A high-glide ram-air parachute for 6,000 kg payloads, tested with the FASTWing CL test-vehicle.

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1 20th AIAA Aerodynamic Decelerator Systems Technology Conference and Seminar<BR> 4-7 May 2009, Seattle, Washington AIAA A high-glide ram-air parachute for 6,000 kg payloads, tested with the FASTWing CL test-vehicle. J. Wim Wegereef 1 Dutch Space B.V., Leiden, The Netherlands Dr Simon Benolol 2 Cimsa Ingenieria de Sistemas, Las Franquesas-Barcelona, Spain Edgar Uhl 3 / Christian Ulbrich Autoflug GmbH, Rellingen, Germany A guided airdrop system using a ram-air parachute with a high-glide ratio enables releases from maximal stand-off distance. During tactical operations this maximal stand-off minimizes the danger from local hostile threats and avoids revealing the target area. In a EU funded cooperation, Autoflug, Cimsa, Dutch Space, National Aerospace Laboratory NLR, DLR, EADS-CESA, CFDn and the Technion University participate in the FASTWing CL project to investigate the application of a 300m 2 high-glide parafoil with a glide ratio >5 for payloads up to 6,000 kg. The project acronym FASTWing CL stands for Folding, Adaptive, Steerable Textile Wing Structure for Capital Loads. In the project the ram-air parachute will be tested in-flight, together with the application of a low-cost Stabilization Parachute. This drogue is used to stabilize the payload immediately after release and decelerate the drop unit down to a maximum velocity of 20 m/s before the main parachute is deployed. In this paper the development of the stabilization chute and the main high-glide ram-air parachute are described, as well as the set-up of the test plan for the flight tests. I. Introduction In general guided airdrop systems with ram-air parachutes are developed to deliver cargo close to a target point where the release point of the system can be arbitrarily selected inside a large air volume. During tactical operations a maximal stand-off distance can be required to minimize danger from local hostile threats and to avoid revealing of the target area. Aerial delivery has been an important means for military operations for many decades. Interest for aerial delivery has increased recently due to new technology coming available. In an EU funded co-operation Autoflug, Cimsa, Dutch Space, National Aerospace Laboratory NLR, DLR, CESA, CFDn and the Technion University participate in the Folding, Adaptive, Steerable Textile Wing Structure for Capital Loads (FASTWing CL) project to investigate the application of a 300 m 2 high-glide parafoil with glide ratio >5 for payloads up to 6,000 kg. The FASTWing CL project is an European development within the 6 th Framework Program for the design of a cargo airdrop system for payloads weighting up to 6,000 kg using a high-glide ram-air parachute. One of the main objectives is to develop this high-glide parafoil and to demonstrate the capabilities of this parafoil in-flight in combination with an autonomous control system. 1 Product Manager, Dutch Space, Operations & Engineering, Mendelweg 30, PO Box 32070, 2303 DB Leiden, The Netherlands, w.wegereef@dutchspace.nl 2 Division Manager, Cimsa, Aerospace Division, Vallès s/n El Ramassar, Las Franquesas- Barcelona, Spain, sbenolol@cimsa.com 3 Project Manager FASTwingCL, AUTOFLUG GmbH, (department RS/E5), address: Autoflug GmbH, Industriestrasse 10, D Rellingen, Germany, e.uhl@autoflug.de 1 Copyright 2009 by the, Inc. All rights reserved.

2 Already in 2005 a 160 m 2 parafoil was designed and tested for 3,200 kg payload in a preceding FASTWing project. This project was also funded by the EC, within the 5 th Framework Program. In the current FASTWing CL project the area of the 27 cells parafoil canopy is extended to 300 m 2 and the parachute is capable to fly at 24 m/s with a total suspended payload weight of 6,000 kg. In Figure 1 on the left the drop unit of the FASTWing parachute for the parafoil deployment verification test is shown for 3000 kg payload. In the picture on the right hand side the parafoil with the guidance unit is shown in-flight. Figure 1: Drop unit of the 160 m 2 FASTWING ready for the parafoil verification test; on the right the parafoil is deployed in-flight and controlled by the guidance unit. The airfoil of the ram-air parachute was selected by means of an advanced vortex-panel based aerodynamic tool [1] and [2], leading to high aerodynamic and inflation performances. The plan form was tapered leading to flexible maneuverability and high gliding characteristics [3]. A scaled model of the parafoil was manufactured and tested in the biggest European wind tunnel at NLR - DNW in the Netherlands. Aerodynamic characteristics of the parafoil were measured for different configurations of the canopy and lines, such as reefing stages, reduced number of lines, turn and brake maneuvers. A wide range of incidence angles of the parafoil was assessed, in order to identify the optimal rigging angle. Figure 2: Two views of the parafoil in wind tunnel tests. For the airdrop tests with the 160 m 2 parafoil an AS 3000 parachute was used as extractor of the system from the carrier aircraft and a reefed G12d parachute was used for stabilizing the payload before deployment of the parafoil. 2

3 II. FASTWing CL In the current project the main objective is to extend the payload-range up to 6,000 kg in combination with a high glide ratio parafoil. The new design of this parafoil system is mainly based on the experience obtained during the analyses of the preceding FASTWing project. In addition a low-cost Stabilization Parachute is designed to replace the G12d parachute. The Stabilization Parachute is based on a cross parachute structure and will be deployed with the aim to stabilize the payload, as well as to decelerate the system down to a maximum velocity of 20 m/s. In parallel to the design of these parachutes a control unit has been developed which can be used to demonstrate the parachutes in controlled flights. At the end of the project it is the objective to demonstrate the FASTWing CL system in fully autonomous flights. Based on this flight-configuration a flight test program has been built up in a step-by-step approach. The flight tests will start with deployment tests without using any control unit. After successful completion of these tests, flights will be carried out including manual controlled maneuvers using the link between a ground station and the flight-unit. From the evaluation of the flight data recorded during these maneuvers the autopilot algorithms shall be derived to prepare the flight unit for autonomous flights. In general for a fully autonomous drop the flight can be schematically subdivided into three phases: 1. the deployment and initialization phase 2. the descent and homing phase 3. the landing approach and landing phase. During the first phase, directly after release, the Stabilization Parachute and the main square ram-air canopy are deployed. These deployments are immediately followed by an initialization or acquisition phase of the control software active on the on-board computer. In this period the autopilot will determine its heading and position and will determine the direction for heading towards the pre-defined target area, which has been entered into the onboard software before flight. After completion of the initialization phase the second phase starts with the descent and homing in on the target. In the third and last phase the flight-system will carry out the landing approach by following the predefined autopilot algorithms in order to get in the right position for a proper landing near the pre-defined landing point. This flight-phase will be completed by a flare maneuver just before landing to minimize the landing shock. In order to limit the risk at smaller drop zones for such a high glide system, an emergency system for the Steering box has been designed as additional measure of safety. The flight configuration is foreseen with a flightabort system, just because of this high glide ratio. In case of abortion the Steering box will be separated from the flight configuration and will be recovered by a stand-alone emergency system using a ballistic parachute. Immediately after separation of the Steering box the main canopy will be disconnected from the payload, which shall fall down ballistically without deceleration. In this paper the Stabilization Parachute and the design of the main 300m 2 high-glide parafoil will be presented respectively. Thereafter, in section V, a discussion will follow on the flight test plan. In this paper results test-flights are not included, since the test-campaigns are scheduled to be conducted during the second half of III. Low-cost Stabilization Parachute The FASTWing CL system consists of at least two sequent parachutes. In order to stabilize the payload after drop and to reduce the velocity of the system, a Stabilization Parachute (SP) with a size of approximately 300 m² precedes the parafoil. It is deployed after extraction from aircraft by a static line or by a preceding extraction parachute and cut after several seconds of stabilization. The subsequent parafoil is then extracted by the leaving SP. 3

4 Figure 3: The Extraction parachute deploys the stabilization parachute. The concept of design is to use low cost material (Polypropylene, Polyester) and to simplify production and assembly by using simple geometries only. This way an economic one-way-parachute is realized, even though the toughness of design and material as well as the extensive modularity of components would allow several reuses. The plan form of the canopy is basically a cruciform with separated gores. In between the gores there is a gap of several centimeters in order to achieve some constructive porosity. Each gore is equal to the others, shaping an individual circle with the suspension lines on both ends. The position of each gore in the network is fixated in a modular textile way in order to realize a maximum of exchangeability among the gores as well as improved handiness during recovery, inspection, repairing and repacking. Since these interfaces are not located in the flow of the main forces, they do not appear as weak points. Figure 4: Inflated Stabilization Parachute versus Simulation. IV. High-Glide Ram-air Parachute The airfoil of the ram-air parachute selected in the former FASTWing project [3], was also chosen for the FASTWing CL project as shown in Figure 5, in order to take into account the aerodynamic results obtained from 4

5 Wind Tunnel tests, on the one hand, and performances from Flight tests, on the other hand, from the former FASTWing project. Figure 5: Airfoil CIM-2016 selected. Although the parafoil area was increased from 160 m 2 up to 300 m 2, no increase was performed in the number of cells (27) and the number of keel attachment points (8), in order to avoid increase of lines and subsequent increase of drag coefficient of the parachute. Aerodynamic and structural analysis of the selected parafoil was performed, using design tools [1] and [2]. The full flight pressure difference profile on the canopy is presented in Figure 6. Figure 6: Pressure difference coefficient in full flight regime. The canopy pressure difference profile is presented in Figure 7 for a turn and a brake maneuver. Figure 7: Pressure difference coefficient for turn and brake maneuvers. Maximum tensions in suspension and control lines were calculated for different payload weights. Full flight, turn and brake configurations were considered as shown in Figure 8 and Figure 9 respectively. The deflection range of control lines is m. 5

6 Figure 8: Full flight shape at maximum payload weight (6000kg). Figure 9: Parachute shape at turn and flare maneuvers at maximum payload weight. The former FASTWing parachute project has demonstrated very high level of reliability, because of the use of long life material and robust construction. No structural failure and no typical damage were found after 7 drop tests with payloads weighting from 1,000 kg up to 3,200 kg. The glide ratio obtained from drop tests was between 3 and 4 as predicted by Wind Tunnel tests. The rigging angle assigned to the parafoil was initially based on theoretical assumptions and experience. In the FASTWing CL project the angle of attack was increased up to approximately 10 deg, according to the rigging angle assessment obtained from Wind Tunnel tests. Under those conditions, it is expected to get a glide ratio higher than 5. The mid-span reefing method was again adopted in the FASTWing CL project, mainly due to the fact that the parafoil deployment and reefing stages are controllable better than using a slider reefing system. V. Flight-test program A. Test philosophy After the development and production of the Stabilization Parachute and the main canopy these parachutes shall be tested in-flight. For the control of the flight unit a Steering Box with on-board control software is developed in parallel. Based on the experience gained in the previous FASTWing project, as well as experience gained during the SPADES airdrop system development, a Steering box is designed to be a test-vehicle for the FASTWing CL experimental and demonstration tests. For the FASTWing CL project a step-by-step test plan has been derived. The basic plan can be subdivided into three different phases: 1. The deployment verification drops 2. The parafoil characterization drops 3. The autonomous controlled verification flight drops During the first series, deployment verification, several drops are carried out (not necessarily in one campaign) to test the full deployment sequence of the complete parafoil system, being the deployment of the extraction parachute (if applicable), the opening of the stabilization drogue and the inflation and de-reefing of the main canopy. These 6

7 tests are carried out without the fully instrumented guidance unit. In this case the parafoil will be set to a fixed a- symmetric steering line setting, so that only a helix type trajectory will be carried out avoiding an unpredictable long-range gliding trajectory. Also the full deployment sequence of the Stabilization Parachute in combination with the main canopy will be tested. As a result from these tests a best estimate can be derived for the complete sequential deployment time of both parachutes. The length of this period will be dimensioning for setting the timer to start the initial control of the onboard steering line actuators. The initiation of the control actuation can only be started in flight after the full completion of both deployments. Since the steering lines are set at a certain fixed a-symmetric steering line setting during these drops, also a first estimate can be derived from the recorded flight data on descent and glide velocity, and as a consequence a first assessment of the in-flight glide ratio. In addition the opening shocks can be verified with the design values. Deployment Verification Drops Without Control Aerodynamic Characterization Drops With Predefined Maneuvers Fully Autonomous Controlled Verification Drops Figure 10: Basic set-up of the test program. In the parafoil characterization drops the in-flight behavior of the flight-unit will be determined from the specifically pre-defined maneuvers. One of the main objectives of this test series is to determine the in-flight turnresponsiveness of the flight unit with respect to commanded steering line deflections. During the descent flight a sequence of several turn- and brake-(pulling symmetrical steering line deflections) maneuvers are commanded manually from the ground station. Based on the evaluation of the flight data recorded on-board during these maneuvers the characteristic aerodynamic data for the flight unit can be derived. In general these characteristics are derived by using drops carried out by payloads of the same weight. Thereafter the characteristics are determined as function of payload mass by conducting flights with different payload weights. The characterization maneuvers are performed by overruling the autopilot homing-commands during the (regular) descent phase when the main canopy is fully deployed. Since the main objective of the characterization drops is to determine flight characteristics of the vehicle in-air, the final landing accuracy is not an objective in these flights. Especially since the autopilot commands are overruled by the pre-defined manual controlled steering commands. By performing these manual maneuvers as function of time it could very well be that the vehicle is steered away from the target area and consequently will not be able to land close to the target point. During this phase the control settings for the flare will also be derived from the flight data. Every drop the initial control setting will be updated. The autonomous controlled verification flight drops can be performed after the update of the autopilot algorithms, using the aerodynamic characteristics of the flying canopy with the suspended load including steering box. The aerodynamic performance can be derived after the evaluation of the recorded flight data during the maneuvers carried out in the previous part of the test program. The system is programmed to find automatically its way to the target after the release of the system, the deployment of the parafoil and a short acquisition period. At the end of the flight a flare will be carried out during the landing. During the campaign of the autonomous flights the autopilot algorithms are tested in-flight to verify the performance with respect to in-flight behavior and precision accuracy of the flight-vehicle. By variation of the different control-parameters, like the initiation timing of the flare at the end of the flight, the fine-tuning of the settings can be completed. As a first step this fine tuning can be carried out using one payload weight, but needs also to be verified for different payload masses within the specified payload-range. 7

8 Deployment and Initialization phase Descent and Homing phase Landing Approach and Landing phase Figure 11: Schematic view of the FASTWing CL descent flight phases. B. Test program Based on the above test philosophy a test plan has been derived to test the FASTWing CL configuration. In total four campaigns are planned: 1. The deployment verification drops shall comprise of drops with payloads of 3,000 kg, 4,500 kg and 6,000 kg payloads, respectively. The releases are from low altitude, sufficient to demonstrate the deployment-sequence. As a step by step approach, the deployment of the Stabilization Chute will be tested first with these three payload masses. Thereafter the deployments of the combined configuration, stabilizer and main canopy, shall be tested also with the same payload weights. 2. The characterization flights tests shall all be carried out with the same 3,000 kg payload. The flight maneuvers shall be conducted with this payload mass in 5 drops from 10,000 ft altitude. The flight properties will be derived from the recorded flight data, including using parameter estimation. Based on this data the autopilot algorithms are designed for this flight configuration. 3. Autonomous drop tests shall be carried out with this autopilot design for 3,000 kg payload. Using the result evaluation of each drop-test to fine tune the flight control parameters. 4. During the last campaign 5 guided drops with 6,000 kg payload are conducted to verify the properties for this heavier payload. The initially used autopilot algorithms for this 6,000 kg configuration are extrapolated from the 3,000 kg payload configuration. During the drops also characterization maneuvers are carried out for fine-tuning of the control parameters The decision, to separate the drops with 6,000 kg payload from the 3,000 kg payload drops, was to minimize development risk during the project. In this way the full flight characterization could be completed with 3,000 kg before the 6,000 kg payload drops are carried out. VI. Conclusion In the FASTWing CL project a low-cost Stabilization Chute and a 300 m 2 high glide ram-air parachute have been developed for payloads up to 6,000 kg. The development is based on the experience gained during a preceding 8

9 FASTWing project for 3,200 kg payloads. The high glide ratio >5 is achieved by increasing the nominal incidence angle of the canopy. The final validation shall be confirmed during planned flight tests in the near future. The FASTWing CL project represents an important increase of knowledge in the parafoil technologies, because it demonstrates how the theoretical design tools and Wind Tunnel tests can be validated by real drop tests, within a wide range of payload mass. Reliability and consistency of the FASTWing CL project results mainly depend on the accuracy of flight data acquisition system to be installed in the flying system, and on the quantity of drops to be performed and the number of maneuvers realized within these drops. (More on the FASTWing CL project is described in parallel papers during this AIAA conference. See reference [4] to [7].) Based on a proven test philosophy a test program is derived to validate the controllability of the parachute in combination with an autonomous guidance system. After the characterization of the flight-performance the autopilot algorithms are designed to enable the autonomous control of the flight configuration. In first instance this will be validated for 3,000 kg payloads. In a fourth and last test campaign the payload range shall be completed up to 6,000 kg. References [1] DVM: Aerodynamic software tool for ram-air parachutes design, Yuri Mosseev, Scientific Technical Center OZON, Moscow, Russia. [2] MONSTR: Structural software tool for ram-air parachutes design, Yuri Mosseev, Scientific Technical Center OZON, Moscow, Russia. [3] The FASTWing Project, Parafoil Development and Manufacturing, 18th AIAA Aerodynamic Decelerator Systems Conference, Munich 2005, Dr. S. Benolol - F. Zapirain. [4] The FASTWing CL Project A self Gliding System for Capital Loads, 20th AIAA Aerodynamic Decelerator Systems Conference, Seattle 2009, Edgar Uhl, Christian Schulte, Christian Ulbrich, Dr. Oliver Burkhardt. [5] Development of Aerodynamic Analysis Software Tools within the FASTWing CL Project, 20th AIAA Aerodynamic Decelerator Systems Conference, Seattle 2009, Ivar J. Oye. [6] Folding, Adaptive, Steerable Textile Wing Structure for Capital Loads: Description of the Guidance, Navigation and Control System,, 20th AIAA Aerodynamic Decelerator Systems Conference, Seattle 2009, Pieter Hollestelle, Arthur Grunwald, Andreas Jiminez Olazabal. [7] Flight Test Instrumentation for Evaluation of the FASTWing CL System, 20th AIAA Aerodynamic Decelerator Systems Conference, Seattle 2009, Thomass Jann, Christian Greiner-Perth 9