The elements of the exhaust cone assembly
are required for inner cone support, these struts
also form fairings around the rods.
consist of an outer shell or duct, an inner cone,
The centrally located inner cone fits rather
and three or four radial hollow struts or fins. Tie
closely against the rear face of the turbine disc.
rods aid the struts in supporting the inner cone
This fit prevents turbulence of the gases as they
from the outer duct.
leave the turbine wheel. The cone is supported by
The outer shell or duct, made of stainless steel,
is attached to the rear flange of the turbine case.
the radial struts, which are usually vertical and
horizontal in relation to the normal position of
This element collects and delivers the exhaust
the engine. In some configurations, there is a small
gases. The gases flow either directly or through
hole located in the exit tip of the cone (fig. 1-40).
a tailpipe to the jet nozzle, depending on whether
This hole allows cooling air to circulate from the
or not a tailpipe is required. There is no need for
exit end of the cone. The pressure of the gases
a tailpipe in some engines. For instance, the
is relatively high in the interior of the cone and
required engine-installation space in wing roots,
against the face of the turbine wheel. The flow
pods, or wings is short and requires very little
of air is positive, since the air pressure at the
tailpipe. In which case the exhaust duct and ex-
turbine wheel is relatively low due to rotation of
haust nozzle will suffice. The construction of the
the wheel, thus air circulation is assured. The gases
duct includes such features as a predetermined
for cooling the turbine wheel return to the path
number of thermocouple bosses for installing
of flow by passing through the clearance between
exhaust gas temperature thermocouples. Also,
the disc and the cone. The clearance between the
there must be insertion holes for the supporting
tie rods. In some cases, there are no requirements
turbine disc and the inner cone must be checked
periodically since the higher pressures aft tend to
for tie rods for supporting the inner cone from
push the inner cone against the turbine wheel.
the outer duct. If such is the case, the hollow struts
The exhaust cone assembly is the terminating
provide the sole support of the inner cone; the
part of the basic engine. The remaining parts (the
struts being spot-welded in position to the inside
surface of the duct and to the inner cone,
tailpipe and jet nozzle) are usually considered air-
frame parts.
respectively.
The tailpipe pipes the exhaust gases out of the
The radial struts actually have a twofold
airframe. Actually, the tailpipe imposes a penalty
function. They not only support the inner cone
on the operating efficiency of the engine in the
in the exhaust duct, they also perform the
form of heat and duct (friction) losses. These
important function of straightening the swirling
losses materially affect the final velocity of the
exhaust gases, which otherwise would leave the
exhaust gases and, hence, the thrust.
turbine at an angle of about 45 degrees. If tie rods
Figure 1-41.-Exhaust system insulation blanket.
1-28
