Cruise Flight Research Articles

Influence of the Earth Rotation on Trajectory of a Returnable Hypersonic Cruise Vehicle

It is of high difficulty for a hypersonic vehicle to implement a hypersonic cruise flight and return to a scheduled airport without power. Accuracy of mission simulation and analysis is more crucial at this time. Under this circumstance, it is meaningful to discuss whether the earth rotation should be considered in the dynamic model and trajectory design. In this research, the dynamic equations in which the earth rotation is taken into consideration are derived for a hypersonic cruise vehicle. The direct shooting method is utilized for parameterization and discretization of the trajectory, so that the trajectory can be analyzed and simulated through numerical integration. Then, two groups of trajectory simulation results are presented. In each group, the only difference between the two trajectories is that whether the earth rotation is involved, and the two trajectories are compared with each other. For a returnable hypersonic cruise vehicle which returns to the ground without power, whether to involve the earth rotation in the dynamic model is discussed on the basis of the numerical results, and relevant suggestions are given for reference.

Longitudinal System Identification of an Avian-Type UAV Considering Characteristics of Actuator

To develop autonomous flapping aircraft, basic mathematical modeling is essential to solve the problem of “uncertainty models” in biomimetic flight dynamics. This study identified the longitudinal linear model of an ornithopter via automated flight tests and sensors onboard the ornithopter to measure angular rates, Euler angles, and total velocity. For accurate flight tests, automated signal input was designed for elevator deflection: doublet and multistep 3211 maneuver. Furthermore, because the flapping motion of the ornithopter’s main wings generates oscillations during cruise flight, fast Fourier transform is used to analyze flight data in the frequency domain, and a Butterworth filter is used to filter out the flapping motion from the data. The characteristics of the actuator are then analyzed using a motion capture camera and applied to the system identification. The structure of the ornithopter linear model is found to be similar to that of a fixed-wing aircraft, which has a periodic oscillation. The results from the flight tests and analysis manifest that an ornithopter has unstable characteristics due to a single right-half plane real pole.

Differentiator based full-envelope adaptive control of air-breathing hypersonic vehicles

Despite the exciting improvement in air-breathing hypersonic vehicles (AHVs), most of the developed control strategies are only for cruise flight. This paper considers the longitudinal maneuver flight of AHVs, whose main purpose is to propose a low-dimension full-envelope adaptive control. In contrast to the existing adaptive back-stepping designs for AHVs, the proposed control synthetically handles the time-varying uncertain coefficients of aerodynamic force and moment that are inevitable during a full-envelope hypersonic flight, while accommodating actuator faults and flexible dynamics as well as circumventing over-parametrization and “explosion of complexity”. The above superiorities are attributed to the combination of the bound estimate mechanism and the sliding mode differentiator in a dynamic surface control scheme. The effectiveness of the proposed control is verified by a simulation study.

Probabilistic aircraft trajectory prediction in cruise flight considering ensemble wind forecasts

The problem of aircraft trajectory prediction subject to wind uncertainty is addressed. In particular, a probabilistic analysis of aircraft flight time and fuel consumption in cruise flight is presented. The wind uncertainty is obtained from ensemble weather forecasts. The cruise is composed of a given number of segments subject to uncertain winds (both along-track winds and crosswinds). The resulting average ground speed of each segment is modeled as a random variable, assuming a Log-Normal distribution. The probabilistic trajectory predictor developed is based on the Probabilistic Transformation Method; the input is the probability density functions of the average ground speeds of the cruise segments, and the output is the probability density functions of the flight time and the fuel consumption. Results are presented for several aircraft of different categories (medium and heavy), for a given trans-oceanic route and a real ensemble weather forecast. The effects of wind uncertainty on flight predictability and on fuel loading are analyzed. A fuel penalty parameter is defined, and the cost of flight unpredictability is quantified. The sample variability of all the results has been quantified by means of standard errors.

Effect of Climb Angle on Aircraft Fuel Consumption and Nitrogen Oxides Emissions

Departure climb angles differ with respect to factors such as obstacles within the departure track, meteorological conditions, and cost index input, most of which have a dynamic nature to some extent. In this sense, it is relevant to perform parametric analyses to capture the outcomes of various climb angles. Therefore, in this Paper, the effects of the departure climb angle, mainly on fuel consumption and nitrogen oxides emissions, are quantified for an increment level as low as 0.25 deg of the departure climb angle. Using actual flight data of a large number of flights, the impacts of climb angle variations are statistically analyzed. The fuel burn and nitrogen oxides emissions tend to increase by 9–19 kg and 0.3–0.7 kg per degree of climb angle for the departure climb phase between takeoff and a further 5 n mile horizontal distance. Furthermore, this trend is a function of aircraft mass, which leads to a (fuel burn) and a (nitrogen oxides) increase for each 2 ton increase in aircraft mass. The current Paper also investigates the effects of the average climb angle in a broader sense, associated with cruise flights. Applying a steeper average climb angle during climb to 30,000 ft, the marginal reductions in fuel burn and nitrogen oxides are found to be 157 and 3.4 kg, whereas they are 65 and 3 kg for the combined climb and cruise phases, respectively.

Uncertainty and sensitivity analysis of flow parameters on aerodynamics of a hypersonic inlet

The performance of the inlet is crucial to the cruise flight of a hypersonic air-breathing propulsion vehicle. The objective of this work is to investigate the uncertainty and sensitivity of pressure field and the performance parameters for a hypersonic inlet due to the uncertainty of five flow parameters, including freestream Mach number, Reynolds number, angle of attack, temperature and wall temperature. The steady Reynolds Averaged Navier-Stokes equations are solved to predict the inlet start and unstart flows within the hysteresis loop. Then, a point-collocation non-intrusive polynomial chaos method (NIPC) is utilized to quantify the uncertainty and sensitivity in the output quantities of interest. The uncertainty analysis in pressure field shows that Mach number and angle of attack of freestream make dominant contributions to the total uncertainty, and the Mach number has remarkable impacts in the isolator. In the start flow, the angle of attack exerts its prominent influence in the post-shock regions, while Mach number mainly dominates these regions ahead of and around the shocks. The reason may be interpreted as the much greater pressure derivatives with respect to angle of attack in the post-shock regions. Significant discrepancies are presented for the unstart flow. The reflected shock waves in the unstart flow are less sensitive to the variations of flow parameters. The external flow field, separation bubble and reflected shocks are significantly affected by angle of attack. Besides, the uncertainties of the performance parameters in the start flow are about twice those in the unstart flow. The sensitivity analysis further reveals that Mach number is the major contributor to the total uncertainty of performance parameters. The correlation coefficients via linear regression method clearly illustrate the relationships between the five input parameters and the performance parameters.

Direct methanol fuel cell (DMFC) and H2 proton exchange membrane fuel (PEMFC/H2) cell performance under atmospheric flight conditions of Unmanned Aerial Vehicles

Abstract Recently, there has been growing interest in fuel cell implementation on aircraft, particularly for Unmanned Aerial Vehicle (UAV) propulsion. The performance of both fuel cell types, cathode air-breathing H2 Proton Exchange Membrane Fuel Cells (PEMFC/H2) and passive Direct Methanol Fuel Cells (DMFCs), is dependent on atmospheric conditions such as pressure, relative humidity and temperature. In this study, models at the single-cell level have been used to simulate the corresponding polarization curves on flight conditions, which constitutes a contribution to the use of fuel cells in UAV. After validating these models, several cases of interest relating to UAV operation have been considered, such as cruise flight at different altitudes and horizontal flight when crossing clouds, to compare the performance of both types of fuel cells. Fuel cell temperature has been controlled to avoid high performance degradation. The results show that the effects of atmospheric flight conditions are more important for PEMFC/H2 than for DMFCs. Low pressure affects PEMFC/H2 performance to a greater extent than DMFC performance. Atmospheric relative humidity affects PEMFC/H2 performance, especially at high cell temperatures, whereas DMFC performance is barely affected. Although performance is lost, it is possible to operate fuel cells in UAV propulsion systems at low-medium altitudes.

Effects of Crosswind Flight on Rotor Harmonic Noise Radiation

To develop recommendations for procedures for helicopter source noise characterization, the effects of crosswinds on main rotor harmonic noise radiation are assessed using a semi-empirical model of the Bell 430 helicopter. Crosswinds are found to have a significant effect on blade-vortex interaction (BVI) noise radiation when the helicopter is trimmed with the fuselage oriented along the inertial flight path, resulting in a “slipped” flight condition. However, the magnitude of BVI noise remains unchanged when the pilot orients the fuselage along the aerodynamic velocity vector, “crabbing” for zero aerodynamic sideslip angle. The effects of wind gradients on BVI noise are also investigated and found to be smaller in the crosswind direction than in the headwind direction. The effects of crosswinds on lower harmonic noise sources at higher flight speeds are also assessed. In all cases, the directivity of radiated noise is somewhat changed by the crosswind. The model predictions agree well with a limited set of flight test data for the Bell 430 helicopter for cruise and approach flight conditions, both measured with and without crosswinds present. The results of this investigation would suggest that flight paths for future acoustic flight testing are best aligned across the prevailing wind direction to minimize the effects of winds on noise measurements when wind cannot otherwise be avoided.

Study on the Mechanism of the Variable-Speed Rotor Affecting Rotor Aerodynamic Performance

The variable-speed rotor has proven to be a promising means to improve helicopter performance. Previous investigations on the aeromechanics of the variable-speed rotor are scarce. This work studies the mechanism of the variable-speed rotor affecting the rotor aerodynamic performance by means of dimensionless parameter analysis and reveals the various effect mechanisms under the various flight speeds and take-off weights. The current work shows that, during hover, the variable-speed rotor improves the rotor aerodynamic performance by reducing the blade dynamic pressure, while the non-uniform thrust distribution is attributed to the reduced rotor speed suppresses the performance improvement. In slow forward flight, the blade dynamic pressure reduction improves the rotor aerodynamic performance. In cruise and fast forward flight, both the blade dynamic pressure and advancing blade tip compression loss reductions improve the rotor aerodynamic performance. The study also shows that in forward flight, the rotor loading is smaller, and the effect of reducing the advancing blade tip compression loss through the variable-speed rotor is greater.

Feasibility Study of Using Flexible Solar Panels for Powered-Parachute Flying Vehicles

Objectives: To assess the potential of using the flexible solar cells to provide the powered parachute vehicles (PPC) with the necessary power for cruise flight. Methods/Analysis: The power required for a typical PPC with three different types of flexible solar cells was determined based on the actuator disk theory. The necessary area and mass of the solar cells needed to generate the required power are also determined. Findings: It was found that the available solar cells in the market can be used to cover the PPC parafoil and generate the required power. However, there is a trade-off between the efficiency, flexibility, and cost of the solar cells. Application/Improvement: The proposed idea of covering the parafoil’s surface with solar cells, with the aim of increasing the endurance of the PPC vehicles, was found to be feasible. This technology can be adopted for military and civilian applications. Keywords: Parafoil, Paraglider, Powered Parachute, Solar, Solar Powered

Upgrade of GLE database: Assessment of effective dose rate at flight altitude

A new database for assessment of radiation doses at cruise flight altitude in the Earth atmosphere, related to ground level enhancement (GLE) events is created under VarSiTi/SCOSTEP support and incorporated to the International ground level enhancement (GLE) database (gle.oulu.fi). The upgraded database provides, for each GLE event, where possible, information on the estimated energy/rigidity spectra of solar energetic particles and the corresponding computed effective doses at cruise flight altitude of 35 kft (10,668 m above sea level). The computations are performed for various reconstructions of solar energetic particles spectra, available in literature, thus for some events there are several results. Computations were performed using a recent model for assessment of effective dose due to cosmic ray particles, applied specifically in the polar region, where the exposure is maximal. This upgrade allows one to estimate the radiation effects at cruise flight altitude caused by major GLE events over several decades.

Solar Cell to Support Perpetual Flight of High Altitude Long Endurance UAV ITB

Research on a High Altitude Long Endurance (HALE) Unmanned Aerial Vehicle (UAV) is currently being conducted at Bandung Institute of Technology to reach the flight duration needed and to get the solution of today’s challenges, minimizing pollution. Besides the good aerodynamic efficiency needed, energy resource is now becoming important. The energy resource must have a good endurance, easy to get, and of course, less pollution. Discussion in this paper is about the analysis of power needed by HALE UAV while takeoff and cruise flight conditions, and then determine the amount of solar cell and battery needed by the UAV.

Comparative Study of Wing Lift Distribution Analysis for High Altitude Long Endurance (HALE) Unmaned Aerial Vehicle

The development of High Altitude Long Endurance (HALE) Unmanned Aerial Vehicle (UAV) has been emerged for both civil and military purposes. Its ability of operating in high altitude with long endurance is important in supporting maritime applications.Preliminary analysis of HALE UAV lift distribution of the wing presented to give decisive consideration for its early development. Ensuring that the generated lift is enough to compensate its own weight. Therotical approach using Pradtl’s non-linear lifting line theory will be compared with modern numerical approach using Computational Fluid Dynamics (CFD). Results of wing lift distribution calculated from both methods will be compared to study the reliability of it. HALE UAV ITB has high aspect ratio wing and will be analyze at cruise flight condition. The result indicates difference between Non-linear Lifting Line and CFD method.

ON THE IMPACT OF FLIGHT SAFETY CERTIFICATION REQUIREMENTS ON THE AERODYNAMIC EFFICIENCY OF COMMERCIAL AIRPLANES

The article considers the issue of aerodynamics efficiency implementation taking into account certification requirements for flight safety. Aerodynamics efficiency means high aerodynamic performance (depending on the airplane size), aerodynamic performance in cruise flight, high aerodynamic performance at takeoff, as well as lift performance at landing. The author estimated the impact on aerodynamics efficiency of both the requirements for aerodynamics performance and requirements for aircraft systems, noncompliance with which may result in significant change of expected operating conditions. It was shown that the use of supercritical wing profiles may result in flight mode limitations due to failure of the required buffeting capacities. It does not allow engaging all the advantages of aerodynamics layout and requires special design solutions to prevent such cases. There were reviewed certification requirements for flight level pressure altitude accuracy and icing conditions warning sysytem. The research presented the methods of aerodynamic efficiency increase by meeting the requirements for reduced vertical separation minima flights and in icing conditions, including requirements for air data probes. Reduced vertical separation minima flight requirements are met by means of efficient air data probes location. Theoretical methods of flow calculation determine areas on the airplane skin surface where static probes minimize errors depending on angle-of-attack and sideslip. It was shown that if certification requirements are not met and in case of flight out of reduced vertical separation minima area, aerodynamics efficiency is significantly reduced and fuel consumption can be increased by 10% and higher. Suggested approaches implementation allows increasing commercial airplanes competitiveness.

Computational Investigation of a Boundary-Layer-Ingestion Propulsion System

The present paper examines the potential propulsive and aerodynamic benefits of integrating a boundary-layer ingestion propulsion system into the Common Research Model geometry and the NASA tetrahedral unstructured software system. The numerical propulsion system simulation environment is used to generate engine conditions for computational fluid dynamics analyses. Improvements to the boundary-layer ingestion geometry are made using the constrained direct iterative surface curvature design method. The potential benefits of the boundary-layer ingestion system relating to cruise propulsive power are quantified using a power balance method, and a comparison to the baseline case is made. Iterations of the boundary-layer ingestion geometric design are shown, and improvements between subsequent boundary-layer ingestion designs are presented. Simulations are conducted for a cruise flight condition of Mach 0.85 at an altitude of 38,500 ft, with a Reynolds number of 40 million based on the mean aerodynamic chord and an angle of attack of 2 deg for all geometries. The results indicate an 8% reduction in engine power requirements at cruise for the boundary-layer ingestion configuration as compared to the baseline geometry. Small geometric alterations of the aft portion of the fuselage using constrained direct iterative surface curvature are shown to marginally increase the benefit from boundary-layer ingestion further, resulting in an 8.7% reduction in power requirements for cruise, as well as a drag reduction of approximately 12 counts over the baseline geometry.

Cessna Citation X Performances Improvement by an Adaptive Winglet during the Cruise Flight

Cessna Citation X Performances Improvement by an Adaptive Winglet during the Cruise Flight

Wind Tunnel Investigation of a Circulation Control Wing with Dual-Radius Flaps

The objective of this research is to investigate the efficacy of circulation control (CC) at low Reynolds numbers () with relatively low and high blowing rates on a circulation control wing (CCW). Four dual-radius flap geometries are developed and tested by varying specific flap parameters from a previously studied baseline configuration. A two-dimensional low-speed wind-tunnel experimental study is undertaken to evaluate the effect of trailing edge upper slot blowing at cruise flight and takeoff (0° and 30° flap deflection). The wind tunnel tests are conducted at Mach numbers of 0.03, with momentum coefficients of blowing () ranging from 0.0 to 0.3. The research presented in this paper is the natural outgrowth of results reported in previous work related to the wind tunnel testing of a CCW with dual-radius flaps. This investigation explores the design of CC dual-radius flaps to improve the performance of existing CC flap configurations. This research also provides insight into how the characteristics of the CC flap geometry affect CC performance.

The high and low comfort peaks in passengers' flight.

Knowing the high and low peaks in comfort during a flight could be useful in prioritizing aircraft interior improvements. The first objective of this study was to identify whether there are differences in comfort experiences during different phases of a flight. The second objective of this study was to identify similarities between recalled and real time reported comfort experiences. 149 participants were asked to rate the comfort in the different phases of their last flight on a scale from 1-10. Additionally, a combination of a self-reporting design probe and generative interview was used to investigate the appraisal patterns of emotions in nine passengers. The 149 subjects reported the highest comfort after take-off and arriving at the destination, the lowest while stowing the luggage and during the cruise flight. The qualitative long haul inflight study showed after take-off and while arriving at the destination the most positive emotions and during the cruise flight there is a negative experience phase. Suggestions are given to improve the cruise flight phase, by for example stimulation of movement or better service.

CFD simulation of contrail formation in the near field of a commercial aircraft: Effect of fuel sulfur content

Aircraft contrails may contribute to the global radiative forcing. In this context, the investigation of contrail formation in the near field of an aircraft may be helpful in developing strategies to reduce undesirable impacts. In this study, three-dimensional Reynolds-Averaged Navier-Stokes (RANS) simulations of contrails produced by commercial aircraft during cruise flights were performed. A realistic geometry (herein a Boeing 737) was taken into account, including the engine core and bypass flows, which allows several parametrical studies and avoids using parameterizations to describe the plume's dilution. The objective was to simulate the early development of contrails in a fresh plume whose dilution was obtained with a spatial simulation of jet/vortex interaction. A coupling was carried out with a chemical and a microphysical model implemented in the numerical simulation code CEDRE to simulate particle growth using an Eulerian approach. The implemented microphysics model can simulate water condensation onto soot particles, taking into account their activation by adsorption of sulfur species. Our simulations show that sulfur dioxide is converted into sulfur trioxide and sulfuric acid at a rate of conversion close to 3 %, which is in good agreement with other studies. Ice-crystal growth was faster when the fuel sulfur content (FSC) increased, allowing a visible contrail to appear earlier. These promising results confirm in situ observations and highlight the model's ability to simulate typical plume chemistry and complex microphysics/chemistry interactions coupled with detailed jet/vortex dynamics.

Full-order terminal sliding-mode control of MIMO systems with unmatched uncertainties

To control MIMO systems with unmatched uncertainties, two sliding-mode controllers are presented in this paper. Firstly, a terminal sliding-mode controller is presented to force the output of an MIMO system to a region near zero in finite-time. With the analysis on the effect of the unmatched uncertainties, a full-order terminal sliding-mode control is further proposed to force the output of the MIMO system to converge to zero rather than a region. The virtual control is utilized to establish the reference for the part of the system states, which can reject unmatched uncertainties completely. To generate continuous virtual control signals, the proposed full-order terminal sliding-mode controller makes the ideal sliding motion as the full-order dynamics rather than the reduced-order dynamics in traditional sliding-mode control systems. Finally, the simulations on the control of an L-1011 fixed wing aircraft at cruise flight conditions validate the effectiveness of the proposed method.