Control force generator

A control force generator for an aircraft using circulation control to a selectively produce lift on an otherwise non-lift surface. The generator employs a novel, double-slot single Coanda surface arrangement for selectively generating the aerodynamic lift.

TECHNICAL FIELD 
This invention generally relates to fluid control surfaces for generating 
control forces and more particularly to a control force generator 
utilizing circulation control in a double slotted, single Coanda surface 
arrangement for selectively generating aerodynamic lift on an otherwise 
nonlifting surface. 
BACKGROUND OF THE INVENTION 
The need to utilize short and narrow, austere landing fields, particularly 
for STOL aircraft, requires accurate glidepath and directional control to 
limit dispersion on landing. While airfield performance is improved with 
lower speed operation, the handling qualities and controllability of STOL 
aircraft diminish significantly at the slower approach speeds experienced 
during a STOL landing. 
Upon certain conditions of aircraft operation, the relatively streamline 
airflow across the upper surface of the wing can become partially or 
substantially separated from the upper surface thereof, resulting in a 
substantial loss of control. This flow separation, or stall condition, 
typically occurs with an aircraft wing at relatively low flying speeds 
found, for example, at landing and takeoff conditions when the wing is 
operated at a relatively high angle of attack and when maximum lift 
generation is particularly critical. This loss of control, resulting from 
the above-noted stall condition, is also applicable to aerodynamic 
stability and control surfaces, such as, for example, ailerons, rudders, 
and elevators. 
Airflow separation from an airfoil is a particularly onerous problem when 
designing an aircraft for STOL operation. Because large pitching moments 
and engine-out yawing and rolling moments are associated with known 
powered-lift arrangements in the STOL mode, the conventional aircraft, 
configured for STOL performance, requires large control surfaces. These 
large control surfaces result in a drag penalty at cruise. Furthermore, 
even with the use of large control surfaces, the airspeed needed for 
minimum control is relatively high compared to that which is theoretically 
possible with the optimum powered-lift arrangements. 
In order to provide a pilot with a greater lateral response for a given 
control input at STOL operation and thus reduce the time required for 
improving lateral tracking errors, enhanced sideforce controls are 
necessary. Known solutions include thrust deflection vanes positioned in 
the slipstream as well as the deflection of ailerons and rudders having 
large control surfaces as previously noted. 
One problem with the movable vane configuration is large thrust losses. 
Additionally, the movable vanes require complex actuators which are 
difficult to maintain, thus providing a reduced reliability of 
performance. 
As noted above, the use of ailerons and rudders having large control 
surfaces has the problem of resulting in a drag penalty at cruise. 
Further, aileron and rudder deflections induce yawing and rolling moments 
which are quite undesirable near the ground and can result in contact with 
obstacles and the loss of the aircraft. 
DISCLOSURE OF THE INVENTION 
It is, therefore, an object of the present invention to provide a control 
force generator for furnishing a control force to an aircraft without the 
attendant roll and yaw normally associated with coordinated use of 
conventional control surfaces such as ailerons and rudders. 
Another object of the present invention is to provide a control force 
generator configured to maximize its aspect ratio and thus minimize thrust 
losses and reducing drag. 
Yet another object of the present invention is to provide a control force 
generator which eliminates the need for increasing the size of 
conventional control surfaces such as ailerons and rudders. 
Still another object of the present invention is to provide a control force 
generator for providing at least a lateral force independent of other 
control forces or in conjunction therewith. 
A further object of the invention is to provide a control force generator 
which is relatively simple in construction and operation to provide 
increased reliability of performance as well as a reduced cost of 
construction and a lightweight configuration. 
One advantage of the present invention is ease with which the control force 
generator is retrofitted to existing aircraft configurations. 
One feature of the present invention is the use of circulation control in a 
novel double slot, single Coanda surface arrangement for selectively 
generating aerodynamic lift on an otherwise non-lifting surface. 
In accordance with these and other objects, advantages, and features of the 
present invention there is provided a control force generator for 
furnishing a control force for an aircraft, the generator comprising a 
source of compressed fluid and a pair of substantially symmetrical, 
spaced, aerodynamic surfaces forming a vane having a given chord length 
and span as well as leading and trailing edges. A fluid discharge slot is 
provided for discharging the compressed fluid from the trailing edge of 
the vane and a plenum adjacent to the discharge slot connects the slot to 
the source of compressed fluid. A fluid control surface, positioned 
adjacent the fluid discharge slot, forms first and second Coanda effect 
circulation control ports each having a given width h. The control surface 
extends beyond the trailing edge and has a substantially rounded trailing 
edge forming a single Coanda surface with a given radius r. Control port 
selection means are provided to selectively discharge the compressed fluid 
from the plenum to one of the control ports. The discharged fluid becomes 
attached to a portion of the Coanda surface adjacent the selected port and 
is deflected substantially tangentially to the Coanda surface resulting in 
the production of lift by one of the symmetrical, aerodynamic surfaces.

BEST MODE FOR CARRYING OUT THE INVENTION 
Referring to FIG. 1, a STOL, powered-lift aircraft 11 is depicted on a 
landing approach to a short and narrow, austere landing field 13. Arrow A 
illustrates the local wind direction which in the case portrayed results 
in a crosswind landing requirement. 
Using the conventional control surfaces, e.g. ailerons 15 and rudder 17, 
the pilot typically compensates for the cross-wind by lowering the 
windward wing 19 using ailerons 15. Additionally, in order to align the 
aircraft with the landing field 13, the pilot must make a forward slip of 
the aircraft 11 into the wind using the rudder 17. 
The above-noted control inputs results in undesirable roll and yaw 
positioning of the aircraft 11. With the windward wing 19 lowered, the 
likelihood of contacting a ground obstacle is greatly increased. Without 
the above-noted control input an apparent sidewise or crab motion results 
with respect to the ground as well as misalignment of landing gear 21, 
because of the direction of travel of the aircraft 11, and the landing 
field 13. 
In accordance with the present invention, aircraft 11 is provided with 
control force generators 23 under each wing 19 and 25 for providing, for 
example, at least a lateral force in addition to the control forces 
provided by ailerons 15 and rudder 17. The number and position of the 
generators 23, illustrated by FIG. 1, is by way of examples only, the 
number and positioning of the generators 23 being determined by the 
aircraft size and configuration as well as the desired amount and 
direction of the control force. Additionally, the control force provided 
by the generator 23 can be utilized in conjunction with or independent of 
the control forces provided by the conventional control surfaces of 
aircraft 11. 
FIG. 2B illustrates a sectional view, taken along line 2--2 of FIG. 2A, of 
the control force generator 23. The generator 23 comprises a pair of 
substantially symmetrical, spaced, aerodynamic surfaces 27 and 29, 
respectfully, which form a vane 31 having a leading edge 33 and a trailing 
edge 35. Further, the vane 31 is provided with a given chord length C and 
a span B as best seen in FIG. 2B. Because the aerodynamic surfaces 27 and 
29 are symmetrical, the vane 31 will not produce any lift when positioned 
in a chordwise flow of fluid. 
A fluid discharge slot, generally indicated at 37, is provided for 
discharging a compressed fluid from the trailing edge 35 of the vane 31. A 
plenum 39, adjacent to the fluid discharge slot 37, connects the slot 37 
to a source of compressed fluid (not shown). 
A fluid control surface 41, positioned adjacent the fluid discharge slot 
37, forms first and second Coanda effect circulation control ports 43A and 
43B, each having a given slot width h. As illustrated, the control surface 
41 extends beyond the trailing edge 35 of the vane 31 and has a 
substantially rounded Coanda surface having a given radius r. 
Control port selection means, generally indicated at 47, selectively 
discharges the compressed fluid from the plenum 39 to one of the control 
ports 43A or 43B, respectively. In the embodiment illustrated by FIG. 2B, 
the control port selection means 47 comprises a member 49 which not only 
divides plenum 39 into two separate plenums 51A and 51B, respectively, but 
also supports control surface 41. Each plenum 51A and 51B is provided with 
a valve 53A and 53B, respectively, to control the passage of compressed 
fluid from the source (not shown) to the respective plenum 51A or 51B and 
thus the discharge of fluid from the selected control port 43. 
Alternatively, as shown in FIG. 2C, the selection means 47 comprises a 
selector vane, generally indicated at 55, which comprises the fluid 
control surface 41, rotatably mounted for movement about its longitudinal 
axis, and a wedge-shaped sealing means 57, positioned in the undivided 
plenum 39. By rotating the selector vane about the longitudinal axis of 
the control surface 41, wedge-shaped sealing means 57 abuts one of the 
side walls 59 of plenum 39 to seal the adjacent control port 43 and permit 
passage of the compressed fluid through the other control port 43. Also 
included is a single valve 61 which selectively permits the passage of 
compressed fluid from the fluid source (not shown) to plenum 39. 
The operation of the generator 23 is best illustrated with reference to 
FIG. 3 wherein control port 43B is selectively connected to a source of 
compressed air, for example, the bleed air from an aircraft engine. As a 
result, a fluid jet 63 is discharged from the selected port. 
Whenever a jet flows in a body of relatively stagnant fluid (i.e. stagnant 
relative to the fluid jet) it entrains some of the surrounding fluid and 
starts it in motion. FIn the case illustrated, as the ambient fluid is 
entrained and carried along the sides of jet 63, replenishing fluid 
continuously moves into this region. 
Along the open air 65, the replenishing fluid continuously moves in 
unimpeded and the average pressure along this side is essentially ambient 
pressure. However, in area 67, adjacent the fluid control surface 41, the 
replenishing fluid must flow down through the restricted opening between 
the Coanda surface 45 and the adjacent jet boundary. The average pressure 
on the Coanda surface side, therefore, is somewhat below ambient. 
The resultant differential in pressure between the two areas 65 and 67 
causes the jet 63 to move closer to the Coanda surface 45, further 
reducing the pressure in area 67 until the jet 63 becomes attached to a 
portion of the Coanda surface 45. The attachment of jet 63 to the Coanda 
surface 45 caused the jet 63 to be deflected substantially tangentially to 
the surface 45. 
The attachment of jet 63 to Coanda surface 45 results in an entrainment of 
the fluid flow stream 69 adjacent to the trailing edge next to the 
selected control port, which in the case illustrated, is control port 43B. 
The entrainment of stream 69 results in the imparting of a flow velocity 
to stream 69 in the direction of Coanda surface 45. 
The downstream deflection of the fluid flow stream 69 by jet 63 effectively 
results in an apparent increase in the angle of attack of the fluid flow 
over the leading edge 33 as experienced by surface 27, adjacent the 
selected control port 43B thus resulting in the production of lift by 
surface 27. Previous to the deflection of jet 63, vane 31 produces no net 
lift because the aerodynamic surfaces 27 and 29 are substantially 
symmetrical. However, with the deflection of jet 63, as shown, surface 27 
produces lift resulting in a net force substantially perpendicular to and 
away from surface 27. 
If vane 31 is mounted vertically on an aircraft, the generator 23 will 
produce a sideforce on the aircraft. Increasing the velocity of stream jet 
63 achieves an increase in te sideforce generated. Selection of the other 
port 43A will change the direction of the force so as to be substantially 
perpendicular to and away from aerodynamic surface 29. 
Referring to FIG. 4, the generator 23 is configured as a sideforce 
generator and mounted to the bottom surface of a wing 71 having an engine 
73. In this embodiment the generator 23 is mounted such that the 25% value 
of the chord C of vane 31 passes through the 35% value of the chord of the 
wing 71. Bleed air from the engines 73 provides the source of compressed 
fluid which is conveyed to plenum 39. 
The generator 23 can be mounted on a wing, as illustraded in FIG. 4, or on 
the fuselage of the aircraft. When mounted to a wing, the generator can be 
positioned to to deflect propeller thrust as illustrated in FIG. 5A or jet 
thrust as shown in FIGS. 5B-5C. Alternatively, the generator 23 can be 
positioned independently of the engine thrust as shown in FIG. 1. 
Additionally, the generator can be positioned above or below the wing, as 
shown in FIGS. 5C and 5B, respectively, or both above and below the wing 
as well as be incorporated in an engine support pylon, as shown in FIG. 
5D, as in, for example, over the wing blowing, or incorporated with a 
control surface such as rudder, aileron, elevator or the like. 
Preliminary studies show that four approximately 6 ft. span by 7 ft. chord 
length circulation control vanes 31 provide a 15-foot sidestep in a 100 
ft. altitude change on a 6-degree glideslope at 90 knots. The vanes 31 can 
also negate an 11-knot crosswind at 90 knots forward speed, thereby 
overcoming drift and permitting a landing without roll or yaw. 
For a vane with an assumed C.sub.L max. =3.0 and C.sub..mu. =0.2, the mass 
fluid flow blowing requirements are calculated as follows: 
EQU r/c=0.01 and 0.01&lt;h/r&lt;0.05 
where 
r=trailing edge radius, 
h=slot width, 
c=7 ft. chord, 
thus 
r=(0.8").perspectiveto.1.5" diameter, and 
h=0.05.times.0.08=0.04 inches. 
Assume the worst case, h=0.1 inches. The mass flux blowing requirements are 
calculated as follows: 
Momentum Coefficient normally used is 
##EQU1## 
where 1/2.rho..sub.0 V.sub.0.sup.2 =q=the dymanic pressure=28 psf 
S=surface planform=40 sq ft 
m=blowing flow rate in lb/sec 
V.sub.j =theoretical jet velocity reached in isentropic 
expansion from duct stagnation pressure P.sub.D to free stream pressure 
P.sub.0. This is given by: 
##EQU2## 
where T.sub.D =duct stagnation temperature (K..degree.) 
P.sub.D =90 psia 
T.sub.D =570.degree. F.=300.degree. C.=573.degree. K. 
so 
V.sub.j =1663 ft/sec for each engine 
thus 
##EQU3## 
In order to sustain this mass flux blowing rate, a small compressor can be 
used in conjunction with the bleed air from an aircraft engine. 
While the invention has been particularly discussed and described with 
reference to preferred embodiments thereof, it will be understood by those 
skilled in the art that various alternation in form and detail will be 
made therein without departing from the spirit and scope of the invention 
as described by the attached claims.