Tayyar MTH-3 Ra'ad

MTH-3 Ra'ad
Type	Low-bypass turbofan
National origin	Riysa
Manufacturer	Tayyar Engine Design Bureau
First run	1978
Major applications	TaH-26 Saika
Status	In production
Produced	1984 - Present

The Tayyar MTH-3 "Ra'ad" (رعد, Thunder) is a Riysian triple-spool low-bypass afterburning turbofan engine, designed by Tayyar to power the TaH-26B deep modernization of the TaH-26 Saika interceptor. It was first flown on a TaH-26A testbed in 1978, and entered full scale production in 1984. Uniquely, it is the only Riysian triple-spool fighter engine, the only triple-spool engine designed by Tayyar, and one of only a few turbofan engines designed for high-altitude supersonic performance.

History

Development of the Ra'ad started in 1975, shortly after the TaH-26A, with its older Tayyar MTH-Kh turbojet engines, had entered service. The MTH-Kh provided superb high-altitude and high-speed performance, allowing the TaH-26 to exceed Mach 3 in ideal conditions, but was overly optimized for that role, leading to extremely poor low-level efficiency and power.

Design

The MTH-3 Ra'ad is a triple-spool turbofan with a relatively high bypass ratio - for a fighter engine - of 0.54, featuring a single-stage low-pressure compressor, six-stage intermediate compressor, annular combustor, single high-pressure turbine, single intermediate-pressure turbine, twin-stage low-pressure turbine, and an afterburner section. It is split into seven field-serviceable modules; consisting of the low-pressure compressor and VIGVs, the intermediate compressor, the "core" of the high-pressure compressor and turbine sections, the bypass air mixer, the afterburner stage, the jet nozzle, and the engine assembly.

Unique to the Ra'ad among fighter turbofans, is that it acts as a sort of turbofan-ramjet hybrid at high altitude and speed, in conjunction with the TaH-26B's variable inlets. At speeds of above Mach 1.5, the airflow into the compressor becomes partially supersonic, massively increasing the pressure ratio of the engine, as well as the bypass ramjet air. Airflow into the compressor is pre-cooled as with the preceding MTH-Kh, . Variable stators are opened and air is bled from the hot core as , such that the majority of the thrust at high speed is generated from the ram airflow, like a ramjet.

Many of the design choices that improve its fuel efficiency and low-altitude profile also contribute to its high-speed performance. A large bypass ratio of 0.54 not only reduces fuel consumption in subsonic flight, but is cooler than a comparable turbojet, and also maximizes ram airflow during supersonic flight.

Due to its specialized features, the thrust output approximately doubles at 20,000 meters and Mach 2.6 compared to sea level, and rapidly increases until its exceeds Mach 3, while fuel consumption drops, a feat not possible by almost any other Riysian turbofan engine. At the same time, it remains efficient at low altitudes and provides high thrust at all flight regimes. Thanks to its turbofan assembly and FADEC control, it does not suffer from runaway acceleration at those speeds like its MTH-Kh predecessor, and is more controllable at all speeds and altitudes. However,