1、.*mNATIONAL ADVISORYCOMMITTEEFOR AERONAUTICSTECHNICAL NOTE 2416THEORETICAL STUDY OF SOME METHODS FOR INCREASING THESMOOTHNESS OF FLIGHT THROUGH ROUGH AIRBy William H. Phillipsand Christopher C. Kraft,Jr.Langley Aeronautical LaboratoryLangley Field,Va.WashingtonJuly1951!.Provided by IHSNot for Resale
2、No reproduction or networking permitted without license from IHS-,-,-NACATN 2416TABLE OF CONTENTSSUMMARY. a71 a71 . . . . . * a71 . a71 a71 a71 a71 a71 a71 a71 a71 a71INTRODUCTION . . . . . . . . . . . . a71 a71 . . a71REQUIREMENTS FOR PROS?ISIONOF SMOOTH FLIGHT . .Factors Influencing Passenger Comf
3、ort . . . .Methods for Reducing Airplane Motion in RoughSYMBOLS. . . . . . . . . . . . . . . . . . . .THEORETICAL ANALYSIS . . . . . . . . . . . . .MethodofAnalysis . . . . . . . . . . . . .Equations of Motion. . . . . . . . . . .Nondimensionalizingof equations . . . . .Form of gust disturbance . .
4、. . . . . . .Approximation to downwash at tail . . . . .Final,form of equations : . . . . . . . . . . .a71 a15a71 a15Air. .*a71 a15.0. .0. .*.a71a15a15a15a15a15a71a15a15_.“-TECHLIBRARYKAFB,Nffl .;.1111111111!11“-”0DLS7QL.a71a15a15a15a15a15a71a71a15a15a15.a71a71a71a71a71a15a15a15a71a15a15a15Calculati
5、on of Response to Sinusoidal Gust DisturbancesTransferfunctions . . . . . . . . . . . . . . . . .Relations between gust frequency and wave length . .Convention for phase angles . . . . . . . . . . . . .Discussion of Limitations of Theory . . . . . . . . . .CALCULATED RESPONSE OF BASIC AIRPLANE TO GU
6、STS . . a71 . .CONTROL MOTIONS REQUIRED FOR ELIMINATION OF ACCELERATIONSDUETOGUSTS . . . . . . . a71 . . . . a71 . . . a71 .Control by Elevator Alone . . . . . . . . . . . .Control byFlapsAlone . . . . . . . . . . . . .Control by Use of Flaps and Elevator . . . . . .CHARACTERISTICSREQUIRED OF FLAPS
7、USED ASACCELERATION ALLEVIATORS . . . . . . a71 a71 .EFFECTIVENESS OF POSSIBLE FLAP CONTROL SYSTEMSACCELERATION ALLEVIATORS . . . . . . . . .Vane-ControlledAcceleration Alleviator . .,ASa71 *a71 .a71a71a15a15a15a71a15a15.a71a15a15a15a15a15.a71a15a15a71a15a15a15a71a71a71a71a15a15a15a15a71a15a15a15a15
8、a15a15a15a15a15.a71a15a71a15a15a15a71a71a71a71a15a71a15a15a15a15a15a15a15a15a15a71a71a71Method of analysis . . . . . . . . . . . . . .Effectiveness of vane-controlled acceleration alleviatorswith various flap characteristics . . . . . . . . . . .Effectiveness of vane-controlledacceleration alleviato
9、rsusing optimum flap characteristics . . . . . . . . . .Effectofairspeed . . . . . . . . . . . . . . . . . . .a71a15a15a15a71a71a15a71a15a15a71a15a15a15a15a15a71a15a15a15a15a15a15a15a71a15a15a15a15a15.a71a15a71a71a71a15a15a15a15a71a15a15a15a71a71a71a15a15a71a71a15a15a15a15a15a71a15a71a71Page1236;101
10、112131516161819192123 .2426293033;:363839iProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-NACA TN 2416Accelerometer-ControlledAcceleration Alleviator . . , . . . .Methodofanalysis . . . . . . . . . . . . . . . . . . . . .Effectiveness of acceleromete
11、r-controlledacceleration alleviators . . . . . . . . . . . . . . . . .Effectoftimelag . . . . . . . . . . . . . . . . . . . . .Effectofairspeed . . . . . . . . . . . . . . . . . . . .STATIC AND DYNAMIC STABILITY AND CONTROL CHARACTERISTICS OFAIRPLANES WITH ACCELERATION ALLEVIATORS . . . . . . . . .
12、. .Provision of Controllability . . . . . . . . . . . . . . . . .Static Longitudinal Stability . . . . . . . . . . . . . . . . .Static longitudinal control characteristicswithvane control . . . . . . . . . . . . . . . . . . . . . . .Static longitudinal control characteristicswithaccelerometer contro
13、l . . . . . . . . . . . . . . . . . . .Examples of Static Longitudinal Control Characteristics . . . .Vane-controlledacceleration alleviators . . . . . . . . . .Accelerometer-controlledacceleration alleviators . . . . . .Effect of maintaining a constant value of the gearingparameter m . . . . . . .
14、. . . . . . . . . . . . . . . .Examples of Dynamic Longitudinal Stability Characteristics . .Basic airplane . . . . . . . . . . . . . . . . . . . . . . .Vane-controlledacceleration alleviators . . . . . . . . . .Accelerometer-controlledacceleration alleviators . . . . . .Effect of time lag in accele
15、rometer-controlledacceleration alleviators . . . . . . . . . . . . . . . . .Response to Control Deflection . . . . . . . . . . . . . . . .Response to control deflection with vane control . . . . , .Response to control deflection with accelerometer control . .Examples of Response to Control Deflectio
16、n . . . . . . . . . .Basic airplane . . . . . . . . . . . . . . . . . . . . . .Vane-controlledacceleration alleviator . . . . . . . . . . .Accelerometer-controlledacceleration alleviator . . . . . .Incorporation of g restrictor . . . . ., . . . . . . . .Stability of the Airplane Equipped with Accele
17、rationAlleviator under Control of a Pilot - . . . . . . . . . . . .Basic airplane . . . . . . . . . . . . . . . . . . . . . .Vane-controlledacceleration alleviators . . . . . . . . .CONCLUI)INGREMARKS . . . . ; . . . . . . . . . . . . . . . .REFERENCES . . . . , . . . . . . . . . . . . . . . . . . .
18、 . . .TABLEI . . . . . . . . . . . . . . . . . . . . . . . . . . . .TABLEII . . . . . . . . . . . . . . . . . . . . . . . . . . . .T4BLEIII. . . ., . . . . . . . . . . . . . . . . . . . . . . .FGS . , . . . , . .*. , , , , , , , , , , . . . .Page3939g42434344444648.50.5051%545555.575759606060%636468
19、71727374if this arrangement is slightly modified to provideincreased static stability, both the control characteristics and dynamicstability characteristics appear desirable. Interconnection of the flap-operating mechanism and the pilots control results in a more rapid“response to control deflection
20、 than is obtained on conventional airplanes.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-2 NACA TN 2416AIn this theoretical study no attempt has been made to considerengineering problems involved in the design of an actual mechanism to .-reduce th
21、e accelerations of an airplane in rough air.INTRODUCTIONThe reduction of accelerations caused by rough air would be ofobvious value for improving passenger comfort in commercialairlineoperation. An airplane capable of smooth flight through rough airwould also be a valuable tool for studying the gust
22、 structure of theatmosphere.Previous studies of devices for reducing the accelerationscausedby gusts (usuallytermed gust alleviators) have been made with theobject of reducing the structural loads due to the most abrupt andsevere gusts. Inasmuch as the provision of such devices complicatesthe normal
23、 control of the airplane, some proposed devices have beendesigned to come into effect only when certain limits of gust severitywere exceeded. Such devices would be of little value for improvingpassenger comfort. In other studies of gust alleviators the problemsof stability and control have not been
24、seriously considered.The present paper contains a theoretical smalysis of various meansfor increasing the smoothness of flight through rough air. Emphasishas been placed on reduction of accelerationsrather than on reductionof structural stresses. An analysis is presented of systems in whichthe wing
25、flaps and elevator are operated through an automatic controlsystem in response to the indications of an angle-of-attackvane or anaccelerometer. The aerodynamic characteristicsof such controls requiredto provide smooth flight through rough air are derived. The responseto gusts and the stability and c
26、ontrol characteristicsof airplanesequipped with these systems are investigated. The effect of intercon-necting the flap-operatingmechanisms with the pilots control as ameans of overcoming the adverse effects of these systems on the controlcharacteristicsof the airplane is also studied.#.Because of t
27、he emphasis placed on reduction of accelerationsrather than structuralloads, the devices considered in this paper havebeen called IIaccelerationalleviators.fThis paper is confined to thedevelopment of a theoretical basis for the design of accelerationallevi-ators. Engineering problems involved in th
28、e design of an actualmechanism are not considered.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a71NACA TN 2L16 3.-.REQUIREMENTS FOR PROVISIONOF SMOOTH lZGIGHTFactors Influenctig Passenger Comfort and SafetyThe design of a device for providing comf
29、ortable flight for thepassengers of an airplane in rough air requires a knowledge of thefactors which contribute to passenger comfort. Unfortunately, verylittle quantitative information is available as to the types of motionor other stimuli that are most often responsible for airsickness. Areview of
30、 the available information on this subject is given by McFarlandin reference 10 The information indicated that slow oscillations oflarge amplitude are more likely to cause sickness than faster oscil-lations of small amplitude. This statement is based mainly on a seriesof tests, reported in reference
31、 2, in which a large number of men weresubjected to vertical oscillations in a device similar to an elevator.With this device, the wave form, the amplitude, and the period of theoscillation could be varied. Some of the results obtained in thesetests are shown in figure 1. This figure shows the perce
32、ntage of themen tested who became sick within a period of 20 minutes when they weresubjected to oscillations of each of the types shown. The results ofthese tests showed that very little sickness was produced by the.ilorest-periodoscillation tested, which had a period of I-.87seconds.The incidence o
33、f sickness reached a maximum at periods of 3 to 4 secondsand decreased slightly at the longest period tested, 4.62 seconds. Inthe data shown in figure 1, the magnitude of the velocity at the mid-point of each cycle was kept constant as the period increased, so thatthe average acceleration over the c
34、ycle decreased with increasing period.If the accelerationwere kept constant as the period increased, still.further adverse effect of the longer-period oscillationswould beexpected.The results of the tests shown in figure 1, while they do notcover a very wide range of conditions, appear to be in acco
35、rd withcommon experience on the subject. Thus, a periodic motion of a smallboat in a rough sea is known to produce sickness in a relatively largepercentage of passengers, whereas the motion of a trolley car on arough track, which involves abrupt jolts and jerks containing componentsof oscillation of
36、 high frequency and fairly large amplitude, causessickness in very few passengers. Reduction of the more prolonged changesin vertical acceleration would therefore appear to be beneficial forminimizing airsickness.Other stimuli may be important in the production of motion sick-ness. These stimuli inc
37、lude lateral or rotational accelerations,motion of objects in the field of vision, and many psychological factorssuch as noise, vibration, temperature, ventilation, and so forth. Therelative importance of lateral and normal accelerations in producingProvided by IHSNot for ResaleNo reproduction or ne
38、tworking permitted without license from IHS-,-,-4 NACA TN 2416motion sickness has apparently not been established. In view of thesefactors it may be expected that even comPlete elination of norlaccelerationswould not necessarily eliminate airsickness. The avail-able evidence indicates, however, that
39、 periodic changes in normalacceleration are a major cause of motion sickness. In flight throughrough air, furthermore, the changes in normal acceleration are rela-tively large, whereas lateral accelerations,rotational accelerations,and changes in orientation are relatively small. Reduction of thecha
40、nges in normal accelerationwould therefore appear to be the mostpromising method of improving passenger comfort.Reduction of changes in vertical accelerationwill also reduce theprobability of passengers being thrown from their seats by unexpectedsevere down gusts. A continuously operating device wou
41、ld not be requiredto prevent this occurrence,but if a continuously operating device isinstalledfor the improvement of passenger comfort, it will provide thisresult as an additional benefit. Reduction of the more prolonged changesin vertical accelerationwould be of greater importance in this connec-t
42、ion also, because the distance a passenger is thrown from his seatwouldincrease with the length of time the accelerationwas applied.Methods for Reducing Airplane Motion in Rough AirIdeally, the airplane should fly in a straight line with no rota-tion about any axis. The conventional autotitic pilot
43、attempts toprevent rotations in roll, pitch, and yaw. Present-day autopilotsgenerally do not have sufficientlyrapid response to suppress completelyrotations due to gusts, but, by increasing the speed of response of theservomechanisins,this condition could in principle, at least, be closelyapproached
44、. Elimination of rotations, however, does not preventvertical motions of the airplane. In fact, maintaining the airplane ata constant angle of pitch increases the response somewhat to low-frequency gusts because a stable airplane tends to relieve changes inaccelerationby pitching into the gusts. In
45、order to avoid the verticalaccelerationsdue to rough air, the additional lift caused by a changein angle of attack from the steady flight conditionmust be eliminated.The following methods(a) Pitching theattack during passage(b) Variation ofattack during passage(c) Operation ofments on the wingmight
46、be consideredto accomplish this result:whole airplane to maintain a constant angle ofthrough the gustswing incidence to maintain a constant angle ofthrough the gustsflaps or other controls to offset the lift incre-Provided by IHSNot for ResaleNo reproduction or networking permitted without license f
47、rom IHS-,-,-NACA TN 2416,.5A. *Method (a) has the advantage that it may be accomplished by the useof the elevators without provision of additional controls on the air-craft. Thetheoretical possibilities of this method will be discussedin a subsequent section of the.paper.In connection with methods (
48、b) and (c), a problem of longitudinalcontrol arises. Normally, control of the airplane by the elevators isaccomplished by pitching the whole airplane to change the angle ofattack. If the lift increment due to change of angle of attack iseliminated, the elevators will be ineffective for producing a c
49、hange inthe direction of the flight path. This problem has not been givendetailed consideration in most previous investigations of gust-alleviatingdevices.Most schemes considered in the past have employed a partialutilization of method (b). If the primaryobject is to reduce wing-root stresses instead of accelerations, a device located near the wingtip may accomp
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