What is Corrugated Aluminum?

A corrugated skin is a skin structure with a corrugated cross section.

An aircraft skin refers to a dimension-shaped member that is surrounded by an aircraft skeleton structure and fixed to the skeleton with an adhesive or rivet to form an aerodynamic shape of the aircraft. The skin structure composed of aircraft skin and skeleton has a large bearing capacity and stiffness, but its own weight is very light, and it plays the role of bearing and transmitting aerodynamic loads. Skin bear

In the 1920s and 1930s, in the history of human aviation, it was in the "golden age" of the beginning of civil aviation, record flying, and the structure of aircraft began to move toward single-wing layout and full metallization. There was a coincidence: the corrugated metal skin seemed to be inextricably bound up with those fashionable transport aircraft of the time.

At that time, the American car king

The corrugated aluminum skin on the aircraft gives people the initial feeling of being durable. In fact, it is indeed true. For Germans who have always been known for its rigor, corrugated aluminum can make them feel a strong industrial atmosphere. Aircraft made of canvas is quite different. Juncker is fond of corrugated aluminum, and its later launched 12-seat three-engine G24 (1923), 16-seat three-engine G31 (1926), and the huge 34-seat four-engine G38 (1929), Both use corrugated aluminum material as the body skin.

The 1920s and 1930s were the years when long-range water jets became popular. In 1930, the German Dornier Aircraft Company made the giant water jet Do-X. It weighs about 52,000 kilograms and can carry 169 passengers. It was the largest behemoth of the world's largest civil aviation aircraft at the time. The upper surface of the "giant" also used corrugated aluminum skin.

In 1932, the Dessau plant built by Juncker also produced another classic that uses corrugated aluminum skin extensively-Junker-52, which was once the only model of Lufthansa. At most, the company was equipped with 52 aircraft. The total output of the Junker 52 is 4,835. In addition to being a passenger aircraft, it has also been widely used as a bomber and tactical transport aircraft. The Junker 52 is widely used by German soldiers for its sturdy structure, excellent battlefield adaptability, and ubiquitous figure. Call it "Auntie Ju". The number of Junker-52s produced exceeds that of any European transport aircraft. After the Second World War, some Junkers-52s continued to be used in some countries. To this day, we can still see the Junker-52s in flight, among which there are ripples. Credit to aluminum.

The corrugated aluminum skin deeply affected the world's aircraft manufacturing industry. In 1925, Ford Motor Co. "Ford Motor Co." purchased an aircraft company and began manufacturing civil aircraft according to Henry Ford's idea. The new aircraft should use 3 engines to ensure safety. In order to avoid ice accumulation, it should adopt a single design and apply metal materials to simplify manufacturing. Based on these ideas, Ford has produced a 4-A Ding civil transport aircraft (A Ding represents Air (Transport, air transport) The aircraft was quickly nicknamed the "Tin Goose" by the public-because it also used a corrugated metal skin fuselage, the "Iron Goose" was one of the earliest all-metal aircraft and was The metal fuselage of this aircraft is rectangular in cross section. Several longitudinal beams are provided. In addition to the fuselage, Shangdanji also uses corrugated aluminum skin. Since then, Ford has successively introduced improved three-engine passenger aircraft such as 7-AT, 9-A Ding. These three-engine passenger aircraft are collectively referred to as Trimotors, and quickly became the selected model of the domestic aviation industry. By 1932, Ford made 200 Trimotors, but even though Ford is already a recognized expert in mass production, the company has not been able to make much profit from Trimotors production. The main reason for this is that the forming and assembly technology of the all-metal aircraft was not yet mature. The biggest contribution of the Ford Trimotor was to allow people to accept the concept of the all-metal aircraft, so that people understand that all-metal aircraft can also have good safety Three years later, the well-known DC-3 passenger aircraft was put into use. This all-metal multi-bill machine became the first profitable civil airliner.

What is the charm of corrugated aluminum? In addition to the appearance of strict and precise appearance, in fact, aircraft with corrugated aluminum material skin is difficult to have a beautiful appearance. This is because when the corrugated aluminum skin is installed along the longitudinal direction of the aircraft, it cannot form a continuous and smooth streamlined appearance, and can only make straight turns and seams. Such a situation outside the aircraft will increase the resistance to flight. In addition, even if the corrugation of the corrugated aluminum skin is completely parallel to the longitudinal axis of the aircraft, the corrugated skin will increase frictional resistance. The increase in flight resistance, of course, for the early civil aircraft and even military transport aircraft, people sought more safety and practicability, and the requirements for flying speed were second. This was from those who did not add any fairings on the Ford Trimotors. The real value of corrugated aluminum can be seen on the huge engine of the engine, which can improve the strength of the skin. The corrugated aluminum body skin can carry part of the structural load. It greatly enhances the rigidity of the structure of the body, but the corrugated aluminum skin also brings For some problems, the installation and coating of corrugated aluminum skin on the surface of the fuselage is not simple. A good technical level is required and the strength of corrugated aluminum is closely related to the direction of the corrugation. Generally speaking. Corrugated aluminum has better strength in the direction along the corrugation, but the strength will be greatly reduced in the vertical direction of the corrugation.

Later passenger planes paid more and more attention to increasing the range and speed of the aircraft. This was even more important for the developers of the United States DC-3 airliner, because the requirement that the aircraft might need to transport passengers from New York to Chicago could not be fully adopted. To achieve a more efficient engine, we must try to make the aircraft more streamlined. The original DC-3 prototype program DC-1 had planned to use three engines, but later researchers thought that too many engines would seriously increase the flight limit. force. In addition, the engine must have a streamlined fairing. In order to reduce the resistance, the corrugated aluminum skin material is naturally not suitable for use. Fortunately, the German engineer Adolf Lorbach has invented a new wing structure methodconstructed in ribs / stringers. The wing frame is covered with a stretched aluminum plate to form a box structure. Tests show that such a wing has good strength, a smooth shape, and low resistance. The wing of the DC-3 successfully withstood the test of heavy pressure, and the testers successfully rolled over the wing with a roller.

Some corrugated materials are still visible today in aircraft skins. The inner skin of the main high-altitude reconnaissance aircraft SR-71 "Blackbird" is corrugated material. However, these corrugated materials are no longer set solely for the purpose of increasing strength. Their functions are more like the wrinkles on the bottom of cans and kettles. Because the "black bird" needs to fly at high speed, the body is bound to withstand extremely high temperatures. High heat can cause the skin to swell, which may cause the skin to tear or curl. The corrugated skin made of corrugated material can stretch in the direction of vertical corrugation in a hot environment to avoid damage caused by stress. At the same time, the corrugated material can enhance the longitudinal strength. Interestingly, because the corrugated material will increase the flight resistance, some aerodynamic experts accused the designer of the "Blackbird" is trying to fly a Ford "Iron Goose" more than 80 years ago to the height of Mach 3 speed.

With the continuous emergence and application of new materials, corrugated aluminum has found no more place on the aircraft skin. But we should not forget that it is corrugated aluminum that helps humans to accept the concept of all-metal aircraft. In the sky, those classic figures wearing "corduroy" coats will never disappear. ^[2]