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Journal Article

Improve Heat Resistance of Composite Engine Cowlings Using Ceramic Coating Materials, Experimental Design and Testing

2018-06-04
Abstract A large amount of heat generated in the engineering compartment in a hovering helicopter may lead to premature degradation of inner skin of its engine cowling and cause serious failure on the engine cowling. This study proposes a solution of improving heat resistance of the helicopter engine cowlings by replacing the currently used intumescent coating with a ceramic coating material, Cerakote C-7700Q. Oven and flame tests were designed and conducted to evaluate the heat resistance of Cerakote C-7700Q. The test results show that the currently used painting scheme of the engine cowlings failed the 220°C oven test while after replacing the epoxy seal coat with the Cerakote, the new painting system passed the 220°C test in regards to painting bubbling. Based on that, a new painting scheme with C-7700Q implemented was recommended.
Journal Article

Modeling of Ducted-Fan and Motor in an Electric Aircraft and a Preliminary Integrated Design

2018-10-04
Abstract Electric ducted-fans with high power density are widely used in hybrid aircraft, electric aircraft, and VTOL vehicles. For the state-of-the-art electric ducted-fan, motor cooling restricts the power density increase. A motor design model based on the fan hub-to-tip ratio proposed in this article reveals that the thermal coupling effect between fan aerodynamic design and motor cooling design has great potential to increase the power density of the motor in an electric propulsion system. A smaller hub-to-tip ratio is preferred as long as the power balance and cooling balance are satisfied. Parametric study on a current 6 kW electric ducted-fan system shows that the highest motor power density could be increased by 246% based on the current technology. Finally, a preliminary design was obtained and experiments were conducted to prove the feasibility of the model.
Journal Article

Power Quality Test Data Analysis for Aircraft Subsystem

2018-12-21
Abstract Aircraft subsystem development involves various combinations of testing and qualification activities to realize a flight-worthy system. The subsystem needs to be verified for a massive number of customer requirements. Power quality (PQ) testing is also an important testing activity carried out as part of the environmental qualification test. It is intended to verify the functionality of subsystems with various kinds of power disturbances and to determine the ability of a subsystem to withstand PQ disturbances. The subsystem being designed should be reliable enough to handle PQ anomalies. A PQ test results in an enormous amount of data for analysis with millions of data samples depending on the test and can be identified as big data. The engineer needs to analyze each set of test data as part of post-processing to ensure the power disturbances during testing are as per the standard requirements and that the functional performance of the subsystem is met.
Journal Article

Landing Response Analysis on High-Performance Aircraft* Using Estimated Touchdown States

2019-04-08
Abstract A novel use of state estimation methods as initial input for a landing response analysis is proposed in this work. Six degrees of freedom (DOF) non-linear landing response model is conceived by considering longitudinal dynamics of aircraft as a rigid body with heave-and-pitch motions coupled onto a bicycle landing gear † arrangement. The DOF for each landing gear consist of vertical and longitudinal motions of un-sprung mass, considering strut bending flexibility. The measurement data for state estimation is obtained for three landing cases using non-linear flight mechanics model interfaced with pilot-in-loop simulation. State estimation methods such as Upper Diagonal Adaptive Extended Kalman Filter (UD-AEKF) with fuzzy-based adaptive tuning and Un-scented Kalman Filter (UKF) were adapted for landing maneuver problem. On the basis of estimation error metrics, aircraft state from UKF is considered during onset of touchdown.
Journal Article

High Power-Density, High Efficiency, Mechanically Assisted, Turbocharged Direct-Injection Jet-Ignition Engines for Unmanned Aerial Vehicles

2019-05-02
Abstract More than a decade ago, we proposed combined use of direct injection (DI) and jet ignition (JI) to produce high efficiency, high power-density, positive-ignition (PI), lean burn stratified, internal combustion engines (ICEs). Adopting this concept, the latest FIA F1 engines, which are electrically assisted, turbocharged, directly injected, jet ignited, gasoline engines and work lean stratified in a highly boosted environment, have delivered peak power fuel conversion efficiencies well above 46%, with specific power densities more than 340 kW/liter. The concept, further evolved, is here presented for unmanned aerial vehicle (UAV) applications. Results of simulations for a new DI JI ICE with rotary valve, being super-turbocharged and having gasoline or methanol as working fuel, show the opportunity to achieve even larger power densities, up to 430 kW/liter, while delivering a near-constant torque and, consequently, a nearly linear power curve over a wide range of speeds.
Journal Article

Stall Mitigation and Lift Enhancement of NACA 0012 with Triangle-Shaped Surface Protrusion at a Reynolds Number of 105

2019-11-21
Abstract Transient numerical simulations are conducted over a NACA 0012 airfoil with triangular protrusions at a Reynolds number (Re) of 100000 using the γ-Reθ transition Shear Stress Transport (SST) turbulence model. Protrusions of heights 0.5%c, 1%c, and 2%c are placed at one of the three locations, viz, the leading edge (LE), 5%c on the suction surface, and 5%c on the pressure surface, while the angle of attack (AOA) is varied between 0° and 20°. Results obtained from the time-averaged solution of the unsteady Navier-Stokes equation indicate that the smaller protrusion placed at 5%c on the suction surface improves the post-stall lift coefficient by up to 59%, without altering the pre-stall characteristics. The improvement in time-averaged lift coefficients comes with enhanced flow unsteadiness due to vigorous vortex shedding.
Journal Article

Limitations of Two-Stage Turbocharging at High Flight Altitudes

2018-09-17
Abstract High-altitude long-endurance (HALE) unmanned aerial vehicles (UAVs) are used for high flight altitudes, which enable low drag and fast flight with minimal fuel consumption. Two-stage turbocharging is necessary to sustain sea-level power at high flight altitudes. In this study, the limitations of two-stage turbocharging at high flight altitudes typical for HALE UAVs are analyzed for the first time. The obtained results show that the minimum available engine power increases as the altitude rises. This will limit the ability of the aircraft to descend rapidly. Furthermore, at high altitudes, if a lower operating point is required for a fast descent, further recovery to full power for climbing or cruising could be unavailable. In the latter cases, a lower altitude must be reached before full power would be available again. A basic algorithm for the assessment and analysis of the limitations of UAV engines with two-stage turbochargers operating at high altitudes is suggested.
Journal Article

Lightweight Carbon Composite Chassis for Engine Start Lithium Batteries

2018-03-07
Abstract The supersession of metallic alloys with lightweight, high-strength composites is popular in the aircraft industry. However, aviation electronic enclosures for large format batteries and high power conversion electronics are still primarily made of aluminum alloys. These aluminum enclosures have attractive properties regrading structural integrity for the heavy internal parts, electromagnetic interference (EMI) suppression, electrical bonding for the internal cells, and/or electronics and failure containment. This paper details a lightweight carbon fiber composite chassis developed at Meggitt Sensing Systems (MSS) Securaplane, with a copper metallic mesh co-cured onto the internal surfaces resulting in a 50% reduction in weight when compared to its aluminum counterpart. In addition to significant weight reduction, it provides equal or improved performance with respect to EMI, structural and flammability performance.
Journal Article

TOC

2020-05-15
Abstract TOC
Journal Article

ERRATA

2020-05-12
Abstract ERRATUM
Journal Article

Conceptual Design, Material, and Structural Optimization of a Naval Fighter Nose Landing Gear for the Estimated Static Loads

2019-12-13
Abstract The Naval Nose Landing Gear (NLG) structural assembly consists of components with complex structural geometry and critical functionalities. The landing gear components are subjected to high static and dynamic loads, so they must be appropriately designed, dimensioned, and made by materials with mechanical characteristics that meet high strength, stiffness, and less weight requirements. This article contributes to the shape, size, and material optimization for the NLG of a supersonic naval aircraft for the estimated static loads. The estimated modal frequency values of the NLG assembly using Finite Element Analysis (FEA) software were compared with available Ground Vibration Test data of an aircraft to literally prove the accuracy and suitability of finite element (FE) model that can be used for any further analysis.
Journal Article

The Missing Link: Aircraft Cybersecurity at the Operational Level

2020-07-25
Abstract Aircraft cybersecurity efforts have tended to focus at the strategic or tactical levels without a clear connection between the two. There are many excellent engineering tools already in widespread use, but many organizations have not yet integrated and linked them into an overarching “campaign plan” that connects those tactical actions such as process hazard analysis, threat modeling, and probabilistic methods to the desired strategic outcome of secure and resilient systems. This article presents the combined systems security engineering process (CSSEP) as a way to fill that gap. Systems theory provides the theoretical foundation on which CSSEP is built. CSSEP is structured as a control loop in which the engineering team is the controller of the design process. The engineering team needs to have an explicit process model on how systems should be secured, and a control algorithm that determines what control actions should be selected.
Journal Article

TOC

2020-06-25
Abstract TOC
Journal Article

Vertical Takeoff and Landing Aircraft, VTOL Ground Effects

2020-08-20
Abstract The ground-effect problems of loss of thrust and fountain-effect instabilities are quantified. Experiments to control and augment ground-effect lift and stability are presented, including jet momentum reflection and fountain redirection using various types of internal and external underbody ventral strakes. By strategically designing the vertical takeoff and landing (VTOL) ventral surface, reflection of the impinging fountain momentum is possible so that instead of losing 10% thrust while in ground-effect, remarkably, thrust is augmented 10% or more to a considerable height above the ground, in addition to stabilizing random pitch and roll moments caused by fountain instability.
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