Report of the Second Piloted Aircraft Flight Control System - Acgsc.org

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IMPROVEMENT OF POWER SURFACE CONTROL SYSTEMS BY STRUCTURAL DEFLECTION COMPENSATION JAMES J. RAHN EVERETT W. KANGAS Boeing Aircraft Corporation Seattle, Washington This paper is based on original work done by Mr. Howard Carson of the Boeing Airplane Company. The authors gratefully aoknowledg the cooperation and assistance of their Engineering colleagues at Boeing Airplane Company in preparation of this paper.
IMPROVEMENT OF POWER SURFACE CONTROL SYSTEMS BY STRUCTURAL DEFLECTION COMPENSATION Power controls for operation of aircraft control surfaces have become a necessity as a result of increased airplane sise, speed, range and control requirements. The direct feedback linkage type of powered surface controls presents the problem of stability versus respome. Thie is especially true when a large surface inertia ie coupled vith a relatively law structural spring rate. Although these systems nrny be eatisfactory for manual operation, they msy prove marginal or u~atisfactory when used with automatic flight control equipment. A moans for improving the performance of a mechanical-Wdraulic control syrtm hoving high surface inertia aad low structural spring rate8 has been dweloped and has proven quite ~uccessful on an airplane installation. In this discuseion we will first cover a basic type powered surface control system; Them it will be shm how a rtructural deflection feedback linkage can be added to the cystom to imprwe performance. A BASIC TTPE PCMER OPERATED CONTROL mTEn A powered surface control system operating a high inertia surface which had a low reaction spring rate me~y be limited in performance. To retain stability of the system the gain must be kept low, resulting in slow response which my make the system Inadequate for 8atisfactoi.g airplane control. This problem was encountered in the dwelopment of a rudder control system which is described belaw and shm In figure 1. operation of the pilot~s pedals rotatee the torque tube Xi by means of cables. A differential linkage ie l0~8ted at the upper en3 of the torque tube. Since the surface ie initially stationary, the movement of the torque tube causes movement of the error link X, which is connected to the Wraulic control valve. Displacement of the control valve admits pressure to one side of the piston ecld opens the other side to return. The resulting pressure differential supplies the force to mom the ndder against inertia, friction, damping and air load. The follou-up or feedbncK link connected to the rudder and to the differential then moves the 3 ifferential to reduce the error to a minimum and closes the tgdraulic control valve. When the CIVW is a dniru, tb. valve ie in neutral and the fluid trapped on both side8 of the pieton holds the rudder in one position against variable loads. This eystem as first installed in the airplane, fignre 2, prwed to be unstable. Any disturbance to the control surface or to the pilot input resulted in a continuous oscillation of the eystem. To overcome this instability the system was slowed d m by reducing control valve gain. The net result wae a deterioration in performance and excessive phase lag. The combined lag of the
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CONTENTS 1, Centering Charauteristi
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CENTERING CHARACTERISTICS OF POWER
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Since pilqt effort and s*face force
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The centering characteristics excep
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-mtla= etlq 30 pwdo o q m ~APA opl
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HELICOPTER POWERED CONTROL SYSTEM P
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Returning to the discussion of the
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loaded by-pass valve closes, and fr
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FUGET RESEARCH ON FORCE WHEEL CONTR
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precisely. The fir at demonstration
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to hare thq coakpit controle comman
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conrtsnt speed). While this ryrtem
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I I SURFACE I AIRCRAFT DYNAMICS LOA
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AUTOMATIC PUT DYNAMICS a LOAD DISTU
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FORCE ME- SERVO. \ - = AMPLIFIER =
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The configuration described above r
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AN ANALYSIS OF FULLY-POWERED AIRCRA
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"W@J@tI pendm ao poqtmeard euofenfo
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Ooeo red em;Co* ey tg areqm - a d m
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Variation of Valve Flcnr with Press
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p - instantaneons density (mare per
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where %, , %+ , fi , and A r' are p
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The error equation (l), with XI * i
Page 61 and 62: C C U P m ZERO - (Bulk Modulus infi
Page 63 and 64: Canparing equation (32) vith eqatio
Page 66 and 67: EFFECT OF ADDRIG A SPEUNC IllbD AT
Page 70: The outtmt 4 is then -tion (a) may
Page 74 and 75: 71 It is of interest to anmine the
Page 77 and 78: It w ill now be shrnm that the quad
Page 79: tp = 4 1' ( 4 include. aU flaxibill
Page 83 and 84: Frequancy Response of Another prore
Page 85 and 86: or, ii the pinton s p w A, in f ~ t
Page 88 and 89: $ - BZ~W~ pfY88WC)* - presstam on e
Page 90 and 91: INTRODUCTION PARAMETERS FOR THE DES
Page 92 and 93: to the piston. When the spool membe
Page 94 and 95: Figure 2 shows an oscillographlc re
Page 96: lication of equations. - The method
Page 99 and 100: The solution to equation (11) , is
Page 101 and 102: I RATIO OF PEAK TRANSIENT CYLINDER
Page 103 and 104: Equations (21) and (22) are written
Page 105 and 106: variation of this rise time with T
Page 107 and 108: CHART ILLUSTRATING EFFECT OF INERTI
Page 109: pa lo=$ $8 uoy$eyQd moy pamwam $ndq
Page 113 and 114: FIG. 2 INSTALLATION - POWER OPERATE
Page 115 and 116: AMPLITUDE RATIO- DB I 0 I 0 I cn 0
Page 117 and 118: The overall reaotien rpring rate ir
Page 119 and 120: FIG.5 - SCHEMATIC -- BASIC TYPE POW
Page 122 and 123: With theae substitutions into equat
Page 124: Although only one type of power oon
Page 127 and 128: 0 AMPLITUDE RATIO- D8 I I I I rU rU
Page 129: In the range ai airplane natural fr
Page 132 and 133: Figure 1. anticipation of the targe
Page 134 and 135: The constant k helped to improve th
Page 137 and 138: to determine if there was behaviora
Page 139 and 140: SYNTHESIS OF FLIGHT CONTROL SYSTEMS
Page 145 and 146: The hydraulic system itself is a hi
Page 147: P :: 7 OT- a- ' 06- 09- . I
Page 150 and 151: Zeros introduced by resonance of th
Page 152 and 153: explicit set of specifications-or a
Page 155: her@ is to lnake the push-rod as st
Page 160:
particular problem. We then choose
Page 164 and 165:
changing flight corditions. Idea-,
Page 166 and 167:
A,. Area of bydraullc jack giston.
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