CO CASE FILE COPY - NASA

NASA TECHNICAL NASATM x-62,073MEMORANDUM

CO

<CO<

CASE FILECOPY

A WIND TUNNEL FLIGHT CORRELATION OF APOLLO 16SONIC BOOM

Frank Garcia, Jr., Raymond M. Hicks, and Joel P. Mendoza

Ames Research CenterMoffett Field, California 94035

February 1973

A WIND TUNNEL-FLIGHT CORRELATION

OF APOLLO 16 SONIC BOOM

By Frank Garcia, Jr.Manned Spacecraft Center

Raymond M. Hicks and Joel P. MendozaAmes Research Center

ABSTRACT

A correlation of sonic boom pressure signatures recorded duringreentry of the Apollo 16 command module with wind-tunnel signatures ex-trapolated to flight distances has been made for Mach numbers of 1.83and 9.71. The flight pressure signatures were recorded by microphoneslocated onboard ships positioned near the ground track whereas the windtunnel signatures were measured during a test of a 0.016-scale model of thecommand module. The agreement between estimates based on wind tunneldata and flight measurements was good at Mach 1.83 and Mach 9.71.

A WIND TUNNEL-FLIGHT CORRELATION

OF APOLLO 16 SONIC BOOM

By Frank Garcia, Jr.Manned Spacecraft Center

Raymond M. Hicks and Joel P. MendozaAmes Research Center

SUMMARY

A correlation of sonic boom pressure signatures recorded duringreentry of the Apollo 16 command module with wind tunnel signaturesextrapolated to flight distances has been made for Mach numbers of 1.83and 9.71. The flight pressure signatures were recorded by microphoneslocated onboard ships positioned near the ground track whereas the windtunnel signatures were obtained from tests of a 0.016 scale model of thecommand module. The average peak overpressure recorded during reentrydiffered from the extrapolated wind tunnel peak overpressures by1.7 N/m2 (.036 psf) at Mach 9.71 and 3.0 N/m2 (.063 psf) at Mach 1.83.The flight signatures exhibited multiple shock waves while the extrapolatedwind tunnel signatures were N-waves. This difference in signature shapeis not understood at this time but may be due to reflected waves fromthe ship superstructure.

NOTATION

h flight altitude, meters

1 length of model or full-scale vehicle, meters

M Mach number

p reference pressure, N/m2

Y flight path angle, degrees, positive above horizon

Ap sonic boom overpressure, N/m2

<(> ray path angle, degrees; the 0 ray direction is down; positiveis left looking forward on aircraft

\p heading angle, degrees, north = 0 degrees; positive toward east

dJdt

-2-

INTRODUCTION

No theoretical methods are available for calculating the sonic boomoverpressures generated by blunt vehicles with detached shock wavemaneuvering at high Mach numbers. Therefore, sonic boom estimates forspace shuttle type vehicles must be based on one of the currently availablesemi-empirical techniques (references 1 and 2; with these techniques near-field pressure signatures measured in wind tunnels are extrapolated to thefar field). In order to extend the range of conditions for which thesetechniques have been validated, experiments were conducted using theApollo 15 and 16 command modules as the test vehicles. The Apollo 15study was reported in reference 3. The Apollo 16 results are reportedherein. Personnel of the Langley Research Center employed microphones placedonboard ships located along the ground track of the command modules toobtain measurements of sonic boom overpressure generated during reentryinto the Earth's atmosphere. These overpressures were compared withestimates based on the wind tunnel data of references 4 and 5 and theextrapolation procedure of reference 1.

TEST CONDITIONS

A photograph of the full-scale command module is shown in figure l(a).A report giving a complete description of the technique used to recordthe pressure signatures generated by the command module during reentry andthe resulting measurements is being prepared by Langley Research Centerand will be published at a later date.

A 0.016-scale model of the Apollo command module (figure l(b)) wastested at Mach numbers of from 1.5 to 10 in the Jet Propulsion Laboratorysupersonic and hypersonic wind tunnels. A complete description of the testconditions along with the wind tunnel pressure signatures are presentedin references 4 and 5.

RESULTS AND DISCUSSION

The reentry trajectory data for Apollo 16 is given in figure 2. Theground track along with the locations of the two ships with onboard micro-phones used to record the sonic boom overpressures generated duringreentry are shown in figure 3.

The flight data (figure 2) and the pressure signatures measured inthe wind tunnel (references 4 and 5) were used to predict the ground over-

-3-

pressures generated by the command module during reentry into the Earth'satmosphere. The signatures for Mach 1.83 and Mach 9.71 shown in figure 4were obtained by interpolation of the wind tunnel data of references 4and 5. In addition, the signatures were extrapolated to an h/l of 9.6(figure 4) using the strong shock theory of reference 5. This was necessarybecause some of the wind tunnel signatures of reference 5 exhibited shockstrengths too large to permit use of the extrapolation technique ofreference 1 which was developed for weak shock waves.

The first step in the calculation of the ground overpressures was todetermine the point on the flight path at which the pressure signalsrecorded by the onboard microphones of both ships originated. This wasaccomplished by choosing a point on the flight trajectory and then cal-culating the ground-ray intersection for the ray emanating from that point.If the intersection was different from the coordinates of the ship anotherpoint on the flight path was chosen and the procedure was repeated. Thisprocedure was repeated until the difference between the calculated ground-rayintersection and the ship's coordinates was less than 100 meters (furtheriteration was found to have a negligible effect on the level of the groundoverpressure). The results of the iteration showed that the pressuresignal recorded onboard the USS Ponchatoula originated at Mach 9.71 andthe signal received by the USS Ticonderoga originated at Mach 1.83.

The accelerations required in the extrapolation of the tunnelsignatures to flight distances were obtained by measuring the slopes ofthe Mach number, flight path angle and heading angle curves shown infigure 2. The atmosphere employed in the extrapolation was taken fromthe 1966 U. S. standard atmosphere supplements for 15 degrees north, annual(reference 6). The wind velocity was assumed to be 0 at all altitudessince atmospheric soundings were not taken during reentry. A total of 8microphones were placed onboard the ships to obtain flight measurements.A photograph showing the location of the microphones on the ships is shownin figures 5(a) and 5(b). The USS Ponchatoula which received the signalthat originated at M = 9.71 had 7 microphones. Five of these were locatedon the deck and two above on the mast. Data from the 5 deck mountedmicrophones only was used in the comparisons of this report. The averageof the five peak overpressures is 15.3 N/m2 (.32 psf) for Mach 9.71. Thecalculated overpressure for this Mach number is 17.0 N/m2 (.355 psf). TheUSS Ticonderoga had only one microphone onboard which measured a peakoverpressure of 31.1 N/m2 (.65 psf) for Mach 1.83. The predicted peakoverpressure for the case is 34.1 N/m2 (.71 psf).

Comparison of extrapolated wind tunnel data with flight measurementsare shown in figures 6 and 7. Only the positive portion of the signaturespredicted from the wind tunnel measurements have been shown at both Machnumbers since Shockwave reflections from the floor of the wind tunnel

-4-

prevented determination of the complete pressure signatures at the Machnumbers of interest in this study (references 4 and 5). The extrapolatedwind tunnel pressure signature for Mach 9.71 is shown superimposed on eachof the flight signatures recorded on the deck of the USS Ponchatoula(see figure 7).

The multiple shock waves suggested by the flight pressure signatures havenot been satisfactorily explained. Some differences in signature shapemight be expected for the following reasons: First, the flow conditions inthe tunnel were different from the conditions present in the atmosphereduring reentry (e.g. temperature, Reynolds' number, density and humidity);second, the model wake was different from the wake behind the full-scalevehicle due to sting effects; and third, shock reflections from the shipsuperstructure may have produced the peculiarities of the signaturesmeasured on board the ships. However, the parameter of primary interestis the peak overpressure and the agreement between estimates and measure-ments for this parameter is good. A summary of the predicted overpressuresfor each Mach number is shown in figure 8. The flight measurements areshown parenthetically.

CONCLUDING REMARKS

A wind tunnel-flight correlation of the sonic boom characteristics ofthe Apollo 16 command module has been made. These results in conjunctionwith those of reference 3 indicate that the maximum overpressure generatedby a blunt, maneuvering vehicle with strong detached shock waves can besatisfactorily predicted using currently available sonic boom extrapolationmethods.

-5-

REFERENCES

1. Thomas, C. L. : . Extrapolation of Sonic Boom Pressure Signatures bythe Waveform Parameter Method. NASA TN D-6832, June 1972.

2. Hayes, W. D., Haefeli, R. C., and Kulsrud, H. E.: Sonic BoomPropagation in a Stratified Atmosphere, with Computer Program.Rept. No. 116, Aeronautical Research Associates of Princeton, Inc.,Dec. 1968.

3. Hicks, Raymond M., Mendoza, Joel P., and Garcia, Frank: A Wind Tunnel-Flight Correlation of Apollo 15 Sonic Boom. NASA TM X-62,111,January 28, 1972.

4. Mendoza, Joel P., and Hicks, Raymond M.: Wind Tunnel PressureSignatures for a .016-Scale Model of the Apollo Command Module.NASA TM X-62,047, July 14, 1971.

5. Hicks, Raymond M., Mendoza, Joel P., and Thomas, Charles L.: PressureSignatures for the Apollo Command Module and the Saturn V LaunchVehicle with a Discussion of Strong Shock Extrapolation Procedures.NASA TM X-62,117, April 6, 1972.

6. U. S. Standard Atmosphere Supplements, 1966. Environmental ScienceServices Administration, National Aeronautics and Space Administration,United States Air Force.

(a) Full scale vehicle.

Figure 1.- Photograph of an Apollo Command Module.

(b) Installation photograph showing model in 20-inch Supersonic Wind Tunnel at the Jet PropulsionLaboratory

Figure 1.- Concluded.

-60 28 r 12 r

-50 24

-40 U 20

o>(U

-30I

*••s-

16

-20 12

-10 8

54

48

36

30

24

J 18

42:00 42:20 42:40 43:00 43:20 43:40 44:00

Time/ Hrs Min

(a) Flight path angle/ heading angle/ Mach number and attitude.

Figure 2.- Apollo 16 reentry flight data.

44:20

10

fc

ooo

3.0 r

2.5

2.0

(U-a

OCO

1.0

157.0 -

156.8 -

156.6 -0)-a

156.4 -

156.2 -

156.0

42:00 42:20 42:40 43:00 43:20 43:40 44:00 44:20

Time, Hrs Min

(b) Longitude and latitude

Figure2.- Concluded.

I I I I

^

1 1 I I

••••.

M i i ;•:AHANCA

tANIHIKI '

-

0°t i i i

MftVIS ISLAND(UNITOtTATB) ,

'

-

5°:

_

10°Tl II 1 Ul 1

vVv°*•• <i"v-v

'-

„

I ] II

"~ O

L°

_

AflANDONEI

EMERGF* " PIEL

^ .̂x'

AOMIIS CLAIJV

/ A

\ 1 '

USS

USS PON

*

'__

j i I ii M

^^-.

ii

r \

1*0

_

•

•* -^ ,

\*

V eotmsoN

r - ,-.M ii Figu

0 NO. 1

Jft||' CHRI

CHRISTMAS ATOLLISTEKEO BY UNITED KIN

ED ALSO BY UNITED STA

I I I 1 1

TICONDEI

CHATOUL

/

/]

0 S

•'PfNIHYN

re 3.- Ree

JMAS ISLAND

JDOM)ESJ

1- 1 i l l

ROGA 13>^

J"

A}<&-fM = 1

= 15;

^""

jntry groun

j-

_ " i1 Degree latitude^lll .2 km ( 60 nm )1 Degree longitude^ 11 1.2 km ( 60 nm )

/f=T

1_|_| !•

o

• "n

i |.i i M ii

*STARBUCK ISLAND(ADMIN BY UK

CLAIMED ALSO BY US)

-— — -

d track of

j

" ' ' I I

: inrin'-i •"•

_

[—

L•MALDEN SLAND7(ADMIN BY UK1AIMED AISO BY US)

•~

;[— ~_>

_

7

Apollo 16

I_

—

-

i M Ii i| i

1 1 1 1 1 - fi .

— <?

<

VOSTOK ISLAND(AOMIN BY UK

CLAIMED ALSO BY US)

c>CAft

(AOMINISTEtEICLAIMED Alt-j- , ^

- 1

.2

ApP

0

M= 1.83h/?= 9.6Bank angle = 57.4°

.8

.6

A_P .4P

.2

0

M=9.71.h//=9.6Bank angle = 49.6C

0 8 12 16

A_xZ

20 24 28

Figure 4.- Wind tunnel pressure signatures,

(a) USS Bonchatoula.

Figure 5.- Photograph showing location of microphones.

(b) USS Ticonderoga.


40(0.836)

20(0.418)

inQ.

CM

-20(-0.418)0 40

Flight measurement - USS Ticonderoga

Extrapolated wind tunnel data

80 120 160 200 240 280 320 360 400 440

Time, msec

Figure 6.- Apollo 16 command module wind tunnel-flight correlation; JA = 1.83> h = 23,652 m (77>599ft) , \|r = 26.3°, 7 = -2^-5°, M = -.0488/sec, ijf = 0.6%ec, 7 = -O.lf3°/sec, bank angle = -57.U°

.20(0.418)

10(0.209)

Q.N_<»

siE

o.<

0

-10(-0.209)Q

Flight measurement - USS Ponchatoula


40 80 120 160 200 240

Time, msec

(a) Microphone 1

280 320 360 400 440

Figure 7.- Apollo 16 command module wind tunnel-flight correlation; M = 9-71, h = UU,113 mft), t = 21°, 7 = -2.7°, M = -.0826/sec, i j r ' = 0.13%ec, y = -.03%ec, bank angle = -^9.

= -1.5

20(0.418)



10(0.209)

CM

Q.

< 0

-10(-0.209)

0 40 80 120 160 200 240 280 320 360 400 440

Time, msec

(b) Microphone 2

Figure 7.- Continued.

20(0.418)

10(0.209)

CO0.

C\J

-10(-0.209)



40 80 120 160 200 240

Time, msec

(c) Microphone U


280 320 360 400 440

20(0.418)

10(0.209)

toa.

<\J

o o

-10(-0.209) 0



40 80 120 160 200 240 280 320 360 400 440

.Time, msec

(d) Microphone 6


20(0.418)



10(0.209)

ino.

Q.

<J

0

-10(-0.209)

^440

Time, msec

(e) Microphone 7


en01-a

*.cu-a

JS

.4-1o

CO

0

.5

1.0

1.5

2.0

2.5

3.0

Note : Overpressure shown in parentheses are flight measurements.

1 psf = 47 .88 N/m2

Ap = 13.0

Footprint for M = 9.71-i

Ap=.34.1(31.1)"

Footprint for M = 1.83

Location of USS Ticonderoga

Ap=20.8 N/m2

Location of USS Ponchatoula

Ap=14.9.

Ap= 13.9 N/m2

M = 11.1

J.

158.0 157.5 157.0 156.5 156.0

West longitude/ deg

Figures.- Apollo 16 ground track with overpressures.

155.5

Documents

CO CASE FILE COPY - NASA