FIELD OF THE INVENTION
The invention relates generally to aircraft, and more specifically,
to systems and methods for control of an aircraft.
Aircraft purposefully built to avoid radar detection are
characterized by shapes with as few different angles as possible. This results in
edges which are parallel to each other even if on opposite sides of the aircraft.
It is also desirable to have a fuselage that is blended into the wing where any
shapes of small radius can be placed on the upper side, unseen by ground radar.
Because of this smooth integration, these aircraft are sometimes referred as "flying
wings." An example of a flying wing aircraft is the B-2 bomber. An aircraft of low
radar cross section is devoid of any unnecessary protuberances such as a vertical
stabilizer, having its function replaced by control surfaces that increase the drag
on one wing or the other only when needed and otherwise lie against the wing to
become part of the wing.
The advantages of all-wing, tailless aircraft are known.
For example, tailless aircraft provide enhanced stealthy operating characteristics
due to their inherent low-observable configuration. Moreover, all-wing aircraft
provide other benefits such as improved efficiency due to reduced weight and drag
and, accordingly, are well suited for use in a wide variety of applications such
as in autonomous (unmanned) aircraft where the bulge for a pilot to look out doesn't
have to be accommodated.
A significant disadvantage of the tailless aircraft configuration
lies in the absence of an aircraft rudder normally incorporated within the vertical
tail section. The rudder is provided in conventional aircraft to provide a side
to side or yaw moment to the aircraft in flight. Therefore, without a rudder, other
means must be provided to impart yaw moment to the tailless aircraft. Traditionally,
tailless aircraft use spoilers in the outboard part of the wing. Either the left
side or the right side can be made to open to control the lateral direction of flight.
These spoilers are either made a part of the existing elevons, elevators or ailerons
in the form of split flaps or they are mounted ahead of these surfaces in the form
of inlay-spoilers. Elevons, ailerons and elevators on all wing aircraft have a minimal
contribution to radar cross section. The spoiler is the largest detractor of stealth
because it forms acute angles with the surface it emerges from. Traditional inlay
spoilers can be low in cross section if they are only opened on the top side. The
wing itself masks the view from balow. But a topside only spoiler of conventional
design produces a down force and, if the spoiler is near the tip of a sweptback
wing, the resulting force will pitch the airplane upward.
As such, based upon the foregoing, there exists a need
in the art for an improved method and device, which improves aircraft yaw control
characteristics without substantially interfering with the aircraft aerodynamic
and radar detectability characteristics.
US Patent No. 2,458,146 discloses an aircraft comprising first and second wings
positioned on opposite sides ofa longitudinal axis; a first control surface attached
by a first hinge to the first wing; and a second control surface attached by a second
hinge to the second wing. US Patent No. 6,491,261 discloses a wing mounted yaw control
device including a spoiler mounted on a first wing surface, and a deflector mounted
on a second wing surface. US Patent No. 4,466,586 discloses the use of rudder-like
surfaces to generate a yaw moment.
This invention provides an aircraft as defined in Claim 1.
The opening of these forward opening surfaces introduces drag on one wing or the
other. It is the drag some distance laterally from the centreline that produces
a yaw force.
The hinges can be canted at an angle of between 20 and
50 degrees with respect to a line perpendicular to the longitudinal axis.
The first and second forward opening control surfaces can
be canted to throw the air outward or inward so that the air can escape sideways
instead of building up in front of the spoiler. If the air was allowed to build
up in front, the surface would produce a down force just like the traditional hinge-in-front
The first forward opening control surfaces can have a substantially
rectangular shape, with an aft edge of each control surface being connected to one
of the wings by a hinge.
The forward opening control surfaces produce drag and a
side force to control yaw without the introduction of any up or down force.
This invention can be applied to an integrated fuselage/wing
structure generally defining the aircraft, wherein the first and second wings are
positioned, on opposite sides of the longitudinal axis with each of the wings including
a substantially straight swept-back leading edge, a lower surface extending aft
from the loading edge, and an upper surface extending aft from the loading edge,
and the control surfaces can be attached by hinges that are canted with respect
to the lateral axis, a direction parallel to the horizon but perpendicular to the
The aircraft can further include additional control surfaces
on the upper surface of the integrated fuselage/wing.
The invention also encompasses a method as defined in Claim
6 of providing yaw control of an aircraft.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is schematic representation of a perspective view
of a swept back aircraft that can be constructed in accordance with this invention.
FIG. 2 is a schematic representation of a top plan view
of the aircraft of FIG. 1, showing inlaid spoilers.
FIG. 3 is a schematic representation of a top plan view
of an aircraft showing yaw control spoilers.
FIG. 4 is a schematic representation of a side view of
a portion of a wing and a vertical spoiler.
FIG. 5 is a schematic representation of a side view of
a portion of a wing and a forward opening spoiler.
DETAILED DESCRIPTION OF THE INVENTION
In accordance with an aspect of the invention, a flying
wing tailless aircraft comprises an integrated fuselage/wing that generally defines
the aircraft and control surfaces integrally formed therewith. FIG. 1 is a schematic
representation of a perspective view of a swept back aircraft 10 that can be constructed
in accordance with this invention. The aircraft 10 has a longitudinal axis 12 and
is provided With a central fuselage 14 positioned along the longitudinal axis. A
pair of opposing swept back wings 16,18 extend laterally and in an aftward direction
from the fuselage 14. The wings 16, 18 have an outer contour which blends smoothly
and continuously with that of the fuselage 14. In this respect, the fuselage 14
is completely integrated with the wings 16, 18. This smooth integration is contemplated
to give the entire aircraft 10 the appearance and functionality of being a single
wing. Thus, the integrated fuselage/wing configuration generally defines the aircraft
10. As such, the aircraft 10 may be characterized by having a relatively low aspect
ratio and a generally triangular or delta-shaped planform.
The aircraft 10 is provided with an upper surface and a
lower surface. The upper and the lower surfaces encompass both the fuselage 14 and
the wings 16, 18. FIG. 1 shows the lower surface 20. In addition, the wings 16,
18 include leading edges 22, 24, respectively. The leading edges 22, 24 are configured
to, for example, form a continuous straight contour. Such a straight contour is
desirable in light of radar signature mitigation considerations, i.e., forming a
low-observable, delta-shaped aircraft. The leading edges 22, 24 of the wings 16,
18 along with the upper surface of the aircraft 10 generally define the aerodynamic
lifting surface of the aircraft 10. As such, the aerodynamic lifting surface is
generally disposed about the fuselage 14 and the wings 16, 18. The wings 16, 18
also include trailing edges 26, 28, respectively.
FIG. 2 is a schematic representation of a top plan view
of the aircraft of FIG. 1. As seen in FIG. 2, the aircraft 10 also includes control
surfaces 30, 32, 34, 36, 38 and 40 that are integrally formed with the upper surface
42 of the fuselage/wing configuration. Specifically, the control surfaces may include,
for example, elevons, ailerons, elevators, rudders, trim tabs, or similar components
that are well known in the art.
In accordance with this invention, some control surfaces
can be positioned in the top surface of the aircraft so as to prevent them from
being seen by ground radar. The particular control surface which should be only
on the top are those that open up so as to create drag. The other surfaces, the
elevator and ailerons, can be hinged to move up and down with little sacrifice in
radar cross section. The topside only control surfaces are called inlay spoilers
and can be operated to control the yaw of the aircraft. A conventional inlay-spoiler
opens up like a hatch door with a hinge on the upwind side. It creates drag but
also creates a force into the wing. In this invention, the yaw control inlay-spoiler
is hinged in the back. In one embodiment, at least some of the control surfaces
can be this hinged-in-the-back inlaid spoiler type that can be operated between
open and retracted positions. When in the retracted position, the surfaces of the
spoilers conform to the surface of the wings.
By operating a pair of conventional inlays 30, 32 (hinged
in the front) in the front of the aircraft, a down-moment can be produced. A pair
of conventional inlays 34, 36 in the back can provide an up-moment. Thus inlays
30, 32, 34 and 36 can be operated in pairs to provide pitch control. Since inlay
spoilers are very high drag devices, trimming in pitch can be done with fuel shifting.
Roll control can be achieved by operating the same four inlays in pairs laterally.
That is, pairs 30 and 34, or 32 and 36 can be operated to provide roll control.
The inlays 38 and 40 near the wing tips 44, 46 provide yaw control.
Inlays 38 and 40 are forward opening inlaid-spoilers. Forward-opening
inlaid-spoilers for yaw control can provide pure yaw and are free of any pitch or
roll moment if their hinges are canted with respect to air flow. If the air were
allowed to build up in front, the surface would produce a down force just like the
conventional hinge-in-front spoilers.
This invention permits a reduction in the aircraft radar
cross-section by eliminating the need for bottom-side spoilers so that surface discontinuities
in the bottom of the aircraft can be minimized. The particular problem with spoilers
with regard to radar signature is that in opening they form an acute angle with
the surface they rise out of. This creates a retro-reflecting structure for radar
to bounce off of.
FIG. 3 is a schematic representation of a top plan view
of an aircraft 50 showing yaw control spoilers 52 and 54. The spoilers are hinged
along edges 56 and 58 so that they open in a forward direction. The spoilers are
canted with respect to the longitudinal axis of the aircraft at angles &thgr;1
and &thgr;2. Angles &thgr;1 and &thgr;2 can
be the same angle. Arrows 60, 62, 64 and 66 show the direction of air flow in the
vicinity of the spoilers. Since the spoilers are canted outward, air is directed
toward the wing tips 68 and 70.
By adjusting the cant angle (the azimuth position of the
inlay) the up or down force can be brought to zero for pure yaw control. This is
important in swept wings because the tips are so far aft. Even vertical spoilers
with all their mechanical complexity produce a down force. FIG. 4 is a schematic
representation of a side view of a portion of a wing 72 and a vertical spoiler 74
positioned in a top surface 76 of the wing. Arrows 78, 80, 82 and 84 illustrate
air flow in the vicinity of the spoiler 74 showing how air is deflected upward with
a consequent down force.
FIG. 5 is a schematic representation of a side view of
a portion of a wing 86 and a forward opening spoiler 88 positioned in a top surface
90 of the wing. Arrows 92, 94 and 96 illustrate air flow in the vicinity of the
FIG. 4 shows that a vertical spoiler 74 causes a net change
in momentum upward, whereas with a canted and tilted surface as shown in FIG 5,
much of the air is withdrawn without going up. This is shown in FIG. 5 where the
arrow 94 shows the air escaping horizontally. Drag is still created but by canting
the surface the airflow is kept from damming up in front of the spoiler, which would
force the air up and over like a vertical spoiler. The side deflection can be outward
or inward. By choosing outward deflection, the air thrown to the side imparts an
inward force that produces a moment, which is in the same direction as the moment
due to drag. By adjusting the cant angle, the down force produced by the forward
opening spoiler can be balanced against the up force of the air piling up in front
of the spoiler.
This invention is particularly applicable to swept back
flying wing aircraft because there is no force down into the wing. Ordinary inlay-spoilers
(hinged in the front) will impart a down force which will pitch the aircraft up.
Since this invention provides a yaw moment without an up or down force it can be
used for wings where the tips are behind the center of gravity.
To demonstrate, in a model, the pure yaw behavior of the
forward opening spoiler, the variable dihedral effect of the sweepback must be overcome.
Otherwise, the yaw will produce a roll which would mask the unwanted roll produced
by any down force. The effect of the sweepback can be overcome by flying the model
with the weight off the wings. A model was built and then test flown at zero lift,
that is, in a ballistic trajectory. That allowed the yaw to occur without affecting
roll. If the model rolled in zero lift, it must be due to the unwanted up or down
To perform that test, a remote control catapult model was
made with a single topside-only forward opening spoiler. This was added to an existing
model that was equipped with normal control surfaces. The normal controls were used
to recover the airplane after the ballistic flight to land it safely. The trajectory
of the airplane upon launch can be judged by the eye to be ballistic. The transmitter's
pitch trim was adjusted until the familiar arc was achieved. Just before hitting
the ground, the control stick was pulled back for a gentle landing.
A shroud was provided in front of the inlay to keep the
leading edge of the new spoiler flush with the skin. The shroud and the spoiler
could be rotated in azimuth or even repositioned on the wing for different test
flights. In practice, the surfaces would not necessarily share the same place on
After several ballistic launches and subsequent recovery
maneuvers, a flight was made where near the top of the trajectory, the forward-opening
spoiler was popped open. Success could be measured by seeing the surface open up
without the airplane rolling, or pitching. A canted angle of about 50 degrees produced
The inlay-spoilers on the top surface of the aircraft are
not matched by anything on the bottom. Inlay-spoilers and topside control surfaces
have been used previously, but they have all been hinged in the front or they rose
vertically. When these conventional inlays are installed on the topside of swept
or delta wings, they must be balanced by inlay-spoilers on the bottom. An unbalanced
surface in the back will affect both pitch and roll. But with this invention, the
yaw control spoilers are self-balancing. The bottom skin need not have any control
surface on it and is thus more easily rendered low in radar cross section.
This wing mounted yaw control device includes spoilers
hingedly mounted on a top surface and canted with respect to the longitudinal axis
of the aircraft. A deployment mechanism can be provided to effect deployment of
the spoilers. During operation, the spoilers can be selectively deployed in order
to impart an unbalanced drag force on one wing, thereby imparting the desired yaw
moment to an aircraft in flight.
The creation of yaw moments, without any down force, has
application in sweptback wings where the tips are behind the center of gravity of
the aircraft. This invention provides the advantage of reducing radar cross section
over traditional (forward hinged, rearward opening) spoilers where there must be
a spoiler on the bottom side to counter the down force created by the top spoiler.
However, this invention can be used on any wing planform.
Using this invention on a swept wing takes advantage of
the canted hinge-line. The discovered phenomenon is that a forward opening spoiler
produces drag without a change in the pitch moment as long as the hinge-line is
canted away from being perpendicular with the airflow. The cant angle can be such
as to dump the air either away from the centerline or toward it. When the surface
is raised, this cant angle produces a lateral force, which is also, either toward
or away from the centerline. It is important to carefully choose whether this force
is toward or away based on the sweep angle. In a swept back wing, the control surface
is aft of the center of gravity, and if the hinge-line is canted so the side force
is inward, a moment is produced that is in the same sense as the moment produced
by the drag. With the same line of reasoning, if the wing is swept forward there
is an advantage in canting the hinge-line of the surface to dump the air inwardly.
If the wing is straight the hinge line must still be canted away, but there is no
advantage to dumping the air in either direction. Only the drag component is useful.
While particular embodiments of this invention have been
described above for purposes of illustration, it will be evident to those skilled
in the art that numerous variations of the details of the present invention may
be made without departing from the invention as defined in the appended claims.