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Design of UAV Systems

System Design c 2002 LM Corporation

Lesson objective - to review the concept ofSystem Design

including...• What is it?• How is it different from other design?• Discuss related concepts

• Requirements• Defined and Derived

• Performance• Allocated and Status

• How to start the process• What are the expectations?• Semester student design projects • Example problem• Homework

Objectives

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Definition

System Design

System Design addresses requirements and their design implementation

Design of a complete system - example, a UAV system and all of its elements

• Air vehicle including• Airframe• Engine• Avionics• Software• Etc.

• Communications

• Control station• Payload• Support system • Training• Logistics• Etc.

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• What a product must or should do (i.e. the documented expectations for a design)

• Example - The mission system software must must employ an open system architecture or …. • The average unit cost for production units 11-20 should not exceed $10 million

• Documents customer, program, functional and designer expectations

• Requirements include performance, cost, schedule and risk.

Definition

Requirement

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Another definition

Requirements based approach• The design of a product from the “Top-Down” - a downward looking activity

• From the highest level of definition to its many layers of subsystems

• At the top-most level - driven by customer expectations and needs

Called “defined requirements”

• At every other level - driven by what is required to meet higher level requirements

Called “derived and/or allocated requirements”

• This is the essence of Systems Engineering

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Provide effective all-weather surveillance of 40,000 square miles in 24 hours at an operating radius of 3000 nm using altitude and standoff distance to enhance survivability.

Example - defined requirement

High Altitude Endurance (HAE) UAV top-level system requirement

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Example - design solution

http://www.fas.org/irp/program/collect/global_hawk.htm

This is not a very good example of a defined requirementGlobal Hawk’s only defined requirement was cost <$10M

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• Air vehicle - Operating altitude - 65,000 feet- Maximum range - 14,000 nm- Maximum endurance - 42 hours- 1 loss in 200 missions- Etc.

• Airframe- 25,600 lb gross takeoff weight- 9,200 lb empty weight- Cruise L/D = 33-35- Etc.

• Engine- Unmodified existing turbofan- Installed thrust (SLS) = 7900

lbf?- Installed thrust (65Kft) = 750

lbf?- Etc.

Generator- Output power = Z

Example - derived requirements


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Example - design solution


• There are two other types of requirements and they

must never be confused• Threshold Requirement - the minimum level of

acceptable performance• Goal Requirement - the maximum level of desired

performance• What customers are telling you when they define

goals and thresholds• If your design does not meet threshold levels it is

unacceptable• If your design exceeds goal performance you get

no benefit (it is “gold plated”)

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Other requirement types

- The lowest level of performance acceptable for of a design. If performance is below a threshold, the design must be changed. If redesign cannot solve the problem within defined cost and risk, something else has to change.

Example - You are responsible for airframe design. Your customer has established a UAV threshold design mission range of 13000 miles. Your project chief systems engineer has allocated you an airframe a weight of 9,200 lbs. When performance is calculated, you discover the airframe weighs 9,200 lbs but it can only fly 12,0000 miles. Your design team has to make a design change

• The deficiency is in a defined requirement (range)

If the deficiency were in a derived requirement (e.g. weight), you might request an increased weight allocation (which might be denied) to allow increased size. The best solution - optimize the existing design to get better performance or try different designs

What you cannot do is hide the problem and hope that you can fix it later.

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Expanded definition

Threshold Requirement

Engineering ethics !

- The highest level of performance needed from a design. If a goal is exceeded, (1) the design is resized until it meets the goal or (2) the design is retained and the excess performance is turned into margin.

Example - You are responsible for airframe design. Your UAV has a goal mission range of 14000 miles and an allocated airframe weight of 9,200 lbs. When performance is calculated, your team discovers it weighs 9,200 lbs but it can fly15,0000 miles. The design team (airframe, payload, support, etc.) has choices, two of which are:

1. Reduce the size of the airframe or…...2. Hold the size and define a performance margin to cover an unexpected (but probable) future performance loss

What you cannot do is to hide the excess performance from the rest of the design team to provide a private margin for unexpected airframe problems.

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Expanded definition

Goal Requirement


• In this course, “performance” can mean more than technical performance (e.g. lift-to-drag ratio). It can also mean cost and risk.

• Performance, cost and risk are all related.

• An example, a UAV might meet a mission range requirement by (1) increasing wing thickness (increased fuel capacity), (2) by using expensive (but existing) advanced materials materials or (3) by developing a potentially low cost (but risky) fuel transfer system to maintain an optimum center of gravity location in flight.

• The designer has responsibility to address solutions across all three areas.

• This can only be done if the designer (and everybody else on the project) understands the requirements in all three areas - technical performance, cost and risk.

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Performance

• There are two types of performance and they also must never be confused

• Allocated performance - the level of performance desired for a design to meet overall requirements. Allocations are expressed in terms of thresholds and goals and they trace directly to requirements• Status performance - the level of performance actually calculated for your design

• What the project is telling you when they allocate performance thresholds and goals

• This is your design space• What the design is telling you when you get status performance • This is what the laws of physics say about how your design performs

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Performance types


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Example - Goals vs. Status

GOAL


STATUS

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Sometimes goals change

• Performance Goals– Range: 12,500 nmi– Endurance: 35 hrs– Endurance @1200nm: 24 hrs

January 2001

International Briefing, August 1999

Endurance at 3200 nm : 24 hrs

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“Performance” measures

Another important performance issue is to make sure our design “performance” levels meet requirements• All systems, whether simple or complex, have multiple

elements designed to meet multiple requirements…and which are drivers and which “fall out”• Example – Thrust required for takeoff may “fall out” of

thrust required to meet an acceleration requirementIt is also important to identify which are most critical • While it is important to monitor all “tracking performance

parameters” (TPMs), the most critical or “key performance parameters” (KPPs) need focused attention and visibility

Therefore, we identify a small number (5-10) of KPPs for system level attention and related sets of TPMs for attention at every other level of the system design• This ensures that the entire team is focused on the most

critical issues at all times and at all levels of the design

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System Design Product

Question - What does the system design process produce?

• A product?

• A design?

• Something else?

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System Design Product

Answer - DOCUMENTED TECHNICAL DECISIONS

• The primary product of any design process

- Everything else (including design, analysis and test) substantiates design decisions

• What the decisions are (drawings and text)• Data to convince others that the decisions are

correct (test and analysis results)• Rationale behind the decisions (results of trade-

off studies)• Instructions on how to implement the decisions

(drawings and specifications)

• Without good documentation, the product is useless

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(1) Design decisions (2) Documentation

• Requirements• Defined• Derived

• ConOps • Description• Effectiveness

• System description• Physical• Functional

• Performance substantiation• Analysis• Test data

• Design rationale/trades• Figures of merit

• KPPs and TPMs

• Cost• Development• Production• Operations & support

• Risk assessment• Identification• Mitigation• Fall back planning

• Development plans• Test & evaluation• Concept/technology demonstrator• Prototype• Initial production• Pre-planned product improvement

(3) Simulation

Expanded list

System design is about more than concepts and analysis – it is also about planning

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1.Define a baseline system concept - System Engineer leads team to decide initial requirements and concepts for

- System- Airframe- Payload- Mission control-Support

2. Develop good initial pre-concept design -Trade requirements and fully explore potential approaches

3. Cycles (1-2) repeat until concept converges ….. 4. Develop Initial Preferred System Concept - System

Engineer leads functional teams in definition of initial baseline - Each team proposes their design approach- All teams discuss and reach agreement (Lesson 2c)- Individual teams define designs to appropriate level for analysis- Individual teams analyze their designs and report results- System Engineer leads effort and assesses system effects

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At this point, customers often define project cost, risk and schedule

- The engineering supporting these estimates better be good!- We will use our parametric methods to ensure good up front decisions

How to start a system design

5. Assess initial system concept design-analysis results• Led by System Engineer• Allocated vs. status performance presented• Some areas will be better than allocated• Some areas will be worse

• Problems and potential solutions are discussed and documented• Trade studies to improve performance are proposed and agreed• Revised allocations are discussed and agreed

6. Systems Engineer documents new allocations7. Cycles (4-6) repeat until design converges

….. (sometimes to an acceptable conclusion)8. Upon convergence, teams evaluate other options until

overall system converges to better performance. Studies continue until improvement stops or budget runs out

9. Results are documented and presented to customer10. Team has party and many beers are consumed

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How to start (cont’d)D

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team lead

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You should now understand the concept of system design

1. Design follows requirements

2. Requirements define what a system needs to do as appropriate for each design phase

3. Requirements do not document a design on an after-the-fact basis

4. Design solutions are traded to ensure that they reflect the best balance of cost, risk and performance

5. Design solutions (and performance) should not be dictated (by the boss or individual designers)

Expectations

Today requirements also evolve with the design

• Even threshold requirements are subjected to trade off studies!

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Next subject - Student projects

• Next generation tactical UAV (TUAV)- Support army/marine type ground operations

• Maritime search UAV- Support navy/coast guard type operations

• Standoff intelligence, surveillance and reconnaissance (ISR) UAV- Global Hawk follow-on type

• Penetrating ISR UAV- Dark Star follow-on type

• Air-to-ground combat UAV (UCAV)- X45 follow-on type

- You will select one of the five as a semester design project- It will also be the basis for your homework problems

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System Design 2002 LM Corporation

Next generation TUAV

Forward based operations from 3000 ft paved runway- Provide continuous (24x7) day/night/under weather near real time

ISR coverage of 100 nm x 100 nm operations area- Able to resolve range of ground moving targets to 10 m anywhere

within combat area and transmit detection data within 2 minutes- Able to provide on-demand positive identification of friendly troops vs.

opponent forces (req’d resolution = 10-20 cm) and transmit imagery to base and/or infantry units within 3 minutes of request

- UAV squadron is based within 70 nm of combat areas- Each squadron provides simultaneous support of 10 infantry units,

each operating in 10nm x 10 nm combat area- Ignore survivability effects

Minimum required trades- Communication architecture- Sensor(s) required- Control architecture- Operating altitude(s)- Time on station

- Air vehicle size and numbers- Air vehicle speed(s)- Propulsion type and size- Aspect ratio- Wing Loading

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Next generation TUAV

100 nm

100

nm

Base

70 nm

Area of operations

10 nm

10 n

m

Combat area

50 nm

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Maritime search UAV

• Land based with 5000 foot paved runway- Squadron is based on the coast- Able to provide continuous day/night/all weather near real time

search capability of 100 x 100 nm ocean surveillance area - Able to launch on distress call or operate from loiter during

periods of heightened alert (24 hrs day/7 days a week)- Able to resolve range of 10 sqm moving targets to 10 m within

surveillance area and transmit movement within 2 minutes- Able to put sensors on target anywhere within search area and

transmit image within 15 minutes or less- Able to ID small boat (req’d resolution = 0.75-1.2m) and identify

occupants as friendly (req’d resolution = 10-20 cm)- Ignore survivability effects

• Minimum required trades- Communication architecture- Sensor(s) required- Control architecture- Operating altitude(s)- Time on station


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Maritime search UAV

100 nm

100

nm

Search area

BaseLoiter location(s)?

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Stand off UAV

Land based with 5000 foot paved runway- Provide continuous (24x7) day/night/under weather near real time

ISR coverage of 100 nm x 100 nm surveillance area- Able to resolve range of ground moving targets to 10 m anywhere

within surveillance area and transmit detection data within 2 minutes- Able to provide on-demand positive identification of 0.5m x 0.5m

targets and transmit imagery within 10 minutes - UAV is based within 200 nm of combat area- Ignore survivability effects

Minimum required trades- Communication architecture- Sensor(s) required- Control architecture- Operating altitude(s)- Time on station- Loiter pattern and location


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Stand off UAV

100 nm

Loiter location(s)? 20

0 n

m

Surveillance area

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Penetrating UAV

Land based with 5000 foot paved runway- Provide continuous (24x7) day/night/under weather near real time

ISR coverage of 100 nm x 100 nm surveillance area- Able to resolve range of ground moving targets to 10 m anywhere

within surveillance area and transmit detection data within 2 minutes- Able to provide on-demand positive identification of 0.5m x 0.5m

targets and transmit imagery within 20 minutes - UAV is based within 200 nm of combat area- Ignore survivability effects



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Penetrating UAV

100 nm

200

nm

Surveillance area

Loiter location(s)?

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Air-to-ground UCAV

Land based with 5000 foot paved runway- Provide continuous (24x7) day/night/under weather ground attack

capability against 10 sqm ground moving targets within a 100 nm x 200 nm operating area

- Able to put eight 500 lb precision guided (GPS) bombs on operator selected target within15 minutes

- Able to provide operator with positive identification of 0.3m x 0.3 m resolution targets prior to weapons release

- UCAV is based within 200 nm of combat area- Ignore survivability effects



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Air-to-ground UCAV

200 nm

200

nm

Target area

100

nm

Loiter location(s)?

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We will use a one continuous example problem throughout the semester to demonstrate:

(1) How to approach the problem(2) How to apply design and analysis methods

First half focus: System requirements analysis- Target coverage- Time on station and response time- Sensor size and performance- Communications architecture and bandwidth- Payload type, size and performance- Manpower

Second half focus: Air vehicle and design trades- Air vehicle size and configuration trades- Propulsion cycle and trades- Performance and technology- Effectiveness- Cost effectiveness and system optimization

Example problem

• Predator follow-on type• Land based with 3000 foot paved runway

- Mission : provide continuous day/night/all weather, near real time, monitoring of 200 x 200 nm area

- Basing : within 100 nm of surveillance area- Able to resolve range of 10m sqm moving targets to 10m and

transmit ground moving target (GMT) data to base in 2 minutes - Able to provide positive identification of selected 0.5m x 0.5 m

ground resolved distance (GRD or “resolution”) targets within 30 minutes of detection

- Ignore survivability effectsMinimum required trades

- Communication architecture- Sensor(s) required- Control architecture- Operating altitude(s)- Time on station- Loiter pattern and location

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Example - surveillance UAV


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Surveillance UAV

200 nm

Loiter location(s)?

100

nm

Surveillance area

200

nm

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Homework assignment

(1) Select one of the 5 student projects- The one that interests you most- All are of approximately equal complexity

• During the first half of the semester you will work as a team of one to define your overall system- During the second half, you will work on (or lead) a

team to define the air vehicle and optimize the system• Team projects (and leads) will be based on mid-term

presentations- The most feasible projects will be selected for

continuation(2) Send Egbert a “capability” email (1 page max)

a. Which project you would like to work onb. Why you want to work on itc. What unique skills and capabilities you think you

have that are applicable to the selected problem

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Intermission

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