Old-school Ball Magnetic Compass Question

[Topaz]

I've said my piece. Don't make it personal. Best of luck to you.

 

[wsimpso1]

How about a light weight LIDAR setup? I know of a project...

It, like you, must have some sort of reference to the horizon. Usually a laser ring gyro that is set while you are on the ground.

 

[TFF]

If one flies an ultralight at bare minimum Class G airspace of one mile Vis and clear of clouds below 1200 ft you are playing with fire. E airspace will have you at standard distance from clouds, and really should be a personal minimum for any UL flight. If you are pressing weather, you will loose without in IFR training. People who fly ULs places have the time to wait for nice weather and don’t attempt those flights without it. They are not anytime anywhere aircraft. Pushing anything less than the minimums will catch up with you faster than you can learn to be safe on your own.

 

[J.L. Frusha]

It, like you, must have some sort of reference to the horizon. Usually a laser ring gyro that is set while you are on the ground.

Only if it needs to know its own location. As a means of scanning ahead and using the Imaging for a display, there is no need for the gyro.

My goal is something simpler that can merely display the area forward, including any detectable horizon. Like watching TV, I can look and see the horizon in the distance in panoramic views, as well as determine the orientation of the 'camera' in comparison to the horizon. Under certain circumstances, a means of seeing forward through, say, a ceiling that has dropped, or where darkness has fallen in circumstances beyond the pilots control.

Take for instance the situation where an unpredicted wind change has blown the ultralight off course, or delayed the landing, or even having to fly around a wildfire, rather than through the area that emergency aircraft are using. **** happens, even to those perfectionists with all their ratings, after all, I am specifically looking for a way to be safer in an ultralight, in extenuating circumstances.

Being able to see is more important than ordinarily unnecessary weight of a gyro-driven artificial horizon for an ultralight.

 

[Dana]

As a student pilot, my instructor told me if I got caught above a cloud layer, trim for approach speed and decent on a 180 degree heading, sit on your hands, and keep the heading with the rudder until you break out the bottom. Compass is most sensitive at the 180 degree heading.

I don't know why it should be more sensitive, but flying 180° (or 360°) eliminates the turning and acceleration errors that are more significant on an E-W heading. (corrected)

Of course if you know there's enough ceiling below the cloud and your airplane is capable, you can just spin down through it. I had to do that once.

To the OP, if you want a cheap attitude indicator, buy or build a Stratux with AHRS and hook it up to Avare on your phone. Avare's PFD screen takes the info from the AHRS.

 

[J.L. Frusha]

Avare

Thank you. I have never heard of Stratux, or the Avare app.

 

[Pops]

I don't know why it should be more sensitive, but flying 180° (or 360°) eliminates the turning and acceleration errors that are more significant on an E-W heading.

Of course if you know there's enough ceiling below the cloud and your airplane is capable, you can just spin down through it. I had to do that once.

To the OP, if you want a cheap attitude indicator, buy or build a Stratux with AHRS and hook it up to Avare on your phone. Avare's PFD screen takes the info from the AHRS.

The needle is most sensitive at 180 degrees and least at 360 degrees.

 

[jedi]

I don't know why it should be more sensitive, but flying 180° (or 360°) eliminates [wrong - see below] the turning and acceleration errors that are more significant on an E-W heading.

Turning errors are a maximum on a 180 or 360 heading.

Acceleration errors are a maximum on an east or west heading.

Flying a heading of 180 degrees in the Northern Hemisphere maximizes the turning error to the pilots advantage. The turning error shows a much larger turn than the aircraft actually makes. When flying an ILS to R/W 18 use of the mag compass can make the approach much smoother. Also when headed any heading near 180 degrees in the approach proceedure is the best time to check and reset, if necessary, the DG.

There is a lot of misinformation in this thread! Get out the books and read. One reference is given in Post # 56.

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/FAA-H-8083-15B.pdf

Page 5-12

"inertia cause magnetic compass errors when accelerating and decelerating on Easterly and westerly headings."

" false southerly turn indication." "false northerly turn indication."

IMHO their explanation is not as clesr as it should be but it is not wrong.

Key words to remember are Accelerate North (turn indication) Decelerate South (turn indication) regardless of heading East or West.

Turning near North the compass lags. Turning near South the compass leads the turn.

These errors are reversed in the Southern latitudes. The amound of the error increases as the latitude increasses numerically.

 

[Dana]

Turning errors are a maximum on a 180 or 360 heading...

Flying a heading of 180 degrees in the Northern Hemisphere maximizes the turning error to the pilots advantage. The turning error shows a much larger turn than the aircraft actually makes.

Hmmm, you're right and I was wrong (been a long time since ground school, and almost as long since I used a compass as anything other than a cross check to pilotage). Had to go back and visualize the angles, now I see what Pops meant about "more sensitive"

 

[Dan Thomas]

Yes, and I do not profess to know it all and that is why I said, "If i remember correctly....."

The older versions of the Instrument FlyingHandbook((FAA H--8083-15B) had more details on the operation of the self-erecting mechanism and the errors. If you need more information I can see if I can find my old copy that gave more detail on the errors. You could with your background study the system and see for yourself why the error cancels out in a 360 degree turn. If you want to check it out in flight you need a fast airplane. It is difficult to see the error in any turn slower than 350 knots.

https://www.faa.gov/regulations_policies/handbooks_manuals/aviation/media/FAA-H-8083-15B.pdf

Page 5-19 The Attitude Indicator
"There is also a possibility of a small bank angle
and pitch error after a 180° turn. These inherent errors are
small and correct themselves within a minute or so after
returning to straight-and-level flight."

Dan,

I would like to hear your comments on the following. Are you currently teaching as a CFII?
Pops said:

You had a good CFI. Every pilot should know this but most do not. I try to spread the word but it is hard to teach those who already know it all.

I quit instructing 15 years ago when the maintenance duties became too much. I still taught the Aircraft Systems course in the college, though, until I left in 2011. Taught it for about 12 years, and covered gyro operations in every semester I taught it. I had attitude and heading indicators, turn coordinators and turn-and-bank instruments all opened up so one could see the operation of the stuff inside them, including the pendulum vanes in the attitude indicator that are fooled by a sustained turn. The attitude indicator has no sense of direction whatsoever, and the FAA's example of a 180-degree turn is an example of a turn sustained just long enough to see the effect of it on those vanes, causing the instrument to read a bit off once you straighten out. A rate-one turn takes one minute to make that 180-degree turn. A steeper turn takes less time but the turn's centrifugal forces are larger and can still get the gyro case tilted somewhat. Continuing the turn to 360 degrees cannot fix it. Turning the opposite direction will pull it back, but by the time you've done that you may as well have just flown straight for a minute and the thing would have fixed itself anyway.

Rent an airplane with a full panel and go play with it and see if a 360-degree turn leaves no error like a 180-degree turn does. You won't find it. Both will leave the error, and the 360-degree turn will leave a bigger error.

I am a Canadian AME. No, not a doctor. An Aircraft Maintenance Engineer, the approximate equivalent of an A&P-IA. Unlike the US, formal training is required here; apprenticeship time alone will not get that license. The equivalent of two years' formal study is required, and a total of four years apprenticeship. If the study is done at an "approved" school, some of that time counts against the apprenticeship. If it's through an "acceptable" training program, the full four years must be done, with a minimum of 150 hours per month, for a total of 7200 hours of apprenticeship. Then 70% of the tasks applicable to the license being applied for must be documented and signed off by a supervising AME. Then exams must be written. I wrote ten exams; they have since consolidated them down to about four. And again, unlike the US, Canada has no books available that have all the possible questions and answers in them; one has to actually know the subject, not just memorize the stuff enough to get past the exams. Here's what we face:
Study and Reference Guide - "M" Rating Technical Examinations

Section 28 covers instruments and instrument systems, including gyros.

The Commercial and IFR groundschools also cover instruments and gyros and their quirks.

It's not as if I don't know what I'm talking about here.

Pops had the right training. A non-IFR pilot caught above an overcast can be in serious trouble. Getting into the cloud and losing sight of the ground is a serious thing. Your brain has, ever since you were born, been getting cues from your inner ear and your eyes, among others, and when the eyes become useless the inner ear signals can fool the brain into thinking that the airplane is turning when it's not, or that it's flying straight when it's turning. People who have never been put under the hood or into cloud don't have a clue about this. They tend to dismiss it. But those sensations are powerfully real, and they have killed many a VFR pilot. Setting up a slow descent, no turns, and keeping it straight with the rudder only is a standard technique. Sometimes the 180-degree setting isn't possible in rougher terrain that isn't lined up north-south. Descending in a turn is asking for a spiral dive, and that is almost guaranteed to kill you.

I remember the first time I was put under the hood. My first IFR lesson. I had earned a PPL more than 27 years before that. Thought it would be a piece of cake. Put the foggles on, and the instructor told me to maintain the current heading and altitude. So I did, but it was getting really difficult, airplane didn't want to cooperate. The instructor took the foggles off and I saw that I was in about a 70-degree bank. See, altitude and heading are only part of it, and this exercise was to show just how quickly the thing gets out of control of the untrained pilot. The attitude indicator is the primary IFR instrument, and you keep coming back to it constantly while scanning all the other instruments. Everything has to add up; if some instrument is giving information that doesn't line up with all the others, it must be eliminated as untrustworthy. Even the tachometer is part of the scan. The whole panel, and the training, is designed so that the loss of one or two instruments isn't fatal. It has to be that way. Stuff does fail, and Murphy ensures that it fails at the worst possible times. In training we were regularly subjected to partial-panel work, sometimes down to nothing but the TC or turn-and-bank, and airspeed. And the mag compass, of course. And the mag compass is no good as an attitude indicator.

 

[Dan Thomas]

In a way, you're both correct and incorrect. I'm looking for a solution to problems I've encountered, regardless, and, yes I HAVE had aviation weather. Been a while and I could use a refresher course, but no prediction is ever 100% accurate. Pop-up storms happen.

You didn't get enough aviation weather. Maybe not recent stuff either.

It's not hard to read the stuff and see the possibilities of stormy weather. Thunderstorms need three things: a steep lapse rate, moist air, and some means of lift: heated ground, or orographic lift, the lift that occurs when the flowing air encounters hills and mountains, or frontal lift, especially cold fronts, and especially rapidly-moving cold fronts. They wedge under that warm moist air and hoist it aloft, and create a terrific lapse rate. You don't want to be flying anywhere near a fast-moving cold front; it generates a squall line, a line of nasty thunderstorms and wicked winds that eat airplanes for breakfast. Tornadoes, too.

The lapse rate we normally get from the FD charts; any more than a two-degree C drop per thousand feet can encourage thunderstorm formation. So if the FD chart (upper winds) shows that the temp at 6000 feet is 12 degrees and the temp at 12,000 is zero, no storms are likely at all. If the temp at 12K is -4, though, watch out. And the moisture in the air is shown by the spread between temperature and dewpoint; if they're close, and the lapse rate is steep, storms are likely, especially if there's any thermal or orographic or frontal lift. If the the dewpoint is far below the temp, not much worry. Too dry. That thunderstorm needs moister air, since part of the energy that builds that storm into the monster it becomes is from the water vapor condensing back into water, and releasing the heat that turned it from water to vapor in the first place. That heat accelerates the upward building of the storm.

Then the GFAs show the isobars (lines of equal pressure); if they're close, wind is the deal. If they're far apart, calmer. If the GFA for six hours from now has the isobars close, maybe don't stay up too long. If there are fronts approaching, especially cold fronts, go home. Wind and storms possible.

There is really no unpredicted weather unless the forecasters and their computers really messed up. Aviation weather forecasters have to get it right. They have airline pilots relying on them for the right stuff. They have thousands of paying customers that expect safety. All of that information is available to every pilot, and there's no excuse to get caught in bad weather.

 

[wsimpso1]

Thank you. I have never heard of Stratux, or the Avare app.

Not legal for IFR, but in an emergency, Stratus or Stratux has ADHR and drives a display with all the bells and whistles. Stratus hooks to iPad/iPhone and ForeFlight. Stratux hooks to many Electronic Flight Bag software, IOS or Android, with Avare being freeware that runs on both platforms. The display can be adjusted to give in-flight traffic, weather, airport weather, etc. It can be a big help on X-Country flight.

Stratus/Stratux run on their own rechargeable battery, has a four channel GPS receiver, and an electronic gyro all built right in. Stratus costs several hundred dollars, Stratux costs around $200 assembled, less if you are willing to assemble it yourself. If you use Avare, throw them a few bucks every three months to keep the servers running. The gyro you keep trying to avoid? It IS inside the box because we do not have other ways to do all this. We need to gyro platform...

I am with the other folks. Part 103 operators should avoid IMC like it will kill you right now, because it will. Tangling with Instrument Meteorological Conditions without a bunch of training and practice typically turns into Loss of Control in less than a minute. If you are lucky, you pop out without losing the wings to overspeed, and you recover. If you are not lucky, maybe you can still deploy the ballistic parachute. There are speed and bank limits on the 'chute too.

Even with the ADHR and display, how do you practice IMC ops Part 103? Single seat, right? Even if you have lots of training and practice with a safety pilot on a regular basis, trying to keep it greasy side down with a tablet already configured before entering IMC is a day that turns what hair you have white. Really.

Billski

 

[J.L. Frusha]

I did say I could use a refresher course. I'm quite certain things have changed considerably in 40 years. That said, down here, the rule of thumb is:
A: How's the weather?
B: ____________________ (current weather report)
C: Wait a while, it'll change.

If weather was really so predictable, stuff like last years polar vortex/'Great Texas Snowpocalyse' would have had more advanced warnings to prevent the loss of life that occurred. The Biden Administration seriously exacerbated things by shutting down natural gas fueled generation capacity (for 'green' reasons) at a crucial moment in time.

Personally, we lost plumbing all the way out to the meter and, because we're in a house built on piers, insurance never paid-up, while FEMA is a cluster-****.

Good thing I have a friend who is a plumber AND needed to get away from the place he lives for a couple of days. He even provided almost all of the materials, parts and tools to repair our plumbing.

 

[jedi]

Rent an airplane with a full panel and go play with it and see if a 360-degree turn leaves no error like a 180-degree turn does. You won't find it. Both will leave the error, and the 360-degree turn will leave a bigger error.

This is off the thread topic but I think it is important to present conflicting opinions to possibly correct the record. I am not alone in my opinion.

The following reference is a more complete discussion of Attitude Indicator gyro errors. It is a good reference for many errors associated with the older mechanical gyro attitude indicators. I have only quoted the section referenced in prior posts about the turn errors. You may find the discussion of other errors also of interest.

attitude indicator (artificial horizon)

"Errors in both pitch and bank indications occur during normal coordinated turns. These errors are caused by the movement of the pendulous vanes by centrifugal force, resulting in the precession of the gyro toward the inside of the turn. The error is greatest in a 180° steep turn. If, for example, a 180° steep turn is made to the right and the aircraft is rolled out to straight-and-level flight by visual references, the miniature aircraft will show a slight climb and turn to the left. This precession error, normally 3° to 5°, is quickly corrected by the erecting mechanism. At the end of a 360° turn, the precession induced during the first 180° is cancelled out by precession in the opposite direction during the second 180° of turn. The slight precession errors induced during the roll-out are corrected immediately by pendulous vane action."

Dan, please comment. Do you disagree with this source?

The intent is not to discredit you. I make errors too. The object is just to set the record straight so as to not propogate misunderstanding. These are obscure fine points that most pilots do not need to know. That is why the revised manuals no longer go into that level of detail. However, if I am teaching the errors I need to teach the facts correctly. You should too. I accept that you are no longer actively teaching as CFII, neither am I but I would if I had the need.

 

[jedi]

I am with the other folks. Part 103 operators should avoid IMC like it will kill you right now, because it will. Tangling with Instrument Meteorological Conditions without a bunch of training and practice typically turns into Loss of Control in less than a minute. If you are lucky, you pop out without losing the wings to overspeed, and you recover. If you are not lucky, maybe you can still deploy the ballistic parachute. There are speed and bank limits on the 'chute too.

There is no substitute for training and knowledge but if you are scud running and know what you are doing it is much safer in an Ultra Light than in a faster, cleaner airplane. One mile clear of clouds at 300 feet AGL is much safer and more legal in an ultralight than it is in a Bonanza. Let's tell it like it is.

I want to know why you think a powered paraglider in a farmers field below 300 feet AGL with a mile visibility is a bad idea. The pilot can see obstacles three away minutes in any direction and their is no danger to IFR traffic. My third most memorable approach was in a powered paraglider. I was VFR on top at 300 feet AGL and landed next to the white pickup in the green field. The next most interesting approach was a Cat II go around at 50 feet in clear skies and unlimited visibility. The control tower was in clear view but no runway in sight.

Did you ever notice what wind and weather it takes to ground the birds?

 

[Dana]

Stratux hooks to many Electronic Flight Bag software, IOS or Android, with Avare being freeware that runs on both platforms.

Avare is Android only.

If weather was really so predictable, stuff like last years polar vortex/'Great Texas Snowpocalyse' would have had more advanced warnings to prevent the loss of life that occurred.

When weather is on the edge, it's hard to predict exactly how it will go, or whether/when the precip will change from rain to snow or vice versa, but you can bet nobody was predicting good VFR weather that day.

There is no substitute for training and knowledge but if you are scud running and know what you are doing it is much safer in an Ultra Light than in a faster, cleaner airplane. One mile clear of clouds at 300 feet AGL is much safer and more legal in an ultralight than it is in a Bonanza. Let's tell it like it is.

I want to know why you think a powered paraglider in a farmers field below 300 feet AGL with a mile visibility is a bad idea. The pilot can see obstacles three away minutes in any direction and their is no danger to IFR traffic.

Quite true; you have a lot more time to think about things, and if it gets really bad you can land an ultralight almost anywhere. A PPG is unique, in that it is completely stable, let go of the brake handles and it stays upright whether climbing or descending.

I remember one memorable flight in my Kolb to a fly-in party about 10 miles from my home field; it was maybe 2 miles viz, 400' scattered, 1000' broken, on the edge of a coastal fog. No problem... but there was always an out by heading inland. I wouldn't have attempted the same flight in a faster airplane. My biggest worry was actually carb ice.

 

[Dan Thomas]

"Errors in both pitch and bank indications occur during normal coordinated turns. These errors are caused by the movement of the pendulous vanes by centrifugal force, resulting in the precession of the gyro toward the inside of the turn. The error is greatest in a 180° steep turn. If, for example, a 180° steep turn is made to the right and the aircraft is rolled out to straight-and-level flight by visual references, the miniature aircraft will show a slight climb and turn to the left. This precession error, normally 3° to 5°, is quickly corrected by the erecting mechanism. At the end of a 360° turn, the precession induced during the first 180° is cancelled out by precession in the opposite direction during the second 180° of turn. The slight precession errors induced during the roll-out are corrected immediately by pendulous vane action."

Dan, please comment. Do you disagree with this source?

If it's true, I cannot see how continuing the turn for another 180° would cancel out the errors. That attitude indicator has absolutely no sense of direction. None. Its gyro spins about a vertical axis, the same axis the airplane turns around, and so it only responds to roll and pitch. Those pendulous vanes pull to the outside of the turn, any coordinated or skidding turn, and cause error, and they don't have any sense of direction either. They only respond to centrifugal force and gravity. The longer they are displaced, the more error they induce.

This wouldn't be the first time the FAA has gotten things wrong in its textbooks, and others---people who have never fooled with this stuff---pick them up and publish them. There are errors in aerodynamic theory in the FAA stuff, too, such as the equal-transit-time theory of airflow over and under a wing. This was disproved many decades ago but it persists in texts and groundschools anyway.

Maybe someone can show me the physics at play that make the second 180° of a turn fix the errors of the first 180°. I would appreciate it. I could see a 180° turn in the opposite direction fixing it, but that is not a 360° turn.

 

[jedi]

Fly VFR. Flights through anything but thin layers were found to destroy airplanes and kill people.

Aneroid airspeed and altimetery were around, but blind flight was made possible by Sperry building gyroscopic instruments for turn rate and heading, and attitude, adding them to the existing instruments. Instrument navigation was by compass, time and airspeed, until radio nav aids were invented still later.

One maneuver that is a pretty reliable way to descend through an undercast without gyroscopic instruments is to spin the airplane until it comes out the bottom of the clouds, then recover from the spin. If you know spins and know you have enough clear air under the clouds it can work. Story is it was used in The Great War both to evade an attacker and to get below a deck.

In the airmail days, they had needle, ball, and airspeed, but not precision approaches. If the clouds were low, fuel was low, and you got caught on top, you ran the ship out of fuel out in the country someplace, spun it, and abandoned it. You would come down under parachute, and the fuel less airplane would spin down and crunch nearby. You survived and the mailbags were retrieved from the wrecked airplane and continued their trip. Story is that Lindberg even did that.

The spin works because drag on the airplane is huge and gravity is straight down, so all velocity except straight down goes away and bird spins down at low airspeed. Fast enough to kill you if you are still on board, but slow enough that airmail bags survive. And usually no fire because the fuel is gone and the engine is cold by the time of the crunch.

All true. But, (that infamous but) if you like you can design the machine to do better. Reference the paraglider discussion above.

Quite true; you have a lot more time to think about things, and if it gets really bad you can land an ultralight almost anywhere. A PPG is unique, in that it is completely stable, let go of the brake handles and it stays upright whether climbing or descending.

And if you would like to make Henryk happy fly a Kasper wing and there is no need to do that stall spin thingy thru the undercast. Just park in a vertical mush and if you see the ground land. If you don't see the ground brace for the crash because you are going to land anyway.

OK, Henryk. Post the video link here;




Drag is a wonderful thing. Without drag the parachute that you trust would let you down.

 

[Dan Thomas]

If weather was really so predictable, stuff like last years polar vortex/'Great Texas Snowpocalyse' would have had more advanced warnings to prevent the loss of life that occurred. The Biden Administration seriously exacerbated things by shutting down natural gas fueled generation capacity (for 'green' reasons) at a crucial moment in time.

There is a difference between predicting the aviation weather for the next 12 to 24 hours and the weather for the next ten days. Big difference. Texas' weather problems would have been known to be approaching for days before the systems all froze up, but Texans don't know what real cold is, and the power and natural gas systems were never designed for the cold and ice like the same types of systems farther north are. There wouldn't have been much they could do about it in time anyway. I would hope that they've done some upgrading since then. It will happen again, maybe soon. The climate is cooling, and it's driven by minimum solar activity.

 

[BJC]

Without drag the parachute that you trust would let you down.

[Groan.]