Condition-based maintenance programs for modern helicopters rely on algorithmic techniques to estimate the useful life remaining for life-limited components. Regime-recognition-based condition-based maintenance programs involve a regime recognition step and a damage estimation step in which damage is calculated based on the identified regimes. Recently, new probabilistic regime recognition algorithms

A study was performed to characterize an optimum return trajectory for a sailplane after a rope-break failure during an aerotow launch procedure. The performance of an SGS 1-26E sailplane was simulated using the equations of motion for quasi-steady flight in a time-stepping routine and published aerodynamic polar data. A gradient-based optimization algorithm was implemented using the simulated trajectory

The channel wing is a lift-enhancement concept pioneered by Willard Ray Custer in the late 1940s in an effort to provide a fixed-wing aircraft with short takeoff and landing (STOL) capabilities. This paper experimentally investigates the possibility of using Custer channel wings for slow flight and STOL of small (under 35 kg) fixed-wing unmanned aerial vehicles. The Custer unmanned aircraft developed

This paper analyzes the effects of the helicopter dynamics on pilots’ learning process and transfer of learned skills during autorotation training. A quasi-transfer-of-training experiment was performed with 14 experienced helicopter pilots in a moving-base flight simulator. Two types of helicopter dynamics, characterized by a different autorotative index, were considered: “hard,” with high pilot compensation

As contemporary aerostructural research for aircraft design trends toward high-fidelity computational methods, aerostructural solutions based on theory are often neglected or forgotten. In fact, in many modern aerostructural wing optimization studies, the elliptic lift distribution is used as a reference in place of theoretical aerostructural solutions with more appropriate constraints. In this paper

Aircraft infrared (IR) signature studies are complex, due to their dependence on several parameters, e.g., line of sight (LOS) and viewing aspect (LOS^). There is no equivalent counterpart of the well-known radar cross section (RCS) that can be easily used for obtaining IR lock-on range, RLO,λ1−λ2. This study introduces the concept of IR cross section (IRCS)λ1−λ2 of complete aircraft as seen by seeker

Journal of Aircraft, Ahead of Print.

This paper presents the results of turbulent flow simulations prepared for the Third AIAA Sonic Boom Prediction Workshop. Solutions were prepared for two geometries that exhibited shock–plume interaction features: the NASA biconvex shock–plume interaction wind-tunnel model, and the NASA C608 low-boom concept aircraft. The unstructured, finite volume Navier–Stokes solver UNS3D was used to predict the

Simulation results are presented for all cases from the Third AIAA Sonic Boom Prediction Workshop. An inviscid, embedded-boundary Cartesian-mesh flow solver is used in conjunction with adjoint-based mesh adaptation to compute near-field pressure signatures. Specialized techniques are applied to maximize accuracy and minimize cost on Cartesian meshes. Regions of the flow most sensitive to discretization

Journal of Aircraft, Ahead of Print.

Tiltrotor aircraft ship suitability and envelope expansion testing aboard a U.S. Navy aircraft carrier is discussed. The purpose was to validate and expand day/night vertical launch and recovery wind envelopes, and the development of short takeoff and minimum run-on landing wind envelopes. The preparation phase incorporated a six-degree-of-freedom motion flight simulator to evaluate flight dynamics

The aerodynamic design and fuel burn performance of a Mach-0.78 strut-braced-wing regional jet is investigated through aerodynamic shape optimization based on the Reynolds-averaged Navier–Stokes equations. Conceptual-level multidisciplinary design optimization is first performed to size the strut-braced-wing aircraft for a design mission similar to the Embraer E190-E2, with a design range of 3100 nmi

Instantaneous force and structural deformation experiments were performed on a flexible, structurally characterized, low-aspect-ratio representative flapping wing. A six-component force balance was used to measure aerodynamic-force time history over a flap cycle. A VICON motion capture setup tracked the wing deformations while flapping. Measured aerodynamic forces and wing deformations were compared

The Third AIAA Sonic Boom Prediction Workshop was held in January 2020, and in the near-field section of the workshop, several simulated near-field pressure signatures of the C608 airplane, an early version of the NASA X-59, were compared. The authors have applied the unstructured/structured overset grid method to the C608 airplane case. In this method, an unstructured grid is used in the vicinity

This work considers the aeroelastic optimization of transport wingbox structures under three different types of design variables: sizing (for example, skin thickness), shape (planform and airfoil twist/thickness), and topology/layout (rib and stringer placement). The numerical optimization is conducted with a nested bilevel method: with a nongradient-based global optimizer at the outer level (a Bayesian

To improve robustness and efficiency of automatic transition prediction in aerodynamic design, a reduced model of linear stability analysis is usually adopted, such as eN-envelope or eN-database method. Nevertheless, building such a model is challenging when it comes to compressible flows, as the transition mechanism is more complex and multiple flow parameters should be taken into consideration. To

In this paper, we develop a computationally efficient frequency-domain model that can be used to compute the required shaft power and vibratory loads for a trimmed helicopter rotor with flexible blades in forward flight. The aerodynamic forces and power are modeled using a vortex-lattice method. A finite element model based on the linearized form of the Hodges–Dowell rotating beam equations is used

Coaxial rotor aeroelasticity is complex due to the counter-rotating wake system, rotor lift offset, periodic blade passage loads, unsteady rotor wake interactions, reduced rotor speed, and stiff hingeless blades. In this study, the aeroelastic stability of a coaxial rotor is examined in hover and forward flight. The rotor wake is modeled with the viscous vortex particle method, a grid-free approach

A Monte Carlo model designed for fixed-wing aircraft takeoff performance uncertainty quantification is benchmarked. The uses of an efficient takeoff simulator of this type range from rapid design variable and constraint sensitivity studies and large-scale conceptual level analyses to operational performance planning and real-time anomaly detection. The accuracy of the model is assessed against high-resolution

The push for more-electric aircraft (MEA) has motivated numerous studies to quantify and optimize the impact of subsystem electrification in early design phases. Past studies on multi-objective optimization of MEA show a clear benefit over conventional architectures when no constraints are placed on the number of subsystems electrified at once. In reality, aircraft manufacturers are more likely to

As distributed electric propulsion has continued to gain popularity as an enabling aircraft technology, further research is required to understand the complete implications of aeropropulsive coupling effects for distributed propulsion systems integrated into actual aircraft geometries. A set of low-speed wind-tunnel tests was performed at the University of Illinois at Urbana-Champaign to characterize

Future aircraft designs look set to use longer wingspans to increase the aspect ratio and therefore overall aerodynamic efficiency of the airframe. Such larger wingspans also reduce roll rates and require increased control surface area to achieve the roll maneuver requirements for certification. In this work, the effect of using flared folding wingtips (FFWTs) on the roll performance of simple aircraft

Propellers used for electric vertical takeoff and landing (eVTOL) aircraft propulsion systems experience a wide range of aerodynamic conditions, including large incidence angles relative to oncoming airflow. In oblique flow, propellers exhibit deviations in thrust and torque oriented along the propeller axis of rotation, as well as significant off-axis forces and moments. Although important for modeling

Compressible cavity flows exist widely in aeronautical vehicles. The cost of the computational fluid dynamics to solve compressible cavity flows is high. To address this issue, in this work, a novel reduced-order model (ROM) combining proper orthogonal decomposition (POD) with the long short-term memory (LSTM) neural network named LSTM-ROM for predicting the compressible cavity flows is proposed. First

New aircraft developments are made to improve aircraft performance and efficiency. One such method is integrating propulsion into the airframe. This allows for boundary-layer ingestion, which shows promise of significant power benefits. However, these benefits are difficult to quantify as the propulsion system and aircraft body become meticulously integrated. The thrust and drag are coupled and cannot

Multi-unmanned aerial vehicle (UAV) cooperative lift systems use multiple UAVs to collectively lift and transport payloads. These systems have unique benefits over standard single-vehicle logistics paradigms in that they distribute lift capacity among several potentially inexpensive and man-portable aircraft, and furthermore provide redundancy to guard against vehicle failure. However, several challenges

This paper presents a conceptual study of a regional aircraft with a turboelectric propulsion system and boundary-layer ingestion. The aircraft has an additional electric propulsor installed at the aircraft tail cone, which is driven by generators installed on both underwing engines, aiming to ingest the fuselage boundary layer and improve the aircraft overall performance. The proposed configuration

The accurate prediction of the sonic boom is essential for the development of a future low-boom supersonic aircraft. In this paper, the best practice for predicting near-field pressure signatures with the German Aerospace Center (DLR) TAU code is applied for geometries and grids provided by the third AIAA Sonic Boom Prediction Workshop. The near-field part of the workshop provided two cases, the biconvex

The PCBoom suite of tools was used to model atmospheric propagation cases and the optional focus case as part of the Third AIAA Sonic Boom Prediction Workshop. The Focused Boom module FOBoom version 7.1.0 was used to complete ray tracing calculations using computational fluid dynamics pressure data as the source. Lossy propagation was modeled using PCBoom’s interactive Burgers equation solver, PCBurg

In this paper, we develop a semiempirical model for predicting degradation in lithium–ion batteries and use it to assess the performance of an all-electric general aviation aircraft over its operational lifetime. The model comprises three parts: a cycle discharge model, a heat transfer model, and a cell-aging model. The discharge model captures the steady-state and transient behaviors of the cell.

Spoilers play a vital role in the flight control systems of modern transport aircraft. Because of their efficiency and fast deflection rates, they are widely used to assist in roll control or for gust load alleviation purposes. Simulating the aerodynamic behavior of spoilers still is a challenging task, as deflecting a spoiler always induces flow separation. The work presented in this paper therefore

Aircraft-mounted gas turbine engines may need to employ a variety of inlet ducts to perform various missions. An inertial particle separator (IPS) is a type of inlet duct that can remove harmful dust and debris from an engine’s flow path. The IPS is a bifurcating duct that is designed to remove particles, but it may also cause undesired flow separation. A novel study on such a bifurcating duct at high

Laboratory experiments were conducted to generate empirical dimensionless correlations for estimating surface roughness of frost formed on a cold flat plate under forced convection. Environmental variables, including wall temperature Ts, air velocity Vair, relative humidity RH, and air temperature Tair, were considered when generating the correlations. The test conditions were chosen to simulate the

The work presented in this paper is a culmination of a multiyear joint experimental and computational effort to explore the feasibility of using active flow control (AFC) on a simple hinged flap system for recovering lift comparable to a conventional high-lift system consisting of Fowler flaps. The baseline configuration chosen for this work is the high-lift version of the NASA Common Research Model

Wind tunnel oscillatory testing is a technique conventionally used for the measurement of dynamic aerodynamic loads on subscale aircraft models. Oscillatory testing is commonly used for identification of dynamic stability derivatives for flight mechanics models. Model oscillation is normally driven by a rig drive mechanism, or with the use of its control surfaces. This paper presents a new test technique

Store separation of a generic, thin-finned, missile through a continuously oscillating shear layer into subsonic flow was conducted experimentally through 100 drop tests to identify potential groups of trajectories and statistical phenomena. Change in store pitch was observed using a high-speed camera. Trajectories were grouped using machine learning with a k-means clustering, followed by a Gaussian

A vehicle-level noise assessment has been performed for the NASA D8 (ND8) concept aircraft in the NASA Advanced Air Transport Technology Project portfolio. The NASA research-level Aircraft Noise Prediction Program was used to predict the noise from each source component on the ND8 to build up a noise estimate for the full aircraft. The propulsion airframe aeroacoustic effects of the ND8 (namely, boundary-layer

This Paper explores the development of a novel hybrid air vehicle for package delivery called the quadrotor biplane tail-sitter. This vehicle uses differential thrust to effect body attitude changes like a traditional quadrotor, ensuring full transitional control between hover and forward flight modes. This method of control also allows the vehicle to remain mechanically simple. A vehicle was designed

Longitudinal vortices are a common flow phenomenon in the flow around aircraft. They emerge wherever sharp edges are encountered and affect the stability of the boundary layers with which they interact. Hence, for an optimal aircraft design, it is necessary to accurately predict not only the formation of these vortices, but also their downstream evolution. This paper presents a numerical simulation

In the context of conceptual design there are low-fidelity lifting line models capable of predicting the maximum lift coefficient of trapezoidal twisted wings. However, more complex geometries like that of the blended-wing–body (BWB) require the introduction of additional geometrical hypotheses. This paper introduces a compound-wing lifting line model that predicts the maximum lift coefficient of geometries

The low-sweep transonic natural laminar flow wing with shock control bumps, namely, LS-NLF-SCB wing, has a promising potential to be applied to future narrow-body commercial aircraft due to its advanced natural laminar wing design combined with shock control. This paper aims to assess the benefits of LS-NLF-SCB wing application from the viewpoint at the aircraft level. Based on the previous published

High-altitude scientific balloons are often prohibited from flying due to the risk associated with flying over populated areas. One solution to this problem is the use of a trajectory control system to control the ground track of the balloon. To assess the performance of one such trajectory control system in a real wind field, a small-scale sail was designed and built to fly beneath a moored balloon

Active flow control (AFC) is conventionally used to reduce flow separation at high angles of attack. A novel alternative form of AFC for controlling rotor blade loads in attached flow is examined. The AFC system employs pulsed fluidic jets near the trailing edge of a VR-12 airfoil on the pressure side and suction side. Each jet has two operating modes: tangential blowing and normal blowing. Unsteady

A flight test with a simplified hybrid laminar flow control (HLFC) system on the vertical tail plane (VTP) of an A320 aircraft was performed in April/May 2018. This HLFC system was a prototype for a simplified system that might be attractive for drag reduction of commercial long-range aircraft. The paper presents the design principles of a simplified HLFC system, including passive suction, and shows

Ice accretion on a helicopter’s aerodynamic surfaces during flight can lead to incidents and fatal accidents. An iced helicopter blade results in a decrease in stall angle, an increase in required torque, as well as potential damage from shed ice. While the high centrifugal forces on a rotor may serve as a natural deicing mechanism, they can also lead to uneven ice shedding, causing rotor imbalances

In an effort to evaluate the accuracy of the finite-state dynamic inflow of Peters and He (“Finite State Induced Flow Models Part II: Three-Dimensional Rotor Disk,” Journal of Aircraft, Vol. 32, No. 2, 1995, pp. 323–333) for use in rotor design, comparisons between dynamic inflow-based calculations and measured test data are presented for a wide variety of single rotor configurations and operating

This paper presents a theoretical investigation into the potential use of structural power composites in regional aircraft passenger cabins and the corresponding challenges to widespread use, including fire resistance, long-term cycling performance, and cost. This study focuses on adapting sandwich floor panels with structural power composite face sheets, designed to power the in-flight entertainment

The modeling and assessment of the community noise impacts of a representative hybrid-electric aircraft implementing windmilling motors as drag generators on approach is presented. An increasing desire to reduce emissions caused by aviation has motivated the development of hybrid-electric aircraft that have some degree of their traditional gas-turbine propulsion replaced with electric propulsion. Turboelectric

Structural optimization technology, as advanced as it has become, is still not used to fully automate the design of airframe components at a level of analysis detail that would be acceptable for certification by regulatory agencies. It is part of the development of certifiable structures but is still just a part, requiring significant manual labor invested by stress engineers working with empirical

Various characteristics of small surface-normal jets (microjets) located on a flap’s pressure-side near the trailing edge are investigated as an active aerodynamic load control technology for multi-element high-lift systems. Two-dimensional computational studies are carried out to investigate the sensitivity of microjet aerodynamic effectiveness to configuration. Initially, the effects of microjet

Mechanical instabilities and elastic nonlinearities are emerging means for designing deployable and shape adaptive structures. Dynamic snap-through buckling is investigated here as a means to tailor the deployment and retraction of a slat-cove filler (SCF), a morphing component used to reduce airframe noise. Upon deployment, leading-edge slats create a cove between themselves and the main wing, producing

In this Paper, the mechanic properties and sealing performance of the aircraft fabric rubber seal during flight are studied. First, the mechanic parameters, geometric structure, loading method of different aircraft cabin door fabric rubber seals, and gas conditions are analyzed. Second, the modified gas leakage rate formula of fabric rubber seal within wide ranges of temperature and gas pressure is

Journal of Aircraft, Ahead of Print.

Many electric vertical takeoff and landing concepts are characterized by nontraditional vehicle layouts with distributed propellers. Two propeller interaction types were distinguished in this Paper, which investigates how propeller interaction in side-by-side and one-after-another configuration affects performance, in terms of thrust, power, in-plane forces, and out-of-plane moments, and how those

The present study numerically explored the hydrodynamic characteristics of a helicopter model experiencing guided ditching on wavy water. The air–water two-phase flow was computed by solving unsteady incompressible Reynolds-averaged Navier–Stokes equations enclosed by the k-ω shear stress transport turbulence model. The effect of water-entry position of the wave, viz., crest, falling, rising and trough

A recent consideration in aircraft design is the use of folding wingtips, with the aim of enabling higher-aspect-ratio wings with less induced drag but also meeting airport gate limitations. A formulation is introduced to account for finite rotations of rigid folding wingtips attached through hinges on a flexible airframe structure including also aerodynamic follower forces for the folding wingtip

A wind tunnel test was performed in the 0.3-Meter Cryogenic Transonic Tunnel at the NASA Langley Research Center to investigate the impact of various boundary layer thickeners on the height and shape of the boundary layer on the aft portion of a half-fuselage model. The present paper discusses USM3D analyses that were performed in support of the wind tunnel test. The results consisted of comparisons

The influence of the lift-share ratio between a rotor and a wing on the aerodynamic performance of a winged compound helicopter in high advance ratio flight is investigated through numerical simulations in this paper. A simplified model constructed with only a rotor and a winged body is considered to focus on the aerodynamic interactions between the rotor and the wing. The effect of the interaction

Journal of Aircraft, Ahead of Print.

Balancing accurate and efficient estimation of aerothermodynamic loads is a significant challenge for multidisciplinary modeling and analysis of high-speed vehicles. This study focuses on this issue by studying the impact of analytical and data-driven model reductions over a broad operational space. Reduced models are compared with Reynolds-averaged Navier–Stokes predictions for steady-state aerodynamic