Rigging the PW2000
Introduced in 1983 for the Boeing 757, the PW2000 is a two-spool, 37,000- to 43,000-pound engine, which has been also applied to military C-32 (757 military equivalent) and C-17 aircraft, as well as the Ilyushin wide-body IL-96M and T passenger and cargo aircraft. The PW2000 is adaptable to any 757 model of aircraft.
Pratt has made a few changes to the PW2000 over the years with a Reduced Temperature Configuration (RTC) offering in 1994, and the PW2043 43,000-pound-of-thrust version, most recently. The RTC version offers improved reliability and durability for long on-wing times and the PW2043 offers the ability to be used on 757 models from the -200 to the -300.
As with any modern jet engine, there is going to be the need to perform some rigging of engine bleeds and variable vane and stator controls.
These tasks may appear difficult, especially if mechanics don't understand the principles of rigging, or don't understand what it is they're trying to accomplish. One mistake can mean that the engine will run poorly or inefficiently. Careful planning and follow-through of all rigging procedures can produce positive results with minimal headaches.
Rigging is required infrequently, but is needed when actuators, brackets, linkage, or other components are changed or damaged or when engine performance problems are noted.
On a PW2000 engine, there are only three areas where rigging is required, explains Norm Jeche, Technical Instructor at Pratt & Whitney's East Hartford Customer Training facility, the Stator Vane Actuator (SVA) assembly, P2.5 bleed ring, and the TCA bleed valves.
VSGVs and VIGVs
The PW2000 engine uses both variable stator guide vanes (VSGVs) and variable inlet guide vanes (VIGVs) to help improve the efficiency of the high compressor. It does this by regulating the volume of air flowing through the engine. According to Jeche, of all the rigging required on this engine, the rigging procedure for these vanes is probably the most critical for satisfactory engine performance.
"Unfortunately this procedure is all to often misunderstood and not followed correctly," Jeche says. "Most of the rigging errors are a result of lack of understanding, using the wrong rigging pins, or using the pins in an incorrect manner."
He continues, "Some mechanics try to line up the rigging holes by sight, or substitute an improper tool for performing the alignment of the rig and check pins. Stator guide vane positioning is very critical and can affect engine performance by being only a few thousandths off. Even using damaged, bent, or worn rig pins can result in rigging errors. The tooling or rig pins used to perform the procedure need to be in good condition in order to conduct the procedure properly."
The first step in performing this procedure is to make sure you have the correct rigging pins and that they are in good condition. "If the rigging pins show signs of being bent or have ridges, scratches, or other damage," Jeche adds, "replace them with new pins immediately."
The stator vane actuator (SVA) is controlled by a torque motor located in the fuel control, which is in turn controlled by the electronic engine control (EEC). The torque motor basically sends fuel to either side of a hydraulic ram in the stator vane actuator system, which in turn moves the unison rings, which then changes the angle of the SGVs and VIGVs.
In order to perform any rigging, you must be able to manipulate the actuator and the bellcrank assembly. There are two methods of actuating the bellcrank. One is to use a hydraulic pump unit and apply hydraulic pressure to the actuator, and the other is to simply use a wrench on one of the flats of the bellcrank. If you use the wrench method, it's important to use a torque wrench and not to exceed 300 inch-pounds of force. Exceeding this value can damage the bellcrank or linkage. You also want to make sure the wrench is on the flat that is near the bellcrank center bearing. If you use other bellcrank surfaces to turn it, you may twist the actuator and damage may occur.
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