Cabin Design

Jan 05 Section 5 – Design Morphology & Preliminary Integration Copyright 2005 by Askin T. Isikveren All Rights Reserved

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Section 5(ii)Design Morphology & Preliminary Integration

Cabin Layout & Fuselage Design


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Cabin Layout & Fuselage Design

General OverviewAll transport aircraft design efforts focus on a philosophy of synthesis and integration from the “inside – out”Geometric definitions dictated by cabin and cockpit ergonomics and functionality determines the cross-section and overall fuselage slenderness

Cabin Layout DefinitionCross-section (seats abreast, personal comfort, ergonomics)WindowsDoors and stairsEnvironmental climate control, air conditioning and sound proofingSeats installation and stowageLavatories, galleys and wardrobesOperational equipment and servicing facilitiesEmergency egress and emergency equipment

Interior Layout ConsiderationsIdentification of the aircraft mission role, i.e. commercial or business applicationPassenger accommodationNumber of flight attendants (therefore seats); general rule is to assume

1 for every 45 PAXThere should always be room for at least 2

Duration of the longest mission; this information will assist in defining the number of meals, hence, required galley spaceThe number of lavatories; general rule is approximately

1 lavatory per 50 PAX for commercial flights economy class1 lavatory per 6 PAX for commercial flight business/first class1 lavatory per 12 PAX for business aircraftIntroduction of an additional lavatory is required for business aircraft flying more than 8 hours (corresponding to facility for crew rest area)

Lavatory width should be no less than 33”


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Cabin Layout & Fuselage Design (cont.)

Seat Pitch - industry surveys show29”-30” for high density economy and up to 33” for “super economy”32” is the industry standard for economy classBusiness class is 34-38”First class is 38-45”For cabins outfitted with sleeper berths 50-72”Business aircraft with club seat arrangements should have seating length of at least 90”

Establishing the Cross-SectionAlgorithm to define wall thickness from outside Outer Mold Lines (OML) to inside wall in the cabin (structure and insulation)

Fuselage diameters up to 70” assume wall thickness of 2.5”Fuselage diameters 70-90” assume wall thickness of 3.5” Fuselage diameters 90-140” assume wall thickness of 4.5”Fuselage diameters larger than 140” assume wall thickness of 5.0” or moreAn additional 0.5” thickness should be incorporated for business aircraft due to more stringent requirements for noise abatement in the cabin

Other useful dimensions areThe lavatory wall should be at least 0.75” thickThe forward/aft galley walls should be 1.0” thick and the inboard/outboard 0.50” thickThe wall for wardrobes are suggested to be 0.50” thick

Width of SeatsTarget minimum design width between armrests should be 18”Minimum design width of armrests is often declared as 2” for economy class

Minimum aisle width is defined by rules under FAR 25.815Passenger seating capacity of 10 PAX or less should have 15”Greater than 20 PAX should have 20”

Carry-on BaggageThe general tendency is for passengers to carry more and more baggage onboard, thus, overhead stowage bins require particular attentionA good target is to stow a standard carry on luggage lengthwiseThe standard IATA carry-on bag is defined as 21.7” x 15” x 7.9”Under-seat volume is suggested to be 1.6-1.8 cu.ft, and, overhead bins are recommended to be at least 2.0 cu.ft per PAX


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Key:G: GalleyW: WardrobeS: StowageL or LAV: Lavatory

Definition of cabin and cross-section sizing parameters required for conceptual design (commercial transport)


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Definition of cabin and cross-section sizing parameters required for conceptual design (business aircraft)

Key:W: Wardrobe


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Window DesignMajor consideration for windows

Maximise natural lightingMaximise the exterior viewing for a wide range of passenger sizes and seat pitches

Generally want to permit >50° of swept sight for a 50-percentile female

There are two approachesRectangular windows spaced between each fuselage frame (therefore restricted cutout width) over the seating length of the cabinLarge oval-shaped windows interrupting fuselage frames resulting in fewer number of cutouts over the seating length of the cabin

Although it is not easy to achieve, for commercial aircraft it is most desirable to have a window for each seat row for various seat pitches and multiple class layouts


Primary geometric considerations for window sizing and placement

a

b

c

dw

x

y

z

A

B

C


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14 x 105000018-30Corporate Shuttle

data not available<20000<20Air-taxi

data not available35000-4700020-49Commuter

14.5 x 10.5 14 x 10

50000-9000050-89Regional

16 x 10 14 x 10 13 x 9

95000-17500090-189Narrow-body

Window Size (H x W) in inches

Max. Takeoff Weight (lb)

Accommodation (PAX)

Category

data not available<100005-6Personal / Micro

19 x 11>300000>200Wide-body

19 x 26 16 x 11 16 x 10 14 x 10 13 x 9

95000-17400013-189Ultra Long-Range

19 x 26 16 x 12 16 x 11

48000-8800012-19Super-Large

19 x 26 16 x 12 14 x 10

41000-480009-19Large

16 x 11 15 x 12

35000-400008-19Super-Midsize

15 x 12 14 x 10

24000-300008-12Midsize

14 x 1020000-210008-11Super-Light

14 x 1014000-200007-11Light

12.5 x 9125006-8Very-Light

Basic survey of window cutout sizes for transport aircraft


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Gauging the Comfort of a Cross-sectionOne visual method to understand the level of passenger cabin comfort is obtained by using a so-called “spider plot”The spider plot is a visual method to compare numbers (usually from a comparison table) using a percentage for each data categoryEach category represents a radius of the spider plot

For each branch, 0% (minimum) data and 100% (maximum) data is shownThe 0% and 100% data are based on certification rules and on what is currently offered in the market respectivelyThe idea is to maximise the area contained within the polygon and avoid 0% ratings on any of the radii

Example of cabin comfort measurement using a spider plot


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Cabin Layout & Fuselage Design (cont.)Cabin comfort categories

Seat pitchSeat width between armrestsPassenger width distance (seat centerline to seat centerline)Shoulder clearance with sidewall (from 95 percentile US man)Head clearance with sidewall (from 95 percentile US man); head clearance from bottom of overhead bin may also be design driverAisle widthAisle heightShoulder clearance with sidewall (from 95 percentile US man)

A definition of each category is given below

Passenger DefinitionThe passenger is generally represented by a 95 percentile US male that corresponds to a height of 73”The human scale dimension, as well as the relationship between weight and seat cushion compression were taken from “Humanscale” Body Measurements by Henry Dreyfuss Associates

Seat Width between Passenger width Shoulder Head clearance Aisle Aisle Head clearancepitch armrests distance clearance with with width height with bin

(center to center) sidewall sidewall

0% 29" 16" 18" 0" 1" 15" 70" 1"

100% 33" 20" 22" 4" 6" 20" 84" 12"

95 percentile US male (73 in. in height); envelop about head andshoulder denotes recommended zones of comfort


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Emergency ExitsEmergency exit location will have significant impact on the interior layout

They must abide by stipulated row widths and are not permitted to be moved around for different seating arrangementsAccordingly, great care has to be taken in their placement and their impact on various seating configurations

The minimum width of access for each door as well as the step-up and step-down heights need to be checked (where applicable)

Emergency door definitions must abide by rules outlined in FAR 25.807 and FAR 25.813

Emergency exits should never be located more than 60 ft from each other on the same sideFor emergency exits serving a “dead-end” area (seats located rear of the last doors) only 75% of the emergency exit capacity can be claimed

For example, two Type III per side, with less than 3 rows between, will allow a maximum capacity of 65 PAX instead of 70 PAX

Although emergency egress analysis may be quite involved, for conceptual design, it is recommended to use at least 20” free row width for Type III exitsEmergency escape slides must be provided

Whenever any emergency exit lower sill is higher than 6 ft from the ground with the gear extendedIn the case of over-wing emergency exits

If the trailing edge of the flap in normal takeoff configuration is higher than 6 feet emergency slides will have to be providedTheir usual location is in the belly fairing and they are automatically deployed when the associated over-wing exit it opened

For aircraft with more than 19 PAXOne overhead emergency escape hatch has to be provided for the flight crew with dimensions of at least 19” x 20”Alternatively, opening windows of similar dimensions must be located on both sides of the aircraft

These are usually referred to as Direct Vision (DV) windowsThey can be opened during the approach phase in case of windshield obscuration

Jan 05Section 5 –

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Cabin Layout &

Fuselage Design (cont.)

Summary of regulations pertaining to emergency exits according to FAR25.807


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Head Injury CriterionSeats just aft of a hard bulkhead must maintain a certain distance to avoid serious injury to those passengers in case of a crashHIC analysis is quite involved since it depends on how “hard” the bulkhead structure isDuring the conceptual design phase, the following rule is suggested

Distance between the forward passenger bulkhead and the intersection of the seat pan and the seat back of the first seat should be at least 40”Alternatively, a minimum of 25” between both the hard partition and front of the seat

General Presentation of the Interior LayoutCabin floor planCabin cross-section showing 95 percentile US maleTable of data including comparison against other aircraft covering

Number of PAXSeat pitchNumber of galley carts and galley volumeOverhead bins volume

Example of a DV window on the Falcon 50EX


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Cabin Layout & Fuselage Design (cont.)Wardrobe volumeTotal carry-on baggage volume (bins + wardrobe)Baggage compartment volume (checked baggage)Cabin volume (generally from cockpit divider to aft cabin)

Other detail drawings such as a side view at the overwing door

A340 ultra-long-haul wide-body cabin interior


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Illustration of interior layout design, both schematic and actual, and, cabin cross-section of Falcon 900C business aircraft


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Rotor burst zone is defined in 3-DRefers to the disintegration of the high speed rotating turbo machinery; this may refer to the main engine and to the APUSmall fragment and fan blade dispersion zone is described by a cone with 15° slant with apex corresponding to the intersection of the fan axis of rotation and fan planeHigh-energy dispersion zone (intermediate size fragments) is assumed to be a cone with 5° slant, apex locale as with small fragment zone It is always good design practice to ensure the passenger seating area is not within the rotor burst zoneHigh-energy dispersion zone cannot interrupt any fuel tanks

Underwing podded engine installations may require the incorporation of a so-called “dry bay” in the wing if the high energy dispersion zone (defined usually by the low-pressure turbine) cuts into any fuel stored aft of the front spar

Other critical systems that affect flight control signalling and/or actuation need to be carefully examinedAdopting an asymmetrical design can actually be detrimental

15° Small Fragment Dispersion Zone

Do not need protected baggage compartment

5° High Energy Dispersion Zone


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There are special rotor burst considerations for aircraft that conduct high altitude operations (above 41,000 ft)

It is easier to meet certification requirements of high altitude operation for an aft fuselage mounted engine configuration provided small fragment trajectory clears the pressure vesselAny other configuration requires heavy shielding; this will incur a large weight penalty

Small and fan blade fragment dispersion zone is permitted to interfere with the baggage area or the lavatory, providing

There is the introduction of a secondary pressure bulkheadSpecial rules during operation are administered, e.g. door must be closed by crew member after 5 minutes of being opened

Information on rotor burst compliance is found in the FAA Advisory Circulars AC25-20 and AC 20-128

15° Rotor Burst Dispersion Zone

Must have protectedbaggage compartment


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Additional ReadingFedEx Fleet and Container Information, 1996

hal90001


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End of Additional Reading

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Cabin Design