AD-787 639

AERODYNAMIC ANALYSIS OF A PROFILE FIGHTER TOW TARGET

J. B. Smith

Naval Air Development Center Warminster, Pennsylvania

22 October 1974

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#1)7X76.39 feEAD WffTR'jrTlONS

BEFORE COHP 2TING FORM 2. OOVT ACCCWION NO »- NCClPICNT't CATALOG NUMSER

«. TITLE (mtä MuhntU)

usaamMic AHLLTSIS or A PBOPIU Ficana TOW

t. TYPE Of REPORT « PERIOD COVERED

msB BiFon «. PERrORNINO ORO. REPORT KUMtKR

•■ CONTRACT OR ORAMT NUMBERCtJ 1. AUTHOR<*>

J. B. a^th

10. PROGRAM ELEMENT. PROJECT. TASK AREA • WORK UNIT NUMBERS

AIMASK MD. A5355351/00ID/ 4W4/S3dÖ00 A

>. PERPORMINO OROANIZATION NAME AND ADDRESS

Air VafeicU Tmchmlogy DcpartMat (Cede 30) lUnral Air D«nr«lopMnt C«nter Vandaatar, Pa. 18974

stte II. CONTROLLING OPPICE NAME AkD ADDRESS

Raval Air Symttm Departarat of the Äavy Wa»hlattont D. C. 20361

U. MONITORING AGENCY NAME * AOORESSfl/«MmiK frön cäntröifiü« O/He«;

12. REPORT DATE 22 October 1974

11. NUMBER OF PAGES -a- %' IS. SECURITY CLASS, (ol ifii« t&aH)

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•«. DISTRIBUTION STATEMENT (el Ihlt Report)

Approved for public release; dletributlon itr.liBlted

IT. DISTRIBUTION STATEMENT (ol tbo mbottoel mlond In Bloek 30, II lUllormtl horn Ktßorl)

IS. SUPPLEMENTARY NOTES t'U'-ofiute.) by

NATIONAL TECHNICA' iNroRMATIOM SFRVTF - S Dppnit^pnf of Convrif..f p

IS. KEY WORDS fContlnu* on nrortt »Ho II noeooomrr and MonHtr by bloek number)

Targets Aarodynaiilce Tow Target«

10. ABSTRACT fCantlm» on reroreo »He It necooetry end Identity by bloek numbef)

This report presents the aerodynaaic characteristics of a proposed aerial tow target configured to aeet the requireaients of the Navy Standard Tow Target Syatea for a large gunnery target. The Profile Fighter Tow Target will be both else and performance representative of potential eneny fighter airplanes.

/6 .:--. 1473 -™ °--v « - —" J UNCUSSIFIED

' * SECURITY CLASSIFICA1 ION OP THIS PAGE (When Dote Knlered)

EDITION OF I NOV SS S/W 0102-014-«601 !

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SUMMARY

la analysis was undartaken to detexaine tha aerodynaaic characteristics of a Profile Fighter Tow Target having as a proposed configuration that of a target which has been produced in limited quantity and flight evaluated by the levy. Included in the analysis were derivations of lift curve slope, pitching aoaent curve slope (center of pressure), side force, yawing aonent, and rolling aonent coefficient variation with sideslip angle, and drag coefficient. The effect of nodifying the proposed configuraeic.t to reduce the drag was also investigated. The results are valid at «ubsonic Mach maibers, and provide aerodynesdc data which can be used to detemlne towllne tension and towllne egress angle at the target for any subsonic flight condition«

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TABLE OF CCTCTEMTS

Page

Simmry 1

List of Figures 3

List of Tables 3

List of Syabolc ..... 4

Introduction * 6

Aerodyiunic Analysis 6

Conclusions 11

Beferenees 11

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UST OP FIGOKES

Figur« Mo. g*g«

1 Profil« Flght«r Tow Target 12

LIST OF TABLES

Tabl« Ho, P*g*

I Smmmxj of Aerodynaaic Derivative« aad Coefficient« for Profile Fighter Tow Target . 13

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LIST Or SYMBOLS

Sf^bol

A «space ratio

b panel «pan (asaaurad froa target ceatarllna to tip of panel)

CJJ drag coefficient, -^

C- friction coefficient

C. lift coefficient, ~ T I

C,' coefficient of force normal to panels, -?

& lift curve slope, %£

C. rolling aoaent coefficient, ^-

C pitching aonent coefficient, -^ Mt

C * coefficient of «ooent nonul to panels.

M

qsC

C- pitching aoaent curve slope, ^*

C yawing aoaent coefficient, -r^r

Y Cv side force coefficient, -rr Y HO

D drag, positive aft

L lift, positive up

L* force normil to panel

HC rolling aioaent, positive, right wing down

I target length (equals 30 ft.)

M pitching noasnt, positive, nose up; or Mach nuabcr

M* aoaenc noraal to panel

N yawing waDent, positive, nose right

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q

«Mt

t/c

Y

y

er

LIST OF SYMBOLS (COW'T)

dyaaaic pr«s»ur«

rafercnc« «r«a (eqiuls 99 ft2)

w«tt«d ar««

thickness to chord rstlc

distsnc« fro« target nose; or distance between center of pressure and center of gravity, positive, center of pressure ahead of center of gravity

side force, positive right

spamrlse distance to panel center of pressure

angle of attack

relative angle of attack nomal to panel

sideslip angle, positive, nose to left of relative wind

wing dihedral angle (equals -30 degrees)

Subscripts

b base

friction

ft forebody

Induced

■iscellaneous

vertical panel

« wing panels

k.

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INTRODUCTION

Th« Profil« Fighter Target ia included as part of the proposed Navy Staadard Tow Target Systea in order to provide a gunnery target that is both sise awl perforaance rapresentative of potential threat vehicles. According to reference (a), a target currently being produced under the trade xumm "FIGAT** (Fiberglass Aerial Target) can fulfill the requireaants for the Profile Fighter Target. The "FIGAT* ia 30 feet long, 8 feet high, has a 9 foot «ingspan and weighs approxiaately 500 pounds. It is described in reference (b). A drawing is shown in figure 1.

Under authority of reference (c), an analysis was undertaken to deteraine the aerodynaaic characteristics, including aerodynaaic derivatives, centers of pressure, and drag for the Profile Fighter Target, as bssed on the "FIGAT** configuration. The effect of a aodification which would reduce the drag was investigated also.

AERODYNAMIC ANALYSIS

The results of the analysis presented below are applicable at subsonic Mach nuabers (up to approxiaately Mach 0.98). The aerodynaaic coefficients are all based on a wing reference area of 99 ft2 with the target length of 30 feet the reference length for the aoaent coefficients. The results are suanar.sed in Table I.

The force and aoaent coefficients noraal to the two wing panels, which have s -30 degrees dihedral, and the vertical panel of the target were calculated as follows using slender thin wing theory. For each panel, the noraal force coefficient,^', is deterained free the equation

where b is the span of each panel (measured froa centerline of carget), S is the reference area, and «' is the angle of attack relative to the respective panel (in radians). The aoaent coefficient corresponding to the aoaent about the nose noraal to each panel, C ', is ieterained froa the equation

v 'I

[ b(x)J Lb'(x)] dx

where I is the target length. The center of pressure of each panel, located aa a fraction of the total target length, is obtained by dividing the calculated

int coefficient by the calculated noraal force coefficient. That is.

K Centers of pressure calculated by this aethod were found to agree with those calculated using charts in reference (d). Because slender thin wing theory aasuass an aspect ratio approaching cero, however, noraal force coefficients

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calculatad by this mthod «ill b« slightly large for s configuration with a finite aspoet ratio. In this ease the difference is smll; nevertheless, the ealevlated nocaal force curve slopes (AC '/«V»') «ere reduced by three percent in order to agree «ith estlaates side using the following equation fro« approzlante lifting surface theory at a Nach nunber of 0.7. (At the Mach mabers of 0.5 and 0.9, there is a variation front this of approxiaately ±Vi percent, idiich is considered negligible^) ...

& 2 v h

In this equation M is the Nach aoaber and A is the aspect ratio of an äquivalent «ing with a seaispan equal to the panel span and an area equal to twice the panel area. The Meent curve slopes (dC '/do') were recalculated by aoltlplying

the respective adjusted nontal force curve slspe by the distance to the center of pressure (noraalised as a fraction of the target reference length).

Lift due to angle of attack (lift curve slope, Cr) cones fro« the vertical

co«ponent of the force on the two wing panels. Since

or' ■ « cos r

where er Is the angle of attack and f is the wing dihedral angle of -30 degrees, and

(^ - 2(0« cos F)

(for the two wing panels) where C. is the lift coefficient, therefore

CL - 2(0.97 TT ~ a) cos2 T

b2 - 4.57 ^ or

Then

b2 C^ - 4.57 i-

- (4.57) ^

• 1.20/radian

The center of pressure of the wing panels, which is also the longitudioai center of pressure, was found to be located 18.4 feet aft of the nose. This is 3.5 feet behind the tow point, which is located at F.S. (fuselage station) 179, and 2.75 feet aft of the center of gravity (F.S. 188). The pitching ■P«ent curve slope about the center of gravity (C- ). was calculated as

nmn^aiv

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S»"0^^ - 1.20 (^jZä)

- -0.110/radUo

Thl« it « stable «onsnt (IncrMSing no«« down pitching ■ownt with Increasing «agl« of attack).

Sid« fore« do« to sideslip angle (Cyg) cone« fro« the force on the vertical

panel and the sideways coaponent of force en the wing panels. For the vertical panel.

<CVv " "^

• -0.80/radlan

For the two wing panels, since

flf» - ß sin F

«here P is the sideslip angle,

(CYp)w - -2 (!%£) 8in2 r

« «0.40/radian

Added together,

CY0 - (CYe)v + (CY0)W

- -0.80 -0.40

- -1.20/radlan

(Side force is positive to the right.)

The center of pressure of the vertical panel «as calculated to be 19,8 feet aft of the nose, and therefore 4.15 feet aft of the center of gravity. The slope of the curve of yawing nowent coefficient (about the center of gravity) versus sideslip angle (Cno) is thus calculated as

- -0.80 i=^) -0.40 (^£)

- 0.111 + 0.037

• 0.148/radlan

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TU* 1« «IM a «tAbl« nommnt (Increasing not« right yawing aoacnt with iacraaaiag aidaslip angle). The net directional center of preeanret with reepeet te the center of gravity, «as calculated as follows:

« -3,7 ft

This is 19.35 feet aft of the nose.

The rolling noasnt about the target centerline produced by sideslip angle (Ctg) «as calculated as

Ctg - «V, + (Ctj),,

«here y is the distance to the spanwlse center of pressure, measured fro« the target centerline, for each panel. Since

^K Ä fr^H and

'v 'w

thus

Ctfi S 0

The drag of the target consists of zero-lift drag plus Induced drag. However, unless the target Is seriously «Isbalanced, the angle of attack will practically always be so low that the Induced drag coefficient, calculated as follows, will be negligible. Using an expression valid for low aspect ratio wings,

=■>! B <^ vt cos r, )

- (1.20 a) (|)

■ 0.6 or2 («In radians)

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Considering only scro-lift drag, then, the total drag of the target la nade up of skin friction drag, base drag, and niscellaneou* drag fro« the varioua protnrberaacea, skids, etc. including any interference drag.

Skin friction drag was calculated according to the nethod of reference (d), using an equation and charts front that reference. Six different sections of the wing and vertical panels (with different lengths) were considered separately. For each section, the Reynolds nuaber was calculated corresponding to an average flight condition of Mach 0.7 at 20,000 fett. This wes coapared to the "cutoff1* Reynolds nunber, which Is a function of the relative surface roughness height. For an estiaated surface roughness height of 0.4 X 10"3

laches (seas as ordinary paint), the "cutoff" Reynolds ouaber Is just slightly less than the calculated Reynolds nuaber. The friction coefficient for each section is deterained as a function of Mach nuaber and Reynolds nuaber, using the lesser of either the calculated Reynolds nuaber or the 'cutoff" Reynolds nuaber, the latter of which was used in this case. The resultant total skin friction drag coefficient was calculated as

C^-ilfc (l + 2|)Swt

- 0.0104

where Cf is the friction coefficient, - is the thickness to chord ratio, and c t

S u is the wetted area of each section. The tern 2 - accounts for the Increase wet c in dynaaic pressure over the surface du» to thickness.

Base drag, arising from the four Inch thich blunt trailing edges of the panels, was calculated according to reference (e). The two-diatenslonal base drag coefficient, based on base area, is deterained froa the «quatlon

C^ - 0.14/3^

where Cp-- is the forebody drag coefficient - that is, drag originating on

the surface ahead of the base - also based on baae area. This equation was applied to each of the panel sections discussed above and Its base. The total base drag coefficient, based on the wing reference area, was found to he

'I>b 0.0132

Miscellsneous drag froa the various proturbstances, skids, etc. was estiaated to provide an additional Increaent in drag coeff< >ient of

CJJ^ - 0.013

of which approxlaately 0.010 coaes froa the forward skid asseably. The total target drag coefficient is

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SIJ)C-74143-3C

cD - C^ + C^ + C^

- 0.0104 + 0.0132 + 0.013

- 0.037

Ihi« ▼«lot 1* rel«tiv«ly unaffected fey Reynolds gguab«r. For exaaple, at a lover loynolds naabor eorresfondlng to «pproxlaately Mach 0.5 at 40,000 foot (also eorrosyoadlag to 4M "cutoff** leynold« mabor for a surface roughness heltfit of 1,0 X 10-5 laches), the target drag coefficient would increase by only 0.001.

It can be noted that a significant portion of the total drag is nede up of base drag. By tapering the trailing edges of the wing end vertical panels to a point or otherwise reducing of eliadnating the blunt bases, this drag could be reduced. As an ezaaple, if the final foot of each panel were to bs tapered saoothly to a point, a decrease in the target drag coefficient of «pproxiMtely 0.012 (301) could be expected. (This would also effect a change in trtu angle of attack of about 0.2 degrees, uhich is not considered significant.)

CONCLUSIONS

An analysis has been «ade to detarsine aerodynaaic derivatives, canters of pressure, and drag coefficient for a proposed Navy Profile Fighter Tow Target confisnration. The results, which are valid at subsonic Mach cunbers, show that the target is statically stable, as expected. In adwition, they provide the aerodynsaic data necessary to detemine towline tenaion and towline egress angle at the target for any subsonic flight condition.

It hat also been detendned that a significant reduction in target drag (as ■nch as 30 percent) could be accooplished by tapering the trailing edges of the wings and vertical panel so as to ellninate, or at least reduce the sise of, the blunt base.

REFERENCES

(a) Carroll, D. W., Proposal for the Development of an Integrated Tow Target Syste», Naval Air Developoent Center Report No. JADC-72192-VT, 23 Mar 1973

(b) Maurer, Willian L., United Evaluation of a Fiberglass Aerial Target (FIGAT) and an Electronic Bullet Scoring System, Air Force Flight Test Center, Edwards Air Force Base, Technical Report FTC-TR-71-53, Dec 1971

(c) AIKIASK No. A5355351/0O1B/4W4733OOOO

(d) DSAF Stability and Control DATCOM, Al; Force Flight Dynamics Moratory, Wrlght-Patteraon Kir Force Base, Oct 1960, Revised Feb 1972

(e) Hoerner, Sjghard F., Fluid-Dynamic Drag, published by the author, 1958

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TABLE I

FOR PKOFIU FIGRTER TOW 1ABGKT

Ci^ t l.20/r«d

C,^ : -oaiO/rad

Cyg : -1.20/r«d

C^p : 0.148/r*d

Ctg J - 0

CD : 0.037

Notts:

1. Derivativ«« «nd coefficients are defined in text and in list of syabols. 2. All coefficients based on an area of 99 ft2. 3. Moasnt coefficients ar« based on target length of 30 ft; ■Meats are about

center of gravity located 15.65 feet back of nose. 4. Surface roughness height assuaed as 0.4 X 10"3 inches.

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