Aeromarine AMC Flying Boat
Single-engine Commercial Flying Boat Biplane
The Aeromarine A.M.C. commercial flying boat was built with a view to supersede the converted war-time HS-2L “Liberty”-engined flying-boat which the Aeromarine Airways were using on their commercial services. As the wooden hole of the HS-2L has the great drawback of water soakage, which seriously impairs performance after a prolonged sojourn in the water, it was decided to use an all-metal hull on the new flying-boat. Other requirements were a greater sturdiness of the hull for operating from beaches and a better all-round performance.
Tests were made for two years with various aluminum alloys, and finally the 17-S alloy (copper, 3.5-5.5; manganese, 0.5-0.8; magnesium, 0.5-0.75; iron, 0.67; silicon, 0.33; aluminum, balance) of the Aluminum Company of America was selected. The metal was used in sheets of sufficient thickness so that the plating of the hull would take the loads imposed on the structure, the frames and longitudinals acting only as stiffeners to carry the load of the skin.
The framework of the hull consists of eighteen frames, five complete water-type bulkheads and fore and aft stiffeners on deck and bottom. All the frames and stiffeners are made of the same size of U sections, thickness 1/32 to 1/16 in., pressed out of flat sheet with flanges to which the covering was riveted on assembly. Adherence to the same size of section greatly simplified the making of all joints between members, and incidentally save lots of space in stock room. The bottom members of the frames (floors) are of box section, built up of two webs and channel, all riveted together.
The covering is of 3/64 in. thickness on sides and top of all and of 1/16 in. thickness on bottom ahead of step. The bottom of the boat is quite smooth and clean, all stiffeners and keelsons being inside where they are protected from damage and handling of boat.
Water-tightness is secured by the use of canton flannel and asphaltum interposed between the thicknesses of metal.
The completed hull is some 100 lbs. lighter than a similar wooden hull, giving accommodation for only four passengers instead of seven in the metal hull.
The hull is wide enough for four persons to sit abreast. The bottom has “V” shape with included angle of 152° at the step, and a still sharper angle toward the bow. The step is 5 in. deep and the bottom back of it rises at the angle of 8° towards the stern, ensuring clean running before take-off.
The wing tip pontoons were constructed of sheet 17S alloy, as was also the framework of the tail plane surfaces, which are lighter and very much stiffer than similar surfaces constructed of wood.
The wing structure, which is of conventional wood and fabric construction, is of externally braced biplane form, with the bottom wing having a smaller chord than the top wing. Ailerons are fitted to the top wing only and are counter-balanced by wind vanes.
The power plant, a 400-hp “Liberty” engine with pusher airscrew, is mounted on heavy steel tubes, with no cable bracing. The radiator is suspended from the center wing panel and is only slightly braced to the motor installation, so as to make it free from vibration. The petrol system consists of two 50 gallon tanks mounted in the center panel above the engine, and of a 70 gallon reserve tank in the hull. Gravity feed is used from the main tanks.
The machine carries seven passengers and fuel for four hours. With five passenger, fuel for seven hours may be carried.
Specification of the Aeromarine A.M.C. Flying-Boat 2
Type of Machine
Weights and Loadings
Historical Notes 2
The A.M.C. has been subjected to extensive trials and the results have been entirely satisfactory. No trouble what ever has been experienced from water soakage or leakage, and though there was some difficulty in making the paint stick to the hull, there have been no indications of corrosion, excepting in the case of some 140 rivets out of the 40,000 used. The defaulting rivets were apparently from a different alloy.
After remaining moored in the open, between flights, for two months, the boat was flown by C. J. Zimmerman (brother of the engineer) early in 1924 from Keyport to San Juan, Puerto Rico, and there placed in the passenger sightseeing service.
The pilot states in a letter that the boat is standing up wonderfully, although the bottom is pretty well covered with barnacles, which will have to be scraped off as they slow down the take-off. Some 8,000 miles have now been flown by the machine.