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8. CONCLUSIONS AND FUTURE
DEVELOPMENTS
This thesis developed a tool for the evaluation of forces and power necessary for the movement of aircraft control surfaces. The integration with EMA models permits the evaluation of the power absorption and the thermal flow.
This tool will be used within the Clean Sky GRA project as a sub-model of the SSE. The scope of the SSE is the design and the validation of the EMS logics in relation to the electrical power absorbed by the A/C subsystems. The thermal flow from the A/C subsystems is an input of the Cabin Thermal Model and it is used by the SSE to evaluate the power absorption of the Environmental Control System.
The mechanical model of each CS takes into account the inertial force, the gravity force and the aerodynamic hinge moment. The weight and the geometrical characteristics, the hinge moment coefficients and the local airflow field have been computed for each CS referring to a reference turboprop transport A/C. In the future such parameters have to be adapted to those of the actual A/C to be considered within the Clean Sky GRA project. Moreover, for the purpose of evaluate the actual influence of the different effects that the model takes into account, some mission profiles have to be generated by flight simulations (to generate inputs in terms of commands, loads, operative modes, mission phases and environmental conditions).
For all the CS the mechanical and aerodynamic models have been developed with reference to a โplainโ control surface, but, for Flaps with a more complex kinematics (e.g. slotted flap), suitable models have to be developed.
In the linear approach used for the evaluation of the hinge moment coefficient (as a function of the local angle of attack and the CS deflection) all the derivatives have been calculated by means of the ESDU method, as a function of the Mach number and the Reynolds number, on the basis of the Net equivalent wing geometry. An exception have been made for the hinge moment coefficient derivatives of the Inboard Flap for which the ESDU equivalent wing has been used as reference. In fact, the ESDU hinge moment coefficient derivatives calculation is valid for a straight-tapered wing but the reference A/C has a cranked wing, thus, for each CS the HM derivatives calculation has been developed by two parallel ways: the first considering the Net equivalent wing and the second considering the ESDU equivalent wing. The comparison of the results has shown that, especially for the IF, the derivatives obtained with the ESDU equivalent wing are the much bigger (percentage variations up to the 15%); thus, these derivatives have been chosen as a
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reference. In any case it is necessary to verify the results of the ESDU hinge moment coefficient derivatives of each CS by using different calculation methods (e.g. Hoerner method, ref. [26]).
A sensitivity analysis of the ESDU hinge moment derivative has been developed as a function of the wing and control surface geometrical characteristics; the analysis shows that the great influence both on ๐1๐ถ๐ and on ๐2โ๐ถ๐ is due to the balance ratio ๐๐โ (percentage variations w.r.t. the minimum absolute value up to 900). Moreover ๐๐ ๐ด๐ ,
๐ฌ50 and ๐ก/๐ cause variation on the same coefficient up to the 100%. Finally
variations due to ๐๐/๐ and ๐๐ are up to the 30%.
The hinge moment coefficient for the Spoilers has been calculated by a method that differs from that used for all the other CS; in this case the computation refers to the normal force acting on an hinged plate (ESDU data has been used as reference) and the hinge moment coefficient is based only on the derivatives w.r.t. the CS deflection and its value is independent from the Mach number and the Reynolds number. The proposed model has to be verified (especially if Spoilers are used also for the A/C dynamic control) by comparison with a more accurate model.
The down-wash angle has been evaluated as a function of the wing lift coefficient (the computation has been developed by means of the RAeS method); it seems to have great influence (especially for high values of the wing lift coefficient) on the horizontal tail angle of attack (variation up to 5 [๐๐๐] for ๐ถ๐ฟ๐ = 2.2) and thus on the Elevators hinge moments. Thus, in order to evaluate the actual horizontal tail airflow variations due to the down-wash angle, the wing lift coefficient, that has been evaluated by a linear approach (using the Roskamโs derivatives), has to be replaced with a more accurate model.
The angular velocities affect the local airflow field especially for the local angle of attack (e.g. for the horizontal tail there is variation up to 10 [๐๐๐] for ๐ = 1 [๐๐๐/๐ ๐๐]).
The engine flow, that has been evaluated as a function of the thrust, seems to affect the local airflow-field with variation lower than the 5% both for the attack angle and the airspeed; in any case a suitable model for the evaluation of the actual engine thrust is necessary to improve the model.
