KR> Tach drives
John said: "use a tooth counter sender off the ring gear" >From observations that is the hardest style to have as a primary or secondary due to the bracketing etc... to keep the air gap correct. Engine vibration tends to knock that one out of reading. Volvo and Chrysler both have used that method as an engine speed sensor, and wear on the ring gear from starters, dirt and such effect it. The best solution if not the coil attached tach, is the Tiny Tach that uses an inductive pickup off of one plug wire. We used these pickups with our Sun Scopes for years with no trouble. It clips around the plugwire and reads the pulses to a digital display. Very simple and reliable. In practice I have not seen any tach failures, and those reported that did fail, did not cause a total ignition failure, just quit reading. Diodes are a couple of bucks each, so applying 2 in each line insures against total failure, and should last a lifetime of flying anyhow. Colin Rainey Independent Loan Officer Branch 2375 Apex Mortgage Company 386.615.3388 Home Office 407.739.0834 Cell 407.557.3260 Fax brokerpi...@bellsouth.net
KR> Tach drives
Sorry Colin, yet again I respectfully disagree :-). Diesel engines often use this method because they don't have coils. They are common on marine installations and many trucks and go for years without problem. Even the Thielert diesel in the demonstration Cessnas use them. They rely on the mass of the steel in each tooth to disturb a magnetic fieldthey are not optical, dirt is irrelevant (especially in our application) and air gap is not critical although the smaller, within limits, the better. I think you might be confusing them with Hall Effect sensors that rely on a magnet being set in the flywheel to create a current in the sender and which are often used on modern cars for electronic timing purposes. A short in your tacho can take your primary to earth irrespective of the existence of diodes and I am sure there are automotive examples that you may have not observed. Tiny Tachs are notoriously unreliable, difficult to calibrate, do not read accurately from suppression leads and can cause radio interference by transporting a sample of the ignition voltage through the firewall. Check the archives on this subject. Finally WW recommends tooth counters and that is good enough for me. I wouldn't bank on a lifetime of flying on a couple of two dollar diodes. John Martindale 29 Jane Circuit TOORMINA NSW 2452 AUSTRALIA phone: 61 2 66584767 (H) 61 2 66869075 (W) mobile: 0403 049990 email:johnja...@optusnet.com.au web: www.members.optusnet.com.au/johnjanet/Martindale.htm - Original Message - From: "Colin Rainey" To: "KRnet" Sent: Thursday, October 12, 2006 1:19 AM Subject: KR> Tach drives > John said: > "use a tooth counter sender off the ring gear" > >>From observations that is the hardest style to have as a primary or > secondary due to the bracketing etc... to keep the air gap correct. Engine > vibration tends to knock that one out of reading. Volvo and Chrysler both > have used that method as an engine speed sensor, and wear on the ring gear > from starters, dirt and such effect it. The best solution if not the coil > attached tach, is the Tiny Tach that uses an inductive pickup off of one > plug wire. We used these pickups with our Sun Scopes for years with no > trouble. It clips around the plugwire and reads the pulses to a digital > display. Very simple and reliable. In practice I have not seen any tach > failures, and those reported that did fail, did not cause a total ignition > failure, just quit reading. Diodes are a couple of bucks each, so applying > 2 > in each line insures against total failure, and should last a lifetime of > flying anyhow. > > Colin Rainey > Independent Loan Officer > Branch 2375 > Apex Mortgage Company > 386.615.3388 Home Office > 407.739.0834 Cell > 407.557.3260 Fax > brokerpi...@bellsouth.net > > ___ > Search the KRnet Archives at http://www.maddyhome.com/krsrch/index.jsp > to UNsubscribe from KRnet, send a message to krnet-le...@mylist.net > please see other KRnet info at http://www.krnet.org/info.html
KR> Tach drives
John said: A short in your tacho can take your primary to earth irrespective of the existence of diodes and I am sure there are automotive examples that you may have not observed. Tiny Tachs are notoriously unreliable, And so the story goes that as many people as we have here on the net, we have experiences that reflect negatively on one type system or another, for virtually every part of the plane. I have never seen a tach drive short a coil down, but have seen starter rings that were chewed and damaged due to starter wear, and these would cause an erratic signal to your tooth counter system. No I am not referring to a Hall Effect switch. If going to the crank for a signal, I would use either the internal method found on many 4 and 6 cylinder GMs or the external mounted to the back of the balancer. MSD makes a universal kit for crank trigger that can be retrofitted onto virtually any engine. Every system will have its strengths and weaknesses. Some guys are using points due to simplicity and low voltage requirements. I find that medieval when systems like one netter is using, the motorcycle CD system (I believe Serge is, sorry if I got it wrong) that is very simple and very reliable. Everyone will have to find their own comfort level with the system they choose, and compromises made with each design. No system is 100% failsafe. Especially in aircraft where they typically do not shim starters and an experienced ear can hear the starter clashing in the ring gear, I would not run a tooth counter, unless you like the same unreliability you say the Tiny Tach has. Colin Rainey brokerpi...@bellsouth.net
KR> Tach drives
At 12:45 PM 10/13/2006, you wrote: >No system is 100% failsafe. >Especially in aircraft where they typically do not shim starters and an >experienced ear can hear the starter clashing in the ring gear, I would not >run a tooth counter, unless you like the same unreliability you say the Tiny >Tach has. >Colin Rainey +++ So run a remote, optical, digital tach rpm checker that could be placed on top of the instrument panel and is powered by a 9 vdc battery. It's quite accurate, is connected to nothing, and is not that expensive when all things considered. Climb out (to see what power I'm getting) and cruise are really about the only times I check my tach anyway. How about one of you electronic wizards finding a way to run an optical sensor to a readout on the dash. Larry Flesner
KR> Tach drives
Hi Colin I agree that chewed teeth could send the signal wonky but surely you would replace that sort of damaged part before flight. In any case that is not really the issue. A wonky signal to the tacho from a tooth counter will never kill your ignition as it's completely independent of it. Using a tacho with or without diodes off the coil primary will always carry that risk even it is is small as you correctly say. I like medieval points also because I understand them and can easily replace them in the field at remote Australian airports if I need to. Each to his own circumstance I guess. Long live the diode :-) John Martindale 29 Jane Circuit TOORMINA NSW 2452 AUSTRALIA phone: 61 2 66584767 (H) 61 2 66869075 (W) mobile: 0403 049990 email:johnja...@optusnet.com.au web: www.members.optusnet.com.au/johnjanet/Martindale.htm > And so the story goes that as many people as we have here on the net, we > have experiences.
