CH652673A5 - HELICOPTER. - Google Patents

Description

The invention relates to a helicopter of the type specified in the preamble of claim 1.

In particular, the invention relates to positioning or adjusting the blade pitch angle of foldable or collapsible helicopter rotor blades prior to locking the blades in their pitch axis to allow the blades to fold or fold onto the helicopter fuselage when the helicopter is not in use, and to automatic positioning the setting angle of the main rotor blades so that they can be locked in their position before folding.

With some helicopters designed for special purposes, such as helicopters stationed on ships, it has long been known to fold back the main rotor blades into positions on the fuselage of the helicopter when the helicopter is not in use. This makes it easier to park the helicopter in a relatively small space and makes the helicopters, which are parked outdoors, less susceptible to wind gusts and the like during parking.

To fold the rotor blades, it is necessary that each blade take a predetermined position with respect to the blade folding hinge and with respect to the fuselage of the aircraft. Therefore, before folding the rotor blades, the main rotor is rotated to a predetermined position, whereby all blades of the rotor are brought into a position in which they can be folded into a position along the fuselage. The setting angle of each sheet is then adjusted to a desired position, and the sheet setting angle is locked with the aid of pins, so that the setting angle of the sheets does not subsequently change when the sheets are folded.

As is known, the setting angle of the main rotor blades of a helicopter is adjusted by means of bumpers, in that they are raised and lowered with a swash plate, the swash plate being able to tilt to a variable extent in each azimuth direction. This inclination of the swashplate causes the blades to have the nominal collective blade pitch with the desired variable periodic blade pitch superimposed on them. When the rotor blades rotate about the main rotor axis in flight, the bumpers connected to the blades and rolling on the swash plate assume different positions depending on the inclination of the swash plate and the azimuth position of the rotor. Thus, the rotor blade movement when the rotor blades are rotating is achieved by the actual change in the blade pitch as a function of the then existing position of the swash plate. Therefore, adjusting the pitch of the rotor blades prior to folding requires the swashplate to be positioned in a manner similar to that achieved by the pilot operated controls and / or an in-flight flight control system.

In the oldest systems, the blade adjustment snap pins were generally shifted by fluid pressure and the blade angle positions were advanced and retracted through the use of manual controls [such as the joystick (for periodic blade adjustment) and the blade adjustment lever (for collective blade adjustment)] pivoted back until the setting angle was locked for each rotor blade. The snap pin was able to snap in and thereby prevent a further change in the angle of attack of the rotor blade. However, snap-in pins cause excessive wear during the flight. Hydraulically operated snap pins are also bulky and hinder the possibility of correctly designing the rotor head for a helicopter. Pins actuated by electric motors are well suited for the rotor head construction, but it is necessary that the

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Enough time for pencils to grip the sheets while holding them in the correct position. This would require the use of pilot lights that indicate to the pilot the correct blade pitch positions for the pen bezel, with the pilot moving the controls very slowly to obtain indicators and to make minute adjustments to the pitch position after the pilot lamps have lit up until the pin is reached. A modern type motorized leaf folding lock has been previously proposed by the applicant (US Patent Application Serial No. 35,364, May 2, 1979).

The object of the invention is to provide a helicopter with an arrangement for automatically positioning the rotor blade pitch angle to facilitate the folding of the rotor blades.

This object is achieved by the features specified in the characterizing part of patent claim 1.

According to the invention, a flight control system of a helicopter provides commands to the pitch, roll and collective blade adjustment trim actuators to thereby position the main rotor blade pitch for locking prior to folding the blades. In one embodiment of the invention, the pitch, roll, and collective trim commands are provided for stored pitch, roll, and collective trim reference values that were determined to be correct in an earlier sheet folding process, and further for reference values for the positions of the swash plate servo devices that are at an earlier sheet folding process was determined to be correct. Furthermore, according to the invention, the positions of the servo devices of the swash plate (hereinafter referred to as swash plate servo positions), which are stored and originate from an earlier sheet folding process, are set positions for positioning in response to the pitch, roll and collective trim commands that originate from the previous sheet folding process are stored, used, and the pitch, roll and collective trim commands are updated using a mixer sweep matrix, if necessary, to achieve the swashplate positioning as indicated by the swashplate servo positions indicated at one earlier sheet folding operations have been saved.

According to a preferred embodiment of the invention, the flight control system delivers commands to the pitch, roll and collective trim channels of the main rotor blade pitch control devices in relation to the positions of the swash plate servo devices at a point in time immediately before the rotor blades are folded, the information being in the form of the deviation of these positions is stored from the nominal positions which are stored in a permanent read-only memory and need not be stored in a non-volatile memory. Furthermore, according to the invention, the movement of the desired swashplate position is achieved by calculating the pitch, roll and collective commands that must necessarily be fed to the mixer (which converts these three commands into separate and separate commands that affect the front, rear and lateral commands or obtain side swashplate servos), eliminating the need to store flight commands used in a rotor blade positioning operation for use as a starting point in a later rotor blade folding operation. Furthermore, according to the invention, an integrator is used in each of the swashplate servo channels to determine a desired swashplate position so that the desired rotor blade pitch angle for locking is achieved and long-term, permanent errors are eliminated, with the pitch, roll and collective trim commands the respective swash plate servo position integrators are generated.

According to yet another aspect of the invention, a coupling between the tail rotor blades and the axis of the periodic longitudinal control (or pitch axis) of the main rotor is achieved in a system in which the pitch trim position detector does not show the actual pitch condition but only the pitch condition in relation to the last synchronization of the Yaw trim position.

The invention avoids the need for the pilot to constantly move the reed lever and joystick while waiting for the pins to randomly engage the lock, causing excessive wear. The invention eliminates the need for the pilot to hold the reed lever and joystick in desired positions, indicated by indicator lights on the control panel, while slower pin locking devices can engage the pins. The invention provides a suitable way of prepositioning the angle of incidence of the main rotor blades, so that the use of relatively slow pin engagement devices is possible, without wear.

The invention can be implemented in a number of ways using equipment and techniques within the scope of the following that are within the skill of the art.

Several embodiments of the invention are described below with reference to the accompanying drawings. It shows:

1 is a simplified block diagram of a helicopter rotor blade pitch angle control system using a flight control computer in which the invention described here can be carried out,

2 is a simplified logic flow diagram of part of a flight control system program in which routines relating to the folding of the rotor blades can be achieved when the aircraft is on the ground.

3 shows a simplified logic flow diagram of a sequence or organization program for controlling the operation of a flight control system during rotor blade folding processes,

4 is a simplified logic flow diagram of a rotor blade folding background program from which computer interruptions can reach utilities in the practice of the invention.

5 is a simplified logic flow diagram of a sheet fold position calculation routine;

6 is a modification of the logic flow diagram of FIG. 2, which includes improvements of the invention;

7 is a simplified logic flow diagram of a routine for storing locked rotor blade positions for use in later rotor blade locking operations.

8 is an alternative to the simplified logic flow diagram of FIG. 3 that includes features used in the invention;

FIG. 9 is an alternative to the logic flow diagram of FIG. 5, illustrating a routine for computing sheet folding positions and commands in accordance with the improvement of the invention; and

10 is a simplified logic flow diagram of a routine used to place yaw pedals (tail rotor pitch) in the center position in a system in which the tail rotor pitch position indicator is a function of the trim engagement point.

Referring to Fig. 1, a conventional helicopter with means that allow the practice of the invention has main rotor blades 12, each of which is pivotable about a longitudinal axis depending on the position of an associated bumper (not shown) contacting a swash plate 13. When the main rotor stops, the degree of inclination set

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and the azimuth position of the inclination of the swash plate 13 in combination with the vertical positioning of the swash plate fixes a position for all the bumpers, whereby a special setting angle is set for each rotor blade. When the rotor blades 12 rotate (the swash plate never rotates), the bumpers cause the pitch angle of each rotor blade to change periodically due to its rotation relative to the swash plate 13.

The swash plate 13 is connected by mechanical linkages 14-16 to a plurality of servo devices 17-19, which are arranged at a mutual distance around the swash plate and can therefore control the positioning of the inclination axis, the degree of inclination and the vertical position of the swash plate 13. The mutual distance of the servo devices can change from case to case, but in the example chosen here it is assumed that the servo devices have the usual configuration in which the servo device 17 in front of the rotor axis, the servo device 18 behind the rotor axis and the servo device 19 is arranged laterally from the rotor axis, which is why these servo devices are referred to below as front, rear or lateral or lateral servo devices. To create a closed control loop with feedback and to determine the setting angle of all rotor blades (by determining the inclination of the swash plate 13), several position detectors 20-22 are provided for the servo devices. These position detectors can include potentiometers that operate on a regulated current source, linear differential voltage transformers, or any other suitable type of known position detectors.

The servo devices 17-19 each have a mechanical input part 23-25 from a mixer 26 which receives mechanical input signals 27-29 from each of the three flight control axes, namely the pitch, roll and collective or lift axis. Depending on the particular helicopter in which the invention described here is carried out, these axes have serial actuators or not. For example, the pitch axis input 27 of the mixer 26 is provided with a pitch bias actuator 30 which is arranged in series with a servo device 31, whereas the roller input signal 28 and the collective input signal 29 are supplied directly by associated servo devices 32 and 33, respectively. The servos 31-33 can have direct series inputs for flight control inputs, which can be provided in the same way as the series actuator 30 described below. The servo devices 31-33 are typically power assist servo devices that receive mechanical input signals 34-36 from the two axes of a joystick (for periodic blade adjustment) 37 or a blade adjustment lever (for collective blade adjustment) 38. Movement of the joystick or reed lever therefore moves the input portion of the servo which hydraulically amplifies the movement so that the desired activity is achieved with a relatively small force applied to the joystick 37 or reed lever 38.

The input to each of the servos 31-33 has a suitable electrically controlled trim actuator 39-41 (either an electric motor or a hydraulic actuator) which is connected via an electrical connection 42-44 to a flight control computer 45 by which it is controlled. The issuance of appropriate command signals over connections 42-44 by computer 44 causes actuators 39-41 to control the angle of incidence of the main rotor blades, thereby adjusting the angle when the helicopter is on the ground to prevent it from locking Allow the rotor blades to fold, or to control the flight profile of the helicopter when it is in the air. The

Flight control computers can be in the form of one of the computers that correspond to an earlier applicant's proposal (U.S. Patent Application Serial No. 938,583, August 31, 1978). A computer of this type has output and input connections 46, 47 with a control panel 48, which may include indicators 49 and switches 50 that allow a pilot to interact with the flight control computer 45, and there is a possibility that the computer may have input signals from inertial devices, such as accelerometers and gyros, and various position indicators. 1, these position detectors 20-22 and likewise the position detectors 51-54 (which are assigned to the corresponding actuators and servo devices 30-33) can be connected to the flight control computer 45 via a plurality of corresponding connections 55. The flight control computer 45 may be connected to other aircraft devices via multiplexed inputs and outputs which include, if necessary, an analog conversion, all of which is state of the art and described in the applicant's earlier prior proposal.

The aircraft, although not shown in detail here, can also have a servo-actuated yaw channel 56, which is connected to the flight control computer 45 via connections 57. This channel contains a setting angle bar for controlling the setting angle of the tail rotor blades, the setting angle bar being positioned in a known manner by a servo device. If, as briefly described below, the tail rotor is tilted, as is known from US Pat. No. 4,103,848, there may be a coupling between the yaw axis and the pitch axis of the helicopter, which requires some consideration in the rotor blade folding process. However, the coupling itself is not part of the invention, is conventional and known and therefore does not need to be described further here.

The manner of carrying out the invention will be described using an example of one of the flight control computers which correspond to the applicant's older proposal mentioned above. According to this older proposal, two identical computers work together in a special way; the use of one of them to perform the functions under consideration (without the functions relating to each other among the computers) is easily made possible from the following explanations.

In the computer according to the older proposal, the flight control functions are carried out during special interruptions. To achieve these programs, a general background routine called a background (HG) program is interrupted in real time, and each interrupt causes a particular sequence of utilities to run. The programs relate to generating autopilot commands, stability commands, bias commands, stick or lever commands, and the like. The programs also provide many functions for determining the health of each computer and the health status communicated to it by the other computer to determine the type determine on which the two computers can handle the workload. In one of the routines achieved in the aforementioned computer, functions to be performed when the aircraft is on the ground are achieved in a third autopilot routine (AP 3), which, modified for rotor blade folding, here in Fig. 2 is shown.

In Fig. 2, the four-digit reference numerals are the corresponding reference numerals found in Fig. 14 of the aforementioned older proposal, while the two-digit reference numerals belong to the invention described here. In FIG. 2, the third autopilot routine AP 3 is reached via an entry point 1401, and a test 1402 determines whether the computer in question is operating in a simplex mode or not.

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If not, then both computers work together, and according to the dual computer reliability scheme according to the older proposal, a pitch outside loop calculation 1403 and a collective outside loop calculation 1404 can be carried out. In the older proposal, however, when only one computer is operating, it is not permitted to perform potentially dangerous functions, such as actuating the autopilot, so that calculations 1403 and 1404 are bypassed by an affirmative result of test 1402. However, in an embodiment of the invention in which only a single computer is used, test 1402 can be eliminated so that pitch and collective outer loop calculation routines 1403 and 1404 are always executed. Of course, using a single computer requires further steps to determine the reliability of the computer's operation. In fact, the pitch outside loop calculation is a calculation that provides the pitch trim command signal on line 42 (FIG. 1) using pitch exit routines (according to the older proposal). Likewise, the collective, roll and yaw routines (including the collective loop calculation routine 1404 and other routines according to the older proposal, which are not shown here) provide the trim command signals on connections 43, 44 and 57 (Fig. 1) in a manner which is described in more detail below.

In Figure 2, a test 1405 determines whether the helicopter is on the ground. A status indicator bit or word indicating the pressure on the helicopter wheels is tested, or the rotor is locked, or other factors are tested. If the test 1405 is negative, then the computer can execute air zero routines 1406 that restore the zeros of various inertial sensors, as well as other routines that are not related to the invention. A step 1408 may then transmit failure and error code words to a service indicator and the program will proceed to other functions via a real time return point 1409, which is the type of real time interrupt triggering through which the third autopilot routine of FIG. 2 is reached to to return to a background program. All of the foregoing is described in much greater detail in the context of an entire flight control computer system in the aforementioned older proposal.

If the helicopter is on the ground, which is indicated by an affirmative result of test 1405 in FIG. 2, then a test 60 determines whether or not the execution control mode of the computer is set to a sheet folding mode. In the example described here, the sheet folding execution mode is assumed to include the service execution mode (as opposed to a non-service mode and a maintenance mode as described in the older proposal). The type and the purpose thereof and the type and the fixing thereof are described below with reference to FIGS. 3 and 4. In a first case, the test 60 will normally be negative, so that the leaf folding execution routine 61 (described below with reference to FIG. 3) is reached. Depending on how routine 61 continues, the execution mode of the computer may be switched to the leaf folding mode, in which case routine 61 will lead to leaf folding program 62 by triggering the real time interrupt within which the third autopilot routine of FIG. 2 arrives has been. Subsequently, the basic computer background program is routine 62, and all normal computer functions are accomplished by interrupting routine 62 (as opposed to interrupting a general background program when the computer is in service mode, in which self-tests on the functionality, such as a checksum, for example).

mentestroutine and an intermediate register test, as shown in Fig. 4 of the aforementioned older proposal). In Fig. 2, if the sheet folding execution routine 61 does not determine that the sheet folding operation is ready to be executed, it will lead to other routines, such as ground zero routines 1407, the routine 1408 for transferring the code words to the maintenance indicator, and then the real time interrupt via the real time return point 1409 break up. Later, routine 61 may determine execution in the sheet folding mode, in which case test 60 will be affirmative, resulting in a sheet folding position calculation routine 63, described below with reference to FIG. 5. This is the routine that actually provides the pitch, roll and collective trim commands required to position the main rotor blade pitch so that they can be locked prior to folding.

In Fig. 3, the leaf folding execution routine 61 is reached via an entry point 64, and a first test 65 determines whether a set angle lock release flag has been set or not. On a first pass through the routine of FIG. 3, the pitch lock enable flag will not normally have been set, so a negative result of test 65 will result in test 66. This determines whether the rotor has been rotated further into the desired position for the blade locking, as indicated by a suitable flag bit, and whether the pilot has actuated a blade folding switch. Typically, during a first pass through the routine of FIG. 3, test 66 will be negative, so that multiple leaf folding initiation steps will be accomplished again and again until the rotor has been turned to the correct position and the pilot has engaged the leaf folding switch. The initiation steps include a step 67 for resetting a new values stored flag, a step 68a for resetting a swashplate position initiated flag, a step 68b for resetting a folding start flag (a local flag that is only in the routine of FIG. 3 is used as described below) and steps 68c and 68d to reset a thirty-second timer and a ten-second timer. Then the program will return to the third autopilot routine of FIG. 3 via a return point 70. The short pass through the leaf folding execution routine 61, which only results in initialization steps 67-68d, is carried out whenever the helicopter is on the ground, unless and until the pilot decides to initiate the folding process by first putting the rotor into the correct position Azimuth position for leaf folding rotates and then carries out the very first step, which is to lock the leaf folding switch so that test 66 can give an affirmative result.

In Fig. 3, if test 66 is affirmative, i.e. is positive, a test 71 determines whether the local folding start flag has been set or not. This flag simply ensures that certain functions are performed once and only once in each sheet folding process. Since the fold start flag in test 67 is reset during prefold initialization, the initial pass through step 71 is always negative. As a result, a test 72 determines whether the pilot has engaged a set angle position switch, which is the second stage of sheet folding that is controlled by the pilot. If the switch has not been latched, a negative result of test 72 results in step 73 which provides a signal which causes indicators 49 (Fig. 1) to indicate the setting angle position enable so that the pilot knows that the Sequence has reached the stage where he should snap the set position switch if he wishes to continue the sheet folding process. In this case, step 73 is the only step performed in sheet folding execution routine 61 during the current cycle,

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and the third autopilot routine is returned via return point 70.

In a subsequent pass through the leaf folding execution routine 61, the pilot will later have engaged the setting angle position switch, so that step 72 delivers a positive result. In this case, step 74 causes the trim system to be turned on (i.e., the computer can cooperate with trim valves 39-41, Fig. 1 to adjust the sheet position for the folding operation). Then step 75 resets the set angle position enable display flag set in step 73 so that the pilot knows that his actuation of the set angle position switch has been detected. The folding start flag is set in a step 76, so that the test 71 will be positive in later runs through the sheet folding execution routine 61 and steps 73-76 are therefore bypassed.

In FIG. 3, after the fold start flag has been set, a test 77 determines whether the real-time interrupt (the interruption of the program that causes the third autopilot routine of FIG. 2 to occur) has been triggered;

if not, a step 78 triggers the real time interrupt. This simply requires releasing all interrupts that have the same priority as the real-time interrupts or a lower priority than the same; and the program will simply continue in a manner that does not result in an interrupt return (so that the return to the normal background program that is effective when the computer's execution mode is in the service mode is not achieved). Then, the execution mode of the computer is set to the sheet folding mode by step 79, and the sheet folding background program is reached through a transition point 80.

In Fig. 4, the sheet folding background program 62, which is reached via the transition point 80, is basically a closed loop, which can only be exited by taking the execution out of the sheet folding mode, which essentially ends the sheet folding process. This may be due to changes in operation or failures that may occur, or due to the fact that the pitch angle positioning function of a sheet folding operation has been completed satisfactorily (which is the only function that the flight control computer 45, Fig. 1, during the sheet folding executes). The sheet folding background program 62 begins with a test 81 to determine if the sheet folding operation is still in progress, which is indicated by the sheet folding switch which is still actuating, i.e. is locked or pressed, and by the rotor, which is rotated further. This is the same as for test 66 in Figure 3. If the rotor is inadvertently rotated out of its folding position or if the pilot changes his mind and disengages the leaf folding switch, then a negative result of test 81 will cause the leaf folding background program to step 82 goes to re-synchronize the trim system to the desired trim positions, thereby eliminating any blade positioning that may have arisen as a result of the blade positioning routines that have been run for several cycles before the pilot has changed his mind. Step 83 causes the sheet fold indicator to be reset, step 84 sets the execution mode to the non-service mode, and step 85 causes the program to branch to an initialization portion of the program, at or near that which occurs during a power reset (which is anywhere 4, in the range of steps 400-405 in FIG. 4 of the aforementioned older proposal), in any way that is appropriate, depending on the particular computer and implementation of the invention. Steps 82-85 effectively turn off the sheet folding positioning process and cause the flight control system to initiate normal flight modes again.

In Fig. 4, a second test in the sheet folding background program 62 is test 86, which determines whether any of the tests that have been performed on the trim system have resulted in a failure, resulting in a trim system failure flag being set. If there has been a trim system failure, test 86 will go to step 87 to set appropriate maintenance code words that may depend on the particular nature of the failure and will cause the sheet folding mode to be terminated by steps 82-85. as described above. Another test 88 will determine if the sheet folding positioning has been completed for less than thirty seconds. If not, the positioning process has been taking too long and cannot be completed due to some condition of the helicopter outside the computer or the inability of the computer to create correct positions. In this case, a negative result of the test 88 results in a font 89 which sets a suitable failure code word, and the sheet folding process is ended by the steps 82-85, as described above.

In Fig. 4, the normal way of leaving the sheet folding background program 62 is through a test 91 which tests a flag generated in the manner described below, which indicates that the swash plate has been positioned within the tolerance and therefore the sheet pitch angle positioning for a sheet folding operation is successful has been completed. A positive result of step 91 leads to step 93, which sets a set angle lock release flag; this is a flag indicating the successful completion of the blade pitch positioning and releasing pitch lock motors to drive the pitch lock pins so that the set blade pitch angle is maintained during the folding process. Then, the sheet folding positioning process of the computer is ended by steps 82-85 as described above.

Generally, after the leaf folding background program 62 of FIG. 4 has entered transition point 80, it will continuously go through tests 81-86, 88 and 91, return to test 81, etc. This is a locked program loop that is only due from test results described immediately above or by program interruptions. The program interrupts are real-time interruptions, causing the computer routine to jump out of the leaf folding background program to execute all normal utilities, including the third autopilot routine of FIG. 2 and the routines reached therein. Therefore, while the flight control computer 45 is actually used to issue commands to connections 42-44 (FIG. 1) to set the swashplate to the correct blade pitch that allows the blades to fold, the utilities, and particularly those, are refer to the sheet folding, all reachable by means of normal real-time interruptions. When these programs have been completed every cycle, the computer automatically branches back to the sheet folding background program 62 by means of an interrupt trigger in the normal manner. All of the routines described above and below make it clear that the only function of the leaf folding program is to monitor the desirability of keeping the computer executing in the leaf folding mode. This is used in the third autopilot routine of FIG. 2 to simply effect the passage through the sheet folding execution program 61 or the passage through the sheet folding position calculation routine 63, as described below. Of course you could

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other programming arrangements can be chosen to provide similar functions, with or without the use of a background program. Again, this may be somewhat dependent on the particular flight control computer used by those skilled in the art to implement the invention.

After the execution program is placed in the sheet folding mode by step 79 within the sheet folding execution program 61 of FIG. 3, each pass through the third autopilot routine of FIG. 2 will cause the test 60 to be positive, so that the sheet folding position calculation routine 63 over an entry point 95 in FIG. 5 is reached. A first test 96 determines whether the position values have been initiated by querying the flag reset in step 86a in Figure 3. If no, step 97 causes the stored pitch, roll, and collective reference values and the stored values the desired swashplate servo positions can be read into the working part of the computer from a non-volatile read / write memory. These are provided in the non-volatile read / write memory at the end of a previous sheet folding process, as described below with reference to FIG. 3.

Then a series of steps 98 cause the nick reference, roll reference, and collective reference values to be used when generating trim commands on connections 42-44 (FIG. 1) equal to the stored pitch, roll, and roll values. and the stored collective values that were determined in the preceding sheet folding process. Then a step 99 sets the position initiated flag that was tested in step 96 so that steps 97-99 are bypassed in later passes through the sheet folding position calculation routine 63.

If any implementation of the invention includes a series actuator, such as pitch bias actuator 30 (Fig. 1), it may be desirable to impose a known position on that actuator so that swashplate positioning repeatability is achieved without any adverse effect from the series actuator. Therefore, a step 100 on each pass through the sheet folding position calculation routine 63 can cause the pitch bias reference value to be equal to the center position of the pitch bias actuator 30 (FIG. 1). This provides a simple method of using the regular pitch bias command generation (such as that shown in the aforementioned older proposal) to open loop, i.e. without returning to the middle position. Then a step 101 will increment the thirty-second timer that was previously reset in step 68c of FIG. 3. Step 102 determines whether the thirty-second timer has been incremented to less than its maximum value; if not, it means that the sheet folding position calculation has taken place over many cycles spanning thirty seconds, which is an indication that something is wrong. Therefore, a negative result of the test 102 will result in a step 103 that sets a failure code group, a step 104 that provides the pilot with an error indication, and a step 105 that forcibly engages the trim system (so that it relates to the 4 as described below as the necessary consequence of an excessive time which ends the sheet folding position operation of the computer can be resynchronized). In this case, the program will return to the third autopilot routine of FIG. 2 via transition point 70.

In a normal case, the thirty-second timer will not have timed out, so test 102 will be positive and will result in a step 106 that increments a ten-second timer. Then a test 107 determines whether the ten-second timer has been incremented a sufficient number of cycles so that it has reached its maximum count or not. If the ten second counter setting is less than its maximum, a positive result of test 107 causes the program to proceed directly to the third autopilot routine via return point 70. This results in ten seconds within which successive computer program cycles can use the reference positions set in steps 98 to cause the generation and use of trim commands, in the manner described with reference to Figure 1 above, so that the swash plate 13 is at desired reference values is set. There is no point in determining whether or not these reference positions have been reached until there is sufficient time for them to be reached. Since the blade pitch positioning system has a response characteristic of 10% of its full adjustment stroke (authority) per second, a time frame of ten seconds will ensure that the rotor blades can be rotated from any blade pitch angle to a desired blade pitch angle within the time frame of ten seconds since 100 % of the full adjustment stroke would be included. If the ten-second timer has been incremented sufficiently to reach its maximum count, test 107 will be negative and cause test 108 to determine whether the series bias actuator, such as a pitch bias actuator, has reached a position equal to a stored middle position. If not, a negative result of test 108 will cause the third autopilot program to be resumed via return point 70. However, if it is assumed that the series actuator can be appropriately positioned within the time frame of ten seconds or shortly thereafter, the test 108 will later be positive and lead to steps 109 which assume the error between the desired swash plate servo positions and the stored swash plate servo positions will determine that they are correct so that leaf locking can occur. A series of tests 110 determine whether all errors in the swashplate servo position are less than 0.2% of the maximum range of positions. If any of them are not within 0.2%, a negative result from one of the tests 110 will cause the position to be corrected via steps 111 and 112. In steps 111, pitch, roll and collective corrections related to the current error in the individual swashplate servos (the front, side and rear) are generated by a matrix related to the function of the mixer 26 (FIG. 1 ) is reversed. In other words, the constants K1-K9 used in steps 111 to cause pitch, roll, and collective correction factors to be generated are those that indicate adjustments to the pitch, roll, and collective commands which are appropriate Adjustments to the positions of the front, rear, and side swash plate servos result, taking into account the effect that mixer 26 (FIG. 1) has on the swash plate servo commands in implementing the helicopter axis commands. This is referred to here as a mixer sweep matrix. Then steps 112 cause the pitch, roll, and collective reference values previously set in steps 98, which control the commands provided to the pitch, roll, and collective trim valves 39-41, to be up to date can be brought about by adding to them the correction factors that were generated in steps 111. The program can then return to the third autopilot program of FIG. 2 via return point 70.

Later, after several passes through the sheet folding position calculation routine 63 of FIG. 5, when the factors that are used and all plant operations

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are correct, the front, rear, and side swash plate servo devices are positioned within 0.2% of the previously stored values, indicating that the blade lock can occur. Tests 110 will therefore be positive, causing step 113 to set a flag indicating the fact that the swashplate has been positioned within tolerance; and step 114 will cause an indication that the blade lock is released so that the pilot can actuate the blade lock pin insertion motors or other devices. The third autopilot routine is then returned via return point 70.

In Fig. 2, the completion of each pass through the sheet folding position calculation routine 63 will result in the code words to the maintenance indicator routine 1408 and the real time interrupt return 1409. This causes the real-time interrupt to be triggered so that the computer returns to the sheet folding background program 62, as shown in FIG. 4. Because the basic loop of the leaf folding background routine consists of only four tests, it can readily be assumed that at computer speeds that are normally encountered, all of these four tests are often performed before the next real-time interruption causes the program to return to the routines. caused by interruptions. It is therefore ensured that the test 91 is made and, since the swashplate-in-tolerance flag was set in step 113, as described above with reference to FIG. 5, this test will be positive. Step 93 will therefore set the set angle lock release flag (which is a significant advance in the routine, as will be described in greater detail below), and steps 82-85 will cause the computer to exit the leaf folder background program and return to the non-service mode for reinitialization purposes . Later, the third autopilot routine of FIG. 2 is reached again during one of the real-time interruptions, and the test 60 will not be negative, so the leaf folding execution routine 61 (FIG. 3) will be reached again. In this case, the test 65 in FIG. 3 will be positive since the setting angle lock release flag has been set in step 93 of FIG. 4. A positive result of the test 65 leads to the reaching of a test 116, in which it is determined whether a local one-time flag has been set, which indicates whether the new values have also been stored or not. First, test 116 will be negative so that multiple tests 117-119 can be achieved to determine if all of the rotor blades have been locked in their pitch. If any of the tests 117-119 is negative, the computer will return to the third autopilot routine via return point 70. Subsequent runs through the third autopilot routine (FIG. 2) leading to the blade folding execution routine 61 (FIG. 3) should later lock all of the rotor blades so that all tests 117-119 will be positive. This will result in a series of steps 120 which will cause the current pitch, roll and collective trim reference values to be saved for use in subsequent sheet folding operations and the end positioning of the front, rear and side swash plate servos for use in a later sheet folding operation becomes. These are the values that are accessed by step 97 in the sheet folding position calculation routine 63 (FIG. 5). After steps 120 are completed, the new values stored flag is set in a step 121. In all subsequent passes through the sheet folding execution routine 61 in FIG. 3, therefore, if the pitch lock release enable flag is still set, step 116 will be positive so that no functions will be performed by the sheet folding execution program.

A system has thus been described which

disc servo devices are positioned using autopilot trim commands so that the blade pitch angle of the helicopter rotor blades can be locked before folding. When the blades are locked, the autopilot trim reference values that have been used to control the swashplate servo are stored for use in a later sheet folding operation, along with the final swashplate servo positions in which the sheets were finally locked.

According to the invention, an improved arrangement for automatically positioning the pitch angle of rotor blades to enable locking prior to folding the rotor blades stores the positions of the swash plate servos that occur at the time the rotor blades are unfolded for use in a later one Sheet folding process. In the embodiment of the invention described below, no autopilot trim reference values are stored for use in later sheet folding operations; instead only the swash plate servo positions are stored and the autopilot trim commands required for the swash plate servo to reach these positions are calculated from the stored positions of the servo devices. This avoids the need to store trim command reference values in the non-volatile read / write memory in which the space is precious. Furthermore, in the embodiment of the invention to be described, the information about the precise swash plate servo reference position is stored as the deviation from the nominal position values. Only the deviations need to be stored in the non-volatile read / write memory, since the nominal values are, in a sense, wired into the computer by being contained in a read-only memory in which the space is not so precious.

The sheet folding positioning described above with reference to FIGS. 2-5 takes place overall during the sheet folding process. In the embodiment of the invention described below, the servo device position deviations are stored at a completely different time for the helicopters, namely at the time at which the rotor blades are to be unfolded or spread. In order to achieve this, the third autopilot program is modified as shown in FIG. 6 so that there are three different paths that the third autopilot program can take when the helicopter is on the ground. In Figure 6, if test 1405 indicates that the helicopter is on the ground, then test 60 can determine whether or not the execution program is in the leaf folding mode. In the normal case it is not in this mode. This leads to the achievement of a test 125 which checks a flag bit which indicates whether the sheets are now being unlocked or not. This flag may be responsive to a spread command switch actuated by the pilot or to some other function at an appropriate point in a procedure of unlocking the sheets after the sheets have been spread out or unfolded for use. During a deployment process, there will be a run through the third autopilot program in which test 125 will be positive. This will result in the program proceeding to a "maintain locked sheet position" routine 126, which will be described below with reference to FIG. 7. However, if the third autopilot routine is not accomplished in a deployment process while the helicopter is on the ground, test 125 will always be negative and will cause the leaf folding execution routine to be accomplished in the manner described above. In the case of the embodiment of the invention described below, however, a sheet folding execution routine 61a is different from the sheet folding execution routine 61 of FIG

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FIG. 3 distinguishes, required, and this routine is described below with reference to FIG. 8.

7, the locked sheet position maintenance routine 126 is reached via an entry point 130. A series of steps 131 produce deviations in the positions of the front, hind and side servos from nominal values of the front, rear and side positions found in a read only memory. This is achieved by reading the values that are displayed by the servo position detectors 20-22 (FIG. 1) and by subtracting the corresponding nominal values read from the read-only memory from these values. A series of tests 132-134 then test each of these deviations to ensure that each of them is less than a maximum allowable deviation. This can be done by comparing the absolute value of each to an unsigned maximum deviation, or by testing each of them to be sure that they are not more positive than a positive value or more negative than a negative value, all of which is known per se. If any of the deviations are too large, a negative result from one of tests 132-134 will cause the locked leaf position retention routine to reach step 135, which will set failure code groups, and step 136, which provides an indication, that there is an error in the arrangement.

However, if all the deviations are less than the maximum allowable value, each of the tests 132-134 will be positive so that step 137 is reached in which a checksum value for the deviations is calculated by adding all three deviations together. The deviations calculated in step 131 and the checksum calculated in step 137 are all stored in a non-volatile read / write memory in step 138. These deviations will therefore be available at a later time when the sheets are to be folded to be used in calculating the necessary flight control system trim commands so that the pitch angle of the rotor blades is adjusted to the positions in which they were located than the deviations have been saved. A step 139 then provides the pilot with an indication that the pitch folding blade positions have been updated so that he can snap a switch to cause the next sheet unfolding sequence to proceed (which is not part of the invention and is not further described here). The program then returns to the third autopilot routine of FIG. 6 via a return point 140.

When the computer repeats a third autopilot routine during normal operations, when the aircraft is on the ground, when the sheet folding has not reached the stage where the computer's execution program is placed in a sheet folding mode, and when the sheets are not being unlocked test 1405 is positive, test 60 is negative, and test 125 is negative, so that the sheet folding execution program 61a shown in FIG. 8 is reached. The only differences between the sheet folding execution program 61a and the sheet folding execution program 61 shown in Fig. 3 is that the storage of values for use in the next operation is eliminated by means of tests and steps 116-121, since these functions instead 7 and during the page unfolding as described with reference to FIG. 7 and, instead of resetting the new values stored flag in step 67 of FIG. 3, initialization includes setting a pedal command to zero in an initialization step 143 . The rest of FIG. 8 is the same and performs the same function as described above with reference to FIG. 3.

In Fig. 8, the sheet folding execution program 61a will not perform any function after the pitch angle positioning has been completed and the sheet folding background program 62 (Fig. 4) has reached step 93 and has set the pitch angle lock release flag. This will cause test 65 (FIG. 8) to always be positive, bypassing the remainder of the sheet folding execution routine 61a.

During the sheet folding sequence control, the sheet folding execution program 61a will later reach step 79 (as described above with reference to FIG. 3), so that execution is placed in the sheet folding mode on the computer. Then, in later passes through the third autopilot routine of FIG. 6, the sheet folding position calculation routine 63a is reached, as described below with reference to FIG. 9. In the embodiment described here as an example, this routine contains a “put pedals into the central position” subroutine 144, as described below with reference to FIG.

In Fig. 9, the sheet fold position calculation routine 63a is reached via an entry point 145 and a first test 146 determines whether or not the swash plate servo positions have been initiated by querying a once-only flag set in the manner described below . On the first pass through the routine, the result of test 146 is negative, so that a series of steps 147 is accomplished to cause the three servo position deviations and their corresponding checksum to be read from the non-volatile memory. Then, in a series of steps 148, values for the desired front, rear and side swashplate positions are set equal to the corresponding nominal positions obtained from the read-only memory. In a test 149, the swashplate position deviations read out in step 147 are added together and the result is compared to the checksum read out in step 147 to see if there is any apparent error in the storage and retrieval of the Swashplate positional deviations have occurred in the non-volatile memory. If the data is still correct, the deviations from the desired positions are added in a series of steps 150. However, if the checksum test 149 indicates an error, then steps 150 are bypassed and only the nominal values can be used as desired values. This use of the nominal swashplate positions causes the servos to adjust the pitch of the rotor blades close to the locking position to assist maintenance personnel in manually adjusting them after initial computer operation or after maintenance. In any event, step 151 sets the swashplate position initiated flag used in test 146, and the swashplate within tolerance flag is reset in step 151a. Therefore, in later runs through routine 63a, tests and steps 147-151a are bypassed, and the program goes from test 146 directly to step 152, which increments the thirty-second timer. A test 153 determines if the thirty-second timer has been incremented to less than its nominal value; if not, it means that an excessive amount of time has passed since the first pass through the sheet folding position calculation routine 63a, so that a negative result of test 153 will lead to steps 154-156, which set failure code words, indicate an error on the control panel and cause the trim to be turned on again to release the resynchronization of the trim after the unsuccessful attempt to position the pitch of the rotor blades for folding.

If the thirty-second timer has not timed out, a positive result of test 153 turns on

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Step 157 reached in which the ten second timer is incremented. A test 158 determines if the ten second timer has been incremented to less than its maximum value. If so, a positive result of test 158 reaches a series of steps 158a to set integrator registers to the desired swash plate servo positions, and further to mid-position pedal subroutine 144, described below with reference to FIG. 10. When subroutine 144 has been passed, a series of steps 159 generates the sweep matrix of mixer 26 using the current integrator values for the front, rear and side swashplate servo devices to provide pitch, roll and collective reference values for use by the computer when generating pitch, roll and collective trim commands to be issued via connections 42, 44 (FIG. 1) to the relevant servo trim actuators 39-41 (FIG. 1). The program will then return to the third autopilot routine via a return point 160. In subsequent passes through the sheet fold position calculation routine 63a, a test 158 will later indicate that more than ten seconds have passed since the first trim reference values were generated in step 159. That is, servos 31-33 (Fig. 1) had ten seconds at this 10% per second speed to achieve up to 100% of their allowable motions, thereby any trim reference value calculated in steps 159 should have been achieved at this point.

When the ten-second timer reaches the maximum, a negative result from test 158 will result in steps 162 which compare the desired swash plate servo positions with the actual swash plate servo positions indicated by position detectors 20-22 (Fig. 1). In a series of tests 163-165, if the swash plate servos are positioned very close to the desired extent, all tests can be positive. However, if any of the servo position errors is greater than 0.2% of the total servo positioning range, then a negative result from any of tests 163-165 will result in steps 166 in which the front, rear and side swash plate servo integrators can be incremented by an integration constant times the corresponding error. This integration is one of the features of the invention, and it avoids any long-term errors, including overshoots, that occur as a result of mechanical errors in trim actuators and linkages that define the swash plate servo positions, and as a result of changes due to non-zero series actuator positioning and Yaw sensor error. In the normal course of events, successive passes through the sheet folding position calculation routine 63a (which is achieved through the third autopilot program in successive computer time interruptions, as described above) will cause the swashplate position servo integrators to be integrated to values that are correct after the sweep matrix calculation (159). , Roll and collective reference values, which bring the system into the desired swash plate servo positions. During the first ten seconds, when steps and tests 162-166 are bypassed, and then when steps and tests 162-166 are performed, center pedal routine 144 (described below with reference to FIG. 10) also executed. Thus, the pedals should later be in the center position, as described below, and later the errors should all be less than 0.2%. A positive result from all three tests 163-166 will therefore lead to a test 168 which determines whether the pedals are actually in the middle position. If not,

the program simply exits via return point 160.

However, if the pedals are in the center position, a positive result of test 168 will result in step 169 which sets the swashplate-in-tolerance flag used in the leaf folding background program of FIG. 4 to the end of the Detect sheet folding mode in the computer. Step 170 commands the blade lock and indicates to the pilot that the blade lock is released.

In the embodiment of the invention described with reference to Figs. 1-5 above, a simple method is shown to open an array in an open loop, e.g. without returning to the center position to eliminate discrepancies in the swash plate servo position due to changes in the row actuator position. There are other design criteria for helicopters that can lead to problems that must be overcome in order to provide the improved pitch angle positioning according to the invention. For example, in the case of an aircraft that has an oblique tail rotor (US Pat. No. 4,103,848), any change in the tail rotor setting and / or speed will affect the pitch axis of the helicopter. There may therefore be a coupling between the tail rotor blade pitch angle commands and the periodic longitudinal control commands to compensate for the effect of the tail rotor on the pitch axis. In a typical case, the coupling is such that there is essentially no effect on the pitch axis when the tail rotor pedals are in the central position, but increments of positive and negative changes can be entered when the pedals are pressed to the right or left . Therefore, the middle pedal position can be taken as a neutral position as far as eliminating the tail rotor coupling in the pitch axis is concerned, to enable the use of the trim system to position the main rotor blade pitch angle according to the invention. In any case where a position detector is directly coupled to the yaw trim servo, the yaw trim servo could be set to a center position in the simple manner described above with respect to the row actuator in FIG. 5. However, in a case where the position detector used to close the servo loop can be snapped into different positions to represent an optionally synchronized trim position, the position detector only shows the relative position with respect to any position of the trim device in which it was snapped into place. The relative position detector therefore provides no indication of where the yaw trim servo is located. In addition, all helicopters have a coupling between the collective blade adjustment and the tail rotor blade adjustment. Another problem that can arise is the inability of a trim system to deliver a command that is equal to 100% of the adjustment stroke (from maximum negative to maximum positive, which is equivalent to controlling the full left pedal to the full right pedal). Therefore, use of the invention described herein requires some degree of consideration of one or more of the above problems.

According to a further aspect of the invention, the middle pedal subroutine 144, which takes the aforementioned problems into account, is reached in FIG. 10 via an entry point 173. In this subroutine, the yaw trim piston is first moved all the way to the left on the left stop (if possible) and then moved back over 50% of the full adjustment stroke, which is indicated by the relative position detector. This overcomes the problem of not knowing the actual trim piston position represented by the relative position detector. However, if the pedals are initially set to or close to the full right position, limiting the trim command will preclude a command signal being sent that is large enough

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to move the pedals fully to the left. Subroutine 144 therefore senses a case where the relative position detector indicates a relative position that is over 90% of the full stroke and will move the piston by 40% of the full stroke, as indicated by the relative position detector. This overcomes the problem of having less than the full adjustment stroke available in the yaw trim channel. In addition, the subroutine of Fig. 10 takes into account that for blade lever positions equal to or greater than 50%, there is a coupling between the blade lever and the yaw pedal stops that can affect the relative pedal positioning related to the stop, which is in the center position pedals Routine to be achieved. If it can be determined that the yaw trim piston has been moved to the left as far as possible, then either a 40% or a 50% adjustment stroke correction is used as a required synchronization position to move the pedals to or near the center position move.

A first test in subroutine 144 of FIG. 10 is a test 174 to determine if any pedal command has been generated. There is no pedal command during the initial stages of the subroutine since it is reset to zero in initialization step 143 (FIG. 8). Therefore, a positive result of test 174 leads to the part of the program that tries to move the yaw trim piston fully to the left so that it can be moved back from there to the center position using a relative position detector. Step 175 resets the pedal-to-center flag, which is queried later in test 168 (FIG. 9); when this subroutine completes its task, the pedal-to-center flag is set so that the blade lock release signal can be generated. Then a test 176 determines if the pedal force is greater than about 8.9 N; when the pedal force reaches about 8.9 N, this is an indication that the trim tab spring is stretched because the yaw trim piston is pushed all the way to the left. It is therefore known that the pedals have reached a stop. Until this is the case, a test 177 is achieved through a negative result of test 176, in which it is determined whether the relative yaw position exceeds 90% of the total adjustment stroke. If so, this is an indication that its zero position has been set to the pedal position fully to the right or in the vicinity of it and that the trim system does not have a sufficient adjustment stroke to drive the yaw trim piston to the left pedal stop, which is why no display of 8.9 N will be available. If test 177 is negative, a yaw trim sync command is generated that is equal to an original yaw trim sync command plus an increment, which is done in step 178. The increment is sized so that the pedals are ordered to move to the left. This increment can be selected to cause the pedals to slowly move to the left stop in the desired manner. Then, the subroutine 144 will return to the sheet folding position calculation routine 63a of FIG. 9 via a return point 179. On the other hand, if, before sensing 8.9 N in test 176, the relative yaw position exceeds 90% of the full stroke in the left direction, test 177 will be positive, so step 180 will generate a pedal command that is equal to the relative yaw position minus Is 40% of the adjustment stroke, which brings the yaw trim piston back close to the middle position. To the extent that the yaw trim piston is not brought into the central position, the pitch, roll and collective reference signals generated in step 159 (FIG. 9) will be incorrect.

so the swashplate servo errors generated in step 162 will be significant. However, these errors are integrated in steps 166 so that the pitch, roll, and collective reference signals are generated later to bring the swash plate servos into the desired positions. A certain error in the pedal center position can therefore be tolerated according to the invention, namely because of the integration of the swashplate servo error when generating the trim commands.

If, on the other hand, the pedal force reaches 8.9 N, test 176 will be positive, so that a test 181 is reached in which it is determined whether the blade adjustment lever position has been brought to a point below 45% of the adjustment stroke. If not, then no functions are performed in subroutine 144, rather the program returns to sheet folding position calculation routine of FIG. 9 via return point 179. Due to the fact that the blade adjustment angle for the blade locking of the rotor blades is selected in such a way that it corresponds to the collective blade adjustment command, the trimming system will later set the blade adjustment lever position to below 45% of the adjustment stroke with the aid of the collective reference signal generated in step 159. If the collective blade adjustment has been carried out to a point below 45% of the adjustment stroke, a positive result of the test 181 results in a step 182 which causes a pedal command to be generated which is equal to the relative yaw position minus 50% of the yaw adjustment stroke. Thus, the first part of subroutine 144 in FIG. 10 simply tries to move the yaw piston to a known position and then uses the relative yaw position to generate a command to drive the yaw trim piston back to the center position (or near it).

If one of the steps 180, 182 has determined a pedal command, its non-zero state will result in a negative result of the test 174, which results in a step 183 in which the yaw trim synchronization is now set equal to the recently generated pedal command. In any case, this pedal command is a relative pedal command since it is based on the relative yaw position detector. The yaw trim piston is therefore adjusted in a closed circuit with feedback, the loop being closed by the relative position detector. This is done each time through the subroutine using a test 184 which determines whether the relative yaw position, which is now indicated by the relative yaw position detector, is within a certain tolerance of the yaw trim synchronization that is commanded repeatedly in each cycle. If the relative yaw position is equal to the given command, step 185 sets the pedal-to-center flag used in the sheet folding position calculation routine of FIG. 9. Depending on the starting conditions and the response times of the different parts of the arrangement, it is possible that the swashplate is positioned almost correctly before the pedals are in the middle position; in this case, the final positioning achieved by the sheet folding position calculation routine of Fig. 9 can only eliminate the errors resulting from the pedals not being in the center position until the pedals reach the center position. In other cases, the pedals can go to the center position long before the swashplate positions are close to their correct setting. In either case, both the swash plate servo positioning and the center position of the pedals are required to effectively recognize that the rotor blades have been correctly positioned by setting the swash plate within tolerance flag in step 169 of FIG 9.

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Claims (5)

652 673 1. Helicopter with foldable main rotor blades (12), the setting angle of which can be positioned by means of bumpers depending on the vertical position and the inclination of a swash plate (13) which interacts with the bumpers, the blades (12) being lockable as a prerequisite for folding at certain setting angles and wherein the swash plate (13) is positioned by a plurality of servo devices (17, 18, 19), each of which can be actuated separately on corresponding output signals of a mixer (26) which in turn receives input signals from pitch, roll and collective channels (27, 28, 29 ), each of which contains an electrically operated trim actuator (39, 40, 41) for emitting a corresponding input signal to the mixer (26) in response to an associated trim command signal (42, 43, 44) from a signal processing device (45), characterized in that that a position detector (20, 21, 22) is provided for each of the servo devices (17, 18, 19) u nd each provides a servo position signal indicative of the position of the corresponding servo device (17, 18, 19) and that the signal processing device (45) includes means (120) for storing a plurality of pitch, roll and collective reference signals which are related to predetermined positions of the servo devices (17, 18, 19), in which positions the rotor blade setting angle has the correct value for locking, and for issuing trim command signals to the pitch, roll and collective trim actuators (39, 40) on the pitch -, Roll- or collective reference signals to thereby cause the mixer (26) to bring the servo devices (17, 18, 19) substantially into the predetermined positions, which are indicated by the corresponding servo position signals. 2. Helicopter according to claim 1, characterized in that the signal processing device (45) contains a device for supplying the reference signals by generating reference signals for all desired position signals which correspond to trim command signals which cause the trim actuators (39, 40, 41) Input signals to the mixer (26) so that the servo devices (17, 18, 19) are brought substantially into the predetermined positions, which are indicated by the servo position signals. 2nd PATENT CLAIMS 3. Helicopter according to claim 2, characterized in that the signal processing device (45) contains a non-volatile read / write memory (138) and a read-only memory, in the latter of which the target position signals each in the form of a nominal target position signal and a deviation signal (131), which is the extent specifies in which the associated target position deviates from the position indicated by the corresponding nominal target position signal. 4. Helicopter according to claim 2, characterized in that the signal processing device (45) delivers a plurality of integrator signals (166), each of which is initially generated so that it is equal to a corresponding target position signal in order to deliver a plurality of error signals (162) from each of which indicates the difference between the position indicated by the associated target position signal and the position indicated by the corresponding servo position signal, to modify each integrator signal to an extent that is dependent on the associated error signal and by each of the reference signals in response to the associated integrator signal to generate. 5. Helicopter according to claim 2, characterized in that a device (125) provides a rotor blade signal which indicates the fact that the main rotor blades (12) have been unfolded after folding and are about to be unlocked, and that Signal processing means (45) stores the servo position signals as the target position signals in response to the rotor blade signal.