Modern High Performance Aircraft Research Articles

Hole diameter variation compensation by integrating computation geometry for helical milling of stacked aerostructure

The stack-ups of composite and metal are used in aircraft manufacturing to produce modern high-performance aircraft, which makes fastener-hole-making more difficult. Helical milling is an advanced machining process to improve the quality of hole-making. This paper seeks to control the hole diameter error and guarantee fastener-hole fitting performance. The setup of automated helical milling for assembling composite/metal aerostructures is first presented. Meanwhile, the helical milling procedure in aircraft wing manufacturing is discussed. Based on the designed helical milling end-effector, a length-gauge-based feedback control mechanism of the orbital eccentricity is designed to reduce the diameter error of an intended fastener hole. For accurate measurement, a least-squares method is used to find the calibration parameters of the length gauge. Then the mathematical model of hole diameter variation extraction based on B-spline curve construction is given for further variation compensation. After that, the feedback control system of the radial feed mechanism is established. Besides, the modeling and compensation system of the hole diameter variation is developed and used. In helical milling of CFRP/Ti stacks in an aircraft assembly, fastener holes tend to achieve the target diameter of 7.9400 mm without extending the range of hole entrance and exit diameters.

Multi-Axis Nose-Pointing-and-Shooting in a Biomimetic Morphing-Wing Aircraft

Modern high-performance combat aircraft exceed conventional flight-envelope limits on maneuverability through the use of thrust vectoring, and so achieve supermaneuverability. With ongoing development of biomimetic unmanned aerial vehicles (UAVs), the potential for supermaneuverability through biomimetic mechanisms becomes apparent. So far, this potential has not been well studied: biomimetic UAVs have not yet been shown to be capable of any forms of classical supermaneuverability, as are available to thrust-vectored aircraft. Here we show this capability, by demonstrating how biomimetic morphing-wing UAVs can perform sophisticated slow-timescale nose-pointing-and-shooting (NPAS). Nonlinear flight-dynamics analysis is used to characterize the extent and stability of the multidimensional space of aircraft trim states that arises from biomimetic morphing. Navigating this trim space provides an effective model-based guidance strategy for generating open-loop NPAS maneuvers in simulation. Our results demonstrate the capability of biomimetic aircraft for air combat-relevant supermaneuverability, and provide strategies for the exploration, characterization, and guidance of further forms of classical and nonclassical supermaneuverability in such aircraft.

МИКРОПРОЦЕССОРНАЯ СИСТЕМА АВТОМАТИЧЕСКОГО УПРАВЛЕНИЯ СРЕДСТВАМИ ПРОТИВОПОЖАРНОЙ ЗАЩИТЫ САМОЛЕТА

Relevance The ever-increasing requirements for the safety of the use of aviation technology are inextricably linked with the problem of providing fire protection for aircraft, both military and civilian. The complexity of the problem of ensuring the fire safety of flights is associated with an increase in the intensity of the use of aviation equipment and the expansion of the range of functional tasks performed by it. The resulting complication of on-board equipment and an increase in the number of energy-intensive devices creates the prerequisites for the occurrence of fires on board the aircraft. At the same time, the remoteness of places where fires are possible, the variety of causes leading to fires, as well as the ambiguity of the conditions for the onset and spread, increase the likelihood of equipment failures, but also complicate the crew's activities. The purpose of the study is to implement a prospective aircraft fire protection system that will increase the effectiveness of existing fire extinguishing equipment. The relevance of this research project lies in the creation of an aircraft fire-fighting system that will provide timely detection of overheating/fire in the nacelles of the main power unit, in the compartments of the auxiliary power unit, baggage and cargo compartments and aircraft toilets; reliability of information from fire detection and elimination systems; increase the effectiveness of existing firefighting equipment. Aim of research The aim of the study is to develop a future aircraft fire protection system that will increase the effectiveness of existing fire extinguishing equipment. The objectives of the research project are: 1. Choosing a hardware complex for electronic indication and signaling of the aircraft fire-fighting system; 2. Integration of the fire protection complex into the general aircraft equipment control system. Research methods Analysis of modern high-performance aircraft fire protection systems and creation of a promising fire protection system based on the data obtained Results In the course of this research project, a hardware complex for electronic indication and signaling of the aircraft fire system was selected, and the integration of the fire protection complex into the control system of general aircraft equipment was carried out.

Fuzzy pid control of electromechanical actuator system

In order to meet the needs of modern high-performance aircraft, the fuzzy PID control strategy was used to design the electromechanical actuator control system. This control strategy combines the advantages of fuzzy control and PID control, and has better adaptability to time-varying complex systems. The electromechanical actuator control system adopted the three-loop structure, and current loop, speed loop and position loop were built on the platform of MATLAB / Simulink. Considering that the discrete universe fuzzy PID control algorithm has good real-time performance with small online computation, the fuzzy PID controller in discrete universe was designed in the position loop and the system was simulated. The simulation results show that the dynamic and steady performance of discrete universe fuzzy PID control is better than that of traditional PID control, and it is more suitable for electromechanical actuator system.

Improvement of Combustion Process of Spark-Ignited Aviation Wankel Engine

This paper deals with the creation of modern high-performance aircraft power units based on the Wankel rotary piston engine. One of the main problems of Wankel engines is high specific fuel consumption. This paper solves the problem of improving the efficiency of this type of engine. The mathematical model of non-stationary processes of transfer of momentum, energy, mass, and the concentration of reacting substances in the estimated volume provides for the determination of local gas parameters in the entire computational region, which are presented as a sum of averaged and pulsation components. The k-ζ-f model is used as the turbulence model; the combustion is described by the coherent flame model (CFM) based on the concept of laminar flame propagation. As a result of the calculation, we obtained the values of temperature, pressure, and velocity of the working fluid in the working chamber cross-sections of a rotary–piston engine. Various options of the rotor recess shape are considered. Based on the data obtained, the rotor design was improved. The offered shape of the rotor recess has reduced emissions of both nitrogen oxides and carbon dioxide.

A thermal management system using ammonium carbamate as an endothermic heat sink

The issue of managing low-quality waste heat onboard modern high-performance aircraft represents a critical performance limitation that can severely restrict flight envelopes, preclude the integration of high-power electronics, or compromise system reliability. The principal engineering challenges to the thermal systems engineer are the large quantities of heat involved, low (and carefully controlled) coolant temperatures required, and the limited availability of heat sinks to which the waste heat must ultimately be rejected. The use of endothermic chemical reactions to serve as controllable, flight envelope-independent heat sinks has considerable potential in addressing the latter of these engineering challenges, but must be integrated as part of a systems-level approach in order to address all three - acquisition, control, and rejection. In this paper, we introduce and demonstrate a thermal management system (TMS) architecture integrating a vapor compression heat pump, phase change thermal energy storage, and heat exchanger-reactor (HEX reactor) to utilize the endothermic decomposition of ammonium carbamate as an expendable heat sink. An experimental proof-of-concept study was conducted to demonstrate acquisition of both static and time- variant thermal loads, coolant temperature regulation typical of electronics cooling applications, and rejection of the thermal load to an expendable heat sink. The proposed TMS successfully managed pulsed and steady thermal loads while maintaining a coolant temperature within 1°C of the target set point. During steady-state operation, the TMS was able to achieve coefficients of performance (COP) in the neighborhood of 3 with nearly 100% efficiency in expendable heat sink utilization; when subjected to dynamic heat loads, the use of a thermal energy storage material allowed simple control schemes to be used to maintain TMS stability.

Acquisition technology research of EEG and related physiological signals under +Gz acceleration

With the continuous improvement of maneuvering performance of modern high-performance aircraft, the protection problem of flight personnel under high G acceleration, the development as well as research on monitoring system and the equipment for human physiological signals processing which include electroencephalogram (EEG) have become more and more important. Due to the particularity of +Gz experimental conditions, the high-risk of human experiments and the great difficulty of dynamic measurement, there is little research on the synchronous acquisition technology of EEG and related physiological signals under +Gz acceleration environment. We propose a framework to execute human experiments using the three-axial high-performance human centrifuge, develop reasonable operation mode and design a new experimental research method for EEG signal acquisition and variation characteristics on three-axial high-performance human centrifuge under the environment of +Gz acceleration. We also propose to build the synchronous real-time acquisition plan of EEG, electrocardiogram, brain blood pressure, ear pulse and related physiological signals under centrifuge +Gz acceleration with different equipments and methods. The good profiles of EEG, heart rate, brain blood pressure and ear pulse are obtained and analyzed comparatively. In addition, the FMS hop-by-hop continuous blood pressure and hemodynamic measurement system Portapres are successfully applied to the ambulatory blood pressure measure under centrifuge +Gz acceleration environment. The proposed methods establish the basis and have an important guiding significance for follow-up experiment development, EEG features spectral analysis and correlation research of all signals.

A strategy for in-flight measurements of physiology of pilots of high-performance fighter aircraft

Some pilots flying modern high-performance fighter aircraft develop "hypoxia-like" incidents characterized by short periods of confusion and cognitive impairment. The problem is serious and recently led to the grounding of a fleet of aircraft. Extensive discussions of the incidents have taken place but some people believe that there is inadequate data to determine the cause. There is a tremendous disconnect between what is known about the function of the aircraft and the function of the pilot. This paper describes a plan for measuring the inspired and expired Po2 and Pco2 in the pilot's mask, the inspiratory flow rate, and pressure in the mask. A critically important requirement is that the interference with the function of the pilot is minimal. Although extensive physiological measurements were previously made on pilots in ground-based experiments such as rapid decompression in an altitude chamber and increased acceleration on a centrifuge, in-flight measurements of gas exchange have not been possible until now primarily because of the lack of suitable equipment. The present paper shows how the recent availability of small, rapidly responding oxygen and carbon dioxide analyzers make sophisticated in-flight measurements feasible. The added information has the potential of greatly improving our knowledge of pilot physiology, which could lead to an explanation for the incidents.

Tank Heating Model for Aircraft Fuel Thermal Systems with Recirculation

Fuel thermal management has become an important consideration in the design and operation of modern high performance aircraft. In many cases, fuel is a primary heat sink for thermal loads associated with the cooling of the airframe as well as propulsion, electronic, actuator, and payload systems. It is now common for thermal systems to recirculate warm fuel to the tanks, resulting in a rise in temperature in the mission fuel mass. In this paper, a model is presented that integrates heat transfer during mission segments to determine the thermal endurance of an aircraft in terms of fuel tank temperature. The model is intended for early-phase trade studies to determine whether a proposed vehicle will be restricted in operational performance by tank temperature limits.

Nonlinear Analysis of Store-Induced Limit Cycle Oscillations

Flight tests of modern high-performance fighter aircraft reveal the presence of limit cycle oscillation (LCO) responses for aircraft with certain external store configurations. Conventional linear aeroelastic analysis predicts flutter for conditions well beyond the operational envelope, yet these store-induced LCO responses occur at flight conditions within the flight envelope. Several nonlinear sources may be present, including aerodynamic effects such as flow separation and shock-boundary layer interaction and structural effects such as stiffening, damping, and system kinematics. No complete theory has been forwarded to accurately explain the mechanisms responsible. This research examines a two degree-of-freedom aeroelastic system which possesses kinematic nonlinearities and a strong nonlinearity in pitch stiffness. Nonlinear analysis techniques are used to gain insight into the characteristics of the behavior of the system. Numerical simulation is used to verify and validate the analysis. It is found that when system damping is low, the system clearly exhibits nonlinear interaction between aeroelastic modes. It is also shown that although certain applied forcing conditions may appear negligible, these same forces produce large amplitude LCOs under specific realizable circumstances.

COMPUTATION OF WORST-CASE PILOT INPUTS FOR CLEARANCE OF FLIGHT CONTROL LAWS

In this paper, global optimisation and nonlinear simulation are used to search for the worst-case control demands which may be input by a pilot flying a modern high performance aircraft with a full authority flight control law. The flexibility of global optimisation is exploited to simultaneously search for worst-case pilot inputs and worst-case combinations of uncertain parameters in the nonlinear aircraft model. The importance of explicitly considering uncertainty in the aircraft model is clearly demonstrated by the results obtained.

A theoretical and experimental investigation of the effects of a steady angle of attack on the nonlinear flutter of a delta wing plate model

Limit cycle oscillations (LCO) of wings on certain modern high performance aircraft have been observed in flight and in wind tunnel experiments. Whether the physical mechanism that gives rise to this behavior is a fluid or structural nonlinearity or both is still uncertain. It has been shown that an aeroelastic theoretical model with only a structural nonlinearity can predict accurately the limit cycle behavior at low subsonic flow for a plate-like wing at zero angle of attack. Changes in the limit cycle and flutter behavior as the angle of attack is varied have also been observed in flight. It has been suggested that this sensitivity to angle of attack is due to a fluid nonlinearity. In this investigation, we study the flutter and limit cycle behavior of a wing in low subsonic flow at small steady angles of attack. Experimental results are compared to those predicted using an aeroelastic theoretical model with only a structural nonlinearity. Results from both experiment and theory show a change in flutter speed as the steady angle of attack is varied. Also the LCO magnitude increased at a given velocity as the angle of attack was increased for both the experiment and theory. While not proving that the observed sensitivity to angle of attack of LCO in aircraft is due to a structural nonlinearity, the results do show that a change in the aeroelastic behavior at angles of attack can be caused by a structural nonlinearity as well as a fluid nonlinearity. In this paper, only structural nonlinearities are considered, but an extension to include aerodynamic nonlinearities would be very worthwhile.

Effects of Angle of Attack on Nonlinear Flutter of a Delta Wing

Limit cycle oscillations (LCOs) have been observed in flight for certain modern high-performance aircraft. The nonlinear physical mechanism responsible for the LCOs is still in doubt, even to the point of it not yet being determined whether the nonlinearity is principally in the flexible elastic structure of the aircraft or due to the fluid behavior in the surrounding aerodynamic flowfield. One observation from flight tests is that by changing the angle of attack of aircraft, the flight velocity at which LCOs begin may be raised or lowered and that the amplitude of the LCOs may be reduced. It has been suggested that this sensitivity to angle of attack indicates the nonlinearity is in the fluid rather than in the structure. We show that such effects of an angle of attack change can be the result of a structural nonlinearity. Specifically, an investigation to determine the effects of a steady angle of attack on nonlinear flutter and LCO of a delta wing-plate model in low subsonic flow has been made. A three-dimensional time domain vortex lattice aerodynamic model and a reduced order aerodynamic technique were used, and the structure is modeled using von Karman plate theory that allows for geometric strain-displacement nonlinearities in the delta wing structure. The results provide new insights into nonlinear aeroelastic phenomena not previously widely appreciated, i.e., LCOs for low aspect ratio wings that have a platelike nonlinear structural behavior. The effects of a steady angle of attack on both the flutter boundary and the LCOs are found to be significant. For a small steady angle of attack, α 0 ≤ 0.1 deg, the flutter onset velocity increases, whereas for larger α 0 , it decreases. Moreover, as α 0 increases, the maximum LCO amplitude decreases substantially. Such effects have been observed by Bunton and Denegri in flight flutter experiments. It is noted that the present theoretical results do not prove that the LCOs phenomena observed in flight are due to structural nonlinearities; however, the results of the present analysis are consistent with those observed in flight and do show that a structural nonlinearity can give rise to the observed effects of angle of attack on the LCOs.

Sensor validation using hardware-based on-line learning neural networks

The objective of this document Is to show the capabilities of parallel hardware-based on-line learning neural networks (NNs). This specific application is related to an on-line estimation problem for sensor validation purposes. Neural-network-based microprocessors are starting to be commercially available. However, most of them feature a learning performed with the classic back-propagation algorithm (BPA). To overcome this lack of flexibility a customized motherboard with transputers was implemented for this investigation, The extended BPA (EBPA), a modified and more effective BPA, was used for the on-line learning, These parallel hardware-based neural architectures were used to implement a sensor failure detection, identification, and accommodation scheme in the model of a night control system assumed to be without physical redundancy in the sensory capabilities. The results of this study demonstrate the potential for these neural schemes for implementation in actual flight control systems of modern high performance aircraft, taking advantage of the characteristics of the extended back-propagation along with the parallel computation capabilities of NN customized hardware.

Experiments characterizing nonlinear shear layer dynamics in a supersonic rectangular jet undergoing screech

Jet screech is the result of a resonant aeroacoustic feedback loop. In modern high-performance aircraft jet screech has given rise to in-flight sonic fatigue failure of nozzle components. For this reason, jet screech has been the focus of numerous investigations. However, the prediction of screech amplitude has been a very elusive goal. A primary objective of the work to be reported is to experimentally characterize the nonlinear instability wave development in the shear layer of a rectangular supersonic jet undergoing screech. Hot-film probes are used to measure the instability wave development in the jet shear layers along a constant Mach number ray. Higher-order polyspectral techniques are employed to determine resonant nonlinear phase locking between multiple instability modes. A detailed comparison of the “inner loop” hot-film measurements with “outer loop” acoustic measurements is made. Such a comparison reveals the importance of incorporating nonlinear effects into a jet screech amplitude prediction method.

Multiple Control Surface Failure Detection Via On-Line Filter Tuning Method

Modern high performance aircraft systems require advanced onboard fault detection, isolation and reconfiguration (FDIR) techniques against system failures. In this paper, we will devise a on-line FDIE (Failure Detection Isolation and Estimation) scheme that could handle multiple and time-varing control surface failure and provide precise health status for future reconfiguration design. This approach combining LQG design with newly developed fuzzy concept would be able to deal with a variety of failure types such as constant failure (hardover), linearly degraded (run-away) and their combination. A big contribution of this approach is unanticipated failure can be successfully detected without prescribing any nominal failure models in memory.

Batch simulation environment for integrated batch and piloted air combat analysis

A batch air combat simulation environment known as the tactical maneuvering simulator (TMS) is presented. The TMS serves as a tool for developing and evaluating tactical maneuvering logics. The environment can also be used to evaluate the tactical implications of perturbations to aircraft performance or supporting systems. The TMS is capable of simulating air combat between any number of engagement participants, with practical limits imposed by computer memory and processing power. Aircraft are modeled using equations of motion, control laws, aerodynamics, and propulsive characteristics equivalent to those used in high-fidelity piloted simulation. Databases representative of a modern high-performance aircraft with and without thrust-vectoring capability are included. To simplify the task of developing and implementing maneuvering logics in the TMS, an outer-loop control system known as the tactical autopilot (TA) is implemented in the aircraft simulation model. The TA converts guidance commands issued by computerized maneuvering logics in the form of desired angle of attack and wind axis-bank angle into inputs to the inner-loop control augmentation system of the aircraft. This article describes the capabilities and operation of the TMS.

On-line learning neural-network controllers for autopilot systems

This paper proposes the implementation of on-line learning neural controllers in the autopilot control laws of a modern high-performance aircraft. A first advantage of this design philosophy consists in avoiding the precomputation, storing, and interpolation between thousands of feedback gains of a typical flight control system. Another advantage is the ability to compensate for nonlinearities and model uncertainties. In addition, an on-line learning time-varying neural architecture will avoid the time-consuming gain recalculation following any modification to the aircraft or to its control system during its operative life. The implementation of these types of alternative controllers is made possible by the recent simultaneous advances in neural-network technology with regard to the availability of efficient and fast learning algorithms, along with progress in digital microprocessors. The approach is shown using a six-degree-of-freedom nonlinear simulation code. The traditional gain-scheduling-based control laws for typical autopilot functions are replaced by on-line learning neural architectures trained with the extended back-propagation algorithm. This algorithm has shown substantial improvements over the conventional back-propagation method in learning speed and accuracy. The results of the simulation with and without a man in the loop are presented and discussed.

Computer Aided Evaluation of Aircraft Handling Qualities

Modern high performance aircraft are designed to be aerodynamically unstable and employ sophisticated digital flight control systems onboard to recover stability and meet the stringent performance requirements over the complete flight envelope. Performance evaluation and verification of these advanced flight control systems require an analytical comparison of system characteristics to various military specifications including handling quality specifications like the MIL-F-8785 and the recent MIL-STD-1797. These evaluations are becoming increasingly complex and difficult as the design trend towards increased control system integration, sophistication and coupling continues. This paper describes the salient features of the interactive computer aided software package developed for the analytical evaluation of handling qualities and generation of lower order equivalent system models for modern high performance aircraft. The software package is based on Mat lab/Fortran and runs on IBM compatible personal computers.

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.