Flight Director Sensitivity - Is it adjustable?

Rick A

Rick A

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Recently had a panel upgrade with a GI 275 being fed by an S-Tec 55X with altitude pre-select. Never have flown one before, and realized how it could be very beneficial in transitioning the two new GI-275's with the AI's vertical tapes and narrowing the instrument scan. Also, still have the round A/S, altimeter, TC and VSI's and have been having a challenging time integrating the vertical A/S and Altitude tapes +VSI) into the scan.

Today I flew over an hour and received my introduction to the FD with a CFI who has been flying Flight Directors for many years in Corporate aircraft, and the airlines. This was his first experience flying a GA plane (Mooney) in the FD mode. After flying the FD today, I believe it has the potential help me bring these panel upgrades all together, as designed.

The CFI believes the FD presentation is way too sensitive for practical use. In mild turbulence it demanded a lot of attention, significantly more than he has ever encountered. He presumes the sensitivity should be able to be adjusted to be less sensitive and more forgiving of minor turbulence deviations.

Also, the GI-275 tape altitude presentation never matches up with the round OEM Aerosonic altimeter (~ 40' difference), and we wondered where GI-275 altitude tape was receiving its altitude input? And which one we should be following.

Before I contact the avionics shop to ask the same questions next week, is anyone here familiar to share a sneak preview? Thanks.
 
In b737's it's not unusual to have the 3 altimeters +-40 ft. The 275 gets its altimeter from the same static system as your other one, but it could be different if you have more than one static port.
 
Rick A said:
The CFI believes the FD presentation is way too sensitive for practical use. In mild turbulence it demanded a lot of attention, significantly more than he has ever encountered.
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Can you be a little more specific on how it was too sensative? And are these "corporate aircraft" all larger jets? When was the last time he's really flown in a smaller GA plane?

You might see if you can find a Mooney CFII in your area or at least fly once with a GA CFI from the local Flight School. See if they agree your FD is too sensative. And 40 feet is enough to go find out which Altimeter is correct. So it sounds like you're headed to the avionics shop anyway, so ask them too about the FD.

For a Mooney CFII, if you can't find any by asking the other Mooney pilots at your airport, you can check the below list. It starts off with traveling CFIs, but keep scrolling down and you'll find a list by state.
https://themooneyflyer.com/cfi.html
 
Rick A said:
Recently had a panel upgrade with a GI 275 being fed by an S-Tec 55X with altitude pre-select. Never have flown one before, and realized how it could be very beneficial in transitioning the two new GI-275's with the AI's vertical tapes and narrowing the instrument scan. Also, still have the round A/S, altimeter, TC and VSI's and have been having a challenging time integrating the vertical A/S and Altitude tapes +VSI) into the scan.

Today I flew over an hour and received my introduction to the FD with a CFI who has been flying Flight Directors for many years in Corporate aircraft, and the airlines. This was his first experience flying a GA plane (Mooney) in the FD mode. After flying the FD today, I believe it has the potential help me bring these panel upgrades all together, as designed.

The CFI believes the FD presentation is way too sensitive for practical use. In mild turbulence it demanded a lot of attention, significantly more than he has ever encountered. He presumes the sensitivity should be able to be adjusted to be less sensitive and more forgiving of minor turbulence deviations.

Also, the GI-275 tape altitude presentation never matches up with the round OEM Aerosonic altimeter (~ 40' difference), and we wondered where GI-275 altitude tape was receiving its altitude input? And which one we should be following.

Before I contact the avionics shop to ask the same questions next week, is anyone here familiar to share a sneak preview? Thanks.
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At what altitude are they 40' off? If they are 40' off at 6,000', they could both be within tolerance. I would recommend doing away with the original 6 pack instruments, so you don't have to scan the same information. The shop who did the install should have verified that the GI 275s were within tolerance in accordance with 14 CFR part 91.411.

-The flight director sensitivity is not adjustable. I can get you a quote to install a Garmin 500 autopilot if you'd like. We can also take a look at your altitude mismatch! Just shoot me a message.
 
Two thoughts.

As already mentioned, the FD in a light GA can be expected to appear more sensitive than in a larger corporate aircraft or airline because the aircraft itself has less inertial momentum and is more sensitive. I’ve never flow large aircraft, but my impression is that FD technique is a bit different because of this. Large AC, “just tuck it under and keep it there.” Light aircraft, “follow its prompts with small, slow, controlled movements.”

The #1 best way to get accustomed to glass of any kind is to cover the analog backup instruments.
 
I’m also curious on the perceived sensitivity comment. Is this the is FD command bars or the speed the ADI (go with it) pitches to match the aircraft pitch. The old mechanical ADI were always a little laggy compared to the new digital. So small pitch/roll is now represented immediately.

Your 275 is a tap off the static line. It sounds like a new pitot static check is in order. Should have been done with the install too.
 
I have an Stec 60-2 with a FD adapter that is interfaced to my G500TXi. There are adjustments in the G500TXi that are used to specify the sensitivity of the FD for both vertical and horizontal. I had to adjust my settings multiple times to get a usable FD presentation. I assume that the GI275 has similar adjustments, but you can confirm with your avionics shop. I expect that you will want to adjust and test fly until you are satisfied with the sensitivity.

Edit, the settings for my system were in the autopilot section and allowed for the FD calibration of V/Deg in both pitch and roll. The install manual settings were useless and tech support from Stec couldn't provide guidance. It was a try and fly iteration.
 
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Not garmin, but my king AP FD is simply giving commands to the AI that it would give to the AP. And that is “adjustable” somewhat with AP gain settings and in my aspen EA100 converter. Does your AP feel too brisk in response also?
 
Every airplane I've ever flown with both a glass panel and a round gauge altimeter shows a difference between the two. And every airplane with two separate static systems shows a difference as well. That's normal. As long as they both pass the check, pick one and use it.

It's like the saying about the person with two watches never knowing what time it is.
 
Spoke to the avionics tech who installed the panel upgrades. Yes, the FD sensitivity can be adjusted on the GI-275's, not the S-Tec 55X. Setting up the GI-275 is done within the STC default settings for the 55X, but they can be adjusted to suit the preference of the pilot. That was great news.

Regarding the altimeter's matching, both altimeters were tested and certified during the panel upgrade, and are legal. The GI-275 is digital and linear as the altitude increases. The old OEM altimeter uses bellows and is not linear, so the accuracy varies with altitude, as per the pressure data graphs supplied following the certifications. He says "take your pick", but the new digital one is more accurate with less variance.

As mentioned on the thread, two altimeters don't often match.
 
Rick A said:
….Regarding the altimeter's… He says "take your pick", but the new digital one is more accurate with less variance...
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The GI275 PFD is primary replacement for your existing analog altimeter. Unless you need the analog to drive the altitude capture on the STEC, it’s not required to be in the panel at all.

Having said that, one technique on the ground is to set the analog altimeter so that is shows the same altitude as the GI-275. When you get to cruise or get an altimeter change, just manually sync the analog altimeter to what’s displayed on the GI275.

Or just ignore the analog altimeter entirely.
 
TCABM said:
Having said that, one technique on the ground is to set the analog altimeter so that is shows the same altitude as the GI-275
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This is a good SOP for any PFD/PFD backup. It’s not just the expected difference due to internal methodology. It’s also easier and more accurate than trying to set 29.93 perfectly in a Kollsman window.
 
TCABM said:
Having said that, one technique on the ground is to set the analog altimeter so that is shows the same altitude as the GI-275. When you get to cruise or get an altimeter change, just manually sync the analog altimeter to what’s displayed on the GI275.
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Yes. That technique is also what the avionics tech suggested could be done. Checked in accordance with the published altitude of the runway (and run-up area) to be used for takeoff.
 
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Rick A said:
Yes. That technique is also what the avionics tech suggested could be done. Set in accordance with the published altitude of the runway (and run-up area) to be used for takeoff.
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I think those are two different techniques.

Unless I missed what was meant, the one @TCABM describes involves setting the PFD's altimeter in accordance with the published Baro (AWOS or ATIS), then copying the altitude to the analog back up rather than using the analog Kollssman (except as a reality check).

What you describe - setting the altimeter to field elevation (AFD or Sectional) is SOP for airports that don't have an official altimeter setting.
 
The comment by your CFI reflects no FD time in one or the other of light vs large aircraft. Large aircraft have mass and so small changes in pitch are “slower” to occur. BTDT.

You’ll master the light aircraft use of the FD, which by virtue of being installed on a platform of 1/70th the mass, is simply going to “move more”.

Just keep flying approaches BY HAND, bt FD, it has a different “reaction time” and you'll “get it”. You CAN do this (two GI-275s in a PA 34…)
 
midlifeflyer said:
I think those are two different techniques.

Unless I missed what was meant, the one @TCABM describes involves setting the PFD's altimeter in accordance with the published Baro (AWOS or ATIS), then copying the altitude to the analog back up rather than using the analog Kollssman (except as a reality check).

What you describe - setting the altimeter to field elevation (AFD or Sectional) is SOP for airports that don't have an official altimeter setting.
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I believe what he meant was a cross check of altitude error, to see if it was within limits. Regardless of how I worded it.
 
My experience with the FD on the Stec autopilots when used with the G500TXi is that the Garmin STC settings are wrong and it absolutely needed fine tuning to get it reasonable. The original STC settings were so sluggish that the FD was absolutely useless. Tuning the sensitivity ranged from hyper sensitive to ultra sluggish. I tried to get specifications for what to expect from Stec in terms of v/degree, but they could not produce them. It is an open loop system and there may be significant differences between Stec FD adapters. If I recall it took 5 or 6 flights to match the Stec FD function with the G500TXi and the result was no where near what the install manual specified.
 
John Collins said:
My experience with the FD on the Stec autopilots when used with the G500TXi is that the Garmin STC settings are wrong and it absolutely needed fine tuning to get it reasonable. The original STC settings were so sluggish that the FD was absolutely useless. Tuning the sensitivity ranged from hyper sensitive to ultra sluggish. I tried to get specifications for what to expect from Stec in terms of v/degree, but they could not produce them. It is an open loop system and there may be significant differences between Stec FD adapters. If I recall it took 5 or 6 flights to match the Stec FD function with the G500TXi and the result was no where near what the install manual specified.
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The avionics tech said the S-Tec 55X is more sensitive than King (as an example), and the 55X output is non-adjustable. According to him, installers of the GI-275's are prompted to enter which autopilot is used, and default voltages are displayed for pitch and roll voltages (and what ever else) determined by Garmin to be appropriate and used by Garmin during their STC process for certification. Which doesn't necessarily mean it's correct, but just there as a default.

This avionics tech is the "go to guy" and very experienced with decades of experience. I've worked with that shop (a very well respected business) for over 30 years, and trust his knowledge and opinions implicitly. He recommends a trial and error of method of flying various "softer" settings, starting with at least 50% softer settings. Then, the pitch and roll display (independently of each other) can be adjusted up or down. He also wants us to take videos of all the flight instruments in various flight conditions (level, turning climbs, descents, etc) to give him a better understanding of the FD presentation. Then, if or when fine-tuning is desired, he knows which way to go.

Will report back after this process and inform anyone interested about the results.
 
Your avionics tech sounds like he knows what he is doing. I was totally unhappy with the STC default settings. I expect similar results and hopefully you should be happy when it is done.
 
John Collins said:
Your avionics tech sounds like he knows what he is doing. I was totally unhappy with the STC default settings. I expect similar results and hopefully you should be happy when it is done.
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My guy said the same thing... Garmin was totally useless in helping to solve this issue.
 
Test flew the non-default GI-275 settings for the Flight Director and they were perfect (according the very FD familiar CFI (airline pilot), on the first try! The pitch and roll settings were softened appropriately 60% less from the default.

We discovered that the 55X would not roll into a standard rate turn when engaged, but showed the bank around 40% shy of standard rate. I had been attributing this shallower bank from the 55X to be from most flying most heading changes of less than 30 degrees, but it has continually seemed sluggish during all changes in headings since the installation of the new boxes.

Flew some intercepts via Heading, and coupled (NAV & NAV GPSS) onto the magenta line and noted when flying intercept angles greater than 30 degrees the bank angle was still producing about 40% less than standard rate.

Apparently there is yet another default setting we now need to increase on the GI-275 to achieve standard rate, then test fly. So not done yet.
 
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