U.S. patent application number 15/706807 was filed with the patent office on 2018-06-07 for active dihedral control system for a torsionally flexible wing.
This patent application is currently assigned to AeroVironment, Inc.. The applicant listed for this patent is AeroVironment, Inc.. Invention is credited to John A. Griecci, Greg T. Kendall, Derek L. Lisoski, Walter R. Morgan.
Application Number | 20180155005 15/706807 |
Document ID | / |
Family ID | 46328637 |
Filed Date | 2018-06-07 |
United States Patent
Application |
20180155005 |
Kind Code |
A1 |
Kendall; Greg T. ; et
al. |
June 7, 2018 |
Active Dihedral Control System for a Torsionally Flexible Wing
Abstract
A span-loaded, highly flexible flying wing, having horizontal
control surfaces mounted aft of the wing on extended beams to form
local pitch-control devices. Each of five spanwise wing segments of
the wing has one or more motors and photovoltaic arrays, and
produces its own lift independent of the other wing segments, to
minimize inter-segment loads. Wing dihedral is controlled by
separately controlling the local pitch-control devices consisting
of a control surface on a boom, such that inboard and outboard wing
segment pitch changes relative to each other, and thus relative
inboard and outboard lift is varied.
Inventors: |
Kendall; Greg T.; (Glendale,
CA) ; Lisoski; Derek L.; (Simi Valley, CA) ;
Morgan; Walter R.; (Simi Valley, CA) ; Griecci; John
A.; (Encino, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
AeroVironment, Inc. |
Simi Valley |
CA |
US |
|
|
Assignee: |
AeroVironment, Inc.
Simi Valley
CA
|
Family ID: |
46328637 |
Appl. No.: |
15/706807 |
Filed: |
September 18, 2017 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14838297 |
Aug 27, 2015 |
9764819 |
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15706807 |
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12804988 |
Aug 2, 2010 |
9120555 |
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14838297 |
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11732109 |
Apr 2, 2007 |
7802756 |
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12804988 |
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10310415 |
Dec 5, 2002 |
7198225 |
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11732109 |
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09527544 |
Mar 16, 2000 |
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10310415 |
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10600258 |
Jun 20, 2003 |
7281681 |
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11732109 |
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10073828 |
Feb 11, 2002 |
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10600258 |
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09826424 |
Apr 3, 2001 |
6550717 |
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10073828 |
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60182165 |
Feb 14, 2000 |
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60241713 |
Oct 18, 2000 |
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60194137 |
Apr 3, 2000 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B64C 2201/028 20130101;
B64C 2201/122 20130101; B64D 27/24 20130101; B64D 31/06 20130101;
B64C 39/024 20130101; B64C 2201/126 20130101; B64C 3/38 20130101;
B64C 2201/165 20130101; B64D 2211/00 20130101; B64C 3/42 20130101;
B64C 17/00 20130101; B64C 2201/127 20130101; Y02T 50/12 20130101;
Y02T 50/44 20130101; Y02T 50/50 20130101; B64C 3/52 20130101; B64C
39/10 20130101; Y02T 50/55 20180501; B64C 2201/146 20130101; H04B
7/18504 20130101; Y02T 50/40 20130101; B64C 2201/042 20130101; Y02T
50/10 20130101; Y02T 50/14 20130101; B64C 2201/102 20130101; B64C
15/02 20130101 |
International
Class: |
B64C 3/38 20060101
B64C003/38; H04B 7/185 20060101 H04B007/185; B64C 17/00 20060101
B64C017/00; B64D 31/06 20060101 B64D031/06; B64C 39/10 20060101
B64C039/10; B64C 15/02 20060101 B64C015/02; B64C 3/52 20060101
B64C003/52; B64D 27/24 20060101 B64D027/24; B64C 39/02 20060101
B64C039/02; B64C 3/42 20060101 B64C003/42 |
Goverment Interests
[0002] This invention was made with government support under ERAST
JSRA Contract NCC-04004 awarded by NASA. The United States
Government has certain rights in the invention.
Claims
1. An aircraft characterized by a flight envelope, comprising: a
laterally extending wing; a plurality of pitch-control devices,
each pitch-control device being mounted at a separate lateral
location along the wing, and each pitch-control device being
configured to apply pitch-control torque at its lateral location,
wherein the wing is characterized by a torsional flexibility
adapted to allow the plurality of pitch control devices to control
localized pitch at their lateral wing locations to a degree
substantial enough to be significant for flight control; and a
control system configured to control the plurality of pitch-control
devices based upon the relative localized pitches at the plurality
of lateral locations.
2. The aircraft of claim 1, wherein each pitch-control device is
adapted to cause a control surface pitch effect and a control
surface flap effect, and wherein each pitch-control device includes
a boom connecting the wing to a control surface aft of the trailing
edge of the wing at a distance adequate to cause the control
surface pitch effect to dominate the control surface flap
effect.
3. The aircraft of claim 1, wherein the control system is
configured to operate the pitch-control devices under a protocol
adapted to control and alter wing dihedral based upon the dihedral
of the wing.
4. The aircraft of claim 3, wherein the protocol actively provides
for dihedral control and alteration that maintains the wing bending
stresses within safety limits.
5. The aircraft of claim 1, and further comprising a plurality of
motors, wherein the control system is configured to separably
control the thrust from the plurality of motors based upon
fore-and-aft wing loads between the motors.
6. The aircraft of claim 1, wherein the pitch-control devices
include both fixed and controllable horizontal surfaces.
7. The aircraft of claim 4, wherein the protocol is configured to
direct outboard pitch-control devices with more downward pitching
pitch-control torques than pitch-control torques of inboard
pitch-control devices.
8. The aircraft of claim 1, wherein the aircraft is controlled
without the use of elevators.
9. An aircraft characterized by a flight envelope, comprising: a
laterally extending wing; a means for separately actuating the
pitch of the wing at a plurality of lateral locations along the
wing, wherein the wing is characterized by a torsional flexibility
adapted to allow the means for separately actuating to actuate
localized pitch at the plurality of lateral locations to a degree
substantial enough to be significant for flight control; and a
means for controlling the means for separately actuating based upon
the relative localized pitches at the plurality of lateral
locations.
10. A method of controlling an aircraft characterized by a flight
envelope, comprising: separately actuating the pitch of a laterally
extending wing at a plurality of lateral locations along the wing,
wherein the wing is characterized by a torsional flexibility
adapted to allow the means for separately actuating to actuate
localized pitch at the plurality of lateral locations to a degree
substantial enough to be significant for flight control; and
controlling the means for separately actuating based upon the
relative localized pitches at the plurality of lateral
locations.
11. The method of claim 10, wherein the step of controlling
includes directing the pitch-control devices under a protocol
configured to control and alter wing dihedral based upon the
dihedral of the wing.
Description
[0001] The present application is a Continuation application of
U.S. patent application Ser. No. 14/838,297, filed Aug. 27, 2015,
which is a Continuation application of U.S. patent application Ser.
No. 12/804,988, filed Aug. 2, 2010, now U.S. Pat. No. 9,120,555,
which is a Divisional application of U.S. patent application Ser.
No. 11/732,109, filed Apr. 2, 2007, now U.S. Pat. No. 7,802,756,
which is a Continuation-in-Part of U.S. patent application Ser. No.
10/310,415, filed Dec. 5, 2002, now U.S. Pat. No. 7,198,225, which
is a Divisional application of U.S. patent application Ser. No.
09/527,544, filed Mar. 16, 2000, now abandoned, which claims
priority from U.S. Provisional Patent Application Ser. No.
60/182,165, filed Feb. 14, 2000, each of which is incorporated
herein by reference for all purposes. U.S. patent application Ser.
No. 11/732,109, filed Apr. 2, 2007, now U.S. Pat. No. 7,802,756, is
also a Continuation-in-Part of U.S. patent application Ser. No.
10/600,258, filed Jun. 20, 2003, now U.S. Pat. No. 7,281,681, which
is a Continuation-in-Part of U.S. patent application Ser. No.
10/073,828, filed Feb. 11, 2002, now abandoned, which is a
Divisional application of U.S. patent application Ser. No.
09/826,424, filed Apr. 3, 2001, now U.S. Pat. No. 6,550,717, which
claims priority from U.S. Provisional Application Ser. No.
60/241,713, filed Oct. 18, 2000, and which also claims priority
from U.S. Provisional Application Ser. No. 60/194,137, filed Apr.
3, 2000, each of which is incorporated herein by reference for all
purposes.
[0003] The present invention relates to aircraft. More
particularly, the present invention relates to aircraft having
unique control mechanisms, and related methods of controlling an
aircraft.
BACKGROUND
[0004] Aircraft are used in a wide variety of applications,
including travel, transportation, fire fighting, surveillance and
combat. Various aircraft have been designed to fill the wide array
of functional roles defined by these applications. Included among
these aircraft are balloons, dirigibles, traditional fixed wing
aircraft, flying wings and helicopters.
[0005] One functional role that a few aircraft have been designed
to fill is that of a high altitude platform. Operating from high,
suborbital altitudes, such aircraft can monitor weather patterns,
conduct atmospheric research and surveil a wide variety of
subjects.
[0006] Three high altitude aircraft that have been constructed are
the well-known Pathfinder, Centurion and Helios aircraft, which
have set numerous flight records. The basic design concepts
underlying these aircraft are discussed at length in U.S. Pat. No.
5,810,284, which is directed toward an unswept flying wing aircraft
having a very high aspect ratio and a relatively constant chord and
airfoil. While these aircraft are quite noteworthy for their long
term flight potential, they do have limits in their available power
and payload.
[0007] Such aircraft may be designed as flying wings that include a
number of self-sufficient wing sections, each generating enough
lift to support its own weight. To minimize weight, the aircraft
structure is highly flexible, and is designed to withstand only
relatively small torsional loads and moderate bending loads along
its lateral axis (i.e., its wingspan). The aircraft's wing has
little or no dihedral while on the ground. However, due to high
flexibility, the large aspect ratio and the constant chord,
in-flight wing loads tend to cause the wing to develop a
substantial dihedral angle at the wingtips, which may not be
optimal for a given wing strength. Thus, there is a tradeoff
between the structural weight of the aircraft and the desirability
of the wing shape.
[0008] There is an inherent relationship between an aircraft's
overall airframe geometry and the design of its airfoils and
control surfaces. Typical aircraft offset negative (i.e.,
nose-down) pitching moments through the use of tail moments (i.e.,
vertical forces generated on empennage horizontal surfaces and
elevators, with a moment arm that is the distance from the wing
center of pressure to the empennage vertical center of
pressure).
[0009] To minimize the torsional loads, the Pathfinder, Centurion
and Helios aircraft include "wing-mounted elevators" along a
substantial portion of their trailing edges (i.e., the trailing
edges of each flying wing segment). These aircraft do not include
rudders or ailerons, and the wing-mounted elevators are not
designed as elevons (i.e., they cannot move in contrary directions
near opposite wingtips). Roll is passively controlled by the
dihedral of the wing, which is developed in flight. Sideslip is
also passively controlled by the dihedral of the wing. As discussed
above, the allowable wing dihedral is limited by the structural
strength of the wing.
[0010] Given the broad range of functions that a long-duration,
suborbital platform has the potential to perform, it is desirable
to design such high-altitude platforms to be capable of handling
larger payloads and power demands. The platforms could be
variations of existing platforms, such as larger variations of the
Pathfinder, Centurion and Helios aircraft, but such platforms will
likely have to handle increased bending loads along the wing as
such larger aircraft have to react against dihedral-causing forces
over a larger wingspan.
[0011] There exists a definite need for a multipurpose aircraft
that can remain airborne for long durations. Preferably, such an
aircraft should be able to operate up to very high, suborbital
altitudes. Importantly, it is desirable for such an aircraft to
have the capability to meet larger payload and/or power supply
requirements. Furthermore, there exists a need for such an aircraft
to be structurally light weight and well controlled. Various
embodiments of the present invention can meet some or all of these
needs, and provide further, related advantages.
SUMMARY OF THE INVENTION
[0012] The present invention addresses the needs mentioned above by
providing an aircraft that can operate at high altitudes, carry
substantial payloads, and/or remain aloft for long periods of
time.
[0013] The aircraft of the invention typically includes a laterally
extending wing, a plurality of pitch-control devices, and a control
system configured to control the plurality of pitch-control
devices. Each pitch-control device is mounted at a separate lateral
location along the wing. Each pitch-control device is configured to
apply pitch-control torque at its lateral location, and the wing is
characterized by a torsional flexibility high enough for each
pitch-control device to separately and substantially control
localized pitch at its lateral wing location, i.e., to a degree
substantial enough to be significant for flight control.
[0014] The pitch-control device may feature a body, e.g., a boom,
connecting the wing to a control surface aft of the trailing edge
of the wing. Advantageously, the control surface is positioned at a
distance from the wing adequate to provide the aerodynamic forces
from the control surface with a pitching effect on the wing to
cause changes in the local lift that dominate (i.e., are much
larger than) the changes in lift that occur from the redirection of
air by the control surface (i.e., the flap effect), over the entire
flight envelope. Thus, aileron reversal is not an issue.
[0015] The invention further features that the control system is
configured to operate the pitch-control devices under protocols
that will actively control wing dihedral. Advantageously, under
such predetermined protocols, a highly flexible wing can be used
while limiting the risk of excessive wing bending.
[0016] Other features and advantages of the invention will become
apparent from the following detailed description of the preferred
embodiments, taken in conjunction with the accompanying drawings,
which illustrate, by way of example, the principles of the
invention. The detailed description of particular preferred
embodiments, as set out below to enable one to build and use an
embodiment of the invention, are not intended to limit the
enumerated claims, but rather, they are intended to serve as
particular examples of the claimed invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is an elevational view of an aircraft embodying the
invention.
[0018] FIG. 2 is a plan view of the aircraft depicted in FIG.
1.
[0019] FIG. 3 is a perspective view of the aircraft depicted in
FIG. 1, in a flexed position that creates moderate dihedral typical
of loading under mild flight conditions.
[0020] FIG. 4 is a perspective, cutaway view showing the
construction of one portion of one wing segment of the wing of the
aircraft depicted in of FIG. 1.
[0021] FIG. 5 is a block diagram showing a control system and
related components from the aircraft illustrated in FIG. 1.
[0022] FIG. 6 is a partial plan view of a second aircraft embodying
the invention.
[0023] FIG. 7 is a partial plan view of a third aircraft embodying
the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] The invention summarized above and defined by the enumerated
claims may be better understood by referring to the following
detailed description, which should be read in conjunction with the
accompanying drawings. This detailed description of a particular
preferred embodiment, set out below to enable one to build and use
one particular implementation of the invention, is not intended to
limit the enumerated claims, but rather it is intended to serve as
a particular example thereof.
[0025] In accordance with the present invention, a number of
preferred embodiments of an aircraft of the present invention are
of designs similar to those of the Pathfinder, Centurion and/or
Helios aircraft, as mentioned above in the Background of the
Invention. While the embodiments' designs, and variations of them,
are described below, further details useful for the practicing of
this embodiment of the invention are provided in U.S. Pat. No.
5,810,284, which is incorporated herein by reference for all
purposes. Nevertheless, it is to be understood that designs for
other embodiments of the invention can differ substantially from
the described aircraft.
[0026] Like the Pathfinder, Centurion and Helios aircraft, the
preferred embodiments may be flying wings. These embodiments
include a plurality of laterally connected, wing segments that
preferably can each support their own weight in flight so as to
minimize inter-segment loads, and thereby minimize required
load-bearing structure. These embodiments have aircraft control
systems configured to control the flexible development of wing
dihedral during flight, and thereby further control inter-segment
loads.
[0027] The Pathfinder, Centurion and Helios aircraft had
trailing-edge control surfaces configured as trailing edge flaps
(or "wing-mounted elevators" on the trailing edge of the wing).
These control surfaces were not configured to act differentially.
The coordination of the wing trailing edge control surfaces to
prevent contrary movement on different portions of the wing was not
utilized. The torsional flexibility of the Pathfinder, Centurion
and Helios aircraft made the use of such control surfaces
relatively impractical. Lacking the torsional rigidity of a normal
aircraft, the Pathfinder, Centurion and Helios aircraft could
suffer from significant control reversal problems if the control
surfaces operated as ailerons. Under some circumstances, these
difficulties also might affect the operation of the control
surfaces as elevators. Thus, the control reversal issue potentially
limited the operability of the aircraft.
[0028] For example, a downward control surface deflection on a
normal, torsionally stiff wing, would typically be expected to
cause additional airfoil section lift (an effect that will be
hereinafter referred to as a "flap effect"). However, such a
deflection will likely cause a significant nose-down pitching
(twisting) moment on the wing, which on a torsionally flexible wing
can lead to a decreased angle of attack, and thereby a reduction in
overall lift (an effect that will be hereinafter referred to as a
"pitch effect"). Under various flight conditions, a control surface
on the trailing edge of a torsionally flexible wing can experience
one, the other and/or both of these two contrary effects to a
significant degree.
[0029] As a result, the response to a movement of the control
surface on a highly flexible (in torsion) winged aircraft can be
unpredictable. Moreover, over the flight envelope (e.g., through
variations in flight speed), the response can vary between having
one of the effects dominate, having the other dominate, having the
two cancel each other out, and having the two cyclically operate
with one lagging the other to drive the wing in a potentially
unstable forced vibration (i.e., flutter) having both bending and
torsional components.
[0030] With reference to FIGS. 1-3, a first preferred embodiment is
a flying wing aircraft 10, i.e., it has no fuselage or empennage
usable to control the overall pitch of the aircraft (as a typical
aircraft would have). Instead, it consists of an unswept, laterally
extending wing 12 similar to that of the Centurion aircraft, having
a substantially consistent airfoil shape and size along the
wingspan. Fourteen motors 14 are situated at various locations
along the wingspan, each motor driving a single propeller 16 to
create thrust. Four vertical fins 18a-18d, or pods, extend down
from the wing, with landing gear at their lower ends.
[0031] The aircraft 10 is longitudinally divided into preferably
five modular wing segments sequentially located along the lateral
wingspan. These include a center segment 20, left and right
intermediate segments 22, 24, and left and right wingtip segments
26, 28. These wing segments preferably range from 39 to 43 feet in
length, and have a chord length of approximately eight feet.
Alternative variations of the embodiment may be highly flexible
flying wing aircraft that are unitary (i.e., not segmented), but
are nevertheless highly flexible.
[0032] With reference to FIGS. 2, 3 and 4, one or more of the wing
segments of the aircraft 10, and preferably at least three wing
segments (as depicted) (and/or up to and including all of the wing
segments) each include a pitch-control device 42, each
pitch-control device being mounted at a separate lateral location
along the wing. The pitch-control device is preferably a boom 44
extending longitudinally aft and holding a preferably horizontal
control surface 46 in a position preferably aft of the trailing
edge of the wing 12. For the purposes of this application, it
should be understood that a "horizontal" surface is one extending
in a direction having a horizontal component, that is adequately
horizontal to impart control forces having a relevant vertical
component. In alternative embodiments, the pitch-control device
could include both a fixed horizontal surface and an active control
surface.
[0033] The three wing segments having pitch-control devices are
preferably an inboard wing segment (e.g., the center segment 20)
and two outboard wing segments (e.g., the end segments 26, 28).
Thus, the flying wing preferably includes at least 3 pitch control
devices, which are preferably located symmetrically across the
wing.
[0034] Each such pitch-device control surface 46 is configured for
rotationally deflecting relative to the boom 44 such that a
controllable, preferably vertical aerodynamic force is applied to
the boom aft of the trailing edge of the wing. The force applied to
the boom is preferably normal to the longitudinal dimension of the
boom, and at a distance from the wing segment on which it is
mounted, such that a torsional force is applied to the wing segment
at or about the lateral location to which the boom structurally
connects to the wing segment.
[0035] Moreover, the wing 12 is characterized by enough torsional
flexibility in the lateral locations of each pitch-control device
42 to separately control localized pitch of the wing at and/or near
its lateral wing location. In this application, the terminology
"separately control" should be understood to mean that the
pitch-control devices are physically independent such that each
could in theory be commanded to operate in a manner different from
the others.
[0036] This control over localized pitch is to a degree substantial
enough to be significant for flight control (i.e., for control of
the response of the aircraft structure to aerodynamic forces, so as
to change the aircraft structural configuration (e.g., wing
dihedral and/or bending load) and/or the aircraft flight or
orientation). The position and configuration of each pitch-control
device preferably limits any flap effect it has on the wing segment
(in response to deflection of the control surface) such that the
pitch effect is dominant over the entire flight envelope of the
aircraft. In other words, the change in vertical force from
movements of the pitch-control device control surface, are
significantly less than the change in lift experienced by the wing
due to the resulting change in local wing pitch.
[0037] Each pitch-control device boom 44 connects the control
surface 46 to the wing 12 at a distance aft of both the spar 40 and
the trailing edge 48 of the wing adequate to cause the control
surface pitch effect to dominate the control surface flap effect.
This is distinctive from a normal aircraft, for which wing-mounted
control surfaces are intended to operate using a dominant flap
effect.
[0038] Optionally (as depicted in FIG. 4), additional, flap-effect
control surfaces 50 could be incorporated into the trailing edge of
the wing, particularly in locations structurally close to (e.g.,
within a spanwise area torsionally affected and/or controlled by) a
pitch-control device 42. These trailing-edge control surfaces could
be limited in use to flight regimes where in their response would
be predictable, or could be used in concert with a pitch-control
device to produce desired effects (e.g., the trailing edge control
surface could control lift while the pitch control device limits
the wing pitch resulting from movements of the trailing edge
control surface). Alternatively, the pitch-control devices may be
the only control surfaces (or the only horizontal control surfaces)
on the aircraft.
[0039] The overall length of the pitch-control device as measured
back from the elastic axis of the wing, and its control surface
size, may be experimentally or analytically determined to meet the
criteria of minimizing overall weight and drag, while providing for
the pitch effect to be the dominant effect over the entire desired
flight envelope. Possible pitch-device lengths that might be
considered, as multiples of the wing fore-and-aft length (i.e.,
chord length), include 1.5 and 3.
[0040] Thus, the aircraft of this embodiment might have a chordwise
length of roughly 20 feet, with a wing segment chordwise length of
eight feet, and a wingspan of approximately 200 feet. The structure
is configured to be lightweight, with significant flexibility in
vertical bending (allowing for significant dihedral bending) and
spanwise torsion (allowing for significant relative pitching).
[0041] With reference to FIGS. 2, 4 and 5, the embodiment includes
an electronic aircraft control system 52 configured to control the
operation of the aircraft. The aircraft control system includes a
structural control system 54 configured to control structural
bending of the aircraft, and a flight control system 56 configured
to control the flight of the aircraft. Because these two functions
may be significantly interrelated, the structural control system
and flight control system are likely to significantly interact
within the overall aircraft control system 52.
[0042] Both the structural control system 54 and the flight control
system 56 receive data from numerous sources. One such source is a
communications unit 61 configured to receive instructions from a
ground controller (e.g., a ground-based pilot). Another source is a
plurality of flight parameter sensors 63, preferably including one
or more of the following sensors: a positional sensor (e.g., a
GPS), a heading sensor, a pitch sensor, a roll sensor, a yaw
sensor, an altimeter, a flight speed sensor, a vertical speed
sensor, a slip sensor, a pitch rate sensor, a roll rate sensor, and
a yaw rate sensor. A third source is a plurality of structural
sensors 65, preferably including one or more of the following
sensors: vertical wing bending sensors, fore-and-aft wing bending
sensors, wing torsion sensors, motor speed and/or thrust sensors,
control surface deflection and/or force sensors, and solar sensors
configured to detect the exposure of the structure to sunlight.
Each of these sensors is of a type either known in the art (e.g.,
strain gauges and positional sensors), or that can be formed with a
combination of known sensors.
[0043] In some cases, one or more sensors of one type may serve the
function of the sensor of another type. For example, a plurality of
pitch sensors and/or pitch rate sensors laterally positioned along
the wing may provide data to analytically determine wing torsion,
which might otherwise be detected with strain gauges.
[0044] The structural control system 54 and the flight control
system 56 may each contribute to command instructions sent to a
number of aircraft systems. The systems receiving command
instructions to control their operation include the control
surfaces (e.g., pitch-control device control surfaces 46, and
flap-effect control surfaces 50) and the motors. As noted above, in
some cases the structural sensors will be of a type to sense the
operation of the control devices (e.g., the control surfaces and/or
the motors).
[0045] Using the aircraft control system 52 and the pitch-control
devices 42, aircraft dihedral is controlled by having the
structural control system 54 cause aircraft control system commands
to be sent to the pitch-control devices to initiate control
movements of their control surfaces 46 using a protocol that
controls the pitch of their respective lateral locations on the
wing, and relatedly affect their wing segments and/or nearby
portions thereof (and possibly the pitch of nearby wing segments).
In particular, outboard pitch-device control surfaces 72 are
directed to actuate downward (i.e., trailing edge down), causing
their respective wing segments 26, 28, or portions of their
respective wing segments to pitch downward (i.e., leading edge
down) and thereby decrease the overall lift generated by the
respective outboard wing segments.
[0046] Simultaneously, inboard pitch-device control surfaces 74 are
directed to actuate upward, causing their respective wing segments,
or portions of their respective wing segments 20 to pitch upward
and thereby increase the overall lift generated by the respective
inboard wing segments. As a result, with inboard lift increased and
outboard lift decreased, overall wing dihedral may be controllably
reduced, eliminated, and/or controlled to achieve desired wing
configurations and desired wing stress levels.
[0047] The aircraft control system is thereby configured to control
the plurality of pitch-control devices under a protocol (i.e., a
detailed plan or procedure) that controls wing dihedral according
to a predetermined program. Such a program will typically include
dihedral limits (e.g., maximums dictated by flight efficiency and
structural limits, and optionally minimums dictated by flight
control issues, possibly varying over the entire flight envelope),
and dihedral schedules (such as ones based on maximizing the
exposure of wing solar cells to sunlight, ones based on optimizing
the positions of onboard instrumentation, or ones based on
stability and control parameters). The protocol may include control
inputs that are symmetric, such as ones to increase or decrease
dihedral, control inputs that are inverted on opposite sides, such
as ones to roll the aircraft, and possibly even control inputs that
are asymmetric.
[0048] In order to optimize flight efficiency by reducing drag, the
aircraft control system dihedral schedule may be configured (i.e.,
the protocol may include command procedures) to cause the dihedral
to be less when the sun is high in the sky, or when it is night.
This allows the aircraft to optimize the tradeoff between power
generation and flight efficiency. To accomplish this end, the
control system determines a dihedral configuration to increase the
power generated by solar cells, should they be present. This can be
done by simply reading a clock signal from a clock within the
aircraft control system and adjusting the dihedral (and possibly
the heading) based on the anticipated light conditions. More
preferably, the control system can detect the light conditions,
either through signals from light sensors, or from indications of
the power levels generated by one or more of the solar cells.
[0049] As suggested above, in some situations it might be desirable
to increase wing dihedral. To do so, the reverse of the
above-recited operation is conducted. More particularly, outboard
pitch-device control surfaces 72 are directed to actuate upward,
causing their respective wing segments, or portions of their
respective wing segments, to pitch upward and thereby increase the
overall lift generated by the respective outboard wing segments.
Simultaneously, inboard pitch-device control surfaces 74 are
directed to actuate downward, causing their respective wing
segments, or portions of their respective wing segments, to pitch
downward and thereby decrease the overall lift generated by the
respective inboard wing segments.
[0050] As a result of the above design, the preferred embodiment of
the aircraft is light, travels at relatively slow air speeds, and
has a configuration controllable to limit stresses on its
individual components. Optionally, the control system may receive
input from sensors configured to detect the configuration (e.g.,
the relative position, orientation, bending and/or torsion) of the
aircraft and/or individual wing segments thereof. Thus, the
aircraft control system may actively control the aircraft
configuration to be maintained within structural safety limits
(e.g., for the bending stresses to be maintained within safety
limits) and within an optimum flight configuration range, even when
the aircraft encounters undesirable flight conditions such as
turbulence.
[0051] Preferably the pitch-control devices 42 are each paired with
(i.e., located substantially aft of) a motor 14, thus potentially
limiting the effects of drag from the pitch-control device on the
wing 12 (i.e., the use of paired motors and pitch-devices limits
the shear forces and fore-and-aft bending of the wing due to moment
arms between the thrust of the nearest motor(s) and the drag of the
pitching device). The depicted outboard pitch-control devices are
paired with motors. Optionally, the wing may include additional
motors that are not paired with pitch-control devices (as depicted
for the inboard pitch-control device). The motors may optionally be
controlled by a motor control system 58, (which may be part of the
aircraft control system) that is configured to control the
operation of the motors such that the unpaired motors (i.e., motors
not paired with a pitch-control device) are operated at a lower
thrust level than the paired motors, the difference being at or
about the anticipated or actual level of pitch-device drag, which
may vary by flight condition and control surface position.
Likewise, two or more motors near an unpaired pitch-control device
may be controlled by the aircraft system controller to provide
relatively increased thrust in a proportional amount based on their
lateral positions relative to the pitch-control device.
[0052] As a result, the motor control system is configured to
separably control the thrust from the plurality of motors to reduce
fore-and-aft wing loads between the motors. Optionally, the motor
control system may optimize this function using flight data and
sensory information regarding wing strain, actual thrust and actual
structural configuration (e.g., wing bending, wing torsion and
other related parameters).
[0053] The aircraft 10 controls yaw, and thereby turns, using
differential thrust from varied motor torque on the propellers 16.
It uses a combination of sideslip and dihedral to control bank
angle. Optionally, the pitch-control devices could be used to
create varied lift over the wingspan, and thereby control bank
angle without large side slip issues. Other known methods or
mechanisms for creating differential thrust could also be used.
[0054] The aircraft relies upon its large wingspan and relatively
low velocities to avoid yaw instability. Roll may be controlled
passively by the wing being maintained with a positive angle of
dihedral, and/or by using the pitch-control devices to create
differential lift across the wingspan.
[0055] The aircraft may further include inter-segment hinge
mechanisms and hinge locks, as described in U.S. patent application
Ser. No. 10/310,415, filed Dec. 5, 2002, which is incorporated
herein by reference for all purposes. The structural control system
may further control the pitch-control devices to actuate the
inter-segment hinge mechanisms (i.e., acting as hinge actuators),
as described in that application. The hinge locks (i.e.,
hinge-rotation locks) can be either within the hinge mechanisms, or
otherwise controlling them. When a rotational lock is in an
unlocked configuration, hinge actuators allow the relative rotation
of respective wing segments. When the rotational lock is in a
locked configuration, the hinge mechanism is restrained, and the
respective wing segments are prevented from rotating with respect
to each other, thereby maintaining the wing's dihedral
configuration.
[0056] The aircraft may optionally feature additional,
non-aerodynamic mechanisms (as described in the above-noted
application), configured to affect the local wing pitch (i.e.,
pitch-control devices) and/or to control the rotation of the hinge
mechanisms, thereby adding further controllability to the wing
configuration and/or the operation of the hinge mechanisms. These
mechanisms may include CG-movement devices (i.e., devices
configured to change the center of gravity in a particular area of
the wing so as to affect its pitch and/or roll). It is preferable
that there be a symmetric arrangement of hinge mechanisms on the
aircraft, along with a symmetric arrangement of pitch-control
devices.
[0057] Additional configurations, such as aircraft configured to
deflect into W-shapes or M-shapes are also within the scope of the
invention. Such configurations having alternating positive and
negative dihedral can reduce wing loading for flight conditions in
which it is desirable to have significant side exposure of the wing
surfaces (such as when the sun is low on the horizon). Furthermore,
aircraft with only two pitch-control devices or only one
pitch-control device are also within the possible scope of the
invention, particularly when combined with a structural control
system implementing protocols as described above.
[0058] While the described embodiments of active dihedral control
are employed on an aircraft having numerous, flexible, non-swept
wing segments of constant airfoil and chord, they can likewise be
employed on other aircraft designs including conventional aircraft,
and even biplanes.
[0059] More particularly, with reference to FIG. 6, another
embodiment may be a conventional aircraft provided with a flexible
wing 401, which supports a fuselage 403, and includes a number of
highly flexible regions 405 capable of significant independent wing
torsion. Each region has a pitch-control device 407 that controls
the pitch of that region, and reacts any negative pitching moments
of that region's cambered airfoil. The aircraft wing 401 will
preferably include at least one pitch-control device 407 on each
side of the fuselage 403 in a symmetric formation. Preferably
(though not necessarily), the fuselage carries an empennage (not
shown) that includes typical horizontal control surfaces, and/or
other fuselage-mounted pitch-control surfaces (e.g., a canard).
[0060] Preferably, the primary function of the pitch-control
devices 407 is controlling and/or preventing local wing torsion and
bending, but overall flight control can also be a primary or
secondary function. Overall aircraft pitching moments can also be
reacted by the fuselage-mounted pitch-control surfaces. An aircraft
control system preferably controls both the pitch-control devices
and any fuselage-mounted pitch-control surfaces to those ends, and
preferably receives input from various sensors, as described with
reference to the first embodiment.
[0061] While the above-described pitch-control devices actively
control local wing pitch, another embodiment of the invention uses
passive controls (i.e., pitch-limiting devices) so as to allow the
use of ailerons on a highly flexible wing without experiencing
aileron reversal. While an aircraft with a fuselage is described in
the embodiment below, other embodiments may be of other
configurations, such as flying wings like those described
above.
[0062] With reference to FIG. 7, another embodiment may be a
conventional aircraft provided with a highly flexible laterally
extending wing 501, which supports a fuselage 503, and includes a
number of highly flexible regions 505 capable of significant
independent wing torsion. A plurality of ailerons 506 are mounted
at various lateral aileron-locations in the highly flexible regions
along the wing.
[0063] A plurality of pitch-limiting devices 507 are mounted at
separate lateral pitch-limiting-locations along the wing. Each
pitch-limiting device is configured to apply a pitch-limiting
torque at its pitch-limiting-location. Each pitch-limiting-location
is proximate the aileron-locations of one or more ailerons. Thus,
each region has a pitch-limiting device 507 that limits the pitch
of that region in response to aileron deflection. The aircraft wing
501 will preferably include at least one pitch-limiting device 507
on each side of the fuselage 403 in a symmetric formation.
Preferably (though not necessarily), the fuselage carries an
empennage (not shown) that includes typical horizontal control
surfaces, and/or other fuselage-mounted pitch-control surfaces
(e.g., a canard).
[0064] It should be understood that a wing that is uniformly (and
highly) flexible can be considered as having a number of highly
flexible regions. The term highly flexible should be understood to
represent a level of torsional flexibility wherein but for any
pitch-limiting devices (i.e., if they weren't there), one or more
ailerons would experience aileron reversal over some portion of the
flight envelope.
[0065] While the pitch-limiting devices could be active horizontal
control surfaces controlled by a control system to limit wing
pitch, or a combination of a control surface and a fixed horizontal
surface, preferably the pitch-limiting devices include only one or
more fixed horizontal surfaces mounted aft of the wing. More
particularly, each pitch-limiting device preferably includes a body
(e.g., a boom) connecting the wing to a fixed surface aft of the
trailing edge of the wing at a distance adequate to cause the flap
effect of the proximate ailerons to dominate the pitch effect over
the entire flight envelope. The primary function of the
pitch-limiting devices 507 is controlling and/or preventing local
wing torsion and bending, and thereby allowing ailerons to function
properly without experiencing aileron reversal.
[0066] Advantageously, the features described above with respect to
the various embodiments can provide various advantages. By allowing
for high torsional flexibility, torsion-carrying wing structure can
be limited, reducing the weight of the aircraft and thereby
potentially increasing its payload capacity. Moreover, by
controlling wing bending loads, wing spar weight can be reduced.
Furthermore, by providing control over the structure, potentially
expanded flight envelopes are available to the aircraft. Improved
stability and control may be obtainable using controlled wing shape
(e.g., dihedral), as well as improved flutter characteristics
(which again provide for expanded flight envelopes). Moreover, the
increased structural weight of the devices may be partially offset
by the elimination of ailerons and/or wing-mounted elevators.
[0067] From the foregoing description, it will be appreciated that
the present invention provides a number of embodiments of a
lightweight aircraft capable of both stationkeeping and flight over
a wide range of speeds, while consuming low levels of power, for an
extended period of time, while supporting an unobstructed
communications platform, and while exhibiting simplicity and
reliability
[0068] Other embodiments within the scope of the invention include
devices comprising forward extending booms configured with canards,
and CG-movement devices. Likewise, other embodiments of the
invention could have other numbers of wing segments, including
variations with an even number of wing segments (e.g., six wing
segments), and other numbers of motors. For example, an embodiment
similar to the Helios aircraft might be configured with six wing
segments, 10 motors, and anywhere from two to six (or possibly
more) independent pitch-control devices. Likewise, a simple
embodiment might include three wing segments with one to three
motors and two or three (or perhaps even one) independent
pitch-control devices, or might even be a very long unsegmented
wing with one or more motors and a plurality of independent
pitch-control devices.
[0069] While a particular form of the invention has been
illustrated and described, it will be apparent that various
modifications can be made without departing from the spirit and
scope of the invention. Thus, although the invention has been
described in detail with reference only to the preferred
embodiments, those having ordinary skill in the art will appreciate
that various modifications can be made without departing from the
invention. Accordingly, the invention is not intended to be limited
by the above discussion, and is defined with reference to the
following claims.
* * * * *