Light Alloys and Composites in Aviation.
Table of Contents Introduction3 The use of Light Alloys in Aviation3 The use of Composites in Aviation4 Comparison between Light Alloys and Composites5 Aircraft Part Identification7 Example of Incorrect Part Installation9 Conclusion11 Bibliography & Referencing12 Introduction 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. 1) 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.
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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 (1).
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 (2) 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 (2) Page 107- 122 (3).
A notable alloy is RZ5 (3) 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 B) 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 (4).
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 (5). 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. Figure 1 – Basic honeycomb construction Image from – http://www. kaskus. us/showthread. php? t=5176868&page=6 (7) 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 (8). 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 (8).
Comparison between Light Alloys and Composites C) 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 (2) 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 (1). 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. 14) 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. Figure 2 – This shows a plain weave, the horizontal fibre passes over and vertical fire creating a strong weave. Above I have mentioned that different weaves can improves strength of the material. http://www. vectorstock. com/royalty-free-vector/132035-abstract-seamless-weaving-pattern-vector (10)
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 (2) Page 197 (4). 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. (2) 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. (2) Page 180. Figure 3 Figure 3 above shows how the composite percentage of structural weight has increase over time, more modern aircraft are now build with more amounts of composites. (9) 2) Aircraft Part Identification A) Safety is arguably the most important thing when it comes to aviation, all aspects have to be considered.
Maintenance is an area of aviation where excessive quality control is put in place to prevent any incidents that can cause damage to the aircraft. Because arcraft components fatigue and have a limited life length, they often need to be replaced. Parts as large as pipe sections and as small as rivets all have a unique code, the code is in place to allow engineers what part of the aircraft that specific component is designed for. The Aircraft Maintenance Manual or Air Publication will identify what specific part needs to be used for a certain job on the aircraft, this allows engineers to get the correct replacement component from the stores. 14) As well as coding there are identification marks on certain components, there are various pipes onboard an aircraft, they carry both liquids and gasses such as hydraulic fluid, fuel and even oxygen. To prevent confusion when replacing a pipe sections, identification tape which shows symbols and colours is used as part of the British Standard BS M23. The tape is applied to each end of the pipe and a two foot gap is left between each piece of tape. When the pipe passes through a bulkhead it is identified on each side to shows the engineer where the pipe continues incase it can’t be tracked trough (2) Page 536.
For a hydraulic pipe information such as the pressure and system it is feeding will be also included, Figure 4 below shows how markings for a hydraulic pipe would look, the black dots show that the fluid inside is hydraulic and the ‘Brake’ shows that the system being supplied is the brakes. 1400 PSI informs the engineer of the operating pressure. (14) Fluid inside pipe, the line in the middle represents on side being blue and the other being yellow. System being supplied System Pressure Black dots are the symbol used on hydraulic pipes Figure 4 – Identifications on aircraft pipe, for the hydraulic System (2).
Although it is the engineers job to carry out the maintenance task correctly, manufacturers of the components and airlines also have to conform to standards put in place by the CAA (UK), this is to prevent bogus parts being used in aviation. All work carried out on aircraft has to be carefully documented and once the task has been completed the inspector has to sign off the work to show the task has been completed safely and correctly. All records of work done are kept, this is to allow investigators to go back and analyse the records if there happens to be a accident involving a part fitted.
If the part fitted turns out to be incorrect the engineer and inspector will be questioned over installation of the part. Wrong parts that have been fitted have caused accidents in the past, an example of this is discussed in question 2B. (14) Example of Incorrect Part Installation B) A notable aircraft incident that was caused due to installation of an incorrect part was on Air Transat Flight 236, the Airbus A330 carrying a total of 306 people on route from Toronto to Lisbon ran out of fuel over the Atlantic, the aircraft had to be diverted to Lajes airport in the Azores where it landed safely.
The investigation conducted by French, Portuguese and Canadian transport authorities immediately after the incident showed there was a leak in a fuel pipe on the Starboard engine, because of the traceability of maintenance the investigators could see that a maintenance procedure had been carried out on the 19th of August five days prior to the incident. The engine had been removed for maintenance which involved installation of a replacement unit sent by Rolls Royce, the engine Manufacturers.
However the engine didn’t include a hydraulic pump assembly so engineers took the part of an older engineer and installed it onto the new one, due to the modifications of the engines the part was only different by a few millimeters which lead the fuel pipe and hydraulic pipe to come into close contact. The pulsations through the hydraulic line effectively wore away at the fuel pipe and a hole was caused, this then lead to a fracture and a major fuel leak close to the right engine.
As investigators traced the engineer from recorded signatures on the job card, the maintenance the engineer said he had raised a question about fitting the older part to the newer engine but higher positioned supervisors said that the airline could not wait for delivery of the correct parts needed and that the aircraft had to be back in service as soon as possible.
The one incorrect part caused more than just a fuel leak on the aircraft, because the right fuel tank had emptied and there way no longer supply to the engine on that side, the cockpit indications showed that there was the expected amount of fuel in the left tank compared to empty right tank, because of this the pilot switched on the fuel cross feed which allows fuel for the left tank to supply the right engine because the fuel to left had now been transferred across to the right where the leak was, the fuel ran out in minutes.
This left the aircraft with no electrical power or hydraulic power as the engines that run the generators and hydraulic pumps flamed out, luckily the aircraft has a back up called a RAT (Ram Air Turbine) that provides limited power to both systems but is enough to operate the aircraft. On the day of the incident, Flight 236 had been ordered by Air Traffic Control to offset its route by 60 miles south, if this change had not occurred the A330 would not of made it to the airport of the island and would have to ditch at sea potentially killing 306 people.
It become evident how one part can put so many lives at risk, for the incorrect maintenance the airline received a $250,000 fine the highest amount in Canadian history. (11) (12) (13) Conclusion From the assignment it is evident how large a part materials play in aviation, even though new aircraft are being produced from some of the most suitable materials ever to be used in the industry, the only way is forward in the future for material engineering within aviation.
Although Composites are largely used in modern day manufacturing there are some areas where metals or ceramics are more beneficial, by combining the best materials for the aircraft the performance levels and passenger comforts can reach new highs, as for the economical side of things, this means emissions can be lowered making air travel for environmentally friendly. Bibliography and Referencing 1. http://www. aviation-database. com/Technical_Aviation_Articles/Aerospace-Alloys .html – accessed 9/3/11 . Module 6 Book – ICAT/Barry College – Chris Strike 3. http://www. azom. com/Details. asp? ArticleID=355 – accessed 9/3/11 4. http://engineers. ihs. com/NR/rdonlyres/AEF9A38E-56C3-4264-980C-D8D6980A4C84/0/444. pdf -accessed 9/3/11 5. http://www. airliners. net/aviation-forums/tech_ops/read. main/211508/ – accessed 9/3/11 6. http://en. wikipedia. org/wiki/Radar-absorbent_material – accessed 10/3/11 7. http://www. kaskus. us/showthread. php? t=5176868&page=6 – Figure 1 – accessed 10/3/11 8. ttp://www2. dupont. com/Kevlar/en_US/uses_apps/mass_transportation. html – accessed 10/3/11 9. http://ftp. rta. nato. int/public/PubFullText/RTO/MP/RTO-MP-069(II)/MP-069(II)-(SM1)-01. pdf – accessed 11/3/11 10. http://www. vectorstock. com/royalty-free-vector/132035-abstract-seamless-weaving-pattern-vectorn – accessed 11/3/11 11. http://www. youtube. com/watch? v=TZe3W_RxvIo&feature=related accessed 14/03/11 12. National Geographic – Aircrash Investigation Season 1 Episode 6 – Flying On empty