The Walter GE M601 turboprop engine and its variants were initially designed for the Let L-410 Turbolet commercial transport and cargo aircraft, dating back to the 60's. The L-410 was designed and built by the Czechoslovak aircraft manufacturer Let Kunovice. The M601 was designed and built at Walter Aircraft Engines, also in the Czech Republic
The M601 engine is reverse flow engine. It has two independent parts: the gas generator and the power part. The gas generator and free turbine shafts are arranged in a tandem layout. Air enters the engine in the rear part, flows forward through the compressor, combustion chamber and turbines and exits through exhaust nozzles near the front of the engine.
Air enters the compressor in a radial direction through a protecting screen and annular plenum to the first stage axial compressor. This compressor consists of two axial stages followed by one centrifugal compressor stage. The combustor chamber is a annular configuration with a low maintenance combustor and fuel distribution system.
During operation, part of the air flow is directed through a flame tube through the perforations in the wall, the remainder passes through the hollow nozzle guide vanes of the gas generator turbine. The fuel is atomized by a special spray ring rotating with the gas generator shaft. A single stage gas generator turbine drives the compressor section through a direct drive shaft. The interturbine temperature (ITT) is measured by 9 thermocouples installed in the flow path at the gas generator turbine outlet.
A tip shrouded single stage axial-flow power turbine drives the propeller through a two stage countershaft reduction gearbox. The reduction gearbox embodies an internal torquemeter which provides a signal to the cockpit installed torque or power indication instruments. The exhaust gases from the power turbine pass through an annular plenum to the atmosphere via two exhaust nozzles. The high velocity and high temperature exhaust gases provide additional jet thrust adding to performance.
Fuel and Starting System
The engine has a low pressure fuel system with an engine driven geared fuel pump. The engine is started by an electric starter/generator. Two torch igniters provide the initial flame for starting.
The oil system is an internal pressure system with an integral oil tank incorporated in the accessory gearbox. It provides lubrication and cooling for bearings and many internal areas of the engine. The engine oil is also used for the torque indication system and propeller governor operation.
Engine Limiter Systems
The engine is equipped with limiters that prevent overheating and overspeeding during starting and reverse thrust operating conditions. The limiters indicate the exceedence of permitted operating parameters of temperature, torque, engine rpm of the gas generator and propeller.
The operation is managed through three cockpit levers. One controls the engine shaft power during positive and reverse propeller blade angle operations. One lever actuates the fuel shut-off valve and if an emergency circuit is on, controls the engine power. The third lever controls the propeller rotation speed and provides emergency feathering and engine shutdown.
The calendar life of M601's is currently 8yrs. Engines can be operated to this limit using field inspection processes defined in the engine maintenance manual. Two mandatory inspections are necessary at the 5th and 7th year of operation. The first inspection after 5yrs extends the calendar life of the engine by 2yrs and the inspection at 7th year extends the calendar life by 1 more year.
These inspections include borescopic inspection of internal parts, replacement of o-rings and other rubber parts, performance and operational checks. The inspection requires only a few man hours by a GE qualified technician and is accomplished with the engine installed on the aircraft.. The calendar limit is then extended by a logbook entry noting approval to continue the engine in service. The logbook shows the calendar life until the next inspection or overhaul.
Legitimate engine overhauls for can only be performed by GE Czech SRO in Prague, or through authorised repair facilities. Major repairs can be done in the US by certified repair facitlities, and general planned inspections and other routine engine work can be done by Authorized Service Centers who employ technicians with proper training.
Other line maintenance is provided by GE a.s. European staff, by the staff at GE or GE Russia. Heavy maintenance up to and including shop revision can be accomplished by GE Overhaul requires the engine to be returned to the GE shop in Czech Republic.
Expired Walter GE M601-B's and M601-D's are available for a low acquisition cost; in some parts, they are abundant - but not for without reason. The cost to replenish a TBO on these turboprop engines is substantial and often makes no sense economically.
However, if you're building an experimental turboprop aircraft and are looking for a sensibly priced engine with at least an 750hr TBO, then read on.
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