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Aviation History
1949
1949 - 1574.PDF
338 Apollo Appraisal. . . pedestal—lowered to 25 deg take-off stop. Between 8,000 and 11,000 r.p.m. the Mambas are treated with some caution on opening up, for it is possible to stall them and roast-up turbine blades. This does not mean, however, that Mambas are unduly "precious." For take-ofi they are opened up reasonably slowly to 11,000 and then banged open, if need be, to the iull 14.500 r.p.m. Brakes are released and, with the nosewheel steering to aid direction- keeping, the Apollo is away in a hurry. The nosewheel will come off at around 60 kt but may be left down, when light, until the aircraft :s ready to unstick at 85-90 kt. With four engines pulling, the rate of climb at 34,000 lb weight is over 2,000 ft/min, and tests to date have shown that an outer engine cut as the aircraft climbs away from the ground at about 100 kt gives no cause for embarrassment to the pilot. There are a number of indicator lights which may wink at the pilot on the ground or in the air. A green one tells him his nosewheel is central, four bright white ones on the pedestal that the withdrawable pitch-stops are engaged, four red ones on the starboard side that the Mambas are "reserve torquing" and four other red ones (day^night type), let into the feathering buttons, give fire warning. Two Feathered on one Side As the Apollo climbed away in pursuit of the photo- graphic Lancaster, and later as it formated with it, it was noticeable that S/L. Franklin handled his aircraft with obvious ease and confidence bespeaking light, responsive controls. He had previously spoken of the simple flying characteristics of his machine, and after some normal de- monstrations two Mambas were feathered on one side. This can be achieved almost instantaneously by cutting the high-pressure cocks. Fuel feed stops at onus, and the reverse-torque warning light flashes on because the air- screw is turning the turbine. The reverse-torque switch also operates at once, moving the airscrew rapidly into full- coarse. Pressing the feathering button then doss the rest. Small turboprops will not usually stop altogether, because they run so freely, and in practice they windmill very slowly (usually backwards), the drag increase being negli- gible. The airscrews also continue to turn for a long time after shut-down on the tarmac. The Apollo remains very handleable on two engines and turns readily against them. Service ceiling on two engines is quoted as 15,000ft and on three, as 26,500ft. Mambas give no trouble in relighting, and the procedure takes approximately nine seconds. The three-bladed D.H. airscrews unfeather in response to pressing the feathering button, and the Mambas pick up readily as soon as the high-pressure cock is switched on and the fire is relighted. During the starting-cycle on the ground, jet-pipe tempera- tures need watching and must not be allowed to exceed 700 deg C, but in the air there is little tendency for this to occur. The maximum jet-pipe temperature allowed for normal running is 590 deg C, and it is not usual to exceed 500 deg C under cruising conditions. Among the relatively few engine instruments on the centre panel are four torquemeters reading in pounds per square inch. Their readings in flight vary between 50 and 80, and, to discover the shaft horsepower developed, one multiplies the torquemeter pressure by the r.p.m. and divides by a constant of approximately 1,940 (the flight crew use the year 1949 to help them remember). Leaving the cockpit and walking back into the furnished cabin, it was possible to consider the ride from the passen- ger s viewpoint, although flying for some 45 minutes at 14,000-15,oooft without pressure or oxygen proved rather a strain, particularly as the climb—and, later, the descent —were rapid. Noise level was found to be a little better than the average for all modern transports, and sounds consisted of a deep rumble mixed with a just discernible whir as of reduction gearing. The whistle mentioned earlier could no longer be heard. Of vibration there was also the average amount, and this, it was said, was chiefly due to the airscrews and will be remedied. FLIGHT. T5 September On one side of the Apollo cabin are standard, solid paired seats by A.S.T., carrying folding tables on-their backs, while on the other side single and paired seats of various makes are provided for trial. Armstrong Whit- worth are to be congratulated on this sensible move. The passengers' view from the large windows is better than previously experienced in any other low-winged aircraft, and the general layout and roominess inside will be appre- ciated. The two toilet compartments at the rear end are too small, but a spacious galley is provided up front. To the occasional passenger with an interest in the air- craft carrying him, the view from the window out over the wings will be unusual. The wing itself is so thick (T/C ratio 18 per cent constant) and of such aspect ratio as to appear humped, thus accentuating the smallness of diameter of the pencil-like Mambas. At the rear, the trailing edge is seen to be cusped and the Mamba jet pipes, naked and unfaired, seem to pop out like afterthoughts. A glance from any window at this juncture of the flight showed the aircraft to be sailing above 10 / ioths cloud— in a north-easterly direction, according to sun and time. The Lancaster was still nearby, although it was not easy to see at its slightly higher level: the windows of the cockpit, from which it was now observed, are so positioned as to give a good view all round and downwards but a somewhat restricted one upwards. No stalls were attempted on the flight, but Franklin reports that warning and recovery are quite satisfactory. A radio bearing for home and a rapid descent through cloud, throttled back and with reverse-torque lights blink- ing, torquemeters reading near zero and fine-pitch-stop lights on (below 27 deg pitch) brought the Apollo back into its base circuit in a very short time. One could not help thinking that when braking airscrews are fitted and if the warning lights for these (already provided for) are on together with all the others, the Apollo cockpit will shame a Christmas tree. At 30 kt on the circuit, flaps were lowered to take-off position and the wheels went down with a resounding clunk. Appropriate trimming followed and now there were the little green undercarriage-warning lights shining. The approach was commenced at 115 kt and 11,200 r.p.m., full flap being dropped at this speed. Over the hedge the needle read 90 kt and the attitude of the aircraft was quite nose-down, giving a very good view of the field ahead. At 80 kt the wheels touched down, the r.p.m. dropped to 8,000, the pitch-stops were withdrawn, and after a few hundred yards the reassuring power of the brakes was felt. If it is necessary to go round again, it is quite in order to open straight up from 10,000 r.p.m., which is con- venient for the approach, but at lower r.p.m. a little time is needed for acceleration. Various power-lever settings are marked on the quadrants, but they are likely to be altered in name and position in the near future. Development of the prototype Apollo will continue as quickly as possible, and a second machine is under con- struction. No firm orders have been announced, but en- quiries from many countries, particularly European and South American, are likely to lead to orders for as many as fifty of these 24 / 40-seat aircraft. ARMSTRONG WHITWORTH APOLLO DATA. Four Armstrong Siddeley Mambas. Span 92ft (28.00 m) Length 71ft li^in (21.90 m) Overall height 26ft (7.9 m) Undercarriage track 17ft. (5.18m) Gross wing area 986 sq ft (91.6 sq m) Aspect ratio 8.5D Fuel capacity (max) 990 gall (4,500 litres) Normal take-off weight 43.000 Ib (19,500 kg) Max payload 10.000 Ib (4,536 kg) Take-off powar 4,040 s.h.p. + 1,228 Ib static thrust (1.024 c.v. + 139 kg x 4) Normal power loading at take-off 8.1 Ib/h.p. 0.62 kg/c.v.) Max speed at 20,000ft 341 m.p.h. (549 km/hr) Economical cruising speed ... ... ... ... 276 m.p.h. (445 km/hr.) Cruising rangs (still air) at 10,000ft 1,100 miles (1,770 km) Cruising range (still air) at 20,000ft 1,400 miles (2,250 km) Stalling speed 88 m.p.h Service ceiling ... " 32,500/t (10.100 m) Take-off run 1,100yd (I 000 m, n h
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