Airplanes And Aircraft Engineering Essay

Aircrafts are capable of flight using forward motion that generates lift as the wing moves through the air. Airplane is propelled by a screw propeller or a high-velocity jet, and supported by the dynamic reaction of the air against its wings. There are many components of an airplane however the essential components are a wing system to sustain it during flight, tail surfaces to stabilize the wing, movable surfaces to control the attitude of the machine in flight, and a power plant to provide the thrust to push the craft through the air.

An enclosed body which is known as the fuselage houses the crew, passengers, and cargo, as well as the controls and instruments used by the navigator. An airplane also requires a support system when it is at rest on a surface and during takeoff and landing.

Airplanes have different shapes and sizes depending on the purpose, but the modern airplanes have some features in common. They are fuselage, tail assembly and control surfaces, wing, power-plant and landing gear.

In this report the prime focus is on the Prime components of the aircraft assuring structural integrity while meeting requirements for optimum operational performance of an aircraft.

The empennage is also known as the tail is the rear part of the aircraft. Usually it includes the stabilizers, rudder and elevator as many other components as seen below.. It is constructed depending on the aircraft for example in fighter jets it may be constructed around the exhaust nozzle. In commercial aircrafts the empennage is built from the cabin pressure-cone and may contain the Flight Data Recorder (“black box”), Cockpit Voice Recorder and the pressure out-flow valve.

There is another design which does not require an elevator. In this design there is a one-piece horizontal stabilizer that pivots from a central hinge point, such a design is known as a stabilator.

2. Wings:

As we can see below is a wing. Wings are airfoils attached to each side of the fuselage and are the main lifting surfaces that help the airplane during flight. There are great variations in the wing designs, sizes, and shapes used by the various manufacturers. Each of these specifications fulfils a certain need with respect to the performance for an airplane.

Wings may be attached at the top, middle, or lower portion of the fuselage and are referred to as high-, mid-, and low-wing, respectively. The number of wings may vary. Monoplanes contain a single set of wings while those with two sets are called Biplanes.

The principal structural parts of the wing are SPARS, RIBS, and STRINGERS.

These are reinforced by trusses, I-beams, tubing, or other devices, including the skin.

The wing ribs determine the shape and thickness of the wing (airfoil).

Attached to the rear, or trailing, edges of the wings are two types of control surfaces referred to as ailerons and flaps.

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2.1 Spars

2.1.1. Definition:

The spar is the main structural member of the wing, in a fixed-wing aircraft, running span wise at right angles to the fuselage. There may be more than 1 spar or none at all.

2.1.2 Uses:

Fight loads and the weight of the wings whilst on the ground is carried by spars. Spars are also used in aerofoil surfaces such as the tail plane, fin and serve a similar function, although the loads transmitted may be different.

2.1.3. Loads:

Upward bending loads – from the wing lift force that supports the fuselage in flight.

Downward bending loads – due to the weights acting.

Drag loads – dependent on airspeed and inertia.

Rolling inertia loads.

Chordwise twisting loads due to aerodynamic effects at high airspeeds.

2.1.4. Materials:

Wooden construction

Early aircraft used spars carved from solid Spruce or Ash. Wooden spar types have been used and tried with such as spars which are box-section in form; or laminated spars which are laid up in a jig, and compression glued to retain the wing dihedral. Wooden spars are still being used in light aircraft such as the Robin DR400.

Metal spars

A common metal spar in a general aviation aircraft generally consists of a sheet aluminium spar web, with “L” or “T” -shaped spar caps being welded or riveted to the top and bottom of the sheet to prevent buckling under applied loads.

Tubular metal spars

The German Junkers J.I armoured fuselage ground-attack sesquiplane of 1917 used a Hugo Junkers -designed multi-tube network of several tubular wing spars, placed just under the corrugated duralumin wing covering and with each tubular spar connected to the adjacent one with a space frame of triangulated duralumin strips riveted onto the spars.

Advantages

Gives substantial increase in structural strength at a time when most other designs were built with wood-structure wings.

Geodesic construction

In aircraft such as the Vickers Wellington, a geodesic wing spar structure was employed which had the advantages of being lightweight and able to withstand heavy battle damage with only partial loss of strength.

Composite construction

Nowadays aircraft use carbon fibre and Kevlar in their construction, ranging in size from large airliners to small aircraft. Companies have employed solid fibreglass spars in their designs but now often use carbon fibre in their high performance gliders such as the ASG 29

Advantages

The increase in strength and reduction in weight compared to the earlier fibreglass-sparred aircraft allows a greater quantity of water ballast to be carried.

2.1.5. Disadvantages:

The wooden spar has a danger of the deteriorating effect that atmospheric conditions, both dry and wet, and biological threats such as wood-boring insect infestation and fungal attack can have on the wooded spars; consequently regular inspections are often mandated to maintain airworthiness.

Similar disadvantages on metal spars limit their use.

2.2 Ribs

2.2.1. Definition:

In an aircraft, ribs are forming elements of the structure of a wing.

Ribs are attached to the main spar, and by being repeated at frequent intervals they form a skeletal shape. Usually ribs incorporate the airfoil shape of the wing. They are the cross-section shape of a wing. The ribs can be classified according to the types of load acting on it.

Lightly loaded ribs are subjected to aerodynamic loads while a rib is subjected to concentrated forces transferred from primary points is considered as moderately loaded rib.

2.2.2 Function:

Maintain the sectional shape of wing box.

Function as panel breakers for stringers.

Provide support for attachment of other systems.

Distribute locally applied air pressure loads.

2.2.3. Stiffness:

The ribs contribute little to the overall stiffness of the wing box and also carry little of global bend and twist loads acting on the wing.

2.2.4. Loads:

Loads acting on the ribs are of three types:

Loads transmitted from the skin-stringer wing panels.

Concentrated forces transmitted to the rib due to landing gear connections, power plants nacelle connections, etc…

Body forces in the form of gravitational forces.

Inertia forces due to wing structural mass.

2.2.5. Materials:

Ribs are made out of wood, metal, plastic, composites, foam.

Carbon reinforced composites (CFC) or Carbon Fibre Reinforced Plastics (CFRP) are used extensively in aircraft structures as they give high stiffness and strength with lower weight.

2.2.6. Advantages and Disadvantages:

Wooden ribs are subjected to atmospheric deterioration.

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2.3. Stringers or Longerons

Interior of a Boeing/ Stearman PT-17 showing small channel section stringers.

2.3.1. Definition:

A longeron or stringer or stiffener is a thin strip of wood, metal or carbon fibre, to which the skin of the aircraft is fastened. Longerons are attached to formers in the case of the fuselage, or ribs in the case of a wing, or empennage. In early aircraft, a fabric covering was sewn to the longerons, and then stretched tight by painting it with dope, which would make the fabric shrink, and become stiff.

2.3.2. Properties:

“Longeron” and “stringer” are used interchangeably.

If the longitudinal members in a fuselage are less in number (usually 4 to 8), they are called “longerons”. The longeron system requires that the fuselage frames be closely spaced (about every 4 to 6 in/10 to 15 cm).

If the longitudinal members are numerous (usually 50 to 100) then they are called “stringers”. In the stringer system the longitudinal members are smaller and the frames are spaced farther apart (about 15 to 20 in/38 to 51 cm).

Longerons are of larger cross-section when compared to stringers.

2.3.3. Advantages:

On modern aircraft the stringer system is more common because it’s more weight efficient despite being complex to construct and analyze. Some aircraft, use a combination of both stringers and longerons.

The stringers carry bending moments and axial forces. They also stabilize the thin fuselage skin.

3. Power Plant:

A power plant consists of propeller and engine.  The main function of the engine is to supply power to run the propeller. It also generates electrical power, provides vacuum source for flight instruments, and provides a source of heat for the pilot and passengers. The engine is covered by a cowling, or in some airplanes, surrounded by a nacelle. Its purpose is to streamline the flow of air around the engine and to help cool the engine by ducting air around the cylinders. The propeller on the front of the engine converts the rotating force of the engine into forward acting force called thrust that helps move the airplane through the air.

4. Landing gear:

Every matter has its base on which it stands. The principle support of the airplane when parked, taxiing, taking off, or when landing is its landing gear. The most common type of landing gear consists of wheels, but airplanes can also be equipped with floats for water operations, or skis for landing on snow.

The landing gear consists of three wheels – two main wheels-tail wheels and a third wheel positioned either at the front or rear of the airplane-nose wheel, the design is referred to as a tricycle gear A steerable nose wheel or tail wheel permits the airplane to be controlled throughout all operations while on the ground.  

5. Fuselage

Fuselage is aircraft’s main body and covers the majority of the airplane, it holds all other pieces of the aircraft together and other large components are attached to it. The fuselage is generally streamlined to reduce drag. Designs for fuselages vary widely. The fuselage houses the cockpit where the pilot and flight crew sit and it provides areas for passengers and cargo. Some aircraft carry fuel in the fuselage; others carry the fuel in the wings.

5.1. Types of Fuselage Structures:

Truss Structure

Geodesic construction

Monocoque Shell

Semi-monocoque

5.5.1. Truss Structure:

This kind of structure is used in lightweight aircraft using welded steel tube trusses.

A box truss fuselage structure can also be built out of wood-covered with plywood.

5.1.2. Geodesic construction:

Geodesic structural elements used by during the wars, World War II, to form the whole of the fuselage, including its shape. In this multiple flat strip stringers are wound about the formers in opposite spiral directions, giving a basket-like appearance. This proved to be light, strong, and rigid and had the advantage of being made almost entirely of wood. Its redundant structure can survive localized damage without catastrophic failure.

5.1.3. Monocoque Shell

In this method, the exterior surface of the fuselage is also the primary structure. A typical early form of this built using moulded plywood, where the layers of plywood are formed over a “plug” or within a mould. A later form of this structure uses fibreglass cloth impregnated with polyester or epoxy resin, instead of plywood, as the skin. A simple form of this used in some amateur-built aircraft uses rigid expanded foam plastic as the core, with a fibreglass covering, eliminating the necessity of fabricating moulds, but requiring more effort in finishing. An example of a larger moulded plywood aircraft is the de Havilland Mosquito fighter/light bomber of World War II. No plywood-skin fuselage is truly monocoque, since stiffening elements are incorporated into the structure to carry concentrated loads that would otherwise buckle the thin skin. The use of moulded fibreglass using negative (“female”) moulds (which give a nearly finished product) is prevalent in the series production of many modern sailplanes.

5.1.4. Semi-monocoque.

This is the preferred method of constructing an all-aluminium fuselage. First, a series of frames in the shape of the fuselage cross sections are held in position on a rigid fixture, or jig. These frames are then joined with lightweight longitudinal elements called stringers. These are in turn covered with a skin of sheet aluminium, attached by riveting or by bonding with special adhesives. The fixture is then disassembled and removed from the completed fuselage shell, which is then fitted out with wiring, controls, and interior equipment such as seats and luggage bins. Most modern large aircraft are built using this technique, but use several large sections constructed in this fashion which are then joined with fasteners to form the complete fuselage. As the accuracy of the final product is determined largely by the costly fixture, this form is suitable for series production, where a large number of identical aircraft are to be produced.

Both monocoque and semi-monocoque are referred to as “stressed skin” structures as all or a portion of the external load (i.e. from wings and empennage, and from discrete masses such as the engine) is taken by the surface covering. In addition, the entire load from internal pressurization is carried (as skin tension) by the external skin.

As stated above we are now familiar with the prime components of an airplane. Now let us get into detail, and understand the components such as the bulkhead, Frames, Ribs, Spars, Stringers (Longerons), and Skins.

5.2. BULKHEADS

5.2.1. Definition:

A bulkhead is the physical partition that divides a plane or a fuselage into different classes or sections. Typically, a bulkhead is a wall but can also be a curtain or screen. In addition to separating classes from one another, i.e. business and economy, bulkheads can be found throughout the plane, separating the seats from the galley and lavatory areas. Bulkheads also contribute to the structural stability and rigidity of a craft.

5.2.2. Uses:

5.2.3. Loads:

5.2.4. Materials:

5.3. FRAMES

5.3.1. Definition:

The airframe provides the structure to which all other components are attached. Airframes may be welded tube, sheet metal, composite, or simply tubes bolted together. A combination of construction methods may also be employed. The airframes with the greatest strength-to-weight ratios are a carbon fibre material or the welded tube structure, which has been in use for a number of years.

5.3.2. Uses:

5.3.3. Loads:

5.3.4. Materials:

Material Selection

Material

Usage

Advantages

Disadvantages

High strength unidirectional graphite/epoxy

Spar caps

High strength, low weight

High cost, low impact resistance, difficult to manufacture

High modulus ±45° graphite/epoxy

Skin (w/foam core), Shear web, Wing ribs

High strength, low weight, low surface roughness, stealth characteristics

High cost, low impact resistance, difficult to manufacture

Aluminum 7075-T6

Bulkheads, Longerons

Low cost, ease of manufacture, good sturctural efficiency

Low strength, not weldable

Stainless steel (AM-350)

Landing gear

Relatively low cost, high strength, corrosion resistance

High weight

Nickel (Hastelloy B)

Nozzles and ducting

Temperature resistance

Low structural resistance

Kevlar

Internal armor

High strength, low weight, high impact resistance

High cost, difficult to manufacture