Blended Wing Body Research Articles

Active gust load alleviation system for flexible aircraft: Mixed feedforward/feedback approach

Lightweight flexible blended-wing-body (BWB) aircraft concept seems as a highly promising configuration for future high capacity airliners which suffers from reduced stiffness for disturbance loads such as gusts. A robust feedforward gust load alleviation system (GLAS) was developed to alleviate the gust loading. This paper focuses on designing a feedback controller which would improve the robust performance of the feedforward controller in reducing the peaks in wing root moments at very short gust lengths. The simulation results show that when the new feedback compensator is engaged with the feedforward controller, the performance of the GLAS system is improved significantly in terms of reduction in wing root moments for shorter as well as for longer gusts. This reduction in the wing root moment's peak provides potential structural benefits and weight savings.

Body Freedom Flutter of a Blended Wing Body Model Coupled with Flight Control System

Aeroservoelastic model is developed for a blended wing body aircraft coupled with flight control system. Body freedom flutter of such aeroservoelastic system is analyzed and trend studies considering varied loop gain value, center of gravity of the balanced weight and wing stiffness are delivered to determine their influence on body freedom flutter characteristics of this aeroservoelastic system. It is found that the closed loop flutter speed decreases dramatically compared to that of the open loop case. The loop gain value and the wing stiffness have strong influence on the closed loop flutter characteristics. It is noted that the static unstable unaugmented blended wing body aircraft can be stabilized by proper designed flight control system, however, the closed loop body freedom flutter speed is still quite low which needs further consideration in flight control system synthesis.

Numerical Simulation of Engine Noise Shielding around Blended Wing Body Aircraft

A numerical simulation of sound propagation around a blended wing body (BWB) aircraft with an open rotor engine is performed to understand the shielding effect of the engine noise. A boundary element method (BEM) code based on the Helmholtz equation is developed for this purpose. The effect of uniform flow and the surface impedance of the aircraft is analyzed in detail. The mean flow showed little effect on the amount of shielding since the approach speed is a relatively low Mach number. On the other hand, when a soft-surface condition is applied to the upper side of the aircraft, a larger amount of shielding is observed throughout the analyzed field when compared to a rigid surface case. Additionally, an effective area for applying the soft-surface condition is clarified in order to reduce the usage of such material.

CONCEPTUAL DESIGN OF BLENDED WING BODY BUSINESS JET AIRCRAFT

Blended Wing Body concept offers several advantages compared to traditional aircraft tube and wing concept. The advantages mainly come from the distributed aerodynamic and structural loads, which leads to better aerodynamic performance as well as lighter structural weight. Most of the existing studies were focused on big transport aircraft carrying 400 to 800 passenger. In this study, a conceptual design of a business jet aircraft applying blended wing body concept is carried out. The market forecast for this category of aircraft can reach up to 24000 aircraft in the next 20 years. The possibility of having larger cross section is one of the competitive advantages, notably in a long-range flight. The requirement stated was to fly a trans-atlantic flight and carrying up to 18 passengers. It has to have a low floor height permitting easy passenger access. The design process consists of initial weight estimation, initial sizing, and preliminary aerodynamics, weight and balance and performance analysis. Some design consideration specially related with Blended Wing Body concept will be discussed, i.e. take-off and landing aerodynamics, structural concept, stability and control. The final design resulted in twin-engine aircraft, a Maximum Take-off Weight of 44 ton, cabin floor area of 6.9 x 10 m, winglet and split rudder for directional stability and control, and elevons for longitudinal and lateral control.

STAMP-based safety control approach for flight testing of a low-cost unmanned subscale blended-wing-body demonstrator

Under tight constraints on cost, during unmanned subscale demonstration flight testing of the novel Blended-Wing-Body (BWB) configurations by our research team, safety was a challenging concern. Earlier accident rates of the prior three demonstrators were high (between 66.7% and 100%), which has proven the ineffectiveness of post-accident learning that we held before. Moreover, considering the status in quo of our team, uncertain vehicle flight characteristics, lack of technical standards and procedures, and especially disorganized team structure made the application of quantitative safety analysis infeasible due to lack of data and technical uncertainties at this engineering stage. Indeed, the BWB demonstrators are not merely technical systems but also have intrinsic organizational dimensions that impact their development and operation processes contributing to the flight safety. As an alternative of even-chain based hazard analysis methods which have limitations on capturing non-failure accidental factors, this paper proposes STAMP/STPA based systems theoretic approach on safety to reduce the number of trials and errors systematically. This method is demonstrated through a case study of the safety control of a new BWB demonstrator called BB-4. This method identifies unsafe scenarios that encompass both the technical system flaws and organizational deficiencies and proposes derived safety control measures in these two dimensions. Since 2011 to date, the accident rates (<5%) maintained by us and other applicators have verified the effectiveness of this approach empirically.

Numerical Prediction of Blended Wing Body Aerodynamic Characteristics at Subsonic Speed

The need for high performance and green aircraft has brought the blended wing (BWB) aircraft concept to the centre of interest for many researchers. BWB is a type of aircraft characterized by a complex blending geometry between fuselage and wing. Recently, many researches had been performed to unlock its aerodynamic complexity that is still not well understood. In this paper, aerodynamic characteristic of a baseline BWB configuration derived from simple conventional aircraft configuration was analysed using the Reynolds-averaged Navier-Stokes computational fluid dynamics (CFD) solver. The main objectives of this work are to predict the aerodynamic characteristics of the BWB concept at steady flight conditions and at various pitch angles. The results obtained are then compared against a simple conventional aircraft configuration (CAC). The results show that the BWB configuration used has 24% higher L/D ratio than the CAC. The increment to the L/D however is mainly due to lower drag than the improvement in the lift.

Acoustic interaction of turbofan exhaust with deflected control surface for blended wing body airplane

Small-scale experiments simulated the elevon-induced jet scrubbing noise of the Blended-Wing-Body platform with a bypass ratio ten turbofan nozzle installed above the wing. The elevon chord length at the interaction zone was similar to the exit fan diameter of the nozzle. The study encompassed variable nozzle position, variable elevon deflection, removable inboard fins, and two types of nozzles—plain and chevron. Far-field microphone surveys were conducted underneath the wing. The interaction between the jet and the elevon produces excess noise that intensifies with increasing elevon deflection. When the elevon trailing edge is near the edge of the jet, excess noise is manifested as a low-frequency bump on the sound pressure level spectrum. An empirical model for this excess noise is presented. The interaction noise becomes severe, and elevates the entire spectrum, when the elevon intrudes significantly into the jet flow. The increase in effective perceived noise level (EPNL) falls on well-defined trends when correlated versus the penetration of the elevon trailing edge into the flow field of the isolated jet. The cumulative takeoff EPNL can increase by as much as 19 dB, underscoring the potentially detrimental effects of jet-elevon interaction on noise compliance.

A hybrid engine concept for multi-fuel blended wing body

Purpose – The purpose of this paper is to present a novel hybrid engine concept for a multi-fuel blended wing body (MFBWB) aircraft and assess the performance of this engine concept. Design/methodology/approach – The proposed hybrid engine concept has several novel features which include a contra-rotating fan for implementing boundary layer ingestion, dual combustion chambers using cryogenic fuel (liquefied natural gas [LNG] or liquid hydrogen [LH2]) and kerosene in the inter-turbine burner (in flameless combustion mode) and a cooling system for bleed air cooling utilizing the cryogenic fuel. A zero-dimensional thermodynamic model of the proposed hybrid engine is created using Gas Turbine Simulation Program to parametrically analyse the performance of various possible engine architectures. Furthermore, the chosen engine architecture is optimized at a cycle reference point using a developed in-house thermodynamic engine model coupled with genetic algorithm. Findings – Using LH2 and kerosene, the hybrid eng...

Airframe integration for an LH2 hybrid-electric propulsion system

Purpose – The purpose of this paper is to explore some of the challenges associated with the integration of an LH2-fuelled advanced hybrid-electric distributed propulsion system with the airframe. The airframe chosen as a case study is an ultra-high-capacity blended wing body configuration. It is designed to represent an A-380 class vehicle but in the 2025-2030 timeframe. The distributed propulsion system is a hybrid-electric concept that utilizes high-temperature superconducting technologies. The focus of the study is the application of LH2 as a fuel, with comment being given to kerosene and LCH4. Design/methodology/approach – The study consists of a conceptual design developed through the preliminary design phase and part way into the detailed design phase. Findings – The relationship between passenger capacity and fuel capacity is developed. Some remaining challenges are identified. Practical implications – The study supports further conceptual design studies and more detailed system studies. Social im...

The Effect of Gust on Blended-Wing-Body Civil Aircraft

In this paper, aerodynamic properties of Blended Wing Body (BWB) civil aircraft are studied by two models: one calls complete model that is computed by numerical simulation coupling equations of motion with the Navier-Stokes equations, and the other doesn’t consider the equations of motion (without dynamic response). The results show that the model without dynamic response can also correctly predict the trend of the dynamic properties compared with complete model. Nevertheless, there are some quantitative differences existing between the complete model and the model without dynamic response.

Aerodynamic Performance of Blended Wing Body Aircraft with Distributed Propulsion

A 350-passenger BWB with a distributed propulsion system configuration is carried out and its aerodynamic performance in cruising and taking off are analyzed and discussed. It is shown from computation that the integrated configuration has a commendable aerodynamic performance in cruising and taking off. The cruise lift to drag ratio is reach to 24.0 in cruising. The ingestion effect of the propulsion system leads to a high lift at a low speed. The maximum lift coefficient CLmax is 1.62 when α=20° in taking off. In addition, the ingestion also delays the flow separation on the upper surface of center body, which contributes to a well stall performance of the configuration at large angle of attack.

Flow control of a boundary layer ingesting serpentine diffuser via blowing and suction

The use of serpentine boundary layer ingesting (BLI) diffusers offers a significant benefit to the performance of Blended Wing Body (BWB) aircraft. However, the inherent diffuser geometry combined with a thick ingested boundary layer creates strong secondary flows that lead to severe flow distortion at the engine face, increasing the possibility of engine surge. This study investigated the use of enabling active flow control methods to reduce engine-face distortion. An ejector-pump based system of fluidic actuators was used to directly manage the diffuser secondary flows. This system was modeled computationally using a boundary condition jet modeling method, and tested in an ejector-driven wind tunnel facility. This facility is capable of simulating the high-altitude, high subsonic Mach number conditions representative of BWB cruise conditions, specifically a cruise Mach number of 0.85 at an altitude of 12,000 m. The tunnel test section used for this experiment was designed, built, and tested as a validation tool for the computational methods.

A multi-input multi-output adaptive feed-forward controller for vibration alleviation on a large blended wing body airliner

Turbulent atmosphere, gusts, and manoeuvres significantly excite aircraft rigid body motions and structural vibrations, which leads to reduced ride comfort and increased structural loads. In particular BWB (Blended Wing Body) aircraft configurations, while promising a significant fuel efficiency improvement compared to wing-tube configurations, exhibit severe sensitivity to gusts. In general, a flexible aircraft represents a lightly damped structure involving a large variety of uncertainties due to fuel mass variations during flight, control system nonlinearities, aerodynamic nonlinearities, and structural nonlinearities, to name just a few. Especially at the beginning of flight testing of a newly developed aircraft type, plant models generally require a lot of verification and adjustment based on obtained flight test data, before they can be used reliably for control law design. Adaptive control already is a well-established method for many active noise and vibration control problems, and thus is proposed here for application to the problem of gust load alleviation. However, safety requirements are significantly higher for gust load alleviation systems than for most noise and vibration control systems. This paper proposes a MIMO (Multi-Input Multi-Output) adaptive feed-forward controller for the alleviation of turbulence-induced rigid body motions and structural vibrations on aircraft. The major contribution to the research field of active noise and vibration control is the presentation of a detailed stability analysis of the MIMO adaptive algorithm in order to support potential certification of this method for a safety-critical application. Finally, the proposed MIMO adaptive feed-forward vibration controller is applied to a longitudinal flight dynamics model of a large flexible BWB airliner in order to verify the derived vibration controller on a challenging control problem.

Flight dynamics models used in different national and international projects

Purpose – The present study aimed to demonstrate different computational models, data and stability results obtained in a wide number of projects of various aircrafts such as unmanned aerial vehicles (UAVs), general aviation and big passenger flying airliners in blended wing body (BWB) configurations. Many details of modeling and computing are shown for unconventional configurations, namely, for a BWB aircraft and for tailless UAVs. Design/methodology/approach – Mathematical models for analysis of static and dynamic stability were built and investigated based on equations of motion in the linearized form using the so-called state variable model for a steady-state disturbed, generally asymmetric, flight. Findings – Flight dynamics models and associated computational procedures appeared to be useful, both in a preliminary design phase and during the final assessment of the configuration at flight tests. It was also found that the difference between thresholds for static and dynamic stability conditions was ...

Aerodynamic Design Optimization Studies of a Blended-Wing-Body Aircraft

The blended wing body is an aircraft configuration that has the potential to be more efficient than conventional large transport aircraft configurations with the same capability. However, the design of the blended wing is challenging due to the tight coupling between aerodynamic performance, trim, and stability. Other design challenges include the nature and number of the design variables involved, and the transonic flow conditions. To address these issues, a series of aerodynamic shape optimization studies using Reynolds-averaged Navier–Stokes computational fluid dynamics with a Spalart–Allmaras turbulence model is performed. A gradient-based optimization algorithm is used in conjunction with a discrete adjoint method that computes the derivatives of the aerodynamic forces. A total of 273 design variables—twist, airfoil shape, sweep, chord, and span—are considered. The drag coefficient at the cruise condition is minimized subject to lift, trim, static margin, and center plane bending moment constraints. The studies investigate the impact of the various constraints and design variables on optimized blended-wing-body configurations. The lowest drag among the trimmed and stable configurations is obtained by enforcing a 1% static margin constraint, resulting in a nearly elliptical spanwise lift distribution. Trim and static stability are investigated at both on- and off-design flight conditions. The single-point designs are relatively robust to the flight conditions, but further robustness is achieved through a multipoint optimization.

NaBH4 (sodium borohydride) hydrogen generator with a volume-exchange fuel tank for small unmanned aerial vehicles powered by a PEM (proton exchange membrane) fuel cell

A proton exchange membrane fuel cell system integrated with a NaBH4 (sodium borohydride) hydrogen generator was developed for small UAVs (unmanned aerial vehicles). The hydrogen generator was composed of a catalytic reactor, liquid pump and volume-exchange fuel tank, where the fuel and spent fuel exchange the volume within a single fuel tank. Co–B catalyst supported on a porous ceramic material was used to generate hydrogen from the NaBH4 solution. Considering the power consumption according to the mission profile of a UAV, the power output of the fuel cell and auxiliary battery was distributed passively as an electrical load. A blended wing-body was selected considering the fuel efficiency and carrying capability of fuel cell components. First, the fuel cell stack and hydrogen generator were evaluated under the operating conditions, and integrated into the airframe. The ground test of the complete fuel cell UAV was performed under a range of load conditions. Finally, the fuel cell powered flight test was made for 1 h. The volume-exchange fuel tank minimized the fuel sloshing and the change in center of gravity due to fuel consumption during the flight, so that much stable operation of the fuel cell system was validated at different flight modes.

Assessment and optimization of an airplane

Purpose – The ratio of the energy transformed to the revenue work done (ETRW) during a flight of an airplane can be employed as a key indicator to assess its environmental impact. It remains constant during the life cycle of the aircraft and is fixed by its designers. The goal of an environmentally optimum airplane is to minimize the ETRW. Design/methodology/approach – For an existing airplane, there are two major parameters that can greatly affect the ETRW, which are the ratio of actual payload to maximum possible payload “c” and the flight range R. The goal of this paper is to study the effect of c and R on ETRW and minimize it by using a genetic algorithm (GA). The study is performed on a Boeing 737-800 and a Boeing 747-400 aircraft as well as recently proposed aircraft designs namely the Boeing second-generation Blended-Wing-Body (BWB) and MIT Double-Bubble D8.2. Findings – It turns out that the maximum possible values of payload and range do not necessarily lead to a flight with minimal environmental...

Conceptual design and analysis of blended-wing-body aircraft

Due to the unconventional nature of the blended wing body (BWB) no off-the-shelf software package exists for its conceptual design. This study details a first step towards the implementation of traditional and BWB-specific design and analysis methods into a software tool to enable preliminary sizing of a BWB. The tool is able to generate and analyze different BWB configurations on a conceptual level. This paper investigates three different BWB configurations. The first configuration is an aft-swept BWB with aft-mounted engines, the second configuration is an aft-swept BWB with wing-mounted engines and the third configuration is a forward-swept BWB with wing-mounted engines. These aircraft comply with the same set of top-level requirements and airworthiness requirements. Each of the designs has been optimized for maximum harmonic range, while keeping its maximum take-off weight constant and identical. Results show that the forward-swept configuration with wing-mounted engines has the highest harmonic range. These findings warrant further investigation in this configuration and other alternative BWB configurations.

Aerodynamic, Stability and Flying Quality Evaluation on a Small Blended Wing-body Aircraft with Canard Foreplanes

Abstract Blended wing-body (BWB) concept promises up to 30 percent increase in aerodynamic efficiency and reduction in fuel cost by having planform geometry optimized to increase lift and to reduce drag. Many claimed to have achieved the target of increasing lift-to-drag ratio better than current conventionally-configured airplanes either large airliners or small unmanned airplane. However, achieving good balance of aerodynamic efficiency, stability and flying quality is harder then one might expect. Over years of studying small BWB aircrafts in Universiti Teknologi MARA (UiTM), it is found that unconventional behaviour of aerodynamic characteristics leads to limitations to BWB aircraft's flight envelope. In this paper, a short overview of aerodynamic, stability and flying quality of UiTM's BWB aircraft design is highlighted. Lessons learned from its unsusual lift-angle of attack curves, stability reversals, the effect of canard to flight stability and poor longitudinal flying quality (short-period mode and phugoid mode) are discussed. A classical control solution to improve it flying quality has been proposed and simulated and the result shows that both short-period and phugoid modes are able to achieve damping ratios within 0.6 to 0.8 exceeding minimum Level 1 damping ratios of 0.35 and 0.04 respectively. Design flaws of this aircraft and recommendations to be implemented on the next evolution of aircraft design conclude this paper.

Blended Wing Body Architecting and Design: Current Status and Future Prospects

Fixed-wing aircraft are viewed as no longer satisfying our needs today. In the past ten years, fuel efficiency and noise reduction have become the two biggest challenges for aircraft manufacturers. The recognition spurred aerospace engineers and system architects to come up with the Blended Wing Body (BWB), a new design for next generation aircraft. In this paper, we discuss the development of BWB from the perspective of design challenges that system architects and engineers faced during the design process, the architecting heuristics employed, and the rationale for design decision. In addition, body material and shape selection procedures, flight simulation, design optimization, and the advantages of the resultant design are also addressed. Thereafter, we look down the line and discuss the evaluation of emergence technologies on BWB aircraft subsystems, and a model for evaluating technology upgrade.