Aircraft Conceptual Design

I. Aircraft Conceptual Design

(1) Aerodynamic Analysis Software Development

VLM513 is a software suite for aircraft aerodynamic and stability/control analysis based on the 

Vortex Lattice Method (VLM). Developed in MATLAB, the entire source code is released here as 

open-source. The primary development work was completed during my doctoral studies, and 

the software is currently updated on an irregular basis. While VLM513 initially referenced Tomas 

Melin's "Tornado" in its early stages, years of continuous development and refinement have 

resulted in over 90% of the current code being distinct from the original Tornado. Key 

improvements over Tornado include:

① Enhanced computational speed. Improved data structures have increased the calculation speed 

when solving for multiple states;

② More convenient input interfaces. Calculation targets can be defined via text files or imported 

from CATIA;

③ Improved numerical stability. The processing logic for calculating downwash at points near vortex 

lines was modified to enhance stability. Additionally, the aerodynamic calculation method for control 

surface deflection was revised to ensure continuous aerodynamic changes from neutral to a specific 

deflection angle;

④ Increased calculation accuracy in specific cases. Placing vortex lattices on the mean camber surface 

rather than the chordal plane has improved accuracy when dealing with high-camber airfoils. The 

inclusion of side-edge vortex analysis has significantly improved aerodynamic calculation accuracy 

when the aircraft is in a sideslip;

⑤ Added stability and control analysis functions. The software can calculate stability and control 

derivatives and conduct longitudinal/lateral-directional modal characteristic analysis by integrating 

inertia information from the input files.

This software can be used for learning aerodynamics courses as well as for aircraft conceptual design 

and optimization. The main interface is in English; for ease of use and learning, critical parts of the code 

include Chinese comments. Every algorithm has its scope and limitations; users must analyze the 

correctness of the results based on their own knowledge. The developer assumes no responsibility for 

any consequences arising from the use of the software.

Learning Tip: The Vortex Lattice Method is an aerodynamic algorithm based on solving linearized 

potential flow equations. Since potential flow does not account for viscosity, it cannot analyze 

viscosity-related effects, such as skin friction drag or flow separation. Because induced drag is 

generated by the deflection of the lift direction under the influence of downwash, it can be solved 

via VLM. The zero-lift drag in VLM is solved using the equivalent skin friction method introduced in 

Raymer's Aircraft Design: A Conceptual Approach, which is an engineering approximation method.

Verification Case for Solver Accuracy (Validated against NASA TM 4640 data)

Publications

[1] SONG Lei, YANG Hua, XIE Jingfeng, et al. Predicting Stability Derivatives of Flying Wing Aircraft Based 

on Improved Vortex Lattice Method [J]. Journal of Nanjing University of Aeronautics & Astronautics, 2014, 

46(3): 457-462.

[2] SONG Lei. Conceptual Design Optimization of Flying-wing Aircraft [D]. Beijing: Beihang University, 2017.

—————————————————————————————————————————————

(2) Parametric Representation Methods for Aircraft Airfoils

In the aircraft design process, aerodynamic optimization is a task that spans from conceptual to 

detailed design. Airfoil parameterization is the foundation for completing aerodynamic optimization; 

on one hand, it determines the coverage of the design optimization search range relative to the actual 

design space, and on the other hand, it significantly impacts the nonlinearity and continuity of the 

optimization problem at the mathematical level. A key goal of airfoil parameterization is to 

mathematically represent the airfoil curve as accurately as possible using fewer parameters.

This research group has proposed an Improved Geometric Parameter (IGP) airfoil parameterization 

method. By separately describing the camber and thickness distributions, this method achieves a 

parametric description of the airfoil using only 8 variables (comparison with other methods is shown 

in Table 2.1). The variables used in this method are easily linked to general airfoil description methods 

in aerodynamic research, making it easier to guide and analyze the airfoil optimization process using 

aerodynamic design experience. Furthermore, because this method decouples the description of 

camber and thickness, it is convenient for use in aerodynamic solvers based on potential flow theory 

(such as VLM). In this context, aerodynamic optimization can be focused solely on the camber curve, 

as thin airfoil theory suggests that the lift characteristics of a wing at small angles of attack are primarily 

determined by its camber. To verify this method, the research group performed fittings using airfoils 

from the Profili database; the fitting accuracy was excellent, as detailed in the published paper linked 

below.

Table 2.1  Comparison of each method's number of parameters.

Publications

[1] Xiaoqiang L, Jun H, Lei S, et al. An improved geometric parameter airfoil parameterization method 

[J]. Aerospace Science and Technology, 2018, 78: 241-247.