Tach Vs. Hobbs Time

Drew Dalgleish wrote:

On Sun, 21 Dec 2003 17:56:56 -0500, "Ron Natalie"
wrote:


"PaulaJay1" wrote in message ...


I got a free program that uses the engine sound to give you RPM. I don't know
the web site but the program says email is . Just
take a laptop to the plane and check it out.


Engine sound or prop sound? How does it work on geared engines?

(just kidding).


Someone suggested using a street light as a strobe to check your tach.
Do the math to figure out what speed will stop the prop and see if
your tach agrees
Drew

I guess you are saying the street light flickers at 60Hz. Than a 2
bladed prop should look stopped at 1800 RPM? I might give this a try but
I think this would be better for calibrating the tach neadle rather than
the tach hour indicator.

John Roncallo

All those posts, and no one answered the question...

"John Roncallo" wrote

I guess this is the question I'm asking. Where does 1:1 occur. On the
particular trip I was running 65% which at that altitude was 2425 RPM.

John Roncallo

It depends on the tach. Typically, you can buy one that's designed for 1:1
at 2300 or 2500... If it's not marked on the faceplate, check the model
number or s/n of the tach, and go to the manufacturer. That's the best way
to tell how the tach is calibrated.

If the tach is calibrated to run at 2300 and you're cruising at 2425, that's
a 5.4% increase, so a trip that took 3.9 would read 4.1, assuming no
takeoff and climb...


"John Roncallo" wrote in message
news
Hello

Im trying to figure out the Tach on our clubs Archer is screwing us. I
just flew down to the Centenial of Flight FFA from Planville CT. Round
trip with all diversions and ATC rerouts was 975nm. The tach said 12.4
hr. I never checked the Hobbs but I do know that for this plane the Tach
usually runs faster than the hobbs on cross countries. Is this normal. I
also did another flight previously at 65% power from Meriden MMK to
Williamsburg W94 in 4.6 Tach time. My watch said 3.9. Also based on the
4.6 my fuel burn was only 8 GPH.

Is there any text book way to check this. Our FBO seems to feel that
calibrating the Tach is a big deal. I'm currently thinking of just
replacing the Tach without tring to calibrate. Right now it looks to me
as if we just replaced and engine at 1700 hr thinking it had 2000 hr.

Thoughts ideas?

"John Roncallo" wrote in message . com...

I guess you are saying the street light flickers at 60Hz.

It flickers at 120 Hz.

Ron Natalie wrote:
"John Roncallo" wrote in message . com...


I guess you are saying the street light flickers at 60Hz.


It flickers at 120 Hz.


I guess this is due to voltage passing through zero 2 time per cycle?
using 60 Hz. AC. Looks like I will only pick up the blade looking like a
4 bladed prop at 1800 RPM.

John Roncallo

Dan Raneri wrote:

All those posts, and no one answered the question...


"John Roncallo" wrote

I guess this is the question I'm asking. Where does 1:1 occur. On the
particular trip I was running 65% which at that altitude was 2425 RPM.

John Roncallo


It depends on the tach. Typically, you can buy one that's designed for 1:1
at 2300 or 2500... If it's not marked on the faceplate, check the model
number or s/n of the tach, and go to the manufacturer. That's the best way
to tell how the tach is calibrated.

If the tach is calibrated to run at 2300 and you're cruising at 2425, that's
a 5.4% increase, so a trip that took 3.9 would read 4.1, assuming no
takeoff and climb...


"John Roncallo" wrote in message
news
Hello

Im trying to figure out the Tach on our clubs Archer is screwing us. I
just flew down to the Centenial of Flight FFA from Planville CT. Round
trip with all diversions and ATC rerouts was 975nm. The tach said 12.4
hr. I never checked the Hobbs but I do know that for this plane the Tach
usually runs faster than the hobbs on cross countries. Is this normal. I
also did another flight previously at 65% power from Meriden MMK to
Williamsburg W94 in 4.6 Tach time. My watch said 3.9. Also based on the
4.6 my fuel burn was only 8 GPH.

Is there any text book way to check this. Our FBO seems to feel that
calibrating the Tach is a big deal. I'm currently thinking of just
replacing the Tach without tring to calibrate. Right now it looks to me
as if we just replaced and engine at 1700 hr thinking it had 2000 hr.

Thoughts ideas?




Thanks, this makes sense. Is there anyway I can tell what is supposed to
be installed in this particular aircraft?

John Roncallo

In article , John Roncallo
wrote:
Why? Do the Archer's engine components wear less at high RPM than an
engine on an Arrow?

Yes they probably do wear less. They are under less load for the given
circumstance. Cylinder pressures are much higher in an engine at 65%
power 2300 RPM than they are at 65% 2480 RPM.

But a far greater effect will be the additional wear from friction of
running at 2480 RPM instead of 2300 RPM - a significant increase in the
number of friction cycles per hour. I'd say the Archer's engine
will wear more quickly.

--
Dylan Smith, Castletown, Isle of Man
Flying: http://www.dylansmith.net
Frontier Elite Universe: http://www.alioth.net
"Maintain thine airspeed, lest the ground come up and smite thee"

"Dylan Smith" wrote in message ...


But a far greater effect will be the additional wear from friction of
running at 2480 RPM instead of 2300 RPM - a significant increase in the
number of friction cycles per hour. I'd say the Archer's engine
will wear more quickly.

The number of revolutions acquired isn't the driving factor in engine
life. Flight school aircraft that are flown frequently and full throttle
tend to far exceed TBO where as babied, infrequently flown single
owner birds tend not to get anywhere near TBO.

Or 50 here in Europe.

Paul

"G.R. Patterson III" wrote in message
...
Any multiple of 60.

To check, you can get one of these:
http://www.aircraftspruce.com/catalo...es/trutach.php

As pointed out, can get get various 1:1 tach RPM settings.
You specify it when you buy one.

Go to http://www.gulf-coast-avionics.com/
and type "tachometer" in the search box. You'll see the
1:1 RPM listed. Maybe a number in the model number
gives it away (like the 3 or 5 at the end in the ones listed).

Paul

"John Roncallo" wrote in message
om...
Thanks, this makes sense. Is there anyway I can tell what is supposed to
be installed in this particular aircraft?

Paul Sengupta wrote:
To check, you can get one of these:
http://www.aircraftspruce.com/catalo...es/trutach.php

As pointed out, can get get various 1:1 tach RPM settings.
You specify it when you buy one.

Go to http://www.gulf-coast-avionics.com/
and type "tachometer" in the search box. You'll see the
1:1 RPM listed. Maybe a number in the model number
gives it away (like the 3 or 5 at the end in the ones listed).

Paul

"John Roncallo" wrote in message
om...

Thanks, this makes sense. Is there anyway I can tell what is supposed to
be installed in this particular aircraft?





Thanks

Our annual is comming up. I will be looking into this.

John Roncallo