Aircraft design initial_sizing_2

Rubber Engine SizingFixed Engine Sizing

Geometry Sizing

Initial Sizing

February 10, 2009

Initial Sizing


Geometry Sizing

Review of sizingRefined Sizing EquationEmpty-Weight FractionFuel WeightSummary of Refined Sizing Method

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1 Rubber Engine SizingReview of sizingRefined Sizing EquationEmpty-Weight FractionFuel WeightSummary of Refined Sizing Method

2 Fixed Engine Sizing

3 Geometry SizingFuselage and WingTail areaControl Surface Sizing

Initial Sizing


Geometry Sizing


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Initial Sizing


Geometry Sizing


Quick method based on configuration sketch and aspect ratio

Crude estimation of Max. L/D.

Approx. SFC, weight change during cruise and loiter.

Weight fractions for takeoff, climb and landing are used fromtable.

We/W0 is estimated from statistical equation.

W0 is calculated iterating W0 =Wcrew +Wpayload

1−“

WfW0

”−

“WeW0

”

Initial Sizing


Geometry Sizing


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Initial Sizing


Geometry Sizing


.

W0 = Wcrew +Wfixed payload +Wdropped payload +Wfuel +Wempty

(1)

W0 = Wcrew +Wfixed payload +Wdropped payload +Wfuel +We

W0W0

(2)

Initial Sizing


Geometry Sizing


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Initial Sizing


Geometry Sizing


Initial Sizing


Geometry Sizing


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Initial Sizing


Geometry Sizing


Engine Start, Taxi and Takeoff

A reasonable estimate is W1/W0= 0.97 to 0.99

Climbing and Accelerating to cruise alt. and Mach number M

Subsonic: Wi/Wi−1 = 1.0065 - 0.0325 MSupersonic: Wi/Wi−1 = 0.991 - 0.007 M - 0.01 M2

Starting at Mach 0.1.For an acceleration beginning at other than Mach 0.1, the weightfraction calculated by the above equation for the given endingMach number should be divided by the weight fraction calculatedfor the beginning Mach number.

Initial Sizing


Geometry Sizing


Cruise Breguet Range Equation

Jet :Wi

Wi−1= exp

[−RC

V (L/D)

](3)

Prop :Wi

Wi−1= exp

[−RCbhp

550ηp (L/D)

](4)

During cruise and loiter - lift = weight

L/D can be expressed as the inverse of the drag divided by theweight:

L

D=

1qCd0W /S + W

S1

qπAe

(5)

Wing loading value should be modified as per the situation.Initial Sizing


Geometry Sizing


Loiter weight fraction

Jet :Wi

Wi−1= exp

[−EC

L/D

](6)

Prop :Wi

Wi−1= exp

[−EVCbhp

550ηp (L/D)

](7)

where E is the endurance or loiter time.

Descent for Landing – Historical value

Wi/Wi−1 = 0.990 to 0.995

Landing and Taxi back – Historical value

Wi/Wi−1 = 0.992 to 0.997

Initial Sizing


Geometry Sizing


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Initial Sizing


Geometry Sizing


Initial Sizing


Geometry Sizing

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Initial Sizing


Geometry Sizing

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Either the mission range or the performance must be considered afallout parameter.

W0 =NTper engine

T/W(8)

Range capability can be determined from Eqn.2 by considering theknown takeoff weight as the guess W0 and varying the cruise legsto match the evaluated W0.Similar process may be taken for the other parameters.

Initial Sizing


Geometry Sizing

Fuselage and WingTail areaControl Surface Sizing

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Initial Sizing


Geometry Sizing


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Initial Sizing


Geometry Sizing


Fuselage

For certain types of aircraft, the fuselage size is determinedstrictly by “real-world constraints” – passenger aircraft.

Initial Sizing


Geometry Sizing


Fuselage fineness ratio

Ratio between the fuselage length and max. diameter.Theoretically, for a fixed internal volume subsonic drag isminimized by a fineness ratio of about 3 while supersonic drag isminimized by a fineness ratio of about 14.

Wing

Wing reference area (including the area extended to aircraft centerline) is determined by

Takeoff gross weight

Takeoff wing loading

Initial Sizing


Geometry Sizing


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Initial Sizing


Geometry Sizing


Definitions

Initial Sizing


Geometry Sizing


Tail volume coefficient

Vertical tail volume coefficient : cVT =LVT SVT

bW SW(9)

Horizontal tail volume coefficient : cHT =LHT SHT

C̄W SW(10)

Initial Sizing


Geometry Sizing


Typical values for cHT and cVT

Initial Sizing


Geometry Sizing


Moment arms LHT and LVT

Engine positions Approx % of fuselage lengthFront mounted propeller engine

60%Engines on the wing 50 – 55 %Aft-mounted engines 45 – 50 %

Initial Sizing


Geometry Sizing



Engine positions Approx % of fuselage lengthFront mounted propeller engine 60%

Engines on the wing 50 – 55 %Aft-mounted engines 45 – 50 %

Initial Sizing


Geometry Sizing



Engine positions Approx % of fuselage lengthFront mounted propeller engine 60%Engines on the wing

50 – 55 %Aft-mounted engines 45 – 50 %

Initial Sizing


Geometry Sizing



Engine positions Approx % of fuselage lengthFront mounted propeller engine 60%Engines on the wing 50 – 55 %

Aft-mounted engines 45 – 50 %

Initial Sizing


Geometry Sizing



Engine positions Approx % of fuselage lengthFront mounted propeller engine 60%Engines on the wing 50 – 55 %Aft-mounted engines

45 – 50 %

Initial Sizing


Geometry Sizing



Engine positions Approx % of fuselage lengthFront mounted propeller engine 60%Engines on the wing 50 – 55 %Aft-mounted engines 45 – 50 %

Initial Sizing


Geometry Sizing


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Initial Sizing


Geometry Sizing


Control Surface Area

Initial Sizing

Engineering

Aircraft design initial_sizing_2