Figure 6-10.-Turbine impingement starting system flow schematic.
BLEED-AIR SYSTEMS (ENGINE)
It is important to understand what is meant
Hydraulic starters, like electrical starters, are
by bleed air and where bleed air comes from.
energy-limited starting systems. Energy-limited
Bleed air is tapped off of pressurized air from the
starting systems are designed to start the engine
in a short time period, and are limited to small
configurations, the air is bled from more than one
engines. They make ideal starters for auxiliary
area of the compressor. This design gives a source
power units (APUs).
for high- and low-pressure air to suit whatever
requirements a particular system may have. Other
Components include a high-pressure accumu-
engines have only one source of bleed air available
lator and a variable displacement motor.
from each engine. That source is often tapped
The variable displacement motor permits high
from the last stage of compression on each engine.
torque to be applied without exceeding cut-
off speed limits. A small electric motor or
The engine has a number of different uses for
hand pump charges the accumulator. The
the air pressure it generates while operating.
accumulator then supplies power to the starter.