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weight and performance calculations for the Junkers J.I
Junkers J.I
role : armoured ground attack aircraft
importance : ***
first flight : operational : August 1917
country : Germany
design : Dr.Hugo Junkers, Prof.Madelung
production : 227 aircraft
general information :
Armoured all-metal ground attack aircraft. Armour : 5mm thick 470 kgs.
The aircraft had two fuel tanks with a capacity of around 120 litres (32 US gal).[5] The main tank (divided in two for redundancy) was supplemented by a smaller, 30-litre (7.9 US gal) gravity tank. This was intended to supply fuel to the engine by gravity feed in the event of an engine fuel pump failure; it contained enough fuel for thirty minutes on full power. There was a manual fuel pump for use when the gravity tank was empty. Underpowered so tricky at take-off and landing from rough grounds, but over the frontline it’s strength and armoured protection made it popular with its crews. Unusual was the thick cantilever upper wing.
It had radio equipment for communication with the rear command post.
The mounting of twin fixed downward firing machine guns proved to be unsatisfactory during operation and it was replaced by two synchronized forward firing machine guns.
users : Germany
crew : 2
armament : 2 synchronized 7.92 [mm] (0.312 in) Spandau LMG 08/15 machine-guns
and 1 movable 7.92 [mm] (0.312 in) Parabellum MG 14 machine-gun for the observer
engine : 1 Benz Bz.IV liquid-cooled 6 -cylinder inline engine 220 [hp](161.8 KW)
dimensions :
wingspan : 16.0 [m], length : 9.1 [m], height : 3.4[m]
wing area : 49.4 [m^2]
weights :
max.take-off weight : 2171 [kg]
empty weight operational : 1762 [kg] bombload : 0 [kg]
performance :
maximum speed : 155 [km/hr] at sea-level
climbing speed : 62 [m/min]
service ceiling : 3300 [m]
endurance : 2.0 [hours]
estimated action radius : 143 [km]
description :
sesquiplane with fixed landing gear and tail strut
upper wingtips supported by slanted struts
two spar upper and lower wing
engines, landing gear, fuel and bombs in or attached to the fuselage
airscrew :
fixed pitch 2 -bladed tractor airscrew with max. efficiency :0.64 [ ]
estimated diameter airscrew 3.00 [m]
angle of attack prop : 14.63 [ ]
fine pitch
reduction : 1.00 [ ]
airscrew revs : 1400 [r.p.m.]
pitch at Max speed 1.85 [m]
blade-tip speed at Vmax and max revs. : 224 [m/s]
calculation : *1* (dimensions)
mean wing chord : 2.06 [m]
calculated wing chord (rounded tips): 2.32 [m]
wing aspect ratio : 7.77 []
estimated gap : 1.71 [m]
gap/chord : 0.83 [ ]
seize (span*length*height) : 495 [m^3]
calculation : *2* (fuel consumption)
oil consumption : 2.1 [kg/hr]
fuel consumption(cruise speed) : 47.3 [kg/hr] (64.6 [litre/hr]) at 87 [%] power
distance flown for 1 kg fuel : 2.95 [km/kg]
estimated total fuel capacity : 150 [litre] (110 [kg])
calculation : *3* (weight)
weight engine(s) dry : 370.0 [kg] = 2.29 [kg/KW]
weight 10 litre oil tank : 1.2 [kg]
oil tank filled with 1.2 litre oil : 1.1 [kg]
oil in engine 9 litre oil : 8.1 [kg]
fuel in engine 1 litre fuel : 0.8 [kg]
weight 30 litre gravity patrol tank(s) : 3.0 [kg]
weight radiator : 24.3 [kg]
weight exhaust pipes & fuel lines 14.5 [kg]
weight self-starter : 4.0 [kg]
weight cowling 6.5 [kg]
weight airscrew(s) (wood) incl. boss & bolts : 24.3 [kg]
total weight propulsion system : 456 [kg](21.0 [%])
***************************************************************
weight 5.0 [mm] armour plating engine, crew and fuel tank (12.1 [m^2]) : 470 [kg]
percentage fuselage armoured : 61.7 [%]
armour plating forms integral part of the fuselage, extra strong wooden frame
fuselage skeleton (wood gauge : 9.78 [cm]): 85 [kg]
bracing : 9.5 [kg]
fuselage covering ( 15.6 [m2] doped linen fabric) : 5.0 [kg]
weight controls + indicators: 7.0 [kg]
weight seats : 6.0 [kg]
weight other details, lighting set, etc. : 5.1 [kg]
weight transceiver : 27 [kg]
weight 120 [litre] main fuel tank empty : 11.5 [kg]
weight engine mounts & firewalls : 3 [kg]
total weight fuselage : 630 [kg](29.0 [%])
***************************************************************
weight wing covering (doped linen fabric) : 32 [kg]
total weight ribs (86 ribs) : 129 [kg]
load on front upper spar (clmax) per running metre : 715.0 [N]
load on rear upper spar (vmax) per running metre : 355.5 [N]
total weight 8 spars : 105 [kg]
weight wings : 266 [kg]
weight wing/square meter : 5.38 [kg]
weight 4 interplane struts & cabane : 118.8 [kg]
weight cables (9 [m]) : 1.5 [kg] (= 165 [gram] per metre)
diameter cable : 5.2 [mm]
weight fin & rudder (3.0 [m2]) : 16.4 [kg]
weight stabilizer & elevator (5.6 [m2]): 30.2 [kg]
total weight wing surfaces & bracing : 432 [kg] (19.9 [%])
*******************************************************************
weight machine-gun(s) : 43.5 [kg]
weight Schneider ring mounting mg :5.5 [kg]
weight ammunition magazine(s) :7.0 [kg]
weight Fokker Zentralsteuerung synchronization gear : 2.0 [kg]
weight armament : 58 [kg]
********************************************************************
wheel pressure : 1085.5 [kg]
weight 2 wheels (860 [mm] by 132 [mm]) : 48.7 [kg]
weight tailskid : 3.8 [kg]
weight undercarriage with axle 52.4 [kg]
total weight landing gear : 104.9 [kg] (4.8 [%]
*******************************************************************
********************************************************************
calculated empty weight : 1682 [kg](77.5 [%])
weight oil for 2.5 hours flying : 5.2 [kg]
weight cooling fluids : 33.3 [kg]
weight 1 drums empty : 4.5 [kg]
weight ammunition (3000 rounds) : 89.2 [kg]
weight signal pistol with cartridges : 3.6 [kg]
weight automatic pistol with spare magazines : 1.2 [kg]
*******************************************************************
calculated operational weight empty : 1814 [kg] (83.6 [%])
published operational weight empty : 1762 [kg] (81.2 [%])
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"
weight crew : 162 [kg]
weight fuel for 2.0 hours flying : 95 [kg]
********************************************************************
operational weight : 2071 [kg](95.4 [%])
estimated bomb load : 50 [kg]
operational weight bombing mission : 2121 [kg]
fuel reserve : 15 [kg] enough for 0.33 [hours] flying
possible additional useful load : 34 [kg]
operational weight fully loaded : 2171 [kg] with fuel tank filled for 100 [%]
published maximum take-off weight : 2171 [kg] (100.0 [%])
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calculation : * 4 * (engine power)
power loading (operational without bombload) : 12.80 [kg/kW]
total power : 161.8 [kW] at 1400 [r.p.m]
calculation : *5* (loads)
manoeuvre load : 1.8 [g] at 1000 [m]
limit load : 3.0 [g] ultimate load : 4.5 [g] load factor : 1.5 [g]
design flight time : 1.64 [hours]
design cycles : 335 sorties, design hours : 550 [hours]
operational wing loading : 411 [N/m^2]
wing stress (3 g) during operation : 229 [N/kg] at 3g emergency manoeuvre
calculation : *6* (angles of attack)
angle of attack zero lift : -1.18 ["]
max. angle of attack (stalling angle) : 12.33 ["]
angle of attack at max. speed : 3.12 ["]
calculation : *7* (lift & drag ratios
lift coefficient at angle of attack 0° :0.10 [ ]
lift coefficient at max. angle of attack : 1.15 [ ]
lift coefficient at max. speed : 0.37 [ ]
induced drag coefficient at max. speed : 0.0073 [ ]
drag coefficient at max. speed : 0.0424 [ ]
drag coefficient (zero lift) : 0.0351 [ ]
calculation : *8* (speeds
stalling speed at sea-level (OW): 87 [km/u]
landing speed at sea-level (OW without bombload): 104 [km/hr]
min. drag speed (max endurance) : 106 [km/hr] at 300 [m](power :55 [%])
min. power speed (max range) : 118 [km/hr] at 300 [m] (power:60 [%])
max. rate of climb speed : 101.2 [km/hr] at sea-level
cruising speed : 140 [km/hr] op 300 [m] (power:78 [%])
design speed prop : 147 [km/hr]
maximum speed : 155 [km/hr] op 100 [m] (power:99 [%])
climbing speed at sea-level (without bombload) : 126 [m/min]
calculation : *9* (regarding various performances)
take-off distance at sea-level : 292 [m]
lift/drag ratio : 11.42 [ ]
max. practical ceiling : 3950 [m] with flying weight :1825 [kg]
practical ceiling (operational weight) : 3025 [m] with flying weight :2071 [kg] line 3385
practical ceiling fully loaded (mtow- 1 hour fuel) : 2850 [m] with flying weight :2124 [kg]
published ceiling (3300 [m]
climb to 1500m (without bombload) : 13.87 [min]
max. dive speed : 440.4 [km/hr] at 1850 [m] height
load factor at max. angle turn 1.56 ["g"]
turn radius at 500m: 82 [m]
time needed for 360* turn 16.6 [seconds] at 500m
calculation *10* (action radius & endurance)
operational endurance : 2.33 [hours] with 2 crew and 84 [kg] useful (bomb)load and 100.0 [%] fuel
published endurance : 2.05 [hours] with 2 crew and possible useful (bomb) load : 98 [kg] and 88.1 [%] fuel
action radius : 257 [km] with 2 crew and 20[kg] photo camera or bombload
max range theoretically with additional fuel tanks for total 504 [litre] fuel : 1089 [km]
useful load with action-radius 250km : 200 [kg]
production : 27.89 [tonkm/hour]
oil and fuel consumption per tonkm : 1.77 [kg]
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Literature :
Warplanes WW1 page 107
Praktisch handboek vliegtuigen deel 1 page 294
Jane’s fighting aircraft WWI page 14,167
German aircraft of the first world war page 154,155,156,157
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 29 February 2020 contact : info.aircraftinvestigation@gmail.com python 3.7.4