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weight and performance calculations for the Savoia-Marchetti S.M.73
SABENA S.M.73
Savoia-Marchetti S.M.73
role : medium weight passenger aircraft
importance : ****
first flight : 4 June 1934 flown by Adriano Bacula operational : June 1935
country : Italy
design :
production : 55 aircraft
general information :
General information :
The S.M.73 could be fitted with different engines:
Gnome-Rhone 9Kfr Mistral 600 hp> prototype and 5 for SABENA
Piaggio Stella P.X. 700 hp > first production aircraft, Ala Littoria
Wright R-1820 770 hp cruise speed 270 km/hr max speed 340 km/hr 1000 km range,
ceiling 6300m , Ala Littoria
Walter Pegasus III MR2V 730 hp Ceskoslovenske Statni Aerolinie (CSA)
Alfa Romeo 125
Alfa Romeo 126RC.10 730 hp max.speed 345 km/hr range : 1000 km ceiling 7000m, Ala
Littoria
Gnome Rhone 14K Mistral Major 900 hp > used in the SABCA licensed built S.73’s,
7 aircraft built from 1936-1937 for the SABENA
users : SABENA (12), Ala Littoria (21), Avio Linee Italiane (6), CSA (3)
crew : 4 passengers : 18
powerplant : 3 Piaggio P.X RC air-cooled 9 -cylinder radial engine 700 [hp](522.0 KW)
normal rating, supercharged engine, low blower, constant power to height : 1000 [m]
and with 670 [hp](499.6 KW) available for take-off
dimensions :
wingspan : 23.99 [m], length : 18.37 [m], height : 4.6 [m]
wing area : 92.97 [m^2]
weights :
max.take-off weight : 9280 [kg]
empty weight operational : 5788 [kg] useful load : 1800 [kg]
performance :
maximum speed :330 [km/u] op 4000 [m]
cruise speed :314 [km/u] op 4000 [m]
service ceiling : 7000 [m]
range : 1600 [km]
description :
low-winged monoplane with fixed landing gear with tail wheel
tapered wing with split flap airfoil : unknown
2 engines attached to the wings 1 in the fuselage, landing gear attached to the wings, useful load inside the fuselage
fuel tanks in the wings
construction : fuselage > steel frame covered with fabric and wood, wooden wing
covered with plywood
airscrew :
ground adjustable 3 -bladed metal Hamilton Standard tractor propeller with max. efficiency :0.73 [ ]
estimated diameter airscrew 3.42 [m]
power loading prop : 101.75 [KW/m]
pitch angle prop : 25.58 [ ]
fixed angle prop : 30.58 [ ]
reduction : 0.62 [ ]
airscrew revs : 1426 [r.p.m.]
pitch at Max speed 3.76 [m]
blade-tip speed at max.continous speed : 271 [m/s]
propellor noise in flight : 94 [Db]
Note the split flap
calculation : *1* (dimensions)
measured wing chord : 4.04 [m] at 50% wingspan
mean wing chord : 3.88 [m]
calculated average wing chord tapered wing with rounded tips: 3.78 [m]
wing aspect ratio : 6.2 []
corrected wing aspect ratio : 6.3 []
seize (span*length*height) : 2027 [m^3]
calculation : *2* (fuel consumption)
oil consumption : 12.5 [kg/hr]
fuel consumption(cruise speed) : 275.3 [kg/hr] (375.6 [litre/hr]) at 58 [%] power
distance flown for 1 kg fuel : 1.14 [km/kg] at 4000 [m] height, sfc : 303.0 [kg/kwh]
estimated total fuel capacity : 2176 [litre] (1595 [kg])
calculation : *3* (weight)
weight engine(s) dry with reduction gear : 1305.0 [kg] = 0.83 [kg/KW]
weight 124.6 litre oil tank : 10.59 [kg]
oil tank filled with 11.7 litre oil : 10.5 [kg]
oil in engine 8.7 litre oil : 7.8 [kg]
fuel in engine 10.7 litre fuel : 7.83 [kg]
weight 159.7 litre gravity patrol tank(s) : 24.0 [kg]
weight Burgess type silencers : 31.3 [kg]
weight starter (compressed air): 12.8 [kg]
weight NACA-type cowling 23.4 [kg]
weight airscrew(s) incl. boss & bolts : 261.9 [kg]
total weight propulsion system : 1695 [kg](18.3 [%])
***************************************************************
fuselage skeleton (steel tubes) : 9.36 [cm]): 1268 [kg]
cabin layout : pitch : 87 [cm] (1+1) seating in 9.0 rows
weight toilet : 8 [kg]
weight 2 fire extinguisher : 6 [kg]
weight pantry : 12.9 [kg]
weight 20 windows : 18.0 [kg]
weight door : 5.0 [kg]
passenger cabin max.width : 1.52 [m] cabin length : 9.50 [m] cabin height : 1.90 [m]
weight cabin furbishing : 57.1 [kg]
weight cabin floor : 86.2 [kg]
bracing : 176.6 [kg]
fuselage covering ( 63.7 [m2] doped linen fabric) : 19.3 [kg]
fuselage (sound proof) isolation : 17.5 [kg]
weight radio transceiver equipment : 7.0 [kg]
weight Sperry gyro auto-pilot - course control equipment : 1.5 [kg]
weight instruments. : 7.0 [kg]
weight lighting : 4.5 [kg]
weight electricity generator : 4.5 [kg]
weight controls : 9.0 [kg]
weight seats : 110.0 [kg]
weight air conditioning : 16 [kg]
weight engine mount and firewall : 26 [kg]
total weight fuselage : 1837 [kg](19.8 [%])
***************************************************************
weight 4.8 [mm] plywood wing covering : 285 [kg]
total weight wooden ribs (130 ribs) : 552 [kg]
weight engine mounts : 52 [kg]
weight fuel tanks empty for total 2016 [litre] fuel : 161 [kg]
load on front upper spar (clmax) per running metre : 1964.1 [N]
load on rear upper spar (vmax) per running metre : 917.3 [N]
total weight 4 wooden spars : 431 [kg]
weight wings : 1268 [kg]
weight wing/square meter : 13.64 [kg]
cantilever wing without bracing cables
weight rubber de-icing boots : 26.4 [kg]
weight fin & rudder (6.7 [m2]) : 92.1 [kg]
weight stabilizer & elevator (10.5 [m2]): 143.3 [kg]
weight split flap (4.6 [m2]) : 34.7 [kg]
total weight wing surfaces & bracing : 1778 [kg] (19.2 [%])
*******************************************************************
wheel pressure : 4640.0 [kg]
weight 2 Dunlop-type wheels (1320 [mm] by 240 [mm]) : 227.7 [kg]
weight tailwheel(s) : 5.9 [kg]
weight wheel-brakes : 7.6 [kg]
weight shock absorbers : 10.1 [kg]
weight undercarriage with axle 168.5 [kg]
total weight landing gear : 419.9 [kg] (4.5 [%]
*******************************************************************
********************************************************************
calculated empty weight : 5730 [kg](61.7 [%])
weight oil for 6.1 hours flying : 76.7 [kg]
calculated operational weight empty : 5807 [kg] (62.6 [%])
published operational weight empty : 5788 [kg] (62.4 [%])
weight crew : 324 [kg]
weight fuel for 2.0 hours flying : 551 [kg]
weight catering : 32.2 [kg]
weight water : 12.9 [kg]
********************************************************************
operational weight empty: 6726 [kg](72.5 [%])
weight 18 passengers : 1386 [kg]
weight luggage & freight : 414 [kg]
operational weight loaded: 8526 [kg](91.9 [%])
fuel reserve : 753.7 [kg] enough for 2.74 [hours] flying
operational weight fully loaded : 9280 [kg] with fuel tank filled for 82 [%]
published maximum take-off weight : 9280 [kg] (100.0 [%])
calculation : * 4 * (engine power)
power loading (Take-off) : 5.93 [kg/kW]
power loading (operational without useful load) : 4.30 [kg/kW]
power loading (Take-off) 1 PUF: 8.89 [kg/kW]
total power : 1566.0 [kW] at 2300 [r.p.m]
calculation : *5* (loads)
manoeuvre load : 4.7 [g] at 1000 [m]
S.M.73 interior with 9 rows of seats
limit load : 3.0 [g] ultimate load : 4.5 [g] load factor : 1.6 [g]
design flight time : 3.57 [hours]
design cycles : 3623 sorties, design hours : 12944 [hours]
operational wing loading : 710 [N/m^2]
wing stress (3 g) during operation : 156 [N/kg] at 3g emergency manoeuvre
calculation : *6* (angles of attack)
angle of attack zero lift : -1.37 ["]
max. angle of attack (stalling angle) : 12.78 ["]
angle of attack at max. speed : 1.20 ["]
calculation : *7* (lift & drag ratios
lift coefficient at angle of attack 0° : 0.11 [ ]
lift coefficient at max. speed : 0.21 [ ]
lift coefficient at max. angle of attack : 1.14 [ ]
max.lift coefficient full flaps : 1.24 [ ]
induced drag coefficient at max.speed : 0.0028 [ ]
drag coefficient at max. speed : 0.0269 [ ]
drag coefficient (zero lift) : 0.0240 [ ]
calculation : *8* (speeds
stalling speed at sea-level (OW loaded : 9005 [kg]): 133 [km/u]
stalling speed at sea-level with full flaps (normal landing weight): 112 [km/u]
landing speed at sea-level (normal landing weight : 6923 [kg]): 129 [km/hr]
max. rate of climb speed : 199 [km/hr] at sea-level
max. endurance speed : 172 [km/u] min.fuel/hr : 180 [kg/hr] at height : 610 [m]
max. range speed : 249 [km/u] at cruise height : 4267 [m]
cruising speed : 314 [km/hr] at 4000 [m] (power:67 [%])
max. continuous speed : 321.75 [km/hr]
maximum speed : 330 [km/hr] at 4000 [m] (power:75 [%])
climbing speed at sea-level (loaded) : 430 [m/min]
climbing speed at 1000 [m] with 1 engine out (PUF / MTOW) : 147 [m/min]
calculation : *9* (regarding various performances)
take-off speed : 161.9 [km/u]
emergency/TO power : 670 [hp] at 2250 [rpm]
static prop wash : 92 [km/u]
take-off distance at sea-level gras field : 696 [m]
take-off distance at sea-level over 15 [m] height : 811 [m]
landing run : 206 [m]
lift/drag ratio : 12.47 [ ]
climb to 1000m with max payload : 2.63 [min]
climb to 2000m with max payload : 5.97 [min]
climb to 3000m with max payload : 10.48 [min]
practical ceiling (operational weight empty 6726 [kg] ) : 7300 [m]
practical ceiling fully loaded (mtow- 30 min.fuel:9142 [kg] ) : 5700 [m]
calculation *10* (action radius & endurance)
published range : 1600 [km] with 4 crew and 1744.2 [kg] useful load and 88.1 [%] fuel
range : 1536 [km] with 4 crew and 1800.0 [kg] useful load and 84.6 [%] fuel
range : 1803 [km] with 18.0 passengers with each 10 [kg] luggage and 99.3 [%] fuel
Available Seat Kilometres (ASK) : 32451 [paskm]
max range theoretically with additional fuel tanks total 4628.1 [litre] fuel : 3925 [km]
useful load with range 500km : 2953 [kg]
useful load with range 500km : 18 passengers
production (useful load): 926 [tonkm/hour]
production (passengers): 5643 [paskm/hour]
oil and fuel consumption per tonkm : 0.31 [kg]
fuel cost per paskm : 0.031 [eur] 
crew cost per paskm : 0.032 [eur]
economic hours : 12775 [hours] is less then design hours
time between engine failure : 557 [hr]
writing off per paskm : 0.036 [eur]
insurance per paskm : 0.001 [eur]
maintenance cost per paskm : 0.092 [eur]
direct operating cost per paskm : 0.193 [eur]
direct operating cost per tonkm : 1.934 [eur]
Literature:
Praktisch handboek vliegtuigen deel 2 page 174,175
Piston-engined airliners page 41
Wikipedia
Maja Stara (1915-1997) was a flight attendant with the CSA, in WWII she worked for the anti-Nazi resistance. In 1948 she fled to Belgium.
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
(c) B van der Zalm 28 November 2021 contact : info.aircraftinvestigation@gmail.com python 3.7.4
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