Trim Type?

[Reticuli]

Just now, Raptor9 said:

 

The pedals have some spring tension in them, but only when the force trim is engaged.  Unlike some other helicopters, you can force trim the 64's pedals. When the force trim is interrupted, they do get much more loose.

So it's got a variable spring 'centering' that changes the center position based the force trim state?  Hmm.  Seems like an odd hybrid solution.  Guardians should have moved over to that Enhanced Apache stuff they were working on.  Guess the Army is going to have to wait for an X2 derivative or Invictus for the really good stuff.

[Raptor9]

2 hours ago, Reticuli said:

So it's got a variable spring 'centering' that changes the center position based the force trim state?  Hmm.  Seems like an odd hybrid solution.

 

No, it's just a similar mag brake system that is used on the cyclic.  The force trim works exactly the same way as other helicopters.  It's just included in all three axes, not just pitch and roll.

[Reticuli]

3 hours ago, Raptor9 said:

 

No, it's just a similar mag brake system that is used on the cyclic.  The force trim works exactly the same way as other helicopters.  It's just included in all three axes, not just pitch and roll.

Now I know why I used the word "spring"... because it was previously used in the thread.  I really just meant to ask about the centering point.  Anyway, controls magnetic lock stuff makes more sense.  I'm gathering now that the centering of the pedal tension is therefore moving around on it upon trimmer button release.  So you could be 50% to the left, it'd hold that, require more pressure to push past, and tend return to that trimmed spot as you ease up pressure until the trimmer button is held down again when it has no particular favored 'centering' point and just a little resistance to movement.  It looks like the only way hardcore players are going to get truly faithful recreation is with a force-feedback cyclic and force-feedback pedals.  And I can't even tell for sure if the collective's got something going on, too, as they talk about the system ignoring movement of that within a certain threshold when altitude hold is on.  I wouldn't be surprised if its collective gets a centering point during altitude hold and commands level changes like the old Penn State experiments with using a normal joystick for collective with vertical hold in GenHel running on MatLab for FlightGear.  Regardless, FFB pedals seems an unlikely market, let alone collectives.  Heck, forget faithful recreation, just not being a convoluted mess of a control system is going to be a challenge for the vast majority of people at home.  Users are having enough issues with just the Hind, and that's more straightforward.  The Blackshark has its quirks, too, just with centering or pressure sticks, and it doesn't even have the complication of a tail rotor and lack of tail-mixing to worry about with centering pedals.  I'm definitely thinking ED ought to go with an optional RC/AH & newer-style of yaw modes.  That'd certainly be a more useful alternative available control scheme than the 'arcade' mode Blackshark uselessly has.  Probably 99% of DCS helo users would go with such new modes.  The 1% of users with self-damped pro long-pole cyclics and also pedals without springs can obviously just go into the simulated Apache's MFD menu where you can turn off the force trim system completely, though.

Edited June 18, 2021 by Reticuli

[Raptor9]

5 hours ago, Reticuli said:

And I can't even tell for sure if the collective's got something going on

 

The collective doesn't have any force trim, nor a collective brake. It does have a friction adjust collar. You can move it a little with the Altitude Hold on, but otherwise any significant movement will automatically disengage Altitude Hold.

[Lurker]

So now that I'm learning the ins and outs of SAS channels in the Hind, and after reading this thread I'm left with one question. In the Hind, the YAW AP SAS channel will hold a heading for a given torque. I.E. when you increase collective the SAS channel will automatically press the power pedal to compensate and keep the helicopter stable and vice versa. 

 

How does this work in the Apache? Does it's yaw channel compensate for torque changes or is it "simpler" which means that it would only hold a heading for a given trim condition at that particular time. I.E. you trim the helicopter for a stable hover, You then increase the collective and would need to push on the power pedal to keep the helicopter stable?

Edited July 8, 2021 by Lurker

[Raptor9]

1 hour ago, Lurker said:

How does this work in the Apache? Does it's yaw channel compensate for torque changes or is it "simpler" which means that it would only hold a heading for a given trim condition at that particular time. I.E. you trim the helicopter for a stable hover, You then increase the collective and would need to push on the power pedal to keep the helicopter stable?

 

The controls (cyclic, collective, and pedals) are all connected to hydraulic flight control servos (4 of them, 3 on the main rotor and 1 on the tail).  You move the controls and through mechanical inputs the hydraulic servos move the main rotor swashplate and tail rotor blade pitch.  Within each of those hydraulic flight control servos there is something called a "SAS sleeve".  It's essentially a small amount of authority that is electromechanically-commanded by the Apache's flight computer for accomplishing such tasks as stability and hold mode logic.  The flight computer uses this small authority to make the aircraft a stable airborne weapons platform, maintain certain hold values, etc.

 

So if you are in a well-trimmed hover, and not interrupting the force trim, the heading hold logic will keep the aircraft on the heading that the aircraft was on the last time the force trim button was released, as long as the directional (yaw) input required to do so does not exceed that small authority amount of the tail rotor/directional servo's "SAS sleeve".  For example, if a strong crosswind picks up and is pushing on the vertical tail, the aircraft will tend to weathervane into the wind.  The directional servo will attempt to counter-act this; but if the wind speed keeps increasing, at some point the SAS sleeve will become saturated to one side of it's allowable authority input, and will no longer be able to compensate.

 

To your question, if you are in a stable hover as in the previous paragraph, and you apply a little collective to initiate a climb, the directional servo will apply an input to the tail rotor in order to counter the increase in torque and to maintain the heading, but if you keep pulling up on the collective the torque from the main rotor will exceed that small authority of the tail rotor/directional servo's "SAS sleeve", in the same manner that the crosswind started to weathervane the vertical tail fin.  As before, the SAS sleeve has reached the limit of its authority and the aircraft will begin to yaw to the right in the opposite direction of the main rotor spin, until the pilot corrects it himself.

 

If at any time, any of the "SAS sleeves" become saturated at the limit of their authority, the crew receives a visual and audio cue to re-trim the aircraft, in which case they will need to interrupt the force trim for several seconds to manually adjust the flight controls to maintain their desired flight condition, while the SAS sleeves re-center themselves.  In the hover you are asking about, small movements of the collective can be compensated for by the heading hold logic via the directional servo's SAS sleeve.  Also, if you manually push on the pedals a slight amount, the heading hold will use the servo SAS sleeve authority to cancel out the yaw movement; but if you move the pedals a certain amount beyond it's force-trimmed position, the heading hold will release and the aircraft will stop trying to hold that heading because it recognizes that the input is deliberate.

[Lurker]

@Raptor9 thank you for that very detailed and very informative explanation! Seems like the Apache is going to be much more hands on than the Hind, which you can basically land without touching the pedals (if you trim it out correctly and when the damn SAS channels behave, that is) I also have a feeling that the controls with the particular design philosophy and solution of the Apache, are probably going to be much more intuitive to operate once we get the hang of it. 

 

I foresee one possible issue though, and that is force trimming the pedals. I have a MSFFB2 joystick which is wonderful for flying choppers, but none of us have force feedback pedals.

 

Which brings me to a follow-up question. Say I'm flying on a given heading once again trimmed out, I push the trimmer and make a 90 degree turn and release the trimmer but I didn't really use the pedals in the turn it was kind of messy and uncoordinated and they aren't really very well trimmed out for the new heading, am I correct in assuming that the SAS computer will try and correct the yaw for this new heading as long as the pedals were not trimmed out previously beyond the so called "SAS sleeve" authority for the current new heading? 

Edited July 9, 2021 by Lurker

[Raptor9]

  

6 hours ago, Lurker said:

I foresee one possible issue though, and that is force trimming the pedals. I have a MSFFB2 joystick which is wonderful for flying choppers, but none of us have force feedback pedals.

 

I have neither a force-feedback stick nor force-feedback pedals, but I get along just fine.  And I believe the vast majority of DCS players probably have some sort of spring-centered gaming stick.  I don't see it as an issue once you understand the methodology ED uses to simulate the force trim functionality/logic.

 

On another note, the Ka-50, Mi-8, Mi-24, and UH-1H all have an option to toggle Trimmer logic on the pedals or not.  I'd be willing to be they include the same option for the AH-64D module for users to tweak their HOTAS setup.

 

6 hours ago, Lurker said:

Say I'm flying on a given heading once again trimmed out, I push the trimmer and make a 90 degree turn and release the trimmer but I didn't really use the pedals in the turn it was kind of messy and uncoordinated and they aren't really very well trimmed out for the new heading, am I correct in assuming that the SAS computer will try and correct the yaw for this new heading as long as the pedals were not trimmed out previously beyond the so called "SAS sleeve" authority for the current new heading? 

 

1) Above 40 knots the Apache uses Turn Coordination logic in the flight computer when performing banking turns.  So outside of any major environmental factors or pilot incompetence, turns are usually quite coordinated by the nature of the flight computer logic.  Small inputs may be necessary on the pedals to keep the trim ball centered because a) the pilot may increase collective slightly to maintain altitude, depending on the steepness of the bank, which will result in the requirement to provide a slight increase in anti-torque by pushing on the left pedal to maintain a centered trim ball; and b) since there is almost always wind of some sort, as the aircraft changes flight direction the crosswind component will also change, which may require a slight pedal adjustment to keep the aircraft in coordinated flight for the changing vector of wind acting on the airframe.  But again, these pedal inputs are usually quite small at higher airspeeds.

2) The Turn Coordination and Heading Hold logic are always enabled (meaning you can't toggle them off unless you turn off the flight computer completely), but they aren't always applied to the flight controls.  Just as the various attitude/altitude hold sub-modes are contextual based on flight condition, the flight computer's logic is also set to assist the pilot in maintaining a stable firing platform while not interfering with the pilot's intentions to deliberately maneuver the aircraft.  Because of this, there are certain flight control reference values the flight computer is looking for to determine what logics to apply, and when, to assist the pilot.  If the pilot is flying straight and level (let's assume >40 knots), with attitude hold off, turn coordination is applied, allowing the crew to smoothly bank and turn as desired.

 

When attitude hold is on in straight & level flight, heading hold is applied assisting the pilot in maintaining the current course, along with the attitude hold itself in pitch and bank.  When any of the controls are moved beyond a certain "breakout value" away from the trimmed reference values, the flight computer determines the pilot is intentionally maneuvering the aircraft, and the attitude hold logics will suspend.  At this point, the heading hold logic will also suspend, and turn coordination logic will be applied in it's place.  At the completion of the turn, when the controls are returned within the original "breakout values", and the yaw rate is below a certain value, turn coordination will be suspended and heading hold will be re-applied.  All of this is happening in the background within the flight computer, while the only actions performed by the pilot was adjusting the cyclic to roll into the turn, and then adjusting the cyclic to roll out of the turn.

______________________________

All of these hold modes in the Apache will suspend if the pilot interrupts the force trim (aka pushing the "trimmer" button in DCS speak), just as all the Ka-50's autopilot modes (pitch/bank/heading hold, Route mode, Hover mode, etc) will suspend when the pilot presses the trimmer button.  When the force trim interrupt button/trimmer button is released, new reference values are assigned for hold modes to maintain.

 

A key difference I've noticed between the Apache and Ka-50 is the role of the flight computer in flying the aircraft.  In the Apache, it's the pilot's job to fly the aircraft and the flight computer's job is to assist the pilot in doing so.  In the single-pilot Ka-50, where the human is performing the role of pilot and gunner, the flight computer has levels of automation to take over some of those navigation/targeting tasks, like a separate crewmember.  In this case, the human pilot's job is to assign navigation tasks to the flight computer, to allow him to re-allocate some of his cockpit workflow to targeting and weapons.  So if you feel like the Ka-50 is fighting you in some cases, such as when it tries to return to the original heading it was holding before you entered the turn yourself, it's because it is trying to perform the task the pilot assigned to it: "Hold this heading value of XXX degrees".  When you release the trimmer button, you are telling the Ka-50 autopilot "Now, hold this new heading value of XXX degrees", and this is why the command heading diamond updates to the new position in the HUD, because you are assigning that new heading value to the flight computer.  Or if the flight computer is navigating to a waypoint in Route mode, and the pilot pushes the trimmer button, it's like the pilot telling the flight computer "I have the controls", but as soon as he releases the trimmer the pilot is essentially saying "You have the controls", and the flight computer goes back to doing what it was last assigned to do, which was navigating to the selected PVI waypoint in Route mode.

 

I know that was a wall of text you didn't ask for, but I wanted to highlight the key differences between how to approach the flight computer logic of the Apache versus the Ka-50.

[zerO_crash]

On 5/6/2021 at 6:17 PM, M1Combat said:

"Fly the stick, hit trim and it would.....trim."

 

In general...   In the shark you want to Press trim, fly the aircraft to a new attitude you'd like to have trim hold for you, then release trim.  the details of that get a little murky depending on your controller (FFB??  No centering Springs??) and which settings you're using in the options page.  But you want to press, fly, release.

 

 

It´s important to mention that this is a efficient way for trimming with the typical flight-gear people fly DCS with. Otherwise IRL, and with a FFB joystick (like my Brunner CLS-E), the "recommended" way of trimming the Ka50 (or any Russian helicopter) is clicking for the reasons explained below (G-forces would make you susceptible to overcorrecting):  

 

 

Not really into western aircraft, but I wouldn´t be surprised if that was the case for Apache too.

Edited July 10, 2021 by zerO_crash

[zerO_crash]

On 5/11/2021 at 2:41 PM, Raptor9 said:

Like the Ka-50, the 64 needs to be in a relatively trimmed hover for the hold mode to keep it there. Otherwise, like the Ka-50, the servos may run out of authority and it may drift.

 

If the helicopter isn´t trimmed within 3km/h, then the AP could start to overcorrect itself leading to a pendulum-effect. It will straighten out over time, but it´s not the real way of doing it. Within 20% of the cyclic´s position, the AP handles everything. The reason why you really want to trim the cyclic to hover before engaging auto-hover, is to have a smooth engagement of auto-hover as well as giving the AP the biggest playfield of the 20% authority that it has across x and y.

Edited July 10, 2021 by zerO_crash

[Raptor9]

2 hours ago, zerO_crash said:

Not really into western aircraft, but I wouldn´t be surprised if that was the case for Apache too.

 

Yeah, the running principle for US helicopters when performing any sort of aggressive combat maneuvers, you either interrupt the force trim and hold it for the entirety of the maneuver, or you leave it un-interrupted and push against the force trim pressure throughout the maneuver, otherwise you encounter "force trim overshoot".

 

1 hour ago, zerO_crash said:

If the helicopter isn´t trimmed within 3km/h, then the AP could start to overcorrect itself leading to a pendulum-effect. It will straighten out over time, but it´s not the real way of doing it. Within 20% of the cyclic´s position, the AP handles everything. The reason why you really want to trim the cyclic to hover before engaging auto-hover, is to have a smooth engagement of auto-hover as well as giving the AP the biggest playfield of the 20% authority that it has across x and y.

 

Yeah, I see the Ka-50 and Mi-24 through the lens of western aviation controls, so I might mis-interpret some of the underlying intent behind the control methodology in the Mi-8, Mi-24, and Ka-50 designs.  I can appreciate the different approaches to accomplishing the same basic tasks in piloting helicopters.

Edited July 11, 2021 by Raptor9

[zerO_crash]

11 hours ago, Raptor9 said:

 

Yeah, the running principle for US helicopters when performing any sort of aggressive combat maneuvers, you either interrupt the force trim and hold it for the entirety of the maneuver, or you leave it un-interrupted and push against the force trim pressure throughout the maneuver, otherwise you encounter "force trim overshoot".

 

 

Yeah, I see the Ka-50 and Mi-24 through the lens of western aviation controls, so I might mis-interpret some of the underlying intent behind the control methodology in the Mi-8, Mi-24, and Ka-50 designs.  I can appreciate the different approaches to accomplishing the same basic tasks in piloting helicopters.

 

 

No worries, much of what you write is indeed true. I find it fascinating to see how the controls are solved on the "other" side. To be honest, I was quite surprised when I saw that the Apache has a force-trim release (i.e. trim) on the upper hat switch on the cyclic. From eastern helicopters, it would be much more natural for me to have the force trim where the flare dispense button is. I am quite sure that it´s a good design too, but its the little differences that make it interesting. The nice effect of that is having attitude-hold and altitude-hold on the same hat, and the respective disengage. I wonder though how natural having a trim button in that position is, when doing a prolonged flight.

 

Even the trim logic seems quite similar in many cases, the difference being in the level of advancement, sophistication, automation and ultimately the methodology as set by the aircraft designers and the mission it is made for. What I cannot find in this helicopter is the engine trim switch. In the eastern aircraft, it´s located on the collective, and gives you the ability to, for a lack of a better word, trim the engine RPM up or down such that you can pull more or less AoA with the collective without demanding as much power from the engines. Does Apache not have anything like that?

Edited July 11, 2021 by zerO_crash

[Raptor9]

1 hour ago, zerO_crash said:

What I cannot find in this helicopter is the engine trim switch. In the eastern aircraft, it´s located on the collective, and gives you the ability to, for a lack of a better word, trim the engine RPM up or down such that you can pull more or less AoA with the collective without demanding as much power from the engines. Does Apache not have anything like that?

 

It doesn't have it.  The rotor is kept at a specific speed once set at flight RPM.

[zerO_crash]

19 minutes ago, Raptor9 said:

 

It doesn't have it.  The rotor is kept at a specific speed once set at flight RPM.

 

But constant rotor speed and engine trim for adjusting engine RPM, is not mutually exclusive per se. I find it kind if weird, as this system of trimming the engine gives you many possibilities, some of which are better top speed and more economic flight. Kind of surprised the AH-64 doesn´t have it then. Does the FADEC lower the engine RPM when reaching higher speeds or so? Or is there any electronic or digital setting for adjusting that in AH-64?

Edited July 11, 2021 by zerO_crash

[Raptor9]

  

1 hour ago, zerO_crash said:

But constant rotor speed and engine trim for adjusting engine RPM, is not mutually exclusive per se.

 

True, but in this case, the engine output is automatically adjusted to keep the rotor speed at a specific reference RPM, without any pilot input to manually adjust it under normal circumstances.  The only time engines are manually controlled are during maintenance test flights or during emergency procedures.

 

1 hour ago, zerO_crash said:

I find it kind if weird, as this system of trimming the engine gives you many possibilities, some of which are better top speed and more economic flight. Kind of surprised the AH-64 doesn´t have it then. Does the FADEC lower the engine RPM when reaching higher speeds or so? Or is there any electronic or digital setting for adjusting that in AH-64?

 

Not all rotorcraft are designed with the same performance objectives, and different designs may have different areas of efficiency.  As for the AH-64, in straight and level flight, if you lower engine RPM, it lowers the rotor RPM, which is counter to the normal mode of operation.  I'm not aware of the original engineering decisions, but the airfoils of the rotor blades are optimized for a specific flight envelope, and I would guess that is based on the assumption of a constant rotor RPM.

 

Aside from that, it may be a case of management by exception, where the entire powertrain system is designed in such a way to minimize crew interaction to allow them to focus on the tasks of flying close to terrain, at night, while managing sensors, weapons, and communications.  So perhaps it was a case of different priorities of where the crew's attentions were intended to be focused.  I'm just speculating though.

Edited July 11, 2021 by Raptor9

[AlphaOneSix]

The manual N2 trim on the Mi-24 and Mi-8 collectives are to correct for errors within the engine fuel control unit. Trimming the N2 manually is performed prior to takeoff in order to ensure that the rotor RPM is set to the correct value (95%). It is not meant to be adjusted during flight or to achieve some other objective. Please keep in mind that these engines are relatively primitive, and requiring the pilot to manually correct the rotor RPM is a symptom of that.

[Lurker]

@Raptor9 thanks again for that extensive reply and explanation! While some may abhor walls of text, I really appreciate the detail and effort and as a result have a pretty clear understanding of the AP logic at work in the Apache. 

Edited July 12, 2021 by Lurker

[Raptor9]

4 hours ago, kgillers3 said:

@Raptor9 do you know if TRC will be implemented or is that in a later version of the aircraft that you guys aren't basing off of? 

 

I'm not on the dev team.

[Lurker]

I have another question, hopefully Raptor9 or kgillers3 can enlighten me

 

I've removed the spring from my Saitek Pro Rudder Pedals, which has allowed me (now that I've adjusted them for proper tension) to move the pedals to their desired deflection and simply leave them there, dispensing with any pedal trim. (Which on the Hind is optional) This works quite well, although with the AP logic that the Hind uses, doesn't let me use the Heading Hold YAW AP channel, which isn't really a problem. 

 

Do you guys foresee spring-less pedals as a problem with the upcoming Apache module? If I understood the gist of the thread correctly, whenever the trim button is released in the real Apache both the cyclic and the pedals are trimmed for the new flight conditions. I'm afraid that with spring-less pedals the game logic might be: "Oh look the pedals are not in neutral position, which means tell the flight computer to disengage all AP logic"

[Lurker]

Maybe some of the early testers who have access to the module will chime in on the control logic within the SIM itself. Let's hope that trimming the pedals is an optional checkbox. Thanks for the reply kgillers3. 

Edited September 20, 2021 by Lurker

[TZeer]

Trying to find some info on how these systems work.

In the quick start manual it says:

• AT (Attitude Hold, Left). Toggles on or off the selected attitude hold mode (position, velocity, or attitude hold). (see TODO)
• AL (Altitude Hold, Right). Toggles on or off the selected altitude hold mode (barometric or radar altitude). (see TODO)

When I go to TODO list on the forum is says that it should be in place before the early access release. 
Had a quick look through through the manual but have failed to find any info on where to change mode, and what they do.

I'm curious if some of it can be used to help you in situation where you wanna be masked behind something before popping up to engage targets, or scanning with the FCR (when it comes). 

I'm also curious if the flight system is in constant need of rudder inputs to hold your heading, or if there are systems to assist you as in the UH-60 Blackhawk, and modeled in the mod. There is a youtube video from The Air Warfare Group, where a former pilot explains how that chopper has a system that basically tries to maintain a certain heading. And as long as you do not manipulate the rudder pedals (combined with a microswitch), the Blackhawk will maintain a certain heading. Making it a very stable and easy platform to fly.

 

 

 

 

[Raptor9]

@TZeer , in this thread I gave several descriptions you can look through.

https://forums.eagle.ru/topic/268393-trim-type/?do=findComment&comment=4658481

[FalcoGer]

Wags' new video ("Setting up controls") confirmed today you have several options for both the cyclic and the rudders. Force feedback joysticks will get stuck in their new center position. You have an option for spring-less sticks that doesn't do anything (?) and you get the new center position option like we have in the ka-50 where you press the force trim release and then move the stick back to center and the position where you set it is the new center position.

[jojo]

If I understood correctly, AH-64 has "Heading Hold" function. It's activated with ATT HOLD with controls neutral/ trimmed position.

It's disabled with control input at more than break through value.

Heading Hold is also active with ATT HOLD OFF at speed < 40kt.

@Raptor9Am I right to think we don't have it yet in DCS ?

[deyv]

I think both AT and AL trims are under development... at least I cant use'em in game (or I dont understand the mechanic and how they work). In manual they are remarked as TODO (not sure what that means but I'm guessing not finished)

Edited March 21, 2022 by deyv