Ever since the invention of aircraft, manufacturers have been uncovering new ways in which the main body of the aircraft and its internal components can be made lighter, which in effect, allows them to carry more passengers, fly faster and increase the range in which they can operate.
As technology has improved materials can now be developed by re- arranging their atomic structure which, makes it possible for aircraft to reach new performance levels as well as lowering emissions. In this assignment I look at how selecting the right material for use benefits airlines and manufactures, before looking at how the wrong materials/ parts can result in disaster.
The use of Light
Alloys in Aviation A) Materials in aircraft need to be both extremely strong and lightweight, this makes light alloys an excellent category of materials to considered when manufacturing the aircraft.
Magnesium and Aluminium are two metals that are both renowned for being lightweight. Although they are not incredibility strong when they are in their pure state, they can be alloyed which provides the material with more strength. The material for the main skin of the aircraft needs to be as strong as possible whilst being as light as possible. Duralumin is an alloy that is used extensively for aircraft skin, it is a Aluminium – Copper based alloy, with 93. 5% Aluminium and 4. 4% Copper in addition there are between 0. 5% to 1. 5% Magnesium and 0. 5% to 1% Manganese, this alloy is also know as 2024.
Its not only the aircraft skin that is made from this specific type of Aluminium alloy, rivets that are used to hold skin panels together can also be made of 2024, however these are heat treated differently and have certain instructions for use. For example, when they are removed from cold storage they have to be used within twenty minutes Page 501- 509. Rivets are also manufactured from a material known as Hidiminium, this is another example of a light alloy used for aircraft components, it has similar strength to steel making it useful for fasteners.
Aircraft piping is another area in which Duralumin is employed, due to it being a soft material is it used for low pressure systems. Along with Aluminium, Magnesium alloys are also present in the aerospace industry. Magnesium alloys are known for there extreme lightness, they are alloyed with metals such as Zincronium, Zinc and Silver which give the alloy superb strength and shock resistance so they are extensively used for aircraft gear box castings Page 107- 122.
A notable alloy is RZ5 which with improved corrosion resistance has been selected as the material to use as the main skin on various helicopters such as Eurocopter EC120, this is because the lightness of the alloy benefits the helicopter as less power needs to be produced to create enough lift to make it airborne. Another area of use for Magnesium alloys is amongst the aircraft undercarriage, mainly the wheels.
Its used in this area because of its ability to be easily cast into shape, the strength and weight are also beneficial as it means weight can be dramatically reduced in the undercarriage area.
The use of Composites in Aviation
Composites have only recently been introduced as the majority material to be used on aircraft, the preferred material was always a metal as manufactures thought this was the optimum material to use. However composites have now been made stronger and with their lightweight properties it becomes a new choice of material for many aircraft manufacturers.
Composite materials play a huge part in construction of the worlds largest passenger airline the Airbus A380, between 22 and 23 percent of the aircraft total weight is composite, the material used on this aircraft is known as GLARE (glass fibre reinforced Aluminium alloy) the material consists of a Aluminium alloy sheet which is combined with glass fibre resin film, this gives the composite the strength to be used on various skin panels, the pressure bulkhead and even flying control surfaces such as the aileron and air brakes.
Although the A380 is a fairly new aircraft and is many of its primary components are constructed from composites, the newer Boeing 787 has took composites in aircraft to a whole new level, 50% of its total weight being composites, the majority of the skin is composite leaving only areas such as the leading edge and engine casing to be made from different materials. Kevlar is another composite that is ever present in aviation, like fibre glass or carbon fibre it is used in many different areas of the aircraft.
Kevlar is also known as aromatic polyamide fibre, the strength and lightweight make it useful for aircraft components. Kevlar is often present with a honeycomb formation, this again, increases the strength of the structure and the gaps between the two layers mean that hardly any weight is added to the material. A lot of the internal aircrafts structure involves a lot of Kevlar, the flooring of the aircraft is an example of an area in which it is used excessively, the over head luggage storage being another.
Due to the fire resistance of Kevlar it makes sense that it is used for these sorts of components, this reduces the risk of a fire spreading on board so not only is it saving cost and weight but it also proves as safety factor. An example of an external component that is constructed Kevlar is the rotor blades on a helicopter, like the internal components they use the honeycomb structure giving them the lightness and stiffness but still enough flexibly for the blades to function correctly.
Comparison between Light Alloys and Composites
To get optimum performance out of the aircraft, manufactures use both the above mentioned materials (Light alloys and Composites) in different area’s of the aircraft, the fundamental reason being that both materials have advantages and disadvantages when used in specific areas. The reason both materials are used on aircraft is due to their excellent strength to weight ratio, however it is said the composites have about 20% weight reduction in comparison to light alloys Page 179 -204.
Both Magnesium and Aluminium are prone to corrosion and for the skin of the aircraft corrosion is a massive problem, to prevent corrosion occurring, additional finishes such as Alc-lad on the Aluminium alloy can be added, although this adds cost to the production of the alloy . Composites such as GLARE are corrosion resistant meaning they do not require any additional coatings and they can be fitted straight to the aircraft without special treatment to prevent the corrosion problem.
Composites can alter there structure to increase or decrease strength, this is done by different ways of weaving or adding more directions to the laminate. This allows composites such as GLARE to be more versatile when it comes to aircraft panels. The composite material can also be moulded into various different shapes, which is useful because it means the skin can be moulded to fit a certain area, light alloys would have to be bent and formed which can effect the atomic structure making them weaker.
GLARE also enables to cabin to be pressurised to a higher level increasing passenger comforts, the comfort of the passenger is a main factor taken into consideration when designing the aircraft making composite a suitable material to achieve this factor.
One problem that has raised concern in the aviation industry regarding composites is the way in which damage can’t easily be detected, with the Aluminium a dent to the material will be visually obvious therefore inspections can be carried out with the naked eye, where as composites might only show a small mark on the surface and more serious damage might be present underneath. If on the visual inspection surface damage is visible then paint or even the panel might have to be removed to enable a more detailed look.
Ultra sonic test equipment can be used to identify damage such as de-lamination in the material. The repair process for Aluminium alloys is considered to be easier than the repair of composite material, if there happens to be damage to a Aluminium panel the panels tend to be a lot smaller so only a small portion of the skin needs to be removed where as composite panels are larger for easier production, but when they need to be replaced it means taking off the whole panel just to replace a small section of damage. Composites also have to be manufactured in the correct conditions.
A special composite bay provides a safe location in which the lay up process can take place, the bay ensures no dirt or impurities get amongst the composite layers which can decrease the strength of the material. Alloys are usually formed in a large industrial process where large amounts of alloys will be produced at one time.
The cost of both materials is a factor that also differs, as previously mentioned composites reduce the weight by about 20% from Aluminium alloys, but due to a more difficult manufacturing process the cost of composites is reasonably higher.
Because finance is a crucial point when producing the aircraft, companies have to carefully select which material to use, whether to pay more a composite structure which has benefits such as passenger comforts or reduce costs and stick to a light alloy which needs more maintaining due to corrosion.