aircraft. The other requirements for stability and control are defined in broad terms, the require ments being of a qualitative character only. In the strength requirements a characteristic typical of rotary wing aircraft is that the man The Air Registration Board's Provisional oeuvring limit load factors are only +3·0 and —0·5. These factors arc based upon the inherent Regulations for Rotating-Wing Aircraft characteristics of the rotor, which in its loadings is much more restricted than a wing of a fixed- In the first sub-section, dealing as usual with British Civil Airworthiness Requirments, Section wing aircraft. It is nearly always possible to general notes and definitions, very much atten G-Rotorcraft [Air Registration Board, Brettenham overstress an aircraft wing by applying large con tion has been paid to the declaration of air House, Strand, W.C.2. 5s.] trol deflexions at high speeds. The speed of the worthiness limitations and information in order airflow over a rotor blade is, however, mainly to make sure that all procedures applying to the The Air Registration Board recently published dependent upon rotor r.p.m. which is kept be operation of the rotorcraft in powered flight as a new section of the British Civil Airworthiness tween close limits. The main factor influencing well is in the emergency case of engine-failure Requirements, dealing with rotorcraft. The issue the aerodynamic forces on the rotor is the pitch shall be properly established. is a provisional one, it being stated in the fore setting. In powered flight the rotor operates word that the first official issue will be published The flight requirements prescribe the take-off fairly closely to its maximum loading and the in approximately eighteen months. space to be determined so that a landing in the , loading case giving rise to the largest loads is the take-off ground area can be made without injury The issue of airworthiness requirements on a flare-out after an antorotative descent, in which to the occupants in the event of failure of the well-defined basis emphasizes the fact that rotary- case normal accelerations of about 3g arc the critical power unit at any point. This phrasing wing aircraft have evolved from the experimental maximum to be reached by full control and pitch implies that it is acceptable for the rotorcraft stage and today arc developed into a means of setting changes. to be damaged in such an emergency, provided transport ready to take its place in the public Ground loads call for a speed of descent of transport system. In 1946 the U.S.A. issued the the occupants escape without injury. At first 6 f.p.s. to be catered for in the normal landing first requirements for rotorcraft in part 06 of the sight this might indicate a slightly lower degree case, a lower value than that for fixed wing air of safety than the requirement for fixed wing Civil Air Regulations. These requirements were craft. transport aircraft which shall be able upon engine of necessity very sketchy and although the A.R.B. These limited loads should enable a rotorcraft failure during take-off either to proceed or to requirements also are a first basis, to be amended to have a lower structural weight than a corre come to a stop before the end of the runway has and amplified as further development requires, sponding fixed wing aircraft. The mechanical been reached, without damaging the aircraft. the rapid advances made in both the theoretical complexity and the need for coping with the The difference is, of course, that in a crash of a and experimental sides of rotary-wing flight be rather severe vibrations have, so far, prevented come apparent when comparing these two sets fixed-wing aircraft upon engine failure during this feature from being exploited to the full of requirements. the take-off the occupants have little chance of extent. escaping unhurt, while in a rotorcraft, due to its The British requirements are based upon drafts, The requirements concerning the vibration and low forward speed, a crash landing can be made prepared by the Rotorcraft Requirements Co fatigue loads reflect the sound practice followed without injury to the occupants, provided the ordinating Committee under the chairmanship by British helicopter designers in prescribing the fuselage structure has been properly designed to of Professor A. G. Pugsley. On this committee authorized life of each component subject to prevent injury from secondary causes during a have been represented the industry (Bristol, fatigue loads to be established by comprehensive crash. This aspect is apparent from the phrasing Cierva, Fairey, Westland), the engine firms con ground testing under simulated flight loads. It is of several paragraphs of the rotorcraft require cerned (Alvis, Rolls Royce), the operators in this respect particularly that the British ap ments. (B.E.A.) and the scientific and administrative proach to helicopter design has been outstanding, official bodies (R.A.E., A.F.E.E., M.o.S. and Climb performance is to be determined for a it having been realized from the beginning that A.R.B.). range of operating conditions, including vertical the success of the development of rotary wing The requirements apply only to normal cate descent after power failure, with the exception aircraft depends to a great extent upon the re gory rotorcraft, but also serve as a basis for the that the region of roughness need not be pene liability of the components under the rapidly trated in the tests. It should be noted that for requirements applicable to other categories. They changing loads occurring in a rotor system. The rotorcraft with more than one power unit at any apply to rotorcraft of conventional design incor experience gathered from these tests constitute a porating flap and drag hinges for individual rotor condition at which the rotorcraft is claimed to sound basis for further development. blades, such as are being used at present on all maintain height with one engine inoperative the Requirements for engine installations, etc., British rotorcraft designs. The requirements to rate and corresponding gradient of climb shall follow closely the corresponding sections of the be applied to rotorcraft embodying rotor designs not be less than 50 f.p.m. and 1 per cent res requirements for fixed wing aircraft. with, for instance, rigidly connected blades, such pectively. For a take-off with all power units The requirements are as complete as could be as the Bell and Hiller types, will be decided by operating the sum of the acceleration in terms of g expected from the available data and experience. and gradient of climb shall be at least 8 per cent. the Board in consultation with the applicant. One point should be mentioned which might be For vertical take-offs a minimum rate of climb The phrasing of the requirements follows amplified in a future amendment. It is not clear in free air shall not be less than 100 f.p.m. modern practice in that it differentiates between whether the maximum speeds on tow with the mandatory requirements and recommendations, The handling requirements reflect the rather engine(s) stopped to be established according to the latter indicating cither accepted means of poor stability characteristics of rotary-wing air sub-section G.1, para. 5.7.4 applies to towing by a demonstrating compliance with the requirements craft in the present stage of development most tractor on the ground or by a fixed-wing aircraft or suggesting certain standards to be achieved clearly in the requirement that the rotorcraft in the air. The latter case may be of importance in but which have not yet been sufficiently estab under smooth air conditions shall exhibit no future operation, especially for long-distance lished to be incorporated as compulsory require dangerous behaviour if at any speed above the rescue flights. It might, therefore, be advisable ments. In this way full use is being made of the best climbing speed in straight trimmed flight the to include requirements both for the loading technical knowledge available without hampering controls are abandoned for a period of 5 seconds! cases following from this condition and for the future development by demanding compliance In this respect much development work still has handling characteristics in towed flight. with requirements based upon insufficiently to be done before the stability characteristics of matured knowledge. rotary-wing aircraft approach those of fixed wing L. II. B.S. No. G.122—Aircraft Magnetic Compass, Remote- By suitable alteration of the operating conditions B.S. SPECIFICATIONS Reading (Gyro-Stabilized). Price 1s. post free. of the anodizing bath, the properties of the film may be varied to suit the requirements of the service con Copies of the following Specifications may be obtained B.S. No. G.123—Aircraft Magnetic Compass, Remote- ditions in which the article is to be used. from the BRITISH STANDARDS INSTITUTION, Reading (Non-Stabilized). Price 1s. post free. The standard covers the methods of testing to be Sales Department, 24 Victoria Street, London, S.W.I These Standards give details of construction and employed, together with the performance requirements at the prices indicated. performance requirements for the various aircraft of films tested by the standard methods. It has been instruments covered. B.S. No. (G.121: 1949.—Hand-Operated Circuit- agreed that it is neither desirable nor practicable to B.S. 1615: 1949.—Anodic oxidation finishes for alu Breakers for Aircraft. standardize the details of the process by which the minium and aluminium alloys. required film is produced. This standard gives details of construction, ratings, The electrolytic process of anodizing or anodic operation and methods of test for the assessment of The characteristics covered are: oxidation was developed after the first world war as the specified performance requirements. Price 2s. post Thickness of anodic coatings, reflection factors, a means of increasing the corrosion resistance of free. resistance to abrasion and fastness to light. aluminium and aluminium-base alloys used on air B.S. No. G.119—Simple Altimeters. Price 2s. post free. Work is still proceeding on the subject of resistance craft. Today it is applied to aluminium and its alloys B.S. No. G.120—Direct-Reading Pressure Gauges. in many industries, with the result that there has to corrosion. developed the need for this new standard. Price \s. post free. Price 3s., post free. 120 A ircraft Engineering
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: Apr 1, 1950
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