AP Altitude Hold

[dmccormack]

A question for those here with A/P with altitude hold...

Do you use it?

I've found that trimming the airplane correctly is more effective that A/P at holding altitude. Maybe it's just the A/Ps I've used?

 

[Everskyward]

A question for those here with A/P with altitude hold...

Do you use it?

Yes.

I've found that trimming the airplane correctly is more effective that A/P at holding altitude. Maybe it's just the A/Ps I've used?

I'm voting for that.

 

[DGlaeser]

I use the A/P all the time for XC flights, especially in my RV. My TruTrack holds altitude great. The KAP 140's and GFC700's in the Cessnas I fly also hold altitude with ease.
What kind of A/P's do you use?

 

[TMetzinger]

I have it, and I use it. Modern autopilots do a fine job of flying the airplane. If your A/P isn't holding altitude, then there may be some slop in your control cable rigging, or your servos may be in need of a refurb.

 

[Areeda]

I use the STec 30 and 55x alt hold, much better than i can do with trim.

I've also used the GFC700 which is even better.

Joe

 

[dmccormack]

I use the STec 30 and 55x alt hold, much better than i can do with trim.

I've also used the GFC700 which is even better.

Joe

OK, Century 2k and now S-TEC 30.

I can trim the airplane to 0 on the VSI and it will stay there for minutes, with only a slight nudge with a finger to maintain within +/- 10 FPM.

 

[RotorAndWing]

If your A/P isn't holding altitude, then there may be some slop in your control cable rigging, or your servos may be in need of a refurb.

Not necessarily. Depending upon the autopilot and what is uses for the output of the altitude hold function. Some autopilots use barometric sensors for the altitude hold function and these can be affected by moisture in the system.

For a little information on autopilots: http://www.avionicslist.com/articles/autopilots.php

http://www.centuryflight.com/manuals/CENTIII.pdf

 

[gismo]

OK, Century 2k and now S-TEC 30.

I can trim the airplane to 0 on the VSI and it will stay there for minutes, with only a slight nudge with a finger to maintain within +/- 10 FPM.

That depends on both the airplane involved and the atmospheric conditions. A Cessna 182 is pretty rock solid in pitch and altitude but a Bonanza or Baron, especially one loaded at or near the aft CG limit will wander if you don't stay on it almost continuously.

Then there's the weather. Smooth air is one thing but unstable air or wave action will cause the most stable airplane to move off altitude rather quickly. I use A/H almost any time I'm not hand flying i.e. most of the time in cruise flight.

 

[nyoung]

My Cherokee only has a wing-leveler, and I'd give almost anything (except the $13k install price) to have a new A/P with altitude hold.

Our family used to have a Seneca II that had the Piper Autocontrol IIIC (which included altitude hold). It worked very well. Climb to altitude, engage, and it would basically hold altitude for 100 miles at a time. On long XC's, eventually the pressure would change enough that you would have to disconnect, recapture the altitude and re-engage. It sure was nice to let the A/P fly the long XCs, while we got to sit back and monitor the plane and traffic.

A friend has an SR22 with an STEC55x. Wow, is all I can say. Altitude pre-select and vertical speed select, GPSS, and so on. An absolutely amazing piece of equipment.

Anyway - to answer your question... Yes, I've used altitude hold and it works quite well when the A/P is working well. Further, after flying 1000hrs (much of it XC) in my current setup without altitude hold, I'd consider it almost a requirement for anyone planning to do traveling.

A question for those here with A/P with altitude hold...

Do you use it?

I've found that trimming the airplane correctly is more effective that A/P at holding altitude. Maybe it's just the A/Ps I've used?

 

[gismo]

Not necessarily. Depending upon the autopilot and what is uses for the output of the altitude hold function. Some autopilots use barometric sensors for the altitude hold function and these can be affected by moisture in the system.

For a little information on autopilots: http://www.avionicslist.com/articles/autopilots.php

http://www.centuryflight.com/manuals/CENTIII.pdf

A friend and I were both flying Barons on the same XC trip. His Century 2000 started making big pitch changes along with altitude excursions in excess of a couple hundred feet. I told him to try opening the alternate static valve and he said that smoothed it right out. No doubt he had moisture in the static lines.

 

[CJones]

I use the A/P all the time for XC flights, especially in my RV. My TruTrack holds altitude great.

^^^ What he said.

I wouldn't want to fly an RV in hard, choppy IFR for extended periods of time without Alt hold.

 

[TangoWhiskey]

I use it. Most autopilots I've used will trim the aircraft to hold altitude; that is, if you disengage the autopilot, it should be in trim and continue to fly and hold the last altitude if you don't touch anything.

That said, I've seen on the Cessna 172's I've flown with the KAP140 Bendix-King autopilot where the altitude I've selected, when locked on to ALT SEL, will end up showing me (on the altimeter) 20 or 40 feet higher or lower than the selected altitude (on the autopilot), despite having the same altimeter setting dialed into both the kollsman window on the altimeter and the autopilot (via the BARO button).

The key here is to use the UP and DN on the autopilot to adjust the altitude reference up or down 20 feet at a time, which makes the altimeter "nail" the altitude you want. I'm often surprised to find how many of the CFII's I've used for IPC's don't know this "trick", which is documented in the manual. One of those nuances you learn by reading the book.

From the KAP140 manual:

To operate in the ALT mode (with autopilot currently in the Vertical Speed mode):

1. ALT button - Press. Note ALT is annunciated and autopilot maneuvers to maintain pressure altitude acquired at button selection.

2. UP or DN button - Select to change altitude. Incremented button strokes will move the reference altitude by 20 feet per press, or if held continuously will command a 500 ft/min altitude change, acquiring a new reference altitude upon button release.

 

[dmccormack]

That depends on both the airplane involved and the atmospheric conditions. A Cessna 182 is pretty rock solid in pitch and altitude but a Bonanza or Baron, especially one loaded at or near the aft CG limit will wander if you don't stay on it almost continuously.

Then there's the weather. Smooth air is one thing but unstable air or wave action will cause the most stable airplane to move off altitude rather quickly. I use A/H almost any time I'm not hand flying i.e. most of the time in cruise flight.

Interesting... the C2 was in an A36 and I found it hunted a bit, but held once all was trimmed up.

Of course trim seemed a bit more "coarse" in the A36...

After flying with the S-TEC in the 205 a while, I've come to appreciate its simplicity and redundancy.

But it's never been able to hold altitude as well as well-trimmed.

 

[Areeda]

OK, Century 2k and now S-TEC 30.

I can trim the airplane to 0 on the VSI and it will stay there for minutes, with only a slight nudge with a finger to maintain within +/- 10 FPM.

We have an Archer and a 182RG with an STec 20 (like the 30 but without alt hold) and yeah they both work like that.

Alt hold in our Cirrus and Arrow keep an altitude for hours or until we make a significant change in baro setting.

Does the plane wander off altitude or do vertical S's around the altitude?

Joe

 

[dmccormack]

We have an Archer and a 182RG with an STec 20 (like the 30 but without alt hold) and yeah they both work like that.

Alt hold in our Cirrus and Arrow keep an altitude for hours or until we make a significant change in baro setting.

Does the plane wander off altitude or do vertical S's around the altitude?

Joe

I can trim it to perfect, hit Alt hold, and we begin the excursions (+/- 100') until the altitude is re-captured.

Annoying and pointless.

 

[tonycondon]

ive never really flown with a fancy new autopilot. have some time in STEC 30's in 172 and 182RG and I think the 421's had Cessna 400 series autopilots. they actually worked, pretty well most of the time. And they had to since we were a single pilot IFR pt. 135 operation.

most of the time that trim would hold altitude acceptably for me is time I would rather be hand flying anyway. that generally would be nice smooth air with a low workload. The autopilot is for turbulence and/or IMC

 

[dmccormack]

ive never really flown with a fancy new autopilot. have some time in STEC 30's in 172 and 182RG and I think the 421's had Cessna 400 series autopilots. they actually worked, pretty well most of the time. And they had to since we were a single pilot IFR pt. 135 operation.

most of the time that trim would hold altitude acceptably for me is time I would rather be hand flying anyway. that generally would be nice smooth air with a low workload. The autopilot is for turbulence and/or IMC

I'm happy using the A/P in IMC or turbulence for heading, but find the excursions are less hand (finger-pressure, really) flying than waiting for the A/P to catch up.

 

[AdamZ]

The AP I used in the Tiger I flew was awesome steady as a rock. The one I used in a Saratoga and in a relativley new Archer III had to be shut off because the oscillations drove me nuts.

 

[SkyHog]

I always flight with 2 autopilots: leftie and rightie, but rightie is still not calibrated properly.

I don't get autopilots, I really don't. I fly because I like flying, not because I like getting somewhere. Maybe that's just me.

 

[TMetzinger]

I always flight with 2 autopilots: leftie and rightie, but rightie is still not calibrated properly.

I don't get autopilots, I really don't. I fly because I like flying, not because I like getting somewhere. Maybe that's just me.

Must be. An autopilot is a big help when your workload gets high, particularly in the descent and approach phases of an IFR flight. At a minimum, it'll keep you straight and level while you go dig out a chart, or brief the arrival, or copy down an amended clearance. A modern autopilot used the way the manufacturer intends puts the equivalent of an ATP first officer in the cockpit. The good news is he never argues with the captain. The bad news is he never argues with the captain, so the captain better be really clear when he gives "George" his instructions via the autopilot mode control panel and/or flight management system.

I don't use the autopilot when I'm buzzing around VFR, or when I'm doing proficiency flying. I'll often "trade legs" when flying IFR solo or with a safety pilot. When I've got pax on board, though, I generally use the autopilot to the max. It frees me up to spend more time monitoring and managing, and that translates to a safer flight, which I think is my duty to my pax.

 

[SkyHog]

Must be. An autopilot is a big help when your workload gets high, particularly in the descent and approach phases of an IFR flight. At a minimum, it'll keep you straight and level while you go dig out a chart, or brief the arrival, or copy down an amended clearance. A modern autopilot used the way the manufacturer intends puts the equivalent of an ATP first officer in the cockpit. The good news is he never argues with the captain. The bad news is he never argues with the captain, so the captain better be really clear when he gives "George" his instructions via the autopilot mode control panel and/or flight management system.

I don't use the autopilot when I'm buzzing around VFR, or when I'm doing proficiency flying. I'll often "trade legs" when flying IFR solo or with a safety pilot. When I've got pax on board, though, I generally use the autopilot to the max. It frees me up to spend more time monitoring and managing, and that translates to a safer flight, which I think is my duty to my pax.

That is one way to look at it.

I prefer to concentrate on flying the airplane as proficiently and smoothly as I can, so that my passengers can recognize me as a good stick, and not George. Also - how does it not get boring flying a 5 hour leg hands off?

 

[Greg Bockelman]

I don't get autopilots, I really don't. I fly because I like flying, not because I like getting somewhere. Maybe that's just me.

Autopilots have their place. If you don't "get" it, you obviously don't need one. There may come a time in the future when you will think, "Man, I sure could use another set of hands here" or "Man, this flight sure was tiring" THEN you will get it.

 

[SkyHog]

Autopilots have their place. If you don't "get" it, you obviously don't need one. There may come a time in the future when you will think, "Man, I sure could use another set of hands here" or "Man, this flight sure was tiring" THEN you will get it.

I agree 100%. Part 135 and 121 definitely need to use autopilots because they have to fly in some pretty crappy weather.

But I can't see any point to Part 91 Autopilot, except in a really long batch of IMC, and even then, it would get boring I'd think.

 

[dmccormack]

I always flight with 2 autopilots: leftie and rightie, but rightie is still not calibrated properly.

I don't get autopilots, I really don't. I fly because I like flying, not because I like getting somewhere. Maybe that's just me.

Do you fly IFR long distances?

If not, then it is rather pointless.

But if you do, it's like having a co-pilot, and helps to reduce overall fatigue and workload, especially in busy airspace or IMC.

That said, let's not let this thread descend into a "real men don't use autopilots" spiral. If you don't have one or use one -- fine.

 

[jtheune]

OK, Century 2k and now S-TEC 30.

I can trim the airplane to 0 on the VSI and it will stay there for minutes, with only a slight nudge with a finger to maintain within +/- 10 FPM.

How much do you weigh? I weigh 250 and I often fly with other like sized people and I find that just leaning forward or reaching into the back seat can throw the trim off enough to cause a altitude change so I like the autopilot to manage it for me.

 

[wsuffa]

I have it (STEC 60-2), use it all the time. It sure helps on the long IFR XCs.

I also do use it occasionally to fly coupled IMC approaches on an ILS - especially after a long flight.

 

[TMetzinger]

That is one way to look at it.

I prefer to concentrate on flying the airplane as proficiently and smoothly as I can, so that my passengers can recognize me as a good stick, and not George. Also - how does it not get boring flying a 5 hour leg hands off?

Well, with the autopilot flying, I spend the time:

• Monitoring flightplan and fuel usage
• Watching the engine gauges
• Monitoring the autopilot.
• Checking weather enroute and destination.
• Wheedling a shortcut from ATC
• Looking for traffic.
• Enjoying the scenery (if not in actual)
• Chatting with pax.
• Posting on POA (just kidding).

A key difference is that I fly differently depending on the mission:

• Proficiency Flying is done by hand, with drills as necessary to ensure I know the automated systems. I operate to the edge of my performance envelope here and try to expand it with a CFI. This is where I develop and maintain the "superior skills" I hope to never need.
• "Fun" Flying is generally done solo, or with other pilots on board. Here I stay somewhat more inside my performance envelope, but still may fly by hand. But everyone on board the plane is a pilot and understands the risks.
• "Pax" Flying puts safety first - I try to think like a captain, and use every tool at my disposal to increase the margin of safety. I'm operating well inside my performance envelope here unless something goes wrong. And I'm conserving myself so I'll be as fresh as possible if something does go wrong.

Now, I'll readily admit that there are those who rely on the automation and cannot operate safely without it. They don't do much/any proficiency flying or fly with a CFI for a review. And when the automation breaks or malfunctions, they don't have the skills to salvage the situation. I try really hard not to become one of them.

 

[Greg Bockelman]

I agree 100%. Part 135 and 121 definitely need to use autopilots because they have to fly in some pretty crappy weather.

But I can't see any point to Part 91 Autopilot, except in a really long batch of IMC, and even then, it would get boring I'd think.

Nick, it isn't just weather. You really don't realize just how much brain power it takes to keep the plane straight and level and navigate on even three hour flights. Even in VMC. I didn't realize that until I had access to a wing leveler in an Archer. I was amazed at just how much better I felt after a three hour VFR cross country with just a wing leveler.

And I won't comment on the 135/121 thing because it isn't really relevant. It doesn't really matter. Flying and navigating is the same no matter what set of rules you operate under.

 

[TMetzinger]

Hey Greg,

Do you have one in the 195? Does using it allow you to monitor your oil level more closely?

 

[gismo]

Nick, it isn't just weather. You really don't realize just how much brain power it takes to keep the plane straight and level and navigate on even three hour flights. Even in VMC. I didn't realize that until I had access to a wing leveler in an Archer. I was amazed at just how much better I felt after a three hour VFR cross country with just a wing leveler.

And I won't comment on the 135/121 thing because it isn't really relevant. It doesn't really matter. Flying and navigating is the same no matter what set of rules you operate under.

+1

Enroute, it's all the other stuff you could be doing to make the flight safer and/or more comfortable for you and your pax that the autopilot allows you to do. In the terminal area an autopilot makes it much easier to brief and set up for an approach, study the airport diagram, etc. And when the fecal matter contacts the rotating air mover they really earn their keep. Case in point: while tooling along on a non-precision MDA to an outlying field that was advertising good VMC on the ASOS you find that it was lying and you're still in the clouds as you pass the MAP. The alternate is only 15 nm away and they just switched to a different approach than you expected to be in use there due to a big wind shift. Approach turns you towards the final and you need to set up the radios and brief the approach. You'll be intercepting the approach in about 3 minutes. Wouldn't you like a little help? Or try this one: As you get close to your destination in pretty bumpy air after winding your way around numerous cells you can see that one storm has just cleared the airport but there's another bearing down on it. You really need to pay close attention to the onboard radar as you prepare to fly the approach but you're also busy working out plan B if the arriving storm gets too close for comfort. Letting George or Otto handle the mechanics of flying removes the panic like feeling and lets you use most of your brain power on managing the flight.

 

[SCCutler]

What Lance said (except, of course, I don't have Radar).

As to altitude hold, I love it, but do not typically engage it until I have trimmed out to straight and level, two or three minutes (at least) after leveling off. Otherwise, if I engaged it early (sloppy practice), when I disengage it, it will "pop" up or down (depending upon whether I had leveled from a climb or descent), and in the meantime, I will have been working the servos needlessly.

 

[Everskyward]

Enroute, it's all the other stuff you could be doing to make the flight safer and/or more comfortable for you and your pax that the autopilot allows you to do. In the terminal area an autopilot makes it much easier to brief and set up for an approach, study the airport diagram, etc. And when the fecal matter contacts the rotating air mover they really earn their keep. Case in point: while tooling along on a non-precision MDA to an outlying field that was advertising good VMC on the ASOS you find that it was lying and you're still in the clouds as you pass the MAP. The alternate is only 15 nm away and they just switched to a different approach than you expected to be in use there due to a big wind shift. Approach turns you towards the final and you need to set up the radios and brief the approach. You'll be intercepting the approach in about 3 minutes. Wouldn't you like a little help? Or try this one: As you get close to your destination in pretty bumpy air after winding your way around numerous cells you can see that one storm has just cleared the airport but there's another bearing down on it. You really need to pay close attention to the onboard radar as you prepare to fly the approach but you're also busy working out plan B if the arriving storm gets too close for comfort. Letting George or Otto handle the mechanics of flying removes the panic like feeling and lets you use most of your brain power on managing the flight.

I agree with all of this but I don't think Nick has an instrument rating, plus I'm guessing the flying he does is different than what you do. I didn't use autopilots until pretty late in life because the airplanes I flew either didn't have one, or the one they had didn't work worth a darn. I think that fighting a cranky autopilot is often times worse than not using it at all.

 

[Clark1961]

What Lance said (except, of course, I don't have Radar).

As to altitude hold, I love it, but do not typically engage it until I have trimmed out to straight and level, two or three minutes (at least) after leveling off. Otherwise, if I engaged it early (sloppy practice), when I disengage it, it will "pop" up or down (depending upon whether I had leveled from a climb or descent), and in the meantime, I will have been working the servos needlessly.

As a contrast, with the Century IIIc, the altitude hold includes an autotrim function. I just engage the altitude hold about fifty feet from my desired altitude and George does the rest. Gotta love the analogue computer and sensors - the fifty feet of offset seems to be required for the system to wake up and notice that I've asked it to do something.

The Century IIIc is ancient and a pain to work on but when it works, it works great. Unfortunately right now the trim amp is in Tulsa for testing and repair.

 

[SkyHog]

I agree with all of this but I don't think Nick has an instrument rating, plus I'm guessing the flying he does is different than what you do. I didn't use autopilots until pretty late in life because the airplanes I flew either didn't have one, or the one they had didn't work worth a darn. I think that fighting a cranky autopilot is often times worse than not using it at all.

That is true, Mari. I think I should revise my belief to say that I don't get why people would use autopilots for VFR flights, Fun flights, or Proficiency flights, passengers or not.

IFR flights (IMC or VMC), Professional Flights, and similar things I can see using the Autopilot.

I get what everyone says, I still think it would sap the fun out of flying to just sit there and let George work the plane for ya.

 

[jesse]

I always flight with 2 autopilots: leftie and rightie, but rightie is still not calibrated properly.

I don't get autopilots, I really don't. I fly because I like flying, not because I like getting somewhere. Maybe that's just me.

Put yourself on an instrument approach, in bumpy clouds, to an unfamiliar airport, single pilot, get your approach switched at the last moment..and you'll wish you had an autopilot.

Flying, communicating, bouncing through clouds, and flipping through an approach book trying to brief yourself is not a fun task.

 

[HPNPilot1200]

Yes I have and it works great. My experience is mainly with the Bendix King KAP140, KFC150, Garmin GFC700, and Collins Proline 21 A/P in the CJ3.

Anytime I'm reading a map or doing something else that requires my focus, the autopilot comes on. That's what it's there for. Single pilot IFR, you can bet I have it on most of the flight.

 

[Sam D]

I've got a question about Century III altitude hold and whether it could be 'upgraded'. If an Aspen can take a gps input and give you GPSS for the autopilot (Century III), is it possible to also eventually have an 'altitude select' upgrade? I know they are working on being able to get attitude information from their own ADHRS. I wonder whether 'atitude select' would even be a possible upgrade.

 

[TMetzinger]

The real issue as I understand it is not the technical bits of getting a new device like the Aspen to send signals to the autopilot computer. It's all the flight testing and documentation needed to certify the combination. I believe as the GA flight decks get more electronic and more modular that the FAA MAY (repeat MAY) start dictating certain interoperability standards for signals and interfaces, and then any two devices certified to meet those standards can be coupled with only an installation flight test to verify, sort of the way IFR GPS installations were done in the early and mid 90s. AMT installs it, tests it on the ground - a test flight is conducted and documented, and all that gets filed with the 337.

 

[Clark1961]

I've got a question about Century III altitude hold and whether it could be 'upgraded'. If an Aspen can take a gps input and give you GPSS for the autopilot (Century III), is it possible to also eventually have an 'altitude select' upgrade? I know they are working on being able to get attitude information from their own ADHRS. I wonder whether 'atitude select' would even be a possible upgrade.

I can fly to and hold an altitude using the pitch hold function and pitch control wheel on the III so I suspect it could be done. I have no idea how smooth it'd be since the darn pitch wheel can be twitchy. It'd be a nice improvement to be rid of (or at least not have to use) the altitude chamber portion of the altitude hold.

 

[Everskyward]

I get what everyone says, I still think it would sap the fun out of flying to just sit there and let George work the plane for ya.

I understand what you are saying, Nick. Many pilots derive a sense of kinesthetic pleasure from flying an airplane. I do and I know a lot of others who do too. But like others have mentioned, that has its place, and there are other times when it is easier to have the mechanical part of flying being done by the autopilot while you are trying to deal with some other more mental aspect of flying.