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Aviation History
1961
1961 - 0704.PDF
714 FLIGHT, 25 May 1961 JET DRAGO de Havilland's DH 125 Executive Jet ONE of the best-kept aviation secrets of recent months hasbeen the date on which de Havilland would make availabledetailed information on their DH 125 executive jet, the existence of which has for many months past been known to thoseclosely connected with the manufacturing industry or to business flying. When it came, the first official release of news was scant indeed—an after-lunch reference to the project in February by Mr H. G. Sturgeon, de Havilland"s managing director. He said that theDH 125 was occupying the thoughts of the company's project engineers and that a Dove customer was anxious to place an order. No decision about production had then been taken, but therumour persisted that metal had been cut and that production was soon to get under way. In April the basis of these rumours wasconfirmed. An illustration was released showing a neat little jet of l8,000lb maximum weight, with a wing of moderate sweep andwith pods enclosing two Viper 20s nestling against the fuselage just forward of a high-set tail. Accompanying the drawing was in-formation that an initial production batch of 30 aircraft was to be laid down, that the Hawker Siddeley investment was of severalmillion pounds, and that DH considered that the type might well remain current for 20 years. This week, in the fullest release of information to date, the nameof the new aircraft is announced as the Jet Dragon, a deliberate association with the first twin-engine de Havilland transport, theDH 84 Dragon of 1932. In years to come the name may be abbre- viated simply to Dragon, the qualification becoming needlessonce the aircraft and its capabilities become well known. The day is passing when the executive jet is a perquisite of themillionaire few. In the USA, Sweden, Switzerland, Israel and Italy, and now in Great Britain, is rising a generation of newbusiness transports with operating economics realistic enough to be compared with those of other tools of industry. On the basis ofaircraft miles flown, de Havilland say, Jet Dragon costs will be almost the same as those for the Dove—about 2s 5d per aircraftmile. The economic argument for a jet as a business aid is that, interms of seat miles flown per year, productivity is very much higher than that of a piston-engine counterpart. Thus, althoughthe Jut Dragon may cost two-and-a-half times as much to operate per hour as the Dove (with which in capacity terms it is broadK comparable) its block speed over average stage-lengths of about500 miles is greater in about the same ratio. From this fact two points arise. First, for an annual commitment ofsay, J20.000 miles of business travel, the Jet Dragon's utilization would be 35Ohr compared to 800hr for a Dove operated at a similartotal cost; and, because utilization in business use is limited by the degree of inconvenience which executives are prepared to accept,on such a high mileage the jet could provide a practical operation where a piston engine aircraft could not. Secondly, the economicsof the jet are very much more critical in respect of stage-length, because stages of several hundred miles must be flown for operatingcost per hour to be balanced or bettered by the greater return in miles of travelling. In practical terms this may mean that muchmore selective analysis may have to be employed by business firms contemplating jet operation, because the jet is less practical overthe very short stages that represent a typical business-aircraft operation today. As projected, the Jet Dragon carries six passengers and baggage,in addition to the crew of two, over a range with reserves of aboui 1.500 miles. Cruising speed will be between 450 and 500 m.p.h.The aircraft is said to be capable of operation from short runways at moderate approach speeds, but no figures have yet been given.In the de Havilland tradition is the promise of "excellent handling characteristics at high and low speeds." The cabin, which has awardrobe and toilet aft and entrance vestibule forward, is 18ft 6in long, 5ft lOin wide and 5ft 9in high. This is substantially largerthan that of the Dove, or of the Beech Queen Air which forms the subject of a handling report in this issue. Air stairs can be suppliedif required, but the vestibule floor is only 40in above ground level. Within the vestibule, space is available for a food and drink cabinetand a cupboard for coats and wardrobes. Cabin space is available for six executive armchairs and an aisle of generous width. Advantage has been taken of the rearward position of theengines to produce a structurally uncompromised wing, built as a single unit from tip-to-tip and passing unbroken beneath thefuselage. A low aspect-ratio and relatively deep section contribute to stiffness and low weight. The top surface of the wing centre-section is dished to receive the cylindrical fuselage, and there is no abrupt discontinuity in either structure. Structurally advantageous,this arrangement also simplifies manufacture. All fuel is contained within the wings. Bristol Siddeley Engines have won the contract for Dragon propulsion with the Viper 20 turbojet. In this drawing of a typical Viper 20 pod, the overall dimensions are: length, 103.Sin; diameter, 32in; and the engine and complete nacelle respectively weigh 810 and 1,1401b. A, 6kW generator; 6, lip anti-icing; C. anti-icing gate valve; D, firewall, £, turbine-blade containment shroud; F, thermocouples; C, drain; H, glowplug; J, igniter; K, pressure-differential switch; L, filter drain; M, l-p fuel filter; N, airlfuel-ratio control; 0, flow control; P. compressor containment shroud; Q, tacho- meter; R, hydraulic pump; S, burners; T, primers * I ' / > PO N M L
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