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The “Flight Template” A tool for Optimization of sailplane aerodynamics at preliminary design stage for cross country flight Prepared and presented by Matthieu Scherrer

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Page 1: Ostiv presentation V2

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The “Flight Template”

A tool forOptimization of sailplane aerodynamics

at preliminary design stage

for cross country flight

Prepared and presented byMatthieu Scherrer

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Contents

IntroductionAerodynamic in sailplane optimization

Flight template TheoryFlight template concept & determination

Using Flight TemplatesFor airfoil selectionFor AR selectionFor airfoil optimization

Conclusion

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Introduction

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Optimizing according flight history

We should optimize the sailplane according toits use during a cross country flight :

h(t) V(t)

Climbing… … straight flight

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Sailplane optimization

Sailplane performance is not only aerodynamics :This is a mixing between mass (ballast capability) andaerodynamics aspects.A method is proposed, that put aerodynamics aspectof performance « in a nutshell ».

-5

-4.5

-4

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

050 100 150 200 250

V (km/h)

V z

( m / s )

50kg/m²

30kg/m²

40kg/m²

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.025 0.05 0.075

CD

C L

Speed polars for differentwing loading …

… correspond to one single equivalent aerodynamic

polar…

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.5 1 1.5 2 2.5 3

1/sqrt(CL)

C D / C L ^ 1

. 5

… and one drag polar.

Performance for the pilot...

...performance for the designer.

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The aerodynamic designerdilemna 1/3

What would be great to do…

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.005 0.01 0.015 0.02

CD

C L

Decrease drag-> straight flight

Increase maximum lift-> climbing

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The aerodynamic designerdilemna 2/3

… and what is possible to do

You cannot win on all the aerodynamic topicsThere is always an “exchange rate”

-> what is best at the end ?

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.005 0.01 0.015 0.02CD

C L

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Given what is possible to do, what is the best between :

An aerodynamic behavior that favors climbing ?

An aerodynamic behavior that favors straight flight ?

This is a compromise : we have to quantify how manyof each aerodynamic component we should have(like a recipe)

There is a need for a «cost function», that gives a figurerepresentative for the global performance.

The aerodynamic designerdilemna 3/3

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Flight Template theory

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Flight template theory

Drag is the force that flies the sailplane down :-> we should try to minimize power absorbed by drag

Airspeed

Lift

Drag

Weight

No more explicit time dependencyTime depandancy embodied by the “Flight template”

L Lt L L D dC C f C V C C S

P rangeC

3

L

)()()(2

)(~1

)( L L

Lt C dC

t d T

C f

dt t V t C T S

T

dE P DFlight

3 )()(2

dt C SV Vdt DdE D32/1

Time dependant

M a t h e m a

t i c a l

t r a n s f o r m a

t i o n

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Flight template interpretation

Building & interpreting flight templateSpeed history

0

50

100

150

200

250

0 20 40 60 80 100t (s)

V a

( k m / h )

CL history

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 20 40 60 80 100t (s)

C L

CL history

Re-ordered CL history

dCL

dt

Flight tem plate

00.20.4

0.60.8

11.21.41.61.8

2

0 0.2 0.4 0.6 0.8 1 1.2 1.4CL

f t ( C L )

ft(CL=1)= 1/T*dt/dCL(CL=1) = 1/100*9/.1 = 0.9

Speed history

CL history ft(C L)= density of each CL

during the flight

)(1

)( L L

Lt C dC dt

T C f

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Performance cost function

For a reasonnably calm flight :

With a function of wing loading

At the end, power dissipated by drag is expressed as :

LC

V V 1

S m

h g

hS m

V )(

2, 1

2/3

31

2 L

D

C

C SV P

L Lt L

L D

L

D dC C f C

C C

C

C

rangeC 2/32/3

L

)()(

Aerodynamically relevant cost function =Weighted C D /C L

3/2

Aerodynamics aspects

Wing loading aspects

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How to get a Flight Template ?

GPS recording is widely used : we can easily get the history ofa flight.CL is extracted from :

2

21

)(

,)()(

W t V

hS m

V t Nz t C L

S m

h g

hS m

V )(

2, 1

2

1cos

1

g

V Nz

Speed history

Sailplane mass

(from path)

Wind estimation

)(1

)( L L

Lt C dC dt

T C f

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Selected flight template examples

Path color Wing loading Scoring Starting airfield

Pink 41kg/m² 464km Nogaro LFCN

Blue 33kg/m² 227km Moissac LFCX

Brown 31kg/m² 167km Bourg Saint Bernard LFIT

50 75 100 125 150 175 200

V

F T ( V )

Denis (454km) Mat thieu (227km) Adrien (167km)

3 Pegasus glider

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Selected flight template examples

50 75 100 125 150 175 200

V

F T ( V )

Denis (454km) Matthieu (227km) Adrien (167km)

0 0.2 0.4 0.6 0.8 1 1.2 1.4

CL

F T ( C L )

Denis (454km) Mat thieu (227km) Adrien (167km)

Transcriptionfrom speed to C

Lreduces dispersion betweenflights, pilots, flying days,sailplanes, etc…

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« Envelope Flight template » strategy

0 0.5 1 1.5CL

F T ( C L )

Enveloppe Flight Template

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Using Flight TemplatesFor airfoil selection

For AR selectionFor airfoil optimization

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Xfoil calculations (GNU licence)2D calculation, from airfoil geometryBoundary layer & transition modelingDirect & indirect design capabilities

Airfoil computation

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Calculated airfoils

Airfoil Sailplane

E603 (public) Astir, Twin Astir

FX S 02-196 (public) LS1c/d,standard cirrus

HQ300 (public) (DG --- ?)

OAP-1 (from photo) Pegase

HX83N80 (from photo) Discus BDuo Discus

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Calculated drag polars

Computed drag polar for various airfoils

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.005 0.01 0.015 0.02

CD

C L

Eppler E603 (public)FX S 02-196 (public)HQ-300GD-mod2 (public)OAP1 (from photo)Discus (from photo)

Xfoil Re*CL^(1/2)=1 250 000

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Sorting airfoilswith Flight template

Computed CD/CL^1.5 polar for various airfoils

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.01 0.02 0.03 0.04 0.05CD/CL^1.5

C L

Eppler E603 (public)FX S 02-196 (public)HQ-300GD-mod2 (public)OAP1 (from photo)Discus (from photo)

Xfoil Re*CL (̂1/2)=1 250 000

Weighted CD/CL^1.5 polar for various airfoils

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.01 0.02 0.03 0.04 0.05

CD

C L

Eppler E603 (pub lic)FX S 02-196 (public)HQ-300GD-mod2 (public)OAP1 (from photo)Discus (from photo)

Xfoil Re*CL^(1/2)=1 250 000

Envelope FlyingTemplate

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.5 1

FT

C LX

=

S i i f il

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Sorting airfoilswith Flight template

Weighted CD/CL^1.5 polar for various airfoils

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.01 0.02 0.03 0.04 0.05

CD

C L

Eppler E603 (public)FX S 02-196 (public)HQ-300GD-mod2 (public)OAP1 (from photo)Discus (from photo)

Xfoil Re*CL (̂1/2)=1 250 000

Detail of weightedpolaras function of C L

Final cost function value

-> Discus airfoil is the bestairfoil according to this criteria

L Lt L

L D

L

D dC C f C

C C

C

C

rangeC 2/32/3

L

)()(

0.0100 0.0110 0.0120 0.0130 0.0140 0.0150 0.0160 0.0170 0.0180

HQ-300GD-mod2 (public)

FX S 02-196 (public)

OAP1 (from photo)

Eppler E603 (public)

Discus (from photo)

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Using Flight TemplatesFor airfoil selectionFor AR selection

For airfoil optimization

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MIAReXNon linear extended lifting lineCoupled with Xfoil

Quick and accurate computation

Wing computation

Local “2,5D” characteristics Alpha polars

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If AR is augmented with fixed span :Induced drag is reducedAirfoil drag is increased

Global result as integrated overpolar needed.

AR effect 1/2

CDi(CL) & CDairfoil(CL)Discus case

-0.25

0

0.25

0.5

0.75

1

1.25

1.5

0 0.005 0.01 0.015 0.02 0.025 0.03

CD

C L

CDi for Discus AR=28.5

CDi for Discus AR=21.6 (Baseline)

CDi for Discus AR=17.3

CDairfoil for Discus AR=28.5

CDairfoil for Discus AR=21.6 (Baseline)

CDairfoil for Discus AR=17.3

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Cost function values as function of AR

AR effect 2/2

From Thomas F,“Fundamental of Sailplane Design”

Cost function as function of AR(modified Discus wing)

0.95

0.975

1

1.025

1.05

1.075

15 20 25 30 35

AR

R e l a t i v e c o s t f u n c t i o n v a l u

Baseline (Discus)

Quasi optimum geometry

0,5%

“Aerodynamic only” optimum

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Using Flight TemplatesFor airfoil selection

For AR selection

For airfoil optimization

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Numerical optimisation

Drag Polar

Aerodyn. Calc.- Xfoil (2D)- MIAReX(2.5D)

Geometryparametrization

Weightingbyflighttemplate

0.0145

OptimizedGeometry

Optimizer

Optimizationcriteria

Cost functionvalue

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Airfoil geometry

Relative thickness fixedRelative camber, position of thickness& position of camber to be optimized together (warping)

Max thicknessshifted backward

Max thicknessshifted forward

Camberincreased

Max cambershifted backward

Max cambershifted forward

Original airfoil

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A new geometry was found by the optimizer

Result of the optimization 1/2

OriginalAirfoil

ModifiedAirfoil

Relativethickness 15.80% 15.80%

Position ofmaximumthickness

41.00% 33.60%

Relativecamber 3.71% 3.29%

Position ofmaximumcamber

45.30% 43.80%

Cost functionvalue 0.01467457 0.01452589 - Decambered

- Camber moved forward- Thickness moved forward

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Result of the optimization 2/2

Computed drag polar

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.005 0.01 0.015 0.02

CD

C L

Discus Airfoil

Modified Discus airfoil

Xfoil Re*CL^(1/2)=1 250 000

Weighted CD/CL^1.5 polar

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.005 0.01 0.015 0.02 0.025 0.03 0.035

CD/CL^1.5

C L

Discus A irfoil

Modified Discus airfoil

Xfoil Re*CL^(1/2)=1 250 000

Aerodynamic characteristicsof the optimized airfoil

0.01467457

0.01452589

- Narrower laminar range- Higher C Lmax- Lower Cm 0

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Conclusion

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Sailplane Optimization

Using science…

… to make pilots happy

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Conclusion 1/3

A new tool is proposed : the “Flight template”

0 0.5 1 1.5CL

F T ( C L )

Enveloppe Flight Template Treatment of many flight recordinghad led to the definition of an

“Envelope Flight template”.

This represents a statistically relevantprogram of a typical cross country flight

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Aerodynamic optimization can be easily performedwith this new tools

Airfoil selection and sorting

Multipoint wing optimization

Airfoil numerical optimization

Aerodynamic only optimization

Conclusion 2/3

Computed drag polar for various airfoils

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 0.005 0.01 0.015 0.02

CD

C L

EpplerE603 (public)FXS 02-196(public)HQ-300GD-mod2(public)OAP1(from photo)Discus (from photo)

Xfoil Re*CL^(1/2)=1250000

Cost functionas functionof AR(modifiedDiscus wing)

0.95

0.975

1

1.025

1.05

1.075

15 20 25 30 35

AR

R e l a t i v e c o s t f u n c t i o n v a l u e

Baseline(Discus)

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Conclusion 3/3

Way forward :

Using the Flight template for computingaerodynamic performance, coupled with otherdisciplines for a multidisciplinary optimizationprocess.

Objective : optimizing the sailplane as a wholething, and not only its aerodynamic.

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Questions ?

Have nice flights !

[email protected]