Requirements analysis

1

• Lesson objective - to discuss
• Requirements analysis
• including
• Basing
• Operational radius
• Operational endurance
• Maximum range
• Speed
• Turn around time
• plus
• Example problem

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Definition

• Requirements analysis
• Quantitative and qualitative engineering analysis
  to translate overall customer goals and
  objectives into a traceable set of design-to
  requirements
• Provides the design team with a consistent set of
  numbers they can work to
• Basically a form of reverse engineering
• Working backwards to determine what combination
  of concepts, design and technology best meet
  customer expectations?
• Usually a cost and risk-based analysis
• What is the highest level of system performance
  achievable at the lowest cost and risk?
• Air vehicle empty weight and payload weight are
  often used as cost surrogates

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UAV system design drivers

• Most top level UAV requirements focus on target
  area coverage, capability and time
• Reconnaissance capabilities are typically defined
  in terms of types or numbers of targets and
  sensor resolution
• Strike capabilities typically are defined in
  terms of types, numbers and distribution of
  targets
• For the UAV air vehicle element this typically
  translates into derived requirements on
• Basing
• Operational radius
• Operational endurance

• Maximum range
• Speed
• Turn around time

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Land Based Operations

• The typical basing mode for aircraft
• Other basing options impose penalties
• Weight and complexity
• ...and/or..
• Operational constraints
• Land based operations are supported by over
  45,000 airports world wide
• Although most runways are short and unpaved
• Very short fields penalize air vehicle design
• Sophisticated high-lift systems are heavy and
  complex
• Unpaved airfields increase the penalty for
  takeoff, landing and ground operations

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Worldwide airport data
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Typical unpaved field
What runway type do you design for?
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It depends on the mission
Example - A Korean venture capitalist sees a
market for overnight aerial delivery of small,
high value products between Korean and Chinese
commercial and industrial airports. An automated
UAV delivery vehicle could have cost benefits
compared to a manned aircraft. - He wants to
operate out of a hub in Sachon - He is familiar
with the runways in Korea and is confident that
they will support his delivery concept - He is
not familiar with the runways in China - He asks
for an initial study to assess UAV takeoff and
landing requirements
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Analysis approach

• - We log on to the internet and access the World
  Fact Book at www.odci/cia/publications/factbook/i
  ndexfld.hmtl and collect runaway data for China
  and Korea
• - A spreadsheet is created to correlate runway
  length and type vs. the number of runways per
  country
• The results are plotted and compared

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Airport data
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Assessment

• Almost all ROK and Chinese airports with runways
  longer than 3000 feet are paved
• - There is no real benefit to having a capability
  to operate from unpaved fields
• 85 of the airports in China are 5000 feet or
  longer
• - There is no real benefit to having a capability
  to operate from shorter fields in China
• But only 33 of the airports in the ROK are 5000
  feet or longer
• Is this enough or should we serve shorter ones?
• Answer Korea is a small country with 54 airports
  with runways gt 5000 feet

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Vehicle Implications

• A subsonic (low wing loading) jet powered UAV
  could operate from a 5000 foot runway in either
  country
• A prop powered UAV could be able to operate from
  a 3000 foot runway in either country
• - 3000 feet is possible for a jet it but
  requires a very low wing loading or a high
  thrust-to-weight (or both)
• see Raymer, Figure 5.4
• Bottom line
• A jet powered UAV could operate from 85 of the
  runways in China and 1/3 of the runways in Korea
• A prop powered UAV could operate from gt90 of the
  runways in China and gt40 of the runways in Korea

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Jet UAV example

• Note that takeoff and landing requirements are
  based on distance over a 50 foot obstacle
• See Raymer, 5.3 through page 103 for more
  information

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Unpaved fields

• Unpaved fields are not as bad as they may sound
• They are designed for aircraft operations
• Typically they are reasonably smooth
• - They may not, however, be level
• - Nor particularly straight
• And they cannot be cleaned
• - This is a problem for jet aircraft with engine
  inlets located near the ground
• They also are generally unusable in wet weather
• And aircraft with high gross weight/tire contact
  area ratios can sink into the ground, whether wet
  or dry
• - Runways and taxi ways generally have a LCN
  (load contact number) rating to indicate how much
  load/tire contact area can be handled

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Unprepared fields

• Unprepared fields are different from unpaved
  fields
• An unprepared field can be anything from a soccer
  field to a muddy pasture
• - A requirement to operate from such fields can
  impose severe penalties on fixed wing aircraft
• Low takeoff and landing speeds
• Heavy duty landing gear
• High flotation tires, etc.
• The requirement can be met with a fixed wing
  aircraft but the result is usually a slow vehicle
  with a low wing loading (like a Piper Super Cub)
  or a faster vehicle with powered lift (e.g. Short
  Take Off Vertical Landing)
• - According to Raymer, STOVL weight penalties are
  10-20 for fighters and 30-60 for transports
• Rotary wing aircraft are often a better option
  for operations from unprepared fields

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Operations at sea

• Operating an air vehicle from a ship is
  complicated
• Manned fighters and fighter bombers have been
  operating from aircraft carriers for years
• - But deck and air operations are complex
• Very high level of pilot proficiency required
• Crowded deck space
• High potential for accidents and injuries
• Helicopters also have been operating from
  smaller ships for years. Operations are less
  complicated but still demanding
• - STOVL aircraft can also operate from smaller
  ships
• - Fixed wing UAVs have operated from smaller
  ships with mixed success
• Cruise missiles have operated from smaller ships
  and submarines but they do not recover back to
  the ship
• - UAV/UCAV operations from subs are being studied

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Benefits

• Ship based air operations
• 70 of the surface of the earth is covered with
  water
• Operating from ships frees operators from
  requirements to build or establish land bases
• Well equipped ships have housing and provisions
  for crew members and facilities and spare parts
  for maintenance and overhaul
• Global mobility is enhanced

But the cost is high and the ships involved are
large and complex
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Aircraft Carriers
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Assault Ships
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Typical assault ship
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UAV ship operations
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Submarines
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UAV operations
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Air launch

• Launching UAVs from aircraft is straight forward
• The UAV benefits are reduced size and weight
• Carrier aircraft adds to operational range
• Engine can be sized for cruise
• Landing gear can be sized for landing weight
• But there are limitations on size and weight
• Under wing mounted (NB-52 with X-15A-2)
• - Length 52.5 ft, span 22.5 ft, height 14
  ft
• - Weight 56.1 Klb
• Upper fuselage mounted (B747 with Shuttle)
• - Length 122 ft, span 57 ft, height 57 ft
• - Weight 180 Klb

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Practical constraints
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More reasonable sizes
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Aerial recovery

• AQM-34 reconnaissance drones were recovered in
  mid air during the Vietnam war
• 65 of the drones were successfully recovered,
  many using a Mid Air Retrieval System (MARS)
  equipped helicopter which performed an aerial
  snatch
• Despite past success, aerial recovery is complex
  and dangerous (for the helicopter)
• I can find no pictures of the recovery system
  but take my word for it, aerial recovery of UAVs
  is very difficult

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Next subject(s)

• Lesson objective - to discuss
• Requirements analysis
• including
• Basing
• Operational radius
• Operational endurance
• Maximum range
• Speed
• Turn around time

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Operational radius and endurance

• Why are they important?
• Operating radius defines how far the UAV operates
  from base
• - Typically sizes the system architecture (comms,
  etc.)
• Endurance (time on station) and operating radius
  typically size the air vehicle
• Example - Global Hawk (RQ-4A) early program goals

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RQ-4A question
Where did 24 hours and 3000 nm come from?
They were driven by customer and crew
considerations - UAV products are generally
needed around the clock (24 hours a day, 7 days a
week) - Air operations are planned in 24 hour
cycles - Crews operate on 8 or 12 hour cycles

• Original Global Hawk endurance would allow 2 air
  vehicles to provide 24/7 coverage at 3200 nm with
  fixed takeoff and recovery times.
• 3200 nm would allow operations from secure bases
  far from a combat zone (Diego Garcia - Kuwait
  2640 nm)

Civilian air crews operate on 8 to 14 hour
cycles
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Expanded explanation

• Preflight checks and maintenance
• - Nominal 1.5 hours (est.)
• Time to taxi and takeoff
• - 30 minutes (from NGC)
• Time to climb
• - 200 nm _at_ 225 kts (135 KEAS average) 1 hr
• Time enroute
• - 3000nm/350 kts 8.6 hrs
• Time on station
• - 24 hours for single vehicle coverage
• Enroute return 8.6 hrs

• Time to descend
• - Nominal 1 hour (est.)
• Landing loiter time
• - 1 hour (from NGC)
• Time to land and taxi
• - Estimate 15 minutes
• Post flight checks - Nominal 1.5 hours (est.)

Single vehicle nominal flight ground time 48
hours i.e. one vehicle can launch every 24 hours
See Chapter 17 for definition
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Maximum range

• Why is it important?
• Defines how far the UAV can deploy from base
• Establishes the support assets required to
  support deployment
• Global Hawk 12500-13500 nm range permits self
  deployment anywhere in the world without aerial
  refueling

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Range and endurance impact

• Range and endurance drive system size, complexity
  and cost
• Range - Communication architecture goes from
  simple to complicated when range exceeds line of
  sight (LOS)
• LOS (nm) 0.87?sqrt 2?h(ft) (see Chapter 9)
  ?
• LOS _at_ 10Kft 123 nm
• LOS _at_ 65Kft 315 nm
• - Beyond line of sight (BLOS) coverage requires
  comm relay (surface or airborne) or satellite
• Endurance (time on station) - 12 hour endurance
  (at 3200 nm) Global Hawk type air vehicle would
  be about 60 the empty weight at the same payload
• - Range and endurance would also drop by 40
• - Number of air vehicles for 24/7 would increase
  50h

Examples
More about this in Chapter 9 (week 14)
Explanation to come - Chapter 24
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Fleet size

• Number of air vehicles required driven by
• Time on station, operating radius and cruise
  speed, turn around and other times. Global Hawk
  example
• - Total ground time 3.75 hrs, time to
  climb/descend/land 3 hrs, time enroute
  2opn radius/speed 17.5 hrs

• If time on station24 hrs, 2 vehicles reqd, one
  launch every 24 hours

• If time on station12 hrs, 3 vehicles reqd, one
  launch every 12 hours

• If time on station 6 hrs, 5 vehicles reqd, one
  launch every 6 hours

24 hour coverage
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Time on station contd
Notional example
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Geographic area coverage?
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Analysis approach

• We randomly select 25 Chinese ICAO airports with
  long runways
• ICAO designations indicate the airports are used
  for commercial operations
• Long runways identify major airports with
  significant airline operations
• We log onto Worldwide Airport Path Finder and
  start to develop a database.

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Example

• This is the output from WAPF at
  http//www2.fallingrain.com.air/
• WAPF has a database of all known airports and
  allows a user to plan a flight between any
  airports with ICAO designators. This example is a
  52 nm flight from Sachon (RKPS) to Pusan (RKPP).
• A data set is created by calculating the
  distances between Sachon and each of the 25
  Chinese airports
• The data set is listed in order of distance, from
  shortest to longest and plotted

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The data set
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The plot
A UAV with an operating radius an 1300 nm can
cover 90 of the airports studied. The radius
has to double to cover the remaining 10. Is
this the result of the small data base used or
does it indicates that a study is needed to
determine if covering the last 10 is cost
effective?
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China is a big country Not many people live in
the western half
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Speed
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Block time

• Why it is important?
• It is what an aircraft gets paid for
• Passenger or freight customers pay by the trip
• Once an aircraft is loaded with freight or
  passengers, it doesnt earn any more money until
  it is loaded again
• But from a revenue standpoint, if an aircraft has
  to sit on the ground for long periods of time
  between flights, it almost doesnt matter if it
  flies fast or slow.
• Time on the ground (ground turn around time) is a
  key mission consideration

Block time Mission distance/block speed
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Sortie length analysis

• Sortie length
• time to service, taxi, load unload
  distance/(block speed)
• Assumptions
• - 1 hour to load and takeoff
• - 1 hour to land and unload
• - 40 knot headwind
• Block speeds
• 60,120 kts (piston engine)
• 240 kts (turboprop)
• 480 kts (subsonic jet)
• 960 kts (supersonic jet)

Min. coverage
50 coverage
90 coverage
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Analysis results

• 60 120 kt UAVs cannot provide overnight service
• A 240 kt UAV can make one (1) flight per night
  (90 coverage)
• A 480 kt UAV can fly two (2) 90 coverage
  missions (one round trip) per night
• Or 1 max. distance mission
• A 960 kt UAV can fly 3 times per night (90
  coverage)

Total time (hr)
Block speed (kts)
Questions - Which speed is most cost
effective? - What are the sensitivities of the
results to the assumption of a 2 hour turn-around
time (international flight)?
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Cost effectiveness

• Best option 240 kts
• Lowest cost to meet requirements

Relative cost (assumption) - 60 kt UAV
1.00 - 120 kt UAV 2.00 - 240 kt UAV
4.00 - 480 kt UAV 8.00 - 960 kt UAV 16.00
Relative income 12hrs?Block time
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Turn around time

• A 240 kt UAV still provides 90 overnight
  coverage with 4 hours on the ground
• With 4 hours on the ground, a 480 kt UAV can now
  make only one overnight flight with 90 coverage
• A 960 kt UAV can make 2 flights per night (one
  round trip) with 2 hour turn around or 1 flight
  if ground time is 4 hours.

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Expectations

• You should now understand
• How simple analysis can provide insight into
  basic customer requirements
• Basing
• Time
• - Distance
• How to develop airport and runway requirements to
  include length and type
• The design implications of operating from unpaved
  fields, ships and air launch
• That requirements analysis is iterative
• - Many analyses raise as many questions as they
  answer
• - It is important to explore these issues and to
  study sensitivities, especially to assumptions

- Area coverage - Speed - Turn around time
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Next subject

• Lesson objective - to discuss
• Requirements analysis
• including
• Basing
• Operational radius
• Operational endurance
• Maximum range
• Speed
• Turn around time
• plus
• Example problem

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Surveillance UAV - review

• 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 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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Review contd
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Review - Customer asking for?

• A system that can monitor a large area of
  interest
• Conduct wide area search (WAS) for 10 sqm ground
  moving targets (GMT), range resolution ? 10m.
  Send back data for analysis within 2 minutes
• A system that can provide more data on demand
• Based on analysis of wide area search information
• Based on other information
• A system that can provide positive identification
  of specific operator selected targets
• Within 30 minutes of request at a resolution of
  0.5 m
• But what is positive identification?
• Does it require a picture or will a radar image
  suffice?
• and what happens to search requirements while
  the UAV responds to a target identification
  request?
• and how often does it respond?
• and what is the definition of all weather?

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Other inputs - review

• Customer guidance
• Positive identification
• Visual image required
• Search while responding to target identification
  request
• interesting question, what are the options?
• ID response frequency Assume 1 per hour
• Weather definition Assume
• Clear day, unrestricted visibility (50 of the
  time)
• 10Kft ceiling, 10 nm visibility (30)
• 5Kft ceiling, 5 nm visibility (15)
• 1Kft ceiling, 1nm visibility (5)
• Threshold target coverage 80 goal 100

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Our first decision

• Will we give the customer a threshold capability
  or will we give them what we think they need?
• The answer will drive system cost and risk
• We bring our team together to discuss and decide

• We decide to design our initial baseline for a
  threshold capability except we will provide a
  simultaneous wide area search and target
  identification capability
• Our decision is based on subjective analysis
• If the system gets one target identification
  request per hour, it will spend all of its time
  doing target identification
• There will be no time left for wide area search
• We can do trade studies to evaluate other options
• i.e. goal performance capability, etc.
• And we need to select a starting concept and
  document our decisions as derived requirements

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Candidate system solutions

• One large UAV with long range WAS sensor
• Minimum WAS range required for 80 target area
  coverage 101nm (187km) h 53.7 Kft

• Communications ranges potentially very long
• Up to 316 nm (h gt 65 Kft)
• Lots of climbs and descents

• And high speed required
• From 262 kts

Note required distance calculations assume no
ID sensor range extension
316 nm
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Another approach

• Two large UAVs, one provides wide area search,
  the other provides positive target identification
• WAS range (80 coverage) 101nm h 53.7 Kft
• One would need very long range communications
• Unless the other also served as a communication
  relay
• Comm. distance reduces to
• 200 nm
• Speed requirements could be
• reduced if UAVs cooperate
• switch roles
• ConOps complexity
• And frequent climbs
• and descents required
• And UAVs have to operate
• efficiently at both altitudes
• - Although not impossible

WAS loiter location
200 nm
Target 2 location
200 nm x 200 nm
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Third approach

• Five medium size UAVs, four perform wide area
  search and ID, a fifth on stays on CAP as gap
  filler
• WAS range (80 coverage) 51nm (95km) h 27
  Kft
• Communications relay distance reduced
• To 158 nm
• Speed requirement can be reduced to 141 kts if
  UAVs cooperate and switch
• roles
• Otherwise 282 kt speed
• required
• Climb and descent reqmnts
• reduced
• WAS and ID
• altitudes closer
• Air vehicle altitude
• optimization a little
• easier

Why?
10 Kft
27 Kft
27 Kft
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Yet another approach

• Twenty small UAVs, sixteen provide wide area
  search, four provide positive target
  identification
• WAS range (80 coverage) 26nm (48km) h 14
  Kft
• Communications relay distance reduced
• To 127 nm
• Speed requirement can be reduced to 70 kts if
  UAVs cooperate and switch roles
• Otherwise 141 kt speed
• required
• Climb and descent reqmnts
• eliminated
• WAS and ID
• altitudes similar
• Air vehicle design
• optimization easy
• Use Predator
• But large numbers required

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Our starting approach

• WAS UAV(s) serve as Comm
• relays

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Requirement summary

• It is important to maintain an up to date list of
  requirements as they are defined or developed

• Defined requirements (from the customer)
• Continuous day/night/all weather surveillance of
  200nm x 200nm operations area 100 nm from base
• Detect 10 sqm moving targets (goal 100,
  threshold 80), transmit 10m resolution GMTI
  data in 2 min.
• Provide 0.5 m resolution visual ID of 1 target
  per hour in 15 min (goal 100, threshold 80)
  
• Operate from base with 3000ft paved runway

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Derived requirements

• Derived requirements (from our assumptions or
  studies)
• System element
• Maintain continuous WAS/GMTI coverage at all
  times
• Assume uniform area distribution of targets
• Communications LOS range to airborne relay 158
  nm
• LOS range from relay to surveillance UAV 212 nm
• Air vehicle element
• Day/night/all weather operations, 100
  availability
• Takeoff and land from 3000 ft paved runway
• Cruise/loiter altitudes 10 27Kft
• Loiter location 158 nm (min) 255 nm (max)
• Loiter pattern 2 minute turn
• Dash performance 141 nm _at_ 282 kts _at_?10 Kft
• Payload weight and volume TBD
• Payload power required TBD

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Derived requirements

• Payload element
• Installed weight/volume/power TBD
• WAS
• Range/FOR /resolution/target speed 95
  km/?45?/10m/2mps
• Uninstalled weight/volume/power TBD
• ID
• Type/range/resolution TBD/TBD/0.5m
• Uninstalled weight/volume/power TBD
• Communications
• Range/type 212nm/air vehicle and payload C2I
• Uninstalled weight/volume/power TBD
• Range/type 158nm/communication relay
• Uninstalled weight/volume/power TBD
• Control Station element
• TBD
• Support element and sortie rates
• To be determined

C2I Command Control and Intelligence
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Individual homework due Thurs.

• Do a first-order requirements analysis of team
  UAV system requirements and propose an initial
  system concept
• How many vehicles are required? Explain why
• What speeds and altitudes are required?
• - Document the calculations that support your
  conclusions.
• Develop an initial ConOps and list of defined and
  derived requirements
• - Use the example problem as a guide
• (4) Submit to your project team for consideration
  and turn in as homework assignment
• Submit via Email by COB next Thursday

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MIETG requirements

• Minimum header information
• Design project name
• Student or team name
• Homework lesson number
• Homework problem number
• Submit electronically by due date/time
• Bring paper copy to class

Make It Easy To Grade .or.. how to get your
homework graded
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Team assignment During class

• Select a team starting baseline system concept
• Evaluate team inputs (from homework)
• Discuss options
• Assess pros and cons
• Agree on one starting baseline ConOps
• Develop an initial list of defined and derived
  requirements
• - Use the example problem as a guide
• (4) Present your project team decision and turn
  in as team homework
• - Email submittal by COB Monday

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Recommended reading/review

• Raymer - Aircraft Design - A Conceptual Approach
• Chapter 3 Sizing from a Conceptual Sketch
• 3.1 - Introduction
• 3.2 - Takeoff Weight Buildup
• 3.3 - Empty Weight Estimation
• 3.4 - Fuel Fraction Estimation
• 3.5 - Takeoff Weight Calculation
• Chapter 12 Aerodynamics
• 12.1 Introduction
• 12.3 Aerodynamic Coefficients (subsonic only)
• 12.4 Lift (subsonic only)
• 12.5 Parasite (Zero-Lift) Drag (subsonic only)
• 12.6 Drag Due to Lift (subsonic only)

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Intermission
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