Armstrong Whitworth F.K.8
role : multi role combat aircraft
first flight : May 1916 operational : January 1917
country : United-Kingdom
design : Frits Koolhoven
production : 1500 aircraft
general information :
The FK8 was a most versatile aircraft and was used with 22 British squadrons , including training. It was developed from the FK3, basically being a scaled up version. No.35 sq. was the first British squadron equipped with the type arriving in France January 1917. It was also used for home defence with 50 sq. And 17 & 47 sq. used the type in Macedonia and 147 sq. in Palestine. The FK8 was contemporary with the RAF RE8 with the FK8 considered superior to the RAF design. The FK8 became known as the “Big Ack”. The FK8 was well built, had a good defence and popular with it’s crews. It was used for reconnaissance, patrol, day & night bombing and ground attack throughout 1917 and 1918. The spacious fuselage made it possible to operate the bulky photo camera’s from the inside. On 27 march 1918 a FK8 was attacked by 8 Fokker Dr.Is. It’s fuel tank and rear cockpit was set ablaze while still carrying its bombload and ammo. Both crew members were seriously wounded but managed to shoot down 4 Dr.Is and finally the pilot Mcleod managed to make a successful crash landing in no-man’s land for which he received a VC.
Landing speed : 72,4 km/u.
At first the Vickers machine gun was synchronized by a mechanic Armstrong Whitworth gear, but this proved unreliable and was later replaced by the hydraulic Constantinesco gear.
users : RFC (35,2,8,10,82,17,47 squadron)
crew : 2
armament : 1 synchronized 7.70 [mm] (0.303 in) Vickers machine-gun
and 1 movable 7.70 [mm] (0.303 in) Lewis machine-gun for the observer
engine : 1 Beardmore liquid-cooled 6 -cylinder inline engine 160 [hp](117.7 KW)
dimensions :
wingspan : 13.26 [m], length : 9.45 [m], height : 3.35[m]
wing area : 50.17 [m^2]
weights :
max.take-off weight : 1275 [kg]
empty weight operational : 869 [kg] bombload : 118 [kg]
performance :
maximum speed : 158 [km/hr] at sea-level
climbing speed : 139 [m/min]
service ceiling : 3962 [m]
endurance : 3.0 [hours]
estimated action radius : 213 [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 2 -bladed tractor airscrew with max. efficiency :0.67 [ ]
estimated diameter airscrew 2.92 [m]
angle of attack prop : 17.03 [ ]
reduction : 1.00 [ ]
airscrew revs : 1250 [r.p.m.]
pitch at Max speed 2.11 [m]
blade-tip speed at Vmax and max revs. : 196 [m/s]
calculation : *1* (dimensions)
mean wing chord : 1.89 [m]
calculated wing chord (rounded tips): 2.10 [m]
wing aspect ratio : 7.01 []
estimated gap : 1.77 [m]
gap/chord : 0.94 [ ]
seize (span*length*height) : 420 [m^3]
calculation : *2* (fuel consumption)
oil consumption : 2.5 [kg/hr]
fuel consumption(cruise speed) : 30.5 [kg/hr] (41.6 [litre/hr]) at 65 [%] power
distance flown for 1 kg fuel : 4.66 [km/kg]
estimated total fuel capacity : 142 [litre] (104 [kg])
calculation : *3* (weight)
weight engine(s) dry : 279.0 [kg] = 2.37 [kg/KW]
weight 13 litre oil tank : 1.1 [kg]
oil tank filled with 0.9 litre oil : 0.8 [kg]
oil in engine 7 litre oil : 5.9 [kg]
fuel in engine 1 litre fuel : 0.6 [kg]
weight 18 litre gravity patrol tank(s) : 2.7 [kg]
weight radiator : 16.9 [kg]
weight exhaust pipes & fuel lines 14.0 [kg]
weight cowling 4.7 [kg]
weight airscrew(s) (wood) incl. boss & bolts : 19.0 [kg]
total weight propulsion system : 343 [kg](26.9 [%])
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fuselage skeleton (wood gauge : 6.80 [cm]): 112 [kg]
bracing : 7.5 [kg]
fuselage covering ( 16.9 [m2] doped linen fabric) : 5.4 [kg]
weight controls + indicators: 6.8 [kg]
FK8 with adapted landing gear and radiators
weight seats : 6.0 [kg]
weight other details, lighting set, etc. : 5.1 [kg]
weight bomb storage : 8.3 [kg]
weight C.F.S4B bomb sight : 1.2 [kg]
weight 124 [litre] main fuel tank empty : 9.9 [kg]
weight engine mounts & firewalls : 6 [kg]
total weight fuselage : 168 [kg](13.2 [%])
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weight wing covering (doped linen fabric) : 32 [kg]
total weight ribs (55 ribs) : 76 [kg]
load on front upper spar (clmax) per running metre : 616.5 [N]
load on rear upper spar (vmax) per running metre : 248.1 [N]
total weight 8 spars : 62 [kg]
weight wings : 170 [kg]
weight wing/square meter : 3.39 [kg]
weight 8 interplane struts & cabane : 24.9 [kg]
weight cables (78 [m]) : 7.7 [kg] (= 98 [gram] per metre)
diameter cable : 4.0 [mm]
weight fin & rudder (2.0 [m2]) : 7.2 [kg]
weight stabilizer & elevator (5.6 [m2]): 19.5 [kg]
total weight wing surfaces & bracing : 229 [kg] (18.0 [%])
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weight machine-gun(s) : 28.6 [kg]
weight Scarff ring mounting mg :6.9 [kg]
weight ammunition magazine(s) :1.8 [kg]
weight Armstrong Whitworth synchronization gear : 1.0 [kg]
weight Aldis gunsight : 0.8 [kg]
weight armament : 39 [kg]
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wheel pressure : 637.5 [kg]
weight 2 wheels (760 [mm] by 95 [mm]) : 29.5 [kg]
weight tailskid : 2.7 [kg]
weight undercarriage with axle 25.6 [kg]
total weight landing gear : 57.8 [kg] (4.5 [%]
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calculated empty weight : 837 [kg](65.7 [%])
weight oil for 3.6 hours flying : 8.9 [kg]
weight cooling fluids : 25.4 [kg]
weight 5 drums empty : 1.0 [kg]
weight ammunition (635 rounds) : 18.5 [kg]
weight Very pistol with cartridges : 3.6 [kg]
weight automatic pistol with spare magazines : 1.2 [kg]
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calculated operational weight empty : 895 [kg] (70.2 [%])
published operational weight empty : 869 [kg] (68.2 [%])
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weight crew : 162 [kg]
weight fuel for 2.0 hours flying : 61 [kg]
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operational weight : 1118 [kg](87.7 [%])
bomb load : 118 [kg]
operational weight bombing mission : 1236 [kg]
fuel reserve : 39 [kg] enough for 1.28 [hours] flying
operational weight fully loaded : 1275 [kg] with fuel tank filled for 96 [%]
published maximum take-off weight : 1275 [kg] (100.0 [%])
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calculation : * 4 * (engine power)
power loading (operational without bombload) : 9.50 [kg/kW]
total power : 117.7 [kW] at 1250 [r.p.m]
calculation : *5* (loads)
manoeuvre load : 3.6 [g] at 1000 [m]
limit load : 3.75 [g] ultimate load : 5.6 [g] load factor : 1.9 [g]
design flight time : 2.40 [hours]
design cycles : 271 sorties, design hours : 650 [hours]
operational wing loading : 219 [N/m^2]
wing stress (3 g) during operation : 193 [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 : 0.81 ["]
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 : 0.19 [ ]
induced drag coefficient at max. speed : 0.0028 [ ]
drag coefficient at max. speed : 0.0300 [ ]
drag coefficient (zero lift) : 0.0272 [ ]
calculation : *8* (speeds
stalling speed at sea-level (OW): 64 [km/u]
landing speed at sea-level (OW without bombload): 76 [km/hr]
min. drag speed (max endurance) : 98 [km/hr] at 1981 [m](power :41 [%])
min. power speed (max range) : 103 [km/hr] at 1981 [m] (power:42 [%])
max. rate of climb speed : 96.4 [km/hr] at sea-level
cruising speed : 142 [km/hr] op 1981 [m] (power:66 [%])
design speed prop : 150 [km/hr]
maximum speed : 158 [km/hr] op 100 [m] (power:98 [%])
climbing speed at sea-level (without bombload) : 223 [m/min]
calculation : *9* (regarding various performances)
take-off distance at sea-level : 129 [m]
lift/drag ratio : 10.68 [ ]
max. practical ceiling : 4525 [m] with flying weight :968 [kg]
practical ceiling (operational weight): 3875 [m] with flying weight :1118 [kg]
practical ceiling fully loaded (mtow- 1 hour fuel) : 3350 [m] with flying weight :1244 [kg]
published ceiling (3962 [m]
climb to 1500m (without bombload) : 7.75 [min]
climb to 3000m (without bombload) : 20.76 [min]
max. dive speed : 372.0 [km/hr] at 2350 [m] height
load factor at max. angle turn 1.92 ["g"]
turn radius at 500m: 39 [m]
time needed for 360* turn 9.8 [seconds] at 500m
calculation *10* (action radius & endurance)
operational endurance : 3.28 [hours] with 2 crew and 118 [kg] bombload and 96.2 [%] fuel
published endurance : 3.00 [hours] with 2 crew and possible useful (bomb) load : 126 [kg] and 88.1 [%] fuel
action radius : 461 [km] with 2 crew and 20[kg] photo camera/radio transmitter or bombload
max range theoretically with additional fuel tanks for total 457 [litre] fuel : 1561 [km]
useful load with action-radius 250km : 228 [kg]
production : 32.37 [tonkm/hour]
oil and fuel consumption per tonkm : 1.02 [kg]
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Literature :
Warplanes WW1 page 99,107td
Praktisch handboek vliegtuigen deel 1 page 198
Jane’s FAWOI page 47fd
Bombers 1914-19 page 64
Armament of British Aircraft 1909-1939 page 5
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 September 2019 contact : info.aircraftinvestigation@gmail.com python 3.7.4