Disclosed is a hollow structure, particularly propeller blade, having excellent productivity, high strength, light weight, and high quality. The hollow structure is made of a resin, and includes: an outer surface; a retaining section; and a space in the structure; wherein at least one of the retaining sections is configured to support the outer surface at multiple points.

An airfoil comprises an airfoil body with an internal cavity and inner and outer covers. The airfoil body defines a first major surface of the airfoil, and a rib extends along the internal cavity. The inner cover is bonded to the airfoil body over the internal cavity, and includes a coupling element extending along the internal cavity in cooperative engagement with the rib. The outer cover is bonded to the airfoil body over the inner cover, and defines a second major surface of the airfoil.

The present invention provides a power device generating greater propelling force and finds that traditional power devices do not include all propelling forces based on the fundamental core propelling force source problem. External pressure is guided to the traditional power devices since the inner speed is higher the outer speed, power consumption for overcoming fluid resistance is high, and mutual contradiction results are obtained. The unique difference between the present invention and general common sense lies in opposite fluid pressure directions; inner fluid channels and outer fluid channels with higher flow speeds are formed to generate pressure differences which guides the fluid pressure to the outside and serve as propelling force, and thus the present invention creatively finds three propelling force sources, two lifting force or propelling force sources of helicopters or airplanes driven by propellers and two propelling force sources for sufficient burning of fuel in combustion chambers of engines.

The present invention provides a power device generating greater propelling force and finds that traditional power devices do not include all propelling forces based on the fundamental core propelling force source problem. External pressure is guided to the traditional power devices since the inner speed is higher the outer speed, power consumption for overcoming fluid resistance is high, and mutual contradiction results are obtained. The unique difference between the present invention and general common sense lies in opposite fluid pressure directions; inner fluid channels and outer fluid channels with higher flow speeds are formed to generate pressure differences which guides the fluid pressure to the outside and serve as propelling force, and thus the present invention creatively finds three propelling force sources, two lifting force or propelling force sources of helicopters or airplanes driven by propellers and two propelling force sources for sufficient burning of fuel in combustion chambers of engines.

A composite airfoil assembly has a composite airfoil, a spar, and a wrap. The composite airfoil has an outer wall and a composite skin. The outer wall extends between a root and a tip. The outer wall defines an interior. The composite skin at least partially defines the outer wall. The spar having a spar centerline axis, a stem, a base, and a transition interconnecting the base and the stem.