Featured Story – Titanium, aerospace and 3D printing: the “ménage à trois” continues to prosper

New designs

The last ten years or so have seen the development and introduction of a new generation of more efficient, quieter planes. They all make use of titanium both to save weight – in wing pylons, fasteners, seats – or to withstand the ever-higher temperatures and pressures of jet engines. Will this rate of innovation continue? Looking at what is on the drawing board, the answer has to be a resounding “yes”. Supersonic flight is set to make a comeback, almost two decades after Concorde was retired. Several projects exist, the most mature being the Boeing-Aerion AS2, a business jet seating 8 to 11 passengers, which will fly at Mach 1.4. The aircraft will be made of carbon fibres (fuselage, wings, engine nacelles, tail), aluminium, steel; titanium will be applied in the wing leading edges to protect against erosion.

Another idea whose time has come is the BWB (blended wing body). In this type of aircraft the body and wings structures are merged, with no clear dividing line between them. The structure is designed to reduce the wind drag and would reduce fuel consumption by around 20%. The concept has been around since the 1920s, and recently NASA took it up, and Airbus is hoping that its BWB design can replace the A320neo family. Its MAVERIC design, launched in 2017, took to the skies in 2019.

E-planes

A promising development, especially for air taxis and urban travel, is the electric and hybrid aeroplane. Progress is hampered by the weight of the lithium-ion batteries, which have a far heavier energy/weight ratio than jet fuel. So whereas long-distance flights and larger aircraft are still offlimits to electric and hybrid aircraft, shorter distances are much more easily attainable. It could well be that the future of aviation lies in more flights made by smaller aircraft and fewer if any made by larger ones. However successful, electric and hybrid are likely to face stiff competition from next-generation jet engines such as the Rolls-Royce UltraFan. Currently being developed at Bristol, it will be significantly lighter thanks to titanium reinforced carbon-fibre fan blades and a composite housing. It will reduce fuel burn and CO₂ emissions by at least 25% compared to the first Trent engine. It is due to enter into service in 2025.

About 90 electric or hybrid projects have existed – starting in 1883! – but the first commercial electric aircraft is probably the magniX, which made its inaugural test flight in Vancouver in July. Sweden is investing heavily in infrastructure to make electric aviation viable. Airbus has teamed up with Rolls-Royce and Siemens for the E-FanX project, a hybrid plane. Boeing has flight-tested its all-electric autonomous (unpiloted) passenger air vehicle, which aims to provide a new model for urban mobility.

Drones

Drones are another relatively new area in which titanium is applied, often with 3D printing. Recent examples include Airbus’s Skyway (trialled from March 2019); Titomic’s XXL machine (extra large), made by cold-spraying titanium particles onto the printing medium at very high speed to fuse them together.

Another example is a unique product from Renishaw, a Mach 0.8 rocket powered drone with very thin titanium walls that can withstand very high pressure. Combining very light weight with very high speed, the rocket could be used to collect meteorological data.

Space

Numerous space projects are under development with the help of the private sector. Titanium is well established in spacecraft, having been used since the early Mercury and Apollo programmes.

Airbus’s satellites have brackets that are 3D-printed in titanium by EOS. These brackets connect the body of the satellite to its reflectors and feeder facilities. They provide insulation and must withstand a temperature fluctuation between -180 and 150°C. An uncrewed Orion spacecraft being developed by NASA in 2018 was installed with a protective heat shield to withstand temperatures nearing 5,000° Fahrenheit during its re-entry into the earth’s atmosphere. Naturally, titanium was specified.

Titanium has long been applied in rockets, but 3D printed titanium is enabling more fuel-efficient designs. For example, New Zealand-based Rocket Lab built a rocket engine that uses electric motors to drive the turbopumps. These pumps, together with the cooled thrust chamber, the injector, the pumps and the main propellant valves, were all 3D-printed in titanium.

By far the most ambitious space projects are those of Elon Musk’s SpaceX company. The company has scored many firsts, including the successful deployment of a reusable launch system.

Its flagship project is to colonize Mars. This involves landing uncrewed cargo ships in 2022 and sending four additional ships in 2024 including the first people. Crucial in this effort will be Starship, a fully reusable second-stage and space vehicle. It will be powered by Raptor, a new family of methane-fueled fullflow staged-combustion cycle engines, which, though complex to construct, should produce fuel savings. Elon Musk is not noted for favouring titanium for the structural components of his spacecraft, even changing the design of the giant grid fins on the Falcon 9 from aluminium to titanium before settling on welded steel. Similarly, the plans for the Starship itself were changed: although the original plan was to construct the frame in carbon fibre, in the end stainless steel type 301 was specified. This was partly to save money, but mainly because it is easier to weld than titanium and can withstand a greater temperature range than carbon fibre or aluminium.

Reference

(1) www.moroccoworldnews.com; figure is for 2018.