Autopilot'n'stuff

[Flagrum]

We have different components that interact with each other:

- Autopilot

- Magnetic Brake Trim

- Gyros

- INS

 

To me, it is not really clear how these components are supposed to work together, especially not when I observe their behaviour in-game. But after spending some time in DCS helos in general and the Gazelle in particular, I would expect them to work like this:

- Autopilot: controls the helo when Altitude hold or Speed hold modes are engaged. Control is exercised independently (within limits?) from pilot inputs.

- SAS: a separate component that has basically nothing to do with the AP. Basically only dampens pilot inputs

- Mag. Brake Trim: "centers" the cyclic in terms of forces that are needed to deflect it. Trim button depressed: no forces (FFB off), button released: current stick position = force center. Unsure, how or if releasing the trim button should interact with SAS and/or the AP. My feeling: the effects should be at least way more "subtle" that they are right now.

- 4-hat trim: only adjusts the helo's attitude. Should probably not affect the force trim? Or maybe it should, but as this way to change the attitude is already rather subtle, it would be ok, I guess? The effects on AP and SAS ... probably should be similar to those when using Mag. Brake trim.

- Gyros: working gyros are a prerequisite for the INS and the AP. But is that true for the SAS then as well? Anyhow, switching off AP and/or SAS must not require the gyros to be shut off as well, right!?

 

Any thoughts?

[Sephyrius]

Don't know much about it, but for one the stick trim buttons affect the position of a ffb joystick, so the pilot trimmer (force trim) and the trim buttons seem to influence eachother/work in tandem. Which I love - after the recent FM changes I've gone back to using DCS ffb instead of SimFFB.

 

Haven't had much reason to turn off the gyros, but on the occasions that it has failed (for whichever reason) it has prevented the use of auto-hover entirely, not sure if it affected SAS much since that one's more subtle, but that's all to be expected.

Edited November 18, 2017 by Sephyrius

[Ramsay]

We have different components that interact with each other:

- Autopilot

- Magnetic Brake Trim

- Gyros

- INS

 

To me, it is not really clear how these components are supposed to work together, especially not when I observe their behaviour in-game. But after spending some time in DCS helos in general and the Gazelle in particular, I would expect them to work like this:

- Autopilot: controls the helo when Altitude hold or Speed hold modes are engaged. Control is exercised independently (within limits?) from pilot inputs.

- SAS: a separate component that has basically nothing to do with the AP. Basically only dampens pilot inputs

This is pure guess work based on how the SA341G, AS332 Super Puma and other helicopters work:-

 

SAS by default controls Attitude, it only functions when the auto-pilot is on and pitch, roll and yaw channels enabled. The cyclic mag brake button is dual function and sets both stick 'feel' and SAS Attitude. Correction signals from the Gyros are used by the SAS to maintain the set Attitude.

 

Auto-pilot 'Speed Hold' and 'Altitude Hold' are 'Higher Functions' of the SAS, both these holds are functions of the Pitch channel, hence only one can be selected at a time. The desired Speed/Altitude is set when the Hold switch is turned on. The Pitch channel receives correction signals to maintain IAS or barometric Altitude rather than from the pitch gyro.

 

AFAIK, once airspeed is above 48kts (89 km/h), the 'Badin switch' disengages the yaw SAS electric actuator as it lacks sufficient control authority.

- Mag. Brake Trim: "centers" the cyclic in terms of forces that are needed to deflect it. Trim button depressed: no forces (FFB off), button released: current stick position = force center. Unsure, how or if releasing the trim button should interact with SAS and/or the AP. My feeling: the effects should be at least way more "subtle" that they are right now.

Releasing the Mag Brake button "centres" cyclic stick feel and sets the desired SAS attitude, so the mag brake button is dual function. Micro switches in the cyclic/linkage ensure the pilot always has control over and above the SAS, even when the mag brake is not depressed.

- 4-hat trim: only adjusts the helo's attitude. Should probably not affect the force trim? Or maybe it should, but as this way to change the attitude is already rather subtle, it would be ok, I guess? The effects on AP and SAS ... probably should be similar to those when using Mag. Brake trim.

I believe the 4-hat trim is used fine tune the Mag Brake. It's not clear if it adjusts SAS Attitude as set with the Mag Brake button but some SFIM systems do have that feature.

- Gyros: working gyros are a prerequisite for the INS and the AP. But is that true for the SAS then as well? Anyhow, switching off AP and/or SAS must not require the gyros to be shut off as well, right!?

The gyros are require for the INS, SAS and AP to function. With the AP/SAS control channels turned off, SAS will no longer work.

 

AFAIK the Autopilot button on the RL cyclic is an 'Autopilot Disconnect' (not a 'AP Toggle') and turns OFF the SAS/AP on the servo control panel and the switch(s) have to be flipped back on there.

 

However, the DCS SA342M SAS seems to work far longer than I would expect i.e. with the AP turned off.

 

Some Ref's but none are specific to the SA342M:

SA341G SAS Diagram: https://i.imgur.com/g8vWO2C.jpg

SFIM Bell Model 407 AP85 Autopilot Presentation: http://slideplayer.com/slide/9967104/

AS332L Autopilot: http://www.finckaviation.com/files/Section_14_-_Autopilot.pdf

Edited May 7, 2020 by Ramsay
Mixed up the AP and Auto-hover buttons on the cyclic, add 'Badin' switch SAS yaw detail. Fix dead link.

[blaster182]

What does the Autopilot button on the cyclic do?

 

I have a question on the 'Autopilot' button on the pilot's cyclic stick, see picture on the right.

 

What does it actually do in the game? I have noticed a small effect when pushing the button on higher speeds and manuevering.

 

Is it the same effect as 'Autopilot master'?

Is it a toggle switch (on/off) or does it have to be held continuously?

[Sprool]

I struggled with this for ages, and am still struggling to grasp the logic in these control systems. There is a master autopilot on/off switch on the dashboard, this activates the SAS, then there is the autopilot button on the stick, which turns autopilot on and off as needed (but you need autopilot master switch on to do anything). How that differs to the trim and mag brake is something thats still evading me.

The autopilot should self-engage at >120 kmh anyway, so what does the little autopilot sick button actually do, and how should it be used correctly? Its almost as if this whole helicopter was designed by French people ;)

[blaster182]

I struggled with this for ages, and am still struggling to grasp the logic in these control systems. There is a master autopilot on/off switch on the dashboard, this activates the SAS, then there is the autopilot button on the stick, which turns autopilot on and off as needed (but you need autopilot master switch on to do anything). How that differs to the trim and mag brake is something thats still evading me.

The autopilot should self-engage at >120 kmh anyway, so what does the little autopilot sick button actually do, and how should it be used correctly? Its almost as if this whole helicopter was designed by French people ;)

 

:lol: Thanks for your response. Well at least I'm not the only person unable to figure out the AP button on the pilot's control stick. It would be nice if one of the developers could shed some light in this.

 

I flew the Gazelle again today and have to say that I like it better and better, even with the flight model and SAS support making it feeling kind of fly-by-wire at times. It is a great addition to the choppers in DCS, very agile.

[Sprool]

With the Mag Brake on, I get the 'usual' Huey-type trim response when I press the trim button I mapped to my X52. It 'sticks' the controls where I set them. Now if I use the POV Hat trim it nudges the trim position very slightly L, R, U, D but not enough to affect the flight of the aircraft. This nudging seems to happen (on the control position display) whether or not I have the master trim button on.

[Sprool]

Well I think its starting to make more sense now. Master power on buttons for trim and autopilot kept on all the time.

Mag Brake switch on , trim hold on pinkie trigger (X52) works just like the Huey, which is perfect. In addition you can nudge the trim making very small corrections/adjustments with the POV Hat switch.

Autopilot normal mode is stability assist, just let it do its thing. The autopilot switch on the stick then acts as an 'attitude hold' to hold a bank angle or pitch. When it is released, you can feel the Gazelle coming back upder the controls of the stability assist, righting itself to a stable position.

[blaster182]

Well I think its starting to make more sense now. Master power on buttons for trim and autopilot kept on all the time.

Mag Brake switch on , trim hold on pinkie trigger (X52) works just like the Huey, which is perfect. In addition you can nudge the trim making very small corrections/adjustments with the POV Hat switch.

Autopilot normal mode is stability assist, just let it do its thing. The autopilot switch on the stick then acts as an 'attitude hold' to hold a bank angle or pitch. When it is released, you can feel the Gazelle coming back upder the controls of the stability assist, righting itself to a stable position.

 

Alright, thanks for going into this again. I'll follow your explanation when I fly the Gazelle next time :thumbup:

[Sprool]

Soz- in addition to the standard autopilot functions you then have the altitude mode or speed mode, which allows you to hold one while varying the other with the collective.

[Volator]

Soz- in addition to the standard autopilot functions you then have the altitude mode or speed mode, which allows you to hold one while varying the other with the collective.

 

I can't activate AP altitude hold or speed hold. Attitude hold works fine with the AP master switch on and pushing the stick autopilot button, but the other modes (altitude/speed) don't seem to kick in when I use the respective switch. Am I doing something wrong, or is it broken?

 

 

[Tanuki44]

I rather consider these modes (altitude, speed) as regulators.

 

For to engage, the speed or altitude must be stable, but if you change the altitude or speed too much, the 'regulator' disengages, although it remains displayed in the controls.

 

Finally that's how I use it ..