The Basics of Aircraft Building !

How to Build an Airplane; The Basics Of Aircraft Building

If you are interested in learning how to build your own aircraft, you might be wondering where to start and what are the essential steps involved. 

In this blog post, we will cover the basics of aircraft building, from choosing a design and materials, to assembling and testing your creation.

The first step in aircraft building is to decide what kind of aircraft you want to build. There are many types of aircraft, such as gliders, ultralights, helicopters, jets, and more. Each type has its own advantages and disadvantages, depending on your budget, skills, and preferences. You should also consider the purpose of your aircraft, whether it is for recreational, educational, or commercial use.

The next step is to choose a design for your aircraft. You can either use an existing design or create your own. There are many sources of aircraft designs online, such as plans, kits, or blueprints. You can also find books and magazines that provide detailed instructions and diagrams for various aircraft models. If you decide to create your own design, you will need to follow some basic principles of aerodynamics, such as lift, drag, thrust, and weight. You will also need to comply with the regulations and standards of your country or region regarding aircraft safety and performance.

The third step is to select the materials for your aircraft. The materials you choose will affect the cost, weight, strength, and durability of your aircraft. Some common materials used in aircraft building are wood, metal, composite, and fabric. Each material has its own pros and cons, depending on the type and size of your aircraft. You should also consider the availability and accessibility of the materials in your area.

The fourth step is to assemble your aircraft. This is the most challenging and rewarding part of aircraft building. You will need to follow the instructions and diagrams of your design carefully and accurately. You will also need to use the appropriate tools and equipment for cutting, drilling, bending, welding, gluing, and fastening the parts of your aircraft. You should also check the quality and alignment of each part before moving on to the next one.

The final step is to test your aircraft. This is the most exciting and risky part of aircraft building. You will need to inspect your aircraft thoroughly for any defects or errors that might compromise its safety or performance. You will also need to obtain the necessary permits and licenses from the authorities before flying your aircraft. You should also find a suitable location and time for your test flight, preferably with the help of an experienced pilot or instructor. You should also prepare for any emergencies or contingencies that might occur during or after your flight.

Building your own aircraft can be a fun and fulfilling hobby or career. However, it also requires a lot of time, money, effort, and patience. You should be prepared for the challenges and risks involved in this endeavor. You should also be proud of your achievement and enjoy the thrill of flying your own creation.

The Basics Of Aircraft Structure

If you are interested in learning how aircraft are designed and built, you need to understand the basics of aircraft structure. Aircraft structure is the framework that supports and shapes the aircraft, and it consists of different components that perform different functions. In this blog post, we will introduce some of the main elements of aircraft structure and explain their roles and characteristics.

The main components of aircraft structure are:

- Fuselage:

 The fuselage is the central body of the aircraft that houses the cockpit, passengers, cargo, and other equipment. It also provides aerodynamic shape and stability to the aircraft. The fuselage can be divided into sections, such as nose, cabin, tail cone, etc. The fuselage can be made of metal, composite, or a combination of both materials.

- Wings: 

The wings are the horizontal surfaces that generate lift and allow the aircraft to fly. They also provide control and stability to the aircraft by changing their shape and angle. The wings can be attached to the fuselage in different ways, such as low-wing, high-wing, mid-wing, etc. The wings can be made of metal, composite, or a combination of both materials.

- Empennage: 

The empennage is the tail section of the aircraft that consists of vertical and horizontal surfaces that provide stability and control to the aircraft. The vertical surface is called the vertical stabilizer or fin, and it has a movable part called the rudder that controls the yaw motion of the aircraft. The horizontal surface is called the horizontal stabilizer or tailplane, and it has a movable part called the elevator that controls the pitch motion of the aircraft. The empennage can be made of metal, composite, or a combination of both materials.

- Landing gear: 

The landing gear is the system that supports the aircraft on the ground and allows it to take off and land. It consists of wheels, tires, brakes, shock absorbers, struts, etc. The landing gear can be fixed or retractable, depending on the type and performance of the aircraft. The landing gear can be made of metal or composite materials.

- Engine: 

The engine is the system that provides thrust and power to the aircraft. It can be located in different positions on the aircraft, such as under the wings, on the fuselage, on the tail, etc. The engine can be of different types, such as piston, jet, turboprop, etc. The engine can be made of metal or composite materials.

These are some of the basic components of aircraft structure that you need to know if you want to learn more about how aircraft are designed and built. Of course, there are many more details and variations that we have not covered in this blog post, but we hope this gives you a general overview and sparks your curiosity. If you have any questions or comments, please feel free to share them below.

Lesson 1C: Aircraft Components & Structure

Aircraft Components & Structure

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Aircraft have changed enormously over the last century from the early Wright Flyer flown at Kittyhawk to the supersonic SR-71 Blackbird flown today. Of course the developments in aeronautical engineering can be broken down into separate divisions that have developed at different rates: a) the aerodynamics, b) power plant engineering, c) control, radios and navigation aids, d) airframe engineering (e.g. hydraulic/electrical systems, interior fittings etc.), and finally e) the structural design. For example, power plants have developed in two large steps separated by a series of sudden burst of ingenuity. In order to facilitate the first successful flight the Wright Brothers had to find a light yet powerful engine system. The next stride was the ingenious invention of the jet engine prior and during WWII by Sir Frank Whittle and Hans von Ohain. In between, the power output of piston engines “increased almost 200 times from 12 bhp to over 2000 bhp in just 40 years, with only a ten times increase in mass (3) “. As will be outlined in this article, the design of aerospace structures on the other hand has only made one fundamental stride forward, but this change was sufficient to change the complete design principle of modern aircraft. Today however, the strict environmental legislation and advent of the composite era may induce further leaps in structural design.

Fig. 1. A schematic drawing of the Wright Flyer (1)

Fig. 2. The modern supersonic SR-71 Blackbird (2)

1) Wire Braced Structures

If we look at the early design of aircraft such as the Wright Flyer in Figure 1 there can really be no misunderstanding of the construction style. The entire aircraft, including most notably the wings, forward and rear structures were all constructed from rectangular frames that were prevented from shearing (forming a parallelogram) or collapsing by diagonally stretched wire. There were two major innovative thoughts behind this design philosophy. Firstly, the idea that two parallel wings would facilitate a lighter yet stronger structure than a single wing, and secondly, that these two wings could be supported with two light wires rather than with a single, thicker wooden member. The structural advantage of the biplane construction is that the two wings, vertical struts and wires form a deep light beam, which is more resistant to bending and twisting than a single wing. Much like a composite sandwich beam it can be treated as two stiff outer skins for high bending rigidity connected by a lightweight “core” to provide resistance to shear and torsion.

Fig. 3. Cutaway drawing of the 1917 Sopwith Camel (3)

Fig. 4. Cutaway drawing of the 1935 Hawker Hurricane (3)

The biplane construction with wire bracing was the most notable feature of aircraft construction for much of the following years and paired nicely with lightweight materials such as bamboo and spruce (Figure 3). Wood is a composite of cellulose fibres embedded in a matrix of lignin and the early aeronautical engineers knew to take advantage of its high specific strength and stiffness. Strangely enough, after the era of metals we are now returning back to the composite roots of aircraft, albeit in a more advanced fashion. The biplane era lasted until the 1930s at which point metal was taking over as the prime aerospace material. Initially the design philosophy was not adapted to take full advantage of thin sheet metal manufacturing techniques such that wooden spars and struts were just replaced by thinner metal tubing. Consequently there remained a striking similarity in construction between a 1917 (Figure 3) and a 1931 (Figure 4) fighter. Even though some thin metal sheets were being used these components generally did not carry much load such that the main fuselage structure featured 4 horizontal longerons supported by vertical struts and wire bracing. This so called “Warren Girder” design can also be seen in some of earliest monoplane wing constructions such as the 1935 Hawker Hurricane. Aeronautical engineers were initially “unsure how to combine the new metal construction with a traditional fabric covering (3)” used on earlier aircraft. The onset of WWII meant that some safe and conservative design decisions were made to facilitate monoplane wings and the “Warren Girder” principle was directly copied to the internal framework of monoplane wings (Figure 5). These early designs were far from optimised and perfectly characterise the transition period between wire-frame structures and the semi-monocoque structures we use today.

Fig. 5. The Hawker Hurricane wing construction (3).

2) Semi-Monocoque Structures

The internal cross-bracing was initially acceptable for the early single or double seater aircraft, but would obviously not provide enough room for larger passenger aircrafts. To overcome this, inspiration was taken from the long tradition and expertise in boat building which had already been applied to construct the fuselages of early wooden flying boats. The highest standards of yacht construction at the time featured “bent wooden frames and double or triple skins…with a clear varnished finish…and presented a much more open and usable fuselage interior (3)”. The well-established boat building techniques were thus passed on to aircraft construction to produce newer aircraft with very smooth, aerodynamic profiles.

Fig. 6. Semi monocoque fuselage construction of an early wooden flying boat (4)

The major advantage of this type of construction is that the outer skin of the fuselage and wing no longer just define the shape and aerodynamic profile of the aircraft, but become an active load-carrying member of the structure as well. Thus, the structure becomes “multifunctional” and more efficient, unlike the braced fuselage which would be just as strong without the fabric covering the girders. As a consequence the whole structure is generally at a uniform and lower stress level, reducing stress concentrations and giving better fatigue life. Finally, as the majority of the material is located at the outer surface of the structure the second and polar moments of area, and therefore the bending and torsional rigidities are much increased. On the other hand, the thin-skinned construction means that compression and shear buckling become the most likely forms of failure. In order to increase the critical buckling loads the skins are stiffened by stringers and broken up into smaller sections by spars and ribs.

Fig. 7. Components of a semi monocoque wing (5)

Because the external skin is now a working part of the structure this type of construction became to be known as stressed skin or semi-monocoque, where monocoque means  “shell in one piece” and “semi” is an english addition to describe the discrete discontinuities of internal stiffeners. The adoption of the semi-monocoque construction and a change from wood to metal naturally coincided since sheet metal production allowed a variety of thin skins to be easily manufactured quite cheaply, with better surface finish and superior material properties. Furthermore, metal construction was conducive to riveting which would overcome the adhesive problems of early wooden semi-monocoque aircraft such as the deHavilland Mosquito.

Fig. 8. Cutaway Drawing of the recently released A400M aircraft (6).

Figure 8 shows the typical construction of a modern aircraft.

 There have been numerous different structural arrangements over the past number of years but all generally feature some sort of vertical stiffener (ribs in the wings and rings in the fuselage) and longitudinal stiffener (called stringers). Over the years the main driver has been towards a) a reduction in the number of rivets by reverting to bonded assembly or ideally manufacturing separate components as a single piece and b) understanding the effects and growth of cracks under static and fatigue loading by building structures that can easily be inspected or have multiple redundancies (load paths). The design and manufacturing methods of semi-monocoque aircraft are now so automated that the development of a new aluminium, medium sized airliner “could be regarded as a routine exercise (1)”. However, the continuing legislative pressure to reduce weight and fuel consumption provides enough incentive for further development.

3) Sandwich Structures and Composite Materials

One of the major disadvantages of thin-skinned structures is their lack of rigidity under compressive loading which gives them a tendency to buckle. A sheet of paper nicely illustrates this point, since it is quite strong in tension but will provide no support under compression. One way of improving the rigidity of thin panels is by increasing the bending stiffness with the aid of external stiffeners, which at the same time break the structure up into smaller sections. The critical buckling load is a function of the square of the width of the plate over which the load is applied. Therefore skins can be made 4 times stronger in buckling by just cutting the width in half. As a wing bends upwards the main compressive loads act on the top skin along the length of the wing and therefore a large number of stringers are visible across the width.

Fig. 8. Buckling analysis of a stiffened wing panel. The stiffeners break the buckling mode shapes into smaller wavelengths that require higher energy to form compared to a single wave (7)

Another technique to provide more rigidity is sandwich construction. This generally features a very lightweight core, such as a honeycomb lattice or a foam, sandwiched between two thin yet stiff outer panels. Here the role of the sandwich core is to carry any shear loads and separate the two skins as far as possible. The second moment of area is a function of the cube of the depth and therefore the bending rigidity is greatly increased with this technique. Ideally, in this manner it would be possible to design an entire fuselage without any internal rings or stringers and the Beech Starship is an excellent example of a successful application. However, there are problems of forming honeycomb cores onto doubly curved shells since the material is susceptible to strong anticlastic curvature, forming a saddle shape when bent in one direction. Furthermore, there are problems with condensation and water ingress into the honeycomb cells and the ability to guarantee a good bond surface between the core and the outer skins. There is the possibility to use foam cores instead, but these tend to be heavier with lower mechanical properties. Perhaps the current trend is away from sandwich construction (10)

This is an Aerospace engineering concerned with the development of aircraft and spacecraft, focused on designing aeroplane and space shutlle and it is a study of all the flying wing used within the earth's atmosphere. Also dealing with the Avionic systems that includes communications, navigation, the display and management of multiple systems. Also dealing with Aircraft mishap such as Accident and Serious Incident.

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Lesson 10: AIRCRAFT STRUCTURAL MATERIALS

The different methods of aircraft structural repair procedures

The importance of knowing the different methods of aircraft structural repair procedures is readily apparent given today’s tight fiscal environment. As a maintenance officer, you will be expected to understand many areas of aircraft structural repair. This lesson concentrates on the different types of aerospace materials used on today’s aircraft and their application.

Key Points:

Structural materials;
Non-ferrous metals;
Filamentary composite materials;
Advanced composites;
Advanced composite repair techniques;
Additional aerospace materials;
Techniques for aircraft structural fabrication and repair;
Temporary structural repair requirements.

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Structural Materials

 METALS.

The metals that are used in the make up of an aircraft must be strong and be able to withstand the stress related with flight. The density of metal is the weight of the metal per volume, measured in pounds per square inch. Strength is the maximum stress that a material can withstand before failure. Here is a basic list of the type of stress or forces that can affect aircraft surfaces:

• Tensile strength is pulling force occurs.

• Compressive strength is pushing force.

• Strain is referred to as the strain of any force over the length of the surface. • Modulus elasticity is referring to the stiffness of the material.

 Ferrous.

 Ferrous metals are those containing iron as the main metal. Iron, itself is heavy, relatively soft, and not used on aircraft. However, steel is an alloyed metal that contains iron, carbon and other non-ferrous metals. Steel, especially stainless steel, is very useful in certain airframe applications. Steel alloys take on the conductive and magnetic characteristics of a ferrous metal.

 Steel.

Steel is rated by its carbon content:

• Low carbon steel (0.1-0.3%) is seldom used except as secondary structural parts and clamps.

• Medium carbon steel (0.3-0.5%) has high strength and is used in landing gear and flight control components.

• High carbon steel (0.5-2.0%) is hard and brittle, rarely used on aircraft, mostly used on coil springs.

Stainless steel is a special class of steel, containing chromium and nickel, and is used in high temperature applications. It can be found in exhaust systems and the hydraulic lines of many aircraft. Stainless steel has a high strength to weight ratio and resists corrosion and heat as well.

Non-Ferrous Metals

 Aluminum.

Aluminum is a light; but strong metal used extensively in structural members and aircraft skin (especially in older aircraft). Aluminum is malleable and relatively easy to work with. Different types of aluminum have been given industry-wide designations by their alloy type. Common alloy-types:

• 2024 – used on many aircraft for secondary structure and skin. • 7075 – found in areas that high strength is required.

Titanium.

Titanium is 43% lighter than stainless steel but stronger. The most popular type of alloy used in the aerospace industry is 6AL-4V (meaning that the titanium is alloyed with 6% aluminum and 4% vanadium). Titanium is very corrosion resistant and is unattached by most acids, by moist chlorine gas, or by common salt solutions. Titanium resists heat extremely well and is therefore used in many high speed aircraft as shown in figure 1-49. It is also expensive, and replacements for titanium are being researched. New alloys for titanium, even composites mixed with titanium (or titanium-matrix’s) are being researched and tested, particularly for use as replacements for steel landing gear actuators and struts.

    

Magnesium.

Magnesium is the lightest structural metal. It is very brittle, porous and seldom used in its pure state. Used widely by aircraft builders in the past, magnesium is being phased out of military aircraft for three reasons: 1. It corrodes easily

2. It is difficult to work with

3. It is highly flammable

Other non-ferrous metals include to clad pr plate parts to protect them from corrosion. Cadmium is commonly used for many parts, though it has a bad reaction with titanium. Nickel, Zinc, and even Aluminum are used to protect parts as well.

NON-METALS.

Nonmetals used in aircraft construction vary widely in type, composition, and application. The earliest aircraft were built with wood and cloth, with some metal parts. New aircraft are being made of advances composite materials, ranging from graphite to experimental uses of titanium/composite matrix to replace steel components.

 Plastics/Acrylics.

 Used for decades in aircraft, plastics offer many advantages over wood and metal structures. Plastics are light, have good strength, and may be used in many non-load bearing areas. Canopies, consoles, and other aircraft parts are frequently made of plastic. There are many different plastics in use today including synthetic resins (such as acrylic, nylon, and vinyl), cellulose plastics (used on older aircraft), thermosetting plastics (those which retain their shape after manufacturing and are not re-formable, such as polyester), and thermoplastics (plastics which may be reheated and reformed).

 Phenolic.

Phenolic is a special type of plastic; it is actually a combination of plastic and wood or paper. When wood based material is set in plastic, it becomes harder and stiffer then plastic alone, but does not have the strength or heat resistance necessary to be used in a primary structure. Phenolics are found in computers (as circuit boards), flight control rigging (pulleys), hydraulics (as clamps to hold lines in place), and many other areas. The advantage of a Phenolic clamp for a hydraulic line over steel on is the pheniloc one will not chaff (scratch) the steel line. The Phenolic clamp will take the damage induced by aircraft vibrations, but will save the hydraulic line from being damaged.

Filamentary Composite Materials

A material consisting of two or more physically different solid constituents, each of which largely retains its original structure and identity. Composites are distinct from alloys in that their structure is engineered by mixing two materials in an intimate solid mixture, with one component being embedded in the other, usually an adhesive or epoxy type of material and a fibrous type of material. A common feature of composite materials is the use of small quantities of a relatively expensive, strong, often fibrous material to reinforce the bulk of a cheap matrix material. The properties of the resulting composite are usually intermediate to those of the components from which it is made. However, certain properties, notably toughness or resistance to fracture, are much better than those of either of the components, giving composites with unique properties. A simple example of a composite is clue on a piece of fabric; it is stronger than either material by itself, but now is a more solid surface type of material. Refer to Figure 1-50, 1-51 and 1-52.

Desired Characteristics of Matrix Resins

Mechanical & Thermal Processing Characteristics

-High strength

-High elastic elongation

-High shear strength

-High modulus

-High heat distortion temp

-Low creep at use temp

-High toughness/impact strength -Thermal expansion near fiber -Resistance to thermal degradation -Low thermal conductivity

 

Chemical Properties:

Good bond to fiber (directly or with coupling agent)

Resistance to solvents & chemicals

-Low enough melt or solution viscosity and surface tension to permit thorough fiber wet-out

-Good flow characteristics

-Rapid cure or solidification

-Suitable for pre-coated reinforcement

-Cure temp. not greatly above use temp

-Low shrinkage during and after molding

-Long shelf life and pot life

Other Factors:

Low cost

Low density

Low dielectric constant

Low moisture absorption

Comparison of Thermoset and Thermoplastic Resins

Thermosets Thermoplastics  

-Most used

-No flow under heat and pressure after cure; scrap discarded

-Amorphous

-Applied to reinforcement as low viscosity liquids or varnishes

-Phenolics and most polyimides emit volatiles on curing

-Stepwise cure possible to permit control of viscosity & handling

-Post curing often necessary for optimum properties

-Higher strength, modulus and average use temperature

-Used with continuous fiber and discontinuous fiber (usually >1/4”) possible with some plastic yielding

-Used mostly with discontinuous fiber (Length usually <1/2”), though much Activity in last 10 years on TP prepregs

-Relatively high tensile elongations -High variability in mechanical properties

-Most suited to automated production

-Softening and/or melting points remolding of scrap usually possible

-May be crystalline

-High viscosity even in the melt; reinforced by dry or melt compounding

-No volatiles emitted during molding

-Viscosity varied only by increase in temperature and/or shear rate

-Post molding shrinkage may be severe due to slow crystallization

-Tougher, less brittle and lower cost -Low tensile elongations

-Variability in mechanical properties  

 Figure 1-50, Figure 1-51, Tensile Strength of Composites Elasticity of Composites

Figure 1-52, Strength of Composites

ADVANCED COMPOSITES

Composites referred to by type of fiber/type of matrix, layers can be fiber only for later “wet” lay-up (adding resin), or can be “prepreg” (already containing the resin)

 Tape - all fibers aligned in single direction

Cloth - fibers aligned in multiple (usually two) directions

Plain weave: over and under one fiber at a time

Satin weave: over several then under one fiber

 Graphite/Epoxy.

Graphite epoxy is produced by subjecting strands of synthetic materials (graphite) to intense heat and pressure, after which the filaments (containing 3,000 to 16,000 strands each) are organized into unidirectional tapes or woven into fabrics. Graphite epoxy materials are extremely stiff, have high tensile strength, and low density. Components made of graphite epoxy are lighter than aluminum, or woven fiberglass, but strong enough to be used as primary structures (and frequently as flight control surfaces or weapons bay/landing gear doors due to their low radar signature). Many newer aircraft are using a substantial amount of graphite epoxy in their primary structures; resulting in lighter, more fuel efficient aircraft.

 Aramid/Epoxy (Kevlar).

 Aramid epoxies are a lightweight polymer material with exceptional tensile strength. They are usually yellow-gold in color. Aramids were developed in 1965 during a research project to design a strong and lightweight fiber.

Used in flight suits and hazardous-material handling gear, Nomex is an example of an Aramid, the most common Aramid used in aircraft, though, is known as Kevlar. Kevlar is 30-35% lighter than fiberglass, but not stiff enough to be used in primary aircraft structure. A distinguishing feature of Kevlar fibers is their low compression strengths, giving the material good energy absorption characteristics. As a result, Kevlar is often used to replace titanium or steel armor plating, being much lighter and having better impact resistance than most metals. Examples of use included bulletproof aircrew seats, high strength ropes, personal armor, helmet, rotor blade bullet resistant coatings, flight control surfaces, and aircraft cowlings. Aramids are repaired with methods similar to those used on fiberglass, though extra care must be taken to limit ultraviolet (sunlight) and moisture penetration on Aramid structures.

 Boron/Epoxy.

Boron epoxy is formed by depositing boron trichloride (as a vapor) onto 0.005-inch tungsten fiber. Boron fibers are stiffer, stronger, harder, and lighter (one-fourth the weight of steel) than conventional metals. In hardness, boron ranks second to only diamonds. Due to its high stiffness, twice that of steel, boron cannot be formed onto a tight radius, that is, parts made of boron are limited to flat surfaces (such as vertical/horizontal stabilizers). Working with boron can be hazardous. The fibers are thin enough and stiff enough to pass through a technician’s hand, or become airborne, if broken off or inhaled. Boron composite materials are easily distinguished by their grayish-black color.

 Figure 1-53, C-17 Composite Material

Newer materials.

Composite materials, as shown in figure 1-53, 1-54 and 1-55 such as carbon- fiber or glass-fiber reinforced plastics, are now widely used, due to their superiority over metals, in applications requiring high stiffness and strength as well as low weight. A major concern about the use of composite laminates for structural applications is however their low-resistance to out-of-plane localized impact loadings, likely to occur during manufacture, service or maintenance. While metal structures may absorb impact energy by plastic deformation, usually without any major effect on the load carrying performance, energy dissipation in composite materials mainly occurs through a combination of fracture modes such as matrix cracks, delaminating and fiber fracture, which may cause significant reductions of residual strength and modify the structural response of the component.

Glass epoxy, glass polyamide, fiberglass polyamide and graphite peek

are just some of the newer materials that are used in construction of modern-day aircraft. Glass epoxy is more of a protective coating for certain panels, used in areas that need less than 400 degree. Glass polyamide and fiberglass polyamide are used for their high temperature resiliency, mainly used in engine areas. Graphite peek is mainly used for its strength and rigidity, works particularly well because its temperature limits, (350– 400°C) is compatible with the range of forming temperatures, 360–500°C, of the super plastic sheets; the sheets used are aluminum alloy 2004.

  

 

Figure 1-54,  Composite Material

     

Advanced Composite Repair Techniques

 Repairing today’s advanced materials can be labor some, time consuming and expensive. In many cases a diamond-dusted tools must be used in order to cut the materials for machining. This type of tool also aids in preventing micro-cracks on the surface of the material, this would allow moisture to possibly penetrate the material.  The temperature that is required to repair and cure (dry) some of the epoxies can be very high, 190-500 degrees. This requires not only special equipment, but a controlled environment as well. Moisture is one of the major causes of failure in any composite, great care must be taken to prevent this when repairing.

Advanced Composites Require Special Safety

Not only are special tools required to make the repairs, but we must also have the proper equipment to protect our personnel making the repairs. Graphite dust can be corrosive, when using, control; must be maintained to prevent the dust particles from escaping, the dust can cause galvanic corrosion. Here is a list of the most common items that are required; goggles, dust respirator and, gloves

 

Additional Aerospace Materials

HONEYCOMB.

Honeycomb, figure 1-56, is a structure sandwich construction that consists of three or more laminations of different materials. Many aircraft use a honeycomb type of construction.

Honeycomb construction is light in weight and used in flight controls and trailing edges of wings. Figure below shows an example of honeycomb construction. Honeycomb structural sheets may be made from many materials, such as fiberglass, plastic, metal (aluminum or steel), graphite or carbon fiber composite.

Figure 1-56, Honeycomb

These materials may be used for both the outer faces and the core. This material is light in weight but very strong.

Many supersonic aircraft use stainless steel and titanium on surfaces and for the core. The metal honeycomb (hexagonal) core is bonded or glued to the faceplates. The material cannot be formed or shaped by bending. The advantage of honeycomb construction is that it has an exceptionally high strength, but very lightweight. Caution is advised when working on or around these surfaces. Stepping on these areas can easily damage them. Aircraft surfaces will be marked or stenciled to show walkway areas. ”No Step” will be stenciled in areas where walking is prohibited.

OTHER MATERIALS.

 Many other materials are utilized in design and manufacture of aircraft. These include protective coatings such as Teflon and rain erosion covers on radomes and metal treatments like a nickel, cadmium, or aluminum plating to protect surfaces from damage and corrosion. Aircraft with special missions such as the F-117 and B-2 utilize Radar Absorbent Materials (RAMS) to complete their stealth features. Ceramics are a class of material that has been used for some time in electrical components and high heat areas, such as augmenter linings and the convergent/divergent exhaust nozzles of afterburning jet engines. Advances in ceramics, such as mixing with certain silicones, are adding strength and flexibility to the otherwise brittle material. These advances are intended to take advantage of the heat resistance properties of ceramics and make them available for use in future engine components to include combustor lines and turbine blades.

Techniques For Aircraft Structural Fabrication And Repair

The following is an example of how detailed and labor some the repair process can be:

Compressed air is applied to the airside diaphragm (for higher pressures, nitrogen gas may also be used). At the same time, air is evacuated from the sandwich pack. Using an electrically heated platen-press, the die and diaphragms are warmed to the forming temperature. Heat and pressure combine to stretch and form the diaphragms to the geometry of the die. By this process, we form the two diaphragms with the composite between them and draw, drape and consolidate the composite between the conforming diaphragms. Forming is not accomplished in a rapid motion like in a stamping operation. Here, the forming operation is relatively slow, making it easier for the fibers to slide into place without breaking or buckling out of the plane. The frictional effect of trying to pull fibers in rapidly can break them. We can make a single monolithic part by integrating multiple details and can co-consolidate parts by raising a finished detail back to its melt point and fusing it together with a new piece. An alternative joining method is dual-resin (amorphous) bonding. This technique is important in bonding the hat-stiffened sections: the hats would collapse if the fabricated section were brought back to their melting temperature. In this case, a plain outer skin and a hat-stiffened inner skin will be bonded together at a temperature below the melting point of the PEEK, using Ultem or another polyetherimide (PEI) interface. Ultem, a product of GE Plastics in Pittsfield, Massachusetts, flows well at a temperature of 265°C to create a 100% bond.

Ply lay-ups are a combination of balanced ply arrangements.

For instance, unidirectional and biaxial material may be arranged to form a 0/90/±45° orientation of the fibers. Parts on the F-22 have thicknesses from 1 mm (0.040 inches) to more than 12.7 mm (0.5 inches) for the main landing-gear doors; each door has more than 100 plies, built up by a combination of co-consolidation and dual bonding of part details.  Many of the materials used to make repairs cannot be just made; they must be formed into replacement parts. The molds or casts to produce the replacement part can be very costly, this greatly limits the type and frequency that certain repairs can be accomplished.

 Permanent repair requirements.

 Repairs must maintain original weight, strength and aerodynamics in order to be effective; changing any portion of this may have catastrophic effects. Many aircraft surfaces are subject to different kinds of stress and forces not only wind but also drag and shock. The aircraft specific –3 TO will list the specific requirements for weight and balance of each component with specifics about the particular component

 Permanent repairs are designed to just that, permanent. Extra time and care is taken so not only the repair is done correctly and right, but will last.

Temporary structural repair requirements.

There are two areas of temporary repairs: primary and secondary aircraft structure. With a primary structure is damage to an integral part of the aircrafts structure causing a safety of flight issue. A temporary repair is mainly made to move an aircraft or to fly it to a depot repair facility. This repair must restore original strength and structural integrity to the surface or aircraft. A RED “X” goes into the aircraft’s forms, only the MXG/CC, AFMC airframe managers must approve this type of repair. A secondary structure is more of a true temporary repair that allows the aircraft’s mission to continue until more down time can be scheduled for a permanent repair. This does not affect any safety of the aircraft’s structure; commonly a diagonal write-up is placed in the aircraft forms. The most common is stop drilling, this prevents a crack from continuing to spread or lengthen.