Aircraft Jet Engine Manufacturing Challenges

The gas turbine jet engines are the most widely used means of aircraft propulsion. The engine burns fuel in the combustion chamber to run a gas turbine to accelerate airflow and in turn create forward thrust. Both the fan and the jet contribute to the process. Normally large airliners and transport aircraft have large fans and a few stages of compressor and turbines and are referred to as the high-bypass engines. Military fighter aircraft engines have to be sleek and have smaller diameter engines and many more stages of compressor and turbines. These are thus low-bypass. Some even use afterburners to augment thrust. Aircraft engines are among the most complex systems on board and there are very few aircraft engine manufacturers. Even emerging major aerospace powers like China and India are still struggling to have their own engines flying.  

Operating Complexities of Aircraft Jet Engine

         The aircraft jet engines have to produce a very high thrust yet remain sleek to reduce in-flight drag. They, therefore, operate at very high rotation speeds (RPM). This requires a very fine balancing of compressor and turbine blades and high-quality bearings which have to be suitably lubricated. The engine burns aviation fuel in combustion chambers and reaches high temperatures requiring special materials technology for hot sections. The engine has to operate efficiently from sea level to very high altitudes up to the stratosphere. Engine must operate at a mix of subsonic, transonic, and supersonic flights. This implies large changes in atmospheric temperatures and pressure conditions. In addition to the temperature and pressure, the engine blades are subjected to very high centrifugal forces. Special alloys, sophisticated air cooling schemes, and special mechanical designs are required. Newer materials like ceramic matrix composites, silicon carbide matrix with silicon-carbide fibres are being used in engines. Efficient engines mostly operate very close to surge levels requiring management of airflow and aerodynamics within the engine. The design of engine air intake is also an important factor for engine efficiency. Fuel injection has to adjust for altitude and thrust requirements. Fuel burn efficiency is very important.  The amount of thrust an engine generates is important. But the amount of fuel used to generate that thrust is also very important. Thrust-specific fuel consumption is thus an engine efficiency indicator. The engine also drives accessories such as fuel and hydraulic pumps and also electric generators.  Engine reliability has to be very high because many fighter aircraft have a single-engine. Shorter turnaround servicing and higher time between servicing are important.  It all requires top-class design and engineering. Modern engines have the Full Authority Digital Engine Control (FADEC). For better aircraft maneuverability, engines have all-aspect thrust vectoring nozzles. Engines have to have low carbon emissions, and low noise and infra-red signature for stealth and environmental reasons.

Major Engine Manufacturers

The turbofan engine market is dominated by a handful of, mostly western, players. These are General Electric, Rolls-Royce, Pratt and Whitney, in order of market share. General Electric and Safran of France have a joint venture, CFM International. Pratt & Whitney also has a joint venture, International Aero Engines with Japanese Aeroengine Corporation and MTU Aero Engines of Germany. Pratt & Whitney and General Electric have a joint venture, Engine Alliance selling a range of engines for aircraft such as the Airbus 380. There are others like Honeywell Aerospace and Russian and Chinese companies in aircraft engine manufacturing. Most engine manufacturers make engines for both civil and military aircraft. It is interesting to look at the product range and size of some of the top engine manufacturers.

General Electric Aviation had 283,000 employees and revenues of US$ 121.6 billion in 2018. In 2019 GE was ranked 21 on the fortune 500 global list.  GE Aviation currently has the largest share of the turbofan civil engine market. GE is also “aggressively researching hybrid-electric and electric propulsion” systems for aircraft. On the military side, GE engines power many U.S. military aircraft, including the F110, powering 80% of the US Air Force’s F-16 fleet. The F404 and F414 engines power the US Navy’s F/A-18 Hornet and Super Hornet. F404 is also onboard India’s LCA ‘Tejas’ and F414 has been chosen for the LCA Mk 2. Rolls-Royce and General Electric were jointly developing the F136 engine to power the Joint Strike Fighter, however, the program has run into uncertainty.

Rolls-Royce Holdings plc. was the world’s 16th largest defence contractor in 2018 by defence revenues. The company is most known for the RB211 (high-bypass turbofans) and Trent series, as well as their joint venture engines. Among their fighter engine was the RB-199 used on Panavia Tornado. The famous thrust vectoring Pegasus (originally a Bristol Siddeley design taken on by Rolls-Royce when they took over that company) is the primary power plant of the Harrier “Jump Jet” and its derivatives.

Pratt & Whitney is third behind GE and Rolls-Royce in market share. It is now a subsidiary of Raytheon Technologies. Pratt & Whitney’s aircraft engines are widely used in both civil and military aviation. The Pratt & Whitney F119 and its derivative, the F135, power the United States Air Force’s F-22 Raptor and the international F-35 Lightning II, respectively. Rolls-Royce is responsible for the lift fan which provides the F-35B variants with a STOVL capability. The F100 engine was first used on the F-15 Eagle and F-16 Fighting Falcon. The Newer Eagles and Falcons also come with GE F110 as an option.

CFM International is a joint venture between GE Aircraft Engines and SNECMA of France. They have created the very successful CFM56 series, used on many civil aircraft. CFM International is now powering ahead with the production of its new Leap-series engines – which span the 23,000-35,000lb (102-155kN)-thrust range. Engine Alliance is a 50/50 joint venture between GE and Pratt & Whitney producing the GP7000 series of engines. International Aero Engines is a Zurich registered joint-venture between Pratt & Whitney, MTU Aero Engines, and Japanese Aero Engine Corporation.  The collaboration produced the V2500, the second most successful commercial jet engine program in production today in terms of volume, and the third most successful commercial jet engine program in aviation history. The FAA-type certification for the V2500 was granted in 1988. Over 7,600 had been built by June 2018.

U.S.-based Williams International is a manufacturer of small gas turbine engines. It produces jet engines for cruise missiles and small jet-powered aircraft. Honeywell Aerospace is one of the largest manufacturers of aircraft engines and avionics and a producer of auxiliary power units (APU) and some other aviation products. Honeywell/ITEC F124 series is used in military jets, such as the Aero L-159 Alca and Alenia Aermacchi M-346. The Honeywell HTF7000 series is used in the Bombardier Challenger 300 and the Gulfstream G280. The ALF502 and LF507 turbofans are produced by a partnership between Honeywell and China’s state-owned Industrial Development Corporation. The partnership is called the International Turbine Engine Co. EuroJet Turbo GmbH is a multi-national consortium, the partner companies of which are Rolls Royce of UK, Avio of Italy, IP of Spain, and MTU Aero Engines of Germany, to manage the EJ200 turbofan engine for the Eurofighter Typhoon. Ishikawajima-Harima Heavy Industries is a Japanese aircraft engine company. The company manufactures F3 for Kawasaki T-4, XF5-1 for ATD-X, and F7 for Kawasaki P-1.

Aviadvigatel is a Russian manufacturer of aircraft engines, and currently offers several versions of the Aviadvigatel PS-90 engine powers Ilyushin Il-96-300/400/400T, Tupolev Tu-214 series, and the Ilyushin Il-76-MD-90. The company is also developing the new Aviadvigatel PD-14 engine for the new Russian MS-21 airliner. Ivchenko-Progress is a Ukrainian aircraft engine company and their engines include Progress D-436 fitted on the Antonov An-72/74, Yakovlev Yak-42, Beriev Be-200, Antonov An-148, and Tupolev Tu-334. The Progress D-18T powers two of the world’s largest airplanes, Antonov An-124 and Antonov An-225. NPO Saturn is a Russian aircraft engine manufacturer, and their engines include Lyulka AL-31, Lyulka, NPO AL-55 and they power many former eastern Bloc aircraft. Saturn also holds a 50% stake in the PowerJet joint venture with Snecma. NPO Saturn engines power many Russian fighters. The latest AL-41F, variable-bypass ratio turbofan engine is the heavily upgraded AL-31F variant and powers the Sukhoi Su-35S and initial serial production Sukhoi Su-57 stealth aircraft. Russia’s Klimov is the manufacturer of the Klimov RD-33 turbofan engines that power the MiG 29 and the Sino-Pak JF-17 fighters.

Chinese turbofans

Three Chinese corporations build turbofan engines. Some of these are licensed or reverse-engineered versions of European and Russian turbofans, and the others are indigenous models. Shenyang Aircraft Corporation manufactures WS-10, Xi’an Aero-Engine Corporation manufactures WS-15, and Guizhou Aircraft Industry Corporation manufactures WS-13 turbofan. Each of these engines is still under development.

As per Chinese media, nearly 300 Shenyang WS-10 have been manufactured for the J-11 program. The WS-10 is derived from the CFM56 with the experience gained from the Chinese Woshan WS-6 turbofan project, which was abandoned in the 1980s. The target was to produce an engine comparable to the Saturn AL-31. After being unable to purchase source code from Salyut, the Chinese aviation industry spent nearly 20 years developing its own source code for the WS-10 engine. The WS-10A reportedly has 120–140 kilonewtons (27,000–31,000 lb) thrust, and FADEC, and first flew on J-8II in 2002. Engine testing on the J-11 began in 2004. The engine’s initial quality was unsatisfactory, and reliability was also poor. The WS-10A matured by 2009 to power the J-11B Block 02 aircraft. The engine now uses new third-generation single-crystal turbine blades and has a life of 1,500 hours. In March 2020, Chinese state media released a video showing a WS-10B-powered J-10C. A test-bed J-10B powered by a WS-10B-3 variant with thrust vectoring was demonstrated at the 2018 China International Aviation & Aerospace Exhibition. By January 2021, Chinese engineers considered the WS-10C to be as good as the AL-31F, with the WS-10C being targeted as a replacement interim engine for the J-20. WS-10G – thrust vectoring variant (152–155 kilonewtons) thrust is intended for the Chengdu J-20. WS-20 is a high-bypass engine with13.8 tons of thrust and uses the WS-10A core. It is meant for the Y-20 strategic airlifted. Xian WS-15 is intended to power and enable super-cruising on the Chengdu J-20.

Chinese Comac’s C919 airliner still continues test flights and looks poised to enter service with Chinese carriers – minus the Chinese engines, for the time being. The prototype of the CJ-1000AX, the alternative power plant manufactured by Chinese engine maker AVIC Commercial Aircraft Engine (ACAE), was first publicised in December 2017, after 18 months of assembly. ACAE had signed a deal with Comac a year earlier to supply engines to the narrow-body program. The CJ-1000AX was touted as the “home-made engine” by the state-owned Global Times newspaper that would “replace imported foreign engines in future”. The C919 will initially be powered by CFM International Leap-1C engines. CJ-1000AX hit a milestone in its development when it achieved power-on. The high-bypass-ratio turbofan engine’s core reached a maximum speed of 6,600 RPM, ­according to Chinese officials. FlightGlobal has previously reported that China plans to build 24 more CJ-1000 prototype engines to support an airworthiness campaign, with entry into service targeted after 2021. Global Times painted a bright future for the turbofan: “The CJ-1000 is designed for the C919, but is expected to power the Boeing 737 or Airbus A320 or a similar newly built aircraft in the world market by 2025.”

Meanwhile, the AEF3500, earlier called the CJ-2000, was first unveiled at the 2018 Airshow China in Zhuhai. The turbofan was pitched as a Chinese engine alternative for the Sino-Russian CRAIC CR929 wide-body program. Little is known about the status of the AEF3500, but media reports suggest it could be put into service on the CR929 by around 2030. Similar to the C919, the CR929 could enter service in 2025 powered by western engines, before a Chinese-made option is offered a few years later. It could, however, face competition from Russia in the form of Aviadvigatel’s PD-35-1. United Engine and Aviadvigatel were picked by Moscow to develop the demonstrator power plant. While AECC continues with work on the two engine types, the aircraft they were supposed to power are moving on with development. It remains to be seen if China can strike a double win with domestically ­manufactured engines on a home-grown aircraft.

India’s Gas Turbine Research Establishment (GTRE)

The GTRE GTX-35VS Kaveri is an afterburning turbofan project developed by the Gas Turbine Research Establishment (GTRE), a lab under the Defence Research and Development Organisation (DRDO) in Bengaluru, India. The Kaveri was originally intended to power production models of the HAL Tejas Light Combat Aircraft (LCA) being built by the Aeronautical Development Agency. However, the Kaveri program failed to satisfy the necessary technical requirements or keep up with its envisaged timelines and was officially delinked from the Tejas program in September 2008. Snecma, on a tie-up with DRDO, is slated to revive and certify the engine as part of the offsets deal for 36 Dassault Rafale jets purchased by India. GTX-35VS Kaveri turbofan is still intended to power later models of LCA Tejas, and the Advanced Medium Combat Aircraft (AMCA). A Kaveri derivative to be developed to power India’s Unmanned Combat Air Vehicle, Ghatak.

Engines Produced by HAL under License

HAL has been manufacturing under license, the Russian AL 31 FP, R-29B, and R25 engines. The spectrum of manufacturing facilities extends literally from the production of nuts and bolts to discs, shafts, blades, forgings, and castings – all that is required to make an Aero Engine right from the Raw materials. They have also been manufacturing spares and doing overhauls, including of RD 33 engine. The Shakti engine for HAL Dhruv helicopters has been co-developed with Safran. HAL engine division has manufactured under license the Adour MK 871, Garrett TPE 331-5, Artouste III B, PTAE-7, DART 533 – 2, and 536 – 2T engines. Orpheus 70105, was indigenously modified by HAL, is a derivative of Orpheus 701 at a lower rating, and is the Power Plant for Kiran MK II Aircraft indigenously designed by HAL. Avon is a Turbo Jet Engine designed and developed by Rolls Royce that was overhauled/repaired under license. The Adour MK 804 Engine is being repaired and overhauled under license from Rolls Royce, UK. This is similar in construction to the MK 811 engine. Similarly, the Gnome 1400 – IT engines are being repaired and overhauled under license from Rolls Royce, UK, and is the Power Plant for Seaking Helicopter.

Challenges for Engine Manufacture

The power-plant makers face conflicting demands for performance, reliability, and high precision production. There are very few major aircraft engine manufacturers who dominate the industry. With many single and twin-engine aircraft, the engine reliabilities have to be very high. The engines have to be very fuel-efficient for better range and endurance and to give greater distance per passenger for fuel expended. Also, fighter engines require high thrust-by-engine weight. There is a requirement for high-quality materials, and precision engineering.

Despite years of investment in R&D, China continues to struggle to have an engine of its own. India’s fledgling attempt at the LCA Kaveri engine has yet to succeed. As can be seen, many major manufacturers have formed joint ventures to access both technology and markets. That perhaps is the best route to follow for India too. It is also a good idea to get into the MRO market, by setting up maintenance, Repair, and Overhaul facilities for existing major engine manufacturers. This could add to the learning curve. All national resources and expertise, including the private sector, must be engaged for the GTX-35VS Kaveri engine to succeed.    

This article had earlier been written by the author for South Asia Defence & Strategic Review for their March-April 2021 Issue

Header Image Source: arcforums.com