8/12/2019 Aerodynamic Analysis and Optimisation of a Servo-Controlled Aileron

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Aerodynamic Analysis andOptimisation of a

Servo-Controlled Aileron

A Dissertation Submitted in Partial Fulllment

of the Requirements for the Degree of

Master of Science in Engineering

at the

University of Cape Town

Student Chris Day

Supervisor Chris Redelinghuys

September 2011

8/12/2019 Aerodynamic Analysis and Optimisation of a Servo-Controlled Aileron

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Abstract

With fuel prices rising while economies crash, and damage to the environmentdue to CO 2 emissions becoming ingrained in our global consciousness, the pres-sure for the airline industry to reduce its consumption of fuel is mounting. Ina collaboration between a leading aircraft manufacturer and four South Africanuniversities, potentially more efficient technologies for aircraft roll control are be-

ing investigated. As purely manually-operated aircraft of a century ago becameheavier, required stick forces for roll control were reduced using a counter-rotatingtab to assist with aileron movement. With the availability of 21st century tech-nology, it has been conjectured that smart materials could be employed to controlthe aileron deections via the tab. This would replace bulky hydraulics with anelectrically-actuated system, contributing to the airliners continuous weight-lossprogramme.

This dissertation involves the aerodynamic analysis component of the collab-oration project. Aerodynamic analyses were undertaken in a number of available

open source programs such as XFoil, a vortex element panel method with cou-pled integral-method boundary layer; TSFoil, a non-linear potential-ow solverusing the transonic small disturbance equations; and using CFD with the Spalart-Allmaras turbulence model. A range of congurations were tested using a double-apped NACA 23012 airfoil, with aileron and tab deected 4 and -4 respectively,and varying the angle of attack and freestream Mach number. It was found thatonly solution of the full Navier-Stokes equations will give practically useful resultsfor typical transonic cruise conditions.

Optimisation of the airfoil geometry in terms of hinge locations as well as

airfoil thickness and camber was performed using the principles of Modern Designof Experiments. PABLO, a vortex panel method, was used to generate responsesfor lift and hinge moment coefficients, and results were compared using a full-factorial analysis and an L 81 orthogonal array. The reduced array was seen to giveaccurate results even with just 11% of the data points of the full array. A meritfunction was evaluated and results suggest that a thick, symmetric airfoil performsbest, while x a should be moved forward and x t back, with the best performancefound at high angles of attack. The applicability of the optimum found is limitedby the inability of the panel method to accurately model transonic ow, but theanalysis illustrates the usefulness of the efficient optimisation method when appliedto a more computationally expensive analysis like CFD.