U.S. patent application number 13/397569 was filed with the patent office on 2013-08-15 for system, apparatus and method for long endurance vertical takeoff and landing vehicle.
This patent application is currently assigned to AURORA FLIGHT SCIENCES CORPORATION. The applicant listed for this patent is Paul Nils Dahlstrand, James Donald Paduano, John Brooke Wissler. Invention is credited to Paul Nils Dahlstrand, James Donald Paduano, John Brooke Wissler.
Application Number | 20130206921 13/397569 |
Document ID | / |
Family ID | 48944819 |
Filed Date | 2013-08-15 |
United States Patent
Application |
20130206921 |
Kind Code |
A1 |
Paduano; James Donald ; et
al. |
August 15, 2013 |
SYSTEM, APPARATUS AND METHOD FOR LONG ENDURANCE VERTICAL TAKEOFF
AND LANDING VEHICLE
Abstract
A vertical take-off and landing (VTOL) aircraft according to an
aspect of the present invention comprises a fuselage, an empennage
having an all-moving horizontal stabilizer located at a tail end of
the fuselage, a wing having the fuselage positioned approximately
halfway between the distal ends of the wing, wherein the wing is
configured to transform between a substantially straight wing
configuration and a canted wing configuration using a canted hinge
located on each side of the fuselage. The VTOL aircraft may further
includes one or more retractable pogo supports, wherein a
retractable pogo support is configured to deploy from each of the
wing's distal ends.
Inventors: |
Paduano; James Donald;
(Boston, MA) ; Dahlstrand; Paul Nils; (Newton,
VA) ; Wissler; John Brooke; (Waltham, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Paduano; James Donald
Dahlstrand; Paul Nils
Wissler; John Brooke |
Boston
Newton
Waltham |
MA
VA
MA |
US
US
US |
|
|
Assignee: |
AURORA FLIGHT SCIENCES
CORPORATION
Manassas
VA
|
Family ID: |
48944819 |
Appl. No.: |
13/397569 |
Filed: |
February 15, 2012 |
Current U.S.
Class: |
244/7C ;
244/4R |
Current CPC
Class: |
B64C 13/16 20130101;
B64C 2201/102 20130101; B64C 3/42 20130101; B64C 29/00 20130101;
B64C 5/02 20130101; B64C 2201/021 20130101; B64C 27/52 20130101;
B64C 29/0091 20130101; B64C 29/04 20130101; B64C 2201/162 20130101;
B64C 29/0033 20130101; B64D 43/00 20130101; B64C 2201/108 20130101;
B64D 27/02 20130101; B64C 2201/187 20130101; B64C 9/00 20130101;
B64C 29/02 20130101; B64C 39/024 20130101; B64C 2201/088 20130101;
B64C 25/10 20130101 |
Class at
Publication: |
244/7.C ;
244/4.R |
International
Class: |
B64C 29/00 20060101
B64C029/00 |
Claims
1. A vertical take-off and landing (VTOL) aircraft, comprising: a
fuselage, wherein the fuselage has a nose end and a tail end; an
empennage located at the tail end of the fuselage, wherein the
empennage comprises a stabilizer configuration; two
counter-rotating engines that are arranged such that one engine is
mounted on the wing at each side of the fuselage; and a wing;
wherein the fuselage is positioned approximately halfway between
the distal ends of the wing; wherein the wing is configured to
transform between a vertical configuration and a horizontal
configuration using at least one pivotal connector positioned on
each side of the fuselage; wherein, during a first phase of
takeoff, the wing is in the vertical configuration thereby causing
the nose end of the fuselage to lift off the ground while the tail
end remains on the ground; wherein, during a second phase of
takeoff, the wing transitions from the vertical configuration to
the horizontal configuration until the fuselage achieves a
predetermined stand-up angle; and wherein, during a third phase of
takeoff, the wing is in the horizontal configuration and the
aircraft is capable of wingborne flight.
2. The aircraft of claim 1, wherein the stabilizer configuration
comprises a vertical stabilizer and an all-moving horizontal
stabilizer
3. The aircraft of claim 1, wherein the wing has a high aspect
ratio.
4. The aircraft of claim 1, wherein each engine is wing-mounted and
located at a point between the pivotal connector and the wing's
distal ends.
5. The aircraft of claim 1, wherein the aircraft comprises a
payload for intelligence, surveillance, and reconnaissance.
6. A vertical take-off and landing (VTOL) aircraft, comprising: a
fuselage, wherein the fuselage has a nose end and a tail end; an
empennage located at the tail end of the fuselage, wherein the
empennage comprises a stabilizer configuration; one or more
engines; a wing; and a retractable pogo support; wherein the
retractable pogo support is configured to deploy from the fuselage
to form a tripod launch and recovery configuration with the
empennage.
7. The aircraft of claim 6, wherein the retractable pogo support is
deployed using a spring.
8. The aircraft of claim 6, wherein the fuselage is positioned at a
predetermined stand-up angle while in the tripod launch and
recovery configuration.
9. The aircraft of claim 8, wherein the predetermined stand-up
angle is between 45 and 90 degrees.
10. The aircraft of claim 9, wherein the predetermined stand-up
angle is between 65 and 75 degrees.
11. The aircraft of claim 6, wherein the wing has a high aspect
ratio.
12. The aircraft of claim 6, wherein the aircraft comprises two
wing-mounted counter-rotating engines, wherein the two
counter-rotating engines are arranged such that an engine is
mounted on each side of the fuselage.
13. The aircraft of claim 6, wherein the aircraft comprises a
payload for intelligence, surveillance, and reconnaissance.
14. The aircraft of claim 6, wherein the stabilizer configuration
comprises a vertical stabilizer and an all-moving horizontal
stabilizer
15. A vertical take-off and landing (VTOL) aircraft, comprising: a
fuselage, wherein the fuselage has a nose end and a tail end; an
empennage located at the tail end of the fuselage, wherein the
empennage comprises a stabilizer configuration; one or more
engines; a wing; wherein the fuselage is positioned approximately
halfway between the distal ends of the wing; wherein the wing is
configured to transform between a substantially straight wing
configuration and a canted wing configuration using a canted hinge
located on the wing at each side of the fuselage; and two or more
retractable pogo supports; wherein a retractable pogo support is
configured to deploy from each of the wing's distal ends.
16. The aircraft of claim 15, wherein the wings are configured such
that, when in the canted wing configuration, the distal ends of the
canted wing form a tripod launch and recovery configuration with
the empennage.
17. The aircraft of claim 16, wherein the retractable pogo supports
are configured to deploy from the distal ends of the canted wings
to form a tripod launch and recovery configuration with the
empennage, such that the fuselage is positioned at a predetermined
stand-up angle.
18. The aircraft of claim 15, wherein the wing has a high aspect
ratio.
19. The aircraft of claim 17, wherein the predetermined stand-up
angle is between 45 and 90 degrees.
20. The aircraft of claim 19, wherein the predetermined stand-up
angle is between 65 and 75 degrees.
21. The aircraft of claim 15, wherein the aircraft comprises a
payload for intelligence, surveillance, and reconnaissance.
22. The aircraft of claim 15, wherein the aircraft comprises two
wing-mounted counter-rotating engines, wherein the two
counter-rotating engines are arranged such that one engine is
mounted on each side of the fuselage.
23. The aircraft of claim 15, wherein the counter-rotating engine
is positioned on each side of the fuselage at a point between the
fuselage and the canted hinge.
24. The aircraft of claim 15, wherein the stabilizer configuration
comprises a vertical stabilizer and an all-moving horizontal
stabilizer
Description
TECHNICAL FIELD
[0001] The present invention relates to system and methods for
vertical takeoff and landing of a long-endurance Unmanned Aerial
Vehicle ("UAV"). More specifically, the present invention relates
to systems and methods for vertical takeoff and landing of
long-endurance Tier 2 UAVs.
BACKGROUND INFORMATION
[0002] There has long been a need, exacerbated by today's overseas
contingency operations, for vertical take-off and landing ("VTOL")
vehicles that are capable of being deployed from confined spaces.
In fact, many situations favor vehicles, specifically UAVs, that
can launch and recover vertically without requiring complex or
heavy ground support equipment. The ability to organically deploy a
UAV is particularly attractive in situations such as
forward-operating bases, clandestine locales, payload emplacement,
and on-the-move situations. Until recently, however, the efficiency
penalty associated with incorporating a hover phase of flight, the
complexity associated with transition from vertical to horizontal
flight, and the necessity to reduce or eliminate exposure of ground
personnel to exposed high-speed rotors have hindered attempts to
develop organically deployable VTOL UAVs, which are expected to be
very important assets. Furthermore, the new competitive landscape
for VTOL vehicles now requires long endurance, which can require
flights in excess of 8 hours.
[0003] As a result, high aspect ratio (i.e., the ratio of a wing's
length to its breadth) fixed-wing designs are gaining advantage
over ducted designs and rotorcraft. An exemplary high aspect ratio
fixed-wing design is the Flexrotor, which is available from Aerovel
Corporation. The Flexrotor is described by Aerovel as a
tabletop-sized robotic aircraft that offers a combination of long
range and endurance, together with VTOL capabilities. For further
information, see, for example, Aerovel Corporation's website at
http://www.aerovelco.com/.
[0004] Despite prior attempts, the need exists for a system, method
and apparatus that allows organic deployment and operation of
long-endurance, high-aspect ratio VTOL UAVs from confined
spaces.
SUMMARY
[0005] The present disclosure endeavors to provide a system, method
and apparatus that allows organic deployment and operation of
long-endurance, high-aspect ratio VTOL UAVs from confined spaces.
Another objective of the present application is to provide a Tier
2-sized long-endurance Robust Efficient Vertical Launch and
Recovery (REVLAR) UAV.
[0006] According to a first aspect of the present invention, a
vertical take-off and landing (VTOL) aircraft comprises: a
fuselage, wherein the fuselage has a nose end and a tail end; an
empennage located at the tail end of the fuselage, wherein the
empennage comprises a stabilizer configuration; two
counter-rotating engines that are arranged such that one engine is
mounted on the wing at each side of the fuselage; and a wing;
wherein the fuselage is positioned approximately halfway between
the distal ends of the wing; wherein the wing is configured to
transform between a vertical configuration and a horizontal
configuration using at least one pivotal connector positioned on
each side of the fuselage; wherein, during a first phase of
takeoff, the wing is in the vertical configuration thereby causing
the nose end of the fuselage to lift off the ground while the tail
end remains on the ground; wherein, during a second phase of
takeoff, the wing transitions from the vertical configuration to
the horizontal configuration until the fuselage achieves a
predetermined stand-up angle; and wherein, during a third phase of
takeoff, the wing is in the horizontal configuration and the
aircraft is capable of wingborne flight.
[0007] According to a second aspect of the present invention, a
vertical take-off and landing (VTOL) aircraft comprises: a
fuselage, wherein the fuselage has a nose end and a tail end; an
empennage located at the tail end of the fuselage, wherein the
empennage comprises a stabilizer configuration; one or more
engines; a wing; and a retractable pogo support; wherein the
retractable pogo support is configured to deploy from the fuselage
to form a tripod launch and recovery configuration with the
empennage.
[0008] According to a third aspect of the present invention, a
vertical take-off and landing (VTOL) aircraft comprises: a
fuselage, wherein the fuselage has a nose end and a tail end; an
empennage located at the tail end of the fuselage, wherein the
empennage comprises a stabilizer configuration; one or more
engines; a wing; wherein the fuselage is positioned approximately
halfway between the distal ends of the wing; wherein the wing is
configured to transform between a substantially straight wing
configuration and a canted wing configuration using a canted hinge
located on the wing at each side of the fuselage; and two or more
retractable pogo supports; wherein a retractable pogo support is
configured to deploy from each of the wing's distal ends.
[0009] In certain aspects, the aircraft may comprise two wing
mounted counter-rotating engines, wherein the two counter-rotating
engines are arranged such that one engine is mounted on each side
of the fuselage. More specifically, at least one of the one or more
engines may be positioned on each side of the fuselage at a point:
(i) between the fuselage and the canted hinge; and/or (ii) between
the pivotal connector and the distal ends of the wing;
[0010] In certain aspects, the wing may be configured such that,
when in the canted wing configuration, the distal ends of the
canted wing form a tripod launch and recovery configuration with
the empennage.
[0011] In another aspects, the retractable pogo supports may be
configured to deploy from the distal ends of the canted wings to
form a tripod launch and recovery configuration with the empennage,
such that the fuselage is positioned at a predetermined stand-up
angle.
[0012] In yet another aspect, the wing may have a high aspect ratio
and/or a payload for intelligence, surveillance, and
reconnaissance.
[0013] In certain aspects, the predetermined stand-up angle may be
between 45 and 90 degrees; more preferably between 60 and 80
degrees, and most preferably between 66 and 75 degrees.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] These and other advantages of the present invention will be
readily understood with reference to the following specifications
and attached drawings wherein:
[0015] FIG. 1a illustrates an aircraft having canted hinges in a
substantially straight wing configuration;
[0016] FIG. 1b illustrates the aircraft of FIG. 1a, wherein the
port side wing has transitions to a canted wing configuration to
deflect wind;
[0017] FIG. 2a illustrates a front angular perspective of a first
REVLAR UAV configuration;
[0018] FIG. 2b illustrates a side perspective of the first REVLAR
UAV configuration;
[0019] FIG. 2c illustrates an exemplary diagram for calculating a
stand-up angle (e.g., launch angle);
[0020] FIG. 3a illustrates a front angular perspective of a second
REVLAR UAV configuration on the ground;
[0021] FIG. 3b illustrates a front angular perspective of the
second REVLAR UAV configuration in a first transitional phase;
[0022] FIG. 3c illustrates a front angular perspective of the
second REVLAR UAV configuration in a second transitional phase;
[0023] FIG. 3d illustrates a front angular perspective of the
second REVLAR UAV configuration in flight;
[0024] FIG. 4a illustrates a front angular perspective of a third
REVLAR UAV configuration on the ground;
[0025] FIG. 4b illustrates a front angular perspective of the third
REVLAR UAV configuration in a first transitional phase;
[0026] FIG. 4c illustrates a front angular perspective of the third
REVLAR UAV configuration in a second transitional phase;
[0027] FIG. 4d illustrates a front angular perspective of the third
REVLAR UAV configuration in flight;
[0028] FIG. 5a illustrates an exemplary avionics system diagram for
controlling a REVLAR UAV; and
[0029] FIG. 5b illustrates an exemplary component diagram of the
avionics system diagram of FIG. 5a.
DETAILED DESCRIPTION
[0030] Embodiments of the present invention will be described
hereinbelow with reference to the accompanying drawings. In the
following description, well-known functions or constructions are
not described in detail because they would obscure the invention in
unnecessary detail. The present disclosure endeavors to provide a
system, method and apparatus that allows organic deployment and
operation of long-endurance, high aspect ratio VTOL UAVs from
confined spaces.
[0031] An objective of the present application is to provide a tier
2-sized long-endurance Robust Efficient Vertical Launch and
Recovery (REVLAR) UAV, a form of VTOL UAV. Additionally, the
present application shall illustrate how a design may be scaled and
shall identify exemplary size, weight, and endurance limits for a
REVLAR UAV. Particular attention shall be paid to control
strategies, especially in the VTOL mode, and associated transition
to long-endurance flight. While the techniques and subject matter
of the present disclosure may be described in relation to USAF Tier
2 UAVs, said techniques and subject matter may be readily applied
to UAVs from the other USAF UAV tiers. For further information on
the USAF tier system, see, for example, Major William W. Bierbaum's
article entitled "UAV", available at
http://www.airpower.maxwell.af.mil/airchronicles/cc/uav.html.
[0032] As will be discussed in greater detail below, employing one
of more techniques disclosed in the present application enables
operation and deployment, including launch and recovery of UAVs,
from confined spaces. This ability greatly encourages organic
deployment of UAVs, thereby eliminating the need for complex and
cumbersome ground support. Organic deployment also eliminated the
need for time that is typically wasted in setting up a UAV and
preparing it for flight. Thus, the qualities of the presently
disclosed REVLAR UAV systems are highly advantageous in the combat
zone since minimal preparation and infrastructure are needed to
facilitate UAV flight and control. For instance, locating a
suitable runway for UAV deployment can be challenging, thus a UAV
capable of achieving flight vertically, or within a minimal area,
is often preferred when space is an issue. Moreover, organic UAV
deployment can eliminate the need for a centralized command center.
In other words, the REVLAR UAVs of the present application may be
readily used and deployed by personnel in the field without
requiring an advanced infrastructure. In fact, the REVLAR UAV may
even be locally controlled via a hand-held remote controller or
mobile command center. Alternatively, the REVLAR UAV may be
configured to be controlled from a greater distance using, for
example, existing communication systems, such as, for example,
L-Band, LAN, WLAN, cellular phone infrastructures, etc.
[0033] As will be discussed in greater detail below, in certain
aspects, a REVLAR UAV may even employ (i) canted wings and/or (ii)
tiltwing configurations. Canted wings may be accomplished by
integrating a hinge or other joint within the wing, thereby
permitting it to flex, curve, and/or pivot in the wind.
Accordingly, canted hinges allow for a UAV to avoid dynamic
transition by remaining trimmed at all flight conditions, from
forward flight to hovering flight.
[0034] Canted wings may be used for a variety of purposes,
including, for example, reducing the angle of attack of the wing
when deflected due to gusts or other disturbances. A first
exemplary wing is disclosed by commonly owned U.S. Patent
Publication No. 2010/0213309, entitled Non-Planar Adaptive Wing
Solar Aircraft, by Robert Parks (the "'309 Publication"). The '309
Publication discloses an aircraft having wings comprising one or
more modular constituent wing panels. Each wing panel of the '309
Publication includes at least one hinge interface that is
configured to rotationally interface with a complementary hinge
interface on another wing panel.
[0035] Another exemplary aircraft equipped with canted wing hinges
is illustrated in FIGS. 1a and 1b. FIG. 1a illustrates an aircraft
100 with both wings 102a, 102b in their normal state (i.e., forming
a substantially straight wing), without interference from, for
example, a wind gust. FIG. 1b, on the other hand, illustrates the
aircraft 100 of FIG. 1a with the port-side wing 102b flexing via
the canted hinge to form a canted wing in response to, for example,
a wind gust. Ignoring the thrust vectoring aspect of the design, as
illustrated in FIG. 1b, the wing 102b, while in the canted wing
configuration, effectively rejects gusts by maintaining constant
moment at the canted hinge point 104, thus delivering constant lift
to the aircraft 100 in the face of gusts.
[0036] As for the tiltwing configuration, a tiltwing aircraft
typically features a wing that is horizontal for conventional
forward flight and rotates up for vertical takeoff and landing. It
is similar to a tiltrotor design where only the propeller and
engine rotate. Tiltwing aircraft are often capable of VTOL
operations. A tiltwing design offers certain advantages in vertical
flight relative to a tiltrotor. Because the slipstream from the
rotor strikes the wing on its smallest dimension, the tiltwing is
able to apply more of its engine power to lifting the aircraft. For
comparison, the V-22 Osprey tiltrotor loses about 10% of its thrust
to interference from the wings. However, the fixed wing of a
tiltrotor aircraft offers a superior angle of attack--thus more
lift and a shorter takeoff roll--when performing STOL/STOVL
operations. A drawback of the tiltwing is control during hover,
because the wing tilted vertically represents a large surface area
for crosswinds to push.
[0037] In designing a REVLAR UAV according to the various aspects
of the present application, nominal target requirements include a
10 ft wingspan, 5 hour endurance, 70 lbs gross take-off weight, and
70 mph cruise speed. The REVLAR UAV should also be enabled to
launch and/or recover within a cylindrical area having a 3 meter
radius and at least 5 meters tall (i.e., 5 meters off the ground).
For example, as the vehicle enters the landing area from about 5
meters off the ground, the REVLAR UAV should be configured to
transition and land without breaching the cylindrical area.
Likewise during take-off it must stay inside this cylinder until it
reaches 5 meters. Moreover, the REVLAR UAV should be able to
operate safely in a confined space around people under field
conditions. Accordingly, there are several potential applications
for such a REVLAR UAV, including, for example, equipping it with a
sensor payload for intelligence, surveillance, and reconnaissance
(ISR).
[0038] An exemplary VTOL UAV that appears to meet the above nominal
target requirements is MLB Company's V-Bat ("V-Bat"). The V-Bat is
a tail-sitter aircraft having a ducted fan in a pusher
configuration powered by a gasoline engine. The V-Bat UAV has a
wingspan of 10 feet, weighs 70 pounds, can fly for up to 5 hours,
and is capable of launching and recovering in an area as small as
6.times.6 meters. For additional information on the V-Bat and its
capabilities, see, for example, the MLB Company's website at
http://spyplanes.com/products-v-bat/. As a result of the
weight-and-balance of the tail-mounted engine, the V-Bat also has a
high aspect ratio straight wing mounted far aft on the
fuselage.
[0039] Additional advantages of the V-Bat include its low center of
gravity, the fact that the rear-mounted duct has a good moment arm
with respect to center of gravity to improve control power in
hover, and potential benefits in drag due to duct ingestion of the
fuselage boundary layer. On the other hand, while the size, weight,
payload, and duration of the V-Bat make it a suitable VTOL UAV, the
V-Bat still suffers from shortcomings that may be overcome by the
teachings of the present application.
[0040] Accordingly, in developing a REVLAR UAV, a first objective
is to improve the efficiency of the propulsion system and reduce
the engine power and weight required for hover by introducing a
ducted fan, for instance using a mixer-ejector to improve hover
thrust, and using a modern efficient heavy fuel engine. A second
objective is to implement configuration modifications that simplify
and stabilize the transition between hover and wing-borne flight.
Once airborne, the aircraft transitions the thrust aft until a
forward airspeed sufficient to support the aircraft is reached, at
which point the aircraft is wing-borne and conventional
aerodynamics may take over.
[0041] Finally, a third objective is to employ full autonomy for
takeoff and landing. For example, the REVLAR UAV may employ a
system capable of landing the UAV, remaining on the ground for a
set period, and launching again in winds without any human
intervention. This may be accomplished by combining a configuration
that does not require dynamic transition between hover and forward
flight (that is, it has a stable trim across the velocity envelope)
with full-envelope flight control laws and robust recovery
procedures.
[0042] Exemplary REVLAR UAVs and configurations capable of
accomplishing vertical takeoff or landing within a minimal area
will now be described in greater detail. Said exemplary
configurations include, for example: (i) resting the REVLAR UAV on
a passively retractable pogo support; (ii) using canted hinges on
the wing to allow the wing tips and tail to form a tripod support;
and (iii) tiltwing configuration where the fuselage may be freely
rotated from the wings and engines. While the term "wing" maybe be
used throughout this application, the wing may be composed of one
or more wing portions, thus, for the purposes of this application,
two wing portions joined together by a fuselage or other components
shall be considered a single wing.
[0043] Aspect ratio and planform (e.g., the shape and layout of a
fixed-wing aircraft's fuselage and wing) can be used to predict the
aerodynamic performance of a wing. As exemplified in Equation 1,
the aspect ratio (AR) is defined as the square of the wingspan b
divided by the area S of the wing planform--this is equal to the
length-to-breadth ratio for constant breadth. For each of the
following REVLAR UAVs, it is preferable to utilize a wing having a
high aspect ratio, thus a high AR value. Accordingly, it may be
preferable to employ a wing having a high AR value of, for example,
at least 10 or, more preferably, at least 15.
AR = ( b 2 S ) Equation 1 ##EQU00001##
[0044] Turning now to FIGS. 2a and 2b, the first REVLAR
configuration involves minimal risk while satisfying each of the
above objectives. The REVLAR UAV 200 is illustrated resting on a
passively retractable pogo support 204. Depending on the design
needs of the aircraft, the pogo support may be of a fixed length or
telescopic (e.g., in direction B)--as illustrated in FIGS. 2a and
2b. While the REVLAR UAV 200 of FIGS. 2a and 2b may be appear
similar to a traditional UAV having a fixed wing 206 and engines
200, the REVLAR UAV's 200 design and aerodynamics allows the
aircraft to have reduced trim drag in cruise. For example, the UAV
200 may comprise one or more inlets for reducing trim drag.
[0045] Furthermore, using the pogo support 204, the REVLAR UAV 200
may be angled toward the sky using a predetermined stand-up angle,
thereby eliminating the need for a runway. In fact, due to the
REVLAR UAV's 200 stand-up angle (e.g., launch angle), which, as
discussed below, may be calculated as taught by FIG. 2c and
Equation 2, the launch configuration may be referred to as an
efficient tripod launch and recovery configuration. This
configuration also facilitated increased stability at all
velocities from zero to cruise (e.g., wingborne).
[0046] To provide thrust, the REVLAR UAV 200 may be equipped with,
for example, twin counter-rotating engines 202. Specifically,
REVLAR UAV 200 may utilize twin ducted fans 202 (e.g., shrouded
mixer-ejector fans) mounted on either side of the fuselage 208,
bringing the center of gravity forward and allowing the
incorporation of a empennage (i.e., tail assembly) for reducing
trim drag during cruise and hover. For a vehicle with a gross
take-off weight of 70 lbs, for instance, The propulsion system
could comprise a FloDesign Inc. Fan and Mixer-Ejector combination,
driven by an XRD Inc. 12hp heavy fuel engine. Similar systems have
been demonstrated to be quiet (propeller noise reduction of 15-20
dB) and reduce engine take-off power by approximately 30%. This is
particularly important for VTOL vehicles, in which the engine size
is virtually always driven by take-off power requirements.
Counter-rotating fans may also eliminate the need to cancel engine
torque in hover. In addition, the wing's inboard section and two
vertical surfaces form a cruciform in the downwash of the ducted
fans; flaps on this cruciform provide control during hover and
transition.
[0047] A purpose of the empennage is to give the aircraft
stability. The empennage 210 generally comprises two fixed parts,
the horizontal stabilizer 210b and the vertical stabilizer 210a.
The horizontal stabilizer 210b may be used to prevent the REVLAR
UAV 200 from pitching up or down. The rear portion of the
horizontal stabilizer 210b may employ an elevator, which is usually
hinged to the horizontal stabilizer 210b. Generally speaking, an
elevator is a movable airfoil that may be used to control the
up-and-down motion of an aircraft's nose during wing-borne
flight.
[0048] The vertical tail structure may be divided into the vertical
stabilizer 210a and the rudder. The vertical stabilizer 210a is the
fixed front section and may be used to prevent the aircraft from
yawing back and forth. In propeller driven UAVs (e.g., single
propeller), the vertical stabilizer 210a may also be used to offset
the tendency of the UAV to roll in the opposite direction in which
the propeller is rotating. The rear section of the vertical
structure often includes a rudder--a movable airfoil that may be
used to turn an aircraft during wing-borne flight.
[0049] However, for a REVLAR UAV 200, the horizontal stabilizer
210b on the empennage 210 may be all-moving. Thus, during low
speed, high angle-of-attack flight, the empennage 210 can remains
unstalled for longitudinal stability and control. An all-moving
horizontal stabilizer is sometimes referred to as a stabilator.
Essentially, an all-moving stabilizer, or stabilator, is an
aircraft control surface that combines the functions of an elevator
and a horizontal stabilizer. Specifically, while most fixed-wing
aircraft control pitch using a hinged horizontal flap--the
elevator--attached to the back of the fixed horizontal stabilizer,
some aircraft make the entire stabilizer movable. Because it
involves a large moving surface, a stabilator can allow the pilot
to generate greater pitching moment with little effort.
[0050] The wing can sometimes present a problem when it is stalled
(e.g., during VTOL and/or transition)--vortex shedding off the wing
can be non-uniform (especially in gusts), and for a high aspect
ratio wing, this can lead to wing rock. Accordingly, if it is
determined, e.g., by an onboard computer or operator, that these
forces cannot be stabilized with the duct vane surfaces alone, the
empennage's all-moving wing tips can be implemented to counter the
instability. In certain aspects, both the horizontal and vertical
stabilizers may be all-moving.
[0051] Upon liftoff, a VTOL vehicle transitions to hover via a
continuous set of trim points, reducing forward speed as more of
its weight becomes supported by vectored thrust. Attitude during
vertical descent is typically about 90 degrees, necessitating
quaternion-based attitude control. After the REVLAR UAV's 202
empennage 210 touches down (e.g., makes contact with the ground
212), which may be detected either by a squat switch or a simple
altitude rate estimator in the flight control system, the pogo
support 204 may deploy from and/or re-stowed (e.g., retracted) into
or alongside the fuselage 208 in the directions of motion A. The
pogo support 204 may be spring-loaded, thereby enabling quick
deployment from the fuselage 208.
[0052] Duct flaps may be used to provide control to smoothly rotate
the vehicle forward, into a stable tripod launch and recovery
configuration on the ground 212. The tripod attitude and overall
weight-and-balance must be such that for takeoff the duct flaps can
cause the vehicle to rotate about the tail 210 and achieve a
vertical attitude with the thrust well below the lift-off
value.
[0053] As with other phases of flight, this transition from
horizontal to vertical flight is expected to be a smooth transition
through a set of trim states. In certain aspects, the set of trim
states may be actively stabilized. Avoiding dynamic transitions is
a tenet that may be employed to increase robustness. The pogo 204
landing support can be re-stowed using a simple pinion mechanism
that overcomes the spring loads in the deployment mechanism--this
simple positive-deploy/servo stow approach is used on general
aviation gear to ensure reliability, since flying with gear
deployed is much safer than landing without gear deployed. However,
other mechanical methods known in the art could be used to re-stow
the pogo 204 inside of along side the fuselage 204 (e.g., retracted
or swung). Exemplary mechanical methods may take advantage of, for
example, one or more of the following gear systems; pinion, worm
drives, sun and planet gears, and the like.
[0054] Turning now to FIG. 2c and Equation 2, the diagram
illustrates exemplary target requirements for a non-skittering
rotation capable of launch, or takeoff. To start, torque T about
the pivot point is computed. Torque T for the vectored component of
thrust must overcome the torque of the vehicle weight. The minimum
stand-up angle .theta. shown here assumes that thrust (T/mg) is
maintained below 80% weight to prevent skittering, and the
application of thrust is at the center of gravity. More
specifically, T is the thrust of the engines, dt is angle that the
thrust can be deflected with respect to the fuselage using flaps or
other thrust-vectoring techniques, L.sub.T and L.sub.g are the
distances from the pivot point on the ground to the point of thrust
application and the center of gravity, respectively. m is the mass
of the vehicle, g is the acceleration of gravity, and .theta. is
the angle that the vehicle make with the ground.
[0055] During vehicle rotation, thrust T should be well below (for
instance, 80 percent of) the weight (mg) to maintain friction at
the pivot point, and the ratio L.sub.T/L.sub.g is approximately one
due to the proximity of the center of gravity to the engines.
Finally, it is assumed that thrust vectoring of about 30 degrees
can be achieved. As illustrated by Equation 2, this results in a
minimum .theta. value (stand-up angle) of 66 degrees for the
on-ground attitude of the vehicle.
( T sin .delta. T ) L T > ( mg cos .theta. ) L g cos .theta.
< ( T mg ) ( L T L g ) sin .delta. T ~ < ( 0.80 ) ( 1 ) ( 0.5
) .theta. > cos - 1 ( 0.4 ) .theta. > 66 .degree. Equation 2
##EQU00002##
[0056] A design trade-off in determining the best overall
configuration for a particular application is to understand the
best landing altitude for stability on the ground, as well as ease
of transition back to hover. The autonomous take-off phase is prone
to complex ground interaction involving `skittering` across the
ground or otherwise accelerating in unwanted ways during transition
from weight-on-skids to air. For example, if thrust vectoring is
sufficient to rotate the vehicle to vertical while significant
weight (perhaps 20% of the vehicle weight) is still supported by
the tail, these effects can be virtually eliminated. This limits
the attitude after landing to at least 66 degrees, as shown in FIG.
2c. Higher attitudes require either less thrust (T) or less thrust
vectoring (dt) to rotate based on Equation 2, but provide less
resistance to tip-over from gusts. Accordingly, an example stand-up
angle value between 45 and 90 degrees may be suitable; more
preferably between 60 and 80 degrees, and most preferably between
66 and 75 degrees.
[0057] Turning now to FIGS. 3a-3d, rather that using the single
pogo support 204 of FIGS. 2a and 2b, a REVLAR UAV 300, according to
a second aspect, may be equipped with canted hinges 308 on the
wings 306, thereby enabling the wing tips, or distal ends of the
wing structure, and tail 312 to form a tripod launch and recovery
configuration. Apart from the lack of the single pogo support 204
and canted hinges 308, which enabled a canted wing configuration,
the REVLAR UAV 300 of FIGS. 3a-3d is otherwise substantially
similar to the REVLAR UAV of FIGS. 2a-2c. Accordingly, the same
propulsion techniques, airfoil designs, angle calculations,
techniques, and the like make be applied.
[0058] Depending on a designer's needs, the distal ends of the
REVLAR UAV's 300 wing 306 may include retractable pogo supports 304
to widen the UAV's 300 stance on the ground and to increase the
stand-up angle without requiring a longer wing. As illustrated in
FIG. 3a, pogo supports 304 may be deployed from the wing tips
(e.g., distal ends), so that the fully folded wing plus pogo
supports 304 form a tripod launch and recovery configuration when
combined with the empennage 312. As will be discussed below, FIGS.
3a through 3d illustrate four exemplary wing-droop settings
encountered when transitioning from ground to wing-borne
flight.
[0059] Specifically, FIG. 3a illustrates the REVLAR UAV 300 on the
ground with the wing 306 in a canted wing configuration. This may
be accomplished by bending the canted hinges 308 to a predefined
maximum bend angle. As illustrated, the resulting REVLAR UAV 300
has a wide stance and low center of pressure on the ground--both
characteristics assist in preventing the REVLAR UAV 300 from
tipping over. As previously mentioned, the stance may be widened by
including retractable pogo supports 304. The retractable pogo
supports 304 also provide the added benefit of increasing the
stand-up angle .theta. without requiring that the wing 306 be
lengthened. As in the REVLAR UAV 200 of FIG. 2b, depending on the
design needs of the REVLAR UAV 300, the retractable pogo support
304 may be of a fixed length or telescopic.
[0060] Turning now to FIG. 3b, the REVLAR UAV 300 is shown as
having entered the second phase of the take-off transition--the
wing's 306 canted hinges 308 have begun to straighten out. In
addition, the retractable pogo supports 304 have been re-stowed
(e.g., retracted) into the wing 306 to avoid, for instance,
unnecessary drag. As described above, in relation to FIGS. 2a and
2b, the pogo supports 304 may be retracted using, for example, a
pinion mechanism that overcomes the spring loads in the deployment
mechanism. Alternatively, electromagnets, solenoids, or other
similar means, may even be used to provide a retracting pulling
force.
[0061] As illustrated, the outboard wing portions (e.g., the span
between the cant hinge 308 and the distal ends of the wing 306) may
be maintained at a low angle of attack (alpha) during the
steady-state transition to hover. FIG. 3c illustrates the third
phase of the take-off transition where the canted wing 306 has
continued to straighten out via the cant hinges 308 as the REVLAR
UAV 300 gains altitude. Finally, FIG. 3d illustrates the fourth and
final phase where the wing 306 and cant hinges 308 have fully
extended and are said to have been straightened out. In other
words, the wing 306 has transformed to a substantially straight
wing configuration. At this point, the REVLAR UAV 300 may enter a
horizontal, wing-borne state.
[0062] Maintaining vehicle stability and control during high-alpha
operation, and the associated potential need to add all-moving tip
surfaces to stabilize wing rock, are some of the drawbacks to
conventional configurations for performing high-alpha `deep stall`
maneuvers to perform high glide-slope landings. As in known in the
art, alpha refers to the angle of attack--the angle between a
reference line on a lifting body (often the chord line of an
airfoil) and the vector representing the relative motion between
the lifting body and the air/fluid through which it is moving.
[0063] The portions of wing 306, which are immediately outboard of
the engines (e.g., propulsors) 302, are used to overcome these
difficulties. The cant (or bend) in the hinge 308 causes the angle
of attack of the outboard section of the wing 306 to be reduced. As
shown in FIGS. 3a-3d, at each vehicle attitude there exists a hinge
bend angle that brings the wing into a low-alpha, lift producing
configuration. Together with the all-moving horizontal tail
empennage, this approach enables the REVLAR UAV 300 to achieve trim
while minimizing wing stall down to very low speed.
[0064] Landing proceeds in a controlled, low-speed descent, but is
more robust than typical tail-sitters due to the very wide stance
of the vehicle on the ground. Besides solving the high-alpha
controllability problem, the canted wing geometry can be used for
active gust load alleviation in up-and-away flight. For landing,
the pogo supports 304 may be deployed from the wing 306 at the tips
as described and illustrated in FIG. 3a.
[0065] Consequently, employing canted hinges 308 in a wing 306
assists in avoiding the necessity for a dynamic transition (e.g.,
untrimmed flight requiring precise maneuvering) during the takeoff
of a REVLAR UAV, while also providing a stable base for the REVLAR
UAV `tail-sitter` take-off and landing configuration show in FIG.
3a. Advantageous features of a REVLAR UAV 300 having canted hinges
include, for example: (1) VTOL takeoff can be accomplished by
rotating the vehicle about the tail boom/ground contact point using
thrust vectoring while transitioning from stationary to vertical
flight; (2) on the ground, the canted hinge-pogo design provides a
broad, stable base with low center of pressure to help prevent tip
over; (3) during landing, outboard panels remain at low angle of
attack, providing trim at low speed.
[0066] A third REVLAR UAV configuration involves a modification of
the free wing concept, and is shown in FIGS. 4a-4d--this type of
wing configuration being more commonly known as tiltwing. Turning
now to FIGS. 4a through 4d, a third REVLAR configuration is shown
that uses a form of tiltwing that involves rotating the fuselage
404 freely from the wings 406 and engines 402 to enable ground
recovery and re-launch. Again, the concept of operations are
substantially the same as the REVLAR UAV of the previous examples,
except for lack of pogo and launch and recovery.
[0067] For launching the REVLAR UAV 400, a mechanical latch device
is released to enable the tiltwing configuration (e.g., the ability
to transition from a vertical configuration to a horizontal
configuration). In a first phase of takeoff, the wings 406 are in
the vertical configuration. As the engine 402 thrust is increased
with the wings 406 in the vertical configuration, the nose end of
the fuselage begins to lift off the ground 408 while the tail end
initially remains on or near the ground 408, thereby causing to
fuselage 404 to be non-parallel to the ground 408. During a second
phase of takeoff, as the engine 402 thrust continues to increase
and the wing 406 begins to transition from the vertical
configuration to the horizontal configuration (e.g., the fuselage
404 freely rotates) until the fuselage 404 has achieved a
predetermined stand-up angle. The standup angle may be calculated
using the methods of FIG. 2c or the standup angle may simple be
substantially vertical to the ground 408 (e.g., .about.90 degrees).
At this point in the transition, the wings are nearing the
horizontal configuration. During a third phase of takeoff, the wing
406 had achieved the horizontal configuration and the aircraft is
capable of wingborne flight. Once the wings are in their horizontal
configuration, the mechanical latch device is enabled, thereby
locking the wings in the horizontal configuration and preventing
the fuselage 404 from freely rotating.
[0068] For recovery, the REVLAR UAV 400 performs substantially the
same phase sequence as the launching procedure, but in reverse
order. Specifically, when the REVLAR UAV 400 contacts the ground
408, whether vertically or at an angle, and as thrust is reduced,
the mechanical latch device is released, thereby re-enabling the
tiltwing configuration and allowing the fuselage 404 to rotate with
respect to the wings 406. Thrust continues to reduce to a value
required to support the wing structure 406, but not the fuselage
404. At this point, the wings 406 begin to drop, and the fuselage
404 rotates or slides out from under the wings 406. The fuselage
404 at the completion of touchdown is horizontal to the ground 408,
but the wings 406 and engines 402 remain oriented vertically. This
configuration has an extremely low center of gravity, and the
recovery procedure can simply be reversed for re-launch (i.e.,
takeoff). As noted, the tiltwing configuration includes a mechanism
for mechanically unlatching-latching that will lock the wing
positively in place during takeoff/wingborne flight, and allow the
wing to unlock during landing or transition. For instance, a
tapered pin that is actuated to protrude from the fuselage. The
tapered pin may be configured to engage a hole in the root spar of
the wing that would both align the wing with the fuselage and hold
it in place. Other mechanisms are possible, including, for example,
direct servo-drive of the wing tilt axis, a spring-loaded latch
mounted on the wing which engages a release mechanism in the
fuselage.
[0069] Specifically, FIG. 4a illustrates the REVLAR UAV 400 on the
ground, in a take-off position where the portions of the wings 406
between the fuselage 404 and the distal ends of the wings 406 are
vertically oriented with respect to the fuselage. The pivoting wing
portions may be pivotally coupled either to the remaining portion
of the wing, or directly to a fuselage using one or more known
techniques. For example, a rotating shaft may be employed. For
example, a rotating shaft that is co-located with the main spar,
may be employed. The shaft may be rigidly and/or internally mounted
to either the outboard or inboard portion of the wing or the
fuselage, and rotating on roller bearings on the other portion.
[0070] As illustrated, the REVLAR UAV 400 has an extremely low
center of gravity and is laying substantially flat on the ground,
thereby virtually eliminating any risk of the REVLAR UAV 400 from
tipping over. Prior to liftoff, the fuselage 404 is substantially
perpendicular to the wings 406 and the pivotable combination of
engine 402 and wing portion are vertical--pointing upward, toward
the sky.
[0071] Turning now to FIG. 4b, the second phase of the take-off
transition is illustrated. As the REVLAR UAV's 400 engines 402
increase the output thrust, the engines 402 and wing portions 406
begin to vertically lift off of the ground 408, causing the nose
portion of the fuselage 404 to point upward, wherein the tail 412
section is still in contact with, or closer to, the ground 408.
FIG. 4c illustrates the third phase of the take-off transition
where the fuselage 404 has continued to pivot and is now almost
parallel with the wings' 406 direction and the direction of engine
thrust. In other words, the outer portions of the wings 406 are
approaching the horizontal configuration. Finally, FIG. 4d
illustrates the fourth and final phase where the wings 406 portions
have fully pivoted and are horizontal with respect to the fuselage
404; in other words, the wing is substantially parallel with the
fuselage 404. At this point, the REVLAR UAV 400 has achieved
wing-borne state.
[0072] For the three REVLAR configurations discussed above and
illustrated in FIGS. 2a through 4d, the weight of the REVLAR UAV
should be about the same, regardless of configuration.
Specifically, the weight breakdown of an exemplary REVLAR UAV is
provided in Table 1 below.
TABLE-US-00001 TABLE 1 Structure (20% GTOW) 14 Payload 5 Twin
Ducted Fans 10 XRDi 12 HP Engine 16 Three Gearboxes 11 Fuel 14
Total 70
[0073] Turning now to FIGS. 5a and 5b, these figures illustrate an
exemplary avionics system 500 component diagram for controlling a
REVLAR UAV 502. For clarity, the complex aircraft power and control
systems are excluded from the figures. Turning now to FIG. 5a, an
exemplary avionics system 500 generally comprises three primary
components: a REVLAR UAV 502; a ground control station 504; and a
ground service module 506.
[0074] Turning now to FIG. 5b, the diagram of FIG. 5a is
illustrated in greater detail. The REVLAR UAV 502 may include any
one of the UAVs disclosed in FIGS. 2a-4d. The REVLAR UAV 502
typically includes an on-board vehicle computer 524 that is
responsible for controlling the various aircraft components and
functions. The vehicle computer 524 may be communicatively coupled
with a remote input/output unit 530 (e.g., Power DNA
Cube--DNA-PPC5), a Inertial Navigation System (INS) 522 (e.g,
Raytheon Advanced Protection Technology Receiver (RAPToR)) that is
communicatively coupled with an inertial measurement unit 526 and
GPS receiver, a user interface panel 532, an on-board memory device
560 (e.g., hard drive, flash memory, or the like), or other
services 520. The remote input/output unit 530 may be
communicatively coupled with Microair UAV Transponder 534, engine
control unit (ECU) 536, Power Switching 538, Power System Status
540 and an Airdata/Mag unit 542. The remote input/output unit 530
may be communicatively coupled with the user interface panel 532
for maintenance and with a payload 528 (e.g., SMEP DRS) for
control.
[0075] To facilitate wireless communication with the ground control
station 504, the REVLAR UAV 502 further comprises an air
communication link 510 enabled to transmit (TX) and receive (RX)
power using one or more antennas (e.g., top and bottom) via a
circulator 516, LNE 512 and RFE 514. To collect data and monitor an
area, the REVLAR UAV may be equipped with a traditional ISR
surveillance payload. For example, the REVLAR UAV 502 may be
equipped with one or more cameras 508, audio devices, and the like.
Any video, or other data, collected by the REVLAR UAV 502 may be
wirelessly communicated to the ground control station 504 in real
time. The REVLAR UAV 502 may be further equipped to store said
video and data to the on-board memory device 560. If the REVLAR UAV
502 is operated in an unfriendly zone, it may be advantageous to
implement a data self-destruction protocol. The REVLAR UAV 502 may
be programmed to erase, or otherwise destroy, the on-board memory
device 560 if the REVLAR UAV 502 determines that it may have fallen
into an enemy's possession. For example, the REVLAR UAV's 502
on-board memory device 560 may automatically erase upon touching
down in a location outside of a predefined radius from the launch
area, based on GPS calculations, or if a crash is detected, e.g.,
based upon a sudden impact.
[0076] The ground control station 504 is used to wirelessly control
the operation of one or more REVLAR UAVs 502, including, at least,
launch, recovery, and flight. The ground control station 504 may be
a portable station such as, for example, a mobile command center,
remote controller, and the like. A portable ground control station
504 may be advantageous in that it enables UAV 502 deployment from
nearly any location with minimal preparation. Alternatively, the
ground control station 504 may be stationary, such as those found
in substantially permanent structures and buildings, whether local,
or remotely controlled from a distance via a communication network
(e.g., the internet, wireless phone network, etc.).
[0077] An exemplary ground control station 504 may comprise a
vehicle control station 552 to a ground communication link 550 for
communication with a REVLAR UAV 502. An exemplary ground
communication link 550 may include the EnerLinksIII.TM.
Intelligence, Surveillance and Reconnaissance (ISR) system,
available form ViaSat, Inc. at
http://www.viasat.com/government-communications/isr-data-links/enerlinks.
The vehicle control station 552, which is communicatively coupled
to the exemplary ground communication link 550, may include one or
more user interface devices, thereby allowing a person to operate
and monitor the REVLAR UAV 502 from the ground control station 504.
Exemplary interface devices may include, for example, one or more
joysticks, throttles, buttons, and any other controllers that may
be useful in controlled flight and/or surveillance. The vehicle
control station 552 may also include one or more audio/visual
devices, thereby permitting the user to monitor the REVLAR UAV 502
from a distance. For example, the video signal from the camera 508
or any other data, including location, may be wirelessly
communicated to the ground control station and displayed using said
audio/visual devices. An exemplary Vehicle Control Station 552 may
employ or incorporate CDL Systems Ltd.'s VCS-4586. For additional
information on the VCS-4586, see, for example, CDL Systems Ltd
website at http://www.cdlsystems.com/index.php/vcs4586.
[0078] The ground communication link 550 may communicate with the
REVLAR UAV 502 using four or more radio interface modules 546 and
pointing systems 544. The ground control station 504 preferably
communicates with the REVLAR UAV, using L band or another spectrum
reserved for military use. L band refers to four different bands of
the electromagnetic spectrum: 40 to 60 GHz (NATO), 1 to 2 GHz
(IEEE), 1565 nm to 1625 nm (optical), and around 3.5 micrometres
(infrared astronomy). In the United States and overseas
territories, the L band is generally held by the military for
telemetry.
[0079] A real-time kinematic (RTK) system 548 may also be coupled
to the ground communication link 550 to provide positioning
information in cooperation with a GPS transmitter and antenna. RTK
satellite navigation is a technique used for land and hydrographic
survey. RTK technology may be based on the use of carrier phase
measurements of the GPS, Globalnaya navigatsionnaya sputnikovaya
sistema (GLONASS) and/or Galileo signals where a single reference
station provides the real-time corrections, providing up to
centimeter-level accuracy.
[0080] The ground service module 506, on the other hand, is
primarily used for ground maintenance. Ground maintenance may
include, for example, updating the REVLAR UAV's 502 software,
firmware, diagnostics, battery charging, and the like. Like the
ground control station 504, the ground service module 506 may be
portable or stationary, depending on the needs of the particular
user. However, because the ground service module 506 is often
connected to the REVLAR UAV 502 using a wired connection, the
ground service module 506 is preferably accessible to the launch
and/or recovery location. The ground service module 506 generally
comprises a battery charger 554, AC-DC converter 556, and ENET
switch 558. The AC-DC converter 556 is enabled to receive AC
current from a ground power source (e.g., 120 VAC) and covert it to
a usable DC power (e.g., 28 volts). The AC-DC converter 556 may be
used to provide power to the REVLAR UAV 502 and/or the battery
charger 554. The REVLAR UAV 502 is typically connected to the
ground service module 504 via a wired connection, such as a cable
bundle or umbilical. This wired connection may be used to carry
both current and data signals. One or more switches or relays may
be used to selectively connect the battery charger 554 and AC-DC
converter 556 to the REVLAR UAV 502. Accordingly, the REVLAR UAV
502 may receive power directly from the AC-DC converter 556 or use
the battery charger 554 to charge any on-board batteries. Finally,
the ENET switch 558 may be used for maintenance (e.g., diagnostics)
and other data transfers (e.g., software updates or backup).
[0081] While avionics systems may be specifically designed for use
in the above REVLAR configurations, existing avionics systems may
be adapted for REVLAR configurations. For example, existing
avionics systems, such as those used for the Aurora GE-50, GE-80,
Excalibur, Orion, Vulture, and Skate, might be adapted for use with
a REVLAR UAV. Avionics components in these architectures may
include the flight control system (GPS-INS and flight computer),
communications, ground servicing equipment, and ground control
station (GCS). Many of Aurora's systems use the TRL 9 VCS-4586
Vehicle Control Station software from CDL systems for the GCS, and
employ an on-board vehicle management computer that houses a
STANAG-4586 compliant Vehicle Specific Module (VSM). Lower cost
implementations such as Skate use Aurora's miniature Autopilot,
which has been adapted to a number of low-cost flight test efforts,
and is part of Skate's military-ready product.
[0082] Verifying the control strategy for the REVLAR vehicle, a
medium fidelity simulation can adequately predict behavior in the
regime from hover to low-speed flight. Trim, stability, and
controllability properties may use the resulting vehicle
aerodynamics, combined with test stand-verified models of ducted
fan performance and control effectors in duct flows.
[0083] Torque commands from the vehicle control laws are
subsequently passed through control allocation software that
performs control surface mixing in the face of saturation and
nonlinearities. In thrust-vectored applications, nonlinearities
arise from kinematic effects at high angles of attack, large thrust
vectoring angles, and from the duct vanes themselves. Saturations
are a primary concern during hover-to-land operations; winds
typically cause saturation in the axis, which must turn the vehicle
into the wind to maintain position.
[0084] Trim calculations, linearizations, and control law designs
should be calculated at a number of representative conditions
across the flight envelope to demonstrate the feasibility of robust
control, for the down-selected REVLAR configuration. For instance,
steady winds from various headings, superimposed with Dryden gust
spectra, may be used to demonstrate the robustness of the
vehicle-controller combination, the adequacy of the control power,
and the repeatability of recovery. Transition from air to ground
may be modeled using ground-interaction approaches developed for
other auto-land programs for VTOL vehicles. Controlled rotation
(vehicle weight balanced at all times) and `gravity-assisted`
rotation (vehicle allowed to accelerate about the touchdown point)
may also be applied to tripod landing.
[0085] Once any problems of trim, stability, and control is solved
through careful vehicle design, robustness to winds and gusts may
be a challenge when developing a fully autonomous vertical takeoff
and landing. However, two solutions may be used to increase
robustness--which may be used together or individually.
[0086] The first method is to descend quickly. Certain aircraft may
be configured to execute a deep stall to affect a precipitous
recovery to a relatively small area. While this approach is not
viable for vehicles much larger than the REVLAR, because this
maneuver can cause catastrophic damage on impact, a controlled
vertical descent at 5 to 10 meters per second (depending on the
prevailing winds and gusts), terminating in a hard, positive
landing, should be robust and repeatable without incurring undue
wear-and-tear on the vehicle.
[0087] The second method is to measure and reject winds and gusts.
While this approach is more complicated in that it requires
additional sensors, this approach provides greater accuracy. For
instance, in very severe wind and gust situations, not only will
alpha and/or beta measurements be extremely useful, but in some
cases distributed measurement, e.g., left vs. right wing, will
significantly improve accuracy and effectiveness. Exemplary sensors
suitable for incorporation are available through Aeroprobe
Corporation. For additional information, see, for example,
Aeroprobe Corporation's website at http://www.aeroprobe.com and
their line of air data probes, available at
http://www.aeroprobe.com/uploads/Air-Data-Applications-for-web.pdf.
[0088] While the present invention has been described with respect
to what are currently considered to be the preferred embodiments,
it is to be understood that the invention is not limited to the
disclosed embodiments. To the contrary, the invention is intended
to cover various modifications and equivalent arrangements included
within the spirit and scope of the appended claims. The scope of
the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures
and functions.
[0089] All U.S. and foreign patent documents, all articles, all
brochures, and all other published documents discussed above are
hereby incorporated by reference into the Detailed Description of
the Preferred Embodiment.
* * * * *
References