Magnetic Brake Trim & FFB

I am reporting an issue that could probably fit in the thread "FFB Implementation" (https://forums.eagle.ru/showthread.php?t=173762) as well. But posting it there seems to be mixing up different issues / a bit off topic - so bear with me when I make a separate thread. :-)

I think, the devs stated it somewhere already, but I noticed this as well: the trim system sets the attitude of the helo, not the position of the controls.

In the Huey, the magnetic brake basically allows you to set the position of the cyclic. The position of the cyclic then causes the helo to assume a certain attitude. For example, I deflect the cyclic, click-trim and the helo follows the cyclic.

In the Gazelle, on the other hand, the trim defines the current(!) attitude of the helo as the desired attitude for the autopilot - even if the current cyclic position does not match that attitude. And then, this is the really weired part, sets the magnetic brake forces to a position that matches that set attitude - again, even if the current position does not match the set attitude.

Example: I want to archieve a steep bank attitude and deflect the cyclic accordingly. Before the helo reaches that banking angle, I click-trim - while the helo is still in a not-so-steep banking angle. The click-trim then causes the mag. brake forces to set the new "center" at a different position than I am trying to hold it. Basically the trim system punches me in my hand holding the cyclic in the opposite direction as I am deflecting the stick (i.e. applying force to).

So, I apply force to push the stick far left, but the mag. trim pushes the stick a bit right.

In real live this would be flat out a health hazard and probably cause broken wrists and what not. And in our simulated world, it causes at least heavy strain on the FFB hardware.

I urge the devs to review this implementation of force feedback. For the gradual 4-way-hat trim, the helo's behaviour might make quite some sense, but I have the strong feeling, that the magnetic brake trim should not work that way. I would rather expect it to be a more separate mechanism that works more like a mechanical solution to trim the helo, much like in the Huey, than a way the AP interferes violently with the pilot's decisions.

Or to put it differently: the magnetic brake should only help the pilot to keep the controls in the desired position. The 4-way-hat trim should be the (only) way to adjust the SAS/AP.

edit: and while we are at it: the "usual" way the mag. trim button works is, that the forces are released when and while it is depressed and re-applied when the button is released. In the Gazelle, the forces remain applied all the time - this makes no sense to me and I suspect that this is not how it works in the real thing...?

I don't have the Gazelle, but the opposite force you feel, can it be the AP actuators trying to move the stick to the position corresponding to the trimmed attitude and not the mag brake?

As I understand it, mag brake only have two modes, hold the stick in position like in the Huey and being released. It's "dumb", only holding the brake or not. It's braking effect is soft enough to allow moving the stick, but with some force.

For the system to actually be able to move the stick to another position you need actuators, that can be controlled by an "intelligent" AP. If the AP is of that kind of system that moves the stick that is. Some AP systems move the control surfaces (i.e. the swash plate) without stick feedback.

But I have no idea how it's working on the Gazelle, only thinking out loud.

I don't have the Gazelle, but the opposite force you feel, can it be the AP actuators trying to move the stick to the position corresponding to the trimmed attitude and not the mag brake?

As I understand it, mag brake only have two modes, hold the stick in position like in the Huey and being released. It's "dumb", only holding the brake or not. It's braking effect is soft enough to allow moving the stick, but with some force.

For the system to actually be able to move the stick to another position you need actuators, that can be controlled by an "intelligent" AP. If the AP is of that kind of system that moves the stick that is. Some AP systems move the control surfaces (i.e. the swash plate) without stick feedback.

But I have no idea how it's working on the Gazelle, only thinking out loud.

Yes, it seems that the current FFB implementation assumes that there are AP controlled actuators that re-position the cyclic. That is in fact exactly what the FFB joystick does: it moves to a position that matches the position that keeps the helo at the attitude at the moment the trim button was pressed.

The problem is that this happens instantly. The FFB stick kicks HARD in your hand if you hold it at a different position at that moment. This puts quite some strain on the hardware, I would suspect. And considering the real forces present in the real helo, such behaviour could easily lead to injuries.

As I understand it, mag brake only have two modes, hold the stick in position like in the Huey and being released. It's "dumb", only holding the brake or not. It's braking effect is soft enough to allow moving the stick, but with some force.

In the SA341G the mag brake circuit also feeds the SAS pitch and roll channels to set the desired attitude, so the mag brake button has a double function. I'd surmise the SA342M SAS works similar.

The problem is that this happens instantly. The FFB stick kicks HARD in your hand if you hold it at a different position at that moment. This puts quite some strain on the hardware, I would suspect. And considering the real forces present in the real helo, such behaviour could easily lead to injuries.

I set 50% FFB Trimmer Force to reduce the effect but mostly leave trim/mag brake untouched as it's almost impossible to read small trim settings in the controls indicator (RCtrl+Enter) in flight and easy to mess the trim up badly.

AFAIK the SA341G has micro-switches to sense pilot input, so the SAS won't fight with pilot. I've read complaints about stick dead zone in DCS, perhaps that centre zone is used to mimic the micro switches on regular joysticks before pilot input takes over from the SAS?

SA341G SAS diagram: https://s25.postimg.org/xev4vcoil/sas.jpg

I view recent Gazelle patches positively and look forward to further improvements.

In the SA341G the mag brake circuit also feeds the SAS pitch and roll channels to set the desired attitude, so the mag brake button has a double function. I'd surmise the SA342M SAS works similar.

Good to know, thanks!

I am reporting an issue that could probably fit in the thread "FFB Implementation" (https://forums.eagle.ru/showthread.php?t=173762) as well. But posting it there seems to be mixing up different issues / a bit off topic - so bear with me when I make a separate thread. :-)

 

I think, the devs stated it somewhere already, but I noticed this as well: the trim system sets the attitude of the helo, not the position of the controls.

 

In the Huey, the magnetic brake basically allows you to set the position of the cyclic. The position of the cyclic then causes the helo to assume a certain attitude. For example, I deflect the cyclic, click-trim and the helo follows the cyclic.

 

In the Gazelle, on the other hand, the trim defines the current(!) attitude of the helo as the desired attitude for the autopilot - even if the current cyclic position does not match that attitude. And then, this is the really weired part, sets the magnetic brake forces to a position that matches that set attitude - again, even if the current position does not match the set attitude.

 

Example: I want to archieve a steep bank attitude and deflect the cyclic accordingly. Before the helo reaches that banking angle, I click-trim - while the helo is still in a not-so-steep banking angle. The click-trim then causes the mag. brake forces to set the new "center" at a different position than I am trying to hold it. Basically the trim system punches me in my hand holding the cyclic in the opposite direction as I am deflecting the stick (i.e. applying force to).

So, I apply force to push the stick far left, but the mag. trim pushes the stick a bit right.

 

In real live this would be flat out a health hazard and probably cause broken wrists and what not. And in our simulated world, it causes at least heavy strain on the FFB hardware.

 

I urge the devs to review this implementation of force feedback. For the gradual 4-way-hat trim, the helo's behaviour might make quite some sense, but I have the strong feeling, that the magnetic brake trim should not work that way. I would rather expect it to be a more separate mechanism that works more like a mechanical solution to trim the helo, much like in the Huey, than a way the AP interferes violently with the pilot's decisions.

 

Or to put it differently: the magnetic brake should only help the pilot to keep the controls in the desired position. The 4-way-hat trim should be the (only) way to adjust the SAS/AP.

 

edit: and while we are at it: the "usual" way the mag. trim button works is, that the forces are released when and while it is depressed and re-applied when the button is released. In the Gazelle, the forces remain applied all the time - this makes no sense to me and I suspect that this is not how it works in the real thing...?

I have noticed the same thing ;)