CN116522593A - Method for calculating take-off track of class-A flight of helicopter - Google Patents
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Abstract
The invention discloses a method for calculating a take-off track of a helicopter class A flying, which is technically characterized by comprising the following calculation steps: s1: counting parameters of the double-engine helicopter and parameters of an engine used by the double-engine helicopter; s2: calculating the front flight power demand of the double-engine helicopter according to the statistical parameters and drawing N xu ‑V 0 A curve; s3: calculating the takeoff safety speed of the double-shot helicopter according to the front flight demand power of the double-shot helicopter and the counted single-shot power of the helicopter; s4: according to the statistical parameters, calculating the lift force and the forward pulling force provided by the helicopter rotor; s5: calculating double-engine helicopter take-offA critical decision point, drawing a helicopter take-off critical decision point curve; s6: according to the calculated takeoff critical decision points of the double-engine helicopter, the takeoff tracks of the class A helicopter are calculated respectively according to the positions of the failure points, and a class A takeoff track curve of the helicopter is drawn.
Description
Technical Field
The invention relates to the technical field of aviation takeoff track calculation, in particular to a takeoff track calculation method for class A helicopter flight.
Background
The helicopter has high maneuvering performance at low altitude and low speed, has wide application in the fields of air warning detection, security inspection, relay communication, inspection and striking integration, middle and short distance transportation, sightseeing tour and the like, and is a main striking product of civil navigation market and emergency rescue departments. Therefore, helicopters are popular worldwide, but this also brings with it strict safety requirements for helicopters.
For a helicopter, engine failure is one of the most main reasons for causing helicopter flight accidents, and how to ensure the flight safety of the helicopter after the engine failure is always the key of helicopter flight safety research. In order to improve safety, the current helicopter generally adopts a double-shot or multiple-shot mode, so that the upward climbing power of the helicopter can be ensured when a single engine fails (OEI), at the moment, the multiple-shot (comprising double shots and accounting for the majority of the double-shot mode) helicopter relates to the class A flight requirement, in particular to the take-off climbing stage, how the helicopter flies after the single-shot failure, and a correct decision needs to be made between landing and flying.
At present, the take-off track of the helicopter A type flying at home and abroad is mainly determined by a flying test method, but the flying test has large risk coefficient and high cost, and the difficulty of determining the take-off track of the helicopter by a test flying test is large; the national part researches are carried out by constructing a helicopter flight dynamics model and calculating the helicopter flight trajectory by adopting an optimal control theory, but the helicopter flight trajectory after single failure is not calculated.
Disclosure of Invention
Aiming at the defects existing in the prior art, the invention aims to provide a method for calculating the take-off track of the class A flight of a helicopter, so as to solve the problem that the method for calculating the take-off track of the class A flight of the helicopter is lacking in the prior art.
In order to achieve the above purpose, the present invention provides the following technical solutions:
a method for calculating a take-off track of a helicopter class A flight comprises the following calculation steps:
s1: counting parameters of the double-engine helicopter and parameters of an engine used by the double-engine helicopter;
s2: calculating the front flight demand power N of the double-engine helicopter according to the statistical parameters xu And draw N xu -V 0 A curve;
s3: according to the front flight required power N of the double-engine helicopter xu And statistical engine single-shot emergency power P OEI Calculating the takeoff safety speed V of the double-engine helicopter toss ；
S4: according to the statistical parameters, calculating the lift force and the forward pulling force provided by the helicopter rotor;
s5: calculating a takeoff critical decision point of the double-engine helicopter according to the takeoff safety speed and the lift force and the forward pulling force provided by the helicopter rotor wing, and drawing a helicopter takeoff critical decision point curve;
s6: according to the calculated takeoff critical decision points of the double-engine helicopter, the takeoff tracks of the class A helicopter are calculated respectively according to the positions of the failure points, and a class A takeoff track curve of the helicopter is drawn.
As a further improvement of the present invention, the parameters of the twin helicopter in the step S1 include: the total weight G of the helicopter, the rotation angular velocity omega of the rotor, the number k of blades, the wing profile of the rotor, the radius R of the rotor and the solidity sigma of the rotor;
the engine parameters used by the double-engine helicopter comprise: engine single-shot emergency power P OEI Single-shot emergency power P of engine 30s OEI-30s Engine 2min single-engine emergency power P OEI-2min Single-engine emergency power P for 30min OEI-30min ；
The step S2 is that the front flight of the double-engine helicopter needs power N xu The method specifically comprises the following steps: power demand P of rotor r Power P required by tail rotor TR Power loss P of speed reducer and transmission system RE.T Installed loss P of engine SET 。
As a further improvement of the invention, the rotor wingPower demand P r Is calculated as follows:
s21: solving the atmospheric density;
the solution of the atmospheric density in the nonstandard atmospheric state is as follows:
ρ＝Δρ 0
wherein H is the flying height, t is the atmospheric temperature, ρ 0 Is sea level standard atmospheric density;
s22: calculate the tension coefficient C T And lift coefficient Cy:
wherein T is rotor wing lifting force; r is the radius of the rotor wing; omega is the rotation angular velocity of the rotor; v (V) 0 Is the forward flying speed of the helicopter; mu is the forward ratio; b is leaf tip loss coefficient, and B is approximately equal to 0.92; sigma is rotor solidity;
s23: solving rotor type resistance power N x The method specifically comprises the following steps:
press-type calculating power coefficient m kx ：
K P ＝(1+5μ 2 )K P0
Wherein K is P Is a hover state resistance correction coefficient; k (K) P0 Approximately 1.0-1.1, is considered type resistanceNon-uniformity in spanwise distribution (typically 1.05); c (C) x7 Is the model drag coefficient at the characteristic section of the blade;
rotor type power N x The method comprises the following steps:
s24: solving for rotor induced power N i The method specifically comprises the following steps:
the induction power coefficient m is calculated according to the following method ki ：
J＝J 0 (1+3μ 2 )
Wherein J is a hover state induced power correction coefficient; j (J) 0 About 1.05 to 1.10, along with C T Variation of sigma;is the relative value of the induction speed at the paddle plane when hovering;
wherein: c (C) T Is the tension coefficient; b is leaf tip loss coefficient;
rotor induced power N i The method comprises the following steps:
s25: solving for waste resistance power N f The method specifically comprises the following steps:
the helicopter waste resistance Q is calculated as follows:
wherein C is x S is the resistance coefficient and the windward area of each windward component on the helicopter respectively;
solving for waste resistance power N f The method comprises the following steps:
N f ＝Q·V 0
power demand P of rotor r The method comprises the following steps: p (P) r ＝N x +N i +N f 。
As a further improvement of the invention, the tail rotor requires power P TR The calculation of (1) specifically comprises: for a helicopter with a single rotor wing and a tail rotor, when flying forwards, the required power of the tail rotor consists of type resistance power and induced power;
s26: tail rotor type resistance N tx The method specifically comprises the following steps:
press-type calculating power coefficient m tkx ：
K p ＝(1+5μ 2 )K p0
Wherein K is P Is a hover state resistance correction coefficient; k (K) P0 Approximately 1.0-1.1, which is to consider the non-uniformity of the profile resistance along the spanwise direction (usually 1.05); c (C) tx7 The model drag coefficient of the characteristic section of the tail rotor blade;
tail rotor type resistive power N tx The method comprises the following steps:
s27: finding tail rotor induced power N ti The method specifically comprises the following steps:
the induction power coefficient m is calculated according to the following method tki ：
J＝J 0 (1+3μ 2 )
Wherein J is a hover state induced power correction coefficient; j (J) 0 ≈1.05-1.10；Is the relative value of the induction speed at the plane of the tail rotor;
wherein: c (C) Tt Is the tail rotor tension coefficient; b (B) t The loss coefficient of the tail rotor blade end;
tail rotor induced power N ti The method comprises the following steps:
power demand P of tail rotor TR The method comprises the following steps: p (P) TR ＝N tx +N ti 。
As a further improvement of the invention, the power loss of the speed reducer and the transmission system refers to friction between gears and in bearings, and loss caused by aerodynamic resistance or wind resistance, and accounts for 2% -4% of the power of the engine.
Installation loss P of the engine SET The engine is arranged on the helicopter, and the output power of the engine is smaller than the test power of the rack and accounts for 3% -6% of the power of the engine.
The calculation of the power required by the front flight of the helicopter is as follows:
N xu ＝P r +P TR +P RE.T +P SET
calculating different forward flight speeds V 0 Lower forward power demand N xu Drawing Nxu-V 0 A curve.
As a further improvement of the present invention, the defining of the takeoff safety speed in the step S3 includes:
in the threshold height interval, calculating the helicopter in stable flight at different speeds and climbing rate of 0.5m/sThe engine needs power to obtain a speed-power curve, and then the engine single-engine emergency power P is used OEI Finding the left intersection point of the single-shot emergency power and the speed-power curve, wherein the corresponding speed is the takeoff safety speed V toss ；
The climbing power coefficient m of the double-engine helicopter is calculated according to the following mode kp ：
C in the formula G Is the weight coefficient of the double-engine helicopter,the relative climbing rate of the double-shot helicopter;
wherein V is y The climbing rate of the double-engine helicopter is the climbing rate;
the climbing power P of the double-engine helicopter is calculated by the following method kp ：
Wherein: p characterizes the atmospheric density.
As a further improvement of the invention, the double-hair helicopter can fly at a certain forward flying speed and maintain the required power N when the climbing rate is stable sum
N sum ＝N xu +P kp
Solving the takeoff safety speed V of the double-engine helicopter toss ：
N sum (V toss )＝P OEI
Wherein P is OEI The emergency power is single-shot for the engine.
As a further improvement of the present invention, the calculation of the lift force and the forward pull force provided by the rotor in the step S4 includes:
s41: the lift force of the rotor wing is recorded as Y, the forward pulling force is recorded as X, the stress of the helicopter in the process of flying is definitely recorded, the aerodynamic resultant force R of the rotor wing is equal to the pull force T of the rotor wing, a slip stream theoretical paddle diagram is constructed, and meanwhile, a helicopter power curve is also constructed;
s42: the rotor wing lift force Y and the forward pulling force X provided by the rotor wing during front flight are calculated:
calculating a hover time curve:
select C T Taking C as a series of calculation points T ＝0.006～0.020；
Calculating blade characteristic profile lift coefficient C according to the following formula y7 ；
From the calculated C y7 Finding out blade polar curve to obtain resistance coefficient C x7 ；
The following calculation type power resistance coefficient:
the relative value of the induction speed at the paddle plane at hover is calculated as follows:
obtaining an induction power coefficient during hovering:
calculating and obtaining the power coefficient required by the wave resistance:
wherein:by blade airfoil drag sudden increase critical Mach number M and lift coefficient C y Obtaining the relation of (2);
the total required power factor is calculated as follows:
m K ＝m Kx +m Ki +m Kb
according to corresponding C T 、m K Make C T -m K A curve;
the corresponding power is the single-engine emergency power P OEI Obtaining the corresponding tension coefficient C T Calculating the relative value of the induction speed at the paddle plane when hovering as follows
The induction speed at the paddle disc is v during forward flight 1 ：
Wherein the formula is the induction speed relative value at the paddle disc;
the fly-forward speed is known as V 0 The rotor tension T after a single failure of the helicopter is calculated by:
T＝2ρπR 2 V 1 v 1
v in 1 Is the deflection airflow velocity value after passing through the paddle disc;
the rotor lift Y and the forward pull X of the rotor are calculated as follows:
X＝T·sinα E
Y＝T·cosα E
alpha in the formula E Is the maximum pitch angle of attack of the rotor.
As a further improvement of the present invention, the takeoff critical decision point in the step S5 is a combination point of the flying height and the flying speed, the takeoff critical decision point forms a critical decision curve in the flying process, and the intersection point of the critical decision curve and the helicopter takeoff track is the takeoff critical decision point corresponding to the takeoff mode.
The invention has the beneficial effects that: the method for calculating the power demand, the takeoff safety speed and the takeoff critical decision point of the helicopter is provided by taking the takeoff track of the helicopter A type flight as a starting point, and the takeoff track of the double-helicopter A type flight is calculated, so that the calculation process is simpler, and the calculation result is more accurate; corresponding flight path references can be provided for different single-shot failure points of the helicopter before the helicopter performs a flight test; particularly, in the flight process, the engine is invalid to help the pilot to make judgment in time, theoretical support is provided for the subsequent flight, and the method has a leading guiding effect on the subsequent flight test. The method can be convenient and reliable for model navigable evidence collection, saves time and labor and material resources.
Drawings
FIG. 1 is a schematic flow chart of the present invention;
FIG. 2 is a graph comparing power demand curves of a helicopter in front of a flight;
FIG. 3 is a schematic view of the safe speed of helicopter takeoff;
FIG. 4 is a plot of UH-60A helicopter forward demand power;
FIG. 5 is a schematic view of the UH-60A helicopter takeoff safety speed;
FIG. 6 is a schematic diagram of a UH-60A helicopter takeoff critical decision point curve;
FIG. 7 is a schematic view of a class A take-off track of a UH-60A helicopter after a single failure;
fig. 8 is a slip flow theoretical paddle diagram.
Detailed Description
The invention will now be described in further detail with reference to the drawings and examples. Wherein like parts are designated by like reference numerals. It should be noted that the words "front", "back", "left", "right", "upper" and "lower" used in the following description refer to directions in the drawings, and the words "bottom" and "top", "inner" and "outer" refer to directions toward or away from, respectively, the geometric center of a particular component.
Referring to fig. 1 to 8, a specific embodiment of a method for calculating a take-off track of a helicopter class a flight according to the present invention includes the following steps:
s1: counting parameters of the double-engine helicopter and parameters of an engine used by the double-engine helicopter;
s2: calculating the front flight demand power N of the double-engine helicopter according to the statistical parameters xu And draw N xu -V 0 A curve;
s3: according to the front flight required power N of the double-engine helicopter xu And statistical engine single-shot emergency power P OEI Calculating the takeoff safety speed V of the double-engine helicopter toss ；
S4: according to the statistical parameters, calculating the lift force and the forward pulling force provided by the helicopter rotor;
s5: calculating a takeoff critical decision point of the double-engine helicopter according to the takeoff safety speed and the lift force and the forward pulling force provided by the helicopter rotor wing, and drawing a helicopter takeoff critical decision point curve;
s6: according to the calculated takeoff critical decision points of the double-engine helicopter, the takeoff tracks of the class A helicopter are calculated respectively according to the positions of the failure points, and a class A takeoff track curve of the helicopter is drawn.
As a further improvement of the present invention, the parameters of the twin helicopter in the step S1 include: the total weight G of the helicopter, the rotation angular velocity omega of the rotor, the number k of blades, the wing profile of the rotor, the radius R of the rotor and the solidity sigma of the rotor;
the engine parameters used by the double-engine helicopter comprise: engine single-shot emergency power P OEI Single-shot emergency power P of engine 30s OEI-30s Engine 2min single-engine emergency power P OEI-2min Single-engine emergency power P for 30min OEI-30min ；
The step S2 is that the front flight of the double-engine helicopter needs power N xu The method specifically comprises the following steps: power demand P of rotor r Power P required by tail rotor TR Power loss P of speed reducer and transmission system RE.T Installed loss P of engine SET 。
As a further development of the invention, the power demand P of the rotor is r Is calculated as follows:
s21: solving the atmospheric density;
the solution of the atmospheric density in the nonstandard atmospheric state is as follows:
ρ＝Δρ 0
wherein H is the flying height, t is the atmospheric temperature, ρ 0 Is sea level standard atmospheric density;
s22: calculate the tension coefficient C T And lift coefficient Cy:
wherein T is rotor wing lifting force; r is the radius of the rotor wing; omega is the rotation angular velocity of the rotor; v (V) 0 Is the forward flying speed of the helicopter;mu is the forward ratio; b is leaf tip loss coefficient, and B is approximately equal to 0.92; sigma is rotor solidity;
s23: solving rotor type resistance power N x The method specifically comprises the following steps:
press-type calculating power coefficient m kx ：
K P ＝(1+5μ 2 )K P0
Wherein K is P Is a hover state resistance correction coefficient; k (K) P0 Approximately 1.0-1.1, which is to consider the non-uniformity of the profile resistance along the spanwise direction (usually 1.05); c (C) x7 Is the model drag coefficient at the characteristic section of the blade;
rotor type power N x The method comprises the following steps:
s24: solving for rotor induced power N i The method specifically comprises the following steps:
the induction power coefficient m is calculated according to the following method ki ：
J＝J 0 (1+3μ 2 )
Wherein J is a hover state induced power correction coefficient; j (J) 0 About 1.05 to 1.10, along with C T Variation of sigma;is the relative value of the induction speed at the paddle plane when hovering;
wherein: c (C) T Is the tension coefficient; b is leaf tip loss coefficient;
rotor induced power N i The method comprises the following steps:
s25: solving for waste resistance power N f The method specifically comprises the following steps:
the helicopter waste resistance Q is calculated as follows:
wherein C is x S is the resistance coefficient and the windward area of each windward component on the helicopter respectively;
solving for waste resistance power N f The method comprises the following steps:
N f ＝Q·V 0
power demand P of rotor r The method comprises the following steps: p (P) r ＝N x +N i +N f 。
As a further improvement of the invention, the tail rotor requires power P TR The calculation of (1) specifically comprises: for a helicopter with a single rotor wing and a tail rotor, when flying forwards, the required power of the tail rotor consists of type resistance power and induced power;
s26: tail rotor type resistance N tx The method specifically comprises the following steps:
press-type calculating power coefficient m tkx ：
K p ＝(1+5μ 2 )K p0
Wherein K is P Is a hover state resistance correction coefficient; k (K) P0 Approximately 1.0-1.1, which is to consider the non-uniformity of the profile resistance along the spanwise direction (usually 1.05); c (C) tx7 The model drag coefficient of the characteristic section of the tail rotor blade;
tail rotor type resistive power N tx The method comprises the following steps:
s27: finding tail rotor induced power N ti The method specifically comprises the following steps:
the induction power coefficient m is calculated according to the following method tki ：
J＝J 0 (1+3μ 2 )
Wherein J is a hover state induced power correction coefficient; j (J) 0 ≈1.05-1.10；Is the relative value of the induction speed at the plane of the tail rotor;
wherein: c (C) Tt Is the tail rotor tension coefficient; b (B) t The loss coefficient of the tail rotor blade end;
tail rotor induced power N ti The method comprises the following steps:
power demand P of tail rotor TR The method comprises the following steps: p (P) TR ＝N tx +N ti 。
As a further improvement of the invention, the power loss of the speed reducer and the transmission system refers to friction between gears and in bearings, and loss caused by aerodynamic resistance or wind resistance, and accounts for 2% -4% of the power of the engine.
Installation loss P of the engine SET Refers to that after the engine is mounted on the helicopter, its output power is less than that of bench testVehicle power, accounting for 3% -6% of engine power.
The calculation of the power required by the front flight of the helicopter is as follows:
N xu ＝P r +P TR +P RE.T +P SET
calculating different forward flight speeds V 0 Lower forward power demand N xu Drawing Nxu-V 0 A curve.
As a further improvement of the present invention, the defining of the takeoff safety speed in the step S3 includes:
in the threshold height interval, calculating the helicopter power demand when the helicopter stably flies at different speeds and climbing rates of 0.5m/s respectively to obtain a speed-power curve, and then obtaining the single-shot emergency power P according to the engine OEI Finding the left intersection point of the single-shot emergency power and the speed-power curve, wherein the corresponding speed is the takeoff safety speed V toss ；
The climbing power coefficient m of the double-engine helicopter is calculated according to the following mode kp ：
C in the formula G Is the weight coefficient of the double-engine helicopter,the relative climbing rate of the double-shot helicopter;
wherein V is y The climbing rate of the double-engine helicopter is the climbing rate;
the climbing power P of the double-engine helicopter is calculated by the following method kp ：
Wherein: ρ represents the atmospheric density.
As a further improvement of the invention, the double-hair helicopter can fly at a certain forward flying speed and maintain the required power N when the climbing rate is stable sum
N sum ＝N xu +P kp
Solving the takeoff safety speed V of the double-engine helicopter toss ：
N sum (V toss )＝P oEI
Wherein P is OEI The emergency power is single-shot for the engine.
As a further improvement of the present invention, the calculation of the lift force and the forward pull force provided by the rotor in the step S4 includes:
s41: the lift force of the rotor wing is recorded as Y, the forward pulling force is recorded as X, the stress of the helicopter in the process of flying is definitely recorded, the aerodynamic resultant force R of the rotor wing is equal to the pull force T of the rotor wing, a slip stream theoretical paddle diagram is constructed, and meanwhile, a helicopter power curve is also constructed;
s42: the rotor wing lift force Y and the forward pulling force X provided by the rotor wing during front flight are calculated:
calculating a hover time curve:
select C T Taking C as a series of calculation points T ＝0.006～0.020；
Calculating blade characteristic profile lift coefficient C according to the following formula y7 ；
From the calculated C y7 Finding out blade polar curve to obtain resistance coefficient C x7 ；
The following calculation type power resistance coefficient:
the relative value of the induction speed at the paddle plane at hover is calculated as follows:
obtaining an induction power coefficient during hovering:
calculating and obtaining the power coefficient required by the wave resistance:
wherein:by blade airfoil drag sudden increase critical Mach number M and lift coefficient C y Obtaining the relation of (2);
the total required power factor is calculated as follows:
m K ＝m Kx +m Ki +m Kb
according to corresponding C T 、m K Make C T -m K A curve;
the corresponding power is the single-engine emergency power P OEI Obtaining the corresponding tension coefficient C T Calculating the relative value of the induction speed at the paddle plane when hovering as follows
The induction speed at the paddle disc is v during forward flight 1 ：
Wherein the formula is the induction speed relative value at the paddle disc;
the fly-forward speed is known as V 0 The rotor tension T after a single failure of the helicopter is calculated by:
T＝2ρπR 2 V 1 v 1
v in 1 Is the deflection airflow velocity value after passing through the paddle disc;
the rotor lift Y and the forward pull X of the rotor are calculated as follows:
X＝T·sinα E
Y＝T·cosα E
alpha in the formula E Is the maximum pitch angle of attack of the rotor.
The calculation of the takeoff critical decision point in the step S5 is as follows:
the motion of the helicopter in the horizontal direction and the motion of the helicopter in the vertical direction are considered separately, the stress condition of the helicopter in the horizontal direction is analyzed, and the acceleration change condition of the helicopter in the horizontal direction can be obtained. The helicopter is subjected to resistance force when flying forward in the horizontal direction and horizontal pulling force generated by the rotor wing. The resistance force applied by the flying front at a certain moment is F f_q (i)：
Wherein: v (V) q (i) For the forward flight speed at different moments, (C) X S) q Is the product of the resistance coefficient and the windward area of each windward component on the helicopter in the horizontal direction.
It can be seen that the forward flight resistance of the helicopter is related to the forward flight speed, and the power demand curve of the helicopter can be obtained, and as the forward flight speed of the helicopter increases, the power demand of the helicopter is firstly reduced and then increased, and the minimum value is obtained at the economic speed. Therefore, when the helicopter engine fails, in order to make the helicopter fly safely, the forward flying speed should be increased as fast as possible so as to reduce the required power of the helicopter. After failure of the helicopter engine, the pilot manipulates the rotor disk, imparting maximum rotor disk longitudinal manipulation to provide maximum forward force component to bring the helicopter to a takeoff safe speed in a minimum amount of time.
The acceleration in the horizontal direction at this time is obtained by the following equation:
wherein X (i) is the horizontal pulling force of the rotor wing when the attack angle of the rotor disc is maximum at the current moment.
Carrying out superposition calculation on the speed change amount in the horizontal direction in the infinitesimal time, and obtaining the forward flight speed after the infinitesimal time through the speed calculation at the previous moment:
V_q(i+1)＝V_q(i)+a_q(i)·Δt
wherein: Δt is the infinitesimal time of 0.1s.
Similarly, the horizontal displacement in the infinitesimal time and the displacement after the infinitesimal time are calculated by the front flying speed at the current moment:
L(i+1)＝L(i)+l_q(i)
iterating the speed and displacement of the helicopter at each moment until the forward speed is greater than or equal to the safe take-off speed, namely V _q (i+1)≥V toss Obtaining the time for accelerating the horizontal speed of the helicopter to the takeoff safety speed after single failure at the moment:
t 1 ＝n 1 ·Δt
wherein: n is n 1 The number of iterations is the horizontal direction velocity.
Establishment oft 1 The motion model of the helicopter in the vertical direction in time needs to be considered firstly, when an engine fails, the lift loss is caused due to the fact that the total rotor pitch is reduced, and the helicopter can be changed in speed and lowered in consideration of the resistance effect. With the increase of the forward flying speed of the helicopter, the required power of the helicopter is gradually reduced, the surplus residual power can provide lift force, and the helicopter can gradually decelerate until climbing begins. However, due to the different speeds of the helicopter in failure, the time for the helicopter to accelerate to the safe take-off speed is different, which results in that when the front flying speed of the helicopter reaches the safe speed, the speed in the vertical direction may be negative (i.e., the helicopter is in a descending state), may be positive (i.e., the helicopter is in an ascending state), and may be just zero. Computational analysis is required for different situations.
The helicopter is in a stable flight state at the moment before failure, and the vertical speed is zero. So the vertical speed at the moment of helicopter failure is zero. As the helicopter descends, the vertical drag will also change:
wherein: v (V) c (j) For the forward flight speed at different moments, (C) X S) c Is the product of the resistance coefficient and the windward area of each windward component on the helicopter in the vertical direction.
The acceleration a_c (j) in the vertical direction at this time is obtained by the following equation:
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the initial speed and the acceleration of each micro-element time period can be used for obtaining the speed after each micro-element time, the descending height in each micro-element time and the vertical displacement after the micro-element time:
V_c(j+1)＝V_c(j)+a_c(j)·Δt
H(j+1)＝H(j)+h_c(j)
wherein: Δt is the infinitesimal time of 0.1s.
t 2 ＝n 2 ·Δt
Wherein: n is n 2 Is the first stage speed iteration times in the vertical direction.
If t is calculated 1 When the vertical speed after the moment is greater than zero, the helicopter is not lowered any more at the moment, and the helicopter is in an ascending trend, which indicates that the helicopter is at the lowest point in the flying process. And calculating the accumulated landing height when the descent speed is zero, namely the maximum landing height after the single failure of the helicopter.
If t is calculated 1 And when the vertical speed after the moment is equal to zero, the helicopter is not lowered any more at the moment and starts to be in an ascending trend, so that the fact that the helicopter is at the lowest height point in the process of flying is indicated. The calculated height is the height of the helicopter falling after single failure. Then adjusting the attack angle of the propeller disk to ensure that the front flying speed of the helicopter keeps V toss And gradually climbing without changing, and completing the flying-away field by performing subsequent operations.
If t is calculated 1 When the vertical speed after the moment is less than zero, the helicopter still descends, but the front flying speed reaches the takeoff safety speed, the helicopter can be controlled to keep the acceleration in the horizontal direction to be zero at the moment, the acceleration in the vertical direction is endeavored to be increased, and the pulling force F provided by the paddle disc, the component Q in the horizontal direction and the component C in the vertical direction are calculated at the moment:
Q＝F f_q (n 1 )
F＝T(n 1 )
since the helicopter is still descending at this time, the fuselage resistance is:
the acceleration in the vertical direction at this time is obtained by the following equation:
the initial speed and the acceleration of each micro-element time period can be used for obtaining the speed after each micro-element time, the descending height in each micro-element time and the total displacement in the vertical direction of the micro-element time:
V_c(k+1)＝V_c(k)+a_c(k)·Δt
H(k+1)＝H(k)+h_c(k)
if the calculated vertical speed is equal to 0, the helicopter is not lowered at the moment and starts to be in an ascending trend, and the helicopter is at the lowest height point in the process of flying. The maximum height of the helicopter falling after single failure can be obtained by accumulating the descending height and the descending height.
The fall time of the whole stage is as follows:
t 3 ＝n 3 ·Δt
wherein: n is n 3 The second iteration number is the vertical direction speed.
The corresponding landing height can be calculated by changing the forward flight speed of the helicopter in single-shot failure, and the minimum point ground clearance height in the flying process after the single-shot failure of the helicopter is regulated in airworthiness regulations is not lower than 4.5m, so that the helicopter take-off safety decision point heights at different failure speeds can be calculated.
Another condition for safe fly-away of helicopters, as specified by airworthiness regulations, is that the preceding flying speed remains V toss When the helicopter climbs, the climbing rate is required to be more than 0.5 m/s. So in the process of climbing up the helicopter, the downward resistance is as follows:
the acceleration in the vertical direction at this time is obtained by the following equation:
the initial velocity and the acceleration of each infinitesimal time period can be used for obtaining the velocity and the vertical displacement after each infinitesimal time:
V_c(m+1)＝V_c(m)+a_c(m)·Δt
H(m+1)＝H(m)+h_c(m)
the horizontal displacement of the process is as follows:
L(m+1)＝L(m)+V toss ·Δt
when the climbing speed of the helicopter reaches 0.5m/s, the corresponding time is as follows:
t 4 ＝n 4 ·Δt
wherein: n is n 4 Is the iteration number of the climbing speed in the vertical direction.
When the helicopter is at t 1 When the descent is stopped within the time period, the total time from the failure point to the point of having a climb rate of 0.5m/s is:
t＝t 2 +t 4
while the opposite helicopter is at t 1 The total time from the failure point to when the helicopter has a climb rate of 0.5m/s is:
t＝t 1 +t 3 +t 4
the total time for completing the process after the helicopter fails is smaller than or equal to the rated time corresponding to the emergency power of a single engine of the helicopter, if the total time exceeds the rated time, the helicopter cannot complete the flying by adopting the emergency power and can only land, and if the total time is smaller than the rated time, the helicopter has the capability of successfully flying at the take-off safety breaking point failure.
The helicopter takeoff critical decision point is a combined point of altitude and speed, so that more than one combination mode is adopted. A different takeoff critical decision point is arranged on the takeoff track corresponding to any specific takeoff mode. The calculation result of the takeoff critical decision point of the helicopter should be a curve, and the intersection point of the curve and the takeoff track of the helicopter is the takeoff critical decision point of the corresponding takeoff mode. And obtaining a helicopter take-off critical decision point according to the calculation result of the calculation model.
The calculation of the class a takeoff track in the step S6 is as follows:
after the climbing rate of 0.5m/s is established, the engine power state is switched to 2minOEI power, and the helicopter is started at V toss The helicopter flies forwards, the climbing rate is kept at 0.5m/s, the helicopter climbs upwards to 10.5m from the ground, and in the time period, the helicopter does uniform linear motion in the horizontal direction and the vertical direction, and the displacement in the horizontal direction and the displacement in the vertical direction are respectively as follows:
L(a+1)＝L(a)+V toss ·Δt
H(a+1)＝H(a)+0.5·Δt
after climbing to a height of 10.5m, switching the engine to a 30minOEI power state, and accelerating the helicopter forward to an economic speed by reducing the attack angle; the tension T of the rotor in this process is calculated in step S4. Through a given angle of attack alpha of the propeller F Calculating to obtain the current edge OY V Directional rotor lift Y and in OX V Forward thrust X of rotor in direction:
X＝T·sinα F
Y＝T·cosα F
the horizontal direction of the helicopter is considered separately from the vertical direction movement, the helicopter is subjected to resistance force when flying forward and horizontal direction pulling force generated by the rotor wing in the horizontal direction, and the helicopter climbs downwards and vertical direction pulling force generated by the rotor wing in the vertical direction. The resistance to flying ahead at a certain moment is:
the acceleration in the horizontal direction at this time is obtained by the following equation:
the speed change amounts in the horizontal direction and the vertical direction are respectively subjected to superposition calculation according to the speed change amount in the infinitesimal time, and the forward flight speed after the infinitesimal time is obtained through the speed calculation at the previous moment:
V_q(b+1)＝V_q(b)+a_q(b)·Δt
V_c(b+1)＝V_c(b)+a_c(b)·Δt
wherein: Δt is the infinitesimal time of 0.1s.
Similarly, the horizontal displacement and the vertical displacement after the infinitesimal time are calculated by the front flying speed at the current moment:
iterating the speed and displacement of the helicopter at each moment until the forward speed is greater than or equal to the economic speed or the advantageous speed, i.e. V_q (b+1) is greater than or equal to V e ，
When the front flying speed of the helicopter reaches an economic speed or a favorable speed, the displacement in the horizontal direction and the vertical direction after the single failure of the helicopter are respectively as follows:
L(b+1)＝L(b)+l_q(b)
H(b+1)＝H(b)+h_c(b)
accelerating forward to the target speed, adjusting the attack angle by the helicopter, keeping the economic speed in the horizontal direction of the helicopter, continuing climbing in the vertical direction, at the moment,
Q＝F f_q (b)
F＝T
since the helicopter is still climbing at this time, the fuselage resistance is:
the acceleration in the vertical direction at this time is obtained by the following equation:
the initial speed and the acceleration of each infinitesimal time period can be used for obtaining the speed after each infinitesimal time and the descending height in each infinitesimal time:
V_c(c+1)＝V_c(c)+a_c(c)·Δt
the displacement of the helicopter in the horizontal direction and the vertical direction in the time period is respectively as follows:
L(c+1)＝L(c)+l_q(c)
H(c+1)＝H(c)+h_c(c)
and climbing to the height of 300m from the ground, completing the flying, and then climbing the flight track to the target height according to the specific flight task requirement, and completing the flying at the corresponding front flying speed.
The following examples are provided:
and (3) selecting the UH-60A helicopter as an example to calculate, and calculating a class A flying and taking-off track when the total mass of the UH-60A helicopter is 9185 kg.
Statistical helicopter parameters and engine parameters used therein are shown in table 1 below:
TABLE 1
Calculating a UH-60A helicopter front flight power demand curve:
the front flight power demand curve of the UH-60A helicopter is saddle-shaped, the power demand is firstly reduced and then increased along with the increase of the front flight speed, and the power demand of the helicopter is minimum and is about 1180kW when the front flight speed is about 140 km/h; see fig. 4;
calculating the takeoff safety speed V of the UH-60A helicopter toss ：
Safe speed V of airworthiness standard pair takeoff toss Is defined as follows: the minimum flying speed with stable climbing rate of at least 0.5m/s can be achieved under the combined conditions of the taking-off weight, the gravity center, the height and the temperature of the helicopter and the residual power after the failure of the key engine.
According to the method, a double-engine helicopter power demand model is established, a speed change curve of the double-engine helicopter power demand along with the front speed is calculated, and then a power demand curve when the helicopter has a climbing rate of 0.5m/s is calculated, as shown in fig. 5, the relation between the emergency power of a single engine of the helicopter and the power demand at the moment can be obtained: when the current flying speed is smaller, the required power of the helicopter is larger than the emergency power of a single engine, and the helicopter cannot climb; with the increase of the forward flying speed, the required power of the helicopter is gradually reduced, when the required power is equal to the emergency power of a single engine, the helicopter can obtain the stable climbing rate of 0.5m/s, and the corresponding forward flying speed is the single-shot failure takeoff safety speed V of the helicopter in a corresponding state toss The calculated value of the takeoff safety speed is 78.214km/h.
Helicopter take-off critical block based on the establishmentBreakpoint model and helicopter OEI state flight trajectory calculation model, and double-engine helicopter takeoff safety speed V is known toss And calculating the takeoff critical decision point of single failure of the UH-60A helicopter when the total mass is 9185kg and the corresponding class A takeoff track.
Calculating a takeoff critical decision point curve of the UH-60A helicopter:
the definition of the takeoff critical decision point is: the helicopter with A-type performance has a first point of continuous take-off capability after single failure on a certain fixed take-off track, and can ensure the last point of safely interrupting take-off. The critical decision point speed of take-off is the maximum speed of taking-off interruption after the critical engine fails, and the minimum speed of taking-off can be continued.
The helicopter takeoff critical decision point is a combination of altitude and speed, with different speeds corresponding to different altitudes. The critical decision speed of take-off can be calculated from the time of acceleration of the failure speed of the helicopter engine to the safe take-off speed and the duration of emergency power of the single engine. The takeoff threshold height can be calculated from the height loss and the minimum ground clearance required by the regulations. Is related to the available energy of the helicopter immediately before the engine fails and the energy loss during acceleration to the takeoff safety speed after that.
The height speed curve formed by UH-60A takeoff critical decision points is shown in figure 6, a certain takeoff critical decision point is selected to perform verification of flight track optimization under the OEI state of the helicopter, and when the front flight speed is selected to be 19.75km/h, the height corresponding to the decision point is 144.1m. And (3) taking the helicopter into an optimized model of the flight trajectory, and calculating to obtain a flight trajectory curve after single failure of the UH-60A corresponding take-off critical decision point, wherein the helicopter is found to have the height of 4.752m when the drop rate of the helicopter is equal to 0, namely the lowest point from the ground, and the result meets the expectation.
Calculating a take-off track of class A flight of the UH-60A helicopter:
as shown in FIG. 7, after a single failure occurs in the helicopter, a pilot starts to operate the helicopter after 1s delay, starts to perform collective pitch operation after 2s delay, and the helicopter reduces the collective pitch, maintains the rotating speed and gives the maximum longitudinal operation to the propeller discThe helicopter is longitudinally converted into kinetic energy by reducing potential energy, the power required by the helicopter is reduced in the process, the height of the lowest point of the helicopter from the ground is 4.752m, when the horizontal speed of the helicopter reaches the safe take-off speed, the attack angle of a propeller disc is adjusted, the horizontal speed is kept constant, the vertical direction climbs at a speed not less than 0.5m/s, and when the ground clearance is climbed from 4.752m to 10.5m, the power of the helicopter engine is switched and V is calculated toss Accelerating to the economic speed, obtaining the maximum climbing rate, at the moment, keeping the forward flying speed at the moment at the ground clearance height of 60m, climbing by adopting the maximum climbing rate, and finishing the flying from 60m to 300 m.
The above description is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above examples, and all technical solutions belonging to the concept of the present invention belong to the protection scope of the present invention. It should be noted that modifications and adaptations to the present invention may occur to one skilled in the art without departing from the principles of the present invention and are intended to be within the scope of the present invention.
Claims (9)
1. A method for calculating a take-off track of a helicopter A-type flight is characterized by comprising the following calculation steps:
s1: counting parameters of the double-engine helicopter and parameters of an engine used by the double-engine helicopter;
s2: calculating the front flight demand power N of the double-engine helicopter according to the statistical parameters xu And draw N xu -V 0 A curve;
s3: according to the front flight required power N of the double-engine helicopter xu And statistical engine single-shot emergency power P OEI Calculating the takeoff safety speed V of the double-engine helicopter toss ；
S4: according to the statistical parameters, calculating the lift force and the forward pulling force provided by the helicopter rotor;
s5: calculating a takeoff critical decision point of the double-engine helicopter according to the takeoff safety speed and the lift force and the forward pulling force provided by the helicopter rotor wing, and drawing a helicopter takeoff critical decision point curve;
s6: according to the calculated takeoff critical decision points of the double-engine helicopter, the takeoff tracks of the class A helicopter are calculated respectively according to the positions of the failure points, and a class A takeoff track curve of the helicopter is drawn.
2. The method for calculating the take-off track of class a helicopter flight according to claim 1, wherein the method comprises the following steps:
the parameters of the double-hair helicopter in the step S1 comprise: the total weight G of the helicopter, the rotation angular velocity omega of the rotor, the number k of blades, the wing profile of the rotor, the radius R of the rotor and the solidity sigma of the rotor;
the engine parameters used by the double-engine helicopter comprise: engine single-shot emergency power P OEI Single-shot emergency power P of engine 30s OEI-30s Engine 2min single-engine emergency power P OEI-2min Single-engine emergency power P for 30min OEI-30min ；
The step S2 is that the front flight of the double-engine helicopter needs power N xu The method specifically comprises the following steps: power demand P of rotor r Power P required by tail rotor TR Power loss P of speed reducer and transmission system RE.T Installed loss P of engine SET 。
3. The method for calculating the take-off track of class a helicopter flight according to claim 2, wherein the method comprises the following steps:
the required power P of the rotor wing r Is calculated as follows:
s21: solving the atmospheric density;
the solution of the atmospheric density in the nonstandard atmospheric state is as follows:
ρ＝Δρ 0
wherein H is the flying height, t is the atmospheric temperature, ρ 0 Is sea level standard atmospheric density;
s22: calculate the tension coefficient C T And lift coefficient Cy:
wherein T is rotor wing lifting force; r is the radius of the rotor wing; omega is the rotation angular velocity of the rotor; v (V) 0 Is the forward flying speed of the helicopter; mu is the forward ratio; b is leaf tip loss coefficient, and B is approximately equal to 0.92; sigma is rotor solidity;
s23: solving rotor type resistance power N x The method specifically comprises the following steps:
press-type calculating power coefficient m kx ：
Wherein K is P Is a hover state resistance correction coefficient; k (K) P0 Approximately 1.0-1.1, which is to consider the non-uniformity of the profile resistance along the spanwise direction (usually 1.05); c (C) x7 Is the model drag coefficient at the characteristic section of the blade;
rotor type power N x The method comprises the following steps:
s24: solving for rotor induced power N i The method specifically comprises the following steps:
the following is used for seeking the attractionConductivity coefficient m ki ：
J＝J 0 (1+3μ 2 )
Wherein J is a hover state induced power correction coefficient; j (J) 0 About 1.05 to 1.10, along with C T Variation of sigma; v dx Is the relative value of the induction speed at the paddle plane when hovering;
wherein: c (C) T Is the tension coefficient; b is leaf tip loss coefficient;
rotor induced power N i The method comprises the following steps:
s25: solving for waste resistance power N f The method specifically comprises the following steps:
the helicopter waste resistance Q is calculated as follows:
wherein C is x S is the resistance coefficient and the windward area of each windward component on the helicopter respectively;
solving for waste resistance power N f The method comprises the following steps:
N f ＝Q·V 0
power demand P of rotor r The method comprises the following steps: p (P) r ＝N x +N i +N f 。
4. A method of calculating a take-off path for class a helicopter flight as claimed in claim 3, wherein: the tail rotor requires power P TR The calculation of (1) specifically comprises: for a helicopter with a single rotor wing and a tail rotor, when flying forwards, the required power of the tail rotor consists of type resistance power and induced power;
s26: tail rotor type resistance N tx The method specifically comprises the following steps:
press-type calculating power coefficient m tkx ：
K p ＝(1+5μ 2 )K p0
Wherein K is P Is a hover state resistance correction coefficient; k (K) P0 Approximately 1.0-1.1, which is to consider the non-uniformity of the profile resistance along the spanwise direction (usually 1.05); c (C) tx7 The model drag coefficient of the characteristic section of the tail rotor blade;
tail rotor type resistive power N tx The method comprises the following steps:
s27: finding tail rotor induced power N ti The method specifically comprises the following steps:
the induction power coefficient m is calculated according to the following method tki ：
J＝J 0 (1+3μ 2 )
Wherein J is a hover state induced power correction coefficient; j (J) 0 ≈1.05-1.10；Is the relative value of the induction speed at the plane of the tail rotor;
wherein: c (C) Tt Is the tail rotor tension coefficient; b (B) t The loss coefficient of the tail rotor blade end;
tail rotor induced power N ti The method comprises the following steps:
power demand P of tail rotor TR The method comprises the following steps: p (P) TR ＝N tx +N ti 。
5. The method for calculating the take-off track of class a helicopter according to claim 4, wherein the method comprises the following steps:
the power loss of the speed reducer and the transmission system refers to friction between gears and in bearings and loss caused by aerodynamic resistance or wind resistance, and the loss accounts for 2% -4% of the power of the engine.
Installation loss P of the engine SET The engine is arranged on the helicopter, and the output power of the engine is smaller than the test power of the rack and accounts for 3% -6% of the power of the engine.
The calculation of the power required by the front flight of the helicopter is as follows:
N xu ＝P r +P TR +P RE.T +P SET
calculating different forward flight speeds V 0 Lower forward power demand N xu Drawing Nxu-V 0 A curve.
6. The method for calculating the take-off track of class a helicopter according to claim 5, wherein the method comprises the following steps:
the defining of the takeoff safety speed in the step S3 includes:
in the threshold height interval, calculating the helicopter power demand when the helicopter stably flies at different speeds and climbing rates of 0.5m/s respectively to obtain a speed-power curve, and then obtaining the single-shot emergency power P according to the engine OEI Finding the left intersection point of the single-shot emergency power and the speed-power curve, wherein the corresponding speed is the takeoff safety speed V toss ；
The climbing power coefficient m of the double-engine helicopter is calculated according to the following mode kp ：
C in the formula G Is the weight coefficient of the double-engine helicopter,the relative climbing rate of the double-shot helicopter;
wherein V is y The climbing rate of the double-engine helicopter is the climbing rate;
the climbing power P of the double-engine helicopter is calculated by the following method kp ：
Wherein: ρ represents the atmospheric density.
7. The method for calculating the take-off track of class a helicopter according to claim 6, wherein the method comprises the following steps: the double-engine helicopter flies at a certain forward flying speed and maintains the required power N when flying at a stable climbing rate sum
N sum ＝N xu +P kp
Solving the takeoff safety speed V of the double-engine helicopter toss ：
N sum (V toss )＝P OEI
Wherein P is OEI The emergency power is single-shot for the engine.
8. The method for calculating the take-off track of class a helicopter according to claim 7, wherein:
the calculation of the lift force and the forward pulling force provided by the rotor in the step S4 includes:
s41: the lift force of the rotor wing is recorded as Y, the forward pulling force is recorded as X, the stress of the helicopter in the process of flying is definitely recorded, the aerodynamic resultant force R of the rotor wing is equal to the pull force T of the rotor wing, a slip stream theoretical paddle diagram is constructed, and meanwhile, a helicopter power curve is also constructed;
s42: the rotor wing lift force Y and the forward pulling force X provided by the rotor wing during front flight are calculated:
calculating a hover time curve:
select C T Taking C as a series of calculation points T ＝0.006～0.020；
Calculating blade characteristic profile lift coefficient C according to the following formula y7 ；
From the calculated C y7 Finding out blade polar curve to obtain resistance coefficient C x7 ；
The following calculation type power resistance coefficient:
the relative value of the induction speed at the paddle plane at hover is calculated as follows:
obtaining an induction power coefficient during hovering:
calculating and obtaining the power coefficient required by the wave resistance:
wherein:by blade airfoil drag sudden increase critical Mach number M and lift coefficient C y Obtaining the relation of (2);
the total required power factor is calculated as follows:
m K ＝m Kx +m Ki +m Kb
according to corresponding C T 、m K Make C T -m K A curve;
the corresponding power is the single-engine emergency power P OEI Obtaining the corresponding tension coefficient C T Calculating the relative value of the induction speed at the paddle plane when hovering as follows
The induction speed at the paddle disc is v during forward flight 1 ：
Wherein the formula is the induction speed relative value at the paddle disc;
the fly-forward speed is known as V 0 By the following constitutionThe rotor tension T after single failure of the helicopter is calculated as follows:
T＝2ρπR 2 V 1 v 1
v in 1 Is the deflection airflow velocity value after passing through the paddle disc;
the rotor lift Y and the forward pull X of the rotor are calculated as follows:
X＝T·sinα E
Y＝T·cosα E
alpha in the formula E Is the maximum pitch angle of attack of the rotor.
9. The method for calculating the take-off track of class a helicopter flight according to claim 8, wherein: the takeoff critical decision point in the step S5 is a combination point of the flying height and the flying speed, the takeoff critical decision point forms a critical decision curve in the flying process, and the intersection point of the critical decision curve and the helicopter takeoff track is the takeoff critical decision point corresponding to the takeoff mode.
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