A method of correcting for indicated airspeed of a helicopter by aerodynamic angle of attack

Abstract

The present application belongs to the technical field of helicopter aerodynamic design, and particularly relates to a method for correcting helicopter indicated airspeed through aerodynamic angle of attack. The method comprises the following steps: S1, installing a front boom on the helicopter to measure the aerodynamic angle of attack and the indicated airspeed; S2, selecting a steady state to calibrate the indicated airspeed of the front boom, and obtaining a relationship curve between the indicated airspeed and the calibrated airspeed of the front boom; S3, selecting a climbing and gliding state, and obtaining the aerodynamic angle of attack AOA of the front boom; according to the relationship curve between the indicated airspeed and the calibrated airspeed of the front boom obtained in S2, obtaining the calibrated airspeed in the climbing and gliding state, and then obtaining the indicated airspeed error in the climbing and gliding state, wherein the indicated airspeed error is the difference between the calibrated airspeed and the on-board indicated airspeed; S4, obtaining the true airspeed TAS and the vertical speed Vz in the climbing and gliding process, and preliminarily calculating the theoretical aerodynamic angle of attack AOA1 of the helicopter; S5, according to the theoretical aerodynamic angle of attack AOA1 calculated in step 4 and the relationship curve between the indicated airspeed error corresponding to different aerodynamic angles of attack obtained in step 3, correcting the on-board indicated airspeed according to the indicated airspeed error corresponding to the theoretical aerodynamic angle of attack AOA1.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of helicopter aerodynamic design, and particularly relates to a method for correcting helicopter indicated airspeed through aerodynamic attack angle. BACKGROUND

[0002] The indicated airspeed of a helicopter is obtained by calculating the total pressure and static pressure measured by an air data computer, and the total pressure is usually measured by a pressure sensor of an airspeed tube. The airspeed tube usually has no airflow angle sensitivity, and the total pressure measured by the common airspeed tube almost does not change with the aerodynamic attack angle within a certain airflow angle range, which directly leads to that the indicated airspeed measured by the air data computer of the helicopter has no airflow angle sensitivity. Within a given attack angle range, the total pressure test has high accuracy, and the airspeed indication has high accuracy. When the attack angle exceeds the airflow angle range of the given airspeed tube, the total pressure test error increases, which directly leads to that the indicated airspeed error increases. The flight states in which the aerodynamic attack angle of the helicopter exceeds the airflow angle range of the given airspeed tube mainly include low-speed climbing, autorotation gliding, maneuvering state and the like, and therefore the airspeed indication error exceeding the airflow angle range of the given airspeed tube needs to be corrected to improve the indicated airspeed accuracy and flight safety. SUMMARY

[0003] The application provides a method for correcting helicopter indicated airspeed through aerodynamic attack angle, uses the forward flight speed and the ascending / descending speed to calculate the attack angle, and corrects the airspeed according to the attack angle-error relationship, so as to improve the indicated airspeed accuracy of the helicopter when the airflow angle exceeds the measurement range of the given airspeed tube in the flight postures such as low-speed climbing, autorotation gliding and maneuvering state, and improve the maneuvering flight safety.

[0004] To achieve the above object, the application adopts the following technical scheme.

[0005] A method for correcting helicopter indicated airspeed through aerodynamic attack angle, the method comprises the following steps:

[0006] S1, a front rod for measuring the aerodynamic attack angle and the indicated airspeed is installed on the helicopter;

[0007] S2, the indicated airspeed of the front rod in the level flight state is calibrated to obtain the relationship curve between the indicated airspeed and the calibrated airspeed of the front rod;

[0008] S3, the aerodynamic attack angle AOA of the front rod is obtained in the climbing and gliding state, the relationship curve between the indicated airspeed and the calibrated airspeed of the front rod obtained in S2 is used to obtain the calibrated airspeed in the climbing and gliding state, and then the indicated airspeed error in the climbing and gliding state is obtained, and the indicated airspeed error is the difference between the calibrated airspeed and the indicated airspeed on the helicopter;

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

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

[0011] Further, in S2, the calculation process of the calibrated airspeed is as follows:

[0012]

[0013] wherein, V GPS is the differential GPS speed, is the density ratio; the pressure ratio: Δ = (1-0.0065*Hp / 288.15) 5.25588 , the temperature ratio: Hp is the absolute air pressure height, and Tamb is the atmospheric temperature.

[0014] Further, in S2, the relationship curve of the indicated airspeed and the calibrated airspeed of the nose boom is obtained, which is specifically as follows:

[0015] According to the measured indicated airspeed Vi_angle of the nose boom and the calculated calibrated airspeed Vc in the flight test, the relationship curve of the measured indicated airspeed and the calibrated airspeed of the nose boom is obtained.

[0016] Further, in S3,

[0017] The given average ground height is used for the reciprocating sawtooth climb, the climb uses the maximum continuous power, the descent uses the unpowered glide, the indicated airspeed on the helicopter ranges from the minimum speed that can be stably indicated to the selected maximum speed, and the speed interval is 10km / h-20km / h flight;

[0018] Through the flight test, the indicated airspeed of the nose boom is obtained, the calibrated airspeed Vc of the climb and glide states is obtained respectively through the relationship curve of the indicated airspeed and the calibrated airspeed of the nose boom in step 2, and then the corresponding indicated airspeed Vi on the helicopter is subtracted to obtain the indicated airspeed error ΔVi of the climb and glide states.

[0019] In combination with the aerodynamic attack angle AOA of the nose boom test, the relationship between the indicated airspeed error and the aerodynamic attack angle is obtained, and polynomial fitting is performed.

[0020] Further, in S4,

[0021] The theoretical aerodynamic attack angle AOA1 calculation formula is as follows: AOA1 = ASIN(Vz / TAS) / π*180

[0022] Wherein, Vz is the lifting speed, TAS is the true speed, and the true airspeed TAS solving formula is as follows: Vc is the calibrated airspeed.

[0023] Further, the method further comprises:

[0024] S6, if the airspeed tube position and the ground level direction exist the included angle with the body parking, then the airspeed tube processing angle of attack AOA_D needs to be obtained according to the airspeed tube installation angle Theta and the body pitch angle Pitch, the indicated airspeed is corrected, and then the indicated airspeed error is corrected according to the relationship between the measured airspeed tube aerodynamic attack angle and the indicated airspeed error.

[0025] Further, the airspeed tube processing angle of attack AOA_D is:

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

[0027] The application also provides a helicopter, which adopts the method to correct the indicated airspeed of the helicopter.

[0028] The method for correcting the indicated airspeed of the helicopter through the angle of attack is proposed in the application, the relationship between the angle of attack and the airspeed error is determined according to the flight test data, and the airspeed is directly corrected by using the theoretically calculated angle of attack. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The comparison schematic diagram of the indicated airspeed before correction and the indicated airspeed after correction provided by the embodiment of the application is shown. DETAILED DESCRIPTION

[0030] The technical scheme of the application is described in detail below with reference to the drawings.

[0031] The method for correcting the indicated airspeed of the helicopter through the aerodynamic angle of attack is proposed in the embodiment of the application, the angle of attack is calculated by using the forward flight speed and the lifting speed, the airspeed is corrected according to the relationship between the angle of attack and the error, so as to improve the precision of the indicated airspeed of the helicopter when the air flow angle measured by the given airspeed tube exceeds the measuring angle range in the flight attitude such as low-speed climbing, autorotation gliding and maneuvering state, and to improve the maneuvering flight safety.

[0032] The method for correcting the indicated airspeed of the helicopter through the aerodynamic angle of attack mainly obtains the relationship between the aerodynamic angle of attack and the indicated airspeed error by combining the flight test, calculates the theoretical aerodynamic angle of attack of the helicopter by using the measured forward flight speed and lifting speed of the helicopter, obtains the relationship between the measured aerodynamic angle of attack and the indicated airspeed error of the helicopter, and embeds the relationship into the atmospheric data system of the helicopter for correction, so as to improve the precision of the indicated airspeed. The specific steps are as follows:

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

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

[0035] Step 2: Select the indicated airspeed of the device for measuring the angle of attack (front boom) for calibration in the steady state.

[0036] Using the steady triangle flight method, start from the minimum stable indicated airspeed, and continue to the maximum steady speed, with an interval of 10 km / h-20 km / h, start flying, through flight test, respectively obtain the DGPS speed V GPS , the front boom measured indicated airspeed Vi_angle, and the calculated calibration airspeed Vc;

[0037] The calculated calibration airspeed Vc (km / h), Hp (absolute air pressure height, m), Tamb (atmospheric temperature OAT, ℃), 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 front boom measured indicated airspeed Vi_angle and the calculated calibration airspeed Vc in the flight test, the relationship curve of the front boom measured indicated airspeed and the calibration airspeed is obtained.

[0043] Vc = a1*Vi_angle + b1

[0044] Step 3: Select the climb and glide state, and obtain the angle of attack AOA tested by the selected device for measuring the angle of attack. According to the relationship between the front boom indicated airspeed and the calibration airspeed obtained in step 2, the calibration airspeed Vc1 of the climb and descent state is obtained, and then the indicated airspeed error of the climb and glide state is obtained. The indicated airspeed error is the difference between the calibration airspeed Vc1 and the on-board indicated airspeed.

[0045] The given average height from the ground is used for the reciprocating sawtooth climb, the climb uses the maximum continuous power, the descent uses the unpowered glide, the on-board indicated airspeed range is from the minimum speed that can be stably indicated to the selected maximum speed, and the speed interval is 10km / h-20km / h flight. Through flight test, the nose boom indicated airspeed Vi_angle is obtained, through the step 2 nose boom indicated airspeed and calibrated airspeed relationship curve, the calibrated airspeed Vc of the climb and glide state is obtained respectively, and then the corresponding helicopter atmospheric machine indicated airspeed Vi is subtracted to obtain the indicated airspeed error ΔVi of the climb and glide state. In combination with the aerodynamic attack angle AOA obtained by the nose boom test, the relationship between the indicated airspeed error and the aerodynamic attack angle is obtained, and polynomial fitting is performed.

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

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

[0048]

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

[0050] AOA1=ASIN(Vz / TAS) / π*180

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

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

[0053] Step 6: Step 5 is applicable to the direction parallel to the horizontal stabilizer of the aircraft body where the airspeed tube is installed. If there is an angle between the airspeed tube position and the horizontal direction of the ground where the aircraft is parked, then according to the airspeed tube installation angle Theta and the aircraft body pitch angle Pitch, the airspeed tube processing theoretical flow attack angle AOA_D can be obtained, and the atmospheric machine indicated airspeed is corrected. According to the relationship between the measured airspeed tube aerodynamic attack angle and the indicated airspeed error, the indicated airspeed error is corrected. Figure 1 is the corrected indicated airspeed effect diagram.

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

[0055] Pitch is the aircraft body pitch angle (°), and Theta is the airspeed tube installation angle (°).

[0056] The method for correcting the indicated air speed of a helicopter by an attack angle is provided, the relationship between the attack angle and the air speed error is determined according to the flight test data, and the air speed is directly corrected by using the theoretically calculated attack angle. The air speed indication error can be reduced, and the accuracy of the air speed system is improved.

Claims

1. A method of correcting for indicated airspeed of a helicopter by aerodynamic angle of attack, characterized by, The method comprises: S1, installing a front rod on the helicopter to measure the aerodynamic angle of attack and the indicated airspeed; S2, selecting a steady state to calibrate the indicated airspeed of the front rod to obtain a relationship curve between the indicated airspeed and the calibrated airspeed of the front rod; in S2, the relationship curve between the indicated airspeed and the calibrated airspeed of the front rod is obtained, specifically as follows: According to the front rod measured indicated airspeed Vi_angle and the calculated calibrated airspeed Vc in the flight test, the relationship curve between the front rod measured indicated airspeed and the calibrated airspeed is obtained; S3, selecting a climbing and descending state to obtain the aerodynamic angle of attack AOA of the front rod; according to the relationship curve between the indicated airspeed and the calibrated airspeed of the front rod obtained in S2, the calibrated airspeed in the climbing and descending state is obtained, and then the indicated airspeed error in the climbing and descending state is obtained, which is the difference between the calibrated airspeed and the on-board indicated airspeed; in S3, The given average ground clearance is used for reciprocating sawtooth climbing, the climbing uses maximum continuous power, the descending uses unpowered descending, the on-board indicated airspeed ranges from the minimum speed that can be stably indicated to the selected maximum speed, the speed interval is 10km / h-20km / h flight; Through the flight test, the indicated airspeed of the front rod is obtained, the calibrated airspeed Vc in the climbing and descending state is obtained respectively through the relationship curve between the indicated airspeed and the calibrated airspeed of the front rod in step 2, and then the indicated airspeed error ΔVi in the climbing and descending state is obtained by subtracting the corresponding on-board indicated airspeed Vi; Combined with the aerodynamic angle of attack AOA tested by the front rod, the relationship between the indicated airspeed error and the aerodynamic angle of attack is obtained, and polynomial fitting is performed; S4, obtaining the true airspeed TAS and the lifting speed Vz of the climbing and descending process, and preliminarily calculating the theoretical aerodynamic angle of attack AOA1 of the helicopter; in S4, The theoretical aerodynamic angle of attack AOA1 solving formula is as follows: AOA1=ASIN(Vz / TAS) / π*180 Wherein, Vz is the lifting speed, TAS is the true airspeed, the true airspeed TAS solving formula is as follows: , Vc is the calibrated airspeed; S5, according to the theoretical aerodynamic angle of attack AOA1 calculated in step 4 and the relationship curve between the indicated airspeed error corresponding to the measured different aerodynamic angles of attack obtained in step 3, the on-board indicated airspeed is corrected according to the indicated airspeed error corresponding to the theoretical aerodynamic angle of attack AOA1.

2. A method of correcting indicated airspeed of a helicopter by aerodynamic angle of attack according to claim 1, characterized in that, In S2, the solving process of the calibrated airspeed is as follows: wherein, is the differential GPS velocity, is the density ratio; pressure ratio: , temperature ratio: , Hp is the absolute barometric height, Tamb is the atmospheric temperature.

3. A method of correcting indicated airspeed of a helicopter by aerodynamic angle of attack according to claim 1, characterized in that, The method further comprises: S6, if there is an included angle between the position of the pitot tube and the horizontal direction of the ground where the body is parked, then the pitot tube processing theoretical flow angle AOA_D is obtained according to the pitot tube installation angle Theta and the body pitch angle Pitch to correct the atmospheric indicated airspeed, and then the indicated airspeed error is corrected according to the relationship between the measured aerodynamic angle of attack and the indicated airspeed error.

4. A method of correcting indicated airspeed of a helicopter by aerodynamic angle of attack according to claim 3, characterized in that, Pitot tube processing theoretical flow angle AOA_D: AOA_D=ASIN(Vz / TAS) / π*180-Pitch-Theta.

5. A helicopter characterized by The helicopter uses the method in any one of claims 1-4 to correct the indicated airspeed of the helicopter.

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