Auto pilot modes

[Flow]

Can someone educate me on auto pilot modes ?

Or maybe there is a bug and they do not work properly ?

 

Here is what I tested :

- Route follow : works, but altitude seems strange ? Also, the plane can climb or dive pretty dramatically in order to reach programmed altitude, isn't there a limit ?

- Altitude hold (barometric) : holds altitude & roll (why does it hold roll ?)

- Attitude hold : holds plane's attitude perfectly, this one does work well

- Flight level hold : goes to 0° roll and holds altitude, works perfectly

 

I did not test the radar altitude hold.

 

Tested with latest stable version, everything up to date.

 

Thank you :)

[Ironhand]

Can someone educate me on auto pilot modes ?

Or maybe there is a bug and they do not work properly ?

 

Here is what I tested :

- Route follow : works, but altitude seems strange ? Also, the plane can climb or dive pretty dramatically in order to reach programmed altitude, isn't there a limit ?

- Altitude hold (barometric) : holds altitude & roll (why does it hold roll ?)

- Attitude hold : holds plane's attitude perfectly, this one does work well

- Flight level hold : goes to 0° roll and holds altitude, works perfectly

 

I did not test the radar altitude hold.

 

Tested with latest stable version, everything up to date.

 

Thank you :)

First, I'm not where I can double check. So I'm relying on memory of a system I don't often use. So some details are a bit fuzzy in my mind.

 

There are two ways to enter ROUTE mode, "A" and "LAlt-6". It's been awhile since I've used either but "A" adds BARALT, while LAlt-6 does not. The last time I used either, "A" had a difficult time settling on the barometric altitude unless I was already pretty well trimmed. LAlt-6, according to the sim's manual, stabilizes on the current pitch and ROUTE. I don't know if I noticed that myself or not.(In other words, if you're in a climb, it'll maintain the climb.) But that does coincide with what I've read so far in the real-world manual. In any case, I did not experience any extreme variations in altitude like I have using "A". And I think I also noticed that I could change altitude by simply using my flightstick without using the override button (which is not how the real-world manual describes the process, if that is actually what I did).

 

BARALT (barometric altitude hold) in the sim stabilizes on your current barometric altitude as well as "0" roll which is half of what the system actually does. The real-world manual indicates that what BARALT does depends on the circumstances:

To enable altitude self-regulation using BARALT, the BARALT (Нбар) button must be pressed with a vertical speed of less than 3 m/sec. When this is done, both the AUTO (АВТОМ) and BARALT annunciators illuminate and, from this point on, the longitudinal (pitch) channel is regulated by the current barometric altitude (BARALT), while laterally either roll is stabilized (provided roll is greater than 7°) or course is stabilized (if roll is less than 7°).

In other words, in the real aircraft, if your roll is greater than 7°, your current roll angle will be held as well as the current barometric altitude. If less than 7°, your roll will be brought to "0".

Edited October 25, 2017 by Ironhand

[Flow]

Thank you for your feedback.

Tried to send you a PM to thank you for all the great Lock On tutorial videos that you can find on youtube where your name is. They are really helpful and very well made.

 

I looked up the auto pilot's modes in the manual, must have been missing from the french version I guess as I cannot recall reading about it.

 

Here is the excerpt :

[A] – Switches on the route following mode and the mode of barometric altitude stabilization. When the ACS is active, this command pushes the "СБРОС" (RESET) button switching off any current mode including the "УПРАВЛЯЙ ВРУЧНУЮ" (MANUAL CONTROL) mode and "УВОД НА ВЫСОТУ" (GROUND COLLISION AVOIDANCE MODE).

 

[H] – Switches on barometric altitude stabilization mode. This is only possible when the bank angle is less than 8 degrees and the heading is stabilized.

 

[LAlt - 1] – Switches on the attitude hold mode (push-light switch "АВТОМ" is on) if the bank angle is less than 8 degrees and the heading is stabilized.

 

[LAlt - 2] – An alternative command to enable barometric altitude stabilization.

 

[LAlt - 3] – Level up to the horizon. In this mode, the ACS is not switched off by control stick overriding and it has no pitch and bank angle limits. If this mode is on, the push-light switch "ПРИВЕД К ГОРИЗ" (Level up to the horizon) is on in the lower right portion of the front cockpit panel.

 

[LAlt - 4] – An alternative command to enable barometric altitude stabilization. Same as [H].

 

[LAlt - 5] – Switches on the radar altitude stabilization mode at altitudes between 300 to 1000m. At a radar altitude of less than 50 meters or vertical velocity of more than -15 m/s, the "УВОД НА ВЫСОТУ" (GROUND COLLISION AVOIDANCE MODE) mode is engaged automatically the bank angle is zeroized and attain positive pitch using a g-load of up to 4 units.

 

[LAlt - 6] – Switches on the route following modes. Simultaneously, the pitch is stabilized based the value at mode initiation is used.

 

[LAlt - 9] –Pushing the "СБРОС" (RESET) button switching off any current mode, including the "УПРАВЛЯЙ ВРУЧНУЮ" (MANUAL CONTROL) mode and "УВОД НА ВЫСОТУ" (GROUND COLLISION AVOIDANCE MODE). It also resets an ACS failure.

 

I will try to test those with that information and report back.

Edited October 26, 2017 by Flow

[Ironhand]

Have fun! :) And thank you. Glad you're finding them helpful.

Edited October 26, 2017 by Ironhand

[WildBillKelsoe]

If you activate route follow after takeoff, it will follow route at your current altitude. If you engage altitude hold, the climb to mission editor point altitude begins. This climb is not split to VSI like airliners, but I guess there is the autopilot override setting for a reason. I think its to adjust parameters. I tried it but depending on your speed the correction to the new say altitude can be coarse or fine depending as I said on airspeed and marginal difference between set and new altitude. The autopilot then goes back to old altitude then moves on its own to the new altitude.

 

 

Sent from my iPhone using Tapatalk

[Ironhand]

If you activate route follow after takeoff, it will follow route at your current altitude. If you engage altitude hold, the climb to mission editor point altitude begins. This climb is not split to VSI like airliners, but I guess there is the autopilot override setting for a reason. I think its to adjust parameters. I tried it but depending on your speed the correction to the new say altitude can be coarse or fine depending as I said on airspeed and marginal difference between set and new altitude. The autopilot then goes back to old altitude then moves on its own to the new altitude.

 

 

Sent from my iPhone using Tapatalk

Hopefully I'll have some time to play with this over the weekend. Like I mentioned, I seldom use the AP--the "H" mostly, when I do. Now that I'm in that section of the real-world manual, it'll be interesting to see where it matches. Pressing the BARALT (H key), for instance, should not cause a climb to the scheduled altitude.

[Flow]

Hopefully I'll have some time to play with this over the weekend. Like I mentioned, I seldom use the AP--the "H" mostly, when I do. Now that I'm in that section of the real-world manual, it'll be interesting to see where it matches. Pressing the BARALT (H key), for instance, should not cause a climb to the scheduled altitude.

 

Feedback will be greatly appreciated when you have time to play around with this :)

[Ironhand]

Feedback will be greatly appreciated when you have time to play around with this :)

Played around with the ACS a bit this evening. I was flying in an Su-27. I'm assuming that other RUSFOR aircraft behave similarly. But I haven't checked that myself. Observations so far:

 

The following mirrors the system described in the real world manual fairly well:

 

• LAlt+1: The sim manual describes this as ATTITUDE HOLD, the real world manual as AUTO (АВТОМ). When engaged, the ABTOM light illuminates and the current orientation of the aircraft is stabilized. If the roll is over 7° (the sim manual states 8°), the roll is stabilized (the degrees of roll is held). If less than 7°, the course is stabilized (roll brought to 0°). Regardless of roll, the current pitch angle is held. The real world manual says it can be no more than 40°. In the sim, though, I've been at 65° and it held. Pressing and holding the combined control switch LShift+A (OVERRIDE in the sim) allows you to alter the aircraft's pitch. When released, the new pitch is held. (Sometimes, however, the aircraft first returns to the old pitch before adjusting to the new.)

 

• LAlt+2, LAlt-4, H: BAROMETRIC ALTITUDE (Нбар) has changed to mirror the description in the real world manual. When engaged, the ABTOM and Нбар lights illuminate. This means that either the roll or course is stabilized as per ABTOM above. However, the longitudinal (pitch) channel is regulated by the current barometric altitude.
   
  CAUTION: When starting on the ground on the Caucasus map, your baro altimeter is set to the runway's QFE. After takeoff (or before) set it to the mission's stated QNH. Otherwise your altimeter reading enroute will be inaccurate and BARALT will stabilize you at the wrong altitude. You can run into moutains that way. This is not an issue with an air start. Nor does it appear to be an issue on the Nevada map. Did not check Normandy.
  

 

• LAlt+6: ROUTE MODE (НАВИГ). When engaged both the ABTOM and НАВИГ lights illuminate. Pitch is stabilized according to the value at the time ROUTE MODE is engaged. Roll varies depending on the direction the aircraft needs to turn to capture and maintain the course. Pressing one of the BARALT key combos adds BAROMETRIC ALTITUDE hold to ROUTE MODE. It's best not to engage it, however, until you have achieved the scheduled altitude. In the sim, BARALT in combination with ROUTE mode tends to climb or descent your aircraft steeply.

 

• A: ROUTE MODE with BARALT. The single keypress to achieve the final result in the above paragraph. I prefer the LAlt-6 method because it allows me to determine the pitch and add BARALT once I've arrrived at the scheduled altitude. Left to it's own devises, "A" tends to climb and descend at 50°.
  

Edited October 29, 2017 by Ironhand

[Ironhand]

The way both the "A" and ROUTE plus BALART combo work in the sim is, as far as I can tell, "magical". The system should not take you to automagically to the scheduled altitude. I have more reading to do but, so far, this is the way you would translate the real world manual into the sim:

 

• First, the aircraft must be trimmed prior to engaging any ACS modes. That being said:
   
   
  
• During the climb, manually bring the current course indicator into line with the scheduled course indicator on the HSI.
   
   
  
• Keep the required bank indicator of the ADI within the center circle and begin your climb to the scheduled altitude. When you have the rate of climb you want, press the ROUTE (НАВИГ) button (LAlt+6) on the ACS panel. If not already switched on, set the Nav system to ENROUTE. When this is done, the aircraft will automatically maintain the required heading and, in the longitudinal channel, will stabilize the current pitch angle's value.
   
   
  
• Once the aircraft attains the scheduled altitude, press and hold the combined control switch (LShift+A) and level out at altitude. Release the switch and press BARALT (H) to stabilize the longitudinal channel on the current barometric altitude.
   
   
  Unfortunately, once you have engaged BARALT in the sim, the only way to follow this proceedure if the subsequent WP has a different altitude scheduled, is to use the RESET key combo and start over.

 

Here's a short video. In reality, to do what we do in the sim, after orienting the aircraft, you would press ABTO, followed by ROUTE on the ACS panel and select one of the ENROUTE modes on the navigation selector panel. At the start of the video, I'm trimming the aircraft:

 

[HwyStar]

Sorry for opening this old thread back up, Ironhand. I am flying in Caucasus Single Player while I am training before I go to Multiplayer. Your statement from above:

"CAUTION: When starting on the ground on the Caucasus map, your baro altimeter is set to the runway's QFE. After takeoff (or before) set it to the mission's stated QNH. Otherwise your altimeter reading en-route will be inaccurate and BARALT will stabilize you at the wrong altitude. You can run into mountains that way. This is not an issue with an air start. Nor does it appear to be an issue on the Nevada map. Did not check Normandy."

After reviewing your video, "I think" what I am needing to do is get the Vertical Velocity Indicator (VVI) to be at "10° or less" via trimming of the aircraft "then" it is okay to engage the AP?

The Su-27 AP is wonky and has no ability to follow RTN, or LNDG modes as I am currently using it. I do trim the aircraft manually but have not been using any of the gauges as a reference(s).

Is there a way to set the QNH on the ground in Caucasus in the Su-27? I do not see anything in the manual about QNH settings for the Su-27. Can we see the mission QNH "in-sim" or is this something I need to take note of on from the Quick Mission generated page?

Sorry for the noob questions. I've got seven hundred hours in MSFS and never had to deal with such poor results using the AP for other planes. I won't mention the Longitude. Cough, cough... Porpoising galore. The Su-27 is acting similarly to that plane in MSFS but more violently.

[draconus]

5 hours ago, HwyStar said:

Is there a way to set the QNH on the ground in Caucasus in the Su-27? I do not see anything in the manual about QNH settings for the Su-27. Can we see the mission QNH "in-sim" or is this something I need to take note of on from the Quick Mission generated page?

Sorry for the noob questions. I've got seven hundred hours in MSFS and never had to deal with such poor results using the AP for other planes. I won't mention the Longitude. Cough, cough... Porpoising galore. The Su-27 is acting similarly to that plane in MSFS but more violently.

You can find QNH in mission briefing (before hitting Fly button) [Lalt+B]. In the controls search for "altimeter pressure" binds. As long as you have the electric power you can set it.

Afaik Su-27S' AP is simulated realistically. Whatever game you played before is irrelevant. And believe me the Su-27 flight behavior is very forgiving compared to many other fighters.

Edited March 14, 2023 by draconus

[HwyStar]

Excellent, Draconus! I had not seen that binding!

Once the paint dries on my sticks new platform (distance and height set for ergonomics) I will give that a whirl. Learn something new every few hours! Thanks, Mate!

[Ironhand]

On 3/14/2023 at 6:38 AM, HwyStar said:

…After reviewing your video, "I think" what I am needing to do is get the Vertical Velocity Indicator (VVI) to be at "10° or less" via trimming of the aircraft "then" it is okay to engage the AP?

The Su-27 AP is wonky and has no ability to follow RTN, or LNDG modes as I am currently using it. I do trim the aircraft manually but have not been using any of the gauges as a reference(s).

Is there a way to set the QNH on the ground in Caucasus in the Su-27? I do not see anything in the manual about QNH settings for the Su-27. Can we see the mission QNH "in-sim" or is this something I need to take note of on from the Quick Mission generated page?

Sorry for the noob questions. I've got seven hundred hours in MSFS and never had to deal with such poor results using the AP for other planes. I won't mention the Longitude. Cough, cough... Porpoising galore. The Su-27 is acting similarly to that plane in MSFS but more violently.

“Wonky” is probably an apt description for the current implementation of the Su-27 ACS (autopilot). To be honest, I’ve seldom used the ACS myself in the past, preferring to trim and fly the aircraft, and use it not at all currently. Depending on what you are attempting to do, though, it works okay if you’re careful. For barometric hold, you need to be well trimmed. If you’re not, the oscillations you experience will be extreme. (Being within 10 m/s on the VVI is far from adequate.) I don’t mind the mild phugoid oscillations that you get once you’re trimmed, when not using the ACS.

Assuming you are trimmed and at constant speed (but not too fast) both baro-hold and route following work fine (assuming the WP transitions for the latter don’t require anything extreme). When I experimented with it yesterday, the transition from enroute to return mode and the return sequence itself worked well.

EDIT: (Inaccurate conclusion concerning landing mode removed.)

The following was only tested on a PRMG enabled runway. The ACS landing mode does work-more or less-though much differently than it used to. Your speed needs to be above 450 km/hr as you leave the IAF. Once you pick up the ILS at 8km on the HSI, you can begin slowing down but stay above 350. Taking manual control prior to reaching a height of 60 m above the ground would probably be best.

It used to be you could leave the IAF at slower speeds but that is no longer the case. The system is unable to adequately adjust to the sudden pitch down requirement as you start down the glide slope at slower speeds. As a result you quickly end up out of phase with increasingly severe oscillations as the system attempts to catch up.

Edited March 16, 2023 by Ironhand

[HwyStar]

Your edit and assessment of the ACS is spot on. I will continue playing around with it. After I am done flying in the hills and shooting at bad-guys I just wanted to engage RTN mode, relax for a bit until "final" then hand stick it onto the runway.

This system doesn't lend itself (IMHO) to flying in bad conditions using ILS to right above the runway. The last thing I would want, is to be distracted by a system that starts porpoising or experiencing bad AOA in the last few seconds in bad weather conditions. Thankfully, the Navigation mark and ILS Deviation marks work great to get us down in one piece.  

Thanks for your insights and advice about speeds at landing time. I will follow those suggestions to the "T"!  

[Ironhand]

1 hour ago, HwyStar said:

…The last thing I would want, is to be distracted by a system that starts porpoising or experiencing bad AOA in the last few seconds in bad weather conditions. Thankfully, the Navigation mark and ILS Deviation marks work great to get us down in one piece…

I suspect that, as far as landing mode is concerned, there is something wrong with the simulation. I took a quick look at the real world manual and have seen nothing warning you about speed restrictions. That sort of stuff is usually given it’s own WARNING section so as not to be missed.

If I was in the habit of using it, I’d probably use the ACS landing mode in bad weather, too. Just keep your speed about 20 km/hr higher (which you should do in bad weather, anyway) than the adjusted speed I mentioned above so that the system can react even more firmly. Don’t forget that it’s the trim system controlling the aircraft. I’d also probably take manual control prior to the inner marker.

Edited March 16, 2023 by Ironhand
Clarify a statement

[HwyStar]

I used to live in Reno Nevada where there is always bad turbulent winds at the airfield. The pilots purposely flew in quickly there to help with lateral winds pushing us around, so I totally understand coming in quick with the Su-27. IRL, I have boltered three times in Reno due to bad winds over the years. Seeing that it is an unstable aircraft I bet ED had to make the decision: fly unstable or allow the ACS to fly it for you. I pick unstable! It is fun to fly in the hills.

[Ironhand]

8 hours ago, HwyStar said:

…Seeing that it is an unstable aircraft I bet ED had to make the decision: fly unstable or allow the ACS to fly it for you…

Not sure what to make of this statement. The real world aircraft does have and uses the ACS for route following, return (either after the last waypoint is passed or when the return button is pressed), and approach down to a height of 50 meters. So ED’s only decision was to model the real world aircraft in that regard. Of course, how the ACS accomplishes that is more complex in the real aircraft than what FC3 aircraft model but the end result (route following, etc.) is there.

Just for chuckles I flew with the ACS again this morning with a 15 m/s crosswind component—the max allowable for the Su-27–to see how it would do. It handled it without any problems. Just had to keep my speed above 450 km/hr (which is the issue) until I took control over the inner marker. 

[HwyStar]

I'm the noob so take everything I say, and just ignore it. Give me a year and I might just catch on.

Biff Tannen: I can't believe you'd loan me your car without telling me it had a blind spot. I could've been killed!
Or
Biff Tannen: Since you're new here, I'm gonna cut you a break; today. So, why don't you make like a tree and get outta here?

Speed up:

[Ironhand]

 Welcome and enjoy.