aircraft structures

Aircraft Structures - Aircraft must be safe to fly. This means that they should not endanger the lives of crew and passengers and people on the ground.

Safety is an important factor in the design and manufacture of an aircraft. Before entering service, the manufacturer must document that the structure it has built will not break or be damaged during operation and that the aircraft's systems will function as designed.

Aircraft Structures

EASA is an organization that defines rules to be followed by engineering offices and makes proposals for aircraft structure and system design.

Aircraft Structural Design & Analysis

All the rules to be followed by manufacturers and operators of large aircraft are grouped by EASA in chapters called CS (Certification Specifications). There are chapters describing engine, propeller, aircraft noise, engine emissions and fuel ventilation, aircraft operation in various weather conditions, navigation, flight simulation training and cabin and flight crew certification requirements for various types of aircraft.

Chapter CS-25 contains certification specifications for the production of large aircraft. It consists of two books. Book No. 1, known as the Certification Specification (CS), contains eight subsections and appendices, the number of which may change when a new number is issued. The subparts specify the general requirements that the aircraft must meet. Clear explanations and descriptions in the appendices ensure that the specifications mentioned in each subsection are well understood. Explanations define terms using sketches, graphs. Book No. 2 is called Acceptable Methods of Conformity (AMC) and contains eleven subsections describing acceptable methods of demonstrating compliance with the requirements of Book No. 1.

The strength required for the airframe is confirmed by physical tests and extensive analysis and simulations performed by engineers. Physical tests are performed on individual parts, sub-assemblies and the entire aircraft on the ground and in flight. EASA certifies the structure as built to withstand the maximum load the aircraft will ever experience in service, without plastic deformation. This means that under this load the structure only deflects elastically, and when the load is stopped it relaxes back to its original shape. This load is called limit load. The structure must also withstand 1.5x limit load without breaking in the first 3 seconds. This is called final weight.

The aircraft loads to be designed are the aerodynamic (lift, drag and moments caused by them) and inertial loads caused by the weight of the structure and equipment, passengers, cargo and fuel.

Materials, Structures And Manufacturing For Aircraft

Aerodynamic loading is obtained by performing airflow tests on scale models in the wind tunnel. The flow test is performed for several flight configurations (level flight, right turn, left turn, climb, dive, etc.). However, airflow tests are expensive and not possible for all configurations that the aircraft may encounter, so in addition, extensive analysis is performed by simulation on powerful computers. The end result is an envelope that describes any stresses that may occur during flight. The number of simulated load cases is typically in the tens of thousands. After the flight is completed, the flight test is performed. These aircraft are equipped with devices that can measure air pressure and main structure load. In this way, the load used to design the aircraft is checked and adjusted if necessary.

Regarding the weight, it is multiplied by an acceleration factor, the value of which varies on the three global axes of the aircraft and depends on the mission for which the aircraft is designed. For example, an airplane intended to carry passengers has a normal (to the wing) axial acceleration factor of 3.0 g (where g is the acceleration due to gravity).

The end result of the engineering design work is the blueprints for each part to be manufactured and further the assembly to the aircraft and a value indicating how safe the component is.

Both show how large the load capacity is in relation to the maximum applied load. For example, if the RF is 2.5, it means that the part can withstand 2.5 times the maximum load that the aircraft can carry in its operational life (called the RF limit in this case). The goal for engineers is to design the structure with as close a reserve factor as possible. This is because when the reserve factor is high, it means that the structure is enlarged and the weight of the material used is more than sufficient. It leads to a heavier aircraft and therefore a lower performance (in terms of speed, fuel consumption, cargo weight and number of passengers).

Aircraft Basics // Aircraft Wings // Aircraft Structure

There are aircraft that are not covered by EASA regulations and remain subject to national regulations. They are listed below:

Another organization called the FAA (Federal Aviation Administration) provides safety certification for aircraft flying in US space. The FAA is responsible for establishing aviation regulations in the United States known as FARs (Federal Aviation Regulations).

Interestingly, military aircraft do not conform to an existing civil type certificate. There are various organizations that define regulations for military aircraft, such as the Military Aviation Authority (MAA) in the UK and the Air Force (AF) in the US.

Aircraft structure and systems can be repaired and modified. However, they must still meet the certification specifications. Repairs can be carried out during production or during operation. For example, a component may develop small scratches due to improper handling at the manufacturer's facility, or a bird may hit the leading edge of the wing in flight and cause a dent. Both damages are reported and repaired following correct procedures. Aircraft modifications can be minor or major and should follow the specifications in the various chapters.

Analysis And Development Of Impact Resistant Light Weight Composite Aircraft Structure

Certified aircraft are periodically inspected and maintained while in service, and this activity is also regulated. The aircraft is certified for a limited number of flight hours. This period depends on the aircraft type and manufacturer. For a large civilian aircraft, it may be in the range of 100,000 hours. This limitation is mainly due to a fatigue phenomenon which can lead to cracking and failure of the structure. At the end of this period, the aircraft may be recertified based on further inspections.

Please note that the certification specifications and acceptable compliance methods presented in this article are for informational purposes only. Please refer to the official documents of the agency operating in your area when it is necessary to issue the air certificate. An aircraft is an instrument used or intended to be used for flight in the air. The main categories of aircraft are airplanes, rotorcraft, gliders, and lighter-than-air vehicles. [Figure 1] Each of these can be further divided by important characteristics, such as aircraft and balloons. Both aircraft are lighter than air, but have different characteristics and operate differently.

The concentration of this article is on the airframe; Specifically fuselage, boom, nacelle, cowling, fairing, airfoil surface and landing gear. Also included are the various devices and controls that accompany these structures. Note that the rotor blades of a helicopter are considered part of the airframe when they rotate. In contrast, an aircraft engine's propellers and rotating airfoils are not considered part of the airframe.

The most common aircraft is the fixed-wing aircraft. As the name suggests, the wings of this type of aircraft are attached to the fuselage and are not intended to move independently in a manner that creates lift. One, two or three blades have been used with success. (Figure 2) Rotating aircraft such as helicopters are also common.

Typical Repairs For Aircraft Structures (part 2)

This section discusses characteristics and maintenance aspects common to both fixed-wing and rotary-wing aircraft categories. Also, in some cases, explanations focus on one or the other specific information. Gliders are very similar to fixed-wing aircraft. Unless otherwise specified, the maintenance practices described for fixed-wing aircraft also apply to gliders. The same applies to lighter-than-air aircraft.

The airframe of a fixed-wing aircraft consists of five main units: fuselage, wings, stabilizers, flight control surfaces and landing gear. (Figure 3) The helicopter's airframe consists of the fuselage, the main rotor and associated gearbox, the tail rotor (on helicopters with a single main rotor) and the landing gear.

Airframe structural components are made from a variety of materials. The earliest airplanes were primarily made of wood. Steel pipes and the most common material, aluminum, followed. Most newly certified aircraft are made of molded composite materials such as carbon fiber. Structural members of an airframe include stringers, extenders, ribs, bulkheads and more. The most important structural element of the wing is called wing spar.

Fly skins can also be made from a variety of materials, from impregnated fabric to plywood, aluminum or composite materials. Under the skin and attached to the structural fuselage are many components that support airframe operation. The entire airframe and its components are connected by rivets, bolts, screws and other fasteners. Welding, glue and special bonding techniques are also used.

Free Aviation Study: Aircraft Structure In The Empennage

History of Aircraft Structures Primary Structural Stresses Fixed Wing Aircraft Wing Empenage Primary Flight Control Surfaces

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