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Lecture 10

Aircraft sizing and designFlight 7 BriefingFlight 5 due

11/19/2001 ASE 167 M lecture 10 2

today’s topicsAircraft sizing and designIntro to fighter.f

Flight 7 Briefing – Level Flight Acceleration performance – F16Flight 5 due

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Aircraft DesignThe Phases of Aircraft Design:

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Aircraft Design (2)Conceptual Design: 7 Pivot Points for sizing

2

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sizingWe are trying to find values for the following equations:

CTW

WLTF

WDTF

z

x

−=

−+=

−−=

∑∑

&

γα

γα

cossin

sincos

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aircraft missionFirst determine for what mission you are designing the aircraft (A/A vs. A/G, long range vs. short range, …)

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mission segmentsThe mission of the aircraft can be divided into

the following segments:Engine start, warm-up, and taxiTakeoffClimb and accelerationCruise and loiterCombat and maneuverDescentLanding

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fuel consumptionFuel burned in each mission segment can be

determined by:

For each mission segment, a weight fraction can be determined

ii

iii W

TCdWWCTdWW

−=−= +

+ 111

Tat thrust duration d thrust T

nconsumptio fuel specific C :where

===

=CTdWif

3

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fuel consumption (2)Engine start, warm-up, and taxi

Usually small fuel consumption

Can be lumped with takeoffAssume ~15 minutes of idle power

99.097.01 −=+

i

i

WW

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fuel consumption (3)Takeoff

Accelerate at Tmax

Acceleration:

Ground roll:

( )[ ]

( )

+−−+

−=

−−−=

22

2VCKCC

WS

WTg

LWDTWga

LLDoµρµ

µ

∫=takeoffV

G dVaVS

0

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Climb and accelerationFrom energy methods:

fuel consumption (4)

( )

+∆=∆

= −∆−

+

2

/11

21 :where Vg

hh

eWW

e

DTVhC

i

ie

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fuel consumption (5)Cruise and loiter

( )

DLEC

i

i

DLVRC

i

i

eWW

eWW

/1

/1

:loiter

:cruise

−+

−+

=

=

where: R = rangeE = endurance time

4

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DescentDescent is usually treated the same as cruise

Landingvery small fuel consumption

fuel consumption (6)

997.0992.01 −=+

i

i

WW

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weightGeneric equations are available to approximate the weight of most aircraft components example:

gear landingmain oflength L factor load landing ultimateN

weightgrossdesign landingW otherwise 1.0

gear for tripod 826.0K

otherwise 1.0gear beam-crossfor 25.2

K

m

l

l

tpg

cb

===

=

=( ) 973.025.0gear landingmain mlltpgcb LNWKKW =

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weight (2)These equations are only good as an initial estimate.Equations for 58 components are given in RaymerOr we can estimate the empty weight by statistics (graphs)

Takeoff weight = ΣWsystem + ΣWfuel

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Performance and configuration layout

Similar equations to get initial estimates are available for aerodynamics, engine performance, …Use the same equations that we have used before for performance.Shape and size of the airplane on a drawing (referred to “as drawn”)

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Optimization: sizing matrixThe current aircraft will have different characteristics and may no longer meet all performance requirements, or exceed them (overdesign, not lightest solution). The performance for this example design are:

Takeoff distance < 500 ftPS = 0 (specific excess power) @ M = 0.95, n = 5g, alt = 30000 ftAcceleration from M = 0.9 to M = 1.5 in < 50s

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sizing matrix (2)Check performance of current design, as well as:

%20%10~

%20%10~

−±

−±

SWWT

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sizing matrix (3)

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sizing matrix (4)Constant weight lines

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sizing matrix (5)Combine constant weight and the 3 performance criteria

T/O distancePS

acceleration

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carpet plot

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carpet plot (2)Determine best designCheck result by recalculating parameters

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fighter.fDesigned to provide a design team with the capability to predict the size of a subsonic/supersonic fighter which is required to perform a given combat mission. The routine can be used before a preliminary aircraft configuration is defined.FORTRAN IV programming language

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fighter.f (2)

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fighter.f (3)Input

design variables (30): Number of crew membersMaximum mach numberStore weight, etc.

Mission variables (8 per mission segment):Mission segment typeAltitudeMach number, etc.

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fighter.f (4)Geometry (subroutine SGEOM)

Determines atmospheric properties

Calculate zero lift drag coefficientCD= Σ drags

2

2VS

WnCW

L ρ=

MaV =

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fighter.f (5)Aerodynamics (subroutine SAERO)

Determine viscosity, maximum lift coefficient, Reynolds number, …

Propulsion (subroutine SPROP)Find maximum thrust, military thrust (maximum thrust with afterburner), specific fuel consumption, …

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fighter.f (6)Performance (subroutine SPERF)

Takeoff performanceClimb performanceCruiseAccelerationTurning performanceSpecific excess powerEtc.

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fighter.f (7)Weights (subroutine SWGTS)Approximate the following:

airframe structural weightpropulsion system weight (engine + fuel tanks)Systems weightMiscellaneous weight (crew, oil, …)Takeoff gross weight (Σabove + fuel)

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γγ

γγ

γ

sincos

cos

sin

VhVx

dtdV

gWWL

dtdV

gWWDT

==

=−

=−−

&&

=−

−

=−−

dtdV

gV

WDTV

dtdV

gWDT

2

21sin

1sin

γ

γ dtg

Vdh

dtdhV

ghh

hWTEEnegySpecific

mVmghTE

EnergyKineticPotentialEnergyTotal

eatedifferentie

e

+= →+=⇒

==

+=

+=

221

21

2

2

2

&

Let’s define:Recall – Nonsteady Climb – Energy Approach

Flight 7 Briefing – Climb Performance

dtdhP e

S =

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Flight 7 Briefing (2)Plot Ps X V (or Mach number)

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Flight 7 Briefing (3)In order to efficiently capture the Pstrend, different altitudes were to be flown in level accelerationProcedures:

Take-off and ascend to 10,000 feetOnce in level flight, cut the power to the engines, maintaining altitude constant while the fighter slows down.Just prior to stall speed, engage full powerRecord the flight data with the onboard flight recorderRepeat previous steps for several altitudesDescend and land

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Flight 7 Briefing (4)

-200

-100

0

100

200

300

400

500

600

0 0.2 0.4 0.6 0.8 1 1.2 1.4

Mach Number

Ps (f

t/s)

h=15,000 ft.h=20,000 ft.h=30,000 ft.

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Flight 7 Briefing (5)Report:

Get data from the Falcon 4.0 ProgramLoad tapes, play video and write down values for time, altitude and velocityGraph Ps versus V or MachCross Plot h versus VDetermine the Level-Flight Envelope for the F16

next week

Review for quiz, Q & A evaluationFlight 6 due