Experiment & Questions

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ahramin
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Re: Experiment & Questions

#76 Post by ahramin » Tue Feb 27, 2018 10:18 pm

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?
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Re: Experiment & Questions

#77 Post by photofly » Tue Feb 27, 2018 10:48 pm

ahramin wrote:
Tue Feb 27, 2018 10:18 pm
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.
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Re: Experiment & Questions

#78 Post by PilotDAR » Tue Feb 27, 2018 11:17 pm

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!
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Re: Experiment & Questions

#79 Post by digits_ » Wed Feb 28, 2018 8:38 am

photofly wrote:
Tue Feb 27, 2018 10:48 pm

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
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Re: Experiment & Questions

#80 Post by ahramin » Wed Feb 28, 2018 8:44 am

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.
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Re: Experiment & Questions

#81 Post by Learning2Fly » Wed Feb 28, 2018 11:16 am

Continuing with the next scenario:

According to some pilots who believe the Earth is flat, in level flight the aircraft would
require continuous nose down corrections to maintain altitude.

The math says about 18 miles of ground coverage results in 200 feet of altitude change.

We know that gravity won't pitch the aircraft to compensate; the VSI and Altimeter is
not affected by gravity.

Imagine the rate of climb at 250 knots cruising speed.

Fighter jet pilots at mach+ speeds and high-speed passenger jets would require even more
frequent inputs.


From what I recall in my limited flight experience no constant adjustments were being made.
The trim wheel wasn't moving continuously, and the yoke wasn't pushed forward constantly.
My "out the window visual" was nose-up attitude; this I recall clearly as it was drilled into my
head to watch the horizon as well as scan the instruments.

Have a listen to these mutli-rated pilots talking about the constant corrections needed to
follow the Earth's curve. Why are these guys so sure? Are they nuts? Please explain your answer.

Listen for about 2 minutes to get most of the idea.
[youtube]https://youtu.be/_dO6HYIPZmk?t=32m00s[/youtube]
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Re: Experiment & Questions

#82 Post by PilotDAR » Wed Feb 28, 2018 12:07 pm

Please explain your answer.
Why?
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Re: Experiment & Questions

#83 Post by Learning2Fly » Wed Feb 28, 2018 12:16 pm

PilotDAR wrote:
Wed Feb 28, 2018 12:07 pm
Why?
Why not? If you believe the airplane is automatically pitching down, explain the concept.

I don't see any control surface adjustment that is consistent with the amount of input required
to maintain -200 ft over every 18 miles of ground.

Do you?
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Re: Experiment & Questions

#84 Post by digits_ » Wed Feb 28, 2018 12:35 pm

Learning2Fly wrote:
Wed Feb 28, 2018 11:16 am
We know that gravity won't pitch the aircraft to compensate; the VSI and Altimeter is
not affected by gravity.
Of course it is. VSI and altimeter work based on air pressure. Without gravity, there would be no pressure and no pressure difference in the atmosphere.

Gravity of earth cancels out lift generated by the airplane wings. The plane will follow the path where these forces are in balance. That means, a fixed height above the earths surface (assuming constant pressure over the flightpath).
Learning2Fly wrote:
Wed Feb 28, 2018 11:16 am
Are they nuts?
Yes
Learning2Fly wrote:
Wed Feb 28, 2018 11:16 am
Please explain your answer.
http://fortune.com/video/2018/02/16/space-x-starman/
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Last edited by digits_ on Wed Feb 28, 2018 12:37 pm, edited 1 time in total.

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Re: Experiment & Questions

#85 Post by PilotDAR » Wed Feb 28, 2018 12:36 pm

I know few pilots who can keep a plane within 200 feet over 18 miles, so how is this a factor? Oh, and even if they are that good, they'll be referencing an altimeter, which will direct them to maintain the same distance from mean sea level. As for airplanes flying further and further from earth on their own if uncorrected.... I've owned a 100HP C 150 for 31 years - I wish!

Your "Learning2fly" is going to be much more time (=money) consuming if you continue to express such an unwillingness to accept clear and understandable facts presented to you in an educational way. For myself, I have declined further training for candidate pilots who refuse to learn what I teach.

I'm working away from home, so bored tonight, and have a bag of good German pretzels, so my willingness to answer silly questions - to a point.
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Re: Experiment & Questions

#86 Post by Learning2Fly » Wed Feb 28, 2018 12:58 pm

digits_ wrote:
Wed Feb 28, 2018 12:35 pm

Of course it is. VSI and altimeter work based on air pressure. Without gravity, there would be no pressure and no pressure difference in the atmosphere.
Right, air pressure...
Gravity of earth cancels out lift generated by the airplane wings. The plane will follow the path where these forces are in balance. That means, a fixed height above the earths surface (assuming constant pressure over the flightpath).
Okay, deal. The force of lift created by air passing over/under the wings exceeds the force of gravity.

The same is true for rudder and elevator.

Where are the control surface changes needed to correct for 200 feet of altitude every 18 miles.

At cruise speed this trim and yoke would require human input every minute or two at typical cruise speeds
according to the pilots in the video.

If my aircraft is trimmed and power is set for cruise, gravity or the curve of the Earth will not compensate
for the change in altitude. So, what gives?
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Re: Experiment & Questions

#87 Post by Learning2Fly » Wed Feb 28, 2018 1:02 pm

PilotDAR wrote:
Wed Feb 28, 2018 12:36 pm
I know few pilots who can keep a plane within 200 feet over 18 miles, so how is this a factor?
I can do the same very easily with manual control. That is not the point.

The point is, the Earth has a curve of 8 inches per mile squared. This equates to 200 feet of altitude increase
about every 18 miles.

Why are we not pushing forward and trimming every minute or thereabouts ( constantly )?

In other words, every 9 miles the altitude would increase 50 feet.

At what point as a pilot would you begin to correct for this change? How close to your assigned altitude to you want to be?
+/- 20? +/-50? 100?
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Re: Experiment & Questions

#88 Post by digits_ » Wed Feb 28, 2018 1:07 pm

Learning2Fly wrote:
Wed Feb 28, 2018 12:58 pm


If my aircraft is trimmed and power is set for cruise, gravity or the curve of the Earth will not compensate
for the change in altitude. So, what gives?
There is no change in altitude over earth surface. The earth can be a sphere, a donut or an infinite flat surface. Doesn't matter. As long as the force pulling towards the earth (gravity) equals the force pulling up away from the earth (lift force of the wings), the plane will stay at a constant altitude above the earth's surface.
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Re: Experiment & Questions

#89 Post by lownslow » Wed Feb 28, 2018 1:15 pm

Learning2Fly wrote:
Wed Feb 28, 2018 1:02 pm
Why are we not pushing forward and trimming every minute or thereabouts?
How do you know you're not?

When you drive your car in a circle to you jerk the wheel to the side every so often? To maintain a constant circle do you have to hold the wheel in one position or do you have to continuously wind it tighter into the direction of the turn?
Learning2Fly wrote:
Wed Feb 28, 2018 1:02 pm
At what point as a pilot would you begin to correct for this change? How close to your assigned altitude to you want to be?
+/- 20? +/-50? 100?
Others may vary, but if I'm off altitude by any measurable amount I put the effort in to get back on.
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Re: Experiment & Questions

#90 Post by Learning2Fly » Wed Feb 28, 2018 1:25 pm

lownslow wrote:
Wed Feb 28, 2018 1:15 pm

When you drive your car in a circle to you jerk the wheel to the side every so often? To maintain a constant circle do you have to hold the wheel in one position or do you have to continuously wind it tighter into the direction of the turn?
Don't know, I've never driven in a constant circle. I would imagine at a constant speed, and turn angle, the car would maintain a perfect circle
if I'm not exceeding the friction of the tires to the ground.

I know I'm not pushing down every minute because I'm not exerting force forward on the stick. Sometimes I'm pulling back to increase altitude.
Much of the time, the aircraft is maintaining when trimmed (over a 1-2 minute period). ie no appreciable altitude change.
Others may vary, but if I'm off altitude by any measurable amount I put the effort in to get back on.
What do you consider measurable amount? 10 feet?

I would personally correct at +/- 20 feet if the trend continued either way.
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Re: Experiment & Questions

#91 Post by Learning2Fly » Wed Feb 28, 2018 1:31 pm

digits_ wrote:
Wed Feb 28, 2018 1:07 pm

There is no change in altitude over earth surface. The earth can be a sphere, a donut or an infinite flat surface. Doesn't matter. As long as the force pulling towards the earth (gravity) equals the force pulling up away from the earth (lift force of the wings), the plane will stay at a constant altitude above the earth's surface.
Okay, so at point A you are at 10,000 feet. Aircraft trimmed, power set.

If left alone, the aircraft would continue level.

The Earth drops away from you.

At point B (18 miles away), the Earth has curved down 200 feet.

How does the aircraft descend with constant power and no change in control surface?

Air density increases as you near sea level which would mean the aircraft would have a tendency to rise, not sink (all things above being steady). Correct?
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Re: Experiment & Questions

#92 Post by digits_ » Wed Feb 28, 2018 1:38 pm

Learning2Fly wrote:
Wed Feb 28, 2018 1:31 pm


If left alone, the aircraft would continue level.

The Earth drops away from you.
It will continue level with a constant distance from the ground. The Earth will not drop away from you.
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Re: Experiment & Questions

#93 Post by PilotDAR » Wed Feb 28, 2018 1:41 pm

How does the aircraft descend with constant power and no change in control surface?
If the constant power was adequate to maintain flight at a constant altitude (fuel burn notwithstanding) it will maintain flight at that altitude, and not descend. Thus, it will maintain the same altitude, or distance from mean sea level. So, to answer your question, it does not descend.
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Re: Experiment & Questions

#94 Post by Chris M » Wed Feb 28, 2018 4:36 pm

Learning2Fly wrote:
Wed Feb 28, 2018 1:31 pm
Okay, so at point A you are at 10,000 feet. Aircraft trimmed, power set.

If left alone, the aircraft would continue level.

The Earth drops away from you.

At point B (18 miles away), the Earth has curved down 200 feet.

How does the aircraft descend with constant power and no change in control surface?

Air density increases as you near sea level which would mean the aircraft would have a tendency to rise, not sink (all things above being steady). Correct?
You didn't descend. You're having trouble grasping that we still aren't talking celestial level navigation. Aircraft are flown relative to the Earth, not the sun or galaxy. As long as you're maintaining a constant altitude above the planet you aren't descending.

If the earth drops away from you it means you're climbing. Climbing means less dense air. Less dense air means less lift.

Air density, simplified, is the result of gravity compressing the atmosphere downward. At sea level you've got lots of atmosphere above you, hence relatively high density. The higher you go the less air there is to weigh down on you and density drops off.

Any plane in level flight will want to remain at the current relative air density - if you climb you'll have less lift and power which will bring you back down. If you descend you'll have more lift and power which will bring you back up.

If you're trully not some flat Earth goof then you accept that the surface of the planet is curved and hence the atmospheric density follows that curve. Therefor as the plane follows the curve of the planet around it's going to seek out a consistent air density, keeping us at a constant altitude above the planet.
Learning2Fly wrote:
Wed Feb 28, 2018 1:25 pm
Don't know, I've never driven in a constant circle. I would imagine at a constant speed, and turn angle, the car would maintain a perfect circle
if I'm not exceeding the friction of the tires to the ground.
Are you being intentionally dense? You've never taken a highway ramp? Were you hammering the wheel back and forth the whole time, or did you find the appropriate amount of steering angle to maintain that radius of turn?
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Re: Experiment & Questions

#95 Post by Learning2Fly » Wed Feb 28, 2018 5:43 pm

Chris M wrote:
Wed Feb 28, 2018 4:36 pm

Are you being intentionally dense? You've never taken a highway ramp?

You call this a circle?

Image


I don't understand why some of you have to be so hostile when I'm asking questions about a subject that I'm not
as experienced with. Excuse me for trying to learn and understand what other high level pilots are questioning
while putting their real names out there.

If I may, I'd like to continue with a couple of other scenarios that are related to this topic, but not necessarily
aviation specific. Most of you seem to have a high level of physics and math education which is perfect.
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Re: Experiment & Questions

#96 Post by AuxBatOn » Wed Feb 28, 2018 6:16 pm

Trim is in relation to the airmass, not the Earth. If you are perfectly trimmed for 150 KCAS and 15,000 ft pressure altitude, the plane will keep these parameters. Since the 15,000 ft pressure altitude follows the curvature of the Earth, you will go around the Earth. And, given a constant aircraft weight (very theoratical discussion), the trim will not change. The attitude reference the Earth immediately underneath the aircraft will not change. The attitude reference your original location will change.
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Re: Experiment & Questions

#97 Post by youhavecontrol » Wed Feb 28, 2018 6:58 pm

Learning2Fly, in all honesty, it's clear that what you need is to discuss this in person with someone, over a whiteboard, who can break down each concept individually, rather than offer explanations piece by piece that get muddied by your own research. Every time an answer is given to you, you counter it with some piece of information with another logical flaw in it. Once that flaw is pointed out, it's as if you forget the first answer someone gave you and you are back to square one again... asking about altitude over distance. It's hopeless discussing in circles without drawing the bigger picture for you. You need a one-on-one lesson, not the internet.

I swear... the flat earth thing is one frustratingly huge echo-chamber where reason and clarity are totally lost with the rest of the crap bouncing around.

It reminds me of the airplane/treadmill thing all over again.
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Re: Experiment & Questions

#98 Post by photofly » Wed Feb 28, 2018 7:00 pm

It reminds me of the airplane/treadmill thing all over again
I like that one. Let’s do that one again.
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Re: Experiment & Questions

#99 Post by lownslow » Wed Feb 28, 2018 7:22 pm

Learning2Fly wrote:
Wed Feb 28, 2018 1:25 pm
I know I'm not pushing down every minute because I'm not exerting force forward on the stick.
That's because you're trimmed to keep the four basic forces in flight in equilibrium at your present pressure level.
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Re: Experiment & Questions

#100 Post by AuxBatOn » Wed Feb 28, 2018 9:16 pm

lownslow wrote:
Wed Feb 28, 2018 7:22 pm
Learning2Fly wrote:
Wed Feb 28, 2018 1:25 pm
I know I'm not pushing down every minute because I'm not exerting force forward on the stick.
That's because you're trimmed to keep the four basic forces in flight in equilibrium at your present pressure level.
Not true. You are trimmed to maintain an angle of attack.
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