U.S. Navy and Marine Corps pilots fly fixed-wing aircraft that are turbine powered, some by internal fans and others by external propellers, with engines requiring service and repair often performed at Fleet Readiness Center Southeast (FRCSE). FRCSE is expanding its manufacturing capabilities using technologically advanced equipment, such as vertical and high-speed grinders and precision measuring machines to ensure reliable power to the military’s high-performance aircraft.
Whether turboprop aircraft like the P-3 Orion Maritime Patrol aircraft powered by four Allison T-56-A-14 engines with propellers or the two F414-GE-400 turbofan internal engines that power the F/A-18 Super Hornet attack fighter, they all must be in tiptop shape to support any mission.
Carl Finger, engine machine shop supervisor in the FRCSE Crinkley Engine Facility, said these power plants are staying on the aircraft longer than ever before. He said the engines division has a dedicated machine shop to rework worn parts to like new condition.
“Our new equipment is producing better engine performance, saving time, and giving Warfighters improved mission capability,” said Finger. “The high speed grinding technology integrated with laser measuring creates a more accurate final product.
In a turbine engine, air is pulled into the engine inlet from the fan. It flows into the compressor where the air pressure is stepped up using many rows of blades rotating 400 times per second. Each fan consists of a hub with a set of blades extending outward from the center. The pressurized air enters the combustion section where it is heated to more than 1,000 degrees, mixed with jet fuel and ignited. The hot exhaust passes through the turbine section made up of small blades and vanes attached to a rotor that extracts mechanical energy to turn the fan (compressor) connected by a central shaft.
The remaining energy provides thrust to the engine by increasing the velocity through the nozzle. Thrust is the force that propels the jet through the air. If additional thrust is required, more fuel can be sprayed into the exhaust and ignited if the engine is equipped with an afterburner.
FRCSE purchased two Reform High Speed Blade Tip Grinders, each turn at 3,000 revolutions per minute. Finger said the high-speed technology allows artisans to grind blade tips on the same axis of rotation that the rotors spin to simulate engine conditions. The engine blades must rotate at high speeds to counteract the force of the grinder. The high-speed feature allows the blades to extend fully during the grinding process for better results.
It is essential that engine blades be machined evenly. Unbalanced grinding can make a blade heavier on one side than on the other, which can lead to heavy vibration, the loosening of internal structural bolts, accelerated engine wear or even failure. The Reform grinder measures every blade at every stage of production with laser technology to ensure grinding accuracy. It generates machining specifications on each serialized part for future engineering purposes.
The machines grind High Pressure Compressor (HPC) rotor blades from a TF34-GE-100 turbofan engine installed on the Air Force A-10 Thunderbolt II and the Navy’s S-3 Viking aircraft. Each aircraft is powered by two engines each capable of producing more than 9,000 pounds of thrust.
In addition, the machine supports the F404-GE-402 engine that powers the F/A-18A-D Hornet with 17,700 pounds of static thrust per engine, and the F414-GE-400 turbofan engines that power the Super Hornet and the EA-18G Growler Airborne Electronic Attack aircraft. Each engine is capable of producing 22,000 pounds of static thrust according to the Navy Fact File.
Another technology solution FRCSE is utilizing is the DANOBAT Vertical Grinder to machine stationary engine components like stator cases. It replaces the Pope Grinding Spindle with its outmoded manual dial indicator and the Electronic Run-Out Machine (EROM) used to perform pre and post production measurements.
“I was happy to see that go,” Finger said of the EROM. “It did really good on the rotors, but when we converted to laser measurements it never really worked. It was touchy; it gave us problems.”
The high-precision DANOBAT integrates different machining options for a wide range of engine components. The machine uses touch probes to provide induction measurements thus ensuring parts can be held to diametric tolerances that can be machined. Artisans use the equipment to grind the TF34 HPC forward and aft stator cases, and finish grind stator vanes that enhance airflow into the engine’s compressor.
FRCSE performs out-of-airframe testing on all jet engines repaired at the facility to ensure maximum reliability and performance to the Fleet. The computer-controlled test cells have a thrust capacity of 40,000 pounds and a bed capacity of 100,000 pounds. All engines are tested through their entire operating range in both automated and manual modes to verify oil pressure, exhaust, gas temperature, vibration, speed, and bearing-vent pressure.
Source: Naval Air Systems Command
Date: Aug 23, 2012