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Aviation History
1962
1962 - 0990.PDF
988 FLIGHT International, 21 June 196: IN THE AIR By Mark Lambert: No 160 of the series POTEZ 840 (Four Turbomeca Astazou of 555 e.h.p.) Span, 66ft 5in; wing area, 376.7sq ft; empty weight, I0,625lb; gross weight, 19,3101b. Performance: Cruising speed at 21,000ft, 310 m.p.h.; initial rate of climb, 1,970ft/mm; take-off run, 2,560ft; max range (with reserves, carrying 24 passengers), 620 miles. POTEZ 840 I N the first prototype Potez 840, F-WJSH, which I flew during the Hanover Air Show with Jacques Grangette, Potez test pilot, the cabin was furnished for 16 people facing forward in two rows. The trench aisle just failed to give one head-room to stand upright, and a series of steps led up to the main spar housing where it crossed the cabin. The cylindrical fuselage section afforded a sizeable shelf outboard of the seats. Windows were of Caravelle ovoid form, but set slightly low. The front row of seats was directly in the line of the four propeller discs. Layout of the flight deck was quite straightforward, except for the Noratlas control wheel and rudder pedals, which were much too large for this aeroplane and are to be changed in production ver sions. A battery of 16 engine controls is a little dismaying, but only four—those controlling propeller pitch—are normally used. The others control engine constant-speed setting and propeller feather ing. Each engine has indicators for propeller pitch in degrees, per cent power and per cent r.p.m., plus an oil-pressure light, combined j.p.t. and oil temperature gauge, and fuel flowmeter. The Lear LIFE instruments and L-5 autopilot controller are on the left panel and normal blind-flying instruments are on the right. Electrics and other controls are in the roof panel; and full airways radio, includ ing CSF radio compass with four preset frequencies, is on the console ahead of the throttles. The tailplane trim-wheel is on the console and electric aileron and rudder-trim controls are there too. Grangette and his engineer went through the starting, taxying and take-off procedure before I was put into the co-pilot's seat to fly the aircraft. With solid cloud cover at 1,500ft, the weather was uninviting; and Hanover Control Zone is no place to frolic about in. The four Astazous were started in turn on internal batteries, simply by setting the pitch levers to zero, pressing a button and working the governor lever up to 80 per cent r.p.m. when the fire had lit. To reduce noise, both inside and outside the cabin, 80 per cent is used for taxying. Normal shaft r.p.m. are 34,500 and propeller r.p.m. 2,200. Just to recapitulate the distinctive Astazou regime: propellers and shafts run at constant governed speed and pitch is electrically set from the pitch lever to a fixed value. Under these conditions only the fuel input can be continuously altered (unless one of the levers is manually moved) and engine power therefore automatically de creases if the nose of the aircraft is pushed down and increases if it is raised. Pitch-lever setting thus produces a power datum suitable for a given speed in level flight. In pitch manoeuvres the power adjusts itself, even reaching negative thrust, and tends to hold airspeed constant. To maintain full power on take-off, pitch has to be progressively coarsened; an automatic full-power regime with automatic pitch change and j.p.t. governing can therefore be selected by pressing a button. The system can be released simply by nudging the pitch levers to trip an electric detent. In the event of failure of the electric pitch control, the propeller is immediately feathered by an emergency hydraulic system. If j.p.t. is exceeded, power is automatically reduced. If an engine loses power in auto full-power setting, the pitch automatically coarsens, in an endeavour to maintain thrust, until the propeller feathers. If the pitch levers are pulled through a gate behind zero pitch, reverse thrust is obtained. We were flying with six people and less than full fuel. Jacques backed out of his parking spot and then taxied along to the runway, where he pressed the automatic full-power button and unleashed the
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