Keith Bergeron

The road ahead: A white paper on the development, testing and use of advanced numerical modeling for aerodynamic decelerator systems design and analysis

Quantitative engineering analysis of parachutes and inflatables has been part of the routine design process since the days of World War II. But in most cases, the shear complexity in which their flexible structure interact both externally and internally with the surrounding air demands that empirical data be used to either validate or supplement such analysis. Advanced modeling embodied in the techniques of Computational Fluid Dynamics (CFD), Computational Structure Dynamics (CSD) and Fluid-Structure Interactions (FSI) has great potential for diminishing such reliance. But even though its application to aerodynamic decelerator systems (ADS) has been under consideration for the past four decades, progress has been painfully slow and the results rarely integrated into todays engineering design practice. This report aims at discussing why advanced modeling has not reached the level of practical use that has occurred in other aerospace fields. Such lack of progress origins partly from advanced modeling requiring substantial human resources that are not usually associated with parachute programs (expertise in computational methods in particular). Moreover, the extensive experimental database for Verification and Validation needed to support advanced modeling development is missing. This white paper begins with a pedagogical review of the most current implementations of CFD, CSD and/or FSI in the context of ADS applications. This is followed by a discussion of both non-ADS and ADS examples in which advanced modeling has been shown to yield interesting and relevant results. The report also identifies the type of data and measurement techniques that are needed for V&V, as well as the most pressing challenges - both theoretical and empirical - that are impeding progress. The paper ends with a series of recommendations for action items to be considered in the near and long terms.

Aerodynamic Effects of Parafoil Upper Surface Bleed Air Actuation

Control of the glide slope of parafoil and payload aircraft is limited with current control mechanisms, which makes the precision landing of autonomous systems extremely challenging. The incorporation of bleed air vents into the upper surface of the parafoil canopy to create aerodynamic spoilers has been shown to be an extremely effective means of obtaining a wide range of glide slope control with minimal actuation effort and complexity. The current work presents physical insight into these novel control mechanisms through a combination of computational fluid dynamic simulation and wind tunnel testing.

Adaptive Control of Damaged Parafoils

Autonomous guided airdrop systems based on steerable, ram-air parafoils generally offer significant improvements in payload delivery accuracy compared to unguided airdrop. However, in the event of a malfunction, the gliding ability of the parafoil canopy can result in extremely large deviations from the target. In particular, damage to the parafoil canopy or rigging during the inherently chaotic canopy inflation is not uncommon. Significant damage can result in large deviations from the assumed flight characteristics, but it is often the case that the parafoil will often retain a significant amount of steerability and gliding ability, even in the event of very large amounts of damage. However, the typical autonomous control logic used for guided airdrop systems is unable to compensate for very large deviations from the assumed flight characteristics. The current work examines the incorporation of simple adaptive control logic into guided airdrop systems to retain reasonable landing accuracy with large deviations from the assumed flight characteristics. Simulation results demonstrate effective autonomous control of guided airdrop systems with large amounts of damage with the proposed adaptive control logic. Monte Carlo simulation results are used to compare landing accuracy for a standard control algorithm and the adaptive control algorithm presented here with various amounts of damage in windy and turbulent conditions. The results demonstrate that even with levels of damage sufficient to create an order of magnitude increase in landing error for a standard control algorithm, the adaptive control algorithm is able to maintain the same landing accuracy expected with no damage at all.

Longitudinal Control for Ultra Light Weight Guided Parachute Systems

† Senior Electrical Engineer, AIAA Member ‡ Electrical Engineer, AIAA Member § Research Engineer, AIAA Senior Member ¶ Research Associate Longitudinal Control for Ultra-Light Weight Guided Parachute Systems Keith Bergeron*, Greg Noetscher, Michael Shurtliff, Steven Tavan US Army Natick Soldier Research, Development and Engineering Center, Natick, MA 01760 Frank Deazley Aerial Delivery Solutions LLC, 2601 Keswick Court, Kissimmee, FL 34744

AccuGlide 100 and Bleed-Air Actuator Airdrop Testing

The Natick Soldier Research, Development, and Engineering Center has been leading an effort to develop precision guided airdrop systems with a CEP under 25-meters. A three-motor airborne guidance unit (AGU) was used on a 100 ft 2 AccuGlide system (AG100) to activate a new longitudinal control mechanism using upper surface bleed air. System Identification methods were applied to populate a drop test database, and dynamic model parameters were determined. It is shown that upper surface canopy spoilers are an effective means of glide slope control for airdrop systems, and spoiler turn rate capability compares favorably with standard differential tail deflection.

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.

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.