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Aviation History
1921
1921 - 0027.PDF
JANUARY 13, 1921 THE GLENN L. MARTIN COMMERCIAL TRANSPORT AIRCRAFT, if it is to be successful commercially, can nolonger be designed solely on the basis of performance as was done during the War, New standards have arisen.The efficient commercial aeroplane of today is judged on its commercial adaptability. Like the locomotive, the auto-mobile and the ocean liner, the commercial features of the aeroplane are paramount. With this all-important factorof commercial aeroplane construction predominating, the Glenn L. Martin Company of Cleveland is designing a newmachine which will incorporate every element of commercial adaptability. Among the principal points that are beingcarefully considered are the factor of safety, life of the 'plane, economy in operation, repair and replacement of parts,minimum work in upkeep, simplicity in housing and towing. The Martin Commercial Transport is a twin-engine tractorbiplane, and is similar in general design to the Martin Bombing and Torpedo 'planes that have proved so successful in the past.The wings, which are of the folding type, are constructed in conventional truss form in the outer sections with frontand rear spars and interplane struts and streamline wire bracing. The upper wing is made in two outer and onecentre section and the lower in two port and two starboard panels—a total of seven panels. The interplane struts, steel, with attached parts brazed and secured to the beamsby through bolts with bearing blocks of metal. Fittings take interplane strut bolts ; flying, landing, incidence andinternal drag, brace wires. The internal wing wires are of solid steel fitted with adjustable terminals. The wings arecovered with grade " A " linen and doped with four coats of acetate and two coats of nitrate dope, in the order named,the latter being impregnated with khaki wing enamel. The wood frames of the wings are wood filled and varnished.The tail surfaces consist of elevator, stabiliser, two rudders and two vertical fins, all built upon the stabiliser. Theelevator is hinged to the trailing edge of the stabiliser, and the rudders and fins are mounted on top of it. Entire unitis mounted on top of the fuselage and braced with steel tubing and steel tie-rods or cables. The tail surface unit may bedetached intact. The stabiliser is adjustable from o° to minus 40 from the pilot's cockpit, during flight. All tailsurface frames are of steel tubing and are channel section. The frames are enamelled and covered with grade " A "linen. The covering is doped and finished with khaki wing enamel. The fuselage is of general rectangular cross section, themaximum depth being 59 ins. and the maximum width 50 ins. AK&I OF fllLEKom .43 " STfiblUZER 62$ GLENN L. MARTIN COMMERCIAL TRANSPORT 2-IZCYL: LIBERTY ENGINES.-400 H.P. EACH. THE GLENN L. MARTIN COMMERCIAL TRANSPORT: Plan, side and front elevations to scale. outside of the folding wing hinge, are of routed spruce ; twofront and two rear on each side of the wings. Tubular steel struts, faired with aluminium, are used at the folding winghinge. The strut system around the motors, on the lower inner panels, consists of a truss work of steel tubes, fairedwith aluminium, which connects the nacelles to the body, to the landing gear, and to the upper wing. The wingtruss wires are of streamline wire, fitted with terminals of clevis form. Wing panels are built on two spruce spars, routed whereverpossible to I-beam sections; the front spar is 10 ins. from the leading edge, and the rear spar 60 ins. In the innerlower wing sections, an auxiliary triangle of steel tubes, inside the wings, carries the stress in the lower rear sparfrom the engine nacelle to the front beam at the body hinge and to the hinge fitting at the rear of the cargo compartment,in the body. The ribs are of truss type, diagonal and vertical bracing, and are built of spruce ; spruce drift struts are usedto carry the drag loads and spruce box ribs, to close the ends of the panels. The four ailerons are attached to the rear spars, upperand lower, at both sides of the machine. The ailerons are unbalanced, and do not extend beyond the contour of thewings. The wing fittings are of plate form, made of sheet outside. The fuselage is built on four spruce and ash longerons,varying from a solid section to an " X " section, in going from nose to tail. The top lovgerons are horizontal in flight andparallel to the axis of the motors. The lower longerons taper upward toward the upper longerons as they approach thenose and tail. The forward section of the longerons is of ash spliced to the spruce. The longerons are solid at fittingbearing points ; the nose is braced with -^-in. 3-ply birch walls and built up plywood bulkheads to "the rear of theaft cargo compartment. The .cargo compartments are lined with plywood, and are braced and reinforced to carryordinary loads. A cradle and slings are provided in the central compartment for carrying heavy concentrated loads.From this point aft, the fuselage struts are spruce and are routed out to I-beam shape. _ These spruce struts are steppedin cup fittings, which, in turn, are brazed to the longeron fittings. The longeron fittings are of strap form, made fromsheet steel, entirely circling the longeron ; each fitting, with exceptions, accommodates six brace wires. The fuselage flooring is of f^-in. 3-ply birch plywood,suitably braced and secured. Where spruce longeron struts are used, that is, from the pilot's cockpit back, the bracingis of solid steel tie rods. Fitted metal cowling is provided around the pilot's cockpit, and metal and plywood doors are
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