Browsing by Author "Cooke, Alastair"

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    The aircraft spin - a mathematical approach and comparison to flight test
    (American Institute of Aeronautics and Astronautics, 2017-06-09) Bennett, Christopher J.; Lawson, Nicholas J.; Gautrey, Jim; Cooke, Alastair
    A Scottish Aviation Bulldog light aircraft operated by the National Flying Laboratory Centre (NFLC) at Cran eld University, modi ed with research equipment including bre optic sensors for wing strain and fuselage pressure measurements, is used to investigate the dynamics of a fully developed spin. A theoretical model is developed to compare with existing ight test data. In particular, the frequency of the aircraft spin is analysed as a function of the mass distribution of the aircraft to determine the e ect of the fuel load. It is found that the spin frequency is minimally a ected by the fuel load since the moments of inertia corresponding to the engine, for example, are far more signi cant. However, it is con rmed that the yawing e ect of the propeller causes the aircraft to spin faster to the right than to the left.
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    Bladesense – a novel approach for measuring dynamic helicopter rotor blade deformation
    (European Rotorcraft Forum, 2018-12-31) Weber, Simone; Southgate, Dominic; Mullaney, Kevin; James, Stephen; Rutherford, Robert; Sharma, Anuj; Lone, Mudassir; Kissinger, Thomas; Chehura, Edmond; Staines, Stephen; Pekmezci, Huseyin; Fragonara, Luca Zanotti; Petrunin, Ivan; Williams, Dan; Moulitsas, Irene; Cooke, Alastair; Rosales, Waldo; Tatam, Ralph P.; Morrish, Peter; Fairhurst, Mark; Atack, Richard; Bailey, Gordon; Morley, Stuart
    Technologies that allow accurate measurement of rotorblade dynamics can impact almost all areas of the rotorcraft sector; ranging from maintenance all the way to blade design. The BladeSense project initiated in 2016 aims to take a step in developing and demonstrating such a capability using novel fibre optic sensors that allow direct shape measurement. In this article the authors summarise key project activities in modelling and simulation, instrumentation development and ground testing. The engineering approach and associated challenges and achievements in each of these disciplines are discussed albeit briefly. This ranges from the use of computational aerodynamics and structural modelling to predict blade dynamics to the development of direct fibre optic shape sensing that allows measurements above 1kHz over numerous positions on the blade. Moreover, the development of the prototype onboard system that overcomes the challenge of transferring data between the rotating main rotor to the fixed fuselage frames is also discussed.
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    Effect of rotor tilt on the gust rejection properties of multirotor aircraft
    (MDPI, 2022-10-18) Whidborne, James F.; Mendez, Arthur P.; Cooke, Alastair
    In order to operate safely in windy and gusty conditions, multirotor VTOL aircraft require gust resilience. This paper shows that their gust rejection properties can be improved by applying a small amount of fixed outward rotor tilt. Standard aerodynamic models of the rotors are incorporated into two dynamic models to assess the gust rejection properties. The first case is a conceptual birotor planar VTOL aircraft. The dependence of the trim and stability on the tilt angle are analyzed. The aircraft is stabilized using a pole-placement approach in order to obtain consistent closed-loop station-keeping performance in still air. The effect of gusts on the resulting response is determined by simulation. The second case study is for a quadrotor with a 10∘" role="presentation" style="max-height: none; display: inline; line-height: normal; word-spacing: normal; overflow-wrap: normal; white-space: nowrap; float: none; direction: ltr; max-width: none; min-width: 0px; min-height: 0px; border-width: 0px; border-style: initial; position: relative;">10∘ outward rotor tilt. The aerodynamic coefficients are analyzed for trimmed station-keeping over a range of steady wind speeds. An LQR controller is used to apply station-keeping that includes integral action, and the gust responses are again obtained using simulation. The results show that the outward rotor tilt causes the aircraft to pitch down into a lateral gust, providing lateral force that opposes the gust and so significantly improving the gust rejection properties.
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    Regressor time-shifting to identify longitudinal stability and control derivatives of the Jetstream 3102
    (Elsevier, 2017-06-20) Yusuf, Sezsy; Lone, Mudassir; Cooke, Alastair; Lawson, Nicholas J.
    The Jetstream 31 G-NFLA aircraft is used as a national flying laboratory test vehicle for flight dynamics research and teaching purposes. It has been the subject of much theoretical and experimental modelling and therefore, the need for generating validation data through flight testing is critical. In this paper, the aircraft's short period pitch oscillation mode characteristics are identified using data from sixteen flight tests. An identification procedure based on the least squares method and reduced order state-space model is used and the need for pre-processing regressors due to the effects of sensor location and instrumentation delays is highlighted. It has been shown that time-shifting the regressors based on relative locations of the angle of attack vanes and the inertial measurement unit results in significant reductions in uncertainty bounds of the estimated aeroderivatives and also a model that provides a closer match to flight test data. The estimated models are validated using separate flight test data and the variations in aeroderivatives over a range of airspeeds and centre of gravity positions are also presented.
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    Simulated pilot-in-the-loop testing of handling qualities of the flexible wing aircraft
    (Taylor and Francis, 2020-02-09) Portapas, Vilius; Cooke, Alastair
    This article aims to indicate the differences between rigid and flexible wing aircraft flying (FQ) and handling (HQ) qualities. The Simulation Framework for Flexible Aircraft was used to provide a generic cockpit environment and a piloted mathematical model of a bare airframe generic high aspect ratio wing aircraft (GA) model. Three highly qualified test pilots participated in the piloted simulation trials campaign and flew the GA model with both rigid and flexible wing configurations. The results showed a negligible difference for the longitudinal HQs between rigid and flexible wing aircraft. However, significant changes were indicated for the lateral/directional HQs of the flexible wing aircraft. A wing ratcheting phenomenon manifested itself during the roll mode tests, the spiral mode exhibited neutral stability and the Dutch roll mode shape changed from a horizontal to a vertical ellipse. The slalom task flight tests, performed to assess the FQs of the aircraft, revealed the degradation of both the longitudinal and lateral/directional FQs.
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    Technical note: recent experiences of helicopter main rotor blade damage
    (Vertical Flight Society, 2019-08-01) Weber, Simone; Lone, Mudassir M.; Cooke, Alastair
    Results of a survey investigating commonly occurring minor rotor blade damage incidents are presented in this paper. Over 100 participants worldwide ranging from test pilots to commercial pilots and licensed engineers answered the survey. The focus of this work was to provide a user-oriented context that can inform the decision-making process for integrating state-of-the-art instrumentation systems for rotor blade health monitoring onboard operational helicopters. This paper highlights the dichotomy faced by designers who have a choice to follow either a reactive strategy based on operational experience or a preventative approach based on technological trends.