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weight and performance calculations for the Junkers G 31
Lufthansa D-1770 “Preussen” entered service in 1929. Gnome-Rhone engines.
Junkers G 31
role : multi-engined passenger aircraft
importance : *
first flight : operational : May 1928
first flight : May 1928 operational : only small number built, not operational used
country : Germany
design : Ernst Zindel , Professor Hugo Junkers
production : 13 aircraft
general information :
All-metal, low wing cantilever monoplane. It was the first Lufthansa airliner with a steward (flight attendant) who served drink and food. For this the airplane got the nickname “fliegender speisewagen”. It had an APU witch gave compressed air to start the engines and drove a generator for electric power.
The seats could be replaced by 10 beds for night flying.
It had trailing edge flaps that reduced the landing speed by 10 percent.
Lufthansa flew the G.31 on routes to Scandinavia up till 1935.
4 G.31’s were sold to Guinea Airways and were used as cargo planes, with a large hatch in the roof for loading bulky cargo (dredging eqpt.).
The G.31 was no commercial success, it was fast and save, but it had a high purchase price and had high operating cost.
users : Lufthansa, Guinea Airways (4)
crew : 4 > pilot & co-pilot, 1 radio operator and 1 steward. passengers : 15
engine : 3 Pratt & Whitney R-1690 Hornet air-cooled 9 -cylinder radial engine 525 [hp](391.5 KW)
without supercharger
dimensions :
wingspan : 30.5 [m], length : 16.5 [m], height : 6.0[m]
wing area : 102.0 [m^2]
weights :
max.take-off weight : 8500 [kg]
empty weight operational : 5250 [kg] useful load : 1500 [kg]
performance :
maximum speed :210 [km/hr] at sea-level
cruise speed :189 [km/u] op 100 [m]
service ceiling : 4400 [m]
range : 850 [km]
description :
low-wing monoplane with fixed landing gear and tail strut
two spar tapered wing
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
airscrew :
three fixed pitch 3 -bladed tractor airscrews with max. efficiency :0.67 [ ]
estimated diameter airscrew 3.08 [m]
angle of attack prop : 14.24 [ ]
fine pitch
reduction : 1.00 [ ]
airscrew revs : 1900 [r.p.m.]
pitch at Max speed 1.84 [m]
blade-tip speed at Vmax and max revs. : 312 [m/s]
calculation : *1* (dimensions)
measured wing chord at root : 4.05 [m]
mean wing chord : 3.34 [m]
wing aspect ratio : 9.12 []
seize (span*length*height) : 3020 [m^3]
11 regular seats, 4 jump seats > 15 passengers
1 jump seat for the steward opposite the toilet, next to the exit door.
Measured wing chord at root : 4.05m
calculation : *2* (fuel consumption)
oil consumption : 18.8 [kg/hr]
fuel consumption(cruise speed) : 285.5 [kg/hr] (389.5 [litre/hr]) at 66 [%] power
distance flown for 1 kg fuel : 0.66 [km/kg] at 2200 [m] cruise height, sfc : 366.4 [kg/kwh]
estimated total fuel capacity : 1988 [litre] (1457 [kg])
calculation : *3* (weight)
weight engine(s) dry : 1086.0 [kg] = 0.92 [kg/KW]
weight 142.3 litre oil tank : 12.10 [kg]
oil tank filled with 8.8 litre oil : 7.9 [kg]
oil in engine 6.5 litre oil : 5.9 [kg]
fuel in engine 8.0 litre fuel : 5.87 [kg]
weight 165.6 litre gravity patrol tank(s) : 24.8 [kg]
weight inertia starter : 9.6 [kg]
weight cowling 15.7 [kg]
weight airscrew(s) (wood) incl. boss & bolts : 191.2 [kg]
total weight propulsion system : 1347 [kg](15.8 [%])
***************************************************************
fuselage aluminium frame : 956 [kg]
cabin layout : pitch : 87 [cm] (2+1) seating in 5.0 rows
weight toilet : 5 [kg]
weight 10.0 windows : 9.00 [kg]
passenger cabin width : 1.95 [m] cabin length : 4.35 [m] cabin height : 1.90 [m]
weight cabin furbishing : 40.42 [kg]
weight cabin floor : 54.28 [kg]
bracing : 199.3 [kg]
fuselage covering ( 51.4 [m2] duraluminium 0.75 mm) : 100.8 [kg]
weight radio navigation equipment : 7.0 [kg]
weight instruments. : 4.0 [kg]
weight lighting : 3.8 [kg]
weight controls : 9.4 [kg]
weight seats : 95.0 [kg]
weight air conditioning : 22 [kg]
weight engine mount and firewall : 20 [kg]
total weight fuselage : 1526 [kg](18.0 [%])
***************************************************************
weight wing covering (painted aluminium 0.75 mm) : 413 [kg]
total weight ribs (130 ribs) : 303 [kg]
weight engine mounts : 39 [kg]
weight fuel tanks empty for total 1822 [litre] fuel : 146 [kg]
load on front upper spar (clmax) per running metre : 2635.1 [N]
load on rear upper spar (vmax) per running metre : 805.9 [N]
total weight 4 spars : 613 [kg]
weight wings : 1329 [kg]
weight wing/square meter : 13.03 [kg]
cantilever wing without bracing cables
weight fin & rudder (10.8 [m2]) : 142.3 [kg]
weight stabilizer & elevator (11.5 [m2]): 150.3 [kg]
total weight wing surfaces & bracing : 1807 [kg] (21.3 [%])
*******************************************************************
wheel pressure : 4250.0 [kg]
weight 2 wheels (1400 [mm] by 175 [mm]) : 209.7 [kg]
weight tailskid : 23.9 [kg]
weight undercarriage with axle 286.5 [kg]
total weight landing gear : 520.1 [kg] (6.1 [%]
*******************************************************************
Junkers G.31 D-1770 “Preussen” op Schiphol, Amsterdam
********************************************************************
calculated empty weight : 5200 [kg](61.2 [%])
weight oil for 5.4 hours flying : 101.4 [kg]
calculated operational weight empty : 5301 [kg] (62.4 [%])
published operational weight empty : 5250 [kg] (61.8 [%])
___o___
"
weight crew : 324 [kg]
weight fuel for 2.0 hours flying : 571 [kg]
********************************************************************
operational weight empty: 6196 [kg](72.9 [%])
weight 15 passengers : 1155 [kg]
weight luggage & freight : 345 [kg]
operational weight loaded: 7696 [kg](72.9 [%])
fuel reserve : 804.0 [kg] enough for 2.82 [hours] flying
operational weight fully loaded : 8500 [kg] with fuel tank filled for 94 [%]
published maximum take-off weight : 8500 [kg] (100.0 [%])
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calculation : * 4 * (engine power)
power loading (Take-off) : 7.24 [kg/kW]
power loading (operational without useful load) : 5.28 [kg/kW]
power loading (Take-off) 1 PUF: 10.86 [kg/kW]
total power : 1174.5 [kW] at 1900 [r.p.m]
calculation : *5* (loads)
manoeuvre load : 2.3 [g] at 1000 [m]
limit load : 2.5 [g] ultimate load : 3.8 [g] load factor : 2.5 [g]
design flight time : 3.60 [hours]
design cycles : 8334 sorties, design hours : 29986 [hours]
operational wing loading : 596 [N/m^2]
wing stress (3 g) during operation : 137 [N/kg] at 3g emergency manoeuvre
calculation : *6* (angles of attack)
angle of attack zero lift : -1.93 ["]
max. angle of attack (stalling angle) : 10.97 ["]
angle of attack at max. speed : 1.34 ["]
calculation : *7* (lift & drag ratios
lift coefficient at angle of attack 0° :0.17 [ ]
lift coefficient at max. angle of attack : 1.14 [ ]
lift coefficient at max. speed : 0.29 [ ]
induced drag coefficient at max. speed : 0.0039 [ ]
drag coefficient at max. speed : 0.0635 [ ]
drag coefficient (zero lift) : 0.0596 [ ]
calculation : *8* (speeds
stalling speed at sea-level (OW loaded : 8215 [kg]): 121 [km/u]
landing speed at sea-level: 142 [km/hr]
min. drag speed (max endurance) at cruise height : 149 [km/hr] at 2200 [m]
min. power speed (max range) : 149 [km/hr] at 2200 [m] (power:45 [%])
max. rate of climb speed : 123.6 [km/hr] at sea-level
cruising speed : 189 [km/hr] op 2200 [m] (power:70 [%])
design speed prop : 200 [km/hr]
maximum speed : 210 [km/hr] op 100 [m] (power:103 [%])
climbing speed at sea-level : 441 [m/min]
calculation : *9* (regarding various performances)
take-off speed : 147.9 [km/u]
static prop wash : 201 [km/u]
take-off distance at sea-level : 202 [m]
lift/drag ratio : 9.49 [ ]
***********plaf with owmin (plafmax) *********
climb to 1000m with max payload : 4.36 [min]
climb to 2000m with max payload : 10.41 [min]
climb to 3000m with max payload : 18.56 [min]
practical ceiling (operational weight 6196 [kg] ) : 6238 [m]
practical ceiling fully loaded (mtow- 30 min.fuel:8357 [kg] ) : 4573 [m]
max. dive speed : 492.6 [km/hr] at 3573 [m] height
turning speed at CLmax : 168.8 [km/u] at 50 [m] height
turn radius at 50m: 95 [m]
time needed for 360* turn 12.7 [seconds] at 50m
load factor at max. angle turn 2.56 ["g"]
calculation *10* (action radius & endurance)
published range : 850 [km] with 4 crew and 1591.1 [kg] useful load and 88.1 [%] fuel
range : 910 [km] with 4 crew and 1500.0 [kg] useful load and 94.4 [%] fuel
range : 1039 [km] with 15.0 passengers with each 10 [kg] luggage and 107.7 [%] fuel
Available Seat Kilometers (ASK) : 15591 [paskm]
max range theoretically with additional fuel tanks for total 4253.6 [litre] fuel : 2064.3 [km]
useful load with range 500km : 2363 [kg]
useful load with range 500km : 15 passengers
production (useful load): 446.55 [tonkm/hour]
production (passengers): 2835.00 [paskm/hour]
oil and fuel consumption per tonkm : 0.68 [kg]
oil and fuel consumption per paskm : 0.11 [kg]
fuel cost per paskm : 0.11 [eur]
crew cost per paskm : 0.11 [eur]
I=I°_°°°°/
°
time between engine failure : 175 [hr]
low risk for emergency landing, can continue flying with 1 engine out
writing off per paskm : 0.12 [eur]
insurance per paskm : 0.034 [eur]
maintenance cost per paskm : 0.2804 [eur]
direct operating cost per paskm : 0.65 [eur]
serious accidents :
Literature :
Piston-engined airliners 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 10 May 2021 contact : info.aircraftinvestigation@gmail.com python 3.7.4