Lesson objective to discuss

1
Objectives

• Lesson objective - to discuss
• Air vehicle parametrics
• including
• Rationale
• Applications
• Limits

Expectations - You will understand when and how
to use parametric relationships
15-1
2
Definitions

• From Websters New Collegiate Dictionary
• Parameter any set of physical properties whose
  value determine the characteristics or behavior
  of something
• Our definition
• Design parametric fundamental design parameter
  the value of which determines the design or
  performance characteristics of a design
• Usually (but not always) a multi-variable
  relationship
• e.g., wing loading (W0/Sref), Swet/Sref, etc.
• Parametric design Parametric based design
  approach to define, size, estimate performance
  and do trade offs on classes of conceptual air
  vehicles
• Different from the traditional approach

15-2
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Why parametrics?

• During pre-concept design we need reasonable, not
  design specific, solutions
• Good enough to support technology readiness,
  cost, risk and schedule estimates
• Parametrics enable Pre-Concept Design studies
  that dont require the user to specify a design
• During conceptual design we need to
  systematically explore a wide range of potential
  concepts
• Parametric design methods allow even small teams
  to evaluate and compare (quantitatively) a wide
  range of concepts and technologies
• During both phases, speed and accuracy are
  critical
• Parametric design methods can significantly
  reduce design and analysis time and produce
  credible results

Customers should avoid the temptation of
specifying the design solution, they almost
always get what you ask for and it may not be the
best available
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The UAV challenge

• Parametric design requires historical data for
  use in preliminary sizing analysis and reality
  checks
• - There is a limited amount of good data
  available on UAVs (from public release sources)
• - A lot of the stuff is marketing hype and
  useless for design
• We will use available UAV data and fill in the
  gaps with manned aircraft data
• - Example problems will be structured to show you
  how to do it

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How is parametric design different?

• Traditional conceptual design starts with a
  sketch
• See RayAD Chapter 3, Sizing from a Conceptual
  Sketch
• The sketch or drawing is analyzed
• Using a variety of techniques
• Aerodynamics from geometry and parametrics
• Weight fraction parametrics from historical
  data
• Propulsion from parametrics or cycle decks
• Performance from fuel or weight fractions and
  Breguet range and/or endurance equations
• The concept is sized to meet mission
  requirements
• - Based on results of the first analysis
• A scaled drawing is made and analysis inputs
  generated
• Higher fidelity analyses is performed
• Based on actual configuration areas and features
• Performance is calculated and compared to mission
  requirements and/or team expectations
• The process is repeated until expectations are
  met

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Whats wrong with this?

• The process is time and data intensive
• Teams plan to evaluate a wide range of concepts
  but often never get beyond the first concept or
  sketch
• Particularly for student design teams
• The first concept gets most of the attention
• Lots of effort expended to make it meet
  expectations
• Teams start to fall in love with the concept
• Alternatives get little attention
• Qualitative comparisons eliminate the
  competition
• Errors and disconnects start to surface and/or
  requirements problems emerge
• Teams scramble to recover, fixing errors gets
  priority
• Trade studies to improve performance are defined
  but seldom completed
• Too much work, not enough time
• Everybody hopes the reviewers wont see the flaws
• - And wish they had more time

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The alternative?

• Use simple analytical geometry models instead of
  concept drawings to generate data for aero,
  weight and propulsion analysis and mission
  performance
• - Physically capture important design variables
  but minimize the time and effort required to
  assess them
• Use full mission integrated spreadsheet analysis
  to evaluate performance
• Size for the actual mission, reduce dependence on
  configuration insensitive rule-of-thumb estimates
• Empty weight fraction, fuel for climb, etc.
• Quickly and systematically evaluate a range of
  concepts
• Select preferred concepts and technologies based
  on data
• Draw and analyze the preferred concept
• Confirm vs. discover how it really performs

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8
Example mission
End cruise at W W0 - (1-Klr)WF
12 13
15
16
17
14
Start cruise at W W0 - KttocWF
4
5
6
7
8
9
10 11
18
0
1
Border - Loiter/Penetrate
Border - Standoff
Border - Penetrate/Loiter
19
3
2
Kttoc (taxi-takeoff-climb fuel)/Wf Klr
landing fuel reserves/Wf Wf fuel weight
For cruise and loiter Lift ? weight Thrust ? drag
Notation
Terminology
15-8
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Many types of parametrics

• Range/endurance related parametrics
• Speed (V)
• Lift-to-drag ratio (L/D)
• Specific fuel consumption (SFC)
• Fuel fraction (FF)
• Range factor (RF)
• Specific range (SR)
• Example problem
• Propulsion related parametrics
• Internal combustion
• Turboprop
• Turbojet turbofan
• Afterburners
• Weight related parametrics
• Fuel
• Payload
• Structure
• Systems

This chapter
Covered under propulsion
Covered under weights
15-9/10
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Range related parametrics

• Based on factors from the Breguet range equation
• - For jet aircraft (See RayAD 3.5)
• R Vcr?(L/Dcr)/TSFCcr?Ln(Wi/Wj) (15.1)
• R Cruise range
• Vcr Cruise speed
• L/Dcr Cruise lift-to-drag ratio (LoDcr)
• TSFCcr Cruise thrust specific fuel consumption
• Vcr?L/Dcr/TSFCcr RF (range factor) W?SR
• SR Specific Range V/Fuel flow)
• - For propeller aircraft (more about this later)
• RF(nm) 325.6??p?(L/Dcr)/SFCcr (15.1a)
• ?p propeller efficiency
• ? 0.8 (for constant speed prop)

where
and
where
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Endurance related parametrics

• Based on Breguet endurance equation factors
• - For jet aircraft (RayAD 3.7)
• E (L/Dlo)/TSFClo?Ln(Wi/Wj)
  (15.2)
• E Endurance (hrs)
• L/Dlo Loiter lift-to-drag ratio (LoDcr)
• TSFClo Loiter thrust specific fuel consumption
• (L/Dlo)/TSFClo EF (endurance factor)
  Wbar/WdotF
• Wbar Average loiter weight (lbm)
• WdotF Fuel flow (lbm/hr)
• - For propeller aircraft (more about this later
  also)
• E EF?Ln(Wi/Wj)
  (15.2a)
• EF 325.6??p ?(L/Dlo)/(Vlo?SFClo
• Vlo Loiter speed ?p propeller efficiency

where
and
where
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Weight fraction version

• The Breguet equation is often expressed in the
  form of weight fractions (more in Chapter 18)
  where
• Empty weight fraction (EWF) ? Empty weight/Gross
  wt.
• Fuel fraction (FF) ? Fuel weight/Gross
  wt.
• Payload fraction (PF) ? Payload wt./Gross
  wt.
• Misc weight fraction (MiscF) ? Misc.
  weight/Gross wt.
• Where by defintion
• Gross weight (W0) ? Empty weight (We) Fuel
  Weight
• (Wf) Payload weight (Wpay) Other weight
  (Wmisc)
• Dividing through by W0 and solving,
• FF 1 - EWF - PF - MiscF
  (15.3)
• Maximum range and endurance occur when
• (Wi/Wj)max (1 - KttocFF)/(1-(1- Klr)FF)
  (15.4)
• Rmax RF?ln(Wi/Wj)max
  (15.5)
• Emax (L/Dlo)/TSFClo?ln(Wi/Wj)max
  (15.6)

or
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Typical weight fractions
Typical value
Caution
- Within any vehicle class, weight fractions can
vary widely - Nonetheless, most initial concept
design procedures start with an assumed empty
weight fraction (EWF) - This can cause problems,
as we will see later - Later we will introduce an
alternative approach
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Database variation examples
15-15
15
Next

• Range/endurance related parametrics
• Speed (V)
• Lift-to-drag ratio (L/D)
• Specific fuel consumption (SFC)
• Fuel fraction (FF)
• Range factor (RF)
• Specific range (SR)
• Example problem
• Propulsion related parametrics
• Internal combustion
• Turboprop
• Turbojet turbofan
• Afterburners
• Weight related parametrics
• Fuel
• Payload
• Structure
• Systems

Covered under propulsion
Covered under weights
15-16
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Cruise speed ranges
BPR Bypass Ratio (Fan airflow/Core engine
airflow) , AB After burner
Typical operating regime - higher speeds have
been demonstrated
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Variation with altitude
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Typical L/D ranges
Condensed from RosAD.1,Table 2.2 Single twin
engine - prop ... STOL Busines
s jets .. Regional turboprop.
Jet transports.. Military
trainers... Fighters Super
sonic cruise.. Average
Cruise 8 - 10 5 - 7 10 - 12 11 - 13 13 -
15 8 - 10 4 - 7 4 - 6 8.9
Loiter 10 - 12 8 - 10 12 - 14 14 - 16 14 -
18 10 - 14 6 - 9 7 - 9 11.4
(25)
Sailplane 20 40 Global Hawk
. 33 - 34
Also see RayAD Fig 3.6 Flight
International, UAVs, page 28,5 /1/01
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Typical SFC ranges
15-20
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Speed and altitude effects
From previous chart
Notation 0 Sea level static cr
Typical cruise altitude speed
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Range factor (RF)
For typical fighters (_at_ subsonic cruise) - we
will derive range factors for UAVs during the
course
F-100 4920NM F-101 4530NM F-102 5390NM F-104 4500N
M F-105 5200NM F-106 5400NM F-111 6450NM
F3D 3750NM F3H 4480NM F4D 3820NM
F-4 4200NM F-86 4870NM F-89 3970NM
From RAND N-2283/2-AF, Dec 1987, approved for
public release
From 15.1 and 15.1a, Range factor (RF) For jets
(nm) ? KTAS(L/Dcr)/TSFCcr For prop (nm) ?
325.6?p(L/Dcr)/SFCcr
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Specific range (SR)

• A simple performance parametric used in many
  flight manuals
• R SR?W (15.7)
• where SR V/Wfdot (NM/Lbm-fuel)
• and Wfdot Fuel flow (lbm/hr)
• - Typically used for optimum (constant Mach)
  cruise above 36 Kft
• - Or high-q dash performance

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Next

• Range related parametrics
• Speed (V)
• Lift-to-drag ratio (L/D)
• Specific fuel consumption (SFC)
• Fuel fraction (FF)
• Range factor (RF)
• Specific range (SR)
• Example problem
• Propulsion related parametrics
• Internal combustion
• Turboprop
• Turbojet turbofan
• Afterburners
• Weight related parametrics
• Fuel
• Payload
• Structure
• Systems

Covered under propulsion
Covered under weights
15-24
24
Example problem - review

• Five medium UAVs, four provide wide area search
  (two are comm. relay), fifth does positive target
  ID
• WAS range required (95km) not a challenge
• No need to switch roles, simplifies ConOps
• No need for frequent climbs and descents
• Base communications and relay distances
  reasonable
• 158nm 212 nm
• Reasonable dash speed (282kts)
• WAS and ID operating altitude
• differences reasonable
• But.

• What kinds of air
• vehicles?
• What propulsion?
• How big will they be?
• How will they perform?
• What will they cost?

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Positive ID - review

• We have a threshold requirement for positive
  (visual image) target identification (ID) 80 of
  the time
• To design our baseline for the threshold
  requirement
• We have to be able to operate at or below 10 Kft
  for 30 of the target identifications
• 50 of the time we can stay at altitude and 20
  of the time we wont see a target (unless we
  image at lt 5 Kft)
• This places 10Kft efficient cruise, loiter and
  climb and descent rate requirements on the air
  vehicle

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Derived requirements - review

• Derived requirements
• System element (from Chapters 5 8, example
  problem)
• Maintain continuous WAS/GMTI coverage at all
  times
• One target recognition assignment at a time
• 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 (from Chapter 8, example
  problem)
• Day/night/all weather operations, 100
  availability
• Takeoff and land from 3000 ft paved runway
• Cruise/loiter altitudes 10 27 Kft
• Loiter location 158 nm (min) 255 nm (max)
• Loiter pattern 2 minute turn
• Dash performance 141 nm _at_ 282 kts _at_?10 Kft
• Payload element (starting assumption more on
  why later) .

• EO/IR 130 lbm _at_ 1.95 cuft
• SAR 455 lbm _at_ 15.6 cuft
• Communications (each) 67.5 lbm _at_ 4.5 cuft

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How do we start ?

• Analyze the problem
• What does the air vehicle have to do?
• Is any information missing?
• Look at some potential solutions
• What are the overall design drivers?
• Payload weight and volume
• Range and endurance
• Speed and propulsion type
• Pick a starting baseline (that should work)
• Analyze it
• Size/weight range/endurance cost and support
• Define and analyze the other approaches
• Compare results and select preferred baseline
• Define/trade preferred overall system
• Reasonable balance of cost, risk and
  effectiveness
• Document results

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What kind of air vehicle?

• One that operates from a 3000 ft paved runway
• One that provides WAS over an area of interest
• At h 27 Kft, 158nm - 255 nm from base,
• Fly circular pattern, 2 minute turns
• Maximum coverage area 50nm x 50 nm each
• One that can ID targets at 141 nm in 30 minutes
• Based on analysis of WAS sensor information
• Based on other information
• One that can image targets from 10 Kft
• Once per hour (at maximum fly out distance)
• But how long must it loiter?
• 6 hours, 12 hours, 24 hours or even longer?
• and what is the definition of all weather?
• Typhoons included?

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Getting answers

• Confer with team and/or ask the customer
• And insist on definitive (quantifiable) answers
• Some typical responses
• Loiter time
• What the team wants to say - interesting
  question, what are the trades?
• What the team needs to say - lets baseline a 12
  hour loiter and do a trade study on the effects
  of from 6 to 24 hours?
• All weather definition Statistics indicate
  terrible (unflyable) weather 10 of the time
• Note this conflicts with our 100 availability
  requirement

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Other resources

• Lessons to follow the basic understanding,
  analysis methods, models and parametric data for
  preliminary sizing and estimating overall mission
  performance
• Chapter 16 (Standard atmosphere) Simple models
  that describe atmospheric properties as functions
  of altitude and speed
• Chapter 17 (Aerodynamics) first-order
  aerodynamic prediction methods that capture key
  configuration features
• Chapter 18 (Parametric propulsion) simplified
  engine models applicable across the performance
  envelope
• Review 19 (Parametric weights) simplified weight
  models that capture key configuration features
• Chapter 20 (Parametric geometry) simplified
  geometry models required to generate aerodynamic
  and weight inputs
• Chapter 21 (Flight mechanics) simplified physics
  based relationships used to predict flight
  performance by mission segment
• Chapter 22 (Integrated performance)
  Spreadsheet models to perform initial sizing and
  calculate overall mission performance
• Plus parametric data from real air vehicles
  needed to test and validate simplified model
  predictions

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Our first decision

• It is a very important one
• What is the best propulsion cycle for the
  mission?
• Internal combustion (ICprop), turboprop (TBProp)
  and turbo fan (TBFan) engines can all meet the
  baseline speed (280 kt) and altitude (10-27Kft)
  requirements
• We bring our team together for the decision
• Speed and altitude at the upper end of IC
  capability, high availability required will be a
  real challenge for IC engines
• TBProp is a good cycle for low-medium altitude
  operations
• TBFan is best at altitudes gt 30 Kft and has best
  reliability
• We select a

• TBProp for our starting
  baseline and agree to evaluate a TBFan as the
  primary alternative
• IC alternative decision will be based on size
  required
• We start with conventional wing-body-tail
  configurations
• - We can evaluate more innovative concepts during
  conceptual design

15-32
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Conflicting requirements

• System analysis thus far assumed 100 air vehicle
  availability and now weather limits availability
  to 90
• This will affect SAR sizing (primarily)
• We assumed SAR operation 100 of the time,
  therefore, the SAR only needed 80 area coverage
• At 90 availability, the SAR would need to
  provide 89 area coverage (range increase to
  102km) to achieve overall 80 (threshold) target
  coverage
• What should the we do, leave the baseline alone
  or resize the payload and start over?

• Answer leave it alone!
• During any design cycle, there will always be
  design and requirement disconnects
• If we change baselines every time we find a
  disconnect, we would never complete even one
  analysis cycle
• Orderly changes occur at the end of an analysis
  cycle

15-33
33
Next decision

• How many engines?
• Generally determined by available engine size
• The smallest number of engines will generally be
  the lightest and lowest drag
• How big will they be?
• Engine size is determined by thrust or
  horsepower-to-weight required to meet performance
  requirements
• One sizing consideration is takeoff others are
  speed, acceleration and maneuver
• Initially we size for takeoff (see RayAD, page
  99)
• We assume a 3000 ft takeoff balanced field length
• Balanced field length means the air vehicle can
  accelerate to takeoff speed, have an engine
  failure and brake to a safe stop within the
  specified length
• We assume half the distance to reach takeoff
  speed
• Later we will calculate performance over the
  entire mission and ensure that all requirements
  can be met

15-34
34
Next decision

• Which mission do we size for?
• WAS with maximum cruise out 255nm at 27.4Kft
• Baseline operational endurance is 12 hr, with
  trade study options for 6 hr and 24 hr endurance
• ID mission with cruise out 200 nm _at_ TBD Kft
• Maximum ID distance constant at 141 nm, 282 kts
• WAS missions are performed at best loiter speed
  (max L/D) and SFC
• ID missions are at max. speed
• (out and back), L/D will be lower
• and SFC will be higher
• Both will have the same take
• off and landing requirements
• Answer.

100 nm
255 nm
158 nm
141 nm
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Mission notation
15-36
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Defined derived requirements
Defined Remain airborne 24/7 ? 90 of the
time Derived payload, distances and
altitudes Payload Wpay 720 lbm Cruise/loiter
altidude Hcr Hlo 27 Kft Operating radius
D3-4 D4-7 D17-14 255 nm Ingress/Egress
D8-14 0 Assumptions typical values (design
independent) Landing fuel reserves Klr 5
MiscF 1 Propeller efficiency ?p 80 First
cut estimates refine later (design
dependent) Taxi/takeoff/climb fuel Kttoc
10 Average rate of climb ROCavg 1500 fpm
(typical TBP) Average climb speed Vcl 0.8 Vcr
(more about this later) Parametric estimates
Next chart (design dependent) Unknowns Gross
weight (W0) Fuel fraction (FF)
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Parametric estimates

• Chart 15-14 shows nominal empty weight fractions
  for manned TBProps (EWF 0.58) and UAVs (EWF
  0.6)
• - Predator B/Altair shows EWF 0.44 probably
  more representative of our concept
• Chart 15-18 shows typical economic cruise speeds
  at 27Kft to be in range of 180-300 kts
• We select lower value (180 kts) to maximize
  performance
• Chart 15-19 shows typical TBProp cruise/loiter
  LoDs
• Regional TBProp LoDcr 11-13, LoDlo 14-16
• Global Hawk LoDlo much higher (33-34) _at_ AR 25
• We will select intermediate L/Dcr value LoDlo
  23
• Charts 15-20 (table) and 15-21 (plot) TBProp
  cruise loiter SFCs conflict (not unusual for
  parametric data)
• The plot is from our engine database (real
  TBProps) so we use it and estimate SFCcr SFClo
  0.4

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Solution approach
Calculate cruise ranges and range factors
(15.1a) Time to climb 27 Kft/1500 fpm 0.30
hr Climb speed ? 0.8?180 144 kts Climb distance
43.8 nm R4-7 255 - 43.8 211.2 nm R14-17
255 nm RFcr 325.6??p?(L/Dcr)/SFCcr 14977.6
nm Calculate outbound initial/final cruise weight
ratios (15.1) R4-7 14977.6 nm?Ln(W4/W7) or.
W4 1.014?W7 Calculate inbound initial/final
cruise weight ratios (15.1) R14-17
14977.6?Ln(W14/W17) orW14 1.017 ?W17 Calculate
initial/final loiter weight ratios (15.2 and
2a) EFlo 325.6??p?(L/Dlo)/(Vlo?SFClo 90.4
hr E7-8 12hrs EFlo?Ln(W7/W8) orW7 1.142
?W14 - Note W8 ? W14 (no ingress/egress)
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Size estimate
By definition the initial and final cruise
weights (W4 and W17) are given by (see chart
15.8) W4 W0?1-FF?Kttoc where Kttoc 0.1 W17
W0?1-FF(1-Klr) where Ktlr
0.05 Therefore W4 W0?1- 0.1?FF 1.014?W7
1.014?1.142 ?W14 1.014?1.142?1.017
?W17 1.014?1.142?1.017?W0?1 -
0.95?FF FF 0.175 Then from 15.3 FF 1 -EWF
-MiscF - PF 1 -0.44 -0.01 -720lbm/W0 or..W0
1918 Lbm And maximum range and endurance (from Eq
15.5-6) are Rmax 2453 nm and Emax 14.8 hrs
or
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Parametric comparison

• Whenever we calculate a performance parameter or
  size a vehicle, we should always ask ourselves if
  the calculation makes sense
• - In this case, the sizing results should make
  sense since we used parametric data from similar
  aircraft as inputs
• Nonetheless, we should still make a reality check
  using our UAV data spreadsheet ASE261.UAV
  data.xls
• Which shows that we have a problem

• Compared to other TBProp UAVs, our calculated FF
  is low for Emax 14.8 hrs
• Other TBProp UAVs require higher FFs for this
  level of performance
• The data shows our inputs may be optimistic

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Issue resolution

• There are many possible explanations for why our
  estimated fuel fraction is low
• LoDs and SFcs were estimated, not calculated
• Ditto for empty weight fractions, speeds, etc.
• What should we do?
• Press on with a higher value of fuel fraction?
• Stop and try to resolve the issues
• Proceed with the knowledge that our performance
  estimates are optimistic

• We can press on and sort it out later
• Our spread sheet design and analysis methods are
  designed to handle uncertainties and disconnects
• Corrections can be made with a few input changes
  or multipliers on performance parameters
• However, if we were using traditional design
  methods, we would need to resolve the issue or
  risk a major down stream redesign or disconnect

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TBFan alternative
Defined Remain airborne 24/7 ? 90 of the
time Derived payload, distances and
altitudes Payload Wpay 720 lbm Cruise/loiter
altidude Hcr Hlo 27.4 Kft Operating radius
D3-4 D4-7 D17-14 255 nm Ingress/Egress
D8-14 0 Assumptions typical values (design
independent) Landing fuel reserves Klr 5
MiscF 1 Propeller efficiency ?p 80 First
cut estimates refine later (design
dependent) Taxi/takeoff/climb fuel Kttoc
10 Average rate of climb ROCavg 1500
fpm Average climb speed Vcl 0.8 Vcr (more
about this later) Parametric estimates Next
chart (design dependent) Unknowns Gross weight
(W0) Fuel fraction (FF)
Same assumptions as TBProp
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TBFan alternative

• Chart 15-14 shows nominal empty weight fractions
  for manned TBFans (EWF 0.55) and UAVs (EWF
  0.6)
• - Predator C shows EWF 0.39 probably more
  representative of our concept
• Chart 15-18 shows jet aircraft economic
  cruise/loiter speeds at 27Kft to be in range of
  250-525 kts
• We select a lower value (300 kts) for both cruise
  and loiter (but not the lowest since RF ? Vcr)
• Chart 15-19 shows typical TBFan cruise/loiter
  LoDs
• BizJet TBFan LoDcr 10-12, LoDlo 12-14
• Global Hawk LoDlo much higher (33-34) _at_ AR 25
• We will select intermediate L/Dcr value LoDlo
  22.5
• Charts 15-20 (table) and 15-21 (plot) TBFan
  cruise loiter SFCs conflict (not unusual for
  parametric data)
• The plot is from our engine database (real
  TBFans) so we use it and estimate TSFCcr TSFClo
  0.65

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44
TBFan contd
Calculate cruise ranges and range factors
(15.1a) Time to climb 27.4 Kft/1500 fpm 0.30
hr Climb speed ? 0.8?300 240 kts Climb distance
72 nm R4-7 255 - 72 183 nm R14-17 255
nm RFcr Vcr?(L/Dcr)/TSFCcr 10385 nm Calculate
outbound initial/final cruise weight ratios
(15.1) R4-7 10385 nm?Ln(W4/W7) or. W4
1.018?W7 Calculate inbound initial/final cruise
weight ratios (15.1) R14-17 10385 ?Ln(W14/W17)
orW14 1.025 ?W17 Calculate initial/final
loiter weight ratios (15.2 and 2a) EFlo
(L/Dlo)/SFClo 36.2 hr E7-8 12hrs
EFlo?Ln(W7/W8) orW7 1.394?W14 - Note W8 ?
W14 (no ingress/egress)
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45
TBFan contd
By definition the initial and final cruise
weights (W4 and W17) are given by (see chart
15.8) W4 W0?1-FF?Kttoc where Kttoc 0.1 W17
W0?1-FF(1-Klr) where Ktlr
0.05 Therefore W4 W0?1- 0.1?FF 1.021?W7
1.018?1.394 W14 1.018?1.394?1.025?W17
1.018?1.394?1.025?W0?1 - 0.95?FF FF
0.354 Then from 15.3 FF 1 -EWF -MiscF - PF 1
-0.39 -0.01 -720lbm/W0 or..W0 2914 Lbm And
maximum range and endurance (from Eq 15.5-6)
are Rmax 3885 nm and Emax 13.5 hrs
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Expectations

• You should understand
• (1) How to analyze requirements to meet mission
  altitude, speed, operating distance and loiter
  time requirements
• What is defined
• What to assume
• What to estimate and later refine
• What to solve for
• (2) How to calculate fuel fraction and gross
  weight
• To meet operating distance and loiter time
  requirements
• (3) How to use parametric data
• To assess/select inputs
• To check results

15-47
47
Homework (individual)

• Select an air vehicle type (one required for
  each individual team member) that you think could
  meet your teams air vehicle initial system
  concept requirements (todays team assignment)
• Select an empty weight fraction and cruise speed
  and L/D for that class of air vehicle.
• Explain your selection.
• Assume a nominal SFC or TSFC for your engine
  type.
• Explain your rationale.
• 2. Size your configuration concept (individual
  grades)
• Use nominal chart 15-37or 15-43 assumptions
• Calculate FF and W0
• Compare your calculations to parametric data and
  assess the results

15-48
48
Intermission
15-49