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Tachometer

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HBaker

Joined: 16 Nov 2008
Posts: 119

Posted: Sun Jan 18, 2009 2:30 pm Post subject: Tachometer

Is there a  mechanical tachometer out there that is not in % of rpm that I can put on the M14P, and does it install in the center of the air start?

_________________
Currently building a Murphy Moose - any help would be appreciated.

dsavarese0812(at)bellsout
Guest

Posted: Sun Jan 18, 2009 8:21 pm Post subject: Tachometer

Why not use a Horizon Instruments Tach?  You can have it  set up any way you want it.  http://www.horizoninstruments.com/prod01.htm.   Many of the people with CJ6's that have an M14 engine have Horizon Tachs  installed.

 Dennis

 [quote]   ---

george(at)gesoco.com
Guest

Posted: Mon Jan 19, 2009 5:49 am Post subject: Tachometer

Mechanical tachs generally work on the speed of the camshaft. That is 50%

of the crankshaft speed. The only place that  the cam speed is available to

drive a tachometer on the M14 is at the center of the air start. The magneto

rotor is the only other part that rotates at 50% of the crankshaft speed.

There are many tachometers that run from magneto electrical pick up will

also work. Be wary of the ones that actually connect to the "p" lead as a

tachometer failure could result in a magneto failure.

	You could also have your Russian tachometer face remarked to actual

RPM instead of % RPM. 

George Coy

Coy Aircraft Sales

714 Airport Rd.

Swanton VT 05488

802-868-5633 off

802-363-5782 cell

george.coy(at)gmail.com

SKYPE george.coy



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mark.bitterlich(at)navy.m
Guest

Posted: Tue Jan 20, 2009 9:55 am Post subject: Tachometer

I agree with George that there is always risk involved when you start

messing around with P Leads and connecting anything to them.  If not

done with careful design and proper caution, hooking anything (else) to

the P Leads can also easily result in a massive increase in radio noise

as well.  That said, this model: HORIZON INSTRUMENTS MODEL P-1000 TACH

has worked extremely well in at least five M-14 equipped aircraft that I

am aware of, and allows you to totally remove the mechanical TACH

TRANSMITTER that attaches to the engine, which in my experiece tends to

have a rather poor track record for long term reliability.  



The P-1000 Tach also gives you a safety BENEFIT in that it will

instantly tell you if you have a failed mag.  I mean really... How many

of us fly along and check the mags while airborne?  This device will

give you an immediate indication of a mag failure, which is a lot better

than finding that out just before taking off when doing your usual mag

check.  In addition, it has engine overspeed LED's that will alert you

should your engine go over a certain "limit" speed.  And, it also

includes engine time recording, etc., etc.  This model includes an

internal opto-isolator design that makes the possibily of it causing a

mag failure to be extremely remote, although of course nothing is

impossible.  



Here is a place to read about it. Out of all the "P Lead" tachs, this is

the only one I would recommend.  Be advised of one big point though...

In every case where someone else installed one of these things on their

own aircraft, there has been a very real and noticable increase in "P

Lead" induced radio noise.  I have had to go back and rip out poor

wiring, and use high quality shielded wire and proper lead bonding and

grounding to deal with this, so it is best the wiring of this device to

an A&P or otherwise highly qualified Avionics type of guy. STRONG

emphasis on this.   



http://www.aircraftspruce.com/catalog/inpages/p1000digitaltach.php

Mark Bitterlich

N50YK



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HBaker

Joined: 16 Nov 2008
Posts: 119

Posted: Mon Jan 26, 2009 12:32 pm Post subject: Re: Tachometer

Thanks Dennis I have decided on the Horizon Instruments tachometer on the Moose, since I only need  the Tack, a lot simpler.

Thanks Henry

_________________
Currently building a Murphy Moose - any help would be appreciated.

Last edited by HBaker on Mon Jan 26, 2009 3:47 pm; edited 1 time in total

HBaker

Joined: 16 Nov 2008
Posts: 119

Posted: Mon Jan 26, 2009 12:33 pm Post subject: Re: Tachometer

What markings of the Horizon Instruments Tachometer is standard for the M-14? Green, Caution, Red (RPM's).

_________________
Currently building a Murphy Moose - any help would be appreciated.

HBaker

Joined: 16 Nov 2008
Posts: 119

Posted: Wed Jan 06, 2010 9:05 am Post subject: Re: Tachometer

Hi Mark



I have a electronics guy hooking up the Horizons tack that I purchased last year, We were going to wire it into the avionics switch,  to be turned on after we have started the engine and have switched to mags, because he heard the booster coil is hard on the micro-processor . any thoughts on this??



Henry

_________________
Currently building a Murphy Moose - any help would be appreciated.

mark.bitterlich(at)navy.m
Guest

Posted: Wed Jan 06, 2010 9:49 am Post subject: Tachometer

I have no personal experience with problems in this regard.  As in...

Booster coil energy damaging the Tach.  No one that I know of who has

installed this Tach has EVER had this problem.  But, he may know

something I do not!  Who knows?  



Keep this in mind if you will.  



The electrical path of the energy supplied by the booster coil for

starting, follows a completely different path than the energy that comes

from the mag AFTER starting.  This is important to understand, so let's

continue.  



The very only things that are used during starting in the mag are: 



1. A retarded rotor point that makes contact with the BOOST COIL energy

through a slip ring.  

2. The mag cap, where the spark plug wires actually connect.  



THAT IS IT!   Nothing else in the mag is used during starting except for

the mechanical parts that make the thing rotate when the engine turns. 



With a good system, you can actually start and run the engine with the

starting circuit alone.  I am not recommending that you DO this,

although I have for testing purposes.  



There is a very brief period of time during starting where the starter

button is pushed, the engine has started on the booster coil energy

firing the spark plugs, the mags are turned on (P LEADS BECOME

UN-GROUNDED) and there is spark energy from both the mag itself (going

to a DIFFERENT contact point on the rotor) AND the boost coil retarded

rotor point.  



So how is this going to impact the P leads and damage a Horizon Tach?  I

don't see any way that it could, except for one thing, shielding.  More

on that in a moment.  



Also, there is no electrical "surge" in these aircraft because there is

no collapsing inductive magnetic field pulse from an electrical starter.

But now we come to shielding.  



If you have bad shielding in ANYTHING... That means Booster Coil High

Voltage, it is ....in theory .....possible that it could get into the

main 28 VDC power source and cause damage to any kind of Avionics.  



That said, let's go in a different direction for a second.  The Horizon

Tach hooks to the P leads.  The P leads contain a TON of RF noise from

the mags.  That is why they are shielded.  However, the actual P leads

themselves... BOTH OF THEM... Run into this Tach.  It is entirely

possible for this noise energy to go into the Tach, and come back out on

the main 28 volt wiring that POWERS this Tach.  Now you have this crap

getting into everything.  Especially if you connect these wires to the

exact same circuits that are powering your RADIOS.  



I am not saying this will happen. The engineers who designed this TACH

just HAD to take great efforts to try and prevent this.  But I am saying

that more than one person has had significant noise problems when using

a Horizon Tach, and most ESPECIALLY with Becker Radios. Not ALL mind

you, but some.   



So, my thoughts are that if you are going to hook it up this way, it

would be wise to put an RF noise filter on the power leads to the

Horizon Tach.  Not to keep outside stuff from getting into the Horizon,

but to keep stuff in the Horizon from getting out and onto main aircraft

power wiring.  



This can be as simple as using a torroidal core with the power wires

wrapped through them several times.  Can't find one of those?  Go look

around for an old computer monitor.  Not the flat screen type, the old

big ones with a CRT.  Look at the cables going to it.  One of them will

have a big BULGE in the cable.  Chop this off and carefully slice it

apart.  Inside you will find a torroidal core with the wires wrapped

through it.  They put it there for the same reason I am suggesting

putting it on the Horizon Tach power leads.  You can also wrap the P

leads through one too. 



 



Mark 



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HBaker

Joined: 16 Nov 2008
Posts: 119

Posted: Thu Jan 07, 2010 12:16 pm Post subject: Re: Tachometer

Mark



    First , thanks for clearing up so many things . I  guess  maybe I should wire it straight in, to prevent it going to the radio circuit at all. I'll will talk it over with the avionics guy. 



Henry

_________________
Currently building a Murphy Moose - any help would be appreciated.

mark.bitterlich(at)navy.m
Guest

Posted: Thu Jan 07, 2010 2:26 pm Post subject: Tachometer

No problem.  Use a few toroids on the power leads.  Even if they are just plain ole donut types.  Your Avionics guys SHOULD know what I am talking about. 



Mark

 



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HBaker

Joined: 16 Nov 2008
Posts: 119

Posted: Thu Jan 07, 2010 6:52 pm Post subject: Re: Tachometer

Yes Mark, he knew exactly what you were talking about as soon as I mentioned it , me I never  had the foggy est  clue:oops:

_________________
Currently building a Murphy Moose - any help would be appreciated.

mark.bitterlich(at)navy.m
Guest

Posted: Fri Jan 08, 2010 12:34 pm Post subject: Tachometer

Nothing to be embarrassed about.  I do this kind of thing for a living. 



Mark



 



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