Albatros L 71
Type
2 seat experimental
Engine
1 Siemens Sh 10 pusher , 2 bladed propeller
Dimensions
Length: 7.20 m, upper wingspan: 10.30 m, lower wingspan: 7.49 m, wing area: 25 m2
Weights
Empty weight: 450 kg, crew 160 kg,  flying weight: 660 kg, fuel capacity: 50 l ( 38 kg), oil 12 kg, wing load 26,3 kg/m2
Performance
Max. speed: 125 km/h, time to altitude:1,000 m 12 min.,
Type
Werk.Nr
Registration
History
 
10055
D-519
Flight tested Jan. 1926
   
D-636
Flight tested Jan. 1926
The Albatros L.71 is a two-seater light 'plane, with u fuselage of mixed const ruction, and with the wing area arranged in the form of a biplane, the lower plane of which is considerably smaller than the top plane in both span and chord. The biplane type was chosen in order to get the greatest practicable wing area into the smallest overall size, and also to keep down the item of wing weight. The competition placed a premium on rate of climb rather than on top speed, and rate of climb was more easily obtained with ligbt wing loading. It was also desired to give the two occupants as good a view as possible, and in order to attain this object the two main planes were very heavily staggered in relation to one another. A glance at the illustrations will show that the stagger is so pronounced indeed that the problem of building a biplane with the usual externall wire bracing would probably have been extremely difficult, Owing to the very poor angle of the inter-plane struts. It was therefore decided to make the machine a cantilever biplane, and the inter-plane struts are intended mainly to stiffen the wings against torsional stresses.
Except lor the unusual stagger, the Albatros L.71 is designed very much as is a flying boat, that is to say, the engine structure is independent of the wing structure to the extent that, although faired into the top wing surface, the engine is earned on four separate tubes, rising from the fuselage. The top plane is supported from the fuselage by two N-struts braced diagonally to centre them over the fuselage, but outside these N-struts there is no wire bracing of the wings.
Both top and bottom planes have wing spars and ribs of spruce, and the spars of both planes run right through. The top plane is perfectly straight, but the bottom plane has a dihedral of 1,5 degrees. Fittings are mainly of duralumin and the inter-plane struts are steel tubes with sheet aluminium fairings. The wing section is a fairly thick one (about 9 in. on the top plane) and was chosen on account of its high value to improvethe climb.
In the construction of the fuselage two distinct methods have been employed. The front portion, in which the cockpits for pilot and passenger are accommodated, is a flat-sided, plywood- covered box, built rather stronger than strictly necessary in order to provide protection for the occupants in case of a crash. The rear portion of the fuselage is in the form of welded steel tubes with piano-wire bracing, and the two halves of the fuselage are joined just aft of the passengers' cockpit.
Incidentally it may be mentioned that the lower plane passes through the welded tube portion where the question of its insertion and attachment is rather easier, owing to the fabric covering.
As already mentioned, the 55 h.p. Siemens radial engine is mounted on four steel tube struts from the top of the fuselage, on a structure independent of the wing structure. A neat aluminium cowl fairs the engine into the top wing surface and a spinner round the propeller boss at the back completes the fairing of the power unit, of which only the outer portions of the cylinders project. The petrol tank is built into the top plane forward of the engine, and although it is stated that gravity feed is employed, provision is made for maintaining a slight pressure in the petrol tank. As the tank is ahead of the engine, presumably the only time when gravity feed would not suffice would be during a steep dive.   The petrol tank has a capacity of 50 litres (11 gals.) and the oil tank which is placed immediately ahead of the engine, has a capacity of 12 litres
The undercarriage is of simple type, the two wheels being carried on short stub axles hinged to the lower longerons of the fuselage and braced forward by tie-rods forming horizontal V's with the axles. Springing is provided by telescopic struts running to the top longerons of the fuselage, and rubber shock-absorbing gear.
The tail planes are of duralumin and steel construction and fabric covered, and provision is made for trimming the tail plane, this obviously being advisable in a machine of this type, where considerable changes in trim may be expected between the " engine on " and " engine on " condition-
It is stated, however, that the machine handles very nicely, and that the only change with engine fully throttled down is a slight tail-heaviness which is easily corrected by slightly increasing the angle of incidence of the trimming tail plane.
From Flight JANUARY 28, 1926