Note: Descriptions are shown in the official language in which they were submitted.
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AIR CONTROL MEANS
This invention relates generally to air control
means for gas turbine engines and~ more particularly, to
means for providing air to the hub region of a rotatable
airfoil.
BACKGROUND OF THB INVENTION
Two types of engines currently available to power
aircraft are the turbofan and the turboprop engines.
Common to both engines is a power generating unit. This
unit typically includes a compressor section, a combustor,
and a turbine section in serial flow relationshipO
Pressurized air from the compressor section is mixed with
fuel and burned in the combustor to produce a high
velocity gas stream which expands through the turbine
where en0rgy is extracted. Some of this energy is used to
power the compressor with the remainder powering the ~an
or propeller.
Although temperature increases occur as a result
of the work done in the compressor, the highest
temperatures in the engine are those in the combustor and
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turbine section. Pressurized air for cooling these
components is typically obtained from the compressor,
fan duct, or otherwise drawn in Erom the
atmosphere.
In most turbofan or propeller driven engines,
the fan or propeller is located generally forward
of the core engine. Thus, in such applications, the
hub structure of the blades of such propulsors
operates in a relatively low temperature environment
obviating the need for hub structure cooling.
However, it is known to locate the
propulsor section generally aft of the core engine
in a so-called "pusher" configuration. For example,
Canadian ~pplication Serial No. 438,676, filed
October 7, 1983, Johnson, discloses novel "pusher"
configurations for both turbofan and propeller driven
engines. Because of the close proximity of propulsor
blades to the turbine and combustor in such
configurations, the blade hub structures will, at
certain flight conditions, be subjected to relatively
high heat loads.
The air temperatures in the hub region will
vary depending upon flight conditions. For example,
during periods of relatively high power demand, such as
takeoff, turbine and combustor temperatures are elevated
resulating in higher blade hub structure temperatures.
Lightweight, cost effective materials and variable
pitch blade hub structures frequently have relatively
low temperature limits. Thus, cooling of this hub
structure may be required during such high power
take-off conditions. In contrast, temperatures
stabilize at a lower level during steady state
cruise operating conditions and cooling may not
be required. Since any cooling system will have a
performance penalty associated with its use, it is oE
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interest to activate cooling only when required. Thus~
means for automatically varying the arnount of cooling air
to the hub region of such blades is desired.
BJ~CTS OF THE INVENTION
It is an object of the present invention to
provide a new and improved air control means.
It is a further object of the present invention
to provide a new and improved means of cooling the hub
structure of a propulsor blade.
~nother object of the present invention is to
provide an automatic means of varying the amount of
cooling air to the hub region of a propulsor blade.
SUM~Y OF TH~ INVBNTION
In accordance with the present invention, air
control means are disclosed for use in a gas turbine
engine with a variable pitch rotatable airfoil and means
for varying airfoil pitch~ The air control means comprise
a platform fixedly attached to a radially inner end of the
airfoil. The plat~orm is generally positioned on a
rotatable annular surface, which surface defines outer and
inner spaces. In a first position, an edge portion of the
platform substantially conforms ~o the surface. In a
second position~ the edge portion is displaced radially
outwardly from ~he surface thereby allowing fluid
communication between the outer and inner spaces.
BRI_F D~SCRIPTION OP THE DRAWINGS
FIGUR~ 1 is a view of a pusher type turboprop
engine embodying one form of the present invention.
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FIGURE 2 is a perspective view of rotating
nacelle and blades shown in Figure 1 with blades set at a
coarse pitch.
FIGURE 3 is a view of the hub region of a blade
shown in ~igure Z.
FIGVRE 4 is a perspective view similar to that
shown in ~igure 2 with the blades set at a flat pitch.
FIGUKE S is a view of the hub region of a blade
shown in Figure 4.
DBTAILED DESCRIP'1`ION OF THE INVENTION
This invention may be used in any gas turbine
engine with a variable pitch rotatable airfoil where it is
desired to control air flow through a rotatable annular
surface relative to which the airfoil is positioned. For
means of illwstration, the invention will be described for
a propeller blade on a rotating nacelle.
A pusher type turboprop engine 10 is shown in
Figure l. The embodiment shows counterrotating propeller
blades 12 and 14 positioned relative to counterrotating
surfaces or nacelles 16 and 18, respectively, and
connected ~o counterrotating turbines 2Z and 24. It will
be clear from the following discussion that the present
invention applies eqllally to gas turbine engines with a
single stage of propulsor blades. The counterrotating
configuration is described by way of example only.
Engine 10 includes a gas generator 20 effective
for producing combustion gases which turn counterrotating
turbines 22 and 240 Each turhine 22 and 24 is connected
to rotatable annular surfaces 16 and 18, respectively.
Each blade 12 and 14 has means ~or varying its
pitch so as to improve engine performance during all
phases of operation. Figures 2 and 3 show greater cletail
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of air control means with blades 12 set at a pitch
for cruise condition of engine 10. A generally disk-
shaped platform 26 is fixedly attached to blade 12
by blade shank 2~ forming a portion, or region, of
surfaces 16 and 13. Thus, as blade 12 changes pitch
by rotation about a radial axis 50, platform 16 moves
therewith. Means 30 for varying the pitch of a
rotatable airfoil are well known in the art. For
example, mechanical, hydraulic, pneumatic, or
electrical means are available to provide torque
to hub structure 32 of blade 12 to provide the
necessary actuation force.
Figures 2 and 3 show the platform being
generally positioned in an opening 27 in rotatable
annular surface 16. Surface 16 together with
platEorm 26 define outer and inner spaces 34 and
36. The tempe~ature in space 36 is generally hot
due to its proximity with turbine 22. The temperature
in region 36 will vary depending upon the operation
state of engine 10. For example, turbine 22 operates
at a higher temperature during takeoff conditions
than during steady state cruise operation. In
contrast to the relatively high temperatures in
space 36, space 34 is generally at much lower ambient
temperature.
The air control means of the present invention
provide varying amounts of cooling air to hub
structure 32 depending upon the pitch setting of
blade 12. As shown in Figures 2 and 3, platform 26
has a generally circular cross section when viewed
radially an~ is positioned with respect to rotatable
annular surface 16. In this first position,
platform 26 is substantially conformal with surface 16.
Thus, in the circumferential direction, the surface
at the perimeter of platform 26 generally flows the
contour of surEace 16. In the embodiment shown in
E'igure 2, surface 16 is generally cylindrical. ~owever,
the invention applies equally to conical as well as
non-linearly sloped surfaces.
Figures ~ and 5 show the air control means as
shown in E'igures 2 and 3 with platform 26 rotated with a
change in the pitch of blade 12 to expose edge portion 38
of platform 26. As is evident from the geometry, edge
portion 3~ is displaced radially outward].y from surface 16
which defines an opening 40 therebetween. Opening 40
thereby allows fluid communication between outer space 34
and inner space 36. This allows cooling air 41 to enter
space 36 and cool hub structure 32.
Under steady state cruise power operation of
engine 10, the pitch of blade 12 will be such that plat-
form 26 and edge portion 3~ substantially conform tosurface 16. During takeoff power OperatiQn of engine 10,
blade 12 will be set to a flatter pitch, shown in
Figure 4, thereby exposing edge portion 33 and opening
40. Thus, while opening 40 is substantially closed during
2Q cruise conditions, increased cooling air is available for
those periods of highest engine operating temperatures.
Nacelle 16 rotates in the direction indicated by
arrow 42. Thus, the di.rection of air flow relative to
nacelle 16 due to the rotation of nacelle 16 is shown by
arrow 44. The direction of air over nacelle 16 due to the
forward motion of engine 10 is generally axially aft as
shown by arrow 43. The relative motion of air with
respect to platform 26 is shown by arrow 46, the vector
sum of arrows 43 and 44. It should be clear from the
foregoing that opening 40 is substantially forwad facing
with respect to the direction 46 of the air. This
orientation provides an increase in available source air
total pressure contributing to increased air flow rates
for hub cooling.
It will be clear to those skilled in the art
that the present inver~tion is not llmited to the spec.ific
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embodiments described and illustrated herein. Nor is the
invention limited to air control means tor propeller or
fan type propulsor blades. Rather, the invention applies
equally to air control means for any variable pitch
rotatable airfoil.
It will be understood that the dimensions and
proportional and structural relationships shown in the
drawings are illustrated by way of example only and those
illustrations are not to be taken as the actual dimensions
or proportional structural relationships used in the air
control means of the present invention.
Numerous modifications, variations, and full and
partial equivalents can be undertaken without dep~rting
from the invention as limited only by the spirit and scope
of the appended claims~
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