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weight and performance calculations for the De Havilland D.H.106 Comet I
BOAC Comet 1 G-ALYP
De Havilland D.H.106 Comet I
role : jet airliner
importance : ****
first flight : 27 July 1949 prototype G-5-1 at Hatfield,flown by John “Cats Eyes”
Cunningham opertational : 02 May 1952 BOAC G-ALYP
country : United-Kingdom
design : led by Ronald Bishop
production : 12 aircraft at Hatfield aerodrome
general information : (mainly taken from Wikipedia)
The Comet was the world's first commercial jet airliner . For the era, it offered a
relatively quiet, comfortable passenger cabin and was commercially promising at its
debut in 1952.
As the Comet represented a new category of passenger aircraft, more rigorous testing was a development priority. From 1947 to 1948, de Havilland conducted an extensive research and development phase, including the use of several stress test rigs at Hatfield Aerodrome for small components and large assemblies alike. Sections of pressurised fuselage were subjected to high-altitude flight conditions via a large decompression chamber on-site and tested to failure. Tracing fuselage failure points proved difficult with this method, and de Havilland ultimately switched to conducting structural tests with a water tank that could be safely configured to increase pressures gradually. The entire forward fuselage section was tested for metal fatigue by repeatedly pressurising to 2.75 pounds per square inch (19.0 kPa) overpressure and depressurising through more than 16,000 cycles, equivalent to about 40,000 hours of airline service. The windows were also tested under a pressure of 12 psi (83 kPa), 4.75 psi (32.8 kPa) above expected pressures at the normal service ceiling of 36,000 ft (11,000 m). One window frame survived 100 psi (690 kPa), about 1,250 percent over the maximum pressure it was expected to encounter in service. The original Comet was the approximate length of, but not as wide as, the later Boeing 737-100 , and carried fewer people in a significantly more-spacious environment. BOAC installed 36 reclining "slumberseats" with 45 in (1,100 mm) centres on its first Comets, allowing for greater leg room in front and behind; Large picture window views and table seating accommodations for a row of passengers afforded a feeling of comfort and luxury unusual for transportation of the period. Amenities included a galley that could serve hot and cold food and drinks, a bar , and separate men's and women's toilets. Provisions for emergency situations included several life rafts stored in the wings near the engines, and individual life vests were stowed under each seat. One of the most striking aspects of Comet travel was the quiet,
"vibration-free flying" as touted by BOAC. For passengers used to propeller-driven airliners, smooth and quiet jet flight was a novel experience. Several of the Comet's
Comet I prototype registration G-5-1, later G-ALVG
avionics systems were new to civil aviation. One such feature was irreversible, powered flight controls , which increased the pilot's ease of control and the safety of the aircraft by preventing aerodynamic forces from changing the directed positions and placement of the aircraft's control surfaces . Many of the control surfaces, such as the elevators, were equipped with a complex gearing system as a safeguard against accidentally over-stressing the surfaces or airframe at higher speed ranges. The Comet had a total of four hydraulic systems : two primaries, one secondary, and a final emergency system for basic functions such as lowering the undercarriage. The undercarriage could also be lowered by a combination of gravity and a hand-pump. Power was syphoned from all four engines for the hydraulics, cabin air conditioning , and the de-icing system ; these systems had operational redundancy in that they could keep working even if only a single engine was active. The majority of hydraulic components were centred in a single avionics bay. A pressurised refuelling system, developed by Flight Refuelling Ltd , allowed the Comet's fuel tanks to be refuelled at a far greater rate than by other methods. The Comet's thin metal skin was composed of advanced new alloys and was both riveted and chemically bonded, which saved weight and reduced the risk of fatigue cracks spreading from the rivets. The chemical bonding process was accomplished using a new adhesive , Redux , which was liberally used in the construction of the wings and the fuselage of the Comet; it also had the advantage of simplifying the manufacturing process. When several of the fuselage alloys were discovered to be vulnerable to weakening via metal fatigue , a detailed routine inspection process was introduced. As well as thorough visual inspections of the outer
The Comet prototype (G-ALVG) had single main wheels, in production aircraft this was replaced by a 4-wheel bogie landing gear.
skin, mandatory structural sampling was routinely conducted by both civil and military Comet operators. The need to inspect areas not easily viewable by the naked eye led to the introduction of widespread radiography examination in aviation; this also had the advantage of detecting cracks and flaws too small to be seen otherwise. Operationally, the design of the cargo holds led to considerable difficulty for the ground crew, especially baggage handlers at the airports. The cargo hold had its doors located directly underneath the aircraft, so each item of baggage or cargo had to be loaded vertically upwards from the top of the baggage truck, then slid along the hold floor to be stacked inside. The individual pieces of luggage and cargo also had to be retrieved in a similarly slow manner at the arriving airport.
The Comet was powered by two pairs of turbojet engines buried in the wings close to the fuselage. Chief designer Bishop chose the Comet's embedded-engine configuration because it avoided the drag of podded engines and allowed for a smaller fin and rudder since the hazards of asymmetric thrust were reduced. The engines were outfitted with baffles to reduce noise emissions, and extensive soundproofing was also implemented to improve passenger conditions.
Placing the engines within the wings had the advantage of a reduction in the risk of foreign object damage , which could seriously damage jet engines. The low-mounted engines and good placement of service panels also made aircraft maintenance easier to perform. The Comet's buried-engine configuration increased its structural weight and complexity. Armour had to be placed around the engine cells to contain debris from any serious engine failures; also, placing the engines inside the wing required a more complicated wing structure. May 1952 BOAC started operating the Comet I, G-ALYP on service from London to Johannisburg. August 1953 BOAC scheduled the 9-stop flight from London to Tokyo at 36 hours with the Comet I. The same trip took 86 hours with BOAC’s DC-4 Argonauts piston-airliners.
Air France Comet IA F-BGNY
An updated Comet 1A was offered with higher-allowed weight, greater fuel capacity, and water-methanol injection; 10 were produced. Fuel capacity : 18144 [kg]. lay out was for 44 passengers. Max. range 6210 [km]. It Was used by Air France and UAT each acquired 3 Comet IA’s.
Work then continued on the Comet Mk.2, with a 0.94 [m] longer fuselage and more powerful Rolls Royce Avon engines. It was ordered by Air India, BCPA, Japan Air lines, Linea Aeropostal Venezolana and Panir de Brasil. The wings were a little larger and it had a higher fuel capacity. A total of 12 of the 44-seat Comet 2s were ordered by BOAC for the South Atlantic route. [158] The first production aircraft (G-AMXA) flew on 27 August 1953. [159] Although these aircraft performed well on test flights on the South Atlantic, their range was still not suitable for the North Atlantic
BOAC Comet Mk.2 G-AMXA
US carriers, Capital airlines, National Airlines and Pan Am placed orders on a planned Mk.3 variant which was even larger and with transatlantic range.
Within a year of entering airline service, problems started to emerge, three Comets being lost within twelve months in highly publicised accidents, after suffering catastrophic in-flight break-ups. Two of these were found to be caused by structural failure resulting from metal fatigue in the airframe , a phenomenon not fully understood at the time; the other was due to overstressing of the airframe during flight through severe weather. The Comet was withdrawn from service and extensively tested. Design and construction flaws, including improper riveting and dangerous concentrations of stress around some of the square windows, were ultimately identified. As a result, the Comet was extensively redesigned, with oval windows, structural reinforcements and other changes. Rival manufacturers heeded the lessons learned from the Comet when developing their own aircraft.
On 26 October 1952, the Comet suffered its first hull loss when a BOAC flight departing Rome's Ciampino airport failed to become airborne and ran into rough ground at the end of the runway. Two passengers sustained minor injuries, but the aircraft, G-ALYZ, was a write-off. On 3 March 1953, a new Canadian Pacific Airlines Comet 1A, registered CF-CUN and named Empress of Hawaii, failed to become airborne while attempting a night take-off from Karachi, Pakistan, on a delivery flight to Australia. The aircraft plunged into a dry drainage canal and collided with an embankment, killing all five crew and six passengers on board. The accident was the first fatal jetliner crash. In response, Canadian Pacific cancelled its remaining order for a second Comet 1A and never operated the type in commercial service.
The Comet's second fatal accident occurred on 2 May 1953, when BOAC Flight 783 , a Comet 1, registered G-ALYV, crashed in a severe thundersquall six minutes after taking off from Calcutta-Dum Dum (now Netaji Subhash Chandra Bose International Airport ), India, killing all 43 on board. Witnesses observed the wingless Comet on fire plunging into the village of Jagalgori, leading investigators to suspect structural failure.
Just over a year later, Rome's Ciampino airport, the site of the first Comet hull loss, was the origin of a more-disastrous Comet flight. On 10 January 1954, 20 minutes after taking off from Ciampino, the first production Comet, G-ALYP, broke up in mid-air while operating BOAC Flight 781 and crashed into the Mediterranean off the Italian island of Elba with the loss of all 35 on board. With no witnesses to the disaster and only partial radio transmissions as incomplete evidence, no obvious reason for the crash could be deduced. Engineers at de Havilland immediately recommended 60 modifications aimed at any possible design flaw, while the Abell Committee met to determine potential causes of the crash. BOAC also voluntarily grounded its Comet fleet pending investigation into the causes of the accident.
On 8 April 1954, Comet G-ALYY ("Yoke Yoke"), on charter to South African Airways , was on a leg from Rome to Cairo (of a longer route, SA Flight 201 from London to Johannesburg), when it crashed in the Mediterranean near Naples with the loss of all 21 passengers and crew on board. The Comet fleet was immediately grounded once again and a large investigation board was formed under the direction of the Royal Aircraft Establishment (RAE). Prime Minister Winston Churchill tasked the Royal Navy with helping to locate and retrieve the wreckage so that the cause of the accident could be determined. The Comet's Certificate of Airworthiness was revoked, and Comet 1 line production was suspended at the Hatfield factory while the BOAC fleet was permanently grounded, cocooned and stored.
In the wake of the 1954 disasters, all Comet 1s and 1As were brought back to Hatfield, placed in a protective cocoon and retained for testing. All were substantially damaged in stress testing or were scrapped entirely.
A large investigation was undertaken to determine the cause of the accidents. G-ALYU was submerched in a watertank at Farnborought to conduct stress test under water pressure. On 24 June 1954 after 3057 flight cycles G-ALYU burst open. The square windows and escape hedges gave more stress in the skin than expected. New variants of the Comet, but also other jetliners would get rounded windows in future. Now metal fatigue was better understood and fuselage could be made stronger with the new insights.
The Mk.II’s were rebuilt with heavier-gauge skin and rounded windows. The Avon engines got larger air intakes. All airlines had cancelled their orders on the Mk.2. With no airlines willing the Mk.2, 8 Mk.2’s were delivered to the RAF as military transport, under designation C2. Deliveries started in 1955.
RAF Comet 2C XK671 “Aquila” at RAF Waterbeach, note the revised rounded windows.
Although sales never fully recovered, the improved Comet 2 and the prototype Comet 3 culminated in the redesigned Comet 4 series which debuted in 1958 and remained in commercial service until 1981. The Comet was also adapted for a variety of military roles such as VIP, medical and passenger transport, as well as surveillance; the last Comet 4, used as a research platform, made its final flight in 1997. The most extensive modification resulted in a specialised maritime patrol derivative, the Hawker Siddeley Nimrod , which remained in service with the Royal Air Force until 2011, over 60 years after the Comet's first flight.
primary users : BOAC Comet IA : UAT, Air France, Canadian Pacific Airlines registrations : Comet I prototype : G-5-1, G-ALVG, second prototype G-ALZK (first flight July 1950), first production aircraft G-ALYP (first flight 9 January 1951), G-ALYS, G-ALYU, G-ALYV, G-ALYY, G-ALYZ (in service September 1952) Comet IA CF-CUN
flight crew : 4 cabin crew : 2 passengers : 36
flight crew consist of pilot, co-pilot, navigator and flight engineer
engine : 4 De Havilland Ghost 50 Mk1 turbojet engines of 22.5 [KN](5058.1 [lbf])
dimensions :
wingspan : 35.05 [m], length : 28.38 [m], height : 8.65 [m]
wing area : 188.3 [m^2]
weights :
max.take-off weight : 47620 [kg]
empty weight operational : 29000 [kg] useful load : 5670 [kg]
performance :
maximum continuous speed : 788 [km/u] op 10700 [m]
normal cruise speed : 725 [km/u] op 10700 [m] (35 [%] power)
service ceiling : 12800 [m]
range with max fuel : 2400 [km] and allowance for 223.3 [km] diversion and 30 [min]
hold
description :
low-wing cantilever monoplane with retractable landing gear with nose wheel
tapered multi-cellular wing with flush-riveted stressed skin
with Fowler flaps airfoil : NACA
sweep angle leading edge: 23.0 [°]
engines in the wingroot and landing gear attached to the wings, fuel tanks in the wings
and fuselage. construction : all-metal aluminium-alloy stressed-skin construction with
pressurized fuselage fuselage shape : O
calculation : *1* (dimensions)
measured wing chord : 5.05 [m] at 50% wingspan
mean wing chord : 5.37 [m]
calculated average wing chord tapered wing with rounded tips: 5.31 [m]
wing aspect ratio : 6.5 []
seize (span*length*height) : 8604 [m^3]
calculation : *2* (fuel consumption)
oil consumption : 45.0 [kg/hr]
fuel consumption (econ. cruise speed) : 3402.0 [kg/hr] (4361.5 [litre/hr]) at 35 [%]
power
distance flown for 1 kg fuel : 0.21 [km/kg] at 10700 [m] height, sfc : 108.0 [kg/KN/h]
estimated total fuel capacity : 17438 [litre] (12782 [kg])
calculation : *3* (weight)
weight engine(s) dry : 3648.0 [kg] = 40.53 [kg/KW]
weight 201.0 litre oil tank : 17.09 [kg]
oil tank filled with 0.6 litre oil : 0.5 [kg]
oil in engine 15.0 litre oil : 13.5 [kg]
fuel in engine 11.1 litre fuel : 8.10 [kg]
weight engine cowling 270.0 [kg]
total weight propulsion system : 3957 [kg](8.3 [%])
***************************************************************
fuselage aluminium frame : 7948 [kg]
typical cabin layout for 36 passengers : pitch : 81 [cm] ( 2+2 ) seating in 9.0 rows
pax density (normal seating) : 1.34 [m2/pax]
high density seating passengers : 68 at 4 -abreast seating in 16.9 rows
weight 1 toilets : 5.2 [kg]
weight 3 hand fire extinguisher : 8 [kg]
weight buffet : 24.8 [kg]
weight 20 windows : 18.0 [kg]
weight 4 emergency exits : 12.0 [kg]
weight 2 life rafts (dinghy) : 45.0 [kg]
weight oxygen masks & oxygen generators : 23.4 [kg]
weight 2 entrance/exit doors : 24.0 [kg]
extra main deck space for freight/mail/luggage etc. : 24.37 [m3]
cabin volume (usable), excluding flight deck : 93.92 [m3]
passenger cabin max.width : 2.78 [m] cabin length : 17.28 [m] cabin height : 1.90 [m]
pressure at cruise height 12192.00 [m] : 0.19 [kg/cm2] cabin pressure : 0.77 [kg/cm2]
weight rear pressure bulkhead : 134.1 [kg]
weight air pressurization system : 22.8 [kg]
fuselage covering ( 177.4 [m2] duraluminium 3.71 [mm]) : 1743.1 [kg]
weight floor beams : 90.9 [kg]
weight cabin furbishing : 141.7 [kg]
weight cabin floor : 320.4 [kg]
fuselage (sound proof) isolation : 150.8 [kg]
weight radio transceiver equipment : 7.0 [kg]
weight radio direction finding (RDF) equipment : 5.0 [kg]
weight artificial horizon : 1.1 [kg]
weight instruments. : 13.0 [kg]
weight APU / engine starter: 11.2 [kg]
weight lighting : 9.0 [kg]
weight electricity generator : 9.0 [kg]
weight controls : 13.0 [kg]
weight seats : 210.0 [kg]
weight 8719 [litre] main central fuel tanks empty : 488.3 [kg]
weight air conditioning : 54 [kg]
total weight fuselage : 11368 [kg](23.9 [%])
***************************************************************
total weight aluminium ribs (453 ribs) : 1698 [kg]
weight engine mounts : 45 [kg]
weight fuel tanks empty for total 8719 [litre] fuel : 488 [kg]
G-ALYU at Schiphol airport, Amsterdam, later this airframe would be used in underwater stress test at Farnborough.
weight wing covering (painted aluminium 2.57 [mm]) : 2616 [kg]
total weight aluminium spars (multi-cellular wing structure) : 3641 [kg]
weight wings : 7955 [kg]
weight wing/square meter : 42.25 [kg]
weight rubber de-icing boots : 38.6 [kg]
weight fin & rudder (14.3 [m2]) : 604.6 [kg]
weight stabilizer & elevator (21.2 [m2]): 896.4 [kg]
weight flight control hydraulic servo actuators: 40.3 [kg]
weight fowler flaps (12.8 [m2]) : 275.5 [kg]
total weight wing surfaces & bracing : 10344 [kg] (21.7 [%])
*******************************************************************
wheel pressure : 5238.2 [kg]
weight 8 Dunlop main wheels (1130 [mm] by 174 [mm]) : 1154.8 [kg]
weight 2 Dunlop nose wheels : 144.3 [kg]
weight hydraulic wheel-brakes : 34.7 [kg]
weight Dowty shock absorbers : 46.2 [kg]
weight wheel hydraulic operated retraction system : 660.4 [kg]
weight undercarriage struts with axle 1228.4 [kg]
total weight landing gear : 3268.7 [kg] (6.9 [%]
*******************************************************************
********************************************************************
calculated empty weight : 28938 [kg](60.8 [%])
weight oil for 4.0 hours flying : 178.8 [kg]
calculated operational weight empty : 29117 [kg] (61.1 [%])
published operational weight empty : 29000 [kg] (60.9 [%])
weight crew : 486 [kg]
weight fuel for 2.0 hours flying : 6804 [kg]
weight catering : 47.7 [kg]
weight water : 19.1 [kg]
********************************************************************
operational weight empty: 36474 [kg](76.6 [%])
weight 36 passengers : 2772 [kg]
weight luggage : 439 [kg]
weight cargo : 2459 [kg]
operational weight loaded: 42144 [kg](88.5 [%])
fuel reserve : 5476.0 [kg] enough for 1.61 [hours] flying
operational weight fully loaded : 47620 [kg] with fuel tank filled for 96 [%]
published maximum take-off weight : 47620 [kg] (100.0 [%])
calculation : * 4 * (engine power)
power loading (Take-off) : 529 [kg/KN]
power loading (operational without useful load) : 405 [kg/kN]
power loading (Take-off) 1 PUF: 705 [kg/KN]
max. total take-off power : 90.0 [KN]
calculation : *5* (loads)
manoeuvre load : 8.6 [g] at 1000 [m]
limit load : 3.0 [g] ultimate load : 4.5 [g] load factor : 2.0 [g]
design flight time : 2.65 [hours]
design cycles : 11110 sorties, design hours : 29424 [hours]
operational wing loading : 2248 [N/m^2]
wing stress (3 g) during operation : 160 [N/kg] at 3g emergency manoeuvre
calculation : *6* (angles of attack)
angle of attack zero lift : -1.84 ["]
max. angle of attack (stalling angle, clean) : 12.19 ["]
Remains of G-ALYP were recovered from the seabed and put on a frame at Farnborough for reconstruction.
angle of attack at max. speed : 0.73 ["]
calculation : *7* (lift & drag ratios
lift coefficient at angle of attack 0° : 0.15 [ ]
lift coefficient at max. speed : 0.21 [ ]
lift coefficient at max. angle of attack : 1.14 [ ]
max. lift coefficient full flaps : 1.41 [ ]
induced drag coefficient at max.speed : 0.0028 [ ]
max.continous speed : 218.8889 [m/s]
drag coefficient at max. speed : 0.0193 [ ]
drag coefficient (zero lift) : 0.0164 [ ]
lift/drag ratio at max. speed : 10.88 [ ]
calculation : *8* (speeds
stalling speed at sea-level (OW loaded : 44218 [kg]): 207 [km/u]
stalling speed at sea-level with full flaps (normal landing weight): 174 [km/u]
landing speed at sea-level (normal landing weight : 38713 [kg]): 200 [km/hr]
max. rate of climb speed : 467 [km/hr] at sea-level
max. endurance speed : 235 [km/u] min. fuel/hr : 214 [kg/hr] at height : 610 [m]
max. range speed : 538 [km/u] min. fuel consumption : 0.789 [kg/km] at cruise height :
10668 [m]
cruising speed : 725 [km/hr] at 10700 [m] (power:31 [%])
max. continuous speed* : 788.00 [km/hr] (Mach 0.74 ) at 10700 [m] (power:37.5 [%])
climbing speed at sea-level (loaded) : 987 [m/min]
climbing speed at 1000 [m] with 1 engine out (PUF / MTOW) : 856 [m/min]
climbing speed at 1000 [m] with 2 engines out (2xPUF / MTOW) : 824 [m/min]
calculation : *9* (regarding various performances)
take-off speed : 257.3 [km/u]
high wheel pressure, can only take off from paved runways
take-off distance at sea-level concrete runway : 1358 [m]
take-off distance at sea-level over 15 [m] height : 1476 [m]
landing run : 783 [m]
landing run from 15 [m] : 1489 [m]
lift/drag ratio : 15.38 [ ]
max. theoretical ceiling : 19100 [m] with flying weight :44218 [kg] line 3359
climb to 1000m with max payload : 1.12 [min]
climb to 2000m with max payload : 2.19 [min]
climb to 3000m with max payload : 3.20 [min]
climb to 5000 [m] with max payload : 5.02 [min]
minimum flying speed at 12800 [m] : 491 [km/hr]
theoretical ceiling fully loaded (mtow- 60 min. fuel: 44218 [kg] ) : 19100 [m]
calculation *10* (action radius & endurance)
published range : 2400 [km] with 6 crew and 6755.0 [kg] useful load and 88.1 [%] fuel
range : 2631 [km] with 6 crew and 5670.0 [kg] useful load and 96.6 [%] fuel
range : 3155 [km] with 36.0 passengers with each 12.2 [kg] luggage
Available Seat Kilometres (ASK) : 113588 [paskm]
useful load with range 500km : 16076 [kg]
useful load with range 500km : 36 passengers
production (theor.max load): 11655 [tonkm/hour]
production (useful load): 4111 [tonkm/hour]
production (passengers): 26100 [paskm/hour]
combi aircraft mail/freight/passengers
oil and fuel consumption per tonkm : 0.296 [kg]
fuel cost per paskm : 0.132 [eur]
crew cost per paskm : 0.029 [eur]
economic hours : 22300 [hours] is less then design hours
time between engine failure : 625 [hr]
can continue fly on 3 engines, low risk for emergency landing for PUF
writing off per paskm : 0.041 [eur]
insurance per paskm : 0.0023 [eur]
maintenance cost per paskm : 0.090 [eur]
direct operating cost per paskm : 0.295 [eur]
direct operating cost per tonkm (max. load): 0.660 [eur]
direct operating cost per tonkm (normal useful load): 1.872 [eur]
Literature :
praktisch handboek vliegtuigen deel 5 page 143 – 146
verkeersvliegtuigen Moussault page 78
encyclopedie van de luchtvaart 1945-2005 page 104,105
De Havilland DH106 Comet 1 & 2 | BAE Systems | International
plane crash ! - Clayton & K.S.Knight page 173 – 192
Air Disasters page 36 - 58
Aeroplane Monthly Sep’88 page 552
Straalverkeersvliegtuigen page 139 – 155
de Havilland Comet - Wikipedia
Straalvliegtuigen page 34 -39, 126 - 133
Aerospaceweb.org | Aircraft Museum - de Havilland Comet
* max. continuous speed : max. level speed maintainable for minimal 30 min.
DISCLAIMER Above calculations are based on published data, they must be
regarded as indication not as facts.
Calculated performance and weight may not correspond with actual weights
and performances and are assumptions for which no responsibility can be taken.
Calculations are as accurate as possible, they can be fine-tuned when more data
is available, you are welcome to give suggestions and additional information
so we can improve our program. For copyright on drawings/photographs/
content please mail to below mail address
Comet C2 in use with RAF transport command
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