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weight and performance calculations for the Lockheed Model 12 Electra Junior
Lockheed Model 12 Electra Junior
role : light passenger / executive aircraft
importance : ***
first flight : 27 June 1936 operational : February 1937
country : United States of America
design :
production : 130 aircraft
general information :
Smaller version of the L.10 Electra, designed as feeder airliner. It was not much used
as airliner, but popular as an executive aircraft. First modern executive aircraft, with
high speed and long range.
Main spar passed through the cabin.
users :
crew : 2 passengers : 6
engine : 2 Pratt & Whitney R-985-SB Wasp Jr air-cooled 9 -cylinder radial engine 400
[hp] (298.3 KW) supercharged engine, constant power to height : 1500 [m]
dimensions :
wingspan : 15.09 [m], length : 11.07 [m], height : 2.97 [m]
wing area : 32.7 [m^2]
weights :
max.take-off weight : 3810 [kg]
empty weight operational : 2615 [kg] useful load : 600 [kg]
performance :
maximum speed :362 [km/u] op 1500 [m]
cruise speed :344 [km/u] op 1500 [m]
service ceiling : 7000 [m]
range : 1300 [km]
description :
low-winged monoplane with retractable landing gear with tail wheel
tapered wing with split flap airfoil : Clark Y
engines and landing gear attached to the wings, fuel tanks in the wings
double fin tail plane
construction : all-metal stressed-skin (duraluminium) airplane
airscrew :
two Hamilton Standard constant speed 3 -bladed tractor airscrews with max. efficiency
:0.74 [ ]
estimated diameter airscrew 2.23 [m]
power loading prop : 89.17 [KW/m]
angle of attack prop at max. speed : 27.56 [ ]
reduction : 1.00 [ ]
airscrew revs : 2200 [r.p.m.]
pitch at Max speed 2.74 [m]
blade-tip speed at Vmax and max revs. : 276 [m/s]
calculation : *1* (dimensions)
measured wing chord : 2.23 [m] at 50% wingspan
mean wing chord : 2.17 [m]
calculated average wing chord tapered wing with rounded tips: 2.15 [m]
wing aspect ratio : 6.96 []
seize (span*length*height) : 496 [m^3]
calculation : *2* (fuel consumption)
oil consumption : 9.5 [kg/hr]
fuel consumption(cruise speed) : 124.7 [kg/hr] (170.1 [litre/hr]) at 68 [%] power
distance flown for 1 kg fuel : 2.76 [km/kg] at 3500 [m] height, sfc : 309.0 [kg/kwh]
estimated total fuel capacity : 730 [litre] (535 [kg])
calculation : *3* (weight)
weight engine(s) dry : 580.0 [kg] = 0.97 [kg/KW]
weight 63.1 litre oil tank : 5.37 [kg]
oil tank filled with 4.5 litre oil : 4.0 [kg]
oil in engine 3.3 litre oil : 3.0 [kg]
fuel in engine 4.1 litre fuel : 2.98 [kg]
weight 72.3 litre gravity patrol tank(s) : 10.8 [kg]
weight starter (E.H.I. - Electric Hand Inertia): 7.3 [kg]
weight NACA cowling 13.4 [kg]
weight variable pitch control : 3.8 [kg]
weight airscrew(s) incl. boss & bolts : 49.2 [kg]
total weight propulsion system : 671 [kg](17.6 [%])
***************************************************************
fuselage aluminium frame : 360 [kg]
cabin layout : pitch : 87 [cm] (1+1) seating in 3.0 rows
weight 1 fire extinguisher : 3 [kg]
weight 6 windows : 5.4 [kg]
passenger cabin width : 1.31 [m] cabin length : 2.61 [m] cabin height : 1.80 [m]
weight cabin furbishing : 12.7 [kg]
weight cabin floor : 21.9 [kg]
fuselage covering ( 38.8 [m2] duraluminium 2.29 [mm]) : 234.0 [kg]
fuselage (sound proof) isolation : 11.3 [kg]
weight radio navigation equipment : 6.0 [kg]
weight Sperry gyro auto-pilot - course control equipment : 1.5 [kg]
weight instruments. : 6.0 [kg]
weight lighting : 1.5 [kg]
weight electricity generator : 3.4 [kg]
weight controls : 5.9 [kg]
weight seats : 40.0 [kg]
weight air conditioning : 9 [kg]
total weight fuselage : 706 [kg](18.5 [%])
***************************************************************
total weight aluminium ribs (90 ribs) : 136 [kg]
weight engine mounts : 30 [kg]
weight two 329 [litre] main fuel tanks empty : 52.6 [kg]
weight wing covering (painted aluminium 1.94 [mm]) : 343 [kg]
total weight aluminium spars (multi-cellular wing structure) : 180 [kg]
weight wings : 658 [kg]
weight wing/square meter : 20.12 [kg]
cantilever wing without bracing cables
weight rubber de-icing boots : 16.6 [kg]
weight fin & rudder (2.6 [m2]) : 53.6 [kg]
weight stabilizer & elevator (3.7 [m2]): 92.8 [kg]
weight split flap(1.6 [m2]) : 19.4 [kg]
total weight wing surfaces & bracing : 923 [kg] (24.2 [%])
*******************************************************************
Can only operate from paved runways
wheel pressure : 1905.0 [kg]
weight 2 wheels (900 [mm] by 138 [mm]) : 95.1 [kg]
weight tailwheel(s) : 5.9 [kg]
weight wheel hydraulic operated retraction system : 18.7 [kg]
weight undercarriage with axle 160.3 [kg]
total weight landing gear : 280.0 [kg] (7.3 [%]
*******************************************************************
********************************************************************
calculated empty weight : 2579 [kg](67.7 [%])
weight oil for 4.5 hours flying : 43.3 [kg]
calculated operational weight empty : 2623 [kg] (68.8 [%])
published operational weight empty : 2615 [kg] (68.6 [%])
___o___
" "
weight crew : 162 [kg]
weight fuel for 2.0 hours flying : 249 [kg]
********************************************************************
operational weight empty: 3034 [kg](79.6 [%])
weight 6 passengers : 462 [kg]
weight luggage & freight : 138 [kg]
operational weight loaded: 3634 [kg](95.4 [%])
fuel reserve : 176.2 [kg] enough for 1.41 [hours] flying
operational weight fully loaded : 3810 [kg] with fuel tank filled for 80 [%]
published maximum take-off weight : 3810 [kg] (100.0 [%])
calculation : * 4 * (engine power)
power loading (Take-off) : 6.39 [kg/kW]
power loading (operational without useful load) : 5.09 [kg/kW]
power loading (Take-off) 1 PUF: 12.77 [kg/kW]
total power : 596.6 [kW] at 2200 [r.p.m]
calculation : *5* (loads)
manoeuvre load : 5.9 [g] at 1000 [m]
limit load : 3.0 [g] ultimate load : 4.5 [g] load factor : 3.1 [g]
design flight time : 3.02 [hours]
design cycles : 15683 sorties, design hours : 47427 [hours]
operational wing loading : 910 [N/m^2]
wing stress (3 g) during operation : 136 [N/kg] at 3g emergency manoeuvre
calculation : *6* (angles of attack)
angle of attack zero lift : -1.82 ["]
max. angle of attack (stalling angle) : 14.05 ["]
angle of attack at max. speed : 0.24 ["]
calculation : *7* (lift & drag ratios
lift coefficient at angle of attack 0° : 0.15 [ ]
lift coefficient at max. angle of attack : 1.31 [ ]
max.lift coefficient full flaps : 1.41 [ ]
lift coefficient at max. speed : 0.17 [ ]
induced drag coefficient at max. speed : 0.0018 [ ]
drag coefficient at max. speed : 0.0250 [ ]
drag coefficient (zero lift) : 0.0233 [ ]
calculation : *8* (speeds
stalling speed at sea-level (OW loaded : 3685 [kg]): 134 [km/u]
stalling speed at sea-level with full flaps (normal landing weight): 119 [km/u]
landing speed at sea-level (normal landing weight : 3124 [kg]): 136 [km/hr]
max. endurance speed : 148 [km/u] min. brpu : 53 [kg/hr] at cruise height : 100 [m]
max. rate of climb speed : 146.9 [km/hr] at sea-level
max. range speed : 255 [km/u] min.fuel cons.: 0.312 [kg/km] at cruise height : 5250 [m]
cruising speed : 344 [km/hr] at 3500 [m] (power:78 [%])
maximum speed : 362 [km/hr] at 1500 [m] (power:103 [%])
climbing speed at sea-level (loaded) : 529 [m/min]
climbing speed at 1000 [m] with 1 engine out (PUF / MTOW) : 169 [m/min]
calculation : *9* (regarding various performances)
take-off speed : 163.0 [km/u]
emergency/TO power : 450 [hp] at 2333 [rpm]
static prop wash : 173 [km/u]
high wheel pressure, can only take off from paved runways
take-off distance at sea-level : 307 [m]
lift/drag ratio : 13.27 [ ]
climb to 1000m with max payload : 2.09 [min]
climb to 2000m with max payload : 4.46 [min]
climb to 3000m with max payload : 7.57 [min]
practical ceiling (operational weight 3034 [kg] ) : 7600 [m]
practical ceiling fully loaded (mtow- 30 min.fuel:3748 [kg] ) : 6400 [m]
calculation *10* (action radius & endurance)
published range : 1300 [km] with 2 crew and 554.2 [kg] useful load and 88.1 [%] fuel
range : 1174 [km] with 2 crew and 600.0 [kg] useful load and 79.6 [%] fuel
range : 1389 [km] with 6.0 passengers with each 10 [kg] luggage and 94.1 [%] fuel
Available Seat Kilometres (ASK) : 8334 [paskm]
max range theoretically with additional fuel tanks total 1509.5 [litre] fuel : 3542 [km]
useful load with range 500km : 925 [kg]
useful load with range 500km : 6 passengers
production (useful load): 318 [tonkm/hour]
production (passengers): 2063 [paskm/hour]
oil and fuel consumption per tonkm : 0.42 [kg]
fuel cost per paskm : 0.042 [eur]
crew cost per paskm : 0.094 [eur]
economic hours : 12775 [hours] is less then design hours
time between engine failure : 118 [hr]
can continue fly on 1 engine, low risk for emergency landing for PUF
writing off per paskm : 0.053 [eur]
insurance per paskm : 0.020 [eur]
maintenance cost per paskm : 0.157 [eur]
direct operating cost per paskm : 0.366 [eur]
direct operating cost per tonkm : 3.659 [eur]
Literature :
Piston-engined airliners page 35
Lockheed Model 12 Electra Junior - Wikipedia
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 2021 contact : info.aircraftinvestigation@gmail.com python 3.7.4