Skip to main content

Foldable, adaptive, steerable, textile wing structure for aircraft emergency recovery and heavy load delivery

Exploitable results

A completely new design based on an extensive structural optimisation and the use of aluminium alloys. The Platform was a 40 % lighter than that developed for the PTD project, and this means that its load carrying capability is enhanced in the same extent; at the same time, this allows to make use of emergency parachutes (capable up to 1100 kg) easily available and inexpensive. The variable payload feature was attained through a safe, cheap and reliable ballast concept. It makes use of inexpensive materials, such as sand and steel pees, which can be ejected in flight in a easy way with minimum risk damage on ground. Design and construction of a cheap damping system, which is made of an inexpensive materials like honeycomb cardboard, and which is a typical material used by parachute armies and thereby, easily available. Moreover, its manufacturing is very simple and cheap: made of several layers of honeycomb cardboard, out cut according to certain pattern, and following glued to get a monoblock which can be easily installed on the Platform. Its design mainly intended to dissipate the energy from vertical landing velocity. However, considering the flight-test data provided by steering flight tests (in particular, flare manoeuvre), we can say that dissipating arrangement has a noticeably ability to cope with pitch and knee-down effects when landing with non-negligible horizontal velocities. Applications: High potential of application on emergency systems as on Tail Bumpers of A/C, and on landing systems to be used only once as Space Ships.
The primary aim of the FASTWing project is the development of an alternate textile wing concept with an increased aerodynamic efficiency to reach a glide ratio greater than five. Another goal is the implementation of a lightweight guidance platform, which has to provide autonomous flight control. In a concept trade off several design concepts for FASTWing system have been discussed. The result of the concept trade off favours the concept of a large parafoil. The autonomous flight control will be provided by the Parafoil Guidance, Navigation and Control (PGNC) software being implemented in the avionics system. To keep the effort to a minimum, for FASTWing already existing PGNC software should be adapted. Thus the FASTWing PGNC software is based on GNC algorithms used in PTD (Parafoil Technology Demonstrator) and X-38 project. The Basic Software (BSW) of the avionics system acts as application service between the hardware (onboard computer, sensors etc.) and the application software (PGNC software). In coordination with NLR the interface between the BSW and the PGNC software has been defined. The application side of the BSW has been documented in terms of an Interface Control Document (ICD). Based on the interface definition the already existing PGNC software has been adapted for FASTWing. To verify accurate operation of the PGNC, the software has been tested first in the development environment (Windows) and second in the avionics system environment (VxWorks). Therefore, based on the simulator for the X-38 parafoil flight control software, a closed loop simulator has been developed for the Windows environment to simulate a FASTWing mission. Due to the BSW/ASW software architecture concept, the PGNC software tested on the Windows platform is fully transportable to the Avionics System of the flight hardware for use in flight tests. Closed loop testing under Windows with the goal of verifying numerical stability and robustness of the control algorithms has been completed in late 2003. Following the first release of the flight application software, the integration and real time testing on the flight hardware was completed in September 2004. Flight Readiness was certified. In addition to the onboard software, a ground station console was developed providing real time visualization and data display to the ground operator. Furtheron, the flight control team provided a mission planning tool that allows to adapt the mission quickly in case of changing meteorological conditions. The first flight of the parafoil guidance system took place 21-Apr-2005 and the second flight was done on 02-May-2005. Post flight analyses has proven that on both flights the parafoil guidance software has worked well without any anomaly. For each flight a detailed post flight analysis has been performed which analyzed - on the basis of flight data recorded on board - the performance of the onboard software with special focus on sensor data acquisition and processing, plausibility of mission management decisions, dynamic response of the guidance and control function. Flights were then reproduced on the simulator to allow an improvement of the system models used for the design of the guidance and control software. The results have shown that in addition to the flawless performance in flight the significant advantage of the applied control development concept is the flexibility w.r.t. configuration changes. With the very limited amount of flight test data available from deployment tests with different load masses it was possible to design a control system, which allowed clearing the system for autonomous operations after only two remote controlled flights. The applied design concept and the resulting flight control software can be used on any parachute landing system. Most obvious applications are the autonomous delivery of personnel and cargo for the military. Space applications include the landing on extraterrestrial bodies with an atmosphere. It is of particular value that the guidance system does not require a square parachute. Any parachute with directional capability such as a modified round canopy can be used. Civilian applications include smart air rescue systems which have a built in capability to actively avoid obstacles of hazardous areas in case of a required bail out of the crew.
In the FASTWing project NLR has developed the hardware platform for the Guidance, Navigation and Control Task. This platform with associated software (partly from EADS, partly from NLR) has been used to navigate the parafoil system to the targeted landing point and consist of COTS equipment and as such can easily follow new developments. Since it is small and light and consumes only a small amount of electric power it has contributed only little to the overhead size and weight of the entire system. The sensor package has been also selected on performance vs. weight and size The system has also been equipped with a so-called Basic Software Package (BSW). This package consists of the operating system and the interface drivers for the outside world (i.e. sensors and actuators) and it provides also an interface to the supplied guidance software using well-defined service calls. In this way the guidance software can be updated without adapting the basic software. In this way a flexible system has been obtained that can be used for a variety of applications, not only for parafoil systems but also for other type of instrumentation.
A main issue for a successful large-scale ram-air gliding parachute system is the quality of the dynamic flare manoeuvre. By an accurately timed pulling of full brakes horizontal velocity and in particular the vertical speed shall tend to zero just at the moment of payload touch down. Of course, this cannot be reached completely in any circumstance, but a limitation of the sink rate at landing to values less than 3 m/s seems to be achievable. The numerical simulation of the behaviour of the parafoil/payload system in this situation requires the solution of the set of equations of motion. The problem can be treated at various levels of physical modelling which adresses the number of bodies, the rigidity and the number of degrees of freedom (n-DoF) of the considered system. At EADS-ST LP46 a two-dimensional (4DoF) and a three-dimensional (8DoF) model describing the parafoil/ payload system are available. As the landing flare manoeuvre shall take place without any lateral motion, i.e. no curved flight during landing, the simulation of this particular phase currently focuses on the 2-D model describing the longitudinal motion allowing two transactional degrees of freedom of the entire system and canopy pitching motion as well as relative payload pitching motion. Once the flight mechanical model is selected, flare initiation altitude, flare speed, and the aerodynamic model are the major parameters to be varied. Numerous simulations were performed and documented showing the influence of the above parameters. As expected the aerodynamic behaviour of the canopy in terms of lift and drag change due to brake deflection clearly determines the flare performance. For the actual FASTWing canopy design only theoretical predictions are available to assess the aerodynamic performance of the canopy and the corresponding brake efficiency. During the wind tunnel test aerodynamic characteristics of the basic design and control deflection efficiency of the FASTWing canopy will be examined in detail. Feeding these coefficients into the 'dynamic flare analysis tool' will enable to further optimise the landing flare manoeuvre with regard to initiation altitude and line travel speed during braking.
AFG laid out the dimension of two Stabilisation Parachutes (one as a spare unit) and realised the reefing system, re-inforcements and attachments to the deployment demonstrator for all agreed payload masses from 1100kg up to 3200kg. Furthermore the reefing system of the parafoil was developed, laid out, manufactured and successfully tested for the two scaled Wind Tunnel parafoils by AFG. The reefing system for the full scale parafoil was laid out, manufactured, tested and attached to the parafoil canopy by AFG. In addition, AFG replaced the metallic confluence fitter by a textile confluence fitter after the first series of deployment tests. During the flight tests the parachute system has been further improved and showed reliable performance.
During the project an interface for exchanging aerodynamic loads (i.e. pressure) and structural deformations was developed. This is on a fairly general format and applies interpolation of data between grids of different element type and topology. The developed structural code was based partly on various public domain software (matrix solvers, precondition and reordering methods) and partly own development.
For several reasons the aerodynamic analysis of ram-air parachute systems is a very intricate and crucial task. The flexible textile wing structure interacts with the pressure distribution resulting from the surrounding external and internal flow field and vice versa. Unsteady processes ranging from canopy deployment, spreading, and filling process to dynamic flight manoeuvres like landing flare or rapid turn initiation are out of reach for nowadays-standard aerodynamic analysis tools. Special features of the parafoil-payload system -e.g. the complex arrangement of large numbers of suspension lines and the close coupling between flight mechanics, (local) free stream velocity resulting from the actual flight path, and changing geometrical shape of the canopy - do not ease the process of aerodynamic analysis. Therefore most of the theoretical methods available focus on description of the aerodynamic behaviour of fully inflated ram-air canopies in steady flight conditions. Only a few computer codes offer the capability to perform an iterative coupling between a solver for the flow and a deformation analysis of the textile wing structure. Unfortunately most of these programs concentrate on one aspect of the coupling, i.e. either a highly accurate flow simulation is coupled with an elementary method for the structural analysis or very simple aerodynamic modelling is combined with highly detailed finite-element methods for the treatment of the textile structure. In the frame of FASTWing an advanced simulation tool will be developed at CFD Norway combining both, an up-to-date flow simulation with an adequate representation of the structural part. Of course, such complex tool cannot be used for all kind of analysis needed during the design process as the corresponding effort w.r.t. man power and computational resources is tremendous. Therefore also an improvement of established methods is followed up. Handbook design procedures as well as singularity (panel) methods at several levels of complexity are applied and, whenever possible, improvements are added. At the same time reduction of empirical corrections to be applied with these type of methods is the major concern, as an increasing independence on empirical data coming from existing (and therefore old) design solutions is the only way to open up the field for innovative design alternatives.
1) The video analysis method was applied to a new system. A new mechanical device with a perspex dome was designed and manufactured for mounting the video camera at the vehicle. The video results have been an important source not only for acquiring the relative motion between parafoil and load, but also for getting valuable information about the opening sequence and general parachute and parafoil behavior. 2) For the analysis of the relative motion a proven and state-of-the-art tracking algorithm was used. As output the relative yawing angle and the relative displacement in x- and y-direction was extracted. The displacements were transformed into relative attitude that was used successfully for the correction of the measurements in the load. The corrected data represents the real motion of the canopy. Using the corrected data instead of the raw data from the load, better results for the parafoil aerodynamic model identification can be expected. 3) The new approach for the post-flight acquisition of the sideslip angle from video measurements of a textile vane did not work as expected. The main problems were poor visibility, partial obstructions and the high frequent fluttering of the textile vane that could not be resolved by the video. For the future this concept will be discontinued.
A ram-air parafoil for heavy load delivery with an optimized airfoil and planform was manufactured by CIMSA Ingenieria de Sistemas, leading to high glide ratio and good manoeuvrability performances. Design works were validated with scaled models by means of jump tests and wind tunnel tests. Drop tests using real size parafoil from carrier aircraft were performed leading to the expected objectives. Loads from 1000kg up to 3500kg weight were dropped using this parafoil and delivered to the target by means of a guiding system connected to the control lines of the ram-air parafoil. The technologies used by CIMSA Ingenieria de Sistemas for the development of this parafoil enable the company to design, manufacture and test parafoils for a wide range of loads varying from tens up to thousands of kilograms.
Regarding the electrical motors, we must admit that there has not been a great forward step. However, gearbox and winch (so- called drum or barrel) have been redesigned in order to mainly reduce the overall weight of actuation system. So, the achieved mass saving is the half one of the homologous PTD actuator assembly through optimisation of both items. The planetary gearbox solution from PTD was replaced by a wormgearbox solution due mainly to - its lower cost and weight for the same torque capacity, - In addition it features a high static irreversibility, so that contributes to the desired locking feature even on presence of high output torque through output shaft when control line must be hold in certain position Despite that control of the system was achieved with no major problems (as proven during flight tests) this type of worm gearbox revealed some drawbacks that shall be accounted for future optimisation stages: - the wormgearbox model shows a behavior clearly non-linear during starting up and stops, which is closely related to the fact of presenting two different efficiencies (static and dynamic) depending of the operation regime. - This is also aggravated by the high degree of intermittency requested. Controller parameters. The programming of servo controllers was optimised in the basis of the new FastWing guiding & flare performances. In particular, The Position Control Loop - proportional, differential and integral terms � was revised, so they were proven to be stable and provide sufficient position accuracy. Actuator performances - The actuation system was successfully tested on ground with the new control parameter set - It was proven that actuator system is able to start up, control, and brake the specified loads for both guiding and flare cases. Applications: Performances optimisation for electrical actuation systems to be used on UAVs (Unmanned Aerial Vehicles).
The deployment analysis tool is capable of modelling the opening shocks and g- loads during deployment of multi stage parachute systems containing both round canopies and parafoils. The necessary calculation techniques for each sequence from aircraft release to the steady flight including free fall phases, the stabilisation phase and reefing stages of the main parachute for variable payload masses were developed. The calculation techniques were translated to implement the calculation into a software tool. The graph force/time for the structural integrity and the analysis of the simulated forces during the entire opening process is the result for the predication of the FASTWing relevant design. This "Deployment Analysis Tool" is capable to calculate with an indefinite number of different parachutes with an indefinite number of reefing stages. Validation showed that the simulation factors for the FASTWing canopy seem to be found. The Deployment Analysis Tool shows good force-over-time development as presented within this document. In most cases there was a slight over prediction of occurring accelerations. For the layout of the parafoil deployment stages and for the material selection of each stage (incl. suspension lines and canopy textiles) the results of this deployment software tool are very satisfying and reliable for development of parafoils in future projects.
Many battery technologies were assessed besides the conventional Ni-Cd type. The best candidate was the Nickel Metal Hydride type owing to its high energy density (and therefore, expected lower weight); however, they were finally discarded due to higher cost and excessive sensitivity to temperature operation � in particular, below cero degrees the performances are rather poor-. So, all battery sets are of Ni-Cd type, and revising and optimizing the mission requirements achieved the attained weight reduction with respect to the previous PTD battery arrangement: - Measuring power demands under different operating conditions; it was done as testing actuators at CESA site on ground - Specifying with more precision the flight profile and actuation times; it was assessed and finally established along Tasks 1.2 and 1.3. - Applications: Weight/size optimisation of power supply for electrical actuation systems to be used on UAVs (Unmanned Aerial Vehicles).