Engine-Ignition Shielding for Radio Reception in Aircraft

The use of highly sensitive receiving equipment on aircraft has made the problem of airplane-engine ignition shielding an important one. Ignition shielding consists of so confining the electrical fields of the ignition system that no interfering signal can be set up in the radio receiving circuits. The problem in ignition shielding is chiefly the electrical and mechanical design of the arrangement for shielding, as it is much more difficult to secure an assembly which will not adversely affect the engine ignition system than to obtain complete freedom from interference for the radio equipment. The Bureau has been in active cooperation with airplane engine, magneto, spark plug and cable manufacturers in an effort to develop a safe method for effecting this shielding and to make the necessary equipment commercially available. As a result of this cooperation shielding assemblies may now be purchased for use on all Wright and Pratt-Whitney airplane engines. A metallic ignition manifold is employed with high tension cable drawn through it in the usual way. The leads from the manifold to the spark plugs and the groups of leads from the manifold to the magneto outlets are enclosed in liquid-proof flexible aluminum tubing with copper braid on the outside to insure effective shielding. Each flexible tubing is suitably fitted to the ignition manifold and to the magnetos or spark plugs, as the case may be. The magnetos are provided with covers which completely enclose the distributor blocks.