The battle of composites in the hottest aircraft

2022-08-07
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The battle of composites in aircraft

Boeing and Airbus, the world's leading aircraft manufacturers, have been fighting for a long time. At present, one of their weapons is composites. George marsh made an investigation

Boeing has indeed taken some time to deal with the challenge of Airbus. Now with the B787 medium-sized airliner, Boeing has begun to take the initiative. In the 1980s, Airbus first used a large number of reinforced plastic structures on aircraft, especially the rudder, tail and wing control surfaces. Recently, what is popular is that on the A380 super large aircraft, solid and light materials account for one quarter of the total weight of the structure. Similarly, at the beginning, Boeing only applied a small amount of composite materials (control surface, wing tip, etc.). By the 1990s, the weight of composite materials on the B777 had accounted for 20%, especially the horizontal tail of the B777 was a large composite component. However, Boeing's boldest attempt is the composite fuselage of the B787. Ketaspire polyether ether ketone (PEEK) will be the first mainstream aircraft with a plastic fuselage with excellent strength, excellent fatigue resistance and a continuous service temperature of up to 240 ℃. (Raytheon's premier 1 and hawker 4000[ex horizon] are also composite fuselages, but they are just commercial jets.) In addition to the large carbon fiber handlebars and cushions that can flexibly adjust the wings and tail wings, the weight of composite materials in the B787 body accounts for about 50%

787 until it reaches the limit position on the right-hand side of the instrument, a large number of composite materials with short correction time are used on its main structure

but the carbon fiber fuselage is controversial. Therefore, Airbus does not use composite materials on A350, a competitor of B787, but uses metal fuselage. Nevertheless, Airbus still hopes that composite materials can account for about 35% of the weight of this model. (in order to respond to the market trend and compete with the B787, Airbus is considering redesigning the A350 from the early A330 series to make it a brand new model with a larger fuselage and wings.)

at first, the airlines were skeptical about the B787 (Boeing called it a dream aircraft), mainly because they were worried about the difficulties in fuselage repair and maintenance. Flight safety foundation said that the damage of ground equipment to low parts of the fuselage costs Airlines $10billion a year, half of which is caused by damage repair and downtime. (casualties account for another half.) This kind of damage is usually very serious, and its repair is really a big problem. Before, airlines worried that composite materials might be more difficult to repair than metal, and there would be more downtime. Another concern is that when the composite is damaged, the surface may not be damaged, while the metal will deform or show obvious dents

despite Airbus' concern, Boeing has achieved great success. Through good customer relations and public relations efforts, B787 has become the fastest selling aircraft in the company's history. Although the early Airbus A350 also received certain orders, Airbus still fell behind Boeing

the recent commitment of Qantas, an Australian airline, has increased the total number of orders for B787 to 400, while the number of orders for Airbus A350, which started late, is 200

air Pacific is the latest customer of Boeing 787. The dispute over ordering 5

fuselages

there have always been two positions of support and avoidance on the issue of using plastics to make important fuselage/pressure cabin of mainstream airliners. The two major competitors regard this as their main difference. Other differences include the viewpoint of using two engines or four engines on large transport aircraft and the prediction of the demand for super large aircraft. The basic principle of Boeing's fuselage is very simple - the world is always very concerned about fuel consumption and emissions, and lighter aircraft will burn less fuel. The composite material structure is lighter than the corresponding metal structure. Therefore, the composite material fuselage can reduce the operating cost and pollution of the aircraft. Boeing also cited other advantages: the composite material can be made into a stronger pressure cabin, so that the pressure in the B787 cabin can be maintained at 6000 feet, rather than the usual 7000-9000 feet. Passengers will feel more comfortable. Because the composite material will not corrode (the biggest enemy of the metal fuselage), the humidity in the cabin can be kept at 10~15%, while the humidity in the metal fuselage can only be kept at 5~10%, which also increases the comfort of passengers

Boeing's composite fuselage can better carry the load brought by larger

windows. (source: Boeing)

the ability of composite materials to adapt to load mode, and larger windows can be installed (about 65% larger) without affecting structural integrity or adding additional weight. Boeing also believes that the corrosion and fatigue resistance of composites will make them more durable than metals. However, when the American aircraft manufacturer claimed that the maintenance cost of composite fuselage was lower, it still caused a controversy

on the issue of composite materials, Airbus took a conservative stance for the first time, believing that Boeing was taking a great risk. Although the American company has faced numerous technical challenges in the past, Europeans believe that it is now facing an unknown. They believe that even if it succeeds, the R & D cost will exceed the budget, the expected price for this aircraft and the expected profit of the operator will be invalidated, and the delivery and performance guarantee may also be a problem. Neutral analysts concluded that Boeing could not afford too many setbacks. If its expectations were confirmed, all the possibilities could be realized one by one

Airbus also grasped the key point of the debate and claimed that although the plastic used on the A350 is less than that of the B787, it is still a leader in the use of advanced materials, and the fuselage will use aluminum titanium alloy skin. According to John Leahy, chief commercial operation officer, the A350 will use 60% of advanced materials, which is ahead of the 787. The use of lightweight alloy as skin reduces the risk and cost, enabling Airbus to offer lower quotations to airlines. Airbus also pointed out that when the fuselage is damaged, airlines can use standard maintenance procedures

recently, the debate about fuselage/composite materials has gradually increased. Airbus' obvious slander of the 787 made Boeing angry, although both companies were taboo about attacks on the safety of their products. This possible violation finally broke out in a safety seminar, after which Boeing decided to prove the visibility of damage to its composite fuselage, requiring only minimal non-destructive testing. A spokesman for the workshop believed that this method could increase safety problems, because damage (such as delamination or cracking) could be hidden in the middle of the laminate without any signs on the surface

the first

b787 composite fuselage at the Boeing developmental center in Seattle. (picture copyright: Ken dejarlais)

Boeing denies any impact on safety and firmly believes that the safety margin is fully considered in the 787 structure, so the undetected damage will not cause catastrophic failure. Just as Justin hale, acting chief machinist of B787 project, believes that the damage in composites tends to stay in one place, on the contrary, the damage in metals will spread rapidly. Composite materials can maintain the integrity of aircraft structure, even with a small amount of undetected damage

continuing his view, hale mentioned the days when Boeing planned to build the sonic cruiser, a supersonic transport aircraft. They have abandoned this plan and focused on what formed the B787. Composite materials have played an important role in the design of high-speed jet aircraft

hale said: "our sonic cruiser task team suggested that if the surface damage of the laminated plate is not obvious by visual inspection, the fuselage design should ensure that it will not prevent the structure from bearing its design load."

this concept has been used in B787. A large number of carbon fiber laminates are used in the fuselage of the 787. The thickness ranges from one inch in the import and export fence and other vulnerable parts (including the lower abdomen of the fuselage), to half an inch at the connection of independently manufactured fuselage parts and 1/10 inch at the top of the fuselage. Due to the different damage tolerance, Boeing pointed out that if the damage is not seen, there is nothing to worry about and the aircraft can operate safely

repair

major crash reports should facilitate more detailed inspections, including signs of damage inside the fuselage. Maintenance personnel may look for signs of fracture in the crossbeam - the crossbeam is a reinforcing member, which is solidified together with the fuselage skin during the manufacturing process. Signs of splitting represent high external impact. If the damage characteristics and extent are still suspected, a non-destructive inspection may be required

for example, the effectiveness of pulse echo evaluation has been demonstrated in the tail and control surfaces, so Boeing is developing a handheld sound device to provide damage signs. This collision damage detector will output information to help the maintenance team refer to the aircraft structure maintenance manual to determine whether the displayed damage should be repaired

airlines are also concerned about the repair of more serious and obvious damage beyond the structural maintenance manual. Justin Hale reassured them by citing several actual case studies in which the metal aircraft was severely damaged. The main causes of accidents include rear impact, front landing gear fracture and service vehicle collision. A Boeing support team moved the same damage photos to the B787 structure, and then estimated the labor and material costs required for a full repair. Hale said that in each case, the repair cost is less than 10% of the repair cost of the corresponding metal aircraft with similar damage

most aircraft need to start major overhaul in the mature period. The maintenance cost of the

b787 is 30% lower than that of the 767, and the saved

cost is increasing year by year. (source: Boeing)

another concern of airlines is that the repair of composite structures may be very different from the existing repair procedures, making it difficult for engineers to adapt. Hale said that is not the case. Technicians can continue to use the current method to repair the damage of the fuselage, that is, their method to repair the bolted metal patch

"we do not want to force operators to use new repair techniques." He explained, "we learned from the sonic cruiser project about six years ago. Service engineers, including structural experts and composite materials experts, believe that it is best for airlines to continue to use the repair methods they are familiar with."

therefore, bolted patches remain in the service manual, although these components may be made of composite materials and titanium - try to avoid using more commonly used aluminum because of its poor compatibility with carbon fiber. Hale stated that the structural maintenance manual would permit large areas (up to 1m × 1m) patch repair. If airlines want to restore the flawless appearance of composite materials in the future, generally when the aircraft lands for major engineering maintenance, they can choose to remove the bolted patch and replace it with bonding repair

Boeing has simplified the procedure as much as possible to ensure that the hot binder can be used to cure commonly used prepreg repair materials without relying on autoclave or furnace curing. Prepregs assigned the same low curing temperature for most repairs do not require preservation of materials with different cooling requirements and shelf life. Boeing is making efforts to

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