Aircraft Design AE 435

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Aircraft Design AE 435
Take-off

• Dr. Wail Harasani
• King Abdul Aziz University
• Aeronautical Engineering Department

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References

• D. How Aircraft Conceptual Design Synthesis
• D. Raymer Aircraft Design, A Conceptual
  Approach
• E. Torenbeek Synthesis of Airplane Design
• J. Roskam Airplane Design Vol. (1-8).

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Sensitivity study (Wto to Wpl, We, R, S.F.C(Cj),
and L/D)
Preliminary sizing (We,Wto,Wf)
Estimating T/W, W/S
Configuration selection
Cost prediction
Landing gear design
Design of cockpit and the fuselage
Design of the empennage
Design of the wing
Selection Integration of the Propulsion system
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Roskam books are organized as follows

• PART I Preliminary sizing of airplanes
• PART II Preliminary configuration design and
  integration of the propulsion system
• PART III Layout design of cockpit, fuselage,
  wing and empennage
• PART IV Layout design of landing gear and
  systems
• PART V Component weight estimation
• PART VI Preliminary calculation of
  aerodynamic thrust and power characteristics
• PART VII Determination of stability, control
  and performance characteristics
• PART VIII Airplane cost estimation design,
  development, manufacturing and operating

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Preliminary Design Sequence I (16 steps)
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Estimating Take-off weight Wto Empty weight
WeFuel weight Wf (p5/I)
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Sensitivity study

• Sensitivity of Take-off Weight to Payload Weight
• Sensitivity of Take-off Weight to Empty Weight
• Sensitivity of Take-off Weight to Range
• Sensitivity of Take-off Weight to Endurance
• Sensitivity of Take-off Weight to Lift to Drag
  Ratio
• Sensitivity of Take of Weight to Specific Fuel
  Consumption

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Why study sensitivity?

• To find out which parameters drive the design.
• To determine which areas of technological change
  must be pursued

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Sensitivity of Take-off Weight to Payload Weight
dWto / dWpl B Wto D - C ( 1 B ) Wto -1
eq 2.27 p70 Where C 1- ( 1
Mff res )( 1 Mff ) Mtfo
eq 2.22 p69 D ( Wpl Wcrew )
eq 2.23 p69 A,B
from table 2.15 Mff res from the mission
specification (i.e. Mff res 0.15) dWto / dWpl
X means that for each pound of payload added,
the airplane take-off gross weight will have to
be increased by X lbs this means the mission
performance stays the same
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Sensitivity of Take-off Weight to Empty Weight
dWto / dWe B . Wto inv.log(log Wto A)/
B-1 eq 2.29 p72 Where A,B
from table 2.15 dWto / dWe X for each pound
of increase in empty, the airplane take-off gross
weight will have to be increased by X lbs this
means the mission performance stays the same, the
factor is the growth factor due to empty weight.
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Sensitivity of Take-off Weight to Range and
Endurance
F - B.W2to C .Wto ( 1 B ) D 1 ( 1
Mres ) Mff eq2.44 p75 Where Mres 0.15 Range
dWto / dR F .Cj ( V. (L / D) )-1
eq 2.46 p78 dWto / dR X
in lbs/n.m The significance of this
sensitivity is that if the range in the mission
specification is decreased from 1500 n.m to 1400
n.m the take off weight can be decreased by
(1500-1400).X lb Note V is in
kts Endurance dWto / dE F .Cj (L / D) -1
eq 2.47 p79
dWto / dE X in lbs/hr. The significance
of this sensitivity is that If the loiter
requirement is increased by (1/2) hr the take off
weight will increased by (1/2). X lb
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Sensitivity study of Take off Weight to S.F.C.
and Lift to Drag Ratio

• For S.F.C.
• dWto/dCj F R ( V (L/D) ) -1
  eq2.52 p83
• dWto/dCj lbs/lbs/lbs/hr
• For Lift to Drag Ratio
• dWto/d(L/D) - F R Cj ( V (L/D) 2 ) -1
  eq2.53 p83
• dWto/d(L/D) lbs
• The mission specification does not call for
  loiter, so the endurance case does not need to be
  examined

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Summary
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Performance Constraint Analysis

• Sizing to take-off distance requirements
• Sizing to landing distance requirements
• Sizing to cruise speed requirements
• Sizing to FAR 25.121 (OEI) requirements

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Sizing to take-off distance
S TOFL 3.75 ( W / S ) / s C L max to ( T / W
) eq.3.8 p98 / I S TOFL take off
distance is in ft CL max to from table 3.1 page
91 s air density ratio 1 for see level
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Sizing to landing distance
VSL 2 ( W / S ) / ? C L max ½
eq.3.1 p90/I Where ? air density slugs
/ ft3 0.002378 slugs / ft3 VA
(Sfl/0.3)1/2, VA is in kts VSL VA / 1.3
in kts Note we substitute in ft/sec
VSL(ft/sec) VSL(kts) 1.688
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Sizing to cruise speed
( T / W ) CDO q / ( W / S ) ( W / S ) / q ?
A e eq.3.60 p167/I Where q dynamic pressure
psf Wto ----fig 3.22 p124----gt Swet Swet ---fig
3.21 p120 assum Cf---gt f Assuming (W/S) calculate
S CDO Zero drag coefficient Calculate CDO f /
S Assuming A Assuming e from table 3.6
p127 ------------------------------------------ Gi
ven (W/S) ---calculating---gt (T/W) (T/W)to
(T/W) / s Where s density ratio
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Sizing to FAR 25.121 one engine inoperative (OEI)
Conditions Required Climb Gradient (CGRgt0.021)
given Landing gear down V 1.5 Vs T/W N / (
N 1 ) ( L / D )-1 CGR ) eq.3.31
p143/I Where CLmaxa 2.1 assumed CLA 2.1
/ (1.52) CLA 0.93 CD 0.792 0.0531 CLA2
CD 0.792 0.0531 (0.93)2 CD
0.125 L/D CLA/CD L/D 7.44 N Number of
engines
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Summary
Max lift coefficient take-off C L max to
table 3.1 page 91 Max lift
coefficient landing CL max L
table 3.1 page 91 Max lift coefficient
clean CL max
table 3.1 page 91 Wing loading (W/S)
lbs/ft2 Thrust loading (T/W)
Aspect ratio A Max take-off
weight Wto lb Empty weight We
lb Fuel
weight Wf
lb Wing area S Wto/(W/S)
ft2 Thrust T (T/W) Wto
lb
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Overall Configuration Selection (p102/II)
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Design of Cockpit and Fuselage Layout (p107/II)
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• Step 1 Referring to the mission specification,
  make a list of all items which need to be located
  in fuselage. (p107/II)
• Example
• Number and weight of the cockpit crew member.
• Number and weight of the cabin crew members.
• Number and weight of passengers.
• Weight and volume of carry-on baggage.
• Weight and volume of the check-in baggage.
• Auxiliary power unit (APU)
• Weight and volume of the fuel carried in the
  fuselage
• A place to perform Salah.

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• Step 2 Propose a dimensioned drawing. II
• That includes or shows the following.
• The cross section to be used. p52/III
• Size and shape of the fuselage.p110/II
• Access doors and emergency exits.p70/III
• Type of seating to be employed first class,
  business class.p52-63/III
• Number of persons abreast.p52-63/III
• Cabin required in terms of closets, toilets,
  overhead storage.p73/III
• See example in p114/II.

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• Step 3 Add the appropriate distance to the cabin
  interior layout. P109/II
• For small commercial airplanes 1.5 inches
• For fighter and trainers 2 inches
• For large transporter 0.2df 1 inches

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Step 4 Draw (sketch) the exterior lines which
define the cabin part of the fuselage See Figure
4.1 and table 4.1 page 110/II See example p118/II
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Step 5 Suggest a design for the cockpit crew
Part III contains detailed data See example
p119/II, and (p29-32)/III
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Step 6 Prepare a dimensioned Drawing of the
entire fuselage, including the rear fuselage cone.
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Step 7 Document the decision made, including
clear, dimensioned drawings (sketches)
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Selection and integration of the propulsion
system p123/II, example p137/II

• Step 1 Check the mission specification for any
  definition of the type of power plant required.
• Step 2 Draw a preliminary speed vs. altitude
  envelope for the airplane.
• Step 3 Compare the airplane speed vs. altitude
  envelope with those of Figure 5.1 p124/II.
• Note If the type of engine is specified in the
  mission specification then step 2, and 3 can be
  omitted. In our case in the mission the power
  plant is specified to be a turbofan engine. So
  step 2, and 3 are omitted.

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• Step 4 Determine the maximum thrust required for
  the airplane. (Look at summary)
• Step 5 Decide on the Number of engines to be
  used.
• Step 6 This step is for propeller engine.
• Step 7 This step is for propeller engine.
• Step 8 Decide on where to mount the engines
• a. the wing
• b. the fuselage
• c. the empennage
• d. any combination

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• Step 9 Obtain the necessary information on the
  engine. (from 1.Jans all world aircraft 2.engine
  manufacturer 3.(p323,324/III))
• (geometry, thrust, attachment point, c.g.
  location,..etc)
• Step 10 Draw the engine installation in a three
  view.
• Step 11 Document the decision made.

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Wing layout design p141/II, p163/III

• From previous summary we have wing area S, and
  aspect ratio Ab2/S
• Step 1,2 If the airplane is a flying wing, then
  all items should be integrated into the wing.
• Step 3 Decide on the overall wing /fuselage
  arrangement.
• (High wing, Low Wing, Mid Wing)
• High Mid
  Low
• Interference Drag Poor Good
  Poor
• Dihedral effect Negative
  Neutral Positive
• Passenger Visibility Good
  Good Poor
• Landing Gear
• If wing mounted Long/heavy
  Short/light
• Loading and unloading easy
  easy need stairs
• p174/III , p142/II

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• Step 4 Select the wing quarter chord sweep angle
  ?c/4 (Forward sweep, aft sweep, None sweep,
  Variable sweep) and wing thickness t/c , see
  table p146/II, and Figure p150/II.
• As for sweep ?c/4.
• 
  Forward None Aft
• Lift Curve slope
  low high low
• Pitch attitude
  high low high
• Ride through turbulence
  good poor good
• Asymmetric stall
  best good poor
• Lateral control at stall
  best good poor
• Compressibility drag
  low high low
• Wing weight
  highest low high
• p174/III

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• For t/c from table p197/II
• Low t/c
  High t/c
• Wing weight High
  Low
• Wing drag low
  high
• Wing fuel volume poor
  good
• Max. left poor
  good
• p188/III
• Step 5 Decide on the wing airfoil to be used.
• See table p197/II

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• Step 6 Decide on the wing taper ratio see table
  6.11 p146/II. (?Ct/Cr)
• High
  Low
• Wing Weight high low
• Tip stall Good
  poor
• Wing fuel volume Good poor
• p192/III
• Step 7,8,9 Due to time constrains these steps
  are Omitted
• Step 10 Compute the wing fuel volume Vwf in ft2
  eq6.2 p153/II
• Step 11 Decide on the wing twist angle. And
  incidence angle iw
• See table 6.7 p146/II. As for twist angle.
• Large
  small
• Induced drag high small
  
• Tip-stall good
  poor
• Wing weight mildly lower mildly higher

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• Step 12 Decide on the wing dihedral angle Gw
• Positive
  Negative
• Spire stability Increased
  decreased
• Dutch roll stability decreased
  Increased
• Ground clearance Increased
  decreased
• Step 13 Draw the wing and fuselage, and Document
  the results.

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Design of the high lift devices p167/II

• Step 1 List the values for the maximum lift
  coefficients.
• CLmax, CLmaxto, CLmaxL.
• Step 2 Verify that the existing wing can produce
  a value of CLmaxw, which is consistent with
  required values of clean airplane CLmax .
• -1- Calculate the reynolds number of the root and
  tip.
• RNt ? V Ct / µ
• ? air density slugs/ft3
• µ coefficient of viscosity lb-sec/ft2
• V velocity at take-off ft/sec

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• -2- from figure 7.1 p169 with t/c, RN
• Get (airfoil) CLmaxt , CLmaxr
• -3- Calculate CLmaxw
• CLmaxw0.95(CLmaxrCLmaxt) / 2
• Note - It does not account for wing
  twist
• - 0.95 is a function of ?
  (assumed ? to be 0.4)
• -4- CLmaxw CLmaxw cos ? c/4
• To account for sweep
• -5- CLmax CLmaxw / F
• F is a number between 1.05 1.1
• CL max for the airplane from CL max of the wing

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• Step 3 Determine the incremental values of
  maximum lift coefficient which need to be
  produced by the high lift devices
• Takeoff
• ?CLmaxto 1.05 (CLmaxto - CLmax)
• Landing
• ?CLmaxL 1.05 (CLmaxl - CLmax)
• 1.05 account for the additional trim penalties.

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• Step 4 Compute the required incremental section
  maximum lift coefficient with flaps
• ?Clmax (?CLmax) (Swf/S) / K?
• -1- assume two arbitrary values for (S/Swf)
• -2- K? factor accounts for sweep angle
• K? ( 1 - 0.08 (cos ?c/4 )2 ) (cos ?c/4
  )3/4
• -3- calculate ?Clmax
• Takeoff flaps landing
  flaps
• (Swf/S)
• ?Clmax

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• Step 5 compute the required value of incremental
  section lift coefficient, ? Cl, which the flaps
  must generate and relate this value to flap type,
  flap angle and flap chord.
• Guess From p172/173
• Cf/C dfTO deg. dfLdeg.
• Then
• From figure 7.4
• By assuming Cf/C, then from figure7.4/p172, K is
  given
• ?Clmax is calculated from previous step then ?Cl
  is calculated
• Takeoff flaps landing flaps
• (Swf/S)
• ?Cl

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WE ARE ALMOST THERE !
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Design of the empennage

• Step 1 Decide on the overall empennage
  configuration
• Step 2 From the fuselage drawing Xh, and Xv are
  guess estimated see p189/II. Figure 8.1.
• Step 3 From tables p197/II, select Vh, Vv.

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• Step 4 Given the wing area S, cord length c, and
  the span b. we calculate the area of the
  horizontal and vertical tail Sh Sv
• Sh Vh Sc/Xh eq8.3 p190/II
• Sv Vv Sc/Xv eq8.4 p190/II
• Step 5 Decide on the following parameters
• Aspect ratio, Sweep angle, Taber ratio p207/II
• Step 6 Prepare a dimensional drawing. And
  document the results.

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Design of the landing gear p217/II

• Step 1 decide on which landing gear system to
  use.
• - Fixed
• - Retractable
• Note As a general rule, if the cruse speed Of
  the airplane above 150 kts, a fixed landing gear
  imposes an unacceptably high drag penalty

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• Step 2 Decide on the overall landing gear
  configuration.
• - Tricycle (i.e. conventional)
• - Tandem
• - Tail wheel

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• Before embarking on the next steps, it will be
  necessary to determine the c.g. rage of the
  airplane.
• There are two geometric criteria which needed to
  be considered in deciding the disposition of the
  landing gear p218/II
• - Tip over Criteria Figure 9.1a
  p219/II
• - Ground Clearance Figure 9.1b
  p219/II
• Due to the lack of time, and manpower the
  following steps has been omitted
• Just assume the c.g. location and draw the
  landing gear.

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Method for estimating airplane component weights
p3/V

• Step 1 List the weight values for the airplane
• (i.e. Wto, We, Wpl, Wcrew, Wf)
• Step 2 From the same aircraft type Identify
  weight fraction from appendix A.
• Step 3 Multiply the selected weight fractions by
  the Wto

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Weight Fraction for the B737-200

• Power plant 0.071
• Fixed equipment 0.129
• Flight control and electrical system
• Auxiliary power unit (APU)
• Furnishings ..etc.
• Empty weight 0.521
• Wing group 0.092
• Empennage group 0.024
• Fuselage group 0.105
• Nacelles 0.012
• Landing gear group 0.038

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Systems Definition

• System list
• 1. Flight control
• 2. Fuel control
• 3. Electrical
• 4. Anti-icing
• 5. Trim system
• 6. High lift control
• 7. Propulsion control
• 8. Pressurization
• 9. Cockpit instrument control
• 10 Flight management and avionics

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• 11. De-icing
• 12. Escape system
• 13. Water and waste
• 14. Fire extinguishing
• 15. In flight refueling
• 16. Hydraulic
• 17. Pneumatic
• 18. Air conditioning
• 19. Oxygen
• 20. Antenna
• 21. Rain removal and defog

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Definition of Cost, Price, and Profit

• COST amount of expenditure needed to manufacture
  the airplane
• PRICE amount paid for the airplane by customer
• PROFIT PRICE COST

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Airplane life cycle

• Planning and conceptual design
• Preliminary design
• Detail design
• Manufacturing
• Operation and support
• Disposal

RDTE Research, Development, Test, and Evaluation
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Operating Cost Break Down
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Operation and support cost

• Total Operation Cost ( TOC )
• Indirect Operation Cost ( IOC )
• Direct Operating Cost ( DOC )
• TOC DOC IOC
• Ways to quote DOC
• /n.m.
• /hr

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Example 1000nm domestic trip 60load factor
(1985)
IOC
DOC
Cost brake down Boeing B737-200
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Direct Operation Cost (DOC) /n.m.

• Direct Operating Cost of Flying
  DOCfly
• Direct Operating Cost Maintenance
  DOCmain
• Direct Operating Cost of Depreciation
  DOCdep
• Direct Operating Cost Of (Landing fees,
  Navigation fees, Taxes) DOClnt
• Direct Operating Cost of Financing
  DOCf
• Direct Operating Cost DOC DOCfly DOCmain
  DOCdep DOClnt DOCf
• DOCfly DOCmain is about 80 of DOC

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Direct Operating Cost of Maintenance

• Labor cost airframe and system
• Clab/ap 1.03 (MHRbl) (R) / V
• MHRbl is the number airframe and systems
  maintenance man hr. needed per block hr.
• MHRbl 3 (0.067 WA)/1000 p95/VIII V is the
  speed in n.m /hr R airline maintenance labor
  rate per man-hour in /hr.
• Ne Number of engines WA WE - Ne Weng
• Labor cost of engine
• Clab/eng 1.03 (1.3) (Ne) (MHRmeng) (Rlg) / V
• MHRmeng MHRbl (0.1/.9) p94Rleng airline
  maintenance labor rate per man-hour in /hr.
• Cost of maintenance materials for the airframe
  and systems
• Cmat/ap 1.03 (Cmat/apbl) / V
• Cmat/apb30 (CEF/CEF1989)0.7910-5AFP p99
• AFPAEP-Ne (EP) where EP engine price. In AEP
  aircraft estimated price assume 20M AFP
  airframe price
• Cost of maintenance materials for the engines
• Cmat/eng 1.03 (1.3) (Ne) (Cmat/engbl) / V
• (Cmat/engbl) 5.43 10-5 EP 1.5 - 0.45
  p100
• Maintenance burden
• Assumed to be zero
• DOCmain Clab/ap Clab/eng Cmat/ap
  Cmat/eng

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Direct Operating Cost of Flying

• Crew
• CcrewS ncj (1kj)/Vbl (SALj/AHj)(TEFj/Vbl)
  p82/VIII
• ncj Number of crew of each type V speed in
  n.m/hr
• Kj Factor that account of items as vacation, and
  training it is suggested to use kj0.26
• SALj Annual salary paid SALj2006SALjCEF2006/C
  EF1990 see table 5-5 p85/VIII
• SAL1 for a captain 70.000 /year SAL2 for the
  first officer 55.000 /year
• AHj Number of flight hours per year assume
  AHj750 hr/year
• TEFj Travel expense factor assume
  TEFj2006TEFjCEF2006/CEF1990
• For CFE2006/CEF see Figure 2.7 p20/VIII assume
  CFE2006 4 and CFE 3
• Fuel and Oil
• Cpol 1.05 (WF/R) (FP/FD)
  p89/VIII
• Wffuel weight lb R Range in n.m
• FPprice of fuel see Figure 5.3 p87 assume
  FP1.5 /gallon
• FDfuel density FD6.7 lbs/gallon p88
• Insurance
• Cins 0.02 (DOC) assume to be 0.239 /n.m
• DOCfly Ccrew Cpol Cins

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Direct Operating Cost landing fees, navigation,
and registry taxes

• Landing fees
• CifCaplf / (V.t)
• Caplf0.002 Wto
• Caplf airplane landing fee per landing
• Navigation fees
• CnfCapnf / (V.t)
• Capnf the navigation fee charged per airplane
  per flight
• Assumed 0 for domestic flight and 10/flight
• Taxes
• Crtfrt (DOC)
• frt0.00110-8Wto
• frt factor
• DOCmain Cif Cnf Crt

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Before Descent
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Landing