Flight Mechanics and Flight Testing

II. Flight Mechanics and Flight Testing

(1) Lateral-Directional Self-Stability Design for Flying Wing Aircraft

Due to the lack of vertical stabilizers, flying wing aircraft exhibit significantly lower directional stability 

than conventional aircraft. Currently, general engineering solutions to this problem include two 

categories: 1. Sideslip angle feedback via automatic control systems (e.g., B-2, X-47B); 2. Adding 

wingtip stabilizers (e.g., X-48B). In our research on flying wing aircraft design, our group has proposed 

a third method distinct from the previous two: lateral-directional self-stability design. This design 

targets the convergence characteristics of the primary lateral-directional modes and employs an 

inverse design of the dihedral distribution across the spanwise sections of the aircraft. By adjusting the 

values of lateral-directional stability derivatives, passive dynamic stability is achieved within the design 

speed range without relying on active control. Meanwhile, because dihedral adjustment does not affect 

the longitudinal aerodynamic coefficients when there is no sideslip, self-stability design does not 

significantly impact the aircraft's lift-to-drag performance.

This technology has been validated through tests on flight platforms of various sizes. During this 

process, new aerodynamic and stability/control issues for flying wing aircraft were discovered, and 

related research is continuously advancing.

Publications

[1] Song L, Yang H, Zhang Y, et al. Dihedral influence on lateral–directional dynamic stability on large 

aspect ratio tailless flying wing aircraft [J]. Chinese Journal of Aeronautics, 2014, 27(5): 1149-1155.

[2] SONG Lei, YANG Hua, YAN Xufeng, HUANG Jun. Lateral-directional Dynamic Stability Design Method 

for Flying Wing without Augmentation [J]. Systems Engineering and Electronics, 2015, 37(11): 2561-2565.

[3] Song L, Yang H, Xie J, et al. Method for Improving the Natural Lateral-Directional Stability of Flying 

Wings [J]. Journal of Aerospace Engineering, 2016, 29(5): 06016003.

[4] SONG Lei. Conceptual Design Optimization of Flying-wing Aircraft [D]. Beihang University, 2015.

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(2) Flight Test Research on Dutch Roll Mode Convergence under Zero 

Directional Static Stability

It is generally believed that directional static stability (weathercock stability) is a necessary condition 

for achieving Dutch roll mode convergence. This study designed an interesting set of experiments to 

verify that an aircraft can achieve lateral-directional Dutch roll dynamic stability even in the absence 

of directional static stability. First, the possibility of Dutch roll mode convergence without directional 

static stability was proven using purely mathematical methods. Subsequently, an RC glider was chosen 

as the research object. By reducing the vertical tail area and adding a vertical stabilizer forward of the 

center of gravity, the directional static stability was adjusted to zero while maintaining a constant 

side-force stability (Cy_beta). After numerical calculations proved that the aircraft could achieve Dutch 

roll convergence, actual flight tests were conducted. The flight test results confirmed the theoretical 

analysis but also revealed new changes in the aircraft's stability and control characteristics after 

modification. These results indicate that, on one hand, the method of emphasizing only directional 

static stability during Dutch roll mode analysis is incomplete, and on the other hand, the impact of 

directional static stability on other stability and control characteristics beyond the Dutch roll mode 

warrants further study.

Publications

[1] Fu J, Huang J, Song L, Yang D. Experimental Study of Aircraft Achieving Dutch Roll Mode Stability 

without Weathercock Stability. International Journal of Aerospace Engineering. 2020;2020.

[2] Fu J, Huang J, Wang L B, et al.Oscillation mode flight data analysis based on FFT [J]. Aircraft 

Engineering and Aerospace Technology, 2018, 91(1): 157-162.

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(3) Sub-scale Flight Testing and Flight Data Measurement

Publications

[1] Hua Y, Lei S, Cheng L, et al. Study on powered-parafoil longitudinal flight performance with a fast 

estimation model [J]. Journal of Aircraft, 2013, 50(5): 1660-1668.

[2] YANG Hua, SONG Lei, WANG Wenjian, et al. Longitudinal Four-Degree-of-Freedom Dynamic 

Simulation of Powered Parafoil [J]. Journal of Beihang University, 2014 (11): 1615-1622.

[3] YANG Hua, SONG Lei, HUANG Jun. Research on Gliding Performance of Ram-Air Parafoil [J]. Flight 

Dynamics, 2014 (6): 510-513.

[4] Hua Y, Lei S, Weifang C. Research on parafoil stability using a rapid estimate model [J]. Chinese 

Journal of Aeronautics, 2017, 30(5): 1670-1680.

[1] Song L, Yang H, Yan X, et al. A study of instability in a miniature flying-wing aircraft in high-speed taxi 

[J]. Chinese Journal of Aeronautics, 2015, 28(3): 749-756.

[2] Fanxing Li, Gang Lin, Xiaoqiang Lu, and Lei Song. Enhancement of Insensitivity for Pitot-Static Probe 

by Static-Pressure Orifices Optimization [J]. IEEE Transactions on Instrumentation and Measurement 71 

(2022): 1-8.

[3] Li F, Song L, Xie J, et al.Preliminary Layout Design Method of Flush Airdata Sensing System [J]. 

IEEE Transactions on Aerospace and Electronic Systems, 2024, 60(6): 9221-9230.

Related Invention Patents

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(4) Flight Simulators for Aircraft Design Education

The team collectively developed the flight simulators for aircraft design education at the "Digital 

Collaborative Innovation Center for Aircraft" on the Shahe Campus, including one transport aircraft 

simulator and two fighter aircraft simulators. All simulators utilize a MATLAB/Simulink-driven 

underlying architecture for aerodynamic and flight dynamics solver development. The visual software 

is based on secondary development of popular modern flight simulation software, achieving 

bidirectional data communication with Simulink. Instruments were developed using rapid 

programming tools to allow students to modify them based on course learning and research needs.

In terms of hardware, the transport simulator employs a multi-monitor display solution to balance wide 

field-of-view with high-resolution requirements. The cockpit layout references modern fly-by-wire 

airliners, with most panels using touchscreen control to simulate various switch effects, while also 

facilitating rapid modifications to the cockpit interface. The fighter simulators utilize Mixed Reality (MR) 

headsets to integrate virtual external scenery with simulated internal cockpit views. The cockpit layout 

references modern 4th-generation fighters based on large-screen touch panels. Both types of simulators 

feature programmable active stick force control systems, which allow for easy force-feel programming 

to implement speed-dependent force gradients, as well as stick pusher and stick shaker effects.

The simulators are currently in use at the "New Generation Fully Digital Aircraft Science and Education 

Collaborative Innovation Center" located in Building 8, Room B119, Shahe Campus.

Promotional Video: https://www.bilibili.com/video/BV1wv4y1c7Qx