FIGURE 10-4. TYPICAL BATTERY CUTOFF AND GENERATOR ALTERNATOR CONTROL
CIRCUIT
1020. QUICK DISCONNECT. Look for and replace the terminal pins when:
a. Excessive pitting or corrosion cannot be removed.
b. Signs of burning or arcing.
c. Cracked part or housing.
d. Excessive wear on contact pins, socket lock pins, or worm screw.
e. Large deposits form on contacts or plastic is discolored.
f. Excessively loose handle and locking assembly.
NOTE: Most manufacturers sell or provide dimensions for tools to check the fit of the quick disconnect sockets.
1021. WEIGHT AND BALANCE. After installation or alteration with the replacement battery the weight and balance of the aircraft should be recomputed if:
a. The weight of the replacement battery is different from that of the original battery.
b. The location of the battery is different from that of the original battery.
NOTE: Weight and balance procedures for aircraft are contained in AC 43.13-1 (as amended), chapter 10.
1022. THRU 1024. RESERVED Par 1020 Page 114
SECTION 3. NICKEL-CADMIUM BATTERY INSTALLATIONS 1025. GENERAL. Nickel-cadmium batteries fulfill a need for a power source that will provide large amounts of current, fast recharge capability, and a high degree of reliability. Nickel-cadmium batteries produce a constant voltage and can operate at lower temperatures. They are generally more expensive to purchase.
1026. ELECTRICAL ANALYSIS. The amperehour capacity of a nickel-cadmium battery is selected to accommodate the aircraft load requirements. When making this selection, the following items should be considered:
a. The low internal resistance permits it to recharge very quickly. This high recharge rate can exceed the generator rated capacity and deprive essential circuits of necessary operating current.
Total system load (battery recharging plus system loads) must not exceed the pre-established electrical capacity of the generator system.
b. Compare the discharge characteristics curves of the batteries to make sure a reduced capacity nickel-cadmium battery is adequate regarding the following:
(1) Ability to provide engine starting or cranking requirements. Some turbine engines require an initial surge of approximately 1200 amperes, which tapers off within 10 seconds to approximately 800 amperes cranking current. Reciprocating engines require approximately 100 to 200 amperes cranking current.
(2) Ability to provide sufficient capacity for low temperature starting. Nickel-cadmium batteries deliver their rated capacity when the ambient temperature range is 70°F to 90°F. For best engine cranking, replacement batteries with increased capacity will offset the lower power or reduced capacity available when the batteries are cold soaked.
(3) Some nickel-cadmium batteries deliver greater power at temperature extremes than comparable rated lead acid batteries; take care not to overload the cables and connectors.
1027. MAINTENANCE CONSIDERATIONS.
To provide for ease of inspection and because nickel-cadmium batteries are generally not serviced in the aircraft, it is important that the battery be located where it can easily be inspected, removed, and installed. Some battery cases are designed with view ports on each side of the case for visual monitoring of the cell electrolyte level. If this type of case is to be used, carefully consider the location of the battery compartment to accommodate this feature.
1028. STRUCTURAL REQUIREMENTS.
Most lead-acid battery compartments provide adequate structure attachment for the installation of nickel-cadmium batteries. However, cantilever supported battery boxes/compartments may not be suitable for nickel-cadmium battery installations unless modified to compensate for an increased over-hang moment. This may be caused by a change in battery shape and center of gravity (CG) location even though the replacement battery may weigh less than the original lead-acid battery. Whenever the total installation weight and/or the overhang moment exceed those of the original installation, perform a static test as outlined in chapter 1. If the battery compartment is to be relocated, follow the location requirement procedures outlined in paragraph 3.
1029. ISOLATION OF BATTERY CASE.
Because of the material from which nickel-cadmium battery cases are generally made (stainless or epoxy coated steel), it is desirable to electrically isolate the case from the aircraft structure. This will eliminate the potential discharge current produced when spillage or seepage of the electrolyte provides a current path between the cell terminal or connector and the exposed metal of the battery case.
Par 1025 Page 115
NOTE: Epoxy coated nickel cadmium battery cases serve to isolate the battery from the airframe thus eliminating electrical leakage to ground. Some batteries use a series of liners that are inside the battery. This isolates the battery from the airframe and helps eliminate electrical leakage to ground.
1030. VENTILATION. During the charging process, nickel-cadmium batteries produce hydrogen and oxygen gases. This occurs near the end of the charging cycle when the battery reaches what is called the gassing potential. To avoid a buildup of these gases, and possible accidental ignition, ventilation should be provided to evacuate this gas from the aircraft. There are two types of nickelcadmium battery cases, one with vent nozzles and one with viewports.
a. The vent nozzle type utilizes vent hoses to evacuate the gas overboard by use of forced air or by venturi effect.
b. Battery cases with viewports or louvers must have airflow sufficient to keep the mixture of air and hydrogen below 4 precent. The gases from this type of case are ev acuated into the battery compartment. Regardless of the ventilation system used, the airflow should be provided at a minimum rate of 0.040 cubic feet per minute (CFM), this equates to 1.13 liters per minute (lpm).
1031. PRE-INSTALLATION REQUIRE- MENTS. Inspect the replacement battery for possible damage incurred during shipment or storage. Give particular attention to signs of spilled liquid within the shipping container, as it may indicate a damaged cell. Follow procedures outlined in section 2 for battery venting and electrical connections.
a. Pre-installation Battery Servicing. Check the following in accordance with the battery manufacturer's instructions:
(1) Remove the shipping plugs (if used) and clean and install the filler cap vent plugs.
(2) Check the tightness of terminal hardware including each cell connector strap to the proper torque values.
(3) Check the polarity of each cell to be sure they are connected in the proper series or sequence.
(4) Prepare the battery for installation in accordance with the manufacturer’s requirements.
b. Compartments or battery boxes which have previously housed lead-acid batteries must be washed out, neutralized with ammonia or a baking soda solution, allowed to dry thoroughly, and painted with alkaline-resistant paint. Remove all traces of sulfuric acid and its corrosive products from the battery vent system to prevent contamination of the potassium hydroxide electrolyte and/or possible damage to the battery case material. Replace those parts of the vent system, which cannot be thoroughly cleansed (hoses, etc.).
1032. NICKEL CADMIUM BATTERY INSTALLATION. Each installation must have provisions to prevent any hazardous effects on structure or essential systems that may be caused by the maximum amount of heat the battery can generate during a short-circuit of the battery or individual cells.
a. Nickel-cadmium battery installations must have:
(1) A system to control the charging rate of the battery automatically to prevent battery overheating;
(2) A battery temperature sensing and over-temperature warning system with a means for disconnecting the battery from its charging source in the event of an over-temperature condition; or
(3) A battery failure sensing and warning system with a means for disconnecting the battery Par 1029 Page 116
Par 1032 Page 117 (and 118) from its charging source in the event of battery failure.
b. In the event of a complete loss of the primary electrical power generating system, the battery must be capable of providing at least 30 minutes of electrical power to those loads that are essential to continue safe flights and landing. The 30-minute time period includes the time needed for the pilots to recognize the loss of generated power and take appropriate load shedding action.
1033. SECURING THE BATTERY. Follow the procedures outlined in section 1. Make certain that the hold down bolts are not drawn up too tightly.
Ensure that the case to cover seal is installed so that the battery case/cover does not become distorted.
CAUTION: In installations where care has been taken to isolate the battery cases, inadvertent grounding may occur through improper or careless use of safety wire.
1034. QUICK DISCONNECT. Look for and replace the terminal pins when:
a. Excessive pitting or corrosion that cannot be removed.
b. Signs of burning or arcing.
c. Cracked part or housing.
d. Excessive wear on contact pins, socket lock pins, or worm screw.
e. Large deposits form on contacts or plastic is discolored.
f. Excessively loose handle and locking assembly.
NOTE: Most manufacturers sell or provide dimensions for tools to check the fit of the quick disconnect sockets.
1035. VOLTAGE AND CURRENT REGULATION. It is essential that the charging voltage and current be checked and, if necessary, the voltage regulator reset to meet the requirements of the nickel-cadmium battery being installed.
IMPORTANT: Improper charging current or voltage can destroy a battery in a short period of time.
1036. WEIGHT AND BALANCE. After installation of the nickel-cadmium battery the weight and balance of the aircraft should be recomputed if:
a. The weight of the nickel-cadmium battery is different from that of the original battery.
b. The location of the nickel-cadmium battery is different from that of the original battery.
NOTE: Weight and balance procedures for aircraft are contained in AC 43.13-1 (as amended), chapter 10.
1037. THRU 1040. RESERVED.
Par 1041 Page 119 SECTION 4. BATTERY INSTALLATION CHECKLIST 1041. STRUCTURAL REQUIREMENTS.
a. Determine if the battery is installed in such a manner that it can withstand the required loads.
The effect on other structure (primary or secondary) should be considered.
b. Determine whether suitable materials are used in the construction, including standard fasteners, confirm that the method of fabrication will result in a consistently sound structure.
c. If a mounting bracket is used, determine if the method used in its fabrication will produce a consistently sound structure.
d. If the equipment is mounted either on the existing structure or on a bracket attached to the existing structure, confirm whether all of the structure (including the bracket, if used) is adequate to support the required loads. This answer can be determined by either of two methods:
(1) By direct comparison with an existing approved installation having the same or similar (approximately the same weight and size) equipment installed.
(2) By structural analysis or static test.
Such installations do not lend themselves readily to analysis, but are normally adaptable to a static test.
In conducting a static test, the following procedure may be used:
(a) Determine the weight and CG position of the equipment item.
(b) Mount the equipment in its position in the airplane or simulate the equipment with a dummy so that th e required loads can be applied at the CG position of the actual equipment.
(c) The required loads should then be applied by any suitable means. If the equipment is light in weight, the inspector could use his own strength and/or weight to determine if the installation will withstand the required loads.
NOTE: All items of mass likely to injure the passengers or crew in a minor crash landing should have their supporting structure designed to the crash load requirements of Title 14 of the Code of Federal Regulations (14 CFR) part 23, § 23.561, insofar as the forward, upward, and sideward directions are concerned. The applicable downward load factor shall be the critical flight or landing load factor specified in §§ 23.341 and
23.473, whichever is greater.
(3) In lieu of a calculated determination of the down load factor, the ultimate factors of 6.6,
6.6, and 9.0 may be used for the normal, utility, and acrobatic categories, respectively. For equipment location not covered by § 23.561, the required loads (ref. § 23.301) are the flight and landing load factors of §§ 23.337, 23.341, and 23.473. In lieu of a calculated determination of these loads, the down load factors referenced above may be used.
(4) Supporting structure of other mass items should be designed to the critical flight or landing load factors of § 23.321, 23.471, 27.321, or
27.471. The values shown in § 23.561 or 27.561 may be used in lieu of determination of these values.
e. Determine if the equipment is installed so that it does not adversely affect another structure (either primary or secondary).
f. Confirm whether means are provided to permit proper inspections of the installation and related adjacent parts as components.
1042. HAZARDS TO THE AIRCRAFT AND ITS OCCUPANTS.
a. Confirm whether the parts of the airplane adjacent to the battery are protected against corrosion from any products likely to be emitted by the battery during servicing or flight.
NOTE: Methods that may be used to obtain protection include: acid-proof paint that will resist corrosive action by emitted electrolyte, drain to discharge corrosive liquids clear of the aircraft, positive pressure vents to carry corrosive fumes and flammable gases outside the aircraft, enclosed battery cases that would contain any amount of electrolyte that might be spilled, or combination of these methods.
b. Determine whether the battery container or compartment is vented in such a manner that any explosive gases released by the battery during charging or discharging are carried outside the airplane.
c. Confirm that the battery container or compartment is vented in such a manner that any noxious gases emitted by the battery are directed away from the crew and passengers.
d. Verify whether the battery connector terminals or other exposed parts are protected against electrical contact with the battery container or compartment.
e. Determine if adequate provision is made for the drainage of spilled or excess battery fluid.
1043. OPERATING ASPECTS. If a battery is the only source of electrical power, determine if the battery has sufficient capacity to supply the electrical power necessary for dependable operation of all electrical equipment essential to the safe operation of the airplane.
1044. DETAIL DESIGN STANDARDS. Verify that the battery is accessible for inspection or servicing on the ground.
1045. RECORDKEEPING.
a. Confirm that a maintenance record entry has been made.
b. Determine if the equipment list and weight and balance has been revised.
1046. THRU 1048. RESERVED.
Par 1042 Page 120
SECTION 5. INSTRUCTIONS FOR CONTINUED AIRWORTHINESS 1049. LEAD-ACID BATTERIES.
a. Airworthiness Limitations.
(1) Battery Inspection. To ensure continued airworthiness, the battery should be removed and capacity tested. Follow the battery manufacturer’s recommended instructions for continued airworthiness (ICA) to determine service periods.
(2) Connector/Wiring Inspection .
Check for mechanical integrity, resiliency, pitted, or corroded mating surfaces, burn marks, condition, and type of wiring.
(3) Electrolyte Levels. Electrolyte levels must be maintained just over the plates at all times.
Replenish consumed water with distilled or demineralized water.
(4) Sump Jar Maintenance. Inspect the electrolyte levels and the sump jar every 100-flight hours.
b. Capacity Test. The capacity test should be performed as follows:
(1) Check for proper battery installation per Supplemental Type Certificate (STC) or manufacturer’s ICA when performing annual and 100-hour inspections and when replacing the battery after a capacity test.
(2) Stabilize the battery at 15°C (59°F) or higher. The battery should be at temperature for at least 24 hours.
(3) Remove the battery from the aircraft and charge it according to the recommended charging instructions. Allow the battery to stand on open circuit for 1 hour.
(4) Connect the fully charged battery to a capacity tester that incorporates a load resistance, ammeter, voltmeter, and a timer.
(5) Discharge the battery at the C1 rate to
1.75 volts per cell (10 volts for a 12-volt battery and 20-volts for a 24-volt battery). Note the discharge time.
(6) The battery is considered airworthy if it meets 80 percent of its C1 (1 hour) capacity rating.
However it is recommended to return batteries to service when their capacity is above the minimum;
i.e., 85 percent minimum or 51 minutes to end point voltage.
(7) If the battery fails to meet the minimum runtime, continue by using the constant current C1 method in the manufacturer’s ICA.
Allow the battery to stand on open circuit for 1 hour.
(8) Repeat the discharge test as indicated.
If the failure persists, replace the battery.
(9) If the battery is found to be airworthy, it must be recharged with constant potential (CP) prior to re-installing it in the aircraft.
1050. NICKEL-CADMIUM BATTERIES.
a. Airworthiness Limitations. T o e n s u r e continued airworthiness, the battery should be removed and inspected per the manufacturer’s recommendations.
(1) Connector/Wiring Inspection .
Check for mechanical integrity, resiliency, pitted or corroded mating surfaces, burn marks, condition, and type of wiring.
(2) Voltage Regulator. Periodic checks to correct out-of-tolerance regulators and replacement of defective units will reduce the possibility of inadvertent increases in charging voltage with the resultant rise in charge current and battery temperature and water consumption.
(3) Battery. Inspect can and cover for dents, damage, epoxy coating separation, vent tube obstruction, latch function, and cover seal condition.
Par 1049 Page 121
Remove the battery cover and clean top of cells and connectors with a nylon brush. Verify torque on every intercell connection. If disassembly is required, discharge the battery first.
(4) Electrolyte Levels. Electrolyte levels should be adjusted during the last 15 minutes of the topping charge and while the current is still flowing, because the cells are at their most uniform electrolyte level at this time. Replenish electrolyte levels with distilled, deionized, or demineralized water only.
Insure that the proper nozzle and syringe assembly are used to level the cells by referring to the component maintenance manual for the syringe/nozzle specifications. Using the incorrect nozzle may impact battery serviceability and longevity.
(5) Electrical Leakage. Determine if external leakage is of such a magnitude as to require a complete battery cleaning. Follow the manufacturer’s recommended procedures.
(6) Sensor Assembly. Inspect the battery for proper placement of thermostats, heaters, thermistors or other sensor elements. Inspect wiring and receptacle for insulation damage, corrosion, and crimping or other defects. If the sensor/harness assembly fails testing or is damaged, it must be replaced. Perform a functional test on the temperature sensor assembly at least once each calendar year.
b. Capacity Test. The capacity test must be performed in accordance with the manufacturer’s recommendations.
1051. THRU 1099. RESERVED.
Par 1050 Page 122
CHAPTER 11. ADDING OR RELOCATING INSTRUMENTS 1100. PURPOSE. This chapter contains structural and design guidance to consider when aircraft alterations are to be accomplished by the addition or relocation of instruments.
1101. HAZARDS AND WARNINGS. The rapid advance of technical progress in the aviation industry has resulted in a virtual explosion of hightech aftermarket instrumentation. In many instances, these innovations are marketed without the support of a proper certification process. As a result, much of the equipment purported to be the most advanced may not be certificated or even certificable for installation on aircraft for which uninformed purchasers have chosen the equipment for installation.
NOTE: The burden of provision of and compliance with approved data falls entirely on the technician approving the aircraft for return to service.
1102. ADDITIONAL REFERENCES. Before initiating an alteration involving the addition or relocation of instruments, the regulatory basis of the aircraft must be considered. The introduction page of this document provides guidance to be considered on the subject of certification basis. For this chapter, the following additional references are provided:
a. Department of Commerce, Aeronautics Branch, Aeronautics Bulletin 7a, section 73(A) through (H) provides regulatory requirements for electrical equipment applicable to the 24 makes and 115 models of aircraft certificated under the provisions of that document. Section 75(B) of the same document provides additional regulatory requirements for instrumentation to be installed on the aircraft listed therein.
NOTE: Exercise care in the use of Bulletin 7a as certification basis proof data. Subsequent changes in ownership and production of some makes and models may have also resulted in changes of certification basis.
b. Department of Commerce, Civil Aeronautics Administration Bureau of Regulation Inspection Handbook, as revised to January 29, 1947, chapter XVII provides a listing of approved type certificated and 609 Group 2 aircraft under those categories. The Group 2 memoranda are identified and briefly described but complete text documentation is not provided. As of this publication no known repository of complete Group 2 memoranda has been identified.
c. Civil Aeronautics Regulation (CAR) 18 and the related Civil Aeronautics Manual (CAM) 18 established and maintained the standards and practices for all maintenance, repair, and alteration of aircraft applicable under the provisions of the CAR. That document remained in effect until the advent of the systemic changes dictated by the Federal Aviation Act of 1958 and the resultant documentary changes.
d. CAR 6, Rotorcraft Airworthiness; Normal Category.
1103. PREPARATION. Before initiating any alteration involving the addition or relocation of instruments the regulatory basis of the aircraft must be considered. For the purposes of this chapter the following references are provided:
• Civil Air Regulation (CAR) 3.661 through 3.676 provides the regulatory basis for installation of instruments in CAR 3 airplanes
• CAR 4a532 through 4a537 provide the regulatory basis for supplemental Par 1100 Page 123
variations for installation of instruments in CAR 4 non-air carrier (NAC) airplanes
• Title 14 of the Code of Federal Regulations (14 CFR) part 23, § 23.1321 provides the regulatory basis for the arrangement and visibility of instruments in part 23 airplanes
a. Structure. Chapter 1 provides guidance by which structural integrit y may be determined.
Chapter 2, paragraphs 202 and 203, provides information pertinent to instrument panel installations.
b. Location. In the absence of specific regulatory requirements, for installation of instruments required for operation under Instrument Meteorological Conditions (IMC), the recommended configuration is in the form of the basic “T” (Figure 11.1).
FIGURE 11-1. THE BASIC “T” VMC
INSTRUMENT CONFIGURATION
(1) The aircraft attitude indicator is located at the top center of the installation.
(2) The air speed indicator is located adjacent to and left of the attitude indicator.
(3) The altimeter is located adjacent to and to the right of the attitude indicator.
(4) The directional indicator is located adjacent to and immediately below the attitude indicator.
NOTE: As instrument panel installations have become more complex, the basic “T” has become more difficult to accomplish. With the relocation of the directional indicator, the relationship of the ASI-ATT-AI combination is assumed.
1104. INSTALLATION. Throughout the development of the complexity of aircraft the requirements for the mounting of all instruments has remained the same. A ll instruments must be mounted so they are visi ble to the crewmember primarily responsible for their use.
a. Structure. Before initiating changes to instrument panel installations, determine the load bearing requirements of the component. In some aircraft the instrument panel is stressed as the primary structure; with the majority, the panel is treated as the secondary structure with load bearing responsibilities limited to instruments and equipment installed. Regardless of the structural nature, the altering technician is responsibility for the installation to its original or properly altered state.
(1) In all cases, where available, refer to the manufacturer’s instructions for continued airworthiness (ICA) when considering alterations to any structure. For aircraft manufactured before the regulatory requirement for the manufacturer to provide such information, refer to AC 43.13-1, Acceptable Methods, Techniques, and Practices (as amended), chapter 4, section 4 and/or chapter 2, of this AC for methods and techniques of retaining structural integrity.
(2) Failing availability or applicability of those sources we recommend that the altering individual have a Designated Engineering Representative (DER) approve the data before accomplishing of the task.
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b. Instrument Plumbing. The majority of CAR 3 and CAR 4 general aviation aircraft use instrumentation identified as “wet” gauges. This term has nothing to do with what is being measured by the gauge, but rather the material to be measured is delivered directly to the gauge. Typical “wet” systems are fuel pressure, engine oil pressure and, when so equipped, hydraulic pressure. While not usually considered “wet” systems, the airspeed and vacuum systems use this same system. The tubing used is generally thin walled seamless aluminum or stainless steel. However, flexible rubber and/or neoprene lines are prevalent in airspeed and vacuum sensing lines.
(1) The most reliable source of information on the material used in a particular aircraft is the manufacturer’s ICA. If that source is not available, AC 43.13-1 (as amended), chapter 8 provides inspection and maintenance guidance on fuel lines, while chapter 9 provides the same level of information on hydraulic systems.
(2) The installation of remote sensing systems per part 23 has replaced the “wet” systems with system pressures being remotely measured by transducers and electrica lly transmitted to the cockpit indicators.
(3) Aircraft with long histories of alteration may contain a mixture of mechanical and/or electrical analogue instruments and digital presentations.
c. Venturi Vacuum Source. A venturi is a relatively low-cost means of producing the vacuum to operate gyroscopic instruments such as the turn and bank, directional gyro, and artificial horizon. It is mounted on the exterior of the fuselage, parallel with the longitudinal axis of the aircraft. As the aircraft moves through the air, an area of reduced pressure, a partial vacuum, is created in the throat of the venturi. The venturi throat is connected by a tube to the gyro instrument case, resulting in a reduction of pressure within the case. Ambient air, entering the instrument through the inlet port of the case, passes over the gyro rotor, causing it to spin rapidly and causes the instrument to activate.
Venturis are available in sizes providing 2”, 4”, and 9” Hg. of vacuum.
(1) The vacuum requirement for the operation of each instrument is generally provided on the data plate attached to its case. If it is not, obtain the data from the manufacturer or another acceptable source, such as AN and MS standards.
(2) If the vacuum available exceeds the requirements of the installation it will be necessary to install an in-line regulator to adjust the flow within requirements.
d. Pumped Vacuum Source. Current aviation technology has produced durable lightweight, mechanically-driven, pump and control systems for providing instrument operating vacuum.
Selection of the correct pump remains dependent on the vacuum requirements of the system being driven. Control is provided by either the system itself or an in-line regulator. Production and aftermarket standby vacuum systems are available to provide operating capabilities in the event of failure of the primary mechanically-driven system.
e. Calculating Vacuum Loads. When a venturi vacuum source is selected, do not assume the venturi selected will provide sufficient flow and negative pressure to operate the instrument package.
Even within the make and model of the venturi selected, tolerance may be insufficient to meet the requirements of the system selected. Therefore, it is essential that the vacuum load requirements be carefully evaluated.
(1) Gyroscopic instruments require optimum value of airflow to produce their rated rotor speed. For instance, a specific bank and pitch indicator required approximately 2.30 cubic feet per minute (CFM) flow and a resistance, or pressure drop, of 4” Hg. If the altering technician has selected a 2” Hg. Venturi, the resultant vacuum would be insufficient to drive the instrument.
(2) The following vacuum driven items are examples for the purposes of calculation:
TABLE 11-1. CFM/VACUUM VALUES instrument flow vacuum Bank and Pitch Indicator 2.3 cubic feet per minute 4.0” Hg Directional Gyro Indicator 1.3 cubic feet per minute 4.0” Hg Turn and Bank Indicator .5 cubic feet per minute 2.0” Hg Total flow required 4.10 cubic feet per minute The above listed instruments are listed in Tables 11-2 and 11-4. Optimum values are shown in Table 11-4. The negative pressure air source must deliver not only the optimum value of vacuum for the instruments, but must also have sufficient volume capacity to accommodate the total flow requirements of the various instruments it serves.
NOTE: The example components listed above and in Tables 11-2 and 11-4 are accepted as viable and the operating parameters related to them as accurate. The nomenclature and the properties related have no effect on the resulting computations.
TABLE 11-2. PROVIDES INSTRUMENT AIR CONSUMPTION FOR AN EXAMPLE VACUUM
DRIVEN AUTOPILOT AND INSTRUMENT INSTALLATION Air consumption at sea level Instrument Differential drop in. Hg suction (Optimum) Cubic feet/per minute Automatic Pilot System (Type A-2, A-3, & A-3A)
Directional gyro control unit across mount assembly 5.00 2.15* Bank & climb gyro control unit across mount assembly 5.00 3.85* Total ― 6.00* Automatic Pilot System (Type A-4) Directional gyro control unit 5.00 3.50* Bank & climb gyro control unit 5.00 5.00* Total ― 8.50* Bank & pitch indicator 4.00 2.30 Directional gyro indicator 4.00 1.30 Turn & bank indicator 2.00 .50 (*) NOTE.― Includes air required for operations of pneumatic relays.
TABLE 11-3. PROVIDES THE EQUIVALENT STRAIGHT TUBE LINE DROPS FOR THE 90-DEGREES ELBOWS INSTALLED IN ANY GIVEN SYSTEM (BY O.D.)
Tubing size Pressure drop in a 90˚ elbow in terms of length of straight tube equivalent to a 90˚ elbow O.D inch Wall thickness inch Feet 1/4 X 0.035 0.28 3/8 X 0.035 0.46 1/2 X 0.042 0.62 5/8 X 0.042 0.81 3/4 X 0.049 0.98 1 X 0.049 1.35
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