Under the TLUH Program TUSAS has completed the design, development and the manufacture of an indigenous twin-engine, 5-ton class medium category (4 to 6 tons), utility helicopter with a maximum take-off weight (MTOW) of 6,050 tons and powered by a pair of 1,400 shp class turboshaft engines. 

Powered by a pair of LHTEC CTS800-4AT turboshaft engines, each generating 1,373 shp during take-off, the T625 TLUH first prototype (dubbed P0) performed its first flight, which lasted 20 minutes, on 6 September 2018 at 6:00am at TUSAS facilities in Ankara. According to Honeywell the CTS800-4AT has almost 95% commonality with CTS800-4A engine, which is being used on T129 Mk-I ATAK helicopters and the 5% difference stems from necessary modifications on the engine and FADEC system (Full Authority Digital Engine Control) System to meet the T625 specific requirements.

Under the Prototype Phase, Turkish Aerospace will manufacture four prototypes for flight and ground tests, and to power these helicopters 10 CTS800-4AT turboshaft engines have been ordered from the Light Helicopter Turbine Engine Company (LHTEC, a 50-50 partnership between Honeywell and Rolls-Royce) under a contract signed on 10 December 2015 between TUSAS and LHTEC. According to Honeywell, as of May 2019 six of these 10 CTS800-4AT engines have already been delivered and the remaining four engines (expected to be used as spares and for ground testing purposes) are scheduled to be delivered during 2019. 

The T625 GÖKBEY TLUH will initially be certified by Turkish Directorate General of Civil aviation (SHGM) & European Aviation Safety Authority (EASA) and then converted with the installation of related mission equipment for Turkish military use to replace the aging AB-205s and UH-1H Hueys. A military version of the T625 GÖKBEY will follow about two years after the first flight. Certification and qualification efforts have been started in 2018 and scheduled to be completed in 2020. Serial production of T625 GÖKBEY TLUH is also expected to start in 2021.

The production of T625 GÖKBEY helicopters are initially expected to be powered by a pair of LHTEC CTS800-4AT turboshaft engines, but once all tests are complete and the required certification is obtained, the serially produced T625 GÖKBEY helicopters will start flying with indigenous TS1400 engines (in 2024-2025 timeframe), which are being developed domestically by TUSAS Engine Industries Inc. (TEI) under the Turboshaft Engine Development Project (TEDP). The TS1400 Turboshaft Engine can also be integrated into the T129 Mk-I ATAK Helicopter with some adaptations.

On February 7, 2017 TEI was awarded a contract by the SSB under the Turboshaft Engine Development Project to develop Turkey’s first indigenous turboshaft engine to power the T625 GÖKBEY TLUH. Under the eight-year (2 years for the development of the turbojet core + 4.5-years for the prototype manufacture + 1.5 years for certification) schedule TEI is to design, develop, produce and certify two 1,400 shp turboshaft engines (TS1400, ITAR-free) prototypes with a team of 250 engineers. The preliminary prototype of the turbojet core to be used on the TS1400 engine which was successfully tested for the first time on a test bench on 11 June 2018. The test cell, where the TS1400 Core Engine Tests are being conducted, was designed, manufactured and made ready for use with fully domestic achievement in cooperation with the 1st Air Maintenance Factory Directorate and TEI.

According to the information we have obtained, 12 to 14 TS1400 prototypes will be produced by TEI under the 8-year Turboshaft Engine Development Project including the core engine prototypes. 

During the Concept Development Phase of the TEI TS1400 Engine, 10 different engine models were examined and the centrifugal (radial) flow compressor design, which is more suitable for the turbocharger, was adopted. Axial compressors, on the other hand, are generally preferred for turbojet engine designs. For example, the Kale ArGe Company product KTJ-3200 Engine, and the French Safran Power Units’ (formerly Microturbo) TR-40 Turbojet Engine features four-stage axial compressors. With the centrifugal design, higher mass flow rates can be obtained in narrower spaces (shorter engine length), however, the centrifugal compressor design requires larger engine diameter than the axial compressor design. The axial flow compressor engines are smaller in diameter, but they are notably longer. Centrifugal compressor engines are considered more robust and stable, while engines with axial compressors are more fuel-efficient than the centrifugal compressor engines. Since the aim of the TS1400 design is to develop a turboshaft engine rather than a turbojet engine, a centrifugal flow compressor design was chosen because the shaft power is more important than the propulsive power (thrust).

The TS1400 Engine consists of a two-stage Centrifugal/Radial Compressor, a Reverse-Flow Combustion Chamber (Combustor), a two-stage High-Pressure Turbine (HPT) and a two-stage Power Turbine (PT). The 2nd core engine prototype in turbojet configuration, which was previously exhibited at IDEF 2019 as well as at the Istanbul Air Show (AIREX) and at the 4th High-Tech Port by MUSIAD in 2018, has an exhaust vent at the rear section instead of a Power Turbine. Power Turbines are required for the transition of the core engine in turbojet configuration to both turboshaft and turboprop configuration. 

The turboprop version of the TS1400 Turboshaft Engine is planned to power TUSAS HURKUS-B/C aircraft. In the turbojet configuration of the TS1400, the core engine can also be converted to turbofan configuration by adding a fan and additional shafts and bearings to the front side and a power turbine to the rear side. Turbofan engines have 30% to 40% lower fuel consumption rates compared to the turbojet engines; however, their production is more difficult, and their unit costs are more expensive than turbojet engines. For example, the unit price of an F107-WR-402 turbofan engine is US$190,000, while the unit price of a turbojet engine in similar class/thrust rates is around US$100,000. 

Among the main purposes of the Turboshaft Engine Development Project (TEDP) is the establishment of a gas turbine engine design and the development of infrastructure and the knowledge to facilitate such a development process. Thus, the core technology of the TS1400 Engine shall also form the basis for the indigenous turbofan engine (in 8,500lbf to 9,500lbf thrust class) needed for the HURJET New Generation Advanced Jet Trainer (AJT) & the Light Attack Aircraft Development Project, and it will be possible to develop the national aircraft engine when needed, upon any necessary technological additions to the capabilities gained under the TEDP. 

However, the TS1400 engine, which prefers a two-stage centrifugal compressor like the LHTEC CTS800-4AT engine with a high-level weight and volume optimization, requires axial (front) air intake assembly changes that are necessary for a turbofan engine design. Although extremely suitable for turboprop (TP) or turboshaft (TS) engines, the two-stage centrifugal compressor architecture has some disadvantages in terms of the cross-sectional area due to both the bypass ratio (the ratio of the air that goes through the core, i.e. the capacity) as well as the placement of the radial air assembly and the combustion chamber. The TS1400 is anticipated to be developed further with a multi-stage axial flow compressor and then a single-stage centrifugal compressor assembly to be able to evolve into a high-performance, low-thrust turbofan (TF) engine.  Announced by TUSAS General Manager Dr. Temel KOTİL during the IDEF ‘19 Fair for the first time, the indigenous 2,500-3,000 shp turboshaft engine, which will power the T129 Mk-II (ATAK-II) Heavy Attack Helicopters, can be expected in a similar configuration. 

According to TEI, the TS1400 Engine has a more robust design thanks to the centrifugal compressor assembly. It allows the air to flow through the core from front to top, not from front to back, creating more efficient negative and positive pressures. Under the TEDP, TEI has been able to effectively produce TS1400 core engine prototypes within two years following the contract and plans to perform the first flight test on the T625 GÖKBEY helicopter in 2021.

Although the contract was signed in February 2017, the history of TEI’s knowledge and infrastructure accumulation for the TS1400 engine goes back to the Core Engine Technology Development Project that was launched in July 2012 with a 3-year schedule. The aim of the project was to develop core engine technology, which would form the basis for a 1,000 hp class turboshaft engine. Under the project, conceptual design software & methodologies for the indigenous compressor, combustion chamber, and turbine were developed by studying different engine architectural concepts. The detailed design studies on the TS1400 started in 2016. The oil lubricated TS1400 engine also features an indigenous FADEC System. The two TS1400 engines on the T625 GÖKBEY will be able to communicate with each other via FADEC. For example, if an engine experiences power loss during the flight, the other engine will be able to increase its power to compensate the lost power of the other engine. The standard engine power of the TS1400 will be 1,400 shp (shaft horsepower) but it will also have the capacity to produce 1,660 shp for a period of 30 seconds in an emergency, such as in the case of the loss of another engine. 

The TEI TS1400 engine is expected to have similar dimensions and weight with the LHTEC CTS800-4A/4AT Turboshaft Engines, which have a reputation for compactness, light weight, reliability, power and durability. In open sources, the dry weight of the LHTEC CTS800-4A Engine (with a length of 86,4 cm and height of 72,9 cm) is stated to be 360 lbs. (163 kg). According to the EASA Type Certification Data Sheet the CTS800-4N version, featuring a reduction gearbox compared to the CTS800-4A/AT versions, with an overall length of 122,2 cm overall width of 60 cm and overall height of 72,9 cm has a dry weight of 408 lbs (185,1 kg). The TS1400 Engine will ensure the shaft output speed conditions of 23,000 rpm and have a service ceiling of 20,000 ft. The process which starts from the engine right through to shutting it off again is known as a cycle, and over the engine’s lifetime there are only a finite number of cycles before something cracks or breaks. The conventional methodology for measuring this lifespan and one that’s used by many engine manufacturers is known as the TAC (Total Accumulated Cycles). One TAC is the equivalent of one cycle of an engine (exactly: one excursion from engine start, passing intermediate power rating and back to engine stop). The average lifespan of the TS1400 is expected to be at least 2,500 cycles, while the target for the service life is 5,000 cycles (TAC). After 2,500 or 5,000 cycles the TS1400 will require a general overhaul.

A team of approximately 250 engineers, all of whom are TEI employees from TEI’s Eskişehir, Ankara and Istanbul Engineering Offices, are involved in the project. The TS1400 turboshaft engine design team includes engineers from the fields of Aerothermal Engineering, Structural Engineering, Product Engineering, Prototype Testing, Electrical/Electronic & Control Engineering, and Embedded Systems Engineering. 

TS 1400 for T129 Mk-I ATAK Helicopters

The TEI TS1400 Turboshaft Engine can also be integrated into T129 Mk-I ATAK Helicopter with some adaptations to replace LHTEC CTS800-4A Engines for which Turkey has been experiencing difficulties for several years in obtaining an export license from the U.S. Government. In 2015 Turkey had finalized negotiations with Turkmenistan for the sale of 2 T129 Mk-I ATAK Helicopters however since the U.S. Government did not provide the export license for the LHTEC CTS800-4A Engines this project was not realized. A similar problem is being experienced for the sale of the T129 Mk-Is to Pakistan. Turkey has been waiting for more than a year for the U.S. export license in order to proceed with the Pakistan T129B Mk-I deal. 

The contract for the sale of 30 T129B Mk-I ATAK Light Attack and Tactical Reconnaissance Helicopters to Pakistan Land Forces was signed on 16 May 2018, yet it has not become effective as of June 2019. Official application to the U.S. Government regarding the export license of the LHTEC CTS800-4A Turboshaft Engine utilized on the helicopter was made, the process was completed with the Foreign Affairs Commission and the request was submitted to the U.S. Department of Defence. The approval process was still underway as of May 2019. Turkish Aerospace previously received the Original License Document from the U.S. Government for the sale/export of the T129B to Pakistan. The Philippine Air Force is another customer for the T129B Mk-I Helicopter. On 18 December 2018, a MoU for Defence Industrial Cooperation between Turkey and the Philippines was signed between the SSB’s Prof. Ismail DEMIR and Philippine Secretary of National Defence Delfin N. LORENZANA at Villamor Air Base in Manila. This MoU will pave the way for cooperation between the two countries in the field of the defence industry and the sale of the Turkish Defence and Aerospace Industry products (including the T129) to the Philippines. The Philippine Air Force will procure 6 (+10 optional) T129 Mk-I Helicopters if the necessary export license for the T129B Mk-I will be received from the U. S. Government.

Even though negative feedback is not expected from the U.S. Government regarding the export license of the CTS800-4A Turboshaft Engine, negotiations with the French Safran Group are being conducted on alternative engine options as a Plan-B. The Safran Helicopter Engine currently has two turboshaft engines which are 1,400 shp class, for twin-engine helicopters in its product portfolio and the company plans to get EASA certification for both of them in 2019. The Ardiden 1H1/Shakti, which powers the twin-engine Dhruv and LCH (Light Combat Helicopter) from India’s Hindustan Aeronautics Limited (HAL) is designed to produce 1,430 shp. With a power range of 1,100 shp to 1,400 shp the Arrano 1A Turboshaft Engine was selected by Airbus Helicopters in early 2015, as sole engine for its new twin-engine helicopter H160, in part, on its ability to deliver extra power when operating in hot-and-high conditions. The Arrano 1A has a dry weight of over 300 kg and features a two-stage Centrifugal Compressor, Reverse-Flow Combustion Chamber, Variable Inlet Guided Vanes, 4th Generation FADEC and a 3D-Printed Fuel Injector. According to Safran Helicopter Engines, depending on the mission, the Arrano 1A Engine can fly almost 5,000 hours before needing a general overhaul (Depot Level Maintenance). Since its first ground test in February 2014, more than 10 test engines have been running at Bordes (France) to demonstrate engine performance. The Arrano-powered H160 (PT2 prototype) made its first flight on 27 January 2016. As of February 2019, the Arrano 1A Engines accumulated more than 7,000 test hours, including 1,100 hours in flight.

Previously, within the scope of the tender that was launched by the SSB in 2014 to meet the engine requirement of the TLUH (both civil and military versions) prototypes, Turbomeca (now Safran Helicopter Engines) competed with LHTEC and had proposed the Arrano Engine. At that time the company had underlined that it was designed for both civil and military rotorcraft and that the Arrano Engine was 100 % ITAR Free and would be civil certified. At that time civil certification (EASA) for the Arrano Engine was planned to be obtained in 2017. Yet, the winner of the tender, which was finalized in April 2015, was LHTEC with their CTS800-4AT Engine.

The Benchmark of T625 GÖKBEY & H160

The T625 GÖKBEY shares several similarities with Airbus Helicopters’ H160 Helicopter. Both of them are medium weight, in twin-engine configuration (powered by a pair of 1,400 shp class turboshafts) utility helicopters and will both have civil and military versions.

The H160 Program of the Airbus Helicopters was launched at Heli Expo in 2015 under the prototype name X6. Airbus Helicopters currently operate three dedicated prototypes (PT1, PT2 and PT3) and two helicopter zero integration test means under the H160 Program and plans to obtain EASA certification by the end of 2019 with an expectation to start deliveries to their launch customer, Babcock, in 2020. About 1,500 flight hours will likely be recorded by the time the aircraft is certified by the EASA. Airbus Helicopters secured 15 sales of this type in 2018.

The H160 has a Fenestron shrouded tail rotor and is powered by twin Safran Helicopter Engines Arrano 1A turboshafts. As of February 2019, the three flight-test prototypes have accumulated over 1,100 hours in the air including customer demonstrations. The first flight-test prototype (PT1) performed its 40-minute maiden flight on 13 June 2015, powered by a pair of Arrano 1A Engines.  The second prototype (PT2), which performed its first ground run on 18 December 2015, joined the flight test program on 26 January 2016. The third H160 prototype (PT3) performed its maiden flight in October 2017. The first serially produced H160, which made its first flight in December 2018, was deployed to Northern Finland in February 2019 for cold-weather tests.

The H160 will have a certified mass of 5,670 kg (12,500 lbs.) for take-off but a flight manual supplement has been drafted to allow operators who wish to have a maximum takeoff weight of 6,050 kg (13,338 lbs.) without significant operational limitations.

While the military version of the H160 — the H160M — has been chosen as the platform for the French military’s tri-service Joint Light Helicopter (Hélicoptère Interarmées Léger/HIL) Program, which has an initial requirement for 169 helicopters (80 for the Army, 49 for the Navy, and 40 for the Air Force). On May 2019 the H160M was designated as Guépard (Cheetah) and French Minister of the Armed Forces, Florence PARLY, announced that the launch of the HIL Program has been brought forward to 2021. Under the HIL Program, for which Airbus Helicopters’ H160M was selected in 2017, was initially scheduled for launch in 2022. The H160M Guépard Helicopter will enter French military service in 2026. The full-scale mock-up of the H160M Helicopter was presented at the French Ministry of the Armed Forces stand at the Paris Air Show 2019. The H160M will replace 5 legacy types (Fennec, Gazelle, Dauphin/Panther, Lynx and Puma/Super Puma) in the French Army (to replace Fennec, Gazelle and Puma), Navy (to replace Dauphin, Panther and Lynx) and Air Force (to replace Fennec and Super Puma). The H160M can carry 5 fully equipped commandos in addition to 2 pilots and in SAR configuration 2 stretchers and 5 passengers in addition to 2 pilots