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Aviation History
1962
1962 - 0991.PDF
FLIGHT International, 21 June 1962 989 840 for a very snappy take-off run. The engines were making their buzz-saw noise and the pressurization was hissing quietly. I was sitting between the propeller discs, but quite comfortable. Lifting off decisively at 80kt, Jacques went straight into a 2,200ft/ min climb at lOOkt. While initially leaving the circuit we had the autopilot on and were flying at 160kt on 70 per cent power with 35° pitch. When we were clear, Jacques again selected auto full- power and we continued the climb under autopilot. At 8,000ft the 840 was put into level flight by autopilot, and autopower retained until the speed had built up to 220kt i.a.s. Then Jacques tripped the auto setting, without actually displacing the pitch levers, so that pitch became fixed. For a while the speed went on building up, but at 230kt i.a.s. we had 87 per cent power and had settled in the cruise without moving the pitch levers. It is quite fascinating to watch these Astazous performing, but I found when I took control that their power response to pitch manoeuvres has a curiously trapping effect if (as I was doing in order to make an assessment of handling) one deliberately tries to change speeds. If I pulled the nose up to slow down, the Astazous produced more power and we simply climbed at constant speed, and vice versa when I tried to increase speed. For normal, straightforward operation this is, of course, extremely useful. At 230kt the 840 showed highish control forces, but there was excellent stability for hands-off flying. For an airliner, this is just as it should be. In this and in other respects the 840 reminded me a good deal of the Avro 748—very smooth and easy, rather a job to throw around at full cruising i.a.s., but light, responsive and delightful at circuit speeds. Slowing down, after firmly retarding the pitch levers, brought considerable trim changes, particularly near lOOkt. I kept on heaving back the stick in level flight until a distinct buffet at around 90kt was followed by the mildest and straightest stall imaginable. Rather than actually stalling, we declined into a stable descent with the nose up. Aileron control remained. I flew around at 120kt, really enjoying the smooth manoeuvr ability, until Jacques told me to fly at lOOkt. Then he brusquely feathered one port engine. There was relatively little reaction, but he next applied auto full-power on the other three, which produced fair control loads all round. Nevertheless I was able to trim hands- off at lOOkt. Failure of an engine does, of course, only reduce power by 25 per cent—a potent safety feature. To make his point about engine-out handling, Jacques then feathered the other engine on the port side, still at lOOkt with full power to starboard; but again I was able to trim hands-off and make easy turns either way. In creasing to 150kt, I found that relatively little trim was needed to hold the asymmetric condition. It felt pretty good to me. Jacques now restarted the two port engines, apparently using the normal automatic starting system, and we prepared to try some flap and undercarriage. The flight was being a little difficult because we were above eight-eighths cloud, navigating by two VORs within the control zone, being watched by radar and constantly told to change height and heading, and also having to keep a weather eye on our eastings—Jacques was naturally wary of getting his prototype netted by the East Germans waiting just down the road. Flaps are operated by an aerofoil-shaped lever in the roof console, with an indicator dial beside it. Actuation is by electric motors and 18° take-off, 37° approach or 45° landing settings are gated on the lever. The shaped undercarriage handle protrudes from the centre of the engine-instrument panel and has its three-light indicator next to it. Maximum speed for take-off flap is 185kt and a strong nose- up trim-change results. Approach flap gave less of a trim change, but landing flap produced a considerable nose-down attitude change. A 60° setting was originally provided, but abandoned because it was excessive. Full flap at 95kt, with power off, gave a rate of descent of no less than l,600ft/min. Flap reduced the power-off stalling speed to about 60kt i.a.s., indicating the remarkable effectiveness of the high-lift system. The slotted flaps move back on curved rails. Stalling characteristics were once again very mild and the aircraft was pleasant to handle even at very low speeds. Undercarriage extension produced no perceptible trim-changes. During a normal airliner approach the Astazous again take over. The drill is 95kt with propeller pitch set at a datum to give a stable rate of descent of 500ft/min. Engine power then automatically compensates for changes in glide-slope angle, so that rate of descent can be increased to l,000ft/min simply by pushing the stick forward, and without the speed rising beyond 1 OOkt. Similarly, the glide-slope can be made shallower without losing much speed. As it happened, the controllers were very busy, the weather was Mtif:- "Flight International" photograph "The four Astazous, giving that certain Viscount turbine airliner feel, should prove a real sales point in the USA..." poor, and we made an ILS approach under autopilot control, Jacques working the autopilot, because the localizer was too wavy for the coupler to follow it accurately. We touched down at 80kt and went straight into reverse pitch for a very short run. Jacques then steered with the brakes, the nose- wheel not having a steering device. From the pilot's point of view I thought the 840 a very pleasant aircraft, easy to fly and fascinating to watch under the control of those Astazou engines. Although I felt distinctly trapped at a fixed speed, as I said, I think this curious characteristic will be useful for airways flying, especially when pilots really learn to make use of the automatics, as Jacques evidently had done. One small point I did not quite like: the curved top of the coaming and the apparent slant of the sharply raked windscreen rather rob one of a level aircraft datum to line up with the horizon in visual flight. I notice that the windscreen geometry is to be slightly different in the second machine, which should be flying by the time these words appear. The four Astazous, giving that certain Viscount turbine airliner feel, should prove a real sales point in the USA, where Turbo-Flight are preparing to sell the aircraft. In Ireland, the new Potez factory is scheduled to turn out two dozen 840s per year. Ten are to be ordered for the French Government VIP flight. The standard 840, furnished with full airways equipment and autopilot, and with the normal 16-seat cabin, will cost around $450,000, about half the cost of anything comparable. Visible in this flight-deck picture is part of the "battery of 16 engine controls" which Mark Lambert found a little intimidating on first acquaintance. Only four are normally used "Flight International" photograph
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