STRUCTURAL DEFORMATIONS IN THE SATURN INSTRUMENT … · 2018. 8. 8. · Data for the uprated Saturn I was taken from references 5 through 11. For yaw vibrations, a similar local effect

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I r

NASA TECHNICAL MEMORANDUM

I .

I.

S T R U C T U R A L D E F O R M A T I O N S I N T H E S A T U R N I N S T R U M E N T UN I T By Larry A. Kiefling

Aero-Astrodynamics Laboratory

NASA

George C. Murshdl S'uce Flight Center,

, .

I

(THRU) V ' h R - 1 2 9 5 6 ,

(ACCESSION NUMBER) I

N.4S.4 TM X- 53673

November 20, 1967

TECHNICAL MEMORANDUM X-53673

STRUCTURAL DEFORMATIONS I N THE SATURN IHSTRUMENT U N I T

Larry A. Kief l ing

George C. Marshall Space F l i g h t Center

Huntsvi l le , Alabama

ABSTRACT

During the Saturn V dynamic t e s t , l o c a l deformations of s i g n i f i c a n t amplitude were measured a t the f l i g h t sensor loca t ions i n the instrument u n i t . The cause is i d e n t i f i e d as a r a d i a l fo rce component a t the j o i n t of t he LM adap te r cone and the instrument u n i t c y l i n d r i c a l s h e l l due t o the axial r e s u l t a n t s from the bending moment. The deformation p a t t e r n s f o r a s h e l l a n a l y s i s of t he s t r u c t u r e . a r e shown. The l o c a l deformation is found to be propor t iona l t o the bending moment only and the propor t ion- a l i t y cons t an t is determined f o r t h ree instrument loca t ions . Typical ampli tudes f o r Saturn V modes and a s e l e c t i o n of po in ts from the Sa tu rn I B dynamic tes t program a re presented.

These l o c a l deformations were prev ious ly thought t o be n e g l i g i b l e .

NASA - GEORGE C, MARSHALL SPACE FLIGHT CENTER

NASA - GEORGE C, MARSHALL SPACE FLIGHT CENTER

Technical M e m o r a n d u m X - 5 3 6 7 3

N o v e m b e r 20, 1967

STRUCTURAL DEFORMATIONS I N THE SATURN INSTRUMENT UNIT

BY

Lar ry A. K i e f l i n g

STRUCTURAL DYNAMICS SECTION DYNAMICS ANALYSIS BRANCH

DYNAMICS AND FLIGHT MECHANICS D I V I S I O N AERO-ASTRODYNAMICS LABORATORY

RESEARCH AND DEVELOPMENT OPERATIONS

TECHNICAL MEMORANDUM X-53673

STRUCTURAL DEFORMATIONS I N THE SATURN INSTRUMENT UNIT

SUMMARY

The l o c a l deformations a t the instrument u n i t measured during the Sa turn V dynamic t e s t a r e found t o be propor t iona l t o the bending moment. Shear has no e f f e c t . The deformation i s due t o radial fo rce components of the a x i a l s t r e s s which ca r ry the bending moment a t the j o i n t between the LM adapter cone and the instrument u n i t c y l i n d r i c a l s h e l l . The p r o p o r t i o n a l i t y constants f o r t he deformations a t the top and bottom halves of the EDS cold p l a t e f o r p i t c h v i b r a t i o n and a t the ST-124 s t a b l e platform f o r yaw v i b r a t i o n a r e der ived from p l o t s of the t e s t da t a . The amplitude of the loca l deformation is shown t o be com- parable t o t h a t of t he bending de f l ec t ions f o r t he Sa tu rn V modes. The d a t a po in t s from the Sa turn I B t e s t program i n d i c a t e t h a t the same l o c a l d e f l e c t i o n phenomena occur fo r that veh ic l e .

I. INTRODUCTION

The Saturn launch veh ic l e s depend on a t h r u s t vec to r con t ro l system f o r a t t i t u d e con t ro l . P o s i t i o n and r a t e s i g n a l s come from sensors loca ted i n the instrument u n i t . Since the sensors measure the t o t a l motion a t t h e i r mounting p o i n t , t h e i r ou tput s i g n a l is the t o t a l due t o v e h i c l e r i g i d body motion plus ove ra l l veh ic l e v i b r a t i o n modes p lus l o c a l deformations. F i l t e r systems, designed from a n a l y t i c a l bending mode p red ic t ions , a r e usua l ly needed t o prevent s t r u c t u r a l feedback i n s t a b i l - i t y of the bending modes. The Saturn V dynamic t e s t program v e r i f i e d the accuracy of the a n a l y t i c a l methods used t o c a l c u l a t e the o v e r a l l bending modes, b u t the l o c a l deformations, which were prev ious ly thought t o be n e g l i g i b l e , were found t o be s i g n i f i c a n t . This r e p o r t p re sen t s t he l o c a l deformations which were measured, expla ins the cause, and provides the d a t a needed t o p r e d i c t l o c a l deformations f o r the f l i g h t v e h i c l e s .

11. DISCUSSION

Locations of the ins t rumenta t ion a r e shown i n f i g u r e 1. During p i t c h e x c i t a t i o n , the ST-124 is on the n e u t r a l axis , and the EDS gyro cold p l a t e i s on the a x i s of motion. A t t he beginning of t e s t i n g , gyro measurements were made a t the fol lowing loca t ions :

(1) Top of ST-124 s t a b l e platform.

(2) Wall b racke t above ST-124.

(3) EDS f l i g h t r a t e gyro l o c a t i o n (Box A i n f i g u r e l ) , va lues a r e r e f e r r e d t o as " top h a l f of p l a t e " i n t e x t .

(4) Locat ion "C" on EDS cold p l a t e , a t es t backup instrument .

L a t e r , a dec is ion was made t o l o c a t e the f l i g h t EDS r a t e gyro a t po in t "B." No s i g n i f i c a n t d i f f e r e n c e s i n the p i t c h rate reading of l oca t ions "B" and "C" were observed. The measurements a t these po in t s w i l l be used interchangeably i n the t e x t and r e f e r r e d t o as "bottom-half-plate ' ' va lues . Notice t h a t the cold p l a t e i s mounted a t f ive po in t s .

The gyro readings a t the ST-124 w a l l b r acke t l o c a t i o n s were i n c lose agreement wi th the c e n t e r l i n e s lopes . The measurements a t the EDS gyro loca t ion d i f f e r e d s i g n i f i c a n t l y from the c e n t e r l i n e v a l u e s , and the measurements on the bottom h a l f of t he cold p l a t e a l s o d i f f e r e d , b u t t o a l e s s e r ex ten t . Since the d i f f e r e n c e s did no t appear t o be frequency-dependent, a q u a s i - s t a t i c cause was sought.

Two causes seemed poss ib le : the shear and bending moment loads appl ied t o the instrument u n i t by the payload. The shea r and moment loads required t o produce a u n i t l o c a l d e f l e c t i o n a t the top h a l f of t he p l a t e were ca l cu la t ed f o r t h ree modes a t th ree time po in t s f o r t he f i r s t s t age v e h i c l e (see f i g u r e 2) . The l o c a l deformation is found t o be a func t ion of bending moment only.

The mechanism of the deformation i s shown i n f i g u r e 3 . The bend- ing moment i s c a r r i e d by compressive s t r e s s e s on one s i d e of the n e u t r a l a x i s and t e n s i l e s t r e s s e s on the oppos i te s i d e . These s t r e s s e s are pro- p o r t i o n a l t o the d i s t a n c e from the n e u t r a l a x i s . The s t r e s s e s on a segment of w a l l w i l l produce forces Fc and F t a c t i n g on the top of the instrument u n i t w i th each of these fo rces having components Fa and Fr. The r a d i a l component causes a l o c a l deformation i n the instrument u n i t and SLA w a l l . The bending shear is c a r r i e d p r imar i ly by the s h e l l near the neu t r a l a x i s and produces no e f f e c t a t the EDS gyro l o c a t i o n .

2

A pre l iminary c a l c u l a t i o n of the l o c a l deformation i s shown i n f i g u r e 4. Cente r l ine and w a l l deformations were found from a s h e l l a n a l y s i s ( r e fe rence 1). The complex curva ture a t the top of the IU is caused by the s t i f f e n i n g r i n g a t t h i s l oca t ion . The loca t ions of a r i g i d EDS cold p l a t e r i g i d l y a t tached a t the four corner mountings and a cold p l a t e hinged i n the middle are shown as d a t u m conf igu ra t ions . The l o c a l d e f l e c t i o n s der ived from t h i s approximate pre l iminary a n a l y s i s are from two t o four times too la rge due t o the s impl i fy ing assumptions made.

Bending moments were ca lcu la ted from a curve f i t of the exper i - Moment va lues a r e g iven

The equat ion f o r the bending moment, M y is mental mode shapes and the mass d i s t r i b u t i o n . i n r e fe rence 2.

where m' is the lumped mass, y is t he modal d e f l e c t i o n , and x" is the d i s t a n c e from the mass po in t t o the top of t he instrument u n i t . The summation i s taken f o r a l l mass poin ts above the instrument u n i t . The s i g n convect ion is shown i n f i g u r e 5. For the mode shown, y" is always p o s i t i v e and hence the moment is p o s i t i v e a l s o . The c e n t e r l i n e s lope i s p o s i t i v e , and the measured s lope i s a l s o p o s i t i v e and l a r g e r than t h e c e n t e r l i n e s lope ; t h e r e f o r e , 'the l o c a l angular d e f l e c t i o n , 4, is also p o s i t i v e . b u t t he t e s t amplitude w a s u s e d ,

A l l modes were normalized f o r a p o s i t i v e bending moment,

Local d e f l e c t i o n s a t the top h a l f of t he cold p l a t e measured during t h e Sa turn V dynamic t e s t are p lo t t ed i n f i g u r e 6 as a func t ion of bend- ing moment. The l o c a l d e f l e c t i o n is taken as the d i f f e r e n c e between the gyro readings a t the top h a l f of the EDS cold p l a t e and a t the ST-124. The use of t he d i f f e r e n c e of two va lues as a v a r i a b l e t e n d s t o cause some scat ter i n the da t a . A l i n e has been drawn through the configura- t i o n I da ta . (Configurat ion I is a s imula t ion of t he v e h i c l e during S-IC s t a g e burn and conf igura t ion I1 a s imula t ion of the S - I 1 burn.) The cons tan t is s l i g h t l y d i f f e r e n t from t h a t given i n f i g u r e 2 s i n c e t h e f i r s t mode va lues , w i th the g r e a t e r moments, a r e emphasized i n f i g u r e 6 . Slope data were taken from re fe rences 3 and 4. The l o c a l angu la r d e f l e c t i o n s a t the bottom h a l f of t he cold p l a t e a r e shown i n f i g u r e 7 . used i n t h i s f i gu re . The l o c a l deformation a t the bottom h a l f of the EDS cold p l a t e are about a third of those a t t h e t o p h a l f .

S c a t t e r of the d a t a is more ev ident a t t he l a r g e r s c a l e

3

Local d e f l e c t i o n s f o r o the r dynamic tes t of Sa turn V and uprated Sa turn I veh ic l e s are shown i n f i g u r e 8, a long w i t h the curves from t h e previous two f i g u r e s . During the f i r s t t es t on the Sa turn V, l a r g e l o c a l e f f e c t s were found. Since the EDS cold p la te was found t o be loose , t he t e s t was re run . The same cond i t ion may have occurred dur ing the SA-202D f i r s t s t a g e t e s t s s i n c e the p o i n t f e l l near the same curve. The SA-202D second s t a g e and SA-500D t h i r d s t a g e r e su l t s i n d i c a t e that the cold p l a t e was p roper ly mounted. The bot tom-half-plate va lues were p lo t t ed f o r t he SA-500D t h i r d s t a g e s i n c e reading f o r the top h a l f p l a t e gyro appeared bad. Data for the uprated Sa turn I was taken from re fe rences 5 through 11.

For yaw v i b r a t i o n s , a similar l o c a l e f f e c t occurs a t the ST-124. Values measured during the Sa turn V dynamic test are shown i n f i g u r e 9.

The s ign i f i cance of the l o c a l deformations during p i t c h v i b r a t i o n s can be seen i n f i g u r e s 10 through 13 (see r e fe rence 12 f o r a n a l y s i s va lues f o r these p l o t s ) , The l o c a l deformations a r e obviously of s i g n i f i c a n t amplitude when compared t o the t o t a l d e f l e c t i o n .

CONCLUSIONS

A l o c a l deformation, propor t iona l t o the modal bending moment, has been shown t o e x i s t i n the Sa turn instrument u n i t . Values f o r t he pro- p o r t i o n a l i t y cons tan t are l i s t e d below.

Bend ing Constant Constant Point D i rec t ion (rad/ l b - i n ) (rad /N-m) -

EDS Cold P la t e , Top p i t c h .32 x 10-l0 .28 x

EDS Cold P la t e , Bottom p i t c h .96 x 10-l' .85 x

ST-124 Stab le P la t form Yaw .62 x 10-l' .55 x 10'11

Because the l o c a l deformations f o r most of t h e modes are of a s i g n i f i c a n t ampli tude, they must be included i n c a l c u l a t i o n s of modal data f o r design purposes.

4

U I U

1

> 0) .-

1 u

5

Shear ( IO Ib.)

5

4

3

2

1

First Mode

Third Mode

I A Second Mode 'I

T 1- 1- I .

.I I

I

I A

I I

I

I

A 1.0 0

0 .5 I Moment (IO" Ib in)

-1 I

A

-2 I

FIG. 2. SHEAR AND MOMENT FOR UNIT LOCAL DEFORMATION AT UPPER HALF OF EDS COLD PLATE SATURN E FIRST STAGE

FT

FA

Neutral

FIG. 3. COMPONENT FORCES ACTING ON TOP OF INSTRUMENT UNIT DUE TO MOMENT LOAD

7

8

0 Center Line

I .I

Hinged Cold Plotc

k- Riqid Cold Plate

/ ," / /

'-t-- .4 .5 .7 .e

--.

e /

-B

D i s p l a c e m e n t (IO* i n ) FIG. 4. L A T E R A L DISPLACEMENTS

FOR U N I T M O M E N T LOAD AT TOP OF S L A , STRUCTURE F IXED AT BASE OF S - E B FORWARD SKIRT

I

c - 0

0 I

h \.. \ --

t

Center L ine s l o p e 1

Measured S lope ( Y Mass Point

FIG. 5. TYPICAL MODE AND S I G N C O N V E N T I O N

+ Y

9

Local Angulor Def lect ion rod) A9 : .96x10"0rad/lb in

.6

.5

.4

.3

.2

.I

0 0 .2 .3 .4 .5 .6 .7

Moment (10' I b i n )

FIG. 6. LOCAL DEFLECTION AT UPPER HALF PLATE A S A FUNCTION OF BENDING MOMENT

10

11

0 Saturn P, T. P. 2 . , First Test With Loose Cold Plate A SA-2020, T= 147

SA-2020, Second Stage + SA-5000, Third Stage (Bottom Half Plate

0

Local Angular Deflection (10-3 rod )

0

/' Y

I I I I I I c .6 .8 1.0

Moment (io7 Ib in)

FIG. 8 LOCAL DEFLECTIONS FOR OTHER TESTS

12

Lo

.3

.2

.I

0

I Angular Deflection rad)

I A # = .62 X 10-" rad Ib/i

0 Configuration I

I

.4 ' Bending Moment ( lo7 Ib i n )

FIG. 9. L O C A L DEFLECTION AT S T - 1 2 4 D U R I N G Y A W T E S T

Slope (10-3 rod / in . )

I I

.6 -

.4

.2

0 - 0

Time ( s e c )

FIG. IO. INSTRUMENT UNIT SLOPES (F IRST MODE, D T V ) VS FLIGHT TIME

14

I

L

rc 0 I

I I >

I-

15

T i m e ( s e e )

0-

-.3.

-.6

-.9

-1.;

4 - /-7

0

\

1

\ \ \

\

I

. '\

Slope (10-3 rad / i n )

FIG. 12. INSTRUMENT UNIT SLOPES ( T H I R D MODE, D T V ) V S FL IGHT T I M E

16

0

Slope r a d / i n )

Time ( D

0 Analysis A Center L i n e

V P l o t e Top H a l f

-- - P l a t e B o t t o m H a l f ----- ---

FIG. 13. INSTRUMENT U N I T SLOPES (FOURTH MODE, D T V ) VS FLIGHT T I M E

17

RE FE REN C E S

1.

2 .

3 .

4 .

5 .

6.

7 .

8 .

9.

Yen, Unpublished Computer P r i n t o u t s , Lockheed HREC.

Pearson, M. L . , "Instrument Uni t Deformation Analysis ,'I Lockheed Report LMSC/HREC 784341. Also unpublished working p a p e r .

Boeing Co. Report , "Saturn V Dynamic Test Vehicle Conf igura t ion I Test Report P i t c h and Yaw Test Resul t s , " Report No. T5-6630-2.

Boeing Co. Report , "Saturn V Dynamic T e s t Vehicle Conf igura t ion 11 Test Report P i t c h and Yaw Tes t Resul t s , " Report No. T5-6633-1.

Chrysler Technical Report , "Dynamic T e s t Resu l t s of SAD-202," Report NO. HSM-Rl48.

Chrysler Report , "Transfer Funct ion Report (SA-202 Vehicle , P i t c h a t 147 Seconds)," Report No. HSM-R607.

Chrysler Report , "Dynamic Tes t Resul t s of SAD-202 Upper Stages , I 1

Report No. HSM-R162.

Chrysler Report , "Transfer Funct ion Report (SA-202 Second F l i g h t Stage, P i t c h , I g n i t i o n , w i t h LES) ,'I Report No. HSM-R656.

Chrysler Report , "Dynamic Tes t Resul t s of S-IVB-D, I . U . , LEM and Apollo," Report No. HSM-R154.

10. Chrysler Report , "Transfer Funct ion Report (Second S-IVB-D, I . U . , and Payload Conf igura t ion , P i t c h a t I g n i t i o n ) , I 1 Report No. HSM-R664.

11. Chrysler Report , "Transfer Function Report (Second S-IVB-D, I . U . , and Payload Concigurat ion, P i t c h a t Cutof f ) , " Report No. HSM-R667.

18

ERRATA

NASA TM X-53673

STRUCTURAL DEFORMATIONS I N THE SATURN INSTRUMENT UNIT

BY

L a r r y A . K i e f l i n g

ERRATA

1. Page 3

Equation should read:

m' y 2. c M = w2

2 . Page 4

The p r o p o r t i o n a l i t y cons tan ts f o r the top and bottom halves of the cold p l a t e have been interchanged i n the t a b l e . The t a b l e should read as follows:

Poin t Bending Constant Constant

D i rec t ion (rad/ lb - i n ) (rad /N-m)

p i t c h .96 x 10-l ' .85 x EDS cold p l a t e , top

EDS cold p l a t e , bottom p i t c h .32 x .28 x 10- l ' -

ST-124 S tab le Platform Yaw .62 x 10-l' .55 x

Please c o r r e c t your copy.

APPROVAL NASA TM X-53673

STRUCTURAL DEFORMATIONS IN THE SATURN INSTRUMENT UNIT

by Larry A. K i e f l i n g

The information i n t h i s r e p o r t has been reviewed f o r s e c u r i t y c l a s s i f i c a t i o n . Review of any information concerning Department of Defense o r Atomic Energy Commission programs has been made by the MSFC S e c u r i t y C l a s s i f i c a t i o n O f f i c e r . This r e p o r t , i n i t s e n t i r e t y has been determined t o be u n c l a s s i f i e d .

This document has a l s o been reviewed and approved f o r technica accuracy.

62uAJig- Robert S. Ryan

Chief , Dynamics Analysis Branch

9 4 s w w bQ H. J. Horn "

Chief, Dynamics and F l i g h t Mechanics Div is ion

/-&"A E. D. Ge i s s l e r Di rec tor , Aero-As trodynamics Laboratory

1 9

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