Document
United States Patent [19] p i ] Patent Number: 4,980,835
Lawrence et ai. [45] Date of Patent: Dec. 25, 1990
CONTROL LAW SYSTEM FOR X-WING [54] pneumatic valving controlling circulation control blow- AIRcR4Fr ing for the rotor. As to the collective axis, the system gives the pilot single-lever direct lift control and insures [75] Inventors: Thomas H . Lawrence, Derby; Phillip that maximum cyclic blowing control power is avail- J. Gold, Shelton, both of Conn.
able in transition. Angle-of-attach de-coupling is pro- [73] Assignee: United Technologies Corporation, vided in rotary wing flight, and mechanical collective is Hartford, Conn.
used to augment pneumatic roll control when appropri- ate. Automatic gain variations with airspeed and rotor [21] Appl. No.: 256,937 speed are provided, so a unitary set of control laws [22] Filed: Oct. 13,1988 works in all three X-Wing flight modes. As to pitch and [51] Int. C L 5 .............................................. B64C 27/12 roll axes, the system produces essentially the same air- [52] U.S. Cl. ................................. 3 6 4 / w 416/20 R craft response regardless of fight mode or condition.
416/90 A, 244A7.11 Undesirable cross-couplings are compensated for in a [58] Field of Search ................... 364/424.01, 433, 434; manner unnoticeable to the pilot without requiring pilot 318/564,565; 416/20 A, 20 R, 90 A, 90 R, 158; action, as flight mode or condition is changed. A hub 244A7.11, 17.13, 17.25 moment feedback scheme is implemented, utilizing a P+I controller, significantly improving bandwidth.
1561 References Cited L i m i t s protect aircraft structure from inadvertent dam- U.S. PATENT DOCUMENTS age. As to pneumatic valving, the system automatically
4,493,612 VI985 D'Anna ............................. 416/20 R
provides the pressure required at each valve azimuth
4,507,050 3/1985 Jeffrey et al. ..................... 416/90 A
location, as dictated by collective, cyclic and higher
4,534,702 8/1985 Johnson, Jr. et al. ............ 416/20 R
harmonic blowing commands. Variations in the re-
4,573,871 3/1986 Krauss et al. ..................... 416/20 R
quired control phase angle are -automatically intro-
4,583,704 4/1986 Krauss et al. .................... 244/17.11
4,594,537 6/1986 Arifian et al. ....................... 318/564 duced, and variations in plenum pressure are compen-
4,596,512 6/1986 Krauss et al. ......................... 416/42
sated for. The required switching for leading, trailing
4,626,171 12/1986 Carter, Sr. et al. .............. 416/90 A
and dual edge blowing is automated, using a simple
4,678,401 7/1987 Bradford et al. ..................... 416/32
table look-up procedure. Non-linearities due to valve Primaly Examiner-Gary Chin characteristics of circulation control lift are linearized by map look-ups.
[571 ABSTRArn Control law system for the collective axis, as well as pitch and roll axes, of an X-Wing aircraft and for the 39 Claims, 18 Drawing Sheets ROLL A X l S
COMMAND - 1
ROTOR AOA
ROTOR RPM 7 1 I
STABILITY AIRSPEED - t AUGMENTATION SYSTEM c o u c n v E I CONTROL ACTUATOR COMMAND
I PILOT I I
I c o - P i L o n
u I +t+ C o u c n V E
CONTROL I I
PNNMATIC PNEUMATIC c o u c n V E . CouEcnVE O P * CONTROL COMMAND LAWS --, TO PNEUMATIC coucnvE LOGIC
1 AUTOPILOT
AIRSPEED CROSS
U.S. Patent Dec. 25,190 Sheet 1 of 18 4,980,835
COMPRESSOR LIMIT ,, /, / , / ' / ' / 2.0 BLADE ROOT 1.6 PRESSURE RATIO 1.4 1.2
F 1 G. 1
-
AZIMUTH ANGLE N DEGREES (AVERAGE RATIO = 1.5)
/ C O M M A N D E D I
2.0 1.8 BLADE 1.6 ROOT PRESSURE I RATIO 1.4 1.2 AZIMUTH ANGLE DEGREES (AVERAGE RATIO = 1.8)
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achieved, a condition analogous to a stall in a conven- CONTROL LAW SYSTEM FOR X-WING tional airfoil.
AIRcRAFr Since an X-Wing circulation control airfoil is sym- metrical about its half chord, the leading edge on the The invention described herein was made in the per- 5 advancing side of the blade path disk becomes the trail- formance of work under NASA Contract No. NAS2- ing edge on the retreating side, and vice-versa. To maxi- 11771 and is subject to the provisions of Section 305 of mize performance as the rotor slows down, it is desir- the National Aeronautics and Space Act of 1958 (72 able that the “local” leading edge slot be closed at all Stat. 435; 42 U. S. C. 2457).
azimuth positions.
1 0 Conventional helicopters provide aircraft pitch and CROSS REFERENCE TO RELATED roll control by varying blade pitch from medium-to- APPLICATIONS high, or medium-to-low to medium at a once “per rev” This application relates to some of the same subject (rotor revolution) rate, as the blades whirl around the matter as the following two applications, both of which rotor disk. The X-Wing aircraft includes 1-per-rev were filed concurrently with this application and the l5 pneumodynamic control and also has more rapid pneu- disclosures of which are incorporated herein by refer- matic variance, at an up to 5-per-rev rate, to system ence.
loads and vibrations.
Ser. No. No. 07/257,474 entitled “X-Wing Fly-By- It achieves rotor control via a pneumatic medium. It Wire Vehicle Management System” by William C.
is a full authority fly-by-wire (FBW) system with, for Fischer; and 2o example, quadruple redundancy for all flight critical Ser. No. No. 07/257,473 entitled “Higher Harmonic functions.
Control System for X-Wing Aircraft” by William C.
The X-Wing aircraft is designed to hover like a heli- Fischer and Kenneth C. Arifian.
copter and cruise at an airplane’s high speeds. It uses a TECHNICAL FIELD stoppable rotor/wing, which, as noted, rotates like a 25 helicopter rotor in low speed flight and stops to become This invention relates to “X-Wing” aircraft and more a fixed wing for high speed cruise. It offers an ideal particularly to a control law system for controlling the compromise for VTOL hover/cn&e capabilities, aircraft. More particularly the present invention relates horsepower/fuel efficiency and ultimate payload capac- to a control law system for the collective a x i s and for the pitch and roll axes for such an aircraft and for the 30 ity- Some exemplary X-Wing related patents, all owned pneumatic valving that controls the edge blowing for by the assignee hereof, are listed below: the rotor of such an aircraft.
GENERAL BACKGROUND Patent No. Patentee@) Issue Date Title Introduction 35 4,493,612 D’Anna 01/15/85 An X-Wing aircraft is a rotary wing aircraft that uses “Axially Slideable Plenum for Circulation Control a rigid rotor/wing utilizing circulation control airfoils. Aircraft” 4,507,050 Jeffery et al 03/26/85 The rotor is driven mechanically, and the rotor may “Pneumatic Valve Control for Circulation Control rotate, as in a helicopter, or it may be stopped and posi- 4o Aircraft” tioned so as to act like a fixed wing.
4,534,702 Johnson et al 08/13/85 Collective and cyclic control is achieved by control “Pneumatic Control Valve Actuator Computer Control of air flowing around a Coanda surface on’the blade Arrangement” 4,573,871 Krauss et al 03/04/86 airfoils. This is done by blowing compressed air “X-Wing Aircraft Circulation Control” through leading edge and trailing edge ducts in the 45 4,583,704 Krauss et al 04/22/86 rotor blades and modulating the amount of air being “Pneumatic System Structure for Circulation Control ejected through span-wise slots on the leading and trail- Aircraft” 4,594,537 Anfian et al 06/10/86 ing edges of the rotor blades.
“Redundant Control System for X-Wing Value Actuators” The rotor system for an X-Wing aircraft includes a 4,596,512 Krauss 06/24/512 hub and attached rotor blades and a pneumatic system “Circulation Controlled Rotor Blade Tip Vent Value” for delivering pressurized air separately to the leading 50 4,626,171 Carteret al 12/02/86 edge and the trailing edge of the individual rotor blades “Rotor Blade Construction for Circulation Control Aircraft” at a desired pressure and mass flow. The pneumatic 4,678,401 Bradford et at 07/07/87 system includes a compressor, a stationary air supply “Rotor Control System” chamber, valving for controlling the flow of air from the chamber to the blades, and a rotating air distribution 5 5 A revolutionary concept such as “X-Wing” requires arrangement for conducting air separately to the lead- innovative approaches to service the technology leap ing edge and trailing edge of the blades.
involved in this type of hybrid aircraft.
In circulation control airfoils, pressurized air is The control laws are one area of such a vehicle which ejected from span-wise openings or slots along the 60 face significant challenges. The control law system upper side of the rounded airfoil leadinghailing edge must first be designed to accommodate the equivalent of Coanda surface. The airflow from the slots attaches to the rounded leadindtrailing edge, which increases the three vehicles, since the X-Wing operates in a rotary wing mode (RW), a fixed wing or stopped rotor mode circulation, to provide a corresponding lift increase (SR), and a conversion state (CV) between the two.
over an airfoil having no ejected air. For a given blade For purposes of this disclosure, it should be under- 65 internal pressure and aerodynamic condition, the lift stood that the phrase “flight mode” refers to the state of change due to circulation control is proportional to the area of the slot opening up to a certain limit. When the the rotor, including its stopped rotor mode (SR), its rotary wing mode (RW) and the conversion state ( C y , slot opening exceeds this limit, no additional lift is 4,980,835 while “fight condition” refers to aircraft air speed and use it to provide roll trim in high speed rotary wing the angle of attack (AOA). In turn, “flight situation” flight.
refers to both rotor mode and aircraft condition.
Pitch & Roll Axes Collective Axis 5 An X-Wing rotor produces pitch and roll moments by varying the pressure at the blade root to change An X-Wing rotor employs both mechanical collec- lift. Higher pressure creates more lift, and lower blade tive pitch and pneumatic collective blowing. Collective pressure reduces lift. In RW mode, the pressure is var- pitch changes the pitch angle on all the blades equally ied azimuthally in a sinusoidal fashion, as discussed i n and simultaneously, in the conventional helicopter way.
the collective axis section. This sinusoidal pressure vari- Pneumatic collective blowing is the average pressure 1 0 ation is analogous to the cyclic pitch variation used on seen by all of the blades.
conventional helicopter rotors. In SR mode, control in Changes in pneumatic collective cause an increase or pitch and roll is achieved by differential fore-to-aft and decrease in rotor lift in all flight modes, i.e., rotary wing right-to-left pressures, respectively.
(RW), conversion (CV) and stopped rotor (SR) modes.
From the point of view of flying qualities, the major While pneumatic collective provides for direct lift con- l5 problem is that a given amount of pressure variation trol, large variations can cause undesirable cross-cou- creates different loads, depending on flight condition pling with pitch and roll control.
and rotor speed. If the flight controls produce the same Pitch and roll control on the X-Wing rotor is pressure variation for a given stick input, then the air- achieved by varying the pressure azimuthally on the craft response to that stick input will vary, depending rotor blades. This is true in all flight modes, but for 2o on aircraft fight condition and rotor speed. These vari- convenience the discussion immediately below will be ations can be very significant and make the aircraft limited to the rotary wing state. In RW mode, blade more difficult to fly, leading to high pilot workload.
pressure is varied around the azimuth, as shown in FIG.
In RW mode, the X-Wing rotor experiences very 1. In this case, the highest blowing is at, for example, 25 high gyroscopic cross-coupling. This is due to the ex- ninety degrees (90”) and the lowest at, for example, two treme stiffness of the blades and their attachment to the hundred and seventy degrees (270”), producing a left hub. For a rotor with conventional rotation (that is, rolling moment. The average or collective pressure with the advancing side of disk to starboard) nose up ’ratio is, for example, one and a half (lS), and the cyclic pitch rates generate right rolling moments, and right variation is plus or minus three-tenths ( + 0 . 3 ) .
3 0 roll rates produce nose down pitching moments. This If, however, the collective pressure ratio is increased type of cross-coupling makes the aircraft very difficult to, for example, one and eight-tenths (1.8) the com- to fly and must be compensated for. In addition, an manded pressure wave will be clipped, as shown in aerodynamic cross-coupling exists such that positive FIG. 2. This situation is called saturation, since higher angle-of-attack changes produce a left rolling moment.
pressure ratios at certain azimuth angles cannot be 35 This can be compensated for by angle-of-attack to me- achieved because of compressor limits.
chanical collective pitch feedback, as discussed in the An analogous situation exists if the collective pres- collective a x i s section below.
sure ratio is reduced, to, for example, one and two- is limiting the hub moments One important concern tenths (1.2), as illustrated in FIG. 3. In this case, the produced. Under some conditions, the hub moments bottom of the desired pressure ratio curve is clipped, 40 generated can be excessive and lead to structural dam- because pressure ratios less than one can not be age. For example, when the aircraft is on the ground, achieved.
large hub moments can not be relieved by aircraft mo- Saturation of the blowing results in two undesirable tion (as they can be in the air), and damage or an acci- effects. First, the desired moment is not produced, be- dent can result.
cause only one side of the disk is performing correctly. 45 Pneumatic Valving Secondly, a change in lift i s produced. When the blow- ing is not saturated, the reduction in lift on one side of In a typical x-wing control system, pilot’s stick com- thi disk is compensated for by the increase on the other mands are converted to mechanical collective pitch and side. In this way, the lift is not strongly effected by collective. bitch and roll blowine commands. These I .
cyclic blowing. If the cyclic blowing is saturated, this 50 blowing commands, however, must be implemented by compensatory effect is reduced and changes in rotor some form of valving. Therefore, there is a requirement thrust result.
for pneumatic valve control laws for controlling the The foregoing also applies in conversion and stopped rotor of the X-Wing aircraft.
rotor flight modes. Of course, in stopped rotor mode the In addition to providing an azimuthal pressure varia- blades are at a fmed azimuth, and cyclic variations in 55 tion to accommodate collective and cyclic commands, pressure are replaced by differential blowing forward to the valve control logic must also include provisions for aft and right to left. But the same effect takes place.
higher harmonic control (HHC) in rotary wing mode.
The effect of mechanical collective pitch on rotor HHC is the application of pressure variations that occur loads varies greatly, depending on the flight mode and at two, three, four and five times per rotor revolution airspeed. In hover, collective pitch changes result in 60 for the purpose of vibration reduction. The control laws large changes in rotor lift. As airspeed increases, varia- which create the HHC commands are not covered here, tions in the collective pitch produce pitch and roll but see the concurrently filed patent application entitled movements, as well as lift changes. At still higher air- “Higher Harmonic Control System for X-Wing Air- speeds, the primary effect of collective pitch is to gener- craft” (S-4208) referred to above.
ate large rolling movements. In stopped rotor and con- 65 Another important requirement for the valving is version flight modes, mechanical collective is primarily providing for selection of trailing edge blowing (TEB), a rolling moment generator. In fact, a basic reason for leading edge blowing (LEB) or dual edge blowing adding mechanical collective pitch to the X-Wing is to (DEB), depending on rotor speed, airspeed and blade
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azimuth position. The reason for this is due to the differ- the rolling moment response noted above is natural. But ences in the airflow over the rotor blades, as the rotor in hover, moving the beeper laterally results in strong changes from rotary wing to stopped rotor modes.
lift changes-again, an unnatural response from the In the rotary wing mode, air is ejected from thin slots pilot’s point of view.
on the trailing edge of each blade, as generally shown in 5 Existing x - w h g designs normally employ FIG. 13 (on the left side). In the stopped rotor mode tal collective as a roll trim device and utilize pneumatic (right side of figure), however, air is ejected from the collective for direct lift control. However, rigid rotor edge slots on the Starboard wings, but from the helicopters (like the X-Wing) experience a large nose- leading edge slots on the port side. Note that the “trail- up pitching moment, % they transition from hover to ing” and “leading” edges are being defined here in the io forward fight. ms moment is generally at a rotary wing way*During conversion, then, as the rotor between, for example, twenty (20) knots and sixty (60) is stopped Or started in fight, the logic has knots forward airspeeds. As the rotor moves into this select the appropriate slots that should be blown.
transition speed range, a si&icant amount of extra lift The way this is done is shown in the sequential dia- is produced by the inflow to the rotor. To maintain lift &rams in 14’ In rotary wing mode is Out l5 trim, pneumatic collective is reduced. However, large Of the trailing edges Only (Ist diagram; mu=o)’ As the amounts oflongitudinal cyclic blowing are required for rotor is ‘lowed down, dual (both ’lots) is intra- pitch control. As a result, the blowing will saturate, as duced on the retreating (port) side by turning the LEB noted above. In this event, pitch control may be lost.
on over a small (2nd mu=o.5). As the at high Weeds (tYPically In rotary wing rotor speed decreases further, the azimuth over which 20 greater than 100 knots) changes in rotor angle-of-attack dual blowing is employed, increases (3rd diagram; result in very large rolling moments being produced. A mu = 0 . 8 ) .
change in angle-of-amk can either be the result of a With further reduction in rotor speed, a central re- gion of leading edge blowing is introduced On the port deliberate pilot action, such as a pull-up, or the result of side by turning off the TEB, flanked by redons of dual 25 atmospheric gusts. In either case, the rolling moment is blowing (4th diagram; mu= 1.5). At very low RPM’~ very undesirable and may be so large that lateral cyclic the region of LEB covers most of the retreating side, blowing cannot control it.
with small dual blowing regions fore and aft (6th &a- Analytical and wind tunnel data show that the opti- mal value of pneumatic collective is different in rotary gram; mu=3.0).
Finally, when the rotor is stopped, the blowing is 30 wing (,,Rw’’) and stopped rotor WR”) modes. In RW, TEB on the starboard side and LEB on the port side, as the best collective pressure ratio is between, for exam- required (6th diagram). When the rotor converts from ple, 1.5 and 1.6, while in SR the best value is around 1.4.
stopped to rotating, the same process is followed but in In existing designs, this change has to be accommodated the reverse order. manually by the pilot. In addition, during conversion, The above discussion referred to reduction in rotor 35 the rotor loses lift at advance ratios of around, for exam- speed as controlling the blowing edge state. In actual- ple, 0.8 to 1.0, corresponding to rotor speeds around ity, the true governing parameter is the advance ratio eighty (80%) percent. To maintain lift trim, the pneu- (mu), that is the ratio of the fight velocity divided by matic collective needs to be increased in this RPM the tip speed. Typically, dual blowing preferably starts region.
at an advance ratio of, for example, one-half (0.51, and Prior X-Wing control laws have attempted to solve leading edge blowing only is introduced at an advance the problems outlined above for the pitch and roll axes ratio of, for example, one (1.0). Thus, i n high speed control by use of hub moment feedback (HMF). This rotary wing fight a small region of dual blowing may basic concept is illustrated in FIG. 7.
exist before the conversion to the stopped rotor mode i s The pilot’s stick input compared to the actual rotor started or at the end of a conversion from stopped rotor 45 hub moment, and the error was integrated. This signal to rotary wing.
was fed to the blowing logic, which adjusted the blade root pressures and changed the rotor hub moment. The PARTICULAR BACKGROUND ART feedback loop assured that this continued until the de- Collective, Pitch and Roll Axes Control sired moment was reached. Imdemented in this fashion.
As noted above, X-Wing and other circulation con- 50 the Control was an acceleration command system, trol rotors employ both mechanical collective pitch and which is very difficult to fly.
pneumatic collective blowing. Historically, pilot activa- The control system i n FIG. 1 C a n be converted to a tion at these two collectives has employed two different rate command system by adding angular rate feedback controls, typically a conventional collective lever and a as shown in FIG. 8. Stick inputs generate an error signal beeper switch. This obviously makes the piloting task 55 which is integrated to produce blowing commands.
They adjust the pressure distribution on the rotor to more difficult.
In addition, since the effect of mechanical collective produce a moment i n the appropriate direction. Once varies greatly, depending on flight mode and airspeed, the moment exists, the aircraft begins to respond, pro- the pilot ends up with one control which does very ducing angular rate. In addition, the aircraft experiences different things at different times. For example, if col- 60 aerodynamic damping, which reduces the applied mo- lective pitch is controlled by a conventional helicopter ment. The aircraft achieves a steady state condition, collective lever, the pilot gets an appropriate response when the aerodynamic damping cancels the applied hub in hover and at low RW speeds. However, in high speed moment and the angular rate feedback cancels the stick RW flight or in SR flight, moving the collective lever input.
causes large rolling moments. For the pilot, this is an 65 While the HMF of the prior a r t is generally a good unnatural response. approach for X-Wing control, it has a number of defi- On the other hand, if collective pitch is controlled by ciencies if implemented as shown in FIG. 8. First, the a lateral motion beeper type switch on the cyclic lever, actual hub moment being measured and fed back has a
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high vibratory content in RW mode. These vibrations fight, and mechanical collective may be used to aug- can be filtered electronically from the feedback signal, ment pneumatic roll control when appropriate. Auto- matic gain variations with airspeed and rotor speed are but this introduces lags in the steady moment portion of HMF integrator must have a provided, so a unitary set of control laws will work i n the signal. In addition, the fairly long time constant in order for the system to be 5 rotor wing (“RW”), conversion (“CV”) and stopped stable. As a result, the HMF system typically has a rotor (“SR”) modes.
bandwidth of one Hertz or less. Detailed mathematical The primary objects of these control laws are to: analyses have shown that such an X-Wing control sys- (a) provide the pilot with a single lever direct lift tem is too sluggish for practical use. control that will provide natural response in all 10 flight modes; Pneumatic Valving (b) maintain the collective pressure ratio at its mid- value in the transition speed range, so that maxi- Prior pneumatic valve control schemes for X-Wing aircraft have been implemented with mechanical l i n k - mum cyclic blowing control authority is available; ages. These systems were able to provide only collec- (c) provide a coupling between angle-of-attack and tive, cyclic and two per revolution (2/rev.) blowing 15 mechanical collective pitch, so that automatic control. In addition, any non-linearities of blade root compensation is provided to cancel the rolling pressure to valve position could not be compensated moments created by angle-of-attack changes i n high speed rotary wing flight; for.
The approach of the invention to X-Wing pneumatic (d) automatically set the pneumatic collective to its control is to use a large number of valves in the station- 20 optimal value in RW, CV and SR flight modes; and ary frame, controlled in a fly-by-wire (FBW) way. (e) cross-couple mechanical collective to lateral stick, Large numbers of valves are needed to provide fidelity so that roll control augmentation is available in in the higher harmonic control, which requires inputs RW, CV and SR flight modes.
up to, for example, five per revolution @/rev.). Use of The exemplary control laws which accomplish the FBW allows for control by sophisticated algorithms, 25 above objectives are described in detail below. For further convenience, the mechanical collective pitch which can allow for variation in control phase angle, account for nonlinearities in valve characteristics and laws and the pneumatic collective laws are described provide for failure monitoring and correction. separately. However, of course, they are both part of Current designs employ twenty-four (24) equally one collective axis control system. A simplified block spaced valves for TEB control and twenty-four (24) for 30 diagram of this system is shown in FIG. 4.
LEB. For further details on an exemplary valving sub- As can be seen in FIG. 4, the collective command system, note U.S. Pat. No. 4,507,050 of Jeffery & Law- signal is the sum of the pilot/co-pilot’s stick input, the rence entitled “Pneumatic Valve Control for Circula- collective stability augmentation system (SAS) and the tion Control Aircraft” noted above. Butterfly valves are collective auto-pilot. If the pilot controls are mechani- used, since they are “self-storing”. Other types of cal, there is only one input for the pilot@). If a fly-by- wire system is utilized, additional pilot-in-command valves, such as, for example, gate valves, require room to move into when open, and this greatly complicates logic is required as shown. This collective command the design of the blowing manifold. signal is then fed to both the pneumatic collective and One feature of any stationary valving scheme is that collective Ditch control laws. Additionallv. the mechan- certain valves may be inactive (closed) for long periods 40 ical collechve control laws receive signis. based on the of time. For example, in low speed rotary wing flight, roll axis command, the rotor angle of attack (AOA), the rotor RPM and the vehicle airspeed, while the pneu- none of the LEB valves are open. Nonetheless, these valves must function properly as the aircraft goes to matic collective control laws receive airspeed and rotor higher speeds and converts to stopped rotor mode. RPM signals.
The collective pitch command is sent to the appropri- DISCLOSURE OF INVENTION to other ate actuator, and a signal for cross-coupling Thus, the present invention provides control laws for axes is also available. The pneumatic collective com- the collective axis, as well as for the pitch and roll axes, mand is sent to the valve control logic, which adjusts of an X-Wing aircraft and control laws for the pneu- the pneumatic control valves (PCV) as required to matic valving for controlling the leading and trailing 50 create the needed pressure at the blade roots. In addi- tion, a pneumatic collective cross-coupling command is edge blowing for the rotor of an X-Wing aircraft. These available for use by other control axes.
will be separately discussed and disclosed below, with some cross-referencing. As an alternative, it may be desirable to design an The control laws preferably are of a “unified” form X-Wing aircraft that did not require mechanical collec- with RW, SR and CV mode laws merged into one set. 55 tive pitch. In this case the blades would be fastened to A prime motivation for this is the reduction of the com- the hub directly without any articulation. Such a rotor puter throughput demand by computing only one set of would be lighter, since no mechanical collective mecha- control laws, particularly during the already computa- nism would be fitted. In addition, it could have less tionally intense conversion phase. aerodynamic drag since the hub could be smaller, and 60 the hubblade junction could have improved streanalin- Collective Axis ing.
Thus, one aspect of the present invention is directed Such a rotor would still have to compensate for the to providing a set of collective axis control laws for an problems noted above-i.e., providing maximum cyclic X-Wing vehicle. blowing control range in the transitional speed regime, These give the pilot single-lever direct lift control 65 compensating for roll moment with airspeed and com- and insure that the maximum cyclic blowing control pensating for roll moments generated by angle-of-attack power is available in the transitional flight regime. An- changes. One possible method for doing this is to blow gle-of-attack de-coupling is provided in rotary wing out of the aerodynamic leading edge slots on the ad-
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vancing side of the disk. Tests have shown that blowing Pneumatic Valving out only the aerodynamic leading edge spoils the lift A still further aspect of the present invention is di- generated by the airfoil.
rected to providing a set of pneumatic valving control Use of such a technique would obviously require laws for controlling the rotor of an X-Wing vehicle.
changes in the control laws. Of course, the mechanical 5 These laws automatically provide the pressure re- collective channel and its interfaces with the other axes quired at each valve azimuth location, as dictated pref- would be deleted. The blowing logic would become erably by the collective, cyclic and higher harmonic more complicated, since it would have to turn o f f TEB blowing commands. Variations in the required control and t u r n on LEB on the advancing side of the disk over 1o phase angle are automatically introduced, and varia- some specified azimuth range. This azimuth range tions in plenum pressure are automatically compensated would have to be calculated to provide the compensa- for. The required switching for LEB, TEB and DEB is tions noted above.
automated, preferably using a simple table look-up pro- cedure. Non-linearities due to valve characteristics of Pitch & Roll Axes 15 circulation control lift are linearized, preferably by map Another aspect of the present invention is directed to lOOk-UpS.
providing a set of pitch and roll axes control laws for an The primary objects of these pneumatic valve control X-Wing vehicle.
laws are to provide control of a large number of pneu- These pitch and roll axes control laws produce essen- matic control valves for an X-Wing rotor that accom- tially the same aircraft response to pilot input regardless 20 plishes the following tasks: of flight mode or fight condition. Undesirable cross- (a) providing azimuthal variations in blade root pres- couplings are compensated for in a manner unnoticed sure in accordance with collective, cyclic and higher harmonic blowing commands; by the pilot and in a way that does not require pilot (b) automatically scheduling TEB, DEB and LEB on action, as the flight mode or condition is changed. A the retreating side as a function of advance ratio; hub moment feedback scheme is implemented, but uti- 25 (c) automatically compensating for the non-linear lizing a proportional plus integral controller, which relationship between valve positionhoot pressure, significantly improves its bandwidth. In addition, hub so that the blade root has the desired value; moment limits are provided so that the structure is pro- (d) automatically compensating for the change in tected from inadvertent damage.
30 cyclic control phase angle required as a function of The primary objects of these control laws are to.
rotor rotational speed; (a) provide the pilot with a rate command control (e) providing for a non-linear correction to the blow- system in pitch and roll which will produce the ing to account for the non-linear nature of circula- same aircraft response to a given stick input regard- tion control lift; and less of fight mode or flight condition; 35 (f) providing continuous commands to all valves, so (b) provide a control system, which automatically that malfunctions can be detected.
compensates for gyroscopic or control cross-cou- The exemplary control laws which accomplish the plings; above objectives are described in detail below.
(c) provide the pilot with a control system, which The foregoing and other features and advantages of provides for sharp and crisp responses to control 40 the present invention will become more apparent from inputs without sluggishness or unacceptable time the following further description and drawings.
delays; BRIEF DESCRIPTION OF DRAWINGS (d) insure that hub moments are automatically limited FIG. 1 is a graph of the blade root pressure ratio to prevent structural damage to the aircraft; and versus the azimuthal angle in degrees for the X-Wing (e) perform the above functions without requiring 45 rotor in its rotary wing (RW) mode, with the collective pilot intervention far selection of fight mode.
pressure ratio at one and a half (1.5); while The exemplary control laws which accomplish the FIG. 2 is a graph of the blade root pressure ratio above objectives are described in detail below. An over- versus the azimuth angle in degrees, with the collective view of the pitch and roll axes control system is pro- 50 pressure ratio raised to one and eight-tenths (1.8), pro- vided below.
ducing saturation above two (2), the compressor l i t ; A simplified block diagram of the pitch and roll axes while control laws is presented in FIG. 9. The command FIG. 3 is a graph of the blade root pressure ratio signal is the sum of the pilot, SAS and auto-pilot inputs.
versus the azimuthal angle in degrees, with the collec- If the pilot controls are mechanical, there is only one 55 tive pressure ratio reduced to one and two-tenth (1.2), input for the pilot@).If a fly-by-wire system is utilized, producing clipping below one (1; “no blowing”).
additional pilot-in-command logic is required as shown.
FIG. 4 is a simplified block diagram of the exemplary The pitch and roll command signals are then sent to embodiment of the collective control system of the their respective control laws. Both axes require cross- present invention.
coupling inputs from the other and from the pneumatic FIG. 5 is a block diagram schematically illustrating collective, and both use airspeed and rotor speed inputs.
the exemplary embodiment of the mechanical collective The pitch axis control laws also have pitch hub mo- control law of the system of the present invention; ment, aircraft pitch rate and mechanical cross-coupling while inputs. The roll axis control laws also have roll hub FIG. 6 is a block diagram schematically illustrating moment, aircraft roll rate and yaw cross-coupling in- 65 the exemplary embodiment of the pneumatic collective puts. control law of the system of the present invention.
The outputs are sent to the pneumatic valve control FIG. 7 is a block diagram schematically illustrating laws. the basic prior art concept of attempting to solve the
4 . 9 8 0 . 8 3 5
, ,
11 12
X-Wing control law problems by the use of hub mo- Because collective pitch is normally zero in SR ment feedback; while mode, the basic map is fed through an RPM fade-in.
FIG. 8 is a block diagram schematically illustrating This is a gain that varies with rotor speed. It is zero for, the basic prior art use of adding angular rate feedback to for example, from zero (0%) to ten (10%) percent rotor the hub moment feedback. 5 speed (omega), then increases with rotor speed until the FIG. 9 is a block diagram schematically illustrating gain gets to one at, for example, ninety (90%) percent the exemplary embodiment of the pitch and roll control (omega), staying at that value to, for example, one hun- laws of the system of the present invention; while dred and ten (1 10%) percent (omega). The advantage of FIG. 10 is a block diagram schematically illustrating using an RPM scheduled gain is that conversion can take place over a broad range of airspeeds (140 to 200 the exemplary embodiment of the pitch axis control law 10 k n o t s ) , and yet the collective pitch will always be at a of the system of the present invention.
suitable value.
FIG. 1 1 is a block diagram schematically illustrating The collective command signal is used to command a proportional plus integral controller.
direct lift changes. As can be seen in the upper middle FIG. 12 is a block diagram schematically illustrating part of FIG. 5, this signal is fed through an airspeed, the exemplary embodiment of the roll axis control law 15 decreasing variable gain. In hover and low speed rotary of the system of the present invention.
wing flight, the collective command effectively is fed FIG. 13 is a generalized, simplified illustration show- directly to the mechanical collective. This compensates ing the leading edge and trailing edge blowing from the for variations in the aircraft weight and allows for verti- edges of the rotor, when the rotor is in its rotating and its stopped dispositions. 20 cal maneuvering. As the airspeed increases, the gain (“K1”) is reduced, going to zero around, for example, FIG. 14 is a diagrammatic view showing the varia- eighty (80) knots in airspeed ( “ V ” ) . This signal is tion in the trailing and leading edge blowing with the summed with the basic map and therefor also is faded changes in the rotor advance ratios.
out in SR mode.
FIG. 15 is a block diagram giving an overview of the As will be seen more fully below in connection with exemplary embodiment of the pneumatic valve control 25 FIG. 6 , the pneumatic collective is faded in to provide laws of the system of the present invention.
direct lift control at higher speeds.
FIG. 16 is a block diagram showing the control phase Compensation for the strong cross-coupling of the angle calculation for the block diagram of FIG. 15.
angle-of-attack to roll moment is accommodated by , FIGS. 17A and 17B are schematic diagrams showing feeding the angle-of-attack (“AOA”) through an air- the calculations of the blowing azimuths for the leading 30 speed varied gain. As can be seen in the lower middle edges and trailing edges, respectively.
part of FIG. 5, out to about, for example, one hundred FIG. 18 is a block diagram showing the blowing flag (100) knots in velocity (“V”), no compensation (Kz=O) calculation for the block diagram of FIG. 15.
is required. At higher speeds, changes in the AOA re- FIGS. 19A and 19B are flag tables for the leading 35 sult in collective pitch inputs, which tend to cancel the edges and the trailing edges, respectively.
induced rolling moment. It should be noted that the FIG. 20 is a schematic, block diagram showing the gain (“Kz”) is negative, i.e., positive AOA (nose-up) valve position calculations for the block diagram of produces negative collective pitch, with the gain in- FIG. 15.
creasing with airspeed.
BEST MODE FOR CARRYING OUT THE 40 Since this aerodynamic crosscoupling occurs only in INVENTION RW mode, the decoupling signal is fed through an RPM fade-in before being summed with the mechanical Mechanical Collective Control Law collective. This performs the same function as the RPM The exemplary embodiment of the mechanical col- fade-in in the primary control path, but a separate func- lective control law of the present invention is presented 45 tion is used to allow for a different shaping of the fade-in schematically in FIG. 5, with the logic, flow and calcu- gain with rotor speed.
lation steps shown in the figure. The primary collective Since mechanical collective pitch in high speed RW, pitch path is shown on top.
CV and SR modes is a strong rolling moment generator, Collective pitch is scheduled with airspeed in RW it is appropriate to use it to augment the pneumatic roll mode. In hover, the pitch ( “ e , ? is set at, for example, six 50 control in these regimes. This is done by cross-feeding ( 6 ) to eight (8) degrees positive. This provides the re- the roll axis command signal to collective pitch.
quired lift, while allowing the pneumatic collective As can be seen in the lower, left hand part of FIG. 5, pressure ratio to be maintained at a mid-value. This the roll axis cross coupling command signal is first scheduling compensates for the increased lift that re- scaled with an appropriate scaling factor (“Ks”), since it sults from forward velocity (“V”); while, at the same 55 is typically in foot-lbs. and the collective pitch com- time, allows the pneumatic collective to remain at its mand is in degrees. Next, the scaled roll command sig- mid-point value.
nal is gained (“K,+”) with airspeed (“V”). No input is By about, for example, eighty (80) knots velocity allowed at low speeds (&=O), with the gain (r‘u’) (“V”)$ the collective set point (,,(I”) is down to zero beginning to be non-zero around, for example, one hun- degrees, and by, for example, one hundred and twenty 60 dred (100) knots velocity ( “ V ” ) . Higher gain is used at (120) knots, it (“0’’) is at minus four (-4) to minus six higher airspeeds. Because the roll movement sensitivity (-6) degrees. At these airspeeds the mechanical coJl’ec- is different in RW and SR modes, provision is also made tive pitch is now functioning to provide roll trim. Be- for an RPM varying gain (“K3”), with a higher value in cause Mach number effects reduce the lift on the ad- RW mode (note difference in function curves) varying vancing blades, the negative pitch (“0”) is reduced 65 gain but not serving as a fader.
slightly at even higher airspeeds, reaching, for example, The frnal collective pitch command signal is the s u m minus two (-2) to minus three (-3) degrees at two of the above signals. As can be seen in the upper, right hundred (200) knots. hand portion of FIG. 5, the summation signal is fed
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through an authority limit (typically f 10 degrees) and large error signals from driving the integrator to unnec- sent to the mechanical collective pitch actuator, as essary high outputs.
shown in the overall system block diagram of FIG. 4. The use of a P + I controller in the HMF loop has signifcant advantages. The integrator part functions in Pneumatic Collective Control Law 5 the normal way, holding the required blowing com- The exemplary embodiment ofthe Pneumatic control mand as the error signal goes to zero. The proportional law O f the present invention i s shown i n FIG. 6. As can path significantly increases bandwidth, since a portion be seen, the P m Path is a map, Which Commands the of the error signal is fed straight to the blowing com- PneUXXlatiC COlkCtiVe aS a function O f rotor speed. In mand and there is no waiting for the integrator. This R w mode. the collective Pressure ratio set point is 10 signifcantly improves the rotor response to stick inputs.
around, for example, 1.55, decreasing to, for example, Referring back to FIG. 10, the next feature of the 1.4 i n SR mode. During conve~ion, the reduced lift pitch control law is gyroscopic &coupling. AS can be state i s compensated for by an increase i n collective Seen in the upper middle part of the figure, this prefera- at around, for example, eighty (80) percent bly is achieved by feeding the roll rate to the pitch rotor speed (omega).
l5 command. In this way, the pitching moments generated Direct lift control is achieved by adding in the collec- by roll rate are for.
‘Omand signal to the primary path pneumatic Use of this feedback has shown, however, that it has collective, as shown in FIG- 6. Since large changes in low bandwidth. problem is solved by also feeding collective blowing are undesirable in RW mode, as can to pitch through a low gain. the roll be seen in the lower left of FIG. 6, the collective com- 20 This coupling anticipates the roll rate that will occur signal is gained as a function Of and signifi-tly reduces the transient c r o ~ ~ ~ ~ o ~ RPM, with the RW gain being about, for example, forty percent Of the SR One* In Order to prevent collec- Since both of these sign& are for gyroscopic decou- tive blowing variation in the transition speed range, the pling, as shown in the figure, they are fed through a
collective Command Signal is also gained (L‘K6”) with 25 linear RPM fade-in. nere is no
when the respect to airspeed (“V”). Control is allowed starting at rotor is stopped, and the amount of feedback is linearly about, for example, sixty knots and increasing with proportional to rotor ’peed* airspeed (“V”) to about, for example, one hundred (100) Another c r o ~ ~ - c o ~ P l ~ g that is compensated for is hots. In this way, direct lift control is automatically transferred from mechanical collective pitch to pneu- 3o collective to pitch. Changes in collective blowing will produce changes in the rotor pitching moment. The matic collective.
ne final pneumatic collective signal is the sum of the pneumatic collective cross-coupling command is fed through an RPM gain schedule, since the collective signals discussed above. As can be Seen in the upper blowing to pitch COUphg iS a fUllCtiOn O f the flight right of FIG. 6, the pneumatic collective is fed through a limit (e.g. limiting the values of the signal 35 mode- similar situation exists with mechanical collective A from 1.0 to 2.1) and then sent to the pneumatic ,,due pitch to aircraft pitch moment coupling. In this case, the control logic, as shown in the overall system block coupling only exists in rotary wing mode and disappears diagram of FIG. 4.
as the rotor stops rotating. In addition, this coupling is Pitch and Roll Control Laws sensitive to airspeed. As can be seen in the lower left of FIG. 1 0 , the mechanical collective feedback is therefore F~~ the detailed above, the prior art approach fed though both an RPM fade-in and a velocity gain of hub moment feedback (HMF), shown in FIG. 8, is not an acceptable control system. It should be noted that the above prior art discussion applies to pitch and The Pitch hub moment used for HMF Contains large roll control and that it is true regardless of the flight 45 vibratory components i n R w mode, typically, with mode-rotary wing, conversion or stopped rotor. The l/rev. and 4/reV. COmpOIIentS, but 2/reV. and 3/reV.
addition of a proportional path around the integrator components may also be Present. These vibratory corn- can significantlyimprove the band width of the control- PonentS must be filtered Out, typically with combina- ler, while r e h g all the intrinsic advantages of HMF. tions Of low pass and notch filters. Since the rotor speed 50 can vary, the notch filters must track rotor speed. All This is discussed in detail below.
this filtering adds considerable phase lag to the basic Pitch Axis Control Law steady moment signal. This would otherwise have re- The pitch axis control law for the overall pitch and sulted i n poor transient response, but the proportional roll axes system of FIG. 9 is shown in FIG, 10. The path in the p + I controller compensates for this, as pitch command signal is scaled and fed through a lim- 55 discussed above.
iter for comparison with the pitch hub moment. The VerY large Cyclic blowing COmmands Only result in error signal drives a proportional plus integral control- saturation of the blowing. For this reason, the fmal ler (P+I), which outputs the pitch blowing command pitch blowing command is limited to, for example, a t 0 . 4 pressure ratio, as can be seen in the upper right of after limiting.
The P+I controller itself is shown schematically in 60 FIG. 1 0 . Because the moments created by the rotor on FIG. 11. The error signal is fed through two paths. One the airframe can be very large, the command signal to is a simple proportional path with a gain. The second the HMF control is limited. In addition, this limit is path is an integral path, where the error signal is inte- further reduced when the aircraft is on the ground. In grated. A separate gain is provided for this path. the air, large hub moments produce angular rates-this As can be seen in the figure, the integrator has both 65 aircraft motion in turn relieves the hub moment. On the an input liiit and an output limit. The input limit pre- ground, no such inertial relief is available, so the com- vents large signals from driving the integrator too fast. mands are further limited using a weight-on-wheels The output limit sets the saturation point and prevents (W.O.W.) switch.
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(i.e. have LEB only) at an advance ratio of one (1.0). It Roll A x i s Control Law should be noted that TEB is always employed on the The current best mode for the roll axis control law of advancing side of the disk, and LEB is always turned off the present invention is shown in FIG. 1 2 . It is essen- on that side.
as the pitch axis and prefera- 5 With the turn-on, turn-off advance ratios defined and tially the same architecture b b has aU of the same major featUres-primarY control with the valve azimuth locations fixed, the advance though m F using a Pi-1 contrOller, explicit gyro- ratios for individual valve turn-on and turn-off can be XOPiC de-coUPb3 using Pitch rate and Pitch command precalculated. The blowing azimuth logic then simply feedback, and Provision for CrOSS-COUP~g from the includes a table for the leading edge valves and a table other axes.
1 0 for the trailing edge valves, which is accessed as a func- In the case of the roll axis, de-coupling of the pneu- tion of advance ratio and sets of flags accordingly.
matic collective is provided by an RPM sensitive gain The blowing flag calculation is graphically shown in as in pitch, but no de-coupling of the mechanical collec- FIG. 18, and sample tables for a twenty-four (24) valve tive is required. In fact, mechanical collective is used to confiwation are shown in FIGS. 1 9 ~ and 1 9 ~ . this generate roll moment, as discussed in the section above 15 case, the valve sets were co-located, i.e., they have the on the collective axis.
same azimuthal location.
Another cross-coupling preferably provided is yaw to roll. This is done to provide the same equivalent C. Valve Position Calculation dihedral in all flight modes and also to provide for im- position calculation is graphically shown
ne
proved turn coordination. Other comments made re- 20 in FIG. 2 0 . ne calculation proceeds as described be-
garding the pitch axis also apply to the roll e in terms
low. It should be noted that this logic assumes that the Of Output limitingy changes in limits with trailing edge and the leading edge valves have the same W.O.W. and filtering of hub moment.
azimuthal locations, and that there are twenty-four (24) equally spaced valves for each set. However, the logic Pneumatic Valving Control Laws 25 could be easily modified to account for differing azi- An overview of the currently preferred, exemplary muthal locations or numbers of valves.
or current best mode of the basic valve control laws of The first step is to calculate the desired pressure ratio the present invention is generally shown in overview in at each valve azimuth as the Fourier series or sum of the FIG. 1 5 . The control phase angle is calculated as a collective, cyclic and higher harmonic blowing com- function of airspeed and rotor speed. The phase angle is 30 mands; that is: used along with the collective, cyclic and higher har- monk commands to calculate a master pressure wave.
A non-linear correction is applied to compensate for PR(Tt)=OP A l p C o s ( T t + + ) the non-linear nature of circulation control lift, and the & p s m ( X i + + ) A2p COS ( 2 1 3 resulting commands are sent to the valve position map. 35 B p S i (2* I ) This calculates the valve position required to achieve A3p COS (31 3 the desired blade root pressure at that azimuth. These B3p S i (3 T 3 - 4 p cos (41 1 ) valve commands are then sent to the blowing azimuth B4p S i (4' 3 logic. This block calculates the azimuths over which Asp COS (5r 3 LEB and TEB should occur. The valve positions are 4 . 0 Bsp Sin ( 5 1 J multiplied by on-off flags to create the TEB and LEB commands.
where: A. Control Phase Angle ar=azimuth angle of irh valve, ~p=COllectiVeblowing command, Cyclic control phase angle can be varied with rotor 45 Alp=PitCh blowing command, RPM and airspeed, as shown in FIG. 16. A map of the %=roll blowing command.
phase angle versus the airspeed is used, which is then
Azp, . . . , B5p=HHC blowing commands, and
fed through an RPM scheduled gain.
(p =control phase angle.
B. Blowing Azimuth Logic 50 The control phase angle, 4, is only applied to the pitch
The blowing aziniuth logic sets flags or switches, and roll blowing COmmandS (Alp, Blp) and not the which determine if a valve is to be set to the com- higher harmonic commands (A2p to B$.
manded valve for that azimuth location (flag= 1) or is to Because O f the intrinsic non-linearity Of circulation remain closed (flag=O). The method for calculating the Control lift with Pressure ratio, the twenty-four (24) valve flag state as a function of advance ratio is shown 55 commanded pressure ratios are corrected by using a in FIGS. 17A and 17B, the former illustrating the lead- map 1ook-w. This basically decreases the low pressure ing edge blowing logic and the later the trailing edge commands and increases the high pressure ones. The exact shaping of this correction map depends on the shut down logic.
As illustrated the reverse flow circle for a given ad- nature of the slot used for blowing on the blade.
vance ratio is drawn. A line is drawn at a radial location 60 The third step is to calculate the valve position re- equal to the advance ratio at which the blowing is to be quired to achieve the commanded root pressure. This is turned on (LEB) or turned off (TEB). The intersection done via a bi-variant map look-up, showing the position of this line and the circle defines the azimuth angle for required as a function of the plenum pressure ratio and that advance ratio. The turn-on and turn-off azimuths the commanded pressure ratio.
use of a bi-variant map has sigdkant advan- can then be defined for all advance ratios of interest. The 65 Analytical studies have shown that LEB should be tages. First of all, even valves with very non-linear started (i.e. dual blowing introduced) at an advance pressure drops versus their position characteristics (e.g.
ratio of one-half (OS), and TEB should be turned off butterfly valves) can be automatically compensated for.
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Secondly, variations in the plenum pressure are also controlled by, for example, either of two computers.
automatically compensated for; although, of course, the Two actuators preferably are housed in an assembly, plenum pressure must be high enough to provide the one for leading edge valve control and the other for maximum demanded pressure with the losses of a fully trailing edge valve control via concentric shafts.
Open Valve. AIIflime insuflticient plenum pressure is 5 Although this invention has been shown and de- available, this logic will provide an open valve.
scribed with respect to detailed, exemplary em- The result i s twenty-four (24) Valve commands, but bodiment(s) thereof, it should be understood by those there are a total of fortyeight (48) valves (24 LEB, 24 in the a r t that various changes in form, detail, skilled m B ) . The flags Calculated by the blowing azimuth methodology and/or approach may be made without logic preferably are used to then determine the com- 10 departing from the and scope of this invention.
mands for each set of valves.
Having thus described at least one exemplary em- bodment of the invention, that which is new and de- D. Other Features sired to be secured by Letters Patent is claimed below.
There are several other, more subtle features of the
we cl-
valve control laws described above. l5 1 . A method of controlling an X-Wing type aircraft First-the same algorithm Preferably is used continu- made up of at least one set of control laws, which air- ously, regardless of the flight mode or flight condition.
craft has a rotary wing c6Rwy9) mode and a stopped There preferably is no switching of control laws with rotor c.SR,,) mode with a conversion (,,cv,,) mode as
airspeed Or rotor ‘wed* The logic is thus simp1er and
the rotor changes between said RW and SR modes faster to execute.
2o during flight of the aircraft, with the rotor having a Second-aU valves are commanded at collective pressure ratio set point and a reduced lift state times. A valve malfunction can be detected, even if the and with the aircraft having a controlled aircraft re- valve is not in use at that particular time.
sponse during flight under a control law system, com- Third-when dual edge blowing (DEB) is employed, prising the following steps: preferably both slots receive the same root pre,.sure 25 (a) utilizing a pneumatic collective control law com- command.
manding pneumatic collective as a function of With respect to the hardware for implementing the rotor speed, and, in said RW mode, making the control law system of the present invention, reference is collective pressure ratio set point a positive value, had to the- co-pending application entitled “X-Wing decreasing but remaining positive in said SR mode, Fly-By-Wje Vehicle Management System” (S-4161) 30 and, during said rotor mode conversion (“CV”), by William C. Fischer, referred to above. In particular compensating for the reduced lift state by an in- it is noted that the major hardware elements of the crease in collective blowing; overall system include the flight control computer (b) utilizing a set of Pitch and roll control laws to (FCC), the actuator control module (ACM), and the essentially producing said aireraft response regard- pneumatic control valve (PCV) actuator. 35 less of flight mode or flight condition by compen- The FCC can be, for example, a 2-8002 microproces- sating for undesirable cross-couplings without re- sor-based computer with a very extensive input/output quiring pilot action, as said flight mode or said signal conditioning complement mandated by the multi- condition i s changed; implementing a hub moment plicity of system sensors and actuators. Two major feedback scheme utilizing a proportional and h e - system challenges, which have been successfully ad- 40 gral (.,,+I”) controller, significantly improving its dressed, are the computational demands on the flight bandwidth; and providing limits to the rotor hub control computers and the magnitude of the software movements protecting the aircraft structure from creation tasks. Throughput in excess of two and one inadvertent damage; and
half million instructions per second (2.5 x 106MIPS) per
(C) Utilizing a Set of Pneumatic ValVing control laws channel can be achieved by, for example, a lattice ma- 45 for controlling the position of the valves for the trix architecture, which provides four microprocessors blowing out of air at the blade edges of the rotor per channel in a parallelho-processor configuration.
and providing the pressure required at each valve Efficiencies are achieved through creation of a task azimuth location, with automated switching for driven_ executive and extensive use of assembly lan- leading edge blowing (.‘LEB9’), tr*g edge blow- guage programming. Software can be treated by a 50 ing (“TEB”) and dual edge blowing (“DEB”) structured development methodology characterized by using a table look-up procedure.
the classical checks and culminating in a jointly struc- 2. The method of claim 1, wherein in conjunction turedhendor conducted verification.
with step “a” there is included the following steps: The complete computer chip set can be comprised of, Utilizing a mechanical collective control law giving for example, four boxes all containing identical primary 55 the pilot single-lever direct lift control, while mak- control and back-up control software (BUCS) for flight ing available at least substantial cyclic blowing critical functions. In addition, two of the boxes prefera- in said conversion (“CV”) from one control power bly contain the automatic flight control system (AFCS); mode to another; providing angle-of-attack de-cou- and the other two boxes preferably contain an active pling in rotary wing flight, and using mechanical higher harmonic control (HHC). 60 collective to augment pneumatic roll control; and The actuator control module (ACM) can be, for ex- providing automatic gain variations with airspeed ample, the standard quadruple electrical/dual hydraulic unitary set of control and rotor speed, resulting in a actuator interface between the FCC and the hydraulic laws making up the control law system working in ram, which would be sized for the load of the specific the rotary wing (“RW”), conversion (“CV”) and application. It exhibits hydrologic, hydraulic shutdown 65 stopped rotor (“SR’) modes of the aircraft.
interlock, and initiated built-in test (IBIT) features.
3. The method of claim 2, wherein there is included The pneumatic control valve (PCV) actuator prefera- bly is a dual electrical/dual hydraulic powered actuator the following step:
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scheduling collective pitch with airspeed in the ro- compensating for the strong cross-coupling of the t a r y wing (“RW) mode, while allowing the pneu- angle-of-attack to roll moment by feeding an angle- matic collective pressure ratio to be maintained at a of-attack (“AOA”) signal through an airspeed de- mid-value.
creasing varied gain before summing said AOA 4 . The method of claim 2 , wherein there is included 5 signal with a mechanical collective signal.
the following step: 1 4 . The method of claim 13, wherein there is included making the maximum cyclic blowing control author- the following steps: itY available by the Collective Pressure providing about a zero AOA signal out to about one ratio at about its mid-value during the conversion hundred (100) knots, and, at speeds higher than (“CV”) mode.
an in- about one hundred (100) knots, providing 5. The method of claim 2 , wherein there is included creasingly negative AOA signal, with changes in the following step: the AOA resulting in collective pitch inputs tend- providing a coupling between anglesf-attack (AOA) ing to cancel any induced rolling moment.
and mechanical collective pitch, providing auto- 1 5 . The method of claim 13, wherein there is included matic compensation to cancel the rolling moments 15 the following steps: created by angle-of-amk changes in high speed feeding the AOA &coupling signal through an RW flight.
RPM fade-in before summing said AOA de-cou- 6 . The method of claim 2 , wherein there i s included pling signal up with the mechanical collective sig- the following step: nal.
automatically setting the pneumatic collective to its 20 1 6 . The method of claim 2 , wherein there is included optimal value in said Rw, cv and SR flight modes.
the following step: 7 . The method of claim 2 , wherein there is included using the collective pitch in high speed the following step; RW, CV and SR modes to augment said pneumatic cross-coupling the mechanical collective to lateral roll control.
stick, making roll control augmentation available in 25 l , . The method of claim 16, wherein there is included said RW, CV and SR flight modes.
the following step: 8 . The method of claim 2 , wherein there is included a cross-feeding a roll axis command signal to collective basic map and wherein there is included the following step: pitch signal.
1 8 . The method of claim 17, wherein the control law feeding the basic map though an RPM fademinthat 3o provides a that with said rotor speed. System includes a roll axis Cross coupling command Signal, and wherein there iS included the fOllOWhg
9. ne method of claim 8, wherein the provided gain
steps: is an RPM scheduled gain, and wherein there is in- scaling said roll axis cross coupling command signal; cluded the following steps: and providing a gain of zero from about zero (0%) to 35 feeding the scaled though an about ten (10%) percent of said rotor speed, then airspeed gain with the gain being about zero at increasing the gain with said rotor speed until the relatively low airspeeds below about one hundred gain gets to about one at about ninety (90%) per- (100) knots velocity and becoming an increasing, cent and maintaining the gain at about that value to Positive value at about One hundred (loo) knots about one hundred and ten (1 10%) percent, using 40 velocity.
the RPM scheduled gain to allow conversion to 1 9 . The method of claim 18, wherein there is included take place Over a broad range of aircraft airspeeds the further from about one hundred and forty (140) to about feeding the airspeed gained and scaled roil command two hundred (200) knots, while maintaining the signal through a RPM Varying gain.
collective pitch at a value that maintains flight of 45 20. The method of claim 1 , wherein in step “a” there the aircraft.
is included the fOllOW~l3 step: 1 0 . The method of claim 2 , wherein there is included increasing the collective blowing at about eighty (80) the following steps: percent rotor speed.
using the collective command signal to command 2 1 . The method of claim 1 , wherein there is included direct lift changes and feeding the signal though 50 a collective command signal and wherein in step “a” an airsped variable g h , and, in hover and low there is included the following step: speed rotary wing flight, feeding the collective adding the collective command signal to the com- command signal directly to the mechanical collec- manded pneumatic collective to produce a pneu- tive compensating for variations in the aircraft matic collective signal, achieving direct lift con- weight and allowing for vertical maneuvering, and, 55 trol.
as said airspeed increases, reducing the gain, ma- 22. The method of claim 21, wherein there is included (80) knots.
neuvering to about zero at about eighty the following preliminary step: 1 1 . The method of claim 10, wherein there is included decreasing the gain of the collective command signal the following step: as a function of RPM.
fading in the pneumatic collective, providing direct 60 23. The method of claim 22, wherein there is included lift control at higher speeds.
1 2 . The method of claim 11, wherein there is included the following step: setting the RW mode gain at about forty (40%) per- the following steps: summing a pneumatic collective signal with a basic cent of the SR mode gain.
24. The method of claim 22, wherein there i s included map and also reducing said pneumatic collective 65 the following supplemented steps: signal in said SR mode.
increasingly gaining the collective command signal as 1 3 . The method of claim 2 , wherein there is included a function of said airspeed, preventing collective the following step:
4,980,835
21 22
blowing variation in the conversion (“CV”) speed 3 7 . The method of claim 1, wherein in step “c” there range. is included the following step: 2 5 . The method of claim 24, wherein there is included providing continuous commands to all said valves for the following steps: said LEB and said TEB, allowing immediate detec- allowing direct lift command control signal to be tion of any malfunctions in the valves.
increased at about sixty (60) knots and further in- 3 8 . The method of claim 1 , wherein there i s further creasing it with said airspeed to about one hundred included the following step: (100) knots, transferring direct lift control from using a unified set of control laws for said RW, CV mechanical collective pitch to said pneumatic col- and SR modes and varying some functions of the lective. control law based on the rotor speed and airspeed 2 6 . The method of claim 1 , wherein there is further to compensate for the modes.
included a pneumatic value control logic circuit and 3 9 . A control system for an X-Wing aircraft made up wherein in step “a” there is included the following of at least one set of control laws, which aircraft has a steps: rotary wing (“RW’) mode and a stopped rotor (“SR’) limiting the pneumatic collective command signal to mode with a conversion (“CV”) mode as the rotor a maximum value and then sending the limited 15 changes between said RW and SR modes during fight pneumatic command signal to the pneumatic value of the aircraft, with the rotor having a collective pres- control logic circuit. sure ratio set point and a reduced lift state and with the 27. The method of claim 26, wherein there is included aircraft having a controlled aircraft response during the following step: fight under the control law system, comprising: limiting the values of the pneumatic collective signal mechanical collective control law signal generating 20 from about 1.0 to about 2.1. means for providing signals giving the pilot single- 2 8 . The method of claim 1 , wherein in step “a” there lever direct lift control, while making available at is included the following steps: least substantial cyclic blowing control power dur- in said RW mode, setting the collective pressure ratio ing said conversion; for providing signals for angle- set point at about 1.55, decreasing to about 1.4 in of-track de-coupling in rotary wing flight, and for said SR mode. using mechanical collective to augment pneumatic 2 9 . The method of claim 1 , wherein in step “b” there roll control; and for providing signals for auto- is included the following step: matic gain variations with airspeed and rotor speed, resulting in a ’unitary set of control laws providing the pilot with a rate command control .
system in pitch and roll which produces said air- working in the rotor wing (“RW’), conversion 3o craft response to a given stick input regardless of (“CV”) and stopped rotor (“SR”) modes of the said flight mode or said flight condition. aircraft; 3 0 . The method of claim 1 , wherein the rotor of the pneumatic collective control law signal generating X-wing aircraft can experience gyroscopic cross-cou- means associated with said mechanical collective plings and wherein in step “b” there is included the control law signal generating means for generating following step: signals commanding the pneumatic collective as a function of said rotor speed, and, in said RW mode, automatically compensating for said gyroscopic cross-couplings. for making the collective pressure ratio set point a 3 1 . The method of claim 1 , wherein there is a blade positive value, decreasing but remaining positive in root pressure on the blades of the rotor and wherein in said SR mode, and, during said conversion, for step “c” there is included the following step: compensating the reduced lift state by an increase in collective blowing; linearizing any non-linearities of said blade root pres- sure to valve position due to the valve characteris- pitch and roll axes control laws signal generating tics of circulation control lift by using map look- means associated with said mechanical collective control law signal generating means and said pneu- ups.
32. The method of claim 1 , wherein in step “c” there 45 matic collective control law signal generating is included the following step: means for generating signals for essentially produc- ing said aircraft response regardless of flight mode providing azimuth variations in blade root pressure in accordance with collective, cyclic and higher har- or flight condition by compensating for any unde- monic blowing commands. sirable cross-couplings without requiring pilot ac- 3 3 . The methodof claim 1 , wherein in step “c” there- 50 tion, as said flight mode or said flight condition is changed; for implementing a hub moment feedback is included the following step: automatically scheduling said TEB, DEB and LEB scheme utilizing a proportional and integral on the retreating side as a function of advance ratio, (“P + I”) controller, significantly improving its which is the ratio of the aircraft’s flight velocity bandwidth; and for providing limits to the rotor divided by the rotor blade tip speed. hub movements protecting the aircraft structure 5 5 34. The method of claim 1 , wherein in step “c” there from inadvertent damage; and pneumatic valving control laws signal generating is included the following step: automatically compensating for the non-linear rela- means associated with said mechanical collective tionship between valve position and root pressure. control law signal generating means and said pneu- 35. The method of claim 1 , wherein in step “c” there matic collective control law signal generating 6o means for generating signals for controlling the is included the following step: automatically compensating for the change in cyclic position of the valves for the lowing out of air at control phase angle required as a function of rotor the blade edges of the rotor and for providing the pressure required at each valve azimuth location, rotational speed and said airspeed.
3 6 . The method of claim 1, wherein in step “c” there with automated switching for leading edge blow- ing (“LEB”), trailing edge blowing (“TEB”) and is included the following step: providing for a non-linear correction to the blowing dual edge blowing (“DEB”) using a table look-up to account for the non-linear nature of circulation procedure.
* * * * *
control lift.
UNITED STATES PATENT AND TRADEMARK OFFICE
CERTIFICATE OF CORRECTION
PATENTNO. : 4,980,835 DATED . : December 25, 1990 INVENTORIS) : Lawrence e t ' a l .
It iscertified that error appears in the above-identified patent and that said Letters Patent is hereby corrected as shown bdow: Col. 1, l i n e 18, d e l e t e one "No."
Col. 1, l i n e 2 1 , d e l e t e one "NO."
Col. 2 , l i n e 48, r e p l a c e "Value" w i t h --Valve-- Col. 2 , l i n e 50, r e p l a c e "Value" w i t h --Valve-- Col. 3 , l i n e 30, r e p l a c e "(+0.3)" w i t h --(+0.3)-- -
Signed and Sealed this
Twenty-fifth Day of August, 1992
Atrest: DOUGLAS B. COMER Attesting Officer Acting Commissioner of Patents and Trademarks