TRADE STUDY METHODS

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Trade Study Methods
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Types of Trade Studies

• Controlled Convergence - Preliminary Method
  Used by Engineering. Quick Method to Compare
  Primitive Design Variables
• Cost Effectiveness - Links Force Structure
  Implications to Top Level Requirements Analysis
• Comprehensive - Considers all Applicable
  Decision Criteria

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Time Frames For Trade Study Methods
--Comprehensive--
------Cost-Effectiveness-------
-Controlled Convergence-
Production Deployment
Pre Concept Tech Dev
A
B
C
Concept Technology Development
System Development Demonstration
Operations Support
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Controlled Convergence Trade Study
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Steps in Applying ControlledConvergence Method
1. Design Alternatives to Same Level of
Detail 2. Choose Comparison Criteria 3. Choose
a Baseline for Comparison Purposes 4. Compare
the Alternatives to the Baseline 5. Sum Pluses
and Minuses 6. Can New Alternative Be Created by
Changing Negative(s) of a Strong
Alternative? 7. Can Weak Alternative Be
Eliminated? 8. Return to Step 4 or Document
Findings and Proceed
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Controlled Convergence Method For Preliminary
Trade Studies
Design
Alternatives
1
2
3
4
5
Comparison
(Baseline)
Criteria
(Design Primatives)
Thrust/Weight (T/W)
S

S


Weight/Wing Ref. Area (W/S)
S




Coef. of Lift (C )
S




L
Cruise Performance (Specific fuel
S
S

S

consumption, range, speed)





Observables (Shaping, materials,
S
S

S

propulsion, etc.)





Payload Capacity
S



S
Agility (maneuverability
S




controllability)
...
TOTAL 's
0
1
5
2
4
TOTAL S's
7
2
1
1
1
TOTAL 's
0
4
1
4
2
Significantly Better
Legend
S About the Same
Significantly Worse
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Strengths and Weaknesses of Controlled
Convergence Preliminary Trade Study Method

• Difficult for Strong-Willed Person to Dominate
  Decision Making
• Encourages Development of Additional Design
  Alternatives
• Time to Converge Can Be Controlled

Repeated Applications of This Method Will Result
in Fuzzy Comparisons of Leading Alternatives
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Cost-Effectiveness Trade Study
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Alternative Configuration Scoring Methods
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Life Cycle Cost Composition
BV41861
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Cost Estimating Methods UsedDuring Acquisition
Phases
Pre Concept Tech. Dev.
Early in System Dev. Demonstration
Early in System Dev. Demonstration
Concept Tech. Dev.
P Primary S Secondary
Prod. Dep.
Parametric Analogy Bottom- Up Eng.
P
S
S
N/A
N/A
S
P
S
N/A
N/A
N/A
S
P
P
P
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Relative Values of LCC Elements(based on 100
aircraft)
Life Cycle Cost
Operations Support (46.1)
RTDE (4.3)
Procurement (49.6)
0.30 Demo/Validation 2.12 Air Vehicle 0.13
Engine 0.22 Offensive Avionics 0.70
Launcher 0.02 Training 0.06 Special Support
Eqpt 0.47 Test Evaluation 0.15 Project
Management 0.13 Data
0.59 Tooling Engineering 31.52 Airframe
8.83 Engine 2.31 Offensive Avionics 2.18
Launcher 0.17 Training 1.94 Special Support
Eqpt 0.36 Test Evaluation 0.07 Project
Management 0.15 Data 1.52 Initial Spares
1.74 Replenish Sppt Eqpt 10.72 Fuel 0.92
Base Level Maint. 11.55 Depot Maint. 3.70
Updating/Mods 0.78 Replenish Spares 0.06
Vehicular Eqpt 12.61 Military Personnel 0.46
Civilian Personnel 1.29 Support Personnel
2.23 Pipeline Costs
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Comprehensive Trade Study
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Principal Steps in ComprehensiveTrade Study
1. Identify Decision Criteria within Broad
Decision Categories 2. Quantify Decision
Criteria for Each Configuration 3. Analyze
Customer Preferences for Each Decision
Criterion 4. Assign Weights to Decision
Criteria 5. Score Each Configuration (Sum
Weights x Preferences) 6. Perform Sensitivity
Analysis on Weights If Configuration Scoring
Is Close
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Sample Configuration Decision Categories
Air Vehicle
Cost
Risk
Effectiveness
Threat Acquisition Avoidance Hit Avoidable Given
Acquisition Sortie Survival Given Hit Target
Acquisition Target Kill Given Acquisition Kills
per Sortie Targets Killed Over Time
Flyaway Weapon System Procurement Program
Acquisition Life Cycle
Technical Cost Schedule Producibility Support
ability Management
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Utility Functions - Preference Indicators

• Utility Functions Provide a Good Technique for
  Translating Diverse Criteria Into a Common Scale.
  (i.e., Range in NMi, MTBF in Hours, etc.)
• Utility Scores Range From 0 to 1 With 0 Being
  Least Preferred and 1 Being Most Preferred.

Examples
Utility for Range
Utility for MTBF
1
1
Threshold Objective
Threshold Objective
Range in MNi
MTBF in hours
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Hints for Determiningthe Shape of Utility
Functions
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After Establishing the Minimum Requirements and
Goal, Draw Neutral Preference Position as Shown
Neutral Preference
1
Critical, Risk Prone
Non-Critical, Risk Average
Req Decision Factor Goal
1
Divide Decision Factor into Quartiles and Assess
25, 50, and 75 Points Relative to Neutral
Preference
2
Req Decision Factor Goal
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Sensitivity Analysis ofConfiguration Preferences

• Select Factor of Interest Such as Performance
  Range
• Increase Weight for Factor of Interest Until
  the Preferred Alternative / Configuration
  Changes
• Incrementally Lower the Weight for Factor of
  Interest Until the Preferred Alternative /
  Configuration Changes

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Exercise
Background As system requirements are
identified and flowed down form the SDR, design
options for the Group A hardware must be
identified and trade studies performed to
determine the best design. Five design options
have been developed for Group A and have been
evaluated by the AFS design team. Documentation
of this first pass design review by the team is
presented below and must now be used to select
the best design in support of entrance criteria
for the program PDR.
Exercise In order to limit the scope of this
Exercise, the design trade study will be
restricted to the Aft Antenna and Radome
assembly. Referring to the Introductory Briefing
material presented on the four subsequent
charts, the Statement of Customer Requirements
Part 2, and the Aft Antenna/Radome Functional
Requirements Baseline, evaluate the designs
provided and perform a comprehensive trade study
to select the best design.
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AJS Statement of Customer Requirements
Customer Kurdish Fighter Program (Peace
Whey) Operational Need Fighter aircraft
operating in a hostile environment require
extensive electronic countermeasures (ECM) to
defeat air-launched and ground-launched threats
to the survivability of the aircraft. These ECM
systems must be capable of generating and
broadcasting radio frequency (RF) energy at
sufficient power levels and in appropriate
patterns to defeat any threat encountered by the
aircraft.
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AJS Statement of Customer Requirements(Cont.)
Description The AJS shall be capable of
installation on a lightweight, high-speed,
multi-role fighter and shall be supportable in
primitive forward operating bases. The system
shall be capable of transmitting radio frequency
signal in the microwave frequency range at
sufficient power levels and in patterns capable
of successfully jamming all identified threats at
the required operational range. The AJS system
shall consist of the following major
components 1. Core Avionics Shall consist of
the jammer, the radar warning receiver, and the
OFP software. Shall be capable of generating the
required RF signal in the microwave band at
required power levels and of detecting radar
emissions from the threat set at the required
ranges. 2. RF Switch H/I/J Band Shall control
selection of broadcast frequency bands as
required. 3. Fire Control Radar Notch Filter
Shall prevent interference of the Fire Control
Radar (FCR) by the AJS system. 4. Forward
Transmit Antenna 5. Aft Transmit Antenna and
Raydome 6. WRD-650D24 Waveguide 7. Coaxial Cable
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AJS Statement of Customer Requirements(Cont.)
Schedule 1. Flight Test The Safety of
Flight(SOF) unit for flight test shall be
available for installation 26 months after
program go-ahead. 2. First Production Delivery
The first production assembly shall be delivered
36 months after program go-ahead. 3. Delivery
Rate Delivery of AJS units shall be at the rate
of 2 units per month. 4. Total Quantity The
total quantity of AJS units shall be 20.
Customer Priorities 1. Power Transmitted. 2.
Weight 3. First production delivery. 4. Cost
not to exceed 125,000/unit (for 20 units).
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Types of Radomes
Types of Construction
Uses and Advantages

• Solid-Wall Construction Laminated Glass
  Cloth/Resin or Filament Wound
• Sandwich-Wall Construction Laminated Glass
  Cloth/Resin Impregnated Skin with Various
  Dielectric Cores

• Narrow Frequency Band
• High Strength
• Optimized Electrical Performance
• Broad Frequency Bandwith
• Lightweight

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Extensive Testing of Antennas ConfirmsThat
Performance Will Be Achieved
Parameters Tested - Electrical Requirements
Antenna Range 1. Radiation Patterns and
Gain 2. Voltage Standing Wave Ratio (VSWR)
3. RF Power Handling 4. Antenna-to-Antenna
Isolation - Environmental Requirements
Engineering Test Labs 1. Vibration 2.
Temperature - Altitude 3. Humidity 4.
Acoustical Noise 5. Mechanical Shock
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Airborne Jamming System (AJS)Statement of
Customer Reqt.s Part 2
Performance 1. Frequency The AJS shall
provide performance over the frequency ranges and
angular pattern as represented in Table 1. The
low-band transmission line shall be coaxial
cable. The high-band transmission line shall be
double-ridge, pressurized Waveguide of type
WRD-650D24. 2. RF Power Handling The AJS,
while operating in any combination of temperature
and pressure consistent with the aircraft
operating envelope (as shown in Figure 1), shall
be capable of handling 1500 watts peak power in a
continuous transmit mode. 3. Antenna
Polarization The transmit antennas shall be
left-hand circularly polarized. 4. Antenna
Gain The gain for each antenna shall be as
specified in Table 1 and Figure 2. The gain is
defined as gain measured at the minimum level of
the axial ratio and is referenced to isotropic
linear polarization.
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Airborne Jamming System (AJS)Statement of
Customer Reqt.s Part 2
Environmental 1. The AJS total system
shall be capable of operation at all points in
the aircraft flight envelope as specified in
Figure 1. 2. The antenna/radome assembly
shall have a mean time between failures (MTBF) of
greater than 50,000 hours.
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Exercise 4 Option 1 Risk Issues
Risk Issues Very good chance additional heat
sink capacity will be needed to sustain power
rating. This creates .4 pound of weight risk.
Schedule risk is assessed as low.
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Exercise 4 Option 2 Risk Issues
Risk Issues Low system weight achieved through
use of spiral antenna impacts power handling
capability and gain. Design of antenna mounting
hardware results in predicted failure of
vibration and acoustic loading spec due to
resonant response within frequency envelope.
Structural design changes required to meet
vibration and acoustic specs result in a highly
likely probability that the total assembly weight
will add 1 pound of weight, exceeding spec.
There is also a better than even chance that two
additional calendar months design/development
time will impact delivery of SOF hardware.
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Exercise 4 Option 3 Risk Issues
Risk Issues Slightly higher-than-spec gain in
the high band is due to an improved dielectric
currently under development. The risk of
additional development and testing costs
resulting in a assessment of a probable AJS
system cost increase per unit of 3. There is
an unlikely probability the qual test
requirements could impact the SOF hardware
delivery schedule, but this is assessed as low
risk.
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Exercise 4 Option 4 Risk Issues
Risk Issues Design Option 4 includes a
solid-wall radome, normally used with
narrow-bandwidth systems. Potential severe
internal heat loads could result from RF energy
reflection from the radome. Performance risk is
assessed as highly likely to reduce power
handling capability by .5 watt.
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Exercise 4 Option 5 Risk Issues
Volume Design consistent with available
installation volume Predicted Unit Cost
19,460 Risk Issues Option 5 includes a
pressurized radome to achieve an operational
altitude greater than required by the specs.
However, this design has a history of pressure
leak problems. Loss of pressure could result in
arcing and system damage impacting performance
and reliability. Upgrade to seals and increased
leak testing would require additional cost and
test time. Assessment indicates probable
additional costs would increase AJS unit cost by
10.
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See Trade Study Example (Excel)