Longitudinal Handling Qualities Research Articles

MODELLING FRAMEWORK FOR FLIGHT DYNAMICS OF FLEXIBLE AIRCRAFT

The flight dynamics and handling qualities of any flexible aircraft can be analysed within the Cranfield Aircraft Accelerated Loads Model (CA2LM) framework. The modelling techniques and methods used to develop the framework are presented. The aerodynamic surfaces were modelled using the Modified Strip Theory (MST) and a state-space representation to model unsteady aerodynamics. With a modal approach, the structural flexibility and each mode’s influence on the structure deflections are analysed. To supplement the general overview of the framework equations of motion, models of atmosphere, gravity, fuselage and engines are introduced. The AX-1 general transport aircraft model is analysed as an example of the CA2LM framework capabilities. The results showed that, according to the Gibson Dropback criterion, the aircraft with no control system lacks the stability and its longitudinal handling qualities are unsatisfactory. Finally, the steps for future developments of the CA2LM framework are listed within conclusions.

Examining the stability derivatives of a compound helicopter

ABSTRACTSome helicopter manufacturers are exploring the compound helicopter design as it could potentially satisfy the new emerging requirements placed on the next generation of rotorcraft. It is well understood that the main benefit of the compound helicopter is its ability to reach speeds that significantly surpass the conventional helicopter. However, it is possible that the introduction of compounding may lead to a vehicle with significantly different flight characteristics when compared to a conventional helicopter. One method to examine the flight dynamics of an aircraft is to create a linearised mathematical model of the aircraft and to investigate the stability derivatives of the vehicle. The aim of this paper is to examine the stability derivatives of a compound helicopter through a comparison with a conventional helicopter. By taking this approach, some stability, handling qualities and design issues associated with the compound helicopter can be identified. The paper features a conventional helicopter and a compound helicopter. The conventional helicopter is a standard design, featuring a main rotor and a tail-rotor. The compound helicopter configuration features both lift and thrust compounding. The wing offloads the main rotor at high speeds, whereas two propellers provide additional propulsive thrust as well as yaw control. The results highlight that the bare airframe compound helicopter would require a larger tailplane surface to ensure acceptable longitudinal handling qualities in forward flight. In addition, without increasing the size of the bare airframe compound helicopter’s vertical fin, the Dutch roll mode satisfies the ADS-33 level 1 handling qualities category for the majority of the flight envelope.

Cybernetic Approach to Assess Aircraft Handling Qualities

This paper presents the experimental behavior measurement method, a novel aircraft handling qualities evaluation method, that enables an objective evaluation and eliminates a number of the disadvantages of current handling qualities assessment methods. The experimental behavior measurement method tries to overcome the omissions of the handling qualities during tracking method and is complementary to the Cooper–Harper rating method. The experimental behavior measurement method determines the aircraft handling qualities based on measurement of the control behavior during target-tracking tasks with an increasing level of difficulty. The main metric of the experimental behavior measurement method is the crossover-regression frequency. This paper will provide the theoretical background of the experimental behavior measurement method and a case study that shows the application of the method. The case study evaluates the effect of the amount of aeroelasticity on the longitudinal handling qualities of three aircraft models, although the experimental behavior measurement method is not limited to aeroelastic handling qualities. The experiment was performed in amotion-based flight simulator with eight Royal NetherlandsAirForce test pilots. The results of the case study revealed significant changes in the crossover frequency matching the altered handling qualities.

A generic control anticipation parameter for aircraft handling qualities evaluation

AbstractThe established control anticipation parameter longitudinal handling qualities criterion is based on the assumption that the short term dynamic response of the aeroplane is classical, or second-order-like. Modern fly-by-wire aircraft often have longitudinal short term dynamics which are not second-order-like and to which it is difficult to apply the criterion. This paper presents a proposed generic control anticipation parameter which is a modified version of the control anticipation parameter and which may be applicable to both unaugmented and augmented aircraft of all types. The appropriateness of the modified criterion was illustrated by designing a number of command and stability augmentation control laws, constrained to meet the criterion, for application to a medium weight fly-by-wire civil transport aircraft. The handling characteristics conferred by the control laws were assessed in a series of flight simulator trials, the results of which are briefly presented.

Optimum aeroelastic design of helicopter rotors for longitudinal handling qualities improvement

This paper describes an optimization study in which the torsional stiffness of a hingeless rotor blade and its cross-sectional offsets are designed to stabilize the phugoid oscillation of the aircraft by increasing the stabilizing effect of the rotor. The real part of the phugoid eigenvalues is minimized at a specified advance ratio, subject to aeroelastic stability constraints hi forward flight, blade root peak-to-peak load constraints for flap bending and torsion, and a longitudinal cyclic response requirement. The aeroelastic analysis and the flight mechanics analysis are connected indirectly to the numerical optimization algorithm through the use of a sequence of approximate optimization problems. A new algorithm to generate a high quality set of starting vectors is presented. The results of the study show that the combined analysis/optimization program can generate designs that have stable phugoid modes and satisfy all the aeroelastic and flight mechanic constraints.

Aircraft design optimization with dynamic performance constraints

This paper describes an integrated optimization procedure for aircraft design in which multidisciplinary criteria are used as performance measures. A composite objective function consisting of a handling qualities parameter and other measures of mission performance is minimized using an unconstrained optimization method. The design variables may include aircraft configuration variables and control system gains. Three example design problems using this methodology are discussed: tail sizing for minimum trimmed drag with longitudinal handling qualities constraints, wing weight minimization with aeroelastic constraints, and oblique wing design for commanded response decoupling. Results show that the integrated design procedure can achieve performance that exceeds that obtained in a sequential design synthesis.

Application of frequency-domain handling qualities criteria to the longitudinal landing task

Under NASA sponsorship, an in-flight simulation of the longitudinal handling qualities of several configurations for the approach and landing tasks was performed on the USAF/AFWAL Total In-Flight Simulator by the Calspan Corporation. The basic configuration was a generic transport airplane with static instability. The control laws included proportional plus integral gain loops to produce pitch-rate and angle-of-attack feedback loops. The evaluation task was a conventional visual approach to a flared touchdown at a designated spot on the runway with a lateral offset. The general conclusions were that the existing criteria are based on pitch-attitude response and that these characteristics do not adequately discriminate between the good and bad configurations of this study. This paper describes the work that has been done to further develop frequency-based criteria in an effort to provide better correlation with the observed data.

A study of vertical motion requirements for landing simulation.

Tests were conducted to determine the significance of vertical acceleration cues in the simulation of the visual approach and landing maneuver. Landing performance measures were obtained for four subject pilots operating a visual landing simulation mechanized in the Ames Height Control Test Apparatus, a device that provides up to ±40 ft. of vertical motion. Test results indicate that vertical motion cues are utilized in the landing task, and that they are particularly important in the simulation of aircraft with marginal longitudinal-handling qualities. To assure vertical motion cues of the desired fidelity in the landing task, it appears that a simulator must have excursion capabilities of at least ±20 ft.

Higher-order control system dynamics and longitudinal handling qualities

An experimental investigation of the effects of higher-order control system dynamics on the longitudinal handling qualities of a fighter airplane are discussed. This research was undertaken using the USAF/CAL variable stability T-33 airplane as an in-flight simulator. Different higher-order responses were simulated by altering the elevator feel system, elevator actuator, and airplane short-period characteristics. Essentially the same configurations were evaluated by two pilots using a revised pilot rating scale. One pilot also rated the configurations for their pilot-induced oscillations (PIO) tendencies. Comments and ratings were related to a response delay parameter. Many of the higher-order control systems investigated produced pronounced PIO tendencies in flight, and some were considered unflyable with certain higher-order characteristics. A comparison of fixed-base and in-flight evaluations indicated that configurations with significant PIO tendencies were rated poorer in flight, and configurations with little or no PIO tendencies were rated better in flight.

Comments on "Navy Variable-Stability Studies of Longitudinal Handling Qualities"

EFERENCE 1 by J. A. Eney contains a misapplication of criteria which leads to erroneous conclusions. Mr. Eney incorrectly states that his Refs. 5 and 6 both have envelopes that are normalized about a steady-state value that is not defined. We found that it was not feasible to specify a single criterion encompassing both the transient and steady-state responses of the longitudinal control system. We therefore specify a criterion for the transient response and a separate criterion for the steady-state response. The envelopes to which Mr. Eney refers are envelopes for transient responses normalized to their own steady-state value. All responses therefore reach a steady-state value of 1.0. By rescaling his curves in Fig. 10, Mr. Eney will find that most of the 2.5 rated responses fall within the envelope. The conclusions reached by Mr. Eney about the inadequacy of the criteria of Refs. 5 and 6 are therefore highly distorted. The steady-state response is governed by stick force per g in the current military specification. As Mr. Eney pointed out, stick force per g is of little consequence in visual landing approach. This is because vertical acceleration is not predominant due to the pilot during landing approach. We found that stick force per C* provides a steady-state criterion that includes landing approach. The steady state FS/C* criterion described below has somewhat arbitrary limits, but it does show how steady-state criterion can be applied separate from the transient criterion. A forward velocity of 1500 fps was selected to set the Fs/n2 limits between 3.32 lb/gr and 8.85 Ib/gr. The corresponding Fs/C* limits were then found to be 2.62 Ib/g and 7.0 Ib/g and were assumed independent of forward velocity. The variation in Fs/nz limits was then computed as a function of forward velocity corresponding to the constant FS/C* limits. A plot of these limits is shown in Fig. 1. Also included on this plot are values of F8/n, and FS/C* for a typical supersonic fighter.

Navy variable-stability studies of longitudinal handling qualities.

A study of longitudinal handling qualities in the simulated carrier approach was performed at Princeton University in a North American Navion so equipped as to vary its static and dynamic longitudinal stability characteristics. Five Navy pilots flew meatball approaches in 24 configurations and gave ratings using the Cooper scale. Short-period dynamics with frequencies greater than 1.4 rad/sec and damping ratios greater than 0.2 were found to be satisfactory. Control sensitivity was variable and was found to be a critical parameter for some configurations. Stick force per g ranged to extremes and was found to be of little consequence in visual landing approach. A comparison is made with several proposed longitudinal handling qualities criteria, with little agreement. Further work in landing approach, as well as high-speed flight, is currently in progress at the Naval Air Test Center, using a variablestability F-8D. Short-period frequencies ranging from 0.2?r to 4?r rad/sec are being flown through typical tactical mission profiles. The handling qualities of higher-order dynamics, typical of augmented aircraft, are of prime interest, and data will be compared with numerous criteria that have been proposed for the longitudinal dynamics of aircraft.

Longitudinal handling qualities criteria - An evaluation.

Compliance with current longitudinal handling qualities criteria is not a guaranteed acceptance of vehicle characteristics. Several criteria for satisfactory characteristics resulting from handling qualities investigations in simulators and variable-stability airplanes are reviewed; in comparison, these criteria reveal significant areas of disagreement. Further, much of the large-airplane data available that reflect satisfactory characteristics in flight would be judged unacceptable to unsatisfactory from these criteria. Consideration of the piloting technique involved in flightpath control indicates the significance of the parameters La/ 15 g/rad also yield good agreement when mapped onto the nza/0}n vs f plane. These three parameters—nza, La/<j3n, and nza/(j}n—-furnish the framework for complete longitudinal handling qualities criteria. These criteria provide the basis for an over-all correlation of pilot opinion data from four sources: 1) airplane characteristics from fixed-base and inflight simulation of airplanes exhibiting high natural short-period frequency, 2) flight experience of commercial jet transports, 3) fixed-base simulation of the B-52, and 4) inflight simulation of very large transports with low natural short-period frequency on the Boeing 367-80 jet transport prototype.

Simulator investigation of the effects of l alpha and true speed on longitudinal handling qualities

The experimental study conducted was directed toward investigating the effects, on pilot rating and optimum longitudinal control gain, of large variations in the relative amplitude and phase of the basic airplane responses to elevator control and to vertical gusts. The variations in relative amplitude and phase were obtained through changes in true speed and the parameter La = (pSF/2ni)CJr,a. Combinations of V and La were examined for each of three short period poles in a fixed-base simulator. True speed was varied from V = 130 knots to V = 1800 knots and La was varied from La = 0.07 I/sec to 4.01/ sec. The steady state ratio of normal acceleration to angle of attack was found to be of significance both to the flying qualities of an airplane and to the optimum longitudinal control gain. Thus the results of previous investigations of the effect of short period dynamics on longitudinal flying qualities must be qualified since the investigations were conducted at specific values of La and V or nz/a. The longitudinal control gain selected by the pilots was found to be a compromise which weighed the often conflicting requirements for good pitch attitude control, adequate g-limiting protection and satisfactory steady forces in turns. It was demonstrated that the primary factors which determine the normal acceleration response to turbulence are JLa, short period frequency, short period damping ratio, and true speed together with the frequency spectrum characteristics of the turbulence.

Prediction of flutter onset speed based on flight testing at subcritical speeds

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