TM 1-410. Technical Manual, Airplane Structures 1941: Section 14 - Shielding and Bonding

SECTION XIV: SHIELDING AND BONDING

55. General.-In order that radio equipment can be operated efficiently in aircraft, ignition and other electrical equipment and related circuits must be shielded properly and the airplane bonded.

56. Shielding.-Shielding is the method of preventing radiation of electrostatic waves by surrounding electrical equipment and related wiring with grounded covers or shields of low-resistance electrical-conducting material.

57. Bonding.-a. Bonding is the term applied to interconnecting electrically isolated metal parts of the airplane by means of good electrical conductors, including connecting shielding to the airplane structure. The principal reasons for bonding airplanes are to

(1) Increase electrical capacity between metal mass of the airplane and radio antenna.

(2) Prevent electrically isolated metal parts from absorbing and thus nullifying some of the energy radiated by radio transmitting set.

(3) Eliminate danger of sparks arcing between unconnected metal members.

(4) Eliminate electrical disturbances resulting from rubbing and vibrating contacts of metal parts.

(5) Lower resistance of shielding so as effectively to localize and ground electrical disturbances.

(6) Prevent reradiation of disturbances which results when large masses of metal are isolated from main mass of the airplane.

b. Bonding connections are attached to flexible braid only by soldering. Metal braid consisting of at least 120 strands of No. 36 (B & S gage)

FIGURE 63.-Bonding strip connection.

tinned copper wire is used for bonding strips. Electrical connections of bonds (fig. 63) may be soldered., bolted, or clamped.

c. The following instructions should be followed in making bonding connections:

(1) Surfaces of all metal parts serving as electrical conductors must be free from protective coating or other insulating materials at point of contact. Required protective coatings are applied at such points only after joining or connecting of parts has been completed.

(2) Care must always be exercised when applying solder to bonding to prevent possible burning of adjacent insulation. The soldering iron must be sufficiently hot that the solder melts and flows at touch of the iron. In no case is it permissible to use an open flame for soldering insulated parts, or for installation or repair work on aircraft.

(3) To minimize corrosion. resin flux is used whenever possible for soldering in place of soldering acids.

(4) Each end of the braid in which a hole must be made to form a terminal connection is tinned to prevent fraying of strands. Lock washers are never placed next to the bonding when the connection is bolted unless a plain washer is placed next to the bonding strip.

d. Parts requiring shielding and bonding may be determined from latest technical publications on this subject.