Use of variable-ratio geared tabs to improve stick-force characteristics in turning flight

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Material Information

Title:
Use of variable-ratio geared tabs to improve stick-force characteristics in turning flight
Alternate Title:
NACA wartime reports
Physical Description:
9, 2 p. : ill. ; 28 cm.
Language:
English
Creator:
Kleckner, Harold F
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:
Airplanes, Military   ( lcsh )
Elevators (Airplanes)   ( lcsh )
Aerodynamics -- Research   ( lcsh )
Genre:
federal government publication   ( marcgt )
bibliography   ( marcgt )
technical report   ( marcgt )
non-fiction   ( marcgt )

Notes

Summary:
Summary: In flight tests of an experimental elevator with geared tabs, a cockpit control over the tab gear ratio was found to be satisfactory for adjusting the stick force per g in turning flight according to the pilot's preference. This type of control appears to have application for increasing the center-of-gravity range for satisfactory stick forces in turning flight. Sample calculations made for a fighter airplane indicated that satisfactory stick forces in turning flight can be obtained for any center-of-gravity position at which the elevator control meets other requirements.
Bibliography:
Includes bibliographic references (p. 8).
Statement of Responsibility:
by Harold F. Kleckner.
General Note:
"Report no. L-85."
General Note:
"Originally issued October 1945 as Restricted Bulletin L5I05."
General Note:
"Report date October 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 - 003633525
oclc - 71753496
sobekcm - AA00006265_00001
System ID:
AA00006265:00001

Full Text

M/AU- Z


RB No. L5105


NATIONAL ADVISORY COMMITTEE FOR AERONAUTICS





WARl TIME REPORT
ORIGINALLY ISSUED
October 1945 as
Restricted Bulletin L5I05

USE OF VARIABLE-RATIO GEARED TABS TO IMPROVE STICK-FORCE
CHARACTERISTICS IN TURNIWN FLICOE
By Harold F. Kleckner

Langley Memorial Aeronautical Laboratory
Langley Field, Va.


NA.d


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 85


DOCUMENTS DEPARTMENT


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I:,CA B 3No. L5I05

NATIONAL ADVISORY COrFITTEE FOR AEROIJATTICS


RESTRICTED BULLETIN

IUTE OF VARIABLE-RATIO GE.,FT.I TABS TO II'PRCVE STICK-:'O.RoE

CHARACTERISTICS IN TjiIT:;G FLIGHT

By Harold F. Kle&c:ner





In flight tests of an experimental elevator with
geared tabs, a cockpit control over the tab gear ratio
was found to be satisfactory for adjusting the stick
force per g in turning flight according to the pilot's
preference. This type of control anpears to have appli-
cation for incr:-asing the center-of-gravity range for
.satisfactory stick forces in turning flight. Sample cal-
culations made for a fighter airplane indicate that sat-
isfactory stick forces in turning flight can be obtained
for any center-of-gravity positionn at which :.he elevator
control meets other requirements.


I .':T ,;CDt CT I O!i


Because of tl-.e increase in eiglt. and in altitude
range, 3st: recent airplanes meet A.rm- and Ui ',vy scecifi-
cations for satisfactnry sticLc forces in turning flight
for -,nly a limited center-of-gravity range. .rttemprts
have been n-i-:oe to o'.ovide satisfactory st'ck f r-ces f or
an increased center-of-gravity rrange by the use cf sprting-
tab elevators and by u reduction in the variation of ele-
vator thing. moment with elevator deflection Ch.-. If any
appreciable increase in center-f-gravi ty raCnge is
obtained by either of these mcthod.s, it is then necessary
to add a bobweicht or to make the va-iation of elevator
hinge mniment with tail angle of Ltt-ack Cha positivL in
order to increase light stick forces in turns at normal
center-of-gravity positions. Arrangements of &his kind
have introduced undesirable control feel in rapid
maneuvers and poor control characteristics irn rough air.
With spring tabs, in addition, difficulty in preventing







NACn R3 I'No. L5I05


flutter and in maintaining the stick force per g suffi-
ciently constant throughout the speed range may be
enc entered.

A methDd is suggested for increasing the center-of-
gravity range for satisfactory stick forces in turning
flight by the use of geared tabs and a cockpit control
over the gear ratio. Flight tsts have been made with an
arrangement of this kind, and pilots' opinions of such a
c-oncrol are no' available.


T7' BOLS


be elevator span, feet

c wing. mean aerodynanuic chord, feet

Ce elevator root-miean-suare chsrd, feet

Ch variation of elevator hinge moment with elevator
deflection h


Cha variation of elevator hinge moment with tail angle
of attack (-6\


Ch elevator hinze-n.Lo.nt coefficient


H hinge r.o:nent foct-pcunds

q dynamic pressure, pounds per square foot

CLT t il lift coefficient

(CLa) tail lift-curve slone, per r-nian _T)


r\ ratLo of stick m!-er.ent to elevator deflection,
feet ser radian








IJACA RB No. L5I05


LT tail length, distance from center-of-gr-vity
position to elevator hinge: line, feet

ST horizontal-tail area (exclusive of area through
fuselage), square feet

W airplane weight, pounds

aT tail angle of attack, radians

6e elevator deflection (positive 'Dwn), degrees

6t tab deflection (positive downn, degrees

6t/6e tab gear ratio


T elevator effectiveness factor
6CLTb/aT


FLIGHT TESTS


A cockpit control over the tab gear ratio was used
urging fli ht tesr.z of an exp:-ri:ental all.-movablR h.ori-
zontal bail on a fighter airplane. '.4ith the all-movable
tail the tabs were used as geared unb,--lancing tabs, und
ratios of tab deflection to v-levat'r deflection 6t/6e
of 0.6 to 1.0 were available. -t thL center-of-ravi ty
location tested, the corresponding stick force per g in
turning flight varied approximately from 6 to 10 pounds
at an altitude of 5000 feet.

The control -.vas found to be satisfactory for adjusting
the stick force per g to the pilot's preference. The
pilots preferred a force of about K pounds per g in the
present flights, which did not involve high accelerations.
The pilots reacted favorably to the control and did not
think it confusing in any way. It is believed that, after
elementary education in the function of the control,
Dilots W'ould use it as instinctively as they use the
trimming controls.








4 IriACA RB i-o. L5105
r
TYPICAL AFFLICATION i'D DI CUSSIOI'


In the f liht tests of the l!l-riovable tail v. ith
-.triable-ratio ^ear,-ed tabs, the control characteristics
could not be determined: over ? l-rge center-of-gravity
'age. In oi-der to illustrate the increased range for
which h sti factory ticti' forces In turns can be obtained,
therefore., calcuations have been made for a typical
fighter airplane .ith co:.n'entioral elevators. The char-
ac eristics of this asiol-ane are given in table I. The
variation -f stic", force per g 'ith center-of-g .ravity
position 'ris calculated from the equation


.Stick force pfer g rc__ _bece 2
Percent change in c. *. position _T(CL, TT


In t-is euatioLnn th.e hI'.ge *-,--Lents of the tab are neg-
1 e a t e I .

Osalculations .'%ere -de for tw.o sets of values of the
elevator hinge-rr..m'.-ijnt coefficients Ch- and CG-h, For
the first exariple it was assur:.-ed that Ci:, = 0 and
C-6 = -0.002. T'ie value of Ch-a 0 nay be obtained in
practice by a suitable choice of the elevator contours.
For the second example it was asstujed that Ch. = -0.001
and Cha = -0.00550 these values are typical of those
obtained on eleva -t rs of several current fighter air-
l anes. For both ct.am-Cpies the elevator hinge-momrent coef-
ficient duie to tab deflection vwas assu:.-ed to be -0.0055;
values close to -0D.0025 have been obtained in practice
with tabs the saTme size as those of the airplane con-
si3d.:-red for the calculati.:.ns.

The curves sh:'..'ing the variationn of stick force
per g *xith center-of-gravit.y positionn for the two examples
are presented in fL.urs 1. The range of satisfactory
stick forces 1i indicated in fiiure' 1 in accordance with
the requirements of reference 1.. T!ie locations of the
stick-fixed neutral point and the stick-fixed maneuver
points were estimated from fli.;ht-test data on an air-
plane of this type. The stick-fixed neutral point is the
center-of-gravity position at which the variation of ele-
vator angle Lith airplane lift coefficient is zero in








NACA R3 1To. L5105 5


straight flight. The stick-fi::ed maneuver p.int is the
center-of-grLavity position at which the variation of ele-
vator angle with airplane lift coefficient is zero in
turning flight.

Figure 1 shows that a greatly increased center-of-
gravity range for satisfactory stick forces in turning
flight is possible with a variable-ratio geared tab con-
trol. In addition the control permits the pilot to adjust
the force to his own preference at any intermediate center-
of-gravity position. The center-of-gravity range can be
extended forward any arbitrary amount if sufficient tab
power and elevator balance are provided. The most forward
center-of-gravity position then .:ill be determinedd not by
limits on stick forces in turning flight but by other con-
siderations, such as the elevator electionin available to
meet lan'.ing requirements. Figure 1 also shows that the
most rearward center-of-gravity position for whichh the
variable-ratio tab control can be used to obtain satis-
factory stick forces in turning flight is somewhat forward
of the stick-fixed maneuver o:int. T:-is limit will be at
least as far rearward as the limit set by the stick-free
or stick-fixed neutral points. With a control over the
gaar ratio of geared elevator tabs, therefore, satisfactory
stick-: forces in .urninc flight c-)uld be provided for any
centor-of-gravity position ac which h the elevator control
would meet 'other requirerrents.

'.hen C!h is negative, a cnridOtion of stick-free
instabt-lity in turns -'.'ould be obtained if the control over
the tab gear rati.io were used in the oDsition to give light
stick forces at a rearvward center-of-gravity position: for
exwcple, if tab gear ratio of -0.5 (fig. 1(')) were used
at 32 -ercent mean aerocyna!:ic chord. This condition
would be dangerous in take-off anda although an item could
be included in the check-off list for take-off to have the
control in position to give heavy stick forces, the possi-
bility of this condition should be avoided by the use of
an elevator with Cha = 0.

A. second advantage is gained if an elevator *,ith
Cha = 0 is used. Then Cha is negative, larger negative
values of Ch. are required to obtain sufficiently heavy
stick forces at rearward center-of-gravity positions and
larger tab gecr ratios or larger tabs are required to
provide a given increase in center-of-gravity range.
(Compare figs. l(a) and (b).)








IACA RB Ho. L5105


It has recently been found that zero is the aooproxi-
mate limit to which Cha can be changed in the positive
direction when Ch6 is small unless some auxiliary device
is used to eliminate the undesirable control feel in rapid
maneuvers. Elevators with Cha = 0 have been found sat-
isfactory \vhen Chn was sufficient to give 5 to E pounds
per g. An elevator with Ch. = 0 and with Ch- large
enough to give only 2 or 5 pounds per g would probably
give unco:'fortaoly light stick force .
;:hen the tab ratio is changed, the stick-free sta-
bility in straight flight (variation of stick force witn
airsr-eed) .'ill change as well as the stick force per g in
tvrning flight. If th, variable-ratio tab control is used
to maintain an essentially c-nstat-t value of stick force
per g through the center-of-gravity range, more nearly
constant stick-free stability in strU-i.hEt flight through
the center-of-gravity ranle will result than is obtained
with conventional elevators.

In addition to improving stick-force characteristics
in turning flight, a variable-ratio geared tab control
may be useful in coinpens-ting for variations in Cha
and Ch,5 due to mranufacturin. tolerances andc other
factors that prevent accurate prediction of hinge-rrmoi'ent
characteristics.


DESIG:; COI'SIDERLTIONS


TEb cwv*er greater than is n.or Cral"y proviJed for
trvmnjg 'a:t,- be necessary if t-:i elevator t-abs are
emrpl o!~c both as geared tabs an.d as trim tabs. If a
reasonable air.ounL of elevator balance is )rn.viJed,
ho'.,.evr,. the necessary tab gear ratio-: will t- sijall and
the cidded dem.anit for t.b Do':.:er will net be difficultl t to
meet. The required cab ratios may be reduced by pro-
viding sufficient elevator balance to alljw the tabs to
be used as unbalancing tabs for r(-ar-vard center-of-gravity
-ositions and as balancing tabs for forward center-of-
gravity posi tions. Tab power additional to ti-at normally provided
may also be necessary to trim the stick force in the landing









NACA RB No. L5I05


approach if the center-of-gravity range is extended for-
ward. The amount of additional tab power for this purpose
will of course depend orn the amount of elevator unbalance
and the size of the tabs, but estimates from flight-test
data indicate that a tab reflection of approximately 10
per percent center-of-gravity movement would be needed for
the elevators assumed in the first example.

In order to avoid large deviations from linearity in
the curves of elevator hin6e moment with elevator deflec-
tion at large elevator deflections, the maxiir.~m tab deflec-
tions should be limited to reasonable values, probably not
greater than 20. A small-chord tab of large span is, in
general, preferable to a large-chord tab of small span.

The job of providing a cockpit control cver the tab
gear ratio is structurally and mechanically similar to
that of providing trim-tab control. A diagrammatic sketch
of an installation that would provide variable tab gear
ratios and tab movement for trimming is shown as figure 2.
Definite stcps should be provided to limit the adjustment
of the tab gear ratio to the amount needed to give satis-
factory stick forces over the center-of-gravity range that
is to be used. If stops are not provided, a condition
of zero or positive Chg might be obtained. This condi-
tion, of course, must be avoided.


CIiCiCUDING RE.,.ARKS


In flight tests a coc;:oit control over the gear ratio
of a geared elevator tab was found to be satisfactory for
adjusting the stick force per g in turning flight according
to the pilot's reference. This type of control appears
to have application for increasing the center-of-gravity
range for satisfactory sticl: forces in turning flight.
Sale calculations made for a fighter airplane indicte
that satisfactory stick forces in turning flight can be
o'bt, inpe for any center-of-..rcvity -mositL _n at .'hi ch the
elevaror c-ntrol -.cet3 -ther requi--:,.?.ts.


Lanley t'emorial neronautic-il Labor'atory
nationall Xdviscry C'-m.nittee for ,eronautics
Langley Field, Va.








c NACA RB Ho. L5105


RJ'EREI-CE

1. Anon.. Stability and Control Ch'aracteristics of Air-
olanes. AAF Specif'cation o. R-18ai-A, April 7,
1945.








I!ACA RB T). L5105


TABLE I


AIRPLAITE r{AXRACTERISTIC.3 USED If CALCULATIONS


Airplane weight, po'mncs . .

V~iin; area, square feet . .

Wing span, feet . .

.'.ing mean aer) yn:anic chord, feet .

Tail length, feet . .

Horizontal-tail area, sj-Ure feet .

Elevator area, square feet .

Elevator span, feet . .

Elevator root-mean-square chard, feet .

Tab span, feet . .

Tab chord, foot .. . ..

Tail lift-curve slope, (CL a) per rardan


* 11,000

* 33554

S. 4. 2.8

. 8.12

. 21.4

. 69.5

. .25.8

. 18.5

. 1.46

S. 4.85

. 0.42

. 3-.7


Elevator effectiveness factor. T

Elevator deflection, degrees


Ratio .of stick rm:ve-.ent to elevator tLeflection,
feet per rar'iian . .


. 0.5


. 1.72


NArIO"iL t.DVISORY
CO!'.ITTITEE FOR AEREOiAUTICS









































































































































































































































































.1.







NACA RB No. L5105


Fig. la,b


;st/ = 0 --Sh ck-flked
neutral point
, __ \ Aihe __ __
4/4 =/ -0 o. 3Y ---
-3. ,000
8 I
__ ____ ____ __ ^__ ,ey/a of
20, 00 0 \safisfactory
4 stfck forces
4. .


SStick f/red '
maneever points7


4 /A /6 20 24 26 32 36 40


Center-o/-y r ,/yl position percent AM. 4C.


(a) C = 0; Ch a= -0.002.


NATIONAL ADVISORY
COMMITTEE FOR AERONAUTICS


Center-of-9ravity position percent M.A.C.
(b) Ch = -0.001; Ch = -0.0035.
Figure 1. Variation cif stick force per g wit. riter-of-gravity
position for a typical fighter ai: .-e.


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Fig. 2 NACA RB No. L5105






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