Aerospace Engineering Commons^™

Utilizing Ground-Based Lidar Measurements To Aid Autonomous Airdrop Systems, Martin Cacan, Edward Scheuermann, Michael Ward, Mark Costello, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Uncertainty in atmospheric winds represents one of the primary sources of landing error in airdrop systems. In this work, a ground-based LIDAR system samples the wind field at discrete points above the target and transmits real-time data to approaching autonomous airdrop systems. In simulation and experimentation, the inclusion of a light detection and ranging (LIDAR) system showed a maximum of 40% improvement over unaided autonomous airdrop systems. Wind information nearest ground level has the largest impact on improving accuracy.

Three-Dimensional Simulation For Fast Forward Flight Of A Calliope Hummingbird, Jialei Song, Bret W. Tobalske, Don Powers, Tyson Hedrick, Haoxiang Luo

Faculty Publications - Department of Biological & Molecular Science

We present a computational study of flapping-wing aerodynamics of a calliope hummingbird (Selasphorus calliope) during fast forward flight. Three-dimensional wing kinematics were incorporated into the model by extracting time-dependent wing position from high-speed videos of the bird flying in a wind tunnel at 8.3 m s⁻¹. The advance ratio, i.e. the ratio between flight speed and average wingtip speed, is around one. An immersed-boundary method was used to simulate flow around the wings and bird body. The result shows that both downstroke and upstroke in a wingbeat cycle produce significant thrust for the bird to overcome …

Experimental Investigation Of Stochastic Parafoil Guidance Using A Graphics Processing Unit, Nathan Slegers, Andrew Brown, Jonathan Rogers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Control of autonomous systems subject to stochastic uncertainty is a challenging task. In guided airdrop applications, random wind disturbances play a crucial role in determining landing accuracy and terrain avoidance. This paper describes a stochastic parafoil guidance system which couples uncertainty propagation with optimal control to protect against wind and parameter uncertainty in the presence of impact area obstacles. The algorithm uses real-time Monte Carlo simulation performed on a graphics processing unit (GPU) to evaluate robustness of candidate trajectories in terms of delivery accuracy, obstacle avoidance, and other considerations. Building upon prior theoretical developments, this paper explores performance of the …

Gust Mitigation Of Micro Air Vehicles Using Passive Articulated Wings, Adetunji Oduyela, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Birds and insects naturally use passive flexing of their wings to augment their stability in uncertain aerodynamic environments. In a similar manner, micro air vehicle designers have been investigating using wing articulation to take advantage of this phenomenon. The result is a class of articulated micro air vehicles where artificial passive joints are designed into the lifting surfaces. In order to analyze how passive articulation affects performance of micro air vehicles in gusty environments, an efficient 8 degree-of-freedom model is developed. Experimental validation of the proposed mathematical model was accomplished using flight test data of an articulated micro air vehicle …

High-Efficiency Thrust Vector Control Allocation, Jeb S. Orr, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

A generalized approach to the allocation of redundant thrust vector slew commands for multi-actuated launch vehicles is presented, where deflection constraints are expressed as omniaxial or elliptical deflection limits in gimbal axes. More importantly than in the aircraft control allocation problem, linear allocators (pseudoinverses) are preferred for large booster applications to facilitate accurate prediction of the control-structure interaction resulting from thrust vectoring effects. However, strictly linear transformations for the allocation of redundant controls cannot, in general, access all of the attainable moments for which there is a set of control effector positions thatsatisfles the constraints. In this paper, the control …

Robust Parafoil Terminal Guidance Using Massively Parallel Processing, Jonathan Rogers, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Terminal guidance of autonomous parafoils is a difficult problem in which wind uncertainty and system underactuation are major challenges. Existing strategies almost exclusively use impact error as the criterion for optimality. Practical airdrop systems, however, must also include other criteria that maybe even more important than impact error for some missions, such as ground speed at impact or constraints imposed by drop zones with restrictions on flight patterns. Furthermore, existing guidance schemes determine terminal trajectories using deterministic wind information and may result in a solution that works in ideal wind but may be sensitive to variations. The work described here …

Projectile Fire-Control Algorithm In A Spatially Varying Wind Field, Lakmal Kaviratna, Mark Costello, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

The fire-control solution is an important element of any modern weapon system, providing precise aiming of the gun to enable highly accurate projectile impact. To be practical, the fire-control solution must be computed rapidly and reliably while simultaneously including all pertinent physical effects that can alter the trajectory and impact point. Current fire-control solutions account for the effect of atmospheric wind in a rudimentary manner, typically assuming a constant crosswind that is estimated in the field or measured at the firing site. With the advent of advanced wind-measurement systems (light detection and ranging, for example), it is now possible to …

Specialized System Identification For Parafoil And Payload Systems, Michael Ward, Mark Costello, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

There are a number of peculiar aspects to parafoil and payload systems that make it difficult to apply conventional system identification procedures used for aerospace systems. Parafoil and payload systems are unique because typically there is very little sensor information available, the sensors that are available are separated from the canopy by a complex network of flexible rigging, the systems are very sensitive to wind and turbulence, the systems exhibit a number of nonlinear behaviors, and the systems exhibit a high degree of variability from flight to flight. The current work describes a robust system identification procedure developed to address …

Evaluation Of Multibody Parafoil Dynamics Using Distributed Miniature Wireless Sensors, Chrystine M. Gorman, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Guided parafoils arc composed of two primary bodies, a payload and parafoil. The payload encompasses the majority ofthe ovcrdll system mass; however, the parafoil generates the majority of aerodynamic loads and is the sole source of control. Despite the canopy being the source of control, the sensor systems used for guidance are located away from the parafoil. Many multi body models exist in literature and use different degrees of freedom to represent parafoil-payload relative motion. However, in many cases, simulations are used to investigate how the relative motion between bodies affects the overall dynamics without experimental validation determining the accuracy …

Terminal Guidance Of Autonomous Parafoils In High Wind-To-Airspeed Ratios, Nathan Slegers, O A. Yakimenko

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Autonomous precision placement of parafoils is challenging because of their limited control authority and sensitivity to winds. In particular, when wind speed is near the airspeed, guidance is further complicated by the parafoils inability to penetrate the wind. This article specifically addresses the terminal phase and develops an approach for generating optimal trajectories in real-time based on the inverse dynamics in the virtual domain. The method results in efficient solution of a two-point boundary-value problem using only a single optimization parameter allowing the trajectory to be generated at a high rate, mitigating effects of the unknown winds. It is shown …

Tethered Aerostat Modeling Using An Efficient Recursive Rigid-Body Dynamics Approach, Brad Hembree, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

A tethered aerostat model is developed using a computationally efficient recursive tether model. The recursive rigid-body tether model results in unconstrained ordinary differential equations and maintains much of the simplicity of simple lumped-mass tether models, while avoiding numerical difficulties associated with using many stiff elastic elements with low mass. Further efficiency is achieved by treating each tether link as a body of revolution and assuming that tether spin is negligible to the dynamics. The tether is attached to a six-degree-of-freedom aerostat model using a single viscoelastic element. The final recursive tethered aerostat model is well suited for a variety of …

On The Benefits Of In-Flight System Identification For Autonomous Airdrop Systems, Michael Ward, Mark Costello, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

A unique feature of airdrop systems is the inherent and large variability in flight dynamic characteristics. The same physical article dropped on two different occasions will exhibit significantly different dynamic response. The problem only becomes worse for different test articles. Control systems for autonomous airdrop systems explicitly or implicitly assume knowledge of the flight dynamic characteristics in some way, shape, or form. A question facing autonomous airdrop designers is whether to use precomputed dynamic characteristics inside the control law, or to compute the needed flight dynamic characteristics in-flight and subsequently employ them in the control law. This paper establishes conditions …

Efficient Tether Dynamic Model Formulation Using Recursive Rigid-Body Dynamics, Brad Hembree, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

A computationally efficient discrete model for low-strain tethers used in many engineering applications is developed without the use of elastic elements. The tether is modelled using N links, with each link treated as a body of revolution where it is assumed the tether spin is negligible to the dynamics, resulting in each link having only two degrees of freedom. A recursive algorithm is developed for the dynamic equations, with the solution procedure being an order N method requiring only a 2 x 2 matrix inversion, resulting in approximately half the computations of the general recursive algorithm. A comparison between the …

Effects Of Canopy-Payload Relative Motion On Control Of Autonomous Parafoils, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

An 8 degree-of-freedom model is developed that accurately models relative pitching and yawing motion of a payload with respect to a parafoil. Constraint forces and moments are found analytically rather than using artificial constraint stabilization. A turn rate controller common in precision placement algorithms is used to demonstrate that relative yawing motion of the payload can result in persistent oscillations of the system. A model neglecting relative payload yawing failed to predict the same oscillations. It is shown that persistent oscillations can be eliminated by reduction of feedback gains; however, resulting tracking performance is poor. A reduced order linear model …

Comment On "Three-Dimensional Ascent Trajectory Optimization For Stratospheric Airship Platforms In The Jet Stream", Nathan Slegers, Ainsmar X. Brown

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

No abstract provided.

Exploiting A Gsm Network For Precise Payload Delivery, Eugene A. Bourakov, Oleg A. Yakimenko, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

This paper introduces the novel concept of using a GSM network for command of and communications with multiple aerial delivery systems. The research prototype of such a system, Snowflake-N, allows communicating with other network clients via a commercial Blackberry Curve 8310 handheld over a Bluetooth connection. A new architecture allows reassigning targets and sending other relevant commands (via web interface, by voice, data, or text messages) to an onboard autopilot, which is within a network reach, from any place in the world. Similarly, a current position of the descending system and target assignment can be viewed from any computer connected …

Development And Testing Of The Miniature Aerial Delivery System Snowflake, Oleg A. Yakimenko, Nathan Slegers, Robyn A. Tiaden

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

This paper discusses the current status of the development of the miniature aerial delivery system to be further employed in a variety of different research projects. It starts from the overall description of the system and proceeds with the discussion of the test results performed so far. Specifically, it addresses the effects of the changing ground winds on touchdown accuracy. The paper ends with conclusions and recommendations.

Performance Of A Fire-And-Forget Anti-Tank Missile With A Damaged Wing, John Harris, Nathan Slegers

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

A mathematical model is developed for an anti-tank missile and its guidance algorithms. The aerodynamic model is separated into two parts, the airframe and external lifting surfaces in order to model damage to the airframe. Radar data is compared to that of the proposed model and it is shown that the model accurately replicates the true flight dynamics. Two types of field handling damage are modeled, a damaged mid-body wing with 50% of its planform area missing, and an un-deployed mid-body wing. Monte Carlo simulations are performed for each type of damage and the eight possible mid-body wing locations. The …

Optimal Control For Terminal Guidance Of Autonomous Parafoils, Nathan Slegers, Oleg A. Yakimenko

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

This paper deals with the development of guidance, navigation and control algorithms for a prototype of a miniature aerial delivery system capable of high-precision maneuvering and high touchdown accuracy. High accuracy enables use in precision troop resupply, sensor placement, urban warfare reconnaissance, and other similar operations. Specifically, this paper addresses the terminal phase, where uncertainties in winds cause most of the problems. The paper develops a six degree-of-freedom model to adequately address dynamics and kinematics of the prototype delivery system and then reduces it to a two degrees-of-freedom model to develop a model predictive control algorithm for reference trajectory tracking …

Use Of Variable Incidence Angle For Glide Slope Control Of Autonomous Parafoils, Nathan Slegers, Eric Beyer, Mark Costello

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Strictly speaking, most autonomous parafoil and payload systems possess only lateral control, achieved by right and left parafoil brake deflection. An innovative technique to achieve direct longitudinal control through incidence angle changes is reported. Addition of this extra control channel requires simple rigging changes and an additional servoactuator. The ability of incidence angle to alter the glide slope of a parafoil and payload aircraft is demonstrated through a flight-test program with a microparafoil system. Results from the flight-test program are synthesized and integrated into a six degree-of-freedom simulation. The simulation model is subsequently used to assess the utility of glide …

The Role Of Diffusive Transport On Low And Intermediate Temperature Hydrocarbon Oxidation: Closed Reactor Experiments Using Equimolar N-Butane + Oxygen Premixtures At Reduced-Gravity, Howard Pearlman, Michael R. Foster

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Experiments were conducted in a closed, spherical reactor aboard NASA's KC-135 reduced-gravity aircraft using an equimolar n-C4H10 + 0 2 premixture ( Le = 1.3) at subatmospheric · pressures to compliment model predictions and further explore the reactive-diffusive structure of cool flames and ignitions. The pressure and radial temperature histories were recorded and analyzed for different initial conditions. In addition, the visible light emission from excited formaldehyde was recorded using an intensified video camera and was observed to be radially symmetric in all cases. Unexpectedly, however, the measured temperature distributions during (and after the passage of) the cool flames and …

The Role Of Diffusive Transport On Low And Intermediate Temperature Hydrocarbon Oxidation: Numerical Simulations Using The Wang-Mou Mechanism, Howard Pearlman, Michael R. Foster

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

The spatio-temporal temperature and species concentration distributions associated with low and intermediate temperature hydrocarbon oxidation are computed using a global thermo kinetic scheme augmented with diffusive transport. The scheme used for the computations was proposed by Wang and Mou and is extended to include diffusion of species and heat. The conservation equations for species and energy are then derived and solved for a one-dimensional and an axisymmetric, spherical domain for temperatures ranging from 540 to 660 Kat subatmospheric pressures. The predictions are then used to develop ignition diagrams for different Lewis ( Le) numbers. Increasing Le is found to promote …

Variable Structure Observer For Control Bias On Unmanned Air Vehicles, Nathan Slegers, Mark Costello

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

No abstract provided.

Cool Flame Propagation Speeds, Michael R. Foster, Howard Pearlman

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Cool flames are studied at reduced-gravity in a closed, unstirred, spherical reactor to minimize complexities associated with natural convection. Under such conditions, transport is controlled by diffusive fluxes and the flames are observed to propagate radially outward from the center of the reactor toward the wall. Intensified video records are obtained and analyzed to determine the flame radius as a function of time for different vessel temperatures (593–623 K) and initial pressures (55.2–81.4 kPa) using an equimolar (Ø = 5) propane-oxygen premixture. Polynomial-fits are applied to the data and differentiated to determine the cool flame propagation speeds. In nearly …

Use Of Dynamic Incidence Angle For Glide Slope Control Of Autonomous Parafoils, Nathan Slegers, Eric Beyer, Mark Costello

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Strickly speaking, most autonomous parafoil and payload aircraft possess only lateral control, achieved by right and left parafoil brake deflection. An innovative new technique to achieve direct longitudinal control through dynamic incidence angle changes is reported. Addition of this extra control channel requires simple rigging changes and an additional servo actuator. The ability of dynamic incidence angle to alter the glide slope of a parafoil and payload aircraft is demonstrated through a flight test program with a micro parafoil system. Results from the flight test program are synthesized and integrated into a 6 degree-of-freedom simulation. The simulation model is subsequently …

Nonlinear Model Predictive Control Technique For Unmanned Air Vehicles, Nathan Slegers, Jason Kyle, Mark Costello

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

A nonlinear model predictive control strategy is developed and subsequently specialized to autonomous aircraft that can be adequately modeled with a rigid 6-degrees-of-freedom representation. Whereas the general air vehicle dynamic equations are nonlinear and nonaffine in control, a closed-form solution for the optimal control input is enabled by expanding both the output and control in a truncated Taylor series. The closed-form solution for control is relatively simple to calculate and well suited to the real time embedded computing environment. An interesting feature of this control law is that the number of Taylor series expansion terms can be used to indirectly …

Cool Flames At Terrestrial, Partial, And Near-Zero Gravity, Michael R. Foster, Howard Pearlman

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Natural convection plays an important role in all terrestrial, Lunar, and Martian-based, unstirred, static reactor cool flame and low-temperature autoignitions, since the Rayleigh number (Ra) associated with the self-heating of the reaction exceeds the critical Ra (approximately 600) for onset of convection. At near-zero gravity, Ra < 600 can be achieved and the effects of convection suppressed. To systematically vary the Ra without varying the mixture stoichiometry, reactor pressure, or vessel size, cool flames are studied experimentally in a closed, unstirred, static reactor subject to different gravitational accelerations (terrestrial, 1g; Martian, 0.38g; Lunar, 0.16g; a n dr e - duced gravity, ∼10−2g). Representative results show the evolution of the visible light emission using an equimolar n-butane:oxygen premixture at temperatures ranging from 320 to 350 ◦C (593–623 K) at subatmospheric pressures. For representative reduced-gravity, spherically propagating cool flames, the flame radius based on the peak light intensity is plotted as a function of time and the flame radius (and speed) is calculated from a polynomial fit to data. A skeletal chemical kinetic Gray-Yang model developed previously for a one-dimensional, reactive– diffusive system by Fairlie and co-workers is extended to a two-dimensional axisymmetric, spherical geometry. The coupled species, energy, and momentum equations are solved numerically and the spatio-temporal variations in the temperature profiles are presented. A qualitative comparison is made with the experimental results.

Model Predictive Control Of A Parafoil And Payload System, Nathan Slegers, Mark Costello

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

No abstract provided.

An Existing Global Heptane Mechanism Augmented With Diffusive Transport, Michael R. Foster, Howard Pearlman

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

The couplings between diffusive transport and the temperature and species concentration distributions associated with low and intermediate temperature heptane oxidation are explored using an existing four-step heptane mechanism, tuned for elevated pressures. The energy and species concentration equations are augmented with diffusive fluxes for heat and species and solved numerically in a one-dimensional domain. The ignition delay times are also tabulated and compared with the zero-dimensional data reported in the literature.

The Cool Flames Experiment: Recent Results At Reduced And Partial Gravity, Michael R. Foster

Faculty Publications - Biomedical, Mechanical, and Civil Engineering

Cool flames at Earth (1g), Martian (0.38g), Lunar (0.18g) and reduced-gravity (10–2g) have been studied experimentally in a closed, unstirred, static reactor to better understand the role of natural convection and diffusive transport on the induction period(s), flame shape, flame propagation speed, pressure history and temperature profile. Natural convection is known to play an important role in all terrestrial, unstirred, static reactor cool flame and auto-ignition experiments when the Rayleigh number exceeds 600 [2,3,6]. At 1g, typical values of the Ra are 10^4-10^6.

In this paper, experimental results from static, unstirred reactor studies conducted at four different gravitational acceleration levels …