Flight, June 1922
THE LONGREN TWO-SEATER BIPLANE
IT cannot be said that American designers have neglected the moderate-priced, low-to-medium-powered aeroplane, for the efforts in this direction, have been numerous. Such machines, it should be noted, are particularly suitable - especially when of the easy-to-fly-and-maintain type - for countries like the States and Canada, where vast tracts of land unserved by regular transport services, ranches, scattered farms, and the like prevail; communication, inspection, and various duties connected with these conditions can easily be carried out by means of the type of machine in question.
One of these machines developed in the U.S.A. is the Longren, described and illustrated herewith. It was designed and built by the Longren Aircraft Corporation of Topeka, Kansas, as a business and pleasure vehicle of moderate price ($2,465) for the individual owner - or owner-pilot. Besides several novel constructional details, low cost of upkeep and operation, small housing space, and facility for obtaining spare parts - all parts are numbered, listed and a full stock always available - are the main features of this machine.
The Longren is a two-seater side-by-side tractor biplane, with its wings arranged to fold back. The fuselage is made of hard vulcanized fibre, moulded to a good streamline form. The fibre is fastened, at the top and bottom centre lines, to two ash longerons, and is reinforced with laminated ash ribs, giving an exceptionally strong and rigid assembly that is resilient and shock resisting. This fibre has a strength-weight ratio that is claimed to be double that of plywood or veneer, and it cannot be shattered or splintered. A combustion point of 650 deg F. is another of its advantages over wood, or fabric-covering, and it is thus practically fire-proof. After assembly, the fuselage is water-proofed inside and out.
The cockpit is immediately beneath the top plane centre section, and is entered by way of a door in the side of the fuselage. This door is so designed that the fuselage is not weakened at this point, where it is reinforced with ash ribs. The pilot's and passenger's seats are of comfortable width, and well upholstered. Standard stick and foot-bar control are fitted, and are arranged to leave no moving parts exposed, making a clean and roomy cockpit, where there is no danger of clothing, etc., catching on any part. In front of the cockpit is an aluminium instrument board, containing a tachometer, altimeter, clock, map case, petrol gauge, oil pressure gauge, motor meter switch and throttle lever. A space is provided under the seat for baggage.
For the main planes the U.S.A. No. 2 wing section, slightly modified, is used, a section giving very satisfactory results with a machine of this type. The top plane consists of two outer sections, and a short centre section; the lower plane is in two sections only. The main spars are built-up I-section spruce, and the ribs are made with ply-wood webs and ash cap strips. The fittings are standardised, and interchangeable. The ailerons, which are fitted to the top plane only, are also interchangeable, and are actuated by a torque tube within the wing and with the operating arm in line with the rear hinge of the wing. Swivels are provided on the arms to allow the wings to fold without affecting the controls. The centre section is supported by four short struts and braced in front by streamline straps, and by a V-tube at the rear.
By the employment of the Warren system of interplane trussing, it is possible to fold the wings without disturbing the setting of the latter or the controls, and no adjustments, or rigging, is necessary, after each operation of folding. The unlocking and removal of four pins is all that is necessary to fold the wings, which when folded back are braced to the fuselage with tubes provided for the purpose. Thus, when the machine is being towed over roads or rough ground the wings are fixed securely against shocks, and are thereby unlikely to be damaged or strained.
The tail surfaces are made thick enough to require a minimum of bracing, only two struts being used and no wires. The horizontal stabiliser is of the divided type, the halves being interchangeable, as are the elevators. The leading edges of the latter, and also those of the rudder and ailerons, serve as operating torque tubes, as well as front spars. The elevator controls are entirely enclosed in the fuselage, and the rudder control has a short arm, and only a very short length of wire exposed.
A tail skid of neat and compact design is fitted consisting of a steel leaf spring, faired, and fastened to the lower longeron, directly under the last transverse rib. The compression load of the skid is carried by a Duralumin compression plate.
A Lawrence 60 h.p. three-cylinder (air-cooled) radial engine is fitted, being bolted directly to the substantial plywood nose panel of the fuselage, giving a strong and simple mounting. The engine is enclosed, except for the cylinder heads, by a metal cone-shaped cowling.
A simple V-type landing gear is fitted, the lower ends of the streamlined struts terminating in Duralumin shock-absorber housings. The axle fairing is given a lifting section, and its leading edge forms the compression member connecting the V's, whilst the trailing edge is attached to the axle and rises and falls with it: both leading and trailing edges are of Duralumin. The chassis is braced by streamline wires.
The Longren flies and handles well, and during the American Legion Flying Meet, held at Kansas City, Mo., last November, one of these machines won the looping contest (38 loops), and at the Omaha Meeting it also won the considerable distinction.
The principal characteristics of the Longren two-seater biplane are :-
Span (upper) 27 ft. 11 ins.
.. (lower) 21 ft. 11 ins.
Chord 4 ft. 3 ins.
Gap 4 ft. 3 ins.
O.A. length 19 ft.
O.A. height 7 ft. 8 ins.
Width folded 9 ft. 8 ins.
Incidence (upper) 3°.
.. (lower) 2°.
Wing section U.S.A. 2 (mod.)
Stabiliser incidence 1 1/2°
Area, main planes (inc. ails.) 189 sq. ft.
.. ailerons (2) 191-1 sq. ft.
.. stabilizer 13-5 sq. ft.
.. elevators 11-4 sq. ft.
.. fin 2-6 sq. ft.
.. rudder 5-6 sq. ft.
Weight (empty) 550 lbs.
.. (loaded) 1,050 lbs.
.. /h.p 17-5 lbs.
.. /sq. ft. 5-55 lbs.