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1、BRITISH STANDARD AEROSPACE SERIES BS 2G 135: 1967 Incorporating Amendment No. 1 Specification for Electrically-heated pitot and pitotstatic pressure heads UDC 629.13.055.2:532.574.3 Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 14:01:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2G 135:1
2、967 This British Standard, having been approved by the Aerospace Industry Standards Committee and endorsed by the Chairman of the Engineering Divisional Council, was published under authority of the General Council on 29 December 1967 BSI 12-1999 The following BSI references relate to the work on th
3、is standard: Committee reference ACE/30 Draft for comment D65/1698 ISBN 0 580 35997 2 Foreword This revision of BS G 135:1955 takes account of new techniques of compensating for pressure errors and of new standards of de-icing requirements. This standard makes reference to the following British Stan
4、dards: BS 3G 100, General requirements for equipment in aircraft. BS G 101, General requirements for aircraft indicators: presentation and case sizes. NOTEWhere metric equivalents are given, the figures in British units are to be regarded as the standard. The metric conversions are approximate. More
5、 accurate conversions should be based on the tables in BS 350, “Conversion factors and tables”. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does
6、 not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages 1 to 8, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. Thi
7、s will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No.Date of issueComments 1225July 1973Indicated by a sideline in the margin Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 14:01:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2G
8、135:1967 BSI 12-1999i Contents Page ForewordInside front cover 1Scope1 2Definitions1 3General construction1 4Particular requirements1 5Aerodynamic accuracy2 6Declarations3 7Tests: General3 8Type tests3 9Production routine tests6 10Production quality tests6 Appendix A Serviceability testsInside back
9、cover Figure 1 Low pressure connectors6 Figure 2 Screwed connections7 Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 14:01:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii blank Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 14:01:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2G 1
10、35:1967 BSI 12-19991 1 Scope 1.1 This British Standard specifies the requirements for two grades of electrically-heated pitot and pitotstatic heads for aircraft. Grade A, heads fully de-iced and suitable for high speeds. Grade B, heads not suitable for flight in severe icing conditions. 1.2 Grade A
11、comprises two classes of head: Class 1, heads not compensated for pressure error. Class 2, heads compensated for pressure error. 1.3 Grade B heads will normally be of the non-compensated type. 2 Definitions For the purposes of this British Standard the following definitions apply: 2.1 pitot pressure
12、 head a tube, having an open aperture at one end, facing in the direction of flight for sensing the total impact pressure, and a pipe connection at the other end for transmitting it to the aircraft pitot pressure system 2.2 pitotstatic pressure head a tube similar to 2.1 with additional circumferent
13、ial slots or holes connected to a separate duct and pipe connection for sensing the static air pressure and transmitting it to the aircraft static system 3 General construction The design and construction of the head shall comply with the relevant requirements of BS 3G 100. 4 Particular requirements
14、 4.1 External shape and contour. The external shape and contour of the head shall be such as to satisfy the aerodynamic accuracy requirements of Clause 5. 4.2 Orifices and pressure ducts 4.2.1 The pitot orifice shall be a single hole of at least 3/16 in (4.8 mm) diameter. 4.2.2 Means shall be incorp
15、orated, in the pitot pressure path from the nose of the head, to ensure that driving rain cannot penetrate down the pitot tube. 4.2.3 Provision shall be made for positive locking of any draining plug which may be incorporated in the head. 4.2.4 The static orifices shall consist of a row, or rows, of
16、 small holes or slots disposed around the cross section of the head. These shall be of such a size that they will not be blocked by driving rain, and account shall be taken also of the mounting and the avoidance of lag errors The finish of the orifices or slots shall be free from burrs or rounding o
17、f edges. 4.2.5 Except on Grade B heads, there shall be no drain hole between the pitot and the static systems (see note). 4.2.6 There shall be no restriction, in the diameter of the pipe leaving the heated region, which could cause blockage of the passage by a drop of condensate. In addition, any re
18、striction to any part of the pressure path shall be kept to a minimum to avoid affecting the time constant or dynamic performance. The preferred pipe connections from the head are 3/8 in (9.5 mm) o.d. for the static line and 5/16 in (7.9 mm) o.d. for the pitot line. If low pressure connectors are us
19、ed they should comply with Figure 1, the correct position of the union on the pipe being indicated when the yellow band is uncovered. Alternatively, if screwed connections are used, e.g. on Grade A heads, they should be in accordance with Figure 2. If any other types of connector are used they shoul
20、d be of an approved design. 4.2.7 The entire pressure ducts of the head shall be designed to withstand a minimum pressure of at least 15 lbf/in2(1.0 kgf/cm2). NOTEWhereas at low Mach number the error in the static pressure system, caused by a drain hole whose area relative to that of the pitot duct
21、is 1 : 50, is of an acceptably low order, the error at higher Mach numbers becomes increasingly unacceptable. 4.3 Location, orientation and locking. The design of the head shall provide for positive location, correct orientation, and locking. 4.4 Heating element 4.4.1 The heating element shall be of
22、 such size and durability as will comply with the performance declared for the particular head. 4.4.2 The whole of the heating system to the external connections shall form a completely sealed unit. 4.4.3 In pitot pressure heads the function of the heating element is to maintain the pitot orifice an
23、d nose, together with any drain hole that may be incorporated, free from ice. In pitotstatic heads the whole of the external surface of the head shall be kept sufficiently free from ice to maintain aerodynamic accuracy. Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 14:01:01 GMT+00:00 2006,
24、Uncontrolled Copy, (c) BSI BS 2G 135:1967 2 BSI 12-1999 The general construction of the head and heater system shall be such that no damage is caused when the head, mounted in a fixture similar to that in which it is mounted on the aircraft, and bonded thermally to a relatively large mass of metal t
25、o simulate the aircraft structure, is energized at the nominal voltage for 60 minutes in still air at 70 C. 4.5 Mechanical stability. The construction of the head shall be such that extremes of temperature cause no leakage, or changes in contour producing aerodynamic errors outside the permitted tol
26、erances, or differential expansion or contraction likely to cause unserviceability. 4.6 Identification. The pitot and static pressure connections shall be permanently marked, on the pipe connections or fittings, with the letters P and S respectively. 5 Aerodynamic accuracy 5.1 The aerodynamic accura
27、cy of the heads shall be determined in terms of the pressure coefficient Cp, the relevant formulae being as follows: 1) Static pressure error coefficient: 2) Pitot pressure error coefficient: 5.2 A pitot or pitotstatic head may be required to sense exactly, within specified tolerances, the local pit
28、ot or static pressure at the head position unaffected by the presence of the head, or to sense pressures which are modified by the geometry of the head (compensation). The degree of compensation required, if any, will normally be specified by the prospective user of the head in conjunction with the
29、manufacturer. When the compensation required has been specified, the following accuracy requirements shall represent the permissible discrepancy from that compensation. In the special case where exact sensing of the local pitot or static pressure is required, i.e. zero compensation, the following ac
30、curacy requirements shall specify the permissible absolute error. These accuracy figures apply for tests in a wind tunnel at speeds up to the maximum at which the head is to be used. 5.2.1 Grade A heads 1) Accuracy with variation of incidence at zero side-slip. Cpp and Cps to be less than 0.005 from
31、 5 to + 15 incidence for speeds up to Mc= 0.4, the incidence range falling linearly from 2; to + 5 at Mc= 0.9 and maintaining this range above Mc= 1.1. For each degree of incidence up to 5 beyond the upper limits of the range quoted above, an additional tolerance in Cpp and Cps of 0.002 for each deg
32、ree is allowed for speeds up to Mc= 0.4 rising linearly to 0.004 for each degree at Mc= 0.9 and above to Mc= 1.1. The performance of the head should have no undesirable characteristics when operated outside the envelope specified of ! between 5 and + 15 and between 10 and + 10 The above definition i
33、s satisfactory for all applications but the magnitudes of the angles could be inadequate for a forward fuselage installation, in this case the maximum angles to be considered could be greater than those specified above, i.e. 5 a 15, 10 + 10 and will normally be specified by the customer. 2) Accuracy
34、 with variation of side-slip at zero incidence. For a range of side-slip of 10 up to Mc= 0.4, falling linearly to a range of 5 at Mc= 0.9 and above Mc= 1.1, an additional tolerance in Cpp and Cps is allowed. This is given by 0.005 multiplied by the side-slip in degrees and is additive to the toleran
35、ces quoted above. 3) Transonic region. An additional tolerance in Cpp and Cps shall be allowed in the transonic region (viz. Mc= 0.9 to 1.1), at the discretion of the purchaser. where S = static pressure error P = pitot pressure error Sc= free stream static pressure Mc= free stream Mach number *= ra
36、tio of specific heats = 1.4 Cps = S * 2 - - ScMc2 - Cpp = P * 2 - - ScMc2 - where: a = The angle measured in the symmetric plane of the aircraft between the relative airflow vector and the axis of the pitot or pitotstatic tube. bThe angle measured in the plane at right angles to the symmetric plane
37、between the relative airflow vector and the axis of the pitot or pitotstatic tube. Licensed Copy: sheffieldun sheffieldun, na, Tue Nov 28 14:01:01 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 2G 135:1967 BSI 12-19993 5.2.2 Grade B heads. The tolerance allowed for Grade B heads is specified for the
38、same incidence and side-slip range as for Grade A heads up to the maximum Mach number for which the Grade B head is declared. The tolerance allowed is that specified above for Grade A heads increased by 0.005. 6 Declarations In addition to the relevant declarations required by BS 3G 100-1, the manuf
39、acturer shall declare the grade and class of head, as applicable. 7 Tests: General 7.1 Tests shall be made to check compliance with all the requirements of this British Standard. It is neither intended nor recommended that complete tests shall be made on every head supplied. Three kinds of test are
40、specified as follows: 1) Type tests (see 8.1 to 8.8), to be made on representative samples of each design and range of head. 2) Production routine tests (see Clause 9), to be made on every head manufactured in accordance with this British Standard. 3) Production quality tests (see Clause 10), to be
41、made on samples as specified in the individual specification. 7.2 In any test in which it is necessary for the heater to be energized, this shall be at the nominal rated voltage, unless otherwise declared. 7.3 For the guidance of users, the minimum tests recommended to verify the serviceability of h
42、eads manufactured to this British Standard are indicated in Appendix A. 8 Type tests 8.1 Heater performance 8.1.1 The performance of the heater shall be measured to determine its ability to fulfil the requirements of the icing test appropriate to its grade. 8.1.2 The power consumption of the head sh
43、all be measured at 20 5 C in still air, and it shall be within 10 % of the nominal value established as necessary to satisfy the icing tests. The test shall be made after the heater has been switched on for 5 minutes. 8.1.3 Type A heads shall be subjected to a life endurance cycling test at an ambie
44、nt temperature of 2030 C at sea level pressure with rated voltage applied for an uninterrupted period of 2 hours and then turned off for a period of one hour. This test shall be repeated for 100 cycles during which the corrosion resistance and proper operation of the head shall not be impaired. At t
45、he conclusion of the test the head body shall be checked dimensionally and for finish to the satisfaction of the Approving Authority. 8.1.4 Type B heads shall be subjected to the test specified in 8.1.3 except that the rated voltage shall be applied for 10 minutes and then turned off for 30 minutes,
46、 and that the test shall be repeated for 50 cycles. 8.2 Performance accuracy. The performance of the head shall comply with the requirements of Clause 5. 8.3 Vibration, acceleration and climatic tests 8.3.1 The head shall be subjected to the grade of vibration, acceleration and climatic tests specif
47、ied in BS 3G 100-2 appropriate to the performance grading declared by the manufacturer. 8.3.2 For the purposes of the vibration and acceleration test the head shall be mounted in a fixture simulating the method of attachment to the aircraft for which it is designed, with the heater energized. If the
48、 applied heater voltage is reduced for the purpose of this test the conditions shall be agreed with the Approving Authority. Heads employing long booms may suffer extreme amplitudes and manufacturers shall carry out additional tests to ensure that the head is satisfactory on the particular aircraft
49、to which it is to be fitted. 8.3.3 The performance of the heater during the vibration test shall be monitored by frequent checks of the electrical circuits for continuity and earth leakage. In addition, the stability of the pressure system shall be checked. 8.3.4 The functioning tests required by BS 3G 100-2 to be made as part of the vibration acceleration and climatic tests shall each consist of a leakage test as described in 8.6. 8.4 Insulation resistance 8.4.1 Insulation resistance (cold