An aircraft propulsion system with a drag reduction portion adapted to reduce skin friction on at least a portion of the external surface of an aircraft. The drag reduction portion may include an inlet to ingest airflow. The aircraft may also have an internally cooled electric motor adapted for use in an aerial vehicle. The motor may have its stator towards the center and have an external rotor. The rotor structure may be air cooled and may be a complex structure with an internal lattice adapted for airflow. The stator structure may be liquid cooled and may be a complex structure with an internal lattice adapted for liquid to flow through. A fluid pump may pump a liquid coolant through non-rotating portions of the motor stator and then through heat exchangers cooled in part by air which has flowed through the rotating portions of the motor rotor. The drag reduction portion and the cooled electric motor portion may share the same inlet.

An aerodynamic body for use on an aircraft including at least a first perforated surface portion (25) and an ice-protection system (31). The first perforated surface portion (25) has perforations. The ice-protection system (31) includes an actuatable element (33) and the actuatable element (33) is movable or deformable between a first position and a second position. In the first position, the actuatable element (33) is thermally coupled to the first perforated surface portion (25) and configured to prevent an inflow or outflow between a boundary layer of an outer aerodynamic airflow and the aerodynamic body through at least one of the perforations. In the second position, the actuatable element (33) is distanced from the first perforated surface portion (25) and configured to allow an inflow from a boundary layer of an outer aerodynamic airflow through at least one of the perforations into the aerodynamic body.

An aerodynamic body for use on an aircraft including at least a first perforated surface portion (25) and an ice-protection system (31). The first perforated surface portion (25) has perforations. The ice-protection system (31) includes an actuatable element (33) and the actuatable element (33) is movable or deformable between a first position and a second position. In the first position, the actuatable element (33) is thermally coupled to the first perforated surface portion (25) and configured to prevent an inflow or outflow between a boundary layer of an outer aerodynamic airflow and the aerodynamic body through at least one of the perforations. In the second position, the actuatable element (33) is distanced from the first perforated surface portion (25) and configured to allow an inflow from a boundary layer of an outer aerodynamic airflow through at least one of the perforations into the aerodynamic body.

An aircraft with wing tip devices, for example, folding wing tips, is disclosed. The folding wing tip may have a flight configuration for use during flight, and a ground configuration for use in ground-based operations. The ground configuration creates a shorter wing span than when the aircraft is in the flight configuration. A hinge arrangement protrudes beyond an outer surface of the fixed wing and wing tip device. In order to reduce the aerodynamic effect of the protruding hinge a fairing may be provided. In the flight configuration the fairing comprises a rear portion with a concave surface, such that the fairing acts as a lift-generating surface when the aircraft is in flight.

An aircraft with wing tip devices, for example, folding wing tips, is disclosed. The folding wing tip may have a flight configuration for use during flight, and a ground configuration for use in ground-based operations. The ground configuration creates a shorter wing span than when the aircraft is in the flight configuration. A hinge arrangement protrudes beyond an outer surface of the fixed wing and wing tip device. In order to reduce the aerodynamic effect of the protruding hinge a fairing may be provided. In the flight configuration the fairing comprises a rear portion with a concave surface, such that the fairing acts as a lift-generating surface when the aircraft is in flight.

Example active flow control systems and methods for aircraft are described herein. An example an active flow control system includes a plenum, a plurality of nozzles fluidly coupled to the plenum, configured to eject high pressure air across a control surface, a compressor to supply pressurized air to the plenum, an electric motor to drive the compressor, and a control system to determine an amount of power input to the electric motor, determine a current speed of the electric motor, and determine a fault has occurred in the active flow control system based on the current speed of the electric motor.

Flow control systems having movable slotted plates are disclosed. A disclosed example apparatus includes a flow control plate to be placed proximate an opening of an aerodynamic body. The opening has a first slot and the flow control plate has a second slot angled relative to the opening. The apparatus also includes an actuator to move the flow control plate relative to the opening in a linear oscillatory motion to vary a flow of fluid exiting the opening over the aerodynamic body. The flow of fluid is to flow from the second slot to the first slot.

Flow control systems having movable slotted plates are disclosed. A disclosed example apparatus includes a flow control plate to be placed proximate an opening of an aerodynamic body. The opening has a first slot and the flow control plate has a second slot angled relative to the opening. The apparatus also includes an actuator to move the flow control plate relative to the opening in a linear oscillatory motion to vary a flow of fluid exiting the opening over the aerodynamic body. The flow of fluid is to flow from the second slot to the first slot.

Methods and apparatus for accelerating an aircraft fuselage boundary layer via a fan powered by an APU of the aircraft are disclosed. An example aircraft includes a fuselage, an APU, and a fan. The fuselage includes an outer skin. The APU is located within the fuselage. The fan includes a plurality of fan blades arranged circumferentially about the APU and projecting radially outward from the outer skin. The fan further includes a fan drive operatively coupled to the APU. The fan drive is configured to rotate the fan blades in response to a supply of electrical energy provided to the fan drive from the APU. The rotation of the fan blades accelerates a fuselage boundary layer traveling rearward along the outer skin from a first velocity to a second velocity greater than the first velocity.

Methods and apparatus for accelerating an aircraft fuselage boundary layer via a fan powered by an APU of the aircraft are disclosed. An example aircraft includes a fuselage, an APU, and a fan. The fuselage includes an outer skin. The APU is located within the fuselage. The fan includes a plurality of fan blades arranged circumferentially about the APU and projecting radially outward from the outer skin. The fan further includes a fan drive operatively coupled to the APU. The fan drive is configured to rotate the fan blades in response to a supply of electrical energy provided to the fan drive from the APU. The rotation of the fan blades accelerates a fuselage boundary layer traveling rearward along the outer skin from a first velocity to a second velocity greater than the first velocity.