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HF.20 at Larkhill
Henri Farman HF.20
role : two-seat unarmed reconnaissance
first flight : 1913 operational : May 1914
country : France
design : Henri Farman
production : 200 aircraft at Billancourt, 167 Rue de Silly.
general information :
The types HF.20 to HF.24 were developed by Henry Farman at the same time as the M.F.7 designed by his brother Maurice Farman. Both types became even popular. The HF.20 did not have much power and could be used only for light reconnaissance duties. It could take some bombs or a machine gun but this reduced performance considerably. Hf.20 to HF.23 differed only in dimensions. The Farman factory could produce the type on a large scale, it was the only factory at that time capable of mass-production. It is said it could turn out 10 aircraft a day and before the war many had been delivered to the France army and taken into service.
The RFC sent Farman F.20’s of 3,5 and 6 squadron to France on 14 august 1914. L.A.Strange of 5sq. flew such an F.20. It was experimentally fitted with a machine gun. For the channel crossing Strange had to take a drunken driver along, together with his gear, a rifle, a bottle of whiskey and his own personal gear. Total weight : 83+30+10+1+80+30+20 = 254 kg. Due to all this extra weight the airplane could barely take off at the start in Gosport (near Portsmouth). Distance to Dover is 175km trough the air (fuel consumption 2.74 km/kg > 64 kg fuel needed)+10 kg reserve. Empty weight : 365 kg + 254 kg useful load + 74 kg fuel = 693 kg > 33 kg above MTOW. At the landing in Dover Strange ran in a ditch and broke a landing-ski. 16 august he crossed the channel with the driver as his passenger. He lands at the airfield at Amiens at 150 km distance and joins the rest of his 5th squadron. On 22 august 1914 L.A.Strange took of with his Farman reg.341 armed with a machine gun to intercept a German aircraft. It was the first time an allied airplane tried to shoot down a German aircraft with a machine gun. Due to the weight of the gun Strange could not climb above 1000m and the German scout escaped.
No.26 sq. RFC went to Africa with the F.20. Two Henri Farman’s and a Caudron G.III directed the fire which sank the Konigsberg in the Rufiji river on 11 June 1915.
30 RFC HF.20’s served in 1914 at the Western front, 55 went to the Middle-East in 1916 and in 1917 still 25 aircraft were used by Home Defence. Also it was used as training aircraft. The French used 30 F.20/21/22’s at the beginning of WWI. The flew with escadrilles 1, 7,13,19 and 28. The Belgian Army used Farman’s with Escadrille 1 and 2. In 1913 the Dutch LVA received 3 F.20’s (reg. LA2/LA3/LA4) and F.22’s.
users : France, RFC, RNAS, Belgium, Netherlands, Rumania, Russia
crew : 2
armament : no fixed armament, hand held guns and 1350 darts/flechettes against ground
forces could be carried
engine : 1 Gnome 7A Monosoupape air-cooled 7 -cylinder Monosoupape rotary engine 80 [hp](58.8 KW)
dimensions :
wingspan : 13.64 [m], length : 8.06 [m], height : 3.1[m]
wing area : 34.84 [m^2]
HF.20 Musee de l’air , Le Bourget
weights :
max.take-off weight : 660 [kg]
empty weight operational : 371 [kg] bombload : 0 [kg]
performance :
maximum speed : 105 [km/hr] at sea-level
climbing speed : 71 [m/min]
service ceiling : 2750 [m]
estimated endurance : 3.5 [hours]
estimated action radius : 165 [km]
description :
2-bay sesquiplane with fixed underwing 4 -wheel landing gear and tail strut
upper wingtips supported by slanted flying wires
two spar upper and lower wing
tail supported by two open tail booms
engine, fuel and bombload in or attached to fuselage, landing gear attached to the wing
airscrew :
fixed pitch 2 -bladed pusher airscrew with max. efficiency :0.62 [ ]
estimated diameter airscrew 2.38 [m]
angle of attack prop : 14.58 [ ]
fine pitch
reduction : 1.00 [ ]
airscrew revs : 1200 [r.p.m.]
pitch at Max speed 1.46 [m]
blade-tip speed at Vmax and max revs. : 152 [m/s]
calculation : *1* (dimensions)
mean wing chord : 1.70 [m]
calculated wing chord (rounded tips): 1.93 [m]
wing aspect ratio : 8.01 []
estimated gap : 1.42 [m]
gap/chord : 0.83 [ ]
seize (span*length*height) : 341 [m^3]
calculation : *2* (fuel consumption)
oil consumption : 6.5 [kg/hr]
fuel consumption(cruise speed) : 18.3 [kg/hr] (25.0 [litre/hr]) at 74 [%] power
distance flown for 1 kg fuel : 5.15 [km/kg]
estimated total fuel capacity : 99 [litre] (73 [kg])
calculation : *3* (weight)
weight engine(s) dry : 109.4 [kg] = 1.86 [kg/KW]
weight 32 litre oil tank : 2.7 [kg]
oil tank filled with 0.4 litre oil : 0.4 [kg]
oil in engine 0 litre oil : 0.3 [kg]
fuel in engine 0 litre fuel : 0.3 [kg]
weight 11 litre gravity patrol tank(s) : 1.6 [kg]
weight cowling 2.4 [kg]
weight airscrew(s) (wood) incl. boss & bolts : 13.5 [kg]
total weight propulsion system : 128 [kg](19.4 [%])
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weight tail boom : 15 [kg]
fuselage skeleton (wood gauge : 4.65 [cm]): 45 [kg]
bracing : 2.7 [kg]
fuselage covering ( 8.0 [m2] doped linen fabric) : 2.6 [kg]
weight controls + indicators: 6.5 [kg]
weight seats : 6.0 [kg]
weight other details, lighting set, etc. : 5.1 [kg]
weight 89 [litre] main fuel tank empty : 7.1 [kg]
weight engine mounts & firewalls : 3 [kg]
total weight fuselage : 77 [kg](11.7 [%])
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weight wing covering (doped linen fabric) : 22 [kg]
total weight ribs (32 ribs) : 39 [kg]
load on front upper spar (clmax) per running metre : 296.3 [N]
load on rear upper spar (vmax) per running metre : 115.8 [N]
total weight 8 spars : 26 [kg]
weight wings : 87 [kg]
weight wing/square meter : 2.50 [kg]
weight 8 interplane struts & cabane : 8.9 [kg]
weight cables (58 [m]) : 2.7 [kg] (= 47 [gram] per metre)
diameter cable : 2.8 [mm]
weight fin & rudder (2.2 [m2]) : 5.7 [kg]
weight stabilizer & elevator (3.3 [m2]): 8.6 [kg]
total weight wing surfaces & bracing : 113 [kg] (17.1 [%])
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weight armament : 0 [kg]
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good soft ground capabilities
wheel pressure : 165.0 [kg]
weight 4 wheels (670 [mm] by 79 [mm]) : 23.4 [kg]
weight tailskid : 1.3 [kg]
weight undercarriage with axle 9.3 [kg]
total weight landing gear : 34.0 [kg] (5.2 [%]
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calculated empty weight : 352 [kg](53.4 [%])
weight oil for 4.2 hours flying : 27.2 [kg]
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calculated operational weight empty : 380 [kg] (57.5 [%])
published operational weight empty : 371 [kg] (56.2 [%])
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weight crew : 162 [kg]
weight fuel for 2.0 hours flying : 37 [kg]
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operational weight : 578 [kg](87.6 [%])
estimated bomb load : 50 [kg]
operational weight bombing mission : 628 [kg]
weight camera : 20 [kg]
operational weight photo mission : 598 [kg]
fuel reserve : 36 [kg] enough for 1.97 [hours] flying
possible additional useful load : 25 [kg]
operational weight fully loaded : 660 [kg] with fuel tank filled for 100 [%]
published maximum take-off weight : 660 [kg] (100.0 [%])
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calculation : * 4 * (engine power)
power loading (operational without bombload) : 9.83 [kg/kW]
total power : 58.8 [kW] at 1200 [r.p.m]
calculation : *5* (loads)
manoeuvre load : 2.1 [g] at 1000 [m]
limit load : 3.75 [g] ultimate load : 5.6 [g] load factor : 1.9 [g]
design flight time : 2.80 [hours]
design cycles : 266 sorties, design hours : 745 [hours]
operational wing loading : 168 [N/m^2]
wing stress (3 g) during operation : 202 [N/kg] at 3g emergency manoeuvre
calculation : *6* (angles of attack)
angle of attack zero lift : -1.17 ["]
max.angle of attack (stalling angle) : 12.23 ["]
angle of attack at max.speed : 2.52 ["]
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 : 0.32 [ ]
induced drag coefficient at max.speed : 0.0053 [ ]
drag coefficient at max.speed : 0.0690 [ ]
drag coefficient (zero lift) : 0.0637 [ ]
calculation : *8* (speeds
stalling speed at sea-level (OW): 55 [km/u]
landing speed at sea-level (OW without bombload): 66 [km/hr]
min. drag speed (max endurance) = minimum speed*1.1 at cruise height : 64 [km/hr] at 1375 [m] (power:37 [%])
min. power speed (max range) : 64 [km/hr] at 1375 [m] (power:37 [%])
max.rate of climb speed : 62.9 [km/hr] at sea-level
cruising speed : 94 [km/hr] op 1375 [m] (power:68 [%])
design speed prop : 100 [km/hr]
maximum speed : 105 [km/hr] op 100 [m] (power:99 [%])
climbing speed at sea-level (without bombload) : 211 [m/min]
calculation : *9* (regarding various performances)
take-off distance at sea-level : 99 [m]
lift/drag ratio : 8.61 [ ]
max. practical ceiling : 5875 [m] with flying weight :470 [kg]
practical ceiling (operational weight): 4800 [m] with flying weight :578 [kg]
practical ceiling fully loaded (mtow- 1 hour fuel) : 4225 [m] with flying weight :642 [kg]
published ceiling (2750 [m]
climb to 1500m (without bombload) : 7.94 [min]
climb to 3000m (without bombload) : 19.51 [min]
max.dive speed : 247.2 [km/hr] at 3225 [m] height
load factor at max.angle turn 2.12 ["g"]
turn radius at 500m: 29 [m]
time needed for 360* turn 7.9 [seconds] at 500m
calculation *10* (action radius & endurance)
operational endurance : 3.73 [hours] with 2 crew and 50 [kg] useful (bomb)load and 93.8 [%] fuel
published endurance : 3.50 [hours] with 2 crew and possible useful (bomb) load : 54 [kg] and 88.1 [%] fuel
action radius : 253 [km] with 2 crew and 20[kg] photo camera/radio transmitter or bombload
max range theoretically with additional fuel tanks for total 272 [litre] fuel : 1027 [km]
useful load with action-radius 250km : 102 [kg]
production : 9.67 [tonkm/hour]
oil and fuel consumption per tonkm : 2.57 [kg]
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Literature :
gevechtsvliegtuigen 14-18 deel 2 page12
Oorlogsvliegtuigen 1914-1918 page 39,49
Van Brik tot Starfighter page 20,21,22,23
Praktisch handboek vliegtuigen deel 1 page135
Jane’s Fighting Aircraft of WOI page111 Tussen vleugels van linnen page 27
Bombers 1914-19 page101,102
The friendless sky page 32
Warplanes WOI page 38
They fought for the sky page 20
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.
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(c) B van der Zalm 04 January 2019 contact : info.aircraftinvestigation@gmail.com python 3.7.2(64-bit)