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• '"1"llh,isi..,;S!;ijäii:iiiiaSi .'i;i,iii!':iii.|ii. ^

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APR No. 3H31

I

ATI No^S NATIONAL ADVISORY COMMITTEE* *§*£ AERONAUTICS

WARTIME REPORT ORIGINALLY ISSUED

August 19^3 a» Advance Festrlcted Report 3H3I

THE EFFECT OF MASS DI3TPIBUTION OH THE LATERAL STABILITY

AND CONTROL CHARACTERISTICS OF AN AIRPLANE AS DETERMINED

BY TESTS OF A MODEL IN THE FPEE-FLICHT TUNNEL

By John P. Campbell and Charles L. Se&cord, Jr.

Langley Memorial Aeronautical Laboratory Langley Field, 7a.

Air Decvtr.wtr DM*», T-2 AMC, WrijM HM

MicrofiU it».

MAC A WASHINGTON

NACA WARTIME REPORTS are reprints of papers originally Issued tu provide rapid distribution of advance research results to an authorized group requiring them tor 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 - 388

KATIOHAt ADVISORY COMMITTEE FOR AERONAUTICS

ADVA:JC3 FTCSTRTCrSD R3P0F.T

\

¥•••*

THE EFFECT OF KA355 DrST-tlBUTIOlT Oil ?IiE LATEHAL STiiSILITY

AND CONTilOL CHAnACTHraSTICS OF AS AIRPLAKE AS DirfSiiHIIJED

BY TESTS CF A IJOE3L IK THE FREE-FLIGHT TUITHEL

By John P. Campbell and Charles L. Seacord, Jr.

SUMMARY

The offsets of iass distribution on lateral stability

and control characteristics of an airplane have been deter-

mined by flight tests of a nodel in the NACA free-flight

tunnel. In the investigation,'the rolling and yawing momenta

of inortia were increased from norrcal values to vr.lues up to

five times nonnal. For each ironent-of-inertia condition,

combinations of dihedral and vertical-tail area representing

a variety of airplane configurations wore tooted.

The results of the flight terts of the model v/ere. cor-

related with calculated stability and control characteristics

and, in general, good agreement was obtained./ The tests

showed the following effects of increased rolling and yawing

»orients of inertia: no appreciable change in 3T/irtil sta-_

bility; reductions in oscillatory stability that tore

serious at hifih values of dihedral; a reduction in the

sensitivity of the model to cust disturbances; and a reduc-

tion in rolling acceleration provided by the ailerons, which.

I-

Mt «TB»

\

caused a narked increase In tine to reach a given angle

of bank. /The general flicht behavior of the model became

worse with increasing monont3 of inertia but, vrith combina-

tions of r.rcall effective dihedral and large vertical-tail

area, satisfactory flight character!sties v.erc obtained at

all moment-of-inertia conditions.

KTwapüonoM A recent trend in design lias hoen to distribute weight

along thfi wing a of an air-plane instead rf concentrating it

in the fuselage. 'Ihin redisfcrlhutier. of weight, which

has be<-n fcrough* about largely by changes fron alngle-

engine to twin-engine design and by the Increased une of

wing guns and wing fuel tanks, has resulted in greater

rolling and yawing moments of inertia for the airplane and

has thereby increased the difficulty of obtaining satisfac-

tory lateral stability. Because of this trend, theoretical

investigations freferences 1 and 2) have recently been

made to determine the effects of large increases in moments

of inertia on lateral stability. The results of those

investigations indicated that the ranr;e of value I of

dihedral and vertical-tail area for ratlsfnctory oscillatory

stability becomes ?>rogreslively mailer «it'i Increasing

moments of inertia.

In order to vurify experimentally ^-he ronults of such

theoretical investigations and to determine the effects of

the indicated stability changes on general flight behavior,

an investigation has been carried out in the IIACA free-

flight tunnel with a l/lO-scale, free-flying dynamic model

loaded to represent a wide ranße of values of rolling and

yawing monents of inertia. For each rnonent-of-inertia

condition, a ranGO of dihedral angles and vertical-tail

areas that represented a variety of airplane conficurationa

«as covered.

Calculations were made to determine the theoretical

stability and control characteristics of the particular

model tested in order that the results obtained by theory

and experinent could be correlated.

SYMBOLS

k radius of gyration about X axis, feet

k_ radius of gyration about Z axis, feet

I moment of inertia about X axis, slug-feet** (mkv*) A

I» moment of inertia about S axis, slug-feet (mk_*)

m mass, slugs

lift coefficient (L/qS)

lateral-force coefficient (Y/q3)

yawing-ir-onent coefficient ^awinj>,gaiowentj

rolline-nor-ent coefficient (^Sili^gEaaSat)

lift, pounds

lateral force, pounds

dynamic pressure, pounds per square foot mPV2)

Ct

[•

;• •• s ;••

w

I

\

n.

'P

lP

ß r

V

P

P>

P

t

wing span, feet

wing chord, feet

winp area, cviare feet

rate of chance of yawtnp-moiaent coefficient with angle

of aide ally, per radian /oCny&ßJ

rate of chanfe of rolling-moment coefficient with angle

of aideslipt per radian (öCj/o ß )

rate of chanpe of lateral-force coefficient with angle

of sidesllr, por radian (cC^/dP/

rate of chance of yawinr-nortent coefficient with yawing

velocity, per wit of rto/2V (öCn/ö ||)

rate of ehanpe of yawiny-nonent coefficient with rolling

velocity, per unit of pb/2V fai/6 ivj

rate of change of rollin^-nonenfc coefficient vrlth rolling

velocity, per unit of pb/2V (^j/0 §v)

rate of chivnr.e of rolling-moment coefficient with yawing

velocity, per unit of rh/2V (oCi/° |v )

anple of 3idegl5.p, radians

yawing antrular velocity, radian* per second

airspeed, feet per second

rolling angular velocity, radians or degrees per second

air density, slups per cubic foot

period of lateral oscillation, seconds

time, seconds

"^J^Si1;*;?:."^; •'•<• JiffiS ^1»«^

:h" '• '.-'••. . '.•^>"vv*i:- 'v,~£i .'' •••••••-•' • •

*; *-T\

I

0 angle of bank, degrees

• angle of yaw, degrees

Ö flap deflection, decrees

R Routh's discriminant

D,S coefficients in stability quartic equation« given In

reference 1

APFARATUS

The investigation was carried out in the NACA free-

flipht tunnel, which is equipped for testinp free-flying

dynamic airplane models. A complete description of the

tunnel and its operation is given in reference 3. Force

tests made to determine the static lateral-stability deriv-

atives »/ere rin on the free-fllfht-tunr.el six-component

balance described in reference 4. A photograph of the

test section of the tunnel showing a r-.odel in flight is

given as finure 1.

A three-view drawing of the model used in the tests

is shown in figure 2, and photopraphs of the model are

presented in figures 3 and 4. The l/lO-scaTe model,

which in over-all dinensions represented a modern fighter

airplane, v/as constructed principally of bal3a and was

equipped with novable control surfaces similar to those

described in references» 3 and 4. For all tosts, the

model was equipped with a split flap 60 percent of the

wing span and 25 percent of the wing chord. The flap

was deflected 60°.

. V:*ft^ •••\.V-V.->

The rolling and yawlnß momenta of inertia of the nodel

were varied by shifting lead weights fro» the fuselage to

the wing tips. The effective dihedral was changed by alter-

ing the peometrin dihedral anple of the outer panel, as

indicated In firmre 2. Four geometrically similar vertical

tails (fir. 2) were used on the r.odel to produce changes in

vertical-tail area.

METHODS

Stability and Control Calculations

Boundaries for neutral spiral stability (?2 = 0), neutral

oscillatory stability (R = o), and neutral directional sta-

bility (D = 0) were calculated for all troment-of-inertia

conditions by means of the stability equations of reference S.

Values of the static lateral-stability derivatives, C„ ,

Oi , and Cv ,used in the calculations were obtained from force P Yß

tests of tiiR model. The value of tho rotary derivative C nr was obtained fron free-oscillation teat? of the nod«1 In the

frre-flight tunnel (reference 6); where;-s, the other rotary

derivatives, C , C. , end C, , were estimated from the charts np P r

of reference 7 rir.ö fror the formulas of reference 1. Values

of the stability derivatives used in the calculations are

given in table I. All the calculated boundaries are shown

ott the stability chart of figure 5.

I •••L&!^'-'.-%y&??'-;,£:ii': '•':.'•• ""•'

••"£-:i'-.-l •••• ••-.-;. •:

\

The period of the lateral oscillation was calculated

for some conditions by use of formula (21) (riven in

reference 5.

The tanking notions of the model following abrupt

aileron Maneuvers with different moment? of inertia were

calculated for a condition of small positive dihedral

and larpe vertical-tail area. For them calculations

the method of reference 8 was used and the model was assumed

to have freedor only in roll.

Testing Procedure

The model »as flown at each test condition and its

stability and control characteristics were noted by the

pilot. In addition, notion-picture records w<?re nade

of some flights In order to supplement the pilot's observa-

tions with quantitative stability and control datfi.

The spiral stability of the nodel was determined by

visual observation during sideslips across the tunnel with

controls fixed. Increasing inward sideslip was taken as

an indication of spiral instability.

General oscillatory stability characteristics with

controls fixed were noted by the pilot, and the damping

and period of the lateral oscillations ai'ter abrupt rudder

deflections were recorded by the cameras for each test

condition.

f-

;:Si#V^'-r?-'--":- • ""•'" •'-•

' A- I ..*ifv" ••:'•? •^i'-T«"-"-'

The directional stability «as judged by the yawing

behavior of the model after gu=t disturbances and by the

amount of adverse yawing produced by aileron control.

The steadiness, or the reaction of the rodel to the

normal trustiness in the air stream, was noted for all test

conditions. This characteristic was apparently not very

closely related to other stability characteristics and was

therefore judged Independently.

The effectiveness of the ailerons in rolling the raodel

was noted by the pilot and was neaaured fron canera records

of abrupt aileron naneuvers. The effect of adverse yawing

on aileron control for the various test conditions v?as

determined by visual observation.

Throughout the investigation, an effort was made to

determine the best conliinations of dihedrcl and vertical-

tail area for each inonent-of-inortia condition and to

establish on the lateral stability chart {-Cj against C )

the boundaries between regions of satisfactory ar.d unsatis-

factory flight behavior. Flight-behavior ratlrgs based on

the pilot's opinion of the general stability and control

characteristics of the nodel -nere recorded fir each test

condition. Although the accuracy of these riting« depended

upon the pilot'a ability to recognize unsatisfactory condi-

tions. It is believod that the ratine? give a true Indica-

tion of the effect of changes in the variables involved because

••eh rating was based on a number of separate flights.

I-

v*~

"V* i

I

IUIJGE OP VARIABLES

The parameters varied during the investigation were

rolling and yawing r.ior.ents of inertia, effective dihedral

, and effective vertic-'.l-ta: 1 area /Cn j. The

weight of the model v.-as held constant to simulate an air-

plane wing loading of 30 pounds per square foot. All the

tests were made at ar. airspeed of 51 feet per second,

which corresponded to a lift coefficient of 1.0.

because the rolling »md yawing moments of inertia

VTP. changed by varying the radii of gyration, ky, and

k , while the weicht was held constant, the inertia changes

in thir Investigation are expressed in terms of ky/b and

k^/b. These ratios or their reciprocal« are the conven-

tional nondinensional expression" for radii of gyration in

stability calculations.

In making the r-onent-of-inertia changes, kv/b and

k^/b v;ere varied in such a nanner that the value of

(b/ " vE> r regained constant. Changing the moments of

inertia in this way corresponds to changing the proportion

of weight carried in the wings. In the tests with high

values of k^/b and k^/b, the r.iodel therefore represented

an airplane with such loads as runs, arm-unit ion, an--i fuel

tanks in^tulled in the winrs instead of the fuselage.

10

Three moinent-of-inertia conditions were tested corre-

sponding to the values of kyA> and k^/b in the following table,

in which the relative values of moments of inertia are also

given lr. ordf-r to afford a l-etter indication of the magnitude

of the inertia changes:

Condition ky/b *x

JCfc/b *V

lx (Condi- tion A>

\<-i (Condi- tion A)

A

B

C

0.1S27

.200

.206

l.co

2.49

5.OS

0.1?7

.247

i

1.00

1.57

2.67

These mor<ent-of-incrtla condition? are represented on

the graph of kj-/b against kj/b In figure 6 by the points

A, B, and C. Condition A is intended to "imulate an aver-

age mass distribution for modern single-er.nine fighter

airplanes. Condition B represents the probable upper

limit of norrents of inertia for present-day conventional

airplanes. Condition C represents the extremely high

values of the parameters ky/b and k-j/b that result in the

case of airplanes with very snail span or vith excep-

tionally larpe loads in the wings* Condition C very

nearly simulates the moments of inertia of a flying wine

with uniform spanvrise na«3 distribution.

I "'•»". "• •• '• .. :• "•';•• ' • -*'*- . ..*"•• ' •-•. ".+tA"*"iv.'^ . . •••• ' '.

11

\

In order to illustrate the trend of present-day

airplanes toward hipher moments of inertia, various

other points are also plotted in figure 6. The squares

connected by arrows show this trend in successive models

of single-engine fighter airplanes of the sane design.

The triangles represent mass distributions of several nodern

twin-erw;iiie and multicrigine designs •

An example is riven in ffifure 6 to rhow the effect

on moments of inertia of adding large bombs or extra fuel

tanks to the wings of a typical flphter airplane. The

position of the mass distribution of this airplane on the

plot is chanred fron Y to Z by the addition of a

2000-pnund bomb or fuel tank midway out on each wing. It

Is evident that an Installation of this kind substantially

increases the rolling and yawing moments of inertia.

Three values of dihedral were used In the tests: a

larpe positive dihedral, a small positive dihedral, fend a

moderate negative dihedral, which are represented by the

symbols L, S, and N, respectively. The value of C. for

each dihedral vnrled slightly with vertical-tall area, as

shown in figure 5. The four vertical tulls used in the

tests? and desipnnted by the numbers 1, 2, 2, and 4 (fig. 2)

provided a ranft of C n„ fron 0.01 to 0.12. Pjtact values

of C_ and C for each nod< 1 confirurntion »fere deter- P lP

mined by force tests of the v.odel and are r.hawn in fir.urc. £•

f"

Y

J

The various configurations are represented by combinations

of symbols, for convenience and brevity; for example, condi-

tion S23 has snail, positive dihedral S, vertical tall 3,

and moment-of-inertia condition E.

KKSULTS AUT) DISCUSSION

Spiral Stability

The spiral stability of the model was not affected toy

ohanges In moments of inertia. The flight te3ts agreed with

theory in this respect for, as indicated in figure 5, the

theoretical spiral stability boundary is not changed by

variation of k/b and kr./b> Ratings for spiral stability

for the various model configurations are presented in

figure 7.

It was interesting to noto that, for the negative

dihedral condition, increaring the rionents of inertia

did not materially increase the difficulty of flying the

model. It night he expected that, because of the spiral

instability with negative dihedral, increasing the rolling

moment of inertia, and consequently reducing the rolling

acceleration produced by the ailerons, would cause diffi-

culty in recovering from a banked attitude. Such was not

the case, however, probably because the acceleration of the

dropping wing after a gust disturbance was also smaller with '

the increased inertia. At tines this reduced rolling

-. .:«.r;\'^ls-^-'s:;!'-.':':- *' '•"''

ÄV; '# *':

.# " •%. ' '• ' \ '. 1"

I-

13

acceleration even caused an apparent Improvement In spiral

stability because the nodel seemed to diverge more slowly

following a rust dlstttrbance.

The flight-teat results emphasized the fact that, for

the range of conditions tested, spiral instability has

virtually no significance in determining general flight

characteristics. It can be seen from figure 7 that the

model was spirally unstable -with both the small positive

and the negative dihedrals. Yet even with the negative

dihedral, no rapid spiral divergence was noted and the

model was not appreciably harder to fly than with the

large positive dihedral.

Oscillatory Stability

Increasing the moments of inertia definitely reduced

the oscillator? stability of the model and for some model

confirurations Introduced conditions of dangerous oscilla-

tory instability. The data of figure 8 show graphically

the changes in the damping of the lateral oscillation with

change in mass distribution for various combinations of and

dihedral/vprtical-tail area. Inasmuch as an accurate

quantitative measure of the damping could not be obtained for

all conditions, the results are presented In the form of

qualitative ratings for dancing at each condition. The

approximate quantitative equivalents of these ratings aret

14

I

Rating Qualitative

rating h; proximate

quantitative equlval

A Stable Damps to or.e-half amplitude In less than two cycles

B llightly stable Dan.pa to ore-haIf amplitude in two cycles or more

C Neutral Zero damping

D Slirhtly unstable Builds up to double amplitude in nore than one cycle

B i i

Dangerously unstable Builds up to double amplitude in one cycle or less

A conparlson of the theoretical oscillatory stability

boundaries (R = 0) In figure 8 with the ratings for damping

of the oscillation obtained in the flight tests of the model

Indicates good agreement between theory and flight results.

Figure 9 shows thut Increasing the moments of inertia

caused an increase in the period of the lateral o?clna-

tion, as indicated by theory. The experimentally deter-

mined values for the period were slightly smaller than the

calculated values.

The ratings in firuro 0 show that, although increasing

the moments of inertia reduced the oscillatory stability for

virtually all model configurations, the mamltude of the

reduction varied greatly for the diffpftnt combinations of

dihedral and vertical-tail area. In general, the effi-cta of

I-

i

15

\

moment of inertia on the oscillation damping wore more

pronounced with the large dihedral and the snail vertical-

tail areaa. This variation in the magnitude of inertia

effects with model configuration «aa in Rood agreement with

the variation indicated by the shifting of the theoretical

oscillatory stability boundaries shr.wn on the stability

charts (-C7 against O, ) in figure 8. With increasing P H

moments of inertia the boundaries move ui'ward and inward

on the charts and thereby show the greatest inertia effects

at large valuer of -C and srrall values of C_ • It lP P

anpears both from these boundary shifts und fror the flight

ratings for oscillation dairping that a complete picture of

the effects of Increased moments of Inertia on oscillatory

stability can be obtained only by an analysis of the effects

over a wide range of model configurations«

Small positive dihedral.- With the small positive

dihedral, the effect of increused moments of inertia on

oscillatory stability was relatively fj^iall for all values

of vertical-tail area. Bran for the condition of least

oscillatory damping With this dihedral (condition SIC),

no unstable oscillations rere noted although the damping

was very light. With the two largest vertical tails

(tails 3 and A) and the small dihedral, r.he oscillatory

stability for conditions D and C, though less than that

for condition A, was conridered satisfactory.

16

\

Lrrrre positive dihedral.- With the large positive dihedral,

increBsinn the moments of inertia caused pronounced reductions

in oscillatory stability for all values of vertical-tail area.

Conditions of dur.eerous ->scillutory instability were encoun-

tered with the smallest tail (tail 11 at loading condition B

and with all tells except the largest (tail 4) at lor.ding

condition C. These unstable conditions wore considered

flanrrerou«? because aii.itP.lned flights were inposslble as a

result of oscillations thai Inoreased, in amplitude despite

intensive efforts of the pilot ";o control the nodel. For

pome conditions, such vs LSB and L4C, unstable OBOillatlOSM

were encountered in flight« with crntrols fired, but these

oselllatlons could ho terminated at will by control applica-

tions and v/ure therefore not considered particularly danger-

ous.

The pronounced effect of moments of inertia on oscil-

latory stability with the larre positive dihedral is illus-

trated graphically in figure 10 hy photographically recorded

time histories of flir-hts at conditions LSA, L3B, and L3C.

The two Upper nets of curves in figure 10 are records of the

lateral oscillations with controls fiatwd, which "ere started

by abrupt rudder deflections. k comparison of the curves

shows that abanging fron raoMent-of-lnertia condition A to

cioment-of-inertla condition B caused the model to baoone

osolllatorlly unstable in flights with controls fixed. As

i

17

I

pointed out in the preceding paragraph« however, this

Instability was not especially dangerous when the lateral

controls were used properly.

The two lower aets of curves in figure 10 show that

Increasing the nonents of inertia from condition A to

condition C produced an unstable oscillation that could

not be stopped by aileron and rudder control. At condi-

tion L3C, the oscillation not only continued to build up

despite aileron-control movements but also was of such

strength that its period was not appreciably altered by

the control applications. The flights at this condition,

of course, were of very short duration and were usually

terminated by an abrupt sideslip to the floor of the

tunnel after the nodel had attained a very steep angle

of bank. The notion-picture record for condition L3A,

which is in sharp contrast with that of condition L3C,

shows the positive and almost instantaneous effect of the

ailerons in returning the model to level flight with

• normal moments of inertia and serves to emphasize the

magnitude of the instability that effectively nullified

the aileron control at condition L3C. The apparently

unstable yaving notion shown in the record of condition

L3A was probably caused by the fact that the rudder

control applied sinultaneously with the aileron control

18

used to bank the model was not always of the required magni-

tude nor In the proper direction for returning the model to

unyawed flight.

Nepatlve dihedral.- With the negative dihedral, the

effects of nonent of Inertia on oscillatory stability were

less than with the positive dihedrals and wore sriall for

all values of vertical-tail area. Y/ith this dihedral, the

lateral oscillation appeared to have a satisfactory rate of

damping for all conditions except with tlie smallest tall

(tall 1). A peculiar und sometines violent fom of insta-

bility was encountered at conditions N1A, NIB, and IUC.

The Instability, v/hich appeared to be more directional than

oscillatory in nature, was usually evidenced by yawing

motions that increased in nacnitude even when the ailerons

and the rudder »'ore used for control. In some flights at

this unstable condition, the model yawed to a larpe anjrle

and then rolled off abruptly with the leadin• win,'* poinß

down. It was interesting to note that the flifht behavior

of the model with the negative dihedral and tail 1 inproved

with increasing nonents of inertia. This surprising offact

appeared to be a direct result of slower, and therefore noro

easily controlled, yawinp motions of the model with the

higher nonents of inertia.

The ratinps for damping of the oscillation In figure

8 for conditions TJ1A, NIB, and NIC are given in parentheses

;>*W;--,

I • &••

!\##S:-,-

*•:*•• ft" *SMÄF*iftv V-. . -•' • . -

19

because of the uncertainty as to whether the Instability

was oscillatory or directional in nature. It should be

noted that these conditions on the stability diagram fall

very near the boundary for neutral directional stability

(D - 0). In the negative dihedral range, and in fact for

all spirally unstable conditions, the R = 0 boundary is

not an indication of neutral oscillatory stability because

E, one of the coefficients of the stability equation, is

negative. An exanination of the roots of the stability

equations for several negative dihedral conditions, however,

reveals that oscillatory stability theoretically exists

well below the D ~ 0 boundary. It appears, therefore,

that over the negative dihedral range directional diver-

gence will occur before oscillatory instability as indicated

by the flight tests of the model.

neaction to Ousts

The reaction of the model to the normal gustiness

In the air stream was improved by increasing the momenta

of inertia. With the high values of kx/b and k„Ai the

model was less sensitive to gust disturbances during

smooth flight and appeared to be steadier both in roll and

in yaw than with the lower moments of inertia. This

effect, which ^7as apparently purely inertial, was considered

beneficial fron a stability standpoint, but like aone aero-

dynamic stabilizing effects was detrimental to lateral

control, as will be shown in the following section.

! I"

20

It should be pointed out that the beneficial effects

of high moments of Inertia on the lateral steadiness of

the model were present only during smooth flight. Once

the smooth flirht of the model was interrupted by a partic-

ularly violent gust or control disturbance, the high momenta

of inertia prolonged the effect of the disturbance and

Increased the difficulty of returning to steady flight.

Lateral Control

Increasing the moments of inertia caused marked

Increases in the tine to reach a riven anfle of bank with

aileron control. It is evident from the time histories

of abrupt aileron maneuvers shown in figure 11 that this

reduction was caused by decreased rolling acceleration.

The model accelerated FO slowly during aileron maneuvers

at conditions B and C that maximum rolling velocities

could not be reached during the limited time and space

available for the maneuvers.

figure 11 shows that the tent results were In excellent

agreement with calculations of the pure banking rmtion

of the model. These calculations, which were based on

the assumption that the model had freedom only in roll,

indicate that the maximum rolling velocity is not affected

by changes in moments of inertia. Complete calculations

of the banking motion of an airplane with three degrees

of freedom (unpublished data) show, however, that increasing

if-

sw-^r-:-.s" ••'•••••••--• -•'••.-•

:*"'7 •-.':•••* ••»'*»;•..

.. ... ...... fc. , ••••..V .**** >'\yf ••^^'•v*'. * •'•^?;

r >•''•.•* .'vc-_v • J.?,»se,*e,y-.• •.. •. » . .*. '*# 1

81

\

the monents of Inertia reduces the final rolling velocity

as well as the acceleration in roll. In any event, it

appears that, with a very high rolling raonent of inertia,

the reduction in rolling acceleration alone is sufficient

to lengthen noticeably the time required to attain a given

angle of banlc with aileron control.

The teat data of figure 11 are made applicable to

the airplane by additional scales for rolling velocity

and tine. By means of these scales, a better indication

can be obtained of the effects of high moments of inertia

on the angle of bank reached in a given tine or on the

time required to reach a given angle of banl: for the full-

scale airplane.

General Flight Behavior

The general flight behavior became worse with increas-

ing monents of inertia, as rtiown by the flight-behavior

ratings in figure 12. It appeared that oscillatory sta-

bility was the predominant factor influencing the pilot's

Opinion of the general flight behavior, as is indicated

by the similarity of the ratings on figures 8 and 12 for

corresponding test conditions. The magnitude of the

detrimental effects of incr«BFed inertia on general flight

behavior, as on oscillatory stability, *vas dependent upon

the model configuration; the greatest effects were observed

with the large positive dihedral and the leant effects

!•

-/vÄ^&^-:<\- ,-.-'A:••••• •;•* . * *-r • •

\-.•;(*&• '.•••••<.•. •.••

^<%#.-

sa

\

were noted with the large vertical tails (tails 3 »n* I4.) used

in combination with the negative or small positive dihedrals.

Combinations of dihedral and vertical-tail area that

gave satisfactory flight behavior at the dilferent moment-

of-inertia conditions are indicated in figure 12 by approxi-

mate boundaries that separate satisfactory and unsatisfactory

regions on the stability charts. It is apparent froin the

mannsr in which the boundaries shift that the number of satis- *

factory combinations of dlhrdral and vertical-tail area

decreased with increasing Inertia. One model configuration

(small positive dihedral and vertical tail 1;.), however, pro-

vided ijood general flight behavior for all moment-of-inertia

conditions tested.

CONCLUSIONS

The effects of increased rolling and yawing moments

of Inertia on the lateral stability and control character-

istics of an airplane as determined by tests of a model

In the free-flight tunnel may be summarized as follows;

1. In general, the test results were in good agree-

ment with theory in regard to the effects of moments of

inertia on lateral stability and control.

33

I

2. Increasing the moments of inertia dici not

affect spiral stability and did not increase the •

difficulty of flying at a condition of rpiral insta-

bility.

3. Increasing the moments of inertia reduced

oscillatory stability. With nepative or pnu.ll

positive dihedral the reduction in stability v/as not

great even with the small vertical tails. With the

large positive dihedral, however, large increases in

tlie moments of inertia introduced dangerous oscillatory

instability, especially with the smaller vertical tails•

4. With high moments of inertia, the model was

less sensitive to gust disturbances and consequently

flew nore smoothly than with the normal r.omcnts of

inertia.

5. Increasing the moments -:f inertiu reduced

the rolling acceleration provided by the ailerons

and thereby caused a narked increase in the time

required to attain a (riven angle of banlc.

6. The reneral flight behavior became worse

T'ith increasing -orient« of inertiu. The grc-atost

effects of increased inertia were observed at

conditions of large dihedral and small vortical-

tall area.

\

3«

7. Satisfactory flight characteristics for all momerit-

of-inertia conditions were obtained with the small dihedral

(Cjß = -O.OSe) and the large vertical tail area (Cn = 0.11).

Langlay Memorial Aeronautical Laboratory, National Advisory Committee for Aeronautics.,

Langlay Field, Va.

I-

t-y'*''' *"

'"'• '• :•.••:.•••»•"

36

IC5FEKRJCES

I

1.

2.

3.

4.

5.

6.

7.

8.

Banher, Hillard J.» Effect of Sone Present-Day Airplane Design Trends on Requirements for Lateral Stability. T. N. Ho. 814, HACA, 1941.

Bryant, L. ti., and Putjalry, A. G.: The Lateral Stability of Highly Loaded Aeroplanes. R. & K. No. 1840, aritish A. ;{. C, 1930.

Shortal, Joseph A., and Österhout, Clayton J.t Preliminary StaMllt;? and Control Te3ts in the HACA Free-Flight Wind Tunnel and Correlation with Full-Scaie Flight Teste. T. H. Ho. 810, IIACA, 1041.

Shortal, Joseph A. and Draper, John V/.: Flight-Tunnel Investigation of t!-.e El

Free- Flight-Tunnel Investigation'of t!-.e Effect of the Fuselage Length ar.d the Aspect Ratio and Size of the Vertical Tail on Lateral Stability and Control. IIACA A.H.H., April 1943.

Zinneman, Charles H.» An Analysis of Lateral Stability in Power-Off Flight with Charts for TJae in Desi(*n. Hep. Wo. 569, IIACA, 15Ö7.

Canpbell, John P. pnd Kathewn, Vlard O.t 55:peri- nental Determination of the Yawing Konent Due to Yav/lng Contributed by the Wing, Fuselage, and Vertical Tail of a Midwing Airplane Model. IIACA A.R.R. Ho. 3F28, 1943.

Pearson, Henry A. arid Jones, Robert T.s Theoretical . Stability and Control Characteristics of V.'lngs with Various Amounts of Taper and Twist. Rop. ITo. G35, HACA, 1938.

Jones, Robert T.s A Simplified Application of the Method of Operators to the Calculation of Disturbed Motions of an Airplane. Rep. Ho. 560, HACA, 1936.

36

\

TABLE I

VALUES OP STAHIIirr DERIVATIVES D33D

lil COMPUTATIONS

JCT le a dependent varlablflj

C np %

C \

C

-0.196 -0.0040 -0.47 -0.0520 0.2530 -0.0472

-.201 -.0022 -.47 -.0517 .2533 -.0434

-.226 .00(55 -.47 -.0503 .2547 -.0545

.'.326 .0415 -.47 -.0431 .as 19 -.O^O

-.426 .07C5 -.47 -.07-06 .2714 -.1035

-.526 .1115 -.<7 -.0217 .2833 -.laoo

-.626 .1435 -.47 -.0070 .2980 -.1526

*&E •vi^:>',*"*v :•••" • •-•*?*r^i.

1 • -

n

NACA v ' Fig.l

1 1 i ••••• r-l

J

r

\r

T^N

ft •H

H n o 1 Tj V

01 s a a

\\

P1 Lm •

• IF H

1 I •H H IJ.J

B V »4

••**

4.1 • 4 M

VI o a o

•H «a a • 01

A' m t)

1

•H

h I •rt K

1 1

. • ' l ' 1 ,• ' 1

V.

IACA <3>

F,q. 2

Vertical tat'/

Area CXS)

Aspec? rafto

/ 52 1.9 Z 1.8 1.9 3 105 1.9 4 /.*>.:. 1.9

Sp/it Hap, 0.6OÖ 0.25c,S,*60°

FIGUHE Z. - Dra wing of model used in free -flight- tunnel mass-distribution investigation

eo oo i

.-i

\

• ACA <2> riBI.,3,4

figure 3.- Side vie» of nodal uud In »««-distribution Invutlgatlo: •ACA • r»«-fil.-nt t ur,„.i n In the

rigure 4.- Flan view or model used in rase-d is in bull or. investigation in the NACA free-flight tunnel.

«0 I NACft

OS? ~ias. 5,7

Stable ^<<<^ Moment- of-inartn ccndrtrsna; £>,hectrate I I 1 |_

.16

.12

$k

.OS

.0*

:

-.08

F/Gu*m S- Stability chart showing stab/My boundar/es and model configurations. CL*/.Otor a/I boundaries and configurations.

IC

IZ

ce

.Of

B Neutral | C Unstable

c* E<. >

c *

Ci

c+ J^i 4-

cv y /* A

^r A _. ._ .

-.03 -.04 04 OB J2 M .20

'*

FIGURE 7. - •Sptrnt-dabit/ly ratings for different model configurations. Q=/.0. (Average ratings tor all moment-af-inertia conditions)

\

en

NACA <§> <g>#€/ Moment-cf-znerf/a lest

Fiq. 6

A/one/ /ni/est/gof/an

WTwayouron each

°>£%»esf4r«>„Jsho» JW£j soccess/fe "xx&s of same aes/Qn)

A Twm-enQ/neanamo/fi-

**%&&% * "*« "fr "V-frcamr*, /n

\

NACA Fiq.8

It 4 ••tr /3+

/I

ua A A S1

1 /rfamenPof~/nert/a.

b* condition A 1

0 a £ -

^"^ /?-0

0 c

•mi g TTTl^

Loterul-osa/Jot/on r ntm

no. A Stable 3 S/iolilNy sta&e

ia C Ateut/at 0 Slightly unstable £ Dangerous// untfat M

/

AR

o —I A. 1

R~0 UO A

R+ *d r 04 on

B D* Momenrof/nerfia condition B

KL £

o ä-S' £

n4

A- J2 y >/?--0

— L r-» /-. H

08 yT

/i .8- v**^ •

04 £ £" Mt vnet

con, it-of-inertia rlitinn r.

CO) £

0

1 ^** £

-C e ^0 4 C ) .0 '2= 'S

6 y< 2 A 6 .2 0 .2 4-

I-

F/GURE 6.- Ratrnqs for damping of /atenpl osc/l/ofion far afferent fest canc/i/tcns. Ci=tO. (Pafmos posstcly influenced by direct/cnal scat-, vbt enclosed m parentheses,

1JACA Fig. 9

\

O •J

5

4

3

1

0

1 -

i rarticcl tai]

i—

1

1 Calculated (ref. 5)

Y U Measured m

1 i H

•3 i 1

| 1

16 —

1 1 1

t

j

1

1 _y 14 i—

_, ...

1 i /

X

12 — / /!

1

10 — / \ A t..oS&nT-<3f-i: condition C

t

iärtlE" B • . e — 1 4.

o 1 r? Ifammt-Of-llUrtJ

1 1 \L^ S 6 — Cl.l IlttOB A 1

\ 1 » 1 Ut-U__

4 — j«»

i. _._ .

: . hoount-of-lsiartia . 'condition 3

2 —

r i

i II 0 —

- -T ,

i 1 1

1 ( ) .1 )S .1

'•* i -: '4 • <. S3

Figure 9.- offset of motänts of inertia on period of lateral oscillation. Small positive dihodral. CL • 1.0.

lo // e /3

7/me,sec

FtsuRE/O.- T/me histories ofbantvnq and yawing motions of model thawing effect of increased moments of inertia on da/npina o* kjfeiat oscillation. LOIQA positive diftedio/. {ferficaf frit 3. CL=I.O.

NACA

Fu/f- scafe

30-

I

* 0-

Fig. I I

Condition Fxper/znento/ Ca/cutofeat S4A o S43 + S4C x

Fu/t- \ xo/e I

0 .2 .4 .6 8 1.0 12 1.4 /.6 to 2.0 Time, t, sec

fiGORE/L- Time histor/es of abrupt ai/eron maneuvers with different moment-of-inert/a conditions. •Smo// positive d/hedrat. Serttcot fait 4. CL*t.O.

1

I

NACA ®

Fig. 12

-.06 -.04- .04 .06 JZ •Qfi

20 24-

f-

Fieufvr /2- Ft/ghf-behavior ratings for different test conditions. Q'/O.

TITLE: The Effect of Mass Distribution On the Lateral Stability and Control Character- istics of an Airplane as Determined by Tests ofa Model in the Free-Filght Tunnel AUTHOR|S): Campbell, J. P.; Seacord, C. L. ORIGINATING AGENCY: Langley Memorial Aeronautical Laboratory, Langley Field, Va. PUBLISHED BY: National Advisory Committee for Aeronautics, Washington, D. C.

AYÖ- »13

(None)

niUOMMO AOD CT Ml

(Same)

iüä. Unclas U.S. Eng. PA03

3$ •tutfi AnoM photos, tables, diagrs. graphs

ABSTRACT:

Rolling and yawing moments of inertia Increased from normal values to values up to five times normal. For each moment-of-Inertia condition, combinations of dihedral and vertical- tail area representing various airplane configurations were tested. Results were correlated with calculated stability and control characteristics, and good agreement was obtained. Flight performance of model became poorer with increasing moments of inertia; but with combination of small effective dihedral and large vertical-tall area, satisfactory flight characteristics were obtained.

DISTRIBUTION: Request copies of this report only from Publishing Agency

DIVISION: Aerodynamics (2) SECTION: Stability and Control (1)

ATI SHEET NO.: R-2-1-S6

SUBJECT HEADINGS: Airplanes - Lateral stability (08470.SS); Airplanes - Design (0B400); Airplanes - Lateral control (08470.5); Airplanes - Rolling moment characteristics (08482.8); Airplanes - Wind tunnel testing (08496.5)

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