water landing impact accelerations for three models of reentry capsules

7/28/2019 Water Landing Impact Accelerations for Three Models of Reentry Capsules

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NASA TN D- 145i.

TECHNICAL NOTE0-145

THREE MODELS O F REENTRY CAPSULESBy Victor L. Vaughan, J r.Langley Research Center

Langley Field, Va.

NATIONAL AERONAUTICS AND SPACE ADMINISTRATIONWASHINGTON October 1959

(PASd-I I ' i -C- IU5) E A ! i E F - L A N C I h G l E E A C T I 09- 70626A C C E L E P A l I C L S FCh IfiBIE BCC E I Z C E GEEITBYCBFS I J L ES ( NA ZA ) 2 9 g Unclas00134 0 1 9 7 1 6 2


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NATI ONAL AERONAUTI CS AND SPACE ADM NI STRATI ONTECHNI CAL NOTE D- 145

WATER-LANDI NG I MPACT ACCELERATI ONS FORTHREE MODELS OF REENTRY W S m SBy Vi ctor L . Vaughan, J r .

SUMMARY

Experi mental i nvest i gat i ons have been conducted to determne theThe mai n bodi es

r i gi d- body i mpact accel erat i ons for three model s of reentry capsul esdur i ng si mul ated parachute- supported water l andi ngs.of the model s were coni cal i n shape.one had a segment of a sphere as a bottomand the other had a 53 coni -cal shape as a bottom The thi rd model was 1/6 scal e and had a convex-coilca1-e t i o t t m .90 (vert i cal ) and 65 to si mul ate parachute l andi ngs w th no w nd andw th w nd, respecti vel y, and nomnal contact at t i tudes of f30, f l 5O,and Oo t o si mul ate at t i tudes that mght occur as a resul t of sw ngi ngof the capsul e under the parachute. Accel erat i ons of the model s ati mpact were measured al ong the X (rol l ) and Z (yaw) axes by accel erometers i nstal l ed at the centers of gravi ty.

Two of the model s were 1/12 scal e;The m6el wer e tested f or nomnal f l i ght paths of

The maxi mumaccel erati ons al ong the X- axi s f or the three f ormswere hi gher for i ncl i ned f l i ght - path angl es t han f or the vert i calf l i ght path, and vari ed as the square of the vert i cal contact vel oci tyf or a gi ven shape, f l i ght path, att i tude, and mass. The maxi mumaccel -erat i ons al ong the X- axi s f or the model w t h the spher i cal bot tomwereabout 5Og at a contact att i tude of 0 and dropped sharpl y t o about l ogw th i ncrease i n contact at t i tude to about f30. The maxi mumaccel era-t i ons f or the model w th the coni cal bot tomwere about l og and werei ndependent of contact at t i tude.The accel erat i ons al ong the Z- axi s were smal l f or the model s w t hthe spheri cal and coni cal bot toms at a contact at t i tude of 0 regard-l ess of f l i ght - path angl e and small (up t o 3g) f or the model w th thespheri cal bot tomf or al l test condi t i ons. The accel erat i ons i ncreasedal ong the Z- axi s of the model w th the coni cal bot tomto about 11gw th departure from the 0 att i tude condi t i on.The maxi mumaccel erati ons al ong the X- axi s of the model w th theconvex-concave bot tomwere about l 7g at a contact at t i tude of Oo andi ncreased t o about 28g w th i ncrease i n contact at t i t ude to *TOo.accel erat i ons al ong the Z- axi s were smal l at a contact atti tuci e of 0f or the model w th the convex-concave bottomand i ncreased to about l 3gat a f 30 contact att i tude.

The


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I NTRODUCTI ONI nterest has recent l y been shown i n obtai ni ng i nf ormat i on on thei mpact accel erat i ons whi ch mght occur on reentry capsul es duri ngparachute- supported water l andi ngs. I n thi s connecti on, experi mentali nvest i gati ons have been made by the Langl ey Research Center to deter-mne water- l andi ng i mpact accel erat i ons on model s of coni cal - shapedreentry capsul es havi ng a vari ety of i mpact bottoms.had a segment of a sphere for a bot tomwhi ch was desi gned to serve asa heat shi el d upon reentry i nto the atmosphere. A f ul l - scal e reentrycapsul e of thi s conf i gurat i on has been test ed and i s reported w th someof the present model data i n ref erence 1. Another model had a 53 coni -cal bottomwhi ch was al so desi gned to serve as a heat shi el d.thi rd model was desi gned for l owaccel erati ons on water i mpact and hada convex-concave bottom

a heat shi el d but coul d be used as a second bottomt hat woul d be exposedf or l andi ng purposes br droppi ng the heat shi el d f romthe capsul e.

One such model

TheThi s bot tomshape has not been devel oped as

Si nce the f i nal descent of the capsul e to a water l andi ng woul d beby means of a parachute, some of the ef f ects of surf ace w nds were si mu-l ated by usi ng vari ous f l i ght paths. A range of contact at t i tudes wastested t o si mul ate the at t i tudes t hat might occur i f the capsul e weresw ngi ng under the parachute at water contact. A w de range of vert i -cal contact vel oci t i es was i nvest i gated t o determne the ef f ects ofvel oci ty on i mpact accel erat i ons.

MODEL DESCRI PTI ONSDraw ngs of the three model s of reentry capsul es w th f i l l - scal edi mensi ons are shown i n f i gure 1. The dynamc model s were const ructedof f i ber gl ass and pl ast i c and the const ruct i on was as r i gi d as possi -bl e to el i mnate structural vi brat i ons. For purposes of i dent i f i cat i onthe model s have been desi gnated as model s A, B, and C.Model A was 1/ 12 scal e and had a segment of a sphere as a bottomThe model had a f ul l - scal e wei ght of 2,270 pounds.model f or whi ch data are reported i n ref erence 1. Thi s i s the sameModel B was 1/ 12 scal e and had a 53O coni cal shape as a bottomThe model had a ful l - scal e wei ght of 2, 000 pounds.Model C was 1/6 scal e and had a convex- concave bot tom Thi s bot tomwas desi gned, by use of the computat i on procedure out l i ned i n ref erence 1,to have a rate of appl i cat i on of accel erati on upon water contact of about

5OOg per second and a maxi mumaccel erati on of l 5g. The other desi gn


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3parameters were a vertical f l ight path, Oo contact atti tude, and a fu l l -scale verti cal contact velocity of 30 feet per second and weight of1,000 pounds.

APPARATUS AND PROCECURE

Two strain-gage-type accelerometers were located at the center ofgravity of each model and ri gi dl y attached t o the bottom of the model.The accelerometers were capable of recording accelerations of 200g and25g along the X-axis and Z-axis , respectively. A drawing showing theaxi s system of the models i s presentedin figure 2. The signals fromthe accelerometers were transmitted through cables to amplifying andrecording equipment. The natural frequency of the 200g accelerometerwas about 900 cycles per second and that of the 25g accelerometer wasabout 350 cycles per second.cent of cr i ti cal damping.f lat to about 2,200 cycles per second.

The accelerometers were damped to 65 per-The response of the recording equipment was

Nominal fl ight paths of 90 (vertical) and 65O and a range of con-tact atti tudes from -30' to 30 were investigated. The f l ight pathsand contact atti tudes are identified in figure 2. The tests for thevertical f l ight path were made by a f ree-fal l method, the models beingdropped from the required heights t o obtain the range of speeds from10 to 45 f eet per second at water contact.path were conducted with a catapult type of test apparatus as shown i nfigure 3 . The catapult consisted of a steel staff which followed thef l i ght path by moving through a ri gidly mounted rol l er cage. A yoke,which held the model by means of pins inserted i nto sleeves at the edgeof the model base, was mounted at the bottom of the staff. The pinswere under spring tension and were retracted at the end of the catapul tstroke to f ree the model. The desired atti tude was set by a sti ng whichw as fixed to the staff and inserted into the top of the model. Desiredspeeds were obtained by varying the catapult stroke or by using a shock-cord drive. The velocity of the catapult was measured by recording thetime for the staff to travel the last 2 inches of the catapul t stroke.An electroni c counter, capable of recording time to 1/ 100, 000 of a second,was used for this purpose. The catapult vel oci ty was combined with theveloci ty computed for the free-fal l height, which was the height betweenthe model release point and the water surface, to obtain the actual con-tact velocity.

The tests f or the 65O f l ight

Most of the tests f or the 90 and 65O f l ight paths were made at aful l -scal e vertical contact velocity of 30 feet per second with a varia-ti on of t l . 5 f eet per second. The other veloci ti es were investigatedt o determine the effects of veloci ty on impact accelerations.paths and contact atti tudes of the models were recorded by a high-speedThe f l i ght


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moti on- pi cture camera.t o 69.The densi ty of the water was 1.94sl ugs/cu f t .The nomnal 65 f l i ght path vari ed f rom65The test s were conducted i n cal mwater i n the Langl ey tank.

RESULTS AND DI SCUSSI ONTypi cal t i me hi stor i es of accel erat i ons al ong the X- and Z- axesf or t he three model s are presented i n f i gures 4 and 5.erat i ons are pl otted agai nst contact at t i tude f or the three model s i nf i gures 6 t o 11.

Maxi mumaccel -A l l val ues shown are f ul l scal e.

The maxi mumaccel erati ons al ong the X- axi s f or model A ( f i g. 6)were about 40g f or a contact at t i tude of Oo and a vert i cal f l i ght pathat a vert i cal contact vel oci ty of approxi matel y 30 f eet per second. Forthe 65 f l i ght path, 0 contact at t i tude, and 30- f eet - per - second vert i -cal contact vel oci ty the maxi mumaccel erati ons were about 3Og. Thei ncrease i n accel erat i ons due to the change to a 65O f l i ght path wascaused by the i ncreased vel oci ty al ong the 65O f l i ght path as comparedw th the vel oci ty al ong the vert i cal f l i ght path. I ncrease i n vert i calcontact vel oci ty to approxi matel y 38 f eet per second f or the 65 f l i ghtpath and 0 contact at t i tude i ncreased the accel erat i ons to about 8Og.I ncrease i n contact att i tude i n ei ther the posi t i ve or negat i ve di rec-t i on f rom0 reduced the accel erat i ons unt i l at f 30 at t i tude the accel -erati ons were about l og f or both f l i ght paths. The l ower accel erat i onsmay be attr i buted to the wedge shape of the i mpact surf ace at TO0 att i -tude as compared w th the bl unt i mpact surf ace at 0 att i tude.

The maxi mumaccel erati ons al ong the Z- axi s for model A ar e shownThere were no measurabl e accel erat i ons al ong the Z- axi sn f i gure 7.f or ei ther f l i ght path at a contact at t i tude of Oo and a vert i cal con-tact vel oci ty of approxi matel y 30 f eet per second. The i ncrease i n con-t act att i tude f rom0 t o about 30 caused very small accel erat i ons,about 2g, f or a vert i cal f l i ght path. I ncrease i n contact at t i tude i nthe negat i ve di recti on f romOo t o 30 at t i tude f or the 65 f l i ght pathgave accel erat i ons of about 3g or 4g. The same val ues of accel erat i onwere obtai ned f or posi t i ve att i tudes; however, the di rect i on of theaccel erat i ons al ong the Z- axi s was reversed. I ncrease i n the vert i calcontact vel oci ty t o approxi matel y 38 f eet per second had a negl i gi bl eef f ect on the accel erat i ons al ong the Z- axi s throughout the ful l rangeof contact att i tudes.

Maxi mumaccel erati ons al ong the X- axi s of model B f or a vert i cal' contact vel oci ty of approxi matel y 30 f eet per second are shown i n f i g-ur e 8, w th data for model A as a ref erence.between model s A and B i s 13 percent , and check test s i ndi cated thatThe di f f erence i n wei ghtsf or a vert i cal f l i ght path and a contact att i tude of 0 the wei ght


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di f f erence caused a very smal l (3g) vari at i on i n the maxi mumaccel era-t i on. Thi s was substant i ated by cal cul at i ons usi ng the computat i onprocedure out l i ned i n ref erence 1.al ong the X- axi s f or model B were about l og f or both f l i ght paths at acontact at t i tude of Oo.w th model A may be at tr i buted to the more poi nted i mpact surf ace of theconi cal - shaped bottomof model B. I ncrease i n contact at t i tude i n ei therthe posi t i ve or negat i ve di rect i on f rom0 to 300 had very l i t t l e ef f ecton the accel erat i ons al ong the X- axi s of model B f or both f l i ght paths.I t may be noted that the accel erat i ons at 30 contact at t i tude were aboutthe same for model s A and B.

Fi gure 8 shows that the accel erat i onsThe l ower accel erat i ons of model B as compared

Maxi mumaccel erat i ons al ong the Z- axi s of model B at a vert i calcontact vel oci ty of 30 f eet per second are shown i n f i gure 9, w th dataf or model A as a ref erence. There were no measurabl e accel erati onsal ong the Z- axi s of model B at a contact at t i tude of 0 f or a vert i calf l i ght path.accel erat i ons of about 7g f or a vert i cal f l i ght path. There were verysmall accel erat i ons, about 2g t o 38, al ong the Z- axi s of model B at acnntact. at. t. i tude of Oo and a 65 f l i ght path.at t i tude i n the negat i ve di recti on f rom0 t o 30 i ncreased the accel -erat i ons to about l l g. I ncreases i n the contact at t i tude i n the posi -t i ve di rect i on f romOo to 30 i ncreased the accel erat i ons al ong theZ- axi s t o about 8g.

The i ncrease i n contact at t i tude f romOo to 30 gaveI ncreases i n the contact

Compari sons between model C and model s A and B have not been madebecause of the di f f erence i n desi gn parameters between the model s.Maxi mumaccel erati ons al ong the X- axi s of model C f or a vert i calcontact vel oci ty of approxi matel y 30 f eet per second ar e shown i n f i g-ure 10. The accel erat i ons al ong the X- axi s at a contact att i tude of 0were about l 7g f or both f l i ght paths w th a rate of appl i cat i on ofaccel erat i on of about 400g per second. Thi s compares very cl osel y w ththe 5OOg per second rate of appl i cat i on of accel erati on and the maxi mumof l 5g f or whi ch the model was desi gned. I ncrease i n contact att i tudei n ei ther the posi t i ve or negat i ve di recti on f rom0 i ncreased theaccel erat i ons al ong the X- axi s unti l at ?Poat t i tude the accel era-t i ons were about 28g f or both f l i ght paths.Maxi mumaccel erati ons al ong the Z- axi s of model C at a vert i calcontact vel oci ty of 30 f eet per second are shown i n f i gure 11. Therewere no accel erat i ons al ong the Z- axi s of model C at a contact at t i tudeof Oo f or a vert i cal f l i ght path.fromOo to 300 gave accel erat i ons of about l 5g f or a vert i cal f l i ghtpath. There were very smal l accel erat i ons, about 2g to 3g, al ong theZ- axi s of model C at a contact att i tude of 0 and a 6 5 O f l i ght path.I ncrease i n contact att i tude i n the negat i ve di rect i on f romOo to 30i ncreased the accel erat i ons to about 13g. I ncrease i n contact at t i tude

The i ncrease i n contact at t i tude


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6i n the posi t i ve di recti on f' romOo t o 30 i ncreased the accel erat i onsal ong t he Z- axi s of model C to about l l g.

The ef f ects of vert i cal contact vel oci ty on the accel erat i ons al ongthe X-axi s of model s A, B, and C at a contact at t i tude of Oo are pre-sented i n f i gure 12.port i onal to the square of the vel oci ty.i nvesti gat i on, f or a gi ven shape, f l i ght - path angl e, att i tude, and mass,the accel erat i ons al ong the X- axi s i ncreased di rectl y as the square ofthe vert i cal contact vel oci ty. Thi s statement al so appl i es for vel oc-

The scal e al ong the absci ssa of f i gure 12 i s pro-Wt hi n the l i mts of the

i t i es al ong the f l i ght path.the square of the vel oci ty i s expected fromthe f act that di spl acementat any gi ven i nstant i s the same regardl ess of contact vel oci ty,vi ded al l other parameters are i nvar i ant .A l i near var i at i on i n accel erat i on w th

pro-Cal cul ati ons by means of thecomputat i on procedure out l i ned i n ref erence 1 veri f y the resul ts gi veni n f i gure 12.Sequence photographs show ng a typi cal l andi ng of model A froma ,650 f l i ght path at a -30' contact att i tude and a vert i cal contact vel oc-i ty of 30 f eet per second are shown i n f i gure 13. At 0. 01 second af tercontact the model penetrat i on i s very smal l w th a negl i gi bl e change i natt i tude. As the penetrat i on i ncreases the model changes at t i tude i na posi t i ve di recti on, and at 0. 48second af ter contact i t has reachedmaxi mumpenetrati on and att i tude change.

Sequence photographs of a l andi ng f or model C f roma 65O f l i ghtpath at a -30' contact att i tude and a vert i cal vel oci ty of 30 f eet persecond are shown i n f i gure 14. The moti ons of the model are very s i m -l ar t o those of model A. Maxi mumpenetrati on and att i tude change occurat 0. 44second af ter contact.the fol l ow ng wave, whi ch st ri kes the back of the model , causes themodel to recover rapi dl y so that at 0.97 second af ter contact the modelhas rebounded to a posi t i on above the water surf ace.

The force of buoyancy and the force of

CONCLUDI NG REMARKSI n general , the maxi mumaccel erat i ons al ong the X- axi s of the

three model s f or a gi ven vert i cal contact vel oci ty were hi gher f or .. i ncl i ned f l i ght - path angl es than f or the vert i cal f l i ght path. For agi ven shape, f l i ght path, al t i tude, and mass the accel erat i ons vari edas t he square of the vert i cal contact vel oci ty.At a contact att i tude of 0 the maxi mumaccel erati ons were 50g forthe model w th the spheri cal bot tomand l og f or the model w th the coni -cal bottom I ncrease i n contact at t i tude i n ei ther the posi t i ve ornegat i ve di recti on resul i ed i n a reducti on i n accel erat i on t o about l og


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7at a 30 att i tude for the model w th the spher i cal bot tom whi l e thei ncrease i n contact at t i tude had l i tt l e ef f ect on the model w th theconi cal bot tom

The maxi mumaccel erati ons al ong the Z-axi s were smal l at a contactat t i tude of Oo for the model s w t h t he spher i cal and the coni cal bot tomsand small (up t o 3g) f or the model wth the spheri cal bot tomf or al ltest condi t i ons. The accel erat i ons al ong the Z- axi s i ncreased t o aboutl l g at a 30 contact at t i tude f or the model w th the coni cal bot tomThe maxi mumaccel erat i ons al ong the X- axi s of the model w th theconvex- concave bot tomwere about l 7g at a contact at t i tude of 0 andi ncreased t o about 28g w th i ncrease i n contact at t i tude to f30 att i -tude. The accel erat i ons al ong the Z- axi s were small at a contact at t i -tude of Oo f or the model w th the convex-concave bottomand i ncreased

t o about l3g at a f30 contact att i tude.Langl ey Research Center,Nat i onal Aeronaut i cs and Space Admni strat i on,Langl ey Fi el d, Va. , J ul y 30, i y33.

REFERENCE1. McGehee, J ohn R. , Hathaway, Mel vi n E. , and Vaughan, Vi ctor L. , J r . :' Water- Landi ng Character i st i cs of a Reentry Capsul e. NASAMEMO 5-23-59LJ 1959.


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8

Model AI

(Spheri cal bottom)

8

Model B (Conical bot t om)Figure 1. - Det ai l s of model s. Di mensi ons ar e fu l l s cal e i n f eet .


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Mo\del C (convex-concave bottom

A0.030.119.296.440- 577- 705.825.9261. 0181. 1001. 172

1. 2501. 5001. 7502. 000

B

0 . 138. 350.654.8631. 0631.2631. 6801.8902. 110 ,2.3402 5252. 8302. 965

1. 470

3 OOO

F i gur e 1. - Concl uded.


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NOTE: X- and Z- axes are i nplane of f l i ght path.

7'Z+Ao

-

N egat ve

atti tude

Fl i ght pathAFigure 2.- Drawings identiming axes, force directions, f l i ght paths,and contact atti tudes.


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YO0 Flight Path30 f ps contact velocity65O Flight Path30 f ps contact velocity38 f ps contact vel oci ty

I I I I0 10 20 30 4040 -30 -20 - 10Cont act atti tude, deg

Fi gure 6. - Maxi mumaccel erat i ons al ong the X- axi s of model A . A l lval ues are ful l scal e.


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00A

I I I

900 Flight Path650 Flight Pat h

30 f p a contact veloci ty30 fpa contact veloci ty38 fpa contact veloci ty

I I I 1-20 - 10 0 10 20 30 4040 -30 Contact atti tude, deg

Fi gure 7. - Maxi mumaccel erati ons al ong t he Z- axi s of model A . A l lval ues are ful l scal e.


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20 -5O f l i g h t pathe- - -0 f l i ght path

I I I I-40 -30 - 20 - 10 0 10 20 30 40Contact atti tude, degFi gure 8. - Compari son of maxi mumaccel erati ons al ong the X- axi s ofmodel s A and B at a vert i cal contact vel oci ty of 30 f eet per second.A l l values are ful l scal e.


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A

L

A 6 5 O f l ight pa t hh- - - 90 f l ight path

rodel A\\\ Model !3

1 I I IContnc t atti ude, deg

Fi gure 9.- Compari son of maxi mum accel erat i ons al ong the Z- axi s ofmodel s A and B at a vert i cal contact vel oci ty of 30 f eet per second.A l l val ues are f u l l scal e.


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C1-- 6 5O f l i ght path-- 0 f l i ght path

-40 - 30 -20 - 10 0 10 2 0 30 40Cont act atti tude, degFi gure 10. - Maxi mumaccel erat i ons al ong the X- axi s of model C at avert i cal contact vel oci ty of 30 f eet per second.f u l l scal e. A l l val ues are


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a- 65O fl1p;ht path0 --- 90 f l i gh t path

\

\\0

1 I I J10 20 30 40.Contact atti tude, de gFi gure 11. - Maxi mumaccel erati ons al ong the Z- axi s of model C at avert i cal contact vel oci ty of 30 f eet per second. Al l val ues aref ul l scal e.


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water landing impact accelerations for three models of reentry capsules

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