How do real apache pilots deal with the SCAS?

[skypickle]

SCAS insulates me from the feel of the aircraft. It makes adjustments to maintain attitude without my awareness. But when i press the trim button and scas is suspended, my attitude goes crazy (because i have not prepositioned my cyclic and pedals to provide what scas was providing). Of course in dcs we have the ‘show controls’ which reports what the pilot and scas are doing. But there is no such display in the real helicopter. How do you real pilots deal with this?

 

The only way i can imagine is to frequently trim- pushing the button almost every time the pedals and cyclic are adjusted. Is there a way to turn down the ‘gain’ of scas? I like that it damps out changes in attitude reducing pilot workload but sometimes wonder if a little dial/or color changing led might be useful instead of just a ‘scas saturated’ warning. Like ‘ how saturated is it?’

[Floyd1212]

13 minutes ago, skypickle said:

But when i press the trim button and scas is suspended, my attitude goes crazy (because i have not prepositioned my cyclic and pedals to provide what scas was providing)

What trimmer mode are you using for the cyclic?  And for the pedals?

[AlphaOneSix]

1 hour ago, skypickle said:

The only way i can imagine is to frequently trim- pushing the button almost every time the pedals and cyclic are adjusted.

Yes, you have to do this in the real aircraft. Otherwise, the controls just return to their last trimmed location. Every control movement requires updating the trim, unless you're just making a small, temporary deviation and plan to return to the previous control position.

[Raptor9]

@skypickle, one needs to realize that the real cyclic and pedals in the AH-64 have force gradients holding them in place when the force trim is not being pressed. Trying to hold the cyclic or pedals in a very precise position against the pressure of this force gradient is difficult, and over a period of time would become tiring, which is the entire reason for having the force trim release.

I think many players, depending on their hardware, develop a false impression of how the force trim is used if their hardware isn't simulating this force gradient. I've seen many videos online of players flying the DCS AH-64D without using the force trim, with the force trim reference remaining at the original locations and never updating. I can infer that these players are using hardware that does not simulate the force gradient of the real AH-64 cyclic and pedals, or at the very least nowhere near the levels of resistance that exists in the real aircraft. If they did, it is highly unlikely those players would be playing for so long without pressing the force trim.

As AlphaOneSix said, when the cyclic or pedals are moved, the force trim is almost always pressed at the onset of such movement. This practice is especially important when making large magnitude movements of the controls to avoid what is called "force trim overshoot". This occurs when the pilot has moved the controls a significant distance from their force trimmed state, and is applying pressure against the force gradient to hold the controls in place. When the force trim release is pressed, this force gradient is immediately removed, which may cause the pilot to inadvertently jerk the cyclic and pedals beyond the intended position when the resistance against the pilot's muscular tension is suddenly removed. This can cause the aircraft attitude to deviate in a somewhat violent manner, as would be the case any other time a sudden and aggressive input were applied to the flight controls.

There are exceptions to this practice of course, in the case where the pilot intends to return the controls to the force trimmed state. The best example would be flying along a route at a constant airspeed and altitude, with the aircraft trimmed in straight and level flight. Without pressing the force trim, the pilot applies cyclic pressure against the force gradient to initiate a turn toward the next leg along the route. This cyclic input is applied and maintained against the force gradient throughout the turn, and then when the pilot intends to roll out on the intended heading, relaxes pressure on the cyclic and lets the force gradient return the cyclic back to the original location, which causes the aircraft to naturally return to the same straight and level flight condition prior to the turn.

If one is properly using the force trim, SAS SATURATED should almost never occur. In real-life, about the only time this would happen is due to atmospheric changes such as sustained wind gusts that cause the aircraft SCAS to flight against unintended attitude or position changes.

[Hiob]

8 minutes ago, Raptor9 said:

@skypickle, one needs to realize that the real cyclic and pedals in the AH-64 have force gradients holding them in place when the force trim is not being pressed. Trying to hold the cyclic or pedals in a very precise position against the pressure of this force gradient is difficult, and over a period of time would become tiring, which is the entire reason for having the force trim release.

I think many players, depending on their hardware, develop a false impression of how the force trim is used if their hardware isn't simulating this force gradient. I've seen many videos online of players flying the DCS AH-64D without using the force trim, with the force trim reference remaining at the original locations and never updating. I can infer that these players are using hardware that does not simulate the force gradient of the real AH-64 cyclic and pedals, or at the very least nowhere near the levels of resistance that exists in the real aircraft. If they did, it is highly unlikely those players would be playing for so long without pressing the force trim.

As AlphaOneSix said, when the cyclic or pedals are moved, the force trim is almost always pressed at the onset of such movement. This practice is especially important when making large magnitude movements of the controls to avoid what is called "force trim overshoot". This occurs when the pilot has moved the controls a significant distance from their force trimmed state, and is applying pressure against the force gradient to hold the controls in place. When the force trim release is pressed, this force gradient is immediately removed, which may cause the pilot to inadvertently jerk the cyclic and pedals beyond the intended position when the resistance against the pilot's muscular tension is suddenly removed. This can cause the aircraft attitude to deviate in a somewhat violent manner, as would be the case any other time a sudden and aggressive input were applied to the flight controls.

There are exceptions to this practice of course, in the case where the pilot intends to return the controls to the force trimmed state. The best example would be flying along a route at a constant airspeed and altitude, with the aircraft trimmed in straight and level flight. Without pressing the force trim, the pilot applies cyclic pressure against the force gradient to initiate a turn toward the next leg along the route. This cyclic input is applied and maintained against the force gradient throughout the turn, and then when the pilot intends to roll out on the intended heading, relaxes pressure on the cyclic and lets the force gradient return the cyclic back to the original location, which causes the aircraft to naturally return to the same straight and level flight condition prior to the turn.

If one is properly using the force trim, SAS SATURATED should almost never occur. In real-life, about the only time this would happen is due to atmospheric changes such as sustained wind gusts that cause the aircraft SCAS to flight against unintended attitude or position changes.

That is probably the most comprehensive explanation of the non-technical part of the whole matter. Thank you. (With technical part I mean, how the hardware actually works, like magnetic couplings etc...)

Edited June 12, 2023 by Hiob

[Floyd1212]

35 minutes ago, Raptor9 said:

the AH-64 have force gradients holding them in place

Can you describe what a "force gradient" is in more (mechanical) detail?  I understand the principles behind what this is doing, but I still don't understand how.  Is this a hydraulic system, or servos, or springs?

[Hiob]

4 minutes ago, Floyd1212 said:

Can you describe what a "force gradient" is in more (mechanical) detail?  I understand the principles behind what this is doing, but I still don't understand how.  Is this a hydraulic system, or servos, or springs?

A force gradient is simply the force, that is pushing the stick back to its trimmed center position. The further away - the stronger the force. When you have a spring loaded Joystick, you also have a force gradient in any direction.

The exact way how the mechanics work, is described in the manual. From the top of my head: "magnetic coupled hydraulic actuators"...

But that is not to take away from Raptors explanations, if he wants to give some. I'm in no way, shape or form a subject matter expert.

[skypickle]

@Raptor9thank you for sharing your experience. Force trim overshoot is the phenomenon i was trying to describe. Frequent trimming is the solution I developed and im glad its the correct habit. Still i never experience force trim overshoot in the huey prob because there is no scas. It just has the magnetic forces hold the stick in place. 
 

Although i use a force feedback stick, its only 5 kg max so sometimes i find myself not pushing the trim button because i can actually be more precise when i am feeling resistance. I guess my sense of proprioception is wearing out w age. Other things that i used to do relatively well like shooting hoops and playing darts  is also not as good anymore. 

[[DE] T-Bone]

@Raptor9

I have a question for you about the FTR and how I am currently using it, I would be interested to know if my method is correct.

 

I am flying along a river (30 knots/50ft) and have the Apache trimmed out. When flying light contours I move cyclic/pedals and then let it return to its original trim position.

On a pop-up, I push the FTR, climb, and turn it 90° to the left over the terrain. Once I'm in my optimal flight attitude, I release the FTR and continue flying at 60 knots.

When I want to go into a hover position, I press and hold the FTR until I get from 60 knots to my position, level it out stable, and then release the FTR again.

 

Is this the correct procedure or am I doing something fundamentally wrong here? I would like to completely understand how to use the FTR.
 

[Raptor9]

57 minutes ago, skypickle said:

Still i never experience force trim overshoot in the huey prob because there is no scas. It just has the magnetic forces hold the stick in place. 

Force trim overshoot is possible in any helicopter that has a force trim system with a force gradient, it is not a product of SCAS but the very fact that you are applying a muscular force against a resistance that is suddenly removed. Have a friend hold up their hand against yours to apply resistance as you try to move it. Tell them to stop resisting against your pressure and then try to keep your hand at its precise location without moving it when they simply stop resisting. Unless your timing is absolutely perfect, your hand will overshoot its position.

It may not manifest the same way in the UH-1 due to the different rotor system and relative responsiveness to control inputs compared to the AH-64.

28 minutes ago, [RENEGADES] T-Bone said:

When I want to go into a hover position, I press and hold the FTR until I get from 60 knots to my position, level it out stable, and then release the FTR again.

Is this the correct procedure or am I doing something fundamentally wrong here? I would like to completely understand how to use the FTR.

That's how I would do it in real-life. However in DCS, I may let go of the FTR a few times during a deceleration to a hover, simply to regain some aft authority of my physical stick on my desk. I don't have a force-feedback stick so as I progressively accelerate forward in the DCS AH-64D (or any helo in DCS), I will intermittently let go of the force trim and let it spring back to center and resume my acceleration. When decelerating I do the same thing but in reverse.

[[DE] T-Bone]

58 minutes ago, Raptor9 said:

Force trim overshoot is possible in any helicopter that has a force trim system with a force gradient, it is not a product of SCAS but the very fact that you are applying a muscular force against a resistance that is suddenly removed. Have a friend hold up their hand against yours to apply resistance as you try to move it. Tell them to stop resisting against your pressure and then try to keep your hand at its precise location without moving it when they simply stop resisting. Unless your timing is absolutely perfect, your hand will overshoot its position.

It may not manifest the same way in the UH-1 due to the different rotor system and relative responsiveness to control inputs compared to the AH-64.

That's how I would do it in real-life. However in DCS, I may let go of the FTR a few times during a deceleration to a hover, simply to regain some aft authority of my physical stick on my desk. I don't have a force-feedback stick so as I progressively accelerate forward in the DCS AH-64D (or any helo in DCS), I will intermittently let go of the force trim and let it spring back to center and resume my acceleration. When decelerating I do the same thing but in reverse.

Roger, thanks for your feedback 

[placsea]

The only time I struggle controlling the aircraft with the ftr depressed is at a hover, so as Im bleeding off the last of my  speed I let go of the ftr and bring it into a hover and land.

[AlphaOneSix]

11 hours ago, Floyd1212 said:

Can you describe what a "force gradient" is in more (mechanical) detail?  I understand the principles behind what this is doing, but I still don't understand how.  Is this a hydraulic system, or servos, or springs?

It's springs. One end of a spring cartridge is attached to the flight controls, the other end is attached to a magnetic brake. Without the force trim being pressed, the end of the spring attached to the flight controls moves with the flight controls, but the other end can't move because of the magnetic brake holding it in place, so any movement of the flight controls is pushing or pulling on the spring cartridge. This spring force is what holds the controls in place. While the force trim switch is being pressed, the magnetic brake allows its end of the spring cartridge to move freely, so the whole spring cartridge just floats along with the flight controls and exerts no force until the force trim switch is released and the magnetic brake end of the spring cartridge is once again prevented from moving.

[McGraw]

What's the point of the force trim at all? Surely without it you're just free to move the controls in the real copter. Why have them almost glued in place?

I use springless and minimal clutch VKB gunfighter. The stick stays where I leave it. Completely intuitive.

[Floyd1212]

12 hours ago, AlphaOneSix said:

It's springs. One end of a spring cartridge is attached to the flight controls, the other end is attached to a magnetic brake.

In that case, these two videos together might help others (like it helped me) to understand what is happening under the hood when FTR is held.  (This looks like some guy's DIY setup, but the principles look to be sound.)

In the second video he plugs in the power to the mag brakes, but in reality this would be the condition when the FTR is not pressed.  Then, when you press FTR you are releasing the mag brakes and the stick moves without any return spring force.

https://www.youtube.com/watch?v=mRCcGSNuoVs

https://www.youtube.com/watch?v=gKBLKjo2E7Y

 

[Floyd1212]

30 minutes ago, McGraw said:

What's the point of the force trim at all?

It gives you the best of both worlds.  Your stick moves and stays where positioned when you want, but then also provides some springy return forces to that new center for minor corrections.

Once you have the aircraft trimmed out at a nice hover you can give it some left stick to slip left 20 feet and then some right stick to counter that movement, then let the spring return the stick back to the trimmed position so you can go back to a hover, instead of having to move the stick around with the dry clutches to find that perfect spot again.

[Raptor9]

1 hour ago, McGraw said:

What's the point of the force trim at all? Surely without it you're just free to move the controls in the real copter. Why have them almost glued in place?

I use springless and minimal clutch VKB gunfighter. The stick stays where I leave it. Completely intuitive.

Because the controls in a real helicopter are exposed to many external forces that do not exist next to your computer, such as vibrations, shock, g-forces, mechanical feedback from the linkages/servos, etc. It helps to have a resistance force that keeps the cyclic from flopping over if the pilot doesn't have a firm grip on it. For example, the AH-64's collective (which does not have a force trim) is under significant tension that normally keeps it from moving when not held in place by the pilot, but when pulling out of a dive, the pilots need to ensure they hold on to the collective to prevent the g-forces from slamming it to the floor and causing a crash, despite the tension that holds it in place under normal flight conditions. And in some cases where the AH-64 is experiencing significant vibrations, the collective can still creep up or down, depending on how the tension is set in that particular airframe. In that case, you can also add additional friction using a sleeve on the collective itself, but then that increases the force required to move the collective.

It's sort of like asking why fixed-wing aircraft have trim tabs since the pilots can simply hold the controls in place, or make the controls stiff enough that they won't move under external forces but then requires significant muscular endurance to fly for several hours. You don't want to have the controls so loose they move around under external forces, but the alternative is requiring significant muscular exertion simply to move the controls at all.

[McGraw]

58 minutes ago, Raptor9 said:

Because the controls in a real helicopter are exposed to many external forces that do not exist next to your computer, such as vibrations, shock, g-forces, mechanical feedback from the linkages/servos, etc. It helps to have a resistance force that keeps the cyclic from flopping over if the pilot doesn't have a firm grip on it. For example, the AH-64's collective (which does not have a force trim) is under significant tension that normally keeps it from moving when not held in place by the pilot, but when pulling out of a dive, the pilots need to ensure they hold on to the collective to prevent the g-forces from slamming it to the floor and causing a crash, despite the tension that holds it in place under normal flight conditions. And in some cases where the AH-64 is experiencing significant vibrations, the collective can still creep up or down, depending on how the tension is set in that particular airframe. In that case, you can also add additional friction using a sleeve on the collective itself, but then that increases the force required to move the collective.

It's sort of like asking why fixed-wing aircraft have trim tabs since the pilots can simply hold the controls in place, or make the controls stiff enough that they won't move under external forces but then requires significant muscular endurance to fly for several hours. You don't want to have the controls so loose they move around under external forces, but the alternative is requiring significant muscular exertion simply to move the controls at all.

Makes sense now.

1 hour ago, Floyd1212 said:

It gives you the best of both worlds.  Your stick moves and stays where positioned when you want, but then also provides some springy return forces to that new center for minor corrections.

Once you have the aircraft trimmed out at a nice hover you can give it some left stick to slip left 20 feet and then some right stick to counter that movement, then let the spring return the stick back to the trimmed position so you can go back to a hover, instead of having to move the stick around with the dry clutches to find that perfect spot again.

Oh yes, now it's making sense

[GremlinIV]

Yeah the only significant external forces the AH64 faces in DCS on your computer is you continually crashing into the ground through pilot incompetence..... 

[Leg2ion]

On 6/13/2023 at 4:42 PM, McGraw said:

What's the point of the force trim at all?

Ultimately, DCS aside - the end game is to reduce pilot fatigue so he can concentrate on flying/fighting the vehicle.

[Nerdwing]

It seems like a huge challenge to recreate with non force-feedback sticks being by far the most commonly used.

[Hiob]

27 minutes ago, Nerdwing said:

It seems like a huge challenge to recreate with non force-feedback sticks being by far the most commonly used.

Actually no, it is pretty easy. The only difference is, that the "trimmed position" aka the force free position is always the center position. Wether you choose instant trim or "center position trimmer mode" is a matter of taste. Other than that it is the same procedure.

When you want to maneuver, press and hold the trimmer (I use the pinky lever on my warthog stick). When you are in your desired attitude, let go of the trimmer -> et voila. SAS is happy, bird is flying straight. No problems. (You need to return the stick back to the center though - other than with a ffb stick)

Edited June 15, 2023 by Hiob

[McGraw]

4 hours ago, Hiob said:

Actually no, it is pretty easy. The only difference is, that the "trimmed position" aka the force free position is always the center position. Wether you choose instant trim or "center position trimmer mode" is a matter of taste. Other than that it is the same procedure.

When you want to maneuver, press and hold the trimmer (I use the pinky lever on my warthog stick). When you are in your desired attitude, let go of the trimmer -> et voila. SAS is happy, bird is flying straight. No problems. (You need to return the stick back to the center though - other than with a ffb stick)

 

I've tried the centre joystick trim method. Can't seem to figure out when to return the stick to centre. Doesn't seem to work for me

[PHMAC]

29 minutes ago, McGraw said:

I've tried the centre joystick trim method. Can't seem to figure out when to return the stick to centre. Doesn't seem to work for me

I don’t think the ‘Instant Trim’ and ‘Centre Joystick Trim’ options are meant for self centering joysticks with springs.

The ‘Joystick without springs and ffb’ option is probably the one that works best for you since you are using a springless, non centering joystick.

Please someone correct me if I’m wrong

Edited June 15, 2023 by PHMAC

[corbu1]

I use a modified stick to stay in place where I leave it and doesn’t self center.

Therefore I use the trim option „Joystick without springs and FFB“ which works nice for me.