Method for determining low-altitude-state large-incidence-angle protection starting threshold of airplane
By calculating the product of the warning angle of attack and the indicated airspeed threshold, the high angle of attack protection activation threshold at low altitudes is determined, which solves the problem of low-altitude aircraft collision risk in existing technologies, realizes safe angle of attack control, and improves aircraft safety.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-29
- Publication Date
- 2026-04-03
AI Technical Summary
Existing technology fails to determine the high angle-of-attack protection activation threshold based on the aircraft's altitude, resulting in a risk of the aircraft crashing into the ground at low altitudes.
By calculating the product of the warning angle of attack, the indicated airspeed threshold, and the delay time, the high angle of attack protection activation threshold at low altitude is determined, and the flight control system implements warnings and controls the elevator to reduce the angle of attack and avoid altitude loss.
By increasing engine thrust at low altitudes, aircraft can safely recover to high angles of attack, improving safety, avoiding the risk of crashing upon touchdown, and saving costs without requiring hardware modifications.
Smart Images
Figure CN121786978A_ABST
Abstract
Description
Technical Field
[0001] This application belongs to the field of flight control system design, and specifically relates to a method for determining the activation threshold of protection at high angle of attack in low-altitude aircraft. Background Technology
[0002] During flight, pilots may lack sufficient monitoring of the aircraft's speed under complex maneuvering conditions, greatly increasing the likelihood of a continuous decrease in speed and consequently, an increase in the angle of attack. When the angle of attack exceeds the stall angle of attack, the aircraft enters a dangerous state. Modern fly-by-wire aircraft typically have high angle-of-attack protection. When the angle of attack exceeds the protection activation threshold, the protection function generates an alarm signal and controls the elevator to pitch the aircraft down, thereby reducing the angle of attack. This process results in a loss of altitude. When the aircraft is at medium to high altitudes, there is sufficient altitude margin to increase speed and reduce the angle of attack through altitude loss. However, when the aircraft is at low altitudes, a significant decrease in altitude could very likely lead to a touchdown and crash. Therefore, the only way to recover from a high angle of attack is to increase engine thrust to increase the aircraft's speed.
[0003] Currently, conventional methods do not determine the high angle-of-attack protection activation threshold separately based on the aircraft's altitude status, which could lead to a risk of the aircraft crashing into the ground when recovering from a low altitude at a high angle of attack.
[0004] Therefore, there is an urgent need for a technical solution to overcome or mitigate at least one of the aforementioned defects in the existing technology. Summary of the Invention
[0005] The purpose of this application is to provide a method for determining the activation threshold of high angle of attack protection at low altitudes of an aircraft, in order to solve at least one problem existing in the prior art.
[0006] The technical solution of this application is:
[0007] A method for determining the activation threshold of high angle-of-attack protection for aircraft at low altitudes includes:
[0008] Step S1: Determine the warning angle of attack based on the stall angle of attack;
[0009] Step S2: Determine the indicated airspeed threshold corresponding to the alarm angle of attack based on the alarm angle of attack;
[0010] Step S3: Obtain the delay time based on the pilot's reaction time and the engine's response time, calculate the product of the delay time and the aircraft's deceleration rate, and obtain the indicated airspeed threshold compensation amount.
[0011] Step S4: Calculate the sum of the indicated airspeed threshold and the indicated airspeed threshold compensation to obtain the alarm indicated airspeed;
[0012] Step S5: When the aircraft is at medium to high altitude, if the current angle of attack of the aircraft is greater than the warning angle of attack, an alarm shall be issued; when the aircraft is at low altitude, if the current indicated airspeed of the aircraft is less than the warning indicated airspeed, an alarm shall be issued.
[0013] In at least one embodiment of this application, in step S1, the alarm angle of attack is equal to the stall angle of attack minus the angle of attack margin.
[0014] In at least one embodiment of this application, step S2, determining the indicated airspeed threshold corresponding to the alarm angle of attack based on the alarm angle of attack, includes:
[0015] Calculate the vacuum velocity corresponding to the alarm angle of attack:
[0016] ;
[0017] Among them, V warn The vacuum velocity corresponding to the warning angle of attack, m is the aircraft mass, g is the acceleration due to gravity, ρ is the aircraft density, and C is the velocity at which the aircraft is launched. L_warn The lift coefficient is the angle of attack corresponding to the warning angle, and S is the wing reference area;
[0018] The indicated airspeed threshold corresponding to the alarm angle of attack is determined based on the vacuum speed corresponding to the alarm angle of attack.
[0019] In at least one embodiment of this application, in step S3, the delay time is the sum of the pilot's reaction time and the engine's response time.
[0020] In at least one embodiment of this application, the pilot's reaction time is 2 seconds.
[0021] In at least one embodiment of this application, the engine response time is the response time from engine idle thrust to maximum thrust.
[0022] In at least one embodiment of this application, in step S3, the aircraft deceleration rate is the wing horizontal deceleration rate or the wing turning deceleration rate.
[0023] In at least one embodiment of this application, the aircraft deceleration rate is determined based on the aircraft roll angle as either the wing horizontal deceleration rate or the wing turning deceleration rate.
[0024] In at least one embodiment of this application, in step S5, when the aircraft's radio altitude is greater than the altitude threshold H0, the aircraft is considered to be at medium to high altitude.
[0025] In at least one embodiment of this application, in step S5, when the aircraft's radio altitude is less than the altitude threshold H0, the aircraft is considered to be at a low altitude.
[0026] In at least one embodiment of this application, the altitude threshold H0 is the sum of the altitude loss when recovering from a high angle of attack and the minimum go-around altitude.
[0027] The invention has at least the following beneficial technical effects:
[0028] The method for determining the activation threshold of high angle of attack protection at low altitude in this application can ensure that the aircraft can safely recover from a high angle of attack state by increasing engine thrust at low altitude, thereby improving aircraft safety. Attached Figure Description
[0029] Figure 1 This is a schematic diagram of the engine thrust response according to one embodiment of this application. Detailed Implementation
[0030] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be described in more detail below with reference to the accompanying drawings. In the drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The described embodiments are some, but not all, embodiments of this application. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application. The embodiments of this application will be described in detail below with reference to the accompanying drawings.
[0031] In the description of this application, it should be understood that the terms "center", "longitudinal", "lateral", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this application.
[0032] The following is in conjunction with the appendix Figure 1 This application will be described in further detail.
[0033] This application provides a method for determining the activation threshold of high angle-of-attack protection for aircraft at low altitudes, including the following steps:
[0034] Step S1: Determine the warning angle of attack based on the stall angle of attack;
[0035] Step S2: Determine the indicated airspeed threshold corresponding to the alarm angle of attack based on the alarm angle of attack;
[0036] Step S3: Obtain the delay time based on the pilot's reaction time and the engine's response time, calculate the product of the delay time and the aircraft's deceleration rate, and obtain the indicated airspeed threshold compensation amount.
[0037] Step S4: Calculate the sum of the indicated airspeed threshold and the indicated airspeed threshold compensation to obtain the alarm indicated airspeed;
[0038] Step S5: When the aircraft is at medium to high altitude, if the current angle of attack of the aircraft is greater than the warning angle of attack, an alarm shall be issued; when the aircraft is at low altitude, if the current indicated airspeed of the aircraft is less than the warning indicated airspeed, an alarm shall be issued.
[0039] Modern fly-by-wire aircraft typically have high angle-of-attack protection. When the angle of attack exceeds the protection activation threshold, the protection function generates an alarm signal to issue warnings via voice and lights, and controls the elevator to pitch the aircraft down, thereby reducing the angle of attack until the angle of attack falls below the protection activation threshold, at which point the protection function deactivates. This process results in a loss of altitude for the aircraft.
[0040] In the method for determining the activation threshold of the aircraft's low-altitude, high-angle-of-attack protection in this application, step S1 involves determining the alarm angle of attack based on the stall angle of attack, where the alarm angle of attack is equal to the stall angle of attack minus the angle of attack margin.
[0041] Through aerodynamic calculations, wind tunnel tests, and flight tests, the angle of attack at which an aircraft reaches maximum lift or experiences buffeting or instability can be obtained; this angle of attack is the aircraft's stall angle of attack. When the aircraft's angle of attack exceeds the stall angle of attack, it enters a stall state, which is a dangerous condition. To prevent the aircraft's angle of attack from exceeding the stall angle of attack, airworthiness regulations or related standards explicitly require a certain angle of attack margin beyond the stall angle of attack, thereby determining the warning angle of attack (AOA_WARN). The warning angle of attack (AOA_WARN) is the high angle of attack protection activation threshold.
[0042] During flight, under complex control conditions, pilots' lack of monitoring of the aircraft's speed can easily lead to a continuous decrease in speed. According to flight mechanics, a decrease in speed results in an increase in the angle of attack. Therefore, it is necessary to increase speed by increasing engine thrust or by sacrificing altitude to gain speed and recover to a high angle of attack. When the aircraft is at medium to high altitudes, there is sufficient altitude margin to increase speed through altitude loss. However, when the aircraft is at low altitudes, a significant decrease in altitude could very likely cause the aircraft to touch down and crash. Therefore, when the aircraft is at a low altitude, due to insufficient altitude margin, it is impossible to increase speed through altitude loss to reduce the angle of attack. Thus, the only way to reduce the angle of attack is to increase speed by increasing engine thrust.
[0043] When the aircraft is at medium to high altitude, the warning angle of attack (AOA_WARN) can be used as the threshold for activating protection at high angles of attack. When the aircraft is at low altitude, due to the dynamic response process of the engine, the factor of the engine thrust increase process needs to be considered on the basis of the warning angle of attack (AOA_WARN) value.
[0044] Specifically, in step S2, determining the indicated airspeed threshold corresponding to the alarm angle of attack based on the alarm angle of attack includes:
[0045] Based on the aircraft's real-time weight, configuration, Mach number, altitude, and the corresponding warning angle of attack (AOA_WARN), the indicated airspeed threshold (VIAS_WARN) corresponding to AOA_WARN can be calculated. During level flight, the aircraft's weight equals its lift; based on the aircraft's aerodynamic data, configuration, and Mach number, the lift coefficient corresponding to AOA_WARN can be obtained.
[0046] Calculate the vacuum velocity corresponding to the alarm angle of attack:
[0047] ;
[0048] Among them, V warn The vacuum velocity corresponding to the warning angle of attack, m is the aircraft mass, g is the acceleration due to gravity, ρ is the aircraft density, and C is the velocity at which the aircraft is launched. L_warn The lift coefficient is the angle of attack corresponding to the warning angle, and S is the wing reference area;
[0049] The indicated airspeed threshold corresponding to the alarm angle of attack is determined based on the vacuum speed corresponding to the alarm angle of attack.
[0050] Based on information such as aircraft pressure altitude, dynamic pressure, and static pressure, and according to the principles of atmospheric data calculation, the indicated airspeed VIAS_WARN corresponding to the vacuum speed at the warning angle of attack can be calculated.
[0051] In the method for determining the activation threshold of the aircraft's low-altitude, high-angle-of-attack protection in this application, step S3 involves calculating the product of the delay time and the aircraft's deceleration rate based on the pilot's reaction time and engine response time to obtain the indicated airspeed threshold compensation amount.
[0052] When an aircraft is at low altitude, engine thrust is typically low. Due to the dynamic response of the engine, it takes time for thrust to increase. After the pilot perceives the aircraft entering a high angle of attack, according to human physiology, the pilot needs a certain reaction time before they can increase throttle. Therefore, the delay T from when the pilot perceives the high angle of attack to when engine thrust increases is the pilot's reaction time. man With engine response time T thrust sum .
[0053] In this embodiment, the pilot reaction time is assessed according to GJB2874-97 (Flight Quality of Aircraft with Fly-by-Wire Control Systems), which requires a 2-second assessment of the pilot's reaction time after an aircraft malfunction. Therefore, the pilot reaction time is selected as 2 seconds. When the aircraft is at low altitude, the engine thrust is usually at a relatively low level. Therefore, the most severe operating condition needs to be considered, i.e., the engine response time is selected as the response time from idle thrust to maximum thrust, which can be determined based on the engine response characteristic curve, such as... Figure 1 As shown.
[0054] During the time delay T, the aircraft may still be decelerating. Therefore, when designing the activation threshold for high angle-of-attack protection at low altitudes, the aircraft deceleration rate needs to be taken into account. The greater the aircraft deceleration rate, the earlier the activation threshold AOA_WARN should be.
[0055] In this embodiment, for large aircraft, the CCAR-25 (Airworthiness Standards for Transport Category Aircraft) and AC25-7 (Flight Test Guidelines for Certification of Transport Category Aircraft) assess stall characteristics based on a 1-knot horizontal deceleration rate and a 3-knot turning deceleration rate. Referring to these requirements, the 1-knot horizontal deceleration rate and the 3-knot turning deceleration rate are selected for the deceleration condition. For other types of aircraft, the relevant specifications can be followed. The aircraft's roll angle distinguishes between horizontal and turning deceleration, thus allowing the selection of either the horizontal or turning deceleration rate.
[0056] In the method for determining the activation threshold of the high angle of attack protection at low altitude of the aircraft in this application, in step S5, if the current angle of attack of the aircraft is greater than the alarm angle of attack when the aircraft is at medium to high altitude, an alarm is triggered; if the current indicated airspeed of the aircraft is less than the alarm indicated airspeed when the aircraft is at low altitude, an alarm is triggered.
[0057] When the aircraft is at medium to high altitude, i.e., when the aircraft's radio altitude is greater than the altitude threshold H0, the warning angle of attack (AOA_WARN) can still be used as the high angle of attack protection activation threshold. When the aircraft is at low altitude, i.e., when the aircraft's radio altitude is less than the altitude threshold H0 (including cases where it is equal to or less than H0), the factor of engine thrust increase needs to be considered in addition to the AOA_WARN value. The altitude threshold H0 is the sum of the altitude loss when recovering from a high angle of attack and the minimum go-around altitude. The altitude loss at high angles of attack can be determined through multiple flight tests at medium to high altitudes, while the minimum go-around altitude is an aircraft performance parameter determined by the aircraft's aerodynamic characteristics and engine capabilities.
[0058] In summary, when the aircraft's radio altitude is below the altitude threshold H0, and the aircraft is in a level wing position (defined as a wing level position when the roll angle is within ±5°), the high angle of attack protection activation threshold is: the aircraft's current indicated airspeed is less than (VIAS_WARN + T × 1 knot). When the aircraft is turning (defined as a turning position when the roll angle is greater than ±5°), the high angle of attack protection activation threshold is: the aircraft's current indicated airspeed is less than (VIAS_WARN + T × 3 knots). Based on the above method, after determining that the aircraft has entered a high angle of attack state, a corresponding warning will be issued. The pilot needs to manually increase engine thrust, or an automatic throttle control system can be designed to automatically increase thrust.
[0059] Based on the above steps, the activation threshold for high angle of attack protection at low altitude can be determined, and this is implemented in the control law.
[0060] This application discloses a method for determining the activation threshold of high angle-of-attack protection at low altitudes. It designs a high angle-of-attack protection activation threshold for low altitudes, ensuring that the aircraft can safely recover from high angle-of-attack states by increasing engine thrust at low altitudes. This application solves the problem of determining the activation threshold for high angle-of-attack protection at low altitudes, improving flight safety at low altitudes. This application requires no hardware modification; the designed high angle-of-attack protection activation threshold can be directly added to the flight control law of the flight control system, saving modification costs and enabling monitoring of high angle-of-attack states at low altitudes, thus improving the safety of high angle-of-attack recovery at low altitudes.
[0061] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.
Claims
1. A method for determining the activation threshold of high angle-of-attack protection for aircraft at low altitudes, characterized in that, include: Step S1: Determine the warning angle of attack based on the stall angle of attack; Step S2: Determine the indicated airspeed threshold corresponding to the alarm angle of attack based on the alarm angle of attack; Step S3: Obtain the delay time based on the pilot's reaction time and the engine's response time, calculate the product of the delay time and the aircraft's deceleration rate, and obtain the indicated airspeed threshold compensation amount. Step S4: Calculate the sum of the indicated airspeed threshold and the indicated airspeed threshold compensation to obtain the alarm indicated airspeed; Step S5: When the aircraft is at medium to high altitude, if the current angle of attack of the aircraft is greater than the warning angle of attack, an alarm shall be issued; when the aircraft is at low altitude, if the current indicated airspeed of the aircraft is less than the warning indicated airspeed, an alarm shall be issued.
2. The method for determining the activation threshold of aircraft low-altitude high angle-of-attack protection according to claim 1, characterized in that, In step S1, the alarm angle of attack is equal to the stall angle of attack minus the angle of attack margin.
3. The method for determining the activation threshold of aircraft low-altitude high angle-of-attack protection according to claim 2, characterized in that, In step S2, determining the indicated airspeed threshold corresponding to the alarm angle of attack based on the alarm angle of attack includes: Calculate the vacuum velocity corresponding to the alarm angle of attack: ； Among them, V warn The vacuum velocity corresponding to the warning angle of attack, m is the aircraft mass, g is the acceleration due to gravity, ρ is the aircraft density, and C is the velocity at which the aircraft is launched. L_warn The lift coefficient is the angle of attack corresponding to the warning angle, and S is the wing reference area; The indicated airspeed threshold corresponding to the alarm angle of attack is determined based on the vacuum speed corresponding to the alarm angle of attack.
4. The method for determining the activation threshold of aircraft low-altitude high angle-of-attack protection according to claim 3, characterized in that, In step S3, the delay time is the sum of the pilot's reaction time and the engine's response time.
5. The method for determining the activation threshold of aircraft low-altitude high angle-of-attack protection according to claim 4, characterized in that, The pilot's reaction time is 2 seconds.
6. The method for determining the activation threshold of aircraft low-altitude high angle-of-attack protection according to claim 5, characterized in that, Engine response time is the time it takes for the engine to go from idle thrust to maximum thrust.
7. The method for determining the activation threshold of aircraft low-altitude high angle-of-attack protection according to claim 6, characterized in that, In step S3, the aircraft deceleration rate is either the wing horizontal deceleration rate or the wing turning deceleration rate.
8. The method for determining the activation threshold of aircraft low-altitude high angle-of-attack protection according to claim 6, characterized in that, The aircraft deceleration rate is determined by the aircraft roll angle, which indicates whether the aircraft deceleration rate is the horizontal deceleration rate of the wing or the turning deceleration rate of the wing.
9. The method for determining the activation threshold of aircraft low-altitude high angle-of-attack protection according to claim 8, characterized in that, In step S5, if the aircraft's radio altitude is greater than the altitude threshold H0, the aircraft is considered to be at medium to high altitude.
10. The method for determining the activation threshold of aircraft low-altitude high angle-of-attack protection according to claim 9, characterized in that, In step S5, if the aircraft's radio altitude is less than the altitude threshold H0, the aircraft is considered to be at low altitude.
11. The method for determining the activation threshold of aircraft low-altitude high angle-of-attack protection according to claim 10, characterized in that, The altitude threshold H0 is the sum of the altitude loss when recovering from a high angle of attack and the minimum go-around altitude.