Aeronautics and astronautics – Aircraft power plants
Reexamination Certificate
1999-10-28
2001-09-18
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Aircraft power plants
C244S129100, C060S322000
Reexamination Certificate
active
06290173
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT
Not Applicable
BACKGROUND OF THE INVENTION
1. Fields of the Invention
The present invention relates generally to apparatuses and methods of preventing cracks and leaks in engine exhaust systems in vehicles, and, more particularly, to a bellows assembly for preventing cracks in the exhaust stack or shroud of an aircraft.
2. Discussion of Background and Prior Art
Shown in
FIGS. 1
,
2
is a small passenger aircraft
10
with dual turbo-prop engines
11
,
12
, such as the King Air 200 and B200 family of aircraft made by Raytheon. A typical turbo-prop engine
20
receives outside air in an air inlet
21
leading to a 3-stage axial flow compressor
22
which sends compressed air to a centrifugal compressor
23
. The highly compressed air is then mixed with fuel and burned in the combustion chamber
24
the exhaust gases from which are accelerated through the nozzles of a compressor turbine
24
and then are finally expanded through the nozzles of a free power turbine
26
which drives a high speed shaft
27
which, after reduction of the shaft rpm in a gear box
28
, drives the propeller shaft
29
and propeller, while the spent gases are exhausted through exhaust outlets
30
to the engine exhaust stacks
42
,
54
(FIG.
3
).
Most OEM aircraft in the King Air 200 class come with an air inlet anti ice system, and the King Air 200 is no exception. In a typical aircraft, the original inlet anti-ice system included a pair of pick up tubes
44
(
FIGS. 7
,
8
), one each (right and left, relative to the nose of the aircraft looking forward) connected between an exhaust stack
42
,
54
adjacent the engine nacelle
32
and an air frame heater duct
74
,
82
in the lower engine cowling
71
. Each pick up tube
44
(
FIGS. 7-12
) is bent about 80° (FIG.
9
), has an upper end
50
,
66
welded around a hole in the stack wall and is fluidly coupled to a scupper portion
46
,
58
mounted inside the stack
42
,
54
, the open end
48
,
60
of which faces upstream relative to the exiting exhaust gases, thereby receiving and directing some exhaust gas forwardly through the elongated portion
45
,
64
of each tube
44
through the lower end
52
,
68
of the tube which is slip joint
84
fastened
87
,
88
,
89
via donut
85
and duct flange
86
(
FIG. 5
) to the airframe ducts
74
,
82
. Ducts
74
,
82
are part of the inlet
77
anti-ice system of each engine and direct the hot exhaust gases through ducts
76
which terminate at splitter vanes
78
which dump the spent exhaust gases to the atmosphere through the opening
80
in exhaust outlet plate
79
in the airframe skin at the bottom of the lower cowling
71
.
One problem with this design is that soot accumulated on the lower surface of the cowling and the underside of the wing. Accordingly, it is an object of the present invention to provide an inlet anti-icing system that eliminates the accumulation of exhaust gas soot inside the cowling and on the exterior skin of the aircraft.
Another problem with this original design was the possibility of exhaust stack cracking. Significant engine vibrations in the X, Y and Z directions, such as during start-up, shut-down, taxiing, take-off, landing, rapid throttle movements, turbulent air conditions, certain sustained engine operating conditions, and the like, and also as a result of repeated expansion and contraction resulting from the combination of extreme weather and operational temperature conditions, place a large amount of stress on the welded connection between the elongated pick up tubes
44
and the stack
42
,
54
walls at the point of attachment. This stress has resulted in the cracking of the pick up tube to stack welded connection allowing further hot exhaust gases and soot to escape into the space between the exterior wall of the stack and the engine cowling creating a potential fire hazard and a dirty, unsightly appearance throughout the entire main engine compartments.
Accordingly it is a further object of the present invention to provide an inlet a anti-icing system that eliminates the cracking of exhaust stacks and associated couplings and the further accumulation of exhaust gas soot inside the entire engine cowling and main engine compartments.
A subsequent prior art system has only partially solved the above described problems. As shown in
FIG. 13
, this prior system modifies the inlet
77
anti-ice system to make it a flow through system in which exiting exhaust gases are picked up on the right side, as in the prior system, but are directed through the hot lip duct in one direction to the left side of the engine where they exit to atmosphere through the left exhaust stack, requiring modifications to the left side scupper, both pick up tubes and the lower cowling discharge area. The modifications made by this prior art system are shown in
FIGS. 13-20
, as explained in greater detail below.
In the modified prior art flow through inlet anti-ice system, the pick up tubes
44
are replaced by a pick up nipple
102
on the right side and exit nipple
124
on the left side. The right scupper
48
remains with its opening facing upstream creating a positive inlet pressure at that end of the system, while the left scupper
58
open face
60
is reversed to point downstream relative to the exhaust gases creating a suction at that end of the system. (FIGS.
16
-
20
). The splitter vanes
78
in the hot lip are removed and blocker dams
126
are installed blocking the old exhaust outlets, leaving duct
76
as a single continuous sealed duct. Cover plate
128
replaces the prior plate
79
completely sealing the lower cowling area from the exhaust gases. Hose assemblies
104
,
114
replace pick up tubes
44
. Each hose assembly
104
,
114
includes a curved tube having a slot
106
,
120
in one end that fits over and is clamped
108
,
122
to the stack nipple
102
,
124
and a flange
112
,
116
at the lower end that is fixedly bolted to a gasketed
113
,
115
airframe duct flange
74
,
82
.
To relieve stress in the rigid connections between the engine, stack, nipple, hose and heater duct, the central portion of each hose body is roughly bent at about 70° and is formed with a plurality of outwardly extending convolutions
110
,
118
which allow the body to flex like a bellows and dampen the engine vibrations previously described. However, in practice while the above solution has relieved the lower cowling problem, the main engine compartment problem previously described has not been solved because the flex in the bellows body itself has been proven to be insufficient to prevent the continued cracking at the nipple-stack welded joints due to the oftentimes severe engine movements in the X, Y, and Z directions. Accordingly, as previously stated, it is an object of the present invention to prevent the cracking of the stacks due to such engine movements.
In view of the failed prior attempts there is a long felt need for and it is an object of the present invention to provide a satisfactory hot inlet lip anti-ice system for small twin turboprop aircraft.
BRIEF SUMMARY OF THE INVENTION
Set forth below is a brief summary of the invention which achieves the foregoing and other objects and provides the foregoing and hereafter stated benefits and advantages in accordance with the structure, function and results of the present invention as embodied and broadly described herein. Applicant's invention includes independently both the apparatus and the methods described herein which achieve the objects and benefits of the present invention. Both formats of the invention are described below and claimed below, and it is applicant's intention to claim both formats even though from time to time below for purposes of clarity and brevity applicant will use either one or the other format to describe various aspects and features of the invention.
One aspect of the invention is in the method of preventing cracks in an aircraft engine stack at or near the stack
Barefoot Galen L.
Commuter Air Technology, Inc.
Lisa Donald J.
LandOfFree
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