30 March 2005 Magneto Test Bench

Magneto Test Bench

Thompson Aircraft Maintenance

San Luis Obispo, California

30 March 2005 Magneto Test Bench

Magnetos 101

• Magnetos are old technology• On cars were replaced by coil

ignition system• Simple system

– Engine driven– Magnetos keep generating spark

even if lose electrical system– Trouble-free

30 March 2005 Magneto Test Bench

Aircraft Engines 101• Air cooled• 4 or 6 cylinder• “Boxer” engine• Doubly-

redundant magneto ignition system– Each magneto

generates spark for all four cylinders

30 March 2005 Magneto Test Bench

Magneto Installations

Magnetos on back side of engine. Notice four spark leads coming from magneto.

Dual mags on six-cylinder twinengine plane.

30 March 2005 Magneto Test Bench

Magnetos Up Close

Engine side of mag showsgear drive. Different makemags have different drives.

Lead side of mag showsspark lead connections.

30 March 2005 Magneto Test Bench

Manually Testing MagsCurrent test procedure is manual and subjective.Spin mag drive and look at spark. Qualitatively assess strength of spark.

Spark test leads formagneto tester

Spin drive gear manuallyAnd observe spark strength

30 March 2005 Magneto Test Bench

Magneto Test Bench

• Want to make testing more quantitative• Want to drive mag with a motor at various

speeds (0-2800 RPM)• Want to be able to measure voltage at spark

leads• Want to be able to accommodate mags of

different makes (Bendix, Slick, etc.)• Want to be able to accommodate 4- and 6-

cylinder engines• Want to be able to drive different mags with

motor• Want to be able to observe spark also

30 March 2005 Magneto Test Bench

Magneto Test Bench

• Make test bench out of off-the-shelf components– 80-20 structural pieces, e.g.– Standard motor and measuring

equipment from McMaster-Carr, e.g.

– Inexpensive

30 March 2005 Magneto Test Bench

Contact Information

Cody Thompson, A&P, IA, 471-1119