U.S. patent application number 09/839260 was filed with the patent office on 2002-10-24 for airframe having area-ruled fuselage keel.
This patent application is currently assigned to The Boeing Company. Invention is credited to Seidel, Gerhard E..
Application Number | 20020153454 09/839260 |
Document ID | / |
Family ID | 25279261 |
Filed Date | 2002-10-24 |
United States Patent
Application |
20020153454 |
Kind Code |
A1 |
Seidel, Gerhard E. |
October 24, 2002 |
AIRFRAME HAVING AREA-RULED FUSELAGE KEEL
Abstract
An aircraft having a fuselage and a wing employs area-ruling of
the fuselage in a vertical direction, with at least a substantial
amount of the area-ruling being accomplished by dishing the keel
area of the fuselage directly below the center portion of the wing.
In one embodiment the aircraft has a main passenger seating deck
and forward and aft upper seating decks located above the main deck
respectively forward and aft of the wing, and both the upper
surface of the fuselage above the wing and the lower surface of the
fuselage below the wing are area-ruled.
Inventors: |
Seidel, Gerhard E.; (Renton,
WA) |
Correspondence
Address: |
ALSTON & BIRD LLP
BANK OF AMERICA PLAZA
101 SOUTH TRYON STREET, SUITE 4000
CHARLOTTE
NC
28280-4000
US
|
Assignee: |
The Boeing Company
Seattle
WA
|
Family ID: |
25279261 |
Appl. No.: |
09/839260 |
Filed: |
April 20, 2001 |
Current U.S.
Class: |
244/119 |
Current CPC
Class: |
B64C 1/00 20130101; B64C
2001/0027 20130101 |
Class at
Publication: |
244/119 |
International
Class: |
B64D 011/00; B64D
013/00; B64C 001/00 |
Claims
What is claimed is:
1. An airframe for a passenger transport aircraft, comprising: a
wing extending transverse to a longitudinal direction of the
airframe; a fuselage formed as a generally tubular structure
extending lengthwise along the longitudinal direction of the
airframe, the fuselage defining a lower keel portion having a lower
aerodynamic surface; wherein the wing includes a center portion
that passes transversely through the fuselage above the keel
portion, the fuselage having forward and aft portions respectively
located forward and aft of the center portion of the wing; and
wherein the lower aerodynamic surface of the keel portion in the
vicinity of the wing is area-ruled such that a waterline height of
said lower aerodynamic surface is greater below the wing than in
the forward and aft portions of the fuselage immediately ahead of
and behind the wing and the waterline height of said lower
aerodynamic surface varies in the longitudinal direction so as to
account for varying cross-sectional area of the wing in the
longitudinal direction.
2. The airframe of claim 1, wherein the fuselage includes a
structural keel beam that extends longitudinally along the keel
portion of the fuselage from the forward portion to the aft portion
of the fuselage for stiffening the fuselage in longitudinal
bending.
3. The airframe of claim 2, wherein the keel beam includes a
portion that passes through a lower part of the center portion of
the wing.
4. The airframe of claim 3, wherein the portion of the keel beam
that passes through the center portion of the wing is sculptured to
be non-linear.
5. The airframe of claim 2, wherein the keel beam includes a
portion that passes beneath the center portion of the wing.
6. The airframe of claim 5, wherein the portion of the keel beam
passing beneath the center portion of the wing is located below the
area-ruled lower aerodynamic surface of the fuselage.
7. The airframe of claim 1, further comprising a set of main
landing gear located aft of the area-ruled lower aerodynamic
surface of the fuselage.
8. The airframe of claim 1, wherein an upper aerodynamic surface of
the fuselage above the center portion of the wing is also
area-ruled.
9. The airframe of claim 1, wherein the fuselage includes a main
passenger seating deck and at least one upper passenger seating
deck located above the main passenger seating deck.
10. The airframe of claim 9, wherein the at least one upper
passenger seating deck is located outside the area-ruled portion of
the fuselage.
11. The airframe of claim 10, wherein the at least one upper
passenger seating deck comprises a forward upper deck located in a
forward part of the fuselage and an aft upper deck located in an
aft part of the fuselage, the forward and aft upper decks both
being located outside the area-ruled portion of the fuselage.
12. The airframe of claim 11, wherein the fuselage isolates the
forward upper deck from the aft upper deck such that the two upper
decks are non-adjoining.
13. The airframe of claim 1, further comprising an environmental
control system located in the fuselage outside of an area below the
center portion of the wing.
14. The airframe of claim 13, wherein the fuselage includes a
passenger seating deck located above the center portion of the
wing, and the environmental control system is located in the
fuselage above the passenger seating deck.
15. The airframe of claim 13, wherein the environmental control
system is located in a lower portion of the fuselage forward of the
center portion of the wing.
16. An airframe for a passenger transport aircraft, comprising: a
wing extending transverse to a longitudinal direction of the
airframe; a fuselage formed as a generally tubular structure
extending lengthwise along the longitudinal direction of the
airframe, the fuselage defining a lower keel portion, the fuselage
including a main passenger seating deck and forward and aft upper
passenger seating decks located above the main passenger seating
deck, a center portion of the fuselage being located longitudinally
between the forward and aft upper passenger seating decks; wherein
the wing includes a center portion that passes transversely through
the center portion of the fuselage above the keel portion, the
fuselage having forward and aft portions respectively located
forward and aft of the center portion of the wing; and wherein the
fuselage in the vicinity of the center portion of the wing is
area-ruled to reduce a cross-sectional area of the fuselage
relative to that of the forward and aft portions of the fuselage so
as to account for presence of the wing, at least a substantial part
of the area-ruling of the fuselage being accomplished by dishing a
lower aerodynamic surface of the fuselage directly below the center
portion of the wing such that said lower aerodynamic surface below
the wing has a concave-downward curvature in the longitudinal
direction.
17. The airframe of claim 16, wherein part of the area-ruling of
the fuselage is accomplished by dishing an upper aerodynamic
surface of the fuselage directly above the center portion of the
wing such that said upper aerodynamic surface is reduced in
waterline height relative to the forward and aft portions of the
fuselage.
18. The airframe of claim 16, wherein the fuselage includes a
structural keel beam that extends longitudinally along the keel
portion of the fuselage from the forward portion to the aft portion
of the fuselage for stiffening the fuselage in longitudinal
bending, and the keel beam includes a portion that passes through a
lower part of the center portion of the wing.
19. The airframe of claim 16, wherein the fuselage includes a
structural keel beam that extends longitudinally along the keel
portion of the fuselage from the forward portion to the aft portion
of the fuselage for stiffening the fuselage in longitudinal
bending, and the keel beam includes a portion that passes beneath
the lower aerodynamic surface of the fuselage below the center
portion of the wing.
20. The airframe of claim 16, wherein the keel portion of the
fuselage defines downwardly protruding forward and aft keel bumps
located respectively forward and aft of the center portion of the
wing and configured to engage the ground during a gear-up landing
and prevent contact between the ground and the center portion of
the wing.
Description
FIELD OF THE INVENTION
[0001] The invention relates to aircraft. The invention relates
more particularly to aircraft having an area-ruled fuselage to
reduce drag of the aircraft at high subsonic Mach numbers.
BACKGROUND OF THE INVENTION
[0002] It is well known that as an aircraft approaches the high
subsonic flight regime, there is a steep rise in aircraft
aerodynamic drag. The onset of the rise in drag results from local
regions of sonic or supersonic flow that occur on parts of the
aircraft because of the contour of the aircraft surfaces; such
regions of locally sonic or supersonic flow typically arise at
flight Mach numbers of about 0.8 or so for many aircraft. As the
Mach number is increased beyond this threshold, the drag begins to
rise at a steep rate.
[0003] It is known that the onset of this drag rise can be delayed
to a higher Mach number by careful design of the aircraft fuselage
and wing. In particular, it is known that so-called area-ruling of
the aircraft fuselage can be effective in delaying the onset of the
transonic drag rise. In accordance with this technique, the
fuselage in the vicinity of the fuselage-wing interface is
contoured so as to locally reduce the fuselage cross-section to
compensate for the cross-section of the wing. The objective in
area-ruling of a fuselage generally is to avoid a steep gradient in
the total cross-sectional area of the aircraft in the longitudinal
direction. Thus, the fuselage preferably has a relatively larger
cross-sectional area forward and aft of the wing than it has in the
area of the wing. As an example, the familiar "coke-bottle" shaped
fuselage has been employed for military fighter aircraft, in which
the fuselage is narrowed in the horizontal direction at the
fuselage-wing interface.
[0004] Area-ruling of the fuselage of a passenger aircraft involves
a number of design considerations, not the least of which is the
desire to provide adequate space for the passengers so that they
will not be cramped. Unfortunately, the desire to area-rule the
fuselage in the vicinity of the wing is at odds not only with the
need to maintain adequate passenger seating space but also with
other design features in this part of the aircraft. For instance,
traditionally the wing-fuselage intersection of a low-wing
passenger transport aircraft includes a large fairing defining the
lower aerodynamic surface of the fuselage in the area below the
center portion of the wing that passes through the fuselage. The
fairing is needed in order to accommodate stowed landing gear, to
house air conditioning units, for structural and aerodynamic
reasons, and to protect the center fuel tank in the wing in the
event of a landing with the landing gear not deployed. The fairing
increases the fuselage cross-section at precisely the longitudinal
station where it would be desirable to reduce the fuselage
cross-section, i.e., at the wing-fuselage intersection.
Consequently, at high subsonic flight Mach numbers (e.g., M=0.85 or
above), the fairing contributes substantially toward overall
aircraft drag.
[0005] On such an aircraft, area-ruling of other regions of the
fuselage at the longitudinal stations corresponding to the wing's
maximum cross-sectional area can be effective in lessening the
deleterious impact of the fairing and the wing with respect to
transonic drag. Area-ruling of the fuselage in the horizontal
direction is not practical, however, because it leads to
inefficiencies in the use of the space in the fuselage for
passenger seating. Accordingly, it has been proposed to area-rule a
passenger transport fuselage in the vertical direction. For
instance, an aircraft is described in U.S. Pat. No. 5,992,797,
assigned to the assignee of the present application and
incorporated herein by reference, in which area-ruling of the upper
portion of the fuselage above the wing is employed in order to
achieve a reduction in aircraft drag at high subsonic Mach numbers.
However, the resulting aircraft, although closer to an optimum
cross-sectional area distribution than an equivalent aircraft
without such area-ruling, is still far from such optimum area
distribution. Accordingly, any measures that could be taken to get
even closer to the optimum area distribution without sacrificing
other important design considerations would obviously be
desirable.
[0006] While this goal is easy to state, achieving it is difficult
in practice because of the many countervailing design constraints.
One very important constraint is the need to protect the center
fuel tank of the aircraft in the event of a gear-up landing. In
such a landing, the aircraft will essentially slide on its belly on
the runway, thus bringing the center fuel tank into close proximity
with the ground. There must be adequate structure between the
ground and the tank to prevent the tank from rupturing. The fairing
described above traditionally plays an important role in this
regard. Thus, the problem becomes how to achieve a greater extent
of area-ruling of the fuselage in the vicinity of the wing-fuselage
intersection, in view of the traditionally required fairing and the
need to maintain adequate passenger space.
SUMMARY OF THE INVENTION
[0007] The present invention addresses the above needs and achieves
other advantages by providing an airframe structure in which
area-ruling of the fuselage is accomplished at least partially by
dishing or sculpting the fuselage in the keel area below the center
portion of the wing that passes through the fuselage. The
traditional fairing can be eliminated or can be reconfigured so
that it does not detract from the objective of area-ruling. In
order to provide the protection for the center fuel tank normally
provided by the fairing, the invention in one embodiment employs
portions of the fuselage keel located forward and aft of the dished
or sculpted portion; contact between the fuselage in this region
and the ground is prevented by the forward and aft portions of the
fuselage. These forward and aft portions can be formed as "bumps"
at the keel area of the fuselage. Advantageously, these keel bumps
are located forward and aft of the longitudinal station at which
the wing's maximum cross-sectional area occurs, and hence do not
hinder the objective of providing area-ruling at that station. In
another embodiment, the center fuel tank is protected by a keel
beam running beneath the lower surface of the fuselage in the
dished or sculpted region; the keel beam thus hangs out in the free
stream air in this region. In this embodiment, the keel beam and
keel bumps can both be used to protect the center fuel tank.
[0008] In accordance with the invention, any air conditioning or
environmental control system that may be used on the aircraft can
be located outside of the space below the center portion of the
wing. For example, the environmental control system can be located
in a lower portion of the fuselage forward of the wing. In another
embodiment directed toward a double-decker aircraft, the aircraft
has a main passenger seating deck and forward and aft upper
passenger seating decks located above the main seating deck and
separated by a middle section of the fuselage having no upper
seating deck. In this embodiment, the environmental control system
can be located in the middle section above the main passenger cabin
between the forward and aft upper decks.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The above and other objects, features, and advantages of the
invention will become more apparent from the following description
of certain preferred embodiments thereof, when taken in conjunction
with the accompanying drawings in which:
[0010] FIG. 1 is a schematic side elevation of a conventional
passenger transport aircraft;
[0011] FIG. 2 is a front elevation of the aircraft of FIG. 1;
[0012] FIG. 3 is a schematic side elevation of an aircraft in
accordance with one embodiment of the invention;
[0013] FIG. 4 is a fragmentary side elevation of the aircraft of
FIG. 3, showing the aircraft executing a gear-up landing;
[0014] FIG. 5 is a front elevation of the aircraft of FIG. 3,
showing the aircraft executing a gear-up landing with one wing
down;
[0015] FIG. 6 depicts an aircraft in accordance with an alternative
embodiment of the invention, executing a gear-up landing with one
wing down;
[0016] FIG. 7 is a view similar to FIG. 4, showing an alternative
embodiment with the environmental control system relocated; and
[0017] FIG. 8 is a plot of total aircraft cross-sectional area
versus longitudinal station, comparing the aircraft of FIGS. 1 and
3 with an ideal Whitcomb body.
DETAILED DESCRIPTION OF THE INVENTION
[0018] The present invention now will be described more fully
hereinafter with reference to the accompanying drawings, in which
preferred embodiments of the invention are shown. This invention
may, however, be embodied in many different forms and should not be
construed as limited to the embodiments set forth herein; rather,
these embodiments are provided so that this disclosure will be
thorough and complete, and will fully convey the scope of the
invention to those skilled in the art. Like numbers refer to like
elements throughout.
[0019] A conventional large passenger transport aircraft is
depicted in FIGS. 1 and 2 and is denoted by reference numeral 10.
The aircraft 10 has a fuselage 12 housing a main passenger seating
deck 14 that extends for most of the length of the fuselage. The
fuselage also houses an upper forward seating deck 16 that extends
from just aft of the cockpit rearward to a station at or slightly
forward of the center section of the wing 13. As known in the art,
the fuselage 12 is area-ruled such that the cross-sectional area of
the fuselage in the portion of the fuselage forward of the wing 13
is larger than the cross-sectional area of the fuselage portion aft
of the wing, and the area decreases in the region corresponding to
the wing location. The objective is to achieve a distribution of
cross-sectional area versus longitudinal station that more closely
approaches an optimum.
[0020] As background regarding the theory of area-ruling, an
important aerodynamic consideration in designing aircraft for
flight at high subsonic Mach numbers is to minimize wave drag,
which is a type of pressure drag resulting from the formation of
shock waves on aircraft surfaces. It has been shown that wave drag
is related to changes in the aircraft's cross-sectional area in the
longitudinal direction, also referred to as the "volume
distribution" of the aircraft. Several advantageous body shapes
have been found that tend to minimize wave drag, one of which is a
Whitcomb body whose volume distribution is shown by the dashed line
15 in FIG. 8. It will be noted that the volume distribution is
characterized by a smooth variation in the gradient or slope of the
curve. Accordingly, it would be desirable from the standpoint of
minimizing wave drag of an aircraft to design the aircraft so that
its volume distribution approaches as closely as possible that of
the Whitcomb body. Since the main contributors to the total
cross-sectional area of an aircraft are the fuselage and wing, and
in view of the fact that the wing's shape cannot be compromised to
any significant extent, area-ruling of an aircraft typically is
accomplished by tailoring the distribution of the fuselage's
cross-sectional area so that the total aircraft cross-sectional
area distribution more closely approaches the optimal distribution.
A common approach used particularly in military fighter aircraft or
the like is to reduce the width of the fuselage in the horizontal
direction in the area of the wing, thus producing an hourglass
shape often referred to as a "Coke bottle" shape. In passenger
transport aircraft, however, this approach is undesirable because
it leads to inefficient use of space.
[0021] For this reason, it is common at least in large passenger
transport aircraft such as the aircraft 10 in FIGS. 1 and 2 to
accomplish the area-ruling not by reducing the fuselage area in the
region of the wing but instead by increasing the fuselage area
forward of the wing and then tapering the area in the wing region.
This can allow the forward part of the fuselage to accommodate an
upper deck as in the aircraft 10. Thus, increased capacity and
area-ruling can be achieved at the same time. The solid line 17 in
FIG. 8 shows the volume distribution for the aircraft 10.
[0022] The assignee of the present application, in U.S. Pat. No.
5,992,797, disclosed an approach particularly suitable for
passenger transport aircraft, in which "Coke-bottling" of the
fuselage is performed in a vertical plane rather than a horizontal
plane. More particularly, the height of the fuselage above the wing
center section is reduced. The '797 patent discloses an
advantageous passenger aircraft having both forward and aft upper
decks above the main seating deck, the forward and aft upper decks
being separated by a center section in the area where the fuselage
height is reduced. This allows a further increase in capacity while
providing area-ruling.
[0023] The present invention represents an improvement to the
technology disclosed in the '797 patent, but is also applicable to
many types of aircraft beyond large dual-deck passenger aircraft.
In accordance with the present invention, area-ruling of the
fuselage is performed in the vertical plane similar to the '797
patent, but at least a substantial amount of the area-ruling is
accomplished by dishing or sculpting the fuselage beneath the
center section of the wing.
[0024] In a conventional aircraft such as the aircraft 10 of FIGS.
1 and 2, there are typically design constraints that would prevent
such dishing or sculpting of the fuselage beneath the wing. For
example, at least in passenger transport aircraft, it is common to
locate the environmental control system (ECS) 20 in a space below
the center section of the wing in a keel region of the fuselage.
Thus, the space required for the ECS would prevent any significant
degree of dishing of the fuselage beneath the wing. Additionally,
at least passenger transport aircraft typically have a keel beam 22
(FIG. 2) that extends longitudinally along the keel region of the
fuselage and typically passes beneath the center section of the
wing. The keel beam 22 would prevent any significant dishing or
area-ruling of the fuselage beneath the wing.
[0025] In accordance with the present invention, however,
area-ruling or dishing of the fuselage beneath the wing of a
passenger transport aircraft is accomplished by relocating such
components that would ordinarily prevent such area-ruling. FIGS. 3
through 5 depict a first embodiment of a passenger transport
aircraft 30 in accordance with the invention. The aircraft has a
fuselage 32 housing a main passenger seating deck 34 extending
substantially the length of the fuselage. The fuselage also houses
a forward upper seating deck 36 and an aft upper seating deck 38.
The forward upper deck 36 extends from just aft of the cockpit
rearwardly to a station at or slightly forward of the wing 33. The
aft upper deck 38 extends from just aft of the wing rearwardly to a
point where the fuselage begins to taper in the tail region. A
middle upper section 40 of the fuselage is located between the
forward and aft upper decks and is preferably not available for
passenger seating. In the illustrated embodiment, the middle upper
section 40 isolates the forward upper deck from the aft upper deck
such that these upper decks are non-adjoining. In this embodiment
of the invention, the ECS 20 is installed in the middle upper
section 40 of the fuselage adjacent to the sidewall, in an
unpressurized compartment. Preferably, the height of the fuselage
in the middle section between the upper decks 36, 38 is reduced
relative to the rest of the fuselage so as to achieve area-ruling
of the fuselage in the area corresponding to the location of
maximum cross-sectional area of the wing 33.
[0026] Additional area-ruling is accomplished by dishing the
fuselage beneath the wing as indicated at 42 in FIGS. 3 and 4. This
is made possible by relocating the ECS as noted above, and by
modifying the keel beam of the aircraft. In the first embodiment of
FIGS. 3-5, the keel beam 44 is sculpted or contoured so that it is
non-linear in the region of the center portion of the wing and the
keel beam 44 in this region passes internally through the center
portion of the wing. Accordingly, there is nothing below the center
portion of the wing preventing the area-ruling of the fuselage in
the vertical plane. The area-ruled region 42 of the fuselage
beneath the wing is characterized by the waterline height of the
fuselage in the area-ruled region 42 being greater than that in the
keel region immediately forward and immediately aft of the
area-ruled region 42. It is also characterized by the curvature of
the area-ruled region 42 in the longitudinal direction being
concave-downward over a substantial part of the length of the
area-ruled portion.
[0027] The aircraft 30 includes a set of main landing gear 49.
Preferably, as shown, the landing gear 49 is located aft of the
area-ruled region 42.
[0028] In the first embodiment of FIGS. 3-5, protection is afforded
to the center fuel tank (not shown) housed in the center section of
the wing by providing the keel area of the fuselage with keel
bumps. Thus, a forward keel bump 46 located just forward of the
area-ruled region 42 projects downward to a substantially lower
waterline height than the area-ruled region; likewise, an aft keel
bump 48 just aft of the area-ruled region projects downward to a
substantially lower waterline height than the area-ruled region. As
shown in FIG. 4, when the aircraft is on the ground with the
landing gear not deployed (e.g., in an abnormal gear-up landing
caused by failure of the gear to deploy and/or lock), the keel
bumps 46, 48 contact the ground G and prevent contact between the
ground and the center section of the wing. Even if the aircraft
lands with one wing down such as when the gear on that side fails
to lock while the gear on the other side is down and locked, the
keel bumps protect the center section of the wing against ground
contact, as shown in FIG. 5.
[0029] FIG. 6 depicts an alternative embodiment of an aircraft 50
in which protection of the center section of the wing is provided
by locating the keel beam 54 below the center section of the wing.
Preferably, the keel beam 54 runs below the lower aerodynamic
surface of the fuselage 52 in the region of the area-ruling; thus,
the keel beam in this region hangs out in the free stream. Unlike
the previously described embodiment, the keel beam 54 can be a
conventional straight beam. It is possible to include both the keel
bumps and the keel beam for protecting the center fuel tank in the
wing.
[0030] FIG. 7 illustrates yet another embodiment of the invention
in which the aircraft 30' is generally similar to the aircraft 30
previously described and depicted in FIGS. 3-5, except that the ECS
20 is located in a lower keel region of the fuselage 32 just
forward of the wing, i.e., generally in the region of the forward
keel bump 46.
[0031] The invention facilitates an increased degree of area-ruling
compared with conventional aircraft. FIG. 8 shows the volume
distribution 55 of the aircraft of FIGS. 3-7. It can be seen that
the volume distribution is closer to the optimum Whitcomb
distribution 15 than is the case for the conventional aircraft
represented by the curve 17. Accordingly, the invention facilitates
a reduction in wave drag for the aircraft.
[0032] Many modifications and other embodiments of the invention
will come to mind to one skilled in the art to which this invention
pertains having the benefit of the teachings presented in the
foregoing descriptions and the associated drawings. Therefore, it
is to be understood that the invention is not to be limited to the
specific embodiments disclosed and that modifications and other
embodiments are intended to be included within the scope of the
appended claims. Although specific terms are employed herein, they
are used in a generic and descriptive sense only and not for
purposes of limitation.
* * * * *