it is free to rotate relative to the drive shaft. The relative rotation is due to transmitted torque, and the
phase angle between the reference surfaces is electronically sensed by two pickups, one sensing five teeth
on the reference shaft, the other sensing five teeth on the drive shaft.
Both stages of each turbine nozzle are cast in segments. The third stage has six segments of
six vanes each, and the fourth stage has 10 segments of five vanes each. The static tip shrouds are
replaceable in four segments each and are of open cell honeycomb arrangement.
Figure 10.1 shows the T700-GE-700 bearing and frame arrangement. The four bearings and
shaft arrangement at the front of the axial compressor isolate the driveshaft from the engine.
Circumferential carbon seals are used on the power turbine shaft, and labyrinth seals are used
on the gas generator shaft. The front frame has eighteen deswirl vanes which are part of the structure.
A schematic of the lubricating system is shown in figure 10.3. The oil tank is built into the
inlet particle separator. All scavenge lines have magnetic chip detection for fault isolation. An
emergency lubrication system has been built into the design for assuring continued bearing operation
after loss of oil from any cause. Small oil reservoirs are included in each bearing sump, and are kept full
during normal operation by the oil pressure pumps. Oil is always bleeding out of these reservoirs at a
slow rate. Air jets, also continuous, act as "foggers" for this oil bleed and provide oil mist lubrication at
all times. This continues for at least six minutes even if the oil supply fails. A fuel-oil heat exchange is
a self-contained oil cooler and fuel de-icer.
The engine has been designed for ease of servicing and maintenance. Borescope inspections
can be made in critical areas where sand and dust erosion and clogging, corrosion, and foreign object
damage can occur and in other critical areas where inspections are necessary.