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-
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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.
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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)
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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.
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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
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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.
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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
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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
\
(
c
OCl DESIGN LOAD FACTOR
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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
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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
..
PLANAR ARRAY RADAR WITH 27 • 8 INCH ANTENNA AND500 WATI DUAL MODE TWT
FORWARD LOOKING lA FOR NAVIGATION AND TAAETINGWITH AUTOMATIC TARGET RECOGNITION
..
PROJECTEDWEI<l*iT (LII)
100
5
2Q
10
32
18
2Q
23
8
(50)
160
280
150
1•5)
955
1,242
VOL (Frl)
1 •2
02
0 25
0 15
1 0
0 4
03
03
N/A
I 2
(0 . ,
36
3 65
36
(1 6)
16 07(18 07!
25.7(28 9)
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.
HINGED ACCESSCOVER
FAULT INDICATORVIEWING WINDOW- - - - - -
IMODULE
FAULTINDICATOR
5.881N.
:li
::>
LINEREPLACEA&E
MOOUlE
Fig. 13 Integrated data processor- VHSIC I.
Winter 1987
• • •7 0 IN
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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)
HRL
Q IQ
1111!11111111111SCALE - INCHES
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
LEGEND
c:::=::J AIR LINE
111111111111111 COOLANOL LINE
a::c::r:::ll FUEL LINEc:z:::::z::l WATER LINE
GROUNDCONNECTION
I8J HEAT EXCHANGER
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)
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(
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.
RHRAM
INLET
NBC ALTER(REMOVED)
Fig. 19 CEF ECS module.
<!lzi5
140
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13
120
110
100
TOTAl HYDRAULICSYSTEM WEIGHT
v
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
I REF NORTHROP N342-3090
80 $
a:
70 2u<'--
60 "l
Fig. 20 Hydraulicsystem pressure, weight,and cost trends.
UlZoil: A..... . i '---.....
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50 z<!lu;-W wa:W> -
"'>- z::>2, z wu
ow:r:w a: a:Ula: ::>Z:!!a: <DOw=> ,_ z,_u
--'Ulu. --'::>'-'-
90
80
70
--'< 10...
0,_0
0
Winter 1987
CEF
"= ITOTAL HYDRAULIC
S[STE.r COST
'URRENT /_TECHNOLOGY RISK FACTOR
/_ .1. I
8 ,...(v2.000 4.000 6.000 8. 000 10.000
RATED SYSTEM PRESSURE PSI
12.000 14.000
40::J<
30
2
1
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0
0
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VISUAL SIGHT GAGE(RESERVOIR FLUID LEVEl)
SEALS
SIN. DIA
ACCUMULATOR
ACCUMULATOR
8 IN. DIA
'
0 958 DIA ACCUM PRESSUREPISTON SENSOR SHAFT
PUMP
I______ __,_______ __,
I
J-- MANIFOLD
VISUAL SIGHT GAGE(RESERVOIR FLUID LEVEL)
5 IN. DIA FLOATINGACCUMULATOR PISTON
WITH BLEEN HOLES
4
SEALS
1.
2.3.4.
5.6.7
8.
MEAN TIME TO REPAIR IS ONE HALF OF CONVENTIONAL SYSTEM
0.958 DIA BOOTSTRAPSENSOR SHAFT
CASE DRAIN FIL TEAHP SUPPLY FIL TEARETURN FIL TEADEAERATION UNITSUCTIONCASE DRAINHIGH PRESSURE SUPPLYLOW PRESSURE RETURN
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-