Tower Tach
05-29-2003 | 10:22 PM
#5
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From: N.E. OREGON
Tower Tach
it should read 3600 rpm. These tachs are optically sensed. Each time a propeller blade passes in front of the sensor, it blocks the light coming in. 120 volt AC electricity cycles on and off 60 times a second and therefore simulates propeller blades blocking the incoming light. 60X60=3600. Some of the ducted-fan guys paint alternating 1/4 of their fan spinners in white and black to get a rpm reading.
05-30-2003 | 11:01 AM
#6
Senior Member
Tower Tachometer
I have a newer, black Tower Hobbies tachometer.
It is sensitive enough to check its calibration even with an incandescent lamp. The AC in my country is 50Hz, as it is in Europe and it registers 3,000 RPM.
When you take a reading with any photocell, optical tachometer, you must verify that it is pointed to the prop blade disk, nearer to the end of the blades. If you point it near the spinner, you will see very surprising readings...
There was an entire thread about a .40 engine, spinning a 10x6 at 25,500 RPM... Obviously a reading error, or a 6.4 horsepower .40 engine.
Sincerely,
It is sensitive enough to check its calibration even with an incandescent lamp. The AC in my country is 50Hz, as it is in Europe and it registers 3,000 RPM.
When you take a reading with any photocell, optical tachometer, you must verify that it is pointed to the prop blade disk, nearer to the end of the blades. If you point it near the spinner, you will see very surprising readings...
There was an entire thread about a .40 engine, spinning a 10x6 at 25,500 RPM... Obviously a reading error, or a 6.4 horsepower .40 engine.
Sincerely,
