Cruise Point Research Articles

Design and flight test of the fixed-flapping hybrid morphing wing aerial vehicle

Bionic aircrafts have become a hot topic in the research on unmanned aerial vehicles (UAVs). By mimicking the flight mechanics and wing morphology of living organisms, bionic aircraft not only improve aerodynamic performance, stealth, and convenience but also enable single aircraft to complete multiple specific tasks. To further improve the practical performance of bionic aircraft, a fixed-flapping hybrid morphing wing aerial vehicle (F-FWAV) is designed, and the aerodynamic and flight mechanics are studied. First, kinematic simulations are conducted on the designed F-FWAV, and the kinematic characteristics of the flapping wing are analyzed. Then, flight tests are conducted on the aircraft model, and time-domain and frequency-domain analyses were performed on the data of the pitch angle and roll angle during level flight, high angle of attack (AOA) maneuvering and landing, indicating that the pitch and roll angles of the F-FWAV are coupled. CFD numerical simulations are used to obtain the cruise points of the F-FWAV under different AOAs, frequencies, and freestream velocities. The results of the mutual interference between the fixed wing and flapping wing sections show that the flapping wing section provides more than 50 % of the lift of the entire flight process, and the downward flapping movement of the flapping wing section increases the edge vortex of the fixed wing section, thereby increasing the lift of the fixed wing section.

Rapid Parametric Modeling and Robust Analysis for the Hypersonic Ascent Based on Gap Metrics

This paper investigates a rapid modeling method and robust analysis of hypersonic vehicles using multidisciplinary integrated techniques. First, the geometrical configuration is described using parametric methods based on the class–shape technique. Aerodynamic forces and moments are estimated for the specific configuration using engineering methods. Moreover, the nonlinear model is simplified by the polynomial fitting expressions, and the linear variable parameter model is obtained for the tracking control design and dynamic characteristic analysis with the aid of the sensitivity analysis and gap metric methods. A velocity-driven trajectory design method is deduced for hypersonic ascent, and the tracking control law is developed to realize the flight process from the initial point to the cruise point. Furthermore, a robust analysis process based on gap margin is proposed for climb trajectory tracking. Simulation results are provided to verify the feasibility of the proposed modeling method and show that the flight control of a hypersonic vehicle is more sensitive to altitude variation.

Variable pitch fan aerodynamic design for reverse thrust operation

Variable pitch low pressure ratio fans could enable higher propulsive efficiency and eliminate the need for heavy thrust reversers. In this paper, the effects of the fan rotor design on reverse thrust capability have been explored by varying key parameters of NASA’s Advanced Ducted Propulsor (ADP) while maintaining cruise point performance. Reverse thrust performance has been assessed using RANS single passage CFD of the variable pitch fan system with an extended domain. This computational approach has been validated using NASA Stage 51B, an experimental variable pitch fan test case. Predicted total pressure and total pressure ratios for this case were found to agree with test data within experimental error, except where large tip region separations occurred at high incidence. Applying individual variations to rotor pitch-to-chord, radial loading distribution, and chordwise camber distribution generated changes to rotor incidence, blockage, and peak surface Mach numbers in reverse operation. An increase in gross reverse thrust of up to 8% was achieved through reductions in rotor pitch-to-chord due to improved loading and lower shock Mach numbers. Controlling section camber distributions was used to move the rotor shock downstream and was found to increase reverse thrust by up to 3%. Increasing rotor loading at the mid span relative to the tip resulted in high tip incidence and a 50% reduction in gross reverse thrust across all rotor speeds. This suggests that tip loaded designs are required for high levels of reverse thrust.

Impact of renewable fuels on heavy-duty engine performance and emissions

The transport sector faces two critical issues: a limited supply of fossil fuels and high greenhouse gas (GHG) emissions. Additionally, the demand for freight transport is steadily increasing, ultimately leading to higher GHG emissions. Since these emissions promote climate change, reducing the GHG emissions from the transport sector is necessary. Renewable drop-in fuels can play an essential role in this regard as those are CO2 neutral. Since these fuels come from so-called renewable sources, this represents a way to reduce carbon dioxide emissions from the current vehicle fleet to meet the EU’s Green Deal goals to become climate neutral by 2050. The drop-in fuels from renewable sources and later the purely renewable fuels serve as a bridging technology in this context.With this in mind, experiments were conducted with a Heavy-Duty Single Cylinder Engine (HD-SCE). The effects of four different renewable fuels or fuel blends – 93% RF/7% UCOME, 60% B0-Diesel/40% RF blend, 70% Diesel/30% Octanol blend and 100% Octanol – on engine performance and raw emissions were studied in comparison to fossil Diesel fuel. The investigations were conducted at three different load points — Rated Power (RP), best Brake Thermal Efficiency (BTE) and Cruise Point, covering all the relevant load points for HD engines. For all load points, the use of renewable fuels resulted in lower carbon dioxide (CO2), hydrocarbon (HC), carbon monoxide (CO) and FSN compared to fossil Diesel due to the fuel-borne oxygen and the lower C/H ratio of these alternative fuels. The blend of 60% B0-Diesel-40% RF shows the highest efficiency due to the paraffinic fuel structure, the fuel-borne oxygen, the higher calorific value, and the high cetane number. 100% Octanol resulted in a reduction in FSN by a factor of 3. All renewable fuels show a GHG emission reduction potential of around 2.5% to 5.5% in the Tank-to-Wheel (TtW) analysis.

Knowledge discovery with computational fluid dynamics: Supercritical airfoil database and drag divergence prediction

Aerodynamic rules and knowledge are often obtained through theoretical research and experiments, which have contributed greatly to aircraft design. For example, Korn's equation predicts the airfoil drag divergence Mach number using the airfoil maximum thickness and the lift coefficient. It is very helpful in the aircraft initial design. However, it neither reveals the key factors of fluid features on the drag divergence nor contributes to the detailed design. This paper designs a supercritical airfoil database that covers the typical free stream Mach number, angle of attack, lift coefficient, and geometry of modern transonic commercial aircraft. Correlation screening and multivariate regression are carried out to discover knowledge about the airfoil drag divergence Mach number and pressure distribution features. A new linear correlation is discovered and validated by existed airfoil databases. Compared with Korn's equation, the discovered correlation reduces the maximum prediction error by approximately 40%. It indicates that the drag divergence Mach number can be increased by obtaining a shock wave that is further upstream in the detailed design. Furthermore, it enables the cruise performance and drag divergence Mach number to be predicted with only one simulation of the cruise point, which will greatly save the computational cost of optimizations.

Fuel burn evaluation of a transonic strut-braced-wing regional aircraft through multipoint aerodynamic optimisation

AbstractThis paper presents a relative fuel burn evaluation of the transonic strut-braced-wing configuration for the regional aircraft class in comparison to an equivalent conventional tube-and-wing aircraft. This is accomplished through multipoint aerodynamic shape optimisation based on the Reynolds-averaged Navier-Stokes equations. Aircraft concepts are first developed through low-order multidisciplinary design optimisation based on the design missions and top-level aircraft requirements of the Embraer E190-E2. High-fidelity aerodynamic shape shape optimisation is then applied to wing–body–tail models of each aircraft, with the objective of minimising the weighted-average cruise drag over a five-point operating envelope that includes the nominal design point, design points at $\pm 10\%$ nominal $C_L$ at Mach 0.78, and two high-speed cruise points at Mach 0.81. Design variables include angle-of-attack, wing (and strut) twist and section shape degrees of freedom, and horizontal tail incidence, while nonlinear constraints include constant lift, zero pitching moment, minimum wing and strut volume, and minimum maximum thickness-to-chord ratios. Results show that the multipoint optimised strut-braced wing maintains similar features to those of the single-point optimum, and compromises on-design performance by only two drag counts to achieve up to 11.6% reductions in drag at the off-design conditions. Introducing low-order estimates for approximating full aircraft performance, results indicate that the multipoint optimised strut-braced-wing regional jet offers a 13.1% improvement in cruise lift-to-drag ratio and a 7.8% reduction in block fuel over a 500nmi nominal mission when compared to the similarly optimised Embraer E190-E2-like conventional tube-and-wing aircraft.

Optimal Cruise Characteristic Analysis and Parameter Optimization Method for Air-Breathing Hypersonic Vehicle

There is an optimal cruise point with the lowest fuel consumption when a hypersonic vehicle performs steady-state cruise. The optimal cruise point is composed of the optimal cruise altitude and the optimal cruise Mach number, and its position is closely related to the aircraft parameters. This article aims to explore the relationship between the optimal cruise point and relevant aircraft parameters and establish a model to describe it, then an aircraft parameter optimization method of adjusting the optimal cruise point to the target position is explored with validation by numerical simulation. Firstly, a parameterized model of a hypersonic vehicle is obtained as a basis, then the optimal cruise point is obtained by the optimization method, and the influence of a single aircraft parameter on the optimal point is investigated. In order to model the relationship between the aircraft parameters and the optimal cruise point, a neural network is employed. Finally, the model is used to optimize the aircraft parameters under multiple constraints. The results show that, after aircraft parameters optimization, the optimal cruise point is located at the predetermined position and the fuel consumption is lower, which provides a new perspective for the design of aircraft.

Robust Design of Transonic Natural Laminar Flow Wings Under Environmental and Operational Uncertainties

The robustness of laminar wings is critical, both against instabilities that can unexpectedly trigger transition and against off-design conditions outside the cruise point. However, current inverse design methodologies not only provide suboptimal configurations but are unable to come up with robust configurations. The objective of this paper is the development and demonstration of a framework for the robust direct design of transonic natural laminar flow wings using state-of-the-art industrial tools such as computational fluid dynamics, linear stability theory, and surrogate models. The deterministic optimization problem, which serves as a baseline, searches for the optimum shape that minimizes drag applying a surrogate based optimization strategy. In that case, crossflow and Tollmien–Schlichting critical factors are fixed according to calibration data. For the robust approach, uncertainties in these critical factors as well as operational conditions are considered to account for situations that could prematurely trigger transition. The framework is able to come up with state-of-the-art natural laminar shapes for a short-haul civil aircraft configuration. The robust configurations are more balanced than the deterministic, as the transition location smoothly moves upstream as the critical factors are reduced. The pressure profiles are more resistant against instabilities, extending the current design envelope of natural laminar flow wings.

Static Aeroelastic Beam Model Development for Folding Winglet Design

Wing shape adaptability during flight is the next step towards the greening of aviation. The shape of the wing is typically designed for one cruise point or a weighted average of several cruise points. However, a wing is subjected to a variety of flight conditions, which results in the aircraft flying sub-optimally during a portion of the flight. Shape adaptability can be achieved by tuning the shape of the winglet during flight. The design challenge is to combine a winglet structure that is able to allow the required adaptable shape while preserving the structural integrity to carry the aerodynamic loads. The shape changing actuators must work against the structural strains and the aerodynamic loads. Analyzing the full model in the preliminary design phase is computationally expensive; therefore, it is necessary to develop a model. The goal of this paper is to derive an aeroelastic model for a wing and winglet in order to reduce the computational cost and complexity of the system in designing a folding winglet. In this paper, the static aeroelastic analysis is performed for a regional aircraft wing at sea level and service ceiling conditions with three degree and eight degree angle of attack. MSC Nastran Aeroelastic tool is used to develop a Finite Element Model (FEM), i.e., beam model and the aerodynamic loads are calculated based on a doublet lattice panel method (DLM).

Perturbation Analysis and Control of Mach Number 2.4-Meter Transonic Wind Tunnel

Because of the large domestic civil aircraft projects started in China a decade ago, there is a greater need to control the accuracy of the Mach number in aerodynamic tests, especially near the designed cruise point of large commercial aircraft. Nowadays the control accuracy of China Aerodynamics Research and Development Center 2.4-meter transonic wind tunnel Mach number is in the range of to when , which is far from the measurement accuracy of drag coefficient required for testing advanced aircraft. This value should result in a better-than-one drag count. As a consequence, it is imperative to improve the control accuracy of Mach number urgently. The nonlinearity, large time delays, and strong coupling of wind tunnel flowfield control, along with the variation of the model angle of attack, could cause the Mach number to deviate from the expected value. To solve these problems, a model predictive control method based on dynamic matrix control algorithm is proposed. This method builds a prediction model based on step response test. The accuracy of Mach number predictive control can be efficiently improved by performance optimization in the form of vector norms, rolling optimization, and feed-forward compensation. This control strategy has been successfully tested in the wind tunnel, and the control accuracy of Mach number has been remarkably enhanced, to the point where it can be controlled to within . This value satisfies the requirements of aerodynamic aircraft testing.

Multi-objective optimization of shock control bump on a supercritical wing

Based on the supercritical “wing1” which was released in the DPW-III conference, multi-objective optimization has been done to increase the lift-drag ratio at cruise condition and improve transonic buffet boundary and drag-rise performance. Hicks-Henne shape functions are used to represent the bump shape. In the design optimization to increase lift-drag ratio, the objectives involve the cruise point and three other off-design points nearby. In the other optimization process to improve buffet and drag-rise performance, three buffet onset points near the cruise point and one drag-rise point are selected as the design points. Non-dominating sort genetic algorithm II (NSGA-II) is used in both processes. Additionally, individual analysis for every selected point on the Pareto frontier is conducted in order to avoid local convergence and achieve global optimum. Results of optimization for aerodynamic efficiency show a decrease of 11 counts in drag at the cruise point. Drag at nearby off-design points are also reduced to some extent. Similar approaches are made to improve buffet and drag-rise characteristics, resulting in significant improvements in both ways.

Aerodynamic Design Methodology for Blended Wing Body Transport

This paper puts forward a design idea for blended wing body (BWB). The idea is described as that cruise point, maximum lift to drag point and pitch trim point are in the same flight attitude. According to this design idea, design objectives and constraints are defined. By applying low and high fidelity aerodynamic analysis tools, BWB aerodynamic design methodology is established by the combination of optimization design and inverse design methods. High lift to drag ratio, pitch trim and acceptable buffet margin can be achieved by this design methodology. For 300-passenger BWB configuration based on static stability design, as compared with initial configuration, the maximum lift to drag ratio and pitch trim are achieved at cruise condition, zero lift pitching moment is positive, and buffet characteristics is well. Fuel burn of 300-passenger BWB configuration is also significantly reduced as compared with conventional civil transports. Because aerodynamic design is carried out under the constraints of BWB design requirements, the design configuration fulfills the demands for interior layout and provides a solid foundation for continuous work.

Optimum Aspect Ratio for Subsonic Air Vehicles

This fundamental study considers airframes engineered to meet range and/or efficiency goals that span several orders of magnitude in size (from approximately 1000 lb to one million lb maximum flight weights). A simplified, analytical model is used to demonstrate the influence of key constraints (maximum ceiling and desired cruise speed) and design parameters (wing loading, wing aspect ratio, wing sweep, wing technology, and allowable excrescence drag) upon aerodynamic performance and fuel volume. This model illustrates factors that drive the optimum wing loading, technology, and aspect ratio for an airframe engineered to meet improved range and efficiency goals. The performance of airframes over a 200,000 lb flight weight is well represented by classical theory. For many airframes under 100,000 lb,flight at the typicalmission cruise point is dominated by zero-lift drag.A statistical design approach to refine these configurations reveals counterintuitive design insight. To simultaneously improve range and efficiency of a conventionally configured zero-lift–drag-dominated airframe, analysis of a full factorial design exploration suggests changes, such as increasing its service ceiling (though larger engines), increasing its certification ceiling, and revisions to the wing planform, that, in some cases, call for a reduction in aspect ratio and wingspan.

Application of total energy control for high-performance aircraft vertical transitions

Energy management guidance algorithms for automated, fast transitions between cruise states are presented. These algorithms use total energy control principles to regulate throttle and flight control inputs. Two principal algorithms are used to perform cruise state transitions: Energy Hold/Altitude Hold - This algorithm consists of two guidance laws which regulate thrust and vertical lift to acquire and maintain a desired height/energy cruise point.

Advanced single-rotation propfan drive system

E CONOMIC and strategic incentives to reduce aircraft fuel consumption have prompted significant government and industry interest in advanced turboprop aircraft for the 1990s. Scale-model wind tunnel testing has shown that large improvements in propulsive efficiency are achievable with a propfan at the high-speed flight conditions of advanced turbofan-powered aircraft. The propfan design concept shown in Fig. 1 is a full-size system for test evaluation in NASA's Propfan Test Assessment (PTA) flight research program in mid-1987. The work described herein is the single-rotation gearbox phase of Allison's Advanced Propfan Engine Technology (APET) study sponsored by the NASA Lewis Advanced Turboprop Office. Today, with the propfan approach of thin-swept highly loaded blades, the flight envelope for commercial turboprop aircraft can be extended in speed and altitude to include the turbofan cruise points. The APET study established the engine cycle trades for an extended turboprop flight envelope. Cost/benefit analyses based on the specific fuel consumption advantages of a high-pressure-ratio cycle showed the advantage of operating in the 30:1 to 40:1 range, which is compatible with 1990's component technology. Turbine inlet temperatures on the order of 2500°F would complement the high pressure and, at the same time, not compromise hotsection life. The APET study also showed that the advanced turboprop propulsion system should be designed using modular concepts to enhance maintenance of components and auxiliary systems. The following discussion describes the preliminary design of a single-rotation (SR) propfan gearbox.

Real model following control

Performance sensitivity may be compensated by adjusting the nominal trajectory to be fuel optimal for the specific variation under consideration. As a first step, optimal cruise points are determined for each variation using Eq. (3). Only variations in the drag coefficients, aircraft weight, and atmospheric conditions cause a shift in the cruise point. The cruise point shifts upward as the drag coefficients and aircraft weight increase, and it shifts downward as the parameters decrease; while a Hot Day atmosphere causes the cruise point to shift upward and a Cold Day atmosphere causes a downward shift. Using the values for (ocDc/Vc) calculated at these adjusted cruise points, the adjusted minimum fuel trajectory for each variation is determined. The fuel performance sensitivity for each variation is given in Table 3. Path adjustment causes very little, if any significant improvement in fuel consumption for any of the parametric or atmospheric variations. For example, when aircraft weight is increased by 20% along the nominal path, fuel consumption increases by 23%. However, when the nominal trajectory is adjusted to be fuel optimal for a 20% weight increase, the fuel consumption is increased by 22% representing a 1% improvement. Obviously, adjusting the nominal trajectory to be fuel optimal for the parameters examined here fails to provide significant improvement in fuel consumption.

Fuel Optimality of Cruise

IN the paper by Schultz and Zagalsky, the solution characteristics for the minimum fuel-fixed range problem are determined for a number of different mathematical models of aircraft dynamics. Different results are obtained for different sets of equations. The energy state equations are shown to not allow a partial throttle, constant velocity, cruise solution; but because the velocity set is not convex, to have a chattering solution which provides the best performance but which may not be realizable with plecewise continuous maximum values of the controls. The equation set with throttle and flight path angle as controls was shown to allow a partial throttle cruise solution. This conclusion was shown to be invalid by Speyer by application of the Generalized Legendre-Clebsch condition. The following analysis shows that for a higher order set of equations which has lift and thrust as controls, the necessary condition for optimization including the Generalized Legendre-Clebsch condition are satisfied at the cruise point so that the partial throttle cruise condition is a candidate solution for the minimum fuel-fixed range problem.