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United States Patent c19] [ll] Patent Number: 6,102,330
Burken et al. [45] Date of Patent: Aug. 15, 2000
Frank W. Burcham, Jr., T.A. Maine, John J. Burken, and EMERGENCY MULTIENGINE AIRCRAFT [54] SYSTEM FOR LATERAL CONTROL USING Drew Pappas, Development and Flgith Test of an Aug- mented Thrust_Only Flight Control System on an MD-II DIFFERENTIAL THRUST CONTROL OF WING ENGINES Transport Airplane, Jul. 1996, pp. i-25, NASA Technical Memorandum 4745.
[75] Inventors: John J. Burken, Tehachapi; Frank W.
John Bull et al., Piloted Simulation Tests of Propulsion Burcham, Jr., Lancaster; John Bull, Control as Backup to Loss of Primary Flight Controls for a Los Altos, all of Calif.
Mid-Size Jet Transport, NASA Technical Memorandum 110374, Dec. 1995, pp. 1-35.
The United States of America as [73] Assignee: represented by the Administrator of the National Aeronautics and Space Primary Examiner--Peter M. Poon Administration, Washington, D.C.
Assistant Etaminer Tien Dinh AttorTw); Agent, or Firm---John H. Kusmiss [21] Appl. No.: 08/905,777 [57] ABSTRACT [22] Filed: Jul. 29, 1997 An emergency flight control system is disclosed for lateral [51] Int. CI. 7 ..................................................... B64C 19/_00 control using only differential engine thrust modulation of [52] U.S. C1 ........................................... 244/76 R; 244/184 multiengine aircraft having at least two engines laterally [58] Field of Search .................................. 244/76 R, 183, displaced to the left and right from the axis of the aircraft in 2441188, 184, 52 response to a heading angle command _,. to be tracked. By continually sensing the heading angle _ of the aircraft and References Cited [56] computing a heading error signal _ as a function of the difference between the heading angle command _ and the U.S. PATENT DOCUMENTS sensed heading angle W, a track control signal is developed 7/1957 Alderson et al..
2,798,682 with compensation as a function of sensed bank angle _, 3/1964 Dornier ..................................... 244/52 3,126,170 bank angle rate ¢_, or roll rate p, yaw rate x, and true velocity 3,176,463 4/1965 Bauger et al............................. 244/52 to produce an aircraft thrust control signal ATC_,_L,e). The 3,361,392 1/1968 Doniger et al..
thrust control signal is differentially applied to the left and 4,106,730 8/1978 Spitzer et al..
right engines with equal amplitude and opposite sign such 10/1991 Nadkami et al..
5,060,889 that a negative sign is applied to the control signal on the 7/1994 Burcham et al..
5,330,131 side of the aircraft to which a turn is required to reduce the OTHER PUBLICATIONS error signal until the heading feedback reduces the error to zero.
EW. Burcham, Jr. & C. Gordon Fullerton, "Controlling Crippled Aircraft-With Throttles," NASA Technical Memo- 4 Claims, 2 Drawing Sheets randum 104238, Sep. 1991, pp. 1-26.
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EMERGENCY MULTIENGINE AIRCRAFT engine throttle servo at the laterally displaced engines for a SYSTEM FoR LATERAL CONTROL USING change in engine pressure ratio (EPR) at each engine.
DIFFERENTIAL THRUST CONTROL OF An object of this invention is therefore to create a suffi- WING ENGINES cient degree of lateral control through differential thrust modulation of laterally displaced engines, i.e., engines ORIGIN OF INVENTION equally spaced on both wings or both sides of the aircraft fuselage to provide directional control of the aircraft inde- The invention disclosed herein was made by two employ- pendent of longitudinal (flightpath angle)control and, in the ees of the United States Government, and may therefore be case of making a landing approach, to make a safe landing manufactured and used by or for the Government for gov- to when only engine thrust control is available.
ernmental purposes without the payment of any royalties therefor, in conjunction with an employee of a contractor of STATEMENT OF THE INVENTION the United States Government in which invention the con- In accordance with the present invention, lateral control of tractor has elected not to seek to retain any title.
a multiengine aircraft is provided in response to a heading 1. Technical Field t5 angle command, _, produced by a pilot through a thumb- The invention relates to an emergency flight control wheel or by an instrument landing system. That command is system using only autocontrol engine thrust modulation for compared to a sensed heading, _, to produce an error signal lateral control of an aircraft in the event of a failure of that corrects the heading sensed after compensation by primary, control effectors, namely wing and tail control feedback signals from selected aircraft dynamic sensors to surfaces. 20 improve dutch-roll damping and closed loop performance.
2. Background Art The compensated error signal is thus transformed into a In the last score of years, aircraft have experienced major thrust command ATCw_L.n) that is applied to the aircraft flight control system failures and have had to use engine engines differentially, i.e,, with a positive sign on the left engine(s) and a negative sign on the right engine(s) or vice throttles for emergency flight control after losing the air- craft's hydraulic system. 25 versa depending on the direction of the heading correction needed to track the command heading _,,,. Bank angle rate In the majority of cases a crash resulted, particularly while is included as a feedback for the dutch-roll damping. Yaw attempting a landing, claiming many lives. To investigate the technique of engine thrust control over flight, the rate x, bank angle • and true velocity vt are included as National Aeronautics and Space Administration, Dryden -0 feedback signals for efficient turn coordination and smooth Flight Research Center, conducted flight and ground simu- ' change in heading.
lator experiments and analytical studies to determine the In a first embodiment, the EPR aut0trim of the digital degree of flight control available with pilot manilJulation of engine control (DEC) at each engine is used with its limi- tation of _-t=5%EPR control, and in order to obviate the need engine throttles for various classes of muhiengine aircraft which have laterally displaced engines from the FI5 to the to make changes there, a +_.5"limiter is imposed on the error B-747 and including the MD-11 which has a third engine signal (_c=_) before compensation for any of the bank angle rate _, yaw rate x, true velocity vt, and bank angle _.
mounted over the fuselage at the base of the tail.
In a second embodiment, the normal autotrim of the DEC In flight, a research pilot was able to use differential may also be used with the +__5% limited autotrim feature but throttle control to generate sideslip which, through the dihedral effect, resulted in a roll and use symmetric throttle 40 without a 5 ° limit on heading change. All of the compen- sation present in the first embodiment for yaw rate x, bank control to climb or descend by increasing or decreasing angle rate qb, and bank angle • are retained in a similar thrust. A research pilot could thus not only successfully fly manner for an efficient turn coordination and smooth change a simulator but could also put a simulator on the runway for in heading with three differences. The three differences in a safe landing. In actual flight, however, both longitudinal 45 the second embodiment are: first the bandwidth filter is and lateral control were almost too difficult for flight and made broader by the coselected to accommodate frequency unsafe for landing. It was thus clear that there was a need for of the yaw rate x; second the scaling of the track command a computerized engine-thrust control system to provide an T_ is made variable by a pilot selected input, Krollmode, for emergency Propulsion Control Aircraft (PCA). The engine- a four engine aircraft, such as a B-747 depending upon thrust control system for longitudinal flightpath angle con- trol is described in a copending application Ser. No. 081886, 50 whether only two inboard engines, only two outboard 656 filed Jul. 1, 1997; by John J. Burken and Frank W. engines or all engines are used, namely 2.20 for onlYinboard Burcham, Jr. titled EMERGENCY CONTROL AIRCRAFT engines, 0.65 for all four engines, and 1.40 for only outboard SYSTEM USING THRUST MODULATION filed Jun. 30, engines; and third the scaling factor K_,,, which corresponds to the same K_,,, of the first embodiment is now modified by 1997. which by this reference is hereby incorporated herein.
The present invention provides an engine-thrust lateral con- 55 the variable vt/g in order for the entire lateral control system to be a function of true velocity for more gentle, smoother trol system that is independent but for the extent both share turns of a four-engine aircraft. The last two features may also the same aircraft dynamics responsive to the PCA control of be used in the first embodiment.
each.
The novel features that are considered characteristic of As disclosed, that PCA system is useful for flightpath this invention are set forth with particularity in the appended angle (y) control _luring all phases of flight, including claims. The invention will best be understood from the landing approach to touch down. However, to provide safe following description when read in connection with the landing capability, a separate PCA system is required for accompanying drawings.
heading angle (_) control using differential engine thrust control. The resulting lateral controI may be combined with BRIEF DESCRIPTION OF THE DRAWINGS the PCA longitudinal control, either at the input of a cockpit FIG. 1 is a functional block diagram of a PCA system for throttle servo, if one is provided separately for each laterally lateral-directional control, i.e., for tracking a heading com- displaced engine on either side of the aircraft, or on each
6,102,330
through a bandpass filter Kwo3S/(Kwo3+l), where K,_03 is a mand signal _, in a multiengine aircraft on which all wash-out time constant that effectively controls the bandpass engines have engine controllers with a normal +__5%engine of the filter. The filtered output, scaled by a constant I<1, v is pressure ratio 0EPR) command limitation.
added to the sensed bank angle rate _ after that angle rate is FIG. 2 is a functional block diagram of a PCA system for 5 scaled by a constant Kt,h_ d. The feedback signal thus devel- lateral-directional control similar to that in FIG. 1 but with oped is subtracted from the heading error lug,.compensated all engines modified to have engine controllers with full- by the bank angle • to further compensate for the bank authority EPR command (FACED).
angle rate _, the yaw rate '_ and g/vt. The fully compensated thrust command signal T,, is then scaled by a constant K_,,, DETAILED DESCRIPTION OF THE INVENTION I0 to produce the ATCv_L. m signal applied differentially to left and fight engines. The functional blocks representing gains The vehicle for which the first embodiment of this inven- of 1 and -1 provide the differential thrist signals applied to tion is designed is the same MD-11 wide-body transport the engines. If ATCv_..R _ is positive, the right engine referred to in the aforesaid copending application which has receives a negative control signal while the left engine a mechanical flight control system with hydraulically pow- 15 receives a positive control signal for a fight turn and vice ered actuators of flight control surfaces and is equipped with versa if ATC_,_L.n_ is negative.
a Flight Control Computer (FCC) that provides a Flight The control law for tracking a command heading angle _,.
Management System (FMS) with autopilot, navigation and is as follows: autoland functions. The autopilot function includes a thum- bwheel for commanding not only flightpath angle, T, hut also 20 (D A TCt_ t R_ = heading angle, _c, during all flight phases, namely climbing, cruising, and descending unless such commands are other- _ K_,ojS + I I _ wise being provided from another source, such as from the FMS during an autoland function that relies on an Instru- Klat ment Landing System (ILS) for guidance control using 25 flightpath angle (T) and heading (_) commands.
Implementation of this control law is preferably in a pro- In the MD-II airplane, two engines are mounted in grammed digital computer. The constants K_,, KI,,_, Kph,a underwing pods equally spaced on each side with the third engine centered at the base of the vertical stabilizer. While and K m are scaling constants initially determined by aircraft 30 aerodynamic analysis and then optimized empirically, vt is all three engines are controlled together by the PCA system true velocity, which is sensed velocity adjusted for altitude for longitudinal control through a cockpit autothrottle servo, pressure and temperature, and K,.o3 is a washout time for lateral control the wing engines are controlled differen- constant.
tially through separate and direct engine thrust or engine As noted above, the output control signal ATC_,¢L_ is pressure ratio (EPR) control in order to provide lateral 35 separated into left and right engine commands by the signs control in response to a heading angle command, _,..
of the gain (+1 and -1) of functional blocks. The +_5°% Consequently, the lateral control system of the present limiter on the error signal _,, provides the necessary limit on invention produces two separate engine thrust modulation the product of _,. and K_,, which, in conjunction with the signals ATC v to be applied directly to respective engines other scaling constants, will limit the engine thrust control differentially to modulate the longitudinal control effected at 40 called for in response to the command ATC_,_L.R_ to be the engines by the longitudinal thrust control signals ATC._ within the EPR range of +_5%.
sent to all engines through the cockpit throttle servo (as The differential lateral control effect thus produced is used shown in the aforesaid copending application) thereby pro- to generate yaw of the airplane, resulting in roll caused by ducing the desired effect of differential lateral control signals the dihedral angle of the airplane wings in order to bank the ATC_, (L,R) at the left and right wing engines, i.e.. produc- 45 airplane for a turn while tracking a heading angle command ing the effect of ATC +v_ATC_, (L,R) for the left and fight _,.. The differential lateral control law uses feedback signals wing engines as though ATC +r_ATCv_L.R) were formed at developed from selected aircraft dynamic sensors to cockpit thrust servos using separate cockpit autothrottle improve closed loop performance. Bank angle rate _ is servos for the wing engines. Because the MD- 11 is equipped included for dutch-roll damping. Yaw rate "L bank angle _, with only one cockpit thrust servo responsive to ATC_. the 50 and vt are included for efficient turn coordination and control signal ATC_,/_.R_ must be sent directly to the engines smooth change in heading angle.
to differentially modulate the engine pressure ratio (EPR) Referring now to FIG. 2, a block diagram is shown of a setting at the left and right wing engines or otherwise second embodiment for lateral control of an aircraft with modulate the engine thrusts.
multiengines, each engine having its separate digital engine The block diagram of the lateral control law shown in 55 control (DEC) computer with its +_5% EPR feature. The FIG. 1 assumes the case of the lateral thrust control signal lateral control law for this embodiment is as follows: ATCv_L.e) applied differentially and directly to the digital engine control (DEC) of each engine. In this case, the DEC Tc=K_=_*K=n=oa_*I(K_*_-K_*4_)-Ke*p-#.._I 12) of each engine is unmodified so that it may accept only normal EPR commands with a +_5% limit. After comparing S a sensed aircraft heading angle _ in degrees with a pilot or 60 /3,,_ = K_. (S__._). g • _b -r, (3) other control input heading angle _c and scaling the result- ing error signal by a constant K/_, the scaled error signal is O_ = K_ . (vt / gX_b_ - _b), 14) passed through a :!:5° error limiter and compared to a sensed bank angle, _, from aircraft dynamic sensors. The resulting 65 where: error signal _ is then further modified as a function of the is roll attitude, deg, difference of x and g=32.2 divided by true velocity vt in order to provide x-g/vt. The result (x-g/vt) is then passed _ is commanded track angle, deg,
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W is the sensed heading, deg, ATCo_L,R_ = is sensed yaw rate, deg/sec, co is selected to set band of highpass filter, + K,..* l--i* it- £1/* X,<,, I|(O__).K,<_,I,]_¢.Kt,, _ : h;.o3S _ , ' tl_,o:S+ IJ _ vt'" P is roll rate, deg/sec, 5 K's are scaling constants, where: K., K_,., Kph_a and Kp. are scaling constants initially EPR ,.--q_'_K,.,,g*TC, determined by aircraft aerodynamic analysis and then opti- K,.,g is a scaling factor for the particular engine, mized empirically, vt is true velocity, which is sensed vt is true velocity Io velocity adjusted for altitude pressure and temperature, and K,,+a3 is a washout time constant.
Kml,,od, = 0.65 for a four engine configuration of a B--747 airplane 3. An emergency flight control system as defined in claim I here said means for compensating said error signal wit..is having two on each wing, implemented in accordance with the following control law: = 2.20 for inboard engines only 15 Tc=K,_j * K,a_,,,.,d¢ * I(K,, *,;/'< -K**¢O-Kp*p-B,,,A = 1.40 for outboard engines only.
_,,o,: x,,,fsl, _,-+ --,, I,S+lo: vt Note: For an MD- 11, the K_,, is on the same order as that for 20 O: = K¢: * (vt / gXqs< - 0), the B-747 inboard engines only. All other constants for the B-747, as for the MD- 11, are determined by aerodynamic where: analysis for the particular aircraft and empirically optimized 0 is roll attitude, deg, for performance.
W is commanded track angle, deg, Although particular embodiments of the invention have 25 been described and illustrated herein, it is recognized that W is the sensed heading, deg, modifications may readily occur to those skilled in the art. • r is sensed yaw rate, degfsec, For example, in both embodiments, the digital engine con- o3 is selected to set band of highpass filter, trol for each engine may be modified to eliminate the +_5% p is roll rate, deg/sec,_ EPR limitation. Both embodiments were designed to work 30 K's are scaling constants, with that feature because most jet aircraft engines are EPR,.=K_,,g*Tc, - provided with an EPR autotrim feature with that limitation, K<.._ is a scaling factor for the particular engine.
but both are capable of working with engines that do not vt is true velocity.
have that limitation. Consequently, it is intended that the 35 claims be interpreted to cover such modifications and Kmt_ = 0.65 for a four engine configuration of a B-747 equivalent_ thereof.
airplane having two on each wing, What is claimed is: = 2.20 for inboard engines only, 1. An emergency flight control system for heading angle W of a multiengine aircraft using engine thrust modulation 4o = 1.40 for outboard engines only.
for differential lateral control of said multiengine aircraft having at least two engines laterally displaced from a longitudinal axis thereof comprising, 4. An emergency flight control system using engine thrust modulation for heading angle W control of a multiengine means for independently entering a heading angle corn- 45 aircraft with differential of at least two engines laterally mand _¢ to be tracked by said aircraft, displaced from a longitudinal axis thereof comprising, means for continually sensing said heading angle _g of means for indepeiident]); entering a heading angle qom_ said aircraft, " ....
- mand _c to be tracked by said aircraft, means for computing a heading error signal W: as a means for continually sensing said heading angle W of function of the difference between said heading angle said aircraft, .. : command _,, and said sensed heading angle W, means for computing a heading error signal W,, as a means for compensating said error signal W_ as a function function of the difference between said heading angle of sensed bank angie_ate _ for dutch roll damping and command W_ and said sensed heading angle W, of Sensed bank angle @, yaw rate x and _,elo-city for 55 means for compensat[ng_d_error signal W,_as a function = efficient turn coordination to produce an aircraft thrust of sensed roll attitude ¢ for dutch roll damping and of sensed bank angle @, roll rate p, yaw rate "r and velocity control signal ATCv<L. m, and means for differentially applying said aircraft thrust con- to produce an aircraft thrust control signal ATCv(, _, and trol signal to said left and right engines with equal amplitude and opposite sign with the negative sign 60 means for differentially applying said aircraft thrust con- applied to the control signal on the side of the aircraft trol signal to said left and right engines with equal to which a turn is required to reduce said error signal amplitude and opposite sign with the negative sign toward zero.
applied to the control signal on the side of the aircraft to which a turn is required to reduce said error signal 2. An emergency flight control system as defined in claim 65 toward Zero.
1 wherein said means for compensating said error signal W_ is implemented in accordance with the following control law: