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UAV - lecture 10 – Zdobyslaw Goraj

Selection of wing section, part 1

Warsaw, 14 May, 2020

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HERON-TP

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Malat’s Customers in Afghanistan

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Selection of wing section • mission-tailored, customized wings –

wing section catalogue as NACA, Wortmanna, Eplera, GAWa

(and derivatives of LS type) are not very useful due to ranges of Re,

CL, Ma;

• interdisciplinary approach must be applied, taking into account many

disciplines as aerodynamics, wing structure (spar location and its

layout), fuel tank arrangement, aeroelasticity, servos locations etc. It is

closely related to so-called MDO (Multi – Disciplinary Optimisation);

• in design and analysis of to-day wing sections the programme MSES

by Mark Drela (MIT) is widely used. This software is based on Euler

equation combined with viscid Boundary Layer equation. In the

internet there is also available the XFOIL software – being an simpler

(linear) version of MSES.

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Flight

endurance:

Endurance – general formula:

1

0ln1

W

W

D

L

cE

t

;

where:

pr

t

Vcc

;

whilst: c – specific fuel consumption of piston engine;

ct – – specific fuel consumption of turbine engine;

pr – propeller efficiency.

For aircraft with piston engine we have:

2/1

0

2/1

1

2/3

2

WWC

CS

cE

D

Lpr

For aircraft with turbine engine we have:

1

0ln1

W

W

D

L

cE

t

Endurance coefficient

efficiency

s

m

s

m

m

s

mkg

m

kgmunit

2

1:

mm

s

sC

sCunit t

11;

1:

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HA-flight – region of development interests

high speed

airfoilshigh altitude

flight

historical

trend

low speed airfoilsRe

M

106 107

0.8

0.6

0.4

0.2

0.0

high speed

airfoilshigh altitude

flight

historical

trend

low speed airfoilsRe

M

106 107

0.8

0.6

0.4

0.2

0.0

manned unmanned

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Wing sections for surveillance aircraft

of high CL and high CD (piston-prop)

)18.0(2

0 tcoefficienOswaldewhere

eA

CCC L

DD

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Wing sections for

surveillance aircraft

of high CL and high

CD (turbo-prop)

AR – aspect ratio

e – Oswalda coefficient

200 cts CD0 = 0.0200

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Two elements (slatted) airfoils: SA

Max.lift (F=0o)= 2.4

Stall characteristics: Mild stall

NLF technology: upper surface – 60% laminar

lower surface – 80% laminar

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Influence of Re on airfoil characteristics (1/2)

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Influence of Re on airfoil characteristics (2/2)

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Endurance factor for different airfoils –

Wind Tunnel results

HQ – variable camber airfoil, for modern sailplane

wings featuring a plain trailing edge flap,

developed at DLR

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Influence of bags on airfoil characteristics

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Influence of flap deflection of airfoil characteristics

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HERON with wing section SA-21

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HERON – wing flaps (1/2)

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HERON – wing flaps (2/2)

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FIREBIRD with wing section SA-19

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Wing section SA-19 – flaps configuration

suited to the mission segment

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Two-element wing sections suited to high

altitude flights: HASA-LT i HASA-HT (1/2)

LOW TRANSONIC (HASA-LT)

propeller-driven aircraft

HIGH TRANSONIC (HASA-HT)

jet-powered aircraft

M = 0.30 - 0.50

high values of endurance factor

Clmax 2.0 - 2.5

M2Clmax = 0.4 - 0.5

maximum

lift

ceil ing

parameter

M = 0.50 - 0.70

high lift-to-drag ratio

Clmax 1.5

M2Clmax = 0.5 - 0.6

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Two-element wing sections suited to high

altitude flights: HASA-LT i HASA-HT (2/2) High Altitude Slotted Airfoil

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Liebeck’s & SA-14 wing sections (1/2)

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Liebeck’s & SA-14 wing sections (2/2)

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Aerodynamic

characteristics at

off-design point –

going down with the

Cl one can decrease

the Cd

Przy zmniejszeniu Cl możemy

też zmniejszyć Cd

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Influence of Mach

number on endurance

coefficient

CL

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High altitude

transonic airfoils

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Influence of

Reynolds number

on drag polars for

high altitude

transonic airfoils

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Influence of

Reynolds number

on aerodynamic

efficiency for high

altitude transonic

airfoils

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Influence of Mach

number on ceiling

parameter for high

altitude transonic

airfoils

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Hinge moments for

high altitude

transonic airfoils

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Two-segment wing section & associated

pressure distribution

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Influence of surface roughness & bugs

(insects) on aerodynamic characteristics

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How wing thickness does change along

wing span on example of HERON

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Wing section configuration best suited to the

mission segment

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Extra space for fuel FT (Fuel Tank – Extended)

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Wing section FT/EX – pressure distribution

& lift coefficient (Fuel Tank – Extended)

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Endurance coefficient dependant on parasite

drag due to external containers

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Altitude Factor:

M2 CL

pTR

pa

s

,

where: R = cp - cv – perfect gas constant (= 287 J/(kg K)); = 1,4 (raio

of specific heats)

From equilibrium of lift and weight one has:

LL CqS

QorazCSqQ

and hence

2

2222

2

2 2

2

1

2

1

aS

QCMorazaCMaC

a

V

S

QLLL

and

LLL CMpp

CMaCMS

Q 2222

2

1

2

1

2

1

or

LL CMSTRCMSpQ 22 )(2

1

2

1

From the above equation one can see that the higher

altitude (and lower pressure) the higher „altitude factor”

M2 CL

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How one can improve the altitude factor: M2 CL

Altitude factor can be increased either due to:

1. Altitude increase (p will decrease and T*

decrease also)

2. Wing loading (Q/S) increase

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Flight at high altitudes (1/2) Smaller S means higher W/S

at the same altitude

The bigger drag of external containers, the higher lift coefficient CL (at loiter)

S

Q

pCM L

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Flight at high altitudes (2/2)

Smaller weight; V=constant;

Flight altitude increases

Smaller weight; smaller speed;

Flight altitude = constant Smaller Re; V=constant;

Flight altitude increases

Smaller Re; smaller speed;

Flight altitude = constant S

Q

pCM L

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