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weight and performance calculations for the McDonnel Douglas MD-81
***** PRELIMINARY FILE ****
a
Swissair MD-81 HB-INS, c/n 49356 at Basle/Mulhouse apt (MLH) august 1986
McDonnel Douglas MD-81
role : jet airliner
importance : ****
first flight : 18 October 1979 operational : October 1980 (Swissair)
country : United States of America
nick name : “Mad dog”
production : 132 aircraft
general information :
Even more extended DC-9 version with new engines, first referred to as Super-80. Certification of the - Super 80 - model, was awarded in July 1981. In 1983, the Super 80 was renamed MD-80, however, this did not stand for a special type, but the designation for a whole series of aircraft, starting with the MD-81, followed by the MD-82 with more powerful engines, etc. The MD-81 was stretched by 4.3m from the DC-9-51 and has a 28% larger wing.
Friday 2 May 1980, DC-9 Super 80 (MD-81) N980DC c/n 48000 carried out landing trials at Edwards afb. RW22 for FAA certification with 7 crew on board. But the aircraft descended to fast with 5 m/s instead of the intended 2.4 m/s. The complete tail empennage broke off behind the engines. The undercarriage was damaged and the fuselage buckled near the nose wheel. Despite this extensive damage the aircraft was repaired and was later used for UDF (Unducted Fan) trials. There were no fatalities, but one crew member was wounded, he broke his ankle in the hard landing. location : 34°54'30"N 117°53'W
Thursday 19 June 1980 landing tests with the DC-9 Super 80, later referred to as MD-81, N1002G c/n 48001 at Yuma apt, Ariziona, USA RW21R with 3 crew on board. Landing test with failed hydraulic systems. The aircraft can only be controlled with the trim surfaces and the flaps do not work. The electric anti-skid system was also switched off because they also need hydraulic pressure and the braking had to be done by the thrust reversers. On landing, however, these did not work well because they need hydraulic pressure !! The aircraft swung to the left. The pilot braked lightly with the right brake pedal. Tires immediately collapsed and the aircraft swung to the right. He braked with the left pedal which resulted in even more blown tires. The aircraft went 180 degrees around the nose wheel and the right main undercarriage breaks off. The DC-9 Super-80 nevertheless received proof of airworthiness in the autumn of 1980. When salvaging the aircraft a 50-ton crane broke and fell on top of the fuselage, the aircraft had to be written off, it only had 6 flying hours. Location : +- 25m 32°39'02.93"N 114°36'52.13"W
primary users : Swissair, SAS
Accommodation:
flight crew : 2 cabin crew : 5
passengers : seating for 143 in two class : 12 business class and 131 economy class seats
( 32 -in pitch) exit limit : 172 passengers
engine : 2 Pratt & Whitney JT8D-209 turbofan engines of 82.3 [KN] (18501.5 [lbf])
dimensions :
wingspan : 32.87 [m], length : 45.06 [m], height : 9.02 [m]
wing area : 112.3 [m^2] fuselage exterior width : 3.34 [m]
weights :
operating empty weight : 35288 [kg] max. structural payload : 18236 [kg]
Zero Fuel weight (ZFW) : 53524 [kg] max. landing weight (MLW) : 58060 [kg]
max.take-off weight : 63502 [kg] weight fuel : 17501 [kg] (21876 [liter])
performance :
Max. operating Mach number (Mmo) : 0.83 [Mach] (927 [km/hr]) at 7620 [m]
normal cruise speed : 873 [km/hr] (Mach 0.80 ) at 9150 [m] (34 [%] power)
economic cruise speed : 821 [km/hr] (Mach 0.75 ) at 9150 [m]
service ceiling : 11278 [m]
range with max fuel : 4056 [km] (ATA domestic fuel reserves - 370.0 [km] alternate)
description :
low-wing cantilever monoplane with retractable landing gear with nose wheel
two main spar fail-safe wing structure
with double slotted flaps with full-span slotted LE flaps (slats) ,with spoilers
airfoil : NACA sweep angle 3/4 chord: 24.5 [°]
engines attached to the tail, landing gear attached to the wings, fuel tanks in the wings
fuselage shape : 0 construction : all-metal aluminium-alloy stressed-skin construction with pressurized fuselage
calculation : *1* (dimensions)
wing chord at root : 7.05 [m]
mean wing chord : 3.42 [m]
calculated average wing chord tapered wing with rounded tips: 3.39 [m]
wing aspect ratio : 9.62 []
seize (span*length*height) : 13360 [m^3]
calculation : *2* (fuel consumption)
oil consumption : 16.5 [kg/hr]
fuel consumption (econ. cruise speed) : 3246.3 [kg/hr] (4057.9 [litre/hr]) at 31 [%] power
distance flown for 1 kg fuel : 0.25 [km/kg] at 9150 [m] height, sfc : 63.0 [kg/KN/h]
total fuel capacity : 21876 [litre] (17501 [kg])
calculation : *3* (weight)
weight engine(s) dry : 4162.0 [kg] = 25.29 [kg/KN]
weight 122 litre oil tank : 10.38 [kg]
oil tank filled with 1.0 litre oil : 0.9 [kg]
oil in engine 2.0 litre oil : 1.8 [kg]
fuel in engine 9.0 litre fuel : 6.58 [kg]
weight fuel lines 40.2 [kg]
weight engine cowling 428.0 [kg]
weight thrust reversers 65.8 [kg]
total weight propulsion system : 4716 [kg](7.4 [%])
***************************************************************
Accommodation cabin facilities:
typical 2-class cabin layout for 143 passengers : economy : pitch : 81.3 [cm] 32.0 [-in]
( 3+2 ) seating in 29.2 rows
weight seats : 750.0 [kg]
high density seating passengers : 170 [pax] at 5 -abreast seating in 34.0 rows,
pitch 73.7 [cm] 29.0 [-in]
pax density, normal seating : 0.65 [m2/pax], high density seating : 0.55 [m2/pax]
weight 3 lavatories : 44.4 [kg]
weight 2 galleys : 143.4 [kg]
weight overhead stowage for hand luggage : 50.0 [kg]
weight 3 wardrobe closets : 28.6 [kg]
weight 60 windows : 54.4 [kg]
weight 4 1.83x0.86 [m] entrance/exit doors : 166.0 [kg]
weight tail entrance stairs : 83.5 [kg]
weight 3 (134.6x127 cm) freight doors (belly) : 135.2 [kg]
McDonnel Douglas MD-81
belly baggage/cargo hold volume front : 12.35 [m3]
belly baggage/cargo hold volume middle : 10.60 [m3]
belly baggage/cargo hold volume rear : 12.52 [m3]
passenger compartment volume : 111 [m3]
passenger cabin max.width : 3.11 [m] cabin length : 30.79 [m] cabin height : 2.06 [m]
floor area : 92.8 [m2]
weight cabin facilities : 1372.0 [kg]
safety facilities:
weight 4 over wing emergency exits (91x51 cm): 79.1 [kg]
weight 7 hand fire extinguisher : 22 [kg]
weight cockpit voice recorder (CVR) and flight data recorder (FDR): 20.0 [kg]
weight oxygen masks & oxygen generators : 93.0 [kg]
weight emergency flare installation : 10 [kg]
weight 3 emergency evacuation slides : 81.4 [kg]
weight safety equipment & facilities : 389 [kg]
fuselage construction:
fuselage aluminium frame : 8444 [kg]
floor loading (payload/m2): 196 [kg/m2]
weight rear pressure bulkhead : 109.2 [kg]
fuselage covering ( 320.2 [m2] duraluminium 2.42 [mm]) : 2024.6 [kg]
weight floor beams : 346.6 [kg]
weight cabin furbishing : 683.0 [kg]
SAS MD-81 SE-DMB at Oslo airport
weight cabin floor : 1237.7 [kg]
fuselage (sound proof) isolation : 230.3 [kg]
weight empty waste tank : 14 [kg]
weight engine mounts : 82 [kg]
weight fuselage structure : 13171.9 [kg]
Avionics:
weight HF and UHF radio : 7.0 [kg]
weight dual cloud-collision radar : 25.0 [kg]
weight VOR/ILS,RMI,Doppler,radio altimeter : 12.0 [kg]
weight Integrated Flight System / auto-pilot : 23.0 [kg]
weight artificial horizons, compass, alti-meters : 7 [kg]
weight engine monitoring gauges & control switches : 6 [kg]
weight avionics : 80.0 [kg]
Systems:
Air-conditioning and pressurisation system maintains sea level conditions up to 5900 [m]
and gives equivalent of 2250 [m] at 10700 [m]. pressure differential : 0.54 [bars] (kg/cm2)
Air Cal MD-81 N476AC
pressurized fuselage volume : 318 [m3]
weight air-conditioning and pressurisation system : 178 [kg]
weight APU / engine starter: 41.1 [kg]
weight lighting : 47.2 [kg]
weight engine-driven 40kVA electricity generators : 35.8 [kg]
weight controls : 18.2 [kg]
weight systems : 320.1 [kg]
total weight fuselage : 15333 [kg](24.1 [%])
***************************************************************
total weight aluminium ribs (949 ribs) : 2265 [kg]
weight 7 fuel tanks empty for total 21876 [litre] fuel : 1225 [kg]
weight wing covering (painted aluminium 3.34 [mm]) : 2023 [kg]
total weight aluminium spars (multi-cellular wing structure) : 2066 [kg]
weight wings : 6353 [kg]
weight wing/square meter : 56.58 [kg]
weight thermal leading-edge anti-icing : 36.2 [kg]
weight ailerons (3.5 [m2]) : 100.2 [kg]
weight fin (15.0 [m2]) : 853.7 [kg]
weight rudder (6.1 [m2]) : 165.5 [kg]
weight tailplane (stabilizer) (29.2 [m2]): 1159.4 [kg]
weight elevators (9.8 [m2]): 149.8 [kg]
weight flight control hydraulic servo actuators: 56.9 [kg]
weight trailing-edge double slotted flaps (19.6 [m2]) : 476.8 [kg]
weight leading edge slats (11.2 [m2]) : 177.3 [kg]
weight spoilers (3.2 [m2]) : 50.5 [kg]
total weight wing surfaces & bracing : 10805 [kg] (17.0 [%])
*******************************************************************
tyre pressure main wheels : 11.95 [Bar] (nitrogen), ply rating : 22 PR
tyre speed limit : 364 [km/hr]
Aircraft Classification Number, MTOW on rigid runway and medium subgrade strength : 76 [ ]
Can only operate from paved runways
SAS MD-81 OY-KGY taking-off. The MD-81 has 33 cabin windows in front of the emergency exits. The fuselage end/tail has a different shape then early production aircraft and the prototypes who had a more pointed tail-end
wheel pressure : 13970.4 [kg]
weight 4 Dunlop main wheels (1130 [mm] by 420 [mm]) : 497.6 [kg]
weight 2 nose wheels : 124.4 [kg]
weight multi-disc wheel-brakes : 53.5 [kg]
weight flywheel detector type anti-skid units : 5.4 [kg]
weight oleo-pneumatic shock absorbers : 71.4 [kg]
weight wheel hydraulic operated retraction system : 634.6 [kg]
weight undercarriage struts with axle 1754.2 [kg]
total weight landing gear : 3141.1 [kg] (4.9 [%]
*******************************************************************
********************************************************************
calculated empty weight : 33994 [kg](53.5 [%])
weight oil for 5.6 hours flying : 106.5 [kg]
weight lifejackets : 64.4 [kg]
weight 3 life rafts : 89.4 [kg]
weight catering : 239.0 [kg]
weight water : 191.2 [kg]
weight crew : 567 [kg]
weight crew lugage,nav.chards,flight doc.,miscell.items : 36 [kg]
operational weight empty : 35288 [kg] (55.6 [%])
********************************************************************
weight 143 passengers : 11011 [kg]
weight luggage : 2288 [kg]
weight cargo : 4937 [kg] (cargo+luggage/m3 belly : 188 [kg/m3])
zero fuel weight (ZFW): 53524 [kg](84.3 [%])
weight fuel for landing (1.4 hours flying) : 4536 [kg]
max. landing weight (MLW): 58060 [kg](91.4 [%])
max. fuel weight : 52789 [kg] (83.1 [%])
payload with max fuel : 115 passengers+luggage 10713 [kg]
published maximum take-off weight : 63502 [kg] (100.0 [%])
SAS with SE-registration, probably a MD-81
calculation : * 4 * (engine power)
power loading (Take-off) : 386 [kg/KN]
power loading (Take-off) 1 PUF: 772 [kg/KN]
max. total take-off power : 164.6 [KN]
calculation : *5* (loads)
manoeuvre load : 6.9 [g] at 1000 [m]
limit load : 3.0 [g] ultimate load : 4.5 [g] load factor : 1.1 [g]
design flight time : 3.34 [hours]
Air Cal MD-81 N475AC
design cycles : 16922 sorties, design hours : 56559 [hours]
max. wing loading (MTOW & flaps retracted) : 565 [kg/m2]
wing stress (2 g) during operation : 187 [N/kg] at 2g emergency manoeuvre
calculation : *6* (angles of attack)
angle of attack zero lift : -1.68 ["]
max. angle of attack (stalling angle, clean) : 13.30 ["]
max. angle of attack (full flaps) : 17.50 ["]
angle of attack at max. speed : 1.59 ["]
calculation : *7* (lift & drag ratios
lift coefficient at angle of attack 0° : 0.15 [ ]
lift coefficient at max. speed : 0.29 [ ]
lift coefficient at max. angle of attack : 1.34 [ ]
max. lift coefficient full flaps : 2.36 [ ]
drag coefficient at max. speed : 0.0352 [ ]
drag coefficient at econ. cruise speed : 0.0385 [ ]
induced drag coefficient at econ. cruise speed : 0.0071 [ ]
drag coefficient (zero lift) : 0.0314 [ ]
lift/drag ratio at max. speed : 8.29 [ ]
calculation : *8* (speeds
take-off safety speed (V2) : 250 [km/u]
take-off (initial climb) speed (Vto) : 301 [km/u]
stalling speed clean at sea-level (OW loaded : 60256 [kg]): 289 [km/u]
max. rate of climb speed : 489 [km/hr] at sea-level
max. endurance speed (Vbe): 444 [km/u] min. fuel/hr : 2519 [kg/hr] at height : 4877 [m]
max. range speed (Vbr): 819 [km/u] min. fuel consumption : 3.553 [kg/km] at cruise height : 10668 [m]
cruising speed : 873 [km/hr] at 9150 [m] (power:34 [%])
max. operational speed (Mmo) : 927.00 [km/hr] (Mach 0.83 ) at 7620 [m] (power:42.8 [%])
McDonnel Douglas MD-81
Friday 27 December 1991 SAS MD-81 OY-KHO c/n 53003
Flight SK751 from Stockholm – Arlanda apt. (ARN) to Copenhagen – Kastrup apt. (CPH) with 7 crew and 122 passengers. first flight : 1991
Airframe hrs : 1608 cycles : 1272 engines : P&W JT8D-217C No people died in the crash, only 42 slightly wounded. location : 700m North of Vangsjoberg farm, near Gottrora, Sweden +-100m 59°46’07.94”N 18°08’24.41”E
McDonnel Douglas MD-81
27 December 1991 MD-81 of the SAS takes off from Arlanda airport near Stockholm with destination Warsaw with 112 passengers and 7 crew members. At 600m both engines fail due to ice forming. The pilot tries in vain to restart the engines. He manages to avoid a forest and makes a successful emergency landing in a field. The aircraft breaks into three pieces and the wings break off. There are no deaths, only 42 mostly slightly injured. Despite the full tanks, no fire broke out, probably due to the light snowfall. All but one of the passengers were able to get out of the aircraft under their own power. A passenger was trapped and could soon be freed. Later it turned out that the aircraft was equipped with an automatic engine power restoration system (ATR), which checked the speed and the position of the gas handless. If these do not match, the fuel supply is adjusted. Both the pilot and the SAS did not know that this system was installed, it was also not mentioned in the manuals! When one engine failed during take-off due to ice formation, the system also adjusted the other engine so rigorously that it also failed. The pilot was surprised by this and could not turn off the system.
airflow at cruise speed per engine : 136.3 [kg/s]
speed of thrust jet : 1612 [km/hr]
initial descent speed 10000 - 7315 [m]: Mach 0.75
descent speed 7315 - 3048 [m]: 537 [km/u]
approach speed 3048 - 500 [m] (clean): 463 [km/u]
stalling speed clean at 500 [m] height at Max.Landing Weight : 58060 [kg]): 290 [km/u]
final approach speed at sea-level with full flaps (normal landing weight) (Vapp): 245 [km/u]
ICAO Aircraft Approach Category (APC) : C
landing speed at sea-level (normal landing weight(Vtd): 57845 [kg]): 217 [km/hr]
stalling speed at sea-level with full flaps (normal landing weight): 189 [km/u]
rate of climb at sea-level ROC (loaded) : 749 [m/min]
rate of climb at 1000 [m] with 1 engine out (PUF / MTOW) : 353 [m/min]
rate of descent: 457 [m/min]
calculation : *9* (regarding various performances)
high wheel pressure, can only take off from paved runways
take-off distance at sea-level concrete runway : 2031 [m]
ICAO Aerodrome Reference Code : 4C
take-off distance at sea-level over 15 [m] height : 2194 [m]
landing run : 1002 [m]
landing run (C.A.R.) from 15 [m] at SL, dry runway : 1382 [m]
landing run (C.A.R.) from 15 [m] at SL, wet runway : 1682 [m]
lift/drag ratio : 13.43 [ ]
climb to 5000 [m] with max payload : 6.18 [min]
climb to 10000 [m] with max payload : 19.01 [min]
descent time from 10000 [m] to 250 [m] : 24.33 [min]
theoretical ceiling fully loaded (mtow- 60 min. fuel:60256 [kg] ) : 15900 [m]
calculation *10* (action radius & endurance)
range with max. payload: 2459 [km] with 18236.0 [kg] max. useful load (57.0 [%] fuel)
range with high density pax: 3087 [km] with 170 passengers (71.0 [%] fuel)
range with typical two-class pax: 3739 [km] with 143 passengers (85.2 [%] fuel)
range with max.fuel : 4426 [km] with 7 crew and 115 passengers and 100.0 [%] fuel
ferry range : 4757 [km] with 2 crew and zero payload (100.0 [%] fuel)
max range theoretically with additional fuel tanks total 36311.5 [litre] fuel : 7628 [km]
Available Seat Kilometres (ASK) : 534687 [paskm]
useful load with range 1000km : 18236 [kg]
useful load with range 1000km : 170 passengers
production (theor.max load): 15920 [tonkm/hour]
production (useful load): 15920 [tonkm/hour]
production (passengers): 124839 [paskm/hour]
oil and fuel consumption per tonkm : 0.205 [kg]
fuel cost per paskm : 0.026 [eur]
crew cost per paskm : 0.007 [eur]
economic hours : 22300 [hours] is less then design hours
time between engine failure : 1030 [hr]
can continue fly on 1 engine, low risk for emergency landing for PUF
writing off per paskm : 0.010 [eur]
insurance per paskm : 0.0007 [eur]
maintenance cost per paskm : 0.014 [eur]
direct operating cost per paskm : 0.058 [eur]
direct operating cost per tonkm (max. load): 0.453 [eur]
direct operating cost per tonkm (normal useful load): 0.453 [eur]
To avoid clear ice braking off the wing and being ingested in the engine at take-off special care must be taken to de-ice the wings before taking-off. Here an American airlines MD-80 is de-iced at Syracuse Hancock apt.
Literature :
KIJK mei’83.
McDonnell Douglas MD-80 - Wikipedia
https://contentzone.eurocontrol.int/aircraftperformance/default.aspx?
https://www.boeing.com/search/results.html?q=airplane+characteristics
Jane’s all the world aircraft 1979-80 page
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/
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(c) B van der Zalm 22 October 2022 contact : info.aircraftinvestigation@gmail.com python 3.7.4