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weight and performance calculations for the Armstrong Whitworth F.K.3
Bulgarian airmen in the British bomber trophy, Armstrong-Whitworth FK3 Nr. 6219 at Airfield Belitsa. On February 12, 1917 2nd Lt A.C.Stopherlanded by mistake on Bulgarian territory. Bulgarian airplane pilots successfully used for 42 missions, night raids against British forces. On May 23, 1918 the engine was struck by anti-aircraft fire, the pilots were forced to land behind the front line and to abandon the aircraft, and then successfully back in the Bulgarian army
Armstrong Whitworth F.K.3
role : primary trainer
importance : ****
first flight : operational : September 1916
country : United-Kingdom
design :
production : 500 aircraft
general information :
Design based on the BE2c for bombing and reconnaissance. During production the crew position was reversed, so now the observer sat behind the pilot and could operate a movable machine gun. Speed, ceiling and flying qualities were superior to that of the BE2c. But it carried a smaller bombload and had a poorer rate of climb. However the FK3 never saw service in France. Only one operational RFC squadron, no.47 in Macedonia, used the FK3 between September 1916 and early 1918 for reconnaissance, patrol and sometimes for a bomb raid. All the other aircraft went to training squadrons in the UK for which role the airplane was well suited.
Pilotīs referred to the aircraft as `Little Ack`.
Armament: One Lewis gun on pillar mounting at the rear of the cockpit; however, when carrying bombs, neither observer nor gun could be carried. Bomb load, one 112 lb or one 100 lb bomb, or up to six 16 lb anti-personnel bombs on external racks.
Landing speed : 61 km/u
users : RFC
crew : 2
armament : 1 movable 7.70 [mm] (0.303 in) Lewis machine-gun for the observer
engine : 1 RAF 1a air-cooled 8 -cylinder V-engine 90 [hp](66.2 KW)
dimensions :
wingspan : 12.19 [m], length : 8.84 [m], height : 3.63[m]
wing area : 42.46 [m^2]
weights :
max.take-off weight : 933 [kg]
empty weight operational : 629 [kg] bombload : 51 [kg]
performance :
maximum speed : 143 [km/hr] at sea-level
service ceiling : 3660 [m]
endurance : 3.5 [hours]
estimated action radius : 225 [km]
description :
2-bay biplane with fixed landing gear and tail strut
two spar upper and lower wing
engines, landing gear, fuel and bombs in or attached to the fuselage
airscrew :
fixed pitch 4 -bladed tractor airscrew with max. efficiency :0.60 [ ]
estimated diameter airscrew 2.72 [m]
angle of attack prop : 24.93 [ ]
reduction : 0.50 [ ]
airscrew revs : 800 [r.p.m.]
pitch at Max speed 2.98 [m]
blade-tip speed at Vmax and max revs. : 121 [m/s]
calculation : *1* (dimensions)
mean wing chord : 1.74 [m]
calculated wing chord (rounded tips): 1.94 [m]
wing aspect ratio : 7.00 []
estimated gap : 1.64 [m]
gap/chord : 0.94 [ ]
seize (span*length*height) : 391 [m^3]
calculation : *2* (fuel consumption)
oil consumption : 1.5 [kg/hr]
fuel consumption(cruise speed) : 21.9 [kg/hr] (29.9 [litre/hr]) at 69 [%] power
distance flown for 1 kg fuel : 5.87 [km/kg]
estimated total fuel capacity : 119 [litre] (87 [kg])
calculation : *3* (weight)
weight engine(s) dry : 204.0 [kg] = 3.08 [kg/KW]
weight reduction gear : 2.6 [kg]
weight 9 litre oil tank : 0.7 [kg]
oil tank filled with 0.5 litre oil : 0.4 [kg]
oil in engine 0 litre oil : 0.3 [kg]
fuel in engine 0 litre fuel : 0.3 [kg]
weight 13 litre gravity patrol tank(s) : 1.9 [kg]
weight cowling 2.6 [kg]
weight airscrew(s) (wood) incl. boss & bolts : 23.2 [kg]
total weight propulsion system : 238 [kg](25.5 [%])
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fuselage skeleton (wood gauge : 6.54 [cm]): 97 [kg]
bracing : 6.0 [kg]
fuselage covering ( 14.8 [m2] doped linen fabric) : 4.7 [kg]
weight dual controls + indicators: 13.7 [kg]
weight seats : 6.0 [kg]
weight other details, lighting set, etc. : 5.1 [kg]
weight bomb storage : 3.6 [kg]
weight 106 [litre] main fuel tank empty : 8.5 [kg]
weight engine mounts & firewalls : 3 [kg]
total weight fuselage : 148 [kg](15.8 [%])
***************************************************************
weight wing covering (doped linen fabric) : 27 [kg]
total weight ribs (44 ribs) : 55 [kg]
load on front upper spar (clmax) per running metre : 517.1 [N]
load on rear upper spar (vmax) per running metre : 197.7 [N]
total weight 8 spars : 44 [kg]
weight wings : 127 [kg]
weight wing/square meter : 2.98 [kg]
weight 8 interplane struts & cabane : 17.4 [kg]
weight cables (72 [m]) : 5.0 [kg] (= 69 [gram] per metre)
diameter cable : 3.4 [mm]
weight fin & rudder (1.7 [m2]) : 5.4 [kg]
weight stabilizer & elevator (4.8 [m2]): 14.6 [kg]
total weight wing surfaces & bracing : 169 [kg] (18.1 [%])
*******************************************************************
weight machine-gun(s) : 12.7 [kg]
weight Scarff ring mounting mg :6.9 [kg]
weight armament : 20 [kg]
********************************************************************
wheel pressure : 466.5 [kg]
weight 2 wheels (740 [mm] by 82 [mm]) : 19.8 [kg]
weight tailskid : 2.5 [kg]
weight undercarriage with axle 28.3 [kg]
total weight landing gear : 50.7 [kg] (5.4 [%]
*******************************************************************
********************************************************************
calculated empty weight : 626 [kg](67.1 [%])
weight oil for 4.2 hours flying : 6.4 [kg]
weight 5 drums empty : 1.0 [kg]
weight ammunition (235 rounds) : 7.5 [kg]
*******************************************************************
calculated operational weight empty : 640 [kg] (68.6 [%])
published operational weight empty : 629 [kg] (67.4 [%])
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weight crew : 162 [kg]
weight fuel for 2.0 hours flying : 44 [kg]
A British pilot, possibly 2nd Lt. A.C. Stopher from No. 47 Squadron RAF, Thessalonika with FK.3.
********************************************************************
operational weight : 846 [kg](90.6 [%])
bomb load : 51 [kg]
operational weight bombing mission : 897 [kg]
fuel reserve : 36 [kg] enough for 1.66 [hours] flying
operational weight fully loaded : 933 [kg] with fuel tank filled for 92 [%]
published maximum take-off weight : 933 [kg] (100.0 [%])
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calculation : * 4 * (engine power)
power loading (operational without bombload) : 12.77 [kg/kW]
total power : 66.2 [kW] at 1600 [r.p.m]
calculation : *5* (loads)
manoeuvre load : 3.3 [g] at 1000 [m]
Early FK3 with the observer still in the front seat.
limit load : 3.75 [g] ultimate load : 5.6 [g] load factor : 2.0 [g]
design flight time : 1.40 [hours]
design cycles : 393 sorties, design hours : 550 [hours]
operational wing loading : 195 [N/m^2]
wing stress (3 g) during operation : 196 [N/kg] at 3g emergency manoeuvre
calculation : *6* (angles of attack)
angle of attack zero lift : -1.45 ["]
max. angle of attack (stalling angle) : 12.40 ["]
angle of attack at max. speed : 1.02 ["]
calculation : *7* (lift & drag ratios
lift coefficient at angle of attack 0° :0.12 [ ]
lift coefficient at max. angle of attack : 1.15 [ ]
lift coefficient at max. speed : 0.20 [ ]
induced drag coefficient at max. speed : 0.0034 [ ]
drag coefficient at max. speed : 0.0241 [ ]
drag coefficient (zero lift) : 0.0207 [ ]
calculation : *8* (speeds
stalling speed at sea-level (OW): 60 [km/u]
landing speed at sea-level (OW without bombload): 72 [km/hr]
min. drag speed (max endurance) : 99 [km/hr] at 1830 [m](power :51 [%])
min. power speed (max range) : 101 [km/hr] at 1830 [m] (power:52 [%])
max. rate of climb speed : 90.9 [km/hr] at sea-level
cruising speed : 129 [km/hr] op 1830 [m] (power:70 [%])
design speed prop : 136 [km/hr]
maximum speed : 143 [km/hr] op 100 [m] (power:99 [%])
climbing speed at sea-level (without bombload) : 131 [m/min]
calculation : *9* (regarding various performances)
take-off distance at sea-level : 210 [m]
lift/drag ratio : 12.21 [ ]
max. practical ceiling : 3950 [m] with flying weight :724 [kg]
practical ceiling (operational weight): 3050 [m] with flying weight :846 [kg]
practical ceiling fully loaded (mtow- 1 hour fuel) : 2600 [m] with flying weight :911 [kg]
published ceiling (3660 [m]
climb to 1500m (without bombload) : 13.42 [min]
max. dive speed : 340.4 [km/hr] at 1600 [m] height
load factor at max. angle turn 1.54 ["g"]
turn radius at 500m: 39 [m]
time needed for 360* turn 11.6 [seconds] at 500m
calculation *10* (action radius & endurance)
operational endurance : 3.66 [hours] with 2 crew and 51 [kg] useful (bomb)load and 92.2 [%] fuel
published endurance : 3.50 [hours] with 2 crew and possible useful (bomb) load : 55 [kg] and 88.1 [%] fuel
action radius : 327 [km] with 2 crew and 20[kg] photo camera/radio transmitter or bombload
max range theoretically with additional fuel tanks for total 300 [litre] fuel : 1291 [km]
useful load with action-radius 250km : 135 [kg]
production : 17.32 [tonkm/hour]
oil and fuel consumption per tonkm : 1.35 [kg]
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Literature :
Praktisch handboek vliegtuigen deel 1 page 212
Jane s FAWOI page 46fd
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 23 November 2019 contact : info.aircraftinvestigation@gmail.com python 3.7.4