what went wrong? - american institute of aeronautics … de havilland dh 106 comet • comet 1:...

What Went Wrong?Why some commercial aircraft programs

didn’t live up to expectations

AIAA Southern California ASAT

Conference

April 30, 2016

Tony Hays

California State University Long Beach

2

“Those who cannot remember the past

are condemned to repeat it”

– George Santayana

2016-04-28

Selected Programs

• De Havilland Comet

• Lockheed Electra

• Convair 880/990

• De Havilland Trident

• Vickers VC10

• Dassault Mercure

• BAC/Sud Aviation

Concorde

• Lockheed L-1011

• VFW-Fokker 61

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1: de Havilland DH 106 Comet

• Comet 1: First flight July 1949

• Entered service May 1952

• Pax: 36-44 Range: 1,300

nmi.

• Two aircraft broke up in flight

in 1964

• Comet 4 entered service in

1958, with 30 year service life

4

Source: www.extremetech.com

Comet 1

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Conceptual Design Studies

5

Source: wikipedia commons

2016-04-28

6

Source: Gunston ‘Commercial Aircraft’

Comet Nacelle Cutaway

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Engines Embedded in Wing Root

7

• V-bomber triad – Vulcan, Valiant, Victor

• First generation of strategic jet bombers

• Contemporaneous with B-47

• British obsession with minimizing wetted area at

expense of everything else

Source:www.telegraph.co.uk Source: en.wikpedia.org

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© Nathan Daws Source: airliners.net

B-47

8

Source: www.aviation-history.com

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Uncontained Engine Failure

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Uncontained Engine Failure

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Source: www.catia.net

Comet Accident Investigation

• Fatigue failure of

frame of escape

hatch

11

Source: www.greatwen.com

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12

Source: www.fugahumana.com

Comet Accident Investigation

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Comet Lessons Learned

• Do as many trade

studies as time and

money permit

• Include the “-ilities”

– Supportability

– Reliability

– Maintainability

– Vulnerability

13

• Design for derivatives

– Payload

– Range

– Propulsion system

• Be prepared for

“unknown unknowns”

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2: Lockheed L-188 Electra

• First flight Dec 1957

• First US commercial

turboprop

• Up to 80 pax / 1,913 nmi.

• Wing root fatigue failure in

Sept 1959 and March 1960

due to loosened engine

mounts

• Public lost faith

• Production ended in 1961 at

170 aircraft

14

Source: commons.Wikimedia.org

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Electra Preceded by Vickers Viscount

• First flight 1948

• Entered service 1950

• 4 X R-R Dart turboprops

• Up to 75 pax / 1200 nmi.

• Total production of 445

15


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1945 1955 1965 1975 1985 1995 2005 2015

De Havilland Trident

Boeing 727

Vickers Vanguard

Lockheed Electra

Vickers Viscount

Service Period and Production Quantity

16

Data source: Wikipedia

2016-04-28

1,832

170

44

445

179

Electra Eventually Replaced by B.727

• Up to 189 pax

• Design development

~1960

• First flight Feb 1963

• Entered service Feb 1964

• Production ended in 1984

with 1,832 aircraft built

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Source: theairlines.net

Success as P-3 ASW

• Total of 734 built

• Eventually to be replaced

by Boeing P-8A (IOC in

late 2013)

18

Source: US Navy

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Model 188 Lessons Learned

• Meet customers’ expectations (they wanted jet

comfort and low vibration levels)

• Too late for a large turboprop (at first flight,

Viscount had been operational for 7 years)

• Be lucky, your design may just have other

applications

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3: Convair 880/990• First flight Jan 1959

• Belated attempt to enter

four-engine transport

market (B.367-80 first flight

in July 1954)

• Five abreast seating

– CV 880 110 pax / 2,943 nmi.

– CV 990 149 pax / 3,124 nmi.

• Mcruise = 0.91 (CV990)

• Production

– CV 880 65

– CV 990 39

20

Source: commons.wikmedia.com

Convair CV 990

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Application of Kücheman

Carrots

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Source: aviation.stackexchange.com

Strong shock on upper surface Shock reduced

GE CJ805-23 Turbofan

22

Source: www.military.ir

• Fan stage at rear of engine

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Convair 880/990 Competition

• Boeing 720

– first flight Nov 1959

– 149 pax (one class)

– Range 3,680 nmi.

• Boeing 727-100

– First flight Feb 1963


• Boeing 727-200


23

Source: commons.wikmedia.com

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1955 1965 1975 1985 1995 2005 2015

Vickers VC10

Convair 880/990

Douglas DC-8

Boeing 707

Service Period and Production Quantity

24

Data source: Wikipedia

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556

104

1010

54

Convair 880/990 Lessons

Learned

• Too late to the party

• Difficult to find niche on payload-range plot that

can’t be filled by derivative of another aircraft type

• GE805 had higher SFC than PWC JT-3C on 707

• Higher cruise Mach didn’t result in significant

reduction in operating cost

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4: De Havilland DH 121 Trident

26

Source: century-of-flight.net

• First flight Jan 1962

• Designed to 1957 BEA

requirement for 88 pax

• 3 R-R Speys

• Trident 1: 101 pax

• Range: 1,170 nmi.

• Entered service March 1964


with 179 aircraft

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Trident 3B

UK Government and Flag Carriers

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Trident Handicaps

• UK government insisted on merger with losing competitor

(to form Hawker Siddeley)

• Too small for worldwide market

• Shared design details with Boeing

• Long flight test cycle (two years vs. one for Boeing)

• Low production rate (12/year vs. 80-100 for Boeing)

• Limited growth potential (couldn’t re-engine)

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Trident 3B had 3½ Engines

29

Source: www.airliners.net

• 3 R-R Speys

Fn = 3 x 11,960 lb.

• 1 RB.162 Fn = 5,250 lb

– Designed as lightweight

lift jet

– Added 15% takeoff thrust

with 5% increase in

TOGW

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© Paul Markman

Trident Lessons Learned

• Don’t allow launch customer to dictate specs

• Don’t show design details to a competitor

• Commit manpower and facilities for quick entry

into service and adequate production rate

• Design for growth in MTOGW

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5: Vickers VC10

31

Source: wikimedia

• First flight June 1962

• Designed to BOAC

requirement ‘hot and high’

airfields on Empire routes

• 4 R-R Conways

• Entered service April 1964


with only 54 aircraft

manufactured (inc. Super)

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VC10 Characteristics

• Clean wing (Vapp approx. 10 kt less than 707)

• Low cabin noise

• BOAC calculated DOC/pax mile ~3% higher than for

707 (and made this public)

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VC10 707-320

TOFL [ft] 8,280 ~10,800

LFL [ft] 6,380 ~7,500

Field Performance

Source: airliners.net Source: Boeing Performance Manual

Wing Root Bending Relief

• Engines mounted on

wing reduce wing root

bending

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Boeing 737

Fuselage And Wing Root Bending

• Additional wing

and fuselage

bending

• Cabin not centered

over wing

• Made worse by

– Stretched fuselage

– Higher BPR

(heavier) engines

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McDonnell Douglas MD-80

Larger C.g. Travel

35

Douglas DC-9-20

• C.g. moves

forward as

aircraft is

loaded

• Problem made

worse with

heavier

engines

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Source: Schaufele

More Difficult to Control C.G. Location

• C.g. location is aft at OEW and forward at MTOGW

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More Difficult to Control C.G. Location

• When defueling, remove fuel from fin tank first

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RAF Brize Norton, Dec. 1997

© Crown Copyright

© Crown Copyright

VC10 Handicaps

• We/Wto = 0.47 compared with 0.44 for B707-320

• Higher cruise drag than predicted due to nacelle/pylon

geometry

• Runways lengthened to accommodate 707/DC8

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• Geometry modified to

maintain (or increase)

isobar sweep at wingtip

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Added Küchemann Wingtips

Source: Küchemann, Aerodynamic Design of Aircraft

Source: http://www.airliners.net/aviation-

forums/general_aviation/print.main?id=6249338

DH Trident 2E modIsobar comparison

VC10 Nacelle and Pylon Mods.

• Extended fairing between engine nacelles

• Extended pylon trailing edge

• Moved nacelles outboard

• Eliminated inboard thrust reversers

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Before After

VC10 Uncontained Failure

41

http://www.vc10.net/History/incidents_and_accidents.html#Engine Disintegrates

• Departed LHR, Nov 1969

• LP turbine blades shed from

No. 3 engine

• Penetrated No. 4 engine

which caught fire (quickly

extinguished)

• Returned to LHR 90K lb over

max landing weight

• Blew fusible plugs

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VC10 Lessons Learned

• Don’t allow launch customer to dictate specs

• Don’t allow a penalty in payload-range unless

commensurate benefit is justified

• Take account of potential changes in the operating

environment

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6: BAC/Aerospatiale Concorde

43


• First flight March 1969

• UK-French government joint

development agreement in

Nov 1962

• 90-120 pax

• Range 3,900 nmi.

• Cruise Mach 2.02

• 4 X B-S Olympus Mk 593

• Production ended at 20 a/c

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Concorde Handicaps

• Development cost 6X original estimate

• Flown supersonically only over water

• 1973 oil shortage deterred buyers

• 15.8 pax miles/gal, compared with B707 33.3 pax

mpg, B747 46.4 pax mpg, DC-10 53.6 pax mpg

• Banned from operation at some airport because of

perceived noise

• In July 2000, AF Concorde crashed at CDG due to

fuel leak/engine fire

• Withdrawn from service 2003

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Concorde Accident at CDG

• In July 2000, AF Concorde crashed at CDG due to

fuel leak/engine fire

45

Source: en.wikipedia.org

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More Concorde Handicaps

• Government to government contract prevented

unilateral withdrawal

• Development costs not adequately controlled

• Profitable operation doubtful, even before 1973 oil

crisis

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Concorde Lessons Learned

• Manufacturers must take responsibility for

success or failure

• There is a big difference between

technological possibility and economic viability

• Safety is paramount

• Pioneers may get all the glory, but they rarely

make all the money

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7: Lockheed L-1011 Tristar

48

Flight test aircraft at Palmdale

• Designed to AA requirement

for ORD-LAX, LGA-ORD

• Capable of operation from

LGA (7000 ft)

• 3 X R-R RB.211

• New production facilities at

Palmdale, CA

• First flight Nov 1970


with 250 aircraft

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Source: www.airlinereporter.com

L-1011 Direct Lift Control

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Source: © DIASpotter

With landing flaps

deployed, spoilers linked

to control column for direct

control of rate of descent

L1011 Direct Lift Control

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Source: www.flightaware.comr

Direct control of rate of

descent without changing

pitch attitude

L-1011 Maneuver Load

Control/Gust Alleviation

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Source: Lockheed

Deflect ailerons t.e.

up to reduce wing

root BM during

maneuver or gust

Overall lift

unchanged

e is reduced

Enables higher wing span (and reduced drag) for

same maximum wing root bending moment

L-1011 All-moving Horizontal Tail

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Source: Green & Swanorough, Commercial Aircraft

Triple-redundant

horizontal tail

hydraulic actuators

Typical T/W vs. W/S plot

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Triple-redundant

horizontal tail

hydraulic actuators

Typical T/W vs. W/S plot

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L-1011-1

124 lb/ft2DC-10-10

118 lb/ft2

L-1011 Handicaps

• Almost identical mission requirement to DC-10

– Fierce competition for sales

– Offered too cheaply

• Bankruptcy of Rolls-Royce during development

• Uneven production required training new labor

• Production facilities too far from source of labor

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History behind Rolls-Royce Downfall

56

CX-LHS Program (1963)

Boeing CX-LHSDouglas CX-LHS

Lockheed C-5AGE TF-39 P&W JT-9D

GE CF-6

Boeing 747-100 Douglas DC-10 Lockheed L-1011 Airbus A300(UK-France MOU signed 1967)

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Difficult to Recruit Labor

57

Source: Google Maps

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Lockheed Plant 10

58

http://www.astrosurf.com/luxorion/vaisseaux-falcon-sls-dragon-orion2.htm

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Theoretical Scissors Plot

59

• Development cost ~$5 B

• Aimed for breakeven at

250 aircraft

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Actual Scissors Plot

60

• Early sale price

reduced to build market

share

• 50 aircraft sold to Air

Holdings Ltd

• When production

picked up, new

employees had to be

trained

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L-1011 Lessons Learned

• Don’t go head to head with an identical

product

• Design for different engine options

• Design for growth in MTOGW

• Build airplane near skilled labor pool

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8: Dassault Mercure

62

Source: wikimedia

• First Dassault airliner

• First flight May 1971

• Designed for 120 – 162 pax

• Stage lengths up to 1100

nmi.

• 2 X JT-8D

• Entered service June 1974

• Production ended in 1979 at

54 aircraft (inc. Super)

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Dassault Mercure Handicaps

63

Source: wikimedia

• Dassault not a recognized

commercial a/c manufacturer

• No significant performance

improvement over B737

• DC-9-50 matched payload-

range of Mercure 100

• We/Wto = 0.57 compared with

0.52 for B737-200

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Mercure Lessons Learned

• Difficult for an unknown commercial

aircraft manufacturer to break into an

established market

• Derivative designs can fill market holes

more cheaply than new designs

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9: VFW-Fokker 614

65


• First flight July 1971

• DC-3 replacement

• 40 – 44 pax

• Range with 40 pax = 645 nmi.

• 2 X R-R/Snecma M45H

turbofans

• Production ended in Dec 1977

with 16 airplanes

• Last flight Dec 2012

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VFW 614 Field Performance

66

Source: http://www.vfw614.de/die_vfw_614_e.html

• Better field performance than DC-3

• Not true STOL (2000 ft TOFL)

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http://www.vfw614.de/die_vfw_614_e.html

Engines Mounted on Top of Wing

• Advantages

– Wing root bending relief

– Short landing gear and airstairs

– Protection from FOD

– Fan noise reduction on ground

• Disadvantages

– Reduced length of t.e. for flaps

– Inlet in high-speed flow

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HondaJet

Hybrid Wing Body

• Lockheed Martin studies

started in 2009

• Carries outsized cargo

lifted by C-5

• Burns 70% less fuel than

C-17

• Over-wing nacelles permit

very-high-BPR engines

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VFW-Fokker 614

source: aviationweek.com

Operating Cost Comparison

69

Seats: Wikipedia

DOC: https://www.flightglobal.com/FlightPDFArchive/1968/1968%20-%200119.PDF

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2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

2.9

3

0 20 40 60 80 100 120

DO

C/s

ea

t m

ile

Maximum seats

Trends in DOC/seat mile vs. Capacity

VFW-614

FH-228

HS.748

F.28

DC-9-10

VFW 614 Handicaps

• DC-3 was cheap and ubiquitous

• VFW 614 had higher price, higher fuel burn

• Rolls-Royce bankruptcy in Feb 1971

• Lost test a/c due to elevator flutter in Feb 1972

• VFW not known as commercial aircraft manufacturer

• Rolls-Royce (Bristol Siddeley) M45H was a new engine

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VFW 614 Lessons Learned

• Very difficult to design viable aircraft at bottom

end of market that meets FAR 25 (i.e., > 20 pax,

or > 12,500 lb TOGW)

• Keep to design goals (including costs)

• Try not to introduce new airframe from unknown

manufacturer with new engine

• Don’t build a Mercedes Benz when a VW is

wanted

712016-04-28

Conclusions

• Be prepared for

“unknown unknowns”

• Do impartial trade studies

• Ensure performance

capabilities will be

utilized

• Don’t compete with an

identical product

• Design for derivatives

• Don’t compete where an

existing product is well

established unless your

product is demonstrably

superior

• Ensure technology is

proven

• Safety is paramount

• Be lucky

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The EndThanks for your interest

2016-04-28

what went wrong? - american institute of aeronautics … de havilland dh 106 comet • comet 1:...

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