The radio modelers have developed a useful market for gadgets.
I bought a tach a while ago, and I keep meaning to mention it
here.

The price was right - around $25.
It's intended for measuring off two or three blade props.
In other words, it counts either two flashes or three as a revolution.

When I point it at this screen (Free Agent News Reader) it registers
1800 rpm i.e 60 flashes / sec if I select two blade, or
1200 rpm if I select 3 blade. If I point it at a compact fluorescent,
it indicates 3600 rpm (120 flashes/sec)

People apparently use it with reflective patches stuck on their props
Half inch numerals on an LCD display with a prop image (2 or 3 blade).
Battery lasts a long long time.

"Tower Hobbies Digital Mini-Tach"

Brian W

Brian Whatcott > wrote in
:

> The radio modelers have developed a useful market for gadgets.
> I bought a tach a while ago, and I keep meaning to mention it
> here.
>
> The price was right - around $25.
> It's intended for measuring off two or three blade props.
> In other words, it counts either two flashes or three as a revolution.
>
> People apparently use it with reflective patches stuck on their props
> Half inch numerals on an LCD display with a prop image (2 or 3 blade).
> Battery lasts a long long time.
>
> "Tower Hobbies Digital Mini-Tach"

I modified one of those some years back... worked quite well. Never needed
any reflective patches for the prop of a real aircraft... works just fine
in daylight.

The two mods I made were:

1. Changed the internal clock frequency so that it read out in tens of
RPM. The stock model I bought (only one they had back then) read out in
hundreds of RPMs. [Lots of model aircraft have props that turn in the tens
of thousands of RPM.]

2. Made the sensor a plug-in. This gave me the option of using it as
originally designed (fine for a SEL single), or on a cable from within the
cockpit (for a twin, with the sensor taped to the wing).

-----------------------------------------------
James M. Knox
TriSoft ph 512-385-0316
1300 Koenig Lane West fax 512-371-5716
Suite 200
Austin, Tx 78756
-----------------------------------------------

Brian Whatcott wrote:

>
>When I point it at this screen (Free Agent News Reader) it registers
>1800 rpm i.e 60 flashes / sec if I select two blade, or
>1200 rpm if I select 3 blade. If I point it at a compact fluorescent,
>it indicates 3600 rpm (120 flashes/sec)
>

What rpm should I expect if I'm using MS Outlook as a newsreader?:-))

Seriously, I've seen several folks using the hobby store tachs at the
airport. As far as I know, they don't require any patches to be stuck to the
prop. The big upside is that they cost about 10% of what specialized
aircraft optical tachs (Prop Tach, TruTach) cost. As with most things, if
it's for an airplane, multiply the normal price by about 10.

John Galban=====>N4BQ (PA28-180)

--
Message posted via http://www.aviationkb.com

On Wed, 20 Aug 2008 22:01:34 GMT, "James M. Knox" >
wrote:

>Brian Whatcott > wrote in
:
>
>> The radio modelers have developed a useful market for gadgets.
>> I bought a tach a while ago, and I keep meaning to mention it
>> here.
>>
>> The price was right - around $25.
>> It's intended for measuring off two or three blade props.
>> In other words, it counts either two flashes or three as a revolution.
>>
>> People apparently use it with reflective patches stuck on their props
>> Half inch numerals on an LCD display with a prop image (2 or 3 blade).
>> Battery lasts a long long time.
>>
>> "Tower Hobbies Digital Mini-Tach"
>
>I modified one of those some years back... worked quite well. Never needed
>any reflective patches for the prop of a real aircraft... works just fine
>in daylight.
>
>The two mods I made were:
>
>1. Changed the internal clock frequency so that it read out in tens of
>RPM. The stock model I bought (only one they had back then) read out in
>hundreds of RPMs. [Lots of model aircraft have props that turn in the tens
>of thousands of RPM.]
>
>2. Made the sensor a plug-in. This gave me the option of using it as
>originally designed (fine for a SEL single), or on a cable from within the
>cockpit (for a twin, with the sensor taped to the wing).
>
>-----------------------------------------------
>James M. Knox
>TriSoft ph 512-385-0316
>1300 Koenig Lane West fax 512-371-5716
>Suite 200
>Austin, Tx 78756
>-----------------------------------------------

I can see the virtue of that remote sensor mod. That would make it a
panel mountable.ay 2.5 X3.5 X 3/4 inch (about)
THe display goes to five digits now, so #1 mod would not be a concern

Brian W