Services PT6 Engine-PT6A Engine Operating Parameters

The PT6A engine is a free turbine engine and is also one of the main variants of the PT6 engine. We all wish that was an economic statement instead of a description of a type of compressor / propeller relationship.

The free turbine compressor is designed to offer the necessary compressed air to the hot section of a PT6A engine for use in fuel-air mixture/combustion and cooling. The compressor’s speed in Revolutions Per Minute (RPM) is controlled by hot gases flowing through the compressor turbine vane ring and power turbine vane ring. These vanes have a specified class number which shows their ability to flow these gases. These class sizes and the condition of the compressor itself figure out the speed of the compressor of PT6A at any given power setting. The class size range for a particular engine is determined by the manufacturer’s technological innovation. The speed of a gas generator is set or fixed to limits during engine overhaul testing or at engine manufacturer. The compressor delivers sufficient air pressure for cooling and combustion to allow the engine to develop the required horsepower/torque.

Since this free turbine compressor is not connected mechanically to the propeller through the power section, what happens when it gets dirty or damaged by foreign objects. The damage or contamination reduces the compressor’s efficiency and results in a higher gas generator speed for the same power setting. The pilot is targeting on Torque and RPM when he applies power. The decreased efficiency of the gas generator will result in the engine requiring more fuel to obtain the same torque and RPM. This implies greater fuel flow, greater temperature and greater gas generator speed for any given power setting. The all three of these parameters are up. The Maintenance Manual identifies this condition as indicating a Cold Section Problem.

Hot weather will result in faster gas generator speeds due to the reduced air density at high temperatures. Assume your engine’s NG speeds have crept up to just beyond the Red Line and a compressor Performance Recovery Wash did not restore the previous settings. Now, you are retarding the throttle at taking off to keep from over-speeding the gas generator. This outcome in less power available, not a good circumstance in the middle of an AG spray season.

The Maintenance Manual cautions to install the same class size vanes when replacing compressor turbine or power turbine vanes. The airflow specifications on these vanes for any PT6 engine are determined and tested in the test cell. Before deciding to re-class an engine on-wing, all possibilities for repair should be exhausted because of recognized inadequate efficiency. All aircraft Gages, such as the gas generator speed indicator should be adjusted before any attempt to re-class an engine. We have corrected at least four performance problems in the last eighteen months by replacing defective gas generator gages. In one of the instances, an engine had already been pulled and sent to the manufacturer, examined and performance-certified before the gage was questioned. Always do the cheap things first when troubleshooting.

For more detail visit here @ www.utpparts.com.

We provide sales and exchanges on a wide variety of engine models and on serviceable turbine engine parts. For example, PT6 engine parts like PT6A-20, PT6 A-21, PT6 A-27, PT6 A-28, PT6 A-34, PT6 A-41, etc.