Method and apparatus for estimating an airspeed of a rotorcraft by analyzing its rotor

Patent metadata

Field	Value
Publication number	US-11796558-B2
Application number	US-202017081439-A
Country	US
Kind code	B2
Filing date	Oct 27, 2020
Priority date	Nov 5, 2019
Publication date	Oct 24, 2023
Grant date	Oct 24, 2023

Abstract

A method and apparatus for estimating an airspeed of a rotorcraft by analyzing its rotor. The rotorcraft includes a fuselage and a main rotor that is equipped with a plurality of blades and that rotates about an axis of a hub of the rotor, and in which the free end or “tip” of each blade describes a path in the vicinity of a tip-path plane. The method makes it possible to determine said airspeed of the rotorcraft in a frame of reference united with the tip-path plane by solving a model of the rotor that puts a pitch angle of at least one blade relative to the tip-path plane into relation with the airspeed of the rotorcraft and with an auxiliary speed. The auxiliary speed may be an induced velocity of the air flowing through the rotor or else an axial airspeed at the upstream infinity of the rotorcraft.

First claim

What is claimed is:

1. A method of estimating an airspeed of a rotorcraft,
the rotorcraft including a fuselage and at least one rotor that rotates about an axis of a mast of the rotor, the rotor being provided with the mast, with a hub and with a plurality of blades, each blade having a connected first end connected to the hub and a free second end, each blade being mounted to pivot at least about a flapping axis and about a pitch axis, the free second end of a blade describing a path in the vicinity of a mean tip-path plane while the blade is rotating, a longitudinal axis X of the tip-path plane extending in a direction going from the tail of the rotorcraft to the nose of the rotorcraft, and a lateral axis Y of the tip-path plane extending in a direction going from left to right perpendicularly to the longitudinal axis X, the rotorcraft further including an anemometer installation having a computer and a sensor, the sensor being arranged on a blade of the rotor,
wherein the method comprises the following steps:
measuring, by the sensor arranged on the blade of the rotor, a pitch angle of the blade relative to the tip-path plane;
determining an auxiliary speed of the rotorcraft, the auxiliary speed being equal
to an axial airspeed at the upstream infinity of the rotorcraft;
determining, by the computer, the airspeed of the rotorcraft in a frame of reference united with the tip-path plane by solving a model of the rotor, the model taking the form of equations putting the pitch angle of the blade into relation with the airspeed of the rotorcraft and with the auxiliary speed;
delivering from the anemometer installation an indication of the airspeed of the rotorcraft for a pilot of the rotorcraft; and
wherein the step of determining the auxiliary speed equal to the axial airspeed at the upstream infinity includes the following steps:
estimating a barometric altitude of the rotorcraft; and
determining the axial airspeed at the upstream infinity that is equal to a time derivative of the barometric altitude of the rotorcraft.

2. The method according to claim 1 ,
wherein the pitch angle can be broken down into a collective pitch of the blade as well as into a longitudinal cyclic pitch and lateral cyclic pitch of the blade.

3. The method according to claim 1 ,
wherein the model of the rotor includes an analytical set of equations of the flight mechanics.

4. The method according to claim 3 ,
wherein the set of equations includes equations expressing the pitch angle as a function of the airspeed of the rotorcraft and of the auxiliary speed.

5. The method according to claim 4 ,
wherein the set of equations is solved by the Newton-Raphson method.

6. The method according to claim 1 ,
wherein the airspeed of the rotorcraft can be broken down into a longitudinal projection and into a lateral projection on the tip-path plane.

7. The method according to claim 1 ,
wherein the method includes a step of transferring the airspeed of the rotorcraft from the frame of reference united with the tip-path plane to a frame of reference united with the fuselage of the rotorcraft.

8. The method according to claim 1 , further comprising the following steps:
measuring a specific force that is being applied to the fuselage of the rotorcraft in a frame of reference united with the fuselage of the rotorcraft;
estimating at least one angle of inclination of the tip-path plane relative to the frame of reference united with the fuselage on the basis of the specific force that is being applied to the fuselage of the rotorcraft;
measuring, by a second sensor, a pitch angle of the blade in the frame of reference united with the fuselage, the pitch angle in the frame of reference united with the fuselage including a collective component and a cyclic component; and
estimating the pitch angle of the blade relative to the tip-top plane as a function of the pitch angle of the blade in the frame of reference united with the fuselage and of the angle(s) of inclination of the tip-path plane.

9. The method according to claim 8 ,
wherein a longitudinal cyclic component of the angle of inclination of the tip-path plane is also estimated on the basis of an estimation of the aerodynamic drag of the fuselage.

10. The method according to claim 8 ,
wherein a lateral cyclic component of the angle of inclination of the tip-path plane is estimated on the basis of the specific force that is being applied to the fuselage of the rotorcraft and of an estimation of lateral thrust from antitorque apparatus of the rotorcraft.

11. An apparatus for estimating an airspeed of a rotorcraft, the rotorcraft including a fuselage and a rotor that rotates about an axis of a mast of the rotor, the rotor being provided with the mast, a hub, and a plurality of blades, each blade having a connected first end connected to the hub and a free second end, each blade being mounted to pivot at least about a flapping axis and about a pitch axis, the free second end of a blade describing a path in the vicinity of a mean tip-path plane while the blade is rotating, a longitudinal axis X of the tip-path plane extending in a direction going from the tail of the rotorcraft to the nose of the rotorcraft, and a lateral axis Y of the tip-path plane extending in a direction going from left to right perpendicularly to the longitudinal axis X, the apparatus comprising:
an anemometer installation on-board the rotorcraft, the anemometer installation including at least one computer and a plurality of sensors suitable for measuring a pitch angle of a blade of the rotor;
wherein a first one of the sensors is arranged on the blade to measure the pitch angle of the blade relative to the tip-top plane;
wherein a second one of the sensors is arranged on a swashplate of the blade to measure the pitch angle of the blade relative to a hub-plane perpendicular to the axis of the mast of the rotor;
the computer being operable to estimate the pitch angle of the blade relative to the tip-top plane based in part on the pitch angle of the blade relative to the hub-plane;
the computer being further operable to determine the airspeed of the rotorcraft in a frame of reference united with the tip-path plane by solving a model of the rotor, the model taking the form of equations putting either the measured or estimated pitch angle of the blade relative to the tip-top plane into relation with the airspeed of the rotorcraft and with an auxiliary speed of the rotorcraft; and
the anemometer installation being operable to deliver an indication of the airspeed of the rotorcraft for a pilot of the rotorcraft.

12. A rotorcraft comprising:
a fuselage and a rotor that rotates about an axis of a mast of the rotor, the rotor being provided with the mast, a hub, and a plurality of blades, each blade having a connected first end connected to the hub and a free second end, each blade being mounted to pivot at least about a flapping axis and about a pitch axis, the free second end of a blade describing a path in the vicinity of a mean tip-path plane while the blade is rotating, a longitudinal axis X of the tip-path plane extending in a direction going from the tail of the rotorcraft to the nose of the rotorcraft, and a lateral axis Y of the tip-path plane extending in a direction going from left to right perpendicularly to the longitudinal axis X;
an anemometer installation including a computer and a plurality of sensors suitable for measuring a pitch angle of a blade of the rotor;
wherein a first one of the sensors is arranged on the blade to measure the pitch angle of the blade relative to the tip-top plane;
a second one of the sensors is arranged on a swashplate of the bla

Assignees

• Airbus Helicopters

Inventors

• Petillon Jean-Paul

Classifications

• G01P5/02 Primary

  by measuring forces exerted by the fluid on solid bodies, e.g. anemometer · CPC title

• B64C27/06

  with single rotor · CPC title

• B64F5/60

  Testing or inspecting aircraft components or systems · CPC title

• G01C23/00

  Combined instruments indicating more than one navigational value, e.g. for aircraft; Combined measuring devices for measuring two or more variables of movement, e.g. distance, speed or acceleration · CPC title

• B64C27/04 Primary

  Helicopters · CPC title