Experiment & Questions

[photofly]

The problem here is that an ascending aircraft, climbing away from the curvature of the Earth does not register on the VSI, or
Altimeter at the rate shown in the chart. Within 50 miles, there is already an apparent change in altitude that exceeds the
typical cruise for most jets.

This is arrant nonsense.

The aircraft in level flight doesn't climb away from the curvature of the earth - it follows the curve of the earth. So there's nothing to register on the VSI, and no change on the altimeter. The air pressure follows the curve of the earth, as does the aircraft.

On the other hand, if the aircraft is ascending, it does register on the VSI and altimeter.

That really is the weirdest thing not to understand!

[Learning2Fly]

You appear to be seeking someone else (other than me, apparently) to tell you how an AI works, instead of seeking understanding in your own head.

I have shown three government/pilot training sources (video and literature) that say ADI instrumentation in an AIRCRAFT DOES NOT POINT TO THE EARTH's CORE.

The gyro does not follow the Earth's surface, it does not care about gravity.

Can YOU please show me a document, or video from a:
- manufacturer
- published book
- credible video

that states a gyro is affected by gravity and points to the Earth's surface?

[youhavecontrol]

This is what happens when you take something concrete, practical and proven through thousands of credible sources and muddy it with technically flawed arguments, impractical math and critically missing background understanding.

This discussion reminds me of a toppled gyro in an old aircraft, in which the only solution would be to stop spinning in circles, take a rest back on earth and get re-calibrated.

[photofly]

Weee this is fun.

I have shown three government/pilot training sources (video and literature) that say ADI instrumentation in an AIRCRAFT DOES NOT POINT TO THE EARTH's CORE.

Your sources say a gyroscope doesn't point to the earth's core. Your sources are 100% correct when they say that.
However, An AI isn't a gyroscope, although it contains one. (Likewise I am not a stomach, although I contain one.)

The gyro does not follow the Earth's surface, it does not care about gravity.

That's again correct. But, again, an AI is not a gyroscope, although it has one inside it. (I am not a gall bladder, although I function better with one inside me.)

Can YOU please show me a document, or video from a:
- manufacturer
- published book
- credible video

that states a gyro is affected by gravity and points to the Earth's surface?

No, I can't, because, one more time, a gyroscope isn't affected by gravity, and doesn't point to the Earth's surface.
I cannot find you a credible document that says what you ask, because it isn't true.

HOWEVER: A gyroscopically stabilized attitude indicator is affected by gravity however, and does point to the Earth's surface.

[Chris M]

Oh there's no problem halting us, just you. We're all peachy with how things work.

Yes, we do adjust the horizon bar on AIs, but that's really only to set a reference point for level cruise flight. I can't even remember the last time I paid it a whole lot of attention... The altimeter is much more useful for maintaining altitude in cruise.

Have you ever noticed an AI spool up with 20 or 30 degrees of bank angle? Remember, the AI is a two-axis instrument, not just a pitch indicator. The answer is no, unless your AI is broken. The same as it never spooling up with gross pitch errors. The reason is that the AI has a universal reference point - gravity. If the AI didn't reference itself to gravity it would always start up in whatever orientation it stopped in. Not tremendously useful.

And yes, if you had some magical plane that could fly fast enough to follow the arc you've drawn the AI would probably lag enough that it would still say you were level all the way out into space. However, at the speeds that real airplanes fly we can't get ahead of that self correcting instrument.

[digits_]

Can YOU please show me a document, or video from a:
- manufacturer
- published book
- credible video

Dude(tte), he made pictures for you to show you the mechanism. He showed you how schematics on how everything works.

Physics doesn't care about who writes the article or publishes the book. I'm sure photofly could write a book about aviation physics and charge you 150 dollars for it to get access to the same info he is writing here for free.

If you disagree with something, again, point out what exactly you disagree/don't understand in his posts. But refusing to accept anything he writes without providing a proper rebuttal is, frankly, pretty insulting.

1) Do you understand the difference between a gyro and an attitude indicator?
2) Why do you think the airvane system doesn't work? "because an oversimplified movie from 1960 doesn't mention it", is not an acceptable answer.

[photofly]

And yes, if you had some magical plane that could fly fast enough to follow the arc you've drawn the AI would probably lag enough that it would still say you were level all the way out into space....

You don't need magic. Any actual spacecraft will do. I already posted a link to how the Apollo Command Module solved this problem. It didn't use gravity to rotate the axis of its attitude reference platform to follow the earth's surface (there's no gravity that will do that in orbit, anyway) but it did use an electric motor.




The actual gravity mechanism in an AI is worth a little thought. You might naively think that all you have to do is attach a little weight to the bottom of the axis of the gyroscope in the AI, and gravity will pull it vertical. Unfortunately that doesn't work. Because of the high angular momentum stored in the rotor, the torque generated by gravity on this putative weight causes the gyro to precess at right angles, and the gyro axis will wobble round like a top instead of straightening up. The cunning thing about the vanes is that they use gravity to release air that exerts a force at right angles to the direction which the axis needs to move, so the precessional effect makes the axis move the way you want. Very clever.

[Chris M]

And yes, if you had some magical plane that could fly fast enough to follow the arc you've drawn the AI would probably lag enough that it would still say you were level all the way out into space....

You don't need magic. Any actual spacecraft will do. I already posted a link to how the Apollo Command Module solved this problem. It didn't use gravity to rotate the axis of its attitude reference platform to follow the earth's surface (there's no gravity that will do that in orbit, anyway) but it did use an electric motor.

I know, I was just trying to come up with something that fit better into the unicorns and pixie dust scenario described (level at 10,000 ft and then able to just continue on in a straight line into space without varying pitch attitude ). Rockets rotate in pitch during launch and I couldn't come up with a vehicle that maintains it's attitude all the way through. Therefor, magic.

[photofly]

I think I might have found what the OP is looking for. The patent for the self-righting mechanism is somewhere available on Google Patents. I can't find that one yet, but I did find this reference: https://patents.google.com/patent/US2669786A/

Which says...

Normally the gyroscope is provided with a pendulous erecting device for continuously precessing the gyroscope to a predetermined reference position relative to the direction of gravity. A; showing of the erecting device, which may be of conventional construction, has been omitted in the interest of simplicity of illustration.

(my emphasis)

Can I now please be released back to work on my masterplan for world domination and the wreaking of havoc on all mankind? Please?

Stop press. I think this might be the one!
https://patents.google.com/patent/US2409188A/
Sperry Gyroscope Co., 1941. So smart.

Gravitationally responsive means in 'the form of pendulums 25 are `provided for each of the ports 23 for controlling the erecting effort or the torque exerted by the air issuing therefrom. Opposite pendulums 25 are secured to a common shaft, the respective perpendicularly arranged shafts being rotatably mounted in the side walls of the erector housing 24. The pendulums 25 which depend from the exterior portion of the housing '24 form blades which normally bisect the respective ports 23, when the spin axis of the gyroscopic rotor element is in a properly erected position, so `that the air exhausting from the erector case through the ports issues in jets that are balanced about all axes, the same consequently exerting no erecting torque on the gyro-vertical. When the rotor of the gyra-vertical tilts, the reactive effect of the air jets is unequalized at the ports to obtain thereby a directed erecting torque which causes the rotor to return to an erected position.

Thank me later.

Actually that patent is even more clever. It describes a method to stop the AI generating any error in turns at all. It has a mechanism that senses whenever the local acceleration is more than 1g, and shuts off the self erection feature regardless of the direction of the force. (I'm actually going to guess that feature never caught on, because if you fly a continuous turn long enough the gyro will run without any self-erection, and topple.)

[PilotDAR]

A gyroscopically stabilized attitude indicator is affected by gravity however, and does point to the Earth's surface.

Yes.

The vacuum driven attitude indicator common to most GA aircraft is stabilized by responding to gravity, and being aligned with the local surface of the earth. Gyroscopes have rigidity in space, vacuum driven AI's are not rigid in space in absolute terms.

[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.