Conceptual Design of an Unmanned Combat Aerial Vehicle (UCAV)

1

Conceptual Design of an Unmanned

Combat Aerial Vehicle (UCAV) by Ray Whitford

Department of Aerospace, Power & Sensors

Royal Military College of Science,

Defence Academy of the UK

with PW-124 Case study by Zdobyslaw Goraj

Warsaw University of Technology

Wykład 15, Warszawa, 16.06.2020

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Topics

• Manned versus unmanned vehicles

• Requirements

• Competition

• Stealth

• Structures

• Powerplant (Engine, Inlet, Nozzle)

• Mass Breakdown

• PW-124 – case study

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Man v Machine (1/2) The pilot against the unmanned vehicle

Pilot Advantages Pilot Disadvantages

Adaptability and flexibility (elastyczność)

Mental processing from wider

variables (Wyższość umysłu nad sztucz.Inteligencją)

Moral and political control (motywacja)

Unpredictable behaviour against the

enemy (Pozytywne reakcje w sytuacjach

nieprzewidywalnych)

Physical shape and frailty (słabości)

Need for rest and sleep (zmęczenie)

Inability to self repair during mission (niemożność samonaprawy)

Fear (strach)

Cost of Training and Currency (koszt

szkolenia, nie domaga się podwyżki!)

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UCAV

Advantages

UCAV

Disadvantages

Durability (długotrwałość misji)

Lack of a vulnerable human (człowiek

jest „urazowy”)

Lower operating cost (niższy koszt

operacyjny)

Expendability (łatwiej uzupełniać braki)

Greater stealth (łatwiej o niskie RCS)

Decision making entity -

undeveloped AI technology (wciąż niedorozwój Artificial Intelligence )

Bandwidth requirements (częstotliwości)

Programmed, lack of flexibility (brak

elastyczności w działaniu)

Smaller warload (słabsze możliwości bojowe)

Limited sensors (niedorozwój czujników)

Man v Machine (2/2)

The pilot against the unmanned vehicle

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Minimum Design Life

Typical system

Current Fighter

design life

UCAV life

Airframe

8,000 hr

300-500 hr

Landing gear

7,500 cycles

300-500 cycles

Radar

10,000 hr

300-500 hr

Environment control

system systemy

Rozpoznawania srodowiska

8,000 hr

300-500 hr

Engine hot section

4,000 cycles

300-500 hr

Engine cold section

8,000 cycles

300-500 hr

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Requirements

• Fully autonomous flight

• In-flight Refuellable

• Combat radius of 1200 nm

• Assorted ordnance up to 2000 lb

• Max speed M=0.9

• Able to operate from 2000m runways

Wyselekcjonowane uzbrojenie

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Possible Roles

• SEAD and DEAD

• Attack from low- medium- & high-altitudes

• Specialist Reconnaissance

• Naval Strike/Reconnaissance

• Electronic Warfare

Suppression of Enemy Air Defence and Destruction of Enemy Air Defence

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Ordnance

• Laser Guided Bombs: Paveway 1000lb

• Anti-Radiation Missiles: ALARM

• Multiple Small Diameter Bombs (SDB)

• Multiple Munitions Dispensers

2000lb JDAM

Paveway

SDB

JDAM: Joint Direct Attack Munition

MMTD: Multi-Mode Threat Detector

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Threats

AWACS & Fighters High Altitude SAMS

Low & Medium Level SAMS MANPADS

High-Altitude Surface-to-Air Missile System (SAM)

1. Man-portable air-defense systems (MANPADS or MPADS)

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The Competition

Predator X-45A

X-47 X-46

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Stealth

• Radar

• Infrared / Thermal Imaging

• Aural

• Visual

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Increased Survivability

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Stealth Design • Straight Parallel Edges

• Continuous Curvature

• Clean Underside (internal weapons)

• Intake & Exhaust Hidden

• Sawtooth Edges on Doors

• Vectored Thrust Trim for Yaw and Pitch

• Cold Air Bypass

• Low Electronic Emissions

• Radar Absorbent Material

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Possible Planforms

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Planforms

• Wing Area: 75 m2

• Span: 21.13 m

• Sweep Angle: 40o

• Fuselage Length: 9 m

• Aspect Ratio: 5.95

• Taper Ratio: 0.29

Early low

aspect ratio design

Early VERY low

aspect ratio concept

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Size Comparison

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Internal Layout This highlights a major problem:

Cutting big holes in the bottom of the

vehicle

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Internal Layout

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Structural Layout

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Structural Layout

FWD

Weapons

Bays

& Engine

Empty space:

Structurally

unsound:

A major problem

Box

Frames

To

withstand

Torsion

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Fuel Tanks

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Internal Layout

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Engine

• Eurojet EJ 200 Selected

• War Mode Produces 65kN (SL ISA)

• T/W : 0.45

• 7% installation Loss

• SFC (M=0.8, 11km) = 28 mg/Ns

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Air Inlet • Mask the Compressor Face

• Low Profile Capture Face

• Use of Blockers and RAM

• Exterior Shaping

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Inlet Treatment

Blocker

Engine

Face

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Versatile Affordable Advanced

Turbine Engine (VAATE)

Versatile Affordable Advanced Turbine Engine

(VAATE)

Stealthy but very poor aerodynamics

due to adverse pressure gradients

Stealthy but poor aerodynamics (so thrust LOSS)

and exhaust duct wants to circularise

Line-of-sight

blockage

Distortion-tolerant fan

Vectoring

nozzle

Wszechstronny (osadzony przegubowo), o umiarkowanej cenie,

Zaawansowany silnik turbinowy

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Air Inlet

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Propelling Nozzle

• High On-Design Thrust

• Low IR Signature

• Low Radar Cross Section

• Thrust Vectoring

• High Aspect Ratio

• Mixer Nozzle

• Upper Surface Location

• Use of Ceramics

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Propelling Nozzle

• Provide For Trimming Of Aircraft

• 3-D Vectoring • Vertical – Fluidic

• Horizontal – Mechanical

FWD

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• Mainly responsible for trim

• Additional pitch or yaw control

• Combination of vanes for directional control and fluidic thrust vectoring allows 3-D vectoring

• Not immediately dependent on engine throttle response, thus relatively fast-acting

Propelling Nozzle

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Mass Breakdown

Fuel

32%

Structure

16%Landing

Gear

4%

Powerplant

11%

Systems and

Equipment

16%

RAM

15%

Payload

6%

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Use of Radar Absorbing Material

RAM Weight: 2300kg

15% MTOW

25% Empty Wt

Polychloroprene + carbonyl iron ferrite

(10% by weight)

Used in parasitic form (not as structure)

for external skin and lining for air inlet

To defeat 3cm (10GHz) radar

requires 7.5mm thick RAM

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Range - Hi Hi Profile

1300 nm

2600 nm

Take-off Landing

45000 ft, M0.82 51000 ft, M0.82

Weapons release

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Range - Hi Lo Hi Profile

630 nm

1460 nm

45000 ft, M0.82 50000 ft, M0.82

Take-off Landing

5000 ft

250 ft, M0.9

200 nm 630 nm

Weapons

release

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UAV flight safety events (based on 120,000 flt hrs of IAI UAVs)

Propulsion

24%

Misc

7%

Flight control

28%

Power

system

8%

Comms

11%

Human error

22%

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PW-124

a high maneuverability, case study UCAV project

anticipated as a future

ground attack aircraft

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Fundamental assumptions 1/3

Main goal: to design, build and prepare

the flight tests of a small, highly manoeuvrable

unmanned aerial vehicle of the reduced radar,

infrared and acoustic signature

First priority: high manoeuvrability Potential future application: ground attack mission

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Fundamental assumptions 2/3

Competitors? Rather niche !

PW-124

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Fundamental assumptions 3/3

Competitors? Rather niche !

•Role of the specialized so-called „ground attack aircraft” is widely

accepted and beyond any discussion. Examples: A10, Su25

•UAVa being now in service or UCAVs in design progress are

multi-mission, so they are not specialized in ground attack.

•Survivability strongly depends on manoeuvrability. Well known

UCAVs as not highly manoeuvrable, can not be very efficient

in ground attack mission. Manned aircraft can be never highly

manoeuvrable ( human g limit!)

•Conclusion: there is a luck of any UCAV specialized for ground attach mission!

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Design assumptions 1/6

•High manoeuvrability (load factor of order 15)

at a relatively small thrust surplus

•Low cost due to small weight and small

dimensions ($1mln is anticipated)

•Cheap turbojet engine (Microturbo TRI 60-5;

SLS 440 kG Thrust)

•Highly sophisticated carbon fibre structure,

light and of high strength

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Design assumptions 2/6

•Compact configuration based on cranked

delta wing, endowed with fixed slots, tab-flaps

and elevons / rudderons, easy to control about

three axes

•Payload compartment of required volume

(width, heigth & length) has to be placed

(hidden) in the central part of the body (CG

position insensitive to the weight change after

the payload is released)

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Design assumptions 3/6

•Reduced RCS is much less weighted now than

manoeuvrability - it will be developed in the

future but under the condition if it does not

change the aerodynamic characteristics

essentially for the worse

•Radius of mission equal to 200 km

•Time of pure combat is limited to 5 min

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Design assumptions 4/6

•Low sensitivity to gust will be achieved due

to relatively low lift-curve slope of order 2.2

per radian and a moderate wing loading of

order 60 kg/m2

•Curved air inlet designed to reduce the RCS

of the engine compressor face

•Essential Ph.D. students participation

in the design effort

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Design assumptions 5/6 Typical UCAV missions

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Design assumptions 5/6 PW-124 - a typical mission

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External layout 1/3

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External layout 2/3

•blended wing body configuration

•Wing control surfaces provide

longitudinal balance

•high wing dihedral (+20; -31)

provide directional stability

•retractable landing gear

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External layout 3/3 Longitudinal control surfaces

Lateral control surfaces Bottom inlet for air & hot gas mixer

Bottom inlet for air

& hot gas mixer

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Configuration of main systems

engine Fuel tanks

battery

Electronic equipment

parachute

EO system

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Main body structure

Payload compartment

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Power unit

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Selected parameters 1/2

Wing span 4,5 m

Wing area 11,8 m2

Body length 5 m

Height (in flight) 0,9 m

Height (on runway) 0,9 m

Aspect ratio 1,76

Payload volume (length x width x height) 2 m x 0,6 m x 0,5 m

Empty weight 300 kg

Payload 200 kg

Fuel weight 400 kg

Nominal take-off weight 800 kg

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Selected parameters 2/2

Maximum take-off weight 900 kg

Maximum manoeuvring weight 650 kg

Take-off thrust 4,4 kN

Take-off wing loading 78 kg/m2

Manoeuvring wing loading 56,5 kg/m2

Manoeuvring thrust loading 148 kg/kN

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Aerodynamic analysis

6200 panels, 28 patches

Body centre airfoil

(with modified both LE

and TE)

NACA

0012-64

Body – outer wing

junction airfoil (in the

plane parallel to the

vertical plane of

aircraft symmetry)

NACA 651-

412

Outer wing airfoil (in

the plane parallel to the

vertical plane of

aircraft symmetry)

NACA 651-

412

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Asymmetric flow

Cp at =3,38o, =0o,

F=0o, E,l=+10o, E,r=-10o

Cp at at =3,38o, =10o

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Lift and pitching moment

CL( )

-0,8

-0,4

0

0,4

0,8

1,2

-10 0 10 20

CLCL_d 0

CL_d 10

CL_d -10

CMY( )

-0,08

-0,04

0

0,04

0,08

-10 0 10 20

CMYCMY_d 0

CMY_d 10

CMY_d -10

Lift coefficient versus angle of attack

for clean configuration (d=0),

flap-tabs deflected down (d=10) and

flap-tabs deflected up (d=-10); Ma=0.5,

Re=28x106

Pitching moment coefficient computed

about a quarter point of MAC versus

angle of attack for clean configu-

ration (d=0), flap-tabs deflected down

(d=10) and flap-tabs deflected up

(d=-10); Ma=0.5, Re=28 mln

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Flight envelope

0 50 100 150 200

-10

-5

0

5

10

15

n

PW-124

V [m/s]

w=15

w=7,5

w=-7,5

w=-15

Cz m

ax

A D

G F

E

Vs1=28

Vs1'=39

VA=107 VD=211

VC=136

VG=124

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Performance

0 200 400 600

Flight speed [km/h]

0

2

4

6

8

10

Fli

gh

t A

ltit

ud

e [

km

]

0 50 100 150

Max rate of climb [m/s], Max climb angle [deg], time to climb [min]

time to climb

Vmax

Vmin

flight speed of max. rate of climb

flight speed of max. climbe angle

rate of climb

climb angle

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Range and endurance PW-124 - Endurance and Range (H=1.5km, W=900kg, WFUEL=350kg)

100 200 300 400 500 600

TAS [km/h]

0

1

2

3

Endurance [h]

0

200

400

600

800

Range [km]

Endurance

Range

60

Sensitivity to gust

tVm

CSq

g

L

eW

W

1

L

gC

V

WWSVWm

2

21

0 0.2 0.4 0.6 0.8 1

time [s]0

0.2

0.4

0.6

0.8

1

vert

ical

dim

en

sio

nle

ss d

isp

lacem

en

t

du

e t

o g

ust

(W/W

gu

st)

small lift-curve slope Cl= 2.2

high lift-curve slope Cl= 4.6

Aircraft of lower aspect ratio

is less sensitive to gust than that

of higher aspect ratio

Aircraft of lower wing loading

(high S/m) is more sensitive to gust

than that of higher wing loading

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RCS has to be minimized

Predicted signature of a generic aircraft

Edges, panels etc. have to be grouped on

a minimum number of alignments. Then the strongest

edge reflections will be seen only at four relatively

narrow azimuth zones

Up to azimuth 30 the box type air

intakes totally dominate the signature

RCS dominated by wing edges

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Stealth Design • Straight Parallel Edges (partly)

• Continuous Curvature

• Clean Underside (internal weapons)

• Intake & Exhaust Hidden (partly)

• Sawtooth Edges on Doors (easy to be done)

• Vectored Thrust Trim for Yaw and Pitch (no)

• Cold Air Bypass (partly)

• Low Electronic Emissions (no)

• Radar Absorbent Material (no)

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Wing design

Double-circuit torsion box,

made of epoxy-carbon composite

takes the torsion loading

Upper and lower skins are made of

sandwich with a filler made

of polyurethane foam

Spar flanges are made of carbon roving

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Configuration (1/8)

Payload containers opened in flight –

both covers are deflected down

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Configuration (2/8)

Internal payload containers are opened,

all undercarriage legs deflected down.

Double covers of each undercarriage

containers are well visible

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Configuration (3/8) A bottom-side view:

Internal payload containers are closed,

all undercarriage legs deflected down.

Double covers of each undercarriage containers

are well visible. Aircraft is ready to land.

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Configuration (4/8)

Internal payload containers

are closed, all undercarriage legs

deflected down. Double covers of

each undercarriage containers

are well visible. Aircraft is ready to

land

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Configuration (5/8)

Elevons deflected asymmetrically

(left elevon deflected down, right deflected up)

Flap-tabs (at the trailing edge of the

blended-wing body) deflected up

(it is typical in horizontal flight for

equilibrium of pitching moments).

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Configuration (6/8)

Horizontal flight – clean configuration

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Configuration (7/8)

Clean configuration from a top-front-side view.

Flight spoilers deflected

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Configuration (8/8)

Clean configuration from a top-back-side view.

Flight spoilers deflected.

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Conclusion (from London conference)

•For successful design project 3 elements are needed:

•bright idea in a proper time

•experienced, well motivated team

•money for research and design activity

•Requirements for PW-124: high manoeuvrability,

low sensitivity to gust, low cost

•Independently on the external support this project

will be continued, because it contain a number

of fascinating subtasks to be solved.

•If the project is successful an interest of governmental

agencies is expected. We are looking for any kind of

cooperation for future business!