L

lr172

Well Known Member
Last week I had my first IFR lesson in my D100 equipped RV-6. There was a decent amount of turbulence and to say I was in task overload would be a major understatement. I deduced that in addition to learning how to fly off instruments, I was additionally learning how my instruments performed and how to manage the interpretation of them. Most of it just seemed like it would take some time to figure them out. The one that surprised me was the attitude indicator. I had expected this to be pretty stable and tightly track the airplane attitude, especially in pitch.

In the end, I was focusing more on the altimeter in order to hold an altitude, which I know is the correct procedure. However, when I went back to cross check the attitude, it was often not where I expected it and was constantly moving.

The following day was the same light chop (no training & VFR) and I observed the attitude indication as I was flying and holding a stable altitude. I observed the cross hairs going above and below the level line (maybe 2 or 3X the bar width). Through my book training, I was led to believe the gyro-based AI's are quite stable.

I am wondering if this is a by-product of a computer algorithm generated indication and something that I just need to learn how it behaves and therefore how to properly interpret it/average it or is there something going on with my D100.

I appreciate any input on the subject.

Larry
 
lr172 said:
In the end, I was focusing more on the altimeter in order to hold an altitude, which I know is the correct procedure.
Larry
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It is not the correct procedure. The altimeter is a 'performance' instrument, which should be used to verify or not the correct altitude. The AI is the control instrument, and should be used to keep altitude where you want it.

If the AI is moving up/down when the nose is not, there is an issue with it.
 
BobTurner said:
It is not the correct procedure. The altimeter is a 'performance' instrument, which should be used to verify or not the correct altitude. The AI is the control instrument, and should be used to keep altitude where you want it.

If the AI is moving up/down when the nose is not, there is an issue with it.
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I am too new to this to understand the expected behavior of the AI in different conditions (I never really look at it much in VFR). Is it possible that the nose is moving up and down with a stable altitude with a light chop if I am holding the stick stable? I don't want to send my unit in for repair if it is just me not understanding the nuances of the behavior.

Larry
 
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Flight Path Marker Use

Hi Larry,
I seriously doubt you have a problem with your D100. I'd get some more time flying with it before you send it in for repair. Maybe have somebody else with more IFR experience go with you or get some video. It's always risky to try and give flying advice like this but here are some thoughts:

Are you using the D100 flight path marker (FPM) to help maintain altitude? Remember, if you put the FPM symbol on the D100 horizon line, you will be in level flight at zero VSI. Keeping it there is another question but it is ALWAYS the best indicator of your flight path, regardless of attitude. Your attitude will change with angle of bank, changes in airspeed, etc. but if the FPM is on the horizon line, you will maintain altitude. Take a turn as an example. As you roll into the turn, if you maintain the same attitude, you will generate a rate of descent and start losing altitude. You have to add some back stick to generate more lift and that means increasing your attitude. As you roll into the turn, watch the FPM. It will start to drop below the horizon line. Use enough back stick to hold it right on the horizon line and you'll get a nice level turn. Same thing as your roll out of the turn. Relax back stick and hold the FPM on the horizon. You'll stay right on your altitude.

Now, our little Vans airplanes aren't the most stable instrument platforms every. Because we are usually bouncing around a little, you're going to see your indications doing the same - moving around a little. Don't react to every twitch of the VSI, Altitmeter, or even the attitude indicator / FPM. You'll need to sort of even out the minor deviations and just correct the trends. Otherwise you'll create a lot of pilot induced oscillations that are unnecessary. Be smooth! Fly with two fingers. All those good tips.
 
f14av8r said:
Hi Larry,
I seriously doubt you have a problem with your D100. I'd get some more time flying with it before you send it in for repair. Maybe have somebody else with more IFR experience go with you or get some video. It's always risky to try and give flying advice like this but here are some thoughts:

Are you using the D100 flight path marker (FPM) to help maintain altitude? Remember, if you put the FPM symbol on the D100 horizon line, you will be in level flight at zero VSI. Keeping it there is another question but it is ALWAYS the best indicator of your flight path, regardless of attitude. Your attitude will change with angle of bank, changes in airspeed, etc. but if the FPM is on the horizon line, you will maintain altitude. Take a turn as an example. As you roll into the turn, if you maintain the same attitude, you will generate a rate of descent and start losing altitude. You have to add some back stick to generate more lift and that means increasing your attitude. As you roll into the turn, watch the FPM. It will start to drop below the horizon line. Use enough back stick to hold it right on the horizon line and you'll get a nice level turn. Same thing as your roll out of the turn. Relax back stick and hold the FPM on the horizon. You'll stay right on your altitude.

Now, our little Vans airplanes aren't the most stable instrument platforms every. Because we are usually bouncing around a little, you're going to see your indications doing the same - moving around a little. Don't react to every twitch of the VSI, Altitmeter, or even the attitude indicator / FPM. You'll need to sort of even out the minor deviations and just correct the trends. Otherwise you'll create a lot of pilot induced oscillations that are unnecessary. Be smooth! Fly with two fingers. All those good tips.
Click to expand...

I didn't think the D100 had a flight path marker. At least they don't call it that or reference that functionality in the documentation. It would explain the behavior though. I was looking at it as pure pitch attitude, but if it is a trend indicator, like vertical speed, I would need to interpret it a little differently. For example, I was dealing with a lot of updrafts that day. I was relatively stable in pitch, but starting getting 500 FPM up with no pitch up. At least I don't think so. I was barely "hanging on" so to say and was in no position to properly assess what was going on.

I recognize that the learning curve is much steeper in the RV and accept that. I am just doing my best to figure out how to interpret my instruments so that I can leverage that as I learn how to do this.

The next time we're in chop, I'll have my instructor look at the attitude indication and tell me if it is doing what it is supposed to.

EDIT: I am pretty sure it is not an FPM, as I was having to hold a pitch up indication in turns to maintain altitude.

Larry
 
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Sounds pretty normal so far, Larry. Get through another few lessons to where the brain starts catching up, and reassess. As you've noticed, the first few hours under the hood are an overload.

Good on ya for making the commitment to get the rating!
 
I think people were confused (I was) by your reference to 'cross hairs' in your first post. The basic instrument should have two bars representing your wings, and a horizon line.
Surely your cfi would have said something if he thought the AI was mal-functioning?
 
BobTurner said:
I think people were confused (I was) by your reference to 'cross hairs' in your first post. The basic instrument should have two bars representing your wings, and a horizon line.
Surely your cfi would have said something if he thought the AI was mal-functioning?
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sorry for that. The airplaen indicator is hollow round with three bars and it moves about separate from the horizon line. It also looks like the FPM on other, newer EFIS'

I suspect my instructor would have said something as well and plan to ask him to specifically observe the behavior next time. I have faith in my instructor, but it is my nature to learn as much as I can and may have gotten ahead of myself in this situation.

Thanks for the input.

Larry
 
lr172 said:
sorry for that. The airplaen indicator is hollow round with three bars and it moves about separate from the horizon line. It also looks like the FPM on other, newer EFIS'
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This is what another member called the "Flight Path Vector". It shows the direction your aircraft is moving through the air, not the current pitch attitude.
 
MercFE said:
This is what another member called the "Flight Path Vector". It shows the direction your aircraft is moving through the air, not the current pitch attitude.
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No, the OP is correct. On the small Dynons the usual 'wing bars plus nose point' is replaced by a small circle, two short wings, and a small vertical stabilizer. I would not call it cross hairs, though. I have a D4 and it behaves normally in turbulence, by which I mean, the same as a mechanical gyro AI.
 
NOT a Flight Path Marker

My apologies. On the D100 that very Flight Path Marker looking thing is NOT. It's just the aircraft reference. Time for a Skyview Upgrade!

Again, my apologies for the bad info but, if you do upgrade to a display with a FPM (which I'd highly recommend) then all that stuff I wrote will apply! :)
 
Thanks for the support guys. I did another flight yesterday with a safety pilot. I had no issues in calm air and even went down for some very light bumps. I am not sure I would call the Attitude indication rock stable, but it was manageable and I felt I was keeping up with the plane. Certainly not ahead of it yet, but didn't feel that I was hanging on by a thread.

I will continue to observe the behavior through my training. I would still expect it to be a bit firmer, but I am not yet sure if it is the plane moving about it's axis or the instrument. Either way, it seems to work quite well in very light chop, so it is most likely me being early on the learning curve.

Thanks,

Larry
 
f14av8r said:
My apologies. On the D100 that very Flight Path Marker looking thing is NOT. It's just the aircraft reference. Time for a Skyview Upgrade!

Again, my apologies for the bad info but, if you do upgrade to a display with a FPM (which I'd highly recommend) then all that stuff I wrote will apply! :)
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No apologies necessary; The effort to assist is appreciated. I considered the upgrade with their new trade in program, but it will still be almost $10K for the upgrade and I built this to be a "budget bird." While it seems the the FPM is much easier to use, it might be best to do the training the hard way so that I have at least some potential to fly a 6 pack some day, should the need arise.

Larry
 
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