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Aviation History
1953
1953 - 0541.PDF
. \ I May 1953 537 The equipment at the navigator's station varies according to the operator's requirements, but this picture is representative. A.D.F. bearing indicator, master receiver controller, Gyrosyn compass master indicator, and intercom station-box can be identified on the main panel. Below them is seen the V.S.C. unit and on the left the oxygen supply, with Rebecca above it. allowed are : engine r.p.m., 10,250; jet-pipe temperature, 725 deg C; oil temperature, 85 deg C; rear-bearing temperature, 160 deg C. If all fuel flowmeters are showing correct flow commensurate with maximum engine r.p.m., then the parking brake is released and the lever moved forward and off, effecting a smooth getaway. At this point, with fuel consumption at its peak, delay must be cut to a minimum. The Comet soon begins to accelerate down the runway, giving a healthy "kick in the back" almost from the beginning of the take off run. Nosewheel steering is used up to a speed of 60 kt, when the rudder is found to be effective. The standard technique for taking-off large tricycle aircraft is used; the captain has his left hand on the steering and his right on the throttles, then moves his right to the wheel; the first officer checks that the throttles are fully open. At 60 kt indicated he places both hands on the wheel and at 80 kt backward pressure on the wheel overcomes the only "feel" characteristic—that of a 40 lb spring strut—and raises the nose. This artificial feel is not representative of control loads imposed, and it behoves the pilot to be cautious in avoiding large control movements and the consequent danger of overstressing at high speed. When the nosewheel rumble ceases a check forward is made on the elevators in order to stabilize the attitude of the aircraft. The nosewheels should be just off the ground, an attitude giving maxi mum acceleration. Depending on the weight, the aircraft will be ready to leave the ground at around 108-115 kt I.A.S. when a steady backward pressure on the control column will ease her off. Distance-run varies, of course, with conditions and weight, but during training in England at maximum landing weight of 75,000 lb (34,019 kg) the run is around the 1,500 yd mark. Naturally, the distance decreases as fuel is burned off at the rate of approximately 1,323 lb (600 kg) per circuit and landing. Once the Comet is airborne it accelerates rapidly and continu ously. The undercarriage is raised by the first officer, and speed is allowed to increase to 150 kt. The flap setting of 15 deg gives greatest angle of climb, and, consequently, maximum obstacle- clearance. Fuel-pump isolation switches are moved to "normal" at 100ft and when the climb-away is satisfactory the r.p.m. are reduced to 9,750, which setting is used throughout the climb to altitude. Flaps are normally raised at between 500 and 1,000ft and speed is allowed to build up to the correct cruising-climb figure (260 kt I.A.S., less 2 kt per 1,000ft a.m.s.l.). In practice, the cap tain aims to arrive at this correct figure by 5,000ft, maintaining a higher rate of climb and lower I.A.S. during the first part of the climb in order to reduce time spent at lower levels. Cruising procedure with the Comet has already been the subject of several excellent articles, but a brief outline may not be out of place here. Normal cruising procedure is to fly at constant incidence, de creasing the indicated air-speed as the fuel is burned off; the true air-speed increases slowly as weight is reduced. The usual incidence is that which gives the value of 1.3 times minimum-drag speed, but for purposes of weather avoidance the i.isVmd cruise may be used; this is also of value when altitude decrease is necessary for other reasons (e.g., when on three engines). This is the sole flexi bility in the cruise procedure, and the fuel reserves carried at present are large enough to cope with one pass at the destination airfield plus climb-out, cruise and descent to one designated alternative airfield, plus a variable holding and residual-fuel figure at that alternative. The three-engined case is not as critical as was at one time thought, thanks to the utilization of the technique whereby the aircraft is "drifted-down" to a new three-engined stabilization altitude. The correct i.i5Vmd airspeed for the Comet's weight at time of engine failure (as shown in the operating tables) will pro duce the optimum rate of "drift down"; on reaching the new height (at, of course, a lower weight, due to use of fuel on descent), the aircraft will begin to climb along the three-engined cruising path as further weight is burned off. Thus, it will be apparent that, given the incidence to fly, be it i.3Vmd or i.isVmd, the Comet is at all times operated at the maximum altitude, and will climb at a con stant 30-40ft min throughout the cruise period. In training, it is usually the practice to give a pilot a complete iA hr period during which a climb to a height of 35,ooo-40,oooft is made. The time taken varies with weight but is around 40 minutes, with initial rate of climb of 2,oooft/min, coming down to 50cft/min in the later stages. After take-off the feet are removed from the rudder pedals, and not replaced until the approach at destination; this is to avoid overstressing the rudder at high speeds (as would occur if ex tremely coarse movements were made) and to give greater pas senger comfort. Control for turns is quite adequate on ailerons alone, and above 20,000ft the recommended rate of turn is ij deg/ sec, or 360 deg in four minutes. This is necessary to limit the angle of bank, which is approximately 29 deg for a rate-half turn at 400 kt T.A.S., and also to limit the^ applied at high T.A.S. A new factor is the inaccuracy of electrically-driven artificial horizons at high altitudes. If the aircraft is levelled out after a sustained turn by reference to a visual horizon, the artificial horizon is seen to be showing a turn in the opposite direction. This can be highly disconcerting to the senses, but reference to the needle-and- ball turn-and-bank instrument soon gives reassurance. The latter, being a "rate" instrument, does not suffer from this error, which is caused by the usual tendency of the artificial horizon to erect with horizon-bar parallel to the wings; on the Comet this effect is accentuated by the large bank-angles and slow rate of turn at high T.A.S. Referred to as the engineer's panel, although the Comet crew does not necessarily include a flight engineer as such : The top dials and switches are concerned with the electrical system of the aircraft; the second panel is for the Ghosts' fuel system; below it again are the controls and indica tors for the cabin pressurization and conditioning system; the levers at the bottom are for fuel coss feed, de-icing and cabin supply-valves.
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