NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS TECHNICAL NOTE 2807 MEASUREMENTS OF TEMPERATURE VARIATIONS IN THE ATMOSPHERE

Transcription

1 jiiwm 'k $ NATINAL ADVISRY CMMITTEE FR AERNAUTICS TECHNICAL NTE 287 MEASUREMENTS F TEMPERATURE VARIATINS IN THE ATMSPHERE NEAR THE TRPPAUSE WITH REFERENCE T AIRSPEED CALIBRATIN BY THE TEMPERATURE METHD By Lindsay J. Lina and Harry H. Ricker, Jr. Langley Aernautical Labratry Langley Field, Va. 6 Si ZQ. C VJ +3 Washingtn ctber 1952 Reprduced Frm Best Available Cpy "Mt hdö-r-tetf

2 !Q " NATINAL ADVISRY CMMITTEE FR AERNAUTICS TECHNICAL NTE 287 MEASUREMENTS F TEMPERATURE VARIATINS IN THE ATMSPHERE NEAR THE TRPPAUSE WITH REFERENCE T AIRSPEED CALIBRATIN BY THE TEMPERATURE METHD By Lindsay J. Lina and Harry H. Ricker, Jr. SUMMARY Detailed measurements f pressure and temperature were made in cnstant-speed level flight, in lw-speed climbing flight, and in a highspeed dive and pull-up with a jet fighter airplane fr the purpse f btaining infrmatin n the accuracy f the temperature methd f airspeed calibratin (NACA TN 246). The measurements were made near the trppause ver land in the vicinity f Langley Field, Va., n clear days with few r n cluds. The data were taken by means f a thermmeter, described in the present paper, which was designed by the Langley Instrument Research Divisin t meet the lw-lag, high-recvery requirements f the temperature methd. Measurements made in lw-speed climbs indicated that the variatins f temperature with pressure were very smth when the lapse rate was clse t adiabatic and several temperature-pressure surveys agreed clsely, althugh spaced several minutes apart with n effrt made t repeat the surveys in the same psitin in the air mass. n the ther hand, when the lapse rate was small (between isthermal and NACA standard fr air belw the trppause), variatins f temperature with pressure were irregular and changed erratically with time and distance. Evaluatin f the airspeed calibratin f the'jet fighter made when the cnditins were least unfavrable t the methd shwed an undesirably large scatter f the static-pressure errr f abut ±2.5 percent f impact pressure at a Mach number f abut.8. INTRDUCTIN A methd f airspeed calibratin in which temperature measurements are used, referred t in this paper as the "temperature methd,"-was described in reference 1. This methd ffers the advantages f flexibility f flight peratin (since all the necessary measurements are made by instruments carried in the airplane) and ease f data evaluatin. The accuracy f the temperature methd, as shwn in reference 1, imprves with

3 NACA TN 287 increased accuracy f the measured quantities, increased recvery factr f the thermmeter, increased speed, and decreased temperature lapse rate in the atmsphere atmsnhere. Althugh the temperature methd was described in reference 1, n experimental verificatin was available at the time f publicatinj furthermre, althugh the accuracy f the methd depends n the variatins f atmspheric temperature ver small vertical and hrizntal distances and small intervals f time, very little infrmatin cncerning these variatins was then available. Measurements f the variatins f temperature and pressure have therefre been made in rder t prvide sme infrmatin n the accuracy f this methd. The data, btained frm flights f a jet fighter airplane ver land in the vicinity f Langley Field, Va., frm February t September 195, included measurements made in lw-speed climbing flights and a dive at high subsnic speeds in the atmsphere near the trppause. An airspeed calibratin was made fr the dive and pullup (the evaluatins fr the dive and pull-up, btained n a day when the variatins f temperature in the atmsphere were believed t be the least unfavrable t the temperature methd, are the nly high-speed data presented) and cvered a range f Mach number frm.6 t.8, with the pullup reaching a maximum nrmal acceleratin f 2g. The thermmeter, which was used fr the tests and described in this paper, was specially cnstructed t meet the lw-lag, high-recvery requirements f the temperature methd. Althugh the thermmeter was designed by the Natinal Advisry Cmmittee fr Aernautics fr use in flight research, it may als prve useful fr detailed meterlgical studies f temperature variatins in the atmsphere. SYMBLS p' measured static pressure p free-stream static pressure q ' measured impact pressure q free-stream impact pressure Ap static-pressure errr M 1 indicated Mach number M Mach number

4 NACA TN 287 K temperature recvery factr T free-stream temperature, abslute units T m measured temperature, abslute units T' temperature defined by equatin (6), abslute units t 1 temperature defined by equatin (6) reduced t C INSTRUMENTATIN The instruments installed in the airplane fr these tests were: a static-pressure and impact-pressure recrder, a statscpe, and the thermmeter. The measurements were recrded n phtgraphic film and all the recrds were synchrnized by a.1-secnd timer. Static-pressure and impact-pressure recrder.- The instrument recrded static and impact pressures measured by means f a pitt-static head munted n a bm abut 1 fuselage maximum diameter ahead f the fuselage nse. The errrs in static and impact pressures caused by the lag in the cnnecting pressure lines were insignificant. The reading accuracy fr static pressure was abut ±.5 millibar and fr impact pressure, abut ±.17 millibar. Statscpe.- The recrding statscpe was used t determine accurately changes in static pressure ver the range f pressures in the surveys} static pressure measured by the altimeter at a starting pint in the surveys was used as a reference pressure. The reading accuracy f the statscpe was abut ±.12 millibar. Thermmeter.- The thermmeter was specially cnstructed t minimize cnductin and radiatin errrs, t have a high recvery factr, and t have as lw a time lag as practical. The thermmeter design incrprated a Wheatstne bridge, ne arm f which was an adiabatic-type resistance sensing element (fig. 1). In rder that errrs in temperature caused by variatins in the pwer supply t the Wheatstne bridge might be made negligible, a pwer supply was develped which cnsisted f a 1.5-vlt ignitin dry cell munted within a bx heated by a 27.5-vlt direct-current supply under thermstatic cntrl. The resultant pwer supply changed its vltage at a rate f.7 percent per hur with a bridge lad f apprximately 1 milliamperes. In rder t ascertain the accuracy f this pwer supply, the battery vltage was read n a high-accuracy ptentimeter immediately

5 NACA TR 287 befre and after each flight, which lasted abut 1 hur. Frm the average f the readings, the accuracy f the pwer supply was believed t be abut.1 percent r better. This variatin in pwer supply resulted in an errr f.2 C r less in temperature. The temperature was recrded n an NACA scillgraph. A check f the temperature measurements during ne f the flights was made by using tw thermmeters and scillgraphs f the same design. The scillgraphs indicated an ccasinal difference in temperature f n mre than.3 C and a standard deviatin f ±.8 C, based n apprximately 2 measurements. The reading accuracy f the scillgraph recrd was abut ±.5 C. The recvery factr f the sensing element was fund t be.99) hwever, the uncertainty f the measurements during calibratin (made in the Langley Instrument Research Divisin wind tunnel) was abut ±.1. Frm measurements made in the wind tunnel, the time lag f the thermmeter was cmputed t be abut.1 secnd fr the cnditins encuntered in these flight tests. The resulting errr in temperature due t time lag was less than.1 C during the dive, and n crrectin fr lag was applied t the data. FLIGHT PRCEDURES Surveys.- Variatins f temperature with atmspheric pressure were measured in climbs f a jet fighter airplane at a cnstant indicated airspeed f abut 2 miles per hur. Surveys f the variatin f air temperature with hrizntal distance parallel and perpendicular t predicted isthermal lines were als made at abut the same speed fr a cnstant nminal altitude f 25, feet. The temperature surveys in the climbs were made frm abut 23, t 31, feet. Surveys frm February 21 t March 1 were made in straightaway climbs, and later surveys were made in spiral climbs. A pilt's lg f the perating cnditins during the surveys is given in table I. In general, the climb surveys cnsisted f shrt recrds f static pressure, impact pressure, and temperature taken by the pilt at 5-ft intervals f altitude; but, fr a few f the surveys, cntinuus recrds were made during the entire climb. The surveys were generally made n clear days) hwever, n a few ccasins thin cirrus appeared in the vicinity f the tests. Dive.- The dive (made n April 13) immediately fllwed the first survey and was made tward the center f the helix described by the spiral climb f the first survey. A range f Mach number frm abut.6 t.8 was cvered in the dive which ended with a 2g pull-up. The dive started at abut 33, feet and ended at abut 27, feet altitude, with an apprximate hrizntal distance f k miles being cvered.

6 NACA TW 287 DATA EVALUATIN +1]W Lw-speed temperature surveys.- Variatins f atmspheric tempera- IfLZl^ free - strean \ stati c pressure were determined frm measurements f impact pressure, static pressure, and temperature by using the fllwing basic relatins: fe P = p' - Ap q c = q c + Ap M = i5 1c + P 1/3.5 1/2 (1) (2) (3) T = T, m 1 +.2KM2 W P re I?r,t +1 T err + r AP had P revlu^y been determined fr the airspeed installatin ver the speed range f the surveys (apprx. 2 mph indicated airspeed) by means f an NACA trailing-airspeed head. The values f atmspheric temperature cmputed frm the preceding equatins were pltted as a functin f hrizntal air distance (cmputed frm true airspeed and time) in figures 2 and 3. The values f atms- llttlä V ITfY*Tk T mve h rat Z e btained ty the Precedin^ e^ati - -re pltted in figure k t shw the variatins f temperature with pressure " the" ELS 8?** Pl^, ln I 1 Ure 5 ^ Part f the Sraphical -l"i n f the temperature methd f airspeed calibratin. Static-pressure errr in dive.- In the graphical slutin f reference L, values f static pressure and temperature are cmputed at a given instant in the dive frm the relatins given in this paper as equatins (3) and (k) by using the measured values f static pressure, bef ZtTZi' an V emperature and Several assumed values f Mach numfa^fl +>, pressure and temperature may then be pltted and Bltt f S T gra? n WMch the data f r the lw-speed surveys are SP t!? in tersectin f this faired line with the line representing the temperature survey btained at lw speeds determines the free-streak static pressure at that instant in the dive

7 NACA TN 287 The graphical slutin suggested in reference 1 may be simplified withut lss P f accuracy. Since, ver a small interval f f^-str^am static pressure and temperature, the cmputed pints fall very nearly n a straight line (within the accuracy f the graphical slutin) nly ne pint and the slpe f the line must be established. The slpe f lit fine may be determined t sufficient accuracy frm the measured values f static pressure, impact pressure, and temperature by using the equatins M' q c - + p'\ l/3 ' 5 1/2 P' - 1 (5) T«= " m (6) 1 +.2KM.2 and the fllwing expressin fr the slpe: dp' = 3-5p' 1 + -gkm.2 dt' KT' 1 +.2M.2 (7) Fr these tests, which cvered a Mach number range frm.6 t.8 and in which a thermmeter having a recvery factr f.99 was used, the slpe was clsely apprximated as dp' = 3-5V dt' T' (8) A line having this slpe was then drawn n the graph (fig. 5) thrugh the pint (p' T') and made t intersect the line representing the lw-speed pressure-temperature survey. If n appreciable change is assumed m the variatin f ambient temperature with ambient pressure in the interval f time between the survey and the dive, the value f the pressure at the intersectin is the free-stream static pressure. The static-pressure errr was then determined as the difference between measured static pressure and free-stream static pressure.

8 NACA TN 287 RESULTS AND DISCUSSIN The variatins f free-air temperature with hrizntal air distance are presented in figures 2 and 3 and the variatins f free-air temperature with atmspheric pressure are shwn in figure k. A sample f the graphical evaluatin used fr the temperature methd f airspeed calibratin f the dive is illustrated in figure 5. The results f the airspeed calibratin are presented in figure 6 as the variatin with indicated Mach number f the static-pressure errr expressed as pressure cefficient. Variatins f ambient temperature with hrizntal distance.- Variatins f free-air temperature with hrizntal air distance (figs. 2 and 3) were btained frm measurements made in nminal level flight at abut 25, feet. The measurements were crrected t a cnstant pressure level f millibars by use f the variatins f temperature with pressure btained frm surveys made in climbing flight n the same day. (See figs. k(a) and Mb).) The results indicated little effect f directin n the maximum variatin f temperature with hrizntal air distance' althugh the surveys were made bth parallel and perpendicular t the predicted directin f istherms. The level-flight surveys made n February 21 shwed very little change in temperature ver an air distance f abut 5 miles (fig. 2). The level-flight surveys f February 27, hwever, shwed larger changes f temperature with hrizntal distance (fig. 3). The mst rapid change f temperature was abut 3/k C ver an air distance f abut l/2 mile. Such a change in temperature during an airspeed calibratin by the temperature methd wuld intrduce undesirably large errrs fr the speed range f these tests inasmuch as an imprtant aspect f the methd is that the temperature at a given pressure level shuld be nearly the same as that encuntered at the same pressure level in the calibratin maneuver. Variatins f ambient temperature with atmspheric pressure.- The surveys made in climbing flight at lw speed are cmpared in figure h with the NACA standard atmsphere pressure-temperature relatinship and with a line (dry adiabat) representing an adiabatic variatin f temperature with pressure. Radisnde data reprted frm Nrflk, Va., althugh btained at a time different frm that f the surveys, are als shwn fr cmparisn. An examinatin f the temperature surveys shws that, when the lapse rate was small r nearly isthermal ver the range f atmspheric pressure surveyed (perhaps a lwered trppause), the variatin f temperature with atmspheric pressure was very irregular and the temperature at a given atmspheric pressure level did nt remain cnstant but changed erratically with time (fr example, the surveys made n February 27, fig. 4(b)). n the ther hand, smth and regular variatins f temperature with pressure

9 8 NACA TN 287 seem t be assciated with a temperature lapse rate nearly equal t the dry-adiabatic lapse rate (fr example, the surveys made n March 1, fig. Mb)). The surveys made under these cnditins were in very clse agreement, althugh spaced several minutes apart with n effrt made t repeat the surveys in the same psitin in the air mass. The results f bth the climb surveys and the level-flight surveys were cnsistent, since bth indicated very little change f temperature with time (r hrizntal distance) at a cnstant pressure level fr the flight made n a day (February 21, figs. 2 and Ma)) when the adiabatic temperature lapse rate prevailed. Under mre nearly isthermal cnditins (February 27, figs. 3 and Mb)) bth the climb surveys and the level-flight surveys indicated larger change's f temperature with time (r hrizntal distance). Evaluatin f airspeed calibratin by temperature methd.- In rder fr the temperature methd t be accurate, the temperature must remain cnstant at a given pressure level and the rate f change f temperature with pressure must be smaller than the slpe representing the adiabatic relatinship. The equatins fr accuracy given in reference 1 indicate that nne f the present climb surveys fully meets the requirements fr an accurate determinatin f airspeed calibratin by the temperature methd cmparable t accuracies attainable by ther methds in the speed range f these tests. The survey f April 13 (fig. Me)), hwever, appeared t be the least unfavrable fr evaluating the temperature methd f airspeed calibratin, since the temperature gradient was small and there were tw cntinuus surveys (ne made befre and ne made after the high-speed maneuver) which shwed changes f temperature that appeared t be small in cmparisn with the surveys made n ther days. Since a small change f temperature ccurred between the time f the survey made befre the dive and the survey made after the dive, the average f the tw surveys was pltted t a larger scale in figure 5 t represent the variatin f temperature with pressure fr the atmsphere thrugh which the dive was made. The graphical evaluatin f static-pressure errr fr the latter part f the dive (that part cnsidered least unfavrable t the methd) and the puli-up made n April 13 is als shwn in figure 5. The varius measured and cmputed values necessary fr the evaluatin f static-pressure errr at ne instant in the dive are als included. The pints n the graph are fr graphical evaluatins made at 1-secnd intervals in the dive and pull-up. The results f the evaluatin f static-pressure errr expressed as pressure cefficient - are shwn in figure 6 alng with the ^c static-pressure errr btained by the NACA trailing-airspeed head at

10 2Q NACA TN 287 a lw speed. Frm previus tests f fuselage-nse-bm installatins f pitt-static heads, the static-pressure errr wuld be expected t remain nearly cnstant up t a Mach number f.8. The limits f uncertainty f the temperature methd were calculated fr an errr in freestream temperature f ±l/k C, with a cnstant static-pressure errr " (equal t 4 percent f impact pressure) being assumed up t a Mach number f.9. The limits f uncertainty fr the case f a free-streamtemperature variatin with atmspheric pressure equal t the standard temperature gradient and fr the isthermal case were calculated by using equatin (7) f reference 1 and equatin (1) f reference 2. The values f static-pressure errr pltted in figure 6 as a functin f indicated Mach number shw appreciable scatter. The maximum.' scatter, abut ±2.5 percent f impact pressure, is undesirably large in cmparisn with ther methds f airspeed calibratin (fr example, ± i'? v percent fr the radar methd at M = - 8 > ref - 2). An examinatin f the pints n the basis f the temperature gradients at the intersectins used in the graphical slutin (fig. 5) indicated as much scatter ir crssings near a small temperature gradient as fr crssings at gradients nearer the adiabatic slpe. The average f the tw surveys therefre prbably des nt truly represent the cnditins f the atmsphere thrugh which the high-speed maneuver was perfrmed. Since the surveys were made n different days in several seasns and n temperature-pressure variatins were fund favrable t an accurate determinatin f an airspeed calibratin by the temperature methd (fr Mach numbers frm.6 t.8), the likelihd f encuntering ; a favrable variatin f temperature with pressure just belw the trppause at a particular time when a calibratin may be desired des nt appear prmising, and, even under apparently favrable cnditins, a very careful selectin 1 ilight data is necessary. A mre thrugh investigatin, hwever, f temperature variatins in the atmsphere at lwer altitudes and in the stratsphere wuld be desirable fr a cmplete evaluatin f the temperature methd at subsnic speeds. The accuracy f the methd shuld imprve cnsiderably at higher speeds. (See fig. 3 in ref. 1.) CNCLUDING REMARKS Measurements f pressure and temperature were made near the trppause ver land in the vicinity f Langley Field, Va., n clear days with few r n cluds fr the purpse f btaining infrmatin n the accuracy f the temperature methd f airspeed calibratin. Measurements made in lw-speed climbs indicated that the variatins f temperature with pressure were very smth when the lapse rate was clse t adiabatic and several temperature-pressure surveys agreed clsely

11 NACA TN 287 althugh spaced several minutes apart vith n effrt made t repeatthe surveyf in the same psitin in the air mass. n the ther hand, when thellpse rate was small (between isthermal and NACA standard fr air helw the trppause), variatins f temperature with pressure were irregular and changed erratically with time and distance, ^aluatin f the data btained when the cnditins were least unfavrable t the methd resulted in an undesirably large scatter f the static P^ssure f abut ±2.5 percent f impact pressure at a Mach number f abut.ö. Since the surveys were made n different days in several seasns and n cnditins favrable t an accurate determinatin f an airspeed calibratin by the temperature methd (fr Mach numbers frm.6_t.ö) were fund, the likelihd f encuntering favrable cnditins in the atmsphere just belw the trppause at a particular time when a calibratin may be desired des nt appear prmising. A mre thrugh investigatin, hwever, f temperature variatins in the atmsphere at lwer KtSudes and in the stratsphere wuld be desirable fr a cmplete evaluatin f the temperature methd at subsnic speeds. Langley Aernautical Labratry, Natinal Advisry Cmmittee fr Aernautics, Langley Field, Va., July 1, REFERENCES 1 Zalvcik, Jhn A.: A Methd f Calibrating Airspeed Installatins n Airplanes at Transnic and Supersnic Speeds by Use f Temperature Measurements. NACA TN 246, Zalvcik, Jhn A.: A Radar Methd f Calibrating Airspeed Installatins n Airplanes in Maneuvers at High Altitudes and at Transnic and Supersnic Speeds. NACA Rep. 985, 195. (Supersedes NACA TN 1979.)

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15 11+ NACA TW 287 Apprximate air distance, miles > u a> a. E ) (a) Parallel t predicted istherms, 23 heading. I Apprximate air distance, miles li T ± li 5 7 Time, sec (b) Perpendicular t predicted istherms, llj- heading. Figure 2.- Variatin f temperature with hrizntal distance at a cnstant pressure level. Surveys made in straight and level flight n February 21.

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17 16 NACA TN 287 CVJ M C <D CM I I -3 Ü a) i-h J U P-H ) ^ P.P s-a is C <H S3 tu fl h p B5 Pi <u a TJ tu cd -p cö <U 1 t> <u ) pv C CM "i 1_ rh X r-l v 7^ T> e\ qi 'a.mss8jd fjaiidem^v J» }j 'apn^t^x«s-mssaaj CNi I Sii p cd *1 cd > cu b

18 3Q NACA TN f-> E-i E-i in u & a r- \ -zr U\ H H rh J t-i 1-1 rh ft p +> P C W H4 H i en tn t H w u r-f c\ f\ CVJ f\ -3" ^J -=T -J H rh r-i P VA r- r- r-l CM en, a 3 3 u,!h C S d s cd c~- C\J u crt n >J '. --t Pi <u Ö <U il PR fr qra 'ajnsssjd Tjaqdstu^y tf 1J 'apn^t^t* a-rssaj,}

19 18 NACA TN 287 vf»? CJ IA V H C Ti,3 ) -p pi a ^H ö -? C (3 & g -P 1 ri p tj Ö C ) fn cd ' 1 1 ^D u Ä 1 fn u <u a5 a ä CM 8 CM -a >»\ c\ qui 'ajnssaad a-piandsnqy v c <*\ t*\ 8 M 1» 1 X H \ CM _L_ I I CM CM CM CM q.j 'apn^tvp? ejnsssjtj

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21 2 NACA TN 287 Survey 1 Survey 2 73 t 736 EST 7l»2 t 7k9 EST 3h xl 3 2I4 r? / Radisnde / 22 EST \ \3 * \ pt \ 32 - _ 31 «* E ) CD 3 ' T <U > a S 2 rt fc 9 93 b JS a«3 28 I ^ NACA Standard \ \ \ \ 1\ Dry adiabat ' Survey 1 ' Survey 2 ' J Njv. \ \ \ i I li8 -hk -1, Free-air temperature, C (e) Cntinuus surveys made April 13. Figure k.- Cntinued.'

22 NACA TN u <D rq r) T3 (1) <L> -P rd P) 2 ) H rn Ö rö ö cd N J -4- -p <u 2 & hi) bi 3 < &4 CH qtn *8nss8jd DT aaqd snny L C 1J 'spniine «nsesjj

23 22 NACA TU X II 3 r- 29 Ö Pints In the dive and pull-up at 1-sec intervals SS in en Average f tw surveys 31( hi -1,6-1,5-1,1, -1(3 Temperature, C Figure 5.- Determinatin f free-stream pressure in the dive by the temperature methd by using the average f the tw surveys made in climbing flight n April 13.

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