Document
[111 4,354,237
United States Patent 1191
[45] Oct. 12, 1982
Lambregts et al.
3,489,378 1/1970 Watson et al. ...................... 244/187
METHOD AND APPARATUS FOR
3,601,339 SA971 Watson ................................ 244/187
PRODUCING AN AIRCRAFJT FLARE PATH
3,604,908 9/1971 Loome et al. ....................... 364/430
CONTROL SIGNAL
3,618,002 11/1971 Stinson ............................ 244/183 X
Inventors: Antonius A. Lambregts, Renton; Rolf 3,626,163 12/1971 Dommasch ......................... 364/429
3,652,835 3/1972 Devlin et al. ....................... 364/429
Hansen, Bellevue, both of Wash.
3,752,967 8/1973 Victor ................................. 364/427
Assignee: The Boeing Company, Seattle, Wash.
3,976,267 SA976 Meyer et al. ................... 364/430 X
4,006,871 2/1977 Simpson .......................... 364/428 X
Appl. No.: 162,451
4,093,158 6/1978 Clews et el. ........................ 244/182
Bliss ................................ 364/428 X
4,106,731 SA978 Filed: Jun. 24, 1980 4,141,522 2/1979 Lambregts .......................... 244/186 .
Int. Cl.3 .......................... G06G 7/78; G05D 1/12
U.S. CI. .................................. 364/428; 73/178 T; Primary Examiner-Jerry Smith 244/183; 244/187; 364/429 Attorney, Agent, or Firm-James P. Hamley; Bernard A.
Field of Search ....................... 364/428, 429, 430; Donahue
340/26; 318/583; 244/183, 186, 187; 73/178 T
VI ABSTRACT
References Cited Aircraft altitude, ground velocity, and altitude rate U.S. PATENT DOCUMENTS signals are input to a computer which, using a unique
....................... 244/187 control law, generates a pitch control surface command
3,169,730 2/1965 Gaylor et al.
8/1966 Montooth ........................... 244/187
3,265,333 signal suitable for guiding an aircraft on its flare path to
3,295,796 1/1967 Gaylor ................................ 244/187
a specified runway touchdown point despite varying
3,310,259 3/1967 Swift et al. ..................... 244/187 X
wind conditions.
3,333,795 8/1967 Hattendorf et al. ................ 244/187
3,437,292 8/1969 Greene ................................ 244/187
3,463,422 SA969 Watson ........................... 244/187 X 2 Claims, 4 Drawing Figures
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?/TCH FLARE A COMMAND __t r L FLARE
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1 2 produced representative of aircraft groundspeed. Third, METHOD AND APPARATUS FOR PRODUCING a signal h is produced, representative of aircraft altitude AN AIRCRAFT FLARE PATH CONTROL SIGNAL rate. Finally, a pitch control surface command signal 6 , is computed according to the relationship: BACKGROUND OF T H E INVENTION 6 , = K i { h + v d ( K h / K d / v G RE.d(h+hB)) The invention described herein was made in the per- No. NAS1- formance of work under a NASA contract where Kh, Kh, v ~ ~ ~ ~ a n d hgare constants selected for 14880 and is subject to the provisions of Section 305 of a given system configuration.
the National Aeronautics and Space Act of 1948, Public Law 85-568 (72 Stat. 435; 42 USC 2457).
BRIEF DESCRIPTION O F T H E DRAWINGS The present invention pertains to the aircraft guid- FIG. 1 is a plot of aircraft altitude h versus altitude ance art and, more particularly, to a system for control- rate h for the prior art flare-out control system; ling aircraft flight during landing flare.
FIG. 2 is a plot of aircraft altitude h versus runway A critical portion of aircraft landing trajectory is 15 distance X and shows the touchdown dispersion of the commonly known as flare-out or flare. Flare is that prior art system from its glideslope intercept point; portion of the landing trajectory between the fixed 3 is a plot of aircraft altitude h versus altitude FIG.
angle glideslope and aircraft runway touchdown. Thus, rate h for an aircraft following a control signal accord- it is desirable, particularly for commercial aircraft, that ing to the instant invention; and the flare profile depart smoothly from the fixed angle FIG. 4 is a block diagram illustrating the preferred glideslope approach providing a smooth transition to runway rollout. embodiment of a system for generating a control signal In commercial aircraft, attempts have been made at according to the instant invention.
generating landing flare commands to be used either as DETAILED DESCRIPTION OF T H E a flight director to the pilot or for automatic, i.e. autopi- PREFERRED EMBODIMENT OF THE lot, landing. The problem with these systems, however, INVENTION is that groundspeed variations affect touchdown disper- sion. That is, since aircraft groundspeed is not taken into In one type of flare control law widely used today, account, the actual touchdown point of the aircraft on the aircraft sinkrate is proportional to altitude. Thus, the runway can vary considerably depending on the excluding damping terms, which are a part of any flare 3 0 groundspeed. This is undesirable both for safety reasons equation, the basic exponential flare control law is of and because reduced touchdown dispersion is essential the form: to effective runway utilization and continued aircraft operation under adverse weather conditions.
6 , , = K i h + K h ( h + h d (1) Another problem with existing flare control systems is that the flare height from which flare is initiated may where be affected by aircraft groundspeed. This has an adverse &=pitch control surface command effect on the ability of the pilot to monitor the system h=altitude rate, for proper operation and may place the start of the flare h=altitude, ahead of the runway threshold where terrain features Ki, Kh, hg=constants selected may make it difficult to use radio altimeters.
for a particular system configuration.
For the condition of a zero pitch control command SUMMARY OF THE INVENTION i.e., the aircraft's servo system reduces the pitch com- It is an object of the present invention, therefore, to mand to zero, the equation takes the following form: provide apparatus for generating, and a method of pro- ducing an aircraft flare path control signal which mini- K i i +Kh(h + h E ) = O . (2) mizes touchdown dispersion due to groundspeed varia- tions. FIG. 1 is a graph of this equation, showing altitude on It is a further object of the invention to provide the the vertical axis versus altitude rate, on the horizontal above described apparatus for, and method of generat- axis. Exemplary values of the various constants are ing an aircraft flare path control signal wherein the selected, i.e. the value of Kh/& is assumed to be 0.205
altitude at which flaie is initiated < independent of
and the value of hB is assumed to be 12.
groundspeed.
Assuming constant control law parameters, the soh- Briefly, according to the invention, apparatus for tion for the above differential equation is producing an aircraft flare path control signal includes h = - r h & - r / T - h B a means for producing a signal h representative of air- 55 craft altitude. Also, suitable means produces a signal . .
h=-h&-r/T (3) VG representive of aircraft groundspeed and further means produces a signal h representative of aircraft where altitude rate. A computer produces a pitch control sur- T = K/;/Kh face command signal 6, according to the relationship: 60 h,=initial sinkrate= -VG tan fi where,
&=K& + v d ( K h / K i ) / VG REFj(h + h d }
VG= groundspeed fi=glidepath angle.
where Ki, Kh, V c ~ E F a n d heare constants selected for The expression for the flare height from which flare a given system configuration. 65 A method for producing an aircraft flare path control must be initiated to satisfy the above equation is signal comprises the first step of producing signal h bo= VG r tan P-hB.
( 5 ) representative of aircraft altitude. Second, a signal VGis
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is produced in a manner discussed herein below, to bc FIG. 1 illustrates this flare height ho for values of 110, coupled to the aircraft's flight dynamics.
125 and 140 groundspeed knots. Thus, since the flare The pitch control command signal computed as height ho varies as a function of groundspeed VG(ab0Ut follows. The altitude signal h is summed with a constant six feet for a 15 knot variation in VG) this has an adverse 5 signal hi, supplied from block 30. Thus, the output from effect on the ability of the pilot to monitor the system summer 14 is of the form h+hi,. This signal is applied as for proper operation and may also place the start of the one input to a multiplier 32.
flare ahead of the runway threshold where terrain fea- The groundspeed block 40 produces an output signal tures may make it difficult to use radio altimeters. VG corresponding to aircraft groundspeed. Such FIG. 2 is a plot of aircraft altitude h versus runway 10 groundspeed signals VG are commonly provided on position X and illustrates the distance X T D between the commercial aircraft and, as such, will not be discussed aircraft actual touchdown point and the glideslope in- here.
tercept point with the runway. It is assumed that the The groundspeed signal VG is multiplied by a factor aircraft is on a glideslope angle P and that flare is initi- l / V ~ R ~ r i n block 42. The signal 1Nc R,pis a constant ated at the altitude h,, which is approximately 42 feet. I5 value depending upon a particular system configura- The total distance is expressed analytically as tion. The signal out of block 42 i s then multiplied by a gain factor Kh/Kj, in block 44. Both Kh and Ki, are Xj-D=(hB/tan p)- V p [ l n ( h e / V ~ T tan p)+ 11. (4) constants selected for a particular system configuration.
Thus, the output from block 44 i s a signal having a Thus, it is evident, assuming a constant hB, r and /3, 20 value that, as with flare heinht altitude h,, the dispersion dis- The basic controlling equation then becomes K h { i + v G [ ( K h / K h / v G REF](h+hB)). (9
Ki,[h + ( 1 / d ( h + ho)l =o
(') This signal is, then, the desired improved control law signal.
and inserting the value for 1 / ~ , this becomes In all aircraft flight guidance control systems, there 40 (9) are certain control law damping signals which are used Ki{k + v G [ ( K h / K d / VG REF](h 4- hB))=O.
to dampen short and long term oscillations. These are This control law is shown graphically in FIG. 3. well understood by those skilled in this art and, as such, Plots are made for three different groundspeeds, as will not be discussed here. Hence, the control law before, 110, 125 and 140 knots. It is apparent from this 45 damping terms are summed with the control signal in a graph that the flare height h,is no longer dependent on summer circuit 52 before being passed as the output groundspeed VG. pitch flare command signal FIG. 4 is a block diagram illustrating the preferred It should be understood that the pitch flare command embodiment of the apparatus for producing the aircraft signal may be used in the aircraft either as an input to flare path control signal in accordance with this newly 50 the flight director to indicate to the pilot a desired air- craft pitch angle or it may be coupled directly to the derived control law.
Here, an altitude block 10 produces an output signal aircraft's autopilot for automatic control of aircraft h representative of aircraft altitude. A suitable means flare-out.
for producing the altitude signal h is commonly avail- In summary, apparatus for, and the method of pro- able in commercial aircraft and, as such, will not be 55 ducing an improved aircraft flare path control signal has been described. This signal is adapted to control discussed here.
The altitude signal h is passed to a pair of summers 12, aircraft flare-out such that the landing flare distance 14. Also passed to an input of summer 12 is the output remains constant despite conditions of varying air- from block 16. Block 16 produces a fixed signal corre- speeds or groundspeeds. In addition, the flare height h, sponding to the altitude height for flare initiation h,. As 60 remains constant despite groundspeed variations.
discussed above, in a system according to the instant While a preferred embodiment of the invention has invention the flare initiation altitude h, is constant re- been described in detail, it should be apparent that many gardless of groundspeed variations. The summer 12 acts modifications and variations thereto are possible, all of to subtract the signal ha from the signal h such that its which fall within the true spirit and scope of the inven- output is negative if and only if the aircraft altitude has 65 tion.
dropped below the flare initiation altitude. Upon this We claim: occurrence, a logic circuit 18 activates a switch 20 1. Apparatus for producing an aircraft flare path which causes the pitch flare command signal t i , , which control signal comprising:
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2. A method for Producing an aircraft flare Path con- means for producing a signal h representative of air- trol signal comprising the steps of: craft altitude; (a) producing a signal h representative of aircraft means for producing a signal VG representative of altitude; aircraft groundspeed; (b) producing a signal VG representative of aircraft means for producing a signal h representative of air- groundspeed; (c) producing a signal h representative of aircraft craft altitude rate; altitude rate; computer means for producing a pitch control sur- (d) computing a pitch control surface command sig- face command signal S , , according to the relation- nal Se, according to the relationship: 10 ship: Gec=KA{h+ V G [ ( K ~ / K I ; ) / V G REF](h+hB)l
6ec=Ki{h + v ~ [ ( K h / K i ) / VG R E d ( h + h d )
where Kh, Kh, VG REF and hg are constants se- where Kh, Kh, V G REF and hg are constants se- lected for a given system configuration; and lected for a given system configuration; and (e) actuating the aircraft control surfaces to track said control means for actuating the aircraft control sur- command signal Se, whereby aircraft landing flare faces to track said command signal 8 , whereby distance is substantially unaffected by the aircraft’s aircraft landing flare distance is substantially unaf- relative groundspeed.
* * * * *
fected by the aircraft’s relative groundspeed.
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