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Aviation History
1964
1964 - 2163.PDF
180 FLIGHT International, 30 July 1964 HAWKER SI DDE LEY HS.125 in the Air . . . inertia-reel shoulder harness. Rudder pedals are also adjustable. There is console space for stowing manuals, cups or for additional controls. Panel space is adequate for the fullest complement of dials in proper layout. There is a central warning system. The aircraft can be flown quite comfortably by one pilot. Two-crew operation is recommended by the ARB in controlled airspace, but the Business Aircraft Users' Association is in process of recommending a "1J" crew system, the second pilot being no more than a PPL with adequate knowledge of radio. Cooling gills, carburetter controls, fuel tank sequencing and other piston-engined housework are absent in the HS.125. Pressurization is additional and at the moment must be manually switched on after take-off, at a time when an IFR departure may keep the pilot very busy, but a speed-sensitive system is to be provided to make even this auto- matic. All pressurization adjustments can be made before take-off. The electrical system includes two starter/generators, two batteries and two inverters, plus a frequency-wild alternator on the right engine to supply the Triplex gold-film windscreen heating system. The edges of the gold panels are, incidentally, wavy to prevent the pilot getting any false datum lines from it, but this seems to produce a little optical distortion. Fire extinguishing is provided for the engines, together with an overheat warning for the equipment bay in the rear fuselage. Hydraulics operate undercarriage, flaps, airbrakes and nosewheel steering, with anti-skid in the normal braking system. There is a stand-by brake system with separate supply lines and accumulator but without anti-skid. This is used for parking too and a single lever selects first stand-by brake and then locks it on for parking. Normal braking applied by toe-pedal is very powerful, but operates rather suddenly as the pedals are progressively depressed. Nose- wheel steering, by tiller wheel on the left console, is effective and light. Both nosewheel and tiller respond to cross-sloping ground like a light car, but the system is designed for use throughout take-off and landing runs. For towing, the steering actuator can be disconnected by removing a pin and the same pin is used to anchor the tow-bar. Final hydraulic stand-by is by hand-pump. Fuel is stowed simply in the "wet" wing box on each side with a single gravity filler neck near each wing-tip. To allow intermediate levels to be set accurately, a glass dip-tube is mounted in each wing. Fuel capacity is 518 Imp gal each side. Cross-feed is available, but the system otherwise requires virtually no in-flight management. Ice Protection Pitot head and mast, the rudder compensator strut and the windscreen are electrically deiced. There is also an alcohol spray for the windscreen. Compressor bleed is used for engine-face, intake and central dorsal intake anti-icing. Otherwise the wing and tail are anti-iced by fluid exuded through porous metal leading- edges. On aerodynamic, power, complexity and effectiveness grounds this is a good system. There are two ice warning devices. A small vane outside the side window shows ice collecting and can be illuminated by a small lamp at night. In addition, a highly effective Napier rotating ice detector will warn within 5sec of the beginning of even light icing. Finally, there is a lamp for inspection of the wing leading-edge at night. Engine starting is possible on internal batteries and the cycle is automatic. There is normally a 5min limit on 100 per cent r.p.m. and 690°C j.p.t., but it can be used continuously at the expense of overhaul life. Normal maximum continuous r.p.m. are 98 per cent. The engines will accelerate from 40 per cent to full r.p.m. in 8sec after the throttles are slammed open. The Viper already has estab- lished an excellent reputation for reliability in RAF training service but, even if one of them fails, automatic rudder compensation and sparkling single-engined performance—far, far better than any piston-engined twin—will take the sweat right out of things. Price is one of the HS. 125's strong points. In Britain the standard aircraft, including six-seat interior with toilet and in flyable con- dition, but without electronics, costs £187,000. A comprehensive radio installation would add approximately another £45,000. For the US market, the aircraft is sold with more equipment and dual controls, engine instruments, pressurization controls, brake indicator and anti-icing, but without electronics or interior, and then costs 5575,000. The instrument panels used for the ferry flight are removed, but Hawker Siddeley provide two blank panels ready for HS-125 Charming femininity is not absolutely nei.ta>oiy for stressing the convenience of the easy-folding airstairs and up-and-over tuck-away door —but it helps customer's instrumentation. An all-in price with custom interior and electronics might be 1750,000, which compares with $lm for an equipped Sabreliner and f 1.15m for a Mystere 20. A Jet Commander with factory-made interior, but without electronics costs 1595,000. The Lear Jet, with its "take it or leave it" all-in electronics package, is cheaper at $495,000, but is admittedly a rather smaller aircraft. The aircraft I flew was the seventh production machine, regis- tered G-ASTY and destined for the French agent. It had everything, including Collins FD-105 director instruments, Collins autopilot, 2 X ADF, 2x VHF nav/com, Bendix transponder, Ekco E.I90 weather radar, duplicated instruments and several stand-by gyro instruments. Starting, lighting, electrics, icing, fuel and air- conditioning controls were in outlined roof panels, but all radio, pressurization and "frequent use" controls were at body level. The passenger cabin was pleasantly coloured and well furnished. A notable HS.125 point are the air-stairs, which can be extended from inside or outside with one gentle pull on a leather loop and are self-restraining in the fall. The main door slides up to lie within the cabin ceiling and leaves very nearly full head-room for my 5ft lOin height in the "vestibule". Though not of generous proportions, the flight deck is not cramped. Radio tuners, trimmers and secondary controls are all on the centre console, except that the undercarriage lever and flap dial, undercarriage lights and airbrake magnetic labels are grouped on the right centre portion of the main panel. Only innovation for an executive aircraft are the "ram's horn" aileron controls—a la Britannia and Trident—which I found pleasant for elevator control but uncomfortable for ailerons. But they d6 give quite a good view of the instruments. Controls in the HS.125 are, of course, all manual, with geared-tab assistance in roll and pitch axes. The tabs on the ailerons are rigged slightly up to prevent up-float and there is a separate trim tab to port. The rudder is split into two halves, each with an anti-balance tab and the lower portion with a trim tab. The elevator carries two combined geared and trim tabs, and there is additionally a bob- weight in the circuit. The wing leading-edge is "hard," but there is a discontinuity from just inboard of the fence marking the beginning of a progressive fixed droop towards the tip. Landing lights are faired into the leading-edge and there is a small breaker strip to induce buffet at the stall. HS.125 maximum operating airspeed (VMO, replacing the former dual VNE and VNO) is 300kt i.a.s. or 294kt e.a.s. and MMO is an indicated Mach 0.735, giving 0.725 true. Flying is simplified, because 210kt is not only the undercarriage-down and take-off flap speed, but also the best turbulence-penetration and best anti- ' icing speed. Normal climb is made at 230kt up to about 26,000ft, when Mach 0.56 is held up to the pressurization-limited ceiling of 40,000ft. Initial rate of climb is well over 4,000ft/min. For performance cruising, 95 per cent r.p.m. will give Mach 0.735 at between 22,000ft
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