NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS
February 1946 as
Restricted Bulletin L5K29a
STATIC-PRESSURE ERROR OF AN AIRSPEED INSTALLATION
ON AN AIRPLANE IN BIGE-SPEED DIVES AND PULL-OUTS
By John A. Zalovcik and Clotaire Wood
Langley Memorial Aeronautical Laboratory
Langley Field, Va.
NACA 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.
Digitized by the Internet Archive
in 2011 with funding from
University of Florida, George A. Smathers Libraries with support from LYRASIS and the Sloan Foundation
'- I / -. .
IJACA RS :o0. L5;29.s: RESTRICTED
'.IATIGN4,L ADVISORY COi::.IITTEE 7FR AER'OIJ1UJTIJCS
STATIC-FRESSURE ERROR OP AI' AIRSPEED III;STLLaTIOIi
I AIT AIF.PL.-.I;E II; HIGH-SPEED DIVES ri.D PULL--'TS
By Jo hn A. Lala;.vic. arnv d 1otaire rood
Tests were made in hid h-speed dives ard pull-o-uts to
determine, by cotmb'ne radar.--,r, tic l tracking equlirjent,
the static--essure error r cf ai a rs eed-head installation
on a P-5i13 air-:PI-ne. The installati.-o included a .itct-
static 'iea-_ mounted on a bo,.om 90' crrcent chord ahead of
the leading ee tne in near t.ee ar tIe tip. The tests were
made in dives t flight Miach numers up t,. 0.75 and in-
cluded pull-o-ts up to 4g nor'rial acceleration.
Tlhe results indicated that the static-pressure error
did not vary,- with M.iach number by,- m.re than about 1 percent
of the im:nact oress.re :.-.'r the range of conditions inves-
I TTR.' DUCTI ON
Flight data on the variation with ?Mach number of the
static-pressure error of pi tot-static-tube installations
have generally been lim-ited by the available testing tech-
niques to sneels attainatic in level flight. Inasmuch as
the imaximrnx' speeds in level flight f -r most present-day
airplanes do not exceed a ,Mach number of j.o, the varia-
tion in static-pressure error with liMach number beyond this
value has not been obtained h-itherto in flight, although
some information is available from wind-tunnel tests
reported in reference 1.
For a recent high-speed investigation of a P-51B air-
olane, an airspeed calibration was required in dives and
pull-outs up to a Mach nu-mber of 0.75. A iiethod 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
2 NACA RB No. L5K29a
supplemented by data obtained up to high speed in level
flight by a method (described in reference 2), which
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 reported herein.
p' static pressure indicated by airspeed installation
p free-stream static pressure or atmospheric pressure
at altitude h
Ps NACA standard atmospheric pressure at altitude h
(from reference 3)
H free-stream total pressure
qc free-stream impact pressure (H p)
M free-stream Mach number
CL airplane lift coefficient
APPARATUS AND :ETH.,D
Airplane equipment.- The airspeed-head installation
of the P-51B airplane is shown in figure 1. A Kollsman
type 651B 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
85 percent semispan from the plane of symmetry, at which
station the wing section had a maximum 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 measure
impact pressure; the static-pressure element was also
connected to a recording altimeter.
The airplane was equipped with an NACA single com-
ponent recording accelerometer, an NACA chronometric timer
to synchronize all records, and a radio to communicate
the timing signals to the ground equipment.
NACAj R3 ;;o. L51K29a
g-rr.indQ equipment.- The track-ing equipment used to
establish the neigh -it .f the arpl.,air consisted of a coIm-
binti.n 7of a radar unit for the ieter:inati:n cf range
an,- a htcttottrheodoli te f:,r the o.etermin tinn of the ele-
Test or.ceure.- Tne first st n in the test .proce.cure
consisted in *obtainin L a survey I. a climb at an i:.:.icated
airspeed of 175 miles z:.r hour over a ran e cf altitude
from about 15,000 to 26,000 feet in cr er t- estaoliish
the relation aotf atmi-spherc c orer.sure tD actual altitude.
In the survey, at intervals in altitudC3e ,f' ar-).-:r,xi.m' tel-,
1000 feet, simultAneous recor-s were ta-ken ;f static
pressure, imp.ict pressure and norim:l aceler-:..L n jn
the airplane anid e.leva.ti;n nle ge and ranIe i:f the
airplane with the tr'aclin;. unit. T'-e airnlains as then
dived t- a flight ;1Much numtber of 0.75 an, pulled -ut wvi h
2g normal acceleration '.vlthin the ranie "f alt itufe sur-
veyed; c.:ntin,.;us :"j si;,iultanieous recorJs .of' static
pressure, impact or:-e:ssre, nr;:al acceler-itio.n, rang ,
and elevarion -ingle 'er.e mads Jdurin,; these .maneuvers.
second div.e w;.s rade over the same ra-ng-e o il titude and
M.ach numriber but ,'Ath .a co'll-.ut :t a nor.1-.ai ,cc leri ti-n
of Ig. After the sccnd :ive and pull-jut the ZLr.'C- in
climb wa. repeated and ,was followed by a survey.' in a
descent at the same speed and over the same r:::nge of
The results of the surveys o.f at.ir-soheric pressure
are shown in figure 3 in which the difference bet,.aen
atmospheric rressutre p and standard atr,.:',srpheric pres-
sure ps is plotted against altitude hi. Th static
pressures obtained in the climbo and curinge the descent
were corrected to atmcscheric pressure b- use r' the
static-pressure error of the airspee.j instaellat'.cn as
deterr.:ined from a low-speed calibrate. n. This T calibration
was made over a range of I'.Iach ni.uuer from 0.2- to 3.45
by a method (described in reference 2; in which level-
flight runs are made past a landmark or a reference air-
plane of i:njwn nressL.re altitude and a sensitive alti-
meter is used t- measure the static pressure indicated by
the airspeed installation.
The 3tatic-pressure error in thp dive and pull-out
was found by taking the difference between the static
pressure measured at a given altitude in the dive and
pull-out and the atmospheric pressure determined from the
pressure surv-es at the saire altitude. .1easure!ments of
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 measurements
RESULTS AND DISCUSSION
The results of the airspeed calibration made at Mach
numbers of 0.24 to 0.L3 in level-flight runs past a land-
mark and also past a reference airplane are presented in
figure 4 as a plot of static-pressure error P' 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
The static-pressure error determined in the two
high-speed dives and pull-outs by means of the radar-
optical tracking equipment is plotted in figure 5 aEainst
airplane lift coefficient for various ranges of Mach
number and in figure 6 against Mach 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 within
the experimental accuracy. At higher lift coefficients
the static-pressure error showed a tendency to increase
slightly with increasing Mach numbers; the increase was
of the order of 1 percent of the impact pressure over the
range of Mach number 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 -.ach numbers from 0.4
to 0,8 and for wing thicknesses up to 15 percent chord.
IIlAC RS ie. L5K2"a
C .' CLU SI. iS
The caliibr.ti .n f an airszpeed installa:i.an with tne
airspeed head -r~uneid 95 percai it ch.orC 'he:-d -,f t=--
P- 13 airplane v.in iwe- r t-.e ti i indj. cted that t he
static-oressure error Ji.j not v'ry ,,lvith M'.ch nutmer L'y
more than :-o.i.it 1 percent: of' the imn aact n re ss3'..ure t.
the highest M:-ch nurmiber (0.75 covered in; the testz.
Langley Miemc.orial .eronrau.t cal Lat'boratry1
flaticnal ..vi )ry Cirmittee f:.r .eronautics
Lan-.i ey Flel,, .:.
RP hR EIrC ES
1. Lin-:sey, "." F.: Effe',-t :.f acn I..ie.b r :n P:.siti-n
Er:.r.r .as replied t: Pit.t-S3:t, tc t L.c: ted
0.55 Chi id .hee: f. an ir p -Ia--e ,.-in.. :.-.C' C3
2. Th 'impso..r, F. L., -r.d Za.. ovei.: J'ohni A.: .-s rsr e
M.'easur'ements in Flight at Hih Sp.eeis 1.C ,-eRR,
. Brcrb acher, J. .: Altitude-Pressure Tatl-s Faset. on
the Unit.e SZtces tanjard Atii.iosph'iEre fi.C RcI.
iL.,. 538, 1 5.
NACA RB No. L5K29a Fig. 1
NACA RB No. L5K29a Fig. 2
NACA RB N.o. L5K29a Fig. 3
4 a- 0I .
0-I M ec
0 Cq4 Co
0______ EP E
---_-- -- --4 F
rlI I 0)
l-1 l-l 1 4
bD Cd -r
----- ------- Q m h or
*> \ *-< P.
9-AV JO q/ C/- Cd
NACA RB No. L5K29a
COMMITTEE FOR AERONAUTICS
0 ./ .2 .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
NACA RB No. L5K29a
Radar-optical tracking, dive 1
Radar-optical tracking, dive 2
Level-flight calibration, M
from 0.24 to 0.45.
(a) M Irom 0.50 t. C.60.
(b) M from 0.60 to 0.70.
(o) M from 0.70 to 0.75.
Figure 5.- Variation of static-pressure error witn
airplane lift coefficient for several ranges of
COMMITTEE FOR AERONAUTICS
NACA RB No. L5K29a
O Radar-optical tracking, dive 1
0 Radar-optical tracking, dive 2
0 Level-flight calibration
(a) CL from 0.03 to 0.10.
(b) OL from 0.10 to 0.20.
(c) OL from 0.20 to 0.30.
.2 .3 .4 .5 .6 .7 .B
) from 00 o NATIONAL ADVISORY
(d) CL from 0.30 to 0.0. COMMITTEE FOR AERONAUTICS
Figure 6.- Variation of static-pressure error with Mach
number for several ranges of airplane lift coefficient.
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