Attitude indicator

Will Kumley

Will Kumley

Line Up and Wait
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Aug 6, 2019
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Will
While flying a rental 172 with a G1000 panel a few days ago I noticed something that surprised me. While cruising at 6000 MSL (VFR Flight following and ATC requested I maintain 6K), flying straight and level, the AI was showing a 3-4 degree nose up attitude and my cruise speed was hovering at the 100 knots indicated. I'll be honest in that I cannot remember right now what the RPMS were at, but I want to say it was around 2450.
If I lowered the nose to show level flight on the AI my airspeed would increase slightly but I would also be in a descent. One thing I really remember was the graph indicated my RPM setting was near the top of the green section just below the yellow.
Stupid question time- shouldn't my AI indicate nose level if I'm actually flying level with such a high power setting? I was trying to get the plane to go faster but every time I lowered the nose, I couldn't get it to fly level unless I put the RPM gauge up into the yellow and close to the red section. I opted for the nose high, slower speed as I figure running in the yellow/red section isn't exactly good for the engine.
 
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If you’re in level flight at 100 KIAS, your AI should indicate what it normally does when you’re at 100 KIAS in level flight, regardless of what power setting is required to maintain it.

The power setting will vary with altitude.
 
The ADI on the G1000 is showing the pitch attitude of the airplane, not your flight-path vector. Some ADIs have a flight-path vector and it would always show on the horizon line when you are level but that an additional indication on the ADI, not the pitch indication.
 
The G1000 uses steady-state sensors and a data computer to compute what shows up on the screens. Meaning it should show nose high if the nose is actually high, with no reference to being in level flight or not. The real issue may have been weight and balance too far aft. Having the CG a little farther back than it should would cause you having to keep the nose up to stay level.
 
Unlike your old mechanical, AI, the G1000 presentation has no user-adjustable level attitude setting. Chances are yours is set up wrong (it wasn't level on the ground when they calibrated it).

Note that aircraft level pitch (with respect to the ground) does not necessarily mean you aren't going to climb or descend. The slower you go, the more pitch up you need to maintain level flight. Eventually, as you slow you'll pitch up so much you'll exceed the critical angle of attack. This is the so-called "stall speed." A large misnomer as speed doesn't cause stalls.
 
Garmin has a leveling procedure as part of their install manual. Some planes have a reference level state, defined by the manufacturer and they require the instrument is set to that. In flight, that is frequently a couple of degrees nose high depending on power settings.
 
Seems like just about any plane would call for some degree of nose up on the gyro in level flight. Yes, with an adjustable horizon one could adjust it some. Sitting on the ramp is a time when it would likely be near zero, right at the line.

That amount of nose up would then vary with airspeed & configuration changes.
 
nrm2430 said:
The G1000 uses steady-state sensors and a data computer to compute what shows up on the screens. Meaning it should show nose high if the nose is actually high, with no reference to being in level flight or not. The real issue may have been weight and balance too far aft. Having the CG a little farther back than it should would cause you having to keep the nose up to stay level.
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It is normal to have a few degrees nose up attitude shown. Aft CG will actually decrease the attitude.

Why Does CG Location Affect Your Airplane's Performance? | Boldmethod

foreward-vs-aft-animation.gif
 
mondtster said:
Does this G1000 have synthetic vision?
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Not sure, this was my second time flying with the G1000 and I haven't had a need for synthetic vision so I'm still just trying to get used to the buttonology on something more advanced than what I'm used to.
 
nrm2430 said:
The G1000 uses steady-state sensors and a data computer to compute what shows up on the screens. Meaning it should show nose high if the nose is actually high, with no reference to being in level flight or not. The real issue may have been weight and balance too far aft. Having the CG a little farther back than it should would cause you having to keep the nose up to stay level.
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W&B was within limits but this is also an A/C at a school so they may have it set for just student and instructor setups. I had my adult son up front and teenage daughter in the backseat so that could have impacted it.
 
flyingron said:
Unlike your old mechanical, AI, the G1000 presentation has no user-adjustable level attitude setting. Chances are yours is set up wrong (it wasn't level on the ground when they calibrated it).

Note that aircraft level pitch (with respect to the ground) does not necessarily mean you aren't going to climb or descend. The slower you go, the more pitch up you need to maintain level flight. Eventually, as you slow you'll pitch up so much you'll exceed the critical angle of attack. This is the so-called "stall speed." A large misnomer as speed doesn't cause stalls.
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I Agree about going slower requires more nose up but I'm also used to a 180hp 172 going faster than 100-105 knots at 2450-ish RPM's. Maybe this plane is just slower than others I've flown.
 
Will Kumley said:
While flying a rental 172 with a G1000 panel a few days ago I noticed something that surprised me. While cruising at 6000 MSL (VFR Flight following and ATC requested I maintain 6K), flying straight and level, the AI was showing a 3-4 degree nose up attitude and my cruise speed was hovering at the 100 knots indicated. I'll be honest in that I cannot remember right now what the RPMS were at, but I want to say it was around 2450.
If I lowered the nose to show level flight on the AI my airspeed would increase slightly but I would also be in a descent. One thing I really remember was the graph indicated my RPM setting was near the top of the green section just below the yellow.
Stupid question time- shouldn't my AI indicate nose level if I'm actually flying level with such a high power setting? I was trying to get the plane to go faster but every time I lowered the nose, I couldn't get it to fly level unless I put the RPM gauge up into the yellow and close to the red section. I opted for the nose high, slower speed as I figure running in the yellow/red section isn't exactly good for the engine.
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Engine speed of 2450RPM at 6,000 feet in a 172S is approximately 61% power. Do you usually fly the S model or a different one?
 
dmspilot said:
Engine speed of 2450RPM at 6,000 feet in a 172S is approximately 61% power. Do you usually fly the S model or a different one?
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This is still a fairly new location for me and most of my Cessna time is in a 172I or L, otherwise I'm usually in a Cherokee of some sort. Maybe it was some sort of mental thing as I saw the tach getting close to the yellow and I assumed it was closer to the top of performance.
I plan to reserve the 172 again for a couple hours and just go solo in an attempt to get more comfortable with it but overall it flies good.
 
Will Kumley said:
This is still a fairly new location for me and most of my Cessna time is in a 172I or L, otherwise I'm usually in a Cherokee of some sort. Maybe it was some sort of mental thing as I saw the tach getting close to the yellow and I assumed it was closer to the top of performance.
I plan to reserve the 172 again for a couple hours and just go solo in an attempt to get more comfortable with it but overall it flies good.
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There's not supposed to be a yellow arc on a 172S tachometer. Is there an STC for a different prop?
 
Will Kumley said:
Not sure, this was my second time flying with the G1000 and I haven't had a need for synthetic vision so I'm still just trying to get used to the buttonology on something more advanced than what I'm used to.
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In the g1000 with synthetic vision the attitude depicted on the screen will appear to be above the surface. It will look similar to what I think you’re describing, although I think what you’re describing is normal for the low power setting you chose to use.
 
It sure seems like the attitude indicator should be easily adjustable in flight to show level pitch attitude for any flight condition, especially for IFR flight.
 
FastEddieB said:
It sure seems like the attitude indicator should be easily adjustable in flight to show level pitch attitude for any flight condition, especially for IFR flight.
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That would potentially defeat many “pitch+power=performance” gouges you may have.
 
FastEddieB said:
Maybe. But once established in level flight for cruising flight in a certain configuration, my preference would be to set the AI to indicate level flight.

Or was I doing it wrong?
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That would give you different pitch attitudes for the same approach, depending upon whether you made it at the end of a normal flight or as an emergency return.
 
You may be right. The Instrument Flying Handbook just says this:

If the miniature aircraft of the attitude indicator is properly adjusted on the ground before takeoff, it shows approximately level flight at normal cruise speed when the pilot completes the level off from a climb. If further adjustment of the miniature aircraft is necessary, the other pitch instruments must be used to maintain level flight while the adjustment is made.
 
It also says:
Procedural Steps in Using Control and Performance
1. Establish an attitude and power setting on the control instruments that results in the desired performance. Known or computed attitude changes and approximated power settings helps to reduce the pilot’s workload.
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and by the way, I don’t intend to imply that the writers at the FAA actually knew what they were supposed to be writing about. ;)
In some places it’s fairly obvious that they didn’t.
 
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FastEddieB said:
You may be right. The Instrument Flying Handbook just says this:
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What you quoted is from the IFH Chapter 7, Section I, Airplane Basic Flight Maneuvers Using Analog Instrumentation. There is also a Chapter 7, Section II, Airplane Basic Flight Maneuvers Using an Electronic Flight Display. In that section it says,

Unlike conventional attitude indicators, the EFD attitude indicator does not allow for manipulating the position of the chevron in relationship to the artificial horizon. The position is fixed and therefore always display the pitch angle as calculated by the AHRS unit.​

This system works better when flying larger, faster airplanes as the required pitch attitude doesn't change based on how you last set the AI. It gives a level of consistency without requiring the pilot to update the level-flight reference. Pilots quickly learn what pitch attitude is a level-flight reference for cruise flight, maneuvering, or approach configurations. The EFIS systems also often have the ability to display a Flight Path Vector symbol which will be on the horizon whenever the airplane is in level flight.
 
I have never flown with the G1000. Does it have a flight director? If so, the FD will show you where to put the attitued. In heading mode with altitude hold selected the FD should be a few degrees above the horizon if you are on altitude.
 
The adjustment on the analog AI's are for Parallax from people of differing heights. No parallax with a screen.
 
dmspilot said:
There's not supposed to be a yellow arc on a 172S tachometer. Is there an STC for a different prop?
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No clue on this plane. But it does in fact have a yellow section of the arc on the digital display on the G1000. I'll definitely be paying more attention to power settings next time I'm flying this particular plane though.
 
You guys are spoiled. I'm happy when the things reads level when the wings are level.
 
As has been mentioned, certificated electronic AI displays (e.g. Garmin G5) are required to be set to zero degrees with the aircraft level on the ground as per manufacturer's guidelines. This may or may not be the attitude of level cruise flight. It may be possible to make a legal fixed adjustment of the AI, but at least for the G5 is is not legal to adjust it in flight. The "adjustment" of mechanical AIs is intended to correct for parallax, not for establishing zero degree attitude.

Having said all that, it is fairly simple to learn new "number" for IFR flight regimes, and the flight attitudes will be 100% reproducible from flight to flight, as the electronic displays do not have any parallax. For my AA-5, level flight at typical cruise speeds and 2 occupants on board is 2 degrees nose up. For level flight at approach speed (90 kt), it is closer to 4 degrees nose up. A 500 fpm descent at 90 kt is 1 degree nose down. And so on for other flight regimes. That's it. The electronic AIs are so precise it is easy to see and make small adjustments in attitude.

With mechanical AIs, you are always flying relative pitch angles from the last manual setting, not absolute pitch angles. Different way of doing things.
 
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