Rev. 1977
BULKHEAD Use standard aircraft practices and procedures for fabrication and attachment of shelf. Reinforce fore and aft corners with gussets or bulb angle.
FIGURE 2.8.-Typical shelf installation.
Fabricate platform using 2017T4(17ST) or equivalent. Apply standard aircraft practices for fabrication and installation.
The equipment manufacturer mounting bases that meet load requirements and can be utilized are acceptable.
27. ELECTRICAL SYSTEMS. The following data in addition to that shown in chapter 11 in AC 43.13-1A is applicable to radio installations.
a. Installation of Wiring.
(1) Use a type and design satisfactory for the purpose intended.
(2) Install in a manner to be suitably protected from fuel, oil, water, other detrimental substances and abrasion damages.
b. Power Sources.
(1) Connect radio electrical systems to the aircraft electrical system at a terminal strip, or use a plug and receptacle connection.
(2) Radio electrical systems must function properly whether connected in combination or independently.
Chap 2 AC 43.13-2A
c. Protective Devices.
(1) Incorporate a "trip free" resettable type circuit breaker or a fuse in the power supply from the bus. Mount in a manner accessible to a crewmember during flight for circuit breaker resetting or fuse replacement.
(2) Select circuit breakers or fuses that will provide adequate protection against overloading of the radio system circuits.
(3) Connect all leads in such a manner that the master switch of the aircraft will interrupt the circuit when the master switch is opened.
(4) Radio system controls are to provide independent operation of each system installed and are to be clearly placarded to identify their function relative to the unit of equipment they operate.
d. Available Power Supply. To preclude overloading the electric power system of the aircraft when additional equipment is added, make an L
1. BULB ANGLE
2. STIFFENING FLANGE OR ANGLE
AT ENDS OF PLATFORM
3. REINFORCEMENT ANGLE FOR BULKHEAD FIGURE 2.9.-Typical rail platform installationaluminum alloy structure.
AC 43.13-2A Rev. 1977 NOTE: AVOID PLACING ADDITIONAL
CLAMPS IN CENTER THIRD
OF TUBE MEMBERS
LOCATE CLAMPS CLOSE TO
WELD CLUSTERS
AN - BOLT
- PLYWOOD AN970- WASHERS AN742-CLAMP -AN 365-NUT
CLAMP DETAIL FrauRE 2.10.-Typical attachment of support structure to tubular frame.
electrical load analysis to determine whether the available power is adequate. Radio equipment must operate satisfactorily throughout the voltage range of the aircraft electrical system under taxi, takeoff, slow cruise, normal cruise, and landing operating conditions. If night and instrument flight is contemplated, compute the electrical load analysis for the above flight regimes under the most adverse operating conditions.
e. Wire Bundle Separation from Flammable Fluid Lines.
(1) Physically separate radio electric wire bundles from lines or equipment containing oil, fuel, hydraulic fluid, alcohol, or oxygen.
(2) Mount radio electrical wire bundles above flammable fluid lines and securely clamp to structure. (In no case must radio electrical wire bundles be clamped to lines containing flammable fluids.)
f. Cable Attachment to Shockmounted Units.
(1) Route and support electrical wire bundles and mechanical cables in a manner that will allow normal motion of equipment without strain or damage to the wire bundles or mechanical cables.
g. Radio Bonding. It is advisable to bond radio equipment to the aircraft in order to provide a low impedance ground and to minimize radio interference from static electrical charges.
When bonding is used, observe the following:
(1) Keep bonding jumpers as short as
(2) Prepare bonded surfaces for best contact (resistance of connections should not exceed .003 ohm).
(3) Avoid use of solder to attach bonding jumpers. Clamps and screws are preferred.
(4) For bonding aluminum alloy, use aluminum alloy or tinned or cadmium-plated copper jumpers. Use brass or bronze jumpers on steel
(5) When contact between dissimilar metals cannot be avoided, put a protective coating over the finished connection to minimize corrosion.
10 Chap 2
Rev. 1977 2017 T4 Bulb Angle or equivalent tubing.
Mounting Base - 2017 T4 or equivalent Plate Nut Airframe Tubing Secure mounting base to airframe tubing with loop-type clamp (AN 742 or equivalent), machine screws, and self-locking nuts.
FIGURE 2.11.-Typical mounting plates for remote location of radio units.
h. Radio Interference. Radio interference generated by aircraft components can be eliminated or reduced by exercising proper precautions.
The following paragraphs contain two major sources of interference which affect audio recep-
(1) Ignition system interference can be minimized with shielding. To be effective, all parts of the ignition system should be shielded in metal in order to eliminate noise resulting from RF radiation.
(a) A metallic braid covering and special end connectors are effective between the magneto and shielded type spark plugs.
(b) Shield the primary lead to the magneto.
(c) Provide a shielded metal cover for the magneto if it is not of a shielded type.
(d) Provide a tight metal-to-metal contact of all connections in the shielding system.
(e) If it is not feasible to shield the engine ignition system, the engine ignition noise may be suppressed by replacing the spark plugs with resistor spark plugs of a type approved for Chap 2 AC 43.13-2A
(f) If it is found that despite shielding of the ignition wiring and plugs an intolerable noise level is present in the radio system, it may be necessary to provide a filter between the magneto and magneto switch to reduce the noise.
This may consist of a single bypass capacitor or a combination of capacitors and choke coils.
When this is done, the shielding between the filter and magneto switch can usually be eliminated and the special shielded magneto switch need not be used.
(g) Supporting brackets and wiring details for magneto filters should be in conformance with standard aircraft electrical practice.
The reliability of the magneto filter installations should be at least equivalent to that of the remainder of the magneto ground lead installation.
(2) Inverter interference is noticeable by a constant noise or hash induced and amplified by the audio circuits of the communication or navigation systems. This noise level can reach such a magnitude that all intelligence of audio reception is lost. Inverter interference can be effectively minimized or eliminated by observing the following precautions during installation:
(a) Locate the inverters in an area separated from other electronic equipment.
(b) Assure that the inverter input and output wires are separated.
(c) Shield the inverter output wires and ground the shields at the inverter end only.
(d) Make sure the inverter case is adequately bonded to the airframe.
i. Mutual Radio Frequency Interference in DME/ ATC Radar Beacon Systems. Distance measuring equipment (DME) and ATC radar beacon (transponder) systems operate within the same frequency range. Therefore, simultaneous operation of two or more of these systems may result in mutual RF interference. Certain makes of DME and transponder equipment have intersystem suppressor circuitry designed to eliminate mutual interference. When such connections are provided, follow the manufacturer's recommendations for use and wire bundle installation.
AC 43.13-2A
28. EMERGENCY LOCATOR TRANSMITTER (ELT) INSTALLATIONS. The ELT unit should be attached to the airframe or other solid structures.
Airframe preparation for either vertical or shelftype mountings is displayed in figures 2.7 and
2.8. The equipment manufacturer mounting bases that meet load requirements and can be utilized are acceptable.
12 Rev. 1977 The installation of the ELT antenna should be located as far as practicable from other installed antennas. Methods for securing whiptype antennas to the structure are shown in figures 3.1 and 3.3. Follow the manufacturer's installation procedures when available.
29.-35. [RESERVED] Chap 2
Rev. 1977 AC 43.13-2A Chapter 3. ANTENNA INSTALLATIONS
36. PERFORMANCE. For proper performance, it is important that the radio equipment manufacturer's instructions be carefully followed in matching and coupling the antenna to the radio equipment.
a. The location of the antenna is of primary importance. When selecting a mounting position, consideration should be given but not limited to the following:
(1) Obstruction to signal reception by aircraft or aircraft components.
(2) Ignition noise (RF radiation pickup).
(3) Vibration.
(4) Flutter.
(5) Instrument static source interference.
b. Attach antenna mounting (masts, base receptacles, and/or supporting brackets) so that the loads imposed (e.g., air, ice, etc.) are transmitted to the aircraft structure.
37. VHF ANTENNA-WHIP.
a. Locate this type antenna so that there is a minimum of structure between it and the ground radio stations. The antenna may be mounted on the top or bottom of the fuselage. It is not advisable to mount the antenna on the cowl forward of the windshield because a lightning strike might possibly blind the pilot.
b. Methods of securing whip antennas to the structure are shown in figures 3.1 and 3.3.
ANTENNA ROD HEX. NUT -FLAT WASHER (BRASS)
MACHINE -GASKET SCREW
CERAMIC BUSHING (FEMALE)
- GASKET
SKIN OF AIRPLANE SKIN OF AIRPLANE
• GASKET
- CERAMIC BUSHING (MALE) HEX. NUT CABLE CLAMP (PART OF ANTENNA CABLE) • GASKET
•FLAT WASHER
LOCK WASHER
• LOCK WASHER ANTENNA CABLE HEX. NUT
ANTENNA CABLE LUG
FLAT WASHER SOLDER LUG •LOCK WASHER (PART OF ANTENNA CABLE) HEX. NUT FIGURE 3.1.-Typical whip antenna installation.
Chap 3 13
AC 43.13-2A Rev. 1977
c. On fabric-covered aircraft or aircraft with other types of nonmetallic skin, the manufacturer's recommendations should be followed in order to provide the necessary ground plane.
An acceptable method of accomplishing this is by providing a number of metal foil strips in a radial position from the antenna base and secured under the fabric or wood skin of the aircraft.
(See fig. 3.2.)
WHIP
ANTENNA
(2) The approximate drag load an antenna is required to withstand can be determined by the following formula:
D=.000327 AV2 (The formula includes a 90 percent reduction factor for streamline shape of antenna.)
Where D is the drag load on the antenna in Ibs., A is the frontal area of the antenna in sq. It., and V is the Ve of the aircraft in m.p.h.
The frontal area of typical antennas are approximately as follows:
Antenna Area (Fig. 3.4) (sq. ft.)
a .073 b .135 C - = J .135 d .025 .045 Example: Antenna "b" at 250 m.p.h.
D=.000327X.135X (250) 2 =.000327 X.135 × 62,500 =2.75 1bs.
METAL FOIL UNDER
FABRIC OR WOOD SKIN NOTE: THE LENGTH OF EACH FOIL ANTENNAS SUPPLIED BENT 45° ARE TO MOUNT
WITH END POINTING TO RADIAL SHOULD BE AT LEAST EQUAL REAR OF AIRCRAFT.
TO THE ANTENNA LENGTH.
FIGURE 3.2.-Antenna ground plane for nonmetallic aircraft.
38. VHF ANTENNA-RIGID.
a. When it is necessary to cover a broader frequency range than can be covered by a whip an- ANTENNA ASS'Y, FLAT WASHER is resonant over a much broader frequency range. tenna, a blade type should be used because it NEOPRENE WASHER ANTENNA MOUNTING However, a broadband antenna is not as efficient BOLT as a small diameter whip antenna and, accord- TRUSS HEAD ingly, should not be used with relatively low output transmitters (under 5 watts). LUTE SKINN
(1) The antennas shown in figure 3.4 are REINFORCING PLATE normally installed at a point on the fuselage - COVER STOP NUT directly above the cabin or baggage compartment. GROUND SHIELDING UNDER MOUNTING BCLT. • LOCK WASHER.
When a rigid antenna is installed on the - BOLT vertical stabilizer, evaluate the flutter and vibration characteristics of the installation. FIGURE 3.3.-Typical shockmounted antenna installation.
14 Chap 3
e FIGURE 3.4.-Typical rigid antennas.
b. Installation of Rigid Antennas.
(1) Place a template similar to figure 3.5 on the fore-and-aft centerline at the desired location.
Drill the mounting holes and the correct diameter hole for the transmission line cable in the fuselage skin.
(2) Install a reinforcing doubler of sufficient thickness to reinforce the aircraft skin. The length and width of the plate should approximate that illustrated in figures 3.6 or 3.8.
(3) Install antenna on fuselage, making sure that the mounting bolts are tightened firmly against the reinforcing doubler, and that the mast is drawn tight against the gasket.
When a gasket is not used, seal the crack between the mast and fuselage with a sealer, such as zinc chromate paste or equivalent.
SUFFICIENT SIZE TO
ACCOMODATE TRANSMISSION
LINE CABLE C/1 NO. 18 DRILL FIGURE 3.5.-Typical antenna mounting template.
Chap 3 251-957 0 - 77 - 2 AC 43.13-2A
(4) Route transmission line cable to the receiver, secure the cable firmly along its entire length at intervals of approximately 2 feet, and take care to prevent fouling of control cables.
39. VHF NAVIGATION RECEIVING ANTENNAS.
Locate antennas for omnirange (VOR), and instrument landing system (ILS) localizer receivers at a position on the aircraft where they will have the greatest sensitivity for the desired signals and minimum response to undesired signals such as electrical energy radiated by the engine ignition system. A good location for the VOR localizer receiving antenna on many small
ANTENNA
FUSELAGE SKIN
EXISTING STRINGERS
VIEW A-A
REINFORCING DOUBLER APPROXIMATELY ONE ALCLAD 2024-T3
INCH SPACING OF 1/8" MIN. DIA. RIVET 1 1/2" EDGE DISTANCE MIN.
FIGURE 3.6.-Typical antenna installation on a skin panel.
AC 43.13-2A Rev. 1977 manufacturer's installation procedures and assure that the balun is properly grounded to the airframe. Refer to AC 43.13-14 'Acceptable Methods, Techniques, and Practices-Aircraft Inspection and Repairi chapter 11, for acceptable bonding practices.
ANTENNA
DIPOLES FIGURE 3.7.-Preferred VOR antenna location for maximum signal pickup with minimum ignition interference.
CUT STRINGER
REINFORCING DOUBLER OF ALCLAD 2024 - I2 BALUN
WIRE WRAPPED AND
SOLDERED TO SHIELD
AIRFRAME GROUND FRAME
STRINGER
STRINGER
DOUBLER FLANGES RIVEIS ADDED
AT LEAST THE HEIGHT AS SHOWN ON
OF CUT STRINGER RAMES, STRINGE
AND DOUBLE
• EXISTING RIVETS FIGURE 3.8.-Typical antenna installation involving a cut stringer.
airplanes is over the forward part of the cabin.
Mount the rigid V-type antenna so that the apex of the "V" points forward and the plane of the "V" is level in normal flight.
a. VOR Antenna Balun and Transmission Lines.
A dual element or balanced antenna system requires a balun or an impedence matching device for maximum signal transfer into an unbalanced coaxial cable. Rigid antennas, as displayed in figure 3.4, incorporate a balun as an integral component of the antenna assembly. Follow the 16 FIGURE 3.9 Typical dipole antenna assembly.
(2) Figure 3.10 is an illustration of a typical VOR antenna balun. A balun made from a section of the transmission line functions as a tuned circuit or transformer which produces a standingwave ratio to provide the desired matching impedence. When the antenna is matched to the line, the line measurement in multiples of wave lengths is not critical.
(2) Radio wave velocity is less in a cable than in air; therefore, the wave length in cable will be shorter than in air. Appropriate test equipment must be used for transmission line measurements because the physical and electrical lengths of lines are not always equal.
Chap 3
Rev. 1977 AC 43.13-2A a lengthwise slit and peel off the outer jacket.
AT TACH Do not nick, cut or damage the shield.
TO ANTENNA DIPOLES
SHIELD (OUTER - DIELECTRIC
CONDUCTOR)
TWISTED SHIELD SHIELD
REMOVED OUTER JACKET
CENTER CONDUCTOR
SINGLE SHIELD
- PROTECTIVE OUTER FIGURE 3.11 Coaxial cable preparation.
COVERING
(2) Comb out the braid and bend back to expose the dielectric. Use a sharp knife to cut the dielectric around the circumference, not quite through to the center conductor. Do not nick or cut the conductor. Remove the dielectric by twisting and pulling.
(3) Solder the contact to the center conductor. Use a clean, well-tinned soldering iron.
ROSIN-CORE WIRE WRAPPED AND SOLDERED TO SHIELD SOLDER 60/40
- AIRFRAME GROUND -CENTER CONDUCTOR OPEN
TO NAVIGATION RECEIVER FICURE 3.10 Typical VOR antenna balun.
(3) The transmission line should be kept as shore a short as possible. Any bends in the cable should have at least a 3-inch radius. Follow the equipment manufacturer's recommendations regarding transmission lines and lengths.
b. Assembly of Coaxial Cable Connectors.
Optimum performance of a radio system is dependent upon the coaxial cable connector assembly. Follow the manufacturer's assembly instructions. Assure that the cable is not distorted or flattened when cutting. The electrical characteristics of the cable change when flattened or bent sharply.
(1) To remove the outer jacket, cut with a sharp knife around the circumference, then make Chap 3 FIGURE 3.12 Coaxial cable tinning center lead.
(4) Do not apply heat too long as this will swell the dielectric and make it difficult to insert into the body of the connector.
FLUSH AGAINST DIELECTRIC 7 CONTACT MUST BUTT
ROSIN-CORE SOLDER 60/40
FEED SOLDER INTO
HOLE ONLY FIGURE 3.13 Coaxial cable soldering center lead.
(5) Install connector body and tighten until secure. Do not overtighten as this will distort the cable.
Rev. 1977 AC 43.13-2A VOR receivers. Typical cable lengths are from 22 to 35 inches and multiples of these lengths.
- 1/4 Another method of coupling two VOR navigation receivers to a common antenna is by utilizing DO NOT BREAK STRANDS. a device called a coupler or diplexer. This de-
DO NOT NICK CENTER CONDUCTOR-
• 1/8
NUT WASHER GASKET CLAMP TRIM STRANDS WITH SCISSORS VERTICAL "V" ANTENNA
FLUSH WITH END OF TAPER → L3/32
CONTACT FLUSH WITH END OF INSULATOR
JACK BODY
INSULATOR -CONTACT FICURE 3.14 Coaxial cable install connector body.
(6) Use only the crimping tool recommended by the manufacturer, or an equivalent tool when installing connectors which utilize a crimp-type contact.
c. Dual VOR/NAV Receiver Installations. Iwo VOR navigation receivers can be connected to a common VOR antenna. This is accomplished by utilizing a coaxial tee connecter (UG-274 A/U) and matched 0.5 wavelength coaxial cable lengths connected from the tee connector to the respective UNDE: JURFACE OF AIRPLANE "p" ANTENNA "L" ANTENNA NOTE: AN "L" TYPE ANTENNA IS SIMILAR TO A "T"
ANTENNA EXCEPT THAT THE LEAD-IN WIRE
IS CONNECTED TO THE END OF THE ANTENNA INSTEAD OF THE CENTER.
FIGURE 3.15.-Typical wire antenna locations.
-TO RECEIVER
SOLDER CONNECTION MINIMUM 16 COPPERWELD ANTENNA WIRE' FiGURE 3.16.- Typical marker beacon receiving antenna.
Chop 3 |
Rev. 1977 1025 STEEL FITTING SPRING
FABRIC WING
• STEEL ROD WASHER NUT
METAL WING 2017 FIGURE 3.17.-Typical wing tip installations.
vice, in addition to impedance matching, also provides isolation between VOR navigation receivers while keeping line insertion losses at a minimum.
40. RANGE RECEIVING ANTENNAS. Mount T", "L", or "V" antennas on top or bottom of the aircraft with approximately 1-foot clearance from the fuselage and wings. Typical wire antenna installations are shown in figures 3.15 through 3.19.
41. MARKER RECEIVING ANTENNA. The marker receiver operates at a frequency of 75 MHz. In order to keep to a minimum the number of antennas on the aircraft, the marker receiver may utilize the same antenna as the range receiver if that antenna is mounted on the underside of the aircraft. However, both receivers should include provisions to permit simultaneous opera- Chap 3 AC 43.13-2A tion without interference. A whip or other vertical type of antenna should not be used for marker reception since the ground facility transmits from a horizontally polarized antenna.
4130
OR AN BOLT AND NUT 1025 STEEL
THIMBLE SPRING
FIN TAIL POST RUDDER:
1025 OR 4130 TUBE
RUBBER TENSION UNIT FIGURe 3.18.-Typical in tip installations.
42. ATC RADAR BEACON (TRANSPONDER) AND
DISTANCE MEASURING EQUIPMENT (DME) AN- TENNAS. Locate these antennas at an unobstructed location on the underside of the fuselage.
preferably at the lowest point of the aircraft when in level flight. To the extent practicable, mount the antenna so that the base is horizontal when the aircraft is in cruise attitude.
a. Installation. Mount the antennas at least 36 inches away from obstructions and as far as possible from other antennas. Tests have shown that the location of the antenna with respect to obstructions is of greater importance than having the antenna installed in a vertical position.
However, signal strength and pattern become noticeably affected as the angle of the antenna approaches 45° from the desired vertical position.
On fabric-covered aircraft or aircraft with other types of nonmetallic skin, it will be necessary to provide a flat metallic surface or ground plane" extending at least 12 inches in all direc- 19
AC 43.13-2A Rev. 1977
ANCHOR CABLE COIL SPRING
INSULATORS
DOUBLER FIGURE 3.19.- Typical wire antenna installations.
FIGURE 3.20.--Preferred position for distance measuring and/or ATO radar beacon antennas.
tions from the center of the antenna. Be sure the antenna makes a good, direct electrical connection with the ground plane. Install gaskets, pressurization seals, and/or sealant as required.
b. Dual System Installations. When dual ATC radar systems, dual DME systems, or combinations of these systems are installed, determine that the separation between their respective antennas is within the manufacturer's prescribed limits. (See paragraph 27i for mutual interference in DME and ATC radar beacon systems.)
c. Antenna Cable. Route the antenna cable in the most direct path practicable. Since losses can be relatively high at these frequencies, follow the equipment manufacturer's recommendations regarding transmission lines and lengths.
43. DIRECTION FINDING ANTENNAS (100 to 1750 KHz). Manual or automatic loop-type antennas are used with direction-finding receivers. The loops are designed for use with a particular receiver. Connecting wires between the loops and receivers are also designed for the specific equipment. Accordingly, only components meeting the specification characteristics of the receiver manufacturer should be used.
Chap 3