What makes the Apache the most difficult helicopter module to fly?

[Rogue Trooper]

I only use the Apache APs or flight stabilisers when I am happy that the airframe is trimmed out in the flight regime I require.

I also tend to hold the trim for 3 or 4 seconds before engaging the APs to ensure the airframe is trimmed out ready for the automated systems.

I love the way the Apache flies, I love the way she drifts off the ground when taking off.... it feels amazingly natural.

I love the way the tail rotor is neutral with a bit of right pedal, the personality of the airframe is superb.

[JetCat]

After three days of Apache training it is now no longer difficult thanks to force trim, and feels almost like the Hind. Landing is still very hard so sitting in the front seat and letting George do the touchdown is the comfortable solution for this task.

[TZeer]

It's great to fly... BUT, there is still some WIP in the flightmodel. Most annoying thing for me is the constant "unstable" yaw channel.

Unless you hold the trim reset or activate the attitude hold in forward flight, the yaw can start chasing left/right. Sometimes it's hard to see, sometimes easy. But if you pay attention to the FPV while flying, one can see the FPV floating left/right while flying straight.

Press the trim reset and it stops. Then after a while it can start doing it again, first small, then increasing over time, up until you can see the entire airframe is turning left/right.

Apart from that, the airframe is really nice to fly. Once that issue is solved, the Apache will become even more stable.

[JetCat]

On 5/3/2024 at 11:39 PM, Rogue Trooper said:

I love the way the Apache flies, I love the way she drifts off the ground when taking off.... it feels amazingly natural.

I love the way the tail rotor is neutral with a bit of right pedal, the personality of the airframe is superb.

It is the best of the best!! I am still thinking about what module would be more interesting for me the A-10 or the Apache, they are both so awesome. And the flight model is so great I have never flown a better and more realistic helicopter simulator. Also thanks to finding out force trim (because some YouTuber made a complete Hind force trim tutorial about this topic) helicopter flying is so much better and so much more natural now. Real helicopters don´t have a control stick that always forces it´s stick into a centered position with a strong spring while the helicopter is in a slightly off center and unstable cyclic and rudder position. Luckily force trim function gets rid of this problem perfect hoovering is now possible.

 

On 5/7/2024 at 1:05 PM, TZeer said:

Press the trim reset and it stops. Then after a while it can start doing it again, first small, then increasing over time, up until you can see the entire airframe is turning left/right.

This is because of helicopter physics. There is no one general tail rotor setting for all flight conditions. The more the collective is pulled to ascent the stronger the torque coming from the steeper blades gets. That´s why the tail rotor needs constant change of input, and the most counter force while hoovering. When force trimming the helicopter to perfect hoover it begins to yaw again when gaining speed and not counteracting with the pedals because the main rotor is giving lower torque to the airframe when flying compared to hoovering. You need to force trim it for hoover, force trim it again for smooth and steady flight forward, and again force trim it when going back into hoover mode or even descending and VTOL-landing.

The Apache has no autopilot feature that auto-corrects tail rotor yaw like the Hind which makes it a bit more unstable to fly with constant smooth corrections necessary. But when getting into the mission zone and when the action begins why not quickly switching seats to the front seat? Pilot George loves to perfect hoover the heli for you while you focus on it´s front cockpit targeting systems...

[jubuttib]

On 5/7/2024 at 2:05 PM, TZeer said:

Most annoying thing for me is the constant "unstable" yaw channel.

Agreed. I often see it just bouncing left/right on its own, neither maintaining a heading nor staying on the ball. I try to keep things steady on my end, and the yaw channel just develops its own oscillations, as if it was a rookie pilot causing pilot induced oscillation.

I've started to turn the yaw channel off completely as a part of my startup procedure. It's perhaps a bit more sensitive to pedals like that, but at least it's a lot more predictable and doesn't do things on its own. Shame that it disables the attitude and altitude hold modes...

 

As for why the Apache is hard to fly vs. the others, for me it comes down to two or three things. One is that yaw channel, as mentioned previously, the other is the tendency of the SAS to _amplify_, not damp your inputs near hover. I've recorded myself multiple times and watching back on the controls overlay you can see how I nudge the cyclic to the left a tiny bit, and the autopilot pushes it further than what I intended. This can make near hover behavior very twitchy. The third is the AFAIK confirmed to be exaggerated lateral push from the tail rotor, which causes the helicopter to crab enough that the canopy structures block visibility forwards when in aerodynamic trim.

BUT overall with the most recent updates it's actually really not that bad! It's very easy to fly and handle when going at anywhere from 30 to 120 knots, it's really only the near hover stuff that's twitchier than I'd  really like. Sedate the yaw channel, reduce the lateral push, and maybe* stop the near hover exaggerations of the AP and there'd be nothing to complain about really. Even now it's by no means uncontrollable near hover, just very sensitive, and the yaw channel is hard to predict.

Oh right, there is one other thing... I need to check whether it's still a bug that exists, but last I checked all trim modes EXCEPT "return to center" had a HUGE effect on how fast you could move the cyclic around. The no-trim and instant trim options caused the maximum speed of the cyclic to be really sluggish when you just moved your stick around, while in center trim mode it responded MUCH faster. This made the helicopter a lot easier and more responsive to fly in center trim mode, but I use an unsprung cyclic so it's not really an option that I can use other than for testing...

[NeedzWD40]

5 hours ago, JetCat said:

This is because of helicopter physics. There is no one general tail rotor setting for all flight conditions.

The problem is that the SAS/SCAS is inducing the sway at speed, not that the helicopter's physics are inducing it. When you press the force trim release, you're telling the SAS/SCAS "hands off, I'm in control" and it no longer tries to hold a heading, pitch, and bank. Thus the issue right now is if you're at cruise speed straight and level, the SCAS will slowly oscillate the yaw channel back and forth. If you press the force trim release, SCAS lets go and the aircraft stabilizes. You can also observe this by killing the yaw SCAS channel in particular. I'd recommend trying the module without any of the SCAS channels engaged at all and you'll quickly see where some of the problems lie.

6 hours ago, JetCat said:

The Apache has no autopilot feature that auto-corrects tail rotor yaw

There's no autopilot for automatic cross-couple, but the yaw SCAS most definitely will try to maintain a heading without input. The manually commanded attitude modes as well as the automatic heading hold modes are described in the manual. You can see one work when you get light on wheels and gently bring the collective up, as the SCAS attempts to maintain a heading within its authority. This is true for most helicopter SCAS configurations and it isn't unique to the Hind.

Technically speaking, the AH-64D would be better described as having an AFCS instead of SAS or SCAS.

[Raptor9]

20 minutes ago, NeedzWD40 said:

Technically speaking, the AH-64D would be better described as having an AFCS instead of SAS or SCAS.

SCAS isn't the AH-64D's equivalent to AFCS. SCAS is just the term that collectively describes two of three primary functions of the Flight Management Computer (FMC), which is for all intents and purposes the AH-64D's AFCS.

Stability Augmentation System (SAS) + Command Augmentation System (CAS) = SCAS. The two functions of SCAS + Hold modes = FMC; which would otherwise leave out the Hold modes and all of their logic for each flight control axis and flight conditions.

AFCS and FMC are just terms to describe the same thing: the system that generates flight control inputs independently of, or in coordination with, the pilot's physical control inputs.

[bradmick]

11 hours ago, NeedzWD40 said:

Technically speaking, the AH-64D would be better described as having an AFCS instead of SAS or SCAS.

Nope. There’s not a single document on the planet that would support this, nor would it help alleviate the confusion that already exists. The terms mean things, AFCS has its own specific traits and characteristics. Please do not inject wrong or incorrect terms when describing things. I’ve literally explained the differences and terms and how the system works across multiple forum threads. Less conjecture and less folks who’ve never interacted with the system describing or talking about the system at this stage is what we need..not more.

[macedk]

Yor medical does not cover injury due to opinionated typing on the internet. 

And to think that your finger arthritis was due to typing nonsense on the internet. 

Have a nice day y'all

[TZeer]

On 5/9/2024 at 1:46 AM, jubuttib said:

BUT overall with the most recent updates it's actually really not that bad! It's very easy to fly and handle when going at anywhere from 30 to 120 knots, it's really only the near hover stuff that's twitchier than I'd  really like. Sedate the yaw channel, reduce the lateral push, and maybe* stop the near hover exaggerations of the AP and there'd be nothing to complain about really. Even now it's by no means uncontrollable near hover, just very sensitive, and the yaw channel is hard to predict.

That's my experience as well. It's really smooth and nice when you get a little speed (except for the issues you mentioned), but below 30 knots it's "unstable".  You hardly need to do anything on the YAW while flying, but when transitioning below 30 knots and in to hover, I feel a lot of the change on the pedals need to happen on a relatively small amount of change in forward airspeed.

There is also still some input from the SCAS while on the ground. According to the manual/documentation, the SCAS input to the YAW channel should not happen until the "weight on wheel" switch indicates that the Apache is in the air. This leads to this unpredictable YAW when taxing. It's amplifying whatever inputs you give, making it very easy to "overshoot" when trying to turn while taxing. It was worse before, but you can still see the SCAS giving inputs while on the ground.

 

BUT, the FM has improved over time. It has gotten more stable, breakout values on the YAW has improved, doesn't "fight" you as it did before. If they can just iron out those 3 last issues it will be really good.

[LorenLuke]

8 hours ago, TZeer said:

That's my experience as well. It's really smooth and nice when you get a little speed (except for the issues you mentioned), but below 30 knots it's "unstable".  You hardly need to do anything on the YAW while flying, but when transitioning below 30 knots and in to hover, I feel a lot of the change on the pedals need to happen on a relatively small amount of change in forward airspeed.

Keep in mind how the control authority changes though. In forward flight, the aircraft is basically one of these:

Always wanting to turn into the wind (which, in forward flight at those speeds is a stiff 40+ knots). It will stabilize in that direction; it's why you can't exactly 'slide' right or left at 80 knots. As a result of that, in order to maintain deflection at speed, you're going to need the rotational force to maintain that sideways aspect. and the required force gets much, much more the faster you go. This is why the rudder seems to barely do anything at 100 knots; the amount of rotational force the tail rotor gives is the same, but the amount it needs to push back is much higher, so the deflection is less.

This is not at all to say that the SCAS systems don't have issues in the yaw channel, I've seen it go plenty squirrelly myself. But the fact that the rudder suddenly seems to lose a significant amount of authority over the aircraft's turning capability at some critical range of speed isn't necessarily the flight systems, it's just largely the physics of the aircraft.

[TZeer]

8 minutes ago, LorenLuke said:

Keep in mind how the control authority changes though. In forward flight, the aircraft is basically one of these:

Always wanting to turn into the wind (which, in forward flight at those speeds is a stiff 40+ knots). It will stabilize in that direction; it's why you can't exactly 'slide' right or left at 80 knots. As a result of that, in order to maintain deflection at speed, you're going to need the rotational force to maintain that sideways aspect. and the required force gets much, much more the faster you go. This is why the rudder seems to barely do anything at 100 knots; the amount of rotational force the tail rotor gives is the same, but the amount it needs to push back is much higher, so the deflection is less.

This is not at all to say that the SCAS systems don't have issues in the yaw channel, I've seen it go plenty squirrelly myself. But the fact that the rudder suddenly seems to lose a significant amount of authority over the aircraft's turning capability at some critical range of speed isn't necessarily the flight systems, it's just largely the physics of the aircraft.

I know how the forces behave. And I fully expect the forces do what you say.

But this behavior with the SCAS/SAS is well documented and known by the SME's. The relative large change in rudder input needed over a short period when crossing the "threshold", can be explained by the excessive lateral push made by the tail rotor. This excessive push is also the reason the Apache has the exaggerated "crabbing" movement when flying in aerodynamic trim.

When that issue is sorted, my guess is that the transition between forward flight and hover will become smoother. It might be something entirely different, but from what I have understood so far after flying and reading the documentation and what the SME's has written, everything is connected with everything in this flightmodel, and it's a complex piece of software to tune.

[JetCat]

53 minutes ago, LorenLuke said:

But the fact that the rudder suddenly seems to lose a significant amount of authority over the aircraft's turning capability at some critical range of speed isn't necessarily the flight systems, it's just largely the physics of the aircraft.

I have watched a bit of this Hind documentary one hour ago and this is called tail rotor loss of authority, and happens in certain cross wind situations. In some wind situations the helicopter tail wants to do whatever it wants and sometimes the helicopter even begins to spin. I haven´t had a good helicopter simulator before until finding DCS therefore I have never spend time learning and understanding helicopter flight dynamics but was flying the Fenix Airbus (and a few jets) only before, so learning all this new helicopter stuff is really exciting! Not only in certain wind conditions but also when the AOA of the main rotor is steep and therefore it´s air resistance and the torque going to the mainframe get´s too high, the tail rotors counteracting force also can become to weak to counteract the main rotor. This happens in a fully loaded Hind sometimes. Love how these physically accurate details are all modeled and simulated in their fully glory and complexity in this sim!

[Blackhawk163]

You know, I'm living out my dreams of actually having joined the AF vs the Army by buying the F16 first and then the A10. For some reason I just had enough of Army Aviation  

However, I remember how much fun me and the crew used to have with Digital Intergrations Apache/Hind and then followed up by Jane's Longbow 2, so I trialed this module, and gosh darn; It's hard! Bought it anyway to support the community. I understand it's a WIP so I won't comment on the Flight Model too much. But I do have a glutton for punishment.

[JetCat]

Today I have noticed that when flying with a certain more strong force trim setting because of a bit of wind the Apache makes a slow 180° turn or more followed by slow yawing back to the direction where the attitude hold mode was switched on.

Is this realistic having the automatic tail rotor stabilizer not kick in immediately when pressing attitude hold mode?