AIRCRAFT PERFORMANCE AND WEIGHT INVESTIGATION >>>> HOME PAGE
weight and performance calculations for the Letord Let.5
Letord Let.5
role : medium-weight bomber
importance : ***
first flight : operational : June 1917
country : France
design : Georges Lepere
production : 51 aircraft
general information :
Letord type I was designed in 1916 to meet a requirement from
Lt.Col Dorand for a twin-engined reconnaissance airplane as replacement for the Caudron R.4. 7 different types emerged, 3 for reconnaissance, 3 for bombing and 1 for escort. All featured backward-staggered wings. The types 1,3 and 4 had an additional nosewheel to prevent nose-overs, but also some type 5’s did have a nosewheel. The Let.IA.3 was the first type, used for reconnaissance and with 2 150hp Hispano Suiza 8A engines. 175 aircraft were ordered in October 1916 and the first entered service in may 1917. The Let.2A.3 had higher power Hispano Suiza 8Ba engines of 200 hp. The Let 3Bn was the first nightbomber also with 200 hp engines but with equal-span 4-bay wings. The Let.4 was again for reconnaissance and now fitted with 2 Lorraine Dietrich 8A’s giving 170 hp. 51 Type 5 bombers were built. Fuelcapacity : 380 kg = litre = 518 litre, endurance : 3.0 hrs. The Let.6Ca.3 was an escort version, with a “cannon” armament , flight tested januar 1918. Only 1 type 7 has been built. First flown in 1918. It was larger with 19.0m span and 275hp engines. Total weight 2860 kgs. 8 France escadrille’s were equipped with Letord of different types. There was also a type 9 but this was a total new design which came to late to take part in the war.
users : France
crew : 3
armament : 3 movable 7.70 [mm] (0.303 in) Lewis machine-guns
engine : 2 Lorraine-Dietrich 8Fb liquid-cooled 8 -cylinder V-engine 220 [hp](161.8 KW)
dimensions :
wingspan : 18.05 [m], length : 11.17 [m], height : 3.7[m]
wing area : 62.2 [m^2]
weights :
max.take-off weight : 2450 [kg]
empty weight operational : 1660 [kg] bombload : 300 [kg]
performance :
maximum speed : 160 [km/u] op 2000 [m]
service ceiling : 5000 [m]
endurance : 4.7 [hours]
estimated action radius : 335 [km]
description :
3-bay biplane with fixed underwing 4 -wheel landing gear and tail strut
upper wingtips supported by slanted flying wires
two spar upper and lower wing
engines,landing gear and fuel attached to the wings, bombload in or attached to
fuselage
airscrew :
two fixed pitch 2 -bladed tractor airscrews with max. efficiency :0.64 [ ]
estimated diameter airscrew 2.58 [m]
angle of attack prop : 16.30 [ ]
reduction : 1.00 [ ]
airscrew revs : 1500 [r.p.m.]
pitch at Max speed 1.78 [m]
blade-tip speed at Vmax and max revs. : 207 [m/s]
calculation : *1* (dimensions)
mean wing chord : 1.91 [m]
calculated wing chord (rounded tips): 2.09 [m]
wing aspect ratio : 9.43 []
estimated gap : 1.75 [m]
gap/chord : 0.91 [ ]
seize (span*length*height) : 746 [m^3]
calculation : *2* (fuel consumption)
oil consumption : 6.5 [kg/hr]
fuel consumption(cruise speed) : 71.9 [kg/hr] (98.1 [litre/hr]) at 59 [%] power
distance flown for 1 kg fuel : 2.00 [km/kg]
estimated total fuel capacity : 518 [litre] (380 [kg])
calculation : *3* (weight)
weight engine(s) dry : 756.0 [kg] = 2.34 [kg/KW]
weight 48 litre oil tank : 6.1 [kg]
oil tank filled with 2.4 litre oil : 2.2 [kg]
oil in engine 18 litre oil : 16.2 [kg]
fuel in engine 2 litre fuel : 1.6 [kg]
weight 42 litre gravity patrol tank(s) : 4.1 [kg]
weight radiator : 46.4 [kg]
weight exhaust pipes & fuel lines 23.8 [kg]
weight self-starter : 4.0 [kg]
weight cowling 6.5 [kg]
weight airscrew(s) (wood) incl. boss & bolts : 48.5 [kg]
total weight propulsion system : 909 [kg](37.1 [%])
***************************************************************
fuselage skeleton (wood gauge : 6.28 [cm]): 113 [kg]
bracing : 9.6 [kg]
fuselage covering ( 23.6 [m2] doped linen fabric) : 7.5 [kg]
weight controls + indicators: 7.9 [kg]
weight seats : 9.0 [kg]
weight other details, lighting set, etc. : 9.1 [kg]
weight bomb storage : 21.0 [kg]
weight Doran/Lafay bomb sight : 1.5 [kg]
weight oxygen/compressed air flasks for high altitude : 15.1 [kg]
weight interior + equipment + fuel lines: 52 [kg]
total weight fuselage : 246 [kg](10.0 [%])
***************************************************************
weight wing covering (doped linen fabric) : 40 [kg]
total weight ribs (105 ribs) : 146 [kg]
weight engine mounts : 16 [kg]
weight two 238 [litre] main fuel tanks empty : 45.7 [kg]
load on front upper spar (clmax) per running metre : 433.7 [N]
load on rear upper spar (vmax) per running metre : 365.2 [N]
total weight 8 spars : 44 [kg]
weight wings : 229 [kg]
weight wing/square meter : 3.68 [kg]
weight 12 interplane struts & cabane : 27.8 [kg]
weight cables (96 [m]) : 6.6 [kg] (= 69 [gram] per metre)
diameter cable : 3.3 [mm]
weight fin & rudder (3.8 [m2]) : 14.5 [kg]
weight stabilizer & elevator (7.0 [m2]): 26.2 [kg]
total weight wing surfaces & bracing : 366 [kg] (14.9 [%])
*******************************************************************
weight machine-gun(s) : 38.1 [kg]
weight pivot mounting mg :12.0 [kg]
weight armament : 50 [kg]
********************************************************************
wheel pressure : 612.5 [kg]
weight 4 wheels (720 [mm] by 85 [mm]) : 49.4 [kg]
weight tailskid : 2.5 [kg]
weight undercarriage with axle 31.6 [kg]
total weight landing gear : 83.5 [kg] (3.4 [%]
*******************************************************************
Letord 5 A.3 with nose wheel !
********************************************************************
calculated empty weight : 1655 [kg](67.5 [%])
weight oil for 5.6 hours flying : 36.1 [kg]
weight cooling fluids : 66.7 [kg]
weight 15 drums empty : 3.1 [kg]
weight ammunition (705 rounds) : 22.4 [kg]
weight signal pistol with cartridges : 3.6 [kg]
weight automatic pistol with spare magazines : 1.2 [kg]
*******************************************************************
calculated operational weight empty : 1785 [kg] (72.8 [%])
published operational weight empty : 1660 [kg] (67.8 [%])
_____________
| | |o| | |
-----------
" "
weight crew : 243 [kg]
weight (electrical heated) clothing for high altitude : 18.0 [kg]
weight fuel for 2.0 hours flying : 144 [kg]
********************************************************************
operational weight : 2190 [kg](89.4 [%])
bombload could not be carried with fuel for 2 hours flying time
fuel reserve : 236 [kg] enough for 3.28 [hours] flying
possible additional useful load : 25 [kg]
operational weight fully loaded : 2450 [kg] with fuel tank filled for 100 [%]
published maximum take-off weight : 2450 [kg] (100.0 [%])
||
||
I||=>|
||
||
calculation : * 4 * (engine power)
power loading (Take-off) : 7.57 [kg/kW]
total power : 323.6 [kW] at 1500 [r.p.m]
calculation : *5* (loads)
manoeuvre load : 2.0 [g] at 1000 [m]
limit load : 3.0 [g] ultimate load : 4.5 [g] load factor : 0.9 [g]
design flight time : 3.25 [hours]
design cycles : 83 sorties, design hours : 270 [hours]
wing loading (MTOW) : 386 [N/m^2]
wing stress (3 g) during operation : 315 [N/kg] at 3g emergency manoeuvre
calculation : *6* (angles of attack)
angle of attack zero lift : -1.13 ["]
max. angle of attack (stalling angle) : 11.63 ["]
angle of attack at max. speed : 2.78 ["]
calculation : *7* (lift & drag ratios
lift coefficient at angle of attack 0° :0.10 [ ]
lift coefficient at max. angle of attack : 1.13 [ ]
lift coefficient at max. speed : 0.35 [ ]
induced drag coefficient at max. speed : 0.0054 [ ]
drag coefficient at max. speed : 0.0536 [ ]
drag coefficient (zero lift) : 0.0482 [ ]
calculation : *8* (speeds
stalling speed at sea-level (OW): 80 [km/u]
landing speed at sea-level (OW without bombload): 96 [km/hr]
min. drag speed (max endurance) = minimum speed*1.1 at cruise height : 100 [km/hr] at 2500 [m] (power:31 [%])
min. power speed (max range) : 113 [km/hr] at 2500 [m] (power:34 [%])
max. rate of climb speed : 98.7 [km/hr] at sea-level
cruising speed : 144 [km/hr] op 2500 [m] (power:53 [%])
design speed prop : 152 [km/hr]
maximum speed : 160 [km/hr] op 2000 [m] (power:72 [%])
climbing speed at sea-level (without bombload) : 343 [m/min]
calculation : *9* (regarding various performances)
take-off distance at sea-level : 160 [m]
lift/drag ratio : 10.73 [ ]
max. practical ceiling : 5575 [m] with flying weight :1874 [kg]
practical ceiling (operational weight) : 5000 [m] with flying weight :2190 [kg] line 3385
practical ceiling fully loaded (mtow- 1 hour fuel) : 4675 [m] with flying weight :2378 [kg]
published ceiling (5000 [m]
climb to 1500m (without bombload) : 4.91 [min]
climb to 3000m (without bombload) : 12.24 [min]
max. dive speed : 451.1 [km/hr] at 3675 [m] height
load factor at max. angle turn 2.28 ["g"]
turn radius at 500m: 66 [m]
time needed for 360* turn 11.4 [seconds] at 500m
calculation *10* (action radius & endurance)
operational endurance : 1.70 [hours] with 3 crew and 300 [kg] bombload and 32.2 [%] fuel
published endurance : 4.65 [hours] with 3 crew and possible useful (bomb) load : 88 [kg] and 88.1 [%] fuel
action radius : 403 [km] with 3 crew and 20[kg] photo camera or bombload
max range theoretically with additional fuel tanks for total 834 [litre] fuel : 1224 [km]
useful load with action-radius 250km : 172 [kg]
production : 24.84 [tonkm/hour]
oil and fuel consumption per tonkm : 3.16 [kg]
_
I_°°>/
°
German soldiers pose amid the remains of a Letord 5
Notes : design cycles : 83 sorties and 270 flying hours is not much. Speculating de Letord 5 was not a very strong and rugged design, could not take to much g-forces.
Literature :
Bombers 1914-19 page 70,149
Jane’s Fighting aircraft WW1 page 114
Mecanique de l’aviation, Lt.Col.Dorand
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/
content please mail to below mail address
(c) B van der Zalm 29 February 2020 contact : info.aircraftinvestigation@gmail.com python 3.7.4