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\

AIM

Paper

NO 73

1

82

DECK HEATING EF F EC TS DUE TO VTOL

JET

EXHAUST IMPINGEMENT

by

0

T .

CASTELLS and R . B. MISHLER

G ener a l

Elec t r ic

Company

Cincinnat i , Ohio

r?

E

w

A l A A l S A E gth

Pronulsion Conference

LA S VEGAS, NEVADA /

NOVEMBER

57,1973

M 73 572

First publication rights reserved b y American Institute of Aeronautics and Astronautics.

1290 Avenue of the Americas, New York,

N.

Y. 10019. Abstracts may be published without

permission if credit i s given to author and to AIA A. (Price: A lA A Member 1.50. Nonmember 2.00)

Note: This paper available at AlAA New York office for six months;

thereafter, photoprint copies

are avai lable a t

photocopy

pr ices

from

AlAA Library,

750

3rd Avenue, New York, New York 10017

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DECK HEATI NG EFFECTS DUE TO VTOL J ET EXHAUST l MPI NGFNENT

OT. Castel l s

R.B. M s hl er

Gener al El ect r i c Company

Ai r craf t Engi ne Cr oup

Ci nci nnati , Ohi o 45215

-

Abstract

Opti mumsupersoni c VTOL ai r cr af t r equi r e hi gh

speci f i c t hr ust engi nes.

vel oci t y and t emper atur e w t h i ncreased heati ng

pot ent i al . The pr esent study i dent i f i es deck

t emperat ure profi l e(s) f or var i ous j et. exhaust

conf i gur at i ons on a deck.

operat i onal modes on t he deck t emper at ure ar e eval -

uated.

w t h j et conf i gur ati on, are found to be t he pri n-

ci pal var i abl es af f ecti ng deck peak t emperat ur e.

Var i ous met hods o f r educi ng peak deck t emper at ure

wer e

consi der ed. Saf e operat i onal usage

of

aug-

ment ed t urboj ets f or supersoni c VTOL ai r craf t ,

appear s t o be f easi bl e w t h mnor constr ai nt s.

Thi s resul t s i n hi gh j et

The ef f ects of var i ous

Run up t i me and cycl e condi t i ons, al ong

Nomencl at ur e

As = Nozzl e exi t area

CN = Adj usted nozzl e coeff i ci ent used i n the

cal cul at i on of J et vel oci ty decay

Cyp

=

Nozzl e vel oci t y coef f i ci ent of non- ci rcul ar

nozzl es

CvSTD= Vel oci t y coef f i ci ent of

a

ci rcul ar nozz l e

Dg = Equi val ent nozzl e exi t di ameter

Dh = Hydr aul i c di ameter

Dhe = J 4nAs/ nozzl e per i meter

g = Accel er ati on of gr avi t y (32. 2 f t l sec )

h = Heat t r ansf er coef f i ci ent

K Thermal conduct i vi t y

I , = I:harac t4vi :; t 5.r i cn~t h or det em ni ng

Mg = Nozzl e exi t Mach number ( f ul l y expanded)

NU = Nussel t Number = hL/ K

PR =

Pr andt l Number

Re = Reynol ds Number

TR = Recover y (adi abati c wal l ) t emper ature

TTR

=

TTN

=

Nozz1. e exhaust t otal t emperat ure

T~w=

VI VB

=

V/ Vj et

=

rat i o of the cent er l i ne vel oci t y

2

Nj arid

IKe

Max i mm

jeC

t otal t e. mper at ur e

e )

own-

st r eamof nozzl e

exi t

downstr eamof t he exi t t o t he nozzl e exi t

vel oci t y

-

Vg ~. Jel euj t vel oci t y, a?so Vj et , Wi,

;: :

3i.:. .mce

dormscream

of: nozal'. exi t.

I

~ C ? ? - ~ O X l ~er.d?Liom.

Tha

USN

has f ormul i i t*, d a cequi . rement for a

supersoni c deck 1; runche. l nter cept or t o be

oper-

at ed f r omt he new

sea

cont rol shi ps. Tho al t er-

nate m ssi ons f or t he ai r craf t i ncl ude t he var i ous

t ypi cal Navy r equi r ement s of subsonic sur f ace

survei l l ance, combat ai r patr ol and var i ous other s.

To meet t hese requi r ement s, sever al VTOL ai r cr af t

have been st udi ed i ncl udi ng t he f ol l ow ng t ypes.

o

Ti l t PodI Tai l Si t t er

o

Advanced Har r i er

o

Augment or W ng

Al l of t hese syst ems have si gni f i cant compra-

m se8

of thei r mul t i - m ss i on capabi l i t i es f orced on

t hemby t he ver t i cal T. O r equi r ement . The var i ous

Syst ems have a great var i at i on

i n

t he heat i ng pr o-

bl ems whi ch t hey cause t o t he shi p' s deck. A sur -

vey paper of t hese pr opul si on syst ems, Ref erence

1,

has

shown a

si gni f i cant advant age f or syst ems whi ch

ut i l i ze al l avai l abl e t hr ust on board at T.O and

t he hi ghest possi bl e speci f i c thrust at T. O , such

a8 i s gi ven by r eheat augmentat i on. Syst ems wi t h

l ow speci f i c thrust at T.O r equi r e a l ar ge por t i on

of t he Al C vol ume to be consumed f or T.O propul -

si on causi ng comprom ses i n t he AI C St r uct ur es,

w ng desi gn and usef ul avai l abl e vol ume f or non-

propul si ve pur poses. An added advant age f or t he

hi gh speci f i c thrust syst ems i s t hdm ni m z i ng of

t he l arge i nstal l at i on penal t i es whi ch ar e associ -

ated w t h VTOL ai rcraft ' s hi gh t hr ust l oadi ngs.

I n t he past , t he magni t ude of t hese l osses has not

been report ed si nce much of t he drag caused by t he

VML pr opul si on has been i ncl uded

i n

t he basi c ai r -

craf t drag pol ar and not at t r i but ed di rectl y t o the

pr opul si ve devi ce. As t he engi ne speci f i c t hr ust

Is i ncr eased t hese f actor s ar e m ni m zed even t hough

t he i nt ernal engi ne crui se per f ormance decr eases.

Proper assessment of the above f act or s t ends t oward

r educed bypass r ati o, beyond t hat whi ch resul t s f r om

an uni nstal l ed opt i m zat i on techni que. Al l

of

t hese

consi derat i ons and a 6ompl ete ai r cr af t s yst emst udy

l ed t o t he desi gn of a composi t e ai rcr af t ut i l i z i ng

r eheat augment at i on i n the take- of f mode whi ch i s

i l l us t rated i n Fi gur e

1. 

Compos i te di rect l i f t p l us l i f t l c rui se

engi ne

Fi g. 1 VlQL Ai rpl ane, 3 Vi ew

1

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The compl et e descr i pti on of t he advant ages and

perf ormance of t hi s ai r craf t i s beyond t he scope

of thi s paper. Here, we wi l l rest r i ct oursel ves to

exam ni ng t he magni t ude of t he probl emf or saf e

operat i on of t hi s ai rcr af t wi t h i t s r esul tant hi gh

exhaust vel oci t i es and temper atur e.

Conf i gurat i on Descr i pt i on

Two

l eaky t ur boj et engi nes of bypass r ati o of

. 2

were

ut i l i zed for t he l i f t l c rui se requi rement

w t h one advanced di r ect l i f t engine l ocated i n the

f usel age. The engi nes are l ocated as cl ose

s

can

be achi eved to t he ai r cr af t CG t o m ni m ze moment s

and al l ow i nf l i ght Vectori ng f or maneuverabi l i t y.

Rro separate i nst al l ati ons were anal yzed to deter-

m ne t he eff ect s of nozzl e desi gn

on

deck. heati ng.

The f i r s t u t i l i z ed a conventi onal r ound nozzl e in-

s t al l ed w t h a t hree bear i ng t ai l pi pe. The second

nozzl e w a s a t wo- di mensi onal desi gn. Per t i nent

geomet r y and t he di f f er ence i n hei ght above deck of

the nozzl es i s i l l ustr ated

i n

Fi gur e 2.   A l ow

carbon st eel deck of 314 i n. t hi ckness was assumed.

CI RCULAR

3- BEARI NG 2- DI MENSI ONAL

i g. 2

VTOL

Nozzl e Conf i gur ati ons

Method of Sol uti on

The

wethod of anal ysi s consi st ed of a sem -

empi r i cal t echni que f or det erm ni ng t he heat t rans-

f er coef f i ci ent s and r ecover y temper atur es whi ch

wer e

used as i nput t o an anal yti cal t r ansi ent heat

t r ansf er comput er pr ogr am Onl y a general descr i p-

t i on of t he t echni ques empl oyed i s pr ovi ded, i n the

i nterest of brevi ty .

A

t r ansi ent heat t r ansf er computer pr ogr amwas

empl oyed (HETRANS) whi ch gave an axi syrometr i c nodal

sol uti on t o the energy bal ance equati on. A pr i mary

si mpl i f i cat i on i n the anal ysi s was consi derati on

of onl y

a

si ngl e j et exhaust . The t emper atur e pr o-

f i l e between nozzl es coul d not be pr edi cted w t h

t hi s method, but as wi l l be di scussed l at er , the

t emperat ure decay away fr omt he j et center l i ne i s

so rapi d t hat t he peak deck t emperatures ar e st i l l

val i d.

Ot her si mpl i f i cati ons and assumpti ons

wer e nec-

essar y i n order t o obt ai n

a

sol ut i on. Ef f ects of

nozzle shape on vel oci t y and t emper at ure decay of

the j et

were

i ncl uded, but not

on

pl ume shape.

Thus, t he characteri st i cs of t he pl ume were based

on par amet er s non- di mensi onal i zed by an equi va-

l ent nozzl e di ameter, i .e.,

a

di amet er whi ch woul d

r esul t i n an equi val ent nozzl e

area.

The

nodal net wor k w a s set up

as

shown

i n

Fi gur e 3.

r equi r ed f o r nor mal t akeof f s and l andi ngs, i t

was

consi der ed necessar y f O K t he abort ed takeof f to

bati c sur f ace exi st ed at t he out er peri phery. The

boundar y condi t i on i mposed at t he l ower surf ace of

t he l aunch deck was t hat of nat ural convect i on wi t h

a

f i l m coef f i ci ent of

1

Bt u/Ft 2

- HR -

OF.

Al t hough t hi s l arge of a net work w a s not

ver i f y the val i di t y of t he assumpt i on t hat an adi a-

. . . .

I

.I I 2 4 7 111 1 5 2 0

25

Fi g.   3 Axi symmet r i c Nodal Net wor k

Pr i mar y i nput r equi r ed f or t he HETRANS program

i s t he heat t r ansf er coeff i ci ent and r ecovery t emp-

erat ure at t he deck surf ace as f unct i on of t i me

and di st ance f r omt he j et cent erl i ne. Vari ous

met hods wer e eval uat ed and composed.

Several i nvest i gat or s have measured

an d

cor r el -

at ed heat t r ansf er. General l y, t he f ormof t he

corr el ati on i s gi ven by:

NU

=

C

. ReA P

f (R/ L) where, 1)

A, B, C,

=

Const ant s of empi r i cal corr el ati on

F(R/ L)

= Functi on of di st ance f r omt he j et

center l i ne

Donal dson' s, et al , (Ref . 2) cor r el ati on and

dat a

on

heat t r ans fer coef f i c i ents , h, f or j et s i m

pi ngi ng

on

a f l at sur f acewas f ound both sat i sf ac-

tory and fai r l y si mpl e to appl y. Donal dson' s t est

dat a i s summar i zed

i n

Fi gur e 4 A smal l t rend w t h

Reynol ds number

i s

apparent . A hi gh Re f ai r i n%of

t he dat a

was

empl oyed.

I n

order to eval uat e the heat t ransf er coef f i c-

i ent , a method f or pr edi ct i ng t he j et vel oci t y and

t emperat ure decay charact eri st i cs

w a s

necessar y.

An empi r i cal equat i on obt ai ned f r omRef erence

3 was

sel ect ed t o predi ct t he j et vel oci t y decay.

wher e,

A1

=

41   8 1 3 ( Da/ Dh -

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Fig. 4

Corre la t ion of Heat Transfe r

Data

The above empi r ical re la t ion ship s were developed

from cold j e t model t e s t s , so t h a t a c o r r e c t i o n f o r

hot j e t s

w s

necessa ry. This was accomplished by

adj us t i ng the coe ff ic i en t (Cn) i n the above equa-

t i o n t o n e a r l y d u p l i c a t e h o t

j e t

r e s u l t s .

s pec i f i c a l l y , t he cu rve l equat l on shown i n  F igure

which was determined from tes t9 of a wide var ie ty

of nozzle shapes

was

used t o de f i ne

Cn.

The quan-

t i t y ( 1

-

CvsTD)

w a s

a d j u s t e d u n t i l e q ua ti o n

2)

nea r l y dup l i ca t ed t he ho t

j e t

tes t

results of

Reference

4.

More

Fig.

Corre la t ion of Veloci ty Coeff ic ien t Data

I t was a l s o neces s a ry t o p red i c t t he t em perat u re

decay of th e j e t with d i s t anc e from the

n o z z l e

e x i t

plane.

ava i l a b l e fo r anyt h ing o t he r t han c i r c u l a r nozz l e s.

A

cor re l a t io n of t emperature decay wi th ve lo ci ty

decay w a s made from the data of Reference 4 wfth

S a t i s f a c t o r y r e s u l t s ( Fi g ur e 6 ) . This Corre la t ion

w a s checked agains t data f rom independent murces

as

No ana l y t i c a l means t o do t h i s was - read i l y

shown i n  

Figure

7  wi t h r eas onab l e ve r i f i ca t i on .

Fig. 6 Velocity Decay Versus Temper ature Decay

Correla t ion .

o CE

nonu

TESTS

CORREUTION

i

2

3 . 4

5

6

. 7

.8 .9 1.0

TOTAL TFhlPERATURE

DECAY-

TT

MAX

To

TT n -

To

Fig. 7 Sub sta nt i at i on of Temperature Decay

C or re l a t i on .

In t h i s s tu d y, t h e t r a n s p o r t p r o p e r t i e s o f a i r

were used t o desc r ibe th ose of

t he j e t Values of

y ,

C ,

,

and v

were

var i ed wi t h s t a t i c temperature

a t t t e

j e t

impingement poin t , co ns ist en t with

Donaldson' s data re duct i on on h e a t t r a n s f e r c o e f f i -

c i e n t .

t o t a l t emperature , which amounts to

a

s l i g h t l y

cons erva t ive approximation .

The recovery temperature w a s taken

a6

t h e

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The e n t i r e p r o c ed ur e f o r c a l c u l a t i n g h e a t t r an s -

f e r coe f f i c i e n t and r ecovery tem pera t ure

was

pro-

grammed on a t ime sh ar ing computer to speed t he

cal cul a t io ns . These parameters

were

i n pu t i n t o t h e

t r a ns i en t hea t t r a n s f e r prog ram a l ong wi t h t h e

nodal network des cr ipt io n and Rppropriate boundary

cond i t i o r s f o r t he ca l cu l . a t ian o f t em pera t u re a s

a

funct ion of t i m e and loc at i on. Teniperatures a t t h e

cen t e r o f

the

nodes

were

computed, s o

a

s l i g h t

ex-

t r apo l a t i on o f

t he ou t put

was

r e q u i r e d t o o b t a i n

s u r fac e and ge t cen t e r l i n e t em pera t u res .

R es u l t s

Ai rc ra f t Opera t i on

Var ious m eans o f ope ra t i ng t he a i r c ra f t i n t he

VTOL mode

were

evaluated . Operat ional exper ience

o n t h e Harrier a i r c r a f t

has

f ou nd t h a t t h e " r o l l i n g

& t i c a l t akeoff" i s th e bes t ov er al l method. This

avoids re ing es t ion , for e ig n object damage, and

a l l

s i p i f i c a n t s u rf a ce h e at in g.

s ho r t l eng th . I f t h i s t echn ique i s not used and

a

p u re v e r t i c a l t a k eo f f i s r e q u i r e d, t h e h e a t i n g

problems

are

wors t .

t o u t i l i z e

a

ho l d down dev ice i n o rde r t o a s s u re

f u l l b a l an ce t h r u s t

i s

avai , lnble prior

t o l i f t

o f f .

This method

w a s

i nves t i ga t ed and t h e

eZ f e L t

of b o l J

down

t i m e

evaluated (F igure

8) .

I n t h i s a n a l y si ~ s ,

augmented t hr us t requi re d fo r

.OR 8 s

a c c e l e r a t i o n

w a s app lie d during th e hold down period .

The

r o l l h a s a very

The most Severe opera t i on i s

Fig. 8 Effec. t of Hold 1 I o m T;me o n Peak

S u r fa c e

Temperature.

A

second method

was

s t ud i ed i n whi ch

the

engine

was

acce l e ra t ed wi t h t he nozz l e f i xed i n t h e V-mrxle

position.

Peak te.npr-ratuv:s

re:irherl

w e v e

:il :gl*t. 'Y

cs5 thap rho our

s ~ m t l ?

old rlowi c as ?

.

p l e Condit ions

The

e f f e c t o

enpine

cjcl,.

cond i t i ons

Pol)

w r l ~

i nves t i ga t ed

1usini: t h v

two-dimensional iiozzle

and

n

four sec md hgl d dorm

opcmt. icn:~l.

procedure.

t h r e e

case:.

used t u o h t a i n t h e t r c n d of Fi.guurc 9

The

correspond t o maximum d ry , pa r t i a l r ehea t and f u l l

reheat condi t ions .

600

500

400

300

200

IO0

2-D

NOZZLE

o TAKEOFF

0

IO00

COO

3000 4000

T - F

T8

Fig.

9

Effect of T T ~ n Peak Deck Temperature

Inc reas e

-akeoff Versus L a d i s

Takeoff i s by f a r t h e c r i t i c a 1 , m o de a€ opera t i on

compared to l anding , s i nc e rehea t

i s

r e q ui r e d f a r

a c c e l e r a t i o n d u ri n g t h i s h i g h e r

gross

weight con-

dit ion. The 2-D nozzle with a ' four second h o l d

down during takeoff ind ica ted

a

peak deck tempera-

tu re 280°F h igher then f a r a l a nd i ng w it h 'a 1 0 f t l

s e c

r a t e

01: s i nk .

T h e

corresponding jet tempera-

r c % w

vere

?? A';' end I 'X i 'F, ' :esm*rti.vrly.

TI,,?

< feci

t1 ~

IC

:ate o f ::lr.k

:R 3) .I,rr.inp.

l.andL-,g was invrsvlg;

tg.1 an,?

f r i i r i i d

m ~ ; . r i n r i l r - l~ :>c iv c

fo

poak tcmperat , rea? but

the

t i ne to peak tempera-

tu re var ie d between 5 .8 seconds fo r R J S - 1 5 f p s t o

12 .0 seconds for

RIS

- 5 fps .

assumed t o be 50 f ee t above t he deck a t t h e

s t a r t

of

th e v e r t i c a l landi .ng descent . Landing power

was

held cons tant F o r two seconds a f t e r 1:ouchdom. and

varied 1 . i n e a r l ~

o

prier 1 F f i n f i v e seccndn.

The a i r c r a f t

was

6

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mx

r

acr oss the sur f ace,

as wel l

as t he expect ed cool i ng

char acteri st i cs of the deck w t h ti me.

Fi gur e 12 shows t he temper ature vers us t i me of

var i ous nodes dur i ng t akeoff w t h t he 2- 0 nozzl e

and t he f our second hol d down ( r ef er t o F i gur e 3 

t he l ar ge t emper atur e gradi ent t hrough t he deck

k

2

3

l rn .

, near t he center l i ne at t he t i me when t he surf ace

2 has r eached i t s peak t emperat ur e. Thi s gradi ent

di sappear s qui ckl y, however . These character i st i cs

are , of course, a f unct i on pri mari l y of t he t hermal

conduct i vi t v of t he mat eri al . The mater i al DroDer-

21111

f or descr i pt i on of node l ocati on). Of i nt erest i s

:

0 -

t i es assumed f or t he l ow carbon st eel

are

as

f ol l ows:

HANOC

Pun18

T h e m1 Conduct i vi t y

K )

= 7 . 5 x

BtuI Ft- Sec' F

3

Materi al Densi t y (

)

=

489

l bs / F t

Speci f i c Heat (C,) = . 10Btu/l 6' F

\

0 i 1 ; ia A6 1s ?o n The t her mal gradi ent s and cor r espondi ng expan-

si ons must be account ed f or i n t he deck desi gn.

IMi-sECwos

F i g .

10 Heat Tr ansf er and Recover y Temperat ur e

f or Node 1 Duri ng Abort ed Takeof f .

2-1) NOZZLE

7

ABORTED TAKEOFF

.

ODf

1 m V L - - U - .

I

0 4 8 12 16 20

24

IW IM

5W

7W

T lM t - S ECONDS

Fi g. 11 Deck Temper at ure Var i at i on Near Cent er-

l i ne Dur i ng Abor t ed Takeof f .

Nozzl e Conf i gur ati on

Under t akeof f condi t i ons w t h a f our second hol d

down, t he ci r cul ar nozzl e pr oduced a peak deck

t emper at ure 90 F hi gher t han the aspect r ati o 2,

2- Di mensi onal nozzl e.

vel oci t y and t emper atur e decay of t he ci r cul ar

nozzl e and i t s

c l oser

ground proxi m t y bef ore l i f t -

of f (1. 73 f t versus

4 . 0

ft). I ncr easi ng t he 2-D

nozzl e aspect r at i o to pr oduced

a

peak t emper a-

t ur e r educt i on

of

40'F,

due to i ncr eased vel oci t y

and j et t emper ature decay. Duri ng l andi ng, t he

ci r cul ar nozzl e resul t ed i n

a

deck t emper at ure 50-F

hi gher, r el ati ve t o the 2- 0 (AR

=

2) nozzl e.

Temperature Prof i l e Characteri st i cs

Thi s was caused by r educed

To thi s poi nt , di scussi on of t he resul t s has

been l i m t ed t o t he peak t emper atur e r i se

of

t he

deck due t o j et i mpi ngement . Of i nter est al so are

t emper ature gradi ent s bot h t hrough t he deck and

v.

NODE

5w

2-0 NOZZLE A

I

8 2

c 3

AKEOFF

D 4

E 5

0 2 4 6---1 0 1 2 +

Irn

3 m rdo liw

TIME - SECON@S

NODL

__

A

21

B

C

D ;i

25

TIME- S fCONOS

Fi g.   1 2 Deck Temper at ure Var i at i on Dur i ng Normal

Takeof f .

I t

shoul d be not ed that r adi ati ve heat t r ansf er

f r omt he j et to t he sur f ace and sur f ace to t he at -

mospher e were i gnored, si nce t he ef f ect woul d have

been sl i ght and cancel i ng.

Not e al so f r omFi gure 12  that t he deck does not

cool o f f very f ast, and that near t he j et cent er-

l i ne l ocat i on the deck sur f ace i s st i l l at

a

t emp-

erat ur e of 250°F af t er 10 m nutes. The cool i ng of f

pr ocess was based, on a f r ee convect i on heat t r ans-

f er coef f i c i ent of 3 .0 Btu/hr-ft' -' F est i mat ed to

exi st f o r

a 2

knot w nd- over- deck.

The hot spot

5

7/27/2019 CFD Deck Heating Effect Due to VTOL Jet Exhaust Impingement.pdf

http://slidepdf.com/reader/full/cfd-deck-heating-effect-due-to-vtol-jet-exhaust-impingementpdf 7/7

i s very l ocal i zed, however,

si nce

at

a

di st ance of

5.5 f eet f r omt he centerl i ne, the deck

i s

onl y

150 F af t er s i x m nut es.

across t he deck' s surf ace i s more vi vi dl y pi ct ur ed

i n Fi gure 13, whi ch shows t hat si gni f i cant heat i ng

of t he deck i s conf i ned to a radi us of i rom

6

t o 8

f eet f romt he nozzl e center l i ne.

The radi al gr adi ent

0

4 8 I2

16

10

Zd 8

D I S I A N C I

FROM

J t l C t N T t R L I N t T T .

Fi g. 13 Radi al Var i ati on of Surf ace Temperatur e

Durlng Takeof f .

A br i ef i nvest i gat i on i nt o materi al pr opert i es

resul ted i n

no

surpri ses. That i s, hi gh conduc-

t i vi ty r esul ted i n l ower peak t emperat ur es and re-

duced gr adi ent s, whi l e l ow conduct i vi t y r esul t ed i n

t he opposi t e. Thus, i f an i nsul ator

were

used to

pr ot ect t he st eel , i t woul d have to have a ver y

hi gh decomposi t i on temperat ure, si nce t emper atur es

r eached woul d be much hi gher t han t he unpr ot ect ed

s t eel .

S u mr y of Resul t s

An overal l compari son of peak deck t emper at ures

r eached for al l t he

cases

i nvest i gated i n thi s

st udy i s pr ovi ded i n Fi gure 14.   Apparent f r om t he

f i gure i s t hat j et t emper atur e and oper ati onal pr o-

cedur es ( hol d down ti me, spool up) ar e t he pri mar y

f act ors af f ecti ng deck heat i ng. Secondary f actor s

are nozzl e desi gn and pr oxi m t y to t he deck.

ConclusionslRecormnend=ti~n~

Deck heat i ng f or augment ed VTOL sys t ems dur i ng

t akeof f cannot be i gnor ed. However, i n Si t uati ons

wher e a s l i ght r ol l can be empl oyed, t he probl emi s

essent i al l y eliminated. In cases wher e pur e vert-

i cal takeof f

is

used, t he deck t emper atur es reached,

whi l e s i gni f i cant , ar e very l ocal i zed and not suf -

f i ci ent t o damage a properl y desi gned l ow carbon

st eel deck.

nozzl e desi gns, l ocat i on and speci al Operati onal

procedures.

andi of t he f l i ght cr ew can el i m nate any saf ety

hazards. For t hese r easons, t her e appear s no need

t o i ncl ude deck heat i ng as a compr om si ng consi der -

ati on i n the engi ne cycl e sel ect i on process f or

m xed ms si on VTOL ai r craft .

Heati ng can be m ni m zed t hrough

Speci al i nstr ucti ons and modus oper-

6W

r-

T AKEO F F S

LANDINGS -

Fi g. 14 summary of Resul t s on Peak Temperat ur e

I ncrease.

More st udy and anal ysi s to veri f y t he resul t s

and concl usi ons of t hi s study ar e desi rabl e. Sev-

eral assumpci ons and s i mpl i f i cati ons were necessar y

to perf ormt he anal ysi s repor t ed, t he most si gni f i -

cant of whi ch wa s consi derati on of onl y a si ngl e

nozzl e exhaust . Heat tr ansf er coef f i ci ent and re -

covery t emper atur e data f or j et i mpi ngement at

hi gher Reynol ds number s

are,

needed.

Ref er ences

1. Kappus, P.G , and Kohn, A. O , Concept ual St udy

of Hi gh Per f or mance V/ STOL Fi ght er s, ASME Paper

73- GT-66, Apri l 1973.

2 Donal dson, C. D , and Snedeker, R. S. , A St udy of

Free J et I mpi ngement , J our nal of Fl ui d Mechan-

i cs

-

Vol . 45, Par t s

2

and 3, 30

January,

15

Februar y 1971.

3 . Uon Gl ahn, U. H. , Geoesbeck, D E. , and Huf f , R.

RG, Peak Axi al Vel oci t y Decay w t h Si ngl e and

Mul t i - El ement Nozzl es, NASA TMS- 67979, J anuar y

1972.

4. Hi ggi ns, C.C., Kel l y, D P., and Wai nwr i ght,

T. W, Exhaust J et Wake and Thr ust Char act er -

Downwash Suppr ess i on, NASA CR- 373, J anuary 1966.

i st i cs of Several Nozzl es Desi gned f or VTOL

6