DE102008046486A1 - Method for landing rotary-wing aircraft, particularly helicopter, involves reducing drive moment on main rotor, such that no blade-rotator interaction effect arises - Google Patents

Abstract

The invention relates to a method for landing a rotorcraft (10) comprising a main rotor (12) and a Fenestron (14), which in normal operation produces a positive tail rotor force (F _F ) and cooperates with at least one vane (50) comprising the steps of: lowering a drive torque (M _drive ) to the main rotor (12) so that no blade vortex interaction occurs, and generating a lateral force (F _Q ) without using the fenestron (14) so that the tail rotor torque Force (F _F ) of the fenestrone (14) remains so large that no blade-wake interaction between a vane vortex of the at least one vane (50) and a Fenestron rotor of Fenestrons (14) is formed.

Description

The The invention relates to a method for landing a rotorcraft, the a main rotor and a Fenestron, which in normal operation a Generated rear rotor force and interacts with at least one vane, includes. According to one second aspect, the invention relates to a rotorcraft, the a main rotor and a Fenestron, which in normal operation a Generated tail rotor force, and cooperates with at least one vane, includes.

such rotorcraft In particular, helicopters, are used for a variety of military and used for civilian purposes. A disadvantage of known rotorcraft is the partly considerable noise that cause them to land. This noise is a hindrance to the further dissemination and use of rotary-wing aircraft for civilian operations, as the population with noise is charged. In military inserts leads the Noise too an increase in Discoverability.

Of the Invention is based on the object that issued by a rotorcraft Noise, in particular when landing, diminish.

The Invention solves the problem by a method with the steps (i) lowering a Driving torque on the main rotor, so no blade-vortex interaction occurs at the main rotor and (ii) generates a lateral force without using the Fenestrons, so that the tail rotor power of Fenestrons remains so large that no leaf-wake interaction between a vane vortex from the at least one vane and the Fenestron arises.

According to one second aspect triggers the invention of the problem by a generic rotorcraft, the a lateral force generating device independent of Fenestron for generating a lateral force which is opposite to that of the tail rotor force Direction works.

Advantageous The invention is that when landing less noise from the Fenestron emanates. It has Namely proved that on an approach that minimizes the noise of the main rotor, especially common dominant Fenestron noise occurs. The solution according to the invention enables a landing maneuver in which both the noise of the main rotor as well as the Fenestrons is particularly low. This reduces the noise pollution the population or discoverability in military operations.

It Another advantage is that the reduction of noise with relatively simple means is possible. The noise, that of a rotorcraft is emitted, stirs usually of very complex, non-linear interactions between rotor blades the main rotor or the tail rotor, such as the Fenestron rotor, on the one hand and by these rotors caused air turbulence on the other ago. It has been shown that despite the highly non-linear Nature of the formation of noise relatively simple strategies suffice to bring about a significant reduction of the noise to reach.

Advantageous In addition, generating the shear force without using the fenestron is automatable, so in this case the pilot no additional Pay attention to the noise reduction got to.

in the The scope of the present description is under a fenestron an enclosed tail rotor of a rotary wing aircraft, in particular a helicopter with tail rotor configuration Understood. The Fenestron balances the torque of the Main rotor and is designed as an impeller. The Fenestron could do that also be referred to as Heckimpeller.

Under the feature that the drive torque is reduced to the main rotor so that no blade-vortex interaction occurs at the main rotor, in particular, it is understood that the collective pitch θ ₀ is changed so that the drive torque decreases. As a result, the flow component from bottom to top through the rotor disk is so large that no blade-vortex interaction occurs on the main rotor, because, for example, the rotorcraft drops or decelerates sufficiently fast. To change the collective angle of attack θ ₀ , in particular the collective control stick is moved accordingly.

Under the feature that the Fenestron in normal operation a tail rotor force produced, it is understood that the Fenestron example in Straight flight produces the tail rotor force, which corresponds to the torque of the Counteracts main rotor. This tail rotor force usually works perpendicular to the tail boom and pointing in the direction of the main rotor blades provisional side, for example, when looking from above at the rotorcraft, to the right. This tail rotor force in normal operation is defined as positive. The Fenestron then works in flow, that is, that Air first through the Fenestron rotor, which represents the tail rotor, flows and afterwards on the at least one vane. The tail rotor power points in other words, in the direction of the trailing rotor blade.

By the feature that the Fenestron cooperates with at least one vane, it is to be understood in particular that air from the Fenestron rotor encounters a structure that is usually designed so that the air flow is comparable is canceled. The Fenestron rotor sits on a shaft, which has a bearing, which in turn is part of the tail boom. It is conceivable that the vane is formed by this suspension. In general, however, several vanes are present to increase the efficiency of the Fenestron rotor.

Under the feature that the drive torque on the Fenestron rotor so it is lowered that no blade-lag interaction occurs is to understand that the drive torque to such a value is lowered, that caused by blade-lag interaction additional noise below of, for example, 6 dB (A). The typical helicopter noise becomes by such blade-vortex interactions (English: blade vortex interaction, BVI) caused. Will that be Drive torque is lowered to a small value, for example is less than 10% of the maximum drive torque, then the decreases rotorcraft so fast that caused by a leaf of the main rotor Swirl sufficiently far up from the rotorcraft have as a subsequent leaf with the vortex in significant Interaction could occur. With sufficiently small drive torque of the rotorcraft is therefore especially quiet.

Under the characteristic that a lateral force without using the Fenestrons is generated so that the tail rotor power of Fenestrons remains so large that no leaf-lag interaction between a vane vortex from the at least one vane and the Fenestron arises, is understood in particular that the Fenestron generated no or a magnitude as small negative tail rotor force. Thereby it is avoided that the Fenestron works in reverse flow. The vane vortex could Also be referred to as vane caster.

Is working the Fenestron in backflow, so air flows first past the at least one vane and then towards the Fenestron rotor. It has been shown that when passing the air one at least a vane vortex arise with which the fenestron rotor interact and noise can generate. The noise caused by this blade-wake interaction is all the more stronger, the bigger the flow rate in backflow through the Fenestron rotor is. In the return flow, the generated as Fenestron Fenestron rotor trained a negative tail rotor force. These negative tail rotor power is needed when the drive torque is lowered to very small values. In this case, there is only one left very small torque necessary to the torque from the main rotor to compensate.

There the tail boom of rotary-wing aircraft usually designed so that a compensating force in straight-line flight is generated to the Fenestron in straight flight Relieve this relieving force with rapid descent due to small drive torque be so great that the Fenestron work in reverse flow would have to keep the sliding angle small. But that leads to unpleasant Fenestron noise. Thereby, that the lateral force is generated without using the Fenestron is ensures that the Fenestron does not or only slightly in reverse flow work that must be the noise pollution remains low.

Prefers is the rotorcraft a helicopter that generates a lateral force generating device for generating a lateral force that is opposite in one of the tail rotor force Direction acts used, the lateral force is generated by that the lateral force generating device is driven accordingly becomes. In such a lateral force generating device is it is preferably a passive device that has an airflow deflected so that the lateral force arises. Alternatively, it is also conceivable to provide an active lateral force generating device, which generates the transverse force by means of an engine.

According to one not shown alternative embodiment includes the lateral force generating device Flow control devices, for example, blowing or sucking air on the tail boom enable and thus generate the necessary lateral force.

To the To finish the landing, the method preferably includes the steps an elevation of the drive torque to the main rotor, so that the cross-flow through the main rotor is so big that no leaf vortex interaction occurs, and one touchdown of the helicopter on the ground.

Prefers the lateral force generating device is driven so that the Shear force is so great that the helicopter is directed with its longitudinal axis in the direction of flight is. In other words, the shift angle β is small, for example, smaller as 10 °.

Preferably, the driving of the lateral force generating device comprises the steps of detecting a speed, in particular a forward speed, of the helicopter relative to the surrounding air and an automatic driving of the lateral force generating device and / or the Fenestron rotor, so that no blade-lag interaction between the vane vortex and the Fenestron rotor arise. This is particularly advantageous if the cross Force generating device is passive, that is, the generated lateral force depends on the speed. For example, when the lateral force generating device is a rudder, the generated lateral force depends on the forward speed relative to the surrounding air.

Conceivable is also that the lateral force generating device is arranged is that the generated lateral force of a sinking speed relative depends on the surrounding air. To relieve the pilot, it is convenient to perform the control automated, so that the helicopter like a non-inventive helicopter can be flown and still Fenestron noise is avoided.

Prefers extends the air flow always from the Fenestron rotor to the at least one Vane too. This way, very little noise is generated because the Fenestron rotor blades are never have to move through your own caster.

alternative or additively, the lateral force can be achieved without using the fenestron Yawing the helicopter are generated. In other words The lateral force generated by this without using the Fenestrons the sliding angle is increased. That way you can Already existing helicopters are landed low noise. adversely is, however, that a corresponding approach for passengers will be unusual can.

at a rotorcraft invention, the if a helicopter is preferred, the lateral force generating device include a rudder. Such a Be tenruder, for example attached to the tail boom and exercises the transverse force characterized by the fact that air flowing from the front of the rotorcraft is redirected to the page. Below a rudder is any airflow redirecting structure understood that to a respect of the coordinate system of the rotorcraft vertical axis pivotable is.

alternative or additively, the lateral force generating device is arranged that it generates a lateral force during a descent. Especially preferred is the lateral force generating device then arranged so that it generates an adjustable transverse force. If the rotorcraft, especially the helicopter, operated with low drive torque becomes, then the rotorcraft sinks quite fast. The resulting high relative flow component from the bottom up in the helicopter coordinate system to the surrounding Air can be used to generate the lateral force. To the lateral force generating device is preferably about a longitudinal axis the rotorcraft pivot stored.

Around relieving the pilot is the lateral force generating device preferably automated operable, so that the pilot to their Do not worry about control must and still low noise can fly to.

Prefers includes the rotorcraft a drive unit which is designed for automatic or semi-automatic performing an above-mentioned method according to the invention.

in the The invention will be described below with reference to exemplary embodiments with reference to the attached Drawings closer explained. Showing:

1 a schematic drawing for explaining a landing method for a helicopter according to the invention,

2 a course of the sliding angle in the landing method to 1 with a constant tail rotor force,

3 a schematic representation of acting on a tail boom of a helicopter according to the invention forces in normal operation,

4 a representation of the forces in the event that the helicopter is operated with a low drive torque and drops quickly and flies straight ahead,

5 an embodiment of a helicopter according to the invention in a view from the side and

6 a view of the helicopter according to 4 from above.

7 shows a second embodiment of a helicopter according to the invention.

1 shows a rotorcraft according to the invention in the form of a helicopter 10 , which is a main rotor 12 and a fenestron 14 has, in a schematic approach plan on a landing site 16 , First, the helicopter flies 10 with a drive torque M _drive of more than 50%, in particular 60% of a maximum drive torque M _{drive, max} to one point 18 , in which the landing approach begins. Before reaching the point 18 For example, the helicopter is in ascent of, for example, more than 2 °, in this case 3 °, at a climb rate of more than 300 ft / min, for example 590 ft / min, at a speed of above 90 kn, in the present case 110 kn.

In point 18 the drive torque M _{drive is} throttled to a value of less than 12% of the maximum _drive torque M _{drive, max} , for example, to 6%. As a result, the helicopter sinks 10 in a descent phase 20 so fast that no leaf-vortex interaction occurs. For example, a trajectory 22 in the descent phase 20 by a rise angle γ _a of less than -10 °, for example -16 °, inclined to the horizontal H. The speed is less than 90 knots, for example 75 knots and the sinking speed above, for example, 1800 ft / min, in this case 2170 ft / min.

The descent phase 20 goes into a short approach phase 24 in which the drive torque M _{drive is increased} to over 50%, for example 60%, and the helicopter 10 on the landing field 16 touches down.

2 shows the dependence of a sliding angle β on the distance from the landing site 16 , It can be seen that the sliding angle β in the descent phase 20 is different from zero. So it is possible that the position of a foot pedal, the Fenestron 14 controls during the full landing phase 26 is kept constant. An advantage of such an approach is in addition to the low noise level, which is a field of vision 28 particularly favorable to the landing field 16 is directed. The Fenestron noise is about as great in this landing maneuver as in the climb.

3 shows the helicopter 10 with those on a tail boom 30 acting forces. The drive torque M _drive that is applied to a main rotor 31 to move with an angular frequency ω leads to a moment force F _M. The moment force F _M is compensated by a tail rotor force F _F (F stands for Fenestron) and a rudder force F _S , that of a rudder 32 is exercised when the helicopter 10 with a forward speed v moved _forward relative to the air. The rudder 32 is rigid in conventional helicopters and serves to provide the straight-line performance of the Fenestron 14 to reduce and thus save fuel.

4 shows the situation in which the moment force F _{M is} significantly reduced, because the drive torque M _{drive has been} greatly reduced for a quiet descent. However, the rudder force is largely unchanged because the forward velocity v _forward , has barely changed. In this case, the Fenestron 14 apply a negative tail rotor force F _F. The above situation occurs with conventional helicopters then when low drive torque M _drive in the in 1 shown descent phase 20 are located.

In the in 4 air flows as shown by the arrow 34 stated, first on in 4 invisible baffles (cf. 7 , Reference number 50 ) and of these on the tail rotor, which is designed as a Fenestron rotor. It then creates unwanted Fenestron noise.

5 shows a helicopter according to the invention 10 comprising two lateral force generating devices, namely a rudder 36 and an adjustable vertical stabilizer 38 , one of which would be sufficient. The rudder 36 and the adjustable vertical stabilizer 38 are provided with associated servomotors and with a drive unit 40 connected. The drive unit 40 in turn is in connection with a speedometer 42 in the form of a pitot tube and an angle sensor 44 on a collective lever to control the helicopter 10 , The drive unit 40 captures the speed and angle and controls the rudder 36 and the adjustable vertical stabilizer 38 so that a lateral force F _Q (cf. 4 ) is generated, which is so large that the tail rotor force F _{F can} again point in the direction in which air flows first through the Fenestron and only then through the baffles.

Alternatively to the use of the rudder 36 Also, the entire upper part of the middle vertical tail can be rotated about the vertical axis to change its angle of attack.

The drive unit 40 may be configured to detect when the collective lever is pulled up, then all the required aerodynamic lateral forces are to be adjusted on the vertical stabilizers in the direction of the side of the leading Haupttrotorblät ter to optimize performance without risking Fenestron noise. With a collective lever position in the lower range, the aerodynamic forces on the vertical stabilizers would be adjusted in the other direction, so that the Fenestron is still loaded in the normal direction and thus remains quiet. The additional consideration of the speed makes it possible to adapt the values of the angles of attack and / or the rudder deflections to the speed in order to obtain the desired lateral forces for different dynamic pressure values on the speedometer 42 to obtain.

6 shows the helicopter according to 5 in the descent phase 20 (see 1 ), in which the adjustable vertical tail 38 and the rudder 36 are set so that the tail rotor force F _{F points} in the same direction as in normal operation, ie in the positive direction.

7 shows a further helicopter according to the invention 10 in which the lateral force generating device is characterized by a about a longitudinal axis L of the helicopter swiveling stabilizer 48 is formed. Moves the helicopter 10 with a sinking speed v _sink , the stabilizer is impinged with air from below and generates the desired lateral force F _Q. The Fenestron 14 can then continue working so that air first through the fenestron and then through the vanes 50.1 . 50.2 , ... streams.

In summary is avoided by the invention that the Fenestron in the state the return flow works. Normally it runs the flow of the Fenestron so that they first (first stage) through the Fenestron rotor (Tail rotor) leads and then (second stage) through the Fenestron stator (vanes). In this case, the sound is due to the interaction from rotors and stators by sucking in the wake of the first stage minimal in the second stage. The formation of sound on a sheet (Rotor or stator) is growing with the time derivative of the pressure on its surface. in the Normally, the tail of the rotor moves with the flow velocity parallel to the Fenestron axis of rotation to the second stage (stator, vanes).

If the angle of attack of the Fenestron rotor blades is set (by Pedal, movement of the pilot) that the flow through the Fenestron in the other direction runs, what needed is going to change the Fenestron thrust direction, then the Caster of the stator in the rotor. This caster can, firstly be highly turbulent (swirled), since the flow of the stator blades in the wrong direction overflowed (first Trailing edge, then leading edge). Second, the stator blade wake on each generates Rotor blade much faster and more intense pressure fluctuations, there the wake not only with the flow rate at the Fenestron the leaves but also with the high rotor blade speed (high Rotation speed). This leads in the consequence to very high values of the time derivation of the leaf pressure and thus high sound radiation from the rotor blades of the Fenestron. The backflow case may be 16 db (A) louder than the normal case described above and the loud Fenestron noise will be particularly disturbing perceived.

Around the torque from the air to the fuselage caused by the air resistance at the main rotor blades is generated, must balance, a lateral aerodynamic force be generated at the rear. To known helicopters in forward flight to keep the overall power requirement minimal and mainly on to concentrate the main rotor, it is necessary to the performance at the Fenestron if possible far to reduce. For this purpose, vertical stabilizers with a fixed Anstellwinkel and / or a single-ended profile used.

Of the Fenestron is for designed this normal case: The air flows through the rotor, the on the starboard side and then through the stator, which on the Port side lies. The distinction of the sides must for the general Case can not be defined by port and starboard, but by the consideration the main rotor rotation direction. Generally expressed, in the normal case, that is called in normal operation, the lateral air forces on the tail boom in Direction of the side of the leading main rotor blades.

The Fenestron backflow can arise when the thrust direction is reversed by the Fenestron got to. That can be for Yaw maneuvers be necessary, but also in flight conditions close to or in the autorotation, for which the aerodynamic side force at the stern will be zero or almost zero should, because here also no torque on the main rotor mast is needed. The main rotor is running almost empty, the air resistance on the leaves is directly on the sheet balanced by the drive due to the flow from bottom to top.

Around to avoid that arise from zero different sliding angle β, the changes Pilot then with the help of the pedals the Fenestron thrust to him in the To face the opposite direction. The autorotation flight is actually too a forward flight, in which the vertical stabilizers are flown at the same time sinking. The Fenestron thrust direction and its flow direction are reversed, which is very loud for the reasons mentioned above.

The control of the lateral force generating device may be done manually or automatically. The automatic solution may be provided by a special controller that takes into account any number of flight parameters, such as the engine or main rotor torque, the speed, air relocate velocities, and so on, and pilot specifications such as pedal or collective lever position. A simple and efficient solution is to couple the lateral force generating device, in particular an adjustable vertical stabilizer or rudder, with the collective lever. The collective angle of attack on the main rotor, which is controlled by the collective lever, also controls the linear rotor torque almost linearly, which in turn determines the need for side forces on the rear. The rudder control can be designed so that for each collective angle of attack on the main rotor, the Fenestron operates with always enough thrust toward the side of the leading main rotor blade and thus can be flown without a slip angle. Compared to today's state, the rudder and / or mounted rudders would then change their angle of attack when the collective lever is lowered. This can, but does not have to, be successful in the context of a linear dependency This dependence of the rudder control on the collective lever could be designed for a mean total speed of, for example, about 75 knots.

The drive unit is preferred 40 designed so that emergency maneuvers, such as the full autorotation landing is not limited by a glitch of the drive unit.

The Control unit of the vertical stabilizer could also be used for other purposes serve, for example, could in case of failure of the Fenestrons the controllable vertical stabilizers allow a replacement control of the heading.

10

helicopter

12

main rotor

14

fenestron

16

landing field

18

Point

20

descent phase

22

trajectory

24

approach phase

26

landing phase

28

field of view

30

Heckausleger

32

fin

34

arrow

36

rudder

38

adjustable fin

40

control unit

42

speedometer

44

angle sensor at the collective club

46

upper part

48

stabilizer

50

vane

M _drive

drive torque

M _{drive, max}

maximum drive torque

αγ _a

angle of climb

β

sideslip

ω

angular frequency

F _M

moment force

F _F

Tail rotor force

F _Q

lateral force

F _s

Rudder force

V _forward

Forward speed relative to the air

V _sink

rate of descent

Claims (13)

Method for landing a rotorcraft ( 10 ), which (a) has a main rotor ( 12 ) and (b) a fenestrone ( 14 ), which generates a positive tail rotor force (F _F ) in normal operation and with at least one vane ( 50 ) comprises, comprising the steps of: (i) lowering a drive torque (M _drive ) to the main rotor ( 12 ) such that no blade vortex interaction occurs, and (ii) generating a lateral force (F _Q ) without using the fenestrone ( 14 ), so that the tail rotor force (F _F ) of fenestrone ( _F 14 ) remains so large that no blade-wake interaction between a vane vortex of the at least one vane ( 50 ) and a fenestrone fenestron rotor ( 14 ) arises. A method according to claim 1, characterized in that the rotorcraft a helicopter ( 10 ). Method according to claim 2, characterized in that the helicopter ( 10 ) comprises a lateral force generating device for generating a lateral force (F _Q ) acting in a direction opposite to the tail rotor force (F _F ), comprising the step of: (iii) driving the lateral force generating device (15) 36 . 38 . 46 . 48 ), so that the lateral force (F _Q ) arises. Method according to one of the preceding claims, characterized by the following steps: (iv) increasing the drive torque (M _drive ) to the main rotor ( 12 ), so the helicopter ( 10 ) slowly sinks, decelerates so fast, rises so fast or accelerates so fast that no blade-vortex interaction occurs, and (v) placing the helicopter ( 10 ). Method according to one of the preceding claims, characterized by the step: - driving the lateral force generating device ( 36 . 38 . 46 . 48 ), so that the lateral force (F _Q ) is so great that the helicopter ( 10 ) is aligned with its longitudinal axis (L) in the direction of flight. A method according to claim 5, characterized in that the driving of the lateral force generating device ( 36 . 38 . 46 . 48 ) comprises the following steps: - detecting a speed, in particular a forward speed (v _forward ), of the helicopter ( 10 ) relative to the surrounding air and - automatic control of the lateral force generating device ( 36 . 38 . 46 . 48 ) and / or the fenestrone ( 14 ) so that no blade-wake interaction occurs between the vane vortex and the fenestron rotor. Method according to one of the preceding claims, characterized in that the air flow through the Fenestron ( 14 ) always from the Fenestron rotor to the at least one vane too runs. Method according to one of the preceding claims, characterized in that generating a lateral force (F _Q ) without using the fenestrone ( 14 ) a yaw of the helicopter ( 10 ). Rotorcraft having (a) a main rotor ( 12 ) and (b) a fenestrone ( 14 ), which generates a tail rotor force (F _F ) in normal operation and with at least one vane ( 50 ), characterized by (c) one of the Fenestron ( 14 ) independent lateral force generating device ( 36 . 38 . 46 . 48 ) for generating a lateral force (F _Q ) acting in a direction opposite to that of the tail rotor force (F _F ). Rotorcraft according to claim 9, characterized in that the lateral force generating device is a rudder ( 36 ). Rotorcraft according to claim 9 or 10, characterized in that the lateral force generating device ( 36 . 38 . 46 . 48 ) so arranged, in particular pivotally mounted, is that it generates a lateral force (F _Q ) during a descent. Rotorcraft according to claim 11, characterized in that the lateral force generating device ( 48 ) about a longitudinal axis (L) of the rotorcraft ( 10 ) is pivotally mounted. Rotorcraft according to one of Claims 9 to 12, characterized by a drive unit ( 40 ), which is designed to carry out a method according to one of claims 1 to 7.