1、AEROSPACE RECOMMENDED PRACTICEARP794 REV.AIssued 1968-12Reaffirmed 2008-02Revised 2001-07Superseding ARP794Airstream Deviation Instrument(ADI)FOREWORDChanges in this Revision are format/editorial only.1. SCOPE:This recommended practice covers an instrument which measures and displays angle of deviat
2、ion of the airstream dependent on mounting location on the aircraft.1.1 Purpose:This Aerospace Recommended Practice recommends the industry standards for an Airstream Deviation Instrument primarily for use with turbine-powered, subsonic transport aircraft, the operation of which may subject the inst
3、ruments to the environmental conditions specified in Paragraph 3.4.2. REFERENCES:NACA Report 1235MIL-I-6181AS425AARP461B3. GENERAL REQUIREMENTS:3.1 Materials and Workmanship:3.1.1 Materials: Materials should be of a quality which experience and/or tests have demonstrated to be suitable and dependabl
4、e for use in aircraft instruments.3.1.2 Workmanship: Workmanship should be consistent with high grade instrument manufacturing practice.SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this repor
5、t is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled.
6、SAE invites your written comments and suggestions. Copyright 2008 SAE International All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the
7、 prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: 724-776-4970 (outside USA) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.org SAE ARP794 Revision A- 2 -3.2 Identification:The following information should be l
8、egibly and permanently marked on the instrument or nameplate attached thereto:a. Name of instrument - Airstream Deviation Instrumentb. SAE ARP794A (show number and revision letter)c. Manufacturers part numberd. Manufacturers serial number or date of manufacturee. Manufacturers name and/or trademarkf
9、. Rangeg. Rating (nominal voltage)h. Explosion Category3.3 Compatibility of Components:If components are individually acceptable, but require matching for proper operation, they should be identified in a manner that will assure proper matching.3.4 Environmental Conditions:The following conditions ha
10、ve been established as design requirements. Tests should be conducted as specified in Sections 5, 6 and 7, to insure compliance with this Aerospace Recommended Practice.3.4.1 Temperature: When installed in accordance with the instrument manufacturers instructions, the instrument should function over
11、 the range of ambient temperature shown in Column A below and should not be adversely affected by exposure to the range of temperature shown in Column B below:3.4.1.1 Housing: (That portion of instrument mounted inside of aircraft)TABLE 1Instrument Location A B Pressurized Areas 0 to 70 C -65 to 70
12、CNon-pressurized Areas -55 to 70 C -65 to 70 CSAE ARP794 Revision A- 3 -3.4.1.2 Sensing Element: (That portion of instrument mounted in airstream)3.4.2 Altitude: When installed in accordance with the instrument manufacturers instructions, the instrument should function from minus 1000 ft up to altit
13、udes and temperatures listed below: Altitude pressure values are per NACA Report 1235. The instrument should not be adversely affected following exposure to extremes in ambient pressures of 50 and 2 inches of mercury absolute respectively.3.4.2.1 Housing:3.4.2.2 Sensing Element:TABLE 2A B External A
14、reas -55 to 70 C -65 to 70 CTABLE 3Instrument Location Altitude TemperaturePressurized Areas 15,000 ft See Paragraph 3.4.1Non-pressurized Areas 60,000 ft See Paragraph 3.4.1TABLE 4A B External Areas 60,000 ft See Paragraph 3.4.1SAE ARP794 Revision A- 4 -3.4.3 Vibration: When installed in accordance
15、with the manufacturers instructions, the instrument should function and should not be adversely affected when subjected to vibrations of the following characteristics:3.4.4 Humidity: The instrument should function and not be adversely affected following exposure to any relative humidity in the range
16、 from 0 to 95% at a temperature of approximately 70 C.3.4.5 Icing: The instrument should function and not be adversely affected when subjected to icing conditions of 1.00 0.25 grams liquid water per cubic meter of air at temperatures of -15 5 C and -30 5 C.3.5 Explosion Category:The instrument compo
17、nent, when intended for installation either in uninhabited areas of non-pressurized aircraft or in non-pressurized areas of pressurized aircraft, should not cause an explosion when operated in an explosive atmosphere. The component should meet the requirements applicable to the explosion category be
18、low. Specifically, any instrument component which can be an ignition source and is intended for installation in an area in which combustible fluid or vapor may result from abnormal conditions, e.g., fuel line leakage, should meet the requirements of Category I. If the intended location is an area wh
19、ere combustible fluid or vapor can occur during normal operation, e.g. fuel tank, the instrument component should meet the requirements of Category II listed below:TABLE 5Maximum Double MaximumInstrument Frequency Amplitude AccelerationLocation cps Inch g Nacelle and NacelleMounts, Wings, Em-pennage
20、 and Wheel Wells5-1000 0.036 10Fuselage:Forward of Spar AreaCenter or Spar AreaAft of Spar Area5-10005-10005-340340-10000.0200.0200.0200.0012368Flight Deck Area 5-1000 0.020 .5SAE ARP794 Revision A- 5 -3.6 Fire Hazard:The instrument should be so designed to safeguard against hazards to the aircraft
21、in the event of malfunction or failure, and the maximum operating temperature of surfaces of any instrument component contacted by combustible fuel or vapor should not exceed 200 C due to self-heating.All materials should be non-combustible and should not liberate gases or fumes which will result in
22、 such corrosion as to cause malfunction of equipment or discoloration of dials or indicia, nor should toxic gases or fumes that are detrimental to performance of the aircraft or health of personnel be liberated under the operating conditions specified herein.TABLE 6Category Definition RequirementI E
23、xplosion proofed: Casenot designed to precludeflame or explosion propa-gation.Paragraph 8.3.1II Explosion proofed: Casedesigned to precludeflame or explosion propa-gation.Paragraph 8.3.2III Hermetically sealed Not applicableIV Instrument not capable ofcausing an explosionShould not be capableof prod
24、ucing a capaci-tive or inductive sparkof more than 0.2 milli0joules of energy or acontact spark of morethan 4.0 millijoules ofenergy.SAE ARP794 Revision A- 6 -3.7 Radio Interference:The instrument should not be the source of objectionable interference, under operating conditions at any frequencies u
25、sed on aircraft, either by radiation or feedback, in the electronic equipment installed in the same aircraft as the instrument, in accordance with the latest revision of MIL-I-6181.3.8 Magnetic Effect:The magnetic effect of the instrument should not adversely affect the performance of other instrume
26、nts installed in the same aircraft and should be in accordance with Paragraph 8.9.3.9 Decompression:When installed in accordance with the instrument manufacturers instructions, the instrument should function and not be adversely affected following exposure to pressure decrease from 22 to 2 inches of
27、 mercury in 2 seconds.3.10 Interchangeability:Instruments and components which are identified in accordance with Paragraph 3.2 should be directly and completely interchangeable.3.11 Definitions:Definitions should be in accordance with AS425A, Flight Control Compartment Nomenclature and Abbreviations
28、, and as noted in the glossary of terms defined in Paragraph 9.4. DETAIL REQUIREMENTS:4.1 Design:The instrument should be designed to measure the angles of airflow with respect to a pre-established aircraft reference line. The total range of measurement should be at least 50 angular degrees.4.2 Oper
29、ational Characteristics:The instrument should respond to a change of 0.1 degree of angular deviation of the local airstream throughout a speed range of 80 to 220 knots with an accuracy of 0.25 degrees. The instrument should respond to a change of 0.1 degree of angular deviation of the local airstrea
30、m throughout the speed range of 220 to 660 knots with an accuracy of 0.2 degrees.SAE ARP794 Revision A- 7 -4.3 Heater:An electrical heating element should be provided for anti-icing purposes. A sufficient area of the heater should be concentrated near the base of the sensing element so that the junc
31、tion of the sensing element and the aircraft fuselage will be kept free of ice. The heater should be automatically regulated so that the power dissipated through the heater is an inverse function of the heater element temperature.4.4 Sensor Electrical Alignment:The mounting surface of the instrument
32、 should provide an indexing arrangement to insure that the sensing element electrical zero position can be related to the reference axis of the aircraft within tolerances specified in Paragraph 4.2.4.5 Power Variation:The instrument should properly function with plus or minus 15% variation in DC vol
33、tage and/or plus or minus 10% variation in AC voltage and plus or minus 5% variation in frequency.4.6 Synchro Requirements:The synchro requirements should be in accordance with the conditions specified in ARP461B.4.7 Fail-Safe Provisions:No single failure or malfunction of the instrument should intr
34、oduce unsafe transients to associated interconnected instruments.5. TEST CONDITIONS:5.1 Atmospheric Conditions:Unless otherwise specified herein, all tests required by this Aerospace Recommended Practice should be made at an atmospheric pressure of approximately 29.92 inches of mercury, an ambient t
35、emperature of approximately 25 C and a relative humidity of not greater than 85%. When tests are conducted with the atmospheric pressure or temperature substantially different from these values, allowance should be made for the variation from the specified conditions.5.2 Power Conditions:Unless othe
36、rwise specified herein, all tests should be conducted at the power rating recommended by the manufacturer.SAE ARP794 Revision A- 8 -5.3 Position:Unless otherwise specified herein, all tests should be conducted with the instrument in its normal operating position.6. INSTRUMENTATION FOR PERFORMANCE CH
37、ECKS:6.1 Vibration Equipment:6.1.1 Vibration Equipment (Turbine-Powered Subsonic Aircraft): Vibration equipment should be such as to allow vibration to be applied along each of three mutually perpendicular axes of the instrument at frequencies and amplitudes consistent with the requirements of Parag
38、raph 3.4.3.6.2 Test Synchros:Synchro transmitters used to provide test output functions of the instrument should be in accordance with the requirements specified in ARP461B - Synchros.6.2.1 Phase Rotation: A positive or clockwise phase rotation of the standard test transmitter should result in incre
39、asing function.6.3 Test Potentiometers:Potentiometers used to provide test output functions of the applicable instrument should be precision potentiometers with an accuracy of 0.02%, a resolution of 0.01%, and a linearity of at least 0.005%. The total impedance of the test potentiometers should be a
40、 function of the instrument design and should be specified by the manufacturer.6.4 Potentiometer Zero:Unless otherwise specified by the instrument manufacturer, where potentiometers are used as output functions, the low impedance end of the potentiometer should correspond to the low end of the funct
41、ion.7. INDIVIDUAL PERFORMANCE TESTS:All instruments should be tested in accordance with the following recommended test procedures to show specific compliance with this recommended practice and any additional tests recommended by the manufacturer.SAE ARP794 Revision A- 9 -7.1 Electrical Zero and Rota
42、tion:When the sensing element is set to the center position (zero degrees with respect to a perpendicular to the reference axis of the indexing arrangement) the output of the instrument should be zero. When the sensing element is rotated in the direction of increasing positive function, the output s
43、hould increase in terms of potentiometer voltage or clockwise test indicator rotation in terms of a synchro output. When the sensing element is rotated in the direction of decreasing positive function, the output should decrease in terms of potentiometer voltage or counterclockwise test indicator ro
44、tation in terms of a synchro output.7.2 Aerodynamic Alignment:The instrument should be mounted in a suitable wind tunnel to simulate the aircraft installation. The airspeed in the working section of the wind tunnel should be adjusted to 110 5 knots. The sensing element should then be displaced in in
45、crements of 5 degrees from 0.3 to 25 degrees inclusive in both directions. After being released, without impulse, the sensing element should return to zero within 0.1 degrees.7.3 Scale Error at Room Temperature:The instrument moving element should be rotated in 5 degree increments throughout the ful
46、l range of travel. The accuracy of the output for each of these positions should be the equivalent of 0.1 degree of angle of attack.7.4 Heater Operation:The heater should be checked to insure proper operation by applying the nominal rated voltage for a period of five minutes. The power consumption s
47、hould meet the rated value.7.5 Dielectric:Each instrument should be tested by the method of inspection listed in Paragraphs 7.5.1 and 7.5.2.7.5.1 Insulation Resistance: The insulation resistance measured at 200 V DC for five seconds between all electrical circuits connected together and the metallic
48、 case should not be less than 5 megohms. Insulation resistance measurements should not be made to circuits where the potential will appear across elements such as windings, resistors, capacitors, etc., since this measurement is intended only to determine adequacy of insulation.SAE ARP794 Revision A-
49、 10 -7.5.2 Overpotential Tests: The instrument should not be damaged by the application of a test potential between electrical circuits, and between electrical circuits and the metallic case. The test potential should be sinusoidal voltage of a commercial frequency with an rms value of five times the maximum circuit voltage. The potential should start from zero and be increased at a uniform rate to its test value. It should be maintained at this value for fiv
