Alan Arnold Griffith facts for kids

Alan Arnold Griffith (13 June 1893 – 13 October 1963) was a very clever English engineer. He was the son of a famous science fiction writer, George Griffith. Alan Griffith is best known for two big ideas. He studied how metals break, which is now called metal fatigue. He also helped create the first designs for the jet engine.

Griffith's advanced designs for axial-flow turbojet engines were key to making Britain's first working axial-flow turbojet. This engine, called the Metropolitan-Vickers F.2, first ran in 1941. Griffith himself didn't build the engine. He moved to Rolls-Royce in 1939.

Early Life and Work

Alan Arnold Griffith studied mechanical engineering at the University of Liverpool. He earned both a master's degree and a doctorate. In 1915, he joined the Royal Aircraft Factory as a trainee. The next year, he moved to the Physics and Instrument Department. This department soon became the Royal Aircraft Establishment (RAE).

Some of Griffith's early ideas are still useful today. In 1917, he and G. I. Taylor found a cool way to study stress. They used soap films to see how stress spreads in objects. Imagine stretching a soap bubble between strings. The colors in the film showed where the stress was. This method was used for many years until computers took over.

Understanding How Materials Break

Griffith is most famous for his studies on how materials break. He looked at brittle materials like glass. People at the time thought materials should be much stronger than they were. Griffith found tiny cracks in every material. He believed these cracks made the material weaker overall.

He realized that any tiny hole or scratch makes stress build up. This stress would get very high at the tip of a crack. This meant the material could break much easier than expected.

Griffith's Theory of Brittle Fracture

From his research, Griffith created his theory of brittle fracture. He used ideas about energy stored in materials. His theory explained how cracks grow by looking at the energy involved. He showed that a crack grows when the energy needed to create new surfaces is balanced by the energy released from the material.

This idea led to Griffith's criterion. It says that a crack will spread and break a material when the energy gained by the crack's surface equals the energy lost from the material's stress. This is a main rule for understanding how brittle things break. If a crack gets past a certain size, it becomes dangerous.

His work, published in 1920, changed many industries. It helped engineers understand why aircraft parts failed. Even if parts were built strong, tiny cracks could cause problems. Designers learned to polish metals to remove these cracks. Later, other scientists expanded Griffith's work to apply to almost all materials, not just brittle ones.

Developing Jet Engines

In 1926, Griffith wrote an important paper called An Aerodynamic Theory of Turbine Design. He explained why early turbines didn't work well. He showed that their blades were not shaped correctly. He suggested a modern airfoil shape for the blades. This new shape would make turbines much better.

His paper also described an engine with an axial compressor and a two-stage turbine. The first part of the turbine would power the compressor. The second part would power a propeller. This early design was a step towards the turboprop engine. Because of his paper, the Aeronautical Research Committee supported experiments. They built a working test design in 1928. This led to many other designs to test different ideas.

Griffith and Whittle's Ideas

Around this time, Frank Whittle was also working on turbine engines. Whittle's design used a centrifugal compressor. He sent his ideas to the Air Ministry in 1930. They asked Griffith for his opinion. Griffith found a small error in Whittle's math. He also thought Whittle's compressor was too big for aircraft. He believed the exhaust wouldn't give much thrust. The Air Ministry told Whittle they weren't interested. Whittle was disappointed, but his friends encouraged him to keep going. Whittle patented his design in 1930 and started Power Jets in 1935.

Griffith later became a lead scientist at the Air Ministry Laboratory. Here, he invented the contraflow gas turbine. This engine had compressor and turbine discs that spun in opposite directions. This design was tricky to build. In 1931, Griffith returned to the RAE to lead engine research. But it wasn't until 1938 that work on an axial-flow engine really began. Hayne Constant joined his team. They worked with a company called Metropolitan-Vickers (Metrovick).

The Metrovick F.2 and Rolls-Royce

Whittle's work at Power Jets started to make big progress. This made Griffith rethink his ideas about using the jet directly for power. In early 1940, he quickly redesigned his engine. This led to the Metrovick F.2. It ran for the first time later that year. The F.2 was ready for flight tests in 1943. It produced a lot of power. It was even tested on a Gloster Meteor plane. The F.2 engine was smaller and performed better. However, it was thought to be too complex to produce widely.

Griffith joined Rolls-Royce in 1939. He worked there until he retired in 1960 as the company's Chief Scientist. He suggested a simple turbojet engine design. It used an axial compressor and a single turbine. This engine was called the AJ.65, later renamed the Rolls-Royce Avon. It became Rolls-Royce's first production axial turbojet. He also proposed different bypass engine ideas, including one used in the Rolls-Royce Conway.

Griffith also did important work on vertical take-off and landing (VTOL) technology. This is about planes that can take off straight up. He suggested using many small, light turbojets to lift aircraft. He also explored how to control planes while hovering. The Rolls-Royce Thrust Measuring Rig helped test these ideas. A plane called the Short SC.1 used four lift engines based on his concepts.

Legacy

Alan Arnold Griffith's contributions are remembered through the annual A. A. Griffith Medal and Prize. This award was given by the Institute of Materials, Minerals and Mining for important work in materials science. The award stopped in 2021.

See Also

• Fracture mechanics
• Jet engine
• Rolls-Royce Limited