Method for correcting indicated airspeed of helicopter through pneumatic attack angle

Abstract

The invention belongs to the technical field of helicopter pneumatic design, and particularly relates to a method for correcting the indicated airspeed of a helicopter through a pneumatic attack angle. Comprising the following steps: S1, additionally arranging a front rod for measuring a pneumatic attack angle and indicating an air speed on a helicopter; s2, the indicated airspeed of the front rod is calibrated in the selected level flight state, and a relation curve of the indicated airspeed and the calibrated airspeed of the front rod is obtained; s3, selecting a climbing state and a gliding state, and obtaining a pneumatic attack angle AOA of a front rod test; s2, according to the relation curve, obtained in S2, of the indicated airspeed and the calibrated airspeed of the front rod, the calibrated airspeed of the climbing state and the calibrated airspeed of the descending state are obtained, then the indicated airspeed error of the climbing state and the indicated airspeed error of the gliding state are obtained, and the indicated airspeed error is the difference value of the calibrated airspeed and the onboard indicated airspeed; s4, the true speed TAS and the lifting speed Vz in the climbing and gliding process are obtained, and the theoretical pneumatic attack angle AOA1 of the helicopter is preliminarily calculated; and S5, according to the theoretical pneumatic attack angle AOA1 calculated in the step 4 and the indicated airspeed error relation curve corresponding to different actually-measured pneumatic attack angles obtained in the step 3, correcting the onboard indicated airspeed according to the indicated airspeed error corresponding to the theoretical pneumatic attack angle AOA1.

Description

Technical Field

[0001] The invention belongs to the technical field of helicopter aerodynamic design, and in particular relates to a method for correcting a helicopter indicated airspeed by using an aerodynamic attack angle. Background Art

[0002] The indicated airspeed of a helicopter is obtained by solving the total pressure and static pressure measured by an atmospheric data machine. The total pressure is usually measured by a pressure sensor of a pitot tube. Pitot tubes are usually not sensitive to airflow angles. The total pressure measured by common pitot tubes hardly changes with the aerodynamic angle of attack within a certain airflow angle range, which directly leads to the indicated airspeed measured by the helicopter atmospheric data machine not being sensitive to airflow angles. Within a given angle of attack range, the accuracy of the total pressure test is high, and the airspeed indication accuracy is high; when the angle of attack exceeds the given airflow angle range of the pitot tube, the total pressure test error increases, which directly leads to an increase in the indicated airspeed error. The flight states where the helicopter's aerodynamic angle of attack exceeds the given pitot tube's measured airflow angle range mainly include low-speed climb, autorotation descent, maneuvering state, etc. Therefore, the airspeed indication error that exceeds the given pitot tube's airflow angle range needs to be corrected to improve the indicated airspeed accuracy and flight safety. Summary of the invention

[0003] The present invention proposes a method for correcting the indicated airspeed of a helicopter by using the aerodynamic angle of attack. The angle of attack is calculated using the forward flight speed and the ascent and descent speed, and the airspeed is corrected according to the angle of attack-error relationship, so as to improve the indicated airspeed accuracy of the helicopter when the airflow angle range measured by a given pitot tube is exceeded in flight attitudes such as low-speed climbing, autorotation descent, and maneuvering states, thereby improving the safety of maneuvering flight.

[0004] In order to achieve the above object, the present invention adopts the following technical solution to achieve it.

[0005] A method for correcting a helicopter indicated airspeed by aerodynamic angle of attack, the method comprising:

[0006] S1, a forward lever is installed on the helicopter to measure the aerodynamic angle of attack and indicated airspeed;

[0007] S2, calibrating the indicated airspeed of the front stick in the level flight state, and obtaining a relationship curve between the indicated airspeed of the front stick and the calibrated airspeed;

[0008] S3, select the climbing and descending states, obtain the aerodynamic angle of attack AOA of the lead stick test; obtain the calibrated airspeed of the climbing and descending states according to the relationship curve between the indicated airspeed and the calibrated airspeed of the lead stick obtained in S2, and then obtain the indicated airspeed error of the climbing and descending states, and the indicated airspeed error is the difference between the calibrated airspeed and the indicated airspeed on the aircraft;

[0009] S4, obtain the true speed TAS and the vertical speed Vz during the climbing and descending process, and preliminarily calculate the theoretical aerodynamic angle of attack AOA1 of the helicopter;

[0010] S5, based on the theoretical aerodynamic angle of attack AOA1 calculated in step 4 and the indicated airspeed error relationship curve corresponding to different measured aerodynamic angles of attack obtained in step 3, correct the indicated airspeed on board according to the indicated airspeed error corresponding to the theoretical aerodynamic angle of attack AOA1.

[0011] Furthermore, in S2, the calculation process of the calibration airspeed is:

[0012]

[0013] Among them, V GPS is the differential GPS velocity, is the density ratio; pressure ratio: Δ = (1-0.0065×Hp / 288.15) 5.25588 , temperature ratio: Hp is the absolute pressure altitude and Tamb is the atmospheric temperature.

[0014] Furthermore, in S2, a relationship curve between the indicated airspeed of the front lever and the calibrated airspeed is obtained, specifically:

[0015] According to the indicated airspeed Vi_angle measured by the front lever in the flight test and the calibrated airspeed Vc obtained by solution, a relationship curve between the indicated airspeed measured by the front lever and the calibrated airspeed is obtained.

[0016] Furthermore, in S3,

[0017] Perform a round trip sawtooth climb using a given average ground clearance, climb using maximum continuous power, and descend using unpowered descent, with the indicated airspeed range starting from the minimum speed that can be stably indicated to the selected maximum speed, with a speed interval of 10km / h-20km / h;

[0018] Through flight tests, the indicated airspeed of the front lever is obtained. Through the relationship curve between the indicated airspeed of the front lever and the calibrated airspeed in step 2, the calibrated airspeed Vc of the climbing and gliding states is obtained respectively, and then the corresponding indicated airspeed Vi on board is subtracted to obtain the indicated airspeed error ΔVi of the climbing and gliding states;

[0019] Combined with the aerodynamic angle of attack (AOA) of the lead rod test, the relationship between the indicated airspeed error and the aerodynamic angle of attack is obtained, and a polynomial fitting is performed.

[0020] Furthermore, in S4,

[0021] Theoretical aerodynamic angle of attack AOA1 solution formula is as follows: AOA1 = ASIN (Vz / TAS) / π * 180

[0022] Among them, Vz is the lifting speed, TAS is the true speed, and the true air speed TAS solution formula is as follows: Vc is the calibrated airspeed.

[0023] Furthermore, the method further comprises:

[0024] S6, if there is an angle between the position of the pitot tube and the horizontal direction of the ground on which the aircraft is parked, it is necessary to obtain the theoretical airflow angle of attack AOA_D of the pitot tube according to the pitot tube installation angle Theta and the fuselage pitch angle Pitch, correct the indicated airspeed of the atmospheric aircraft, and then correct the indicated airspeed error according to the relationship between the aerodynamic angle of attack at the measured pitot tube and the indicated airspeed error.

[0025] Furthermore, the pitot tube calculates the angle of attack AOA_D:

[0026] AOA_D=ASIN(Vz / TAS) / π*180-Pitch-Theta.

[0027] The present invention also provides a helicopter, wherein the helicopter adopts the method to correct the indicated airspeed of the helicopter.

[0028] This paper proposes a method to correct the indicated airspeed of a helicopter by using the angle of attack. The error relationship between the angle of attack and the airspeed is determined based on the test flight data, and the airspeed is corrected directly using the theoretically calculated angle of attack. This can reduce the error of the airspeed indication and improve the accuracy of the airspeed system. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A schematic diagram comparing the indicated airspeed before correction and the indicated airspeed after correction provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is described in detail below with reference to the accompanying drawings.

[0031] An embodiment of the present invention proposes a method for correcting the indicated airspeed of a helicopter by using the aerodynamic angle of attack. The angle of attack is calculated using the forward flight speed and the ascent and descent speed, and the airspeed is corrected according to the angle of attack-error relationship to improve the accuracy of the indicated airspeed of the helicopter when it exceeds a given airspeed tube-measured airflow angle range in flight attitudes such as low-speed climb, autorotation descent, and maneuvering states, thereby improving the safety of maneuvering flight.

[0032] The method of correcting the indicated airspeed of a helicopter by aerodynamic angle of attack is mainly to obtain the relationship between the aerodynamic angle of attack and the indicated airspeed error by combining flight tests, and calculate the theoretical aerodynamic angle of attack of the helicopter by measuring the forward flight speed, lifting speed, etc. of the helicopter, and then obtain the relationship between the aerodynamic angle of attack and the indicated airspeed error measured by the helicopter according to the relationship between the measured aerodynamic angle of attack and the indicated airspeed error, and embed it into the helicopter atmospheric data system for correction to improve the accuracy of the indicated airspeed. The specific steps are as follows:

[0033] Step 1: Select the device for measuring aerodynamic angle of attack, DGPS and install it on the helicopter.

[0034] The commonly used calibrated angle of attack and sideslip angle sensor is installed on the front side of the helicopter nose. This device is usually called a front rod and is used to measure the airflow angle of attack AOA relative to the flight direction of the helicopter. The differential GPS transceiver is installed to measure the GPS speed.

[0035] Step 2: Select the indicated airspeed of the device (front stick) that measures the aerodynamic angle of attack in level flight and calibrate it.

[0036] The level flight triangle flight method was adopted, starting from the minimum stable indicated airspeed to the maximum level flight speed, with an interval of 10km / h-20km / h. Through the flight test, the DGPS speed V GPS , measure the indicated airspeed Vi_angle with the front lever, and calculate the calibration airspeed Vc;

[0037] Calculate the calibration airspeed Vc (km / h), Hp (absolute pressure altitude, m), Tamb (atmospheric temperature OAT, °C), V GPS

[0038] Pressure ratio: Δ = (1-0.0065×Hp / 288.15) 5.25588

[0039] Temperature ratio:

[0040] Density ratio:

[0041]

[0042] According to the indicated airspeed Vi_angle measured by the front lever in the flight test and the calibrated airspeed Vc obtained by solution, a relationship curve between the indicated airspeed measured by the front lever and the calibrated airspeed is obtained.

[0043] Vc=a1*Vi_angle+b1

[0044] Step 3: Select the climb and descent state, obtain the aerodynamic angle of attack AOA tested by the device for measuring the aerodynamic angle of attack, and obtain the calibrated airspeed Vc1 of the climb and descent state according to the relationship between the indicated airspeed on the front bar and the calibrated airspeed obtained in step 2, and then obtain the indicated airspeed error of the climb and descent state. The indicated airspeed error is the difference between the calibrated airspeed Vc1 and the indicated airspeed on the aircraft.

[0045] A round trip sawtooth climb is performed using a given average ground clearance. The maximum continuous power is used for climbing, and the power-free descent is used for descent. The indicated airspeed range on the aircraft starts from the minimum speed that can be stably indicated to the selected maximum speed, and the speed interval is 10km / h-20km / h. Through the flight test, the indicated airspeed Vi_angle of the front lever is obtained. Through the relationship curve between the indicated airspeed of the front lever and the calibrated airspeed in step 2, the calibrated airspeed Vc of the climbing and gliding states is obtained respectively, and then the indicated airspeed Vi of the corresponding helicopter atmospheric machine is subtracted to obtain the indicated airspeed error ΔVi of the climbing and gliding states. Combined with the aerodynamic angle of attack AOA of the front lever test, the relationship between the indicated airspeed error and the aerodynamic angle of attack is obtained, and a polynomial fitting is performed.

[0046] Step 4: Obtain the true speed TAS and vertical speed Vz during the climb and descent process, and preliminarily calculate the theoretical aerodynamic angle of attack AOA1 of the helicopter.

[0047] The true airspeed TAS calculation formula is as follows:

[0048]

[0049] The theoretical aerodynamic angle of attack AOA1 solution formula is as follows:

[0050] AOA1=ASIN(Vz / TAS) / π*180

[0051] Vz(m / s),TAS(m / s)

[0052] Step 5: Based on the relationship between the indicated airspeed errors corresponding to the theoretical aerodynamic angle of attack AOA1 calculated in step 4 and the measured different aerodynamic angles of attack obtained in step 3, correct the indicated airspeed on board according to the indicated airspeed error corresponding to the theoretical aerodynamic angle of attack AOA1.

[0053] Step 6: Step 5 is applicable to the direction where the pitot tube installation position is parallel to the horizontal stabilizer of the aircraft. If there is an angle between the pitot tube position and the horizontal direction of the aircraft parking ground, it is necessary to obtain the theoretical airflow angle of attack AOA_D of the pitot tube according to the pitot tube installation angle Theta and the fuselage pitch angle Pitch, and correct the indicated airspeed of the atmospheric aircraft. Then, according to the relationship between the aerodynamic angle of attack at the pitot tube and the indicated airspeed error, correct the indicated airspeed error. Figure 1 This is the effect diagram of the corrected indicated airspeed.

[0054] AOA_D=ASIN(Vz / TAS) / π*180-Pitch-Theta

[0055] Pitch is the fuselage pitch angle (°), Theta is the pitot tube installation angle (°).

[0056] The embodiment of the present invention proposes a method for correcting the indicated airspeed of a helicopter by the angle of attack, determines the error relationship between the angle of attack and the airspeed based on test flight data, and uses the theoretically calculated angle of attack to directly correct the airspeed, thereby reducing the error of the airspeed indication and improving the accuracy of the airspeed system.

Claims

1. A method for correcting helicopter indicated airspeed by aerodynamic angle of attack, characterized in that: The method comprises: S1, a forward lever is installed on the helicopter to measure the aerodynamic angle of attack and indicated airspeed; S2, calibrating the indicated airspeed of the front stick in the level flight state, and obtaining a relationship curve between the indicated airspeed of the front stick and the calibrated airspeed; S3, select the climbing and descending states, obtain the aerodynamic angle of attack AOA of the lead stick test; obtain the calibrated airspeed of the climbing and descending states according to the relationship curve between the indicated airspeed and the calibrated airspeed of the lead stick obtained in S2, and then obtain the indicated airspeed error of the climbing and descending states, and the indicated airspeed error is the difference between the calibrated airspeed and the indicated airspeed on the aircraft; S4, obtain the true speed TAS and the vertical speed Vz during the climbing and descending process, and preliminarily calculate the theoretical aerodynamic angle of attack AOA1 of the helicopter; S5, based on the theoretical aerodynamic angle of attack AOA1 calculated in step 4 and the indicated airspeed error relationship curve corresponding to different measured aerodynamic angles of attack obtained in step 3, correct the indicated airspeed on board according to the indicated airspeed error corresponding to the theoretical aerodynamic angle of attack AOA1.

2. A method for correcting helicopter indicated airspeed by aerodynamic angle of attack according to claim 1, characterized in that: In S2, the calculation process of the calibration airspeed is: Among them, V GPS is the differential GPS velocity, is the density ratio; pressure ratio: Δ = (1-0.0065×Hp / 288.15) 5.25588 , temperature ratio: Hp is the absolute pressure altitude and Tamb is the atmospheric temperature.

3. A method for correcting helicopter indicated airspeed by aerodynamic angle of attack according to claim 2, characterized in that: In S2, the relationship curve between the indicated airspeed of the front lever and the calibrated airspeed is obtained, which is specifically: According to the indicated airspeed Vi_angle measured by the front lever in the flight test and the calibrated airspeed Vc obtained by solution, a relationship curve between the indicated airspeed measured by the front lever and the calibrated airspeed is obtained.

4. A method for correcting helicopter indicated airspeed by aerodynamic angle of attack according to claim 3, characterized in that: In S3, Perform a round trip sawtooth climb using a given average ground clearance, climb using maximum continuous power, and descend using unpowered descent, with the indicated airspeed range starting from the minimum speed that can be stably indicated to the selected maximum speed, with a speed interval of 10km / h-20km / h; Through flight tests, the indicated airspeed of the front lever is obtained. Through the relationship curve between the indicated airspeed of the front lever and the calibrated airspeed in step 2, the calibrated airspeed Vc of the climbing and gliding states is obtained respectively, and then the corresponding indicated airspeed Vi on board is subtracted to obtain the indicated airspeed error ΔVi of the climbing and gliding states; Combined with the aerodynamic angle of attack (AOA) of the lead rod test, the relationship between the indicated airspeed error and the aerodynamic angle of attack is obtained, and a polynomial fitting is performed.

5. A method for correcting helicopter indicated airspeed by aerodynamic angle of attack according to claim 4, characterized in that: In S4, Theoretical aerodynamic angle of attack AOA1 solution formula is as follows: AOA1 = ASIN (Vz / TAS) / π * 180 Among them, Vz is the lifting speed, TAS is the true speed, and the true air speed TAS solution formula is as follows: Vc is the calibrated airspeed.

6. A method for correcting helicopter indicated airspeed by aerodynamic angle of attack according to claim 5, characterized in that: The method further comprises: S6, if there is an angle between the position of the pitot tube and the horizontal direction of the ground on which the aircraft is parked, it is necessary to obtain the theoretical airflow angle of attack AOA_D of the pitot tube according to the pitot tube installation angle Theta and the fuselage pitch angle Pitch, correct the indicated airspeed of the atmospheric aircraft, and then correct the indicated airspeed error according to the relationship between the aerodynamic angle of attack at the measured pitot tube and the indicated airspeed error.

7. A method for correcting helicopter indicated airspeed by aerodynamic angle of attack according to claim 6, characterized in that: Pitot processing airflow angle of attack AOA_D: AOA_D=ASIN(Vz / TAS) / π*180-Pitch-Theta.

8. A helicopter, characterized in that: The helicopter uses the method according to any one of claims 1-7 to correct the helicopter indicated airspeed.

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