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Aviation History
1960
1960 - 0049.PDF
1O 1 12 45\ 7 ! 19 S 25 123 ! 29 ! 39 I 35 1O 2 13 42 | 43 53 55 52 51 SO9 22 16 26 26 31 35 4O 36 56 41 47 49 44 This diagram gives an indication of the profusion of access panels on the underside of the fuselage 1, 2, Radio, electrical and fire control (left and right); 3, controls, stations 194/208; 4, controls, stations 208/235; 5, 6. controls, stations 235/253 (I, r); 7, oxygen convertor filler; 8, 9, lower equipment stations 253/277 (I, r); 10, forward radar (I, r); 11, pylon electrical connecter; 12, 13, equipment bay, station 185/194 (I, r); 14, nosewheel door; 15, mainwheel door (I, r); 16, 17, hydraulic check valve (I, r); 18, inboard hydraulics, stations 318/325; 19, fuel FLIGHT, 8 January 1960 49 selector valve; 20, fuel drain valve; 21, fuelling coupling; 22, controls tunnel, stations 284/325; 23, wing attach points (I, r); 24, fuel probe (four more mounted dorsally); 25, forward tank; 26-34, speedbrake panels; 35, flap actuators and wing attach bolts (I, r); 36, control tunnel, stations 390/445; 37, 38, gearbox (I, r); 39, throttle quadrant; 40, fuel drain; 41, engine oil fill and drain; 42, aft fuel tank; 43, aft wing attach bolt (I, r); 44, hydraulic equipment; 45, tailplane torque tube; 46, 47, tailplane and hydraulic equip- ment (I, r); 48-50, flying controls (I, r and centre); 51, air for starting engines (I, r); 52, controls, station 482; 53, controls, stations 464/471; 54, 55, engine speed adjustment (I, r); 56, controls, stations 471/478 (I, r); 57, controls, station 475. power remains after failure of either powerplant. An externalground power receptacle is provided. Two 25-amp transformer/ rectifiers supply 28V DC power to charge the nickel-cadmiumbattery, which energizes a single-phase 115V 400c/s inverter supplying ignition during engine starts. Hydraulic System: There are two completely independentpower systems, the flight-control system and utility hydraulic system. Each is of the pressurized closed-centre 3,0001b/sq intype, with a pressurized reservoir. The flight-control system is powered by a pump driven by the right-hand engine while theutility system is supplied by the left-hand engine, both being in operation at all times. Under normal operation each systemsupplies half the force needed for control-surface movement, following failure of one system, the other is capable of controllingthe aircraft in normal flight, the transfer being automatic without pilot action or crossover power, each circuit having independentdistribution. The utility system, in addition to providing half the power for the flight controls, serves the landing gear and its doors,speedbrakes, stability augmenters and nosewheel steering. Full power controls are provided for the aircraft's ailerons,tailplane and rudder. The ailerons each have a dual hydraulic actuator, controlled by a cable system from the control stick. Therudder pedals are connected by cables and push-rods to servo valves on dual actuators. In order to avoid large vertical-tailloads during yaw manoeuvres, pedal travel is restricted when the landing gear is retracted. A subsystem provides Dutch-roll damp-ing, and interconnection between the rudder and ailerons com- pensates for non-linear inertia forces during roll manoeuvres, andprovides rudder trim authority. Spring and a bob-weight provide the stick forces and centeringaction for the tailplane, which is powered by two tandem hydraulic actuators. One cylinder of each actuator is poweredby the flight-control hydraulic system, the other by the Utility. Controls from the stick to the servo valves are duplicated, andpitch damping is provided. Freeplay is eliminated by preloading the actuators through the torque tube. Automatic trim-change takes place when the flaps are loweredor raised, and a push-button control allows the pilot to select the correct tailplane angle for take-off with hands off the stick.Trim is provided for all three surfaces, operation of switches on the stick grip controlling the tailplane and ailerons, while apotentiometer on the left-hand console trims the rudder. Move- ment of the trailing-edge flaps also actuates the leading-edge flaps,both systems being electrically driven. The speed brakes are located under the centre fuselage, and can be depressed to anyangle up to 46°. Each is actuated by its own hydraulic jack, but both are controlled by a single switch on the r-h. power lever. Northrop pioneered fully powered controls from the B-35 on-wards (British Messier manufacture full power servos under Northrop licence). A new feature incorporated in the N-156F's The first N-156F is here seen at Edwards, with two YT-38 Talons system is the use of a Teflon high-pressure cup-type seal, backedup by a low-pressure O-ring with a return leakage drain between the two. These seals have proved effective at up to 350° F, andto have a life of over 5,000,000 cycles. Provided in the navigation and communication system areUHF, Tacan, IFF, range radar, infra-red search equipment and a bomb director system for use with the LABS technique. Thepilot is seated in a rocket powered, zero-altitude ejection seat of Norair design. It is capable of ejecting through the canopy ifnecessary, and a single pin safeties it on the ground. The seat has been sled-proven at up to Ml at Hurricane Mesa.Particular emphasis has been placed throughout the design on ease of maintenance. To collect data on actual field experience,Norair sent teams of engineers out to bases operating Century- series aircraft. Based on the wealth of data thus gained, studieswere made of the degree of skill necessary to service the N-156F anywhere in the world, taking a conservative level as representa-tive. These studies show that maintenance manhours per flight are only 21.5, compared to two Century figures of over 40. It is worthy of note that there are 111 access panels on the fuse-lage alone, comprising some 25 per cent of the surface area (see illustration above). All operational fittings and connections arereadily reached. Components liable to frequent replacement are located in the most accessible positions and all others can betested in situ (e.g., the boost-pump pressure output can be checked through a convenient port on the fuel-valve manifold). Very littleground support equipment is required to service the aircraft be- cause virtually all systems are located at waist or chest-height.Perhaps the best evidence of the fighter's small demands is that even in the testing phase Northrop's ground staff consists only ofa crew chief and four mechanics. A high degree of safety is designed into the N-156F, based onstudies of other operational fighters. As the two engines energize two independent electrical systems, failure of one merely reducesavailable performance. USAF accident statistics show that twin- engined fighters suffer approximately one-quarter the attritionrates of single-engined types. Moreover, the handling characteris- tics of the fighter during take-off and landing are markedlysuperior to those of competitive aircraft. No ram-air turbine is needed in the event of complete power-plant failure; the windmilling engines supply sufficient hydraulic and electric power to maintain control down to and including thelanding. The aircraft can also be landed on one aileron. From its inception the N-156F has been regarded as an advancedarmament-launching platform to provide versatility in its role as a counter-air fighter (counter-air is the USAF definition forthe destruction of enemy airpower both in the air and on the ground). So, although the basic armament consists of two Side-winder IR air-to-air missiles mounted at the wing tips, the air- craft has the capacity to utilize at least 48 different combinationsof external stores (see sketch, page 48). In keeping with the overall concept, Northrop's humanengineering personnel have developed a new type of non-com- pensating optical sight called Norsight. It is of minimum weightand bulk, and can thus be mounted close to the pilot without obstructing the primary panel. While dispensing with the cus-tomary expensive electronic computer, it provides for delivery of all the weapons that the fighter can carry. The design of the N-156F was based on three main operationalconcepts: that operational and maintenance facilities are fewer and less complete in NATO and SEATO than in the USA; thatthere was a shortage of skilled technical personnel, but a good supply of non-rated or low-skilled personnel; and that the aircraftwould be built under licence in NATO and SEATO countries. It thus represents Northrop's solution to these varied requirements,while minimizing the unit price in order to attract the largest number of customers, but without sacrificing performance oroperational effectiveness. Two main missions are envisaged. The first presupposes the use of fixed bases with a reasonable level of engineering support, while
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