The first prototype of the DeHavilland Comet logged more than 100 hr. of test flying during the last half of the year. The first machine was designed for payload sufficient for 36 passengers for its maximum range. Plans to increase its capacity to 40-50 passengers for shorter-range operation were under consideration. Power plant of the Comet is four DeHavilland Ghost turbojet engines having a total thrust of 20,000 lb.
The 11,000-lb. payload in the Comet prototype and early production versions is carried in two passenger cabins and three cargo compartments. An 8-seat passenger section is located forward of the front spar structural bulkhead. Main cabin aft will seat 28 passengers in 7 double seats which are separated by a 6 ft. 5½-in. high center aisle. Two windows in the forward cabin and two of the seven main cabin windows are fitted as emergency exits. The main passenger entry door will be on the port side at the rear with a wardrobe to hang coats just inside the door.
Another door located forward on the starboard side provides access to the flight deck, galley, and main cargo compartment without disturbing the passengers. Hat racks will be fitted in the cabin with a 5 ft. head clearance. The floor of the passenger compartment and the rear belly hold are stressed for a loading of 37 lb. per sq. ft. The forward cargo compartment is built to take 120 lb. per sq. ft. A total of 585 cu. ft. storage space is provided in three cargo and baggage compartments: one located between the flight deck and the passenger cabin with a special compartment for diplomatic mail and bullion; another in the tail section; and the third in the fuselage belly aft of the wing. Forward belly compartment is used to hold pressurization and electrical equipment. The galley is located forward with two lavatories in the tail.
The Comet’s present fuel load of about 7,200 U. S. gal. is contained in two integral wing tanks outboard of the engines and cell-type tanks in the center wing section which runs under the fuselage. The fuel system is designed for under-wing pressure refueling at a rate of 150 gal. Per min. but can also use normal top wing methods. Air for tank venting is drawn from a leading edge intake in the wing, which can also be used to blow out fuel by ram pressure for emergency jettisoning.
A mechanical lever is fitted on the underside of the engine cowling where it will be the first part of the plane to contact the ground in a wheels-up landing. When lever makes contact it will cut off the fuel supply of all four engines, cut off electric power and operate the fire-extinguisher systems. Methyl bromide fire-extinguishing system is used to protect the engines, leading edge wing equipment zones, and the de-icing bay. Cabin fire protection comes from carbon dioxide and water glycol extinguishers. All under-floor compartments have access hatches and observation windows allowing entry in flight.
Storage space is provided for medium, high and very high frequency radio equipment; duplicate ADF; ILS and omnirange receivers; radio altimeters; distance-measuring equipment; Loran; and an intercom system. All antennas are flush to reduce drag. They are located in the vertical and horizontal fins, nose wheel doors, fuselage top and the underside of the wing-root fillets. Wing space between the engine tail pipes contains two 15-ft. dinghies equipped with radio and emergency rations, and actuated by an automatic release.
Comet controls are power-operated by completely duplicated hydraulic boosters with duplicate sources of power for both systems. A Smith autopilot is installed. Split flaps are fitted over the inboard section of the wing with plain flaps outboard. Automatic aileron droop is applied when lowering flaps. Four pair of air breaks are installed upper and lower on each side of the wing at the front and rear positions. There are four hydraulic power systems each with separate power supplies and a 24-volt electrical system operated by engine-driven generators.
The cabin pressurization system is designed for maximum working differential pressure of 8.25 lb. per sq. in. to give maximum cabin altitude of 8,000 ft. at 40,000 ft. The pressurization system is installed in duplicate with each system capable of independent functioning. Fresh air supply for the cabin is tapped from the compressors of the four engines and cooled before passing into the cabin. Air supply system in each wing can be operated independently and either system can supply sufficient air for pressurization. Heat for cabin air is bled off the engines. The Comet is equipped with an emergency oxygen system that permits a descent from 40,000 ft. to 15,000 ft. at maximum rate. Four portable oxygen systems are also provided.
Specifications of the Comet follow: span 115 ft.; length, 93 ft.; height, 28 ft. 4.5 in.; wing area, 2.015 sq. ft.; root chord, 29.5 ft.; tip chord, 6.75 ft.; sweepback at ¼ chords, 20 deg.; fuselage max. Internal dia., 9.75 ft.; fuselage max. External dia., 10.25 ft.; tail span, 42.67 ft.; and payload, 11,000 lb.
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