Edward Scheuermann

Autonomous Airdrop Systems Employing Ground Wind Measurements for Improved Landing Accuracy

Aerial cargo delivery, also known as airdrop, systems are heavily affected by atmospheric wind conditions. Guided airdrop systems typically employ onboard wind velocity estimation methods to predict the wind in real time as the systems descend, but these methods provide no foresight of the winds near the ground. Unexpected ground winds can result in large errors in landing location, and they can even lead to damage or complete loss of the cargo if the system impacts the ground while traveling downwind. This paper reports on a ground-based mechatronic system consisting of a cup and vane anemometer coupled to a guided airdrop system through a wireless transceiver. The guidance logic running on the airdrop systems onboard autopilot is modified to integrate the anemometer measurements at ground level near the intended landing zone with onboard wind estimates to provide an improved, real-time estimate of the wind profile. The concept was first developed in the framework of a rigorous simulation model and then validated in the flight test. Both simulation and subsequent flight tests with the prototype system demonstrate reductions in the landing position error by more than 30% as well as a complete elimination of potentially dangerous downwind landings.

Combined Lateral and Longitudinal Control of Parafoils Using Upper-Surface Canopy Spoilers

Precision placement of guided airdrop systems necessarily requires some mechanism enabling effective directional control of the vehicle. Often this mechanism is realized through asymmetric deflection of the parafoil canopy trailing-edge brakes. In contrast to conventional trailing-edge deflection used primarily for lateral steering, upper-surface bleed air spoilers have been shown to be extremely effective for both lateral and longitudinal (i.e., glide slope) control of parafoil and payload systems. Bleed air spoilers operate by opening and closing several spanwise slits in the upper surface of the parafoil canopy, thus creating a virtual spoiler from the stream of expelled ram air. The work reported here considers the autonomous landing performance of a small-scale parafoil and payload system using upper-surface bleed air spoilers exclusively for both lateral steering and glide slope control. Landing accuracy statistics computed from a series of Monte Carlo simulations in a variety of atmospheric conditi...

Aerodynamic Characterization of a Microspoiler System for Supersonic Finned Projectiles

To create highly maneuverable projectiles, some physical control mechanism is needed that is capable of altering the projectile trajectory in a desired manner. The work reported here considers a small flow control device, termed a microspoiler system, located between the rear stabilizing fins of a projectile. Such a mechanism relies on the boundary-layer shock interaction between the projectile body, rear stabilizing fins, and microspoilers to provide a multiplicative effect on controllable forces and moments. To investigate performance of the microspoiler control mechanism, projectile trajectories with microspoilers were generated both computationally using a coupled CFD and rigid-body dynamic simulation and experimentally from spark range testing. Using this computational and experimental trajectory information, aerodynamic coefficients both with and without microspoilers were estimated and found to be in good agreement where the major effect of the microspoiler system is the addition of trim forces and...

Use of Ground-Based Wind Measurements for Improved Guided Airdrop Accuracy

Uncertainty in atmospheric winds represents one of the primary sources of landing error in airdrop systems. While guided airdrop systems can compensate for uncertainties in the wind profile, unexpected winds in the drop zone can still result in large errors in landing location, and they can even lead to damage or complete loss of the cargo if the system hits the ground while traveling downwind. This work examines the impact of real-time knowledge of the winds in the drop zone on guided aidrop landing accuracy and landing quality. Measurements of the horizontal wind profile at multiple altitudes above the target provided by a ground-based LIDAR are considered in addition to a simple ground wind measurement. The guidance logic running on the airdrop system’s onboard autopilot is modified to integrate the wind measurements near the intended landing zone with onboard wind estimates to provide an improved, real-time estimate of the wind profile. The strategy is first developed in the framework of a rigorous simulation model and then validated in flight test. In both simulated and actual flight tests, knowledge of the wind profile near the target provided from the LIDAR unit improved landing accuracy by 40%. Knowledge of the ground winds alone provided by a low-cost, lightweight, highly portable device, again in both simulated and actual flight tests, is enough to improve landing accuracy by 33% and completely eliminate potentially dangerous downwind landings.

Shared Control of a Guided Parafoil and Payload System

The direct inclusion of human pilots into airdrop operations has a strong potential to increase the landing accuracy of conventionally autonomous guided airdrop systems. Human pilots have significant mental flexibility and an innate ability to prioritize requirements to aid safe and accurate landings. Autonomous algorithms on the other hand, are generally rigid in nature and cannot handle situations not directly programmed into the software. This paper outlines the work done to develop an integrated human-machine interface that combines the flexibility of human control decisions with the powerful ability of autonomous systems to measure data on the aircraft and generate key estimates. Two interfaces are presented melding a first person view camera mounted to the payload of the airdrop system and a birds eye GPS based map of the drop zone with relevant system estimates overlaid. Flight testing of these digital feedback methods to the pilot are studied to identify the ability of human operators to successfully and accurately control an airdrop system to the ground. Results indicated that a trained human operator has the ability to improve landing accuracy over a conventionally autonomous system by 36%.

High Fidelity In-Flight Pressure and Inertial Canopy Sensing

In order to effectively understand airdrop system dynamics, analysis and verification beyond simulation alone must be pursued. This requires accurate experimental data for both the canopy and payload. Measurement of parafoil-payload relative motion has always been challenging due to the flexible nature of the canopy and requires a sensing system that does not interfere with canopy packing, does not significantly increase the canopy mass, and requires no physical connection between the canopy and payload. In 1999, Strickert and Jann [1] successfully used video-image processing techniques to measure parafoil-payload relative motion. Post flight analysis demonstrated the difficulty in estimating the differences in the orientation of the payload and canopy. Later in [2] and [3], using the same videomeasurement system, a multi-body simulation was used primarily to investigate relative longitudinal displacement, lateral displacement, and yawing. In this paper, the authors take a different approach by embedding multiple miniature low power wireless inertial sensors into the canopy. After release, the canopy sensors transmit inertial data to a main payload flight computer in during flight. As in [4], information provided from each sensor includes: magnetometer data, angular velocity, and accelerations; however, new to this work is the addition of pressure sensors which can also measure individual cell pressures and multiple GPS modules. The miniature canopy sensors were installed in an MC-4/5 canopy that mated with an autonomous guidance unit (AGU). Data was collected first for two drops with three sensors, with an emphasis on working out communication logistics between all of the sensors and the main payload module and evaluating the most recent sensor upgrades. A final drop was completed with 14 sensors embedded in the canopy (two GPS sensors and 12 pressure-inertial sensors). The experimental miniature wireless canopy sensors platform used in the parafoil and payload system is outlined in Section 2. Section 3 details the first two drops and analyzes the trajectories of each, followed by the pressure measurements and their analysis in Section 4. Section 5 highlights the performance of the system with 14 embedded sensors.

Utilizing ground-based LIDAR measurements to aid autonomous airdrop systems

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.

Global Positioning System Denied Navigation of Autonomous Parafoil Systems Using Beacon Measurements From a Single Location

Precision-guided airdrop systems have shown considerable accuracy improvements over more widely used unguided systems through high-quality position, velocity, and time feedback provided by global positioning system (GPS). These systems, like many autonomous vehicles, have become solely dependent on GPS to conduct mission operations. This necessity makes airdrop systems susceptible to GPS blackout in mountainous or urban terrain due to multipathing issues or from signal jamming in active military zones. This work overcomes loss of GPS through an analysis of guidance, navigation and control (GNC) capabilities using a single radio frequency (RF) beacon located at the target. Such a device can be deployed at the target by ground crew on site to retrieve package delivery. Two novel GNC algorithms are presented, which use either range from or direction to a RF beacon. Simulation and experimental flight testing results indicated that beacon-based methods can achieve similar results as GPS-based methods. This technology provides a simple and elegant solution to GPS blackout with best method studied showing only a 21% decrease in landing accuracy in comparison to GPS-based methods. [DOI: 10.1115/1.4037654]

Flight Testing of Autonomous Parafoils Using Upper Surface Bleed Air Spoilers

Upper surface bleed air spoilers are a novel control mechanism for guided airdrop systems. In contrast with conventional trailing edge deflection mechanisms, upper surface bleed air spoilers have been shown to be extremely effective for both lateral (turn rate) and longitudinal (glide slope) control of parafoil aircraft. Bleed air spoilers operate by opening and closing several span-wise slits in the canopy upper surface thus creating a virtual aerodynamic spoiler from the stream of expelled ram air. The work reported here investigates the autonomous landing performance of parafoil aircraft in both computer simulation and flight testing using upper surface bleed air spoilers exclusively for lateral steering control and combined lateral and longitudinal control. Additionally, a novel incanopy bleed air actuation system has been designed and successfully flight tested on a variety of larger parafoil aircraft ranging in payload weight from 300 lb to nearly 1000 lb. The in-canopy system consists of several small, specifically designed winch actuators mounted inside the parafoil canopy capable of opening one or more upper surface bleed air spoilers completely independent of the system AGU. Details of the in-canopy hardware, unique internal rigging structure, and resulting flight performance using the in-canopy system are also presented with excellent results.

Beacon Based Autonomous Airdrop Systems: Back to the Future

Current autonomous airdrop systems critically rely on GPS feedback for inertial position and velocity information. Future airdrop missions will involve scenarios where it is desired to aerially deliver payloads accurately in an area where GPS is not available. In these situations, a pressing need exists to create useful feedback information from a non-GPS source for use by the autonomous airdrop system guidance and control algorithm. This work addresses this issue through implementation of radio beacons which can be deployed by ground crew on site to retrieve package delivery. Current radio beacon technology is presented in addition to two control algorithms designed around different levels of radio beacon feedback information.