Rockets and Flight

Where were rockets first used and by whom? What were these early rockets used for?
The first recorded use of rockets was by the Chinese, in the battle of Kai-Keng (The place is now known as Kaifeng) against the Mongols, in 1232. They were used as weapons (rockets mounted on arrows), which were used to repel, create a sense of fear and potentially injure and the Mongols.

Explain the difference between the way a rocket achieves flight and the way an aeroplane does.
An aeroplane achieves flight through the meticulous design of the wings that allow lift. Lift is created through these wings due to the fact that the top of the wing has a larger/longer surface area than the bottom of the wing (aerofoil design). This increases the speed of the moving air (above the wing) which decreases the pressure on top and combined with the thrust produced by the plane –through is engines- thus allowing the plane to “lift off”. The pressure underneath pushed the wing upwards resulting in flight. The plane flies horizontally. A rocket, however, does not use this type of aerodynamic design to achieve flight. A rocket has large amounts of fuel which is used in a combustion chamber to create thrust. A rocket relies mainly on thrust to lift off. The thrust is used as propulsion out of the earth (upwards). It is overcomes the downward force/pressure exerted from gravity – and the weight of the rocket- allowing it to take off. Put simply, the exhaust propulsion is fast and powerful resulting in a high acceleration and eventually flight/lift off. The rocket flies vertically.

 Rockets have fins that usually have an aerofoil shape. Aerofoils are used on rockets, aeroplanes and helicopters. Explain how the air flowing over an aerofoil creates lift. 
Aerofoils create lift by making the pressure above the wing lower than the pressure under the wing.
This will cause the pressure below to overpower the pressure above and make the plane lift off. This is done by making the top of the wing curved outward and keeping the bottom wing fairly flat. When the plane moves, the air particles need to get around the wing. However, because the top of the wing is curved outwards, there is more area that the air particles above the wing have to cross. This increases the speed of the air particles above the wing which decreases pressure (Bernoulli’s Principle). The air above the wings thins out as well, also reducing pressure. Now the plane can lift off. The air on top is moving fast to reach the same place as the air on the bottom.

Explain why aluminium alloys and titanium alloys are used in plane bodies more than steel.
Titanium alloys and aluminium alloys have more desirable properties for plane bodies than steel. Titanium alloys and Aluminium alloys are usually quite strong reducing the change of parts/the body breaking during flight. Planes need this strength as they are under much stress during flight. They also have a very good strength to weight ratio reducing the cost for construction and fuel while maintaining the low mass of the plane. In addition, both alloys are flexible which is  needed in plane wings during liftoff, landing and general flying. Aluminium alloys and titanium alloys are both corrosion resistant which can allow a plane to fly/be in use for longer periods of time before replacement or repairs. This can greatly reduce the cost of repairs and ensure safety while flying through the atmosphere which contains large amounts of water vapour and similar corrosive substances. Steel on the other hand corrodes quite quickly compared to Aluminium and titanium alloys.

Composite materials such as carbon fibre and KevlarTM are used extensively in many aviation applications. Explain why high performance planes are moving to composite structures.
Composite materials are able to be moulded much better than regular metal alloys. This means that plane designs can be more streamlined, reducing fuel costs and fastening speed. Many composite structures are lighter than regular metal alloys which reduce mass, increases speed and increases fuel costs. Composite materials allow the ability to possess both properties of the materials meaning that it is more desirable. Composite materials are often resistant to corrosion and fractures due to their atomic structure and properties. These traits are necessary in the design of high performance planes.

Explain the difference between an aerospace and aeronautical engineer. Then list a current project for both and aerospace and aeronautical engineer.
An aerospace engineer deals with the construction, design, observation and knowledge that concerns aircraft and spacecraft. An aeronautical engineer however, deals with the study, knowledge, design and manufacturing of machines (e.g. planes) and technologies that are capable of flight which are used within the earths atmospheric regions (i.e. in the sky and not in space). Currently a lot of aeronautical engineers are working on NASA’s Aeronautics Research Mission Directorate Project which aims to solve the current problems that we have in air transportation and development. Some aerospace engineers would be working on the ASRI’s Ausroc 4 project which is aiming to launch a micro-satellite orbital vehicle.

Since WWII there have been three different engine designs used for commercial aircraft: the piston engine, the turbojet engine and the turbofan. Explain why each motor design has superseded the preceding design.
The piston engine had performance issues in the fact that it could not fly quite as fast as people wanted it to. The propellers literally had a speed limit as they neared the speed of sound. Once close, the propellers of the piston engine would not allow the plane to go any faster. This was fixed by the introduction of the turbojet engine, which used an exhaust propulsion-like system that allowed planes to reach speeds much faster than those of a piston engine. They were also somewhat more reliable than piston engines. Piston engines would sometime fail whereas the new turbojet engines would barely every fail. It used less fuel for the same distance compared to piston engines as well.
When fuel prices began rising a newer, more fuel efficient plane engine was needed. The turbofan engine was the answer. It provided reduced fuel consumption as well as increased thrust, more control over speed and quieter engine sound. The turbofan engines also allowed anti-icing and bleed air systems to be fitted which were needed for cold temperatures and pressurisation.

The DeHavilland Comet airliner was the first jet airliner, why did it suffer from explosive decompression at high altitude and how did they solve the problem?
It suffered from explosive decompression due to metal fatigue that would cause the metal of the fuselage and air frames to split which would cause the plane to explode. This metal fatigue was experienced at high altitudes when flying for long periods of time. The material used was not tested for stress/fatigue. Another factor for the explosive decompression is the square window design which allowed splits to occur. The square windows had obvious stress points and could easily cause fractures in the fuselage. The rivets on the plane were also too close together meaning that if one small crack appeared it would spread into a much bigger crack quickly. This was fixed with the introduction of square windows, placing the engines on pylons instead of inside the wing, increased pressurisation testing, spreading the rivets apart and making the fuselage skins thicker and more resistant to splits.

The Boeing 787 Dreamliner and the Airbus A350 are revolutionary because of newer materials and is being promoted as a more efficient plane for commercial transport. Explain why Boeing can make this claim.
The Boeing 787 has newer features which both enhances the passengers comfort (necessary in commercial transport) as well as increasing safety, speed and reducing costs to both the environment and monetarily to the aviation companies. Its structure is 50% composite material (by weight), making it the first commercial plane to have the majority of its structure made out of composite materials. Carbon Sandwich is one of the abundant types of composite materials used. It has a high bending stiffness, low density and a high strength to weight ratio meaning it is lighter and less fuel is needed to lift/move the plane. All the materials used in the plane is recyclable, reducing the impact on the environment. Smaller fairings on the plane are used which reduce drag and fuel consumption. The composite materials used on this plane are also very malleable and mouldable, meaning the plane design can be more streamlined, thus reducing drag and eventually reducing fuel consumption and costs. Overall 20% less fuel is used (compared to similar sized planes) which is both better for the environment as well as the commercial flight companies. The wings of 787 are also designed for speed and efficiency, with the aspect ratio of the wing higher than other aircrafts.

The plane also has a new “Smoother Ride Technology” which turns on at the sense of turbulence. The wings and its control surfaces will engage reducing the impact of turbulence. This is also better for the plane structure as it will decrease stress on the wings. The plane also has equipped technologies which reduce sound and vibrations. This softer sound is desirable for future commercial transport as aviation becomes more popular and extensive.


Sources:



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