The objective of this project work was to construct and implement an algorithm into the program ADAPDT to calculate the zero-lift drag profile for defined aircraft geometries. ADAPDT, short for AeroDynamic Analysis and Preliminary Design Tool, is a program that calculates forces and moments about a flat plate geometry based on potential flow theory. Zero-lift drag will becalculated by means of different hand-book methods found suitable for the objective and applicable to the geometry definition that ADAPDT utilizes.

Drag has two main sources of origin: friction and pressure distribution, all drag acting on the aircraft can be traced back to one of these two physical phenomena. In aviation drag is divided into induced drag that depends on the lift produced and zero-lift drag that depends on the geometry of the aircraft.

How reliable and accurate the zero-lift drag computations are depends on the geometry data that can be extracted and used. ADAPDT‟s geometry definition is limited to flat plate geometries however although simple it has the potential to provide a huge amount of data and also deliver good results for the intended use. The flat plate representation of the geometry proved to be least sufficient for the body while wing elements could be described with much more accuracy.

Different empirical hand-book methods were used to create the zero-lift drag algorithm. When choosing equations and formulas, great care had to be taken as to what input was required so that ADAPDT could provide the corresponding output. At the same time the equations should not be so basic that level of accuracy would be compromised beyond what should be expected from the intended use.

Finally, four well known aircraft configurations, with available zero-lift drag data, were modeled with ADAPDT‟s flat plate geometry in order to validate, verify and evaluate the zero liftdrag algorithm‟s magnitude of reliability. The results for conventional aircraft geometries provided a relative error within 0-15 % of the reference data given in the speed range of zero to Mach 1.2.

While for an aircraft with more complicated body geometry the error could go up to40 % in the same speed regime. But even though the limited geometry is grounds forun certainties the final product provides ADAPDT with very good zero-lift drag estimation capability earlier not available. A capability that overtime as ADAPDT continues to evolve has the potential to further develop in terms of improved accuracy.

Source: Mälardalen University

Author: Bergman, David