Flight, November 1923

NEW AMERICAN NIGHT FLYING MAIL 'PLANES

A LITTLE while back the U.S. Air Mail Service issued tenders for a certain number of aeroplanes designed specially to meet the various requirements for night mail service. As a result three types of machines have already materialised, one from each of three well-known American aircraft constructors - the Aeromarine Plane and Motor Co., of Keyport, N.J., the Curtiss Aeroplane and Motor Co., of Garden City, N.Y., and the Glenn L. Martin Co., of Cleveland. We give below brief descriptions of these three machines, together with illustrations. It may be mentioned that these machines are intended for use on the "night section" of the New York-San Francisco air mail service, that is, the section between Chicago and Cheyenne.
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   The Glenn L. Martin Night Mail 'Plane. - The Glenn L. Martin machine is also a tractor biplane, of the single bay type, with a Wright E4 200 h.p. engine. It is of sturdy construction, having a fuselage of rectangular section, veneer covered. The pilot's cockpit, which is comfortable and roomy, is located well back of the wings, about midway of the fuselage. In front of this cockpit is the mail compartment in the upper part of the fuselage, having 31 cubic ft. of space, sufficient for 600 lbs. of mail. Below the mail compartment are two petrol tanks, with a combined capacity of 64 gals.
   The engine is mounted on ash bearers supported by a tubular steel structure attached to the longerons and front bulkhead of the fuselage. The radiator is directly below the engine, and completely cowled in with the exception of the front cooling surface. The radiator shutter is a novel trapdoor arrangement with a positive rack-and-pinion control in the cockpit. A 5-gal. oil tank is mounted on the front bulkhead at the rear and below the engine. Between this tank and the engine is a special oil radiator. An aluminium fire wall separates the engine from the mail compartment and fuel tanks.
   The cowling is arranged to allow quick accessibility to all parts of the engine, large hinged doors held in place by tension fasteners being provided on each side.
   A large portion of the unusual efficiency of this machine is due to the wing section used. This is a recent development of the Martin Co., a thick section known as Martin No. 15. The main spars are of the box type, built up of spruce, with plywood sides and the typical Martin type built-up spruce ribs.
   There are two lower wing sections, each attached to the bottom of the fuselage, and the upper wing is in three sections, there being a narrow cabane section the width of the fuselage to which the outer sections are attached. The centre section is supported over the fuselage by two inverted U-struts. There is only one interplane strut each side of the I type. These are built up N's covered with plywood. The interplane bracing is composed of four streamline rods on each side.
   Ailerons are fitted to both upper and lower planes, the upper ailerons being balanced by means of auxiliary vanes or panels. The tail surfaces are of the same construction as the wings, the stabiliser being adjustable from the pilot's cockpit.
   The landing gear is of robust construction, and with a wide track in order to meet the special requirements of night landings, etc. It is of steel tubing with large aluminium alloy castings and riveted and welded steel fittings. The axle is of the centre-hinged type.
   Several improvements have been embodied in the control system. No pulleys are employed, every cable running in a straight line, and the controlled parts are operated by levers and bell cranks, thus giving a positive action with little or no wear on the cables. The tail skid is of the steerable type.
   Characteristics :- Span, 42 ft.; chord, 5 ft. 4 ins.; gap, 6 ft.; o.a. length, 28 ft.; height, 12 ft. 1 in.; area, 430 sq. ft.; weight empty, 2,020 lbs.; speed range, 38-105 m.p.h.; climb, 6,000 ft. in 11 mins.; ceiling, 17,000 ft.

Flight, October 1924

THE MARTIN MODEL 70 COMMERCIAL BIPLANE

   A NEW commercial aeroplane has just been completed by the Glenn L. Martin Co., of Cleveland, Ohio, the builders of the famous Martin twin-engined bombers extensively used by the U.S. Air Services. This machine, known as the Model 70, has been designed for either cargo or passenger carrying, and represents an efficient combination of speed and load capacity. Fitted with a 200 h.p. Wright model E4 engine, it has a speed range of 45-112 m.p.h., with a pay load of 750 lb., and has a cruising range of 550 miles. It was designed bv L. C. Milburn, chief engineer of the Glenn L. Martin Co.
   The Model 70 is a further development of the experimental night mail 'plane, which the Martin Co. produced last year for the U.S. Air Mail Service (described in FLIGHT for Nov. 1, 1923). Numerous minor changes have been made in the "70," with the object of improving its serviceability. The wings are entirely new, having about 65 sq. ft. less area, while the tail surfaces have been modified to correspond. Its landing speed is slightly higher than that of the "night 'plane," mainly for the reason that it has been found that many pilots prefer a higher landing speed for general work.
   As will be seen from the accompanying illustration, it is an equal-span tractor biplane, with a single pair of "N" interplane struts each side. The wings are built up on birch plywood box-type spars, with Martin trussed spruce ribs. They are fabric-covered and the leading edge is reinforced with plywood back to the front spar. A 2-ft. "walk-board" is also fitted on the left-hand side of the fuselage in order that free access to the cargo or passenger compartment may be obtained without damage to the wings. Glenn Martin No. 15 wing section is employed. The interplane struts are of streamline steel tubing, and the strut connections are submerged in the struts. All members of the wings are designed to sustain eight times normal load.
   The fuselage, which is well streamlined, is constructed of birch plywood supported by a spruce frame. The pilot's cockpit is located well aft of the main planes, and is exceptionally roomy and comfortable; excellent vision is obtained from this position for all conditions of flying and landing. In front of the pilot's cockpit is an enclosed cargo compartment of 28 cub. ft. Provision is made in this compartment for the rapid installation of two comfortable passenger seats. When passengers are carried, the flush turtle deck over this portion of the fuselage is replaced by a suitable cockpit-type of cowling.
   A large manhole is provided in the middle of the bottom of the fuselage, the door of which is hinged and latched, and can be opened at once to permit access to the entire inside of the fuselage aft of the pilot's seat. A locker is provided behind the pilot's seat for carrying small luggage, spare tyre, tools, etc., and a space is left open behind the instrument-board to permit the connection and disconnection of any instrument without difficulty.
   The engine mounting is of steel tube, with wood bearers. The radiator is mounted in the bottom of the fuselage below the engine, where it receives the full blast of the slip-stream through a specially-designed opening. After passing through the radiator, the air is drawn out through louvres in the side and bottom of the engine cowling. This latter is provided with extra large doors on each side, fastened with quick-release spring latches. When these doors are opened, the entire engine compartment is exposed, and all connections of the oil and water systems are conveniently reached. The petrol and oil filler-spouts are located outside the fuselage, and are fitted with quick-opening caps.
   The control system is extremely simple, and is fitted with extra large pulleys and ball bearings, resulting in easy and rapid operations. The rudder bar is provided with an adjustable tension to compensate for engine torque and slip-stream effects. The tail skid is steerable, and is operated from the rudder foot bar. Amongst the "refinements" on this machine may be mentioned the following: Anchor rings are provided at the wing tips in order to facilitate the machine being staked down in the open should this be necessary, while rings are also provided in the top surface of each wing panel so that these may easily be swung into place during assembly; accurate spirit levels are built into the wings and fuselage to permit rapid rigging and adjustment.
   The landing gear, of the divided-axle type, is substantially built and braced. It is made of steel tube, and has a comparatively wide track. The brace struts join the axle through a fork fitting which permits the shock-absorber unit to be wound on the bench. The wheels are 30 ins. by 5 ins.
   Several of these machines have been built, and have been given commercial service tests by Test-pilot C. C. Caldwell between Cleveland-Chicago and Cleveland-New York, on which very favourable reports were given by the pilot.
   The principal characteristics of the Glenn-Martin M.70 are :-
   Span 38 ft.
   Chord 5 ft. 4 1/2 ins.
   Gap 4 ft. 10 ins.
   Overall length 27 ft.
   Height 12 ft.
   Total wing area 365 sq. ft.
   Area of ailerons (four) 36 sq. ft.
   Area of tail plane 28-2 sq. ft.
   Area of elevators 10-4 sq. ft.
   Area of rudder 11-4 sq. ft.
   Area of fin 9 sq. ft.
   Weight fully laden 3,500 lbs.
   Weight empty (with water) 2,100 lbs.
   Useful load 1,400 lbs. (40 per cent.)
   Weight per horse-power 17-5 lbs.
   Weight per square foot 9-5 lbs.
   Speed range 45-112 m.p.h.
   Climb (zero) 800 ft./min.
   Climb in 10 mins. 6,500 ft.
   Ceiling 17,000 ft.
   Normal petrol capacity (64 gals.) 385 lbs.
   Cruising radius 550 miles.