Actualización de noticias del mes de abril, primera quincena.
BAE Systems ha realizado con éxito un disparo de prueba del APKWS en Eurofighter Typhoon, marcando un hito en la búsqueda de soluciones de armamento de bajo coste y alta precisión.
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Se espera que la próxima fase de pruebas incluya enfrentamientos contra objetivos aéreos, consolidando el uso de este armamento en misiones de defensa aérea. El APKWS ya ha sido desplegado operativamente en plataformas como el F-16 y el A-10, así como en helicópteros, ofreciendo una alternativa de menor coste frente a los misiles guiados tradicionales.
"UK Typhoons and F-35 jets, supported by Voyager and Royal Navy Merlin and Wildcat helicopters, have continued their defensive missions over the Eastern Mediteranean, Jordan, Bahrain, and the UAE," the post read.
Four RAF pilots have achieved the "ace" status due to the mission, the ministry added in a separate statement, having "aving blasted Iranian drones out of the sky during operations in the Middle East, protecting British interests, partners, and personnel in the region."
On early engines, something called ‘fretting corrosion’, between tight-fitting parts in the EJ200 compressor, was cutting component life down to a mere 400 hours, rather than the 4,000 they’d been designed for. This occurred due to wear between the tight-fitting compressor blades and disc subject to colossal cyclic stresses, and needed to be eliminated somehow.
The solution was to change how they were made: Rolls-Royce elected to replace the conventional compressor disc (with retaining slots for the blades) with a single-piece, fully machined bladed disc, called a ‘blisk’. The rationale was simple: You can’t get wear between tight-fitting parts if there is only one part! To achieve this, Rolls-Royce needed to pursue a new and very unusual type of welding.
Simply put, it needed to use friction, -ridiculous friction!- to join the jewel-like blades to the machined disc. Think of it like rubbing your hands together to keep warm on a cold winter’s day, but taken to absurd extremes, ending with your hands becoming merged together. Uncomfortable body horror, but impressive.
Friction welds were already performed on the shafts that run up the middle of jet engines, to join multiple pieces by spinning them up and forcing them together until frictional heating, and ludicrous pressure, bonded shafts together. The advantages of this are significant: Friction welding creates minimum heat affected zones (HAZ), extremely low porosity and high quality welds with favourable microstructure that’s well-suited to highly-loaded assemblies like jet engines. It also works well with dissimilar metals, and can be done very, very quickly, with low-ish energy costs.
In linear friction welding, a specialized fixture holds a part such as a compressor blade and applies it to the workpiece with many tens of tons of compressive force, while vibrating 20-125 times a second at very low amplitudes of just a few millimetres. This rapidly generates exactly the same kind of frictional and compressive load that woks so well with rotating friction welding, and lets you weld blades onto compressor discs, which can be further machined down into finished ‘blisks’ at leisure, saving weight and adding extra life to the engine.
But it’s not straightforward. Friction welding is one of those weird hyper-specialised processes that’s thrives in strange niches, too awkward and specialised for mere mortals. The capital cost of friction welders, especially LFW machines, is nothing short of astronomical, so you only pick this as a weld method if the output justifies the expense… as it does with jet engine compressor blisks, where it nets you a juicy weight saving as well as eliminating fretting corrosion risk.
In 1995, when Arthur Schäffler first unveiled the new full-blisk low-pressure compressor to the four Eurofighter customers for their EJ200 jet engine, the response was less than enthusiastic. “Heated discussions broke out immediately,” recalls the then Technical Director of the EJ200 consortium Eurojet, thinking back to that meeting in London. The representatives from Spain, Germany, Italy and the United Kingdom had some grounds for their skepticism. Although a first blisk had already been used in a helicopter engine back then, the blisks that MTU’s Schäffler was proposing had a much greater diameter than the helicopter component. “With the EJ200 blisks, we’d gone out to the very frontier of development technology,” says the engineer, who is now 81 years old. Driven there by necessity, the MTU engineers were forced to try the new technology in order to fulfill the service life requirements for the EJ200. The high rotational speeds of the rotors in the jet engine—and thus the centrifugal forces—were so great that fretting corrosion became a problem for the conventional individual blade technology. Fretting corrosion here refers to the formation of little pits on the surfaces of the blade root and rotor groove, which can lead to cracks and ultimately to loss of the blade.
“The first 85 EJ200 engines that were delivered without blisks in the high-pressure compressor in stages 1 and 2 were thus limited to 400 flight hours—whereas the design had planned for 4,000 hours,” says Christian Köhler, who joined MTU in 1990 and is today the Chief Engineer of the EJ200 program. The blisks resolved the problem and fully convinced the customers of the integrated disk-blade solution. By the start of 2019, 558 jets had already been delivered with the EJ200 engines—and more are on order. MTU’s blisk experience was then further utilized in an experimental high-pressure compressor that was developed as part of the HDV12 technology program and which fit more or less exactly into the PW6000 engine for the A318. “This allowed us to show Pratt & Whitney our technological abilities,” Köhler says. With a few modifications, the high-pressure compressor is a standard component in the PW6000 today, and for blisk technology this represented the leap into commercial business.
