Wing structures of training aircraft, strength calculation of wing elements

Contents

Table of contents

Introduction

1. Selection of aircraft prototype by its characteristics

2. Establishment of mass and geometric characteristics of the aircraft, wing layout

3. Purpose of overload and safety factor

4. Determining Wing Loads

4.1. Determination of aerodynamic loads

4.2. Define mass and inertial forces

4.2.1. Determination of distributed forces based on own weight of wing structure

4.2.2. Determination of distributed mass forces from fuel tanks weight

4.2.3. Building Epures from Concentrated Forces

4.3 Calculation of moments acting relative to the conditional axis

4.3.1 Determination of Mz due to aerodynamic forces

4.3.2. Determination of Mz EMI from distributed wing mass forces (Mz EMI and Mz EMI)

4.3.3 Determination of Mz from concentrated forces

4.4 Determination of design values of Mizg and Mkr for assigned wing section

5. Selection of structural-power scheme of the wing, selection of parameters of design section

5.1 Selection of structural-power diagram of the wing

5.2 Selection of wing design section profile

5.3 Selection of section parameters (approximate calculation)

5.3.1 Determination of normal forces acting on wing panel

5.3.2. Determining Skin Thickness

5.3.3 Determination of the pitch of stringers and ribs

5.3.4 Determination of section area of stringers

5.3.5 Determination of cross-sectional area of spars

5.3.6 Determination of spar wall thickness

6. Calculation of wing section for bending

6.1 Calculation Procedure for the First Approach

6.2 Determination of stringer critical voltages

7. Calculation of wing section for shear

7.1 Calculation Procedure

8. Calculation of wing section for torsion

8.1 Determination of wing section stiffness center position

8.2 Determination of tangent force flow from torsion

9. Check of skin and walls of spars for strength and stability

Conclusion

List of sources used

Appendix A

Introduction

The wing is the bearing surface of the aircraft, which serves to create the aerodynamic lift necessary to ensure flight and maneuvers of the aircraft in all modes provided for by tactical and technical requirements.

The relevance of this topic is that the wing takes part in ensuring the transverse stability and controllability of the aircraft and can be used to attach the landing gear, engines and fuel placement, etc.

Wing represents thin-walled reinforced shell and consists of frame and skin. The frame consists of spars, walls and stringers (longitudinal set) and ribs (transverse set).

Various requirements are imposed on the aircraft. Many of these requirements are contradictory, for example, an aircraft must have good flight data and at the same time must be quite strong in operation and have a minimum mass.

The continuous increase in the speed and altitude of aircraft has a decisive effect on changes in their aerodynamic layout and structural and power schemes. This effect leads to significant changes in the shape in plan and thickness of the wing profiles, shape and extension of the fuselages. All this requires further development and improvement of methods for calculating the strength of aircraft structures.

The purpose of course design is to develop the wing design of a mainline passenger aircraft and perform strength calculation of wing elements.

The following tasks will be considered during the course project:

selection of aircraft prototype by its characteristics;

determination of the weight and geometric characteristics of the aircraft, necessary for load calculation, according to the selected prototype, wing layout;

assignment of operational overload and safety factor for the specified design case;

determination of loads acting on the wing when the aircraft performs the specified maneuver, construction of symbols;

selection of the type of structural-power scheme of the wing and selection of section parameters;

calculation of wing section for bending;

calculation of wing section for shear;

calculation of wing section for torsion;

check of wing skin and spar walls for strength and stability.

5. Selection of structural-power scheme of the wing, selection of parameters of design section

5.1 Selection of structural-power diagram of the wing

The choice of structural-power scheme of the wing is determined by a number of conditions:

layout of the wing itself (presence of panels in the skin for maintenance of equipment units located in the wing, presence of fuel tanks inside the wing, niches for LG retraction, etc.);

fuselage layout (availability of sufficient volumes for the wing central part in the fuselage);

stiffness requirements

The most common are the following structural-power schemes of free-bearing wings:

single-spar;

monoblock or caisson;

single-spar with an "inner brace";

multibeam.

The single-member scheme is very suitable for use in light sports and other aircraft with straight wings and a sufficiently large relative profile thickness (more than 8%), in which, due to the limited volume of the fuselage, it is difficult to pass through the fuselage of an all-in-one block or caisson, as well as in all cases when cuts are inevitable in the wing skin.

The difference between the monoblock wing and the caisson wing is that in the monoblock wing normal bending forces are perceived by the skin and its supporting stringers along the entire outline of the cross-section of the wing, and in the caisson wing normal forces are perceived by the skin and stringers only along a part of the outline, for example by a sock or, as usual, by the middle part.

The caisson scheme is very useful for obtaining greater torsional stiffness of the wing. With the same weight, the wing of the caisson circuit will have a torsional stiffness of about 10% greater than the single-wing wing. For aircraft with a swept wing and a large extension, the caisson wing can be used with greater efficiency, since for such wings with a large load, rigidity is of great importance in view of the possibility of the phenomenon of aileron reversal on such wings. With small loads on the wing, the caisson circuit is inferior in weight capabilities to the single-wing. However, it should be taken into account that with increasing speed, with increasing wing load, the caisson circuit is made more profitable by weight, since the thickness of the skin and stringers with increasing load increases, and critical stresses are made to lose local stability higher.

In arrow-shaped wings, the ribs can be located:

parallel to the axis of symmetry of the aircraft or along the flow;

perpendicular to the leading edge or to the axis of the spar.

The arrangement of the ribs in the first case has some drawbacks, for example, the ribs in the arrow-shaped wings are longer than in the second case, so it is more difficult to make them. If the wings are caisson, that is, the ribs approach the spars or walls at very sharp angles, which creates structural and technological complexity.

At the same time, there are some reasons to assume that the flexural stiffness of the wings with the location of the ribs "downstream" is slightly higher than that of the wings with ribs perpendicular to the spar. When the ribs are located downstream in any power scheme - single-generon with an internal brace, single-generon or caisson reinforced, there will be only one nerve - on-board. This rib will be loaded firstly by forces from the torque acting in the section along the side rib, and secondly by forces directed in the plane of the rib, resulting from the decomposition of forces acting in the direction of the belts of spars and stringers (in the caisson scheme) at the point of fracture of the spar and stringers.

7. Calculation of wing section for shear

The calculation of the wing section for shear is carried out without taking into account the influence of torsion (the transverse force of the Q∑ is considered to be applied in the center of the section stiffness, believing that the spar walls and skin work on the shift).

Conclusion

In this course project, the wing of the training aircraft was calculated.

Values of loads acting on the wing, bending moments relative to the conditional axis were obtained. The structural power scheme of the wing is chosen - caisson (with two spars).

In this work, the parameters of the skin, stingers, spars were selected according to the estimated area in the stretched and compressed zones. The number of stringers in the compressed panel is 7, in the stretched panel - 6. As a result of calculating the wing section for bending, it was revealed that the stress of the stringers in the compressed panel and stretched does not exceed the stress of the total stability loss. Calculations of the wing section for shear and torsion were carried out.

Checking the skin and walls of spars for strength and stability showed that the strength conditions are met.