Martin China Clipper

Самолет Model 130 China Clipper, предназначенный для длительных трансокеанских перелетов, представлял собой четырехмоторный моноплан, спроектированный по схеме летающей лодки с двухреданным корпусом совершенно новой конструкции.
  По экономическим ДальшеMore>>> критериям Model 130 превосходил DC-3, и три лодки закупила в 1935 году авиакомпания "Pan Am". Экипаж каждого гидроплана состоял из четырех человек, лодка в дневной полет могла брать на борт до 48 пассажиров. Силовая установка включала четыре мотора Pratt & Whitney R-1830 Twin Wasp мощностью по 600 л. с., установленных на передней части крыла.
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Flight, January 1935

AMERICA'S LATEST "CLIPPER"
The New Martin Trans-oceanic Flying Boat: Accommodation for Fifty Passengers: Mail Range of 4,000 miles

  A MAXIMUM range of about 4,000 miles is calculated for the new “Clipper” flying boat launched recently by the Glenn Martin Company for Pan American Airways. This figure is for mail-carrying purposes. When the craft is used as a carrier of both mails and passengers the range is estimated at 3,000 miles. The estimated maximum speed is about 180 m.p.h. and the cruising speed 160 m.p.h. At 75 per cent, of the available power the duration should be slightly over 20 hours, and at that power the calculated speed is 145 m.p h.
  The general arrangement drawings, for which we are indebted to our American contemporary, Aero Digest, show the shape of hull and wings, and it will be seen that a slight "gull's wing" shape has been given to the centre-section.
  For ordinary ranges the machine can be equipped with passenger accommodation for fifty, but at present the cabin layout is being arranged for eighteen, with settees so designed that they can be converted into berths. This arrangement has been chosen with the trans-Pacific service in view. By carrying the engine exhaust pipes back over the top of the wing, and by suitably lagging the walls of the cabins, the noise level has been reduced to 72 decibels, which is approximately equivalent to the noise in a Pullman carriage on a straight and fairly good track.

The First Test

  On the first test flight, carried out by Mr. W. K. Ebel, the Martin company's test pilot and assistant chief engineer, the machine left the water in twelve seconds.
  Interesting features of the Martin "Clipper" are the use of sponsons for maintaining lateral stability on the water, and the stowage of the fuel (4,000 American gallons) in the hull. In this country it has for many years been the practice to put the fuel tanks in the wings, well away from the hull, so as to reduce fire risk. In the Martin the lower portion of the hull itself forms the petrol tanks, and it is probable that a considerable amount of weight has thereby been saved. It will be remembered that in the giant Dornier "Do. X" twelve-engined flying boat the tanks were also housed in the lower part of the hull. During the discussion on Dr. Dornier's lecture at the Royal Aeronautical Society several speakers expressed doubts as to the wisdom of this placing of large quantities of petrol. Presumably the Martin engineers have decided that the fire risk is smaller in practice than might be expected, there is certainly something to be said for the arrangement from the aircraft designer's point of view, for not only does he save most of the weight of the fuel tanks, but he lowers the centre of gravity of the boat a great deal when the tanks are full. This is of importance when sponsons are used for lateral stability.
  If the figures published are to be believed, the Martin engineer must have saved a very great deal of structure weight, not only in this manner, but in many others, as the empty weight of the machine is given as 23,100 lb., while the gross weight is 51,000 lb. This would give a ratio of gross weight to tare weight of 2.205. In other words, the machine carries as disposable load approximately one and one-fifth times its own weight. If the figures are correct they show very great skill on the part of the designers. An average value is 65 per cent.
  Power is supplied by four fourteen-cylinder Pratt and Whitney "Twin Wasp" engines of 800 h.p. each. The engines are located slightly forward of the leading edge of the wing, carried in streamline nacelles, and enclosed in long N.A.C.A. cowls. As already mentioned, most of the fuel is carried in the lower part of the hull, but a certain amount is carried in the sponsons. Engine-driven pumps transfer the petrol to service tanks in the wing. Three-bladed Hamilton Standard controllable-pitch airscrews are fitted.
  The span of the monoplane wing is 130 ft., and the total wing area is 2,315 sq. ft., of which the sponsons account for 145 sq. ft. The overall length is 90 ft. At full gross weight the wing loading is just over 22 lb. per sq. ft., and the power loading 16 lb. per h.p. The machine has been designed to fly at 6,000 ft. with full load on any three of its four engines.