I still think Kamov got the AP wrong

[Dr_Arrow]

Well, I would recommend to read this article for many posters in this thread to understand the basic concepts of autopilots and how it works in Ka-50:

 

http://www.simhq.com/_air13/air_429a.html

[mvsgas]

...Correct me if I'm wrong, but as far as I remember, there is a similar "panic button" on F-16. It's a pinkie switch, which works as a temporary AP disable, to correct maintained attitude, as well as a mean to save the aircraft, if AP tries to do something weird while flying at low level in terrain following mode...

It is a paddle switch in the base of the side stick controller. Nor really a panic switch, just a way to correct AP if there is a need to.

 

 

I can only comment on my experience in DCS:BS. I do not feel the AP fight my inputs. I'm not arguing some of you see it that way. Maybe is a combination of you joystick and something in the game. I have no idea how the real KA-50 work. But in BS, if I give the aircraft an input it responds accordingly with any hesitation. When turning, there are certain times where the turning rate increases (180 degrees from initial point of turn) but I never had to hold the trim button the entire flight. I do trim a lot. Speed changes, attitude changes etc. Have you guys tried different joysticks? Maybe a setting in the game? Are there any weather conditions that may cause the issues you guys describe?

[dsobbe]

Whenever you are having trouble controlling the aircraft remember: "When you are doing it right, you are hardly doing anything".

I've always found that idea to be a good indicator of control "quality". When you find yourself fighting the controls, review what you are doing in the manual. Are the V speeds, attitudes and rates within operating limits, etc? Are the systems properly and correctly set?

[HellToupee]

Feels fine to me, try flying without AP, feels like your fighting the chopper just to hold it straight :P

[Frederf]

The evidence of AFS inputs counter to those desired by the pilot is there for you to witness in a 30 second flight: With flight director on, lift off to a stable hover, accelerate forward to 100 kps, turn 360 degrees, and decelerate back to a hover. Perform this little flight agressively--not as you would your 172 but as you would in a high powered killing machine. Now, do the same with the FD off. See the differece?

 

I never said that the AP (AFS? what does this stand for?) doesn't provide inputs. I simply said that your statement that the AP will always override pilot inputs in an attempt to return to the hold-function attitude is patently false. You have distinctly said that the AP will provide input up to its maximum authority to return the aircraft to the hold attitude regardless of pilot input. If this were true then a 0° pitch hold would be maintained by the AP's authority on a very weak cyclic pitch down command as the AP exercises its pitch up authority to make the aircraft's pitch again 0°. I suggested this rather straight forward test to prove the AP does not exhibit this behavior but it has been ignored. Did you create 2 accounts to get to 11 rep or what?

 

Also, no, I don't see any difference in maneuverability between FD and non-FD modes. I've tried rapid maneuvers in both modes and the aircraft completes them so similar that I cannot tell the difference. There's nothing I can get the aircraft to do in FD mode that I can't in non-FD mode.

 

Ok Frederf, I think I see why you resist the term 'fighting', since it seems that to you it would mean that the AP channel actually 'won' the fight, and produced a result totally opposite to pilot input. Did I understand you right? Because that's not what I mean by 'fighting'. To me, that means that not all of my control input was allowed to be exerted, ie the AP took something away from me, and I don't mean filtered the result (ie an AP moderated rate of onset), I mean genuinely exerted itself against my input and ultimately reaching a kind of 'stalemate' (regardless of the fact that I 'won' the fight, and the helo did ultimately move in the direction I told it to, abeit not at my commanded rate, and eventually stopping the commanded roll/pitch)

 

Right, fighting would be the AP "punching back" with all it had after you punched the controls. You punch, it punches, this is fighting. I can be sure that the AP is not fighting the pilot around the vicinity of the 0% stick zone. Testing if it's doing anything counter-stick at the 100% perimeter zone is extremely difficult as these inputs are quickly changing the flight parameters and even damaging the aircraft. What you're describing is the AP absorbing your punches as it was a lump of inert mashed potatoes blocking the punches from getting through the rotors. Like I said, I believe the AP stab and/or hold functions are, by design, not only diminishing your inputs in rate of onset but also absolute magnitude which may be confused with but is distinct from the situation of a contrary input.

 

I have however noticed some distinct limiting behavior relating to the pitch hold function. It's a very easy test to do. When trimmed and held at 0° pitch (you can make sure your trim is good if it stays at 0° pitch with the pitch hold off, otherwise you don't know if the trim is good or if it's just "close enough" for the AP to modify the trim-zero position for the hold. This eliminates a possibly extraneous variable) you weakly pitch down, stabilizing at minus 5-10° or so. Then you depress-and-hold the trim button in order to disable the hold function on the pitch channel while keeping the stick in exactly the same position. You get a little more pitch down to 15-20°. Clearly the hold function had something to do with how much pitch authority commanded (at that specific cyclic position) you had as it noticeably jumped when disabled.

 

This suggests that the hold, while not completely countering small control inputs about a held attitude, does have some limiting, weakening, or saturating effect. I still believe that full authority is possible in either mode but perhaps there are dissimilar curves between 0% and 100%. Is the stabilization program is stronger when the hold program is in effect, as in, is a portion of the stab program's influence realized only through the hold program's authority? Is the stick sensitivity less when the hold channel is on than off?

 

What I'm trying to ultimately say, is that FD mode feels more like the way it should be all the time - watching the RL Kamov videos doesn't show the FD HUD mode. I shouldn't have to press the trim button to be allowed to move the helo - the AP channels should take cyclic pressure/deflection commanded by the pilot into account when stabilising and not attempt to counter this. It's just a gut feel, ED may have it totally correct. In which case, Kamov, what were you thinking?! :)

To be fair the RL Kamov videos are likely unarmed with 25% fuel with a pilot of 10+ years experience. Playing the Ka-50 at sea level with a lightened load makes a huge difference in game compared to a combat load. It practically dances around like a ballerina on crack no matter what mode the AP is set to.

 

Well, I would recommend to read this article for many posters in this thread to understand the basic concepts of autopilots and how it works in Ka-50:

 

http://www.simhq.com/_air13/air_429a.html

 

I've read that and there are a few factual errors. It's a pretty high quality resource for the "all simulators" crowd that simhq caters to but A16's knowledge for example is definately a notch or two higher.

 

Other note: The F-16 has an AP disable paddle because when the F-16's AP is in control... it's IN CONTROL. This is very much unlike the Ka-50 where you can avoid an obstacle with the AP on by simply jerking at the stick in panic. The F-16 doesn't even flinch with a panic stick input because the stick is dead in AP mode. Thus a handy panic disable paddle is needed in the F-16 while the "soft autopilot" in the Ka-50 doesn't.

Edited December 26, 2009 by Frederf

[ericinexile]

AFS=Auto Flight System. A general term for the systems installed to make flight easier for the pilot, up to and including the autopilot.

 

...There's nothing I can get the aircraft to do in FD mode that I can't in non-FD mode...

 

Same here. Its just easier with the autopilot off. Now why is that? Really think about that question. The autopilot is there to help me, right? And usually it does. I use Route mode and Autohover and Turn-on-Target all the time and would have died a thousand (more) deaths were it not for those features. But at other times during general maneuvering flight why is flying different with the FD on than it is with the FD off. That difference is obviously the AP right? Is that difference helping? Well if it is then why all the force trim inputs to either countermand the autopilot or to lock it into another mode?

 

Let us say you are driving on a straight road and ask your wife to reach over and take the wheel while you open another beer, check the map, and fiddle with the GPS. Do you then constantly make steering inputs for her? Do you slap her hand (trim) every time you want to adjust your course then immediately have her take the wheel back? No right!? You either let her drive or you say, "I got it, thanks?" In other words, there was a point where she made driving easier. Then later, there was a point where her steering made driving harder for both of you and you took over completely with zero further input from her...other than perhaps, "We're lost AGAIN?" That's what the FD does in DCS. It is our way of saying, "thanks babe. You made my life a little easier for awhile. But flying isn't done by committee and its my turn for awhile." Again, I happen to think this is a "DCS thing", and that Kamov designed the AFS so that any cyclic input is registered as a pilot's desire to take full, unaltered control. Then, after a short time elapses and no more cyclic input is sensed, the autopilot resumes flying.

Edited December 26, 2009 by ericinexile

[Frederf]

Personally, the maneuvers themselves are the same ease in FD or non-FD mode. It may require that I push to stick a little more to the side to get the aircraft to perform but that's fine by me because that essentially lowers the sensitivity and increases my control and smoothness. Often my goal in maneuvering is to pull the least Gs to accomplish the same task which keeps my speed up and lowers airframe stress.

 

I find the autopilot a great help when a maneuver is finished to stabilize in the new regime. In FD-mode stabilizing at an attitude out of a turn is a wobbly, time-consuming affair. With the holds an attitude is reached in a much shorter time allowing my series of actions greater frequency.

 

Trimming is such a natural and habitual thing that I have never simply released the controls and had the aircraft wander back to a previously scheduled attitude for lack of trimming. I imagine it might be frustrating if one's disposition was fervently against updating the hold schedules, but it doesn't apply to me. The one exception is when, in Auto Hover, when the trim button does not update the scheduled heading hold value but instead remains on the DH PVI task direction but that has nothing to do with my trim button practices.

 

If there was one thing on my wish list from Kamov it is a separate trim button and hold schedule update button. The mechanical trim and AP use the same button which limits you to updating both at the same time. It might be nicer and faster to be able to hold in a hard pedal input to get to a new heading and then set that as the current heading hold value before the pedals were fully relaxed. Of course doing that now would lock in a mechanical rudder trim of a strong pedal input and would do you no good. Right now the best way to use the trim button is to hold your control inputs static until the aircraft is both stable and on the proper course and then trim.

 

It is also notable that maneuvering with the altitude hold on causes weak response at best and foolhardy at worst. I'm not exactly in the habit of grabbing the collective brake every time I move the collective handle or even when I want to suspend the altitude hold function. It would be nice to have an option to automatically apply collective brake lever whenever the collective axis moves.

 

I see utility in adjusting the conditions of the controls-flight surfaces linkage depending on all manner of mode. For example the F-16 will reduce input gains when the landing gear is down for an easier landing. I have noticed that cyclic pitch input with the Ka-50 is reduced when in ROUTE mode. This makes it much easier to precisely and confidently accelerate while in ROUTE mode while maintaining cruise (level) flight. More authority does not always mean more control.

 

I believe unaltered control is overvalued in most cases. If the control authority is sufficient for the mission then it is pilot ego to want more control that could potentially have harmful consequences. Flying the aircraft yourself has no intrinsic value; if the autopilot can fly the aircraft then so much the better. I have no special interest in being in control of the aircraft, just happy if it's getting the job done. The less flying I have to do the more fighting I can do.

 

The various control sensitivity (Channel Off, Hold Off, Normal, and Route) levels all have their place in my mind. 90% of my flying happens where Normal and Route control sensitivities make the most sense as the best compromise between control-&-maneuverability and safety-&-workload. Canyon carving at low altitude (which is often unnecessary at a mission level) often justifies Hold Off and emergencies justify Channel Off.

Edited December 26, 2009 by Frederf

[ericinexile]

Trimming is such a natural and habitual thing that I have never simply released the controls and had the aircraft wander back to a previously scheduled attitude for lack of trimming. I imagine it might be frustrating if one's disposition was fervently against updating the hold schedules, but it doesn't apply to me. The one exception is when, in Auto Hover, when the trim button does not update the scheduled heading hold value but instead remains on the DH PVI task direction but that has nothing to do with my trim button practices.

 

If there was one thing on my wish list from Kamov it is a separate trim button and hold schedule update button. The mechanical trim and AP use the same button which limits you to updating both at the same time. It might be nicer and faster to be able to hold in a hard pedal input to get to a new heading and then set that as the current heading hold value before the pedals were fully relaxed. Of course doing that now would lock in a mechanical rudder trim of a strong pedal input and would do you no good. Right now the best way to use the trim button is to hold your control inputs static until the aircraft is both stable and on the proper course and then trim...

 

I see your point about a second button even though many modern large helicopters use that same trim button logic to communicate pilot desires to the AFS. I like the idea just so people stop using the term "trim" when half the time they are really refering to autopilot updates. Unlike an airplane, a helicopter doesn't need trimming. Triming isn't for the helicopter, it's for the pilot--his fatigue level and and ability to fly with precision. But back to the thread and the question, "is the AP modeled correctly?" I fly with fighter guys, helo guys, and bomber guys all the time. They are more than willing to answer all my technical (non-classified) questions about their old jobs. Aren't there plenty of players on the Russian side of the forum in similar situations? This seems like such an easy question to answer even considering the rarity of the Ka50.

[Martillo1]

Well, I have recently changed my X52 profile to use the pinkie switch for trim instead of C button and it is now more flyable. It halves the functions I can use in each mode, but the thumb is now gripping the stick while trimming instead of pressing a button, and it gives me the edge over the aircraft so it is worth the loss of functions.

 

Ergo...nomics rule :joystick:

 

As for whether it is Kamov's or ED's fault, if any, I do not know and I think I will not ever :D

Edited December 28, 2009 by Martillo1

[My Fing ID]

Figured I'd chime back in though I know this thread is running its own course. I think it's the heading hold that really gets me. With AP on bank left, pull back and try to go 90 degrees, level out, and then you're floating right back to where the AP wants to go. Trim, and you're screwing up your AP. With the FD you don't have that problem, and, though I'll admit I haven't played with it, you probably wouldn't have that problem with the heading hold.

 

Again, since this keeps coming up, I can fly with the AP and usually do, I still feel more comfortable with the FD on though. The helicopter just feels more responsive and I feel like I'm more in control. With no AP it's much more of a pain. You can osculate the copter very easily and before you know it you're on a roller coaster until you just stop input and ease back into controlling the copter.

[EtherealN]

Actually, that sounds familiar to an experience I had in flight school, even though that was fixed wing and without any AP: overcompensation. Basically, the aircraft does something unexpected and you instinctively compensate, which exacerbates the problem and you end up in ever worse yaw oscillations (which on an 18-metre wingspan straight-wing aircraft also means differential lift since one wing is moving faster through the air than the other, causing roll oscillations as a secondary effect).

 

The solution, mostly, is to just let go and allow the oscillations to settle. This takes a bit of practice since the "corrections" that caused it aren't necessarily counscious. (My instructor basically said "stop flying, just let go of the controls", which feels very weird when you are a thousand meters up in the air. :P )

 

While that was not on a helicopter, and without any AP, I suspect one might get a similar situation if there is AP input going in that one feels isn't quite in sync with one's own commands. My recommendation in that case would actually be to fly more with the AP on and FD off, since flying FD on just means you never get the practice needed to become accustomed to how the aircraft behaves with FD off.

 

Though of course, it's also possible that the issues are only superficially similar.