Radio altimeter height measurement precision test flight verification method based on laser range finder

Abstract

The invention belongs to the technical field of flight tests of aircrafts, and discloses a radio altimeter height measurement precision test flight verification method based on a laser range finder, which comprises the following steps of: 1, measuring a position difference value between a radio altimeter and the laser range finder; 2, measuring a mounting roll angle L theta 1 and a mounting pitch angle L theta 2 of the laser range finder; 3, adding data acquisition equipment on the aircraft, and synchronously acquiring the height H1 of the laser range finder, the radio height H2, the roll angle theta1, the pitch angle theta2 and the indicated airspeed Vi; 4, collecting an initial height value H0 of the laser range finder when the aircraft is in a ground shutdown state; recording an aircraft roll angle initial value I theta 1 and a pitch angle initial value I theta 2 output by the inertial navigation system at the same time; 5, controlling the flight of the aircraft, and collecting the collected data through a data collection device; step 6, calculating the measured value deviation delta H1 (t) of the radio altimeter signal transceiving system and the laser range finder caused by the pitch attitude change; calculating the measured value deviation delta H2 (t) of the radio altimeter signal receiving and transmitting system and the laser range finder caused by the roll attitude change; 7, calculating the actual terrain clearance H (t) measured by the laser range finder; 8, calculating the test flight precision delta H (t) of height measurement of the radio altimeter; and 9, calculating the mean value and the standard deviation of the test flight precision in the flight time period.

Description

Technical Field

[0001] The invention belongs to the technical field of aircraft flight test, and in particular relates to a high-precision test flight calibration method for a radio altimeter based on a laser rangefinder. Background Art

[0002] The radio altimeter (Low Range Radio Altimeter), also known as the radar altimeter, is used in the field of aircraft to measure the height relative to the ground or water surface. The radio altimeter is particularly important during the take-off, climb, low-altitude flight, and slow approach flight stages of the aircraft. It provides pilots with real-time information on the aircraft's altitude above the ground, which helps prevent ground collisions. The radio altimeter can work normally in various complex meteorological environments such as fog, clouds, and rainy days. It is an indispensable general navigation basic equipment on modern aircraft. The basic working principle of the radio altimeter is based on radar technology. It works by emitting electromagnetic waves and receiving reflected waves reflected from the ground or water surface.

[0003] The performance indicators of the radio altimeter include: sampling rate, transmission power, altitude measurement range, altitude measurement accuracy, etc. The sampling rate and transmission power are generally verified through laboratory tests, and the altitude measurement range and altitude measurement accuracy require special test flight verification. The altitude measurement range test flight verification method is relatively simple: the aircraft continuously climbs the altitude until the radio altimeter does not display the altitude or the displayed value is fixed to a value and no longer updated. After the flight, the radio altimeter altitude measurement range can be obtained by downloading the flight parameter data and analyzing the radio altimeter cutoff height in the flight parameter data. The altitude measurement accuracy test flight verification method is relatively complex.

[0004] The mainstream radio altimeter high-precision test flight calibration method uses a total station or differential GPS system for measurement. The total station test flight method can obtain higher measurement accuracy, but its disadvantage is that it cannot obtain continuous benchmark data, the number of sampling data points is often small, and it can only measure hovering aircraft, and cannot measure the radio altimeter high accuracy of level-flying aircraft. The differential GPS test flight method can obtain higher measurement accuracy, and the data obtained is continuous, and the amount of sampling data meets the data analysis requirements. Its disadvantage is that it can only measure hovering helicopters, and cannot measure the radio altimeter high accuracy of level-flying aircraft, and before the test flight test, the aircraft must be parked still on the hovering site for high-precision differential positioning, and the measurement site is limited. Summary of the invention

[0005] Purpose of the invention: The present invention proposes a test flight calibration method for the altitude measurement accuracy of an aircraft radio altimeter based on a laser rangefinder. The laser rangefinder is used to measure and calibrate the altitude measurement accuracy of the radio altimeter during the test flight. By correcting the system error, continuous test data that meets the data analysis requirements is obtained, and then the altitude measurement accuracy of the radio altimeter in hovering and level flight states is obtained.

[0006] Technical Solution

[0007] The high-precision test flight calibration method of a radio altimeter based on a laser rangefinder comprises the following steps:

[0008] Step 1: Measure the position difference between the radio altimeter and the laser rangefinder;

[0009] Step 2: Measure the installation roll angle L of the laser rangefinder θ1 and installation pitch angle L θ2 ;

[0010] Step 3: Install data acquisition equipment on the aircraft to synchronously collect laser rangefinder altitude H1, radio altitude H2, roll angle θ1, pitch angle θ2, and indicated airspeed Vi;

[0011] Step 4: When the aircraft is parked on the ground, collect the initial altitude value H0 of the laser rangefinder; at the same time, record the initial value of the aircraft roll angle I output by the inertial navigation system θ1 and the initial value of the pitch angle I θ2 ;

[0012] Step 5: Control the aircraft to fly and collect data through data acquisition equipment;

[0013] Step 6: Calculate the measurement value deviation ΔH1(t) between the radio altimeter signal transceiver system and the laser rangefinder caused by the pitch attitude change; calculate the measurement value deviation ΔH2(t) between the radio altimeter signal transceiver system and the laser rangefinder caused by the roll attitude change;

[0014] Step 7: Calculate the actual ground height H(t) measured by the laser rangefinder;

[0015] Step 8: Calculate the test flight accuracy ΔH(t) of the radio altimeter.

[0016] Step 9: Calculate the mean and standard deviation of the test flight accuracy during the flight period.

[0017] Furthermore, the method also includes: Step 10: repeating steps 5 to 9, performing multiple flights, and respectively calculating the average values ​​of the mean and standard deviation of the multiple flight test accuracies to obtain the height measurement accuracy of the radio altimeter.

[0018] Furthermore, in step 1, the position differences between the radio altimeter and the laser rangefinder in the longitudinal, lateral and heading directions are measured and recorded as L1, L2 and L3 respectively.

[0019] Furthermore, in step five, the aircraft is controlled to hover and take off, about 5 meters above the ground, and hover stably for 5 minutes to collect a set of data.

[0020] Furthermore, in step five, the aircraft is controlled to perform stable level flight at an altitude of 40 m above the ground and an indicated airspeed of 150 km / h for 1 min, and a set of data is collected.

[0021] Furthermore, in step 6, the calculation process of the measurement value deviation caused by the pitch attitude change is as follows:

[0022] ΔH1(t)=(L2+L3)sin[θ2(t)-(Iθ2-Lθ2)].

[0023] Furthermore, in step 6, the calculation process of the measurement value deviation caused by the roll attitude change is as follows:

[0024] ΔH2(t)=(L1)sin[θ1(t)-(Iθ1-Lθ1)].

[0025] Further, in step seven, the actual height above the ground is calculated as follows:

[0026] H(t)=H1(t)cos[θ2(t)-(Iθ2-Lθ2)].

[0027] Further, in step eight, the high precision calculation process is as follows:

[0028] ΔH(t)=H(t)+ΔH1(t)+ΔH2(t)-H2(t).

[0029] In summary, the beneficial effects of the present invention are as follows:

[0030] The present invention uses a laser rangefinder to achieve the measurement and verification of the radio altimeter's altitude precision in an aircraft test flight state, has a high sampling rate, high measurement precision, reliable implementation of the method, and the obtained test data is continuous data, meeting the test flight data analysis requirements. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of data measured by radio altimeter and laser rangefinder.

[0032] Figure 2 This is a graph showing the change in radio altimeter accuracy over time. DETAILED DESCRIPTION

[0033] The present invention provides a method for testing and verifying the height accuracy of an aircraft radio altimeter based on a laser rangefinder, including basic data measurement, test data collection, hovering and level flight test flights, and height accuracy analysis and calculation. The test flight verification method mainly includes the following steps:

[0034] 1) Due to the installation location restrictions, the laser rangefinder cannot be installed at the same location as the radio altimeter. The laser rangefinder is installed under the aircraft.

[0035] 2) Measure the position differences L1, L2, and L3 between the radio altimeter signal transceiver system and the laser rangefinder in the lateral, longitudinal, and heading directions of the helicopter;

[0036] 3) Use a level to measure the inclination angle L of the laser rangefinder installation θ1 and pitch angle L θ2 ;

[0037] 4) Installing airborne data acquisition equipment on the aircraft can collect parameters such as laser rangefinder altitude H1, radio altitude H2, aircraft roll angle θ1, aircraft pitch angle θ2, aircraft indicated airspeed Vi, and flight control parameters. The aircraft indicated airspeed, among which the indicated airspeed is used for test flight status identification, and other parameters are used for accuracy calculation.

[0038] 5) The aircraft is powered on while the ground is shut down, and the laser rangefinder's range height value H0 is collected; at the same time, the initial value of the helicopter's roll angle I output by the aircraft's inertial navigation system is recorded. θ1 and the initial value of the pitch angle I θ2 ;

[0039] 6) The aircraft takes off in a hovering position, about 5 meters above the ground, and hovers stably for 5 minutes. The onboard data acquisition equipment continuously records various measurement parameters;

[0040] 7) At a height of about 40m above the ground, the aircraft performs a stable level flight at an indicated airspeed of 150km / h for 1min, and the onboard data acquisition equipment continuously records various measurement parameters;

[0041] 8) Steps 6) and 7) are repeated three times each, the aircraft returns to the landing site, and the measurement data recorded by the onboard data acquisition device is downloaded;

[0042] 9) Identify the time period when the helicopter performs stable hovering and stable level flight through parameters such as indicated airspeed, flight attitude and flight control, and extract the change history of laser rangefinder height H1(t), radio altitude H2(t), helicopter roll angle θ1(t), helicopter pitch angle θ2(t), aircraft indicated airspeed Vi(t) and other data over time t in the corresponding time period from the measurement data;

[0043] 10) Using the data extracted in step 9), the variation history of the deviation of the measured value between the radio altimeter signal transceiver system and the laser rangefinder caused by the change of the helicopter pitch attitude over time is calculated according to formula (1):

[0044] ΔH1(t)=(L2+L3)sin[θ2(t)-(Iθ2-Lθ2)] (1)

[0045] 11) Using the data extracted in step 9), the variation history of the deviation of the measured value between the radio altimeter signal transceiver system and the laser rangefinder caused by the helicopter's roll attitude change over time is calculated according to formula (2):

[0046] ΔH2(t)=(L1)sin[θ1(t)-(Iθ1-Lθ1)] (2)

[0047] 12) The data extracted in step 9) is used to calculate the actual height above the ground measured by the laser rangefinder according to formula (3). The measurement result of the laser rangefinder is the actual distance from the laser beam to the ground reflection point, not the actual height above the ground of the aircraft, and needs to be corrected:

[0048] H(t)=H1(t)cos[θ2(t)-(Iθ2-Lθ2)] (3)

[0049] 13) Calculate the test flight accuracy of the radio altimeter by using the data extracted in step 9) and the results calculated in steps 10), 11) and 12) according to formula (4):

[0050] ΔH(I)=H(l)+ΔH1(l)+ΔH2(l)-H2(l) (4)

[0051] 14) The radio altimeter altitude measurement accuracy in stable hover and stable level flight is calculated according to steps 10) to 13) respectively;

[0052] 15) Calculate the mean value of the radio altimeter height measurement accuracy data obtained in step 13) according to formula (5), where n is the total amount of data collected;

[0053] ΔH a =∑ΔH(t) / n (5)

[0054] 16) Calculate the standard deviation of the radio altimeter height accuracy data obtained in 13) according to formula (6):

[0055] (6)

[0057] 17) Calculate the average value of the mean and standard deviation of the height measurement accuracy data obtained from three repeated tests of stable hovering and stable level flight, and give the height measurement accuracy characteristics of the radio altimeter in the form of (mean ± standard deviation).

[0058] During the test flight, the installation and measurement errors of the laser rangefinder, and the errors caused by the installation positions of the laser rangefinder and the radio altimeter due to changes in the aircraft's flight attitude during the flight can all be accurately calculated using the above-mentioned test flight verification method, thereby obtaining the height measurement accuracy of the aircraft's radio altimeter during the test flight.

[0059] By calculating the mean of the radio altimeter's height measurement accuracy data, the error caused by chance can be effectively eliminated. By calculating the standard deviation of the radio altimeter's height measurement accuracy data, the concentration of the data can be checked, and then the measurement quality of the radio altimeter can be fed back.

[0060] Example

[0061] The laser rangefinder was installed on the short wing on the right side of the aircraft, and the UMA2000 data acquisition device was installed inside the aircraft. The power supply was connected to the 28V DC power on the aircraft, and the airspeed bus data of the atmospheric data system, the inertial navigation system, the aircraft roll angle, the pitch angle, and the radio altimeter altitude bus data were respectively extracted. After the test modification was completed, the test equipment was powered on for inspection, and the basic data was measured. The longitudinal, lateral and heading position differences between the radio altimeter and the laser rangefinder were obtained, L1 = 2.2m, L2 = 4m, L3 = 1.1m, and the installation roll angle L θ1 =-0.23°, installation pitch angle L θ2 =0.4°, initial value of roll angle I θ1 =0°, initial value of pitch angle I θ2 =0.83°, the initial height value of the laser rangefinder H0 = 0.84m.

[0062] The aircraft conducted a hovering test flight, collecting data at a sampling rate of 20Hz for a total of 3 times. The first test flight lasted 388s, with a total of 7771 data points, the second test flight lasted 394s, with a total of 7869 data points, and the third test flight lasted 396s, with a total of 7901 data points. The test flight data was calculated according to the test flight verification method, and the average accuracy of the radio altimeter in the test flight state was 0.21m, and the standard deviation was 0.10m.

[0063] The aircraft conducted a level flight test and collected data at a sampling rate of 20Hz for 3 times. The first test flight lasted 49s, with a total of 967 data points, the second test flight lasted 51s, with a total of 1001 data points, and the third test flight lasted 52s, with a total of 1031 data points. The test flight data was calculated according to the test flight verification method, and the average accuracy of the radio altimeter in the test flight status was 0.39m, and the standard deviation was 0.12m.

Claims

1. A high-precision test flight calibration method for a radio altimeter based on a laser rangefinder, characterized in that: The following steps are involved: Step 1: Measure the position difference between the radio altimeter and the laser rangefinder; Step 2: Measure the installation roll angle L of the laser rangefinder θ1 and installation pitch angle L θ2 ; Step 3: Install data acquisition equipment on the aircraft to synchronously collect laser rangefinder altitude H1, radio altitude H2, roll angle θ1, pitch angle θ2, and indicated airspeed Vi; Step 4: When the aircraft is parked on the ground, collect the initial altitude value H0 of the laser rangefinder; at the same time, record the initial value of the aircraft roll angle I output by the inertial navigation system θ1 and the initial value of the pitch angle I θ2 ; Step 5: Control the aircraft to fly and collect data through data acquisition equipment; Step 6: Calculate the measurement value deviation ΔH1(t) between the radio altimeter signal transceiver system and the laser rangefinder caused by the pitch attitude change; calculate the measurement value deviation ΔH2(t) between the radio altimeter signal transceiver system and the laser rangefinder caused by the roll attitude change; Step 7: Calculate the actual ground height H(t) measured by the laser rangefinder; Step 8: Calculate the test flight accuracy ΔH(t) of the radio altimeter. Step 9: Calculate the mean and standard deviation of the test flight accuracy during the flight period.

2. The method according to claim 1, characterized in that: The method also includes: step 10: repeating steps 5 to 9, performing multiple flights, respectively calculating the average values ​​of the mean values ​​and standard deviations of the multiple flight test accuracies, and obtaining the height measurement accuracy of the radio altimeter.

3. The method according to claim 2, characterized in that: In step 1, the position differences between the radio altimeter and the laser rangefinder in the longitudinal, lateral and heading directions are measured and recorded as L1, L2 and L3 respectively.

4. The method according to claim 3, characterized in that: In step five, the aircraft is controlled to hover and take off, about 5 meters above the ground, and hover stably for 5 minutes to collect a set of data.

5. The method according to claim 4, characterized in that: In step 5, the aircraft is controlled to perform stable level flight at an altitude of 40m above the ground and an indicated airspeed of 150km / h for 1min, and a set of data is collected.

6. The method according to claim 5, characterized in that: In step 6, the calculation process of the measured value deviation caused by the pitch attitude change is as follows: ΔH1(t)=(L2+L3)sin[θ2(t)-(Iθ2-Lθ2)].

7. The method according to claim 6, characterized in that: In step 6, the calculation process of the measurement value deviation caused by the roll attitude change is as follows: ΔH2(t)=(L1)sin[θ1(t)-(Iθ1-Lθ1)].

8. The method according to claim 7, characterized in that: In step 7, the actual height above the ground is calculated as follows: H(t)=H1(t)cos[θ2(t)-(Iθ2-Lθ2)].

9. The method according to claim 8, characterized in that: In step eight, the high precision calculation process is as follows: ΔH(t)=H(t)+ΔH1(t)+ΔH2(t)-H2(t).

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