Flight measurements to determine effect of a spring-loaded tab on longitudinal stability of an airplane

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Material Information

Title:
Flight measurements to determine effect of a spring-loaded tab on longitudinal stability of an airplane
Alternate Title:
NACA wartime reports
Physical Description:
13, 25 p. : ill. ; 28 cm.
Language:
English
Creator:
Hunter, Paul A
Reeder, John P
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:
Bombers   ( lcsh )
Stability of airplanes, Longitudinal   ( lcsh )
Aeronautics -- Research   ( lcsh )
Genre:
federal government publication   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
Summary: In conjunction with a program of research on the general problem of stability of airplanes in the climbing condition, tests have been made of a spring-loaded tab, which is referred to as a "springy tab," installed on the elevator of a low-wing scout bomber. The tab was arranged to deflect upward with decrease in speed, which caused an increase in the pull force required to trim at low speeds and thereby increased the stick-free static longitudinal stability of the airplane. It was found that the springy tab would increase the stick-free stability in all flight conditions, would reduce the danger of inadvertent stalling because of the definite pull force required to stall the airplane with power on, would reduce the effect of center-of-gravity position on stick-free static stability, and would have little effect on the elevator stick forces in accelerated flight. Another advantage of the springy tab is that it might be used to provide almost any desired variation of elevator stick force with speed by adjusting the tab hinge-moment characteristics and the variation of spring bobweight, the springy tab would provide stick-free static stability without requiring a pull force to hold the stick back while taxying. A device similar to the springy tab may be used on the rudder or ailerons to eliminate undesirable trim-force variations with speed.
Statement of Responsibility:
by Paul A. Hunter and John P. Reeder.
General Note:
"Report no. L-210."
General Note:
"Originally issued February 1946 as Advance Restricted Report L5I20."
General Note:
"Report date February 1946."
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 - 003594145
oclc - 70915707
System ID:
AA00009505:00001

Full Text

ARR No. L51I20


NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS





WARTIME REPORT
ORIGINALLY ISSUED
February 1946 as
Advance Restricted Report L5120

FLIGHT MEASUREMENTS TO DETERMINE EFFECT OF A SPRING-LOADED
TAB ON LONGITUDINAL STABILITY OF AN AIRPLANE
By Paul A. Hunter and John P. Reeder

Langley Memorial Aeronautical Laboratory
Langley Field, Va.


^ ^ ^:.C'?, ,. T ...?- ** *
17" ~r nt~l N.,4~~
NACI
.. "


WASHINGTON

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.


L 210


DOCUMENTS DEPARTMENT







































Digitized by the Iniernet Archive
in 2011 Wilh Iunding from
University ol Florida, George A. Smathers Libraries wilh support from LYRASIS and Ihe Sloan Foundation


hilp: www.archlive.org details flighirmeasuremenOOlang





~, ~,


IIACA ARR Ho. L5120

IIATIDONAL ADVISORY CO.'TTITTEC T 9,- .LDT.,'TCS


HDV!;NCE EESTRICTED ?_LF.T


FLIGHT I7ZASR C1'1iTS T_, D7TE'T-,I.E ';C i C ''-' A T:'- .:-L-,ADD
-.T. I L.i T i TVDLIZ.L ST .-.T T IL ,, AIRPLO. E'

3- Laul .-. center andr Jl.I P. FReeder





In conj 'iuictl''n ;.i th a or. :. of research on the
general prr 1 .e:r;. :' tabi it'1 _-, planes in the cli :r'ti~g
condit .on, tests have been .,aUe -f a spring-loaded tab,
which is referred t:. as a "s'rinr tao," in Ltll.-r on the
elevat-:r :..f a lo'*-winz scout Lo:;i._-r. -he tab ,.,is arranged
to reflect uov.arJ ith ,ecrease 1.1 speed, which caused an
increase in the p7)ll f1rce requlr-c to trim a6t low speeds
and there, increased t-hLe stL c,-fre, static lon:l ;gtudinal
stability the &irilane.


It was found t-.Sa t.-r sp,-ingy tab ':.':ld increase the
stick>-free stability. in ..1 'l;iht conditions, would
reduce the danger of in,:.vert.n- staIli. bect.sie of the
def'inte pdll f.rce re-vi.reJ.i .-, stall the airplane ,'ith
,ojuer on, wuld- re-uce 'he effect of center-of-gravit5
position on srick-free Ztatic stabilityr, and v,ould have
little effect on tie l.\-atr stick forces in accelerated
flight. Ano.thlier 'akvaiTae ". the prringy tab is that it
might be used t: *rov:i.~e siL-t any desired variation :-'
eleva:or stic." frice with s -e,' adjustbi," the tab
hinre-...:cr..ent c Ircteristics end the variation of springg
moment with tab deflect in. 1inlike the burgee L..i t.v:.
bobv ei.;i,-.t, the spriln.; t Lab i'ul- provide sticl:-freE
static stability ..'ith),:) re'[uiring a .:..ll f,.ce to L.-ld
thr. st ick bac *:hil .c t A:-'-inr,. device similar to ,,e
spn'ingy t a :, a.y u uSed J n L: r*-.'der or ailerons to
eliminate undesiranle trimi-'-,rce variations with s-eed.


T.TR'DOiCTTC.::


The I;ati-nal .a, visry 'm. ttee for Aeronautics .as
initiated a ro-zra.: of re-se:arc I. '- .- ;~cneroal or',.'.lem 1 .'f









2 N'-Ci ,R NJ. .'5120


the s-a:'. litv of airplanes in the clir.bing c n,-ri tion. In
conjunction N with this pro,.r' e ....,- ; ;. ..,. .,t-fi'
s. ;est*.:' a fev ece that increas:- tl 'j I.- -ir'-:-.
stability at low spe,:"'s in-' yet -es n-t -ifc :t the 3tick-
fr e sta'i:lity at hl-"i soe-ds. hiLs E vice c-r.n:;ist.: f
a spri-.-r-l aded tab on the el.-v-tor. ;i.. ;:-ab is arr.-njed
to _> _'lect vupw "'., with respect to th. le '-r an, :*
cause an increasr,-' 7-i1l force for trir at los, sfeds. As
the :c-.. is increased, the i,. ., t-il' ,*. c .. r nd
rL.,?r.-fore the incremenc t of :i-'ll fore?, is c. uc ;2..s, uL until
at hl- '. s.--od the ta, reaches a store '. its, ne tr-l r osi-
tion ..'r. has no further effect on th, <- v-.:r l-rces.

A tab of this tr-e, referred to ,I.~" r .s .a "c ringy
tab," 1 as built and init.ll- on th i1-i'.t v.1 :- -r f -f
low-wi.n. scout bh' .er. .- 1ht -fli I t' t: .-ere r-.ade of
-he a r,-lane *..1th the 11-Ii,_,-tao ir-t .lu -l :. dta
obtained in these fl1 I-.ts ure c .:.red h:-.e'n .'a:h data
previously obtained for the sa&-e airpl.c ,ci t; pr'iduc-
tion t-..b locked.





A si:; view of t'~-. airplane used in thi- i:::.\sti,,a-
tion is shown in figure 1. The ucti r. ro s-is '.2 the
airol-.-ine tested inc corporate a tab on th' ri.t le';al:r
that is designed as a balancing tab c.ut is --'a.:ally l:,-e:ed.
T._s tab was utilized for the spring :;-t.., installation.
Ti,: sprin:: tab was staticall-: and oyna-"icall-,- over-
r-ianc.-d '.Y mov'n.,-- its hin line re.Earv r.- 1 .-- inc. and
'.., a"i.d 1 v -. ht to its le .a:. el ,e. .-' t.e s 7.. 1 ';,y-
tab installation, the elevator .'ss b.lce a.;';s :-.cieased
to obtain the crilIn-al mass overbalance .--f i: elevator.
A olan vies. of the stabilizer, elevmac-r, a:-d ta" is shown
in fi ';e 2.

A sprin, was installed as shown in f:.i 'ire t, pro-
vide a moment 'A:ut the tab hi.n I-i:e '.e lir!: con-
nec- -n: the soprin., to the tab as iv:.t.ee .':.i .e tab at
a .-Aint bL..iAl' the .ir.- line so th~7 t the ;ra,.i-tnt -,f tab
hiin e moment with deflection co'l-.1. mide ci her stable
or unstable by !. justin the ometry f L e .,-.- re. -.rnd
the sar-..-' characteristics. A s.-Ill .-ubtr .v attached
to the trailin- e.-. of the so.in'T L.b in 'jrr-.r to adjust
the loat!... angle of .,. t b, ?.n st ps .r.ere r"'id':d -C .3
limit the ,i.r..7s'd deflection of the spr.-ing tab tL 21l and








NACA ARR :Io. L'.120 3


the ,roPna'rd ef election to 00o P-i to rans of the springy-
tab installation are given as figures 4 and 5. Unles-:
other'.,ise n-'te', ti-e variation of s-.ingy-tab lirn l moment
with s rin-y-t2 b anjle (as measured on the ground) was as
sh-,jn in fieur.e 6 and the -an-.le of te subtab upward from
the soringy-tab center line was approximately 6.50.

The relation between the elevator angle, measured
from the stabilizer, and the sti :- position is shown in
figure 7. The friction in the elevator system is indi-
cated in figure ":' to be of the order of 2- pounds. The
2
airplane .as fitted with a bobweight that required a
stic'-: pull f-ore -.f approximately 5 pounds. The bob-
ei.ht, which ..as installed for the tests of the airplane
..ith the -.rigiinal tab and with the s,-in.' tab, is a pro-
cLi.cti :.n instill-.tion and had no effect on the relative
stabillti .2f the t;.o confi..irations. Elevator angle,
elevator stic_ f'rce, springy-tab an.^le, velocity,
a...eerati-', in:' time were deternrined from standard iC, 'A
recording instruments. Elevator -,an les were measured from
the stabilizer in all cases. The airspeed used through-
out, called correct service indicated airspeed, is the
airsre.?d that would be given by a standard A; airspeed
meter if it were connected to a pitot-static system free
fr1::,. position error and is defined by


Vis = 45.0O fU Q


*;n' re

Vs correct devicee indicated airns,e:." miles :,er -'ur
s

to sta n. rd sea-level compressibility correction
factor

q c measure.- difference between total and static
pressures correcte, for 'tot-static p--sition
error, inches of water

The elevator- -y-t.tern mechanical advantage was .nr.ned
between the timr_ that the tests of the airplane with. the
ori~,i'-,l tab and the tests of the airplane with the
springy tab were made. T.et stick forces for the airplane









4 C.;-.C. a:'.R :: L I.O120


with the original tab, h-.-::ever, have 'ree c-jrrected to
corres7Fnd to Ie mecl..nical advanta e31 the alr l-.e
with the sprin.y tab installed.


RETTLTS .-tD .'T .CU .. :.

Static Lon::.tudinal S.a':i11t;'


The first several flights were ma.'e t.- ufI- ,st tihe
characteristics of the springy tab t:, Live the desired d
effects on the static lon:Itudinal sta ll.ty. Tn these
f li-t.s, the speed r..'.r. e over which ":'-: e:, .:. .ited ,-s
found to be too small and the fricti.. in t-.e -.l :,'t mn,
too large. These faults were corrected o .-: j.~r in the
tension in the spri.', by adjl,.-..ig h.- n I. "f chh-
s'-ttab, by chn.-:ing the c.:sition of cn. l n,-: j 1it ..n the
tab, and by installing ball be-rings it. .ll ri-.:'n joints
of the sprin,-y-tab system. Unless c:er.'..ILse n5c, the
data on static longitudinal st.,i'-,litfv .re frr: i'liL hts
trade subsequent to these changes.

Figures 9(a), 10(a), 11(a) and i.1',. an- 12(a)i sh.w
the static lor. tudinal stability ch a:rteris-tis of the
alrolane at both forward and rearward crntsr--f-,.;ravity
positions with the sorr..y taao instLi. The te-t fli:'ht
conditions are defined in table I. ,C.: .-.ir.ble c.;:e "re-
viously obtained with the airplane h&.vi,- T.o 'r,, iinl
tab locked at zero deflection are sh."''i in -ures (o),
10(b), 11(c) ani (d), and 12(b). The s.ick-freo :ta'ility
characteristics of the airplane with I .r. :1.i n.l t:,:c _~nd
of t.:e airplane with the s-..'i. .' tab .r" ca ..-'-red n
fi:ur? 13 for the climbing and _.l'.in c'n.:l i:ins t trine
rearward center-of-.r.vity position. r" S1..r.ts i. 1 ated
as srnt runs were obtained from short rec.:r ; taWien ',. ile
the airplane was in equilibrium in a -[ i.n .li .ht conit-
tion. "--.. .-'>ints c'- si, :.ated co t- I nu : s '.:.. re ad
f:.'-'. lon or records dur:i..- which the :- ...a' S- :'1;'
decreased.

The effects of tre s : n '; c 1 ii -
tudinal stability of the U.r"-lane as c. r..rw. th the
effects of the ori,.l-. l tab (f1'Z. 9 c 1i) ..;y b1
summarized as follows:

(1) The springy tab increas-.c tr' : 'L .: -r.-. L.ta';"lity
in all fli ht co;-1i Lions as manifesto '' l, r,er :igative









NACA ARR Iro. L5120


slopes of the curves of elevator stic:_ force against air-
speed. In po.wer-)L-i fligh t with the crncei'- r 'f-ravit:
position at approximately -2 rnrcent :f the ir.e; a,.=ro'y-
nanic chord a ccn:i tin in Vhl-ich the ai-rc:lane v.ith the
original tab had a large degree of instability both sticl:
fixed and stick free t.ie va,-iatic-n of stic.: f',Irc.e with
airspeed became stable trcughi.: ut the speed range. T.I
the poA'--r-cff conditions, for i:hich the airplane with the
original tab Aas stable, t he ull fr'1rces required to trim
at lcw seed were increased o-,, the srlin,;y talb to an
extent thLt was considered so..ie,.hat 'b'iectioiAble by the
pilots, although the pull -ircee never exceeded JO pounds.
Some li.-hteninr -,f the pull f rce at the stall occurred
in cases in vhich the sfr'ngyr tab r-eached its maximum
deflect c. a few'i miles -er ho' -r a:D-,e th:. st-l lirn speed
but stickc-force r:-.v;rsal ,cc.:u:e' d riily in the lanr-di rg
cond.iti'in at the rearward center--.:-_-,ra vit c.osition.
Because the springy tab reached its stw:. at zero deflec-
tion at aCp ro.-:i...ateoly 2'-Ju miles -.,r .ur, the hit-hest
speed :.f the srringy-tbo tests, it ...:uld be expected to
have n- effect on the staL ili t, at nir h,'r :ose.ds.

(2) Tbe spring.;, tab tenderd to reach maximum :ef lec-
tion at a speed near the stall.In.r speed for all fli-,ht
conditions despite the variation of staliin:, speed .with
flight cnr.d.ition. The increased dynamic pressure on the
tail in ',-wer-on conditions probably accounts for the
fact that the tab reached its maximum deflection at a
l.vcer speed in these conditions.

(3) The springy tab reduce' the effect of center-of-
gravity position on the stick-;fre static stability. The
curves of elevator stick force against airspeed, with the
s-r-in:y tab installed, almost coincide in -.c. lo,.-sc:--ed
ran ,e at the two center-of--ravity positions testey-. The
increased up-elevator deflections required for trim with
the i.,ore-forward center- f-gravit.y positions :r-:;,ult-l in
smaller u-ward defl-',_tions of the tab because of ti.-u- aero-
dyn.wu.ic hin.-_e moment, due to elevator deflection, action
on tIhe tab.

(4) The stick-fixed static lon .itudinal stoiblity
was slightly decreased by the action cf the springy tab,
as sh:)wn by the smaller up-elevator or l-r-er do-n-
el t-:et :.r cc flectic.ns req.1rej :"or ".I: at low, -:-,eds with
the srrinc. tab in operation.









UR CA K-JRFR 1D. L5120


Dynamic Longitudinal Stability

r:.e results of tl.e s.atic-stability-. i rer.ents
indicate. that the airplane with t.he sn.ri.ny tab installed
was stable ..-ith the stick free in all fli.:ht cn;i-t.il.ns.
For co:--.itions in which a large ca'".unt of tic':-fixed
instabilit-r existed, it was c.sidered de3tr.abkl to
investi -ate whether the air-lane with the scrl.i,:y tab
installed would tend to return to its tri.-2 seed if the
seed were chan ed slightly ar.' the c ,:trol stick released.
T-. results of tests made in the cll Binging sliding
cci:1Itions in which h the stick was released at a s-eed
sli htly above the trim s-e-e are 1i1'ei i: figure 14. In
the climbing c.-,nition (fig. lL(a)), the ainlane uid not
tena to return to its trim sne,.?, but .nstelC t,.e s.,eeb
increased slightly at first. : sta"-le vr.ilaton If
stick force with s:me in 'i .s condition (:'... ,(a)) vould
I've a cni a-e in stick force of less than 2 o-w- nis for-
this cl.an.re in trim speed. ",.s amount -,f c'_an-e in stick
force is less than the fritlon in the -lev-.-r cTmtrol
system. T..:e elevator -h-erefore remained. ess.nt.allY fixed
c.urin.n this maneuver and the initial dci-.:r-j-.ce :'r :: the
trP', s-.eed was caused b, the stick-fixed -.iLsta 11 ty in
this fli-.ht con-.ition, S.s'e s11 ht up-el tr.r. '.. tion
occurred near the- end of the .rm.e'uvE. a-.; n*revented' the
speej fr:.i cont'nuilng to increase; in fcact. Tne s3'eed
apparently be.-a.in to decrease sl.-'.htly.

In the -li ing; condit-on (fi-.. 14(b)) t'.e airplane
initially ten-ed to return to its trim S-ee,-. Ti'.at this
state tend':ency was due largely to the ect....n of tiLe
sprlny tab ray be seen rr.- the motion -: t'= elevator
when the stick was released. The airplane also had a
small amount of stick-fixed sta..ility in t..is c.in' Ition
(fig:. 10(a)). S'o:-e 1.-.-: in trUe action of t:ie tob is
indicated in fi'ir lii(b) 'nr may have beL- cursd partly
t v th? small a;.-unt of friction in the tab ..ystea, an'
partly by tht elevator -otion. ,T'e"use t~e airoicir.e as
not in steady flight, the elevator anr lis in t-.-ie tests
did not bear the same relation to aIr'-eed in the
static-stability tests (fiG. 10(a)). 'ie 1-. in the
action of the tab rmray :ive.caused tLv: inr stAility ,-f the
lor,--eriod oscillation shown in this fi-u, e. Thii: sta-
bility of the oscillation fJr the a:"li-. ne ;,-lth the
ori;i.-l 1 ;.: was not investl,:-'ted-.. .ir:.'.e -zr c'l racter-
istics of the l.:n,:-:eriod oscillation hv_ be 1cen .vlL.A?,;i by
previous invest _.ations to have no corri.l ul?-.n ,itlh the









IJACA ARR :T.o. L5120


hand,'.' n qualities of an air-olne, the oscillation shL.wn
in figure 1(oi) is not believed to be objectionable.

The failure of the smrir.-" tab to cu'.-:e the i'.' lane
to ten,'" to return to ts tirr. speed ,-hen disturbed i:
f'liht con.cditi.orns in which the airplane was ver',- unstable
witn stic: fixed, inicati-? t" it this device cannot o:cer-
cc:r:e r deficiency in stic.c-fixe stabilit-v', t l1 i:st ;:ot
with the 3at e a:.cunt -f friction as was '.,r.sent in "t,:
control svstei. during these tests. The r-lots 'd not
cornsLder the cL'rse:! ] st. cs of the airplAi' to 'e satis-
factor:y. f,'r an7 rli1;ht -o -i'Ition in which h it was U.n3st.ble
with st-ic'" fixed, alt-. :i tl:y belie-e.:.' that the c::-tr:l
characteristics .,ere ".r..-,,d the u"ri" .7 tab.

.',re adrvint .-e f t.he -.'"iri. tab is the r- :-.ced
daner ~f' in.''.'rtent :tall:r. Vlith the springy tab in
operation, *- e-"inite :.;.ll f: rce was re:iuired to stall
the airpla:ie ; herea v.ith the criJinal t: ., a la:-e
oush :'rce 'a required t: .-,revent the stall in .>,.i.?er-on
cornJdi t..crs.


O *; ,3 1-' t f d .' I ght

The variati:, i ,a : r stick force ,': srir.- -
tab an.--le wirh- normal acceleration in turns at 196 mil:'s
-7.tr h-ur is shown in figure 15. Comparable cata for the
airp lane with the ori- n~l tab are given in fii,-,e l6.
The soringy tab appeared to have little effect on the
elevator stici- forces in accelerated fl:'i-.. -.r the
s')ringy-tab system, the test results showed a sl'.. tly
lower slope of the curve :. elevator stick force with
normal acceleration at rearward center-of- :-.vity p:c."-
ti:,ns, as may be seen b- conoarli fi 'A.s 15 ,ni 16.
The effect of the ".b on the force -Lr 3 normal accelera-
tion .vw-uld be expected to be greater with the more--":r..-ar,
center-of-.r, .-lty positions because a larger -..:_;e in
el-.vator a ;.-le would 'e r -"' e." to ,':.'. ce a ivon accel-
errati)n and a f-r:-ter ten ency for the tt.b to .1--at down
S,,ul..* exist. The slight friction in the tab system : '-
hive caureO -.. flight measurements to differ frontn the
exoc rte.,i tender.-:,-.









,:CA A.R yD. L5120


TkF- iffs

T '-ie hist -ries of tLke-of;" of trhe i-_.lane ',-ith a
forward center-of-..'Iav'ty -:siscon are i'.n in
fi '.es 17(a) -Ancd (b) for the -orinV-,-t-an_ inst21iati:..'-n
Sn." ;-r the original tab inr.st la.t i *n; rs.'ecti ve 1 The
time history y of a take-off with a redr..ard center-:.f-
grivity positiono n an. the sprin-7-tio nstllatior. is givenn
in fi i. re 17(c). .:lth th'e s:i.n.yv 1 b, t.e ai rpla,-.- v.-as
sai:. t.. -:.-.ibit a tei; -r to :.- i'd a to;,. ': t ':e- .i'.
Several of the pilots stated that -t the start of tihe
take-off the elevator ii.,ved -:..n ant th. i at atn airs:.eed
of about 80 miles Der hour mlove';F. un *-'f its :.wn. acc;,rd and
pulled the airplane off the gro-n ,. The ctL '., :f the
snriirng tab that proci ced this te.n5.-v : ."-: De feen in
figUrres 17(a) and 17(c). At the start "' tle ta;e-.ff
the s : in ;r tab was at its 'r. :L ..::u. up li: i ectl:.n, *:ich
pr a.ce& a down-elevator moveiaent; -t aci t ,J :'.-iles per
hour, the sprin,.,- tab st2-.rted to m:.v.- c.vn ai.ci t'.er'by
permitted the e]..-ator to rove up. r'.!r.-ir' '...f he
elevator stick forces for tlIe spri,:!y-t'": Inst.ll.ation
(fig. 17(a)) with those of the air ^l-.. 1 .lth the original
tab (fi... 17(b)) shows the forces rqi re- :'-r the air-
plane with the sprilin. tab to '- less 3 :.,n [1.)-se f )r the
airplare with the oriIn,~al tab. A.-rc;:l: .atelly one-half
as much rush force was required witi t!:-- 2.rij,y tcb to
lift the tail off the ground althou.-.h t.-e n..c.'.:n--lev, tor
dceflections were greater with hLs -ist.llati.:,.


Trim-Force Ah=an.:,cs

All pilots v.h-, flew the airpln.- .v. it. the springy
tab commented on the Larr,-rently lar ., t:li.-'...rce c'n-ie
v.lth Po.' -er This and other trim-f, -2c c:an,_.e s r com-
.ared in table II with those for th ;.ir::i.lne .iLh the
original tab for speeds of 123 and 1 i llh o'r L"'r.
Th .se data were obt ii red oy tr:'.r inj trA.o ro.:'l ivr first
in the climbing condition .-n .:-kii ; i.cces-ivc c.ianies
in confi duration and then trim:.:, in t. iiniin, conc.i-
tion and .kin, successive h':.Anz.t:s ,'i c:..ifi,.hur:tit n, iith
recor'.-s taken after each Tc:;--. T l- i r r 'euired
to maintain tr'. on clos'Lii the thr'r LCl ..Lth tn- fl.r-s
ur were considerably lar-er wi:h tc- sri: .7n ta s installed
(t .-le IT). T. T'u "- forces reui-r-e.., i. .- e'.cr, -n a pplying
f'ull ._-r with the fla-s down were ".nall=r ,.' t. the
.:r]u v tab install,-7 The amount -i :r'.:.,-t L .'efle tiCon
for rri is _*,ter Lv the amount .-qu.i red tc ..f.set the









ITACA ARR :Io. L5T20


effect of the springy tab at trirn 2 ee. The mnnim; u
speed at which h the airolane with thie sprirn.gy t'o. cc..ild be
trimmed, .when the r:aax.irmu.n tri'n-t.ab defle-tticr. is us-: In
the landin. condition (fig. lli'a ) at c-ither center-.-,f-
Cravi.ty .,osi tion and inP the ar-ac co ndi 7 tic. n ."i 11ib))
at the fr-r'ard center-.f-gor.vi-ty _o si ticion, as t.-.ther
high, particularlyy in the iani:L i c : titi?:. As s'.o.vn in
figure ll(a), a ,:.rce c.f 22 co:uns 3u repaired for trim
in t-:> lanr lng c ntit io-n at. 1,3 *.ile 3 .-er *-- ur, s:. t._
trin forces sh,.;n in t c le II f.or :;, n c-a.: 1' tiiin d: n...t
correspond to tr-r-f r',e chanlx es fr-.. a tri.'. 'e! c o, li ia.
The da.ta ivc-n fo'.r the airol.-.ne Ai t t.e :ri'iinal tab
trima.:ed at ICO ..i' les oer h7ur in the ar, '1. :., cc.n:diLtt i.n
we re o- tai ned ov inter' lat'. : fr.. '.. .11 ish = .t a i:'r
an air-lane -f t ie s:.. ty-e as t.c u ,f th.:. tinve tig ati n
becauc ?e -at'a -oDr he ir. -1 ne '.i i t;-i, criminal t ac .:e
not avai'.'dlable.


C ..'ari ', a -f -:ri n.." '.,r : h their Le':...cEs

r.. '.,.'in t c.-:- r. e 2.ta ili t

In a & -r..ussi-n of the zs r .i._ t:'. it .i ht b"e
anr r' ate t c. ',r re it .'.it. :t. r -.ices .sec L:
i:-'rv.e sti ck-fre stat c lo.acit' ir.al t r.ilit 'ne
..c-vice t' r t.is -, r..:,3s s e .'- iz L i '-L ,.,:tr'-1
s3:.:te I *--.at ...rt.. .-.:. ient i:'Lich ':-e Ls r.- .*--iress the
elevator, Alth -u h this '' ev 'ce c-ill. J trh:' t:', e ill
irncresc. the stick-free stability, it has disadvantages:
A *ull :frce must be exerted by the pilot to hold the
sick bca-ck while taxying and the high push forces that
r1-, be rcquirc.,d in high-speed flight would result in
excessi.'e accelerations if the stie: ,were rele.,s'd in an
.ut-o.f-tri, dive. The same disa:1- ...t-1 jes a.-,ly to a o:.b-
w-lht ecce.' that it produces an a:'.tional incr'e-e of
stick force with an increase in normal acceleration, ,.,'ii.ch
w.':',ld r.rve'.t exess ^i ve accelerations in this :maneuver.
Tnen =rinr.-7 t:;b ill not c. -- .': r-cabe pull force
while t.:~in-: : :-...e the dy-. ic :-3sure on the tab at
t:-Z-i-in2 -n-eels is low. In -A'i1tion, the springy t b -.11
r.t c-use lr .-.e uni.T forces at hi :, s:reed because it will
then be defleccd .: its r:'utr'.1 position.

Anth-,r var-.vnit-"i.e of the -:.in tab over the -:ng'.ee
?'r bct.weilht is tna.t tht stick-f-r e characteristics ,',
be djLuIsted t: -.tain l:.''-t .;,- i"--- r el' "'.'tor -tick-
fo.rce va-ria.titon with so:ec,. This adj'..tmer.t may ct












acco::'li shed by chairing the a.trodyna..ic char-Acteristics
Df the tab, the spr .nr .icrient at zero tab *:.e fl ctit.'n, and
the variation of the mf.:ient e-..erte.. by the s ')rinr- with
zab .ef'lectic'n. A rce incre:-,en-t -of alir. st any valie
can be an"lied at .Any riart of the need ran',e of tnc air-
plane. The variat -r. of hinge :ro .Ce Lnt i.th *.e'leczion fr
the initial spring.j-tab ccnfi,:.Lrition is s.o).va i n fie.gure I1.
The static lov,'itui'nal stability crc, -i-cter13tics Af the
airrl:, ne -ith the initial snrn y- t:-,b c :i' i'ra-tisn Peftre
the chnarnes i-,icated .on ...-e L. iere nmi e are s.:,wn in
ft ;ure 19. A co'. s r .,'rs n f .i re 1, '. tn fl,:ure a).
shows the wi. 1e variL t L: f el .-v tr stic:-f:t..ce c r rac-
teristics obtu?-ned .itA i the S-:,'_ tab f.ri t .e cnanLe in
hi..e momentt between th-it a -. *_, li- u. e 1,' .;. C.1 t
s?' .m in fi ,a 6, It -..-.ul1 be a t.d tcr.t i ar.e
increase in stic'-:-fL-- sta:.i l.Lty :Lv th' .:,.,-s Med rane,
where adverse effects "- c..-r are ,r..lly rt.,test, may
be obtained without ._re tl -' .c .:._. th,- st.: ilicy at
hbi.h.cr S )ceIs by th-: t s .... I c.ar I :n -. s '. i.i.i',ent
with t-;-,- deflection in .l ic-. t.:hc sri ng iT /n-' thnit tends
to nove the t.b .p.;-Jrc L. cr- e.s. w ,- th. lr .er u --.eab
deflections.

_e.' ,se a -,rIr.,'y t.:L ...-y be i n 6 t : acivist the
control-,?-rce variant' ri .:th -.r,, ..'ithia .i.2 li,.its, it
can be usea on the ru6c,, r i ilerr-rn2 t -climi.ln.-te
unj-lirable trim-f.:rce r --.,'..p ".itfln iO.e,.


"':.CLU ''T.'S


r 1" flizzit tests t3 ..eten..ine the er z :f a
spnrimn-lo:dF>.F cTab :.n ti-~i- l-.t.i ti, l l :ta ilit:' ch ric-
teristics of a lwv-''ng sc:ut I':fbrer, tle llc.ing con-
clus:ons were reached:

1. Compared wit;" th- ri .:t1 tab .instai -T.i :,n the
spri:],. y tab increased the utic'c-free st 'L.!it- in 11
flijh1 conditions aq :I..-U :este?.' .7 t.h l rU er ,'i', tive
slYes of the curves e le:'. tr stick: fo'ce al...ln3t air-
sT" .. In the cli :' i.n c..f : :it0'1 1 : r :r.' i.r'd c atc.r-
of-,-ra-.vity position a 2... itl u in ..h..:h rte -irpl:.ne
with the uorl. ;:>. tn sh:.;,cd s t c,:-'z ic ins t'ti ty
throu 1. ,ut the spe.-i i -.n e *.u l :1.-e. I .,i t.h e c-nringy
tab exhibited satis:'ct :.ry Itj- :-x ..;a \'r-iat l n 'i. i.


i.,CI \i l*:. LM1IL








NACA ARR 4o. L5120


2. The pilots did no consi,'er the characteristics
of the airplane to be satisfactory for an;. flight c.::'i-
tlin inr which 5t was unstable with stick fixed, alt.-,ugh
the-y believed that the c_'ntr:.l characteristics were
impr.:.ved by the springy tab.

5. The springy,, tab reduced the danger of ia rv& -'tent
stalling because of the definite pull i.:rce required to
stall the airplane .,itlh po-:'er Dn.

l.. The sprint-y tub .nay be used to provide almost any
desired variation f elevar'r 3Lic.c force with siped by
adjusting the tab hinge-inmrrient characteristics and the
variation of sprig mii.ent with tai deflection.

5. The springy tub tenried to reach maximum deflection
at a seed near the stallln7 sEeed for all flight condi-
tions clespite the variati:n of stalling speed with flight
condition.

6. The springy tco reduced Lhe effect of center-Df-
gravity positiD on stick-free static stability.

7. The stick:-fi ed sta-c l :-git & nal stability was
slightly decreased by the a.cti n of zte springy tab.

8. The springy tab had little effect on the elevator
stick forces in accelerated flight.

9. Pull forces required to maintain trin on closing
the throttle with flaps up were considerably larger with
the soringy tab installed than with the ori finall configu-
ration. The push forces required, however, on applying
full po'w'er aith flaps down were smaller ;.ith the sprin,-j;
tab installed.

10. :h r -pringy tab would prv-:ide stick-free static
stability without requiring a pull force to hold the
stick back ..h- le t..:-.y_-., as wo-1 e required the
b..e e arnd rhe be'bweight.


L e..l ev' emorial Aeronautical T' .rratory
_'tional Advisor- Comnittee for Aeronautics
.... 'y i eid, V .









12 NACP ARR No. L.,1 0



,0 0 T .0
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NACA ARR No. L5120


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NACA ARR No. L5I20 Fig. 2





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NACA ARR No. L5120


0 4

S'a

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Fig. 3










NACA ARR No. L5120 Fig. 4























En





bo

id







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NACA ARR No. L5120


















01

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tbo
-I





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.-.-'" "i'!" ". -




: i ii:C,







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Fig. 5








NACA ARR No. L5120F


NATIONAL ADVISORY
COMMITTEE FOI AERONAUTICS


) --- ---- ---- ---- ---- ---- ---- ---- ---- ----______________
0 4 8 /e /6 0
Up
Springy-tab angle, deg







Figure 6.- Variation of springy-tab hinge moment with
springy-tab angle (as measured on the ground).


Fig. 6







NACA ARR No. L5120


3Q


20










0-
/O-
/o ----- --









NATIONAL ADVISORY
COMMITTEE FOR AERONAUTICS
0


8 4 0 4 8 12


Forward


Back


Stick position, in.





Figure 7.- Variation of elevator anble, n.easured from
trne stabilizer, with stick position for the test
ai rplane.


Fig. 7








NACA ARR No. L5120 Fig. 8






us


La
04
tPrr 0 z





4.$ 4 ,-
S () _o
0






C)O
S00 C




qCIbO
o a> ot







0 -0







0 0




LI I U .o A? D1







NACA ARR No. L5I20.


/C Max. up deflection, 2?S



043 "-- __ Q-- -B


c.g. position Elevator
(percent M.A.C.' trim tart


26.0
e08


2. 90, ose iup
0.1", nose up


Spot Continuous
runs runs
c0 cf
a rf


--- Ll ax down defl ec L i on,

T1


/60


200


240


280


,'orret pervi.;e indic ated airspeed, mpn

(a) Airplane itn. spring y ta r, instal led on elevator.
Figure 9.- Stat 12 longituirinal statI11t it' characterist ics in
the cl irmrt.ing cond it i on .


J1 1111


FTT-kZ4-F----


'-I


03
P1.


'-4
(U
'-4
cd
;q
0
(U
,-4 0


IIy


/0


20




/0




0


' \ NATIONAL ADVISORY
% .X.. 1 COMMITTEE FOR AERONAUTICS
,- -- -


Fig. 9a


3









NACA ARR No. L5120


.0



r'
ca
P4-

0p.
0)

r-.1 I
c.J


31.4
24.5




Max. up deflection, 31


Spot Continuous
runs runs


0
1.4o, nose down o 6a.
2.u ,nose up o Ef


10-- --- -- -- -- ---- -- --





0-- -- -- -







NATIONAL ADVISORY
COMMITTEE FOR AERONAUTICS

Max. down deflection, 210
Q00/


200


240


Correct service indicated airspeed, mph



(b) A'irplane with original tab on elevator locked.
Figure 9.- Concluoed.


Fig. 9b


c.g. position Elevator
(percent M.A.C.) trim tab


20


Na

bo
P
01



14
0)


60 120 /60


320


3
3

j







NACA ARR No. L5120


40 L c.g. position Elevator Spot Continuous L|_J
(percent M.A.C) trim tab runs runs
o
31.7 5.7 ,nose up o d
Q 1 2b.6 9.2 ,nose up o Of

/0 Max. up deflection, 28



-n .


20
:R


/20 /60 200 240 280
Correct service indicated airspeed, mph


(a) Airplane with springy tab installed on elevator.
Figure 10.- Static longitudinal stability characteristics in
the gliding condition.


Fig. lOa








NACA ARR No. L5120


c.g. position Elevator Spot Continuous
(percent M.A.C.) trim tab runs runs


30.9
24.0


)r----,- Max.


0
0.90,nose up
5.0 ,nose up


o d
O EU


320


Correct service indicated airspeed, mph


(b) Airplane with original
Figure 10.- Concluded.


tab on elevator locked.


!


Fig. 10b







Fig. lla,b


0



2(
:3
P.
20


b3
O O -



OO -=
S/-


0



Cj








r-.

0 -





6


____ ______- ---___-


c.g. position Elevator
__(percent M.A.C.) trim tab

31. 15.0 nose
26.2 15.2 ,nose
S 1.1 12.90 nose
S6.7 15.0 nose


100


ion, 28


Spot Continuous
runs runs


/40


/00


Correct service indicated airspeed, mph


(a) Landing condition;
springy tab installed
on elevator.


(b) Approach condition;
springy tab installed
on elevator.


Figure 11.- Static longitudinal characteristics.


NACA ARR No. L5120


/40








NACA ARR No. L5120


s- 2
,-I


0
'4-
., 0
o
4a


>m
W 2(C
,-4
I.*-


c.g. position Elevator
(percent M.A.C.) trim Lab


26.2
25.7


15.C', nose up
S.7,nose up


0
-Max. up deflection, 28


Spot Continuous
runs runs


A s


/00


Correct service indicated airspeed, mph


(c) Landing condition;
original tab on
elevator locked.


(d) Approach condition;
original tab on
elevator locked.


Figure 11.- Concluded.


NATIONAL ADVISORY
CONNITTEE FOR AERONAUTICS


60 /00 40


140


"BIC


Fig. llc,d







NACA ARR No. L5120


Elevator
) trim tab

9.0o,nose up
12.5 ,nose up


Spot
runs


Continuous
runs

Cu


--Max. down deflection, 150


NATIONAL ADVISORY
COMMITTEE FOR AERONAUTICS

60 /00 /40
Correct service indicated airspeed, mph

(a) Airplane with springy tab installed on elevator.
Figure 12.- Static longitudinal stability characteristics in
the wave-off condition.


30.8
26.5


r- Max.


Fig. 12a








NACA ARR No. L5120


c.g. position Elevator
(percent M.A.C.) trim tab


25.6


4.b ,nose up


Spot Continuous
runs runs

El]


NATIONAL ADVISORY
COMMITTEE FOR AERONAUTICS
o
n, 15
-i
/60
airspeed, mph


(b) Airplane with original tab on elevator locked.
Figure 12.- Concluded.


40 80 120
Correct service indicated


Fig. 12b







NACA ARR No. L5120


c.g. position Elevator
(percent M.A.C.) trim tab


32.0
31.7
31. 4
30.9


2.qO, nose
5.70,nose
1.4 ,nose
0.9O, nose


Spot Continuous
runs runs


up
up
down
up


Elevator with springy
tab installed
Elevator with original
tab locked


20
V ^NATIONAL ADVISORY
COMMITTEE FOI AERONAUTICS






(b) Gliding condition .
20
L --


I20


/60


200


240


Correct service indicated airspeed, mph

Figure 13.- Comparison of stick-free static longitudinal
stability characters ic-s of airplane with springy tab
installed and of airplane with original tab locked.


320


Fig. 13










NACA ARR No. L5120 Pig. 14a



IC

















M 10
,' I I

I f l I / - -
= /a0.1 Ia, i'.M


C)


0


-0 &.


-0J


aJ


01

I I-

o -- -- -- -- -


NATIONAL ADVISORY
CONNITTEE F1 AEMONAUTICS
I- .

0 J. .

a, 140

S- 0 8 6 24 32 40 48 56
Time, sec

S1 l I i rg ri i. or,; center of cira'itj ai. 30.3
t r,r aer.-jr.i. --'nor r g, tab
FLgure I1. 7".e r.,ft:r. f ,rl>tion following stick release
t .-,r -I slightly above trim.







NACA ARR No. L5120


9


Fig. 14b








NACA ARR No. L5120


0"




c') ia


I NATIONAL ADVISORY
I _COMMITTEE FOR AERONAUTICS

0 \ 2 3 4




Fio.re .. .. :.?7 .: r i; -. r .r ,

rr.s a-. 2 -.ileo :- r .".cur. -: r w :. -
scro: ;:" "sr in.s.al :" .n e-eva::r.


Fig. 15







NACA ARR No. L5I20


c.g. position Elevator
(percent M.A.C.)trim tab


30.0
25.7


- 0.2 nose down
1. 7,nose up


0 / 2 3 4 5
Normal acceleration, g


Figure 16.- Variation of elevator stick force.with
normal acceleration in turns at 196 miles per
hour. Airplane with original tab on elevator
locked.


Fig. 16









NACA ARR No. L5120


Fig. 17a


0














0-














2O





120
10 -- / -- -


























NATIONAL ADVISORY
COMMITTEE FOR AERONAUTICS
__ T--
,r-,-- --I-- -]---
4 -
NATINALADVSOA
CONMT-- -FDA -- --IC


Ir
'-C


-;4 32


(7.- r. 'r r v i : I-' -.. : r- [ r n- r ,-, L r -
. I :-. : -r'. r [ r r 'ir
u. I r r. I r F









Fig. 17b


NACA ARR No. L5120


S20


0 8 16 24 32
T e 5


rn c. C r, i, t I 2 lev ror-lrir-t. b .-e rin ,
I' r ir ne ? rr. ori inal t lat .:n Al v t.r
I .I' e .
FiE.,r ',-'. ~'"r, it Lead.


c 10






20
0 O



0




0 0


--_
























/











----





NAT IONAL ADVISORY
COMMITTEE FOR AERONAUTICS










NACA ARR No. L5120


20



























2C
0-
0----

- --------






















80
-----













C \
2 -------^--^-__--






I? -


80--- ---- -- -- -- -



4C-
NATIONAL ADVISORY
COMMITTEE FM AEONIIAUTICS


I I --


8 16 24 32
T i w'c, ne c


40 48 56


Icj CenLT.r of gr3vilt at -.1 Derert rLean aPr,,-
1yr. m c.ord ;e evat or-trim-lac. e't. ing,
.Il (nose ur.) i airpflane w tr. springl ti,
in.E.al lea cri ei leva or.
Figure 17.- Concludea.


Fig. 17c







NACA ARR No. L5120


(


03 2


Springy-tab angle, deg


Figure 18.- Variation of springy-tab hinge moment with
springy-tab angle as measured on the ground for the
initial springy-tab configuration.


20


Fig. 18


C- --i-i-i- --- -- ---- --




4------ -- -






5---- -- --7





















NATIONAL ADVISORY
COMMITTEE FOR AERONAUTICS


--- --- -- --- -- -- -- -


0








NACA ARR No. L5120





,-I


"b o
. -Max. up deflection, 28
o 0-






----- Max. down deflection, 150


c- .g. position Elevator
(percent M.A.C.)trim tab


32.1


2.3 ,nose up


Spot Continuous -
runs runs
0 d -


NATIONAL ADVISORY
CONNITTEE FOR AERON0UtTICS


-I- (--- --- -- n--


160


200


240


280


Correct service indicated airspeed, mph


Figure 19.- Static longitudinal stability characteristics
in the climbing condition with the initial springy-tab
configurat ion.


Fig. 19


OL
8C


01


0




I





























































I







ERSI1 O R


UNt.'ERSITY OF FLORIDA
DOCUMENTS DEPARTMENT
120 MvARSTON SCIENCE LIBRARY
P.O. BOX 117011
GAINESVILLE, FL 32611-7011 USA


k