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Aviation History
1957
1957 - 1722.PDF
812 FLIGHT, 22 November 1957 Close-up of a BOr.3 intake, showing twin starter cartridges. On the right is seen the front face of the main intake, showing the wheelcase and compressor intake guide vanes. BRISTOL ORPHEUS ... aircraft are foreseen and clearly there are many duties both in thefields of military training and communications, as well as that of civil transport, that this ten-seat swept-wing aircraft could per-form exceedingly well. Another American aeroplane for which the Orpheus has beenselected as one of two alternative powerplants is the North American Model 249 jet trainer which at N.A.A.'s ColumbusDivision is being developed for the U.S. Navy as the T2J. In Japan the Orpheus-powered Fuji TIF-1 trainer is likely to fly inthe near future, and the BOr.4 is also scheduled for certain other trainer aircraft including the Fiat G91T, the Gnat Trainer andtwo-seat versions of the Etendard and Taon. Future Orpheus- powered intercepters include the Folland Gnat Mk 2, the ItalianAerfer Leone and the Spanish Hispano HA.300. Yet another application concerns the Short SB.5 research aircraft, which nowhas a wing swept at no less than 69 deg. It would also be reason- able to suppose that the Orpheus would be suitable for generatingdirect lift in VTO applications. Development of the Orpheus engine was originally intended tobe completed when the BOr.3 had been proven at its design rating of 4,850 lb. However, the demand for ever higher aircraft per-formance has changed the picture, and Bristol Aero-Engines are now developing two advanced versions, designated BOr.ll and BOr.12. The former is rated at 5,760 lb thrust, and has the samediameter as the earlier engines (32.4in) and is slightly longer, at 79.27in. The BOr.12 is rated at 6,810 lb dry thrust, with a take-offfigure, using a lightweight form of reheat, of over 8,000 lb. The BOr.12 is also of the same diameter but has a length of 82.7in. There have been proposals that production versions of theBreguet Taon, Dassault Etendard VI and Fiat G91 should be equipped with the BOr.12, an engine which has not yet reachedthe production stage. In addition, two-seater versions of the Taon and Etendard with the BOr.12 are being offered, to combineadvanced training with an operational role. With this engine, the thrust/weight ratio of the aircraft will be restored to the valuecorresponding to the gross weight specified in the original NATO specification. Moreover, both the Etendard IV and the Sud Avia-tion Baroudeur have since been offered with the BOr.12 for NATO purposes.In addition to the current marks of the engine which are being manufactured in increasing numbers, Bristol Aero-Engines ispinning its faith to these advanced marks for the future. Although in military installations these are likely to be equipped withreheat (in which form there is undoubtedly a big future for the Orpheus) there are perhaps, even greater possibilities for civil ver-sions, where the engine's inherent toughness will be translated into the long overhaul life and exceptional reliability for which Bristolengines have been renowned for more than thirty years. HELICOPTER RADIO INSTALLATIONS A PLEA addressed to helicopter designers for greater considera-tion of radio equipment installation problems was the keynote of a discussion held in London by the Helicopter Association onNovember 8. Five short lectures were delivered under the general title of Problems Relating to the Installation and Operation ofRadio Equipment in Helicopters. The speakers were Mr. D. W. Griffiths, radio supervisor, Airwork, Ltd.; Mr. M. P. Kitson,Murphy Radio, Ltd.; Mr. R. A. Burberry, Standard Telephones and Cables, Ltd.; Mr. P. P. Creek, Marconi's Wireless TelegraphCo., Ltd.; and Mr. G. Hinchliffe, Decca Navigator Co., Ltd. The chairman was W/C. R. A. C. Brie. MR. GRIFFITHS began by outlining the general problem and the otherfour speakers dealt with the detailed aspects of different items of equip- ment. MR. KITSON described the installation and operation of two-wayV.H.F. communications equipment—which was, he said, an essential item for the majority of aircraft. The most significant installation prob-lem to be overcome, apart from the siting of aerials, was that of vibration. Care had to be taken to avoid using flexible mountings having a naturalfrequency near the cruising r.p.m. of the rotor or its second or third harmonic. Otherwise vibratory oscillations tended to build up andfailures be caused. The difficulties of siting aerials most advantageously were explainedby MB. BURBERRY. Because of its relatively large forward structure and low ground-clearance, the single-rotor helicopter was the most difficultto eater for. The best location for an aerial was below the fuselage, where it was unaffected by rotor modulation. If there was insufficientground clearance forward, it had to be fitted below the tail boom, with consequent shielding by the fuselage in a wide arc ahead of the machine.There was not usually sufficient rotor-blade clearance for a V.H.F. aerial above the fuselage. This position, however, was favoured by the speaker following,MR. CREEK, for mounting the smaller loop aerials for A.D.F. equipment. The radio compass, said Mr. Creek, had been installed in a number ofhelicopters and he had carried out a series of tests to determine the most suitable aerial locations on the first installation. Ideally, the loopaerial had to be as far as possible from surface discontinuities and as far as possible from the rotor assembly and sources of electrical noise.It had to be mounted, on the fore-and-aft line of the fuselage. The sensing aerial had to be as near as possible to the centre of plan areaand as far as possible from the rotor assembly, two requirements which were not easy to meet. If the sensing aerial had to be mounted aft of theideal position it usually resulted in the bearing-indicator needle reversing after the aircraft had passed over the beacon. On a single-rotor helicopter, the loop aerial could be mounted eitherabove the cabin or on the upper side of the tail boom abaft the rotor head. The latter position had been found to give less susceptibility to modula-tion effect and random errors. Instrumental accuracy of the radio com- pass was approximately ± 1 deg and overall operational accuracies in 'heregion of + 3 deg had been obtained. MR. HINCHLIFFE described installation and operation of the DeccaNavigator. Again, aerial location was of prime importance and was complicated by the fact that the first valve of the receiving unit had tobe within one foot of the aerial. Therefore, apart from other considera- tions, there had to be space inside the fuselage adjacent to the aeiialattachment point to accommodate the aerial amplifier unit; but the P™°' lems were not insurmountable, and many successful installations baabeen made. Mr. Hinchliffe re-iterated the plea of the other speakers in asking for more consideration from helicopter designers in the ea»ystages of any new type. More "systems engineering" was needed, the helicopter, its instruments, radio communication system and navigatio iaiaids being considered as an integrated whole.
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