Explanation and differences between: trim, AP hold, AP mode, AP override

[Igneous01]

Are there any veteran black shark flyers that can explain to me the semantic differences between all these terms? I'm trying to understand why for example auto turn to target conflicts with heading hold when at cruising speed, yet responds without issue in a hover.

 

1. How does trim interact with autopilot hold like heading hold?

 

2. Whats the difference between an AP hold and an AP mode? For example how does route mode interact with heading hold? Why can you enable flight director mode and route mode at the same time but not hover hold-mode? (btw is this a mode, override, or a hold?)

 

3. Whats the difference between an AP override like auto turn and AP mode and AP hold? How do these interact with each other?

 

For example: If I enable the 3 common AP holds (pitch, bank, heading) and enable route mode without task (heading stabilizer) and engage auto turn to target override, auto turn is extremely responsive at cruising speeds. Why does it work like this? I heard that auto-turn + disabling heading hold will achieve the same result (will test when at home).

 

I've looked at forum posts regarding descriptions of these modes. But I have not found anything that explains how these interactions work. Can someone offer any insights?

[Flagrum]

To not having to repeat what others probably can explain better ... you have read these excellent articles already?

 

http://www.simhq.com/_air13/air_428a.html

http://www.simhq.com/_air13/air_429a.html

http://www.simhq.com/_air13/air_430a.html

 

If you have still questions then, I'd gladly try to help.

[Igneous01]

Thank you flagrum for these links. Extremely informative and what I was looking for.

 

Now I have some questions:

 

1. If I engage route mode, does this mean that attitude mode is overwritten? as in, stability is applied on the ap channels, but the attitude is now being commanded by route mode?

 

2. When in altitude hold, if I hold down collective brake and increase collective, the auto-pilot is still exerting its 20% authority on my collective. It says otherwise in those articles. Is this a bug, or does this happen only when in hover-hold?

 

3. If I engage auto-turn to target, does this override the route mode attitude settings, which are overwritten from the attitude hold mode? Like a form of data transfer between the 3 modes?

[Bucic]

Also, Section 8 in Rookie pilots - Quick Intro

[ShuRugal]

Are there any veteran black shark flyers that can explain to me the semantic differences between all these terms? I'm trying to understand why for example auto turn to target conflicts with heading hold when at cruising speed, yet responds without issue in a hover.

 

For this example, auto-turn to target only produces command input on the yaw channel. At a hover, all you use to turn is yaw, so this works. At cruise speed, you need to make coordinated turns to change heading, so yaw is not enough. For auto-turn to work when flying at forward speed, you must engage auto turn (tell the helicopter where you want it to point) and route mode (tell the helicopter to use all three steering axis to get there)

 

 

1. How does trim interact with autopilot hold like heading hold?

 

The trimmer commands autopilot hold to maintain the heading, pitch, and bank angles when the trimmer button is released. Holding the trimmer down tells the AP that you want control of the aircraft.

 

2. Whats the difference between an AP hold and an AP mode? For example how does route mode interact with heading hold?

 

Setting the AP in route mode tells the aircraft that you want it to use all three channels of steering to achieve a certain heading and direction. the AP gets heading information from the following places, in order of priority (least to greatest):

 

• PVI-800 waypoints/target point
  
• Datalink target point (when DL Ingress mode is active)
  
• Shkval azimuth (when auto-turn to target is selected)
  

 

Additionally, when following PVI-800 waypoints, the PVI-800 generates a tracking angle, and selecting the DTA (desired tracking angle) switch on the AP panel will cause the AP to generate steering commands to follow the exact path.

 

 

Why can you enable flight director mode and route mode at the same time but not hover hold-mode? (btw is this a mode, override, or a hold?)

 

Hover-hold and route mode do opposite things. Hover mode tells the AP to use all steering axis to maintain a specific point over the ground. Route mode tells the AP to use all steering axis to maintain forward flight in a certain direction. Obviously both of these cannot be done at the same time by the same helicopter.

 

Flight-Director mode tells the AP not to put any steering commands to the helicopter, but to instead display them on the HUD so you can do it manually.

 

 

3. Whats the difference between an AP override like auto turn and AP mode and AP hold? How do these interact with each other?

 

not sure what you mean by "an AP override". The AP override switch on the cyclic kills all AP and flight-stab channels and returns the helicopter to pure manual control.

 

 

For example: If I enable the 3 common AP holds (pitch, bank, heading)

 

it is important to remember that these three channels are not only "holds". Without using te AP modes (route, auto-turn, or auto-hover), they function as holds, but they also allow the AP modes to work. If you turn off one of those channels and turn on the AP, the AP won't work right.

 

and enable route mode without task (heading stabilizer) and engage auto turn to target override, auto turn is extremely responsive at cruising speeds.

 

I mentioned this above, but what you are seeing is the AutoPilot Route Mode taking the heading information generated by Auto Turn, and turning it into fully-coordinated steering commands. Without route mode, Auto Turn only tries to yaw the helicopter to achieve the desired heading.

 

Why does it work like this? I heard that auto-turn + disabling heading hold will achieve the same result (will test when at home).

auto-turn and disable heading hold will do nothing. the heading hold button enables the yaw channel of the AP. if you disable this channel, auto-turn wont work.

 

 

Thank you flagrum for these links. Extremely informative and what I was looking for.

 

Now I have some questions:

 

1. If I engage route mode, does this mean that attitude mode is overwritten? as in, stability is applied on the ap channels, but the attitude is now being commanded by route mode?

 

yes.

 

2. When in altitude hold, if I hold down collective brake and increase collective, the auto-pilot is still exerting its 20% authority on my collective. It says otherwise in those articles. Is this a bug, or does this happen only when in hover-hold?

Not sure if it is a bug or not, but it has always behaved that way. Collective brake -should- tell the AP to let go of the collective, the same way trimmer tells AP to let go of cyclic and rudders, but it doesn't.

 

3. If I engage auto-turn to target, does this override the route mode attitude settings, which are overwritten from the attitude hold mode? Like a form of data transfer between the 3 modes?

 

 

order of priority for route-mode steering points (least to greatest) is as follows:

 

• PVI-800 waypoints/target point
  
• Datalink target point (when DL Ingress mode is active)
  
• Shkval azimuth (when auto-turn to target is selected)
  

 

So if you are following waypoints, but point the shkval somewhere and turn on auto-turn, the shkval azimuth becomes your new route-mode heading.

Edited December 14, 2014 by ShuRugal

[Igneous01]

Thank you ShuRugal for explaining this to me, now its starting to make more sense!

 

I was discussing this with someone on the DCS facebook group, and they told me this:

 

"You can not "engage" auto turn without having something in the auto pilot first. It is an override, not a mode. What is your auto pilot mode in the first example, where you get no turn? An override in route mode will work well, yes, but it should work to some extent in any mode, I believe."

 

"Auto turn to target IS NOT A MODE. It is an OVERRIDE.

 

With all those switches off your auto pilot is in "attitude hold" mode. It will not attempt to change your heading. I am surprised you get anything out of ATtT in that mode. The auto pilot ought not try to change heading at all then."

 

"When you have heading stability on and move at speed, you have told the auto pilot to maintain attitude over everything else. It may turn, but it will be slow. In route mode you have told the auto pilot to maintain direction to the waypoint over everything else, and sacrifice attitude to accomplish this.

 

Then you turn on the override of ATtT, and the auto pilot, still obeying your primary command (the mode) will try to accomplish this *as well*.

 

It's not all that obvious unless you remember both that ATtT is an override and that the auto pilot is very stubborn and will do exactly what you tell it to do through the mode."

 

So, I'm not exactly sure if he is correct on all these aspects. I will point him to this forum post just in case.

[ShuRugal]

ATtT is not an "override". All it does is tell the yaw channel to point the helicopter at where the shkval is looking. With route mode disabled, this is the same as using the rudder pedals (and only the rudder pedals) to steer the nose of the helicopter.

 

With route mode engaged, the AP takes the heading generated by ATtT and treats it the same way it treats the headings generated by the PVI-800 or the Datalink Automatic-Ingress. The only way in which ATtT could be considered an "override" is that the heading generated by ATtT will be used first, even you already have the PVI-800 or the DL-Ingress (or both) turned on.