Experiment & Questions

[photofly]

Hey, PilotDAR, welcome to the party! Help yourself to pretzels.

[Chris M]

Not a huge pretzel fan... Do we have any chips?

[Learning2Fly]

Thank you for the sources, Photofly. I wouldn't bring out the pretzels just yet as I'm more into pizza.

I find it strange that after finding a fourth source, our references have discrepancies regarding mechanisms
for aircraft instrumentation. This article from the Aircraft Electronics Associaton, 2005 states what my
prior links state. I'll link the screen shot below.

For the sake of furthering the discussion, let's assume my links are incorrect and yours are accurate.

Back to the values in my chart. Do you [Photofly], or anyone else agree with the figures with respect
to the curvature of the Earth? If yes, I'll respond with the next question. If no, please state the error(s),
and corrections. Thanks.

Source: https://www.aea.net/AvionicsNews/ANArch ... Sept05.pdf

[Tips Up]

Just stop. I am running out of pretzels. I had a similar discussion at a family function with a true flat earth believer and short of shooting him into space no argument presented would satisfy him. I did offer to provide part of the ride up to about 20,000 ft but he would have to do the rest....

[Learning2Fly]

Just stop. I am running out of pretzels. I had a similar discussion at a family function with a true flat earth believer and short of shooting him into space no argument presented would satisfy him. I did offer to provide part of the ride up to about 20,000 ft but he would have to do the rest....

Lucky for us, I'm a believer in the globe...but many questions after this weekend's chat. Sit back and grab some more food.

Do you mind verifying the values in this chart, or do you not care to play anymore?

[upnatem]

Wow, this has to be the weirdest thread on this forum - and there have been some dillies.

Disregarding all the wonderful information photofly has provided as well as the absurd intransigence of learning2fly - how can someone continue to argue a point of view when AIs actually work exactly as they should and have done so since they were invented. As was mentioned earlier, someone not understanding exactly (or even partly) how something works doesn't mean it doesn't work. It simply means that someone should give it a rest. But trolls don't do that, do they?

[photofly]

Source: https://www.aea.net/AvionicsNews/ANArch ... Sept05.pdf

Well, that's a lousy article, full of elementary errors.


"Rigidity is another important property of a gyro. The primary trait of a rotating gyro rotor is its rigidity in space, or gyroscopic inertia. Newton's first law states in part A body in motion tents to move in a constant speed and direction unless disturbed by some external force."

Comment: Newton's first law isn't particularly applicable to gyroscopes any more than non-rotating bodies, and is not able to explain why a rotating mass demonstrates rigidity-in-space while the same mass not rotating does not. The writer demonstrates no understanding of what he's writing about.

"To compensate for real or apparent precession in the ADI gyro we add weight or torque to the gyro gimbals to induce a reverse precession"

Comment: For reasons I've already discussed, adding weight to the gimbal is entirely the wrong thing to do to stabilize an attitude indicator, and will cause the axis to precess in circles and not to erect. The writer is incorrect.

In this case we use what should be a perpendicular position from the earth's surface to the aircraft's center of gravity (CG)... The precession of the ADI gyro is constantly corrected by the erection mechanism to the aircraft's CG."

Comment: the aircraft centre of gravity plays no part in the operation of the instrument. This section is utter bullshit. Again, nobody who understands the operation of this instrument could write such a thing.

I'm going to leave it there, except to say that people need to be more discerning about what they believe. Just because it appeared in print somewhere doesn't mean it's correct.

[PilotDAR]

I like figure #3, which states "rotor upright". Upright is relative to local earth. And, the statement that "the ADI gyro is constantly corrected by the erection mechanism to the aircraft's CG". The "G" in CG is for "gravity", meaning that the gyro is correcting itself relative to local earth. If there were no gravity, and no precession, then the rigidity in space would assure that the attitude indicator would show you not flying away from earth by an increasing pitch indication error as you flew around earth.

My bag of pretzels says "Brezel", because I'm in the land of pretzels this week. I'll have a few now....

[Learning2Fly]

Interesting as one member slams the article, while another likes it.

We'll move on using the ADI corrects to Earth's core then. Grab more pretzels!

[photofly]

Now if you want a real puzzle, see if you can explain to yourself *why* a spinning mass exhibits rigidity in space. It doesn't have anything much to do with Newton's first law, but what does it have to do with?

[Bede]

I'm pretty sure Learning2Fly is a flat earth troller. I've heard this argument before. A friend of mine (not a pilot, not a flat-earther) asked me this because one of his friends, who is fond of flat earth nonsense, brought it up.

The answer is very simple. The gyro shows a plane normal to a vector from the aircraft to the center of the earth. On earth, we use a terrestrial frame of reference. When you're climbing, it is relative to this plane, not some celestial frame of reference.

P.S. I'm always impressed with photofly's knowledge. I'm less impressed by his willingness to suffer fools. I would have ended this nonsense after the first response.

[photofly]

Without passing any comment on on the original poster's mental capacity, I can say that fools are extremely effective tools for sharpening ones own understanding. Kind of like diamond whetstones for the mind. If you can explain something to a fool, you can explain it to anyone.

[Learning2Fly]

I'm pretty sure Learning2Fly is a flat earth troller. I've heard this argument before. A friend of mine (not a pilot, not a flat-earther) asked me this because one of his friends, who is fond of flat earth nonsense, brought it up.

Sorry to get your man shorts in a knot, I'm really not a troll...and you have the story wrong. It wasn't a friend, it was your mom. Tell her I said hello.

There are several things that were mentioned that raised questions in my mind. Does discussing it and ensuring my position on the globe make me a troll?

It's not as if the title says, "TRUTH FLAT EARTH EXISTS". You almost had me.

Photo, the answer to your question is angular velocity.

[ahramin]

Photo that was an epic effort, loved it. I was particularly tickled with the patent link, a beautiful touch. I would say we all learned a lot of useful things about Gyros except that we're talking about old vacuum driven round things and I prefer to relegate to bin 99 any knowledge obsolete by current equipment standards and not old enough that most people still know about it.

Thank you and well done.

[photofly]

It's funny that you say it's not relevant, but most of what I know about how Attitude Indicators work I learned while writing software for a home-made solid-state AHRS. (Using the "usual" MEMS gyros, accelerometers and magnetometers.) The problems that used to have to be solved mechanically - preventing precession, self-erection at startup, recovering from a topple, minimizing accumulated errors in a turn - now have to be solved in software. But they're still there. The software in your state-of-the-art Garmin G5 owes a lot to the Sperry Gyroscope Company.

[ahramin]

Very true.

Recently attended a lecture by Dynon and I was surprised to discover that instead of using super fancy top of the line sensors, they just use lots and lots of really cheap ones.

How does a solid state reference system topple?

[photofly]

Very true.

Recently attended a lecture by Dynon and I was surprised to discover that instead of using super fancy top of the line sensors, they just use lots and lots of really cheap ones.

How does a solid state reference system topple?

If the drift overcomes the correction rate, or it's subject to rotations too fast to integrate, or ...

Also, depending on how you model the orientation internally, there are orientations for which some of the operations you need to carry out on the direction cosine matrix become unstable. If I remember right. It's the mathematical equivalent of gimbal lock. Of course there are ways to fix it, I suppose you'd call them a mathematical equivalent of a four-gimbal setup. But it adds complexity.

Did Dynon say they heat their sensors in an oven? My project foundered because I couldn't find a way to keep the correction rate small enough so that errors in the turn were adequately small to meet TSO-4c requirements, and still cope with the thermal drift of the MEMS gyro. I figured the best solution was to put the sensor in an oven and keep it at 60 degrees. But that's not really practical for a battery powered instrument. Do you know how they solved that one?

Another way is to use a high correction rate, but use GPS to detect when the instrument is really accelerating, so you can extract the gravitational component from the acceleration vector. Every time you see a solid-state AI that requires a GPS antenna, you know they're "cheating" that way. I was determined to do it without GPS.

I think that the sensors that are around now are considerably better than they were in 2012, from the point of view of drift, so perhaps it's not such a big issue any more.

[PilotDAR]

I think the best information in this thread is:

If you can explain something to a fool, you can explain it to anyone.

Perhaps one of things I have not really been taught, maybe I should take the flight instructors course, and get these little wisdoms!

[digits_]

Did Dynon say they heat their sensors in an oven? My project foundered because I couldn't find a way to keep the correction rate small enough so that errors in the turn were adequately small to meet TSO-4c requirements, and still cope with the thermal drift of the MEMS gyro.

Was the problem with the correction rate caused by imperfections by the MEMS, and thus randomly distributed if you used different MEMS? If it is, you should theoretically be able to build for example 3 gyro systems and average them out. That's probably in line with ahramin's Dynon comment.

If it is a theoretical limit, then I have no idea.

On the other hand, if heating it up works, you might be able to "just" add a tiny heating blanket around the part of the chip that needs to be at constant temperature. It is probably a very small part anyway, so the power usage would be similar to one old fashioned instrument light.
Or more fancy, although you probably already tried stuff like this, https://www.sciencedirect.com/science/a ... 7487870026

[ahramin]

No oven. My GRT cheats by using GPS but Dynon insists that they don't. When I pressed him further on it he explained they use airspeed and altitude data to supplement the mems. This lead to problems where doing a pitot static test on the aircraft could screw up the attitude for hours. They now require you to turn off the unit between each data point so that the unit doesn't see large changes in vertical soeed with no pitch change.