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TACH READING HELP

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Old 12-23-2006 | 10:24 AM
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Default TACH READING HELP

Hi all now this may sound stupid but when using a tach where do you hold it on the prop? If hold it near the bottom im reading 7900rpm but if i hold it near the top im reading 13000rpm. Any help would be great thanks.....
Old 12-23-2006 | 12:24 PM
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Default RE: TACH READING HELP

While the tip velocity may be faster than the root velocity the same number of prop blades pass a given point per second so it really shouldnt matter.
Old 12-23-2006 | 12:45 PM
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Default RE: TACH READING HELP

Hi!
Shouldn't matter where you point it...what kind of strange tach do you have?
Old 12-23-2006 | 01:09 PM
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Default RE: TACH READING HELP

I doubt if the different readings you get actually depend on where in the prop arc you point the tach. Tachs can give you wildly erratic readings sometimes. Try sitting in the shade with the front of the plane pointed towards a sunny area of your field. Sit behind your plane when reading your tach --- safer than in front.
Old 12-24-2006 | 07:49 AM
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Default RE: TACH READING HELP


ORIGINAL: perreback

I doubt if the different readings you get actually depend on where in the prop arc you point the tach. Tachs can give you wildly erratic readings sometimes. Try sitting in the shade with the front of the plane pointed towards a sunny area of your field. Sit behind your plane when reading your tach --- safer than in front.
perreback has the best analysis here,

Another point to consider is that these tachs have a swicth to change from 2-3 bladed propellers - where is your switch positioned? Is it working properly? Are you changing it accidentily? []
The math would indicate that this is a possibility...
Old 12-24-2006 | 09:15 AM
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Default RE: TACH READING HELP

Are you near any flourescent lights?
It could be picking up the pulses from them.
KW_Counter
Old 12-24-2006 | 12:25 PM
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Default RE: TACH READING HELP

hi i have the hanger 9 tach. it was a cloudy day so i guess i will try it again in better conditions. it worked on another model ok so i guess a bit of trial and error is needed.
Thanks for the replys all.

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