Author Topic: Tachometers (Read 19613 times)

leshoman · « **on:** November 08, 2013, 07:15:40 AM »

I have been in question of my tach (s) for some time. Finally broke down and got a westach unit to read directly off the mag hoping it would be somewhat accurate. After some testing I again temporarily installed my high tech auto tach that runs off battery and spark plug wire. Had to temporary a 12 volt battery, in my jacket to power the thing. Results indicate the 3 tachs I have, the high tech digital, westach and the TTO, (similar to a tiny tach) all indicate almost identical up to 2,800 rpm. Above 2,800 the TTO reads low and the westach reads high. At full power level flight the hi tech reads 3,640, TTO reads 3460 and the westach reads 4,400. More to come as testing and calibration continue. I am going to trust the hi tech unit at this time.

Steve · « **Reply #1 on:** November 08, 2013, 08:08:16 AM »

Les:
There is an optical tach included with the Wood Bar Dyno package... Check with Joe Spencer on the accuracy... You might get Joe to split it out of the kit and send it your way for bench marking...

Have you considered Steve Bennett's method of installing the spark driven Tach's on a mag?:

http://www.greatplainsas.com/ittach.html

My personal experience with Tiny Tach's has been good... I run the impulse lead away from other wires or grounds over the top of F1 thru the windscreen and go across space to the mid span of a plug wire with one or two wraps around it...

Steve

leshoman · « **Reply #2 on:** November 08, 2013, 09:05:37 AM »

Steve
I have tried about 5 different methods and the one based on the great plains aircraft is the one I am using now. I ran the Tiny tach and the TTO tach for while to compare them but both had similar readings so went back to just the TTO.

Steve · « **Reply #3 on:** November 08, 2013, 09:39:18 AM »

Les:

I think this extract from the Bennett Install spec is where you are at "Note: spark plug wires that are not shielded cannot be touching each other. The secondary false signal will cause the tach to read improperly. Likewise, when going through baffling, the wires must not touch the pick up spark plug wires. Wires must be insulated from the baffling also as the baffling will cause a false signal to be transmitted."

You may be getting signals from your mag kill switch lead / switch or even the header tank - try mounting the TT readout head out on the top of the engine...

Steve

leshoman · « **Reply #4 on:** November 08, 2013, 09:47:27 AM »

Steve
My mag is in the cockpit, between rudder pedal area. The two plumb wires are on opposite sides of the mag and one of left goes to hole in firewall on left and one on right goes thru hole on right, not anywhere near each other. The TTO tach wire only nears spark plug wires as it goes thru the housing at mag. Mag wires to westach leave mag and run direct to tach. other than steel in fuselage it is clear of other wires. I will be working on this more this weekend.

Steve · « **Reply #5 on:** November 08, 2013, 12:34:05 PM »

Les:
I have 2 thoughts:

1) The plug wires are talking to each other thru the firewall metal or engine case... To test get a long plug wire and run one lead over the firewall thru the windscreen...

2) Here's the way my grounding is laid out... The firewall is fixed to the tube structure with 5 metal clamps... The engine case is bonded to a central ground hub on the footwell diagonal tube with a dedicated braided ground wire... All ground wires in the cab run to that central ground hub...
Steve

leshoman · « **Reply #6 on:** November 08, 2013, 01:16:16 PM »

Steve
I am going to put my tiny tach back on and run it all exterior and keep it well away from the firewall and other wires. Will also do the same with the TTO tach. Not much choice with the westach it is about as straight and clear as possible. The Hi Tech tach is external wiring up to spark plug wire and should not be getting any interference. Let you know results as the weekend progresses.

Steve · « **Reply #7 on:** November 08, 2013, 01:46:33 PM »

Les:
I may be covering old territory for you but it's worth putting out one more time in this type of discussion... The tachs that run from the mag primary can sometimes fail and ground the mag - often the failure appears as an intermittent engine miss first and that's a good thing if you have provided a way to disconnect the tach in the cab... Look around the net on this - there may be a best practices way to provide the tach disconnect...
Steve

leshoman · « **Reply #8 on:** November 08, 2013, 02:42:30 PM »

Steve. Been there do that. Long years ago. Had dual mags I have a 1/4 amp in line fuse on the westach from mag

Steve · « **Reply #9 on:** November 08, 2013, 03:23:20 PM »

Les:
For some reason both Spruce & Wicks will answer a search argument for the #381 fuse holder but not show it in inventory - curious... Anyway, I know you are going to get to the bottom of the failure - almost everything has a reason & work-around... I've begun to wonder if these New/Old mags are starting to radiate a lot of EMF from the coil...
Steve

leshoman · « **Reply #10 on:** November 08, 2013, 03:47:37 PM »

Well I would say that may be a possibility except I have the same problem on the 12 volt auto system on LEU-81and LEXL B-69, mag type. I talked to Scott Cassler and understand the mags are brand new, from the factory. As we have been talking today I believe I will also try a better ground between engine and airframe.

rockiedog2 · « **Reply #11 on:** November 08, 2013, 06:16:36 PM »

hi guys
i had the westach on mine for a while and it started an unexplainable miss which ceased after removing the westach which was wired in the P lead to the switch. ive sworn off that kinda setup. i didnt have a fuse and dont know how thats wired but wonder if it blows i guess that makes the mag hot at all times right? well that sounds good...all i know is after a few engine stopages i realize it happens so fast there's no catching it with some sort of planned reaction. but i suspect yall already know that...
the TTO lasted i think it was about 10 or 15 hours for me. my original tiny tack went almost 175 hours. am now running a commercial version of the tiny tack which is doing ok at about 40 hours. the TT tech guy told Sam to only wrap it one time.
Les i will get the test club setup out to you. curious to knwo what yours pulls

Joe

leshoman · « **Reply #12 on:** November 09, 2013, 06:47:38 PM »

Well after a productive day of testing tachs I can say the following.
If engine is making noise it must be running. More noise more RPM, less noise less RPM.
I added a ground from fuselage to engine.
set the tiny tach up and run exterior to aircraft and wrapped it around plug wire adjacent to plug and ground.
The TT (Tiny Tach) and the TTO (trail tech, similar to tiny tach) read the same within about 5 or 10 rpm except for some reason the tiny tack was reading 1/2 the RPM, but both agreed thru out the RPM ranges.
The HTDT, (high tech digital tach) agreed with the WT (westach) and the TT and TTO up to about 2,800 RPM, then things got strange.
Full power in level flight resulted in 3,600 on the HTDT, 3480 on TT and TTO and 4400 on the WT, my hall effect meter, which seems to agree with the GPS in two direction flight and averaging was showing 63-65 mph.
Pointed down hill at full power till HTDT read 3,700, TT and TTO read 3,600, WT read 4400.
At 3000 on the TT and TTO, HDTD 3400, WT 4000.
I have concluded the WT readings are totally worthless.
I suspect the HTDT is most accurate but it is very possible all are off.
If it was not for the high fuel consumption and working with Frank to get a new prop for this thing I would not worry about this stuff and throw the tachs away.
Back to the Drawing board.
Got some good video later in the day.

Steve · « **Reply #13 on:** November 09, 2013, 07:26:02 PM »

Les:

Are you using the TT- model 2A?... Spec sheet attached:

Steve

weasel · « **Reply #14 on:** November 16, 2013, 09:20:03 AM »

As a data point I had trouble with my standard version Tiny Tach when I first installed it.

Running on a 4 cyl Cassler VW with a slick mag.

I messed around with the pick-up lead and the final set-up that works for me is:

Make certain there is no exposed antenna area prior to wrapping around the Ignition lead.
Only wrap it 1-2 turns
Cut off excess wire

Works great. Verified accuracy with an optical tach.

This one