Aircraft Lateral Trim Using Internal Fuel Transfer & Differential Thrust In Formation Flight

In order to shorten the wake safe separation, numerical simulation technology with aerodynamic response models and strip models have been combined to calculate wake hazard zone. As a realistic case, a medium aircraft ARJ21 following a heavy aircraft A330-200 is considered, and the Reynolds-averaged Navier-Stokes (RANS) method is used to explore the wake vortex evolution process of the leading aircraft at the decision height. A strip algorithm is proposed to calculate the rolling moment coefficient and overload increment of the ARJ21 after encountering the wake of the front aircraft in the three-dimensional space. The proposed algorithm identifies the area where the wake of the front aircraft can cause risks to the following aircraft and analyzes the evolution process of the hazard zone of the section where the decision height is located. The minimum safe separation of the ARJ21 following the A330-200 is 1.32 nmile, which is 26.4% of the ICAO separation standard of 5 nmile. When the average runway occupancy time (ROT) is reduced to match the separation of 1.32 nmile, the capacity of runway 02R/20L in Tianfu International Airport could theoretically reach 102.37 sorties/h under this aircraft pair combination. Compared to original 27 sorties/h, the runway capacity can be improved up to 279.14%, which will increase the airport operation efficiency.

Measurements were made in the NASA-Ames 40- by 80-foot wind tunnel of the rolling moment induced on a following model in the wake 13.6 spans behind a subsonic transport model for a variety of trailing edge flap settings of the generator. It was found that the rolling moment on the following model was reduced substantially, compared to the conventional landing configuration, by reshaping the span loading on the generating model to approximate a span loading, found in earlier studies, which resulted in reduced wake velocities. This was accomplished by retracting the outboard trailing edge flaps. It was concluded, based on flow visualization conducted in the wind tunnel as well as in a water tow facility, that this flap arrangement redistributes the vorticity shed by the wing along the span to form three vortex pairs that interact to disperse the wake.

This paper presents a trajectory optimization study that has been conducted using a recently developed tool for the synthesis and analysis of extended flight formations of long-haul commercial aircraft, with the aim to minimize overall fuel consumption. In extended flight formations, trailing aircraft can attain an appreciable reduction in induced drag and associated reduction in fuel burn by flying in the upwash of the lead aircraft’s wake. In the present study, a previously developed multi-phase optimal control (MOC) framework for the synthesis of two-ship flight formations has been extended to include the assembly of three-ship flight formations. Using the extended tool, various numerical experiments have been conducted in relation to the assembly of two-ship and three-ship flight formations in long-haul operations across the North-Atlantic Ocean. Additionally, numerical experiments have been carried out to examine the impact of wind fields on the synthesis and performance of flight formations. Additionally, a parametric investigation has been conducted to assess the sensitivity of the solutions with respect to the degree of the induced drag reduction that might be attained by the trailing aircraft in a formation. The results of the various numerical experiments reveal that formation flight can result in appreciable reductions in fuel burn in comparison to flying solo—particularly when larger formation strings are permitted.

Significant resources (about 100 tcf in place) of natural gas are entrapped in low-permeability, low-pressure reservoirs at depths less than 3,000 ft (900 m) in Montana and the Dakotas. The gas occurs in fine-grained sequences of Late Cretaceous age deposited on a shallow, open-marine shelf. The low-permeability reservoirs were deposited during progradations and consist of discontinuous lenses and laminae of siltstone and sandstone enclosed by silty clay shale. The siltstone and sandstone layers are porous and permeable, whereas the enclosing shale is impermeable. The large proportion of allogenic clay, including highly expansive mixed-layer illite-smectite, causes extreme water sensitivity as well as high measured and calculated water saturation values in the reservoir s quence. Gas production has been established in sweet spots on structural highs where the reservoirs are best developed. Recurrent tectonic movement resulted in winnowing of coarser grain sizes on the highs by southward-flowing, geostrophic currents. In the future, exploration will occur off structure for lower quality reservoirs. The gas was generated in the marine environment by decomposition of organic matter by anaerobic microorganisms and is referred to as biogenic gas. The most important mechanism of methane generation in marine sediments is reduction of CO2. Organic carbon values, rates of sedimentation, and products of early diagenesis indicate that biogenic gas production was widespread during deposition. Most of the gas was initially retained in solution in the pore waters because of higher methane End_Page 520------------------------------ solubility at higher hydrostatic pressures owing to the weight of the overlying water column; the gas subsequently exsolved because of uplift and erosion during the Tertiary. End_of_Article - Last_Page 521------------

of wind tunnel walls and Reynolds number scaling. A formation of two and three aircraft is considered with a separation distance of 10 to 100 spans. It is demonstrated that in some earlier simulations, discussed in open literature, an incorrect lift coecient is used which leads to erroneous prediction of the induced drag reductions. The application of positive sweep, taper and winglets are all found to have benecial eects on formation ight induced drag reduction, while aircraft trim causes a slight decrease of induced drag reduction. Furthermore, the wing aspect ratio was not found to have a signicant inuence. According to the calculation model, a typical medium aircraft exhibits a total drag reduction around 13% when ying behind an identical aircraft. Good agreement between scaled and full scale simulation induced drag reduction is found in terms of both trend and induced drag reduction at the so-called sweet spot. The addition of wind tunnel walls causes a large increase in maximum induced drag benets, which signies the need for accurate windtunnel wall corrections in case of future windtunnel tests.

Formation flight is currently being investigated as a means to reduce drag and improve fuel efficiency in commercial aviation. In an attempt to approximate passenger impact in formation flight, a simple aerodynamic model for two aircraft in formation was developed. The wing trailing vortices were assumed to shift in an ideal fashion within atmospheric turbulence resulting in aerodynamic disturbance loads acting on the trailing aircraft. As the sensitivity of the human body to vibrations is frequency dependent, a spectral representation of atmospheric turbulence was incorporated. Monte Carlo simulations were done for various levels of turbulence intensity. The predicted acceleration responses of the trailing aircraft were used to determine the passenger comfort levels by applying the criteria of standard 2631-1 from the International Organization for Standardization and comparing with comfort levels experienced in an aircraft flying in isolation in the same turbulent atmosphere. A significant increase in discomfort was predicted for the lateral separations corresponding to the location for optimum drag benefit. Seating locations forward and inboard (closer to the lead aircraft) of the mass center showed the greatest increase in discomfort.

: In this research the close formation flight control problem is addressed. The formation consists of a lead and wing aircraft, where the wing flies in close formation with the lead, such that the lead's vortices produce aerodynamic coupling effects, and a reduction in the formation's drag is achieved. A controller, i.e., a formation-hold autopilot for the wing aircraft, is designed such that the formation's geometry is maintained in the face of lead aircraft maneuvers. In the formation flight control system, the wing and lead aircraft dynamics are coupled due to kinematic effects, and, in the case of close formations, additional aerodynamic coupling effects are introduced. In the research these additional aerodynamic coupling effects are properly modeled. The most significant aerodynamic coupling effect introduced by close formation flight entails the coupling of the lateral/directional channel into the altitude-hold autopilot channel. It is shown that formation hold autopilots designed ignoring the aerodynamic coupling effects, yield satisfactory performance in close formation flight.

Many theoretical and experimental studies have shown that aircraft flying in formation could experience significant reductions in fuel use compared to solo flight. To date, formation flight for aerodynamic benefit has not been thoroughly explored in flight for large transport-class vehicles. This paper summarizes flight data gathered during several two ship, C-17 formation flights at a single flight condition of 275 knots, at 25,000 ft MSL. Stabilized test points were flown with the trail aircraft at 1,000 and 3,000 ft aft of the lead aircraft at selected crosstrack and vertical offset locations within the estimated area of influence of the vortex generated by the lead aircraft. Flight data recorded at test points within the vortex from the lead aircraft are compared to data recorded at tare flight test points outside of the influence of the vortex. Since drag was not measured directly, reductions in fuel flow and thrust for level flight are used as a proxy for drag reduction. Estimated thrust and measured fuel flow reductions were documented at several trail test point locations within the area of influence of the leads vortex. The maximum average fuel flow reduction was approximately 7-8%, compared to the tare points flown before and after the test points. Although incomplete, the data suggests that regions with fuel flow and thrust reduction greater than 10% compared to the tare test points exist within the vortex area of influence.

This paper presents identification, control synthesis and simulation results for an YF-22 aircraft model designed, built, and instrumented at West Virginia University. The ultimate goal of the project is the experimental demonstration of formation flight for a set of 3 of the above models. In the planned flight configuration, a pilot on the ground maintains controls of the leader aircraft while a wingman aircraft is required to maintain a pre-defined position and orientation with respect to the leader. The identification of both a linear model and a nonlinear model of the aircraft from flight data is discussed first. Then, the design of the control scheme is presented and discussed with an emphasis on the amount of information, relative to the leader aircraft, needed by the wingman to maintain formation. Using the developed nonlinear model, the control laws for a maneuvered flight of the formation are then simulated with Simulink® and displayed with the Virtual Reality Toolbox®. Simulation studies have been performed to evaluate the effects of specific parameters and the system robustness to atmospheric turbulence. The conclusions from this analysis have allowed the formulation of specific guidelines for the design of the electronic payload for formation flight.

: Automatic formation flight involves controlling multiple wing aircraft equipped with standard Mach-hold, altitude-hold, and heading-hold autopilots in order to maintain a desired position relative to a lead aircraft throughout formation maneuvers. Changes in the lead aircraft's states, including formation heading, velocity, altitude, and geometry changes, are treated as disturbance and are rejected by the formation flight control system. The work in this thesis is a continuation of five previous theses, dealing with the design of formation flight control systems. The goal of the optimal formation flight control design is to achieve robust formation maintenance in the face of formation maneuvers and the presence of full system nonlinearities. Second-order aircraft/autopilot models are included in the design and a new control law is employed. A constrained optimization for determining the optimal controller gains of fixed structure controllers is employed. The two controllers considered are a Proportional plus FeedForward (PFF) controller, previously developed at AFIT, and a new Proportional plus Integral and FeedForward (PIFF) controller, which uses less feedforward information. Finally, the constrained optimization is applied to a wide variety of formation maneuvers and geometry changes initiated from both the tight, closely spaced, and loose, more widely dispersed, types of formations.

In recent decades, micro aerial vehicles (MAVs) have spread rapidly, initially developed for military applications and now serving a wide range of civilian purposes. MAVs in use today come in various forms, including multicopters, fixed-wing vehicles, and coaxial-rotor helicopters, among many others. Their compact size makes them attractive for surveillance and agility tasks, as they exhibit higher accelerations and greater stability compared to their larger counterparts. This work presents a theoretical and numerical study of an innovative propulsion system technique capable of obtaining attitude control authority while removing the swashplate, reducing the number of actuators, and greatly simplifying the mechanical complexity of the MAV’s propulsion system. This concept introduces a pair of coupled antisymmetric lag-pitch hinges that are combined with a synchronized sinusoidal input to the motor. The passive response of the blades allows a differential thrust between them, resulting in a pitching or rolling moment for the vehicle. We developed a Reduced Order Model (ROM) based on the Blade Element Momentum Theory (BEMT) that permits the calculation of the forces and moments generated by these rotors at a reduced computational cost. This model was verified using a higher-fidelity, six-degrees-of-freedom computational fluid dynamics (6-DOF-CFD) simulation carried out with STAR-CCM+, a commercial CFD software. • Higher fidelity coupled CFD 6-DOF simulations used to inform the development of ROM. • Azimuthally resolved BEM predict accurately moments generated by torque modulation. • Friction in the hinge is responsible for a phase delay in control moments.

Rates of release of nitric oxide from HbSNO and internal electron transfer

Flight control system design for two F/A- 18 aircraft flying in closed-coupled formation is the subject of this paper. Developed by Boeing - Phantom Works as an integral part of NASA revolutionary concept program called Autonomous Formation Flight (AFF), the Formation Flight Control System (FFCS) provides autonomous aircraft operation and flight testing capability. Using two specially instrumented Boeing-built F/A-18 Hornets research aircraft, AFF Phase I flight demonstrations are scheduled for the fall of 2002 at NASA's Dryden Flight Research Center, Edwards Air Force Base, in California. It is expected that the trailing aircraft equipped with FFCS would sustain 15-20% drag reduction if it is flown in the wake vortex created by the lead aircraft wingtips. This paper presents the baseline FFCS design, analysis, and evaluation using high fidelity 6-DoF nonlinear aircraft simulation environment. Aircraft vortex modeling is discussed. An alternative adaptive formation flight control system design is proposed. The adaptive system is shown to improve the formation tracking performance.

The article describes an approach to ensuring stability and controllability of unmanned aerial vehicle (UAV) with unknown aerodynamic characteristics by computer simulation of the airplane flight along a given route in the meteorological standard atmosphere. This computer model takes into account the programmed flight of an unmanned aerial vehicle in the meteorological atmosphere along a given route with waypoints. For this purpose the model incorporates 5 feedback systems (FS) with autopilot (AP) that ensure the stability and controllability of an airplane. Besides the autopilot and the airplane glider the control system encompasses the Kalman filter and a strapdown inertial navigation system. The appropriate structure and parameters of the control system of the model were chosen on the basis of practical technical solutions of the de veloped UAVs. The closed control systems of the model are developed according to the equations considering generation of aerodynamic forces and moments, a model of the standard atmosphere, the routing scheme and the feedback system with autopilot. The stability and controllability of the model were analyzed according to the theory of feedback systems with the graphic plotting of Bode magnitude plot and Bode phase plot. With a view to the assessment of dynamic and fluctuation errors of the control systems the model is represented by stochastic differential control system with the Kalman filter and the strapdown inertial navigation system in quaternions. The results of the computer simulation showed that the Kalman filter estimates the measured parameters with the noise reduction under 10 dB. The strapdown inertial navigation system influences the general dynamics of the control system during the assessment of its stability and controllability. Changing the band of the control system at the expense of external perturbations affecting the plane can lead to instability, and in order to avoid it the robust autopilot is recommended.

The development of sustained, long-term endothermy was one of the major transitions in the evolution of vertebrates. Thermogenesis in endotherms does not only occur via shivering or activity, but also via non-shivering thermogenesis (NST). Mammalian NST is mediated by the uncoupling protein 1 in the brown adipose tissue (BAT) and possibly involves an additional mechanism of NST in skeletal muscle. This alternative mechanism is based on Ca2+-slippage by a sarcoplasmatic reticulum Ca2+-ATPase (SERCA) and is controlled by the protein sarcolipin. The existence of muscle based NST has been discussed for a long time and is likely present in all mammals. However, its importance for thermoregulation was demonstrated only recently in mice. Interestingly, birds, which have evolved from a different reptilian lineage than mammals and lack UCP1-mediated NST, also exhibit muscle based NST under the involvement of SERCA, though likely without the participation of sarcolipin. In this review we summarize the current knowledge on muscle NST and discuss the efficiency of muscle NST and BAT in the context of the hypothesis that muscle NST could have been the earliest mechanism of heat generation during cold exposure in vertebrates that ultimately enabled the evolution of endothermy. We suggest that the evolution of BAT in addition to muscle NST was related to heterothermy being predominant among early endothermic mammals. Furthermore, we argue that, in contrast to small mammals, muscle NST is sufficient to maintain high body temperature in birds, which have enhanced capacities to fuel muscle NST by high rates of fatty acid import.