CN103192996A - Method for determining drift-down flight path of large airplane - Google Patents

Abstract

The invention belongs to the field of aviation large aircraft design, relates to the flight test of large aircraft, and in particular relates to a method for determining the flight track of large aircraft. Firstly, the drift-down performance is determined, and then the drift-down performance is used for flight test verification to obtain the drift-down track. The invention obtains the drifting trajectory of the aircraft by first determining the favorable drifting speed to obtain the favorable drifting performance, and then conducting a flight test verification. The calculation method of the ^favorable drifting speed V is simple and easy to obtain. The result is characterized as a correction speed, which is only related to the flight weight of the aircraft. It is not only easy for the pilot to remember and use, but also easy to write the aircraft user manual. At the same time, it has important guiding significance for flight test verification, which can save test flight sorties, shorten test flight cycle, and save a lot of test flight funds. This method is comprehensive in consideration and strong in versatility, and is applicable to large transport aircraft and large passenger aircraft of turbofan class with twin engines or more.

Description

A Method for Determining the Drifting and Landing Track of Large Aircraft

technical field

The invention belongs to the field of large-scale aviation aircraft design, relates to the test flight of large-scale aircraft, and in particular relates to a method for determining the flight track of large-scale aircraft.

Background technique

According to the requirements of the International Civil Aviation Organization and the CCAR-121 of the Civil Aviation Administration of China (operating qualification certification rules), in order to ensure the flight safety of aircraft routes, flights on high-altitude routes must undergo safety inspections for drifting. It is beneficial to improve the obstacle-crossing altitude of the aircraft, ensure flight safety, and is beneficial to increase the flight limit weight of the aircraft's routes, and increase the economic benefits of the airlines. Abroad, there is no clear method for the test flight of large aircraft's drifting performance, and due to technical blockade, relevant technical information cannot be obtained from open channels. Through the patent website query, there is no similar or related patent, and there is no relevant research result in China. The method proposed by the present invention has been verified on specific models.

Contents of the invention

The purpose of the invention is to provide a method for determining the flight path of a large aircraft drifting down, so as to solve the problem that there are no definite performance evaluation means and flight test verification methods for large aircrafts in the process of drifting down.

The technical proposal of the present invention is: a method for determining the drifting track of a large aircraft. Firstly, the drifting performance is determined, and then the drifting performance is used for flight test verification to obtain the drifting track.

C_D＝f(C_L)，

C_D为C_L的函数，通过试验获取并考虑发动机失效后引起的阻力系数C_D的增量；其中：The specific content of determining the drift-down performance is: by determining the remaining thrust ΔP, the speed V at the time when the remaining thrust ΔP is the largest is selected as the _favorable drift-down speed V, and the aircraft flies under the _favorable V to obtain the optimal drift-down performance; wherein, ΔP=P _Available -P _required , P _available is available thrust, P _required is required thrust, P _available =nP(V)η,

C _D =f(C _L ),

_CD is a function of C _L , which is obtained through experiments and takes into account the increase in drag coefficient C _D caused by engine failure; where:

G - aircraft weight;

S - wing area;

P - engine thrust;

ρ - atmospheric density;

C _L - lift coefficient;

C _D - drag coefficient;

n-number of working engines;

η- engine installation correction factor

P _required —required thrust;

P _available - available thrust;

V - flight speed.

The specific content of the flight test verification is: at a typical cruising altitude, decelerate the flight speed from the current favorable cruising speed V _cruise to V _favorable , and then fly at the V _favorable speed. During the flight, the flying altitude gradually decreases until the flying altitude reaches a balance , to complete the flight test verification.

The advantage of the present invention is that the present invention obtains the drifting trajectory of the aircraft by first determining the favorable drifting speed to obtain the favorable drifting performance, and then conducting flight test verification. The calculation method of the _favorable drifting speed V is simple and easy to obtain. The result is characterized as a correction speed, which is only related to the flight weight of the aircraft. It is not only easy for the pilot to remember and use, but also easy to write the aircraft user manual. At the same time, it has important guiding significance for flight test verification, which can save test flight sorties, shorten test flight cycle, and save a lot of test flight funds. This method is comprehensive in consideration and strong in versatility, and is applicable to large transport aircraft and large passenger aircraft of turbofan class with twin engines or more.

Description of drawings

Figure 1 is a schematic diagram of the selection of drifting speed.

Detailed ways

The present invention will be described in further detail below in conjunction with the accompanying drawings and examples, please refer to the drawings.

A method for determining the drift-down track of a large aircraft includes firstly determining the drift-down performance, and then using the drift-down performance for flight test verification to obtain the drift-down track. Drifting down of a large aircraft refers to the transition process from the original cruising altitude to the new cruising altitude when one engine (or several engines) stops, and the cruising altitude and cruising speed must be reduced. Large aircraft drifting down. The drifting process consists of three stages: deceleration, drifting down, and leveling off. When one engine (one engine) stops, the engine that is still working pushes the throttle to the rated state to compensate for the thrust lost by the stopped engine. The aircraft begins to decelerate. When the drifting speed is reached, the aircraft begins to drift down until leveling off.

C_D为C_L的函数，没有具体的算法，是通过试验获取并考虑发动机失效后引起的阻力系数C_D的增量而得出两者之间的关系；其中：The specific content of determining the drift-down performance is: by determining the remaining thrust ΔP, the speed V at the time when the remaining thrust ΔP is the largest is selected as the _favorable drift-down speed V, and the aircraft flies under the _favorable V to obtain the optimal drift-down performance; wherein, ΔP=P _Available -P _required , where P _available is available thrust, P _required is required thrust, P _available =nP(V)η, where C _D =f(C _L ),

_CD is a function of _CL , there is no specific algorithm, and the relationship between the two is obtained through experiments and considering the increase in drag coefficient C _D caused by engine failure; where:

G - aircraft weight;

S - wing area;

P - engine thrust;

ρ - atmospheric density;

C _L - lift coefficient;

C _D - drag coefficient;

n-number of working engines;

η-engine installed capacity correction factor;

P _required —required thrust;

P _available - available thrust;

V - flight speed.

The specific content of the flight test verification is: at a typical cruising altitude, decelerate the flight speed from the current favorable cruising speed V _cruise to V _favorable , and then fly at the V _favorable speed. During the flight, the flying altitude gradually decreases until the flying altitude reaches a balance , to complete the flight test verification.

The typical cruising altitude is generally between 9km and 12km. After the aircraft reaches the expected cruising altitude and cruising speed, the critical engine will be placed in the air idle, and the other engines will be placed in the maximum cruising state, and the current flying altitude will be maintained until the flying speed changes from the current favorable cruising. _Cruise at speed V and decelerate to V _{is favorable} , maintain V _favorable speed until the aircraft reaches the cruise ceiling after a single engine failure under the current weight, that is, the flight altitude reaches balance, and the flight test verification is completed; relevant flight parameters are collected and recorded throughout the process .

Example:

For an aircraft with a wing area of 300m ² , a flight weight of 150,000kg, and an air density of 0.332kg/m ³ where it flies, and 4 engines of a certain type installed, the available thrust P _{can be} calculated in Table 1, and the required thrust P _{can be} calculated in Table 2. See Table 3 for remaining thrust. It can be seen from Table 3 that when the speed is 480km/h, the remaining thrust ΔP is the largest, which is -450kgf, and this speed is the favorable drifting speed.

Table 1 Available Thrust P _Available Calculation

Table 2 Required Thrust P _Required Calculation

Table 3 Calculation of residual thrust ΔP

Claims (3)

1. A method for determining the drift-down track of a large aircraft is characterized in that firstly the drift-down performance is determined, and then the drift-down performance is used for flight test verification to obtain the drift-down track. 2. The method for determining the flight path of a large aircraft drifting down according to claim 1, wherein the specific content of determining the drifting down performance is: by determining the remaining thrust ΔP, the speed V when the remaining thrust ΔP is selected to be the largest is favorable. Drift-down velocity V _{is favorable} , and the aircraft flies under V _favorable to obtain optimum drift-down performance; wherein, ΔP=P _{is available} -P _{needs to be used} , and P _{can be used} as available thrust, and P _{needs to be used} as required thrust, and P _{can be used} =nP( V) η,

C _D =f(C _L ),

_CD is a function of C _L , which is obtained through experiments and takes into account the increase in drag coefficient C _D caused by engine failure; where: G - aircraft weight; S - wing area; P - engine thrust; ρ - atmospheric density; C _L - lift coefficient; C _D - drag coefficient; n-number of working engines; η- engine installation correction factor P _required —required thrust; P _available - available thrust; V - flight speed. 3. according to claim 1 or the determining method of a kind of large-scale aircraft drifting down track described in any one, it is characterized in that, the specific content of flight test verification is: under the typical cruising height, the flight speed is changed from current favorable cruising _Cruise at speed V and decelerate until V _{is favorable} , and then fly at V _favorable speed. During the flight, the flight altitude gradually decreases until the flight altitude reaches balance, and the flight test verification is completed.