---------------------------------------------------------- Yak-List Digest Archive --- Total Messages Posted Mon 09/30/19: 4 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 09:01 AM - Re: Stock Nanchang Prop (Gary Luther) 2. 10:53 AM - Re: Re: CJ6 Heading Adjustments (Mark Bitterlich) 3. 11:11 AM - Re: Re: CJ6 Heading Adjustments (Mark Bitterlich) 4. 02:45 PM - In Search Of 2 Needle RPM Gauge For CJ6 (bmiles) ________________________________ Message 1 _____________________________________ Time: 09:01:30 AM PST US From: Gary Luther Subject: Re: Yak-List: Stock Nanchang Prop I have a set I took off of mine Jon. Give me a call On Sun, Sep 29, 2019 at 7:56 PM JON wrote: > Looking for a new or used prop for a stock CJ-6. Pass the word that is > like two. > > Jon Blake > saber369@comcast.net > > Sent from Xfinity Connect Application ________________________________ Message 2 _____________________________________ Time: 10:53:29 AM PST US From: "Mark Bitterlich" Subject: RE: Yak-List: Re: CJ6 Heading Adjustments Actually TTail, I must agree with Walt. In order to adjust a compass, you need at a minimum a north/south line, and for General Aviation typically an accurate compass rose. IE. You need an accurate physical reference to "swing" a compass. If you are only trying to check the accuracy of your compass it is commonly acceptable to use your GPS True heading, add or subtract Magnetic Variation (as you said) and then compare your compass reading with your GPS readings. If you have a WAAS GPS, or perhaps two built in GPS's this will work, but you have to be moving because GPS has to derive Heading from movement, and does not compute it sitting still. Thus if you fly anything but straight and level, GPS heading can also be skewed. Never-the-less, you can get a pretty good idea of your compass accuracy if you are flying straight and level and fly right along an Isogonic Line. With a calibrated North/South line and a calibrated Compass Calibrator it is possible to park an aircraft on that line, plumb bob it for alignment and using the calibrator fool the compass into believing any one of the 24 cardinal points and adjust N/S, E/W compensation magnets accordingly, and create a compensation card as required by the FAA. Very very few facilities have this device, although the military does. Even then, the North South line must be surveyed on a regular basis using something like a MC-2000. What is interesting is that by FAA Regs our compass systems or ... in most cases a simple magnetic compass... must have an up to date compass calibration card attached in plain sight. I've always laughed at this, mainly because FAA Inspectors have not got a clue in this regard. Supposedly completed by an A&P or better, just how was it done, and how does the FAA know it was not just made up and never done in the first place? Add to that what Walt said about a compass rose and not only painting one but to keep it accurate. Compass Rose's for many decades were a really big deal on military bases. So important in fact that no REBAR was allowed in the concrete that the rose was painted on. Why should be obvious, but suffice it to say there is natural magnetic deviation and then there is "local influence" and these are referred to as single and dual cycle errors. Bottom line, any ferrous metal around you, to include buildings, other aircraft, REBAR, etc., will also skew magnetic lines of flux, which throw the compass out of accuracy, thus why the Flux Valve Walt is referring to is generally put as far away from the engine as possible. So bottom line, "Swinging a compass" is no small matter, assuming you really want to do it right, and/or you want an accurate compass calibration correction card. Doing it on the ground requires special considerations and an accurate rose which is extremely hard to find, let alone construct. So in reality there is no way to get there from here and I would venture to say that most compass's in most GA aircraft fail to meet FAA mandated accuracy standards, the good news being they have no way to actually prove that! FYI, the majority of military aircraft today use an Embedded GPS Inertial Navigation System (or "EGI" for short) that derive Mag Heading using True Heading from the INS corrected for Mag/Var and tend to ignore the Standby Compass as regards accuracy. In the end, given all the very real problems involved, I would be tempted to calibrate a standby compass using GPS in flight, and if you have an older model flux valve system, well... good luck with that. You'll need a compass rose, and someone who really knows what they are doing, and a whole day doing it. Conversely, I have read about some of the brand new flux valves that compensate themselves with only a N/S, E/W physical alignment. In the end, it is highly unlikely that we will be doing any time/distance/speed navigation these days based on compass heading, ala Charles Lindbergh ... instead we just pretty much keep the line straight on the GPS. Mark -----Original Message----- From: owner-yak-list-server@matronics.com [mailto:owner-yak-list-server@matronics.com] On Behalf Of Ttail Sent: Sunday, September 29, 2019 9:40 PM Subject: Yak-List: Re: CJ6 Heading Adjustments The True heading hasent changed :) so applying the latest Mag var should result in an acceptable mag heading. In my part of the world the variation drift is pretty sedate. ________________________________ Message 3 _____________________________________ Time: 11:11:13 AM PST US From: "Mark Bitterlich" Subject: RE: Yak-List: Re: CJ6 Heading Adjustments And then there is this: https://www.faa.gov/documentlibrary/media/advisory_circular/ac_43-215.pdf -----Original Message----- From: Mark Bitterlich [mailto:markbitterlich@embarqmail.com] Sent: Monday, September 30, 2019 1:52 PM Subject: RE: Yak-List: Re: CJ6 Heading Adjustments Actually TTail, I must agree with Walt. In order to adjust a compass, you need at a minimum a north/south line, and for General Aviation typically an accurate compass rose. IE. You need an accurate physical reference to "swing" a compass. If you are only trying to check the accuracy of your compass it is commonly acceptable to use your GPS True heading, add or subtract Magnetic Variation (as you said) and then compare your compass reading with your GPS readings. If you have a WAAS GPS, or perhaps two built in GPS's this will work, but you have to be moving because GPS has to derive Heading from movement, and does not compute it sitting still. Thus if you fly anything but straight and level, GPS heading can also be skewed. Never-the-less, you can get a pretty good idea of your compass accuracy if you are flying straight and level and fly right along an Isogonic Line. With a calibrated North/South line and a calibrated Compass Calibrator it is possible to park an aircraft on that line, plumb bob it for alignment and using the calibrator fool the compass into believing any one of the 24 cardinal points and adjust N/S, E/W compensation magnets accordingly, and create a compensation card as required by the FAA. Very very few facilities have this device, although the military does. Even then, the North South line must be surveyed on a regular basis using something like a MC-2000. What is interesting is that by FAA Regs our compass systems or ... in most cases a simple magnetic compass... must have an up to date compass calibration card attached in plain sight. I've always laughed at this, mainly because FAA Inspectors have not got a clue in this regard. Supposedly completed by an A&P or better, just how was it done, and how does the FAA know it was not just made up and never done in the first place? Add to that what Walt said about a compass rose and not only painting one but to keep it accurate. Compass Rose's for many decades were a really big deal on military bases. So important in fact that no REBAR was allowed in the concrete that the rose was painted on. Why should be obvious, but suffice it to say there is natural magnetic deviation and then there is "local influence" and these are referred to as single and dual cycle errors. Bottom line, any ferrous metal around you, to include buildings, other aircraft, REBAR, etc., will also skew magnetic lines of flux, which throw the compass out of accuracy, thus why the Flux Valve Walt is referring to is generally put as far away from the engine as possible. So bottom line, "Swinging a compass" is no small matter, assuming you really want to do it right, and/or you want an accurate compass calibration correction card. Doing it on the ground requires special considerations and an accurate rose which is extremely hard to find, let alone construct. So in reality there is no way to get there from here and I would venture to say that most compass's in most GA aircraft fail to meet FAA mandated accuracy standards, the good news being they have no way to actually prove that! FYI, the majority of military aircraft today use an Embedded GPS Inertial Navigation System (or "EGI" for short) that derive Mag Heading using True Heading from the INS corrected for Mag/Var and tend to ignore the Standby Compass as regards accuracy. In the end, given all the very real problems involved, I would be tempted to calibrate a standby compass using GPS in flight, and if you have an older model flux valve system, well... good luck with that. You'll need a compass rose, and someone who really knows what they are doing, and a whole day doing it. Conversely, I have read about some of the brand new flux valves that compensate themselves with only a N/S, E/W physical alignment. In the end, it is highly unlikely that we will be doing any time/distance/speed navigation these days based on compass heading, ala Charles Lindbergh ... instead we just pretty much keep the line straight on the GPS. Mark -----Original Message----- From: owner-yak-list-server@matronics.com [mailto:owner-yak-list-server@matronics.com] On Behalf Of Ttail Sent: Sunday, September 29, 2019 9:40 PM Subject: Yak-List: Re: CJ6 Heading Adjustments The True heading hasent changed :) so applying the latest Mag var should result in an acceptable mag heading. In my part of the world the variation drift is pretty sedate. ________________________________ Message 4 _____________________________________ Time: 02:45:16 PM PST US Subject: Yak-List: In Search Of 2 Needle RPM Gauge For CJ6 From: "bmiles" Looking for a 2 needle rpm gauge for my cj6. The single needle gauge has smaller pins in the back and will not fit. Thoughts. Miles Read this topic online here: http://forums.matronics.com/viewtopic.php?p=491553#491553 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message yak-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/Yak-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/yak-list Browse Digests http://www.matronics.com/digest/yak-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.