Investigation of the effects of wing and body deformation on aircraft motion equations
 

In common mechanics references and books, the equations of motion of the aircraft are generally obtained by assuming the rigidity of the aircraft structure and neglecting the effects of the flexibility of the structure.

In cases where the natural frequencies of the dynamics of the plane assumed to be rigid are very different from those of the vibrational natural frequencies of the structure, the assumption of rigidity for dynamic analysis of the plane shall be reasonably consistent with reality. But with increasing structural flexibility and decreasing the natural vibrational frequencies of the structure, this difference is reduced and the assumption of structural rigidity is no longer acceptable. This has led experts in the field to take into account the flexibility of the structure in obtaining aircraft equations.
With the development of larger aircraft with much longer body and wing span in the 1950s, as well as the use of jet engines and increased aircraft speeds, numerous problems arose that resulted in fatal accidents. Also, the use of new alloys and emerging composites in the following years significantly increased the structural flexibility, so that the lack of structural flexibility in high-speed aircraft and supersonic fighter jets not only reduced The accuracy of the analysis was accurate, but it gave the analysts completely false results.

In fact, the dynamic modes of flight and the vibrational modes of the structures are coupled together [1], [15]. But this dependency is typically much lower in small and low-speed aircraft than in large and high-speed aircraft. Because in small and low-speed aircraft the natural frequencies of longitudinal and transverse flight modes including short period and Fogoid [3], roll [4], dochrol [5] and spiral [6] are much less than the natural vibrational frequencies of structures. So that the dependence of the flight modes and vibration of the structure is neglected and the lack of structural flexibility does not cause a significant error.

 In this project the effect of flexibility of aircraft body in both static and dynamic modes was studied. In the second chapter, assuming bending in the body by horizontal and vertical tail, the longitudinal and transverse stability derivatives of the aircraft were obtained and, as shown, flexibility of the body reduced the stability of the aircraft and also reduced the power of the tail control surfaces. This decrease increases with increasing speed. So that at higher speeds these effects are noticeable. In the fourth chapter, the natural frequencies of the aircraft structure are obtained by dividing the continuous masses into discrete concentrated masses, and as it can be seen, as the number of masses increases, the obtained results become more accurate and converge to the true value. According to the analysis carried out, the reduction in power of Elvitor and Rader increases significantly with increasing speed. This can put flight safety at risk in critical situations when the aircraft enters unintended and critical maneuvers. As shown in the reviews, Iran 041 passenger aircraft has relatively high rigidity. So that the flexibility effect on the flight of the aircraft cruise is not noticeable. But if the aircraft dive into an unintended maneuver in critical conditions and given the fact that the aircraft was not designed for such maneuvers, the flexibility of the body would be significant in such circumstances.

[1] Coupled

[2] Short Period

[3] Long Period

[4] Roll

[5] Duch-roll

[6] Spiral

Table of Contents

1. Introduction............................................... ................................................... ................................................... ........................ 2

1-1- Introduction ............................................. ................................................... ................................................... ................. 2

Effects of Structural Flexibility on Aircraft Dynamics and Control .................................... ........................................ 4

1-2-1- Flyer ........................................... ................................................... ................................................... ......... 5

1.2.2- Alan Reverse Effect ......................................... ................................................... .......................................... 5

1-2-3- Reduce the power of Alvator and Rader ....................................... ................................................... ............................. 6

Structural Fatigue ......................................... ................................................... ....................................... 10

1.2.5- Dynamics and controllability of aircraft ...................................... ................................................... ......... 10

2. Static analysis of the effect of body flexibility on longitudinal and lateral stability ..................................... ...................... 13

2-1- Introduction ............................................. ................................................... ................................................... .............. 13

2-2- The effects of bending of the body due to the power of the power on the power of the pilot and the longitudinal stability of the aircraft ... 14

Effects of bending of the body due to vertical tail force and radar on vertical tail strength and plane side stability .........