A comparison of data obtained by two flight techniques for determining the sideslip characteristics of a fighter airplane

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Material Information

Title:
A comparison of data obtained by two flight techniques for determining the sideslip characteristics of a fighter airplane
Alternate Title:
NACA wartime reports
Physical Description:
6, 4 p. : ill. ; 28 cm.
Language:
English
Creator:
Johnson, Harold I
Langley Aeronautical Laboratory
United States -- National Advisory Committee for Aeronautics
Publisher:
Langley Memorial Aeronautical Laboratory
Place of Publication:
Langley Field, VA
Publication Date:

Subjects

Subjects / Keywords:
Fighter planes   ( lcsh )
Airplanes -- Control systems   ( lcsh )
Aerodynamics -- Research   ( lcsh )
Genre:
federal government publication   ( marcgt )
bibliography   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
Summary: In order to determine the validity of sideslip data obtained in flight by the continuous-record method, sideslip data obtained from a fighter airplane in slowly increasing sideslips have been compared with sideslip data obtained from the same airplane in sideslips in which all the flight conditions were stabilized. The results of the comparison showed no essential difference in the sideslip characteristics obtained by the two flight techniques even though the continuous sideslips were purposely executed with a yawing velocity about double the usual rate of 1° per second in order to accentuate the effects of the small yawing and rolling velocities inherent in the method. Approximate theoretical calculations confirmed the experimental results but indicated that rates of yawing or rolling lower than 1° per second are desirable if the continuous-sideslip technique is employed in testing airplanes much larger than current fighters. The method of measuring sideslip characteristics under steady conditions is preferred to the method of measuring sideslip characteristics in slowly increasing sideslips when the airplane is directionally unstable, when is has a large pitching moment due to sideslip, or when a poor relationship exists among the rudder, aileron, and elevator control forces in sideslips.
Bibliography:
Includes bibliographic references (p. 6).
Statement of Responsibility:
Harold I. Johnson.
General Note:
"Report no. L-87."
General Note:
"Originally issued August 1945 as Restricted Bulletin L5F25a."
General Note:
"Report date August 1945."
General Note:
"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 previously held under a security status but are now unclassified. Some of these reports were not technically edited. All have been reproduced without change in order to expedite general distribution."

Record Information

Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 003613545
oclc - 71214417
sobekcm - AA00006263_00001
System ID:
AA00006263:00001

Full Text
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RB No. L5F25a


NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS




WAIRTIM'IE RE PORT
ORIGINALLY ISSUED
August 1945 as
Restricted Bulletin L5F25a

A COMPARISON OF DATA OBTAINED BY TWO FLIGHT TECHNIQUES
FOR DRTMRMJIjjG THE SITSLIP CHARACTERISTICS
OF A FINGER AIRPLANE
By Harold I. Johnson

Langley Namarial Aeronautical Laboratory
Langley Field, Va.







NACA


WASHINGTON
SNACA 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-
hically edited. All have been reproduced without change in order to expedite general distribution.


L 87


DOCUMENTS DEPARTMENT



































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


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NACA- RB No. L5725a

NATICKAL ADVISORY CC.'IrT_-E OR A?.1C'1:A.TICS


RESRICT:D r31LLETI::


A CO"PA ISC';N OF DATA CB't'-NED BY T'JC FLI'"T T' CiNI-iES

F:'R DET R TTI 'IG THE SIDEoI.iP CHEAACTERISTICS

0o A FIGHTER AIFPLU.CE

37 Hsrola I. Jchnzcn





In orderr r deter-.inf. the v7li-.ity cf sile: lip data
obtained 5in LV .-,.t bh ta,? cr.nt lr'-..o-s-r'?cr5 -r.ethc 1, side-
slip J o.;a obtained i2,c_ fi.:re-r ..-r'il ne rin i'.vly
increpsin" sidesli-, YSv2- t en co 'r..red ith sides3lip
d-a. ob cb 9 ed ro.. che sar-.e airp.lne in ide lips it vnich
all the "li.zhT c-. I tcns we2e st -oi -lize:1. he results
cf the ccmnc.-riscr -hc'.-.i t.o 7vsen.isl .iferen-ce in the
sis ]. .i i ch r.F cteri t Ics tained by the two licht
techniques e'.,n t'.hou h th-e .c.ntinuruns sideli'sz were
put-rcsely executed ':ith a yvawir veloci vbo'.t -it ble
the .ut-al r.ce of I.C J second in -rder to accent :cte
the effects of the srnall ; rW.inz, anj rcllin; velocities
inherent. in t.ia, method. Approxir.ace there i l cilcu-
lations confirr.ed the e.- erim.-nti ri:SuiLs but inlicet d
t.hl-.t ras es cf yewin. cr -c.lli., l:.6r t.r. 1i" e; r scccnd
are desirSble it the continuous-siJ.s1Zli technique is
em,:.loyed in testin- .-ir'l;-nz s much _rg"er thrn cur-ent
fightL rs. Trie ir.tho:i of r.ess-.rini sideslic characteristics
under steady conditions 5: .referr,, to -.e meth:d of
nmesa.rins sir slio chFr cteristics in .lo .1 y increain
sidegsins whmn t.he -ir:,lne is directic.-:;'iy unstale,
when it hns a i:rge nitchinz ;e!i-nc iJue to si,=alip, or
when E poor irei -tiornsh.i, exist-: non-g tre rudIer, siler.on,
end elevator 2:,r.trol fcrces in siie-iips.


INTRCD.JCTIC r


from til.: tc tire questions -.'e j-isen corncer-nin
the validity of dca.- on sideslip charactsrlst is obtained
by the continuous-reccd odtaod as aiI:f'f'r:enti ted from
tho usual staqdy-record :;;ethod. The usual flight technique









2 NACA RB No. L5F25a


for measuring sideslip characteristics consists in taking
records of control forces and anrles under steady condi-
tions of airspeed, herdin"., angle of bank, and angle of
sideslip, at various attitudes of the airplane within the
sideslip range to be covered. Although this method of
testing obviously yields the desired results, it is
uneconomical with regard to flight and instrument time
consumed because only a relatively limited number of runs
can be obtained in any one flig-ht. In order to speed up
the test program materially, sideslip characteristics have
often been determined by the continuous-record method.
This method consists in switching the recording instruments
on at laterally level flight trim and then slowly mC' ing
the three controls together in such a way as to maintain
constant airspeed and -eiding while causing the angle of
sideslip or bank to increase at a slow rate (not exceeding
1 per sec) until one of the controls is fully deflected,
or I--h control forces or other limitations are reached -
at which time the instruments are '-,itched off. The
resulting data are handled under the assumption that the
variables measured at any particular instant during the
maneuver represent the stel-:iy sideslip values. The error
of this assumption, of course, lies in the neglect of the
small incremental control forces and deflections required
to maintain the small angular velocities of the airplane
during the sideslipping maneuver.


DESCRIPTION OF E'7LT


In order to investigate the m--.r.itude of the error
involved in the continuous-record technique for deteri.ining
sideslip characteristics, flight tests were made with a
current fightsr-tv-le airplane (fi.7. 1) and sideslip data
were recorded during the tests by both the steady-record
and the continuous-record techniques. Sideslip records
were taken at indicated airsc-eds of 152 5 3 iles per
hour .ith normal rated power at about 50C0 feet altitude.
The slowly increases' sideslips wire purposelyy executed
with a yawirn- velocity about double the usual rate in
order to accentuate the differences between the results
obtained by the steady-record and continuous-record
techniques. All control positions were measured at the
control surfaces and the control forces were measured: at
the stick and rudder pedals.









NACA R. ITo. L5F25a


RESULTS .'J: DIS CSSI3T


.es'-uits cl' tne tests are shown in figure 2. These
results indicate th.t v:-ry little error is incurred in
sidesii,-char.cteristics data beca.:se of the use of the
continuous-rccrd metnod. A cucuid be expected, the test
points obtained fr.-,. the co, ntinuO.u. records, vhen cocr-,-red
with the test ocoints fror,, La ste-. reecc.ds, generally
indicate th:t slightly y greFter rul-ter- and :i ler ron-cng.'L
and control-force diffe.:-ences from: the-3 values corr-es- ending
to laterall/ level fli-ht trim eLr rnequlred for a given
si:ieslip Lnle. The slight a -.sc ntinuitv. that s:.ear. s in
the curves where the direction of side 3 1pp.',n- is reversed
is ...rtl the re-.ult of th.: control def- sections 3nd forces
requ.ird to f"ccele'rt: the -r:.-1 ne fron st-:d' fight to
the condition of si,,li un.,if-rm. :p Vir- nd rolling veloc-
iries. Conrrl. fri-.cti.n el:o conlrib \Lces to the discon-
tiinuitr in the ce7t-.n-cl-f:rc r-e curv-e. In-asmr.ch ?s the
co tint u ec c o .1'ire 1' '0'.'r'no- o'.ts: ned for :a yew.inp:
velocity s"noroxiatelw tw'ic. es r-re.t s the reccimrT.ended
maxijnui:m rate for fishte:--tye -ir; 3nes (lo sideslip ,er
sec at low aIrsree..s) it beecces evident thft, for the
size end flight sw-ieed of' the !irlane tested, the dis-
cr'.,:'ancy to be expected bet.veen 2lde1li., datE obtained
by tne LVo -methods is within the Fscatter to be expected
from successively recsated tests ,ades by either of the
methods.

Approximpate theoretical celcu.. -tions ha-ve been .iasde
of the veri.ticn of rudder- angle qnd totl-qiRleron-?.nj1le
errors with service indicated eir'sed for the ssrne
fic.htr t irplane in slow::ly incr.as-ing sidslips. Only
the two most imoortent ;.qwinj- or rolling derivt ivss were
considered in calculetinr- the ru-dder- or alleron error,
respectively. For the rudder-angle error, these deriv-
atives :.re the rte of cl.ante o[' iirplcn:- y- ,inr -xnomnent
coefficient with yewing velocity d.,.-: to the ver icCl tail
and the rate of change 0 yv.wing-n:o,.int coeffic ient with
rollin,; velocity due to the .ving. For the totel-rileroin-
ang-le error, these derivatives include the variation of
wing rollin-.'-r.c.een coefficient with rollin? velocity itnd
the variation of ;.inb rollini-moi.ert coefficient with
yaw.ing velocity. Vlu,. fr trne v',-,in; derivatives were
determined from the charts of r1furencn 1. TVertice.l-tail
effectiveness w ts esti-mated from refer-,nce 2. Aileron
e-fectiveness was obtained from :-reviou- flight .tests on
the same airrlene ren frc.n the theoret ical charts of









DACA RB No. L5F25a


reference 3. The side-force characteristics of the
fighter airplane used were assumed to be similar to those
measured for another fighter airplane having nearly
identical -eometric and weight characteristics. This
assumption was necessary because no data were available
for the airplane used in the tests from. which to determine
the ratio of rolling velocity to yawing velocity as a
function of speed in properly executed sideslips. The
errors were calculated both for a constant rolling
velocity of 1 per second at all speeds and for a constant
yawing velocity of 1 per second at all speeds. In
practice, the rate of executing continuous sideslips is
generally set by limiting the rolling velocity to
r: i hly 1 per second at high speeds and by limiting
the yawing velocity to about 10 per second at low speeds.

Results of the calculations for errors in r-i der
iand aileron anrles caused -: use of ,hi continuous-record
method with tho fi 1ter airpl.ne tested are presented in
the curves of f.igurs 3 and respectively. The
errors are given as functions of service indicated
airspeed. A positive error indicates that more control
deflection from the initial trim condition is required
in a slowly increasing sideslip than in a steady sideslip.
As noted previously, the rrts of executing continuous
sideslips is controlled by limiting the rolling velocity
at high speeds pnd 1c- limiting the -awing velocity at
low spee ds. An inspection of the calculated curves
indicates th_.t, if neither the rolling nor the yewing
velocity were allowed to exceed 10 '..r second, the error
in rudder-angle measurements should not exceed 0.20 at
100 miles per Lour service indicated airspeed and should
nearly vanish at high speeds; similarly, the error in
total-aileron-. s measurements should not exceed 0.60
at 100 miles per hour service indicated airspeed and
should become .ruch less at high speeds.

If the rates of yawlr, and rollinQ and the airplane
seed are held const-nt and the airplane size is increased,
the error's in r..d .-angle and aileron- r.le !measurements
in continuous sid zsliop' increase. -rora rel.ti'" to the
wi0.1 yar.-' or rolling derivatives increase in direct
proportion to the incranze in i..'. span, whereas z .ne
rudder- ,- ]e error de to vertical-tail damping increases
in direct proportion to the increase in distance between
the center of gravity and the vertical tail. Hence, if
the continuous-rec-.)-- method for deter,a"i:in sideslip
characteristics is used "n testing~ airplanes much larger










.ACA .RB No. L.F'25a


than current fiaht ,. tines (.pan, appro-,'iP'cely 40 ft;
vertical-tsil len trt, p:,rc.imratel- 20 ft), the miximriun
allow.ble rates of yawing or rollinF. robb-ly should be
r~ui.ced belo.: the 1' -er second liruit recor.merded herein.

Ib is de 'ir-ble to use the ste i-. .etho-. for
.,e aarin sides, char c teristicZ fo- any fli1hc con-
di-ri,.n il' the reliLcionship ,miong the various control
forces io door, if the ,-1-ir7 ine ia s Ziec i-n.il-l unstable,
or if there is a9 lrge pitching ;:o, '.enrt ,.e to sideslo
present. Nher. none cf these .,bjecionible ronditicns
are present rand ien orj-.t inuou.s-r'eccrir.g instru-e.ts
a-e evaijlable, the con-tinuo.!-recor .,, thcd for jet .r' ,ning
sides la, characteristics csn be used ,d'.':.ntc gecusly to
s-ve tiie in tli-ht- testing.





?ne conr-i e.--rec.id re-ho for meas :-.ng sieslip
ch.racterist ics in fli!-.t v ei:]s cou-.:'.e res .t1 for
current fijhrer -irdr1nrs jif th? :- ete of y' v.ing :r rolling
.s not llo.;ed to xceed 1 .C s.:,o:1., l ". r tes of
ys .'.:in cr r o in-. re desir-'.le ii t-ie conti.nuous-sideslip
technique., is e.ioied in tesrinl 1 :rcr- *r -i l-1r-n s in
si esli'.s. W,:~n he rel :t i nshin ) smioi: the various con-
trol forces in sideslips is -.oor, when the ?irplan? is
directiorsllv unstable, or wrinen the pitching. moerr.nt due
to sidcslio is unusLiually lEr- the sterc..y-ecori method
for dezercinirig s.i.es lip ch'r_--cte-i tics is pr-efersble
to the co:ntinuc-s-record meth.d.


Leniley H'exr.-,'i2al A-i-ronoutical Lsaorstory
N:-tiona, Advisory Comrriutte. for A rcnu.atics
Leng.ley: Field, Va.









6 NACA RB No. L5F25a

REFERENCES

1. Pearson, Henry A., and Jones, Robert T.: Theoretical
Stability and Control Characteristics of Wings with
Various Amounts of T :.er end Twist. NACA Re'-.
No. 655, 1938.

2. Pass, H. R.: Analysis of Pi nd-Tunnel Data on
Directional Stability and Control. NACA TN H,.' 775,
1940.

5. Gilruth, R. R., ran Turner, W. !.: Lateral Control
Required for Setisfactory Flying Qualities Based
on Flight Tests of Numerous Airplanes. YFAA Rep.
No. 715, 1941.








Fig. 1


NACA RP No. L5F25a


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NATIONAl. ADVIsoRY
COMOITTE fO AEONWTICS


Figure 1.- Throe-view drawing of fighter airplane use n the test.


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NACA RB No. L5F25a


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