Bud Nelson Supersonics

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Design Scope for

Student Supersonic ProjectsBUD D. NELSONNorthrop Aircraft Division, Hawthorne, California

Abstract

In the course of judging student designs for theSupersonic Executive Jet Competition, it has been

recognized that most formal training has empha-

sized aerodynamics, propulsion, and structures but

has ignored two significant learning experiences:design with the area rule and exposure to major

subsystems. In light of ongoing supersonic cruise

engine developments, many new product opportu-

nities are on the horizon. In addition to the execu-

tive jet, there are supercruise fighters, supersonicshort takeoff and vertical landing (STOVL) fight-

ers, supersonic transports, and transatmospheric

vehicles. The AIAA Aircraft Design Committee,

through its industry members; can do much to aid

in this training by providing lessons learned with

area ruling techniques and a data base for advanced

subsystems. This paP._er is a first installment to en-large the scope for undergraduate designers.

BUD D. NELSON got an early startin engineering at the stutient-operatedUniversity of Washington Aero-

nautical Laboratory where he servedas Operations Chief while attendingundergraduate classes. A B.Sc. in

Aeronautical Engineering (1956) was

· followed by assignments in perfor-mance, structural design, preliminarydesign, system conceptual design,and program management. Nelson'sparticipation in major projects in-

cludes TFX, B-52, X-20 Dyna-Soar, USFIFRG VSTOL,SST, C-14, VTXITS, and ATF. His early student AIAAactivities have been followed by continuous participationand national committee duties. In addition to Nelson's cur-

rent management job at Northrop Aircraft Division, he is aregular lecturer at Aircraft Design Short Courses.

Winter 1987

Introduction

This paper is intended to add information for thestudent design data base and to support the move

for new student competition in fighter design. Stu-

dent designs submitted for competition show a lack

of emphasis on area ruling techniques and major

There are several reasons for this situ-

ation. In designing with the area rule, little has beenpublished about conceptual level techniques, and

only in schools close to fighter companies has therebeen any transfer of knowledge. Subsystems de-

scriptions are limited generally to statistical weight

buildup using the methods of Nicolai's "Funda-

mentals of Aircraft Design" (Ref. 1), but compet-

ition rules never request specific subsystems perfor-

mance. Furthermore, there has been no data basepresented that is easy to use in a conceptual design

school project. Subsystems recognition by the stu-

dent is important for three reasons.1) Subsystems represent a major part of vehicle

volume, weight, and cost. This is particularly true

for fighters.2) Student designers should confirm that major

subsystems fit within the volume and weight con-straints of their design project.

3) Technologies are changing the character of

major subsystems toward increased modularity.To prepare this data base several engineering in-

vestigations have been reviewed to collect informa-

tion directly useful to student design concepts.Next-generation (ATF technology) and far-term

technology projections were considered before se-lecting the far-term compact fighter class as a base-

line data base.The following sections review a professional con-

ceptual design process to scope the magnitude of ef-

5



WEEK

1 1 2 3 1 c 5 & 1 a 9 110111 L12113 1c115 11&!17!1&!19 20 21 22 23 2c

e SYSTEMS ANALYSIS-MISSIONS I rt Ei'i' EVAL I DOC I

ll.f'/SIZ:NG t ' / /OFF DES /A IVEHICLE SYNTHIPERF

e CONFIGURATIONS GA ,ft ' D : i I I!"' lrWPNS/1 1f INST"L DWG !COC KPIT FUEL HYO ELEC. WEAPON CARRIAGE.SUBSYSTEM DESCRIPTIONS

e STRUCTURES LAYOUT -iC. OIAG AV I rC t If I EVA'L .u '

Il

- C ONCEPTS EVAL J [@

e SURVIVABILITY ANALYSIS t '"1- INPUT t' te COST ESTIMATES

e LOGISTICS lA. M & Si

e AERODYNAMICS

e MANUFACTURING

e AVIONICS

1111111WPNS. STAB CONTROL

1+ SENSOR H:_ .SYS, L ' ' J

e PROPULSION

I It ! t " i , ATA BOOK

e WEIGHTS

e DOCUMENTATION

e MARKET SURVEYS

e PARAMETRIC$

e REVIEW MEETINGS

VSENSITIVITY'/1

I IFEASIBILITY l;

I I I

Fig. 1 Conceptual design process for a fighter system.

VEHICLECONFIGURATION AIRFRAME

e AERO GEOMETRY e WING STRUCTURE

e SUBSYSTEM e BODY & COCKPITINTEGRATION STRUCTURE

e VEHICLE INTEGRATION e EMPENNAGE

e MOCKUPSIMOOELS

o FLIGHT SIMULATION

o COST ENGINEERING

o R&M ENGINEERING

STRUCTURE

e LANDING GEAR

o FITTINGS &MECHANISM

e TEST ASSEMBLIES

e MANUFACTURING

Fig. 2 Conceptual design projeCt.

PROPULSION

e INTAKE SUBSYSTEMS

e POWERPLANTINSTALLATION

e SECONDARY POWER

SUPPLY

e EXHAUST SUBSYSTEM

e FUEL SYSTEM

e EMERGENCY POWER

e TEST PLANS

fort required, describe lessons learned and guide-

lines for designing with the area rule, and provide

some of the modular subsystems useful in super-

sonic projects.

Conceptual Design Process

A professional concept design process is sum-

marized in Fig. 1. The purpose of this figure is to

show design scope and schedules. The shaded ele-

ments represent design characteristics which stu-

dents generally are expected to include in their

projects. The student team project, while massive

relative to other student efforts, represents less than

one-tenth the expected scope and depth of a profes-sional fighter concept design.

VEHICLE MANAGEMENT

e FLIGHT CONTROLS

e MECHANISMS

e POWER DISTRIBUTION

e COCKPIT CONTROLLERSe UTILITY CONTROLS

e SYSTEM SIMULATION

e LIFE SUPPORT

e ENVIRONMENTALCONTROL

CROSS

SECTIONAREA

A

I INPUTS TO- FOLLOW ON

I BRIEFING I I .,

d s Y J T J DELN

CONCEPT REVIEW

MISSION SYSTEMS

e ATIACK SUBSYSTEMS

e INTEGRATED AVIONICS

e STORES MANAGEMENT

e ARMAMENT SUBSYSTEMSe SYSTEM SIMULATION

e LOGISTIC SUPPORT

Conceptual design is usually conducted by a proj-

ect team led by a configuration designer who has Fig. 3 Designing with the area rule.

6 A!AA Student Journal



50

p

NET DENSITYLlllf"fl

30

LOWVOLUMETRIC EFFICIENCY

Fig. 4 Volumetric efficiency.

HIGH

an overall understanding of total design and a talent

for integrating the requirements of project special-

ists. A project organizat ion is shown in Fig. 2. Each

of the specialists will contribute to the conceptual

level data base and will later add design detail dur-ing preliminary design if concept development pro-

ceeds. The data base covers all disciplines to allow a

quick start for each new concept and is vital to the

early definition of total vehicle volume.

Designing with the Area Rule

What should the student designer Jearn about

area plots?

INITIAL CHARACTERISTICS I

1) Two principal methods for initial estimates of

vehicle volume; element buildup vs statistical gross

weight/ density.

2) Area ruling techniques to distribute total vol-

ume for minimum wave drag.3) The use of Sears/Haack curves as a simple

graphic tool for shaping volume distribution and to

account for major configuration variations such as

engine location.

The area rule for complete aircraft assumes that

all volume can be expressed within a body of revol-

ution, Fig. 3, and from that the far-field wave drag

can be estimated using the NASA methods from

Ref. 2. Combining this theory with Sears/Haack

area distributions has produced very-low-drag air-

craft. 3•4 The airplane must be designed to fill the

area distribution without surface discontinuities or

large slope changes that could cause local pressuredrag. Early consideration of critical minimum cross

sections is essential and will be influenced by con-

figuration arrangement.

Step one in the process is an initial weight estimate

that can be estimated by techniques such as Ref. 1,

Chapter 5. Initial volume may be estimated by either

of the two methods shown in Figs. 4 and 5. In Fig. 4,

a simple statistical sample shows that fighter net den-

EST FOGW • ---- L8 FULL INTERNAl FUEL • ---- L8

T/W • DESIGN MACH NO. •· __ At FT

WING GEOMETRY • ----------------AAREF • s - lie • ----

PROPULSION • __ YCLE • _ · _ INLET • __ OZZLE • --VOLUME SUMMARY

ELEY£NT

FOREBOO'I' (W'COCKPIT. NOSE GEAA. RAOOME)

WEAPONS BAY (CAP • L8)

GUN BAY

MAIN GEAA (CBR • __ ASSES • __EQUIPMENTCONTROL RUNS

WING SWEEP MECHANISM

TAIL CARR'f.I"HROUGH

INLETS

ENGINE BAY

BOOY FUEL VOLUME

SUB'TOTAL

STRUCTUfiAL & UNUSED VOLUME

(0.15 X GROSS 800'1' VOLUME)

EXPOSED WING VOLUME

GROSS WING • BOOY VOLUME

5TREAM'f\JBE

NET VOLUME. WING + 800'1' (FT3)

Fig. 5 Volume buildup.

Winter 1987

CRITICAL LENGTH (FT)

7



Table 1 Weapon carriage volume

CRITICAL

COHI'IGURATIOH A YOt.IBOOV U:NGTH

e AU EXTERNAL PYLON 0 0CAARIAGE

e TANGENT CONFORMAL 15 n3t1,000'LB 3F TCARRIAGE: SUBMERGEDEJECTOR WITH ACCESS.

e SEMI-SUBMERGED AIRBAG &-3 n3n.ooo LB MAX WPN

EJECTOR CARRIAGE LENGTH

e INTERNAL BAY·TUSE 20 n3t1.000 LB MAX WPNLAUNCH LENGTH + 6 IN.

e INTERNAL BAY-EJECTOR 33 n3n.ooo LB MAX WPNLAUNCH LENGTH + 6 IN.

Table 2 Armament volume

INIITAUATIOH CIIITlCALUNINIBTAU.BI I' ACT DR

e 20MM MK81 7n3 X2 GIJN+2FTGATl.JNG GUN

e 20MM Nllll/0 (LINK· 0.01 n3t X 1.3LESS OAIJM) ROUND

e 30MM OERLIKON 1.en3 X3 GUN+2FT(1 BARRELl

e 30MM OERLIKON 0.04 n3t X 1.3AMMO, BOX 6 LINKS ROUND

sities will range from 30 to 45 lb/ft3. Most produc-

tion fighters have values between 32 and 38 lb/ft3,

where net density is determined from the net volume

without propulsion stream tube.

Volnet = Volgross- (Acaplure X Lpropulsion)

The second method employs a volume. buildup as

shown in Fig. 5. A format is shown for a new fight-

er concept where the volume may evolve through

iteration. Minimum volume estimates of each ele-

ment are derived graphically or from the equations

described in the following paragraphs. Recording

of component lengths will allow early estimate of

the minimum length. (Note: Critical lengths do not

accumulate for total length.) This list of elements

also includes those of critical cross section that must

be considered for volume distribution. Volume esti-

mates described in the following paragraphs are in-puts to Fig. 5. The equations are from Ref. 5 plus

data from the authors to reflect both current and

future technology where applicable.

Cockpit

Minimum volume requirement for each crew

member, in a tandem arrangement, is currently 70

ft 3 with at least 14-ft2 cross section at the pilots

design eye body station. Future technologies allow

50 ft3 each with ll-ft2 cross section for upright and

7 ft 2 for semisupine seating. This volume allocation

includes provisions for avionics, controls, and dis-

8

plays. The nose gear is often stowed under the cock-

pit section. If so, add at least 3 ft 2 and 15 ft3 to this

section of forebody volume.

AvionicsThe airplane volume requirements for avionics

equipment excepting displays and antennas is 1.6

times the volume of the bare equipment. That is, it

requires a 60% allowance for rack, cooling, connec-

tors, and clearance. This is true for current boxes

and future modules. Equipment examples are de-

scribed later in the subsystem section.

Antennas

The principal antenna volume requirement is that

for the nose radome. Ordinarily fuselage cross sec-

tions in this region are circular and the area vari-

ation with length has been simplified to a constantvalue of 1.4 ft 2/ft to give a parabolic radome shape.

The diameter at the fuselage station that will ac-

commodate the radar dish is assumed to be 4 in.

larger than the dish itself. Thus the volume of fuse-

lage considered to accommodate the radome is

Radome volume=[;

where the tadome volume is in ft 3and Dis the radar

dish diameter in feet.

Weapon Provisions

Body volume requirements can be estimated fromTable 1.

Gun and Ammunition

Gatling guns, single barrel, and two barrel guns

are in service and may be replaced with lighter more

powerful versions of each type. For initial sizing use

Table 2 as a guide. Installation factors account for

routing of ammo, ammo storage, and gun bay

purging.

Landing Gear

The volume of the landing gear, sized for 36

passes at a given California bearing ratio (CBR)

field surface condition, is given by

VLG =9+ 10- 6(2.56 CBR- 4.86)TOW(L924 CBR)- 0·158

where Vw is the volume of the landing gear (ft3)

and TOW is the design takeoff weight (lb).

Miscellaneous Equipment

Carrier based airplanes must have a volume allow-

ance of 4 ft3 for arresting gear.

Initial volume requirements of other equipment

and systems can be estimated using Table 3.

AIAA Student Journal

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\

Table 3 Subsystem volume estimates

CURN!NT FUTURI!I!OUII'UI!NT Tla4ftOLOGY T£CMMOt.OGY

HYOAAULIC AND PNEUMATIC 0.46 FT't1,000 0.46 FT'I1.000(CU. FT. PER 1,000 LB T.O.W.)

ELECTRICAL 4FT ' 1 FTJ (ENGINEBAY)

ARMOR 1FT' 1FT'

ENVIRONMENTAL CONTROL SYS. 15FT' 18 Ffl (CBR)

AUXILIARY GEAR 2FT' 2FT'

OXYGEN (08005 OR 081GGS) 6 FT'tEA. 6 Ff'JEA.

Future fighters will require increased hydraulic

horsepower for active flight controls; but increase

system pressure, as high as 8000 psi, will reduce unit

weight and volume requirements.

Electrical system components will be hidden with-

in engine bay volume; direct mounting to engine gearbox.

Environmental control systems (ECS) will require

additional filters to counter chemical and biological

environments. Onboard oxygen generating system

(OBOGS) and onboard inert gas generating system

(OBIGGS) are accounted for separately.

System Runs

The volume required to carry control cables, push

pull rods, and electrical and hydraulic lines through

the fuselage is derived as the product of an average

cross section and the length of the fuselage. For in-

itial sizing, use I ft2 over 85% of fuselage length; no

runs in the forward radome or aft nozzle tail cone.

Tail Carry-Through

The volume required for tail carry-through struc-

ture is 0.002 ft 3 /lb of airplane gross weight, which

also applies to canard designs.

Wing Sweep Mechanism

I f variable sweep is employed, provision for the ac-

tuation system and mechanism is included as follows:

where C is the chord of the extended wing at the

pivot, ti c is the thickness rat io at the pivot, and W8

·s the body width at the wing carry-through. Struc-

ural carry-through of the wing is accounted for in

structural allowances.

Propulsion

Volume requirements include inlet, engine bay,

and accessories. The inlet volume is the product of

capture area and length from the cowl lip to the

compressor face. The engine plus accessories vol-

Winter 1987

ume is based on the length and average cross section

of the compressor face and nozzle at maximum

AlB position. The stream tube volume is the prod-

uct of capture area times overall propulsion system

length and will be deducted from gross volume toproduce net total volume.

Body Structure

Volume for body structure is based on I) the

fuselage fineness ratio, and 2) the approximate wet-

ted area of a prolate spheroid.

Vbody structure= O.I3(f/d) bodyA wet body

Vbody structure= 0. I3(fld) body 1.33 [ 3( Vrusclfrusc)

+ 2. 7 Vfuse X frusc]

At this point, or before, some rough estimate

should be made of body length and equivalent diam-eter. Body width will establish exposed wing area and

volume. For supersonic shapes assume body f/d 2!:

II . Exposed wing volume is left to the student.

Unused Volume

Any airplane has a certain amount of volume that

cannot be charged to the required volume for useful

items. This unused or wasted volume is a result of

shape irregularities in components that prevent

compact stacking. Wasted volume has been deter-

mined in a number of representative fighter designs

by subtracting the accountable volume from the

total. The quantity correlates well with fuselage sur-

face area. The expression is

where Vruse is the total summation of component

volume requirements for the fuselage (ft3) and Lruse

is the overall fuselage length (ft).

Fuel Volume

Body fuel volume should assume a volumetric

efficiency no greater than 85-870Jo to account for

expansion, structure, fuel boost pumps, and wasted

space. Assume fuel density at 40.5-41.5 lb/ft3 for

integral tanks.

Wing fuel should occupy no more than 42% of

exposed wing volume (outside the body). For vari-

able sweep wings initial estimates can use 4707o of

the wing volume outboard of the pivot.

Summing the Volume

The gross volume, Fig. 5, is the sum of body

components, wing volume, and strake or leading

edge extension (LEX) if employed. Tail surface

volume is not included in any area ruling because of

9



1.0

0.8 0.8

0.6 0.6A

dmaxifmax "'max •.4 0.4

0.2 0.2

0

0.5 0.6 0.7 0.8

Xll

lldltCtfdW IIMUUI'III! OIUQ Vot. • C"n_ ll Amu X L

TYPE I co.

9

8

TYPE II C o .

TYPE Ill Co • 312

rFig. 6 Sears bodies.

CROSSSECTIONAL

AREA SEARS TYPE 1(A)

GIVEN LENGTH & VO L

LENGTH & OIA

OIA & VOL

CpI

• 0.59

cPu• 0.51111

Cplll - 0.392

CROSSSECTIONAL

AREA

FIRST STAGE AIRPLANE Ct'IOU SECTION DEFINITION (TARGEn

MINI UMFUSELAGE

NET AIRPLANE CROSS SECTIONFOR RESTRICTED FUSELAGE

INITIAL AREA OEANED BYVOLUME AND LENGTH

REQUIREMENTS

INLET STREAMTUBE

LCINGIT\JOII'W. STATION

SECONO STAClill! Ct'IOU SECTION DEFINITION

Fig. 7 Area plot-graphic standards.

10 AIAA Student Journal

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/I

SEARS-HAACK SHAPECRITICAL CROSS SECTIOHS (1st ESTIIIIATE)

xAMAX

CONFIGURATION TYPE FOAEIIOOY MIOIIOOY AFT IIOOY FOAEIIOOY AFT IIOOY L 11 (FIG 7)

FORWARD ENGINE AFTTAIL RAOOME OR COCKPIT WING CARRY-THROUGH TAIL SUPPORT TYPE II TYPE II Q.50.0.56

OR MAIN GEAR

AFT ENGINE AFT TAIL RADOME OR COCKPIT WING CARRY-THROUGH ENGINE CUSTOMER TYPE II TYPE I 0.55-0.60OR MAIN GEAR CONNECT AND TAIL

SUPPORT

AFT ENGINE TAILLESS RADOME OR COCKPIT WING MID-SPAR AND WING REAR SPAR TYPE II TYPE I 0.55-0..60MAIN GEAR

AFT ENGINE CANARD RADOME COCKPIT OR MAIN GEAR OR WING WING REAR SPAR TYPE II TYPE I 0.55-0.60CANARD CARRY THRU FRONT SPAR

Fig. 8 Critical control points.

aftbody adverse pressure gradients, except for stag-

gering horizontal and vertical surfaces to minimize

cross-sectional area buildup. With airplane gross

volume estimated, area ruling with required cross

sections can begin.

Area Distribution

The most common area plots are defined bySears/Haack area distributions.2·3 These are widely

employed in the design of transonic and supersonic

ADVANCED FLIGHT COHTAOUI

••

e MISSION PlANNING

e MULTITHAEAT WARNINGe INTERNETTINGe ADVANCED ANTENNAS

" ICNIAe INT£GRA TED V1.lW'MSIC

AEAOMECHANICAL

• VAAIAIILE CAMBER WINGe RELAXED STATIC STAIIIUTYe TAILLESS DESIGNe AEROELASTIC TAILORINGe CONI'OAMAUINTERNAL

WEAPON CARRIAGEe INTEGRA TED CONTROLS• ADVANCED INLE T DESIGN

AOVAHCED MOOUI.ARCOCICP1T

e AUTONOMOUS FUGHTSUIT !II'SI

e FLAT PANEL DISPLAYSANO SWITCHES

e VOICE CONTROLe HELMET MOUNTED

DISPLAYe SEMI-SUPINE SEATING

e ADAPTIVE PASSIVE GEARe AOUGHISOFT Fi£1.0e HIGH PRESSURE

HYDRAULICSe ADVANCED INTEGRATED

IIRAKINGISTEERINGe HIGH DEFLECTION TIRES

Fig. 9 Compact fighter promis ing technologies.

Winter 1987

airplanes because of the good correlation of theory

and flight results and the systematic approach pos-

sible in the application of this tool throughout the

vehicle design life. Three basic Sears shapes are

shown in Fig. 6 with respective pressure drag equa-

tions and prismatic coefficients CP for combina-

tions of length, volume, and equivalent diameter. A

primary value of these shaping options is realizedwhen critical cross sections along the body create

control points in the area distribution. Control

ADVANCEDMOOUI.AR ECS INTEGRAL V ARIAIILE

DISPlACEMENTFUEL TANK

ADVANCED MOOULARSECONDARY POWER

e ELECTRIC LINKe INTEGRA TED POWER UNIT

ADVANCED MOOULARCOMPOSITE/METAL AIRFRAME

e HOT SIZING .PRESSINGe ALAM£NT W1NDIHGe ADVANCED AIIL.i MATERIALe ADVANCED COMFOSITES

ADVANCED PROPULSICIN

MOOULAR WEAPONS

e FOLDING FIN TUBE

LAUNCHEDe AIR BAG EJECTORe TELESCOPED AMMOe ADVANCED MUNITIONS

11



J.x0.6la

..+.......SEARS TY [;.7 " " DENSITY APPROX-36 LSICUBIC FT

CAPTURe AREA • 800 SO IN. REMOVED

·' -

. / ' 1/ WINGr.t

• 1.0r\\·-..../ --- \ \ EARS T PE I

v...- / ........ \CANOPY /

"'-\ -"'-\/ FUSELAGE

"'-\"f t , \

/

'"- / /W I NG M • 1.0

/ v. . :L / v

4200.0

1oo--140 180 ' 2 2 0 _ 280 __ 300_ .

FUSELAGE STATION-INCHES

IBA&IC DATA

IIAIPCIIIIIPACIIS U08TII - V1!RT TAll.

A!l'Ef'IEHCE N'IEA 90FT 2878 285 EA

ASPI!CT RATIO AA 10 4 084

TAPER RATIO TR 0.204 03 2

THICI<HESS RATIO TIC.._ • 3

L.E. SWI:EP AHGl.f DEG 88 -C/4 SWI:EP AHOl£ OEG -OIHEOAAUCANT AHGLE DEG 000 -15 0

INClOEHCE AHGl.f OEG 24 00 0

TWIIIT AHGl.f DEG 58 000

AIIOFOI\. HACAeo!A woo 85A

PAO.IECTI!O SPAN ... 2080 -AOOTCHOAO ... 3150 0 105 81

TP CHOfiO ... 71 •7 3318

- AEPIO CHORD IN 232.12 -

480

\ EXIT AREAL

i SO IN .I .

500 540 580 620 eeol 700

( . .

1 <43• TURNOVERANGLE

Fig. 10 General arrangement-future compact fighter conceptual design.

12

\

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c

OCl DESIGN LOAD FACTOR




2.000

I 1,600

F-15AFIA·18A 1990J TECHNOLOGY

tTECHNOLOGY

-t14% REDUCTION

1,200

1:1

!- f"' UL

46%

REDUrTION

CAPABILITY

< 6000w........

tJ) 400

!!:

-

1-

085

EQUIVALENT

CAPABILITY

70

EOUIJLENT

I

"'"j""I

75 80 85 90 95

TECHNOLOGY AVAILABILITY DATE

Fig. 11 Technology application-avionics.

points are often created by the cockpit, the wing

carry-through structure, the inlet duct, and theinterface between airframe and engine nozzle (the

customer-connect point). The choice of three shape

descriptions for initial target values allows the de-

signer to produce smooth longitudinal distributions

through the control points while minimizing excess

volume created by the fairing technique.

For the initial target volume, the equation for net

cross section forward and aft of the maximum is a

function of the maximum cross section, position of

the maximum cross section, length of the fuselage,

and the difference between the engine exit area and

inlet area as shown in the upper part of Fig. 7. The

maximum cross section A max is determined fromthe required net volume, the prismatic coefficient of

the selected shape (Fig. 6), and a selected value for

fineness ratio fld.

In subsequent phases during layout design, body

OPTIMUM FIELD-OF-REGARD REQUIREMENTSFOR VARIOUS OFFENSIVE AND DEFENSIVESENSORS IACTlVE AND PASSIVE) ABOARD

A HIGH PERFORMANCE AIRCRAFT

Fig. 12 Multirole sensor field o f regard.

Winter 1987

constraints and exposed wing volume may cause a

mismatch like that illustrated in the lower part ofFig. 7. This is a common occurrence which causes

the designer to I) re-examine the configuration gen-

eral arrangement, and 2) re-evaluate the initial

target area distribution. In most cases, a single

iteration of target or configuration will produce ad-

equate closure of the student design.

Critical Control Points

In the initial layout, longitudinal area distribu-

tion will be selected for the forebody and aftbody.

Selection of Sears/Haack shapes will be influenced

by wing planform and engine location; the aftbody

is most affected (see Fig. 8). A shape for minimumwave drag (type II from the area distribution chart,

Fig. 6) can generally be fitted to the critical cross

sections required for the forebody. The aftbody

area distribution is more sensitive to engine loca-

lASTTAIL

WARNING

13



Table 4 Multirole avionics configura tion

SUBSYSTEM-EQUIPMENT

e COMM/NAVIIDENT- ICNIA

UHFNHF RADIOMK XV-NISTACANVORMLSJTIDSENHANCED JTIDSGPSSINCGARS

- LOW COST HIGHLY ACCURATE ALG INERTIALNAV UNIT

- CNI ANTENNAS AND CONTROLLER

- ADVANCED AIR DATA SENSORS

e DATA PROCESSING

- INTEGRATED AJC COMPUTER SYSTEM

- HELMET DISPLAY ELECTRONIC PROCESSOR

e CONTROLS AND DISPLAYS

- VOICE INTERACTIVE CONTROL SYSTEM

- FLAT PANEL DISPLAYS PLUS CONTROLS

- HELMET MOUNTED DISPLAY/EYE SENSOR-TRACKER

e DEFENSIVE SYSTEM

- MULTI-THREAT WARNING SYSTEM

- CHAFF/FLARE/EXPENDABLE JAMMERDISPENSER (2)

- ELECTRONIC COUNTERMEASURES SYSTEM

e OFFENSIVE SYSTEM

- PLANAR ARRAY RADAR

- NAV/ATIACK FLIA

- WEAPONS CONTROL SYSTEM

UNINSTALLED TOTAL IN SENSOR AND AVIONIC BAYSTOTAL (INCLUDING ALL REMOTE SYSTEMS)

INSTALLED TOTAL

( ) NOT LOCATED IN AVIONICS BAY

TECHNOLOGY FEATURES

VHSIC CHI SYSTEM

LOW COST INERTIAL REFERENCE UNIT WHICH USED RINGLASER GYRO TECHNOLOGY AND GPS UPDATES TOACHIEVE ACCURACY INCLUDES NAV PROCESSOR

ADAPTIVE NULL STEERING ANTENNAS. MULTIPLE BAND.LOW PROFILE

TUBELESS DIGITIZED AIR DATA SYSTEM-REDUNDANCYMANAGED

VHSIC. FIBER OPTIC BUS

VHSIC. BUS

VOICE CONTAOUAIACAAFT COMPUTER RESPONSESYSTEM. VHSIC BASED. + 200 WOAD VOCABULARY

HIGH RESOLUTION COLOR FLAT PANEL DISPLAYS(7 x 7 INCHES)

FULL COLOR HOLOGRAPHIC HELMET VISOR DISPLAY WITHINSTRUMENT PANEL AND HUDON IT EYE SENSOR-TRACKERBORESIGHTS EYES TO HUD AND INSTRUMENT PANEL ONVISOR

ALL FREQUENCY. ALL ASPECT. VHSIC BASED THREATWARNING SYSTEM

DUAL VHSIC CONTROLLED EXPENDABLE DISPENSERSYSTEM

THREAT JAMMING SYSTEM. VHSIC MULTIMODE

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tion. With aft-mounted engines ·it is recommended

that a type I shape be selected initially. This shape

provides more cross section for the critical aftbody

stations and fits smoothly to the maximum area

generated by forebody requirements.

1) Many emerging subsystem technologies con-

tribute to down sizing full capability fighters.

Subsystem Data Base-Future Compact Fighter

In the previous section guidelines were presentedfor estimating component and subsystem volume in

an effort to ensure more realistic student designs. In

this section subsystems are presented that may be

applied to future fighter concepts. Fighter subsys-

tems were selected because the impact of technology

development will appear in fighter design first. The

technologies indicated in Fig. 9 are manifested

generally as subsystems made possible by major

advancements in digital electronics, structural ma-

terials, propulsion, and advanced weapons. Com-pact fighters, beyond the next generation, are used

for this example because of the following trends.

14

2) Fighter cost, survivability, and availability

will benefit directly by down sizing.

3) Cost reduction concepts are possible with

modular subsystems and airframes, directly ap-plicable to vehicle size reduction.

4) Future fighters will emphasize new reliabilityand maintainability technologies to produce high-

sortie generation rates at forward operating siteswith little or no maintenance.

5) The compact fighter is easier to design for ef-

fective forward basing. Its size requires smaller sup-

port systems (fuel, weapons, and maintenance),offers easier ground handling, makes avail more

operating sites, and smaller subsystems that areeasier to modularize.

Baseline Concept

A high-performance compact fighter is used to il-


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lustrate use of the area plot and the impact of ad-

vanced subsystems that will be described later.

Figure 10 shows a typical general arrangement that

results from the design process described in the

introduction.For supersonic cruise vehicles, cross-sectional

area distribution is used as the initial control for

minimum wave drag. Sears target area distributions

are shown on the baseline to employ type II for the

forebody and type I for the af tbody. Note also that

Amax occurs at 600Jo of body length in agreement

with the guidelines discussed in Fig. 8. The varia-

tion shown between target and measured cross sec-

tions will produce accuracies in far-field drag that

are adequate for conceptual design estimates. Con-

tinued area tailoring would be appropriate before

entering preliminary design or wind-tunnel tests.

Nozzle exit area also contributes to wave drag.Supersonic cruise conditions will require that pro-

pulsion systems produce high nozzle pressure ratios

and large expansion ratios. This particular variable

wedge nozzle with fixed cowl assures minimum

boattail drag at the loss of some internal perfor-

mance. Its impact on the area plot is to improve aft-

body fineness ratio. This design has an overall net

fineness ratio e!d of IO, considered by most to be a

minimum for efficient supersonic operations.

An additional benefit of the area plot design tool is

for center of gravity control. During initial layout,

the vehicle can be assumed to have a constant den-

sity; thus, the centroid of the area plot is approx-

imately the vehicle center of gravity with full internal

fuel. Initial fuel volume may also be sketched withinthe area plot to allow estimates of empty weight e.g.

Subsystems for this compact baseline feature

modularity to reduce subassembly size and cost and

to improve vulnerability and supportability. Most

evident in this general arrangement are modular

low-profile cockpit, weapons carriage, secondary

power generation, and propulsion. These and other

subsystems are described in the following sections.

Critical Major Subsystem Technologies

The technology development of selected major

subsystems is summarized in this section along with

design data to add to the students' data base.

Modular Avionic Concepts

Modularity and quick change benefits of digital

avionics will provide multirole capability with siz-

able reduction in avionics load carried on each mis-

sion. Avionic system developments and trends are

indicated in Fig. II where future systems are com-

pared to current F-I5 and F-18 system technologies.

Multirole avionic suites will provide sensor field

of regard capability such as those shown in Fig. 12.

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Winter 1987

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15



Multiwavelength offensive sensors include radar

and infrared search and track (IRST) for air-to-

air combat, and forward-looking infrared (FLIR),

millimeter wavelength (MMW) and laser radars for

air-to-ground combat. Defensive systems will in-

clude fore and aft warning systems in the IR and

radar frequencies. Installation and location of these

sensors to achieve required field of regard must be

considered early in the design layout process.A typical multirole avionics suite can be pro-

jected to have the weight and volume indicated in

Table 4. Major reductions in ove_rall system volume

are now emerging, due in large part to very-large-

scale integration (VLSI) and very-high-speed inte-

grated circuit (VHSIC) technologies that greatly

requce signal processor volumes for Common/

NA V IDENT functions (ICNIA technology) and

data processing. Cockpit display volume (instru-

mental panel) will almost be eliminated in favor of

helmet-mounted displays. Such installation benefits

are illustrated in Fig. 13 and in the following section

on crew station design.

Modular Crew Systems

Future compact fighters will owe much to the de-

velopment of modular low-profile cockpits and as-

sociated crew protection technologies. Crew station

design will be all new, driven by semisupine seating

(50- to 60-deg seat back angle). Performance bene-

fits will be evident from forebodies with much

reduced cross section and lower wave drag. Radical

performance advances will push cruise and maneu-

ver portions of the flight envelope to levels that will

obsolete current fighters.

16

e TfiANSPAAENCIES

e RESPIRATOR (BREATHING /PRESS SYS)

e HELMET DISPLAYS

e PNEUMATICRESTRAINT

e CONTROlS ANDDISPLAYS

e 800 KT/15G SEAT

e MODULAR SEA TICOCI<PIT

e INTERFACES- ELECTRONIC- ELECTRICAL- ECSIMSOGS- UOVID LOOP

Fig. 14 Low-profilecrew systems integra-tion.

The modular low-profile crew station is shown in

Figs. 14 and 15. As indicated, the crew station is es-

sentially all mounted to the seat module. Controls and

display technology will integrate the helmet-mounted

visor as the primary display. Backup multipurpose

displays and all controls will be seat mounted as are all

crew protection interfaces for pneumatic restraint,

high-altitude escape, high-g escape, anticipatory "g"

protection, and chemical-biological-radioactive (CBR)protective ensemble.

A semisupine seat permits the low-profile cockpit

MOLD LINE AT <t_ FOOT

(8 IN. FROM ACFT <t_. 19 IN. FUSELAGE RADIUS)ENVELOPE-95TH

(NO CLEARANCE)

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Fig. 15 Low-profile cockpit geometry.

Fig. 16 Upright seat in future compact fighter.

AJAA Student Journal

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CABINEXHAUST

that has a reduced forebody volume distribution

with minimum hump due to the canopy (see Fig.

10). To illustrate the aerodynamic payoffs with the

layback seat, an upright seat was installed in the

future compact fighter (FCF) as shown in Fig. 16. A

comparison was made of the FCF sized to a super-

sonic design mission with the upright seat and the

supine seat. The MTOW of the supine seat FCF was

2211/o lighter and the empty weight was 21% lighter.

The reduction in supersonic wave drag producedperformance improvements that increased with

supersonic Mach number, especially in dry power.

Differences at M = 1.6 and 30,000 ft include 50%

improvement in specific excess power Ps and 15%

more sustained turn capability with dry power.

Environmental Control System

The ECS provides the following functions:

temperature, pressure, humidity control, avionics

cooling, cooling and pressurization for the pilot's

integrated protective system, canopy seal, r adar and

ECM waveguide pressurization, internal and exter-

nal fuel pressurization, windshield and canopydefogging, and self-generating oxygen system. The

onboard oxygen generating system (OBOGS) pro-

vides for pilot survival in CBR environments, elim-

inates frequent service operations required by

present-day LOX system, and is effective up to the

aircraft's 60,000-ft plus service ceiling.

A projected closed-loop air cycle system, Fig. 17,

uses low- and high-pressure bleed air from the

high-pressure spool to eliminate the need for an

ECS precooler. Cooling of critical avionics is by

cold plate technique, while pilot temperature con-

Winter 1987

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trol is provided by cool suit technique. Both the

cold plate and cool suit techniques use liquid heat

transfer media that interface with the air cycle

system through liquid to air heat exchangers.

The self-generating oxygen system uses molecular

sieves to separate oxygen from processed air provided

by the ECS system. A gaseous oxygen bottle is located

in the ejection seat to provide oxygen for emergency

backup and high-altitude ejection. Filtration of CBR

contaminants is provided within the OBOGS.The ECS and OBOGS systems are located aft of

the cockpit between the avionics bay and weapons

pallet (Fig. 10). Access to the ECS and oxygen sys-

tems is through the bottom of the aircraft by low-

ering the weapons module.

Environmental Control System Modularity

The closed-loop environmental control system

was configured to adapt to a modular installation.

Figure 18 shows the fundamental modular break-

down for FCF configurations and Fig. 19 shows the

module; interchangeable modulars are identified in

Fig. 18. The primary heat exchanger and relatedram air inlets, ducting, and outlets are too con-

figuration-dependent to permit interchangeability.

The same is true for the secondary heat exchanger

and the emergency ram and dump circuits.

When compared to current designs, modular in-

stallation exhibits significant improvements in

damage tolerance and repair for moderate structure

weight penalties. The module is slightly less vulner-

able because of added system structural weight. It

has a marked advantage in maintainability; mean

time to repair is approximately one-half that of a(Continued on page 39)

17



(

Design Scope fo r Student Supersonic Projects

(Continued from page 17)

conventional system due to easy access and quick

remove and replace characteristics.

Modular Hydraulic System

A high-pressure hydraulic system will signifi-cantly reduce the size of key hydraulic system com-

ponents, such as reservoirs and accumulators, and

HEAT SIN!<UOUIO CONTIIOL HX MOOULE

COOLING MODULEMODULE

Fig. 18 Modular environmental control system concept.

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Fig. 19 CEF ECS module.

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TOTAl HYDRAULICSYSTEM WEIGHT

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ease installation packaging problems due to smaller

tubing diameters compared to a conventional 3000-

psi hydraulic system. Trends in hydraulic system

weight, cost, and risk related to system pressure for

medium-sized, twin-engine fighter are depicted inFig. 20 and summarized as follows.

I) An 8000-psi hydraulic system is considered the

highest risk.

2) A 6000-psi hydraulic system is considered

minimum technical risk.

3) Approximately 28o/o weight reduction and a

volume reduction of approximately 40% is pro-

jected to 8000 psi, compared to an equivalent 3000-

psi system.

4) The 8000-psi system was selected for the com-

pact fighter because advanced development is being

funded by the U.S. Air Force.

Active flutter suppression and direct drive servo-valve-controlled actuators are considered critical pre-

requisite requirements for the successful develop-

ment of an 8000-psi hydraulic system. Included in

system cost is the engineering time and money re-

quired to develop the servoactuators and appropriate

software for each individual flight control surface.

For the FCF class aircraft, two redundant hy-

draulic systems are required to have a maximum

output capability of 70 hp each. This requires that

two main hydraulic pumps, rated at 8000 psi, have a

maximum flow rate capability of approximately 15

gpm. (This horsepower compares to the current F-5

requirements of 40 hp, total, and is indicative offuture performance regimes with active controls.)

The right-hand system boot-strap reservoir (util-

ity) is required to have a displaced volume of 350

in. 3 , and the left-hand system reservoir a displaced

volume of 250 in. 3 • Each system has one accumula-

IMEDIUM-SIZE. TWIN-ENGINE 1-FIGHTER AIRCRAFT

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Winter 1987

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VISUAL SIGHT GAGE(RESERVOIR FLUID LEVEl)

SEALS

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Fig. 2 I 8000-psi hydraulic system power supply (manifold with boot-strap, 270-in. 3 reservoir).

SIN

10 IN DIA

40 AIAA Student Journal

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Fig. 22 Modular weapons carriage.

tor having a displaced volume of approximately 50

in.3 • This assures retention of system pressure in the

boot-strap reservoirs to preclude pump cavitationduring pump startup.

A common module design, Fig. 21, was selectedto provide the following benefits.

1) Easy access for checkout inspection and main-tenance, because cartridge units can be readily re-

placed or the entire module can be removed and

checked on a test bench.

2) Improved reliability with fewer parts and

fewer potential leakage points.

3) Weight savings; less complex and more

compact.

4) Decreased vulnerable area over individualcomponents.

Modular Weapons Carriage

Continued development of folding fin weapons

and lock-on-after launch (LOAL) guidance pack-ages will greatly improve the overall cost of owner-

ship for future fighters. Down-sized weapons such

as illustrated in Fig. 22 will allow payload modules

that are configured for rapid loading, quick: config-

uration changes, low signature, and low-drag inter-

nal carriage. The module concept shown here

measures 36 in. wide, 15 in. average height, and 125

in. long. Volume is approximately 39 ft3 with a

weapon capacity of 2000 lb.

Concluding Remarks

AIR-TQ.AIR MISSILE(CAPACITY 4)

duced only a few of the graphic techniques used to

achieve low-drag vehicle configurations. Area ruling

can be much more sophisticated than shown here,however, the author's aim was to keep it simple.

Others will surely have even simpler methods to

share with undergraduate designers.

A wealth of data also exists for advanced sub-systems, but it should be collected in a common for-

mat, to educate and to make it easier for aspiring

student designers to use. Perhaps professional sub-

system designers should lecture directly to student

design teams.

AIAA's Aircraft Design Committee can play the

key role. They have sponsored many design com-

petitions and will soon publish a design manual. As

a clearinghouse for this and other follow-up infor-

mation, this activity would seem to fit their group

charter, and, at the same time, boost AIAA's objec-

tives for better design education. f/1

References1Nicolai, L.M., "Fundamentals of Aircraft Design,"

METS, Inc., 6520 Kingsland Court, San Jose, CA 95120.2Harris, R.V. Jr., "An Analysis and Correlation of Air-

craft Wave Drag," NASA TM X-947, Langley ResearchCenter, Hampton, VA.

3Sears, W.R., "Projectiles of Minimum Wave Drag,"Quarterly ofApplied Mathematics, Vol. 4, No. 4, 1947.

4 Shapiro, A.H., "The Dynamics and Thermodynamicsof Compressible Fluid Flow," Vol. II, Figs. 17.16 and17.7, Ronald Press Co., 1945.

SJensen, S.C. and Painter, E., "Design Synthesis ofTwin Engined Fighter Physical Characteristics forParametric Studie s," BoeingDOC D6-2044TN, 1968 (un-

Documents

Bud Nelson Supersonics