English Nlr Tr 83150 L Design Guidelines For

ORIGINAL: ENGLISH

NLR TR 83150 L

DESIGN GUIDELINES FOR HANDLIITG QUALITIES OF FUTURE TRANSPORT AIRCRAFT WITH ACTIVE CONTROL TECHNOLOGY by W.P. de Boer, M.F.C. van Gool, C. La Burthe, O.P. Nicholas and D. Schafranek

This report contains the provisional findings of an Action Group created by the GARTEUR Flight Mechanics Group of Responsables to study the handling qualities of future actively controlled transport aircraft. The responses of Industry to a questionnaire drawn up by the Action Group are presented. Based on these, present and future manual control piloting tasks are defined. Handling qualities criteria, currently used in the design of transport aircraft are presented. A flight simulator experiment is proposed to establish their applicability to ACT transport aircraft. It is anticipated that useful handling qualities guidelines for the design of those aircraft will be generated.'

Prepared under the auspices of the Responsables for Flight Mechanics of the Group for Aeronautical Research and Technology in Europe (GARTEUR).

Division: Flight Completed : 840401 Prepared: WCVG/& Ordernumber : 533.002 Approved : "dB/& '&P. : PTP -2-

CONTENTS

PREFACE

LIST OF SYMBOLS AND ACRONYMS 1 INTRODUCTION 2 SUMMARY AND INTERPRETATION OF RESPONSES TO THE QUESTIONNAIRE 2.1 General 2.2 Questions and responses

3 DEFINITION OF PRESENT AND FUTURE MANLJAL CONTROL TASKS

4 EVALUATION OF AVAILABLE ANALYTICAL METHODS DESCRIBING THE PILOT-AIRCRAFT SYSTEM 4.1 General 4.2 Methods available at NLR 4.3 Methods available at RAE 4.4 Methods available at DFVLR 4.5 Methods available at ONERA

5 EXISTING CRITERIA FOR LONGITUDINAL HANDLING QUALITIES 5.1 General 5.2 Criteria using frequency domain characteristics 5.3 Criteria using time domain characteristics 5.4 Miscellaneous criteria

6 THE GENERATION OF NEW HANDLING QUALITIES GUIDELINES 6.1 Objective 6.2 Plan for a simulator investigation 6.3 Data analysis 6.4 Program size and time table

7 CONCLUSIONS AND RECOMMENDATIONS

8 REFERENCES 16 Fimres Appendix A: Terms of Reference

(66 pages in total) PREFACE

An Action Group was created by the GARTEUR Flight Mechanics Group of Responsables with the objective of establishing a basis for handling qualities guidelines for future transport aircraft, taking particularly into account the influence of advanced flight control systems. It is emphasized that the expression "design guidelines" used in the title has been chosen in accordance with the firm intent ofthe Group of Respons- ables not to deal with certification criteria in the present studies.

The Action Group consisted of the following members:

NETHERLANDS

W.P. de Boer National. Aerospace Laboratory (NLR) M.F.C. van Goo1 1

FRANCE

C. La Burthe Office National d7Etudes et de Recherches A6rospatiales (ONERA) UNITED KINGDOM

O.P. Nicholas *) Royal Aircraft Establishment (RAE)

FEDERAL REPUBLIC OF GERMANY

D. Schafranek Deut sche Forschungs- und Versuchsanstalt fiir Luft- und Raumf ahrt (DFVLR)

*) O.P. Nicholas replaced D.E. Fry, who was a member for the first five months. LIST OF SYMBOLS AND ACRONYMS

* C Weighted sum of two aircraft variables Drb Dropback Longitudinal stick force Fe g Acceleration due to gravity G Amplitude of frequency characteristic h Altitude h Altitude command C Altitude error he Gain factor in normal acceleration equivalent Kn Z system approximation Gain factor of the pilot model in the pitch angle control loop Gain factor in pitch rate equivalent system approximat ion Mismatch of equivalent system approximation Normal load factor Limit load factor

Normal load factor measured at the pilot position

Normal load factor change per unit change of angle of attack Pitch rate Laplace variable Longitudinal stick displacement

Time Time-to-peak pitch rate

Time delay of pilot model

Equivalent time delay of normal acceleration response

System time delay Equivalent time delay of pitch rate response Time to double Airspeed Crossover velocity True airspeed

Pilot model transfer function in the altitude (pitch angle) control loop Flight path angle Phase angle Damping ratio parameter of the equivalent system

Pitch angle Pitch angle command

Pitch angle error

Pilot lead time constant

Pilot lag time constant

Numerator time constant used in the equivalent system Angular frequency Undamped natural frequency of the equivalent system

Minimum bandwidth frequency Subscripts e Equivalent s s Steady state

Acronyms

ACT Active Control Technology AG Action Group DFVLR Deutsche Forschungs- und Versuchsanstalt fiir Luft- und Raumfahrt DLC Direct Lift Control FCS Flight Control System HOS High Order System m Head Up Display ILS Instrument Landing System IMC Instrument Meteorological Conditions LOS Low Order System MLS Microwave Landing System NLR Nationaal Lucht- en Ruimtevaartlaboratorium ONERA Office National dlEtudes et de Recherches A6rospatiale RAE Royal Aircraft Establishment RMS Root Mean Square THETA Typical Heavy Electrical Transport Aircraft VMC Visual Meteorological Conditions 1 INTRODUCTION

In order to establish whether there was a need for an Action Group in the area of handling qualities guidelines for future transport aircraft the GARTEUR Flight Mechanics Group of Responsables created an Exploratory Group. The findings of this Exploratory Group have been reported in reference 1 and resulted in the establishment of an Action Group. The Terms of Reference for this Action Group have been incorporated in appendix A of the underlying report. According to the Statement of Work of these Terms of Reference the work performed in the first year was aimed at the definition of present and future manual control piloting tasks (Task-1) on the one hand and the evaluation of available analytical methods describing the pilot- aircraft system a ask-2) on the other hand. The underlying report can be considered as the formal report on Task-1 and Task-2. The information provided leads to a recommendation for the execution of a comprehensive flight simulator programme aimed at the generation of handling qualities guidelines for future transport aircraft equipped with advanced flight control systems.

The outline of the report is as follows: Results of a questionnaire presented to the aircraft industries in the participating countries are given in section 2. Section 3 contains a description of the present and expected future manual control piloting tasks. Section 4 contains a survey of analytical methods, mainly in the form of computer programs, available in the participating institutes, in order to describe the pilot-aircraft system. Because longitudinal control has been selected as the main subject of investigation, existing criteria for longitudinal hanaing qualities to be used in pre and post-experimental analysis, are dealt with in section 5. In section 6 a proposal for the generation of new handling qualities guidelines is presented, based on a simulator investigation. Section 7 contains the conclusions and recommendations. 2 SUMMARY AND INTERPRETATION OF THE RESPONSES TO THE QUESTIONNAIRE

2.1 General A questionnaire was drawn up by the Action Group (AG) at the beginning of 1983 and presented to Industry. In this section a summary and interpretation of the responses given will be presented. Parts of the responses that reflect the existing FAR/JAR requirements have not been mentioned. Responses have been received from the following sources: Aerospatiale (Toulouse) Airbus Industrie British Aerospace, Manchester Div. (pilot's response) British Aerospace, Manchester Div. (engineer's response) British Aerospace, Hatfield British Aerospace, Weybridge Messerschmitt - BBlkow - Blohm Fokker and Dutch certification pilots

Where appropriate the Action Group interpretation of responses is presented after AG:

2.2 Questions and responses

I : Do you think that the next generation transport aircraft will be basically unstable?

Engineers have in mind that the definition of stability may differ according to the case: stability versus speed, angle of attack or Mach number. Some of today's aircraft are already unstable: military, most transport aircraft in the transonic regime, etc... In terms of static pitch stability, there is almost an agreement to concentrate on the neutrally stable aircraft for two reasons : a) basic instability is not necessary for economics b) difficulties with general design: position of wheels, demon- strating reliability of fuel transfer, etc... AG: The static stability of the basic aircraft will be about neutral in cruise conditions, it will be made stable by fuel transfer for landing. The aircraft will never be dynamically unstable.

I1 : Do you think that such aircraft will have handling problems?

Responses agree that by the time such aircraft are certified they will have handling qualities at least as good as those of today's aircraft in a no-failure case. Based on fighter experience, it is anticipated that special care must be taken near the edges of the flight envelope.

111: Is it allowable that handling qualities are degraded after a failure in the primary flight control system?

Everybody agrees that there will be some degradation of handling qualities after failure, and that there must be a relationship between failure probability and the associated degradation in handling qualities that can be accepted. Some have the opinion that in a manual back-up mode situation handling qualities should be at least as good as today's. It is expected by some that the flight envelope will be limited when using a back-up system in order to retain a satisfactory level of handling qualities, such that specific training of pilots on back-up systems can be avoided. Also some concern is mentioned over the possibility that there will be a decrease of piloting skill due to lack of experience with manual back-up modes.

AG: The handling qualities of electrical back-up systems are expected to be at least as good as those of today's mechanically controlled aircraft.

IV : Will future aircraft handle differently from today's aircraft?

The question intended to address handling characteristics, however, some responses consider handling qualities instead. The main opinion is that the handling characteristics will be different but the handling qualities will be the same. Mention is made of more use of automatic modes and of flight condition dependent control laws. Some see the mini-stick and advanced displays as major changes. All-automatic flight is only seen as long-term future.

V : Have any existing aircraft poor handling characteristics? If so, what are they? (e.g. low level of short-period damping, period too long, sluggish response etc.)

Existing transport aircraft are mentioned, having defects that pilots can cope with (poor damping of Dutch Roll, pitch moments due to thrust, sluggishness of engine response, etc .. . ) . The remark was made that old aircraft were probably much worse than today's and would possibly not have been certified today.

VI : Will more use be made of automatic modes?

All agree that automatic modes will be used more and more, however, some say flight is already so automated that little more use can be made unless the flight management system is connected to the autopilot. Some mention the need for automatic systems providing better com- fort for the passengers, better ride qualities for the crew and a reduction of structural loads. Automation of take-off is presented as a possibility but still envisaged with caution, because of failure cases. However, again difficulties are foreseen in the ability of pilots to take manual control after failure.

VII: Are there merits in applying military specifications in the civil field (AVP 970, Mil-F-8785 C)?

The responses to this question varied widely from some who are strictly against their application, to others who consider the use of military specifications to be possibly beneficial as a phi- losophical base providing information, guidelines, etc... Some consider FAR 25 as much better suited to accommodate the new technology.

AG: It is believed that those who oppose using military specifications as guidelines are mainly concerned about the possibility of having to satisfy additional requirements.

VIII: Is pilot workload increasing or decreasing?

There is general agreement that the level of handling workload is low to very low and still decreasing. Some see management workload as low, some as high, but all as increasing. Possible overload is foreseen in the case of complex systems' failure. Some are concerned by the increase of communication workload, especially in the terminal area. It is foreseen that pilots will probably devote more time to flight safety and management. Mention is made of the experience with pilot workload assessment in the efforts made with the forward facing crew cockpit concept.

IX : Is there a need for more accurate performance of piloting tasks (e.g. approach, beam holding, terminal area control, etc.)?

Some respond with a very explicit No, because manual control of the aircraft will be an exceptional case (failure case). The others consider that,if terminal flow is to be increased, greater precision will be required (e.g. microwave landing systems, 4-D navigation ...)

X : Is the pilot adequately informed regarding his performance?

The question was interpreted in two different ways: handling and navigation performance. As far as the first is concerned most responses consider the information as sufficient. Those who considered navigation performance regard information as inadequate for the future on such matters as 4-D navigation, descent information, etc... However, it is also stated that care should be taken that the presentation of the information does not become too complex.

XI : What are the important parameters in measuring performance and pilot workload?

Two questions in one: performance and workload. When performance is understood as system's performance or aircraft's performance, there is a general agreement on measuring it by study of devi- ations of the desired path. However, difficulties exist in defining the desired path, because pilot strategies differ. Many responses did not include answers to the workload question. Those who responded consider it difficult to measure meaningfully. F%ysiological measures, which are still under development and other methods like time line analysis or spare mental capacity are mentioned. Some aircraft manufacturers are developing three kinds of tools for workload assessment: static analysis, dynamic analysis and physiological measures, in case these may be required for future purposes.

XI1 : What emphasis should be placed on the reliability of augmentation systems for relaxed stability aircraft?

General agreement exists on the necessity of having a very high level of reliability. Use can be made of the current FAR 25 failure probability and effect requirements where the probability of a failure must be less than if consequences are catastrophic. A lower level of reliability will be acceptable if the consequences are less serious.

XIII: Would pilots prefer alternative modes of control, e.g. flightpath control?

The general feeling is: Yes, but only as additional modes and only if the pilots see any benefit. For example, to see any benefit from adding flightpath control, it would probably be necessary to provide accurate flightpath information on a head-up display (HUD). Some are doing specific research in the field of system integra- tion, looking for the proper combination of control system mechani- zation and pilot's display. The aim is to establish an adequate definition of the total loop, including pilot, and hence how to train the pilot.

XIV : Is there a case for the mini-controller? Force or compliant?

Almost all responses are positive. In almost all responses the compliant stick is preferred because it provides displacement cues and protection against sharp inputs. It is interesting to mention that introduction of the side-stick in newly proposed aircraft was asked for by the airlines. One negative pilot comment was given due to personal experience with side-stick control. It is mentioned that to provide mechanical synchronization of two sticks, compliance will be necessary. It is recognized that there is a lack of requirements for mini- controllers.

XV : Is it important to include advanced display concepts in advanced flight control system investigations?

All responses are positive, but some are very short (just Yes!). Some mention research being performed on different kinds of flightpath visualisation. Many consider optimization of display content as essential and the influence of the dynamic characteristics of the display as important. Some believe that display of control surface position may be necessary with fly-by-wire flight control systems. XVI : What is the area in which study is needed most concerning future aircraft with advanced controls? Are there areas not mentioned that should be studied?

Again two questions in one. Some decided to concentrate on the areas not mentioned, whereas others mentioned areas already discussed on which attention should be concentrated.

Areas mentioned in order of frequency: - Lightning or electromagnetic protection - Keeping the pilot in the loop, particularly to cope with failure conditions - New modes (direct lift, load alleviation, etc.. .) - Turbulence, wind shear - Cockpit design with side-stick - Design and shaping of the mini-stick - Display formats - Requirements for stability and safety

XVII: Would Industry participate in a GARTEUR handling qualities guideline investigation?

One aircraft manufacturer is ready to share its opinions about today's requirements and proposes to formulate new ones. Some would accept participation at a low level. Others are afraid that the results of the study could develop into handling qualities requirements for certification purposes. Almost all are very doubtful about the usefulness of a general study on the subject .

XVIII: Would Industry participate in a simulation exercise at a later date?

Responses are similar to XVII, but generally less unfavourable. Most pilots would not refuse to participate in a simulator exercise. It is emphasized that it is necessary to have a good aircraft model. Some are prepared to participate by providing aircraft data sets. One aircraft manufacturer is prepared to consider to offer the use of its facilities. The level of participation would depend on its interest in the study.

3 DEFINITION OF PRESENT AND FUTURE MANUAL CONTROL TASKS

Task-1 from the approved terms of reference (29 Sept. 1982) included in appendix A reads:

Definition of present and future manual control tasks including control systems, displays, environment, and performance levels.

The following is a summary of the diverse contributions made to Task-1 during AG meetings.

The AG drew up a questionnaire to seek Industry's views on handling qualities of future aircraft. The questionnaire and a summary of the responses are presented in Section 2 of this report. These responses form the basis for the present section. Discussing the various aspects of Task-1 the AG members, looking at the simulator experiment to be executed as Task-3, decided on the type of aircraft to be used. The AG agreed to take the available data of an existing heavy transport aircraft as a basis for the intended investigations. Configurations both with maximum landing weight and with a low weight were proposed for evaluation. The configuration studied should inherently have relaxed static stability in pitch. Industry regard neutral static stability as the practical limit. Stability augmentation systems will normally provide the pilot with a stable configuration possessing excellent handling qualities.

The inherent stability of the original aircraft would be changed by centre of gravity movement to the rear to produce a configuration having a realistically relaxed stability. At first it was thought that the amount of stability reduction might be limited by the available control power for augmentation purposes, due to realistic and representative limiting values for the deflection and the deflection rate of elevator and stabilizer. However, an initial study showed that this was not the case. The possibility of reducing longitudinal static stability and simultaneously reducing pitch damping by reducing the horizontal tail surface area was considered, but the AG decided that it was not necessary to include this in their studies. The AG members also decided not to deal with the influence of the elastic behaviour of the aircraft on handling qualities.

Only a few tasks are left for manual control because more and more use will be made of automatic control. modes with advanced transport aircraft. Pilots will have to fly manually only in a few flight phases including take-off, emergency approach and landing, overshoot, and special approaches into airfields without suitable ground equipment.

Because the accomplishment of the piloting task is most difficult in terminal flight phases and all aircraft must be landed, independent of the given condition of their augmentation systems, the AG agreed to concentrate on take-off, landing approach, landing, and overshoot. The definition of landing approach piloting task should not be confined to the standard ILS. Since MLS (microwave landing system) will replace today's ILS in the future, the investigations to be carried out by the AG should consider MLS as well as decelerated and curved approaches.

The AG discussed the problems of incorporating a representative model of ground effect and the question of the validity of pilot's assessments of the flare manoeuvre on the simulator. A final decision has not yet been reached on the approach to this aspect of Task-3.

With any stability and control augmentation system handling of the aircraft will be affected by time delays in the control system.

Problems will arise in the case of system failure and degradation of the control system down to a back up system. This will particularly be the case if the degradation involves a mode change, e.g. from flightpath control to pitch-rate control. Therefore the case of flying the aircraft with failed primary FCS is a most important aspect for the definition of the Task-1 piloting task. Due to the possibility that the total primary FCS may fail, the degradation of both longitudinal and lateral-directional control should be considered.

During the discussion of Task-1 the question came up whether the AG should investigate handling problems associated with the failure transients. The AG agreed not to consider this a major problem, assuming that the control system designer would ensure that such transients were innocuous.

The AG discussed non-linear control laws, manoeuvre limiting, etc. While recognising their important implications, it was considered that these were very concept-dependent and would unreasonably expand the AG's work. They were therefore excluded.

An engine failure in combination with an FCS failure would aggra- vate the piloting task. However, this would be a multiple failure case, so the AG agreed to exclude that problem from the investigation.

Future transport aircraft will be equipped with a fully electrical FCS (fly-by-wire) implying the possibility of designing the aircraft's responses, and hence handling qualities, in a desired way. For the purpose of the Task-l formulation the AG decided to: - Define two sets of pitch control laws for the primary FCS, body-rate control and flight-path control. - Define the lateral/directional control law for the primary FCS as roll-rate control with bank angle hold, plus sideslip suppression and bank compensation. - Consider the effects of control system time delays. - Use fixed control loop gains (because only low speed flight phases will be considered). - Concentrate on rigid airplane without manoeuvre load control and gust load alleviation. - Consider the auto-pilot modes, like airspeed hold (autothrottle) as a part of the FCS under investigation. - Define a fully electrical back up system (AG members are convinced that mechanical back up systems will only be used during a transitio- nal period). A back up control system will be defined regardless of the possibility that the primary FCS of future aircraft might be so reliable that a failure would be extremely improbable. Since the back up system should use the minimum of sensors a single rate feedback in each axis, based on a very reliable rate-gyro, is considered as one possible solution. In the pitch loop an integral of rate could be used as a substitute for pitch attitude feedback. Operation of the autothrottle mode in conjunction with the back up system is a parameter to be varied.

The AG agreed that the pilot should use pedals for directional control and a ministick for lateral and longitudinal control. The discussion on whether the ministick should be located in the centre in front of the pilot or at the side of the pilot's seat is still open. An indication of Industry's view on ministick position is the sidestick controller now under investigation (including flight tests) for the use with Airbus A-320. The AG decided that it should be a compliant stick. Because of the importance of the stick characteristics for handling qualities investigations, stick filter design and signal shaping belong to the parameters to be varied, together with the system control laws and time delays.

Advanced displays of future transport aircraft will undoubtedly influence pilots' opinion about the aircraft's handling qualities. Application of head-up displays can provide the pilot with important information, particularly regarding flightpath. For the case of failed augmentation systems, which the AG is dealing with, it is reasonable to assume that the pilot is then dependent on the pure basic instruments. It was decided not to concentrate the AG attention on the field of advanced displays. When investigations are carried out by the AG, use will be made of the most appropriate display concepts available.

The definition of the environment belonging to Task-I can be sub- divided into two areas, first the outside environment, and second the pilot's environment inside the cockpit. The AG agreed that variation of environmental parameters is an essential part of the intended investigations. Atmospheric disturbances like turbulence, discrete gusts and if possible windshear have to be included in any investigation. Attempts should also be made to consider disturbances such as dis- tractions arising from air traffic communication and from failed radio and navigation equipment.

The problem of pilot workload, especially its increase following upon an unexpected situation like the occurrence of a FCS failure, was realized to be important but would not be assessed quantitatively by the AG.

The wording of Task-I also required the definition of performance levels. It has been found to be very difficult to define exact levels, because for instance control strategies of pilots performing the same task are different. One possible way of defining practical performance levels is to use the existing performance requirements for automatic control systems as a general basis. A final decision has yet to be made.

During the preceded discussions the AG has identified and defined many problem areas to be considered in the Task-1 formulation. The AG- members are conscious of the fact that a simulator experiment cannot cover all areas and that the results cannot give answers to all problems. The investigations will be confined to the variation of a few important parameters influencing the handling qualities of aircraft.

The AG recommends that the possibility of a subsequent in-flight simulator experiment to validate some of the conclusions resulting from the ground based simulator experiment should be considered.

4 EVALUATION OF AVAILABLE ANALYTICAL METHODS DESCRIBING THE PILOT- AIRCRAFT SYSTEM.

4.1 General Methods describing the pilot-aircraft system can be used for the purpose of flight control system design in the development phase and for the analysis of an existing system in the certification phase. In all cases the methods are used to predict or to analyse the handling qualities or the performance of a system, based on certain characteristics that are considered valuable. In this section a summary will be given of the available methods in the institutes participating in GARTEUR. In many respects these methods are very similar because the underlying principles are the same. However, differences exist in the applicability of the methods with respect to the longitudinal handling qualities criteria. A summary of relevant existing criteria on longitudinal handling qualities, for which the computer programs mentioned in this section can provide the tools, is presented in section 5.

4.2 Methods available at NLR A software package, called DRACOLA (~esignof Regulator Algorithms for the Control of Linearised Aircraft) has been developed especially for application to the subject under study. The set of computer programs applies the classical control theory methods to multi-input, multi- output, multi-feedback linear time-invariant systems. DRACOLA is primarily capable of general linear system analysis and control system design and evaluation. For any given linear time- invariant system the transfer functions (eigenvalues , eigenfrequencies , residues, etc. ) may be computed. The frequency responses of these transfer functions are available in the form of Bode, Nichols, Nyquist and power spectral density plots. In the time domain, responses to pulse, step-, ramp-, block-type and random inputs may be calculated and plotted.

In the design stage a root-locus technique may be used for quick assessment of the effect of application of feedback loops in a specific system. firthermore it is possible to reduce the order of a system by computing an "equivalent" low-order system approximation.

All characteristics of a system, necessary for comparison with the handling qualities criteria mentioned in section 5, can be computed with a procedure in DRACOLA in a very simple manner. The program package DRACOLA has been written in the programming language FORTRAN-4 and has been implemented on the central computer of NLR, the Cyber 170-855. Plots generated by the program can be dis- played on a PLOT-10 compatible graphics terminal. A description of the program and a user's guide is presented in reference 2.

4.3 Methods available at RAE A software package is available for computer-aided design of flight control systems called TSIM2. The package allows simulation, analysis and design of continuous or discrete control systems based on either linear or non-linear models of the aircraft dynamics. It provides a means of linearising the equations of motion at any flight conaition, after which it is possible to apply a range of linear systems analysis techniques, providing eigenvalues, frequency responses, etc . The following options are available: - Simulation of a set of linear or non-linear dynamic equations. - Automatic trimming for non-linear aircraft simulation. - Mixed continuous and discrete system simulation. - Mixed continuous and discrete system time response generation. - Automatic linearisation of simulation equations leading to: - mixed continuous and discrete system eigenvalue generation - mixed continuous and discrete system frequency response generation - mixed continuous and discrete system integral square error generation - mixed continuous and discrete system transfer function generation - mixed continuous and discrete system pole assignment - Parameter optimisation.

The package is based upon a Fortran-like simulation language for a VAX 11/780 digital computer. When run the package is controlled through a command language that allows the user to change parameters interactively. The package includes graphical output which has been written with respect to a Teletronix 4025 terminal, although the plotting software for this is accessible and may be adapted for different displays. A description of the program and a user guide is presented in reference 3.

4.4 Methods available at DFVLR A number of computer programs for the calculation of handling qualities parameters are available on the Siemens 7.870 computer of Dm. Programs are written in FORTRAN using many subroutines of the internal program library. They are suitable for: - Calculation of transfer function coefficients and the corresponding poles and zeros. - Simulation of the behaviour of nonlinear dynamic systems (plots of time responses to optional inputs), calculation of the eigenvalues of a linearized subsystem. - Determination of the coefficients of transfer functions including time delay. Equivalent low-order systems of given high-order dynamic systems can be derived using maximum likelihood methods. The computed mismatch is compared with gain and phase envelopes, presented by J. Hodgkinson and J.R. Wood (Ref. 4). Handling qualities parameters calculated in connection with the transfer function coefficients are compared with the US military specifications for handling qualities. This program was primarily developed to analyse flight test data recorded on magnetic tape. A description of the program and a user guide is presented in reference 5.

4.5 Methods available at ONERA At the moment no programs comparable to those in the other institutes are available at ONERA. A pilot-aircraft model, different in its approach, has been used some years ago. The program is not yet implemented on the new Cyber 160 computer of ONERA. The ONERA handling qualities research is aimed at making a model of pilot's behaviour in flight which, connected to an aircraft model, can be used to form the basis for a computer program for the study of handling qualities problems and related topics: new displays, new cockpits, workload assessment, etc... It was estimated that in the development of modern aircraft more and more evaluation tools are needed. As opposed to other existing models, single axis transfer functions, or multivariable optimal control techniques, the ONERA model is based on a heuristic approach. That means that the model decides on the actions to be undertaken after an analysis of the proposed situation and a selection of prelearned rules. The process is a discrete one, and is adapted to a multivariable task by means of a seriousness function which is used by the model to select the specific parameter which has to be corrected first. Another specific feature of the ONERA model is the "operating insight". Its meaning is that the model is not considering the real aircraft state for his decisions, but a mental image of it. Updating that image is specific of the flight phase, the used strategy and, in the end, the workload. The pilot model was qualitatively validated by two kinds of tests (it should be noted that an objective validation of such a subjective tool is impossible and meaningless). One was a statistical comparison of the controls deflections of the model with those of human pilots. The other was a study of beam holding performances as the static margin of the aircraft model was progressively decreased. As in real flight, the amount of missed approaches in the model increased rapidly as the static margin approached zero. A more extensive description of the program is presented in reference 6. 5 EXISTING CRITERIA FOR LONGITUDINAL HANDLING QUALITIES

5.1 General The AG required a source of quantitative information on existing handling qualities criteria. The prime documents for this purpose are the US military flying qualities specifications contained in Mil-F- 8785 C (~ef7) and the Standard and Handbook (~ef8) that is proposed as future format for these specifications. In many respects the Standard and Handbook form only a reformulation of the existing Mil-F-8785 C specifications in a more consistent format. The Handbook contains a large amount of design guidance information concerning the application of criteria in the case of aircraft equipped with advanced flight control systems. It is therefore a very valuable source of information on the subject of the Action Group. Since many of the criteria to be presented in this section use definitions from the military specifications, these are presented first.

For application of criteria in the US Military Specifications an airplane shall be placed in one of the following classes:

Class I : Small, light airplanes

Class I1 : Medium weight, low-to-medium manoeuvrability airplanes such as light or medium transport, cargo or tanker

Class I11 : Large, heavy, low-to-medium manoeuvrability airplanes such as heavy transport, cargo or tanker aircraft

Class IV : High-manoeuvrability airplanes such as fighter, interceptor and attack aircraft

Three categories of flight phases, which are referred to in the requirement statements can be distinguished:

Category A : Those non-terminal flight phases that require rapid manoeuvring, precision tracking, or precise flight path control Category B : Those non-terminal flight phases that are normally accomplished using gradual manoeuvres and without precision tracking, although accurate flightpath control may be required

Category C : Terminal flight phases, normally accomplished using gradual manoeuvres and usually requiring accurate flightpath control. Included in this category are amongst others take off, approach and landing

The requirements are stated in terms of three values of the stability or control parameter being specified. Each value is a minimum condition to meet one of three levels of acceptability related to the ability to complete the operational missions for which the airplane is designed. The levels are:

Level 1 : Flying qualities clearly adequate for the mission flight phase

Level 2 : Flying qualities adequate to accomplish the mission flight phase, but some increase in pilot workload or degradation in mission effectiveness, or both, exists

Level 3 : Flying qualities such that the airplane can be controlled safely, but pilot workload is excessive or mission effectiveness is inadequate, or both. Category A flight phases can be terminated safely, and category B and C flight phases can be completed.

The existence of degraded flying qualities (~evel2 and 3) is treated on a probability basis, recognizing various aircraft failure states. Moreover the effect of atmospheric disturbances is incorporated in the qualitative description of the flying qualities by changing the requirements for increased levels of disturbance. Apart from the Military Specifications a number of other criteria have been used with varying degrees of success in the reported handling qualities literature. In general the criteria can be divided into frequency domain and time domain criteria. Frequency domain criteria mainly use characteristics of aircraft transfer functions (often pitch rate and normal acceleration over pitch control input ) , both alone (open-loop) and in combination with a human pilot (closed-loop), as shown in section 5.2. Time domain criteria mainly use time histories of responses of aircraft quantities to step- or block-type manipulator inputs, as shown in section 5.3. Additionally, some criteria that do not fit either of the above descriptions are of importance and these are presented in section 5.4.

In the remainder of this section criteria will be described in more detail. Where possible, emphasis will be put on criteria for Class 11-111 aircraft in Category C flight phases, as this is the main subject of the study.

5.2 Criteria using frequency domain characteristics Criterion I: Aircraft transfer function criterion based on low-order equivalent system approximat ion. (Ref. 7, Mil-F-8785 C: 3.1.12, 3.2.2.1.1, 3.2212 3.5.3 andRef 8, Standard and Handbook: 3.2.1.1)

The background of this criterion is that if the characteristics of the airframe-flight control system combination are similar to those of unaugmented aircraft, the contemporary Military specifications should be applicable. For this purpose the high-order aircraft-flight control system transfer functions should be replaced by low-order "equivalent systems", which have responses most closely matching those of the actual aircraft. The numericai requirements, stated in terms of linear system parameters (such as frequency, damping ratio and time constants) apply to the parameters of that equivalent system rather than to any particular mode of the actual high-order system. Since pitch control and flight path control are vital elements of flying qualities, the equivalent systems for pitch rate q and normal acceleration n (at the centre of rotation) response to pitch control z force input F are used for the definition of criteria as follows: e

The equivalent systems are to be obtained from simultaneous matching of the pitch rate and normal acceleration high-order transfer functions over a frequency range of approximately 0.1 to 10 rad/s. In using reduced-order models the question of allowable mismatch is important. Mismatch is defined as:

'I LOS HOS LOS

where G(oi) = amplitude in dB at frequency w.1

'P(wi) = phase in deg at frequency w.I. Amplitude and phase differences are computed at 20 discrete frequencies between 0.1 and 10 rad/s, evenly spaced on a logarithmic scale.

A value for K equal to 0.02 has been used in many applications. It attaches equal significance to an amplitude mismatch of 1 dB and a phase mismatch of approximately 7 degrees.

The parameters of the equivalent systems can be compared to the following requirements in the Military Specifications:

i Limits for the equivalent short-period damping ratio 5 : 9

CATEGORY A AND C CATEGORY B FLIGHT PHASES FLIGHT PHASES LEVEL MINIMUM MAXIMUM MINIMUM MAXIMLJM

1 0.35 1.30 0.30 2.00

2 0.25 2.00 0.20 2.00

3 T > 6 sec* -- T > 6 see* -- 2 2

T2 applies to the value of an unstable first-

order root (= time to double)

* In the presence of one or more other Level 3 flying qualities, 5 shall be at least 0.05. q ii Limits for the equivalent short-period undamped natural frequency w : n 9

Limits are presented for w as a function of n for each n a 9 combination of airplane class and category flight phase. The boundaries for Category C flight phases are presented in figure 1. For application with the equivalent system parameters an equivalent n can be defined by: a e

A different way to present the requirements using combinations of three equivalent system parameters is shown for Category C flight phases in figure 2. . . . 111 Limits for the equivalent time delay parameters T and T : 9 nz The maximum of the time delays of the pitch rate and normal acceleration equivalent systems shall not exceed the following values :

LEVEL Allowable delay

1 0.10 s

2 0.20 s

3 0.25 s

It should be mentioned that these values are the result of experience with fighter aircraft and that indications exist that the allowable delay for (heavy) transport aircraft is larger.

Criterion 11: Pilotlaircraft closed-loop dynamic performance A: (~ef.9, Calspan-SCR: 3.5.71, B: (Ref. 10, Neal-Smith, Ref. 1 1, Douglas and Ref. 12, NLR). Instead of using only the characteristics of the aircraft-flight control system, these two criteria use a model of the human pilot to close the pitch attitude control loop. Figure 3 shows the model used. The pilot model consists of a gain, a time delay and a compensation element with lead or lag characteristics. The essence of both criteria is to select the pilot model characteristics that provide good closed-loop performance of the pilot-aircraft combination. Good closed-loop performance is obtained if the closed-loop amplitude ratio and phase angle are maintained close to zero up to reasonably high frequencies. The Neal-Smith criterion (B) requires the closed-loop amplitude ratio to stay above -3 dB ("droop" less than 3 dB) and the closed-loop phase angle to remain above -90 degrees up to a frequency indicated as

"minimum bandwidth" : w BW The pilot model compensation parameters (using a fixed time delay of 0.3 s) are selected such that for a given maximum bandwidth (depending upon the piloting task) these performance standards are just met. In doing so it is possible that the pilot-aircraft system has resonant peaks in the vicinity of the bandwidth. The parameters pilot compensation, vpc (phase angle of the compensation element at the minimum bandwidth frequency), and the e system resonance - are used in a handling qualities criterion I Bc I max as shown in figure 4. The boundaries indicated in the figure are a a result of fighter Category A flight phases, using a minimum bandwidth of 3.5 rad/s. In several studies a value of 1.2 rad/s has been used as minimum bandwidth for transport aircraft in landing approach. A shift of the Level 2/Level 3 boundary is proposed by Douglas (Ref. 11) and a shift of the Level l/Level 2 boundary by NLR (~ef.12) as indicated in the figure. The closed-loop criterion in Calspan SCR (A) is conceptually the same but is uses slightly different standards. The pilot model includes a time delay of 0.25 s and minimum bandwidth is defined as 2.5 rad/s for landing and 1.5 rad/s for all other flight tasks. Contrary to the Neal-Smith criterion this criterion does not put a limit to the pilot compensation parameter, and only resonance boundaries of 3 dB for Level 1 and 9 dB for Level 2 flying qualities are indicated in a Nichols diagram as shown in figure 5.

Criterion 111: Pilot/aircraft "inferred" closed-loop dynamic performance (Ref. 13, ~shkenas). This criterion is a simplified version of the closed-loop performance criteria using only the characteristics of the pitch response to pitch control inputs in the neighbourhood of 1 rad/s, including the effects of a (~ilot)time delay of 0.3 s, as indicated in figure 6.

Criterion IV: Bandwidth (Ref. 14, Hoh and Ref. 8, Standard and Handbook: 3.2.1.2). Bandwidth is defined as the maximum frequency at which closed-loop tracking can take place without threatening stability. This criterion is another form of the closed-loop criteria mentioned earlier (Neal- Smith, Calspan SCR), with the difference that instead of specifying a bandwidth and looking at pilot compensation and system resonance, the available bandwidth itself is used as criterion parameter. For this criterion, bandwidth is defined as the frequency for which the pitch attitude over pitch control input transfer function has a phase margin of 45 degrees or a gain margin of 6 dB, whichever frequency is lower, as shown in figure 7. Moreover, the shape of the phase curve at frequencies above the frequency for which the phase angle becomes less than -180 degrees is used to estimate the value of system time delay T by assuming that P all phase lag beyond -180 degrees is caused by time delay. The bandwidth criterion is presented in the form of boundaries in a plot of time delay versus bandwidth and the proposed criterion for Category C flight phases is shown in figure 8.

Criterion V: Precision flightpath control (~ef.12, NLR). This criterion was introduced to explain the results of experiments in which the manoeuvrability of transport aircraft with a low value of the normal acceleration sensitivity was enhanced through the application of blended direct lift control, but it can be used to indicate the flightpath tracking ability of any aircraft. The principle of this criterion consists of establishing the available altitude loop bandwidth, once the pitch attitude inner-loop has been closed by a pilot model, such that "satisfactory" inner-loop characteristics are obtained. (For transport aircraft in landing approach the Neal-Smith pilot model for a bandwidth of 1.2 rad/s can be applied). Assuming a "series" model pilot-aircraft altitude loop closure, as indicated in figure 9, the available altitude loop bandwidth can be computed using the frequency for which the closed loop phase angle reaches -90 degrees. The results of reference 12 indicate that for Level 1 handling qualities in the landing approach, the altitude loop bandwidth should be larger than 0.5 rad/s.

Criterion VI: Attitude/flightpath consonance (Ref. 15, Hanke and Ref. 8, Standard and Handbook 3.3.1.1 ) This criterion is directed at flightpath control, assuming that the pilot has to close a pitch attitude inner loop to control flightpath angle. It uses the phase angle between flightpath and pitch attitude at the short-period frequency. It is based on the experience that when a pilot controls flightpath by pitch attitude a clear separation of the bandwidths between pitch- and flightpath loops is important and that the path response should lag the attitude response. A transformation has been performed of the Mil-F-8785 boundaries for Category C flight phases, as presented in figure 1, into boundaries in a plane of equivalent short-period frequency versus phase angle between flightpath and pitch attitude at the equivalent short-period frequency as shown in figure 10.

5.3 Criteria using time domain characteristics The time response criteria mainly use boundaries on the form of the responses of aircraft variables to Step control inputs. In most cases a normalization of the response with respect to the steady state value is required. However, because the criteria are mainly directed at the short-term aircraft response, it is important that the steady state value does not include the influence of long-period (phugoid) aircraft modes. For that reason it is advisable to compute the responses from two degrees-of-freedom equations of motion. (constant speed approximation) .

Criterion VII: Aircraft open-loop time response (~ef.9, Calspan-SCR: 3.5.6.1, 2 and 3) This criterion uses boundaries on the form of the pitch rate response to a step input of pitch controller force. The response, calculated from two degrees-of-freedom equations of motion (i.e. with speed constrained) exhibits the characteristics indicated in figure 11.

Time t, from the instant of the step input to the time corresponding to the intersection of the maximum slope line with the time axis is considered as an equivalent time delay and shall be within the limits specified in Mil-F-8785 C.

Time t is measured from the instant of the step input to the time 2 corresponding to the intersection of the maximum slope line with the steady state line. The rise time parameter, defined as the difference between t2 and t, shall have a value between the following limits: =true airspeed in m/s) : (VT

Nonterminal Flight Phases Terminal Flight Phases

Level Min At Max Level Min At Max

1 1 2.746At< -152.4 =_

2 m5,A,, -487.7 2 Da~t,-196.6 v~ v~ v~ v~

The transient peak ratio, defined by the ratio of q1 and q 2' being the maximum pitch rate minus the steady state and the steady state minus the first minimum respectively, shall be equal or less than the following:

Level

0.85 Criterion VIII: C* time history envelope (Ref. 16, Tobie) The C* variable is composed of a weighted sum of normal acceleration at the pilot station and pitch rate as follows:

The relative contributions of normal acceleration and pitch rate vary with velocity as a result of the inherent variation of the two mathematical expressions for the two transfer functions. The velocity for which the steady state contributions from each term in the ex- * pression for C are equal is called the crossover velocity V This CO . criterion as presented in reference 16 for a crossover velocity of 122 m/s is presented in figure 12.

Criterion IX: Large supersonic aircraft (Ref. 17, Sudderth) For low speed flight phases this criterion consists of envelopes in time histories of pitch rate to step pitch controller inputs plus additional constraints on the time to reach maximum pitch rate and total pitch damping for landing approach, as indicated in figure 13.

Criterion X: Shuttle pitch rate time history envelope (Ref. 18, Rockwell) This criterion used in the development of the closed-loop flight control system of the Space Shuttle for the terminal flight phase consists of a time history envelope for the pitch rate response to a step pitch control input as indicated in figure 14. Comparison of this criterion with the Supersonic Aircraft criterion shows that in the Shuttle criterion much less pitch rate overshoot is allowed.

Criterion XI: Dropback (Ref. 19, Gibson) Another criterion concerned with characteristics of the pitch rate response to a step pitch control input is using pitch attitude "dropback" or "overshoot" (the inverse of dropback) after the input is removed. Figure 15a shows the pitch rate and pitch attitude response to a block input for different amounts of dropback. Gibson has proposed boundaries in a plane of normalized dropback and pitch rate overshoot ratio, based on fighter up and away precision attitude tasks as shown in figure 15b.

Criterion XII: Rise time and settling time (~ef.12, NLR) Results of experiments using transport aircraft equipped with pitch rate command/attitude hold flight control systems controlled by side stick controller have resulted in boundaries for pitch rate rise time and settling time as shown in figure 16. The definitions of rise time and settling time adopted for this criterion are the following:

Rise time = the time in which the pitch rate response to a step control input reaches 90 percent of the steady state value. Settling time = the time after which the pitch rate response remains within 10 percent of the final steady state value. Level 1 handling qualities are obtained if rise time is less than 1 second and if settling time is less than 4 seconds.

5.4 Miscellaneous criteria

Criterion XIII: Longitudinal static stability (Ref. 7, Mil-F-8785 C: 3.2.1.1 and Ref. 8, Standard and Handbook: 3.4.1) For Levels 1 and 2 there shall be no tendency for airspeed to diverge aperiodically when the airplane is disturbed from trim with the cockpit controls fixed and with them free. This requirement will be considered satisfied if stability with respect to speed is provided through the flight control system, even though the resulting pitch control force and deflection gradient may be zero. For Level 3 the requirement may be relaxed, however, in no event shall its time to double be less than 6 seconds.

Criterion XIV: Steady manipulator forces in manoeuvring flight (~ef.7, Mil-F-8785 C: 3.2.2.2.1, Ref. 8, Standard and Handbook: 3.2.9.1 and Ref. 9, Calspan SCR: 3.5.12) The steady-state "stick force per g" requirement is based on the premise that it represents a necessary tactical cue for elevated values of load factor. Low values of stick force per g result in excessive sensitivity with a tendency toward exceeding the airplane structural limites. High values lead to pilot fatigue during manoeuvring. At constant speed in steady turning flight, pullups and pushovers, the variations in pitch control force with steady state normal acceleration shall have no objectionable nonlinearities within the normally used load factor range (specified more precisely in the references). The force gradients are required to be within the limits of the following table for one-handed centre stick controllers: (nL = limit load factor)

Level Maximum Gradient, Minimum Gradient (Fe/n)max, pounds per g pounds per g

1 -24 0 The higher of n 21 a - but not more than 28.0 n -1 L nor less than 56 * and 3.0 n -1 L

2 360 The higher of n 18 a but not more than 42.5 n -1 L nor less than 85 and 3.0 n -1 L

3 56.0 The higher of -12 n -1 L and 2.0 * For nL<3, (Fe/n),,, is 28.0 for Level 1, 42.5 for Level 2.

Since the range of acceptable force gradients for side stick controllers varies with the control-deflection gradient and the signal shaping the contractor is required to show that the control force gradients produce suitable flying qualities. Flight tests in the usAF/calspan variable stability T-33, in air-to-air tracking indicate that the Level 1 area for side stich controllers is close to that for centre stick controllers, i.e. 2-14 lb/g.

Criterion XV: Dynamic manipulator forces in manoeuvring flight (~ef.7, ~il-~-8785C: 3.2.2.3.1, Ref. 8, Standard and Handbook: 3.2.9.2 and Ref. 9, Calspan SCR: 3.5.9) This requirement accounts for the possibility that stick force per g for high frequency inputs may be reduced considerably below the steady state limits in criterion XIV, thus possibly leading to pilot- induced oscillations. It is directed against unfavourable characteristics of artificial feel systems (e.g. bobweights). The frequency response of normal acceleration at the c.g. to pitch control force shall be such that the inverse amplitude is greater than the following for all frequencies greater than 0.5 rad/s (Calspan SCR) or 1 rad/s (Military Specifications):

Centre stick controller (one handed operation):

LEVEL Maximum gradient F /n e 14 Level 1 n-1 lb/g L

-12 Level 2 n -1 lb/g L

8 Level 3 n-1 lb/g L n = the limit load factor. L

In addition, the cockpit control position shall not lead the pitch control force for any frequency or force amplitude.

Criterion XVI: Compatibility of steady manipulator forces and pitch acceleration sensitivity (Ref. 9, Calspan SCR: 3.5.8, Ref. 12, NLR) This criterion recognizes the fact that the control gains for pitch attitude control and steady manoeuvring must be compatible. The product of the control force per g at the pilot position in steady manoeuvring flight and the maximum amplitude of the transfer function of pitch acceleration over stick force shall not exceed the following limits:

e Calspan SCR NLR transport Fe X- n Non terminal Terminal Terminal Fe ss max flight phases flight phases flight phases

Level 1 Q 3.6 rad/s2.g Q 2.5 rad/s2.g Q 0.7 rad/s2.g

Level 2 and 3 Q 10 rad/s2 .g Q 3.6 rad/s2 .g -

The limits are independent of the type of controller.

6 THE GENERATION OF NEW HANDLING QUALITIES GUIDELINES

6.1 Objective The objective of the AG is to generate handling qualities guidelines for the design of future heavy transport aircraft with active control technology. A flight simulator experiment is proposed to provide information which will permit existing criteria to be critical- ly reviewed and if necessary new ones to be proposed. The studies should cover all major system elements, including flight control systems, displays and inceptors. Through post- experimental analysis of recorded pilot ratings and performance data, regions in suitable formats defining areas of desirable handling qualities should be established. -39-

6.2 Plan for a simulator investigation

6.2.1 Simulator description: The NLR moving base flight simulator is proposed for the intended investigations. The simulator facilities include a side by side two man cockpit with a conventional instrument panel, pedals for directional control and a compliant side stick controller for roll and pitch control. A TV-terrain model visual system provides the pilot with outside view. The symbols of a head-up display (HUD) can be superimposed on the visual scene presented to the pilot.

6.2.2 Simulated aircraft: The AG proposes to simulate a Typical Heavy Electrical Transport Aircraft (THETA) for the GARTEUR investigations, so the available data of an existing civil transport aircraft will be fed into the simulation computer. Although only a low speed model of the rigid aircraft will be used, all known nonlinearities associated with equations of motion, aerodynamic characteristics, actuator dynamics and engine behaviour should be considered. Ground effect influencing the aerodynamic coefficients will be included as far as known. The centre of gravity will be moved to the rear by way of calculation to represent an aircraft with relaxed longitudinal static stability. The flight control system will provide a stable aircraft in all cases. Centre of gravity location and weight of the aircraft are potential parameters to be varied.

6.2.3 Flight control system: Taking into account the assumption that future transport aircraft will be equipped with fully electrical flight control systems (FCS) two sets of control laws, one for a primary FCS and one for a back-up system, have already been designed (based on existing criteria) using the assigned data for the aircraft. Operation of the primary FCS will allow the pilot to fly a rate command attitude hold mode for roll and yaw and either a rate command attitude hold mode or a flightpath command mode for the pitch axis. The system will provide sideslip suppression, pitch compensation due to bank angle and autothrottle. The back-up system will rely upon rate gyro signal feedbacks only, to provide rate command modes for the three control axes. Operation of the autothrottle as part of the back-up system will be a parameter to be varied.

The main parameter to be varied during the intended investigations concerning the influence of FCS lay-out on handling qualities will be the magnitude of time delay occurring due to data sampling and signal processing in the FCS, consisting of sensors, flight control computers and actuators.

6.2.4 Piloting task: Only manual control tasks in terminal flight phases will be considered in the simulator investigations. The evaluation pilot will have to fly manually a landing approach under bad weather conditions (beginning with IMC followed by VMC below a certain height), then possibly perform a go-around and second approach before landing.

A failure of the primary FCS will be simulated during the approach, degrading the longitudinal and lateral control systems down to the back- up system. A mode change from flight path control to pitch rate control will occur in conjunction with the FCS degradation, in those cases where the pilot was making his landing approach using the flightpath mode. The mode of the primary FCS at the beginning of the landing approach, i.e. pitch rate command or flight path command, is a parameter that will be varied.

The landing approach will not be confined to standard ILS; MLS and curved approaches will also be considered in the simulation programme. Take-offs will also be studied. 6.2.5 Displays and instrumentation: Depending on the flight simulator equipment the cockpit instrumentation will be the most appropriate available at the time of the execution of the GARTEUR investigations. Application of a head-up display (HUD) , e.g. for flightpath indication, will be possible through creation and presentation of the corresponding signals on the TV screen used for outside view.

6.2.6 Environment : Various levels of turbulence including discrete gusts and wind shear can be generated by the simulation computer. Intensity and nature of turbulence will be varied to investigate their influence on handling qualities ratings.

6.2.7 Collected data: Pilots1-comments, effort ratings and Cooper-Harper ratings for the aircraft configuration under investigation will be asked and tape recorded using a voice recorder. State variables, flightpath data, signals of the guidance system and control activities will be measured and recorded on magnetic tape during simulation runs. Serial statistical data (mean value, standard deviation, RMS, range, frequency distribution, etc.) will be computed from the recorded data.

It will be checked if heart rate measurement devices can be installed in the cockpit. Analysis of such data can possibly give an objective indication of pilots workload.

6.3 Data analysis Pilot ratings will be compared with the existing criteria and performance measurements will be used to assist the interpretation. If disagreements are apparent, it will be necessary to reject or modify the existing criteria. The AG will then be in a position to propose design guidelines for future ACT transport aircraft. 6.4 Programme size and timetable The programme size will mainly depend on the number of configurations to be evaluated and on the number of pilots who will fly the various configurations. The AG suggests that a total of 100 hours of simulator flying time be provided for the intended programme, which would be executable in a 4 to 6 week period. A minimum of 4 experienced test pilots will be necessary. Up to 5 hours of flying time in the simulator may be reasonable for familiari- zation for each of the pilots. Assuming that all pilots will carry out the whole programme, this means that at least 20 hours per pilot are available for formal evaluation. In order to obtain reliable pilot commentary, 4 replications per pilot per configuration must be taken into consideration. It is estimated that with this set-up a total of 25 to 30 configurations (combinations of experimental variables) can be evaluated.

If a simulator programme of this form is to be executed, the AG proposes the following timetable: ." M 0 * w C* 0 '" Cd 8 $2 .Si '; m aM .d fiF4 3 $ .d ." * 51 $? cd dcd V] * k dX *& cds a aJ $2 MV] 3 OW Ed Cdr~ 2 ms rnd 0 EaJ do kid *Ld F4 U* UaJ Xo'il k%, .dF: k o* CdC aJ hro hm n ao mu a@ ha, ncd a 7 CONCLUSIONS AND RECOMMENDATIONS

The GARTEUR Action Group on handling qualities guidelines for future transport aircraft has completed two of the three tasks specified in the Statement of Work of the Terms of Reference. Task-1 dealt with a definition of the present and future manual control piloting tasks, including, among other things, flight control systems. Because early involvement of Industry in the activities of the Action Group was considered of great importance, aircraft industries within the participating countries were approached with a questionnaire on the subject of Task-I. From the responses to this questionnaire and from discussions held within the Action Group it can be concluded that manual control will be performed only in a few flight phases: take-off, (emergency) approach and landing and go-around. The application of fully electrical primary flight control systems (with an electrical back-up system) in transport aircraft is foreseen, allowing for aircraft designs with higher aerodynamic efficiency due to relaxed static stability. Improvement in handling qualities will be achieved by application of fly-by-wire flight control systems. Task-2 consisted of an evaluation of available analytical methods for describing the pilot-aircraft system. It can be concluded that within the participating institutes ample methods, mainly in the form of computer programs, are available for that purpose. The execution of Task-3 is recommended, consisting of a comprehensive flight simulator investigation to form the basis for the generation of new handling qualities guidelines for the design of future transport aircraft. For this investigation it is planned to concentrate on the handling qualities during the terminal flight phases of a heavy transport aircraft with reduced longitudinal static stability and equipped with a fly-by-wire flight control system controlled by a side- stick. A prime topic will be operation with a back-up flight control system, assuming failure of the primary flight control system. It is proposed to use the moving-base flight simulator facility of the National Aerospace Laboratory (NLR) for this investigation. Some concern was expressed by Industry that the results aimed at by the Action Group could possibly develop into additional requirements to be applied by the certifying authorities. However, the Action Group is convinced that the application of ACT brings with it such wide possibilities that guidelines will be necessary for the design of ACT transport aircraft. Useful, generally applicable, handling qualities design guidelines can be generated as a result of the proposed flight simulator experiment (Task-3).

8 REFERENCES

1. Mooij, H.A., Hanke, D., Fry, D.E. and Leblanc, G.: Handling qualities guidelines for future ACT transport aircraft NLR TR 82072 L, GARTEUR/TP-03 (1982)

2. Geest, P.J. van der: DRACOLA, a software package for application of classical control theory methods to multi-input, multi-output systems. Description and user's guide NLR memorandum vS-83-008 L ( 1983)

3. Winter, J.S., Corbin, M.J. and Murphy, L.M.: Description of TSIM2: a software package for computer aided design of flight control systems RAE TR 83007 ( 1983)

4. Wood, J.R. and Hodgkinson, J.: Definition of acceptable levels of mismatch for equivalent systems of augmented CTOL aircraft MDC Report ~6792(1980)

5. Wulff, G. and Marchand, M.: POLYKO, ein Verfahren zur Bestimmung der Koeffizienten und Totzeiten von Uebertragungsfunktionen aus Frequenzgangwerten DFVLR IB 11 1-83/53 (1983)

6. La Burthe, C. and Cavalli, D. : Rapport technique de synthese sur l'e'tude de modelisation du pilote humain ONERA document 7. Military Specification, Flying Qualities of Piloted Airplanes Mil-F-8785 C (1980) (Criteria I, XIII, XIV, XV)

8. Proposed Mil Standard and Handbook-Flying qualities of air vehicles AFWAL-TR-82-3081 VOL I and IS (1983) (criteria I, IV, VI, XIII, XIV, XV)

9. Chalk, C.R.: Calspan Recommendations for SCR Flying Qualities design criteria (Calspan Report No 6241-F-5 (April 1980) (Criteria IS, VII, XIV, xv, XVI)

10. Neal, T.P. and Smith, R.E.: An in-flight investigation to develop control system design criteria for fighter airplanes, Vol I and 11. AFFDL-TR-70-74 (1970) (Criterion 11)

11. Rickard, W.W.: Longitudinal flying qualities in the landing approach 12th Annual Conference on Manual Control, NSA TM X-73, 170 ( 1976) (Criterion IS)

12. Mooij, H.A., De Boer, W.P. and Van Gool, M.F.C.: Determination of low-speed longitudinal manoeuvring criteria for transport aircraft with advanced flight control systems NLR TR 79127 U ( 1979) (Criteria 11, V, XII, XVI)

13. Ashkenas, I.L., Hoh, R.H. and Craig, S.J.: Recommended revisions to selected portions of Mil-F-8785 B (ASG) and background data AFFDL-TR-73-76 ( 1973) (Criterion 111)

14. Hoh, R.H., Mitchell, D.G. and Hodgkinson J.: Bandwidth - A criterion for highly augmented airplanes AIM paper 81-1890, (Aug 1981) (Criterion IV) 15. Hanke, D., Wilhelm, K. and Lange, H.-H.: Handling qualities aspects of CTOL aircraft with advanced flight controls AGARD-CP-333 criteria for handling qualities of military aircraft .(1982) pp. 10-1 to 10-17 (Criterion VI)

16. Tobie, H.N., Elliot, E.M., and Malcom, L.G.: A new longitudinal handling qualities criterion Proceedings of the 18th National Aerospace Electronics Conference (NAECON), Dayton (1966) (Criterion VIII)

17. Sudderth, R.W., Bohn, J.G., Caniff, M.A. and Bennet, G.R.: Development of longitudinal handling qualities for large advanced supersonic aircraft NSA CR-137635 ( 1975) (Criterion IX)

18. ~e~uirements/Definition Document; Flight Control, Part 1: Configuration, performance and functional requirements Rockwell International Space Division Report SD 72-SH-0105, Vol. 1, Book 2, Part 1A (JU~Y 1977) (Criterion X)

19. Gibson, J.C.: Piloted handling qualities design criteria for high-order flight control systems AGARD-CP-333 Criteria for handling qualities of military aircraft (1982) pp. 4-1 to 4-5 (Criterion XI)

Fig. 2 U.S. Military specifications for short-term pitch response to pitch controller for land-based aircraft in category C flight phases FCS PLUS AIRFRAME PILOT

Fig. 3 Definitions used in the pilot-aircraft closed-loop dynamic performance criteria I SLUGGISH RESPONSE. ABRUPT RESPONSE. STRONG PI0 TENDENCIES. STRONG PI0 HAVE TO OVERDRIVE IT. TENDENCIES. STRONG PI0 12 HAVE TO FLY IT TENDENCIES. iSMOOTHLY.

PROPOSEDBY

TO OSCILLATE OR OVERSHOOT

TO PREDICT. TENDENCY TO OVERCONTROL OR DIG IN. HAVE TO OVERDRIVE IT. INITIAL FORCES HEAVY, LIGHTENING UP AS RESPONSE DEVELOPS.

-40 -20 -0 20 40 60 80 PILOT COMPENSATION pp, ((deg)

1) DOUGLAS USES INDICATED BOUNDARIES WlTH wBW= 1.2 rad 1 s 2) NLR USES INDICATED LEVEL 1 BOUNDARY WlTH wBW=1.2 rad 1 s

Fig. 4 Neal-Smith criterion format 30

20 CLOSED LOOP RESONANCE

(dB)

-10

RE PERMITTED BELOW THIS LINE

-20

-30 -240 -180 -90 0

Fig. 5 Calspan SCR closed-loop criterion format (Nichols diagram) Fig. 6 Inferred closed-loop criterion Fig. 7 Definition of Bandwidth Frequency, w BW From Open Loop Frequency Response

LEVEL 2

0 1 2 3 4 5

WBW (rad / s)

Fig. 8 Bandwidth Requirements Fig. 9 Block diagram of series closure structure for altitude control

Fig. 10 Conversation of MIL-F-8785 C CAT. C requirements into the y/8-Phase diagram of the attitude/flightpath consonance criterion TANGENT AT MAX SLOPE k?? TRANSIENT PEAK RATIO

t, EFFECTIVE TIME DELAY At EFFECTIVE RISE TlME

1 2 3 TlME (sl

INTERSECTION OF MAX. SLOPE LlNE AND ZERO AMPLITUDE t, INTERSECTION OF MAX. SLOPE LlNE AND STEADY STATE t,

Fig. 11 Definition of parameters used in the Calspan SCR time response criterion * : "It Fig. 13 Large advanced supersonic aircraft criterion

Drb=DROPBAC

0 DEG OVERSHOOT

TIME Fig. 15a Responses for various amounts of "dropback"

OVERSHOOT 0 DROPBACK I I I I I I I -0.4 -02 0 0.2 0.4 0.6 0.8 9. A SATISFACTORY B ABRUPT, BOBBLE TENDENCY C CONTINUOUS BOBBLING D SLUGGISH

Fig. 15b Dropback criterion

APPENDIX A Terms of Reference GROUP FOR AERONAUTICAL RESEARCH AND TECHNOLOGY IN EUROPE

GARTEUR +) Terms of Reference for the Action Group on Handling Qualities (29 September 1982)

Title: Handling qualities guidelines for future transport aircraft with active control technology.

I. Objective

To establish a basis for the handling qualities guidelines to be applied to future transport aircraft, particularly taking into account the influence of advanced flight control systems.

The category of aircraft to be considered are those which for manual flight are controlled either through a "manual mode" of the automatic flight control system (AFCS) when no failures have occurred and through a "back-up system" in the case of failure of the AFCS. Application of electrical signal transmission without mechanical back-up is supposed here.

11. ' Statement of Work

Based on the findings of Exploratory Group 2 the need for an Action Group on handling qualities for future transport aircraft with active controls is clearly indicated. The proposed framework of tasks is broken down into two parts. The work to be performed in the first year does not require special facilities (besides the computers already available at the research establishments) and is aimed at the formulation of manual control piloting t- t- (tasks-1) on the one hand and the evaluation of analytical methods -describing the pilot-aircraft system (task-2) on the other hand. These studies culminate in data and information essential for the execution of a comprehensive flight simulator programme aimed at the generation of information on design handling qualities guidelines for a certain category of future aircraft (task-3). This will take place in the second and third year period. A high quality research simulator is required for the execution of such a programme. + ) Based on the proposal for the establishment of an Action Group by the Group of Responsables for Flight Mechanics (20 Nov.'81). Task description:

Task-1 - Definition of present and future manual control tasks including control systems, displays, environment and performance levels ; Task-2 - Evaluation of available analytical methods describing the pilot-aircraft system to be used in pre- and post-experimental analysis of Task-3; Task-3 - Generation through flight simulator experiments of information on design handling qualities guidelines for the category of aircraft given under item I, using the results of Task-1.

Boundaries in suitable formats defininp: areas of

the -.satisfactory handling qualities (for the "manual modes" of the AFCS) and acceptable handling qualities (for the "hack-up system" situation) should be established. Attention should be paid to probability-based procedures.

The breakdown of work between the participating nations is given on page 65.

111. Resources Establishment : Effort, man-months (MM) DFVLR 10 MM/year NLR 10 MM/year + one time extra sim. effort ONERA 5 MM/year RAE 5 MJiI/year

Specialization : Aircraft operation, analytical models of the pilot-aircraft system, handling qualities criteria formats flight simulation.

Use of facilities: Computer facilities (pilot-aircraft models, flight simulator data analysis programs). Research flight simulator (NLR) during the second year: + 150 hrs simulator computer for programme dev~lopment,5 200 hrs total simulator for formal experiment. st nd Other costs: Adequate travel funds; 1 and 2 year up to 6 meetings per year. -64-

IV. Membership

The Netherlands

(see "break-down o work.. page 65) La Burthe .",

United Kingdom

In principle subject-pilots will be drawn from the four nations. Liaison with industry will be through the points of contact for FRG, Neth. and U.K. In France there will only be informal contacts with industry.

V. Chairmanship

The following is proposed: Chairman : de Boer Vice Chairman : Fry The AG will be monitored by the French Responsable for Flight Mechanics.

VI . Timetable

See bar chart attached (page 66). At the end of the first year a detailed review will be made by the Group of Responsables. They will make recommendations to the Executive Committee as to the continuation or termination of the AG activities for Task-3.

VII. Reporting

Brief progress notes will be produced quarterly. The first report (Task 1 and 2) will be produced in the beginning of the second year. rd The second and final report will be published in the 3 quarter of the srd year.

VIII. Security

The meetings will be unclassified as will be all reports also. FRG France Neth. U.K.

Task-1 x x x x

Task-2 x x Formal Report, Task-1 and -2 x x x x

Task-3 Test plan x x x x Simulator-programming/ briefing guide, etc x Check-out x Experiment x Data-report x Computer processing x x Data-analysis, interpr. x x x x Formal Report Task-3 x x x x

Bre-ak-down of work between the participating nations