Cooperation in Aircraft Design

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Res Eng Des (1992) 4:115-130 Research in Engineering Design

Theory, Applications, and Concurrent Engineering

Cooperation in Aircraft Design

A l a n H B o n d 1'* a n d R i c h a r d J R i c c i

~Manufacturing Engineering Program, University of California, Los Angeles, California, USA; and 2Automation

Systems, Lockheed Aeronautical Systems Company, Burbank, California, USA

Abstract We describe how aircraft are designed in a large

organization We discuss the different phases of design

and interaction with the customer We then describe the

models used by each specialist department and the interac-

tions among departments during the design process We

observe that the main design choices are refinement opera-

tions on the design We then briefly describe how the

negotiation process is controlled by an organizationally

agreed sequence of commitment steps We then describe

negotiation at higher levels in the organization What deci-

sions are made, the compromises worked out, and the

effect of these higher-level commitments on the design

process

We conclude that: (I) aircraft design proceeds by the

cooperation of specialists (specialist teams or depart-

ments); (2) each specialist has its own model of the design,

and may use several different models or partial models for

different purposes; (3) specialists have limited ability to

understand each other's models They communicate using

a shared vocabulary, but not necessarily.shared technical

knowledge; (4) design proceeds by successive refinement

of the models, which are coordinated and updated to-

gether; (5) the design decisions, which are acts of commit-

ment and model refinement, are negotiated by the special-

ists among themselves; (6) one way this negotiation

process is organized and controlled is by the use of com-

mitment steps; (7) negotiations occur at higher levels in

the organization, resulting in commitments which greatly

influence and constrain the design process and its organi-

zation, and which have the greatest effect on the cost of

the product

1 Introduction

t i The Problem o f Collaborative Design

W h e r e a s t h e r e is some existing published research

on c o n c u r r e n t design requirements and on c o m p u t e r

systems for the support o f c o n c u r r e n t design (see,

Offprint requests: 4173C Engineering 1, Department of Com-

puter Science, University of California, Los Angeles, CA 90024-

1596, USA

e.g., [I] and [2]), we k n o w of v e r y little previous work that has reported on existing collaborative design in manufacturing organizations

We perceive the problem as to first describe collaborative design, then to manage it (i.e., to control action and allocate resources so as to optimize re- source use, subject to real-time requirements) As part of this, we can then determine h o w to support this activity, by changes in procedure, culture, and

computer support

1.2 Separate Models

An illustrative example arises in our work on collaboration in wing section design H e r e a stress engineer and a producibility designer interact using a diagram on a CAD system T h e stress engineer needs a solution which transmits loads well through the structure, and the designer needs a structure that

is easy to fabricate, using, for example, an automatic riveting machine T h e criteria used b y each specialist are private to them in that they are c o m p l e x and

c o n c e r n e d with their particular technologies

In the case o f the collaboration o f a producibility designer and a stress engineer, the producibility designer is c o n c e r n e d with arranging forms and fasteners so that the design realizes (or " s i z e s " ) a given layout and function, and is producible (i.e., manu- facturable on the machines currently available using techniques and tooling currently in use in the organization) His description c o n c e r n s the use o f the part, and its production T h e producibility engineer tries

to make joints which are straight, and accessible with k n o w n riveting gun types H e also needs to keep rivet spacing constant, or at least to a small

n u m b e r or different rivet spacings, in o r d e r to limit tooling set-up cost

T h e stress engineer is c o n c e r n e d with arrangements such that the loads carried in the elements are well formed, in that internal load is transmitted throughout the structure, which satisfies a given external load specification His description c o n c e r n s

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116 Bond & Ricci: Cooperation in Aircraft Design

loads, stresses, transmission, and techniques for

finding them The stress engineer works privately

with a finite element model which calculates load

patterns satisfying differential equations derived

from physical principles These must match the load

transmission properties of the sized geometry

The common language of their collaboration is

simply a drawing, that is, geometric elements and

their relations; in addition, indications of what is

right or wrong with a given geometry, and possibly

suggested changes in the geometry

In aircraft design, there are many other special-

ists, each with their own technology and language

For example, there are aerodynamicists who use

surface models and flow-field equations; there are

maintainability engineers concerned with access,

disassembly, and replacement; there are hydraulic

engineers; and thermodynamic experts They do not

understand each other's specializations, but they

have to collaborate to produce a single design ac-

ceptable to all

The aim of collaboration is to produce a design

which is agreed to by each agent This means that

each agent has a justification of the design that he is

satisfied with In organizational practice, it is very

important to validate designs Manufacturing is very

much concerned with validation, specification, and

standardization, as organizational mechanisms The

design must satisfy' contractual requirements and

must also meet safety and other legal and govern-

ment-dictated requirements

1.3 Conflict

We shall ignore any problems of conflict and decep-

tion in collaboration, and assume benign, nonantag-

onistic collaboration This is, in any case, what hap-

pens in organizations At a given organizational

level, one department can assume that the informa-

tion given by other departments is "correct." It is

not held responsible for inaccuracies or errors of

judgment of other departments Problems of compe-

tence and conflict of interest among departments are

usually assumed to be dealt with at higher organiza-

tional levels

1.4 Outline of This Paper

In Section 2, we discuss how the collaborative prod-

uct design process is initiated by specification with

the customer Sections 3 and 4 describe the different

specialists involved in aircraft design, the models

they use, and their interactions Section 4.3 draws

conclusions on the overall structure of the collabora-

tive design process Section 4.4 discusses model re-

PHASE

~ONCEPT DESIGN

PRELIMINARY DESIGN

P R O D U C T I O N D E S I G N

MAIN DECISIONS I~equh'eluent s Spex:itic~t&~ns Fuel/Stores/Engine ()ug~l,o, rd Sy~telnx hdm~rd Profile

Fuel/Stllres/Engines Flight Station/Envirmunent Ctm~rots/Hydraulics Primary Stnu:turM Joints ElectricM/B[ack Boxes Detailed Inboard Profile

Same as gbow~ except De~ailed parts released for pr(ld u(C.ion Dimenslmts with all parts

MAIN TECHNOLOGIES

Design Str~c~,,r~'~ (Stre~/L~ad,s ~, VCeights

Aeronlechanic~

Mission AnMysis

Design Al~rodyl~ulics Structures (Stress/Loads] Weighg~

Al~romechal~ics Tllermodyn~mii:s RMar Imagiug

I Propulsion

R, M aud S

Fig 1 Design phases, main decisions, and main technologies involved

finement Section 5 lays out a typical complete scheme of design goals and steps in the design of aircraft to prototype stage Section 6 briefly raises the issue of higher level negotiation By higher level,

we mean (1) at a higher level of abstraction, such as policies for choice of materials, and also (2) concerned with organization and support of the design process Section 7 summarizes and concludes

2 Specifying the Product

2.I Phases of Design

The design of an aircraft usually has three main distinguishable phases, Concept Design, Prelimi- nary Design, and Production Design The main decisions made in each phase and the main departments involved in each phase are listed in Fig 1 The general idea of these phases is in relation to the customer, the determination of feasibility, and tim- ing and cost estimates Originally, a concept design was sufficient to allow a commitment of resources

by the customer A proof of concept is that a viable product can be produced to perform the mission

"Based on this specification, we are convinced that

we can achieve this design at this cost." As airplanes became more expensive and their introduction also involved major technological and production process investment, the negotiation with the customer became more protracted Preliminary design in- volves a major detailed design, perhaps taking 50 people and six months to complete, and costing several million dollars Another approach is to design

to the point of producing a prototype plane This is

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Bond & Ricci: Cooperation in Aircraft Design 117

sometimes called a "demonstrator" or "valuation"

project by the Department of Defense (DOD)

The specification of the mission may be generated

by a military customer and given in a request for

proposal For commercial customers, an unsolicited

proposal may be made, based on a survey of industry

needs made by the airplane company A commit-

ment (e.g., to buy 50 planes if they meet this specifi-

cation) can sometimes be obtained

From the specification, a concept design is done

and submitted to the customer, from which an award

may be made for the next step The next step is

usually not a full preliminary design, but a design to

the level of a paper prototype This is again submit-

ted to the customer, who makes a further award,

usually to more than one contractor in competition,

to produce an actual prototype This is a preliminary

design of the production version It results in a physi-

cal "demonstrator" (i.e., an actual plane that per-

forms to the specification, but which is "hand

made"), as well as many other aspects of the design,

including:

1 Demonstration that the company has sufficient

" k n o w h o w " to produce the planes

2 Demonstration that key types of people are

available

3 Demonstration that the plane can be made within

schedule

4 Demonstration that the plane is maintainable

If a production contract is then awarded, since

this is often 2 - - 3 years later, a redesign is done to

take into account new technological advances, to

give a production design, and to manufacture a given

number of planes

2.3 High-Level Analysis and Synthesis

A small team of concept designers does the first-cut analysis of the possibilities Early key decisions are:

I Major manufacturability choices

Material policy Fastening policy types of fastener, whether to use automatic fastening machines, whether to use sealant

Sizes of parts Fly by wire or not

2 Structural design policy

3 Major items of supportability

Built-in test equipment Major spares versus repairable rudders, eleva- tors, landing gear, doors, etc

These decisions are more important than exact ad- herence to schedules An attempt is made to make

a "level playing field" for the design by estimating the three main aspects of the design all into dollar figures:

DESIGN weight, strength;

M A N U F A C T U R I N G - - m a n - h o u r s , fixed assets; SUPPORT man-hours, spares

The team determines:

1 Overall size, weight, and power

2 Basic spatial style and shape or approach

3 Basic materials and processes

4 Basic structural philosophy

5 From the set of missions, a set of scenarios is developed These determine the number of times

a stress is applied and allow fatigue measures to

be developed

2.2 Customer Specification

The customer specification contains the following

types of information:

1 Stores (i.e., cargo) weight, size There may be 20

or 30 different types of stores to be carried at any

one time

2 At this stage, a description of a set of missions,

which includes speed regime, distance, time in

air, and payloads

3 Extreme performance conditions, speeds, accel-

erations, etc

4 Volume

5 Performance characteristics, maneuvrability,

fuel efficiency

6 Target cost, profit, cost/effective design

2.4 The Initial Cartoon

The designer takes the output from the team, and the customer specification, and produces an initial

cartoon The cartoon contains the following types

of information:

1 Location of major systems/components

2 Location of major structural members (structural arrangement drawing)

3 Planform

4 Cross-section of various critical sections; more specifically:

1 Basic geometry

2 Size information

3 Basic location of main systems such as fuel, stores, landing gear, flight station, and engine(s)

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ACES 11 EJECTION SEAT

AFT

FWD

WEAPONS ADVANCED

AAM

FWD AVIONICS

B A Y

FUSELAGE FUEL TANKS

- - 1.]2 Ai

~ _ , / / q - ~ J \ ,

WING TANK P~W CCD,II78

20MM GUN

• ~ , B Z >,-.-' = I

, ~ i '

ENGINE FEED TANKS AFT AVIONICS FWO

AVIONICSBAY ~ F ~ F BAY ~ B r " D

APU

L.A

RECEPTACLE

Fig 2 Surface definition of initial cartoon given as three-view drawing

4 Basic location of electronics

5 Wing cross-sections

6 Number and location of engines

7 Basic radar configuration

The designer gives the cartoon its first main geomet-

ric representation as a three-view drawing, where

the cross-sections at critical sections are developed,

as given in Fig 2

3 Different Models for Different Specialists

The set of specialists departments involved in each

design phase was shown in Fig 1 In this section,

we discuss the models used by each department in

each phase

Each specialist department constructs, from the

cartoon, its own specialized model A model will

usually have a geometric representation, but in gen-

eral will be abstraction, and will contain a lot of nongeometric information

3.1 Designer

The main taks of the design department is the development of three-view drawings, with preliminary inboard profile This contains:

• Location of major systems/components

° Location of major structural members (structural arrangement drawing)

• Planform

• Cross-sections at various critical sections The main task is to develop, update, and maintain spatial arrangements and geometry

3.2 Aerodynamics

The main question being answered by aerodynamics

is "Will it fly?" More specifically, estimates of the flight characteristics of the design so far

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In the concept design phase, this model

• is a 2D plan (planform)

• with minor allowances for airfoil (e.g., angle of

attack of wings)

• and rough approximations of cross-section area

progression

The main outputs are lift/drag profiles and effi-

ciency assessments This gives more exact fuel esti-

mates, wing area, and wing sweep angle

In the preliminary design phase, more detailed

models are used Aerodynamic models consist of a

considerable amount of vehicle description, up to

and including some inlet detail and wind-tunnel

models:

• 3D surface models

° Some 3D flow models (simplified)

• Sophisticated cross-sectional area progression (for

wave drag)

A quadpan model uses a mesh of 3D surface ele-

ments, and a full 3D finite element model is eventu-

ally used

3.3 Structures

The structures department is concerned with the

strength and structural integrity of the aircraft under

all required conditions of use The structures model

° is a 3D finite element model

• is a lumped model (e.g., 2-3 lumped stringers rep-

resent 20 actual stringers, 200 degrees of freedom

represent 5000 degrees of actual freedom, parame-

ters are lumped)

° has abstract structural members

• and abstract plates

In the concept design phase, it is a fairly sparse

model, used primarily for rough sizing of main load-

carrying members Main critical joints are defined,

and main load paths are found The main outputs

generated are required cross-sectional areas of

structural members, and their moments of inertia

The values of loads in each member are found From

these, stresses in each member can be easily deter-

mined The loads transmitted through each joint are

also found

In preliminary design phase, a model is eventu-

ally developed (called a full " b o n e s " drawing),

which represents each actual structural member by

a modeled structural member:

• Much more sophisticated external loading models,

including a significant set of flight conditions

• Much more detailed structural " b o n e s " model,

including all primary load-carrying members and many of the secondary load carying members

• Significant study done on both critical and secondary joint areas (not to rivet level)

• Significant amount of detailed structural analysis done on critical members, includes crippling, buckling, bending analysis (very local analysis)

In the production phase, detailed individual stress analyses are performed for all important substruc- tures throughout the aircraft

3.4 Weights

The weights department is concerned with the static weight distribution Their model contains the following types of information:

° A lumped model with point masses and moments

of inertia

• A representation of the 1 g loading configuration (i.e., just to lift off the ground)

° The center of gravity (cg)

• The center of lift (provided by aerodynamics)

In the concept design phase, the lumped masses and moments of inertia represent the main components of the vehicle The model is used to generate rough 1 g loading for structural applied loads Many

of these numbers are based upon phenomenological formulae obtained empirically The main outputs are the balance (cg), and the total weight

In the preliminary design phase:

• Significant detailed weight calculations for 1 g loading Major vendor part information is used Exact x,y,z cg locations are used where possible

• Total weight calculations become more realistic and critical, as to meet performance requirements

3.5 Aeromechanics

Aeromechanics are concerned with the dynamic re- sponse of the system under given excitation regimes The model:

• is an inertia model

° is generally simpler than a structures model

• is a stick diagram with lumped masses and stiffnesses

It is used to generate nodal vibration relationships and vehicle stability characteristics The outputs contain vibration amplitudes throughout the vehicle for given flight conditions which are used as multipli- ers for inertial effects on applied structural loads

In the concept design phase, a simplified mass- stiffness stick model representing the vehicle is used

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to generate nodal vibration relationships and vehicle

stability characteristics

In the preliminary design phase:

• A significantly enhanced mass-stiffness stick

model is used to determine stability

• More detailed analysis of vibration/stability prob-

lems relating to major components (i.e., engine

and wings) is carried out

3.6 Mission Analysis

Mission analysis is used mainly in the concept design

phase It uses parametric characteristics of vehicle

layout to perform sizing iterations to determine opti-

mal geometric shape

3.7 Radar lmaging

This technology determines detectability by radar

The model consists of panelized data used to repre-

sent the vehicle shape The model must be extremely

accurate and dense (number of elements) in order to

accurately find true reflectance values

3.8 Thermodynamic Analysis

This model is concerned with heat absorption, con-

ductance, and emittance throughout the vehicle, and

how these affect the structural, environmental, and

reliability characteristics of the aircraft In the con-

cept design phase, it consists of a space model con-

sisting of major components represented as lumped

masses as conductors and resistors In the prelimi-

nary design phase, a much more detailed model is

used:

• it contains many components

• the vehicle is broken into regions and

• localized systems, such as fuel systems and electri-

cal systems, are studied individually

3.9 Mechanism Analysis

The mechanisms of the aircraft consist of the opera-

tion of all moving mechanical systems in the vehicle

In the concept design phase, the model:

• defines moving surfaces

• models landing gear

• includes control systems and

• specifies the motion of the large main members

In the preliminary design phase, the model is the

same as above except:

• motion ranges are defined in much greater detail

• minor components, such as hydraulic pumps, are included

• large attention is paid to fitting working mechanisms within volume constraints and

• structural aspects are studied and determined (sizing, life cycle, etc.)

3.10 Manufacturability

Manufacturing specialists are involved already at the concept level, as described in Section 2.3 Manu- facturing specialists do not have a separate model, but criticize the main design model In the preliminary design phase, the main criticisms concern whether the design could be built in the given fabrication shops Considerations include material choices and whether special fabrication processes

or techniques would be involved

During the last phase of prototype design, they are involved in all the detailed specifications of parts and assemblies

1 Correct specifications for manufacturing have to

be generated

2 Assignments of manufacturing processes have to

be determined These have to satisfy manufacturability criteria

3 Detailed assembly processes have to be determined to ensure that assemblies can actually be assembled

4 Detailed cost factors are determined at the part level

Thus, in this last phase, there is a manufacturing model which is the set of process plans for fabricat- ing parts, and the set of assembly plans for assem- bling them These plans do not contain detailed tooling designs, but contain an outline tooling design or tooling concept

3.1t Quality Assurance

Checking is done by QA specialists to criticize designs

3.12 Reliability, Maintainability, and Supportability

Checking is done by RM&S specialists They use

"lessons learned" feedback from the field in the form of case reports, to criticize designs

3.13 Cost Estimation and Control

Cost specialists are involved in all phases They use analytical models to derive estimated costs from designs so far

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4 Interactions Among Specialists

In this section, we describe the interactions and in-

terfaces among the different specialists and their

models

4.1 Informal Overview of Interactions

Among Specialists

We can give an overall illustration by briefly describ-

ing a typical scenario in a preliminary design envi-

ronment At this point in the design, the designer

has developed a shape concept with significant detail

as far as the location of the vehicle primary systems

and vehicle surface components/control surfaces

are concerned

A " b o n e s " diagram determining rib stations, fu-

selage ring stations, major pressure bulkheads, ma-

jor joints, and major load carrying members has been

developed

A typical course of action might be as follows

The aero-engineer, who has already made previous

preliminary runs, now creates a more detailed model

and runs the more expensive flow codes to get a

better feel of the vehicle performance He comes

back with data which indicate the improvements can

be made by modifying certain areas of the vehicle

shape

The designer examines these suggested changes

relative to their effect on the packaging of the vehicle

systems and the support structure used to hold these

systems in place

The stress engineer examines the designer's

changes to the structure needed to fulfill aerody-

namic recommendations and runs an upgraded

stress finite element model reflecting these changes

The feedback from the F E M analysis is reported to

the designer, denoting any trouble areas which may

arise

The three organizations will now sit down to-

gether, usually in a meeting to discuss variations of

the proposed changes which could alleviate problem

areas Compromises will be suggested All these or-

ganizations will then return to their respective disci-

plines to make further studies on the recommended

compromises These new studies will necessitate

further meetings to reconcile continuing problem

areas This iteration process will continue until all

parties are satisfied that they can live with the de-

scribed changes

Throughout this process, time and cost of analysis

play an important role as to the depth of analysis

actually undertaken and the number of iterations

allowed In the end, these two factors are what

closes off further development and the development

community settles into a "make this w o r k " situ- ation

4.2 Descriptions of Input and Output to Each Specialist

4.2.1 Designer The designer bases his design primarily on the information obtained from the proposal specifications From this information and previous experience, concepts, etc., the designer generates a three-view cartoon concept which forms the basis of the first analysis Thereafter, he/she updates and refines the spatial layouts in interaction with the technology specialists Input is received from all other departments and the designer's task

is to constantly resynthesize a good design The model used is a set of drawings, on a CAD system, which represent the actual geometry of the aircraft,

as it is estimated so far

4.2.2 Aerodynamics

Input: The aerodynamics specialist will query geometry (2D and/or 3D) for specific geometry points (x,y,z), which will be used to represent the surface shape of the vehicle, and can be used to demonstrate airflow over the surface

Model elements: From input data, a 3D quadrilat- eral grid of points will be developed to represent the airflow system about the vehicle

Output: Life, drag, and pressure distribution of the vehicle for a given set of flight conditions From the output, the viability of the vehicle to fulfill the flying requirements will be determined and required changes recommended

4.2.3 Structures The philosophy behind the structures model is that it is created for two basic reasons:

1 To prove, through analysis, the viability of the design (i.e., will the structure fail to fulfill its strength requirements)

2 To help in the optimization of the design (i.e., reduce weight, reduce cost, reduce complexity, etc.)

The level of detail varies as the design proceeds toward greater definition and completion The reasons for the variation in detail include:

1 Lack of completeness of design

2 Cost of running analysis

3 Time required to create and run model

Input: The structures specialist will query geometry (2D and/or 3D) for specific geometric points

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(x,y,z), which can be used to represent the

strength components of the structure These

include load paths, physical locations, type of

loads transferred, and strength of load path

Structures will also receive external pressure

distribution data from the aerodynamics and

loads departments

Model elements: From input data, a "bulk data

deck" representing the model is created This

includes:

1 Grid points representing physical locations

2 Connectivity elements representing the

physical structure through which the loads

pass

3 Material properties representing the

strength and stiffness characteristics of the

material of each component

4 Structural properties representing the physi-

cal shape and size of each component

5 Applied external loads from aerodynamic/

loads pressure curves

Output: Internal loads and configuration deflec-

tions From this output, the viability of the con-

figuration is determined, and required changes

are recommended

4.2.4 Weights and loads The inputs, model and

outputs for weights analysis are as follows:

Input: The weights model is generated from sev-

eral sources including the central design layout,

empirical data based on existing aircraft and

vendor data on included parts/segments of the

airplane, such as engines, radar systems, etc

Model elements: The model assigns weights in a

lumped model

Output: A gravitational loading distribution

which is lumped and/or provides an envelope

In addition, there is a loads group which elabo-

rates the dynamic loading cases

Input: The loads data is a direct result of combin-

ing aerodynamically derived pressure distribu-

tion data with different speed regimes and flight

conditions which impose certain g forces and

air forces on the vehicle

Model elements: A lumped model

Output: A set of load cases

4.2.5 Aeromechanics The inputs, model, and

outputs for aeromechanics analysis are as follows:

1 The aeromechanics model is derived from the

components of the three-view created by the de-

signer (determines stiffnesses) and the I g weights

developed by the weights group

2 The model is a simpler lumped model representing the basic structure only It typically ignores major systems and has fewer structural members than other structural models It uses lumped weights and inertia

3 Mathematical stimuli are applied to the resulting model to determine system vibration and stability characteristics for each flight condition This is used to make recommendations on altering the parameters of structures in the wing and fuselage

4.2.6 Manufacturability During design, manufacturing specialists relate to the cooperative design process more as checkers with vetoing ability than design drivers They act to stabilize cost and time Checking is done by manufacturing specialists to criticize designs

Input: The main design model

Output: Criticisms of the form of vetoing or sug-

gested modifications of given aspects of the design

During the last phase of prototype design, they are involved more interactively in all the detailed specifications of parts and assemblies

A lot of manufacturability criticism and constraint

is actually achieved from the training of central designers in the principles of manufacturability; in addition, there are design handbooks, used for the guidance of designers, which contain manufacturability criteria Thus, the interaction is via the transfer

of knowledge through education

4.2.7 Quality assurance Checking is done by

QA specialists to criticize designs

4.2.8 Reliability, maintainability, and supportability Checking is done by RM&S specialists to criti-

cize designs

4.2.9 Cost estimation and control Cost specialists are involved in all phases

Model elements: Cost estimates for assemblies

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Structures

bigger wing box "~

more ribs

I, moment

A s:ctioo~

baiance

total weight

Weights

i speed regime volume, weight distance ,performance

Aerodynamics more exact

wing area / sweep angle / geometl]

-o4 e net

Final Conceptual Design

mission

• inertia distribution [ Aeromechanics

Fig 3 C o n c e p t u a l design

Output: Cost estimates for given aspects of the

design

4.3 Overall Structure o f the Design Process

4.3.1 Interacting specialists During conceptual

design, the initial cartoon is refined up to the point

of a fairly detailed layout During this process, the

specialized models are constructed in their initial

forms, and then also refined so as to reflect and

to incorporate the changes and progression of the

central design This is diagrammed in Fig 3

Further, the sets of experts involved gradually

change as the design proceeds Some leave and some

join the dance

4.3.2 Coordinated refinement o f models The

process of refinement, where each specialist refines

his model, and works to keep his model up to date

with the central model, is depicted in Fig 4 This

also shows the input of specification changes, and

their distribution to the relevant specialists

4.4 Model Refinement

A model may be changed to correct it, but most of

the changes are in the refinement of the model We

give some examples of refinement:

specialist model

i specification changes

specialist model model changes

evaluations suggestions

Fig 4 T h e p r o c e s s o f c o o r d i n a t e d r e f i n e m e n t o f models

4.4.1 Envelope to more detailed geometry The initial model specifies an approximate volume, which can be an envelope or a bounding cuboid for the refined model

4.4.2 More exact numerical estimates As an example, fuel capacity 15,000 gal is a representation of

an interval such as 14,000-16,000 A more exact estimate might be 15,500 gal, which might at this level of refinement corresponds to the interval 15,250-15,750

4.4.3 Single to multiple elements The mapping from the initial model, which lumps elements into abstract elements, may not be a direct expansion of each element into several more detailed elements

We have depicted a lumped model with four elements being expanded into a more detailed model with 14 elements We also show that single element expansions have to be merged to produce a refinement, and that additional elements may be added during this process

4.4.4 Putting in explicit fuel, power, and hydraulic lines These may have a nonnegligible diameter and other requirements and may need to be consid- ered at a nondetailed level

4.4.5 SuJface geometry specification Surfaces are at first approximated by a series of defining curves comprising planar cross-sections and primary longitudinal lines Finally, these are converted into surface patches in which the areas between the defining curves are mathematically defined The analysis models represent these surfaces using planar facets connected to x,y,z coordinate data

4.4.6 Articulation and fastening A 3D form will

at first exist in a simplified shape, and will then be refined, and optimized for manufacture, by articulat- ing it into an assembly of component parts This may

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124 Bond & Ricci: Cooperation in Aircraft Design

Customer

Project management

D ~ i g n ~nd sys%ems

Loft

I Aerodynamics

Propulsion

Weights

Generate requirements

Prom customer requirements and advanced technology assessment, coordinate configuration concept, Generate ba~e|ine drawings, general arrangement, inboard profile (support tool - CADAM}

Wing proportions + (~) W i g chord lengtb/sutface area

(b) thickness/chord tength~ (c) Aspec~ Ratio

Empennage size, Thrust to weight r~tio T / W Engine selection~ ta, nge of cycle parameters

Engine installation criteria

Approx gross weight Approx empty weight

Strtlct ure~

Ae~omechanics

Materials and producibility

Model specifications

Laboratories

Engineering shop

Plight test

Other disciphnes

Evaluate configuratiou for

{I) toad paths for low cost light weight structures, and (2) reasonable and consistent design parameters, Provide criteria guidelines

Participate in design:

11) evaluation for loads (2) aeroelastic and flutter effects (support tool - loads programs),

Fig 5 Step 1: Initial design parameters

require specification of fasteners for stress calcula-

tions at a nondetailed level

replaces a center line specification by a volume ge-

ometry This may at first exist as a width and height

specification only, and then an exact cross-sectional

geometry After this, modifications such as light-

ening holes may be added

have a simplified representation at the initial level,

and thus the model is refined by enhancing them An

example, in the design area, is of adding the cockpit

elements such as seats and console There may be

intermediate refinements, such as specifying the

angle of inclination of the back of the seat, and the

pilot's viewing window

5 Organization of Design Using Committed Steps

The way the grouping of design departments is usu-

ally organized is related to the schedule steps in

design A step is defined as a set of design choices

that must be committed to by a given time

5.1 Steps in Advanced Aircraft Design

We show, in Figs 5-13, an organization into six

steps sometimes used in aircraft design These steps

are:

1 Initial design parameters

2 Generate data/preliminary point design

3 Parametric and trade-off analysis

Customer Project managemettt

Design al~d systems

Give approval at design review

Change configuration collcept, revise design par~lueters,

do design review

Update general arrangement, update inhoard profile, find wetted areas and area distribution, functional systenl8 considerations (1} flight controls (2) fuel (3} hydraulic (4) electrical (5) avionics (6) environmental control (6) weapons

(Use0 CADAM support tool)

(May use Asset support tool)

Produce updated baseline drawings, genera/ arrangements, inboard profile, Loft

~ - d y x ~ a a n i c s Determine

(1) eppennage scaling data (2) drag data (3) low speed lift data

(4} control surface sizes

{U~es aerodynamic programst Propulsion

Weights

- S ~ t : t u r ~

Aeromechanics

~ a T e r i a l s and producibility Model specifications Laboratories -E'~l~gin ear i ug shop Flight test Other disciplines

Determine (1) parametric installed engine, performance data versus (b) bypass ratio (el turbine entry temperature (2) Loom flow field col~ditions (3) inlet and exhaust nozzle performance data (4) Scaling data

(5) Installed engine weigh data (6) Performance and weight scaling 7} Initial structural temperatures

(Uses propulsion programs}

Determine (11 component weight relationship~

(21 payload and operating equipnmnt weights (3) effects of configuration peculiar items (4) C.G location and limits (5) F~el volume relationships

(use mass distrihutio~ tool}

Define structural design criteria

Perform trade-off studies to define (1) basic structural concepts (21 material usage, Provide effects on asset weight equation~ due to ( ~ structurM technology (b) structural arrangements (c) structural design requirements, Provide parametric basic loads

Participate in design evaluation Preliminary aeroielastic assessment

(use loads programs, detailed load~ programs and aeroelastic program)

Fig 6 Step 2: Generate data/preliminary point design

4 Detail point design studies

5 Refine selected configuration

6 Design and build prototype

Within each step, and for each goal, we indicate which of the many available computer support tools are used

5.2 Commitment Steps

We summarize the above six steps in Fig 14

grammed in Fig 15, the notion of commitment step

is that a set of joint commitments is made by all the design agents at the end of each step These are public commitments to best estimates for decision choices These estimates are then used by all agents during the next step

Tiêu đề	Cooperation in Aircraft Design
Tác giả	Alan H. Bond, Richard J. Ricci
Trường học	University of California, Los Angeles
Chuyên ngành	Manufacturing Engineering
Thể loại	Research
Năm xuất bản	1992
Thành phố	Los Angeles

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Số trang	16
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