Tachometer, New Old Stock PN 656K-03, P-51, P-47

Here is an authentic original WWII-era Electrical Tachometer Indicator Kollsman part number 656K-03 (US Army Type E-9), as used in US Army Air Force fighters P-38 Lightning, P-39 Airacobra, P-47 Thunderbolt, P-51 Mustang, and P-63 King Cobra. This specimen is New Old Stock and was received by Aero Antique in its original sealed carton dated November 28, 1944, and we are the first to have opened it since then.

The Army type E-9 tachometer indicator consists of a three phase alternating current  synchronous motor and an indicating element. By using the magnetic drag principle, the speed of the synchronous motor is transmitted to the indicating element, which registers it on a dial marked in revolutions per minute.  Indicates engine speed from 0-3500 RPM. 

This design of the E-9 has two pointers: the long pointer indicates RPM in 100's.  The short pointer indicates RPM in 1000's along the same scale. Some E-9 designs had a single pointer indicating 100's RPM with a small inset window at the 9 o'clock position with rotating numbers 1-3 indicating 1000's RPM. 

The instrument is in mint condition. The dial measures 3.25 inches diameter and is approximately 5 inches deep.