Aircraft Flight Test Research Articles

Prediction and occurrence of pilot-induced oscillations in a flight test aircraft

Flight testing of a high-performance aircraft was conducted several years ago and again during the past two years. During the first flight tests, a pilot-induced oscillation was experienced in the pitch axis during the time between the landing flare and touchdown. During the more recent flight tests two pilot-induced oscillations were experienced in the pitch axis during up-and-away flight. One of these occurred while the pilot attempted to track a cockpit display. Math models of the aircraft were used with three handling qualities criteria to determine the predicted handling qualities of the aircraft. These predictions were compared with flight test results. The handling qualities criteria used were the equivalent systems, bandwidth, and R. Smith criteria. The handling qualities predicted by each of these criteria agreed well with flight test results. The R. Smith criteria were especially interesting because they predicted the likelihood of pilot-induced oscillation explicitly and correctly and also predicted the frequency of each pilot-induced oscillation correctly. The predictions and flight test results also highlighted the impact that pilot displays can have on handling qualities. g n/a.

Telemetry—a Powerful Tool for Aircraft Flight Testing

This paper describes the Evolution of the Flight Test Telemetry system with Real-time processing capabilities at the Design Bureau of HAL. In this paper is described the development of an Indigenous Telemetry System jointly by ISRO-HAL called “HIPFIT” standing for HAL and ISRO project on Flight Test Instrumentation Telemetry. A brief description is given of the various sub-systems. Their capabilities with applications of the Telemetry Systems to Aircraft Flight Testing and the Real Time processing capability is mentioned. Some grey areas of the Telemetry System are pointed out which commonly occur during the development phase of a project of this nature.

OPERATIONAL CONSIDERATIONS FOR OPTIMUM DEPOSITION EFFICIENCY IN AERIAL APPLICATION OF DISPERSANTS

ABSTRACT The growing worldwide recognition of the value of aircraft for application of dispersants to marine oil spills has resulted in a number of tests and field trials, but they have developed new concerns regarding control of depositional efficiency. These are similar to those extensively studied by the agricultural aviation industry, and involve anything influencing placement of a calculated dosage on a given area with minimum variation or loss due to aircraft turbulence, drift, or other factors. Aerial application of dispersants differs from agricultural practice in the physical properties of the fluids sprayed, the dosage generally required, and operational factors such as altitude, speed, swath, and total area to be covered. Consideration of these may result in need for special mechanical designs or alterations in the spray system. The major requirement for depositional efficiency is the droplet size distribution, which is affected by at least five factors. The most critical are nozzle diameter, viscosity of the fluid sprayed, and its exit velocity relative to the aircraft speed. These, together with pressure and pump rates, result in two shear regimes which are the ultimate controllers of droplet size. This report presents evidence for the above from mathematical model studies, laboratory windstream tests, and flight tests of both piston and turbo-powered aircraft. The data are used to propose a framework of requirements for optimal aerial dispersant application operations.

XH‐59A ABC™ Aircraft Flight Tests at Ft. Rucker, Alabama

The XH‐59A ABC™ demonstrator aircraft is a research vehicle designed to investigate the unique characteristics of the Advanced Blade Concept. The aircraft, shown in Fig. 1, has now completed an extensive flight test programme investigating its full airspeed, altitude, and manoeuvring envelope. Aircraft design was initiated in 1972, with first flight in July 1973, with certain interruptions to review and analyse flight data and make modifications to the aircraft. The culmination of the flight test programme was a 12.7 hour evaluation of the aircraft by the US Army Aviation Development and Test Activity at Ft. Rucker, Alabama. This evaluation is the subject of this technical report. Reference 1 is the Army report documenting their evaluation. The XH‐59A programme has been jointly funded by the US Army, Navy and Air Force, the National Aeronautics and Space Administration, and Sikorsky Aircraft. The majority of funding has come from the Army.

On matching the systems identification technique to the particular application

Several maximum likelihood and multiple regression parameter estimation programs are currently being used at the Langley Research Center of the NASA to analyze aircraft flight test data. Based on this wealth of experience, the pertinent features of these programs are investigated and some of the difficulties involved in their use are discussed. By comparing computational time, data requirements and accuracy needed, a strategy for determining which program can be used to the best advantage of the flight test engineer is discussed.

Guest editorial: Mini-issue in NASA's advanced control law program for the F-8 DFBW aircraft

The six papers in this “mini-issue” are primarily concerned with the synthesis of digital autopilot logic for adaptive stabilization of straightand-level flight. Some of the logic developed in these papers will be implemented on the unique digital fly-by-wire control system of NASA’s F-8 research aircraft as part of an advanced control law research program sponsored by NASA’s Langley and Dryden Research Centers. The need for adaptive control on aircraft has been debated for many years. The alternative of scheduling autopilot gains accordmg to sensed pressure altitude and Mach number (air data) appears to work well for most aircraft and is relatively simple to implement. To my knowledge the X-15 was the only previous aircraft that had an adaptive control system. While it worked reasonably well, there were problems [I]. Curiously, there is little mention of that project in these papers. Adaptive control appears attractive to handle less predictable things such as changes in atmospheric gustiness @articularly wind shears on final approach) and changes to aircraft weight and mass center (e.g., due to unusual loading distributions or dropping of external stores). To make the present task more challenging, some of the authors assumed only rate gyro and accelerometer information were available. NASA stipulated that only subliminal test inputs could be used for identification. Surprisingly, even with these constraints, key quantities like dynamic pressure and pitching moment due to angle of attack are identifiable to about 10 percent accuracy, which is adequate for the designated task. However, it seems unlikely that a commercial or private pilot would fly without functioning air data sensors, and a military pilot would not be too concerned about detectable test inputs if his air data sensors had failed. Furthermore, an aircraft that could afford adaptive control could probably afford inertial measurement units which give accurate attitude and velocity information. Detection and identification of sensor failures is the subject of one of the papers. The need for this type of adaptation is much less controversial and is part of a larger area of concern, namely, designing for reliability. Detection and identification of engine and actuator failures is another subject of current interest. Developing improved methods for identifying stability derivatives from flight tests of new aircraft is also not too controversial. In this connection it is interesting that the present authors clearly recognize the importance of identifying an “equilibrium offset vector” or “trim disturbance” vector. If control were the objective instead of identification, such constant disturbances are, of course, readily handled using integral-error feedback or lag compensation. I believe it is sigmficant that the authors find it important for identification to use either: 1) “fading memory” or “moving window” algorithms or 2) “fictitious noise” such as Brownian motion models for stability derivatives. This appears to be associated with the “undisturbable mode” difficulty which occurs in the design of steady-state Kalman filters [2]. NASA, IFXE, and the present authors are to be commended for this interesting start on using advanced control concepts in an expenmental aircraft. I hope the program continues and gets into other areas such as sample rate reduction, automatic landing, controlling flexible aircraft, gust alleviation, and controlling aircraft with many inputs and outputs.

Remote Sensing of Ocean Color

Remote sensing of ocean color offers the potential of monitoring some of the characteristics of the upper layer of the ocean, on a global basis, by use of sensors on satellites or aircraft. Color sensing has been shown to be of use for parameters such as chlorophyll and sediment concentration and the location and motion of pollutants due to ocean dumping. A major obstacle to remote sensing of ocean color from satellites or high altitude aircraft is backscatter of sunlight by the atmosphere. This backscatter, consisting of reasonably predictable Rayleigh scattering and unpredictable Mie scattering, will constitute the majority of the signal seen by a high altitude sensor. In addition, some of the sunlight scattered from the ocean is scattered out of the sensor field of view by the atmosphere. The result is a low contrast signal with the oceanographic information contained in 20% or less of the total detectable signal. Aircraft flight tests, with concurrent surface truth measurements, have been carried out at altitudes up to 19.8 km with spectrometers and multispectral imagers. Analysis techniques have been developed that allow meaningful, quantitative calculation of ocean water content to be made from the remotely sensed color. The results have led to a satellite sensor, the Coastal Zone Color Scanner, to be flown on Nimbus G in 1978.

The Use of Computers in Flight Testing

Flight testing of modern high performance aircraft has generated an increasingly complex data handling workload and this contributes significantly to the duration and cost of flight test programmes. Automation of this critical data handling process can reduce the high cost of such a programme by reducing its duration. The effects of automation of data flow at the ground station can be enhanced by the use of immediate flight analysis of data telemetered from the aircraft.

Lifting body flight test

The concept of manoeuvrable re-entry vehicles capable of controlled re-entry from earth orbit to tangential landing is attractive to a number of military and civilian space missions. One of the several manoeuvrable re-entry techniques that has been proposed is the lifting body concept. Early studies on lifting body configurations indicated that unpowered horizontal landings would be feasible since subsonic lift/drag ratios of four or better were consistently obtained from model tests in wind tunnels. In 1962 the NASA Flight Research Center initiated a programme to investigate the capability of a pilot to control, manoeuvre, and land a lifting body vehicle. I would like to compare the philosophies and procedures used in the lifting body flight test programme at Edwards Air Force Base with those more commonly used in the flight testing of high performance aircraft. Also I would like to discuss limited results of the M2/F2 flight programme and give one pilot's opinion of the requirements for operational lifting bodies.

Signal Transduction with Differential Pulse Width Modulation

The Differential Pulse Width Modulation System presented here is a signal transduction scheme applicable to a wide range of data acquisition processes for either large systems such as industrial process control, aircraft flight testing, computerized medical information centers, etc. or individual users seeking low cost, compact measuring instruments. In this scheme, a variable capacitance or equivalent sensor, actuated by the physical quantities to be measured, is combined with an integrated circuit containing mainly logic elements, to generate a series of pulses with fixed height in voltage but varying width in time so that the difference/sum ratio of the width between two adjacent pulses is proportional to the input. Signals thus modulated can be converted readily into analog output by simple low-pass filtering and can also control a simple up-down counter to give digital output, bypassing the conventional analog-digital converter. For portable recording, this differential pulse width scheme facilitates the use of inexpensive tape recorders at no sacrifice in accuracy, since there is no need for precision speed control.

Initial military flight tests of the X-22A VSTOL research aircraft

The X-22A aircraft was evaluated to establish the status of its development and its potential usefulness for conducting flight research using a variable stability system. The more significant aspects and results of the tests are covered in this paper. Ground familiarization and planning conducted prior to the flight tests included the use of a fixed-based simulator programmed with X-22A design data. Test techniques were developed and/or refined during both ground simulator work and actual flight tests as necessary to adapt to the unique characteristics of the aircraft. Quantitative and qualitative evaluation of the stability and control characteristics in terms of their effect on the aircraft to perform its intended mission of flight research have shown that it is acceptable in all respects considered. Unusually high sideforce, with no means of variation, was the most detrimental characteristic of the aircraft noted relative to its potential use as a variable stability flight research vehicle.

Cables for aircraft. Pressure-type connections

The paper discusses the techniques adopted by Britain aircraft constructors for terminating cables by pressure-type connections. After a brief historical introduction, the various factors which influence design are dealt with in some detail. The various forms of high-pressure (permanent) connection used for aircraft cables are reviewed. As one type of termination can be used for several different cables, the subject is dealt with under the respective conductor temperatures as stated in BS2G.178. The termination of special-purpose (i.e. thermocouple, screened and r.f.) cables is also described.High-density semipermanent connectors are dealt with briefly and the systems employed for reprogramming multicircuit flight and ground tests of new aircraft are reviewed. No attempt has been made to review the practices employed for multiway circular connectors, as such a subject would demand a separate discussion.Finally, the paper anticipates the development of high-temperature preinsulated terminals and pressure-type terminations for semirigid coaxial cables.

Comments Relative to the Application of PCM to Aircraft Flight Testing

The pending widespread use planned for PCM telemetry has caused some confusion in the area of PCM or digital standards. It is the purpose of this paper to discuss proposed PCM standards on a realistic basis and to show by example the organization of an integrated digital flight test system using these standards. Consideration is given to the variety of testing applications and ultimate usage of digital flight test data.

A High-Speed, Airborne Digital Data Acquisition System

This paper describes a transitorized airborne PCM/FM data acquisition system. The prototype version of this system has, in the past few months, been subjected to a flight evaluation program, and the final version is now in the process of assembly and test. The system is primarily digital; however, the technical areas of switching and amplification of low-level analog signals will be emphasized and system aspects will be discussed. The airborne system is part of a larger system designed to provide an accurate and reliable means of collecting information from a large number of transducers during aircraft flight testing, and to transfer this information in the most efficient manner to a digital computer for final data reduction. The Airborne portion collects, stores, and transmits flight-test data in digital form to the ground control record station trailer which monitors the progress of the flight test. The recorded data is then carried to the computer station which organizes and controls the selection of data in a form compatible with the requirements of an IBM type 704 computer.

Completely transistorized strain gage oscillator

Described is a completely transistorized strain gage oscillator (S.G.O.). Its primary use is in conjunction with a resistive-type strain bridge transducer to furnish a frequency modulated signal that is directly proportional to an applied force such as stress or pressure. It is expected that due to desirable characteristics it will find major application in the fields of telemetry and remote control, primarily in flight testing of aircraft and missiles. While the S.G.O. vas designed primarily for airborne use, it also has applications (see text) in the fields of spectroscopy, thermmodynamics, and mechanics. The theory of operation of the S.G.O., including mathematical analyses, is described in considerable detail. Special emphasis is placed on the incorporation of transistors. The uses, applications, and performance of the S.G.O. are also discussed together with its electrical and physical characteristics. The transistorized S.G.O. was developed for the AFFTC as a portion of Project DATUM under USAF Contract No. AF 04(611)-683.

Application of telemetry to flight testing at Boeing Airplane Company, Wichita division

Although relatively new at Boeing-Wichita, telemetry has justified its past use and indicated its future potential for the flight testing of piloted aircraft. It is the intent of this paper to discuss the air-borne package and ground receiving units operated by Boeing-Wichita, the use made of these units on various flight tests as a means of data transmission, and finally, to evaluate the system as to its limitations and capabilities.

A complete system for the flight-testing of piloted aircraft

Early in 1948 the Douglas Aircraft Co., Inc., M Testing Division, began an investigation to determine a method by which large amounts of flight test data may be accumulated, observed, and recorded in proper form for rapid analytical scrutiny.

A Complete Telemetry System for the Flight Testing of Aircraft

A Complete Telemetry System for the Flight Testing of Aircraft

Film Reader for Data Analysis

With the increased use of photographic recorders for military aircraft flight testing, there has been a need for an efficient film reading device to enable rapid evaluation of the recorded data. This paper not only introduces a projector-reader that meets this demand, but also suggests that, with certain modifications, it will be of use to the following: 1. draftsman or engineer, 2. film editor, 3. animator, and 4. rush film reviewer.

Aeronautical Quarterly

THE Royal Aeronautical Society has produced the first issue (May) of a new publication called the Aeronautical Quarterly. The purpose of the journal is to make available reports on new and original work of a scientific nature, and also papers reviewing progress m the various specialized branches of the application of fundamental aeronautical science. The Council of the Society feels that the development of aeronautical science and engineering has now become so rapid that the means of disseminating the knowledge acquired are inadequate ; it is intended that the papers in the new journal will present results of original work done in Government research establishments, universities and the industry, not always suitable for presentation before the Society's meetings. Under the terms of its charter the Society is charged, among other things, "to facilitate the exchange of information and ideas amongst the members of the Society and others", and the editorial board expresses the hope that workers will be encouraged to submit details of their researches, so that the results may be available to others concerned with the development of the many aspects of aviation. A distinguished Editorial Board with the necessary editorial executives have been appointed, and they are advised by panels of referees upon aerodynamics (general, fluid motion, and stability and control), structures, materials, aircraft design, instrumental and electrical equipment, vibration and flutter, aircraft propulsion, air transport, meteorology, flight testing, helicopters and propellers, aircraft accessories, fuels and oils, aviation medicine, performance, and radio and radar. The publication will be available to the public, and contributors need not necessarily be members of the Society.