Low speed autogyro yaw control apparatus and method
Apparatus and methods for controlling yaw of a rotorcraft in the event of one or both of low airspeed and engine failure are disclosed. A yaw propulsion device, such as an air jet or a fan may be used. A pneumatic fan may be driven by compressed air released into a channel surrounding an outer portion of the fan. Power for the yaw propulsion device and other system may be provided by a hydraulic pump and/or generator engaging the rotor. Low speed yaw control may be provided by auxiliary rudders positioned within the stream tube of a prop. The auxiliary rudders may one or both of fold down and disengage from rudder controls when not in use. Apparatus for generating horizontal lift imbalance induced a tail boom positioned within the downwash of a rotor may also be used, including compressed air vents or lateral or trailing edge flaps.
1. An autogryro comprising:
an airframe defining a flight direction;
an engine mounted to the airframe;
a lift rotor rotatably mounted to the airframe, the lift rotor defining an axis of rotation and being selectively coupled to the engine;
a propulsion source selectively powered by the engine and oriented to generate thrust parallel to the flight direction; and
a yaw flap positioned within a downwash of the lift rotor:
the yaw flap offset from the axis of rotation and mounted to the airframe to be pivotable about a flap axis and effective to redirect air from the downwash;
the yaw flap selectively pivotable to be effective to generate a corresponding yaw moment on the airframe about the axis of rotation;
a rudder pivotably mounted to the airframe to pivot about a rudder axis substantially perpendicular to the flight direction; and
a control system configured to receive yaw control inputs from a pilot, the control system having a first mode in which the yaw control inputs are coupled to the yaw flap and a second mode in which yaw control inputs are not coupled to the yaw flap.
2. The autogyro of claim 1 , wherein the flap axis is oriented substantially parallel to the flight direction.
3. The autogyro of claim 1 , wherein the rudder is positioned outside the downwash of the lift rotor.
4. The autogyro of claim 1 , wherein:
the airframe comprises a fuselage and a tail boom extending therefrom, the tail boom mounting the rudder to the fuselage; and
the yaw flap is mounted to the tail boom.
5. The autogyro of claim 4 , wherein:
the tail boom has an upper surface and a lower surface; and
the yaw flap is mounted proximate the lower surface of the tail boom.
6. A method for operating an autogyro comprising:
rotating a lift rotor at a first angular velocity, the lift rotor rotatably mounted to an airframe and rotatable about an axis of rotation, the first angular velocity being greater than a sustained autorotative angular velocity corresponding to a current airspeed of the airframe and orientation of the lift rotor;
receiving a first yaw control input;
modulating a velocity component of an air stream perpendicularly away from the airframe, according to the first yaw control input, effective to generate a reactive force on the airframe and a corresponding yaw moment;
determining that an air speed of the autogyro is above a threshold;
receiving a second yaw control input; and
in response to determining that the air speed of the autogyro is above the threshold, coupling the second yaw control input to a rudder of the autogyro and refraining from modulating the velocity component of the air stream perpendicularly away from the airframe, according to the second yaw control input.
7. The method of claim 6 wherein modulating the velocity component perpendicularly away from the airframe comprises adjusting an orientation of a flap positioned within a downwash of the lift rotor.
8. The method of claim 7 , wherein:
the airframe comprises:
a fuselage,
a vertical stabilizer, and
a boom mounting the vertical stabilizer to the fuselage, and
the flap is rotatably mounted to the boom.
9. The method of claim 8 , wherein:
the boom has a lower surface;
the flap is positioned on the lower surface;
the flap has a flap axis of rotation extending substantially parallel to the longitudinal axis of the boom.