Flight, September 1920

THE GLENN-MARTIN NAVY TORPEDO 'PLANE

   THE Glenn L. Martin Co., of Cleveland, Ohio, U.S.A., recently completed a new type of torpedo 'plane for the U.S. Navy. Final trials, before Army and Navy officials, were carried out with success on May 6 last at McCook Field, Dayton. This type of machine is intended for operation either with the fleet or directly from shore stations. It is not fitted with floats, but in addition to the specially designed landing gear it is provided with emergency flotation bags, inflated by compressed air, so that it can, when required, alight on the water.
   When operating with the fleet, the machine, fully loaded, can, it is claimed, take off from the deck of a warship or seaplane carrier. Its cruising radius of 480 miles permits a reconnaissance of several hundred miles, during which communication with the base can be maintained by means of radio equipment. On sighting an enemy ship, the plane sweeps down and launches its torpedo at comparatively close range, and then flies back to the mother ship. Having returned - all being well! - it alights on the water on the lee side of the ship, and is hoisted on board by means of attachments on the top plane.
   As a coast defence unit it, practically speaking, takes the place of coast defence guns, and the average range of the latter being 20 odd miles, the 'plane scores somewhat with its 200-mile range - to say nothing of the difference in cost. Should an engagement take place so far out to sea as to make a return trip impossible, the 'plane can alight on the water, by means of its flotation gear, and signal its home station, or any nearby ship, as to its location.
   The Martin Navy torpedo 'plane is essentially a land-type, twin-motored, tractor bi-plane, designed to carry a 2,100-lb. torpedo (or the equivalent weight in torpedo and bombs), two machine-guns complete, radio equipment, a crew of three men (pilot, navigator, and gunner), and sufficient fuel for 480 miles cruising radius. In addition, it carries 450 lb. of, bombs, two Lewis machine-guns, a radio set, and a complete equipment of instruments and accessories.
   This new type of torpedo 'plane has several recent developments, such as folding wings, which when folded reduce the over-all width of the 'plane to 35 ft. 10 in. - thus minimizing the space required for housing. Another new feature is found in the landing-gear, which is divided in the middle so as to permit the torpedo cradle, carrying the torpedo, to be suspended underneath the fuselage.
   The two 12-cylindered Liberty engines are mounted on the lower front wing beams just outside of the first wing strut away from the fuselage. By mounting the motors in this manner the centre of gravity is lowered, the flying efficiency is increased, and the motors are made more accessible than they would be if they were suspended from the upper wings or between the struts.
   The principal characteristics of the Martin torpedo 'plane are :-
   Span, over all 71 ft. 5 ins.
   Width, wings folded 35 ft. 10 ins.
   Over-all length 46 ft. 4 ins.
   Over-all height 14 ft. 0 ins.
   Weight, empty 6,533 lb.
   Load, useful 4,950 lb.
   Weight, gross 11,487 lb.
   Crew 4 men
   Factor of safety 5 to 7.
   Maximum speed 107 m.p.h.
   Economical speed (at sea-level) 95 m.p.h.
   Landing speed 60 m.p.h.
   Climbing speed (from sea-level in 10 mins.) 5,100 ft.
   Cruising radius 480 m.
   Service ceiling 12,000 ft.
   Absolute ceiling 10,000 ft.

Flight, January 1921

THE GLENN L. MARTIN COMMERCIAL TRANSPORT

   AIRCRAFT, if it is to be successful commercially, can no longer 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 automobile and the ocean liner, the commercial features of the aeroplane are paramount. With this all-important factor of commercial aeroplane construction predominating, the Glenn L. Martin Company of Cleveland is designing a new machine which will incorporate every element of commercial adaptability. Among the principal points that are being carefully 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 tractor biplane, 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 front and rear spars and interplane struts and streamline wire bracing. The upper wing is made in two outer and one centre section and the lower in two port and two starboard panels - a total of seven panels. The interplane struts, outside of the folding wing hinge, are of routed spruce; two front and two rear on each side of the wings. Tubular steel struts, faired with aluminium, are used at the folding wing hinge. The strut system around the motors, on the lower inner panels, consists of a truss work of steel tubes, faired with aluminium, which connects the nacelles to the body, to the landing gear, and to the upper wing. The wing truss wires are of streamline wire, fitted with terminals of clevis form.
   Wing panels are built on two spruce spars, routed wherever possible to I-beam sections; the front spar is 10 ins. From the leading edge, and the rear spar 60 ins. In the inner lower wing sections, an auxiliary triangle of steel tubes, inside the wings, carries the stress in the lower rear spar from 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 used to carry the drag loads and spruce box ribs, to close the ends of the panels.
   The four ailerons are attached to the rear spars, upper and lower, at both sides of the machine. The ailerons are unbalanced, and do not extend beyond the contour of the wings. The wing fittings are of plate form, made of sheet steel, with attached parts brazed and secured to the beams by through bolts with bearing blocks of metal. Fittings take interplane strut bolts; flying, landing, incidence and internal drag, brace wires. The internal wing wires are of solid steel fitted with adjustable terminals. The wings are covered 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. The elevator is hinged to the trailing edge of the stabiliser, and the rudders and fins are mounted on top of it. Entire unit is mounted on top of the fuselage and braced with steel tubing and steel tie-rods or cables. The tail surface unit may be detached intact. The stabiliser is adjustable from 0° to minus 4° from the pilot's cockpit, during flight. All tail surface 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, the maximum depth being 59 ins. and the maximum width 50 ins. 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 longerons are horizontal in flight and parallel to the axis of the motors. The lower longerons taper upward toward the upper longerons as they approach the nose and tail. The forward section of the longerons is of ash spliced to the spruce. The longerons are solid at fitting bearing points; the nose is braced with 3/32-in. 3-ply birch walls and built up plywood bulkheads to the rear of the aft cargo compartment. The cargo compartments are lined with plywood, and are braced and reinforced to carry ordinary 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 stepped in cup fittings, which, in turn, are brazed to the longeron fittings. The longeron fittings are of strap form, made from sheet steel, entirely circling the longeron; each fitting, with exceptions, accommodates six brace wires.
   The fuselage flooring is of 3/16-in. 3-ply birch plywood, suitably braced and secured. Where spruce longeron struts are used, that is, from the pilot's cockpit back, the bracing is of solid steel tie rods. Fitted metal cowling is provided around the pilot's cockpit, and metal and plywood doors are provided for the cargo compartments. The tail skid is mounted on a swivel post and secured for shock absorption with 5/8-in. elastic cord and 3/8-in. rebound rubbers. The skid is of hickory, provided with a cast steel shoe. All walls of the fuselage, not built with plywood, are covered with grade "A" linen, doped and finished in khaki enamel. The exterior plywood walls are also finished with khaki enamel; the interior wood parts are filled and varnished; interior metal parts are zinc plated, are covered with blue lacquer or both; the exterior metal parts are zinc plated and enameled in khaki; wearing surfaces, etc., are greased.
   The landing chassis is attached under the fuselage and engine nacelle, and consists of two 44 in. by 10 in. wheels and two nickel steel tubular axles. The axles are held in place laterally by the medium of sway braces attached under the fuselage, and support the machine by means of "A" struts. These struts are vertical, two being attached under each nacelle. The landing gear "A" struts are of nickel steel tubing, and are braced from the rear. Each wheel is shock-absorbed with 5/8-in. elastic cord, and the shock absorber is enclosed in a streamline case; mud guards are provided for each wheel. The landing gear "A" struts are streamlined with wood and covered, where necessary, with grade "A" linen, doped and finished in khaki enamel. The sway braces are streamlined with aluminium and magnesium fairing, and are provided with steps to facilitate work upon the motor when the engines are not running.
   Each engine is mounted in the forward portion of its nacelle. The engine bed is built in the top of a vertical plywood bulkhead, braced laterally by a horizontal plywood bulkhead, connecting it to the nacelle longerons. A sloping bulkhead connects the forward end of the engine bearers to the front spar of the wing. The oil tanks are carried beneath the motors. The batteries are carried beside the starters at the rear end of the motors. Directly behind the rear end of the starters is an aluminium covered plywood fire wall, which runs from the top to the bottom of the nacelle. On top of the fire wall and outside of the nacelle is the radiator. Behind this firewall, and separated from it by an air space, is the petrol tank. The latter ends at the rear spar where there is another vertical bulkhead. Behind this bulkhead is a fairing to streamline the nacelle. A removable cover is provided for this, making it available for the storage of tools, etc. Detachable cowling is also provided over the motors. All cowling on the nacelles is sheet aluminium.
   The engine controls are carried to the fuselage through the wings, being run over pulleys at the nacelles and at the inner end of the wings and being run through straight aluminium tubes between these points. All controls are standard cable. A gravity tank is provided in the upper wing over each motor, and a sight-glass in the overflow line enables the pilot to determine at all times, whether petrol is being pumped to the gravity tank.
   The entire petrol system is designed to withstand a pressure of 5 lbs. per square inch.

The general specification of the Martin Commercial Transport is as under :-
   Span, overall, both wings 74 ft. 2 ins.
   Length, overall 43 ft. 8 ins.
   Height, overall 15 ft. 6 3/4 ins.
   Chord 7 ft. 11 ins.
   Gap 8 ft. 6 ins.
   Dihedral angle 176° from folding hinge out in lower wing
   Angle of wing setting to propeller axis 2°
   Wing curve Albatros
   Upper wing area, including ailerons 577 sq.ft.
   Lower wing area, including ailerons 544 sq.ft.
   Total wing area, including ailerons 1,121 sq.ft.
   Ailerons (4) 130 sq.ft.
   Elevator area 43 sq.ft.
   Stabiliser area 62.25 sq.ft.
   Rudders (2) 39.5 sq.ft.
   Fins (2) 18 sq.ft.
   Total weight of machine, fully loaded 12,000 lbs.
   Weight of machine, empty 6,840 lbs.
   Total useful load 5,160 lbs.
   Crew (pilot and mechanician) 360 lbs.
   Cargo capacity 3,000 lbs.
   Weight carried per sq. ft. of supporting surface 10.7 lbs.
   Weight per brake h.p. 15.0 lbs.
   Fuel capacity (2 main tanks) 280 gals.
   Gravity tanks (2) 20 gals.
   Oil capacity (2 tanks) 22 gals.
   Speed, maximum, horizontal flight 110 m.p.h.
   Speed, economical 100 m.p.h.
   Speed, minimum landing 52 m.p.h.
   Climb from sea level in 10 mins., fully loaded 5,000 ft.
   Radius of operation, fully loaded under full power, 4 1/2 hrs.
   Radius of operation, at cruising speed 600 miles. .
   Ceiling 13,000 ft.

The equipment includes :-
   Air speed indicator, oil temperature thermometers, altimeter compass, water temperature thermometers, clock, self-starters, inclinometer, navigation lights, lateral indicator, instrument lights, tachometers, trouble lamps, petrol level gauges, fire extinguishers, oil pressure gauges, ammeter, compass, all necessary switches, wiring, etc., safety belts, life preserver seat cushions, thermos bottles.