1、BRITISH STANDARDAEROSPACE SERIES BS2G 135: 1967 Incorporating Amendment No.1 Specification for Electrically-heated pitot and pitotstatic pressure heads UDC 629.13.055.2:532.574.3BS2G135:1967 This BritishStandard, having been approved by the Aerospace Industry Standards Committee and endorsed by the
2、Chairman ofthe Engineering Divisional Council, was published under authority of the General Councilon 29December1967 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference ACE/30 Draft for comment D65/1698 ISBN 0 580 35997 2 Foreword This revision of BS G 1
3、35:1955 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 BritishStandards: BS 3G 100, General requirements for equipment in aircraft. BS G 101, General requirements for aircraft indicator
4、s: 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 accurate conversions should be based on the tables in BS350, “Conversion factors and tables”. A British Standard does
5、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 not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside
6、 front cover, pagesi andii, pages1 to8, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date of i
7、ssue Comments 1225 July1973 Indicated by a sideline in the marginBS2G135:1967 BSI 12-1999 i Contents Page Foreword Inside front cover 1 Scope 1 2 Definitions 1 3 General construction 1 4 Particular requirements 1 5 Aerodynamic accuracy 2 6 Declarations 3 7 Tests: General 3 8 Type tests 3 9 Productio
8、n routine tests 6 10 Production quality tests 6 Appendix A Serviceability tests Inside back cover Figure 1 Low pressure connectors 6 Figure 2 Screwed connections 7ii blankBS2G135:1967 BSI 12-1999 1 1 Scope 1.1 This BritishStandard specifies the requirements for two grades of electrically-heated pito
9、t 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 comprises two classes of head: Class1, heads not compensated for pressure error. Class2, heads compensated for pressure erro
10、r. 1.3 Grade B heads will normally be of the non-compensated type. 2 Definitions For the purposes of this BritishStandard the following definitions apply: 2.1 pitot pressure head a tube, having an open aperture at one end, facing in the direction of flight for sensing the total impact pressure, and
11、a pipe connection at the other end for transmitting it to the aircraft pitot pressure system 2.2 pitotstatic pressure head a tube similar to2.1 with additional circumferential slots or holes connected to a separate duct and pipe connection for sensing the static air pressure and transmitting it to t
12、he aircraft static system 3 General construction The design and construction of the head shall comply with the relevant requirements of BS3G100. 4 Particular requirements 4.1 External shape and contour. The external shape and contour of the head shall be such as to satisfy the aerodynamic accuracy r
13、equirements of Clause5. 4.2 Orifices and pressure ducts 4.2.1 The pitot orifice shall be a single hole of at least 3 / 16in(4.8mm) diameter. 4.2.2 Means shall be incorporated, in the pitot pressure path from the nose of the head, to ensure that driving rain cannot penetrate down the pitot tube. 4.2.
14、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 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
15、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 of 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 Ther
16、e 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 restriction to any part of the pressure path shall be kept to a minimum to avoid affecting the time constant or dynamic performance. T
17、he preferred pipe connections from the head are 3 / 8in(9.5mm) o.d. for the static line and 5 / 16in(7.9mm) o.d. for the pitot line. If low pressure connectors are used they should comply with Figure 1, the correct position of the union on the pipe being indicated when the yellow band is uncovered.
18、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 should 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 least15
19、lbf/in 2 (1.0kgf/cm 2 ). 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 is1:50, is of an acceptably low order, the error at higher Mach numbers becomes increasingly unacceptable. 4.3 Location, orientation a
20、nd 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 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
21、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 and nose, together with any drain hole that may be incorporated, free from ice. In pitotstatic heads the whole of the external surface of t
22、he head shall be kept sufficiently free from ice to maintain aerodynamic accuracy.BS2G135:1967 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 b
23、onded thermally to a relatively large mass of metal to simulate the aircraft structure, is energized at the nominal voltage for60minutes in still air at70 C. 4.5 Mechanical stability. The construction of the head shall be such that extremes of temperature cause no leakage, or changes in contour prod
24、ucing aerodynamic errors outside the permitted tolerances, 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.
25、 5 Aerodynamic accuracy 5.1 The aerodynamic accuracy of the heads shall be determined in terms of the pressure coefficient C p , 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
26、 exactly, within specified tolerances, the local pitot 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 p
27、rospective user of the head in conjunction with the 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 i
28、s required, i.e.zero compensation, the following accuracy 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 zer
29、oside-slip. C ppand C psto be less than0.005 from5 to+15 incidence for speeds up to M c =0.4, the incidence range falling linearly from2; to+5 at M c =0.9 and maintaining this range above M c =1.1. For each degree of incidence up to5 beyond the upper limits of the range quoted above, an additional t
30、olerance in C ppand C psof0.002 for each degree is allowed for speeds up to M c =0.4 rising linearly to0.004 for each degree at M c =0.9 and above to M c =1.1. The performance of the head should have no undesirable characteristics when operated outside the envelope specified of! between5 and+15 and
31、between10 and+10 The above definition is satisfactory for all applications but the magnitudes of the anglescould be inadequate for a forward fuselage installation, in this case the maximumanglestobe considered could begreater than thosespecified above, i.e.5 a15,10 +10 and will normally be specified
32、 by the customer. 2) Accuracy with variation of side-slip at zero incidence. For a range of side-slip of 10 up to M c =0.4, falling linearly to a range of 5 at M c =0.9 and above M c =1.1, an additional tolerance in C ppand C psis allowed. This is given by0.005 multiplied by the side-slip in degrees
33、 and is additive to the tolerances quoted above. 3) Transonic region. An additional tolerance in C ppand C psshall be allowed in the transonic region (viz. M c =0.9 to1.1), at the discretion of the purchaser. where S =static pressure error P =pitot pressure error S c =free stream static pressure M c
34、 =free stream Mach number * =ratio of specific heats=1.4 C ps= S * 2 - S c M c 2 - C pp= P * 2 - S c M c 2 - 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. b The angle measured in the plane at ri
35、ght angles to the symmetric plane between the relative airflow vector and the axis of the pitot or pitotstatic tube.BS2G135:1967 BSI 12-1999 3 5.2.2 Grade B heads. The tolerance allowed for Grade B heads is specified for the same incidence and side-slip range as for Grade A heads up to the maximum M
36、ach number for which the Grade B head is declared. The tolerance allowed is that specified above for Grade A heads increased by0.005. 6 Declarations In addition to the relevant declarations required by BS3G 100-1, the manufacturer shall declare the grade and class of head, as applicable. 7 Tests: Ge
37、neral 7.1 Tests shall be made to check compliance with all the requirements of this BritishStandard. It is neither intended nor recommended that complete tests shall be made on every head supplied. Three kinds of test are specified as follows: 1) Type tests (see8.1 to8.8), to be made on representati
38、ve samples of each design and range of head. 2) Production routine tests (see Clause9), to be made on every head manufactured in accordance with this BritishStandard. 3) Production quality tests (see Clause10), to be made on samples as specified in the individual specification. 7.2 In any test in wh
39、ich 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 heads manufactured to this BritishStandard are indicated in Appendix A. 8 Type tests
40、 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 shall be measured at20 5 C in still air, and it shall be within10% of the nominal valu
41、e established as necessary to satisfy the icing tests. The test shall be made after the heater has been switched on for5minutes. 8.1.3 Type A heads shall be subjected to a life endurance cycling test at an ambient temperature of2030 C at sea level pressure with rated voltage applied for an uninterru
42、pted period of2hours and then turned off for a period of one hour. This test shall be repeated for100cycles during which the corrosion resistance and proper operation of the head shall not be impaired. At the conclusion of the test the head body shall be checked dimensionally and for finish to the s
43、atisfaction of the Approving Authority. 8.1.4 Type B heads shall be subjected to the test specified in8.1.3 except that the rated voltage shall be applied for10minutes and then turned off for30minutes, and that the test shall be repeated for50cycles. 8.2 Performance accuracy. The performance of the
44、head shall comply with the requirements of Clause5. 8.3 Vibration, acceleration and climatic tests 8.3.1 The head shall be subjected to the grade of vibration, acceleration and climatic tests specified in BS3G 100-2 appropriate to the performance grading declared by the manufacturer. 8.3.2 For the p
45、urposes 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 applied heater voltage is reduced for the purpose of this test the conditions shall be agreed with the
46、 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 to which it is to be fitted. 8.3.3 The performance of the heater during the vibration test shall be mon
47、itored 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 BS3G 100-2 to be made as part of the vibration acceleration and climatic tests shall each consist of a le
48、akage test as described in8.6. 8.4 Insulation resistance 8.4.1 Insulation resistance (cold). The insulation resistance between the heating element and the frame shall be greater than3megohms when measured using a500voltd.c. source at a temperature of20 5 C.BS2G135:1967 4 BSI 12-1999 8.4.2 Leakage cu
49、rrent (hot). The leakage current shall be measured using a500voltd.c. source for heaters designed to operate from115volts supply and using a250voltsd.c. source for heaters designed to operate from a28volts supply. The head shall be run at rated voltage for20minutes in still air at an ambient temperature of20 5 C, the head being mounted in a fixture similar to its aircraft mounting. The power dissipated when500voltsd.c. or250voltsd.c., as appropriate, is applied between the heating element a
