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AIAA Team Aircraft Design Competition 2009-2010

Introductory Lectures on Aerospace Design Oct. 23rd, 2009

University of Southern California

Sina Golshany


Lecture-2 Anatomy of Aircraft, Descriptive Geometry & Modern Configuration,


Configuration – Ultimate goal of engineering analysis – Almost all analysis procedures are performed to determine the safest, most optimum geometry (i.e. configuration) – Creating a working, optimum, and safe geometric construction to perform a given mission. – Working Geometry: It has to be geometrically valid (parameterized and matching views, etc…) It has to be manufactured with most simplicity

– Optimum Geometry: Minimum drag, weight, fuel burn and/or cost

– Safe Geometry: Satisfies safety requirements and agrees with safety regulations: (Emergency Egress, Floatation, Fire Hazard, Engine Failures, and Crashworthiness)


Descriptive Geometry – To describe the important geometric features of an aircraft to be used to perform the analysis with very high accuracy (sometimes as high as ±0.0005 inches) – This includes: • Fuselage geometric construction – – – – – –

Cockpit and transparencies (visibility) Contours (top and side) Forebody section (nose) Constant cross-section of the fuselage Wing-fuselage fairing Aftbody section (tail)

• Geometry of wing and other aerodynamic surfaces • Landing Gear • Engine Installation


Goals of This Lecture – Reasoning for each feature of the aircraft geometry is not discussed in this lecture. – Theoretical reasoning for Each geometric feature/parameter is explained in the lecture related to it’s specific discipline. – The goal of this lecture is to introduce you to the parameters used to define aircraft geometry, so later concepts which are usually formulated in terms of the geometric properties could be described. – In a nut shell: How do we define airplane geometry?


Aircraft Anatomy Exploring Tranquillus in CAD Environment


Descriptive Geometry The Essential Elements


Descriptive Geometry: Fuselage – To describe the important geometric features of an aircraft to be used to perform the necessary analysis – This includes: • Fuselage geometric construction – Constant cross-section of the fuselage – Cockpit and transparencies (visibility) – Contours (top and side) – Forebody section (nose) – Wing-fuselage fairing – Aftbody section (tail) • Geometry of wing and other aerodynamic surfaces • Landing Gear • Engine Installation


Descriptive Geometry: Fuselage – General Definitions

– Various mathematical definitions could be used for forebody and aftbody geometries. – Possible geometric trade-studies: Closure angle (τ), forebody fineness ratio (lf/D) and aftbody fineness ratio (la/D) to see their effect of drag-rise Mach number – Also trade studies on nose radiuses to body diameter ratio (ρ0/D)


Significant Forebody Geometries:

- Type 5, Power Law

r  x =  R l

m

-Type 6, Ellipsoidal forebody: n

r   x   = 1 − 1 −  R   l   - Type 7, ESDU I (ESDU 2

α10.5 r77028) = 15 − 10α1 + 3α12 8 R 2 x  x   where α1 =  + k1    (1 + k1 ) l  l    

(

)


Cockpit integration and transparencies: – Fore body is modified to allow low curvature regions for transparency (i.e. cockpit windshield) installation. – To get completely flushed transparencies, topologic optimization is usually performed (by mathematicians) – Curved transparencies (1d or 2d) are often avoided – Very complex process – Room for avionics, cockpit consuls and controls – Trade off between cost, visibility & aerodynamics – Visibility requirements by FAR-25 must be satisfied


Irregular forebody geometry : – High Droop Side Profile – Simple Power Law for top profile --Highly Integrated & Packed with systems -- Safe, providing for pilot’s emergency egress -- Structurally & Geometrically


Irregular forebody geometry :


Irregular forebody geometry :


Concept of visibility patterns:


Significant Aftbody Geometries: - Type 8, ESDU II (ESDU 77028)

(

r = α 2 3 − 3α 2 + α 22 R

)

- Type 9, Myring profile (cubic) r  = 1 − (3 − 2 A)1 − R 

2

x  x ( ) + 2 1 − 1−  A   l  l

- Type 10, Spherically Blunted

cone

3


Sears-Haack Bodies: - Developed by Germans during the Second World War to increase the range of heavy artillery shells. (Operation Paper Clip) -Special case of an Ellipsoidal forebody with n=(3/4) also written as the following in x-y plane:

sin( 2θ ) R θ− + C sin 3 θ 2 y=

π

 2x  θ = cos 1 −  l   -For C=0.3333 drag is minimized for the volume enclosed inside the geometry (LV Haack) -For C=0 drag is minimized for a given value of R (maximum fuselage radius) and l (forebody or aftbody length) (LD Haack) −1


Comparison of nose shapes: - Each is specifically optimized for a particular speed range

Rankings are: superior (1), good (2), fair (3), inferior (4). [From USAF DATCOM]


Sears-Haack Application: - F-16 nose cone matches closely with a modified Sears-Haack


Fuselage Cross-sections – Constant cross-section – 2 main geometric constructs: Elliptical and Doublebubble cross-sections.


Example of Fuselage Cross-section

– Non regular cross-section: ‘8 arc’ cross-section is selected for the lifting fuselage. Note that the cross-section is not constant throughout the length of the cabin, due changes of the outer geometry of the fuselage


Example of Fuselage Cross-section

– Exterior geometry of the lifting body


Example of Fuselage Cross-section

– Non regular cross-section: ‘8 arc’ cross-section is selected for the lifting fuselage. Note that the cross-section is not constant throughout the body


Example of Fuselage Cross-section

– Regular cross-section: a slight ‘Double Bubble’ cross-section is selected for Tranquillus. Note that the cross-section is constant throughout the length of the cabin


Example of Fuselage Cross-section

– Exterior geometry of Tranquillus


Interior Arrangement


Configuration Drawing

– The Final Product of preliminary configuration – Describes the most important geometric features of the airplane


Parameters: Aerodynamic Surfaces – Reference area (Sw): – Almost all major aerodynamic, performance and stability parameters depend of the reference surface area – Different methods to compute them exist: • Trapezoidal Approximation • ESDU Approximation (Straight Tapered & Cranked geometries) • Industrial Approximations (Each company uses a different way of computing the reference area)


Trapezoidal Approximation – Trapezoidal Reference area (Sw), Span (b), tapper ratio (λ) and Aspect Ratio (AR or A): – Simplifying the wing geometry to a simple trapezoid, by extending the outboard trailing edge as shown: – General Parameters: c_bar, span, Leading edge and c/4 sweep angle, root chord & tip chord.


ESDU Approximation – Adopted by Roskam’s aircraft design methodology – Geometry for a straight tapered wing:


ESDU Approximation – Adopted by Roskam’s aircraft design methodology – Input Geometry for a cranked wing:


ESDU Approximation – Conversion of geometry for a cranked wing:


Example of equivalent planform:

– ESDU Method applied to obtain the equivalent trapezoidal planform


ESDU Generalized Method – To analyze more complex wing planform geometries wing is broken down to multiple analytic panels:


Dihedral & An-hidral angles: – Angle between the wing and fuselage – Added to adjust a particular rolling behavior (i.e. roll stability) -- It’s value is usually very small (2-6 deg. Positive or negative) – Depending on the configuration this angle can be: • positive ( upward, Dihedral). Examples: Boeing 737,747,… • negative (downward, an-hidral): Lockheed F-104, Boeing C-17


Wing Cross-Section: Airfoils – Examples of General Shape of Transonic Airfoils:


Wing Cross-Section: Airfoils – Pictures are exaggerated to show variation of thickness – t/c parameter – Camber line (i.e. maximum camber percentage) – installation angle – Geometric Twist of the wing.


Wing 3d Geometry


Wing ‘Jig geometry’ vs. ‘Elastic geometry’ – Effects of flight loads causes the geometry of wing during flight to be different than the unloaded geometry


Configuration for efficiency Present day case studies


Configuration, Notable Examples: – Configurations under study today for similar requirements to that of the RFP – Airbus: Using High BPR Turbofans – A30X project, Low Noise, Low emission, Low fuel burn – H-tail to suppress noise


Configuration, Notable Examples:

– Remember Tranquillus? It was configured prior to the release of the Airbus images


Configuration, Notable Examples: – Configurations under study today – Airbus: Using Open Rotor engines (AKA Propfans) – Main Elements: – Forward Sweep – Canards – Wing is attached to the aft body -Prop fans and engine exhausts are covered by the empennage


More radical examples from Airbus: – Configurations under study today – Airbus: Using Open Rotor engines (AKA Propfans)


Concepts From Boeing: – Low Noise Concept: – Lifting Fuselage, Sweep Forward Wings + H-tail – Low Fuel Burn Concept: – Propfan engines, High AR wing, Laminar flow, Pi (π) tail engine installation – Low Emission Concept – High BPR Turbofans – Ultra High AR + folding wings – Aft engine mounting + T-tail


Hierarchical Elimination might be the way:


DSM Completed


Questions?

2 - Configuration, Descriptive Geometry, and aircraft anatomy  
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