Dissertations / Theses on the topic 'Aircraft engineering'

Aircraft developers like other development and manufacturing companies, are experiencing increasing complexity in their products and growing competition in the global market. One way to confront the challenges is to make the development process more efficient and to shorten time to market for new products/variants by using design and development methods based on models. Model Based Systems Engineering (MBSE) is introduced to, in a structured way, support engineers with aids and rules in order to engineer systems in a new way.

In this thesis, model based strategies for aircraft and avionics development are studied. A background to avionics architectures and in particular Integrated Modular Avionics is described. The integrating discipline Systems Engineering, MBSE and applicable standards are also described. A survey on available and emerging modeling techniques and tools, such as Hosted Simulation, is presented and Modeling Domains are defined in order to analyze the engineering environment with all its vital parts to support an MBSE approach.

Time and money may be saved by using modeling techniques that enable understanding of the engineering problem, state-of-the-art analysis and team communication, with preserved or increased quality and sense of control. Dynamic simulation is an activity increasingly used in aerospace, for several reasons; to prove the product concept, to validate stated requirements, and to verify the final implementation. Simulation is also used for end-user training, with specialized training simulators, but with the same underlying models. As models grow in complexity, and the set of simulation platforms is expanded, new needs for specification, model building and configuration support arise, which requires a modeling framework to be efficient.

Modern unmanned aerial vehicles (UAV) are made of lightweight structures, owing to the demand for longer ranges and heavier payloads. These lightweight aircraft are more susceptible to vibrations caused by atmospheric turbulence transmitted to the fuselage from the wings. These vibrations, which can cause damage to the payload or on board avionics present a serious problem, since air turbulence is expected to increase over the next few decades, due to climate change.

The objective of this thesis is to predict the vibration of an aircraft fuselage by establishing a relationship between wing and fuselage vibration. A combination of ANSYS^® and MATLAB^® modeling are used to simulate aircraft vibrations. First, the displacement of a lumped mass aircraft model to step and sinusoidal forces acting on the wings are compared to displacements calculated using modal superposition equations. Next, a state space representation of this system is found using system identification techniques, which uses wing displacement as input, and provides fuselage displacement as output. This state space model is compared to a derived state space model for validation. Finally, a three dimensional aircraft with distributed displacement sensors on its wings is modeled. A state space representation is established using the wing displacement output from the sensors as its input and the motion and rotation of the fuselage along the X, Y and Z axes as the output.

It is seen that the displacement results of the lumped mass system match with those calculated using modal superposition equations. The state space model can also accurately predict the fuselage vibration of the lumped mass system, when provided with wing displacement as input. More importantly, results have shown that the distributed vibration sensors on the three dimensional plane model are able to measure the wing displacements. Using the output from these distributed sensors, the motion and rotation of the fuselage about all three axes can be effectively predicted.

Aircraft attitude estimation requires fusing several sensors in order to recover both high and low frequency information in an observable manner. This thesis explores the fusion of gyroscope integration, gravity vector estimation, and magnetic field vector estimation using a complementary filter and an extended Kalman filter (EKF), both of which use a unit quaternion to represent the attitude portion of the state.

First, a set of models, which contain bias, scale factor errors, alignment errors, and Gaussian white noise, is introduced to govern the available sensors. The gyroscope bias is modeled as a random walk. A calibration routine is then established to minimize scale factor and bias errors. After some definitions and derivations for quaternion algebra are established, the attitude solution is then estimated using the complementary filter. Then the EKF is introduced and used to estimate both the quaternion state and gyroscope bias.

The thesis is concluded with a Monte Carlo run to compare the complementary filter with the EKF. Due in large part to the estimation of gyroscope bias in the EKF, this filter is shown to give a significantly more accurate state estimate. The robustness is also evaluated, with both filters initialized with the incorrect initial quaternion and gyroscope bias estimate. The EKF is shown to converge relatively quickly, while the complementary filter does not reliably converge due to the lack of gyroscope bias estimation.

This thesis presents the work done to implement new computational tools and methods dedicated to aircraft conceptual design sizing and optimization. These tools have been exercised on different aircraft concepts in order to validate them and assess their relevance and applicability to practical cases.First, a geometry construction protocol has been developed. It is indeed essential to have a geometry description that supports the derivation of all discretizations and idealizations used by the different analysis modules (aerodynamics, weights and balance, stability and control, etc.) for which an aircraft concept is evaluated. The geometry should also be intuitive to the user, general enough to describe a wide array of morphologies and suitable for optimization. All these conditions are fulfilled by an appropriate parameterization of the geometry. In addition, a tool named CADac (Computer Aided Design aircraft) has been created in order to produce automatically a closed and consistent CAD solid model of the designs under study. The produced CAD model is easily meshable and therefore high-fidelity Computational Fluid Dynamics (CFD) computations can be performed effortlessly without need for tedious and time-consuming post-CAD geometry repair.Second, an unsteady vortex-lattice method based on TORNADO has been implemented in order to enlarge to scope of flight conditions that can be analyzed. It has been validated satisfactorily for the sudden acceleration of a flat plate as well as for the static and dynamic derivatives of the Saab 105/SK 60.Finally, a methodology has been developed to compute quickly in a semi-empirical way the buffet envelope of new aircraft geometries at the conceptual stage. The parameters that demonstrate functional sensitivity to buffet onset have been identified and their relative effect quantified. The method uses a combination of simple sweep theory and fractional change theory as well as the buffet onset of a seed aircraft or a provided generic buffet onset to estimate the buffet envelope of any target geometry. The method proves to be flexible and robust enough to predict within mainly 5% (and in any case 9%) the buffet onset for a wide variety of aircrafts, from regional turboprop to long-haul wide body or high-speed business jets.This work was done within the 6^th European framework project SimSAC (Simulating Stability And Control) whose task is to create a multidisciplinary simulation environment named CEASIOM (Computerized Environment for Aircraft Synthesis and Integrated Optimization Methods), oriented toward stability and control and specially suited for aircraft conceptual design sizing and optimization.

An analytical technique for investigating transport aircraft handling qualities is exercised in a study using models of two such vehicles, a Boeing 747 and Lockheed C-5A. Two flight conditions are employed for climb and directional tasks, and a third included for a flare task. The analysis technique is based upon a “structural model” of the human pilot developed by Hess. The associated analysis procedure has been discussed previously in the literature, but centered almost exclusively on the characteristics of high-performance fighter aircraft. The handling qualities rating level (HQRL) and pilot induced oscillation tendencies rating level (PIORL) are predicted for nominal configurations of the aircraft and for “damaged” configurations where actuator rate limits are introduced as nonlinearites. It is demonstrated that the analysis can accommodate nonlinear pilot/vehicle behavior and do so in the context of specific flight tasks, yielding estimates of handling qualities, pilot-induced oscillation tendencies and upper limits of task performance. A brief human-in-the-loop tracking study was performed to provide a limited validation of the pilot model employed.

The purpose of this research was to investigate the cybersecurity controls needed to protect Unmanned Aircraft Systems (UAS) to ensure the safe integration of this technology into the National Airspace System (NAS) and society. This research presents the current vulnerabilities present in UAS technology today along with proposed countermeasures, a description of national and international rules, standards, and activities pertaining to UAS and cybersecurity, and a minimum set of safety operational requirements which are recommended to be implemented by manufacturers of small UAS and mandated by governing agencies. UAS attacks are defined in three categories: hardware attack, wireless attack, and sensor spoofing. The future influx of small and hobby oriented UAS should consider a minimum set of regulated cyber safety standards right out of the box, such as Geofencing technology and isolated auto safety measures. The commonality between national and international cyber related activities point to several operational requirements, hardware limitations, and heightened UAS vulnerabilities. These include type of radio frequency spectrum that is used during operation, methods for detect and avoid, safety measures, lost link procedures, and corrupted data communications.

Westhelicopter INC. has an aviation workshop providing qualified helicopter maintenance in accordance with PART-145. Maintenance and administrative base is situated in Luleå at Kallax airport. The types that Westhelicopter INC are currently authorised to service are: Eurocopter AS 350 Base/Line Maintenance, Eurocopter EC 120 Base/Line Maintenance and Robinsson R44 Base/Line Maintenance.

The thesis work has been to make new maintenance programme for Westhelicopter INC. This maintenance programme will be used to follow-up the time of the components, service bulletins and ADs. Existing materials, as maintenance manuals and interviews with technical staff, was used to make more efficient maintenances programme. Work will be applied to all helicopters that Westhelicopter AB supplies.