, a first gas stream including a first metal powder at a first speed below supersonic speed. The method further includes applying a cold spray deposit layer to the bond layer by emitting, with the supersonic nozzle, a second gas stream including a second metal powder at a second speed above supersonic speed.

A method of constructing a cured composite assembly includes positioning a composite assembly within a bonding tool, wherein the composite assembly comprises an uncured composite spar and a skin and performing a curing cycle on the composite assembly to simultaneously cure the uncured composite spar and bond the skin to the cured composite spar.

An apparatus for securing first and second skins to a core in a composite rotor blade includes an elongated member configured to be installed through a passage in the core of the composite rotor blade. The elongated member has a first end configured to be attached to an outer surface of the first skin and a second end configured to be attached to an outer surface of the second skin. The apparatus also includes a first patch configured to adhere the first end to the outer surface of the first skin, and a second patch configured to adhere the second end to the outer surface of the second skin such the elongated member extends from the outer surfaces of the first and second skins through the passage in the core.

A method for reducing the resistivity of a carbon nanotube nonwoven sheet includes providing a carbon nanotube nonwoven sheet comprising a plurality of carbon nanotubes and applying pressure to the carbon nanotube nonwoven sheet to reduce air voids between carbon nanotubes within the carbon nanotube nonwoven sheet.