/1-c/h i ' f 3 / NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS WARTIME REPORT ORIGINALLY ISSUED rel)ruary 19lf6 as Eestrlcted Bulletin L5K29a STATIC -PRESSDEE ERROR OF M AIESPEED INSTAUATIOK OK AN AIRPLAHE IN HICffl-SPEED DIVES AHD PDLL-OTJTS By John A, ZaloTClk and Clotalre Wood Langley Memorial Aeronautical Laboratory Langley Field, Ta. NACAP^ WASHINGTON NAC A WARTIME REPORTS are reprints of papers originally issued to provide rapid distribution of advance research results to an authorized group requiring them for the war effort. They were pre- viously held under a security status but are now unclassified. Some of these reports were not tech- nically edited. All have been reproduced without change in order to expedite general distribution. L-43 DOCUMENTS DEPARTMENT Digitized by tlie Internet Arcliive in 2011 witli funding from University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation http://www.archive.org/details/staticpressureerOOIang KACA R3 No . L5K29a RESTRICTED NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS RESTRICTED BITLLETIN STATIC -PRESSURE ERROR OP AK AIRSPEED INSTALLATION ON AN AIRPLANE IN HIGH-SPEED DIVES AND PULL-OUTS By John A. Zalovcik and Clotaire Vvood SUMMARY Tests were made in high-speed dives and pull-outs to determine, by combined radar-optical tracking equipment, the static-pressure error of an airspeed-head installation on a P-5IB airplane. The installation included a pitot- static head miounted on a boom 95 percent chord ahead of the leading edge of the vving near the tip. The tests were made in dives at flight Mach numbers up to 0.75 ^^^ in- cluded pull-outs up to Lj.g normal acceleration. The results indicated that the static-pressure error did not vary with Mach number by more than about 1 percent q£ the impact pressure over the range of conditions inves- tigated. INTRODUCTION Plight data on the variation with Mach number of the static-pressure error of pi tot-static-tube installations have generally been limited by the available testing tech- niques to speeds attainable in level flight. Inasmuch as the maximum speeds in level flight for most present-day airplanes do not exceed a Mach number of 0.6, the varia- reported in reference 1. por a recent high-speed investigation of a P-5IB air- plane, an airspeed calibration viras required in dives and pull-outs up to a Mach number of 0.75* A inethod was there- fore devised for obtaining such a calibration by use of radar-optical tracking equipment to establish the reference altitudes. The calibration obtained by this method was RESTRICTED 2 NAG A RB NOc L5K29a supplemented by data obtained up to high speed in level flight by a method (described in reference 2), V'/hich makes use of a landmark or another airplane to provide the reference altitude. The results of these calibrations are believed to be of general interest and are therefore reoorted herein. Syi^BOLS p' static pressure Indicated by airspeed installation p free-stream static pressure or atmospheric pressure at altitude h Pg NACA standard atmospheric pressure at altitude h (from reference J) H free-stream, total pressure G(, free- stream impact pressure (H - p) M free- stream Mach nijmber Cl alvolane lift coefficient APPARATUS AND METHOD Airplane equipment . - The airspeed-head installation of the P-5IB airplane is shown in figure 1. A Kollsnan type 65IB airspeed head (fig. 2) was used and was mounted 95 percent chord ahead of the leading edge of the wing. The boom supporting the airspeed head was located 65 percent sem.ispan from the plane of syinmetry, at v/Mch station the vving section had a maximLim thickness equal to 12 percent of the chord. Pressure leads from the static- and total-pressure elements of the airspeed head were connected to an NACA airspeed recorder to m.easure im.pact pressure; the static-pressure element 'vvas also connected to a recording altimeter. The airplane was equipped with an NACA single com- ponent recording accelerome ter , an NACA chronometric timer to synchronize all records, and a radio to cormnunicate the timing signals to the ground equipment. NACA R3 IIo. L5K29a Gr oun d e qui pm e nt . - The trackliig equipiTient used to establish the height of the airplane consisted of a com- bination of a radar vinlt for the determination of range and a phototheodollte for the detemiination of the ele- vation angle. Test procedure .- The first step In the test procedure consisted In obtaining a survey in a climb at an Indicated airspeed of 175 miles per hour over a range of altitude from about 15,000 to 2b, 000 feet in order to establish the relation of atmospheric pressure to actual altitude. In the survey, at intervals in altitude of approximately 1000 feet, simultaneous records were taken of static pressure, impact pressure, and normal acceleration in the airplane and of elevation angle and range of the airplane with the tracking unit. The airplane was then dived to a flight Mach number of 0.75 ^^d pulled out with 2g normal acceleration within the range of altitude sur- veyed; continuous and simultaneous records of static pressure, impact pressure, normal acceleration, range, and elevation angle were iiJ8.de during these m.aneuvers . A second dive Vi^as m.ad.e over the same range of altitude and Mach number but with a pull-out at a normal acceleration of [|.g. After the second dive and pull-out the survey in climb was repeated and was followed by a survey in a descent at the same speed and over the same range of altitude . The results of the surveys of atmospheric pressure are shown in figure 3 i^ which the difference betjveen atmospheric pressure p and. standard atmospheric pres- sure pg is plotted against altitude h. The static pressures obtained in the climbs and curing the descent were corrected to atmospheric pressure by use of the static-pressure error of the airspeed installation as determined from a low-speed calibration. This calibration v^as m:ade over a range of Mach number from 0.2Lj_ to .J+J by a method (described in reference 2) in which level- flight runs are m.ade past a landmark or a reference air- plane of known r^ressure altitude and a sensitive alti- meter is used to m.easure the static pressure indicated by the airspeed Installation. The static-pressure error in the dive and pull-out viras found by taking the difference between the static pressure measured at a given altitude in the dive and pull-out and the atmospheric 'oressure aetermined from the pressure surveys at the same altitude. Measurements of k- NACA RB No. L5K29a static pressure, impact pressure, and normal acceleration were used to evaluate the Mach number and lift coefficient corresponding to the determined static-pressure error. A ground check of the lag of the airspeed installa- tion indicated that the effect of lag on the measureLients was negligible. RESULTS AND DISCUSSION The results of the airspeed calibration made at Mach numbers of 0.2.^. to O.llJ in level-flight runs past a land- mark and also past a reference airplane are presented in figure [i. as a plot of static-pressure error 2 — . ~ P against airplane lift coefficient Cl- The flight Mach numbers corresponding to the airplane lift coefficients are plotted above the curve for static-pressure error. The static-pressure error was constant over the range of the test conditions and was 1.0 percent of the impact pressure. The static-pressure error determined in the tvvo high-speed dives and pull-outs by m.eans of the radar- optical tracking equipment is plotted in figure 5 against airplane lift coefficient for various ranges of Mach number and in figure 6 against I.Iach number for various ranges of airplane lift coefficient. The results of the level-flight calibration are also included in figures 5 and 6. At a lift coefficient of about 0.1, the static- pressure error showed no variation with Mach number vvithin the experimental accuracy. At higher lift coefficients the static-pressure error showed a tendency to increase slightly vfith increasing Mach nxmabers; the increase was of the order of 1 percent of the impact pressure over the range of Mach num.ber tested. These results are in agroe- ment with those obtained from the wind-tunnel tests reported in reference 1, which indicated that for a static-pressure tube located 55 percent chord or more ahead of an airplane wing the variation of static-pressure error with Mach number was no more than about 1 percent of the impact pressure, at least for Mach numbers from O.l], to 0,8 and for wing thicknesses up to 15 percent chord. NACA R3 No. L5K2qa CONCLUSIONS The calibration of an airspeed installation with the airspeed head counted 95 percent chord ahead of the P-5IB. airplane v/ing near the tip indicated that the static-pressure error did not vary with Mach nurriber by more than about 1 percent of the impact pressure up to the highest Mach number (0.75) covered in the tests. Langley Memorial Aeronautical Laboratory National Advisory Committee for Aeronautics Langley Field, Va . RSPERSNCES 1. Lindsey, W. P.: Effect of Mach Number on Position Error as Applied to a Pi tot-Static Tube Located 0.55 Chord Ahead of an Airplane Vvln^. N.-iCA C3 No. lL^E29, 19U^. 2. Thom.pson, ?. L., and Zalovcik, John A.t Airspeed Measurements in Flight at Kigh Speeds. NaCA ARR, Oct. 19)^2 . J. Brombacher, IV. G.: Altitude-Pressure Tables Based on the United States Standard Atmosphere. NACa Rep. No, 538, 1955= NACA RB No. L5K29a Fig. 0) c «3 .-I CL u •H (0 n i-H I Cm O bo S (M O t3 cd tu x: cd e o o C o OJ c 3 O e •o 0) OJ 0) CL to u 0) bo NACA RB No. L5K29a Fig. 2 X3 QJ x: T3 QJ 0) Q. m aa . — I in y3 >2 c E CO o be; I 0) NACA RB No. L5K29a Fig. 3 HOJ -P H a a o •r4 ^ CO iH H © OO Q O DO qp "0 ■ H « 2 O z 52 o > * - -J P < '^ Z ui O {^ ii o CM < ^ ^ > c (U to (0 oi » -p (D (U M ^ ;3 CQ (U CO o a •H ai 4^ ■p r-i CO cd TJ ■ x: G CO ■p 03 >. •H M (-1 c d d o CO CD •H CO 43 0) s (b ^H o .r4 PifH ^ o •H -o h 0) 1 0) c • 43 •iH K^PiB CD M — n- o -Ci r — O— "-^ C ; ■Gr O ./ .Z .3 4 Figure 4-.- Variation of static-pressure error with lift coefficient determined in level flight. Mach number corresponding to each value of lift coefficient also shown. NACA RB No. L5K29a Fig. 5a-c .04 O \ .04\ ^ O O Radar-optical tracking, dive 1 D Radar-optical tracking, dive 2 Level-flight calibration, M from 0.24 to 0.43. Q— ,Q .. ^ol)--- (a) M from O.5O to 0.60. °^. (b) M from 0.60 to 0.70. .LMt # . □ ° E 33 EH n Sd J .2 .3 .4 Cl (o) M from 0.70 to 0.75. .S NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS Figure 5.- Variation of static-pressure error with airplane lift coefficient for several ranges of Mach number. Fig. 6a-d NACA RB No. L5K29a 04 O O Radar-optical tracking, dive 1 D Radar-optical tracking, dive 2 O Level -flight calibration Q I^ bO^ % ^.o .O^ ^ (a) Ct from 0«03 to 0.10. -O- O O -^ <9 e G (b) 0^ from 0.10 to 0.20. G GG3 .04^ ^ xi «. D d s / (c) Oj^ from 0.20 to O.3O, ^1 .^^ □ □EH ^ \ > .3 Ai .6 y .8 „ ,,„ NATIONAL ADVISORY (d) Cl from 0.30 to 0.40. COMMITTEE FOft AERONAUTICS Figure 6.- Variation of static-pressure error with Mach number for several ranges of airplane lift coefficient. UNIVERSITY OF FLORIDA " "illllllMI 3 1262 08104 958 6 UNIVERSITY OF FLORIDA DOCUMENTS DEPARTMENT 1 20 MARSTOM SCIEiNCE LIBRARY P.O. BOX 117011 GAINESVILLE. FL 32611-7011 USA V